WorldWideScience

Sample records for incident flow velocity

  1. Experimental and Computational Study of the Flow past a Simplified Geometry of an Engine/Pylon/Wing Installation at low velocity/moderate incidence flight conditions

    Science.gov (United States)

    Bury, Yannick; Lucas, Matthieu; Bonnaud, Cyril; Joly, Laurent; ISAE Team; Airbus Team

    2014-11-01

    We study numerically and experimentally the vortices that develop past a model geometry of a wing equipped with pylon-mounted engine at low speed/moderate incidence flight conditions. For such configuration, the presence of the powerplant installation under the wing initiates a complex, unsteady vortical flow field at the nacelle/pylon/wing junctions. Its interaction with the upper wing boundary layer causes a drop of aircraft performances. In order to decipher the underlying physics, this study is initially conducted on a simplified geometry at a Reynolds number of 200000, based on the chord wing and on the freestream velocity. Two configurations of angle of attack and side-slip angle are investigated. This work relies on unsteady Reynolds Averaged Navier Stokes computations, oil flow visualizations and stereoscopic Particle Image Velocimetry measurements. The vortex dynamics thus produced is described in terms of vortex core position, intensity, size and turbulent intensity thanks to a vortex tracking approach. In addition, the analysis of the velocity flow fields obtained from PIV highlights the influence of the longitudinal vortex initiated at the pylon/wing junction on the separation process of the boundary layer near the upper wing leading-edge.

  2. Flow of nanofluid by nonlinear stretching velocity

    Science.gov (United States)

    Hayat, Tasawar; Rashid, Madiha; Alsaedi, Ahmed; Ahmad, Bashir

    2018-03-01

    Main objective in this article is to model and analyze the nanofluid flow induced by curved surface with nonlinear stretching velocity. Nanofluid comprises water and silver. Governing problem is solved by using homotopy analysis method (HAM). Induced magnetic field for low magnetic Reynolds number is not entertained. Development of convergent series solutions for velocity and skin friction coefficient is successfully made. Pressure in the boundary layer flow by curved stretching surface cannot be ignored. It is found that magnitude of power-law index parameter increases for pressure distibutions. Magnitude of radius of curvature reduces for pressure field while opposite trend can be observed for velocity.

  3. CORRELATION BETWEEN UTERINE ARTERY FLOW VELOCITY ...

    African Journals Online (AJOL)

    CORRELATION BETWEEN UTERINE ARTERY FLOW VELOCITY WAVEFORMS AND ENDOMETRIAL HISTOPATHOLOGY IN WOMEN WITH PERIMENOPAUSAL AND POSTMENOPAUSAL BLEEDING. Dr. Ebtesam Saied, Dr. Ismail El Garhy(MD), Dr. Farid I. Hassan(MD), Dr. Adel-Gamil Abd-Allah, Abd El Shafy Ibrahim ...

  4. STARE velocities: 2. Evening westward electron flow

    Directory of Open Access Journals (Sweden)

    M. Uspensky

    2004-04-01

    Full Text Available Four evening events and one morning event of joint EISCAT/STARE observations during ~22h are considered and the differences between observed STARE line-of-sight (l-o-s velocities and EISCAT electron drift velocities projected onto the STARE beams are studied. We demonstrate that the double-pulse technique, which is currently in use in the STARE routine data handling, typically underestimates the true phase velocity as inferred from the multi-pulse STARE data. We show that the STARE velocities are persistently smaller (1.5–2 times than the EISCAT velocities, even for the multi-pulse data. The effect seems to be more pronounced in the evening sector when the Finland radar observes at large flow angles. We evaluate the performance of the ion-acoustic approach (IAA, Nielsen and Schlegel, 1985 and the off-orthogonal fluid approach (OOFA, Uspensky et al., 2003 techniques to predict the true electron drift velocity for the base event of 12 February 1999. The IAA technique predicts the convection reasonably well for enhanced flows of >~1000m/s, but not so well for slower ones. By considering the EISCAT N(h profiles, we derive the effective aspect angle and effective altitude of backscatter, and use this information for application of the OOFA technique. We demonstrate that the OOFA predictions for the base event are superior over the IAA predictions and thus, we confirm that OOFA predicts the electron velocities reasonably well in the evening sector, in addition to the morning sector, as concluded by Uspensky et al. (2003. To check how "robust" the OOFA model is and how successful it is for convection estimates without the EISCAT support, we analysed three additional evening events and one additional morning event for which information on N(h profiles was intentionally ignored. By accepting the mean STARE/EISCAT velocity ratio of 0.55 and the mean azimuth rotation of 9° (derived for the basic event, we show that the OOFA performs

  5. Channel flow analysis. [velocity distribution throughout blade flow field

    Science.gov (United States)

    Katsanis, T.

    1973-01-01

    The design of a proper blade profile requires calculation of the blade row flow field in order to determine the velocities on the blade surfaces. An analysis theory is presented for several methods used for this calculation and associated computer programs that were developed are discussed.

  6. Plasma flow velocity measurements using a modulated Michelson interferometer

    International Nuclear Information System (INIS)

    Howard, J.

    1997-01-01

    This paper discusses the possibility of flow velocity reconstruction using passive spectroscopic techniques. We report some preliminary measurements of the toroidal flow velocity of hydrogen atoms in the RTP tokamak using a phase modulated Michelson interferometer. (orig.)

  7. Stationary velocity distributions in traffic flows

    International Nuclear Information System (INIS)

    1997-01-01

    We introduce a traffic flow model that incorporates clustering and passing. We obtain analytically the steady state characteristics of the flow from a Boltzmann-like equation. A single dimensionless parameter, R=c 0 v 0 t 0 with c 0 the concentration, v 0 the velocity range, and t 0 -1 the passing rate, determines the nature of the steady state. When R 1, large clusters with average mass left-angle m right-angle ∼R α form, and the flux is J∼R -γ . The initial distribution of slow cars governs the statistics. When P 0 (v)∼v μ as v→0, the scaling exponents are γ=1/(μ+2), α=1/2 when μ>0, and α=(μ+1)/(μ+2) when μ<0. copyright 1997 The American Physical Society

  8. Parallel ion flow velocity measurement using laser induced fluorescence method in an electron cyclotron resonance plasma

    International Nuclear Information System (INIS)

    Yoshimura, Shinji; Okamoto, Atsushi; Terasaka, Kenichiro; Ogiwara, Kohei; Tanaka, Masayoshi Y.; Aramaki, Mitsutoshi

    2010-01-01

    Parallel ion flow velocity along a magnetic field has been measured using a laser induced fluorescence (LIF) method in an electron cyclotron resonance (ECR) argon plasma with a weakly-diverging magnetic field. To measure parallel flow velocity in a cylindrical plasma using the LIF method, the laser beam should be injected along device axis; however, the reflection of the incident beam causes interference between the LIF emission of the incident and reflected beams. Here we present a method of quasi-parallel laser injection at a small angle, which utilizes the reflected beam as well as the incident beam to obtain the parallel ion flow velocity. Using this method, we observed an increase in parallel ion flow velocity along the magnetic field. The acceleration mechanism is briefly discussed on the basis of the ion fluid model. (author)

  9. The Effect of Flow Velocity on Waveform Inversion

    Science.gov (United States)

    Lee, D.; Shin, S.; Chung, W.; Ha, J.; Lim, Y.; Kim, S.

    2017-12-01

    The waveform inversion is a velocity modeling technique that reconstructs accurate subsurface physical properties. Therefore, using the model in its final, updated version, we generated data identical to modeled data. Flow velocity, like several other factors, affects observed data in seismic exploration. Despite this, there is insufficient research on its relationship with waveform inversion. In this study, the generated synthetic data considering flow velocity was factored in waveform inversion and the influence of flow velocity in waveform inversion was analyzed. Measuring the flow velocity generally requires additional equipment. However, for situations where only seismic data was available, flow velocity was calculated by fixed-point iteration method using direct wave in observed data. Further, a new waveform inversion was proposed, which can be applied to the calculated flow velocity. We used a wave equation, which can work with the flow velocities used in the study by Käser and Dumbser. Further, we enhanced the efficiency of computation by applying the back-propagation method. To verify the proposed algorithm, six different data sets were generated using the Marmousi2 model; each of these data sets used different flow velocities in the range 0-50, i.e., 0, 2, 5, 10, 25, and 50. Thereafter, the inversion results from these data sets along with the results without the use of flow velocity were compared and analyzed. In this study, we analyzed the results of waveform inversion after flow velocity has been factored in. It was demonstrated that the waveform inversion is not affected significantly when the flow velocity is of smaller value. However, when the flow velocity has a large value, factoring it in the waveform inversion produces superior results. This research was supported by the Basic Research Project(17-3312, 17-3313) of the Korea Institute of Geoscience and Mineral Resources(KIGAM) funded by the Ministry of Science, ICT and Future Planning of Korea.

  10. Daily rhythm of cerebral blood flow velocity

    Directory of Open Access Journals (Sweden)

    Spielman Arthur J

    2005-03-01

    Full Text Available Abstract Background CBFV (cerebral blood flow velocity is lower in the morning than in the afternoon and evening. Two hypotheses have been proposed to explain the time of day changes in CBFV: 1 CBFV changes are due to sleep-associated processes or 2 time of day changes in CBFV are due to an endogenous circadian rhythm independent of sleep. The aim of this study was to examine CBFV over 30 hours of sustained wakefulness to determine whether CBFV exhibits fluctuations associated with time of day. Methods Eleven subjects underwent a modified constant routine protocol. CBFV from the middle cerebral artery was monitored by chronic recording of Transcranial Doppler (TCD ultrasonography. Other variables included core body temperature (CBT, end-tidal carbon dioxide (EtCO2, blood pressure, and heart rate. Salivary dim light melatonin onset (DLMO served as a measure of endogenous circadian phase position. Results A non-linear multiple regression, cosine fit analysis revealed that both the CBT and CBFV rhythm fit a 24 hour rhythm (R2 = 0.62 and R2 = 0.68, respectively. Circadian phase position of CBT occurred at 6:05 am while CBFV occurred at 12:02 pm, revealing a six hour, or 90 degree difference between these two rhythms (t = 4.9, df = 10, p Conclusion In conclusion, time of day variations in CBFV have an approximately 24 hour rhythm under constant conditions, suggesting regulation by a circadian oscillator. The 90 degree-phase angle difference between the CBT and CBFV rhythms may help explain previous findings of lower CBFV values in the morning. The phase difference occurs at a time period during which cognitive performance decrements have been observed and when both cardiovascular and cerebrovascular events occur more frequently. The mechanisms underlying this phase angle difference require further exploration.

  11. Plasma flow velocity measurements using a modulated Michelson interferometer

    NARCIS (Netherlands)

    Howard, J.; Meijer, F. G.

    1997-01-01

    This paper discusses the possibility of flow velocity reconstruction using passive spectroscopic techniques. We report some preliminary measurements of the toroidal flow velocity of hydrogen atoms in the RTP tokamak using a phase modulated Michelson interferometer. (C) 1997 Elsevier Science S.A.

  12. Liquid velocity in upward and downward air-water flows

    International Nuclear Information System (INIS)

    Sun Xiaodong; Paranjape, Sidharth; Kim, Seungjin; Ozar, Basar; Ishii, Mamoru

    2004-01-01

    Local characteristics of the liquid phase in upward and downward air-water two-phase flows were experimentally investigated in a 50.8-mm inner-diameter round pipe. An integral laser Doppler anemometry (LDA) system was used to measure the axial liquid velocity and its fluctuations. No effect of the flow direction on the liquid velocity radial profile was observed in single-phase liquid benchmark experiments. Local multi-sensor conductivity probes were used to measure the radial profiles of the bubble velocity and the void fraction. The measurement results in the upward and downward two-phase flows are compared and discussed. The results in the downward flow demonstrated that the presence of the bubbles tended to flatten the liquid velocity radial profile, and the maximum liquid velocity could occur off the pipe centerline, in particular at relatively low flow rates. However, the maximum liquid velocity always occurred at the pipe center in the upward flow. Also, noticeable turbulence enhancement due to the bubbles in the two-phase flows was observed in the current experimental flow conditions. Furthermore, the distribution parameter and the void-weighted area-averaged drift velocity were obtained based on the definitions

  13. Blood flow velocity in migraine attacks - a transcranial Doppler study

    International Nuclear Information System (INIS)

    Zwetsloot, C.P.; Caekebeke, J.F.V.; Jansen, J.C.; Odink, J.; Ferrari, M.D.

    1991-01-01

    A pulsed Doppler device was used to measure blood flow velocities in the common carotid artery, the extracranial part of the internal carotid artery, the external carotid artery, the middle cerebral artery, and the anterior cerebral artery in 31 migraneurs without aura (n=27) and with aura (n=4), both during and ouside an attack. The aims were to compare blood flow velocity during and between migraine attacks and to study asymmetries of the blood flow velocity. Compared with blood flow velocity values obtained in the attack-free interval, blood flow velocity was lower during attacks without aura in both common carotid arteries, but not in the other extra- and intracranial vessels which were examined. However, during attacks of migraine with aura, blood flow velocity tended to be lower in all examined vessels. There were no asymmetries of the blood flow velocity. It is suggested that during migraine attacks without aura there is a dissociation in blood flow regulation in the common carotid and middle cerebral arteries. 20 refs., 2 tabs

  14. Turbulent flow velocity distribution at rough walls

    International Nuclear Information System (INIS)

    Baumann, W.

    1978-08-01

    Following extensive measurements of the velocity profile in a plate channel with artificial roughness geometries specific investigations were carried out to verify the results obtained. The wall geometry used was formed by high transverse square ribs having a large pitch. The measuring position relative to the ribs was varied as a parameter thus providing a statement on the local influence of roughness ribs on the values measured. As a fundamental result it was found that the gradient of the logarithmic rough wall velocity profiles, which differs widely from the value 2.5, depends but slightly on the measuring position relative to the ribs. The gradients of the smooth wall velocity profiles deviate from 2.5 near the ribs, only. This fact can be explained by the smooth wall shear stress varying with the pitch of the ribs. (orig.) 891 GL [de

  15. Real gas flows with high velocities

    CERN Document Server

    Lunev, Vladimir V

    2009-01-01

    Gasdynamic Model and Equations Outline of the Gasdynamic Model Basic Equations and Postulates Equations of State Kinetic Theory Second Law of Thermodynamics Speed of Sound Integral Equations of Motion Kinematics of Fluid Media Differential Equations of Gasdynamics Rheological Model Initial and Boundary Conditions Similarity and Modeling in Gasdynamics Euler Equations Navier-Stokes Equations Turbulent Flows Viscous and Inviscid Flow Models Inviscid Gasdynamics Stream Function, Potential,

  16. Simultaneous Temperature and Velocity Diagnostic for Reacting Flows Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A diagnostic technique is proposed for measuring temperature and velocity simultaneously in a high temperature reacting flow for aiding research in propulsion. The...

  17. Simultaneous Temperature and Velocity Diagnostic for Reacting Flows, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — A diagnostic technique is proposed for measuring temperature and velocity simultaneously in a high temperature reacting flow for aiding research in propulsion. The...

  18. Measurement of gas flow velocities by laser-induced gratings

    Energy Technology Data Exchange (ETDEWEB)

    Hemmerling, B.; Stampanoni-Panariello, A. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Kozlov, A.D.N. [General Physics Institute, Moscow (Russian Federation)

    1999-08-01

    Time resolved light scattering from laser-induced electrostrictive gratings was used for the determination of flow velocities in air at room temperature. By measuring the velocity profile across the width of a slit nozzle we demonstrated the high spatial resolution (about 200 mm) of this novel technique. (author) 3 figs., 1 ref.

  19. Maximum Likelihood Blood Velocity Estimator Incorporating Properties of Flow Physics

    DEFF Research Database (Denmark)

    Schlaikjer, Malene; Jensen, Jørgen Arendt

    2004-01-01

    )-data under investigation. The flow physic properties are exploited in the second term, as the range of velocity values investigated in the cross-correlation analysis are compared to the velocity estimates in the temporal and spatial neighborhood of the signal segment under investigation. The new estimator...... has been compared to the cross-correlation (CC) estimator and the previously developed maximum likelihood estimator (MLE). The results show that the CMLE can handle a larger velocity search range and is capable of estimating even low velocity levels from tissue motion. The CC and the MLE produce...... for the CC and the MLE. When the velocity search range is set to twice the limit of the CC and the MLE, the number of incorrect velocity estimates are 0, 19.1, and 7.2% for the CMLE, CC, and MLE, respectively. The ability to handle a larger search range and estimating low velocity levels was confirmed...

  20. Measurement of LBE flow velocity profile by UDVP

    International Nuclear Information System (INIS)

    Kikuchi, Kenji; Takeda, Yasushi; Obayashi, Hiroo; Tezuka, Masao; Sato, Hiroshi

    2006-01-01

    Measurements of liquid metal lead-bismuth eutectic (LBE), flow velocity profile were realized in the spallation neutron source target model by the ultrasonic Doppler velocity profiler (UVDP) technique. So far, it has not been done well, because both of poor wetting property of LBE with stainless steels and poor performance of supersonic probes at high temperatures. The measurement was made for a return flow in the target model, which has coaxially arranged annular and tube channels, in the JAEA Lead Bismuth Loop-2 (JLBL-2). The surface treatment of LBE container was examined. It was found that the solder coating was effective to enhance an intensity of reflected ultrasonic wave. This treatment has been applied to the LBE loop, which was operated up to 150 deg. C. The electro magnetic pump generates LBE flow and the flow rate was measured by the electro magnetic flow meter. By changing the flow rate of LBE, velocity profiles in the target were measured. It was confirmed that the maximum velocity in the time-averaged velocity distribution on the target axis was proportional to the flow rate measured by the electro magnetic flow meter

  1. Slip velocity of large neutrally buoyant particles in turbulent flows

    International Nuclear Information System (INIS)

    Bellani, G; Variano, E A

    2012-01-01

    We discuss possible definitions for a stochastic slip velocity that describes the relative motion between large particles and a turbulent flow. This definition is necessary because the slip velocity used in the standard drag model fails when particle size falls within the inertial subrange of ambient turbulence. We propose two definitions, selected in part due to their simplicity: they do not require filtration of the fluid phase velocity field, nor do they require the construction of conditional averages on particle locations. A key benefit of this simplicity is that the stochastic slip velocity proposed here can be calculated equally well for laboratory, field and numerical experiments. The stochastic slip velocity allows the definition of a Reynolds number that should indicate whether large particles in turbulent flow behave (a) as passive tracers; (b) as a linear filter of the velocity field; or (c) as a nonlinear filter to the velocity field. We calculate the value of stochastic slip for ellipsoidal and spherical particles (the size of the Taylor microscale) measured in laboratory homogeneous isotropic turbulence. The resulting Reynolds number is significantly higher than 1 for both particle shapes, and velocity statistics show that particle motion is a complex nonlinear function of the fluid velocity. We further investigate the nonlinear relationship by comparing the probability distribution of fluctuating velocities for particle and fluid phases. (paper)

  2. Scaling Effect on Velocity Profiles in Capillary Underfill Flow

    Science.gov (United States)

    Ng, Fei Chong; Abas, Aizat; Abdullah, M. Z.; Ishak, M. H. H.; Yuen Chong, Gean

    2017-05-01

    In this paper, the scaling effect of ball grid array (BGA) device on the capillary underfill (CUF) flow and its velocity profiles is thoroughly investigated by means of fluid-structure interaction (FSI) numerical simulation. It is found that generally the flows front profiles attained from device of different scale sizes are comparable to the actual miniature BGA, with relative error approximately under 10%. Based on dimensionless number analysis, the scaling limit is estimated at 20, to maintain low scaling error. The velocity profiles attained on the CUF flow in each models of different scales are relative similar in magnitude and trend. Although the increases in gap height reduces the strength of capillary flow, the flow’s velocity still be maintained and the scaling effect is counter-balance with the increases in driving pressure force. The magnitude of entrant velocity is higher at earlier stage of CUF (less than 40% filling); while higher magnitude of exit velocity is found at later stage of CUF (beyond 60% filling). Additionally, the pressure and velocity distributions of CUF flow in miniature device were also studied thoroughly.

  3. An Approach to Predict Debris Flow Average Velocity

    Directory of Open Access Journals (Sweden)

    Chen Cao

    2017-03-01

    Full Text Available Debris flow is one of the major threats for the sustainability of environmental and social development. The velocity directly determines the impact on the vulnerability. This study focuses on an approach using radial basis function (RBF neural network and gravitational search algorithm (GSA for predicting debris flow velocity. A total of 50 debris flow events were investigated in the Jiangjia gully. These data were used for building the GSA-based RBF approach (GSA-RBF. Eighty percent (40 groups of the measured data were selected randomly as the training database. The other 20% (10 groups of data were used as testing data. Finally, the approach was applied to predict six debris flow gullies velocities in the Wudongde Dam site area, where environmental conditions were similar to the Jiangjia gully. The modified Dongchuan empirical equation and the pulled particle analysis of debris flow (PPA approach were used for comparison and validation. The results showed that: (i the GSA-RBF predicted debris flow velocity values are very close to the measured values, which performs better than those using RBF neural network alone; (ii the GSA-RBF results and the MDEE results are similar in the Jiangjia gully debris flow velocities prediction, and GSA-RBF performs better; (iii in the study area, the GSA-RBF results are validated reliable; and (iv we could consider more variables in predicting the debris flow velocity by using GSA-RBF on the basis of measured data in other areas, which is more applicable. Because the GSA-RBF approach was more accurate, both the numerical simulation and the empirical equation can be taken into consideration for constructing debris flow mitigation works. They could be complementary and verified for each other.

  4. Divergence instability of pipes conveying fluid with uncertain flow velocity

    Science.gov (United States)

    Rahmati, Mehdi; Mirdamadi, Hamid Reza; Goli, Sareh

    2018-02-01

    This article deals with investigation of probabilistic stability of pipes conveying fluid with stochastic flow velocity in time domain. As a matter of fact, this study has focused on the randomness effects of flow velocity on stability of pipes conveying fluid while most of research efforts have only focused on the influences of deterministic parameters on the system stability. The Euler-Bernoulli beam and plug flow theory are employed to model pipe structure and internal flow, respectively. In addition, flow velocity is considered as a stationary random process with Gaussian distribution. Afterwards, the stochastic averaging method and Routh's stability criterion are used so as to investigate the stability conditions of system. Consequently, the effects of boundary conditions, viscoelastic damping, mass ratio, and elastic foundation on the stability regions are discussed. Results delineate that the critical mean flow velocity decreases by increasing power spectral density (PSD) of the random velocity. Moreover, by increasing PSD from zero, the type effects of boundary condition and presence of elastic foundation are diminished, while the influences of viscoelastic damping and mass ratio could increase. Finally, to have a more applicable study, regression analysis is utilized to develop design equations and facilitate further analyses for design purposes.

  5. Effects of local flow field on flow accelerated corrosion. Effect of flow velocity on corrosion rate

    International Nuclear Information System (INIS)

    Nagaya, Yukinori; Nakamura, Akira; Murase, Michio; Utanohara, Yoichi

    2010-01-01

    Flow accelerated corrosion (FAC) is one of important issues for aging of nuclear power plants. In this study, in order to evaluate the effects of flow field on corrosion rate due to FAC, corrosion rates downstream of an orifice were measured using an electric resistance method. In these experiments, a test loop under high temperature and high pressure conditions was used. The pipe inner diameter was 50 mm and the ratio of orifice diameter which was 24.3 mm to the pipe diameter was about 0.5. The water temperature was controlled at 150 within ± 1 degC. To evaluate the effect of flow velocity on FAC rate, we carried out two series of measurements. During each period of measurements, we changed the flow velocity from 1.4 to 5.0 m/s, or from 2.1 to 3.5 m/s. In these results, FAC rates downstream of the orifice increased remarkably by increasing the flow velocity, while the changes of FAC rates upstream were little. The results show a possibility that the effect of flow velocity on FAC rate in the upstream of the orifice is different from that in the downstream. It turned out that the maximum FAC rate downstream of the orifice is proportional to Re 0.82 in the range of Reynolds number, Re=3.5x10 5 - 1.3x10 6 . However these measurement results might be different on the little difference of water quality or the difference of initial conditions of sensor surface, therefore we have to evaluate these effects in the future. We confirmed that FAC rates downstream of the orifice can possibly be evaluated by the parameter based on the flow velocity. (author)

  6. Reduced retinal blood flow velocity in diabetic retinopathy.

    Science.gov (United States)

    Burgansky-Eliash, Zvia; Nelson, Darin A; Bar-Tal, Orly Pupko; Lowenstein, Anat; Grinvald, Amiram; Barak, Adiel

    2010-05-01

    The purpose of this study was to compare the retinal blood flow velocities of patients with diabetes and healthy control subjects. We used a novel device offering a noninvasive diagnostic of retinal function. Flow velocities in retinal arterioles and venules were quantitatively analyzed by retinal function imager scanning in 58 eyes of 42 patients with nonproliferative diabetic retinopathy and 51 eyes of 32 normal subjects. Group differences were assessed by the mixed-model effect. Average velocity in arterial compartments (in mm/s) was 3.74 +/- 1.09 for the diabetic group and 4.19 +/- 0.99 for the control subjects. The average velocity of all segments, taking associated heart rate and individual segment widths into account, was 17% slower in the diabetic group (P velocity was lower than the arterial velocity (2.61 +/- 0.65 for the diabetic group; 3.03 +/- 0.59 for the control subjects). Individual vein velocities, taking heart rate and segment widths into account, was 17% slower, on average, in the diabetic group (P velocities in the retinal arterioles and venules of patients with diabetes compared with healthy control subjects, supporting the view of abnormal vessel function in eyes with nonproliferative diabetic retinopathy.

  7. Measuring surface flow velocity with smartphones: potential for citizen observatories

    Science.gov (United States)

    Weijs, Steven V.; Chen, Zichong; Brauchli, Tristan; Huwald, Hendrik

    2014-05-01

    Stream flow velocity is an important variable for discharge estimation and research on sediment dynamics. Given the influence of the latter on rating curves (stage-discharge relations), and the relative scarcity of direct streamflow measurements, surface velocity measurements can offer important information for, e.g., flood warning, hydropower, and hydrological science and engineering in general. With the growing amount of sensing and computing power in the hands of more outdoorsy individuals, and the advances in image processing techniques, there is now a tremendous potential to obtain hydrologically relevant data from motivated citizens. This is the main focus of the interdisciplinary "WeSenseIt" project, a citizen observatory of water. In this subproject, we investigate the feasibility of stream flow surface velocity measurements from movie clips taken by (smartphone-) cameras. First results from movie-clip derived velocity information will be shown and compared to reference measurements.

  8. Viscous flow solutions for slender bodies of revolution at incidence

    Science.gov (United States)

    Vatsa, Veer N.

    1991-01-01

    Flow over slender prolate spheroids at incidence is examined. The incidence angle is chosen high enough to cause streamwise separation of the flow in addition to crossflow separation generally observed at lower incidence angles. The freestream Mach number for the cases investigated here is subsonic, thus precluding the use of parabolized procedures. Laminar, transitional and turbulent flow cases are investigated.

  9. Numerical Simulation Modelling for Velocity Measurement of Electromagnetic Flow Meter

    International Nuclear Information System (INIS)

    Wang, J Z; Gong, C L; Tian, G Y; Lucas, G P

    2006-01-01

    An induced voltage EMF in the area of measuring single-phase flow rate in pipes has been used in many industrial areas. To measure the continuous phase velocity profile in multiphase flows where the continuous phase is an electrical conductor, Electrical capacitance and resistance tomography has been comprehensively investigated, except for continuous phase velocity profile measurement. This paper tries to design the numerical simulation model according to the basic electromagnetic induction law and to investigate the relationship between induced electric potential or potential drop and the velocity distribution of the conductive continuous phase in the flow. First, the 3-Dimenssion simulating module for EMF is built. Given the most simple velocity profile of the fluid in the pipe, the value of the induced potential difference between electrodes is obtained by simulation and theoretical computation according to J A Shercliff's weight function. The relative error is 6.066 . This proves that the simulation model is accurate enough to investigate the characteristic of the induced potential difference of EMF. Finally, the relationship between induced potential difference and the velocity profile is analysed in detail where the complicated velocity profile is expressed as vz = 1m/s when 0.022< x2+y2< = 0.02652 and vz = 5m/s when x2+y2< = 0.022

  10. Investigation of the Velocity Distribution in Sediment-Laden Flow

    Directory of Open Access Journals (Sweden)

    S. Khodadoust Siuki

    2016-02-01

    Full Text Available Introduction: For a velocity profile in turbulent flows, the flow conditions in the vicinity of the wall are described by logarithmic law of the wall. However, it has been extensively verified that the log-law does not apply in the outer region of the boundary layer. For example, in free surface flows, the law of the wall holds only for 20 percent of the flow depth from the wall. Coles (1956 conducted an important advancement and argued that away from the wall, the deviations of the profiles of measured velocity from those obtained from the law of the wall could be explained by another universal law, called the wake-law. Combining both laws (wall and wake, a complete approximation to the time-averaged velocity profile in turbulent flows is then feasible (White, 1991. On the other hand, the fundamental problem of characterizing the mean velocity profile in sediment-laden flows remains unresolved. While existence models have been developed to estimate velocity profile, but there is a lack of generalization in the sediment-laden flows. For several decades, it has been controversial about the effects of suspended sediment on hydraulic characteristics of the flow, including flow resistance and velocity distribution. Fig. 1 shows the variations of velocity distribution due to introduction of the suspended sediment. As it is seen in this Figure, the suspended sediment moves faster than the water in the inner layer; on the other hands, there is a velocity-lag due to the introduction of sediment into the outer layer. Accurate estimate of the rate of sediment loads is important in sediment-laden flow. Because velocity distribution is one of the required parameters to estimate the sediment discharge. Until now, many equations have been introduced by many researchers for estimating the velocity distribution in open channels. Generally, there are two different views about the velocity distribution in sediment-laden flows. The first view suggests that the log

  11. Dynamic exercise enhances regional cerebral artery mean flow velocity

    DEFF Research Database (Denmark)

    Linkis, P; Jørgensen, L G; Olesen, H L

    1995-01-01

    Dynamic exercise enhances regional cerebral artery mean flow velocity. J. Appl. Physiol. 78(1): 12-16, 1995.--Anterior (ACA) and middle (MCA) cerebral artery mean flow velocities (Vmean) and pulsatility indexes were determined using transcranial Doppler in 14 subjects during dynamic exercise after...... a focal response but depended did not demonstrate a focal response but depended on the muscle mass involved during exercise. The data demonstrate a significant increase in Vmean for the artery supplying the cortical projection of the exercising limb. Insignificant and marginally significant increases...

  12. Recent advances in blood flow vector velocity imaging

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt; Nikolov, Svetoslav; Udesen, Jesper

    2011-01-01

    been acquired using a commercial implementation of the method (BK Medical ProFocus Ultraview scanner). A range of other methods are also presented. This includes synthetic aperture imaging using either spherical or plane waves with velocity estimation performed with directional beamforming or speckle...... Medical 8804 transducer. This resulted in a relative standard deviation of 1.2% for a fully transverse flow. Plane wave imaging was also implemented on the RASMUS scanner and a 100 Hz frame rate was attained. Several vector velocity image sequences of complex flow were acquired, which demonstrates...

  13. Assessing the velocity of the groundwater flow in bedrock fractures

    International Nuclear Information System (INIS)

    Taivassalo, V.; Poteri, A.

    1994-10-01

    Teollisuuden Voima Oy (TVO) is studying the crystalline bedrock in Finland for the final disposal of the spent nuclear fuel from its two reactors in Olkiluoto. Preliminary site investigations for five areas were carried out during 1987-1992. One part of the investigation programme was three-dimensional groundwater flow modelling. The numerical site-specific flow simulations were based on the concept of an equivalent porous continuum. The results include hydraulic head distributions, average groundwater flow rate routes. In this study, a novel approach was developed to evaluate the velocities of the water particles flowing in the fractured bedrock. (17 refs., 15 figs., 5 tabs.)

  14. Measurement of Plasma Ion Temperature and Flow Velocity from ...

    Indian Academy of Sciences (India)

    304. Xu Wei where ν0 is the flow velocity vector. The uniform flow in the absence of any other mechanism is delta function (Xu 2003): f (λ) = δ. [ λ − λc. (. 1 − ν0 c cos θ. )] = δ. [ x + λc ν0 c cos θ. ] , where x = λ − λc. The line profile due to Doppler broadening and Doppler shift is the convolution of the two profile functions: f (y) =.

  15. Estimating Stream Surface Flow Velocities from Video Clips

    Science.gov (United States)

    Weijs, S. V.; Brauchli, T.; Chen, Z.; Huwald, H.

    2014-12-01

    Measuring surface flow velocities in streams can provide important information on discharge. This information is independent of water level, the most commonly used proxy for discharge and therefore has significant potential to reduce uncertainties. Advances in cheap and commonly used imaging devices (e.g. smartphone cameras) and image processing techniques offer new opportunities to get velocity information. Short video clips of streams can be used in combination with optical flow algorithms to get proxies for stream surface velocities. Here some initial results are presented and the main challenges are discussed, especially in view of using these techniques in a citizen science context (specifically the "WeSenseIt" project, a citizen observatory of water), where we try to minimize the need for site preparation and additional equipment needed to take measurements.

  16. Coronary Flow Velocity Reserve Assessed by Transthoracic Doppler

    DEFF Research Database (Denmark)

    Michelsen, Marie M; Peña, Adam; Mygind, Naja D

    2016-01-01

    BACKGROUND: Coronary flow velocity reserve (CFVR) measured by transthoracic Doppler echocardiography is a noninvasive measure of microvascular function, but it has not achieved widespread use, mainly because of concerns of validity and feasibility. The aim of this study was to describe the feasib...

  17. Influence of flow velocity on the removal of faecal coliforms in horizontal subsurface flow constructed wetland.

    Science.gov (United States)

    Lohay, W S; Lyimo, T J; Njau, K N

    2012-01-01

    In order to determine the influence of flow velocity on the removal of faecal coliforms (FC) in constructed wetlands (CWs), removal rate constants of FC (k(FC)) were studied at various flow velocities (u). Membrane filtration technique was used during analysis. Values of k(FC) were determined using Reed's equation of pathogen removal; the results were compared with the plug flow equation. According to Reed's equation, k(FC) values ranged from 1.6 day⁻¹ at a velocity of 4 m/day to 34.5 day⁻¹ at a velocity of 42.9 m/day. The removal rates correlated positively with flow velocity (r = 0.84, p < 0.05). On assuming a plug flow equation, removal rates constants ranged from 0.77 to 11.69 day⁻¹; a more positive correlation (r = 0.93, p < 0.05) was observed. Optimum removal rate constants were observed for the velocity ranging 36 to 43 m/day. Generally, the increase of flow velocity improved FC removal rate constants: implying that pathogen removals are influenced by diffusion of the microorganisms into the biofilms on CW media. The velocity dependent approach together with the plug flow equation is therefore proposed for incorporation in the design of CW in a tropical climate where temperature variations are minor.

  18. A flow meter for ultrasonically measuring the flow velocity of fluids

    DEFF Research Database (Denmark)

    2015-01-01

    The invention regards a flow meter for ultrasonically measuring the flow velocity of fluids comprising a duct having a flow channel with an internal cross section comprising variation configured to generate at least one acoustic resonance within the flow channel for a specific ultrasonic frequency......, and at least two transducers for generating and sensing ultrasonic pulses, configured to transmit ultrasonic pulses at least at said specific ultrasonic frequency into the flow channel such that the ultrasonic pulses propagate through a fluid flowing in the flow channel, wherein the flow meter is configured...... to determine the flow velocity of the fluid flowing in the flow channel based on a change in transit time, phase and/or pulse such as amplitude and/or form, of the ultrasonic pulses....

  19. Flow velocity measurement with the nonlinear acoustic wave scattering

    Energy Technology Data Exchange (ETDEWEB)

    Didenkulov, Igor, E-mail: din@appl.sci-nnov.ru [Institute of Applied Physics, 46 Ulyanov str., Nizhny Novgorod, 603950 (Russian Federation); Lobachevsky State University of Nizhny Novgorod, 23 Gagarin ave., Nizhny Novgorod, 603950 (Russian Federation); Pronchatov-Rubtsov, Nikolay, E-mail: nikvas@rf.unn.ru [Lobachevsky State University of Nizhny Novgorod, 23 Gagarin ave., Nizhny Novgorod, 603950 (Russian Federation)

    2015-10-28

    A problem of noninvasive measurement of liquid flow velocity arises in many practical applications. To this end the most often approach is the use of the linear Doppler technique. The Doppler frequency shift of signal scattered from the inhomogeneities distributed in a liquid relatively to the emitted frequency is proportional to the sound frequency and velocities of inhomogeneities. In the case of very slow flow one needs to use very high frequency sound. This approach fails in media with strong sound attenuation because acoustic wave attenuation increases with frequency and there is limit in increasing sound intensity, i.e. the cavitation threshold. Another approach which is considered in this paper is based on the method using the difference frequency Doppler Effect for flows with bubbles. This method is based on simultaneous action of two high-frequency primary acoustic waves with closed frequencies on bubbles and registration of the scattered by bubbles acoustic field at the difference frequency. The use of this method is interesting since the scattered difference frequency wave has much lower attenuation in a liquid. The theoretical consideration of the method is given in the paper. The experimental examples confirming the theoretical equations, as well as the ability of the method to be applied in medical diagnostics and in technical applications on measurement of flow velocities in liquids with strong sound attenuation is described. It is shown that the Doppler spectrum form depends on bubble concentration velocity distribution in the primary acoustic beams crossing zone that allows one to measure the flow velocity distribution.

  20. Measurement uncertainty budget of an interferometric flow velocity sensor

    Science.gov (United States)

    Bermuske, Mike; Büttner, Lars; Czarske, Jürgen

    2017-06-01

    Flow rate measurements are a common topic for process monitoring in chemical engineering and food industry. To achieve the requested low uncertainties of 0:1% for flow rate measurements, a precise measurement of the shear layers of such flows is necessary. The Laser Doppler Velocimeter (LDV) is an established method for measuring local flow velocities. For exact estimation of the flow rate, the flow profile in the shear layer is of importance. For standard LDV the axial resolution and therefore the number of measurement points in the shear layer is defined by the length of the measurement volume. A decrease of this length is accompanied by a larger fringe distance variation along the measurement axis which results in a rise of the measurement uncertainty for the flow velocity (uncertainty relation between spatial resolution and velocity uncertainty). As a unique advantage, the laser Doppler profile sensor (LDV-PS) overcomes this problem by using two fan-like fringe systems to obtain the position of the measured particles along the measurement axis and therefore achieve a high spatial resolution while it still offers a low velocity uncertainty. With this technique, the flow rate can be estimated with one order of magnitude lower uncertainty, down to 0:05% statistical uncertainty.1 And flow profiles especially in film flows can be measured more accurately. The problem for this technique is, in contrast to laboratory setups where the system is quite stable, that for industrial applications the sensor needs a reliable and robust traceability to the SI units, meter and second. Small deviations in the calibration can, because of the highly position depending calibration function, cause large systematic errors in the measurement result. Therefore, a simple, stable and accurate tool is needed, that can easily be used in industrial surroundings to check or recalibrate the sensor. In this work, different calibration methods are presented and their influences to the

  1. Deployable Emergency Shutoff Device Blocks High-Velocity Fluid Flows

    Science.gov (United States)

    Nabors, Sammy A.

    2015-01-01

    NASA's Marshall Space Flight Center has developed a device and method for blocking the flow of fluid from an open pipe. Motivated by the sea-bed oil-drilling catastrophe in the Gulf of Mexico in 2010, NASA innovators designed the device to plug, control, and meter the flow of gases and liquids. Anchored with friction fittings, spikes, or explosively activated fasteners, the device is well-suited for harsh environments and high fluid velocities and pressures. With the addition of instrumentation, it can also be used as a variable area flow metering valve that can be set based upon flow conditions. With robotic additions, this patent-pending innovation can be configured to crawl into a pipe then anchor and activate itself to block or control fluid flow.

  2. Data adaptive estimation of transversal blood flow velocities

    DEFF Research Database (Denmark)

    Pirnia, E.; Jakobsson, A.; Gudmundson, E.

    2014-01-01

    The examination of blood flow inside the body may yield important information about vascular anomalies, such as possible indications of, for example, stenosis. Current Medical ultrasound systems suffer from only allowing for measuring the blood flow velocity along the direction of irradiation......, posing natural difficulties due to the complex behaviour of blood flow, and due to the natural orientation of most blood vessels. Recently, a transversal modulation scheme was introduced to induce also an oscillation along the transversal direction, thereby allowing for the measurement of also...... the transversal blood flow. In this paper, we propose a novel data-adaptive blood flow estimator exploiting this modulation scheme. Using realistic Field II simulations, the proposed estimator is shown to achieve a notable performance improvement as compared to current state-of-the-art techniques....

  3. Thermistor based, low velocity isothermal, air flow sensor

    Science.gov (United States)

    Cabrita, Admésio A. C. M.; Mendes, Ricardo; Quintela, Divo A.

    2016-03-01

    The semiconductor thermistor technology is applied as a flow sensor to measure low isothermal air velocities (sensor is subjected to heating and cooling cycles controlled by a multifunctional timer. In the heating stage, the alternating current of a main AC power supply source guarantees a uniform thermistor temperature distribution. The conditioning circuit assures an adequate increase of the sensors temperature and avoids the thermal disturbance of the flow. The power supply interruption reduces the consumption from the source and extends the sensors life time. In the cooling stage, the resistance variation of the flow sensor is recorded by the measuring chain. The resistive sensor parameters proposed vary significantly and feature a high sensitivity to the flow velocity. With the aid of a computer, the data transfer, storage and analysis provides a great advantage over the traditional local anemometer readings. The data acquisition chain has a good repeatability and low standard uncertainties. The proposed method measures isothermal air mean velocities from 0.1 ms-1 to 2 ms-1 with a standard uncertainty error less than 4%.

  4. Volumetric velocity measurements on flows through heart valves

    Science.gov (United States)

    Troolin, Daniel; Amatya, Devesh; Longmire, Ellen

    2009-11-01

    Volumetric velocity fields inside two types of artificial heart valves were obtained experimentally through the use of volumetric 3-component velocimetry (V3V). Index matching was used to mitigate the effects of optical distortions due to interfaces between the fluid and curved walls. The steady flow downstream of a mechanical valve was measured and the results matched well with previously obtained 2D PIV results, such as those of Shipkowitz et al. (2002). Measurements upstream and downstream of a deformable silicone valve in a pulsatile flow were obtained and reveal significant three-dimensional features of the flow. Plots and movies will be shown, and a detailed discussion of the flow and various experimental considerations will be included. Reference: Shipkowitz, T, Ambrus J, Kurk J, Wickramasinghe K (2002) Evaluation technique for bileaflet mechanical valves. J. Heart Valve Disease. 11(2) pp. 275-282.

  5. On the measurement of lateral velocity derivatives in turbulent flows

    Science.gov (United States)

    Antonia, R. A.; Zhu, Y.; Kim, J.

    1993-01-01

    Direct numerical simulation data for the lateral velocity derivative delta(u)/delta(y) at the centerline of a fully developed turbulent channel flow provide reasonable support for Wyngaard's analysis of the error involved in measuring this quantity using parallel hot wires. Numerical data in the wall region of the channel flow also provide a useful indication of how to select the separation between the wires. Justification for this choice is obtained by comparing several measured statistics of delta(u)/delta(y) with the corresponding numerical data.

  6. Study on flow parameters of fractal porous media in the high-velocity fluid flow regime

    Science.gov (United States)

    Qi, Mei; Xu, Hui; Yang, Chao; Qu, Tailai; Kong, lingxiao; Wu, Shucheng; Zeng, Baoquan; Xu, Haixia

    2017-12-01

    High-velocity fluid flow, which will result in the region of the wellbore or fracture, is generally in the turbulent flow regime and has drawn tremendous attention in petroleum engineering field. Turbulent factor is the key parameter, which is widely used to describe high-velocity flow in porous media. In this work, a theoretical model for turbulent factor in fractal porous media in the high-velocity fluid flow regime is developed. Moreover, a novel analytical expression for the permeability in porous media based on Wu's resistance model is also derived. Then, the analytical Kozeny-Carman constant with no empirical constant is obtained. The predictions of permeability-porosity relation by the current mathematical models have been validated by comparing with available experimental data. Furthermore, the effects of structural parameters of porous media on the curve of velocity and pressure drop are discussed in detail.

  7. Assessment of orbital blood flow velocities in retinopathy of prematurity.

    Science.gov (United States)

    Ozcan, Pehmen Yasin; Dogan, Ferit; Sonmez, Kenan; Con, Rahim; Dokumaci, Dilek Sen; Seyhanli, Eyüp Sabri

    2017-08-01

    The purpose of this study is to evaluate whether the presence of any stage retinopathy of prematurity (ROP) alters central retinal artery (CRA) and ophthalmic artery (OA) blood flow parameters in premature infants. The patients were divided into two groups according to the development of ROP; those who have ROP were defined as group I, those without ROP were defined as group II. Ninety eyes of 45 patients in group I and 40 eyes of 20 patients in group II were investigated. The blood flows in the CRA and OA were measured using ultrasound color doppler imaging (CDI) that allows to evaluate the peak systolic velocity (PSV), end diastolic velocity (EDV), and resistivity index (RI). The results were compared between two groups of subjects. There were no significant differences in the PSV, EDV, and RI of CRA between two groups (P = 0.09, P = 0.20 and P = 0.63, respectively). The mean PSV value of OA in group I was found to be significantly higher than the one in group II (P  0.05), whereas the difference in the mean PSV values of OA were found to be significant among the eyes with stage 1 ROP, eyes with stage 2 ROP, and eyes without ROP (P = 0.03). This study demonstrated significant alterations in systolic flow velocities in the OA predicted by CDI in infants with ROP.

  8. Fourier analysis of cerebrospinal fluid flow velocities: MR imaging study. The Scandinavian Flow Group

    DEFF Research Database (Denmark)

    Thomsen, C; Ståhlberg, F; Stubgaard, M

    1990-01-01

    images. The phase information in the resultant image was converted to flow velocity with a calibration curve with the slope 26.5 radian.m-1.sec. The velocity versus time function was Fourier transformed and a continuous curve was fitted to the measured data with use of the first three harmonics...

  9. Discharge estimation combining flow routing and occasional measurements of velocity

    Directory of Open Access Journals (Sweden)

    G. Corato

    2011-09-01

    Full Text Available A new procedure is proposed for estimating river discharge hydrographs during flood events, using only water level data at a single gauged site, as well as 1-D shallow water modelling and occasional maximum surface flow velocity measurements. One-dimensional diffusive hydraulic model is used for routing the recorded stage hydrograph in the channel reach considering zero-diffusion downstream boundary condition. Based on synthetic tests concerning a broad prismatic channel, the "suitable" reach length is chosen in order to minimize the effect of the approximated downstream boundary condition on the estimation of the upstream discharge hydrograph. The Manning's roughness coefficient is calibrated by using occasional instantaneous surface velocity measurements during the rising limb of flood that are used to estimate instantaneous discharges by adopting, in the flow area, a two-dimensional velocity distribution model. Several historical events recorded in three gauged sites along the upper Tiber River, wherein reliable rating curves are available, have been used for the validation. The outcomes of the analysis can be summarized as follows: (1 the criterion adopted for selecting the "suitable" channel length based on synthetic test studies has proved to be reliable for field applications to three gauged sites. Indeed, for each event a downstream reach length not more than 500 m is found to be sufficient, for a good performances of the hydraulic model, thereby enabling the drastic reduction of river cross-sections data; (2 the procedure for Manning's roughness coefficient calibration allowed for high performance in discharge estimation just considering the observed water levels and occasional measurements of maximum surface flow velocity during the rising limb of flood. Indeed, errors in the peak discharge magnitude, for the optimal calibration, were found not exceeding 5% for all events observed in the three investigated gauged sections, while the

  10. The in situ permeable flow sensor: A device for measuring groundwater flow velocity

    International Nuclear Information System (INIS)

    Ballard, S.; Barker, G.T.; Nichols, R.L.

    1994-03-01

    A new technology called the In Situ Permeable Flow Sensor has been developed at Sandia National Laboratories. These sensors use a thermal perturbation technique to directly measure the direction and magnitude of the full three dimensional groundwater flow velocity vector in unconsolidated, saturated, porous media. The velocity measured is an average value characteristic of an approximately 1 cubic meter volume of the subsurface. During a test at the Savannah River Site in South Carolina, two flow sensors were deployed in a confined aquifer in close proximity to a well which was screened over the entire vertical extent of the aquifer and the well was pumped at four different pumping rates. In this situation horizontal flow which is radially directed toward the pumping well is expected. The flow sensors measured horizontal flow which was directed toward the pumping well, within the uncertainty in the measurements. The observed magnitude of the horizontal component of the flow velocity increased linearly with pumping rate, as predicted by theoretical considerations. The measured horizontal component of the flow velocity differed from the predicted flow velocity, which was calculated with the assumptions that the hydraulic properties of the aquifer were radially homogeneous and isotropic, by less than a factor of two. Drawdown data obtained from other wells near the pumping well during the pump test indicate that the hydraulic properties of the aquifer are probably not radially homogeneous but the effect of the inhomogeneity on the flow velocity field around the pumping well was not modeled because the degree and distribution of the inhomogeneity are unknown. Grain size analysis of core samples from wells in the area were used to estimate the vertical distribution of hydraulic conductivity

  11. Velocity profiles of fluid flow close to a hydrophobic surface

    Science.gov (United States)

    Fialová, Simona; Pochylý, František; Kotek, Michal; Jašíková, Darina

    The results of research on viscous liquid flow upon a superhydrophobic surface are presented in the paper. In the introduction, the degrees of surface hydrophobicity in correlation with an adhesion coefficient are defined. The usage of the adhesion coefficient for the definition of a new boundary condition is employed for expressing the slip of the liquid over the superhydrophobic surface. The slip of the liquid was identified on a special experimental device. The essence of the device consists of a tunnel of rectangular cross section whose one wall is treated with a superhydrophobic layer. The other walls are made of transparent organic glass whose surface is hydrophilic. Velocity profiles are measured by PIV. The methodology is drawn so that it allows the speed determination at the closest point to the wall. The measurements were performed for different Reynolds numbers for both laminar and turbulent flow. Based on the measured velocity profiles, marginal terms of use have been verified, expressing slippage of the liquid on the wall. New forms of velocity profiles considering superhydrophobic surfaces are shown within the work.

  12. Development of Hydroxyl Tagging Velocimetry for Low Velocity Flows

    Science.gov (United States)

    Andre, Matthieu A.; Bardet, Philippe M.; Burns, Ross A.; Danehy, Paul M.

    2016-01-01

    Hydroxyl tagging velocimetry (HTV) is a molecular tagging technique that relies on the photo-dissociation of water vapor into OH radicals and their subsequent tracking using laser induced fluorescence. Velocities are then obtained from time-of-flight calculations. At ambient temperature in air, the OH species lifetime is relatively short (PIV) measurements recorded in identical conditions. Single shot and averaged velocity profiles are obtained in an air jet at room temperature. By modestly raising the temperature (100-200 degC) the OH production increases, resulting in an improvement of the signal-to-noise ratio (SNR). Use of nitrogen - a non-reactive gas with minimal collisional quenching - extends the OH species lifetime (to over 500 µs), which allows probing of slower flows or, alternately, increases the measurement precision at the expense of spatial resolution. Instantaneous velocity profiles are resolved in a 100degC nitrogen jet (maximum jet-center velocity of 6.5 m/s) with an uncertainty down to 0.10 m/s (1.5%) at 68% confidence level. MTV measurements are compared with particle image velocimetry and show agreement within 2%.

  13. Velocity distribution in a turbulent flow near a rough wall

    Science.gov (United States)

    Korsun, A. S.; Pisarevsky, M. I.; Fedoseev, V. N.; Kreps, M. V.

    2017-11-01

    Velocity distribution in the zone of developed wall turbulence, regardless of the conditions on the wall, is described by the well-known Prandtl logarithmic profile. In this distribution, the constant, that determines the value of the velocity, is determined by the nature of the interaction of the flow with the wall and depends on the viscosity of the fluid, the dynamic velocity, and the parameters of the wall roughness.In extreme cases depending on the ratio between the thickness of the viscous sublayer and the size of the roughness the constant takes on a value that does not depend on viscosity, or leads to a ratio for a smooth wall.It is essential that this logarithmic profile is the result not only of the Prandtl theory, but can be derived from general considerations of the theory of dimensions, and also follows from the condition of local equilibrium of generation and dissipation of turbulent energy in the wall area. This allows us to consider the profile as a universal law of velocity distribution in the wall area of a turbulent flow.The profile approximation up to the maximum speed line with subsequent integration makes possible to obtain the resistance law for channels of simple shape. For channels of complex shape with rough walls, the universal profile can be used to formulate the boundary condition when applied to the calculation of turbulence models.This paper presents an empirical model for determining the constant of the universal logarithmic profile. The zone of roughness is described by a set of parameters and is considered as a porous structure with variable porosity.

  14. Velocity flow field and water level measurements in shoaling and breaking water waves

    CSIR Research Space (South Africa)

    Mukaro, R

    2010-01-01

    Full Text Available levels were measured using capacitive waves gauges, while the instantaneous velocity flow fields were measured using video techniques together with digital correlation techniques. The instantaneous velocity flow fields were further analyzed to yield...

  15. Application of velocity filtering to optical-flow passive ranging

    Science.gov (United States)

    Barniv, Yair

    1992-01-01

    The performance of the velocity filtering method as applied to optical-flow passive ranging under real-world conditions is evaluated. The theory of the 3-D Fourier transform as applied to constant-speed moving points is reviewed, and the space-domain shift-and-add algorithm is derived from the general 3-D matched filtering formulation. The constant-speed algorithm is then modified to fit the actual speed encountered in the optical flow application, and the passband of that filter is found in terms of depth (sensor/object distance) so as to cover any given range of depths. Two algorithmic solutions for the problems associated with pixel interpolation and object expansion are developed, and experimental results are presented.

  16. Middle cerebral artery flow velocity waveforms in fetal hypoxaemia.

    Science.gov (United States)

    Vyas, S; Nicolaides, K H; Bower, S; Campbell, S

    1990-09-01

    In 81 small-for-gestational age fetuses (SGA) colour flow imaging was used to identify the fetal middle cerebral artery for subsequent pulsed Doppler studies. Impedence to flow (pulsatility index; PI) was significantly lower, and mean blood velocity was significantly higher, than the respective reference ranges with gestation. Fetal blood sampling by cordocentesis was performed in all SGA fetuses and a significant quadratic relation was found between fetal hypoxaemia and the degree of reduction in the PI of FVWs from the fetal middle cerebral artery. Thus, maximum reduction in PI is reached when the fetal PO2 is 2-4 SD below the normal mean for gestation. When the oxygen deficit is greater there is a tendency for the PI to rise, and this presumably reflects the development of brain oedema.

  17. Ultrasonic 3-D Vector Flow Method for Quantitative In Vivo Peak Velocity and Flow Rate Estimation.

    Science.gov (United States)

    Holbek, Simon; Ewertsen, Caroline; Bouzari, Hamed; Pihl, Michael Johannes; Hansen, Kristoffer Lindskov; Stuart, Matthias Bo; Thomsen, Carsten; Nielsen, Michael Bachmann; Jensen, Jorgen Arendt

    2017-03-01

    Current clinical ultrasound (US) systems are limited to show blood flow movement in either 1-D or 2-D. In this paper, a method for estimating 3-D vector velocities in a plane using the transverse oscillation method, a 32×32 element matrix array, and the experimental US scanner SARUS is presented. The aim of this paper is to estimate precise flow rates and peak velocities derived from 3-D vector flow estimates. The emission sequence provides 3-D vector flow estimates at up to 1.145 frames/s in a plane, and was used to estimate 3-D vector flow in a cross-sectional image plane. The method is validated in two phantom studies, where flow rates are measured in a flow-rig, providing a constant parabolic flow, and in a straight-vessel phantom ( ∅=8 mm) connected to a flow pump capable of generating time varying waveforms. Flow rates are estimated to be 82.1 ± 2.8 L/min in the flow-rig compared with the expected 79.8 L/min, and to 2.68 ± 0.04 mL/stroke in the pulsating environment compared with the expected 2.57 ± 0.08 mL/stroke. Flow rates estimated in the common carotid artery of a healthy volunteer are compared with magnetic resonance imaging (MRI) measured flow rates using a 1-D through-plane velocity sequence. Mean flow rates were 333 ± 31 mL/min for the presented method and 346 ± 2 mL/min for the MRI measurements.

  18. Ultrasonic 3-D Vector Flow Method for Quantitative In Vivo Peak Velocity and Flow Rate Estimation

    DEFF Research Database (Denmark)

    Holbek, Simon; Ewertsen, Caroline; Bouzari, Hamed

    2017-01-01

    Current clinical ultrasound (US) systems are limited to show blood flow movement in either 1-D or 2-D. In this paper, a method for estimating 3-D vector velocities in a plane using the transverse oscillation method, a 32×32 element matrix array, and the experimental US scanner SARUS is presented....... The aim of this paper is to estimate precise flow rates and peak velocities derived from 3-D vector flow estimates. The emission sequence provides 3-D vector flow estimates at up to 1.145 frames/s in a plane, and was used to estimate 3-D vector flow in a cross-sectional image plane. The method...... is validated in two phantom studies, where flow rates are measured in a flow-rig, providing a constant parabolic flow, and in a straight-vessel phantom ( ∅=8 mm) connected to a flow pump capable of generating time varying waveforms. Flow rates are estimated to be 82.1 ± 2.8 L/min in the flow-rig compared...

  19. Peritumoral interstitial fluid flow velocity predicts survival in cervical carcinoma

    International Nuclear Information System (INIS)

    Hompland, Tord; Lund, Kjersti V.; Ellingsen, Christine; Kristensen, Gunnar B.; Rofstad, Einar K.

    2014-01-01

    Background and purpose: High tumor interstitial fluid pressure (IFP) is associated with poor outcome in locally advanced carcinoma of the uterine cervix. We have recently developed a noninvasive assay of the IFP of tumors, and in this assay, the outward interstitial fluid flow velocity at the tumor surface (v 0 ) is measured by Gd-DTPA-based DCE-MRI and used as a parameter for IFP. Here, we investigated the independent prognostic significance of v 0 in cervical cancer patients given cisplatin-based concurrent chemoradiotherapy with curative intent. Patients: The study involved 62 evaluable patients from a cohort of 74 consecutive patients (Stage IB through IIIB) with a median follow-up of 5.5 years. Results: The actuarial disease-free survival (DFS) and overall survival (OS) at 5 years were 67% and 76%, respectively. Significant associations were found between v 0 dichotomized about the median value and DFS and OS, both in the total patient cohort and a subcohort of 40 Stage IIB patients. Multivariate analysis involving stage, tumor volume, lymph node status, and v 0 revealed that only v 0 provided independent prognostic information about DFS and OS. Conclusion: This investigation demonstrates a strong, independent prognostic impact of the pretreatment peritumoral fluid flow velocity in cervical cancer

  20. Flow velocities and bed shear stresses in a stone cover under an oscillatory flow

    DEFF Research Database (Denmark)

    Stenanato, F.; Nielsen, Anders Wedel; Sumer, B. Mutlu

    2010-01-01

    layers of stones. The flow velocities in the pores of the stones were measured using LDA (Laser Doppler Anemometer). In addition to the velocity measurements, the bed shear stresses were also measured using a hotfilm (Constant Temperature Anemometry). It is found that the boundary layer of the outer flow...... current boundary layer without any externally generated turbulence. The bd shear stress is found to be very low, more than ten times smaller than in the case of a smooth base bottom without stone cover....

  1. Modelling of two-phase flow based on separation of the flow according to velocity

    Energy Technology Data Exchange (ETDEWEB)

    Narumo, T. [VTT Energy, Espoo (Finland). Nuclear Energy

    1997-12-31

    The thesis concentrates on the development work of a physical one-dimensional two-fluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model one-dimensional two-phase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. In the SFAV approach, the two-phase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for non-uniform transverse profile of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on two-phase flow wave phenomena Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtual-mass models that are typically optimized for special flow regimes like bubbly flow. The SFAV model has proved to be applicable in describing two-phase flow physically correctly because both the dynamics and steady-state behaviour of the model has been considered and found to agree well with experimental data This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors. 45 refs. The thesis includes also five previous publications by author.

  2. Modelling of two-phase flow based on separation of the flow according to velocity

    International Nuclear Information System (INIS)

    Narumo, T.

    1997-01-01

    The thesis concentrates on the development work of a physical one-dimensional two-fluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model one-dimensional two-phase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. In the SFAV approach, the two-phase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for non-uniform transverse profile of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on two-phase flow wave phenomena Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtual-mass models that are typically optimized for special flow regimes like bubbly flow. The SFAV model has proved to be applicable in describing two-phase flow physically correctly because both the dynamics and steady-state behaviour of the model has been considered and found to agree well with experimental data This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors

  3. Model-assisted measurements of suspension-feeding flow velocities.

    Science.gov (United States)

    Du Clos, Kevin T; Jones, Ian T; Carrier, Tyler J; Brady, Damian C; Jumars, Peter A

    2017-06-01

    Benthic marine suspension feeders provide an important link between benthic and pelagic ecosystems. The strength of this link is determined by suspension-feeding rates. Many studies have measured suspension-feeding rates using indirect clearance-rate methods, which are based on the depletion of suspended particles. Direct methods that measure the flow of water itself are less common, but they can be more broadly applied because, unlike indirect methods, direct methods are not affected by properties of the cleared particles. We present pumping rates for three species of suspension feeders, the clams Mya arenaria and Mercenaria mercenaria and the tunicate Ciona intestinalis , measured using a direct method based on particle image velocimetry (PIV). Past uses of PIV in suspension-feeding studies have been limited by strong laser reflections that interfere with velocity measurements proximate to the siphon. We used a new approach based on fitting PIV-based velocity profile measurements to theoretical profiles from computational fluid dynamic (CFD) models, which allowed us to calculate inhalant siphon Reynolds numbers ( Re ). We used these inhalant Re and measurements of siphon diameters to calculate exhalant Re , pumping rates, and mean inlet and outlet velocities. For the three species studied, inhalant Re ranged from 8 to 520, and exhalant Re ranged from 15 to 1073. Volumetric pumping rates ranged from 1.7 to 7.4 l h -1 for M . arenaria , 0.3 to 3.6 l h -1 for M . m ercenaria and 0.07 to 0.97 l h -1 for C . intestinalis We also used CFD models based on measured pumping rates to calculate capture regions, which reveal the spatial extent of pumped water. Combining PIV data with CFD models may be a valuable approach for future suspension-feeding studies. © 2017. Published by The Company of Biologists Ltd.

  4. Determination of groundwater flow velocity by radon measurements

    International Nuclear Information System (INIS)

    Hohn, E.; von Gunten, H.R.

    1990-01-01

    The groundwater resources of glacio-fluvial perialpine valleys are recharged significantly by the infiltration from rivers. The groundwater residence times between rivers and wells should be known in groundwater management problems. Short residence times can be estimated using radon. Radon concentrations in rivers are usually very low. Upon filtration and movement of the water in the ground, radon is picked up and its concentration increases by 2-3 orders of magnitude according to radioactive growth laws. Residence times and flow velocities can be estimated from the increasing radon concentrations measured in groundwater sampling tubes at different distances from the river. Results obtained with this method agree with the results from experiments with artificial tracers

  5. Meta-analysis on Macropore Flow Velocity in Soils

    Science.gov (United States)

    Liu, D.; Gao, M.; Li, H. Y.; Chen, X.; Leung, L. R.

    2017-12-01

    Macropore flow is ubiquitous in the soils and an important hydrologic process that is not well explained using traditional hydrologic theories. Macropore Flow Velocity (MFV) is an important parameter used to describe macropore flow and quantify its effects on runoff generation and solute transport. However, the dominant factors controlling MFV are still poorly understood and the typical ranges of MFV measured at the field are not defined clearly. To address these issues, we conducted a meta-analysis based on a database created from 246 experiments on MFV collected from 76 journal articles. For a fair comparison, a conceptually unified definition of MFV is introduced to convert the MFV measured with different approaches and at various scales including soil core, field, trench or hillslope scales. The potential controlling factors of MFV considered include scale, travel distance, hydrologic conditions, site factors, macropore morphologies, soil texture, and land use. The results show that MFV is about 2 3 orders of magnitude larger than the corresponding values of saturated hydraulic conductivity. MFV is much larger at the trench and hillslope scale than at the field profile and soil core scales and shows a significant positive correlation with the travel distance. Generally, higher irrigation intensity tends to trigger faster MFV, especially at field profile scale, where MFV and irrigation intensity have significant positive correlation. At the trench and hillslope scale, the presence of large macropores (diameter>10 mm) is a key factor determining MFV. The geometric mean of MFV for sites with large macropores was found to be about 8 times larger than those without large macropores. For sites with large macropores, MFV increases with the macropore diameter. However, no noticeable difference in MFV has been observed among different soil texture and land use. Comparing the existing equations to describe MFV, the Poiseuille equation significantly overestimated the

  6. Optical Flow Cell for Measuring Size, Velocity and Composition of Flowing Droplets

    Directory of Open Access Journals (Sweden)

    Sammer-ul Hassan

    2017-02-01

    Full Text Available Here an optical flow cell with two light paths is reported that can accurately quantify the size and velocity of droplets flowing through a microchannel. The flow cell can measure the time taken for droplets to pass between and through two conjoined light paths, and thereby is capable of measuring the velocities (0.2–5.45 mm/s and sizes of droplets (length > 0.8 mm. The composition of the droplet can also be accurately quantified via optical absorption measurements. The device has a small footprint and uses low-powered, low-cost components, which make it ideally suited for use in field-deployable and portable analytical devices.

  7. Thermal particle image velocity estimation of fire plume flow

    Science.gov (United States)

    Xiangyang Zhou; Lulu Sun; Shankar Mahalingam; David R. Weise

    2003-01-01

    For the purpose of studying wildfire spread in living vegetation such as chaparral in California, a thermal particle image velocity (TPIV) algorithm for nonintrusively measuring flame gas velocities through thermal infrared (IR) imagery was developed. By tracing thermal particles in successive digital IR images, the TPIV algorithm can estimate the velocity field in a...

  8. Dual-beam optical coherence tomography system for quantification of flow velocity in capillary phantoms

    Science.gov (United States)

    Daly, S. M.; Silien, C.; Leahy, M. J.

    2012-03-01

    The quantification of (blood) flow velocity within the vasculature has potent diagnostic and prognostic potential. Assessment of flow irregularities in the form of increased permeability (micro haemorrhaging), the presence of avascular areas, or conversely the presence of vessels with enlarged or increased tortuosity in the acral regions of the body may provide a means of non-invasive in vivo assessment. If assessment of dermal flow dynamics were performed in a routine manner, the existence and prevalence of ailments such as diabetes mellitus, psoriatic arthritis and Raynaud's condition may be confirmed prior to clinical suspicion. This may prove advantageous in cases wherein the efficacy of a prescribed treatment is dictated by a prompt diagnosis and to alleviate patient discomfort through early detection. Optical Coherence Tomography (OCT) is an imaging modality which utilises the principle of optical interferometry to distinguish between spatial changes in refractive index within the vasculature and thus formulate a multi-dimensional representation of the structure of the epi- and dermal skin layers. The use of the Doppler functionality has been the predominant force for the quantification of moving particles within media, elucidated via estimation of the phase shift in OCT A-scans. However, the theoretical formulation for the assessment of these phase shifts dictates that the angle between the incident light source and the vessel under question be known a priori; this may be achieved via excisional biopsy of the tissue segment in question, but is counter to the non-invasive premise of the OCT technique. To address the issue of angular dependence, an alternate means of estimating absolute flow velocity is presented. The design and development of a dual-beam (db) system incorporating an optical switch mechanism for signal discrimination of two spatially disparate points enabling quasi-simultaneous multiple specimen scanning is described. A crosscorrelation (c

  9. Behavior of instantaneous lateral velocity and flow pulsation in duct flow with cylindrical rod

    International Nuclear Information System (INIS)

    Lee, Chi Young; Shin, Chang Hwan; Park, Ju Yong; Oh, Dong Seok; Chun, Tae Hyun; In, Wang Kee

    2012-01-01

    Recently, KAERI (Korea Atomic Energy Research Institute) has examined and developed a dual cooled annular fuel. Dual cooled annular fuel allows the coolant to flow through the inner channel as well as the outer channel. Due to inner channel, the outer diameter of dual cooled annular fuel (15.9 mm) is larger than that of conventional cylindrical solid fuel (9.5 mm). Hence, dual cooled annular fuel assembly becomes a tight lattice fuel bundle configuration to maintain the same array size and guide tube locations as cylindrical solid fuel assembly. P/Ds (pitch between rods to rod diameter ratio) of dual cooled annular and cylindrical solid fuel assemblies are 1.08 and 1.35, respectively. This difference of P/D could change the behavior of turbulent flow in rod bundle. Our research group has investigated a turbulent flow parallel to the fuel rods using two kinds of simulated 3x3 rod bundles. To measure the turbulent rod bundle flow, PIV (Particle Image Velocimetry) and MIR (Matching Index of Refraction) techniques were used. In a simulated dual cooled annular fuel bundle (i.e., P/D=1.08), the quasi periodic oscillating flow motion in the lateral direction, called the flow pulsation, was observed, which significantly increased the lateral turbulence intensity at the rod gap center. The flow pulsation was visualized and measured clearly and successfully by PIV and MIR techniques. Such a flow motion may have influence on the fluid induced vibration, heat transfer, CHF (Critical Heat Flux), and flow mixing between subchannels in rod bundle flow. On the other hand, in a simulated cylindrical solid fuel bundle (i.e., P/D=1.35), the peak of turbulence intensity at the gap center was not measured due to an irregular motion of the lateral flow. This study implies that the behavior of lateral velocity in rod bundle flow is greatly influenced by the P/D (i.e., gap distance). In this work, the influence of gap distance on behavior of instantaneous lateral velocity and flow

  10. Exploiting LSPIV to assess debris-flow velocities in the field

    Science.gov (United States)

    Theule, Joshua I.; Crema, Stefano; Marchi, Lorenzo; Cavalli, Marco; Comiti, Francesco

    2018-01-01

    The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

  11. Exploiting LSPIV to assess debris-flow velocities in the field

    Directory of Open Access Journals (Sweden)

    J. I. Theule

    2018-01-01

    Full Text Available The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek. Free software has been employed for preliminary treatment (orthorectification and format conversion of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

  12. Accelerated and Decelerated Flows in a Circular Pipe : 1st Report, Velocity Profile and Friction Coefficient

    OpenAIRE

    Kurokawa, Junichi; Morikawa, Masahiro

    1986-01-01

    In order to determine the flow characteristics of a transient flow in a circular pipe, an accelerated and a decelerated flow are studied, and effects of acceleration upon the formation of a velocity profile, transition and a friction coefficient are determined for a wide range of accelerations. The results of the accelerated flow show that there are two patterns in the formation of a sectional velocity profile and transition, one of which is observed when the acceleration is relatively large ...

  13. Velocity bias induced by flow patterns around ADCPs and associated deployment platforms

    Science.gov (United States)

    Mueller, David S.

    2015-01-01

    Velocity measurements near the Acoustic Doppler Current Profiler (ADCP) are important for mapping surface currents, measuring velocity and discharge in shallow streams, and providing accurate estimates of discharge in the top unmeasured portion of the water column. Improvements to ADCP performance permit measurement of velocities much closer (5 cm) to the transducer than has been possible in the past (25 cm). Velocity profiles collected by the U.S. Geological Survey (USGS) with a 1200 kHz Rio Grande Zedhead ADCP in 2002 showed a negative bias in measured velocities near the transducers. On the basis of these results, the USGS initiated a study combining field, laboratory, and numerical modeling data to assess the effect of flow patterns caused by flow around the ADCP and deployment platforms on velocities measured near the transducers. This ongoing study has shown that the negative bias observed in the field is due to the flow pattern around the ADCP. The flow pattern around an ADCP violates the basic assumption of flow homogeneity required for an accurate three-dimensional velocity solution. Results, to date (2014), have indicated velocity biases within the measurable profile, due to flow disturbance, for the TRDI 1200 kHz Rio Grande Zedhead and the SonTek RiverSurveyor M9 ADCPs. The flow speed past the ADCP, the mount and the deployment platform have also been shown to play an important role in the magnitude and extent of the velocity bias.

  14. Directional velocity estimation using focusing along the flow direction II: Experimental investigation

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt; Bjerngaard, R.

    2003-01-01

    A new method for directional velocity estimation is investigated through a number of flow rig measurements. The method uses beamformation along the flow direction to generate data, where the correct velocity magnitude can directly be estimated from the shift in position of the received consecutive...

  15. Carotid flow velocity/diameter ratio is a predictor of cardiovascular events in hypertensive patients

    DEFF Research Database (Denmark)

    Bellinazzi, Vera R; Cipolli, José A; Pimenta, Marcio V

    2015-01-01

    OBJECTIVE: The aim of this study was to evaluate the performance of common carotid artery diameter, flow velocity and flow velocity/artery diameter ratio as predictors of major adverse cardiovascular events (MACEs) in a sample of hypertensive patients. METHODS: A cohort of 403 hypertensive patien...

  16. Cardiac and extra-cardiac flow velocity waveforms in the growth-retarded human fetus

    NARCIS (Netherlands)

    I.A.L. Groenenberg (Irene)

    1991-01-01

    textabstractThe central theme in this thesis is the documentation of Doppler flow velocity waveforms in a number of cardiac and extra-cardiac arterial vessels with emphasis on changes in the flow velocity waveforms relative to intrauterine growth retardation and fetal and neonatal condition. The

  17. A Raman anemometer for component-selective velocity measurements of particles in a flow

    NARCIS (Netherlands)

    Florisson, O.; de Mul, F.F.M.; de Winter, H.G.

    1981-01-01

    An anemometer for the measurement of the velocity of particles of different components in a flow, separate and apart from that of the flow itself, is described. As a component-selective mechanism Raman scattering is used. The velocity is measured by relating the autocorrelated scattering signal to

  18. Laser transit anemometer measurements of a JANNAF nozzle base velocity flow field

    Science.gov (United States)

    Hunter, William W., Jr.; Russ, C. E., Jr.; Clemmons, J. I., Jr.

    1990-01-01

    Velocity flow fields of a nozzle jet exhausting into a supersonic flow were surveyed. The measurements were obtained with a laser transit anemometer (LTA) system in the time domain with a correlation instrument. The LTA data is transformed into the velocity domain to remove the error that occurs when the data is analyzed in the time domain. The final data is shown in velocity vector plots for positions upstream, downstream, and in the exhaust plane of the jet nozzle.

  19. Influence of slip velocity in Herschel-Bulkley fluid flow between parallel plates - A mathematical study

    International Nuclear Information System (INIS)

    Sankar, D. S.; Lee, U Sik

    2016-01-01

    This theoretical study investigates three types of basic flows of viscous incompressible Herschel-Bulkley fluid such as (i) plane Couette flow, (ii) Poiseuille flow and (iii) generalized Couette flow with slip velocity at the boundary. The analytic solutions to the nonlinear boundary value problems have been obtained. The effects of various physical parameters on the velocity, flow rate, wall shear stress and frictional resistance to flow are analyzed through appropriate graphs. It is observed that in plane Poiseuille flow and generalized Couette flow, the velocity and flow rate of the fluid increase considerably with the increase of the slip parameter, power law index, pressure gradient. The fluid velocity is significantly higher in plane Poiseuille flow than in plane Couette flow. The wall shear stress and frictional resistance to flow decrease considerably with the increase of the power law index and increase significantly with the increase of the yield stress of the fluid. The wall shear stress and frictional resistance to flow are considerably higher in plane Poiseuille flow than in generalized Couette flow.

  20. High resolution measurement of the velocity profiles of channel flows using the particle image velocimetry technique

    International Nuclear Information System (INIS)

    Nor Azizi Mohamed

    2000-01-01

    The high resolution velocity profiles of a uniform steady channel flow and a flow beneath waves were obtained using the particle image velocimetry (PIV) technique. The velocity profiles for each flow were calculated for both components. It is shown that the profiles obtained are very precise, displaying the point velocities from a few millimeters from the bottom of the channel up to the water surface across the water depth. In the case of the wave-induced flow, the profiles are shown under the respective wave phases and given in a plane representation. High resolution measurement of point velocities in a flow is achievable using PIV and invaluable when applied to a complex flow. (Author)

  1. Entropy-Based Modeling of Velocity Lag in Sediment-Laden Open Channel Turbulent Flow

    Directory of Open Access Journals (Sweden)

    Manotosh Kumbhakar

    2016-08-01

    Full Text Available In the last few decades, a wide variety of instruments with laser-based techniques have been developed that enable experimentally measuring particle velocity and fluid velocity separately in particle-laden flow. Experiments have revealed that stream-wise particle velocity is different from fluid velocity, and this velocity difference is commonly known as “velocity lag” in the literature. A number of experimental, as well as theoretical investigations have been carried out to formulate deterministic mathematical models of velocity lag, based on several turbulent features. However, a probabilistic study of velocity lag does not seem to have been reported, to the best of our knowledge. The present study therefore focuses on the modeling of velocity lag in open channel turbulent flow laden with sediment using the entropy theory along with a hypothesis on the cumulative distribution function. This function contains a parameter η, which is shown to be a function of specific gravity, particle diameter and shear velocity. The velocity lag model is tested using a wide range of twenty-two experimental runs collected from the literature and is also compared with other models of velocity lag. Then, an error analysis is performed to further evaluate the prediction accuracy of the proposed model, especially in comparison to other models. The model is also able to explain the physical characteristics of velocity lag caused by the interaction between the particles and the fluid.

  2. Comparison of fluid-dynamic modeling of flow with velocity-encoded MR imaging

    International Nuclear Information System (INIS)

    Sun, Y.; Hearshen, D.O.; Rankin, G.W.; Haggar, A.M.

    1990-01-01

    This paper develops a fluid dynamic model using finite difference methods characterizing flow in phantoms simulating in vivo conditions and to compare those results with velocity encoded MR images. The phantom consisted of 1-inch (2.5-cm) tubing with semicircular insert and fluid with viscosity, T1, and T2 comparable to blood. Numeric solutions to Navier-Stokes equations for this system were obtained using finite difference methods, with velocity input function of zero at walls and parabolic at both ends. In resulting color raster (CR) images, color temperature represented velocity value. In velocity-encoded MR images acquired under the same flow conditions, phase is proportional to average velocity during application of flow-encoding gradients. Because these gradients are applied along one direction per acquisition, magnitude and direction of velocity are obtained

  3. Effect of stone content on water flow velocity over Loess slope: non-frozen soil

    Science.gov (United States)

    Ban, Yunyun; Lei, Tingwu; Gao, Yuan; Qu, Liqin

    2017-06-01

    Stony soils are commonly found worldwide and are considerably studied for their hydrological characteristics and effect on soil erosion. Water flow velocity is an important parameter in understanding the effect of stone content on hydrodynamics and soil erosion. In this study, laboratory experiments were used to measure rill flow velocity by using electrolyte tracer method under different hydraulic conditions: flow rates of 1, 2, 4, and 8 L/min, slope gradients of 5°, 10°, 15°, and 20°, and stone mass contents amounting to 0%, 10%, 20% and 50%. Nine sensors, which were 1 m apart along the 8 m long rill, were used to measure flow velocity by tracing solute transport. Measured flow velocity increased with slope gradient and flow rate. The highest increase in flow velocity was measured from 15° to 20° which were also affected by flow rate. Effects of discharge rate on flow velocity presented the largest difference when flow rate increased from 2 L/min to 8 L/min at slope gradients higher than 5°. The effects of different factors were quantified by a regression model with high accuracy of 0.99. Maximum flow velocity of water was predicted at 15.23% of stone content. Flow velocity increased with 0-15.23% of stone content but decreased at higher values. This study aims at further understanding the hydrodynamics of soil erosion and sediment transport behaviors in hillslopes with different stone contents to obtain information for quantifying soil erosion on stony slopes.

  4. Velocity profile variations in granular flows with changing boundary conditions: insights from experiments

    Science.gov (United States)

    Schaefer, Marius; Bugnion, Louis

    2013-06-01

    We present results of detailed velocity profile measurements in a large series of granular flow experiments in a dam-break setup. The inclination angle, bead size, and roughness of the running surface were varied. In all experiments, the downstream velocity profiles changed continuously from the head to the tail of the avalanches. On rough running surfaces, an inflection point developed in the velocity profiles. These velocity profiles cannot be modeled by the large class of constitutive laws which relate the shear stress to a power law of the strain rate. The velocity profile shape factor increased from the head to the tail of the avalanches. Its maximum value grew with increasing roughness of the running surface. We conclude that flow features such as velocity profiles are strongly influenced by the boundary condition at the running surface, which depends on the ratio of bead size to the typical roughness length of the surface. Furthermore, we show that varying velocity profile shape factors inside gravitationally driven finite-mass flows give rise to an additional term in the depth-averaged momentum equation, which is normally solved in the simulation software of hazardous geophysical flows. We therefore encourage time dependent velocity profile measurements inside hazardous geophysical flows, to learn about the importance of this "new" term in the mathematical modeling of these flows.

  5. Scaling of peak flows with constant flow velocity in random self-similar networks

    Science.gov (United States)

    Troutman, Brent M.; Mantilla, Ricardo; Gupta, Vijay K.

    2011-01-01

    A methodology is presented to understand the role of the statistical self-similar topology of real river networks on scaling, or power law, in peak flows for rainfall-runoff events. We created Monte Carlo generated sets of ensembles of 1000 random self-similar networks (RSNs) with geometrically distributed interior and exterior generators having parameters pi and pe, respectively. The parameter values were chosen to replicate the observed topology of real river networks. We calculated flow hydrographs in each of these networks by numerically solving the link-based mass and momentum conservation equation under the assumption of constant flow velocity. From these simulated RSNs and hydrographs, the scaling exponents β and φ characterizing power laws with respect to drainage area, and corresponding to the width functions and flow hydrographs respectively, were estimated. We found that, in general, φ > β, which supports a similar finding first reported for simulations in the river network of the Walnut Gulch basin, Arizona. Theoretical estimation of β and φ in RSNs is a complex open problem. Therefore, using results for a simpler problem associated with the expected width function and expected hydrograph for an ensemble of RSNs, we give heuristic arguments for theoretical derivations of the scaling exponents β(E) and φ(E) that depend on the Horton ratios for stream lengths and areas. These ratios in turn have a known dependence on the parameters of the geometric distributions of RSN generators. Good agreement was found between the analytically conjectured values of β(E) and φ(E) and the values estimated by the simulated ensembles of RSNs and hydrographs. The independence of the scaling exponents φ(E) and φ with respect to the value of flow velocity and runoff intensity implies an interesting connection between unit hydrograph theory and flow dynamics. Our results provide a reference framework to study scaling exponents under more complex scenarios

  6. Scaling of peak flows with constant flow velocity in random self-similar networks

    Directory of Open Access Journals (Sweden)

    R. Mantilla

    2011-07-01

    Full Text Available A methodology is presented to understand the role of the statistical self-similar topology of real river networks on scaling, or power law, in peak flows for rainfall-runoff events. We created Monte Carlo generated sets of ensembles of 1000 random self-similar networks (RSNs with geometrically distributed interior and exterior generators having parameters pi and pe, respectively. The parameter values were chosen to replicate the observed topology of real river networks. We calculated flow hydrographs in each of these networks by numerically solving the link-based mass and momentum conservation equation under the assumption of constant flow velocity. From these simulated RSNs and hydrographs, the scaling exponents β and φ characterizing power laws with respect to drainage area, and corresponding to the width functions and flow hydrographs respectively, were estimated. We found that, in general, φ > β, which supports a similar finding first reported for simulations in the river network of the Walnut Gulch basin, Arizona. Theoretical estimation of β and φ in RSNs is a complex open problem. Therefore, using results for a simpler problem associated with the expected width function and expected hydrograph for an ensemble of RSNs, we give heuristic arguments for theoretical derivations of the scaling exponents β(E and φ(E that depend on the Horton ratios for stream lengths and areas. These ratios in turn have a known dependence on the parameters of the geometric distributions of RSN generators. Good agreement was found between the analytically conjectured values of β(E and φ(E and the values estimated by the simulated ensembles of RSNs and hydrographs. The independence of the scaling exponents φ(E and φ with respect to the value of flow velocity and runoff intensity implies an interesting connection between unit

  7. Effect of stone content on water flow velocity over Loess slope: Frozen soil

    Science.gov (United States)

    Ban, Yunyun; Lei, Tingwu; Feng, Ren; Qian, Dengfeng

    2017-11-01

    Soils in high-altitude or -latitude regions are commonly rich in stone fragments, which are frequently frozen. The hydrodynamics of water flow over frozen, stony slopes must be investigated to understand soil erosion and sediment transportation. The objective of this laboratory experiments was to measure water flow velocity over frozen slopes with different stone contents by using electrolyte trace method. The experiments were performed under slope gradients of 5°, 10°, 15°, and 20°; flow discharge rates of 1, 2, 4, and 8 L/min; and stone contents of 0%, 10%, 20%, and 50% on mass basis. Nine equidistant sensors were used to measure flow velocity along flume from the top of the slope. Results indicated that stone content significantly affected flow velocity under increasing slope gradient. The increase in stone content rapidly reduced the flow velocity. The flow velocities over frozen slopes were 1.21 to 1.30 times of those over non-frozen slopes under different slope gradients and flow rates. When the stone content increased from 0% to 20%, proportions gradually decreased from 52% to 25% and 13%. Additionally, flow velocities over frozen and non-frozen soil slopes became gradually similar with increasing stone content. This study will help elucidate the hydrodynamics, soil erosion, and sediment transport behaviors of frozen or partially unfrozen hillslopes with different stone contents.

  8. The influence of flow velocity on electrochemical reaction of metal surface

    Science.gov (United States)

    Li, Zhen; Zhang, Jiding

    2017-12-01

    In order to find out the effect of fluid flow velocity on electrochemical reaction, the electrochemical parameters of super 13Cr stainless steel in 3.5% NaCl aqueous solution were measured by a jet flow system at different flow velocities. The electrochemical characters such as open-circuit potential and polarization curve were monitored online using a three-electrode electrochemical system. The results show that the increase of wall shear stress caused by the high flow velocity leads to the rupture of passive films and the exposure of fresh metal in the corrosive media, which causes the increase of corrosion rate. Meanwhile, the corrosion rate shows a significant growth when the flow velocity is less than 0∼10.0 m/s. But it gradually decreases after reaching a maximum value.

  9. A 2D particle velocity sensor with minimal flow disturbance

    NARCIS (Netherlands)

    Pjetri, O.; Wiegerink, Remco J.; Krijnen, Gijsbertus J.M.

    2016-01-01

    A 2D sound particle velocity sensor, consisting of a cross of two connected, heated wires is presented. We developed a fabrication process by which the wires become freely suspended 350 micrometer above the chip surface. This largely eliminates the influence of boundary layer effects and increases

  10. Reduced frequency of embolic signals in severe carotid stenosis with poststenotic flow velocity reduction.

    Science.gov (United States)

    Goertler, Michael; Blaser, Till; Guhr, Susanne; Lotze, Heike; Heisinger, Jane; Kropf, Siegfried; Wallesch, Claus-Werner

    2005-01-01

    We aimed to investigate the effect of poststenotic low blood flow in patients with recently symptomatic severe carotid stenosis on arterio-arterial embolism. Analyses based on a series of 206 consecutive patients (155 men and 51 women, mean age 65.3 years) with a nondisabling ischemic event in the anterior circulation or =30% local diameter reduction). All patients underwent Doppler/duplex sonography, which included measurement of poststenotic flow velocity as an indicator for poststenotic blood flow as well as a 1-hour transcranial Doppler monitoring for the detection of embolic signals. Thirty-seven of two hundred and six patients had very severe stenosis which was associated with reduced poststenotic flow velocity ( or =90% local diameter reduction if poststenotic flow velocity was not reduced. Reduced poststenotic flow velocity in patients with very severe stenosis was associated with a significantly lower frequency of embolic signals compared to patients with the same degree of stenosis but no velocity reduction (adjusted odds ratio 0.15, 95% confidence interval 0.025-0.897, p = 0.038, adjustment for antiplatelet medication and time since ischemia). Low poststenotic flow velocity behind very severe internal carotid stenosis reduces the otherwise high frequency of embolic signals in recently symptomatic patients corroborating the hypothesis that reduced blood flow across carotid stenosis causes reduced embolism. Copyright 2005 S. Karger AG, Basel.

  11. Improved flow velocity estimates from moving-boat ADCP measurements

    NARCIS (Netherlands)

    Vermeulen, B.; Hoitink, A.J.F.; Sassi, M.G.

    2014-01-01

    Acoustic Doppler current profilers (ADCPs) are the current standard for flow measurements in large-scale open water systems. Existing techniques to process vessel-mounted ADCP data assume homogeneous or linearly changing flow between the acoustic beams. This assumption is likely to fail but is

  12. GALAXY CLUSTER BULK FLOWS AND COLLISION VELOCITIES IN QUMOND

    Energy Technology Data Exchange (ETDEWEB)

    Katz, Harley; McGaugh, Stacy; Teuben, Peter [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Angus, G. W., E-mail: hkatz@astro.umd.edu, E-mail: stacy.mcgaugh@case.edu, E-mail: teuben@astro.umd.edu, E-mail: angus.gz@gmail.com [Astrophysics, Cosmology and Gravity Centre, University of Cape Town, Private Bag X3, Rondebosch 7700 (South Africa)

    2013-07-20

    We examine the formation of clusters of galaxies in numerical simulations of a QUMOND cosmogony with massive sterile neutrinos. Clusters formed in these exploratory simulations develop higher velocities than those found in {Lambda}CDM simulations. The bulk motions of clusters attain {approx}1000 km s{sup -1} by low redshift, comparable to observations whereas {Lambda}CDM simulated clusters tend to fall short. Similarly, high pairwise velocities are common in cluster-cluster collisions like the Bullet Cluster. There is also a propensity for the most massive clusters to be larger in QUMOND and to appear earlier than in {Lambda}CDM, potentially providing an explanation for ''pink elephants'' like El Gordo. However, it is not obvious that the cluster mass function can be recovered.

  13. Discrete Velocity Method for Simulating Rarefied Gas Flows with Plasma

    Data.gov (United States)

    National Aeronautics and Space Administration — I am proposing to develop a low cost computational method capable of simulating conditions during atmospheric reentry, where the flow is rarefied and ionized. To do...

  14. Pressure and velocity dependence of flow-type cavitation erosion

    CSIR Research Space (South Africa)

    Auret, JG

    1993-12-01

    Full Text Available for chemically corrosive waters, the disc, test chamber, stators, drive shaft, valves, reservoir and all connections were made of stainless steel, while pump ~mponents were nickel plated. The flow system was completed by reinforced...

  15. Blood flow velocity imaging of malignant melanoma by micro multipoint laser Doppler velocimetry

    Science.gov (United States)

    Ishida, H.; Andoh, T.; Akiguchi, S.; Shirakawa, H.; Kobayashi, D.; Kuraishi, Y.; Hachiga, T.

    2010-09-01

    We have developed a laser Doppler velocimeter to measure blood flow, the micromultipoint laser Doppler velocimeter (μ-MLDV). This equipment can measure absolute velocity and, based on this, can display the course of blood vessels. In this study, we attempted to perform blood flow velocity imaging of malignant melanoma transplanted to the mouse ear. We found that blood flow velocity of the formed blood vessels originating in the melanoma was much greater than that of the capillary vessels in normal skin. Furthermore, the form of the tumor was clearly visible from the blood flow velocity image. These experimental results suggest that μ-MLDV has potential as a diagnostic method for distinguishing benign nevi from malignant melanomas.

  16. Flow Velocity and Morphology of a Submerged Patch of the Aquatic Species

    NARCIS (Netherlands)

    Cornacchia, L.; Licci, S.; van de Koppel, J.; van der Wal, D.; Wharton, G.; Puijalon, S.; Bouma, T.J.

    2016-01-01

    The interaction between macrophytes and hydrodynamic conditions is animportant feature in many aquatic ecosystems. Submerged macrophytes can formmonospecific patches that interact with the flow and alter current velocity; withinthe same vegetation patch, plants are exposed to different levels of

  17. Effect of electrical stimulation on blood flow velocity and vessel size

    Directory of Open Access Journals (Sweden)

    Jin Hee-Kyung

    2017-03-01

    Full Text Available Interferential current electrical stimulation alters blood flow velocity and vessel size. We aimed to investigate the changes in the autonomic nervous system depending on electrical stimulation parameters.

  18. Outer region scaling using the freestream velocity for nonuniform open channel flow over gravel

    Science.gov (United States)

    Stewart, Robert L.; Fox, James F.

    2017-06-01

    The theoretical basis for outer region scaling using the freestream velocity for nonuniform open channel flows over gravel is derived and tested for the first time. Owing to the gradual expansion of the flow within the nonuniform case presented, it is hypothesized that the flow can be defined as an equilibrium turbulent boundary layer using the asymptotic invariance principle. The hypothesis is supported using similarity analysis to derive a solution, followed by further testing with experimental datasets. For the latter, 38 newly collected experimental velocity profiles across three nonuniform flows over gravel in a hydraulic flume are tested as are 43 velocity profiles previously published in seven peer-reviewed journal papers that focused on fluid mechanics of nonuniform open channel over gravel. The findings support the nonuniform flows as equilibrium defined by the asymptotic invariance principle, which is reflective of the consistency of the turbulent structure's form and function within the expanding flow. However, roughness impacts the flow structure when comparing across the published experimental datasets. As a secondary objective, we show how previously published mixed scales can be used to assist with freestream velocity scaling of the velocity deficit and thus empirically account for the roughness effects that extend into the outer region of the flow. One broader finding of this study is providing the theoretical context to relax the use of the elusive friction velocity when scaling nonuniform flows in gravel bed rivers; and instead to apply the freestream velocity. A second broader finding highlighted by our results is that scaling of nonuniform flow in gravel bed rivers is still not fully resolved theoretically since mixed scaling relies to some degree on empiricism. As researchers resolve the form and function of macroturbulence in the outer region, we hope to see the closing of this research gap.

  19. Ultrasonic Measurement of Velocity Profile on Bubbly Flow Using Fast Fourier Transform (FFT) Technique

    Science.gov (United States)

    Wongsaroj, W.; Hamdani, A.; Thong-un, N.; Takahashi, H.; Kikura, H.

    2017-10-01

    In two-phase bubbly flow, measurement of liquid and bubble velocity is a necessity to understand fluid characteristic. The conventional ultrasonic velocity profiler (UVP), which has been known as a nonintrusive measurement technique, can measure velocity profile of liquid and bubble simultaneously by applying a separation technique for both phases (liquid and bubble) and transparent test section is unnecessary. The aim of this study was to develop a new technique for separating liquid and bubble velocity data in UVP method to measure liquid and bubble velocity profiles separately. The technique employs only single resonant frequency transducer and a simple UVP system. An extra equipment is not required. Fast Fourier Transform (FFT) based frequency estimator paralleled with other signal processing techniques, which is called as proposed technique, was proposed to measure liquid and bubble velocity separately. The experimental facility of two-phase bubbly flow in the vertical pipe was constructed. Firstly, the Doppler frequency estimation by using the FFT technique was evaluated in single-phase liquid flow. Results showed that FFT technique showed a good agreement with autocorrelation and maximum likelihood estimator. Then, separation of liquid and bubble velocity was demonstrated experimentally in the two-phase bubbly flow. The proposed technique confirmed that liquid and bubble velocity could be measured efficiently.

  20. Reference values of fetal peak systolic blood flow Velocity in the ...

    African Journals Online (AJOL)

    Objectives: The objectives of this prospective cross sectional study are (i) to establish new reference values of peak systolic blood flow velocity measurement in the fetal middle cerebral artery (MCA-PSV) following validated methodological guidelines (ii) to correlate peak systolic velocity with gestational age and (iii) to ...

  1. Middle cerebral artery flow velocity and blood flow during exercise and muscle ischemia in humans

    DEFF Research Database (Denmark)

    Jørgensen, L G; Perko, M; Hanel, B

    1992-01-01

    Changes in middle cerebral artery flow velocity (Vmean), measured by transcranial Doppler ultrasound, were used to determine whether increases in mean arterial pressure (MAP) or brain activation enhance cerebral perfusion during exercise. We also evaluated the role of "central command......, they support the hypothesis that cerebral perfusion during exercise reflects an increase in brain activation that is independent of MAP, central command, and muscle metaboreceptors but is likely to depend on influence of mechanoreceptors.......," mechanoreceptors, and/or muscle "metaboreceptors" on cerebral perfusion. Ten healthy subjects performed two levels of dynamic exercise corresponding to a heart rate of 110 (range 89-134) and 148 (129-170) beats/min, respectively, and exhaustive one-legged static knee extension. Measurements were continued during 2...

  2. Measurement of Flow Velocity and Inference of Liquid Viscosity in a Microfluidic Channel by Fluorescence Photobleaching

    DEFF Research Database (Denmark)

    Carroll, Nick J.; Jensen, Kaare Hartvig; Parsa, Shima

    2014-01-01

    We present a simple, noninvasive method for simultaneous measurement of flow velocity and inference of liquid viscosity in a microfluidic channel. We track the dynamics of a sharp front of photobleached fluorescent dye using a confocal microscope and measure the intensity at a single point...... theological properties of the liquid. This technique provides a simple method for simultaneous elucidation of flow velocity and liquid viscosity in microchannels....

  3. Middle cerebral artery flow velocity increases more in patients with delayed intraparenchymal hemorrhage after Pipeline.

    Science.gov (United States)

    Brunozzi, Denise; Shakur, Sophia F; Hussein, Ahmed E; Charbel, Fady T; Alaraj, Ali

    2018-03-01

    Pipeline Embolization Devices (PED) are commonly used for endovascular treatment of cerebral aneurysms but can be associated with delayed ipsilateral intraparenchymal hemorrhage (DIPH). The role that altered intracranial hemodynamics may play in the pathophysiology of DIPH is poorly understood. We assess middle cerebral artery (MCA) flow velocity changes after PED deployment. Patients with aneurysms located proximal to the internal carotid artery terminus treated with PED at our institution between 2015 and 2016 were retrospectively reviewed. Patients were included if MCA flow velocities were measured using transcranial Doppler. Bilateral MCA flow velocities, ratio of ipsilateral to contralateral MCA flow velocity, and bilateral MCA pulsatility index before and after PED deployment were assessed. 10 patients of mean age 52 years were included. Two patients had DIPH within 48 hours after PED deployment. We observed that these two patients had a higher increase in ipsilateral MCA mean flow velocity after treatment compared with patients without DIPH (39.5% vs 5.5%). Additionally, before PED deployment, patients with DIPH had a higher ipsilateral MCA pulsatility index (1.55 vs 0.98) and a higher ratio of ipsilateral to contralateral MCA mean flow velocity (1.35 vs 1.04). After PED, ipsilateral MCA mean flow velocity increases more in patients with DIPH. These flow velocity changes suggest the possible role of altered distal intracranial hemodynamics in DIPH after PED treatment of cerebral aneurysms. Further data are required to confirm this observation. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

  4. Flow Scales of Influence on the Settling Velocities of Particles with Varying Characteristics.

    Directory of Open Access Journals (Sweden)

    Corrine N Jacobs

    Full Text Available The settling velocities of natural, synthetic, and industrial particles were measured in a grid turbulence facility using optical measurement techniques. Particle image velocimetry and 2D particle tracking were used to measure the instantaneous velocities of the flow and the particles' trajectories simultaneously. We find that for particles examined in this study (Rep = 0.4-123, settling velocity is either enhanced or unchanged relative to stagnant flow for the range of investigated turbulence conditions. The smallest particles' normalized settling velocities exhibited the most consistent trends when plotted versus the Kolmogorov-based Stokes numbers suggesting that the dissipative scales influence their dynamics. In contrast, the mid-sized particles were better characterized with a Stokes number based on the integral time scale. The largest particles were largely unaffected by the flow conditions. Using proper orthogonal decomposition (POD, the flow pattern scales are compared to particle trajectory curvature to complement results obtained through dimensional analysis using Stokes numbers. The smallest particles are found to have trajectories with curvatures of similar scale as the small flow scales (higher POD modes whilst mid-sized particle trajectories had curvatures that were similar to the larger flow patterns (lower POD modes. The curvature trajectories of the largest particles did not correspond to any particular flow pattern scale suggesting that their trajectories were more random. These results provide experimental evidence of the "fast tracking" theory of settling velocity enhancement in turbulence and demonstrate that particles align themselves with flow scales in proportion to their size.

  5. Magnetic resonance velocity mapping of 3D cerebrospinal fluid flow dynamics in hydrocephalus: preliminary results

    Energy Technology Data Exchange (ETDEWEB)

    Stadlbauer, Andreas [Landesklinikum St. Poelten, MR Physics Group, Department of Radiology, St. Poelten (Austria); University of Erlangen-Nuremberg, Department of Neurosurgery, Erlangen (Germany); Salomonowitz, Erich [Landesklinikum St. Poelten, MR Physics Group, Department of Radiology, St. Poelten (Austria); Brenneis, Christian [Landesklinikum St. Poelten, Department of Neurology, St. Poelten (Austria); Ungersboeck, Karl [Landesklinikum St. Poelten, Department of Neurosurgery, St. Poelten (Austria); Riet, Wilma van der [European MRI Consultancy (EMRIC), Strasbourg (France); Buchfelder, Michael; Ganslandt, Oliver [University of Erlangen-Nuremberg, Department of Neurosurgery, Erlangen (Germany)

    2012-01-15

    To investigate the detectability of CSF flow alterations in the ventricular system of patients with hydrocephalus using time-resolved 3D MR velocity mapping. MR velocity mapping was performed in 21 consecutive hydrocephalus patients and 21 age-matched volunteers using a 3D phase-contrast (PC) sequence. Velocity vectors and particle path lines were calculated for visualisation of flow dynamics. CSF flow was classified as ''hypomotile flow'' if it showed attenuated dynamics and as ''hypermotile flow'' if it showed increased dynamics compared with volunteers. Diagnostic efficacy was compared with routine 2D cine PC-MRI. Seven patients showed hypomotile CSF flow: six had non-communicating hydrocephalus due to aqueductal stenosis. One showed oscillating flow between the lateral ventricles after craniotomy for intracranial haemorrhage. Seven patients showed normal flow: six had hydrocephalus ex vacuo due to brain atrophy. One patient who underwent ventriculostomy 10 years ago showed a flow path through the opening. Seven patients showed hypermotile flow: three had normal pressure hydrocephalus, three had dementia, and in one the diagnosis remained unclear. The diagnostic efficacy of velocity mapping was significantly higher except for that of aqueductal stenosis. Our approach may be useful for diagnosis, therapy planning, and follow-up of different kinds of hydrocephalus. (orig.)

  6. A simple measuring technique of surface flow velocity to analyze the behavior of velocity fields in hydraulic engineering applications.

    Science.gov (United States)

    Tellez, Jackson; Gomez, Manuel; Russo, Beniamino; Redondo, Jose M.

    2015-04-01

    An important achievement in hydraulic engineering is the proposal and development of new techniques for the measurement of field velocities in hydraulic problems. The technological advances in digital cameras with high resolution and high speed found in the market, and the advances in digital image processing techniques now provides a tremendous potential to measure and study the behavior of the water surface flows. This technique was applied at the Laboratory of Hydraulics at the Technical University of Catalonia - Barcelona Tech to study the 2D velocity fields in the vicinity of a grate inlet. We used a platform to test grate inlets capacity with dimensions of 5.5 m long and 4 m wide allowing a zone of useful study of 5.5m x 3m, where the width is similar of the urban road lane. The platform allows you to modify the longitudinal slopes from 0% to 10% and transversal slope from 0% to 4%. Flow rates can arrive to 200 l/s. In addition a high resolution camera with 1280 x 1024 pixels resolution with maximum speed of 488 frames per second was used. A novel technique using particle image velocimetry to measure surface flow velocities has been developed and validated with the experimental data from the grate inlets capacity. In this case, the proposed methodology can become a useful tools to understand the velocity fields of the flow approaching the inlet where the traditional measuring equipment have serious problems and limitations. References DigiFlow User Guide. (2012), (June). Russo, B., Gómez, M., & Tellez, J. (2013). Methodology to Estimate the Hydraulic Efficiency of Nontested Continuous Transverse Grates. Journal of Irrigation and Drainage Engineering, 139(10), 864-871. doi:10.1061/(ASCE)IR.1943-4774.0000625 Teresa Vila (1), Jackson Tellez (1), Jesus Maria Sanchez (2), Laura Sotillos (1), Margarita Diez (3, 1), and J., & (1), M. R. (2014). Diffusion in fractal wakes and convective thermoelectric flows. Geophysical Research Abstracts - EGU General Assembly 2014

  7. New sensor for measurement of low air flow velocity. Phase I final report

    International Nuclear Information System (INIS)

    Hashemian, H.M.; Hashemian, M.; Riggsbee, E.T.

    1995-08-01

    The project described here is the Phase I feasibility study of a two-phase program to integrate existing technologies to provide a system for determining air flow velocity and direction in radiation work areas. Basically, a low air flow sensor referred to as a thermocouple flow sensor has been developed. The sensor uses a thermocouple as its sensing element. The response time of the thermocouple is measured using an existing in-situ method called the Loop Current Step Response (LCSR) test. The response time results are then converted to a flow signal using a response time-versus-flow correlation. The Phase I effort has shown that a strong correlation exists between the response time of small diameter thermocouples and the ambient flow rate. As such, it has been demonstrated that thermocouple flow sensors can be used successfully to measure low air flow rates that can not be measured with conventional flow sensors. While the thermocouple flow sensor developed in this project was very successful in determining air flow velocity, determining air flow direction was beyond the scope of the Phase I project. Nevertheless, work was performed during Phase I to determine how the new flow sensor can be used to determine the direction, as well as the velocity, of ambient air movements. Basically, it is necessary to use either multiple flow sensors or move a single sensor in the monitoring area and make flow measurements at various locations sweeping the area from top to bottom and from left to right. The results can then be used with empirical or physical models, or in terms of directional vectors to estimate air flow patterns. The measurements can be made continuously or periodically to update the flow patterns as they change when people and objects are moved in the monitoring area. The potential for using multiple thermocouple flow sensors for determining air flow patterns will be examined in Phase II

  8. Wind-induced flow velocity effects on nutrient concentrations at Eastern Bay of Lake Taihu, China.

    Science.gov (United States)

    Jalil, Abdul; Li, Yiping; Du, Wei; Wang, Jianwei; Gao, Xiaomeng; Wang, Wencai; Acharya, Kumud

    2017-07-01

    Shallow lakes are highly sensitive to respond internal nutrient loading due to wind-induced flow velocity effects. Wind-induced flow velocity effects on nutrient suspension were investigated at a long narrow bay of large shallow Lake Taihu, the third largest freshwater lake in China. Wind-induced reverse/compensation flow and consistent flow field probabilities at vertical column of the water were measured. The probabilities between the wind field and the flow velocities provided a strong correlation at the surface (80.6%) and the bottom (65.1%) layers of water profile. Vertical flow velocity profile analysis provided the evidence of delay response time to wind field at the bottom layer of lake water. Strong wind field generated by the west (W) and west-north-west (WNW) winds produced displaced water movements in opposite directions to the prevailing flow field. An exponential correlation was observed between the current velocities of the surface and the bottom layers while considering wind speed as a control factor. A linear model was developed to correlate the wind field-induced flow velocity impacts on nutrient concentration at the surface and bottom layers. Results showed that dominant wind directions (ENE, E, and ESE) had a maximum nutrient resuspension contribution (nutrient resuspension potential) of 34.7 and 43.6% at the surface and the bottom profile layers, respectively. Total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) average concentrations were 6.38, 1.5, and 0.03 mg/L during our field experiment at Eastern Bay of Lake Taihu. Overall, wind-induced low-to-moderate hydrodynamic disturbances contributed more in nutrient resuspension at Eastern Bay of Lake Taihu. The present study can be used to understand the linkage between wind-induced flow velocities and nutrient concentrations for shallow lakes (with uniform morphology and deep margins) water quality management and to develop further models.

  9. Axial and radial velocities in the creeping flow in a pipe

    Directory of Open Access Journals (Sweden)

    Zuykov Andrey L'vovich

    2014-05-01

    Full Text Available The article is devoted to analytical study of transformation fields of axial and radial velocities in uneven steady creeping flow of a Newtonian fluid in the initial portion of the cylindrical channel. It is shown that the velocity field of the flow is two-dimensional and determined by the stream function. The article is a continuation of a series of papers, where normalized analytic functions of radial axial distributions in uneven steady creeping flow in a cylindrical tube with azimuthal vorticity and stream function were obtained. There is Poiseuille profile for the axial velocity in the uniform motion of a fluid at an infinite distance from the entrance of the pipe (at x = ∞, here taken equal to zero radial velocity. There is uniform distribution of the axial velocity in the cross section at the tube inlet at x = 0, at which the axial velocity is constant along the current radius. Due to the axial symmetry of the flow on the axis of the pipe (at r = 0, the radial velocities and the partial derivative of the axial velocity along the radius, corresponding to the condition of the soft function extremum, are equal to zero. The authors stated vanishing of the velocity of the fluid on the walls of the pipe (at r = R , where R - radius of the tube due to its viscous sticking and tightness of the walls. The condition of conservation of volume flow along the tube was also accepted. All the solutions are obtained in the form of the Fourier - Bessel. It is shown that the hydraulic losses at uniform creeping flow of a Newtonian fluid correspond to Poiseuille - Hagen formula.

  10. Velocity estimation using synthetic aperture imaging [blood flow

    DEFF Research Database (Denmark)

    Nikolov, Svetoslav; Jensen, Jørgen Arendt

    2001-01-01

    Presented an approach for synthetic aperture blood flow ultrasound imaging. Estimates with a low bias and standard deviation can be obtained with as few as eight emissions. The performance of the new estimator is verified using both simulations and measurements. The results demonstrate that a fully...

  11. Magnetic and velocity fields MHD flow of a stretched vertical ...

    African Journals Online (AJOL)

    Analytical solutions for heat and mass transfer by laminar flow of Newtonian, viscous, electrically conducting and heat generation/absorbing fluid on a continuously moving vertical permeable surface with buoyancy in the presence of a magnetic field and a first order chemical reaction are reported. The solutions for magnetic ...

  12. Efficient use of the velocity gradients tensor in flow modelling

    NARCIS (Netherlands)

    Passchier, C.W.

    1987-01-01

    For models of fabric development in rocks, with vorticity as a variable parameter, the choice of an unsuitable reference frame for instantaneous flow can hamper clear presentation of results. The orientation of most fabric elements which develop in deforming rocks is attached to some principal

  13. Scaling of the velocity profile in strongly drag reduced turbulent flows over an oscillating wall

    International Nuclear Information System (INIS)

    Skote, Martin

    2014-01-01

    Highlights: • Scaling analysis is used to derive a log-law for drag reduced flow. • The slope of the log layer is directly linked to the drag reduction. • The result is only valid for wall manipulated flows – not fluid altering methods. • Extensive comparison with data found in the literature is made. - Abstract: Scaling analysis of the velocity profiles in strongly drag reduced flows reveals that the slope of the logarithmic part depends on the amount of drag reduction (DR). Unlike DR due to polymeric fluids, the slope changes gradually and can be predicted by the analysis. Furthermore, the intercept of the profiles is found to vary linearly with the DR. Two velocity scales are utilized: the reference (undisturbed) and the actual friction velocity. The theory is based on the assumption that the near-wall linear region is only governed by the actual friction velocity, while the outer part is governed by the reference friction velocity. As a result, logarithmic part is influenced by both velocity scales and the slope of the velocity profile is directly linked to the DR. The theoretically obtained results are verified by data from six previously performed direct numerical simulations (DNSs) of boundary layers over spatial and temporal wall oscillations, with a wide range of resulting DR. The theory is further supported by data from numerous investigations (DNSs as well as experiments) of wall-bounded flows forced by various forms of oscillating wall-motion. The assumption that the outer part is unaffected by the actual friction velocity limits the validity of the proposed log-law to flows not fully adapted to the imposed wall forcing, hence the theory provides a measure of the level of adjustment. In addition, a fundamental difference in the applicability of the theory to spatially developing boundary flow and infinite channel flow is discussed

  14. Directional velocity estimation using focusing along the flow direction - I: Theory and simulation

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt

    2003-01-01

    velocity of 0.5 m/s is simulated for different beam-to-flow angles and for different emit foci. At 45degrees the relative standard deviation over the profile is 1.6% for a transmit focus at 40 mm. At 90degrees the approach gave a relative standard deviation of 6.6% with a transmit focus of 80 mm, when......A new method for directional velocity estimation is presented. The method uses beamformation along the flow direction to generate data in which the correct velocity magnitude can be directly estimated from the shift in position of the received consecutive signals. The shift is found by cross...

  15. Modification of Turbulent Pipe Flow Equations to Estimate the Vertical Velocity Profiles Under Woody Debris Jams

    Science.gov (United States)

    Cervania, A.; Knack, I. M. W.

    2017-12-01

    The presence of woody debris (WD) jams in rivers and streams increases the risk of backwater flooding and reduces the navigability of a channel, but adds fish and macroinvertebrate habitat to the stream. When designing river engineering projects engineers use hydraulic models to predict flow behavior around these obstructions. However, the complexities of flow through and beneath WD jams are still poorly understood. By increasing the ability to predict flow behavior around WD jams, landowners and engineers are empowered to develop sustainable practices regarding the removal or placement of WD in rivers and flood plains to balance the desirable and undesirable effects to society and the environment. The objective of this study is to address some of this knowledge gap by developing a method to estimate the vertical velocity profile of flow under WD jams. When flow passes under WD jams, it becomes affected by roughness elements on all sides, similar to turbulent flows in pipe systems. Therefore, the method was developed using equations that define the velocity profiles of turbulent pipe flows: the law of the wall, the logarithmic law, and the velocity defect law. Flume simulations of WD jams were conducted and the vertical velocity profiles were measured along the centerline. A calculated velocity profile was fit to the measured profile through the calibration of eight parameters. An optimal value or range of values have been determined for several of these parameters using cross-validation techniques. The results indicate there may be some promise to using this method in hydraulic models.

  16. Fish responses to flow velocity and turbulence in relation to size, sex and parasite load.

    Science.gov (United States)

    Hockley, F A; Wilson, C A M E; Brew, A; Cable, J

    2014-02-06

    Riverine fish are subjected to heterogeneous flow velocities and turbulence and may use this to their advantage by selecting regions that balance energy expenditure for station holding while maximizing energy gain through feeding opportunities. This study investigated microhabitat selection by guppies Poecilia reticulata in terms of flow characteristics generated by hemisphere boulders in an open channel flume. Velocity and turbulence influenced the variation in swimming behaviour with respect to size, sex and parasite intensity. With increasing body length, fish swam further and more frequently between boulder regions. Larger guppies spent more time in the areas of high-velocity and low-turbulence regions beside the boulders, whereas smaller guppies frequented the low-velocity and high-turbulence regions directly behind the boulders. Male guppies selected the regions of low velocity, indicating possible reduced swimming ability owing to hydrodynamic drag imposed by their fins. With increasing Gyrodactylus turnbulli burden, fish spent more time in regions with moderate velocity and lowest turbulent kinetic energy which were the most spatially and temporally homogeneous in terms of velocity and turbulence. These findings highlight the importance of heterogeneous flow conditions in river channel design owing to the behavioural variability within a species in response to velocity and turbulence.

  17. Fish responses to flow velocity and turbulence in relation to size, sex and parasite load

    Science.gov (United States)

    Hockley, F. A.; Wilson, C. A. M. E.; Brew, A.; Cable, J.

    2014-01-01

    Riverine fish are subjected to heterogeneous flow velocities and turbulence and may use this to their advantage by selecting regions that balance energy expenditure for station holding while maximizing energy gain through feeding opportunities. This study investigated microhabitat selection by guppies Poecilia reticulata in terms of flow characteristics generated by hemisphere boulders in an open channel flume. Velocity and turbulence influenced the variation in swimming behaviour with respect to size, sex and parasite intensity. With increasing body length, fish swam further and more frequently between boulder regions. Larger guppies spent more time in the areas of high-velocity and low-turbulence regions beside the boulders, whereas smaller guppies frequented the low-velocity and high-turbulence regions directly behind the boulders. Male guppies selected the regions of low velocity, indicating possible reduced swimming ability owing to hydrodynamic drag imposed by their fins. With increasing Gyrodactylus turnbulli burden, fish spent more time in regions with moderate velocity and lowest turbulent kinetic energy which were the most spatially and temporally homogeneous in terms of velocity and turbulence. These findings highlight the importance of heterogeneous flow conditions in river channel design owing to the behavioural variability within a species in response to velocity and turbulence. PMID:24284893

  18. Color Doppler myocardial imaging demonstrates reduced diastolic tissue velocity in growth retarded fetuses with flow redistribution.

    Science.gov (United States)

    Larsen, Lene U; Petersen, Olav B; Sloth, Erik; Uldbjerg, Niels

    2011-04-01

    In fetuses suffering from intrauterine growth retardation with cerebroplacental redistribution (IUGR CPR), the diastolic heart function may be particularly susceptible to hypoxemia as described in postnatal pathological conditions. Using the newly introduced ultrasound technique, color Doppler myocardial imaging (CDMI), we investigated the correlation between diastolic tissue velocities and diastolic blood flow velocities and compared diastolic myocardial tissue velocities in fetuses with IUGR CPR and normal fetuses. Peak early and active atrial tissue velocities (E' and A') were acquired from both ventricular free walls in 18 fetuses with IUGR CPR and 42 normal fetuses. In 35 normal fetuses, blood flow across the atrio-ventricular valves was also recorded. Umbilical artery (UA), middle cerebral artery (MCA) and ductus venosus (DV) flows were obtained in all fetuses. Nonparametric tests were used for statistical analysis. There was a tendency towards increased E' and A' with fetal age in normal pregnancies. No correlation between tissue velocity and blood flow velocity was established. IUGR CPR fetuses had significantly lower E' and A', but when indexing to heart length, only A' remained significantly lower. E'/A' ratio was increased in the left ventricle but unchanged in the right. CDMI is easily applicable during standard fetal echocardiography and provides new information on the diastolic properties of the fetal myocardium. In fetuses with IUGR CPR, diastolic tissue velocities are abnormal and especially A' may be a marker of diastolic dysfunction. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.

  19. Enhancing the Velocity Data From 4D Flow MR Images by Reducing its Divergence.

    Science.gov (United States)

    Mura, Joaquin; Pino, A Matias; Sotelo, Julio; Valverde, Israel; Tejos, Cristian; Andia, Marcelo E; Irarrazaval, Pablo; Uribe, Sergio

    2016-10-01

    Velocity measurements from 4D flow MRI are prone to be affected by several imperfections of the MR system. Assuming that blood is incompressible, we propose a novel method for enhancing the velocity field by reducing its divergence. To enhance the velocity data, we added a corrector velocity to each voxel such that the divergence is minimized. The method was validated using an analytical Womersley flow model for different settings of resolution and noise levels. The performance of the proposed method was also assessed in volunteers and patients. Results demonstrated a significant reduction of the divergence depending on the size of the regularization term, obtaining a reduction close to 50% of the mean divergence with negligible modification of flow parameters. Remarkably, we found that the reduction of the divergence, in percentage, was independent of volunteers, resolution or noise.

  20. Correlation and spectral measurements of fluctuating pressures and velocities in annular turbulent flow. [PWR; BWR

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, R.J.; Jones, B.G.; Roy, R.P.

    1980-02-01

    An experimental study of the fluctuating velocity field, the fluctuating static wall pressure and the in-stream fluctuating static pressure in an annular turbulent air flow system with a radius ratio of 4.314 has been conducted. The study included direct measurements of the mean velocity profile, turbulent velocity field; fluctuating static wall pressure and in-stream fluctuating static pressure from which the statistical values of the turbulent intensity levels, power spectral densities of the turbulent quantities, the cross-correlation between the fluctuating static wall pressure and the fluctuating static pressure in the core region of the flow and the cross-correlation between the fluctuating static wall pressure and the fluctuating velocity field in the core region of the flow were obtained.

  1. Methodology for the determination of underground water velocity, direction and flow, by using radioactive tracers

    International Nuclear Information System (INIS)

    Aoki, P.E.

    1983-01-01

    A basic route determining velocity and direction of ground water flow by using radioactive tracers is presented. Emphasis has been given to hydrology and nuclear energy concepts, to the construction of some specific equipment, to the calibration of radiation detectors and to the practical applications in borehole. 82 Br and 51 Cr have been chosen as tracers for the Darcy's velocity and direction determinations, respectively. From the obtained value of Darcy's velocity, the laminar flow was confirmed according to the admitted hypothesis. Comparisons of the Darcy's velocity values and flow direction have been made with values obtained using pumping tests and survey of the equipotential curves, where it can be concluded that they are of the same largeness and then, from a practical view, approximate. (Author) [pt

  2. Measurement of gas flow velocity: anemometer with a vibrating hot wire.

    Science.gov (United States)

    Kiełbasa, Jan

    2010-01-01

    I propose a new method to measure velocity of a gas flow, which utilizes the time derivative of the voltage observed on a vibrating hot-wire sensor. The wire vibrates with an amplitude a and a frequency f, and is kept perpendicular to the gas flow direction in the plane containing the flow velocity vector v(g). When the parameters of vibrations are tuned, the number of zeros per vibration period of the hot-wire voltage function changes. I demonstrate that at the point of change, the unknown gas velocity is directly expressed by the parameters of vibrations v(g)=2pifa. Therefore, the velocity can be measured without any prior calibration of the hot-wire speed-voltage curve and the method can be used for gases of slowly changing temperature or composition.

  3. Water velocity and the nature of critical flow in large rapids on the Colorado River, Utah

    Science.gov (United States)

    Magirl, Christopher S.; Gartner, Jeffrey W.; Smart, Graeme M.; Webb, Robert H.

    2009-01-01

    Rapids are an integral part of bedrock‐controlled rivers, influencing aquatic ecology, geomorphology, and recreational value. Flow measurements in rapids and high‐gradient rivers are uncommon because of technical difficulties associated with positioning and operating sufficiently robust instruments. In the current study, detailed velocity, water surface, and bathymetric data were collected within rapids on the Colorado River in eastern Utah. With the water surface survey, it was found that shoreline‐based water surface surveys may misrepresent the water surface slope along the centerline of a rapid. Flow velocities were measured with an ADCP and an electronic pitot‐static tube. Integrating multiple measurements, the ADCP returned velocity data from the entire water column, even in sections of high water velocity. The maximum mean velocity measured with the ADCP was 3.7 m/s. The pitot‐static tube, while capable of only point measurements, quantified velocity 0.39 m below the surface. The maximum mean velocity measured with the pitot tube was 5.2 m/s, with instantaneous velocities up to 6.5 m/s. Analysis of the data showed that flow was subcritical throughout all measured rapids with a maximum measured Froude number of 0.7 in the largest measured rapids. Froude numbers were highest at the entrance of a given rapid, then decreased below the first breaking waves. In the absence of detailed bathymetric and velocity data, the Froude number in the fastest‐flowing section of a rapid was estimated from near‐surface velocity and depth soundings alone.

  4. Magnetic particle imaging for in vivo blood flow velocity measurements in mice

    Science.gov (United States)

    Kaul, Michael G.; Salamon, Johannes; Knopp, Tobias; Ittrich, Harald; Adam, Gerhard; Weller, Horst; Jung, Caroline

    2018-03-01

    Magnetic particle imaging (MPI) is a new imaging technology. It is a potential candidate to be used for angiographic purposes, to study perfusion and cell migration. The aim of this work was to measure velocities of the flowing blood in the inferior vena cava of mice, using MPI, and to evaluate it in comparison with magnetic resonance imaging (MRI). A phantom mimicking the flow within the inferior vena cava with velocities of up to 21 cm s‑1 was used for the evaluation of the applied analysis techniques. Time–density and distance–density analyses for bolus tracking were performed to calculate flow velocities. These findings were compared with the calibrated velocities set by a flow pump, and it can be concluded that velocities of up to 21 cm s‑1 can be measured by MPI. A time–density analysis using an arrival time estimation algorithm showed the best agreement with the preset velocities. In vivo measurements were performed in healthy FVB mice (n  =  10). MRI experiments were performed using phase contrast (PC) for velocity mapping. For MPI measurements, a standardized injection of a superparamagnetic iron oxide tracer was applied. In vivo MPI data were evaluated by a time–density analysis and compared to PC MRI. A Bland–Altman analysis revealed good agreement between the in vivo velocities acquired by MRI of 4.0  ±  1.5 cm s‑1 and those measured by MPI of 4.8  ±  1.1 cm s‑1. Magnetic particle imaging is a new tool with which to measure and quantify flow velocities. It is fast, radiation-free, and produces 3D images. It therefore offers the potential for vascular imaging.

  5. Proposed method for reconstructing velocity profiles using a multi-electrode electromagnetic flow meter

    International Nuclear Information System (INIS)

    Kollár, László E; Lucas, Gary P; Zhang, Zhichao

    2014-01-01

    An analytical method is developed for the reconstruction of velocity profiles using measured potential distributions obtained around the boundary of a multi-electrode electromagnetic flow meter (EMFM). The method is based on the discrete Fourier transform (DFT), and is implemented in Matlab. The method assumes the velocity profile in a section of a pipe as a superposition of polynomials up to sixth order. Each polynomial component is defined along a specific direction in the plane of the pipe section. For a potential distribution obtained in a uniform magnetic field, this direction is not unique for quadratic and higher-order components; thus, multiple possible solutions exist for the reconstructed velocity profile. A procedure for choosing the optimum velocity profile is proposed. It is applicable for single-phase or two-phase flows, and requires measurement of the potential distribution in a non-uniform magnetic field. The potential distribution in this non-uniform magnetic field is also calculated for the possible solutions using weight values. Then, the velocity profile with the calculated potential distribution which is closest to the measured one provides the optimum solution. The reliability of the method is first demonstrated by reconstructing an artificial velocity profile defined by polynomial functions. Next, velocity profiles in different two-phase flows, based on results from the literature, are used to define the input velocity fields. In all cases, COMSOL Multiphysics is used to model the physical specifications of the EMFM and to simulate the measurements; thus, COMSOL simulations produce the potential distributions on the internal circumference of the flow pipe. These potential distributions serve as inputs for the analytical method. The reconstructed velocity profiles show satisfactory agreement with the input velocity profiles. The method described in this paper is most suitable for stratified flows and is not applicable to axisymmetric flows in

  6. Determination of filtration velocity and direction of groundwater flow using tracer technique, Port Dickson, Negeri Sembilan

    International Nuclear Information System (INIS)

    Md Shahid Ayub; Roslan Mohd Ali; Kamarudin Samuding

    1996-01-01

    The filtration velocity of the groundwater was determine by introducing I mCi Br-82 into a borehole. Br-82 was in the form of potassium bromide. The result showed that the filtration velocity varies from 2.3 to 4.5 cm/day depending on the soil matrix with the clayey layer posting more resistance to flow. Au-198 in the form of aurium chloride was introduce into two other boreholes to determine the direction of flow. The general trend of flow was in the direction between N140E and N160E

  7. An Instrument for the Simultaneous Measurement of Velocity, Temperature and Density in Unseeded Air Flows.

    Science.gov (United States)

    1989-01-31

    Fluorescence Modulation Technique for Velocity Measurements in Gas Flows ", FQ.i Fuids . Vol.5, P.240- 246, 1987. 18. P.H.Krupenie, ’The Spectrum of Mo...TABLE OF CONTENTS 1. Introduction 1 2. Flow Tagging with Carbon Atoms 3 2.1 Single Pulse Carbon Velocimetry 5 2.2 Results 10 2.2.1 Fluctuations in the...distribution across the laser beam. Fig.3. Total fluorescence at 247.8 nm vs the flow velocity for the three different intensity distribution functions. The

  8. Real-Time GPU Implementation of Transverse Oscillation Vector Velocity Flow Imaging

    DEFF Research Database (Denmark)

    Bradway, David; Pihl, Michael Johannes; Krebs, Andreas

    2014-01-01

    Rapid estimation of blood velocity and visualization of complex flow patterns are important for clinical use of diagnostic ultrasound. This paper presents real-time processing for two-dimensional (2-D) vector flow imaging which utilizes an off-the-shelf graphics processing unit (GPU). In this work...... vector flow acquisition takes 2.3 milliseconds seconds on an Advanced Micro Devices Radeon HD 7850 GPU card. The detected velocities are accurate to within the precision limit of the output format of the display routine. Because this tool was developed as a module external to the scanner’s built...

  9. In vivo lateral blood flow velocity measurement using speckle size estimation.

    Science.gov (United States)

    Xu, Tiantian; Hozan, Mohsen; Bashford, Gregory R

    2014-05-01

    In previous studies, we proposed blood measurement using speckle size estimation, which estimates the lateral component of blood flow within a single image frame based on the observation that the speckle pattern corresponding to blood reflectors (typically red blood cells) stretches (i.e., is "smeared") if blood flow is in the same direction as the electronically controlled transducer line selection in a 2-D image. In this observational study, the clinical viability of ultrasound blood flow velocity measurement using speckle size estimation was investigated and compared with that of conventional spectral Doppler of carotid artery blood flow data collected from human patients in vivo. Ten patients (six male, four female) were recruited. Right carotid artery blood flow data were collected in an interleaved fashion (alternating Doppler and B-mode A-lines) with an Antares Ultrasound Imaging System and transferred to a PC via the Axius Ultrasound Research Interface. The scanning velocity was 77 cm/s, and a 4-s interval of flow data were collected from each subject to cover three to five complete cardiac cycles. Conventional spectral Doppler data were collected simultaneously to compare with estimates made by speckle size estimation. The results indicate that the peak systolic velocities measured with the two methods are comparable (within ±10%) if the scan velocity is greater than or equal to the flow velocity. When scan velocity is slower than peak systolic velocity, the speckle stretch method asymptotes to the scan velocity. Thus, the speckle stretch method is able to accurately measure pure lateral flow, which conventional Doppler cannot do. In addition, an initial comparison of the speckle size estimation and color Doppler methods with respect to computational complexity and data acquisition time indicated potential time savings in blood flow velocity estimation using speckle size estimation. Further studies are needed for calculation of the speckle stretch method

  10. Measurement system of bubbly flow using ultrasonic velocity profile monitor and video data processing unit

    International Nuclear Information System (INIS)

    Aritomi, Masanori; Zhou, Shirong; Nakajima, Makoto; Takeda, Yasushi; Mori, Michitsugu; Yoshioka, Yuzuru.

    1996-01-01

    The authors have been developing a measurement system for bubbly flow in order to clarify its multi-dimensional flow characteristics and to offer a data base to validate numerical codes for multi-dimensional two-phase flow. In this paper, the measurement system combining an ultrasonic velocity profile monitor with a video data processing unit is proposed, which can measure simultaneously velocity profiles in both gas and liquid phases, a void fraction profile for bubbly flow in a channel, and an average bubble diameter and void fraction. Furthermore, the proposed measurement system is applied to measure flow characteristics of a bubbly countercurrent flow in a vertical rectangular channel to verify its capability. (author)

  11. Video imaging measurement of interfacial wave velocity in air-water flow through a horizontal elbow

    Science.gov (United States)

    Al-Wazzan, Amir; Than, Cheok F.; Moghavvemi, Mahmoud; Yew, Chia W.

    2001-10-01

    Two-phase flow in pipelines containing elbows represents a common situation in the oil and gas industries. This study deals with the stratified flow regime between the gas and liquid phase through an elbow. It is of interest to study the change in wave characteristics by measuring the wave velocity and wavelength at the inlet and outlet of the elbow. The experiments were performed under concurrent air-water stratified flow in a horizontal transparent polycarbonate pipe of 0.05m diameter and superficial air and water velocities up to 8.97 and 0.0778 m/s respectively. A non-intrusive video imaging technique was applied to capture the waves. For image analysis, a frame by frame direct overlapping method was used to detect for pulsating flow and a pixel shifting method based on the detection of minimum values in the overlap function was used to determine wave velocity and wavelength. Under superficial gas velocity of less than 4.44 m/s, the results suggest a regular pulsating outflow produced by the elbow. At higher gas velocities, more random pulsation was found and the emergence of localized interfacial waves was detected. Wave velocities measured by this technique were found to produce satisfactory agreement with direct measurements.

  12. Evaluation of multiple tracer methods to estimate low groundwater flow velocities.

    Science.gov (United States)

    Reimus, Paul W; Arnold, Bill W

    2017-04-01

    Four different tracer methods were used to estimate groundwater flow velocity at a multiple-well site in the saturated alluvium south of Yucca Mountain, Nevada: (1) two single-well tracer tests with different rest or "shut-in" periods, (2) a cross-hole tracer test with an extended flow interruption, (3) a comparison of two tracer decay curves in an injection borehole with and without pumping of a downgradient well, and (4) a natural-gradient tracer test. Such tracer methods are potentially very useful for estimating groundwater velocities when hydraulic gradients are flat (and hence uncertain) and also when water level and hydraulic conductivity data are sparse, both of which were the case at this test location. The purpose of the study was to evaluate the first three methods for their ability to provide reasonable estimates of relatively low groundwater flow velocities in such low-hydraulic-gradient environments. The natural-gradient method is generally considered to be the most robust and direct method, so it was used to provide a "ground truth" velocity estimate. However, this method usually requires several wells, so it is often not practical in systems with large depths to groundwater and correspondingly high well installation costs. The fact that a successful natural gradient test was conducted at the test location offered a unique opportunity to compare the flow velocity estimates obtained by the more easily deployed and lower risk methods with the ground-truth natural-gradient method. The groundwater flow velocity estimates from the four methods agreed very well with each other, suggesting that the first three methods all provided reasonably good estimates of groundwater flow velocity at the site. The advantages and disadvantages of the different methods, as well as some of the uncertainties associated with them are discussed. Published by Elsevier B.V.

  13. Ultrasonic velocity profiling rheometry based on a widened circular Couette flow

    International Nuclear Information System (INIS)

    Shiratori, Takahisa; Tasaka, Yuji; Oishi, Yoshihiko; Murai, Yuichi

    2015-01-01

    We propose a new rheometry for characterizing the rheological properties of fluids. The technique produces flow curves, which represent the relationship between the fluid shear rate and shear stress. Flow curves are obtained by measuring the circumferential velocity distribution of tested fluids in a circular Couette system, using an ultrasonic velocity profiling technique. By adopting a widened gap of concentric cylinders, a designed range of the shear rate is obtained so that velocity profile measurement along a single line directly acquires flow curves. To reduce the effect of ultrasonic noise on resultant flow curves, several fitting functions and variable transforms are examined to best approximate the velocity profile without introducing a priori rheological models. Silicone oil, polyacrylamide solution, and yogurt were used to evaluate the applicability of this technique. These substances are purposely targeted as examples of Newtonian fluids, shear thinning fluids, and opaque fluids with unknown rheological properties, respectively. We find that fourth-order Chebyshev polynomials provide the most accurate representation of flow curves in the context of model-free rheometry enabled by ultrasonic velocity profiling. (paper)

  14. Evolution of star-bearing molecular clouds: the high-velocity HCO+ flow in NGC 2071

    International Nuclear Information System (INIS)

    Wootten, A.; Loren, R.B.; Sandqvist, A.; Friberg, P.; Hjalmarson, Aa.

    1984-01-01

    The J = 1-0 and J = 302 lines of HCO + and H 13 CO + have been observed in the molecular cloud NGC 2071, where they map the dense portions of a bidirectional molecular flow. The high resolution (42'') of our observations has enabled us to determine the distribution of mass, momentum , and energy in the flow as a function of projected distance from the cluster. Both momentum and energy diminish with distance from the central cluster of infrared sources. The highest velocities at a given intensity in this dense flow occur in a limited region coincident with an infrared cluster and the densest part of the molecular cloud. Higher resolution (33'') CO and 13 CO observations reveal that the extreme velocities in the flow occur in regions displaced on opposite sides of the cluster, suggesting that the flow only becomes visible in molecular line emission at distances approx.0.1 pc from its supposed source. Lower velocity material containing most of the mass of the flow is found over larger regions, as expected if the flow has decelerated as it has evolved. Assuming conservation of momentum, the historical rate of momentum injection is found to have been roughly constant over a period of 10 4 years, suggesting a constancy of the average luminosity of the central cluster over that time. The J = 3--2 HCO + profile does not show the absorption which is a prominent feature of the J = 1--0 profile, and the J = 3--2 line appears to be a useful probe of conditions specific to the dense cores of clouds. The high velocity HCO + emission correlates very well with spatial and velocity events of molecular hydrogen emission. The abundance of HCO + [X(HCO + )approx.10 -8 ], and by inference the electron density, is similar in material at all velocities

  15. Influence of hemodialysis on the mean blood flow velocity in the middle cerebral artery.

    Science.gov (United States)

    Stefanidis, I; Bach, R; Mertens, P R; Liakopoulos, V; Liapi, G; Mann, H; Heintz, B

    2005-08-01

    Several effects of hemodialysis, including hemoconcentration, alterations of hemostasis or hemorheology and endothelial activation, could potentially interfere with cerebral blood flow (CBF) regulation. These treatment-specific changes may also be crucial for the enhanced incidence of stroke in uremic patients. Nevertheless, the influence of hemodialysis on CBF has not been yet adequately studied. We registered mean blood flow velocity (MFV) in the middle cerebral artery (MCA) during hemodialysis treatment in order to evaluate its contribution on CBF changes. Transcranial Doppler ultrasonography (TCD) of the MCA was performed continuously during hemodialysis treatment in 18 stable patients (10 males and 8 females, mean age 62 +/- 11 years) with end-stage renal disease of various origin. Blood pressure (mmHg), heart rate (/min), ultrafiltration volume (ml), BV changes (deltaBV by hemoglobinometry, %), arterial blood gases (pO2, blood oxygen content, pCO2), hemostasis activation (thrombin-antithrombin III complex, ELISA) and fibrinogen (Clauss) were measured simultaneously at the beginning of treatment and every hour thereafter. Before the hemodialysis session the MFV in the MCA was within normal range (57.5 +/- 13.0 cm/s, ref. 60 +/- 12) and was mainly dependent on the patients' age (r = -0.697, p delta%MFV) were interrelated to the ultrafiltration volume (r = -0.486, p delta%acO2, r = -0.420, p delta%fibrinogen, r = 0.244, p < 0.05). A significant continuous decrease of the MFV in the MCA was observed during hemodialysis treatment, which inversely correlated both with ultrafiltration volume, BV changes and changes of plasma fibrinogen. The ultrafiltration-induced hemoconcentration with concomitant rise of hematocrit and oxygen transport capacity, may partly explain the alterations in the cerebral MFV observed during hemodialysis.

  16. On the theoretical velocity distribution and flow resistance in natural channels

    Science.gov (United States)

    Moramarco, Tommaso; Dingman, S. Lawrence

    2017-12-01

    The velocity distribution in natural channels is of considerable interest for streamflow measurements to obtain information on discharge and flow resistance. This study focuses on the comparison of theoretical velocity distributions based on 1) entropy theory, and 2) the two-parameter power law. The analysis identifies the correlation between the parameters of the distributions and defines their dependence on the geometric and hydraulic characteristics of the channel. Specifically, we investigate how the parameters are related to the flow resistance in terms of Manning roughness, shear velocity and water surface slope, and several formulae showing their relationships are proposed. Velocity measurements carried out in the past 20 years at Ponte Nuovo gauged section along the Tiber River, central Italy, are the basis for the analysis.

  17. Velocity measurements and identification of the flow pattern of vertical air-water flows with light-beam detectors

    International Nuclear Information System (INIS)

    Luebbesmeyer, D.; Leoni, B.

    1980-07-01

    A new detector for measuring fluid velocities in two-phase flows by means of Noise-Analysis (especially Transient-Cross-Correlation-technique) has been developed. The detector utilizes a light-beam which is modulated by changes in the transparency of the two-phase flow. The results of nine measurements for different flow-regimes of vertical air/water-flows are shown. A main topic of these investigations was to answer the question if it is possible to identify the flow-pattern by looking at the shape of different 'Noise-Analytical-functions' (like APSD, CPSD, CCF etc.). The results prove that light-beam sensors are good detectors for fluid-velocity measurements in different flow regimes and in a wide range of fluid velocities starting with values of about 0.08 m/s up to values of 40 m/s. With respect to flow-pattern identification only the time-signals and the shape of the cross-power-density-function (CPSD) seem to be useful. (Auth.)

  18. ANALYTICAL METHODS FOR VELOCITY DISTRIBUTION AND DIP-PHENOMENON IN NARROW OPEN-CHANNEL FLOWS

    OpenAIRE

    Absi, Rafik

    2009-01-01

    International audience; In this study, we present analytical tools for velocity distribution in steady uniform open-channel flows. Simple dip-modified laws are presented. An ordinary differential equation based on an analysis of the Reynolds-averaged Navier-Stokes (RANS) equations is proposed. Comparisons of predicted velocity profiles with experimental data show good agreement. It is well known that dip-phenomenon depends on aspect ratio Ar (ratio of the channel width b to the water depth h)...

  19. Measurement system of bubbly flow using Ultrasonic Velocity Profile Monitor and Video Data Processing Unit. 3. Comparison of flow characteristics between bubbly cocurrent and countercurrent flows

    International Nuclear Information System (INIS)

    Zhou, Shirong; Suzuki, Yumiko; Aritomi, Masanori; Matsuzaki, Mitsuo; Takeda, Yasushi; Mori, Michitsugu

    1998-01-01

    The authors have developed a new measurement system which consisted of an Ultrasonic Velocity Profile Monitor (UVP) and a Video Data Processing Unit (VDP) in order to clarify the two-dimensional flow characteristics in bubbly flows and to offer a data base to validate numerical codes for two-dimensional two-phase flow. In the present paper, the proposed measurement system is applied to fully developed bubbly cocurrent flows in a vertical rectangular channel. At first, both bubble and water velocity profiles and void fraction profiles in the channel were investigated statistically. In addition, the two-phase multiplier profile of turbulence intensity, which was defined as a ratio of the standard deviation of velocity fluctuation in a bubbly flow to that in a water single phase flow, were examined. Next, these flow characteristics were compared with those in bubbly countercurrent flows reported in our previous paper. Finally, concerning the drift flux model, the distribution parameter and drift velocity were obtained directly from both bubble and water velocity profiles and void fraction profiles, and their results were compared with those in bubbly countercurrent flows. (author)

  20. Measurement system of bubbly flow using ultrasonic velocity profile monitor and video data processing unit. 2. Flow characteristics of bubbly countercurrent flow

    International Nuclear Information System (INIS)

    Aritomi, Masanori; Zhou, Shirong; Nakajima, Makoto; Takeda, Yasushi; Mori, Michitsugu.

    1997-01-01

    The authors have developed a measurement system which is composed of an ultrasonic velocity profile monitor and a video data processing unit in order to clarify its multi-dimensional flow characteristics in bubbly flows and to offer a data base to validate numerical codes for multi-dimensional two-phase flow. In this paper, the measurement system was applied for bubbly countercurrent flows in a vertical rectangular channel. At first, both bubble and water velocity profiles and void fraction profiles in the channel were investigated statistically. Next, turbulence intensity in a continuous liquid phase was defined as a standard deviation of velocity fluctuation, and the two-phase multiplier profile of turbulence intensity in the channel was clarified as a ratio of the standard deviation of flow fluctuation in a bubbly countercurrent flow to that in a water single phase flow. Finally, the distribution parameter and drift velocity used in the drift flux model for bubbly countercurrent flows were calculated from the obtained velocity profiles of both phases and void fraction profile, and were compared with the correlation proposed for bubbly countercurrent flows. (author)

  1. Measurement of bubbly flows in vertical channels using ultrasonic velocity profile monitor

    International Nuclear Information System (INIS)

    Aritomi, Masanori; Zhou Shirong; Takeda, Yasushi; Nakamura, Hideo; Kukita, Yutaka

    1998-01-01

    The authors have been developing measurement technique, using the Ultrasonic Doppler effect and applicable for a bubbly flow in vertical channels in order to understand their multi-dimensional flow characteristics and to offer a data base to validate numerical codes for multi-dimensional two-phase flow. Our developed measurement system is composed of an ultrasonic velocity profile monitor with a video data processing unit, which can measure simultaneously velocity profiles in both gas and liquid phases, a void fraction profile for bubbly flow in a channel, and an average bubble diameter and void fraction. In this paper, our proposed measurement system was applied to bubbly countercurrent flows in a vertical rectangular channel the followings are discussed: (1) the measurement principle, (2) the data processing process, (3) measurement accuracy and (4) further problems. (author)

  2. Animal models of surgically manipulated flow velocities to study shear stress-induced atherosclerosis.

    Science.gov (United States)

    Winkel, Leah C; Hoogendoorn, Ayla; Xing, Ruoyu; Wentzel, Jolanda J; Van der Heiden, Kim

    2015-07-01

    Atherosclerosis is a chronic inflammatory disease of the arterial tree that develops at predisposed sites, coinciding with locations that are exposed to low or oscillating shear stress. Manipulating flow velocity, and concomitantly shear stress, has proven adequate to promote endothelial activation and subsequent plaque formation in animals. In this article, we will give an overview of the animal models that have been designed to study the causal relationship between shear stress and atherosclerosis by surgically manipulating blood flow velocity profiles. These surgically manipulated models include arteriovenous fistulas, vascular grafts, arterial ligation, and perivascular devices. We review these models of manipulated blood flow velocity from an engineering and biological perspective, focusing on the shear stress profiles they induce and the vascular pathology that is observed. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  3. Cross-tail velocity component in the plasma sheet fast flows

    Directory of Open Access Journals (Sweden)

    N. P. Dmitrieva

    2008-06-01

    Full Text Available The flux transfer in the magnetotail plasma sheet is mainly provided by the tail-aligned fast plasma flows (Bursty Bulk Flows – BBFs. In this paper we study the events with a large cross-tail velocity component, including their occurrence and relationship to the standard BBFs. We found out that a significant part of large Vy events are a subgroup connected with the BBFs propagation. The maximal deviation of the velocity vector from the X direction (about 40–50 degrees, on average is observed near the BBFs' leading front in the sheath, where the fast flow interacts with surrounding plasma. The average variation of the velocity direction in the vicinity of the BBF resembles a plasma vortex. Our results support the model, in which the BBF represents a polarized, bubble-like flux tube, propagating through the plasma sheet.

  4. Flow velocity of the superior sagittal sinus is reduced in patients with idiopathic normal pressure hydrocephalus.

    Science.gov (United States)

    Kuriyama, Nagato; Tokuda, Takahiko; Yamada, Kei; Akazawa, Kentaro; Hosoda, Makoto; Sakai, Koji; Watanabe, Yoshiyuki; Nakagawa, Masanori

    2011-10-01

    The pathogenesis and diagnostic methods for idiopathic normal pressure hydrocephalus (iNPH) have been active areas of research in recent years. This study was performed to determine whether there is a venous return abnormality in the intracranial circulation of patients with iNPH. The subjects were 20 patients with iNPH (Group N) and 24 normal controls (Group C). MR venography (MRV) was performed at the superior sagittal sinus 2 cm above the confluence of the sinuses, and the flow velocities were compared between Groups N and C. During normal breathing, the maximum velocities were significantly lower in Group N (18.8 cm/second) than in Group C (22.9 cm/second; (P velocity decreased in both groups, but both the maximum (Max V) and minimum (Min V) velocities were significantly lower in Group N than in Group C (P velocity at the superior sagittal sinus was lower and the flow velocity during the Valsalva maneuver decreased more in patients with iNPH than in controls. The results may reflect the presence of abnormal intracranial venous flow in iNPH. © 2010 by the American Society of Neuroimaging.

  5. TECHNICAL DESIGN NOTE: Three-component velocity measurement in microscale flows using time-resolved PIV

    Science.gov (United States)

    Erkan, N.; Shinohara, K.; Someya, S.; Okamoto, K.

    2008-05-01

    The measurement of a three-component (3C) velocity field in microfluidic devices with conventional techniques and conventional micro-PIV (particle image velocimetry) is still difficult due to limited optical access. Since Santiago et al (1998 Exp. Fluids 25 316-9), micro-PIV flow velocity measurements have remained mainly limited to 2C velocity vector field realizations. In this study, the third component of the velocity, i.e. out-of-plane velocity extraction from two-dimensional time-resolved (TR) micro-PIV images, is proposed. The method is based on PIV and performs cross-correlation (CC) peak height tracking inside the small ensembles of the TR-PIV flow images. This concept was verified basically by an experiment performed on a microscale fluid flow inside a 100 µm diameter inclined micro tube. Despite the inevitable background noise which affects the measurement negatively, the extracted steady-state depthwise velocity profile was in agreement with the analytical result.

  6. Three-component velocity measurement in microscale flows using time-resolved PIV

    International Nuclear Information System (INIS)

    Erkan, N; Shinohara, K; Someya, S; Okamoto, K

    2008-01-01

    The measurement of a three-component (3C) velocity field in microfluidic devices with conventional techniques and conventional micro-PIV (particle image velocimetry) is still difficult due to limited optical access. Since Santiago et al (1998 Exp. Fluids 25 316–9), micro-PIV flow velocity measurements have remained mainly limited to 2C velocity vector field realizations. In this study, the third component of the velocity, i.e. out-of-plane velocity extraction from two-dimensional time-resolved (TR) micro-PIV images, is proposed. The method is based on PIV and performs cross-correlation (CC) peak height tracking inside the small ensembles of the TR-PIV flow images. This concept was verified basically by an experiment performed on a microscale fluid flow inside a 100 µm diameter inclined micro tube. Despite the inevitable background noise which affects the measurement negatively, the extracted steady-state depthwise velocity profile was in agreement with the analytical result. (technical design note)

  7. Tunable diode laser absorption sensor for temperature and velocity measurements of O2 in air flows

    Science.gov (United States)

    Philippe, L. C.; Hanson, R. K.

    1991-01-01

    A fast and nonintrusive velocity and temperature diagnostic based on oxygen absorption is presented. The system uses a GaAlAs tunable diode laser, ramped and modulated in wavelength at high frequency. Detection is performed at twice the modulating frequency, leading to second harmonic absorption lineshapes. Velocity is inferred from the wavelength shift of the absorption line center due to the Doppler effect. Temperature is determined by comparing experimental and calculated lineshapes. Capabilities of the technique for studies of transient high-speed flows are demonstrated in shock tube experiments. Good agreement is obtained with predicted temperatures and velocities when pressure-induced shifts are accounted for.

  8. Numerical simulation of bubble behavior in subcooled flow boiling under velocity and temperature gradient

    International Nuclear Information System (INIS)

    Bahreini, Mohammad; Ramiar, Abas; Ranjbar, Ali Akbar

    2015-01-01

    Highlights: • Condensing bubble is numerically investigated using VOF model in OpenFOAM package. • Bubble mass reduces as it goes through condensation and achieves higher velocities. • At a certain time the slope of changing bubble diameter with time, varies suddenly. • Larger bubbles experience more lateral migration to higher velocity regions. • Bubbles migrate back to a lower velocity region for higher liquid subcooling rates. - Abstract: In this paper, numerical simulation of the bubble condensation in the subcooled boiling flow is performed. The interface between two-phase is tracked via the volume of fluid (VOF) method with continuous surface force (CSF) model, implemented in the open source OpenFOAM CFD package. In order to simulate the condensing bubble with the OpenFOAM code, the original energy equation and mass transfer model for phase change have been modified and a new solver is developed. The Newtonian flow is solved using the finite volume scheme based on the pressure implicit with splitting of operators (PISO) algorithm. Comparison of the simulation results with previous experimental data revealed that the model predicted well the behavior of the actual condensing bubble. The bubble lifetime is almost proportional to bubble initial size and is prolonged by increasing the system pressure. In addition, the initial bubble size, subcooling of liquid and velocity gradient play an important role in the bubble deformation behavior. Velocity gradient makes the bubble move to the higher velocity region and the subcooling rate makes it to move back to the lower velocity region.

  9. Ground water flow velocity in the bank of the Columbia River, Hanford, Washington

    International Nuclear Information System (INIS)

    Ballard, S.

    1995-12-01

    To properly characterize the transport of contaminants from the sediments beneath the Hanford Site into the Columbia River, a suite of In Situ Permeable Flow Sensors was deployed to accurately characterize the hydrologic regime in the banks of the river. The three dimensional flow velocity was recorded on an hourly basis from mid May to mid July, 1994 and for one week in September. The first data collection interval coincided with the seasonal high water level in the river while the second interval reflected conditions during relatively low seasonal river stage. Two flow sensors located approximately 50 feet from the river recorded flow directions which correlated very well with river stage, both on seasonal and diurnal time scales. During time intervals characterized by falling river stage, the flow sensors recorded flow toward the river while flow away from the river was recorded during times of rising river stage. The flow sensor near the river in the Hanford Formation recorded a component of flow oriented vertically downward, probably reflecting the details of the hydrostratigraphy in close proximity to the probe. The flow sensor near the river in the Ringold Formation recorded an upward component of flow which dominated the horizontal components most of the time. The upward flow in the Ringold probably reflects regional groundwater flow into the river. The magnitudes of the flow velocities recorded by the flow sensors were lower than expected, probably as a result of drilling induced disturbance of the hydraulic properties of the sediments around the probes. The probes were installed with resonant sonic drilling which may have compacted the sediments immediately surrounding the probes, thereby reducing the hydraulic conductivity adjacent to the probes and diverting the groundwater flow away from the sensors

  10. Determine of velocity field with PIV and CFD during the flow around of bridge piers

    Directory of Open Access Journals (Sweden)

    Picka D.

    2013-04-01

    Full Text Available The article describes the processing of specific junior research FAST-J-11-51/1456 which dealt with physical and CFD of the velocity field during the flow around of bridge piers. Physical modelling has been carried out in Laboratory of water management research in Institute of Water Structures in Brno University of Technology – Faculty of Civil Engineering. To measure of the velocity field in profile of bridge piers were used laser measuring method PIV (Particle Image Velocimetry. The results of PIV served as a basis for comparing experimental data with CFD results of this type of flow in the commercial software ANSYS CFX.

  11. Characteristics of low-mass-velocity vertical gas-liquid two-phase flow

    International Nuclear Information System (INIS)

    Adachi, Hiromichi; Abe, Yutaka; Kimura, Ko-ji

    1995-01-01

    In the present paper, characteristics of low mass velocity two-phase flow was analyzed based on a concept that pressure energy of two-phase flow is converted into acceleration work, gravitational work and frictional work, and the pressure energy consumption rate should be minimum at the stable two-phase flow condition. Experimental data for vertical upward air-water two-phase flow at atmospheric pressure was used to verify this concept and the turbulent model used in this method is optimized with the data. (author)

  12. Exercise Tl-201 myocardial scintigraphy and coronary blood flow velocity in patients with hypertrophic cardiomyopathy

    Energy Technology Data Exchange (ETDEWEB)

    Sugihara, Hiroki; Umamoto, Ikuo; Harada, Yoshiaki (Kyoto Prefectural Univ. of Medicine (Japan)) (and others)

    1992-03-01

    In 22 patients with hypertrophic cardiomyopathy not associated with coronary stenosis, findings of exercise Tl-201 myocardial scintigraphy were reviewed in relation to coronary blood flow velocity. Blood flow velocity of the left antero-inferior segment was recorded by using a Doppler catheter. From time velocity integration in systolic and diastolic phases, both % systolic fraction (%SF) and %diastolic 1st third fraction (%d1F) were obtained. A decreased perfusion was visually assessed on exercise Tl-201 myocardial images. In addition, transient dilation of the left ventricular cavity was quantitatively assessed by expressing it as a transient dilation index (TDI) for subendocardial ischemia. Coronary blood flow velocity was characterized by a decrease in both %SF and %d1F and negative systolic flow. Both %SF and %d1F were inversely correlated with TDI. Coronary negative systolic flow was frequently associated with a decreased perfusion. These results suggest factors such as left ventricular relaxation impairment, other than coronary small vessel lesions, may also be involved in the occurrence of myocardial ischemia in hypertrophic cardiomyopathy. (N.K.).

  13. A Continuous-Flow Polymerase Chain Reaction Microchip With Regional Velocity Control

    Science.gov (United States)

    Li, Shifeng; Fozdar, David Y.; Ali, Mehnaaz F.; Li, Hao; Shao, Dongbing; Vykoukal, Daynene M.; Vykoukal, Jody; Floriano, Pierre N.; Olsen, Michael; McDevitt, John T.; Gascoyne, Peter R.C.; Chen, Shaochen

    2009-01-01

    This paper presents a continuous-flow polymerase chain reaction (PCR) microchip with a serpentine microchannel of varying width for “regional velocity control.” Varying the channel width by incorporating expanding and contracting conduits made it possible to control DNA sample velocities for the optimization of the exposure times of the sample to each temperature phase while minimizing the transitional periods during temperature transitions. A finite element analysis (FEA) and semi-analytical heat transfer model was used to determine the distances between the three heating assemblies that are responsible for creating the denaturation (96 °C), hybridization (60 °C), and extension (72 °C) temperature zones within the microchip. Predictions from the thermal FEA and semi-analytical model were compared with temperature measurements obtained from an infrared (IR) camera. Flow-field FEAs were also performed to predict the velocity distributions in the regions of the expanding and contracting conduits to study the effects of the microchannel geometry on flow recirculation and bubble nucleation. The flow fields were empirically studied using micro particle image velocimetry (μ-PIV) to validate the flow-field FEA’s and to determine experimental velocities in each of the regions of different width. Successful amplification of a 90 base pair (bp) bacillus anthracis DNA fragment was achieved. PMID:19829760

  14. Erectile dysfunction in healthy subjects predicts reduced coronary flow velocity reserve.

    Science.gov (United States)

    Borgquist, Rasmus; Gudmundsson, Petri; Winter, Reidar; Nilsson, Peter; Willenheimer, Ronnie

    2006-09-20

    Erectile dysfunction is associated with, and may be the first sign of coronary artery disease. We aimed to assess whether men with erectile dysfunction but without cardiovascular disease have reduced coronary flow reserve, as a sign of early coronary atherosclerosis. We investigated 12 men aged 68-73 years with erectile dysfunction, and 12 age-matched controls. Erectile function was evaluated using the validated IIEF-5 questionnaire. A score or = 21 was considered normal. Patients with neurological or psychological reasons for erectile dysfunction were excluded, as were patients with symptoms of or prescribed medication for cardiovascular disease, hypertension or diabetes. Coronary flow velocity reserve was measured non-invasively by Doppler in the left anterior descending artery, before and during adenosine infusion. Coronary flow velocity reserve was significantly reduced in subjects with erectile dysfunction: 2.36 versus 3.19; P=0.024. In logistic regression analysis, compared to control subjects, men with erectile dysfunction had significantly increased risk of reduced coronary flow velocity reserve (reduced coronary flow velocity reserve, P=0.016. Men with erectile dysfunction but without diabetes or clinical cardiovascular disease have early signs of coronary artery disease. Our findings suggest that a cardiac risk evaluation may be indicated in men with suspected vasculogenic erectile dysfunction, and these individuals should be considered for primary prevention measures regarding cardiovascular disease risk factors.

  15. Effect of jet-mainstream velocity ratio on flow characteristics and heat transfer enhancement of jet on flat plate flow

    Science.gov (United States)

    Puzu, N.; Prasertsan, S.; Nuntadusit, C.

    2017-09-01

    The aim of this research was to study the effect of jet-mainstream velocity ratio on flow and heat transfer characteristics of jet on flat plate flow. The jet from pipe nozzle with inner diameter of D=14 mm was injected perpendicularly to mainstream on flat plate. The flat plate was blown by mainstream with uniform velocity profile at 10 m/s. The velocity ratio (jet to mainstream velociy) was varied at VR=0.25 and 3.5 by adjusting velocity of jet flow. For heat transfer measurement, a thin foil technique was used to evaluate the heat transfer coefficient by measuring temperature distributions on heat transfer surface with constant heat flux by using infrared camera. Flow characteristics were simulated by using a computational fluid dynamics (CFD) with commercial software ANSYS Fluent (Ver.15.0). The results showed that the enhancement of heat transfer along downstream direction for the case of VR=0.25 was from the effect of jet stream whereas for the case of VR=3.5 was from the effect of mainstream.

  16. Vector velocity volume flow estimation: Sources of error and corrections applied for arteriovenous fistulas

    DEFF Research Database (Denmark)

    Jensen, Jonas; Olesen, Jacob Bjerring; Stuart, Matthias Bo

    2016-01-01

    A method for vector velocity volume flow estimation is presented, along with an investigation of its sources of error and correction of actual volume flow measurements. Volume flow errors are quantified theoretically by numerical modeling, through flow phantom measurements, and studied in vivo....... This paper investigates errors from estimating volumetric flow using a commercial ultrasound scanner and the common assumptions made in the literature. The theoretical model shows, e.g. that volume flow is underestimated by 15%, when the scan plane is off-axis with the vessel center by 28% of the vessel...... to cross-sectional scans of the fistulas, the major axis was on average 10.2 mm, which is 8.6% larger than the minor axis. The ultrasound beam was on average 1.5 mm from the vessel center, corresponding to 28% of the semi-major axis in an average fistula. Estimating volume flow with an elliptical, rather...

  17. Middle cerebral artery blood flow velocity in elite power athletes during maximal weight-lifting.

    Science.gov (United States)

    Dickerman, R D; McConathy, W J; Smith, G H; East, J W; Rudder, L

    2000-06-01

    Cerebral blood flow velocity (CBFV) has been shown to significantly increase during dynamic exercise (running) secondary to increases in cardiac output. Static exercise (weight-lifting) induces supraphysiological arterial pressures up to 450/380 mmHg, and thus may alter CBFV. Catastrophic brain injuries such as stroke, cerebral hemorrhage, subarachnoid hemorrhage, retinal hemorrhage and retinal detachment have been associated with weight-lifting. A recent study has shown that intra-ocular pressure (IOP), which is an indirect measure of intracranial pressure, elevates to pathophysiologic levels during weight-lifting. Recent CBFV studies instituting Valsalva have demonstrated decreases in CBFV from 21%-52%. To date, no studies have examined CBFV during maximal weight-lifting to elucidate the cerebrovascular responses to extreme pressure alterations. We recruited nine elite power athletes, including a multi-world record holder in powerlifting, for a transcranial Doppler study of middle cerebral artery blood flow velocity at rest and during maximal weight-lifting. All subjects' resting blood flow velocities were within normal ranges (mean 64.4 +/- 9.5 cm sec2). Blood flow velocities were significantly (p < 0.0001) decreased in all subjects during maximal lifting (mean 48.4 +/- 10.1 cm sec2). Linear regression analysis demonstrated a significant inverse linear relationship in the net change of blood velocities from rest to maximal lift for each subject (r = 0.8585, p < 0.001). This study demonstrates that blood flow velocities are significantly decreased during heavy resistance training. The drop in CBFV during weight-lifting was significantly less than previous Valsalva studies, which likely reveals the cardiovascular, baroreflex, and cerebrovascular system adaptations occurring in these elite power athletes.

  18. Investigation of joule-heating flow using ultrasound velocity profiler-effect of cold cap condition

    International Nuclear Information System (INIS)

    Duong, T.T.; Tsuzuki, N.; Kikura, H.

    2015-01-01

    The High Level Radioactive Wastes (HLWs) are vitrified in a glass melter. However, sometimes the glass melter operation is not stable due to abnormal phenomena. If this happens, the glass melter has to be shut down. Understanding the flow behavior in glass melter is important to improve the applicability of the melter operation. Ultrasonic Velocity Profiler (UVP) is appropriate to observe the Joule-heating flow behavior which is scaled into experiment and conducted in Laboratory scale. The cubic cavity for Joule heating flow has dimension of 100 mm with a top surface condition is under cooling condition and the other walls is set as adiabatic condition. The effect of cold cap condition on the flow behavior is investigated by changing the top surface as fully or partly cooling as 50%, 75%. As a result, Joule-heating flow convection is observed by UVP and displayed in color scale (so-called spatio-temporal velocity profile). This information is very useful to observe the unstable flow convection. It is revealed that cold cap boundary conditions affect the flow field in the whole cavity. In case of full cooling on the top wall, the flow behavior is unstable by multi-vortex inside the cavity. However, the main vortex has a diameter of about 90 mm in both cases of 50% cooling and 75% cooling. These characteristics are also confirmed using a Computational Fluid Dynamic, named GSMAC-Finite Element Method that combined three fields: Flow field, Thermal field and electromagnetic field. (author)

  19. A New Imaging Tool for Realtime Measurement of Flow Velocity in Intracranial Aneurysms

    Science.gov (United States)

    Petridis, Athanasios K.; Kaschner, Marius; Cornelius, Jan F.; Kamp, Marcel A.; Tortora, Angelo; Steiger, Hans-Jakob; Turowski, Bernd

    2017-01-01

    With modern imaging modalities of the brain a significant number of unruptured aneurysms are detected. However, not every aneurysm is prone to rupture. Because treatment morbidity is about 10% it is crucial to identify unstable aneurysms for which treatment should be discussed. Recently, new imaging tools allow analysis of flow dynamics and wall stability have become available. It seems that they might provide additional data for better risk profiling. In this study we present a new imaging tool for analysis of flow dynamics, which calculates fluid velocity in an aneurysm (Phillips Electronics, N.V.). It may identify regions with high flow and calculate flow reduction after stenting of aneurysms. Contrast is injected with a stable injection speed of 2 mL/sec for 3 sec. Two clinical cases are illustrated. Velocity in aneurysms and areas of instability can be identified and calculated during angiography in real-time. After stenting and flow diverter deployment flow reduction in the internal carotid aneurysm was reduced by 60% and there was a reduction of about 65% in the posterior cerebral artery in the second case we are reporting. The dynamic flow software calculates the flow profile in the aneurysm immediately after contrast injection. It is a real-time, patient specific tool taking into account systole, diastole and flexibility of the vasculature. These factors are an improvement as compared to current models of computational flow dynamics. We think it is a highly efficient, user friendly tool. Further clinical studies are on their way. PMID:28839527

  20. A new imaging tool for realtime measurement of flow velocity in intracranial aneurysms

    Directory of Open Access Journals (Sweden)

    Athanasios K. Petridis

    2017-08-01

    Full Text Available With modern imaging modalities of the brain a significant number of unruptured aneurysms are detected. However, not every aneurysm is prone to rupture. Because treatment morbidity is about 10% it is crucial to identify unstable aneurysms for which treatment should be discussed. Recently, new imaging tools allow analysis of flow dynamics and wall stability have become available. It seems that they might provide additional data for better risk profiling. In this study we present a new imaging tool for analysis of flow dynamics, which calculates fluid velocity in an aneurysm (Phillips Electronics, N.V.. It may identify regions with high flow and calculate flow reduction after stenting of aneurysms. Contrast is injected with a stable injection speed of 2 mL/sec for 3 sec. Two clinical cases are illustrated. Velocity in aneurysms and areas of instability can be identified and calculated during angiography in real-time. After stenting and flow diverter deployment flow reduction in the internal carotid aneurysm was reduced by 60% and there was a reduction of about 65% in the posterior cerebral artery in the second case we are reporting. The dynamic flow software calculates the flow profile in the aneurysm immediately after contrast injection. It is a real-time, patient specific tool taking into account systole, diastole and flexibility of the vasculature. These factors are an improvement as compared to current models of computational flow dynamics. We think it is a highly efficient, user friendly tool. Further clinical studies are on their way.

  1. Ratio of left ventricular peak E-wave velocity to flow propagation velocity assessed by color M-mode Doppler echocardiography in first myocardial infarction

    DEFF Research Database (Denmark)

    Møller, J E; Søndergaard, E; Seward, J B

    2000-01-01

    OBJECTIVES: To determine the ability of the ratio of peak E-wave velocity to flow propagation velocity (E/Vp) measured with color M-mode Doppler echocardiography to predict in-hospital heart failure and cardiac mortality in an unselected consecutive population with first myocardial infarction (MI...

  2. Determination of drift-flux velocity as a function of two-phase flow patterns

    International Nuclear Information System (INIS)

    Austregesilo Filho, H.

    1986-01-01

    A method is suggested for the calculation of drift-flux velocity as a function of two-phase flow patterns determined analytically. This model can be introduced in computer codes for thermal hydraulic analyses based mainly on homogeneous assumptions, in order to achieve a more realis tic description of two-phase flow phenomena, which is needed for the simulation of accidents in nuclear power plants for which phase separation effects are dominant, e.g., small break accidents. (Author) [pt

  3. Simultaneous measurement of particle and fluid velocities in particle-laden flows

    International Nuclear Information System (INIS)

    Jin, D. X.; Lee, D. Y.

    2009-01-01

    For the velocity measurement in a particle-laden fluid flow, the fluid velocity and the inherently dispersed particle velocity can be analyzed by using PIV and PTV, respectively. Since the PIV result statistically represents the average displacement of all the particles in a PIV image, it is inevitable that the PIV result includes the influence of the dispersed particles' displacement if a single CCD camera is used to simultaneously measure the fluid velocity and the dispersed particle velocity. The influence of dispersed particles should be excluded before the PIV analysis in order to evaluate the fluid velocity accurately. In this study, the optimum replacement brightness of dispersed particles to minimize the false influence of dispersed particles on the PIV analysis was theoretically derived. Simulation results show that the modification of dispersed particle brightness can significantly reduce the PIV error caused by the dispersed particles. This modification method was also verified in the analysis of an actual experimental case of the particle-laden fluid flow in a triangular grooved channel

  4. Whole blood viscosity and cerebral blood flow velocities in obese hypertensive or obese normotensive adolescents.

    Science.gov (United States)

    Akcaboy, Meltem; Nazliel, Bijen; Goktas, Tayfun; Kula, Serdar; Celik, Bülent; Buyan, Necla

    2018-01-26

    Obesity affects all major organ systems and leads to increased morbidity and mortality. Whole blood viscosity is an important independent regulator of cerebral blood flow. The aim of the present study was to evaluate the effect of whole blood viscosity on cerebral artery blood flow velocities using transcranial Doppler ultrasound in pediatric patients with obesity compared to healthy controls and analyze the effect of whole blood viscosity and blood pressure status to the cerebral artery blood flow velocities. Sixty patients with obesity diagnosed according to their body mass index (BMI) percentiles aged 13-18 years old were prospectively enrolled. They were grouped as hypertensive or normotensive according to their ambulatory blood pressure monitoring. Whole blood viscosity and middle cerebral artery velocities by transcranial Doppler ultrasound were studied and compared to 20 healthy same aged controls. Whole blood viscosity values in hypertensive (0.0619±0.0077 poise) and normotensive (0.0607±0.0071 poise) groups were higher than controls (0.0616±0.0064 poise), with no significance. Middle cerebral artery blood flow velocities were higher in the obese hypertensive (73.9±15.0 cm/s) and obese normotensive groups (75.2±13.5 cm/s) than controls (66.4±11.5 cm/s), but with no statistical significance. Physiological changes in blood viscosity and changes in blood pressure did not seem to have any direct effect on cerebral blood flow velocities, the reason might be that the cerebral circulation is capable of adaptively modulating itself to changes to maintain a uniform cerebral blood flow.

  5. Colloid release and clogging in porous media: Effects of solution ionic strength and flow velocity.

    Science.gov (United States)

    Torkzaban, Saeed; Bradford, Scott A; Vanderzalm, Joanne L; Patterson, Bradley M; Harris, Brett; Prommer, Henning

    2015-10-01

    The release and retention of in-situ colloids in aquifers play an important role in the sustainable operation of managed aquifer recharge (MAR) schemes. The processes of colloid release, retention, and associated permeability changes in consolidated aquifer sediments were studied by displacing native groundwater with reverse osmosis-treated (RO) water at various flow velocities. Significant amounts of colloid release occurred when: (i) the native groundwater was displaced by RO-water with a low ionic strength (IS), and (ii) the flow velocity was increased in a stepwise manner. The amount of colloid release and associated permeability reduction upon RO-water injection depended on the initial clay content of the core. The concentration of released colloids was relatively low and the permeability reduction was negligible for the core sample with a low clay content of about 1.3%. In contrast, core samples with about 6 and 7.5% clay content exhibited: (i) close to two orders of magnitude increase in effluent colloid concentration and (ii) more than 65% permeability reduction. Incremental improvement in the core permeability was achieved when the flow velocity increased, whereas a short flow interruption provided a considerable increase in the core permeability. This dependence of colloid release and permeability changes on flow velocity and colloid concentration was consistent with colloid retention and release at pore constrictions due to the mechanism of hydrodynamic bridging. A mathematical model was formulated to describe the processes of colloid release, transport, retention at pore constrictions, and subsequent permeability changes. Our experimental and modeling results indicated that only a small fraction of the in-situ colloids was released for any given change in the IS or flow velocity. Comparison of the fitted and experimentally measured effluent colloid concentrations and associated changes in the core permeability showed good agreement, indicating that the

  6. Blood flow velocity in the Popliteal Vein using Transverse Oscillation Ultrasound

    DEFF Research Database (Denmark)

    Bechsgaard, Thor; Lindskov Hansen, Kristoffer; Brandt, Andreas Hjelm

    2016-01-01

    Chronic venous disease is a common condition leading to varicose veins, leg edema, post-thrombotic syndrome and venous ulcerations. Ultrasound (US) is the main modality for examination of venous disease. Color Doppler and occasionally spectral Doppler US (SDUS) are used for evaluation of the venous...... flow. Peak velocities measured by SDUS are rarely used in a clinical setting for evaluating chronic venous disease due to inadequate reproducibility mainly caused by the angle dependency of the estimate. However, estimations of blood velocities are of importance in characterizing venous disease....... Transverse Oscillation US (TOUS), a non-invasive angle independent method, has been implemented on a commercial scanner. TOUS’s advantage compared to SDUS is a more elaborate visualization of complex flow. The aim of this study was to evaluate, whether TOUS perform equal to SDUS for recording velocities...

  7. Nonlinear output feedback control of underwater vehicle propellers using feedback form estimated axial flow velocity

    DEFF Research Database (Denmark)

    Fossen, T. I.; Blanke, Mogens

    2000-01-01

    Accurate propeller shaft speed controllers can be designed by using nonlinear control theory and feedback from the axial water velocity in the propeller disc. In this paper, an output feedback controller is derived, reconstructing the axial flow velocity from vehicle speed measurements, using...... a three-state model of propeller shaft speed, forward (surge) speed of the vehicle, and the axial flow velocity. Lyapunov stability theory is used to prove that a nonlinear observer combined with an output feedback integral controller provide exponential stability. The output feedback controller...... compensates for variations in thrust due to time variations in advance speed. This is a major problem when applying conventional vehicle-propeller control systems, The proposed controller is simulated for an underwater vehicle equipped with a single propeller. The simulations demonstrate that the axial water...

  8. Visualisation of air–water bubbly column flow using array Ultrasonic Velocity Profiler

    Directory of Open Access Journals (Sweden)

    Munkhbat Batsaikhan

    2017-11-01

    Full Text Available In the present work, an experimental study of bubbly two-phase flow in a rectangular bubble column was performed using two ultrasonic array sensors, which can measure the instantaneous velocity of gas bubbles on multiple measurement lines. After the sound pressure distribution of sensors had been evaluated with a needle hydrophone technique, the array sensors were applied to two-phase bubble column. To assess the accuracy of the measurement system with array sensors for one and two-dimensional velocity, a simultaneous measurement was performed with an optical measurement technique called particle image velocimetry (PIV. Experimental results showed that accuracy of the measurement system with array sensors is under 10% for one-dimensional velocity profile measurement compared with PIV technique. The accuracy of the system was estimated to be under 20% along the mean flow direction in the case of two-dimensional vector mapping.

  9. Middle cerebral artery blood velocity and cerebral blood flow and O2 uptake during dynamic exercise

    DEFF Research Database (Denmark)

    Madsen, P L; Sperling, B K; Warming, T

    1993-01-01

    . To investigate this controversy, we applied the Kety-Schmidt technique to measure the global average levels of CBF and cerebral metabolic rate of oxygen (CMRO2) during rest and dynamic exercise. Simultaneously with the determination of CBF and CMRO2, we used TCD to determine mean maximal flow velocity...

  10. Voluntary respiratory control and cerebral blood flow velocity upon ice-water immersion

    DEFF Research Database (Denmark)

    Mantoni, Teit; Rasmussen, Jakob Højlund; Belhage, Bo

    2008-01-01

    In non-habituated subjects, cold-shock response to cold-water immersion causes rapid reduction in cerebral blood flow velocity (approximately 50%) due to hyperventilation, increasing risk of syncope, aspiration, and drowning. Adaptation to the response is possible, but requires several cold immer...

  11. Influence of caffeine and caffeine withdrawal on headache and cerebral blood flow velocities

    NARCIS (Netherlands)

    Couturier, EGM; Laman, DM; vanDuijn, MAJ; vanDuijn, H

    Caffeine consumption may cause headache, particularly migraine. Its withdrawal also produces headaches and may be related to weekend migraine attacks. Transcranial Doppler sonography (TCD) has shown changes in cerebral blood flow velocities (BFV) during and between attacks of migraine. In order to

  12. Voluntary respiratory control and cerebral blood flow velocity upon ice-water immersion

    DEFF Research Database (Denmark)

    Mantoni, Teit; Rasmussen, Jakob Højlund; Belhage, Bo

    2008-01-01

    INTRODUCTION: In non-habituated subjects, cold-shock response to cold-water immersion causes rapid reduction in cerebral blood flow velocity (approximately 50%) due to hyperventilation, increasing risk of syncope, aspiration, and drowning. Adaptation to the response is possible, but requires seve...

  13. Correction factor to dye-measured flow velocity under varying water and sediment discharges

    Science.gov (United States)

    Dye-tracing technique was a widely used method to measure velocity of overland flow in soil erosion studies under both laboratory and field conditions. Few studies were performed to quantify the effects of sediment load on correction factor on steep slopes. The objective was to investigate the poten...

  14. Constitutive Curve and Velocity Profile in Entangled Polymers during Start-Up of Steady Shear Flow

    KAUST Repository

    Hayes, Keesha A.

    2010-05-11

    Time-dependent shear stress versus shear rate, constitutive curve, and velocity profile measurements are reported in entangled polymer solutions during start-up of steady shear flow. By combining confocal microscopy and particle image velocimetry (PIV), we determine the time-dependent velocity profile in polybutadiene and polystyrene solutions seeded with fluorescent 150 nm silica and 7.5 μm melamine particles. By comparing these profiles with time-dependent constitutive curves obtained from experiment and theory, we explore the connection between transient nonmonotonic regions in the constitutive curve for an entangled polymer and its susceptibility to unstable flow by shear banding [Adams et al. Phys. Rev. Lett. 2009, 102, 067801-4]. Surprisingly, we find that even polymer systems which exhibit transient, nonmonotonic shear stress-shear rate relationships in bulk rheology experiments manifest time-dependent velocity profiles that are decidedly linear and show no evidence of unstable flow. We also report that interfacial slip plays an important role in the steady shear flow behavior of entangled polymers at shear rates above the reciprocal terminal relaxation time but has little, if any, effect on the shape of the velocity profile. © 2010 American Chemical Society.

  15. Flow characteristics in an expansion tunnel as inferred from velocity measurements

    Science.gov (United States)

    Miller, C. G.; Friesen, W. J.

    1977-01-01

    A photoionization technique was used to study flow characteristics in an expansion tunnel. Vertical surveys of the axial component of flow velocity just downstream from the nozzle exit were obtained, and estimates of freestream density were inferred from the velocity measurement technique. The pitot pressure was measured and compared to the average axial component of velocity as a function of time for the two cases when air and CO2 were used as test gases. Vertical velocity and static density profiles at the nozzle exit are presented for the case when CO2 was used as test gas. Experimental results were used to determine the diameter and uniformity of the test core at the nozzle exit and the duration of the quasi-steady flow period. These data are relevant to evaluation of the suitability of operating an expansion tube as an expansion tunnel. The expansion tunnel is an expansion tube with a conical nozzle positioned at the exit of the acceleration section, so that nozzle entrance flow conditions are hypersonic and characterized by hypervelocity.

  16. Surface ice flow velocity and tide retrieval of the amery ice shelf using precise point positioning

    DEFF Research Database (Denmark)

    Zhang, X.H.; Andersen, Ole Baltazar

    2006-01-01

    Five days of continuous GPS observation data were collected in the frontal zone of the Amery ice shelf and subsequently post-processed using precise point position (PPP) technology based on precise orbit and clock products from the International GNSS service. The surface ice flow velocity...

  17. Statistics of the perceived velocity gradient tensor in a rotating turbulent flow

    International Nuclear Information System (INIS)

    Naso, Aurore; Godeferd, Fabien S

    2012-01-01

    The dynamics and structure of rotating homogeneous turbulence is investigated through the statistical properties of the ‘perceived’ velocity gradient tensor, defined by interpolation from the locations and velocities of a set of four particles. The results of direct numerical simulations of forced homogeneous rotating turbulence at different Rossby numbers are presented. We thus provide a multi-scale analysis of the dynamics of rotating turbulence and some of its important features. We present scaling laws for second- and third-order moments of the perceived velocity gradient tensor. We relate the distribution of the enstrophy and strain variance, and of their production terms, to the topology of the flow, thanks to conditional probability density functions. These quantities demonstrate the role played by the Zeman scale in the elementary processes of rotating turbulence, when compared to the scale at which the perceived velocity gradient tensor is measured. (paper)

  18. Numerical Investigation of Viscous Flow Velocity Field around a Marine Cavitating Propeller

    Directory of Open Access Journals (Sweden)

    Zhifeng Zhu

    2014-11-01

    Full Text Available Velocity field around a ship cavitating propeller is investigated based on the viscous multiphase flow theory. Using a hybrid grid, the unsteady Navier-stokes (N-S and the bubble dynamics equations are solved in this paper to predict the velocity in a propeller wake and the vapor volume fraction on the back side of propeller blade for a uniform inflow. Compared with experimental results, the numerical predictions of cavitation and axial velocity coincide with the measured data. The evolution of tip vortex is shown, and the interaction between the tip vortex of the current blade and the wake of the next one occurs in the far propeller wake. The frequency of velocity signals changes from shaft rate to blade rate. The phenomena reflect the instability of propeller wake.

  19. Electromagnetic velocity gauge: use of multiple gauges, time response, and flow perturbations

    International Nuclear Information System (INIS)

    Erickson, L.M.; Johnson, C.B.; Parker, N.L.; Vantine, H.C.; Weingart, R.C.; Lee, R.S.

    1981-01-01

    We have developed an in-situ electromagnetic velocity (EMV) gauge system for use in multiple-gauge studies of initiating and detonating explosives. We have also investigated the risetime of the gauge and the manner in which it perturbs a reactive flow. We report on the special precautions that are necessary in multiple gauge experiments to reduce lead spreading, simplify target fabrication problems and minimize cross talk through the conducting explosive. Agreement between measured stress records and calculations from multiple velocity gauge data give us confidence that our velocity gauges are recording properly. We have used laser velocity interferometry to measure the gauge risetime in polymethyl methacrylate (PMMA). To resolve the difference in the two methods, we have examined hydrodynamic and material rate effects. In addition, we considered the effects of shock tilt, electronic response and magntic diffusion on the gauge's response time

  20. Velocity statistics in holographic fluids: magnetized quark-gluon plasma and superfluid flow

    Energy Technology Data Exchange (ETDEWEB)

    Areán, Daniel [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut),Föhringer Ring 6, D-80805, Munich (Germany); Zayas, Leopoldo A. Pando [The Abdus Salam International Centre for Theoretical Physics,Strada Costiera 11, 34014 Trieste (Italy); Michigan Center for Theoretical Physics, Department of Physics, University of Michigan,450 Church Street, Ann Arbor, MI 48109 (United States); Patiño, Leonardo; Villasante, Mario [Departamento de Física, Facultad de Ciencias, Universidad Nacional Autónoma de México,A.P. 70-542, México D.F. 04510 (Mexico)

    2016-10-28

    We study the velocity statistics distribution of an external heavy particle in holographic fluids. We argue that when the dual supergravity background has a finite temperature horizon the velocity statistics goes generically as 1/v, compatible with the jet-quenching intuition from the quark-gluon plasma. A careful analysis of the behavior of the classical string whose apparent world sheet horizon deviates from the background horizon reveals that other regimes are possible. We numerically discuss two cases: the magnetized quark-gluon plasma and a model of superfluid flow. We explore a range of parameters in these top-down supergravity solutions including, respectively, the magnetic field and the superfluid velocity. We determine that the velocity statistics goes largely as 1/v, however, as we leave the non-relativistic regime we observe some deviations.

  1. Velocity and Temperature Distribution in Flow from an Inlet Device in Rooms with Displacement Ventilation

    DEFF Research Database (Denmark)

    Jacobsen, T.V.; Nielsen, Peter V.

    Measurements are performed in a full-scale test room with displacement ventilation with focus on the velocity and temperature field in the region close to the inlet device. Investigations based on these detailed measurements have been made in order to see if it is possible to describe the velocit...... decay and the shape of velocity and temperature profiles in front of the inlet device by traditional jet theory, by stratified flow theory or by a combination of the two theories.......Measurements are performed in a full-scale test room with displacement ventilation with focus on the velocity and temperature field in the region close to the inlet device. Investigations based on these detailed measurements have been made in order to see if it is possible to describe the velocity...

  2. Lid-driven cavity flow using a discrete velocity method for solving the Boltzmann equation

    Science.gov (United States)

    Sekaran, Aarthi; Varghese, Philip; Estes, Samuel; Goldstein, David

    2016-11-01

    We extend the discrete velocity method for solving the Boltzmann equation previously used for one-dimensional problems to two spatial dimensions. The collision integral is computed using collisions between velocity classes selected randomly using a Monte Carlo method. Arbitrary post-collision velocities are mapped back onto the grid using a projection scheme which conserves mass, momentum, and energy. In addition, a variance reduction scheme is implemented to decrease noise and further reduce computational effort. The convection part of the equation is computed using first order upwind finite differences. We apply this discrete velocity scheme to the 2D lid-driven square cavity flow problem with Ar as the fluid medium and explore the effect of the additional flexibility available in this quasi-particle based stochastic method on the accuracy and noise level in the solutions obtained.

  3. In-vivo Examples of Flow Patterns With The Fast Vector Velocity Ultrasound Method

    DEFF Research Database (Denmark)

    Hansen, Kristoffer Lindskov; Udesen, Jesper; Gran, Fredrik

    2009-01-01

    Purpose: Conventional ultrasound methods for acquiring color flow images of the blood motion are limited by a relatively low frame rate and are restricted to only giving velocity estimates along the ultrasound beam direction. To circumvent these limitations, the Plane Wave Excitation (PWE) method...... has been proposed. Material and Methods: The PWE method can estimate the 2D vector velocity of the blood with a high frame rate. Vector velocity estimates are acquired by using the following approach: The ultrasound is not focused during the ultrasound transmission, and a full speckle image...... of the blood can be acquired for each pulse emission. The pulse is a 13 bit Barker code transmitted simultaneously from each transducer element. The 2D vector velocity of the blood is found using 2D speckle tracking between segments in consecutive speckle images. Implemented on the experimental scanner RASMUS...

  4. Optical Feedback Interferometry for Velocity Measurement of Parallel Liquid-Liquid Flows in a Microchannel

    Science.gov (United States)

    Ramírez-Miquet, Evelio E.; Perchoux, Julien; Loubière, Karine; Tronche, Clément; Prat, Laurent; Sotolongo-Costa, Oscar

    2016-01-01

    Optical feedback interferometry (OFI) is a compact sensing technique with recent implementation for flow measurements in microchannels. We propose implementing OFI for the analysis at the microscale of multiphase flows starting with the case of parallel flows of two immiscible fluids. The velocity profiles in each phase were measured and the interface location estimated for several operating conditions. To the authors knowledge, this sensing technique is applied here for the first time to multiphase flows. Theoretical profiles issued from a model based on the Couette viscous flow approximation reproduce fairly well the experimental results. The sensing system and the analysis presented here provide a new tool for studying more complex interactions between immiscible fluids (such as liquid droplets flowing in a microchannel). PMID:27527178

  5. The feasibility of substituting left atrial wall strain for flow velocity of left atrial appendage.

    Science.gov (United States)

    Miyoshi, Akihito; Nakamura, Yoichi; Kazatani, Yukio; Ito, Hiroshi

    2017-07-28

    Non-valvular atrial fibrillation (NVAF) is frequently complicated by thromboembolism. Left atrial appendage (LAA) flow is a predictor of LAA thrombosis. LAA flow is measured by transesophageal echocardiography (TEE), which is a semi-invasive diagnostic tool. Recently, speckle-tracking methods have been adapted for the evaluation of local cardiac function. We hypothesised that if we could determine LAA wall motion utilising a speckle tracking technique, we could non-invasively analyse LAA flow. Sixty-three NVAF patients including 38 with chronic atrial fibrillation (CAF), 14 with paroxysmal AF (PAF) and 11 with atrial flutter (AFL) were enrolled in this study. Normal sinus rhythm (NSR) patients with non-thromboembolic cerebral infarction were also included. Immediately after obtaining a 2D movie of the LAA through the aortic oblique short axis view by transthoracic echocardiography, LAA flow velocity was measured by TEE. Mean strains between the posterior and anterior walls were measured using a speckle-tracking technique. Ten patients exhibited a thrombus and 11 had spontaneous echo contrast (SEC) in the auricle. Mean strain value was similar between CAF and PAF, although LAA flow velocity for CAF was significantly reduced compared with PAF (median value 13.7 cm/s versus 36.1 cm/s, p = reduced compared with NSR patients (median value 1.52% versus 3.17%, p = .00181). Furthermore, mean strain was correlated with LAA flow velocity (R = 0.399, R2 = 0.1595, p = .000615). LAA wall strain identified via speckle-tracking methods may presage LAA peak flow velocity. This technique may contribute to stratification of thrombosis risks in the LAA.

  6. Visualization of velocity field and phase distribution in gas-liquid two-phase flow by NMR imaging

    International Nuclear Information System (INIS)

    Matsui, G.; Monji, H.; Obata, J.

    2004-01-01

    NMR imaging has been applied in the field of fluid mechanics, mainly single phase flow, to visualize the instantaneous flow velocity field. In the present study, NMR imaging was used to visualize simultaneously both the instantaneous phase structure and velocity field of gas-liquid two-phase flow. Two methods of NMR imaging were applied. One is useful to visualize both the one component of liquid velocity and the phase distribution. This method was applied to horizontal two-phase flow and a bubble rising in stagnant oil. It was successful in obtaining some pictures of velocity field and phase distribution on the cross section of the pipe. The other is used to visualize a two-dimensional velocity field. This method was applied to a bubble rising in a stagnant water. The velocity field was visualized after and before the passage of a bubble at the measuring cross section. Furthermore, the distribution of liquid velocity was obtained. (author)

  7. Comparison of thermal, salt and dye tracing to estimate shallow flow velocities: Novel triple-tracer approach

    Science.gov (United States)

    Abrantes, João R. C. B.; Moruzzi, Rodrigo B.; Silveira, Alexandre; de Lima, João L. M. P.

    2018-02-01

    The accurate measurement of shallow flow velocities is crucial to understand and model the dynamics of sediment and pollutant transport by overland flow. In this study, a novel triple-tracer approach was used to re-evaluate and compare the traditional and well established dye and salt tracer techniques with the more recent thermal tracer technique in estimating shallow flow velocities. For this purpose a triple tracer (i.e. dyed-salted-heated water) was used. Optical and infrared video cameras and an electrical conductivity sensor were used to detect the tracers in the flow. Leading edge and centroid velocities of the tracers were measured and the correction factors used to determine the actual mean flow velocities from tracer measured velocities were compared and investigated. Experiments were carried out for different flow discharges (32-1813 ml s-1) on smooth acrylic, sand, stones and synthetic grass bed surfaces with 0.8, 4.4 and 13.2% slopes. The results showed that thermal tracers can be used to estimate shallow flow velocities, since the three techniques yielded very similar results without significant differences between them. The main advantages of the thermal tracer were that the movement of the tracer along the measuring section was more easily visible than it was in the real image videos and that it was possible to measure space-averaged flow velocities instead of only one velocity value, with the salt tracer. The correction factors used to determine the actual mean velocity of overland flow varied directly with Reynolds and Froude numbers, flow velocity and slope and inversely with flow depth and bed roughness. In shallow flows, velocity estimation using tracers entails considerable uncertainty and caution must be taken with these measurements, especially in field studies where these variables vary appreciably in space and time.

  8. Flow velocity effect on the corrosion/erosion in water injection systems

    International Nuclear Information System (INIS)

    Jimenez, C.; Mendez, J.

    1998-01-01

    The main causes of fails at water injection lines on the secondary petroleum recovery systems are related with corrosion/erosion problems which are influenced by the flow velocity, the presence of dissolved oxygen, solids in the medium and the microorganisms proliferation. So too, this corrosion process promotes the suspended solids generation which affects the water quality injected, causing wells tamponage and loss of injectivity, with the consequent decrease in the crude production. This situation has been impacted in meaning order at the production processes of an exploration enterprise which utilizes the Maracaibo lake as water resource for their injection by pattern projects. Stating that, it was developed a study for determining in experimental order the effect of flow velocity on the corrosion/erosion process joined to the presence of dissolved oxygen which allows to determine the optimum range of the said working velocity for the water injection systems. This range is defined by critical velocities of bio layers deposition and erosion. They were realized simulation pilot tests of the corrosion standard variables, concentration of dissolved oxygen and fluid velocity in the injection systems with filtered and non filtered water. For the development of these tests it was constructed a device which allows to install and expose cylindrical manometers of carbon steel according to predetermined conditions which was obtained the necessary information to make correlations the results of these variables. Additionally, they were determined the mathematical models that adjusts to dynamical behavior of the corrosion/erosion process, finding the optimum range of the flow velocity for the control of this process, being necessary to utilize the following techniques: Scanning Electron Microscopy (SEM), X-ray dispersion analysis (EDX) for encourage the surface studies. They were effected morphological analysis of the surfaces studies and the values were determined of

  9. The influence of the tangential velocity of inner rotating wall on axial velocity profile of flow through vertical annular pipe with rotating inner surface

    Directory of Open Access Journals (Sweden)

    Sharf Abdusalam M.

    2014-03-01

    Full Text Available In the oil and gas industries, understanding the behaviour of a flow through an annulus gap in a vertical position, whose outer wall is stationary whilst the inner wall rotates, is a significantly important issue in drilling wells. The main emphasis is placed on experimental (using an available rig and computational (employing CFD software investigations into the effects of the rotation speed of the inner pipe on the axial velocity profiles. The measured axial velocity profiles, in the cases of low axial flow, show that the axial velocity is influenced by the rotation speed of the inner pipe in the region of almost 33% of the annulus near the inner pipe, and influenced inversely in the rest of the annulus. The position of the maximum axial velocity is shifted from the centre to be nearer the inner pipe, by increasing the rotation speed. However, in the case of higher flow, as the rotation speed increases, the axial velocity is reduced and the position of the maximum axial velocity is skewed towards the centre of the annulus. There is a reduction of the swirl velocity corresponding to the rise of the volumetric flow rate.

  10. Improved Blood Pressure Prediction Using Systolic Flow Correction of Pulse Wave Velocity.

    Science.gov (United States)

    Lillie, Jeffrey S; Liberson, Alexander S; Borkholder, David A

    2016-12-01

    Hypertension is a significant worldwide health issue. Continuous blood pressure monitoring is important for early detection of hypertension, and for improving treatment efficacy and compliance. Pulse wave velocity (PWV) has the potential to allow for a continuous blood pressure monitoring device; however published studies demonstrate significant variability in this correlation. In a recently presented physics-based mathematical model of PWV, flow velocity is additive to the classic pressure wave as estimated by arterial material properties, suggesting flow velocity correction may be important for cuff-less non-invasive blood pressure measures. The present study examined the impact of systolic flow correction of a measured PWV on blood pressure prediction accuracy using data from two published in vivo studies. Both studies examined the relationship between PWV and blood pressure under pharmacological manipulation, one in mongrel dogs and the other in healthy adult males. Systolic flow correction of the measured PWV improves the R 2 correlation to blood pressure from 0.51 to 0.75 for the mongrel dog study, and 0.05 to 0.70 for the human subjects study. The results support the hypothesis that systolic flow correction is an essential element of non-invasive, cuff-less blood pressure estimation based on PWV measures.

  11. A GIS-based Computational Tool for Multidimensional Flow Velocity by Acoustic Doppler Current Profilers

    International Nuclear Information System (INIS)

    Kim, D; Winkler, M; Muste, M

    2015-01-01

    Acoustic Doppler Current Profilers (ADCPs) provide efficient and reliable flow measurements compared to other tools for characteristics of the riverine environments. In addition to originally targeted discharge measurements, ADCPs are increasingly utilized to assess river flow characteristics. The newly developed VMS (Velocity Mapping Software) aims at providing an efficient process for quality assurance, mapping velocity vectors for visualization and facilitating comparison with physical and numerical model results. VMS was designed to provide efficient and smooth work flows for processing groups of transects. The software allows the user to select group of files and subsequently to conduct statistical and graphical quality assurance on the files as a group or individually as appropriate. VMS also enables spatial averaging in horizontal and vertical plane for ADCP data in a single or multiple transects over the same or consecutive cross sections. The analysis results are displayed in numerical and graphical formats. (paper)

  12. Magnetic resonance velocity imaging of liquid and gas two-phase flow in packed beds.

    Science.gov (United States)

    Sankey, M H; Holland, D J; Sederman, A J; Gladden, L F

    2009-02-01

    Single-phase liquid flow in porous media such as bead packs and model fixed bed reactors has been well studied by MRI. To some extent this early work represents the necessary preliminary research to address the more challenging problem of two-phase flow of gas and liquid within these systems. In this paper, we present images of both the gas and liquid velocities during stable liquid-gas flow of water and SF(6) within a packing of 5mm spheres contained within columns of diameter 40 and 27 mm; images being acquired using (1)H and (19)F observation for the water and SF(6), respectively. Liquid and gas flow rates calculated from the velocity images are in agreement with macroscopic flow rate measurements to within 7% and 5%, respectively. In addition to the information obtained directly from these images, the ability to measure liquid and gas flow fields within the same sample environment will enable us to explore the validity of assumptions used in numerical modelling of two-phase flows.

  13. Blood flow velocity in the middle cerebral artery during transnasal endoscopic skull base surgery performed in controlled hypotension.

    Science.gov (United States)

    Sieskiewicz, Andrzej; Lyson, Tomasz; Drozdowski, Andrzej; Piszczatowski, Bartosz; Rutkowski, Robert; Turek, Grzegorz; Lewczuk, Anna; Rogowski, Marek; Mariak, Zenon

    2014-01-01

    To assess blood flow velocity in the middle cerebral artery (MCA) during transnasal endoscopic procedures performed with decreased hemodynamic parameters. In 40 patients who underwent endoscopic skull base surgery in controlled hypotension (studied group) and in 13 patients operated without reduction of hemodynamic parameters (control group), blood flow velocity in MCA was assessed with transcranial color Doppler sonography. Blood flow velocity in MCA remained within the range of age-specific reference values in all patients before operation. It decreased significantly in both groups after induction of anesthesia and then dropped even further in studied group of patients when hemodynamic parameters were reduced; the systolic velocity fell below the normal reference values in 25% of patients, the mean velocity in 50% and the diastolic velocity in 57% of patients. The diastolic velocity was much more heavily influenced by diminished hemodynamic parameters than systolic velocity in the studied group as opposed to the control group where reduction of blood flow velocity pertained equally systolic and diastolic velocity. During transnasal endoscopic procedures performed in moderate hypotension, in addition to significant drop of blood flow velocity to values well below the normal reference range, a divergent reduction of systolic and diastolic velocity was detected. Since divergent systolic and diastolic velocity may indicate an early phase of cerebral autoregulation compromise, and the decrease of mean blood flow velocity in MCA corresponds with a decrease of cerebral blood flow, further investigations in this field seem warranted. Copyright © 2014 Polish Neurological Society. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.

  14. Measurements of flow velocity and temperature profile in a propane-oxygen combustion MHD channel

    International Nuclear Information System (INIS)

    Aoki, Yoshiaki; Kayukawa, Naoyuki; Yamazaki, Hatsuo

    1986-01-01

    In a propane-oxygen combustion MHD channel, experimental measurements were made of the plasma flow velocity by means of a cross-correlation function analysis and of the boundary-layer temperature-profile by a newly-devised light-polarization line-reversal method. The following results were obtained: the velocity decreased gradually, the temperature profile of the boundary layer varied appreciably as the magnitude of the externally applied magnetic field increased, and the temperature increased from Joule heating, making the boundary layer profile steeper. (author)

  15. Point and planar LIF for velocity-concentration correlations in a jet in cross flow

    DEFF Research Database (Denmark)

    Meyer, Knud Erik; Özcan, Oktay; Larsen, Poul Scheel

    2002-01-01

    velocities, mean concentration and Reynolds fluxes in the symmetry plane of the jet are presented for PIV and PLIF measurements. The LIF measurements performed with the LDA equipment was in general in good agreement with the PIV/PLIF measurements. The cross sections selected for comparison are challenging......, since these involve areas with high velocity- and concentration gradients, which in turn amplifies the effect of a finite measurement volume in the two measurement systems. In addition, the concentration measurement was realized by injecting clean water into the dye seeded main flow. This "inverse...

  16. MR velocity mapping measurement of renal artery blood flow in patients with impaired kidney function

    DEFF Research Database (Denmark)

    Cortsen, M; Petersen, L.J.; Stahlberg, F

    1996-01-01

    . MR velocity mapping was performed in both renal arteries using an ECG-triggered gradient echo pulse sequence previously validated in normal volunteers. Effective renal plasma flow was calculated from the clearance rate of PAH during constant infusion and the split of renal function was evaluated...... by 99mTc-DTPA scintigraphy. A reduction of RBF was found, and there was a significant correlation between PAH clearance multiplied by 1/(1-hematocrit) and RBF determined by MR velocity mapping. Furthermore, a significant correlation between the distribution of renal function and the percent distribution...

  17. Experiment on effect of water flow velocity on migration of strontium

    International Nuclear Information System (INIS)

    Wang Zhiming; Guo Qian; Li Shushen; Jiao Zhilan; Meng Liping; Guo Zhiming

    2003-01-01

    Tracer migration experiment of stable elements, strontium, is conducted in both unsaturated and saturated columns with undisturbed loess. It is found from the experiment that retardation coefficient, R d , of Sr can be joined up very well. It can be seen that retardation coefficient, R d , of Sr in loess is not constant and increases with water flow velocity either in unsaturated columns or in saturated columns, as well as migration velocity of Sr at unit sprinkling rate decreases with sprinkling rate according to positions of either peaks or mass centers. It is shown that to use equilibrium adsorption model is not proper for describing migration of Sr in loess

  18. Flow field velocity measurements for non-isothermal systems. [of chemically reactive flow inside fused silica CVD reactor vessels

    Science.gov (United States)

    Johnson, E. J.; Hyer, P. V.; Culotta, P. W.; Clark, I. O.

    1991-01-01

    Experimental techniques which can be potentially utilized to measure the gas velocity fields in nonisothermal CVD systems both in ground-based and space-based investigations are considered. The advantages and disadvantages of a three-component laser velocimetry (LV) system that was adapted specifically for quantitative determination of the mixed convective flows in a chamber for crystal growth and film formation by CVD are discussed. Data from a horizontal research CVD reactor indicate that current models for the effects of thermophoretic force are not adequate to predict the thermophoretic bias in arbitrary flow configurations. It is concluded that LV techniques are capable of characterizing the fluid dynamics of a CVD reactor at typical growth temperatures. Thermal effects are shown to dominate and stabilize the fluid dynamics of the reactor. Heating of the susceptor increases the gas velocities parallel to the face of a slanted susceptor by up to a factor of five.

  19. The Three-Dimensional Velocity Distribution of Wide Gap Taylor-Couette Flow Modelled by CFD

    Directory of Open Access Journals (Sweden)

    David Shina Adebayo

    2016-01-01

    Full Text Available A numerical investigation is conducted for the flow between two concentric cylinders with a wide gap, relevant to bearing chamber applications. This wide gap configuration has received comparatively less attention than narrow gap journal bearing type geometries. The flow in the gap between an inner rotating cylinder and an outer stationary cylinder has been modelled as an incompressible flow using an implicit finite volume RANS scheme with the realisable k-ε model. The model flow is above the critical Taylor number at which axisymmetric counterrotating Taylor vortices are formed. The tangential velocity profiles at all axial locations are different from typical journal bearing applications, where the velocity profiles are quasilinear. The predicted results led to two significant findings of impact in rotating machinery operations. Firstly, the axial variation of the tangential velocity gradient induces an axially varying shear stress, resulting in local bands of enhanced work input to the working fluid. This is likely to cause unwanted heat transfer on the surface in high torque turbomachinery applications. Secondly, the radial inflow at the axial end-wall boundaries is likely to promote the transport of debris to the junction between the end-collar and the rotating cylinder, causing the build-up of fouling in the seal.

  20. Effect of flow velocity on the photoacoustic detection for glucose aqueous solutions

    Science.gov (United States)

    Ren, Zhong; Liu, Guodong; Ding, Yu; Yao, Qingkai

    2018-01-01

    The blood glucose non-invasive detection has become the research hot-spot. The photoacoustic spectroscopy is a well-promising, high-efficient and noninvasive detection method because it combines the advantages of the pure optic and pure ultrasonic. In practice, the photoacoustic detection of blood glucose is impacted by many factors because the human body is a complicated bio-system. To study the effect of flow velocity in the blood vessel on the photoacoustic detection of blood glucose, a photoacoustic detection system based on optical parameter oscillator (OPO) pulsed laser induced ultrasonic was established. In this system, a 532nm pumped Nd: YAG OPO pulsed laser was used as the excitation source, and the photoacoustic signals of glucose were captured by ultrasonic transducer. Moreover, a set of blood circulation system was built to simulate the real blood flow situation in the human body. The experiments of the photoacoustic detection of glucose aqueous solutions with different concentrations at different flow velocities were experimentally investigated. Experimental results show that the photoacoustic peak-to-peak value linearly increases with the glucose concentration, but it decreases with the increase of the flow velocity although the profiles of photoacoustic signals don't change.

  1. Cerebral blood flow velocity in migraine and chronic tension-type headache patients

    Directory of Open Access Journals (Sweden)

    Karacay Ozkalayci S

    2018-04-01

    Full Text Available S Karacay Ozkalayci, B Nazliel, HZ Batur Caglayan, C Irkec Department of Neurology, Faculty of Medicine, Gazi University, Ankara, Turkey Introduction: The present study seeks to use transcranial Doppler ultrasound to evaluate cerebral blood flow velocities in anterior and posterior circulation arteries, during an attack-free episode in migraine patients, with and without aura, as well as in chronic tension-type headache patients who were not receiving prophylactic medication. Methods: A total of 50 patients (35 female, 15 male were evaluated during a headache-free episode: 30 migraine patients without aura (mean age: 32±8 years, 10 migraine patients with aura (mean age: 34±4 years, and 10 patients with chronic tension-type headache (mean age: 34±5 years. Results: No significant difference was present between anterior, middle, and posterior cerebral and vertebral arteries’ blood flow velocities between migraine patients, with and without aura, or in patients with a tension-type headache, and normal controls (p>0.05. However, a significant increase in basilar artery cerebral blood flow velocities relative to controls was present in patients with a tension-type headache (p>0.001. Conclusion: It is difficult to predict the main reason for the significant increase in basilar artery blood flow velocities in patients with chronic tension-type headache. It may be due to constriction of conductance or the dilatation of the resistance vessels. Keywords: cerebral blood flow, migraine without aura, migraine with aura, tension-type headache, transcranial Doppler ultrasonography 

  2. Semi-Empirical Estimation of Dean Flow Velocity in Curved Microchannels.

    Science.gov (United States)

    Bayat, Pouriya; Rezai, Pouya

    2017-10-20

    Curved and spiral microfluidic channels are widely used in particle and cell sorting applications. However, the average Dean velocity of secondary vortices which is an important design parameter in these devices cannot be estimated precisely with the current knowledge in the field. In this paper, we used co-flows of dyed liquids in curved microchannels with different radii of curvatures and monitored the lateral displacement of fluids using optical microscopy. A quantitative Switching Index parameter was then introduced to calculate the average Dean velocity in these channels. Additionally, we developed a validated numerical model to expand our investigations to elucidating the effects of channel hydraulic diameter, width, and height as well as fluid kinematic viscosity on Dean velocity. Accordingly, a non-dimensional comprehensive correlation was developed based on our numerical model and validated against experimental results. The proposed correlation can be used extensively for the design of curved microchannels for manipulation of fluids, particles, and biological substances in spiral microfluidic devices.

  3. Statistics of spatial derivatives of velocity and pressure in turbulent channel flow

    Science.gov (United States)

    Vreman, A. W.; Kuerten, J. G. M.

    2014-08-01

    Statistical profiles of the first- and second-order spatial derivatives of velocity and pressure are reported for turbulent channel flow at Reτ = 590. The statistics were extracted from a high-resolution direct numerical simulation. To quantify the anisotropic behavior of fine-scale structures, the variances of the derivatives are compared with the theoretical values for isotropic turbulence. It is shown that appropriate combinations of first- and second-order velocity derivatives lead to (directional) viscous length scales without explicit occurrence of the viscosity in the definitions. To quantify the non-Gaussian and intermittent behavior of fine-scale structures, higher-order moments and probability density functions of spatial derivatives are reported. Absolute skewnesses and flatnesses of several spatial derivatives display high peaks in the near wall region. In the logarithmic and central regions of the channel flow, all first-order derivatives appear to be significantly more intermittent than in isotropic turbulence at the same Taylor Reynolds number. Since the nine variances of first-order velocity derivatives are the distinct elements of the turbulence dissipation, the budgets of these nine variances are shown, together with the budget of the turbulence dissipation. The comparison of the budgets in the near-wall region indicates that the normal derivative of the fluctuating streamwise velocity (∂u'/∂y) plays a more important role than other components of the fluctuating velocity gradient. The small-scale generation term formed by triple correlations of fluctuations of first-order velocity derivatives is analyzed. A typical mechanism of small-scale generation near the wall (around y+ = 1), the intensification of positive ∂u'/∂y by local strain fluctuation (compression in normal and stretching in spanwise direction), is illustrated and discussed.

  4. Experimental investigation of acceleration and velocity fields in turbulent channel flow

    Science.gov (United States)

    Christensen, Kenneth Thor

    2001-12-01

    Time-resolved particle-image velocimetry measurements are made in the streamwise-wall-normal plane of turbulent channel flow at Reτ = 547, 1133, and 1734. These measurements are meant to complement efforts in the development of a new class of large-eddy simulation (LES) subgrid-scale models for the simulation of high-Reynolds-number wall turbulence. Optimal formulations of LES are based upon minimizing the mean-square error associated with estimating the short- term dynamics of the resolved scales of the turbulence. However, due to the empirical nature of optimal LES, extension of optimal formulations to higher Reynolds number requires experimental documentation of the statistical and structural behavior of both the velocity and the evolution of the flow at higher Reynolds numbers. It is found that coherent arrangements of hairpin-like vortices in the outer layer leave their imprint upon the statistics of the flow. Estimates of the conditionally- averaged velocity field associated with a spanwise vortex core consist of a series of swirling motions located along a line inclined away from the wall. This pattern is consistent with the observations of outer-layer turbulence in which groups of hairpin/hairpin-like vortices occur aligned in the streamwise direction. The velocity time derivatives are associated predominantly with small scales in both space and time. Examination of instantaneous and estimates of the conditionally averaged velocity time-derivative fields indicates that the smaller-scale vortices leave a convective imprint upon the time derivatives. Further, the streamwise spectra of the velocity time-derivative support the notion that convective effects dominate the smaller scales of the flow. Comparison between the bulk convective-derivative and time-derivative spectra illustrate this behavior. At low wavenumbers, the bulk convective-derivative and time-derivative spectra coincide with one another, implying that the larger scales are dominated by

  5. High-velocity two-phase flow two-dimensional modeling

    International Nuclear Information System (INIS)

    Mathes, R.; Alemany, A.; Thilbault, J.P.

    1995-01-01

    The two-phase flow in the nozzle of a LMMHD (liquid metal magnetohydrodynamic) converter has been studied numerically and experimentally. A two-dimensional model for two-phase flow has been developed including the viscous terms (dragging and turbulence) and the interfacial mass, momentum and energy transfer between the phases. The numerical results were obtained by a finite volume method based on the SIMPLE algorithm. They have been verified by an experimental facility using air-water as a simulation pair and a phase Doppler particle analyzer for velocity and droplet size measurement. The numerical simulation of a lithium-cesium high-temperature pair showed that a nearly homogeneous and isothermal expansion of the two phases is possible with small pressure losses and high kinetic efficiencies. In the throat region a careful profiling is necessary to reduce the inertial effects on the liquid velocity field

  6. A local sensor for joint temperature and velocity measurements in turbulent flows

    Science.gov (United States)

    Salort, Julien; Rusaouën, Éléonore; Robert, Laurent; du Puits, Ronald; Loesch, Alice; Pirotte, Olivier; Roche, Philippe-E.; Castaing, Bernard; Chillà, Francesca

    2018-01-01

    We present the principle for a micro-sensor aimed at measuring local correlations of turbulent velocity and temperature. The operating principle is versatile and can be adapted for various types of flow. It is based on a micro-machined cantilever, on the tip of which a platinum resistor is patterned. The deflection of the cantilever yields an estimate for the local velocity, and the impedance of the platinum yields an estimate for the local temperature. The velocity measurement is tested in two turbulent jets: one with air at room temperature which allows us to compare with well-known calibrated reference anemometers, and another one in the GReC jet at CERN with cryogenic gaseous helium which allows a much larger range of resolved turbulent scales. The recording of temperature fluctuations is tested in the Barrel of Ilmenau which provides a controlled turbulent thermal flow in air. Measurements in the wake of a heated or cooled cylinder demonstrate the capability of the sensor to display the cross correlation between temperature and velocity correctly.

  7. Satellite angular velocity estimation based on star images and optical flow techniques.

    Science.gov (United States)

    Fasano, Giancarmine; Rufino, Giancarlo; Accardo, Domenico; Grassi, Michele

    2013-09-25

    An optical flow-based technique is proposed to estimate spacecraft angular velocity based on sequences of star-field images. It does not require star identification and can be thus used to also deliver angular rate information when attitude determination is not possible, as during platform de tumbling or slewing. Region-based optical flow calculation is carried out on successive star images preprocessed to remove background. Sensor calibration parameters, Poisson equation, and a least-squares method are then used to estimate the angular velocity vector components in the sensor rotating frame. A theoretical error budget is developed to estimate the expected angular rate accuracy as a function of camera parameters and star distribution in the field of view. The effectiveness of the proposed technique is tested by using star field scenes generated by a hardware-in-the-loop testing facility and acquired by a commercial-off-the shelf camera sensor. Simulated cases comprise rotations at different rates. Experimental results are presented which are consistent with theoretical estimates. In particular, very accurate angular velocity estimates are generated at lower slew rates, while in all cases the achievable accuracy in the estimation of the angular velocity component along boresight is about one order of magnitude worse than the other two components.

  8. Satellite Angular Velocity Estimation Based on Star Images and Optical Flow Techniques

    Directory of Open Access Journals (Sweden)

    Giancarmine Fasano

    2013-09-01

    Full Text Available An optical flow-based technique is proposed to estimate spacecraft angular velocity based on sequences of star-field images. It does not require star identification and can be thus used to also deliver angular rate information when attitude determination is not possible, as during platform de tumbling or slewing. Region-based optical flow calculation is carried out on successive star images preprocessed to remove background. Sensor calibration parameters, Poisson equation, and a least-squares method are then used to estimate the angular velocity vector components in the sensor rotating frame. A theoretical error budget is developed to estimate the expected angular rate accuracy as a function of camera parameters and star distribution in the field of view. The effectiveness of the proposed technique is tested by using star field scenes generated by a hardware-in-the-loop testing facility and acquired by a commercial-off-the shelf camera sensor. Simulated cases comprise rotations at different rates. Experimental results are presented which are consistent with theoretical estimates. In particular, very accurate angular velocity estimates are generated at lower slew rates, while in all cases the achievable accuracy in the estimation of the angular velocity component along boresight is about one order of magnitude worse than the other two components.

  9. Effect of flow velocity, substrate concentration and hydraulic cleaning on biofouling of reverse osmosis feed channels

    KAUST Repository

    Radu, Andrea I.

    2012-04-01

    A two-dimensional mathematical model coupling fluid dynamics, salt and substrate transport and biofilm development in time was used to investigate the effects of cross-flow velocity and substrate availability on biofouling in reverse osmosis (RO)/nanofiltration (NF) feed channels. Simulations performed in channels with or without spacer filaments describe how higher liquid velocities lead to less overall biomass amount in the channel by increasing the shear stress. In all studied cases at constant feed flow rate, biomass accumulation in the channel reached a steady state. Replicate simulation runs prove that the stochastic biomass attachment model does not affect the stationary biomass level achieved and has only a slight influence on the dynamics of biomass accumulation. Biofilm removal strategies based on velocity variations are evaluated. Numerical results indicate that sudden velocity increase could lead to biomass sloughing, followed however by biomass re-growth when returning to initial operating conditions. Simulations show particularities of substrate availability in membrane devices used for water treatment, e.g., the accumulation of rejected substrates at the membrane surface due to concentration polarization. Interestingly, with an increased biofilm thickness, the overall substrate consumption rate dominates over accumulation due to substrate concentration polarization, eventually leading to decreased substrate concentrations in the biofilm compared to bulk liquid. © 2012 Elsevier B.V.

  10. A new phase coding method using a slice selection gradient for high speed flow velocity meaurements in NMR tomography

    International Nuclear Information System (INIS)

    Oh, C.H.; Cho, Z.H.; California Univ., Irvine

    1986-01-01

    A new phase coding method using a selection gradient for high speed NMR flow velocity measurements is introduced and discussed. To establish a phase-velocity relationship of flow under the slice selection gradient and spin-echo RF pulse, the Bloch equation was numerically solved under the assumption that only one directional flow exists, i.e. in the direction of slice selection. Details of the numerical solution of the Bloch equation and techniques related to the numerical computations are also given. Finally, using the numerical calculation, high speed flow velocity measurement was attempted and found to be in good agreement with other complementary controlled measurements. (author)

  11. Models for assessing the relative phase velocity in a two-phase flow. Status report

    International Nuclear Information System (INIS)

    Schaffrath, A.; Ringel, H.

    2000-06-01

    The knowledge of slip or drift flux in two phase flow is necessary for several technical processes (e.g. two phase pressure losses, heat and mass transfer in steam generators and condensers, dwell period in chemical reactors, moderation effectiveness of two phase coolant in BWR). In the following the most important models for two phase flow with different phase velocities (e.g. slip or drift models, analogy between pressure loss and steam quality, ε - ε models and models for the calculation of void distribution in reposing fluids) are classified, described and worked up for a further comparison with own experimental data. (orig.)

  12. Effects of solid inertial particles on the velocity and temperature statistics of wall bounded turbulent flow

    DEFF Research Database (Denmark)

    Nakhaei, Mohammadhadi; Lessani, B.

    2016-01-01

    is reduced by the presence of particles,and in spite of the additional heat exchange between the carrier fluid and the particles, the total heattransfer rate stays always lower for particle-laden flows. To further clarify this issue, the total Nusseltnumber is split into a turbulence contribution...... Eulerian–Lagrangianapproach is adopted to solve the carrier flow field and the motion of dispersed particles. Three differentparticle Stokes numbers of St = 24, 60, 192, at a constant particle mass loading of φm = 0:54, are considered.The mean and rms profiles of velocity and temperature for fluid...

  13. Visualizing flow fields using acoustic Doppler current profilers and the Velocity Mapping Toolbox

    Science.gov (United States)

    Jackson, P. Ryan

    2013-01-01

    The purpose of this fact sheet is to provide examples of how the U.S. Geological Survey is using acoustic Doppler current profilers for much more than routine discharge measurements. These instruments are capable of mapping complex three-dimensional flow fields within rivers, lakes, and estuaries. Using the Velocity Mapping Toolbox to process the ADCP data allows detailed visualization of the data, providing valuable information for a range of studies and applications.

  14. Cross-correlation based time delay estimation for turbulent flow velocity measurements: Statistical considerations

    International Nuclear Information System (INIS)

    Tal, Balazs; Bencze, Attila; Zoletnik, Sandor; Veres, Gabor; Por, Gabor

    2011-01-01

    Time delay estimation methods (TDE) are well-known techniques to investigate poloidal flows in hot magnetized plasmas through the propagation properties of turbulent structures in the medium. One of these methods is based on the estimation of the time lag at which the cross-correlation function (CCF) estimation reaches its maximum value. The uncertainty of the peak location refers to the smallest determinable flow velocity modulation, and therefore the standard deviation of the time delay imposes important limitation to the measurements. In this article, the relative standard deviation of the CCF estimation and the standard deviation of its peak location are calculated analytically using a simple model of turbulent signals. This model assumes independent (non interacting) overlapping events (coherent structures) with randomly distributed spatio-temporal origins moving with background flow. The result of our calculations is the derivation of a general formula for the CCF variance, which is valid not exclusively in the high event density limit, but also for arbitrary event densities. Our formula reproduces the well known expression for high event densities previously published in the literature. In this paper we also present a derivation of the variance of time delay estimation that turns out to be inversely proportional to the applied time window. The derived formulas were tested in real plasma measurements. The calculations are an extension of the earlier work of Bencze and Zoletnik [Phys. Plasmas 12, 052323 (2005)] where the autocorrelation-width technique was developed. Additionally, we show that velocities calculated by a TDE method possess a broadband noise which originates from this variance, its power spectral density cannot be decreased by worsening the time resolution and can be coherent with noises of other velocity measurements where the same turbulent structures are used. This noise should not be confused with the impact of zero mean frequency zonal flow

  15. A new car-following model for autonomous vehicles flow with mean expected velocity field

    Science.gov (United States)

    Wen-Xing, Zhu; Li-Dong, Zhang

    2018-02-01

    Due to the development of the modern scientific technology, autonomous vehicles may realize to connect with each other and share the information collected from each vehicle. An improved forward considering car-following model was proposed with mean expected velocity field to describe the autonomous vehicles flow behavior. The new model has three key parameters: adjustable sensitivity, strength factor and mean expected velocity field size. Two lemmas and one theorem were proven as criteria for judging the stability of homogeneousautonomous vehicles flow. Theoretical results show that the greater parameters means larger stability regions. A series of numerical simulations were carried out to check the stability and fundamental diagram of autonomous flow. From the numerical simulation results, the profiles, hysteresis loop and density waves of the autonomous vehicles flow were exhibited. The results show that with increased sensitivity, strength factor or field size the traffic jam was suppressed effectively which are well in accordance with the theoretical results. Moreover, the fundamental diagrams corresponding to three parameters respectively were obtained. It demonstrates that these parameters play almost the same role on traffic flux: i.e. before the critical density the bigger parameter is, the greater flux is and after the critical density, the opposite tendency is. In general, the three parameters have a great influence on the stability and jam state of the autonomous vehicles flow.

  16. New observations from MR velocity-encoded flow measurements concerning diastolic function in constrictive pericarditis

    Energy Technology Data Exchange (ETDEWEB)

    Bauner, Kerstin; Horng, A.; Reiser, M.; Huber, A. [Ludwig-Maximilian University, Department of Clinical Radiology, University Hospitals-Campus Grosshadern, Munich (Germany); Schmitz, Ch. [Ludwig-Maximilian University, Department of Cardiac Surgery, University Hospitals-Campus Grosshadern, Munich (Germany)

    2010-08-15

    To assess diastolic function in patients with constrictive pericarditis (CP) by using velocity-encoded flow measurements at the atrioventricular valves and to evaluate whether conclusions regarding increased ventricular pressure can be drawn. Twenty-two patients with CP and 20 healthy subjects were examined on a 1.5-T MR system. In addition to evaluation of pericardial thickness, ventricular volumes and septal movement, velocity-encoded flow measurements were performed at the level of the atrioventricular valves for assessment of diastolic function. Amplitudes of the e- and a-waves were measured and e- to a-wave ratios were calculated. The correlation of transtricuspid e- to a-wave ratios and right ventricular end-diastolic pressures (RVEDP) was calculated. Right ventricular volumes were significantly smaller in patients with CP (p < 0.001). Abnormal septal movement was detected in all patients except one with CP and in none of the healthy subjects. In patients with CP mean transtricuspid e- to a-wave ratios were significantly smaller compared with healthy subjects. Individual transtricuspid e- to a-wave ratios were highly correlated with RVEDP (r = 0.6, p = 0.01). An elaborate MR examination can identify patients with CP. Velocity-encoded flow measurements with calculation of transtricuspid e- to a-wave ratios are a valuable tool for detection of diastolic dysfunction in patients with CP. The value of e- to a-wave ratios may indicate elevated RVEDP. (orig.)

  17. Effect of Electrical Stimulation on Blood Flow Velocity and Vessel Size

    Science.gov (United States)

    Jin, Hee-Kyung; Hwang, Tae-Yeon; Cho, Sung-Hyoun

    2017-01-01

    Abstract Interferential current electrical stimulation alters blood flow velocity and vessel size. We aimed to investigate the changes in the autonomic nervous system depending on electrical stimulation parameters. Forty-five healthy adult male and female subjects were studied. Bipolar adhesive pad electrodes were used to stimulate the autonomic nervous system at the thoracic vertebrae 1-4 levels for 20 min. Using Doppler ultrasonography, blood flow was measured to determine velocity and vessel size before, immediately after, and 30 min after electrical stimulation. Changes in blood flow velocity were significantly different immediately and 30 min after stimulation. The interaction between intervention periods and groups was significantly different between the exercise and pain stimulation groups immediately after stimulation (p<0.05). The vessel size was significantly different before and 30 min after stimulation (p<0.05). Imbalances in the sympathetic nervous system, which regulates balance throughout the body, may present with various symptoms. Therefore, in the clinical practice, the parameters of electrical stimulation should be selectively applied in accordance with various conditions and changes in form. PMID:28401194

  18. Effect of Electrical Stimulation on Blood Flow Velocity and Vessel Size.

    Science.gov (United States)

    Jin, Hee-Kyung; Hwang, Tae-Yeon; Cho, Sung-Hyoun

    2017-01-01

    Interferential current electrical stimulation alters blood flow velocity and vessel size. We aimed to investigate the changes in the autonomic nervous system depending on electrical stimulation parameters. Forty-five healthy adult male and female subjects were studied. Bipolar adhesive pad electrodes were used to stimulate the autonomic nervous system at the thoracic vertebrae 1-4 levels for 20 min. Using Doppler ultrasonography, blood flow was measured to determine velocity and vessel size before, immediately after, and 30 min after electrical stimulation. Changes in blood flow velocity were significantly different immediately and 30 min after stimulation. The interaction between intervention periods and groups was significantly different between the exercise and pain stimulation groups immediately after stimulation (p<0.05). The vessel size was significantly different before and 30 min after stimulation (p<0.05). Imbalances in the sympathetic nervous system, which regulates balance throughout the body, may present with various symptoms. Therefore, in the clinical practice, the parameters of electrical stimulation should be selectively applied in accordance with various conditions and changes in form.

  19. Measurement of cardiac valve and aortic blood flow velocities in stroke patients: a comparison of 4D flow MRI and echocardiography.

    Science.gov (United States)

    Wehrum, Thomas; Guenther, Felix; Fuchs, Alexander; Schuchardt, Florian; Hennemuth, Anja; Harloff, Andreas

    2018-01-11

    4D flow MRI is an emerging technique that allows quantification of 3D blood flow in vivo. However, comparisons with methods of blood velocity quantification used in clinical routine are sparse. Therefore, we compared velocity quantification using 4D flow MRI with transthoracic and transesophageal echocardiography at the mitral and aortic valves and the aorta. Forty-eight stroke patients (age 67.3 ± 15.0 years) were examined by 4D flow MRI. Blood flow velocities were assessed using standardized 2D analysis planes positioned in the mitral valve (MV), aortic valve (AV), ascending aorta (AAo), and descending aorta (DAo) and were compared with echocardiography. MRI showed moderate-high correlations of systolic velocity values for the MV (r = 0.67, p flow velocities compared with echocardiography by 8.6% for the MV (p = 0.07), 3.1% for the AV (p = 0.48), 10.7% for the AAo (p = 0.09), and 15.0% for the DAo (p = 0.01). Blood flow velocities obtained using 4D flow MRI and echocardiography at the MV, AV, and the ascending and DAo showed moderate to high correlations. Underestimation of absolute velocity values by MRI was low. Thus, 4D flow MRI seems ideally suited to comprehensively assess cardiac and aortic pathologies and related hemodynamic changes in future studies.

  20. Heat-flow and lateral seismic-velocity heterogeneities near Deep Sea Drilling Project-Ocean Drilling Program Site 504

    Science.gov (United States)

    Lowell, Robert P.; Stephen, Ralph A.

    1991-11-01

    Both conductive heat-flow and seismic-velocity data contain information relating to the permeability of the oceanic crust. Deep Sea Drilling Project-Ocean Drilling Program Site 504 is the only place where both detailed heat-flow and seismic-velocity field studies have been conducted at the same scale. In this paper we examine the correlation between heat flow and lateral heterogeneities in seismic velocity near Site 504. Observed heterogeneities in seismic velocity, which are thought to be related to variations in crack density in the upper 500 m of the basaltic crust, show little correlation with the heat-flow pattern. This lack of correlation highlights some of the current difficulties in using seismic-velocity data to infer details of spatial variations in permeability that are significant in controlling hydrothermal circulation.

  1. The effect of lipid emulsion of different concentration on blood flow velocity: an experimental study

    International Nuclear Information System (INIS)

    Li Qiang; Wang Maoqiang; Duan Liuxin; Song Peng; Ao Guokun

    2009-01-01

    Objective: To investigate the function mechanism of lipid emulsion (LE), used as a carrier, by observing the effect of intra-arterial infusion of LE in different concentration and dosage on blood flow velocity. Methods: According to the concentration and dosage used in arterial infusion, the experiments were divided into four groups:group A (20% LE, 2 ml), group B (20% LE, 20 ml), group C (30% LE, 2 ml) and group D (30% LE, 20 ml). Two healthy hybrid dogs were used for the study. Under DSA guidance, the 4 F catheter was placed in the splenic artery and in the hepatic artery respectively. DSA frames were counted in order to calculate the time that the contrast took from the catheter tip to the selected tertiary branches of the splenic or hepatic artery. Results LE infusion, regardless of its concentration level or its dosage, could reduce the blood velocity. The lasting time and the maximal peak value of the blood velocity reduction were significantly different among groups (P < 0.05). The lasting time was 5 minutes, 5-10 minutes, 20 minutes and 20-30 minutes among group A, B, C and D, respectively. The peak value of the reduction appeared at the 18th frames (1.44 s), 30th frames (2.4 s), 9th frames (0.9 s) and 14th frames (1.12 s) in group A, B, C and D, respectively. Conclusion Intra-arterial infusion of LE can reduce the blood flow velocity. The lasting time of the reduction in 30% LE groups is longer than that in 20% LE groups, while the blood velocity reduction in 30% LE groups is less than that in 20% LE groups. (authors)

  2. Maximizing flow velocities in redox-magnetohydrodynamic microfluidics using the transient faradaic current.

    Science.gov (United States)

    Weston, Melissa C; Nash, Christena K; Homesley, Jerry J; Fritsch, Ingrid

    2012-11-06

    There is a need for a microfluidic pumping technique that is simple to fabricate, yet robust, compatible with a variety of solvents, and which has easily controlled fluid flow. Redox-magnetohydrodynamics (MHD) offers these advantages. However, the presence of high concentrations of redox species, important for inducing sufficient convection at low magnetic fields for hand-held devices, can limit the use of redox-MHD pumping for analytical applications. A new method for redox-MHD pumping is investigated that takes advantage of the large amplitude of the transient portion of the faradaic current response that occurs upon stepping the potential sufficiently past the standard electrode potential, E°, of the pumping redox species at an electrode. This approach increases the velocity of the fluid for a given redox concentration. An electronic switch was implemented between the potentiostat and electrochemical cell to alternately turn on and off different electrodes along the length of the flow path to maximize this transient electronic current and, as a result, the flow speed. Velocities were determined by tracking microbeads in a solution containing electroactive potassium ferrocyanide and potassium ferricyanide, and supporting electrolyte, potassium chloride, in the presence of a magnetic field. Fluid velocities with slight pulsation were obtained with the switch that were 70% faster than the smooth velocities without the switch. This indicates that redox species concentrations can be lowered by a similar amount to achieve a given speed, thereby diminishing interference of the redox species with detection of the analyte in applications of redox-MHD microfluidics for chemical analysis.

  3. Investigation of the velocity distribution in the flow of a journal bearing model

    Science.gov (United States)

    Nobis, Matthias; Reinke, Peter; Schmidt, Marcus; Riedel, Marco; Redlich, Marcel

    2014-03-01

    In many previous studies the main focus was put on the pressure distribution in the lubricating gap. Due to the limited space in the gap an investigation of the velocity distribution is very difficult or rather impossible. Based on the geometrical shapes of a real journal bearing, a bearing model test rig with an increased relative gap width has been developed. Thus, it is possible to detect the distribution of the flow speed within the gap by using a Laser Doppler Velocimeter (LDV). The comparability of the flow to the flow in a real journal bearing is ensured by observing the Reynolds similarity. Due to a targeted eccentricity in the system and the circumferential groove over 180°, there is in connection with the outlet hole in the rotating shaft a permanent change in the outflow conditions. The consequence is a periodically varying system pressure with effects to the pressure and volumetric flow rate at the inlet and outlet. The velocity measurements with a triggered LDV are done by considering these transient boundary conditions at the system boundaries. In this paper the experimental setup, the expiration of the investigations and some exemplary results are presented. Attendant to the experiment, numerical simulations are carried out and the results are compared with the experimental data.

  4. Investigation of the velocity distribution in the flow of a journal bearing model

    Directory of Open Access Journals (Sweden)

    Nobis Matthias

    2014-03-01

    Full Text Available In many previous studies the main focus was put on the pressure distribution in the lubricating gap. Due to the limited space in the gap an investigation of the velocity distribution is very difficult or rather impossible. Based on the geometrical shapes of a real journal bearing, a bearing model test rig with an increased relative gap width has been developed. Thus, it is possible to detect the distribution of the flow speed within the gap by using a Laser Doppler Velocimeter (LDV. The comparability of the flow to the flow in a real journal bearing is ensured by observing the Reynolds similarity. Due to a targeted eccentricity in the system and the circumferential groove over 180°, there is in connection with the outlet hole in the rotating shaft a permanent change in the outflow conditions. The consequence is a periodically varying system pressure with effects to the pressure and volumetric flow rate at the inlet and outlet. The velocity measurements with a triggered LDV are done by considering these transient boundary conditions at the system boundaries. In this paper the experimental setup, the expiration of the investigations and some exemplary results are presented. Attendant to the experiment, numerical simulations are carried out and the results are compared with the experimental data.

  5. [Time lag effect between poplar' s sap flow velocity and microclimate factors in agroforestry system in West Liaoning Province].

    Science.gov (United States)

    Di, Sun; Guan, De-xin; Yuan, Feng-hui; Wang, An-zhi; Wu, Jia-bing

    2010-11-01

    By using Granier's thermal dissipation probe, the sap flow velocity of the poplars in agroforestry system in west Liaoning was continuously measured, and the microclimate factors were measured synchronously. Dislocation contrast method was applied to analyze the sap flow velocity and corresponding air temperature, air humidity, net radiation, and vapor pressure deficit to discuss the time lag effect between poplar' s sap flow velocity and microclimate factors on sunny days. It was found that the poplar's sap flow velocity advanced of air temperature, air humidity, and vapor pressure deficit, and lagged behind net radiation. The sap flow velocity in June, July, August, and September was advanced of 70, 30, 50, and 90 min to air temperature, of 80, 30, 40, and 90 min to air humidity, and of 90, 50, 70, and 120 min to vapor pressure deficit, but lagged behind 10, 10, 40, and 40 min to net radiation, respectively. The time lag time of net radiation was shorter than that of air temperature, air humidity, and vapor pressure. The regression analysis showed that in the cases the time lag effect was contained and not, the determination coefficients between comprehensive microclimate factor and poplar's sap flow velocity were 0.903 and 0.855, respectively, indicating that when the time lag effect was contained, the determination coefficient was ascended by 2.04%, and thus, the simulation accuracy of poplar's sap flow velocity was improved.

  6. Measuring flow velocity on frozen and non-frozen slopes of black soil through leading edge method

    Directory of Open Access Journals (Sweden)

    Chao Chen

    2017-09-01

    Full Text Available Flow velocity is a major parameter related to hillslope hydrodynamics erosion. This study aims to measure flow velocity over frozen and non-frozen slopes through leading edge method before being calibrated with accurate flow velocity to determine the correct coefficient for convenience of flow velocity measurement. Laboratory experiments were conducted on frozen and non-frozen soil slopes with flumes involving four slope gradients of 5°, 10°, 15°, and 20°and three flow rates of 1, 2, and 4 L/min with a flume of 6 m long and 0.1 m wide. The measurements were made with a stopwatch to record the time duration that the water flow ran over the rill segments of 2, 4 and 6 m long. Accurate flow velocity was measured with electrolyte trace method, under pulse boundary condition. The leading edge and accurate flow velocities were used to determine the correction coefficient to convert the former to the latter. Results showed that the correction coefficient on frozen soil slope was 0.81 with a coefficient of determination (R2 of 0.99. The correction coefficient on non-frozen soil slope was 0.79 with R2 of 0.98. A coefficient of 0.8 was applicable to both soil surface conditions. The accurate velocities on the four frozen black soil slopes were approximately 30%, 54%, 71%, and 91% higher than those on non-frozen soil slopes. By contrast, the leading edge flow velocities on the frozen soil slopes were 23%, 54%, 67%, and 84% higher than those on non-frozen soil slopes. The flow velocities on frozen soil slopes increased with flow rate at all four slopes, but they increased from 5 to 15° before getting stabilized. Therefore, rill flow velocity can be effectively measured with leading edge method by multiplying the leading edge velocity with a correction coefficient of 0.80. This study provides a strategy to measure rill flow velocity for studies on soil erosion mechanisms.

  7. Vibrationally-Fluidized Granular Flows: Impact and Bulk Velocity Measurements Compared with Discrete Element and Continuum Models

    Science.gov (United States)

    Hashemnia, Kamyar

    A new laser displacement probe was developed to measure the impact velocities of particles within vibrationally-fluidized beds. The sensor output was also used to measure bulk flow velocity along the probe window and to provide a measure of the media packing. The displacement signals from the laser sensors were analyzed to obtain the probability distribution functions of the impact velocity of the particles. The impact velocity was affected by the orientation of the laser probe relative to the bulk flow velocity, and the density and elastic properties of the granular media. The impact velocities of the particles were largely independent of their bulk flow speed and packing density. Both the local impact and bulk flow velocities within a tub vibratory finisher were predicted using discrete element modelling (DEM) and compared to the measured values for spherical steel media. It was observed that the impact and bulk flow velocities were relatively insensitive to uncertainties in the contact coefficients of friction and restitution. It was concluded that the predicted impact and bulk flow velocities were dependent on the number of layers in the model. Consequently, the final DE model mimicked the key aspects of the experimental setup, including the submerged laser sensor. The DE method predictions of both impact velocity and bulk flow velocity were in reasonable agreement with the experimental measurements, with maximum differences of 20% and 30%, respectively. Discrete element modeling of granular flows is effective, but requires large numerical models. In an effort to reduce computational effort, this work presents a finite element (FE) continuum model of a vibrationally-fluidized granular flow. The constitutive equations governing the continuum model were calibrated using the discrete element method (DEM). The bulk flow behavior of the equivalent continuum media was then studied using both Lagrangian and Eulerian FE formulations. The bulk flow velocities predicted

  8. Quasi-direct numerical simulation of a pebble bed configuration. Part I: Flow (velocity) field analysis

    International Nuclear Information System (INIS)

    Shams, A.; Roelofs, F.; Komen, E.M.J.; Baglietto, E.

    2013-01-01

    Highlights: ► Quasi direct numerical simulations (q-DNS) of a pebble bed configuration has been performed. ► This q-DNS database may serve as a reference for the validation of different turbulence modeling approaches. ► A wide range of qualitative and quantitative data throughout the computational domain has been generated. ► Results for mean, RMS and covariance of velocity field are extensively reported in this paper. -- Abstract: High temperature reactors (HTR) are being considered for deployment around the world because of their excellent safety features. The fuel is embedded in a graphite moderator and can sustain very high temperatures. However, the appearance of hot spots in the pebble bed cores of HTR's may affect the integrity of the pebbles. A good prediction of the flow and heat transport in such a pebble bed core is a challenge for available turbulence models and such models need to be validated. In the present article, quasi direct numerical simulations (q-DNS) of a pebble bed configuration are reported, which may serve as a reference for the validation of different turbulence modeling approaches. Such approaches can be used in order to perform calculations for a randomly arranged pebble bed. Simulations are performed at a Reynolds number of 3088, based on pebble diameter, with a porosity level of 0.42. Detailed flow analyses have shown complex physics flow behavior and make this case challenging for turbulence model validation. Hence, a wide range of qualitative and quantitative data for velocity and temperature field have been extracted for this benchmark. In the present article (part I), results related to the flow field (mean, RMS and covariance of velocity) are documented and discussed in detail. Moreover, the discussion regarding the temperature field will be published in a separate article

  9. Capabilities of optical SIV technique in measurements of flow velocity vector field dynamics

    Science.gov (United States)

    Mikheev, N. I.; Dushin, N. S.; Saushin, I. I.

    2017-11-01

    The main difference between Smoke Image Velocimetry (SIV) technique and the conventional PIV is that higher concentration of tracer particles typical of smoke visualization techniques is used in SIV. Not separate particles but smoke structures with continuous pixel intensity are visible in the recorded images. Owing to better smoke reflectivity, higher spatial and temporal resolution is obtained in the case when relatively simple equipment (camera and laser) is used. It is simple enough to perform SIV measurements of velocity vector field dynamics at the frequency exceeding 15000 Hz, which offers new opportunities in unsteady flow examination. The paper describes fundamentals of SIV technique and gives some new results obtained using this method for the measurements that require high spatial and temporal resolution. The latter include frequency spectra of turbulent velocity fluctuations, turbulence dissipation profiles in the boundary layer and higher-order moments of velocity fluctuations. It has been shown that SIV technique considerably extends the potential of experimental studies of turbulence and flow structure in high-speed processes.

  10. Numerical performance analysis of acoustic Doppler velocity profilers in the wake of an axial-flow marine hydrokinetic turbine

    Energy Technology Data Exchange (ETDEWEB)

    Richmond, Marshall C.; Harding, Samuel F.; Romero Gomez, Pedro DJ

    2015-09-01

    The use of acoustic Doppler current profilers (ADCPs) for the characterization of flow conditions in the vicinity of both experimental and full scale marine hydrokinetic (MHK) turbines is becoming increasingly prevalent. The computation of a three dimensional velocity measurement from divergent acoustic beams requires the assumption that the flow conditions are homogeneous between all beams at a particular axial distance from the instrument. In the near wake of MHK devices, the mean fluid motion is observed to be highly spatially dependent as a result of torque generation and energy extraction. This paper examines the performance of ADCP measurements in such scenarios through the modelling of a virtual ADCP (VADCP) instrument in the velocity field in the wake of an MHK turbine resolved using unsteady computational fluid dynamics (CFD). This is achieved by sampling the CFD velocity field at equivalent locations to the sample bins of an ADCP and performing the coordinate transformation from beam coordinates to instrument coordinates and finally to global coordinates. The error in the mean velocity calculated by the VADCP relative to the reference velocity along the instrument axis is calculated for a range of instrument locations and orientations. The stream-wise velocity deficit and tangential swirl velocity caused by the rotor rotation lead to significant misrepresentation of the true flow velocity profiles by the VADCP, with the most significant errors in the transverse (cross-flow) velocity direction.

  11. Pressure-sensitive paint on a truncated cone in hypersonic flow at incidences

    International Nuclear Information System (INIS)

    Yang, L.; Erdem, E.; Zare-Behtash, H.; Kontis, K.; Saravanan, S.

    2012-01-01

    Highlights: ► Global pressure map over the truncated cone is obtained at various incidence angles in Mach 5 flow. ► Successful application of AA-PSP in hypersonic flow expands operation area of this technique. ► AA-PSP reveals complex three-dimensional pattern which is difficult for transducer to obtain. ► Quantitative data provides strong correlation with colour Schlieren and oil flow results. ► High spatial resolution pressure mappings identify small scale vortices and flow separation. - Abstract: The flow over a truncated cone is a classical and fundamental problem for aerodynamic research due to its three-dimensional and complicated characteristics. The flow is made more complex when examining high angles of incidence. Recently these types of flows have drawn more attention for the purposes of drag reduction in supersonic/hypersonic flows. In the present study the flow over a truncated cone at various incidences was experimentally investigated in a Mach 5 flow with a unit Reynolds number of 13.5 × 10 6 m −1 . The cone semi-apex angle is 15° and the truncation ratio (truncated length/cone length) is 0.5. The incidence of the model varied from −12° to 12° with 3° intervals relative to the freestream direction. The external flow around the truncated cone was visualised by colour Schlieren photography, while the surface flow pattern was revealed using the oil flow method. The surface pressure distribution was measured using the anodized aluminium pressure-sensitive paint (AA-PSP) technique. Both top and sideviews of the pressure distribution on the model surface were acquired at various incidences. AA-PSP showed high pressure sensitivity and captured the complicated flow structures which correlated well with the colour Schlieren and oil flow visualisation results.

  12. Peak negative myocardial velocity gradient in early diastole as a noninvasive indicator of left ventricular diastolic function: comparison with transmitral flow velocity indices.

    Science.gov (United States)

    Shimizu, Y; Uematsu, M; Shimizu, H; Nakamura, K; Yamagishi, M; Miyatake, K

    1998-11-01

    We sought to assess the clinical significance of peak negative myocardial velocity gradient (MVG) in early diastole as a noninvasive indicator of left ventricular (LV) diastolic function. Peak systolic MVG has been shown useful for the quantitative assessment of regional wall motion abnormalities, but limited data exist regarding the diastolic MVG as an indicator of LV diastolic function. Peak negative MVG was obtained from M-mode tissue Doppler imaging (TDI) in 43 subjects with or without impairment of systolic and diastolic performance: 12 normal subjects, 12 patients with hypertensive heart disease (HHD) with normal systolic performance and 19 patients with dilated cardiomyopathy (DCM), and was compared with standard Doppler transmitral flow velocity indices. In a subgroup of 30 patients, effects of preload increase on these indices were assessed by performing passive leg lifting. In an additional 11 patients with congestive heart failure at the initial examination, the measurements were repeated after 26+/-16 days of volume-reducing therapy. Peak negative MVG was significantly depressed both in HHD (-3.9+/-1.3/s, p indices failed to distinguish DCM from normal due to the pseudonormalization. Transmitral flow velocity indices were significantly altered (peak early/late diastolic filling velocity [E/A]=1.1+/-0.5 to 1.5+/-0.7, p indicator of LV diastolic function that is less affected by preload alterations than the transmitral flow velocity indices, and thereby could be used for the follow-up of patients with nonischemic LV dysfunction presenting congestive heart failure.

  13. Synchrotron X-ray PIV Technique for Measurement of Blood Flow Velocity

    International Nuclear Information System (INIS)

    Kim, Guk Bae; Lee, Sang Joon; Je, Jung Ho

    2007-01-01

    Synchrotron X-ray micro-imaging method has been used to observe internal structures of various organisms, industrial devices, and so on. However, it is not suitable to see internal flows inside a structure because tracers typically employed in conventional optical flow visualization methods cannot be detectable with the X-ray micro-imaging method. On the other hand, a PIV (particle image velocimetry) method which has recently been accepted as a reliable quantitative flow visualization technique can extract lots of flow information by applying digital image processing techniques However, it is not applicable to opaque fluids such as blood. In this study, we combined the PIV method and the synchrotron X-ray micro-imaging technique to compose a new X-ray PIV technique. Using the X-ray PIV technique, we investigated the optical characteristics of blood for a coherent synchrotron X-ray beam and quantitatively visualized real blood flows inside an opaque tube without any contrast media. The velocity field information acquired would be helpful for investigating hemorheologic characteristics of the blood flow

  14. Exploring the velocity distribution of debris flows: An iteration algorithm based approach for complex cross-sections

    Science.gov (United States)

    Han, Zheng; Chen, Guangqi; Li, Yange; Wang, Wei; Zhang, Hong

    2015-07-01

    The estimation of debris-flow velocity in a cross-section is of primary importance due to its correlation to impact force, run up and superelevation. However, previous methods sometimes neglect the observed asymmetric velocity distribution, and consequently underestimate the debris-flow velocity. This paper presents a new approach for exploring the debris-flow velocity distribution in a cross-section. The presented approach uses an iteration algorithm based on the Riemann integral method to search an approximate solution to the unknown flow surface. The established laws for vertical velocity profile are compared and subsequently integrated to analyze the velocity distribution in the cross-section. The major benefit of the presented approach is that natural channels typically with irregular beds and superelevations can be taken into account, and the resulting approximation by the approach well replicates the direct integral solution. The approach is programmed in MATLAB environment, and the code is open to the public. A well-documented debris-flow event in Sichuan Province, China, is used to demonstrate the presented approach. Results show that the solutions of the flow surface and the mean velocity well reproduce the investigated results. Discussion regarding the model sensitivity and the source of errors concludes the paper.

  15. Magnetic Resonance Flow Velocity and Temperature Mapping of a Shape Memory Polymer Foam Device

    Energy Technology Data Exchange (ETDEWEB)

    Small IV, W; Gjersing, E; Herberg, J L; Wilson, T S; Maitland, D J

    2008-10-29

    Interventional medical devices based on thermally responsive shape memory polymer (SMP) are under development to treat stroke victims. The goals of these catheter-delivered devices include re-establishing blood flow in occluded arteries and preventing aneurysm rupture. Because these devices alter the hemodynamics and dissipate thermal energy during the therapeutic procedure, a first step in the device development process is to investigate fluid velocity and temperature changes following device deployment. A laser-heated SMP foam device was deployed in a simplified in vitro vascular model. Magnetic resonance imaging (MRI) techniques were used to assess the fluid dynamics and thermal changes associated with device deployment. Spatial maps of the steady-state fluid velocity and temperature change inside and outside the laser-heated SMP foam device were acquired. Though non-physiological conditions were used in this initial study, the utility of MRI in the development of a thermally-activated SMP foam device has been demonstrated.

  16. Deterministic nonlinear characteristics of in vivo blood flow velocity and arteriolar diameter fluctuations

    International Nuclear Information System (INIS)

    Parthimos, D; Osterloh, K; Pries, A R; Griffith, T M

    2004-01-01

    We have performed a nonlinear analysis of fluctuations in red cell velocity and arteriolar calibre in the mesenteric bed of the anaesthetized rat. Measurements were obtained under control conditions and during local superfusion with N G -nitro-L-arginine (L-NNA, 30 μM) and tetrabutylammonium (TBA, 0.1 mM), which suppress NO synthesis and block Ca 2+ activated K + channels (K Ca ), respectively. Time series were analysed by calculating correlation dimensions and largest Lyapunov exponents. Both statistics were higher for red cell velocity than diameter fluctuations, thereby potentially differentiating between global and local mechanisms that regulate microvascular flow. Evidence for underlying nonlinear structure was provided by analysis of surrogate time series generated from the experimental data following randomization of Fourier phase. Complexity indices characterizing time series under control conditions were in general higher than those derived from data obtained during superfusion with L-NNA and TBA

  17. The Design Method of Axial Flow Runners Focusing on Axial Flow Velocity Uniformization and Its Application to an Ultra-Small Axial Flow Hydraulic Turbine

    Directory of Open Access Journals (Sweden)

    Yasuyuki Nishi

    2016-01-01

    Full Text Available We proposed a portable and ultra-small axial flow hydraulic turbine that can generate electric power comparatively easily using the low head of open channels such as existing pipe conduits or small rivers. In addition, we proposed a simple design method for axial flow runners in combination with the conventional one-dimensional design method and the design method of axial flow velocity uniformization, with the support of three-dimensional flow analysis. Applying our design method to the runner of an ultra-small axial flow hydraulic turbine, the performance and internal flow of the designed runner were investigated using CFD analysis and experiment (performance test and PIV measurement. As a result, the runners designed with our design method were significantly improved in turbine efficiency compared to the original runner. Specifically, in the experiment, a new design of the runner achieved a turbine efficiency of 0.768. This reason was that the axial component of absolute velocity of the new design of the runner was relatively uniform at the runner outlet in comparison with that of the original runner, and as a result, the negative rotational flow was improved. Thus, the validity of our design method has been verified.

  18. Velocity-intermittency structure for wake flow of the pitched single wind turbine under different inflow conditions

    Science.gov (United States)

    Crist, Ryan; Cal, Raul Bayoan; Ali, Naseem; Rockel, Stanislav; Peinke, Joachim; Hoelling, Michael

    2017-11-01

    The velocity-intermittency quadrant method is used to characterize the flow structure of the wake flow in the boundary layer of a wind turbine array. Multifractal framework presents the intermittency as a pointwise Hölder exponent. A 3×3 wind turbine array tested experimentally provided a velocity signal at a 21×9 downstream location, measured via hot-wire anemometry. The results show a negative correlation between the velocity and the intermittency at the hub height and bottom tip, whereas the top tip regions show a positive correlation. Sweep and ejection based on the velocity and intermittency are dominant downstream from the rotor. The pointwise results reflect large-scale organization of the flow and velocity-intermittency events corresponding to a foreshortened recirculation region near the hub height and the bottom tip.

  19. Numerical simulation of unsteady flow around rectangular cylinders at incidence

    OpenAIRE

    García Buitrago, Arturo

    2012-01-01

    Flows around varied barriers are involved in many practical areas such as bridges, flow meters, towers, cables... The prediction of both the efforts exerted on the structure and main frequencies is of great importance in terms of engineering, especially in aeroacoustics. Development and validation of flexible numerical tools allowing an easy evaluation of different geometries can be very useful. La interacción entre una corriente de aire y un obstáculo está presente en muchos a...

  20. Velocity measurement by vortex shedding. Contribution to the mass-flow measurement

    International Nuclear Information System (INIS)

    Martinez Piquer, T.

    1988-01-01

    The phenomenon of vortex shedding has been known for centuries and has been the subject of scientific studies for about one hundred years. It is only in the ten last years that is has been applied to the measurement of fluids velocity. In 1878 F. Strouhal observed the vortex shedding phenomenon and shown that the shedding frequency of a wire vibrating in the wind was related to the wire diameter and the wind velocity. Rayleigh, who introduced the non-dimensional Strouhal number, von Karman and Rohsko, carried out extensive work or the subject which indicated that vortex shedding could form the basis for a new type of flowmeter. The thesis describes two parallel lines of investigation which study in depth the practical applications of vortex shedding. The first one deals with the measure of velocity and it presents the novelty of a bluff body with a cross-section which has not been used until this day. This body is a circular cylinder with a two-dimensional slit along the diameter and situated in crossdirection to the fluid's stream. It possesses excellent characteristics and it is the most stable as a vortex shedder, which gives it great advantage to the rest of the shapes used until now. The detection of the vortex has been performed by measuring the pressure changes generated by the vortex on two posts situated just beside the slit. To calculate the frequency of the vortex shedding, we obtain the difference of the mentioned signals, which are the same and 180 out of phase. Finding out the period of the autocorrelation function of this signal we can estimate the velocity of the fluid. A logical equipment based on a microprocessor has been designed for the calculation using a zero-crossing time algorithm implemented in assembler language. The second line of research refers to a new method of measure mass flow. The pressure signal generated by the vortex has an intensity which is proportional to the density and to the square of the velocity. Since we have already

  1. An extended macro traffic flow model accounting for multiple optimal velocity functions with different probabilities

    Science.gov (United States)

    Cheng, Rongjun; Ge, Hongxia; Wang, Jufeng

    2017-08-01

    Due to the maximum velocity and safe headway distance of the different vehicles are not exactly the same, an extended macro model of traffic flow with the consideration of multiple optimal velocity functions with probabilities is proposed in this paper. By means of linear stability theory, the new model's linear stability condition considering multiple probabilities optimal velocity is obtained. The KdV-Burgers equation is derived to describe the propagating behavior of traffic density wave near the neutral stability line through nonlinear analysis. The numerical simulations of influences of multiple maximum velocities and multiple safety distances on model's stability and traffic capacity are carried out. The cases of two different kinds of maximum speeds with same safe headway distance, two different types of safe headway distances with same maximum speed and two different max velocities and two different time-gaps are all explored by numerical simulations. First cases demonstrate that when the proportion of vehicles with a larger vmax increase, the traffic tends to unstable, which also means that jerk and brakes is not conducive to traffic stability and easier to result in stop and go phenomenon. Second cases show that when the proportion of vehicles with greater safety spacing increases, the traffic tends to be unstable, which also means that too cautious assumptions or weak driving skill is not conducive to traffic stability. Last cases indicate that increase of maximum speed is not conducive to traffic stability, while reduction of the safe headway distance is conducive to traffic stability. Numerical simulation manifests that the mixed driving and traffic diversion does not have effect on the traffic capacity when traffic density is low or heavy. Numerical results also show that mixed driving should be chosen to increase the traffic capacity when the traffic density is lower, while the traffic diversion should be chosen to increase the traffic capacity when

  2. Flow instability originating from particle configurations using the two-dimensional optimal velocity model

    Science.gov (United States)

    Ishiwata, Ryosuke; Sugiyama, Yuki

    2015-12-01

    The two-dimensional optimal velocity model has potential applications to pedestrian dynamics and the collective motion of animals. In this paper, we extend the linear stability analysis presented in a previous paper [A Nakayama et al., Phys. Rev. E. 77, 016105 (2008), 10.1103/PhysRevE.77.016105] and investigate the effects of particle configuration on the stability of several wave modes of collective oscillations of moving particles. We find that, when a particle moves without interacting with particles that are positioned in a diagonally forward or backward direction, the stable region of the particle flow is completely removed by the elliptically polarized mode.

  3. Measuring the cosmological bulk flow using the peculiar velocities of supernovae

    International Nuclear Information System (INIS)

    Dai, De-Chang; Kinney, William H.; Stojkovic, Dejan

    2011-01-01

    We study large-scale coherent motion in our universe using the existing Type IA supernovae data. If the recently observed bulk flow is real, then some imprint must be left on supernovae motion. We perform a Bayesian Monte Carlo Markov Chain analysis in various redshift bins and find a sharp contrast between the z 0.05 data. The z +39 −31 °,20 +32 −32 °) with a magnitude of v bulk = 188 +119 −103 km/s at 68% confidence. The significance of detection (compared to the null hypothesis) is 95%. In contrast, z > 0.05 data (which contains 425 of the 557 supernovae in the Union2 data set) show no evidence for the bulk flow. While the direction of the bulk flow agrees very well with previous studies, the magnitude is significantly smaller. For example, the Kashlinsky, et al.'s original bulk flow result of v bulk > 600km/s is inconsistent with our analysis at greater than 99.7% confidence level. Furthermore, our best-fit bulk flow velocity is consistent with the expectation for the ΛCDM model, which lies inside the 68% confidence limit

  4. A meshless scheme for incompressible fluid flow using a velocity-pressure correction method

    KAUST Repository

    Bourantas, Georgios

    2013-12-01

    A meshless point collocation method is proposed for the numerical solution of the steady state, incompressible Navier-Stokes (NS) equations in their primitive u-v-p formulation. The flow equations are solved in their strong form using either a collocated or a semi-staggered "grid" configuration. The developed numerical scheme approximates the unknown field functions using the Moving Least Squares approximation. A velocity, along with a pressure correction scheme is applied in the context of the meshless point collocation method. The proposed meshless point collocation (MPC) scheme has the following characteristics: (i) it is a truly meshless method, (ii) there is no need for pressure boundary conditions since no pressure constitutive equation is solved, (iii) it incorporates simplicity and accuracy, (iv) results can be obtained using collocated or semi-staggered "grids", (v) there is no need for the usage of a curvilinear system of coordinates and (vi) it can solve steady and unsteady flows. The lid-driven cavity flow problem, for Reynolds numbers up to 5000, has been considered, by using both staggered and collocated grid configurations. Following, the Backward-Facing Step (BFS) flow problem was considered for Reynolds numbers up to 800 using a staggered grid. As a final example, the case of a laminar flow in a two-dimensional tube with an obstacle was examined. © 2013 Elsevier Ltd.

  5. The effects of squat exercises in postures for toilet use on blood flow velocity of the leg vein.

    Science.gov (United States)

    Eom, Jun Ho; Chung, Sin Ho; Shim, Jae Hun

    2014-09-01

    [Purpose] The purpose of this study was to identify the effects of squat exercises performed in toilet-using postures on the blood flow velocity of the lower extremities for the prevention of deep vein thrombosis. [Subjects] The subjects were 28 students who were attending B University in Cheonan. They were divided into a group of 14 subjects of sitting toilet users and a group of 14 subjects of squat toilet users. [Methods] The subjects performed squat exercises in different toilet-using postures and we investigated the changes in blood flow velocity. [Results] The variations in blood flow velocities before and after the exercises showed significant differences in both groups but the differences between the two groups were not significant. [Conclusion] Based on the results of this study, we consider squat exercises are effective at improving the variation in lower-extremity blood flow velocity when using a toilet.

  6. Heart rate and flow velocity variability as determined from umbilical Doppler velocimetry at 10-20 weeks of gestation.

    Science.gov (United States)

    Ursem, N T; Struijk, P C; Hop, W C; Clark, E B; Keller, B B; Wladimiroff, J W

    1998-11-01

    1. The aim of this study was to define from umbilical artery flow velocity waveforms absolute peak systolic and time-averaged velocity, fetal heart rate, fetal heart rate variability and flow velocity variability, and the relation between fetal heart rate and velocity variables in early pregnancy.2.A total of 108 women presenting with a normal pregnancy from 10 to 20 weeks of gestation consented to participate in a cross-sectional study design. Doppler ultrasound recordings were made from the free-floating loop of the umbilical cord.3. Umbilical artery peak systolic and time-averaged velocity increased at 10-20 weeks, whereas fetal heart rate decreased at 10-15 weeks of gestation and plateaued thereafter. Umbilical artery peak systolic velocity variability and fetal heart rate variability increased at 10-20 and 15-20 weeks respectively.4. The inverse relationship between umbilical artery flow velocity and fetal heart rate at 10-15 weeks of gestation suggests that the Frank-Starling mechanism regulates cardiovascular control as early as the late first and early second trimesters of pregnancy. A different underlying mechanism is suggested for the observed variability profiles in heart rate and umbilical artery peak systolic velocity. It is speculated that heart rate variability is mediated by maturation of the parasympathetic nervous system, whereas peak systolic velocity variability reflects the activation of a haemodynamic feedback mechanism.

  7. Slip velocity and Knudsen layer in the lattice Boltzmann method for microscale flows.

    Science.gov (United States)

    Kim, Seung Hyun; Pitsch, Heinz; Boyd, Iain D

    2008-02-01

    We present mesoscopic fluid-wall interaction models for lattice Boltzmann (LB) model simulations of microscale flows. The exact solution of the slip velocity for the LB equation with the Bhatnagar-Gross-Krook collision operator is obtained for Poiseuille flow at finite Knudsen numbers. With a consistent definition of the Knudsen number, the slip coefficients of the LB equation with the standard D2Q9 scheme are found to be slightly larger than those of the Boltzmann equation with the same boundary condition, which makes the standard LB method remain quantitatively accurate only for small Knudsen numbers. By modifying the nonequilibrium energy flux or introducing the effective relaxation time, the LB method is analytically shown to reproduce the slip phenomena up to second order in the Knudsen number. For the standard LB method, the Knudsen layer is captured only with modification of the relaxation dynamics such as in the effective relaxation time model.

  8. Technique for velocity vector field dynamics measurement on the basis of smoke visualization of flow

    Science.gov (United States)

    Mikheev, N. I.; Dushin, N. S.; Saushin, I. I.

    2017-09-01

    The main difference between Smoke Image Velocimetry (SIV) technique and traditional PIV is that the smoke with continuous intensity in the image is seeded into the flow instead of separate particles. Owing to better smoke reflectivity, relatively primitive equipment is enough to measure the dynamics of velocity vector fields with the frequency of 25 kHz and higher. The image processing algorithm is adapted to high tracer concentration and relatively large displacement of smoke patches between two consecutive frames. The results of SIV testing are presented, including the estimations of the most measurement noise sensitive characteristics of turbulence calculated from spatial derivatives of fluctuations of small-scale turbulence. The measurement results have been shown to agree well with the data obtained by other methods. Application of SIV technique opens new possibilities in the research of flow pattern and turbulence in unsteady and fast processes.

  9. Investigation of Velocity Distribution in Open Channel Flows Based on Conditional Average of Turbulent Structures

    Directory of Open Access Journals (Sweden)

    Yu Han

    2017-01-01

    Full Text Available We report the development of a new analytical model similar to the Reynolds-averaged Navier-Stokes equations to determine the distribution of streamwise velocity by considering the bursting phenomenon. It is found that, in two-dimensional (2D flows, the underlying mechanism of the wake law in 2D uniform flow is actually a result of up/down events. A special experiment was conducted to examine the newly derived analytical model, and good agreement is achieved between the experimental data in the inner region and the model’s prediction. The obtained experimental data were also used to examine the DML-Law (dip-modified-log-law, MLW-Law (modified-log-wake law, and CML-Law (Cole’s wake law, and the agreement is not very satisfactory in the outer region.

  10. One-dimensional transient unequal velocity two-phase flow by the method of characteristics

    International Nuclear Information System (INIS)

    Rasouli, F.

    1981-01-01

    An understanding of two-phase flow is important when one is analyzing the accidental loss of coolant or when analyzing industrial processes. If a pipe in the steam generator of a nuclear reactor breaks, the flow will remain critical (or choked) for almost the entire blowdown. For this reason the knowledge of the two-phase maximum (critical) flow rate is important. A six-equation model--consisting of two continuity equations, two energy equations, a mixture momentum equation, and a constitutive relative velocity equation--is solved numerically by the method of characteristics for one-dimensional, transient, two-phase flow systems. The analysis is also extended to the special case of transient critical flow. The six-equation model is used to study the flow of a nonequilibrium sodium-argon system in a horizontal tube in which the nonequilibrium sodium-argon system in a horizontal tube in which the critical flow condition is at the entrance. A four-equation model is used to study the pressure-pulse propagation rate in an isothermal air-water system, and the results that are found are compared with the experimental data. Proper initial and boundary conditions are obtained for the blowdown problem. The energy and mass exchange relations are evaluated by comparing the model predictions with results of void-fraction and heat-transfer experiments. A simplified two-equation model is obtained for the special case of two incompressible phases. This model is used in the preliminary analysis of batch sedimentation. It is also used to predict the shock formation in the gas-solid fluidized bed

  11. The dependence of Pi2 waveforms on periodic velocity enhancements within bursty bulk flows

    Directory of Open Access Journals (Sweden)

    K. R. Murphy

    2011-03-01

    Full Text Available Pi2s are a category of Ultra Low Frequency (ULF waves associated with the onset of magnetic substorms. Recent work has suggested that the deceleration of bulk plasma flows in the central plasmasheet, known as bursty bulk flows (BBFs, are able to directly-drive Pi2 oscillations. Some of these studies have further shown evidence that there is a one-to-one correlation between Pi2 magnetic waveforms observed on the ground and periodic peaks in flow velocity within the BBF, known as flow bursts. Utilising a favourable conjunction between the Geotail spacecraft and the Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA magnetometer array on 31 May 1998, we examine the causality of the link between BBF flow bursts and Pi2 waveforms. Using a series of analytical tests in both the time and frequency domains, we find that while the Pi2 and BBF waveforms are very similar, the ground response for this event occurs prior to the observed flow enhancements in the magnetotail. We conclude that during this specific case study the temporal variations of the flow bursts within the BBF are not directly-driving the observed ground-based Pi2 waveforms, despite the fact that a visual inspection of both time-series might initially suggest that there is a causal relationship. We postulate that rather than there being a direct causal relation, the similar waveforms observed in both Pi2s and BBFs may result from temporal variations in a common source for both the BBFs and the Pi2s, such as magnetic reconnection in the tail, this source modulating both the Pi2 and BBF at the same frequency.

  12. A netFlow scoring framework for incident detection

    CSIR Research Space (South Africa)

    Sweeney, M

    2017-09-01

    Full Text Available Vault and are made available as regularly updated feeds. Whitelists are lists of IP hosts that are known to be reliable or common destinations that are not likely to be a risk. Examples of these are Google, Facebook and Amazon. The suggested approach is that flows... based on the outcome of the test. A benefit of this approach is that many different potential threat identification approaches can be combined in order to identify high-risk flows with a strong level of confidence. In addition, the scoring has allowed us...

  13. Application and evaluation of LS-PIV technique for the monitoring of river surface velocities in high flow conditions

    OpenAIRE

    Jodeau , M.; Hauet , A.; Paquier , A.; Le Coz , J.; Dramais , G.

    2008-01-01

    Large Scale Particle Image Velocimetry (LS-PIV) is used to measure the surface flow velocities in a mountain stream during high flow conditions due to a reservoir release. A complete installation including video acquisition from a mobile elevated viewpoint and artificial flow seeding has been developed and implemented. The LS-PIV method was adapted in order to take into account the specific constraints of these high flow conditions. Using a usual LS-PIV data processing, significant variations...

  14. Burst Speed of Wild Fishes under High-Velocity Flow Conditions Using Stamina Tunnel with Natural Guidance System in River

    Science.gov (United States)

    Izumi, Mattashi; Yamamoto, Yasuyuki; Yataya, Kenichi; Kamiyama, Kohhei

    Swimming experiments were conducted on wild fishes in a natural guidance system stamina tunnel (cylindrical pipe) installed in a fishway of a local river under high-velocity flow conditions (tunnel flow velocity : 211 to 279 cm·s-1). In this study, the swimming characteristics of fishes were observed. The results show that (1) the swimming speeds of Tribolodon hakonensis (Japanese dace), Phoxinus lagowshi steindachneri (Japanese fat-minnow), Plecoglossus altivelis (Ayu), and Zacco platypus (Pale chub) were in proportion to their body length under identical water flow velocity conditions; (2) the maximum burst speed of Japanese dace and Japanese fat-minnow (measuring 4 to 6 cm in length) was 262 to 319 cm·s-1 under high flow velocity conditions (225 to 230 cm·s-1), while the maximum burst speed of Ayu and Pale chub (measuring 5 cm to 12 cm in length) was 308 to 355 cm·s-1 under high flow velocity conditions (264 to 273 cm·s-1) ; (3) the 50cm-maximum swimming speed of swimming fishes was 1.07 times faster than the pipe-swimming speed; (4) the faster the flow velocity, the shorter the swimming distance became.

  15. Comparison of Simultaneous PIV and Hydroxyl Tagging Velocimetry in Low Velocity Flows

    Science.gov (United States)

    Andre, Matthieu A.; Bardet, Philippe M.; Burns, Ross A.; Danehy, Paul M.

    2016-01-01

    Hydroxyl tagging velocimetry (HTV) is a molecular tagging velocimetry (MTV) technique that relies on the photo- dissociation of water vapor into OH radicals and their subsequent tracking using laser-induced fluorescence. At ambient temperature in air, the OH species lifetime is about 50 micro-s. The feasibility of using HTV for probing low- speed flows (a few m/s) is investigated by using an inert, heated gas as a means to increase the OH species lifetime. Unlike particle-based techniques, MTV does not suffer from tracer settling, which is particularly problematic at low speeds. Furthermore, the flow needs to be seeded with only a small mole fraction of water vapor, making it safer for both the user and facilities than other MTV techniques based on corrosive or toxic chemical tracers. HTV is demonstrated on a steam-seeded nitrogen jet at approximately 75 C in the laminar (Umean=3.31 m/s, Re=1,540), transitional (Umean=4.48 m/s, Re=2,039), and turbulent (Umean=6.91 m/s, Re=3,016) regimes at atmospheric pressure. The measured velocity profiles are compared with particle image velocimetry (PIV) measurements performed simultaneously with a second imager. Seeding for the PIV is achieved by introducing micron-sized water droplets into the flow with the steam; the same laser sheet is used for PIV and HTV to guarantee spatial and temporal overlap of the data. Optimizing each of these methods, however, requires conflicting operating conditions: higher temperatures benefit the HTV signals but reduce the available seed density for the PIV through evaporation. Nevertheless, data are found to agree within 10% for the instantaneous velocity profiles and within 5% for the mean profiles and demonstrate the feasibility of HTV for low-speed flows at moderate to high temperatures.

  16. Velocity correlations and spatial dependencies between neighbors in a unidirectional flow of pedestrians

    Science.gov (United States)

    Porzycki, Jakub; WÄ s, Jarosław; Hedayatifar, Leila; Hassanibesheli, Forough; Kułakowski, Krzysztof

    2017-08-01

    The aim of the paper is an analysis of self-organization patterns observed in the unidirectional flow of pedestrians. On the basis of experimental data from Zhang et al. [J. Zhang et al., J. Stat. Mech. (2011) P06004, 10.1088/1742-5468/2011/06/P06004], we analyze the mutual positions and velocity correlations between pedestrians when walking along a corridor. The angular and spatial dependencies of the mutual positions reveal a spatial structure that remains stable during the crowd motion. This structure differs depending on the value of n , for the consecutive n th -nearest-neighbor position set. The preferred position for the first-nearest neighbor is on the side of the pedestrian, while for further neighbors, this preference shifts to the axis of movement. The velocity correlations vary with the angle formed by the pair of neighboring pedestrians and the direction of motion and with the time delay between pedestrians' movements. The delay dependence of the correlations shows characteristic oscillations, produced by the velocity oscillations when striding; however, a filtering of the main frequency of individual striding out reduces the oscillations only partially. We conclude that pedestrians select their path directions so as to evade the necessity of continuously adjusting their speed to their neighbors'. They try to keep a given distance, but follow the person in front of them, as well as accepting and observing pedestrians on their sides. Additionally, we show an empirical example that illustrates the shape of a pedestrian's personal space during movement.

  17. Comparative study of the discrete velocity and lattice Boltzmann methods for rarefied gas flows through irregular channels.

    Science.gov (United States)

    Su, Wei; Lindsay, Scott; Liu, Haihu; Wu, Lei

    2017-08-01

    Rooted from the gas kinetics, the lattice Boltzmann method (LBM) is a powerful tool in modeling hydrodynamics. In the past decade, it has been extended to simulate rarefied gas flows beyond the Navier-Stokes level, either by using the high-order Gauss-Hermite quadrature, or by introducing the relaxation time that is a function of the gas-wall distance. While the former method, with a limited number of discrete velocities (e.g., D2Q36), is accurate up to the early transition flow regime, the latter method (especially the multiple relaxation time (MRT) LBM), with the same discrete velocities as those used in simulating hydrodynamics (i.e., D2Q9), is accurate up to the free-molecular flow regime in the planar Poiseuille flow. This is quite astonishing in the sense that less discrete velocities are more accurate. In this paper, by solving the Bhatnagar-Gross-Krook kinetic equation accurately via the discrete velocity method, we find that the high-order Gauss-Hermite quadrature cannot describe the large variation in the velocity distribution function when the rarefaction effect is strong, but the MRT-LBM can capture the flow velocity well because it is equivalent to solving the Navier-Stokes equations with an effective shear viscosity. Since the MRT-LBM has only been validated in simple channel flows, and for complex geometries it is difficult to find the effective viscosity, it is necessary to assess its performance for the simulation of rarefied gas flows. Our numerical simulations based on the accurate discrete velocity method suggest that the accuracy of the MRT-LBM is reduced significantly in the simulation of rarefied gas flows through the rough surface and porous media. Our simulation results could serve as benchmarking cases for future development of the LBM for modeling and simulation of rarefied gas flows in complex geometries.

  18. Synchronous Surface Pressure and Velocity Measurements of standard model in hypersonic flow

    Directory of Open Access Journals (Sweden)

    Zhijun Sun

    2018-01-01

    Full Text Available Experiments in the Hypersonic Wind tunnel of NUAA(NHW present synchronous measurements of bow shockwave and surface pressure of a standard blunt rotary model (AGARD HB-2, which was carried out in order to measure the Mach-5-flow above a blunt body by PIV (Particle Image Velocimetry as well as unsteady pressure around the rotary body. Titanium dioxide (Al2O3 Nano particles were seeded into the flow by a tailor-made container. With meticulous care designed optical path, the laser was guided into the vacuum experimental section. The transient pressure was obtained around model by using fast-responding pressure-sensitive paint (PSPsprayed on the model. All the experimental facilities were controlled by Series Pulse Generator to ensure that the data was time related. The PIV measurements of velocities in front of the detached bow shock agreed very well with the calculated value, with less than 3% difference compared to Pitot-pressure recordings. The velocity gradient contour described in accord with the detached bow shock that showed on schlieren. The PSP results presented good agreement with the reference data from previous studies. Our work involving studies of synchronous shock-wave and pressure measurements proved to be encouraging.

  19. Simultaneous measurement of 3D zooplankton trajectories and surrounding fluid velocity field in complex flows.

    Science.gov (United States)

    Adhikari, Deepak; Gemmell, Brad J; Hallberg, Michael P; Longmire, Ellen K; Buskey, Edward J

    2015-11-01

    We describe an automated, volumetric particle image velocimetry (PIV) and tracking method that measures time-resolved, 3D zooplankton trajectories and surrounding volumetric fluid velocity fields simultaneously and non-intrusively. The method is demonstrated for groups of copepods flowing past a wall-mounted cylinder. We show that copepods execute escape responses when subjected to a strain rate threshold upstream of a cylinder, but the same threshold range elicits no escape responses in the turbulent wake downstream. The method was also used to document the instantaneous slip velocity of zooplankton and the resulting differences in trajectory between zooplankton and non-inertial fluid particles in the unsteady wake flow, showing the method's capability to quantify drift for both passive and motile organisms in turbulent environments. Applications of the method extend to any group of organisms interacting with the surrounding fluid environment, where organism location, larger-scale eddies and smaller-scale fluid deformation rates can all be tracked and analyzed. © 2015. Published by The Company of Biologists Ltd.

  20. Interfacial area, velocity and void fraction in two-phase slug flow

    International Nuclear Information System (INIS)

    Kojasoy, G.; Riznic, J.R.

    1997-01-01

    The internal flow structure of air-water plug/slug flow in a 50.3 mm dia transparent pipeline has been experimentally investigated by using a four-sensor resistivity probe. Liquid and gas volumetric superficial velocities ranged from 0.55 to 2.20 m/s and 0.27 to 2.20 m/s, respectively, and area-averaged void fractions ranged from about 10 to 70%. The local distributions of void fractions, interfacial area concentration and interface velocity were measured. Contributions from small spherical bubbles and large elongated slug bubbles toward the total void fraction and interfacial area concentration were differentiated. It was observed that the small bubble void contribution to the overall void fraction was small indicating that the large slug bubble void fraction was a dominant factor in determining the total void fraction. However, the small bubble interfacial area contribution was significant in the lower and upper portions of the pipe cross sections

  1. Two different approaches for creating a prescribed opposed-flow velocity field for flame spread experiments

    Directory of Open Access Journals (Sweden)

    Carmignani Luca

    2015-01-01

    Full Text Available Opposed-flow flame spread over solid fuels is a fundamental area of research in fire science. Typically combustion wind tunnels are used to generate the opposing flow of oxidizer against which a laminar flame spread occurs along the fuel samples. The spreading flame is generally embedded in a laminar boundary layer, which interacts with the strong buoyancy-induced flow to affect the mechanism of flame spread. In this work, two different approaches for creating the opposed-flow are compared. In the first approach, a vertical combustion tunnel is used where a thin fuel sample, thin acrylic or ashless filter paper, is held vertically along the axis of the test-section with the airflow controlled by controlling the duty cycles of four fans. As the sample is ignited, a flame spreads downward in a steady manner along a developing boundary layer. In the second approach, the sample is held in a movable cart placed in an eight-meter tall vertical chamber filled with air. As the sample is ignited, the cart is moved downward (through a remote-controlled mechanism at a prescribed velocity. The results from the two approaches are compared to establish the boundary layer effect on flame spread over thin fuels.

  2. Two different approaches for creating a prescribed opposed-flow velocity field for flame spread experiments

    Science.gov (United States)

    Carmignani, Luca; Celniker, Greg; Bussett, Kyle; Paolini, Christopher; Bhattacharjee, Subrata

    2015-05-01

    Opposed-flow flame spread over solid fuels is a fundamental area of research in fire science. Typically combustion wind tunnels are used to generate the opposing flow of oxidizer against which a laminar flame spread occurs along the fuel samples. The spreading flame is generally embedded in a laminar boundary layer, which interacts with the strong buoyancy-induced flow to affect the mechanism of flame spread. In this work, two different approaches for creating the opposed-flow are compared. In the first approach, a vertical combustion tunnel is used where a thin fuel sample, thin acrylic or ashless filter paper, is held vertically along the axis of the test-section with the airflow controlled by controlling the duty cycles of four fans. As the sample is ignited, a flame spreads downward in a steady manner along a developing boundary layer. In the second approach, the sample is held in a movable cart placed in an eight-meter tall vertical chamber filled with air. As the sample is ignited, the cart is moved downward (through a remote-controlled mechanism) at a prescribed velocity. The results from the two approaches are compared to establish the boundary layer effect on flame spread over thin fuels.

  3. Continuous time random walks for the evolution of Lagrangian particle velocities in heterogeneous porous and fractured media flows

    Science.gov (United States)

    Dentz, M.; Kang, P. K.; Comolli, A.; Le Borgne, T.; Lester, D. R.

    2016-12-01

    We develop a continuous time random walk (CTRW) approach for the evolution of Lagrangian velocities in steadyheterogeneous porous and fractured media flows based on a stochastic relaxation process.This approach describes persistence of velocities over a characteristic spatial scale, unlike classical random walk methods,which model persistence over a characteristic time scale.We first establish the relations between Eulerian and Lagrangian velocities for both equidistant and isochronal sampling along streamlines,under transient and stationary conditions. Based on this, we develop the CTRW approach for the spatial and temporaldynamics of Lagrangian velocities. Unlike classical CTRW formulations, the proposed approach quantifies both stationaryand non-stationary Lagrangian velocity statistics, and their evolution from arbitraryinitial velocity distributions. We provide explicit expressions for the Lagrangian velocity distributions,and determine the behaviors of the mean particle velocity, velocity covariance andparticle dispersion. We find strong correlation and anomalous dispersion for velocity distributions which are tailedtoward low velocities. The developed CTRW approach and thus the Lagrangian particle dynamics are fully determined by the Eulerian velocitydistribution and the characteristic correlation scale. The developed framework is applied to particle transport in two-dimensionalrandom fracture networks.

  4. Development and validation of a measurement technique for interfacial velocity in liquid-gas separated flow using IR-PTV

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sang Geun; Kim, Hyung Dae [Dept. of Nuclear Engineering, Kyung Hee University, Seoul (Korea, Republic of)

    2015-07-15

    A measurement technique of interfacial velocity in air-water separated flow by particle tracking velocimetry using an infrared camera (IR-PTV) was developed. As infrared light with wavelength in the range of 3-5 um could hardly penetrate water, IR-PTV can selectively visualize only the tracer particles existing in depths less than 20 um underneath the air-water interface. To validate the measurement accuracy of the IR-PTV technique, a measurement of the interfacial velocity of the air-water separated flow using Styrofoam particles floating in water was conducted. The interfacial velocity values obtained with the two different measurement techniques showed good agreement with errors less than 5%. It was found from the experimental results obtained using the developed technique that with increasing air velocity, the interfacial velocity proportionally increases, likely because of the increased interfacial stress.

  5. Development of ultrasonic velocity profile method for flow rate measurements of power plant (effect of measurement volume on turbulent flow measurement)

    International Nuclear Information System (INIS)

    Hiroshige, Kikura; Gentaro, Yamanaka; Tsuyoshi, Taishi; Masanori, Aritomi; Yasushi, Takeda; Michitsugu, Mori

    2001-01-01

    Ultrasonic Velocity Profile method has many advantages for flow rate measurement of power plant over the conventional flow measurement methods, such as measurement of the instantaneous velocity profile along the measuring line and its applicability to opaque liquids. Furthermore, the method has an advantage of being non-intrusive. Hence, it is applicable to various flow conditions, although it requires a relatively large measurement volume. In this paper, the effects of the measurement volume on the mean velocity profile for flow rate measurements of power plant and the Reynolds stress measurement have been investigated for fully developed turbulent pipe flows in a vertical pipe. The results are then compared with data obtained by Direct Numerical Simulation (DNS). (authors)

  6. Study of Estimation Method for Unsteady Inflow Velocity in Two-Dimensional Ultrasonic-Measurement-Integrated Blood Flow Simulation.

    Science.gov (United States)

    Kadowaki, Hiroko; Hayase, Toshiyuki; Funamoto, Kenichi; Taniguchi, Nobuyuki

    2016-02-01

    Information on hemodynamics is essential for elucidation of mechanisms and development of novel diagnostic methods for circulatory diseases. Two-dimensional ultrasonic-measurement-integrated (2D-UMI) simulation can correctly reproduce an intravascular blood flow field and hemodynamics by feeding back an ultrasonic measurement to the numerical blood flow simulation. In this method, it is critically important to give the correct cross-sectional average inflow velocity (inflow velocity) as the boundary condition. However, systematic study has not been done on the relative validity and effectiveness of existing inflow velocity estimation methods for various target flow fields. The aim of this study was to examine the existing methods systematically and to establish a method to accurately estimate inflow velocities for various vessel geometries and flow conditions in 2D-UMI simulations. A numerical experiment was performed for 2D-UMI simulation of blood flow models in a straight vessel with inflow velocity profiles symmetric and asymmetric to the vessel axis using existing evaluation functions based on Doppler velocity error for the inflow velocity estimation. As a result, it was clarified that a significantly large estimation error occurs in the asymmetric flow due to a nonfeedback domain near the downstream end of the calculation domain. Hence, a new inflow velocity estimation method of 2D-UMI simulation is proposed in which the feedback and evaluation domains are extended to the downstream end. Further numerical experiments of 2D-UMI simulation for two realistic vessel geometries of a healthy blood vessel and a stenosed one confirmed the effectiveness of the proposed method.

  7. In situ calibration of an interferometric velocity sensor for measuring small scale flow structures using a Talbot-pattern

    Science.gov (United States)

    König, Jörg; Czarske, Jürgen

    2017-10-01

    Small scale flow phenomena play an important role across engineering, biological and chemical sciences. To gain deeper understanding of the influence of those flow phenomena involved, measurement techniques with high spatial resolution are often required, presuming a calibration of very low uncertainty. To enable such measurements, a method for the in situ calibration of an interferometric flow velocity profile sensor is presented. This sensor, with demonstrated spatial resolution better than 1 μm, allows for spatially-resolving measurements with low velocity uncertainty in flows with high velocity gradients, on condition that the spatial behavior of the interference fringe systems is well-known by calibration with low uncertainty, especially challenging to obtain at applications with geometries difficult to access. The calibration method described herein uses three interfering beams to form the interference fringe systems of the sensor, yielding Doppler burst signals exhibiting two peaks in the frequency domain whose amplitude ratio varies periodically along the measurement volume major z-axis, giving a further independent value of the axial tracer particle position that can be used to determine the calibration functions of the sensor during the flow measurement. A flow measurement in a microchannel experimentally validates that the presented approach allows for simultaneously estimating the calibration functions and the velocity profile, providing flow measurements with very low systematic measurement errors of the particle position of less than 400 nm (confidence interval 95%). In that way, the interferometric flow velocity profile sensor utilizing the in situ self-calibration method promises valuable insights on small scale flow phenomena, such as those given in shear and boundary layer flows, by featuring reliable flow measurements due to minimum systematic and statistical measurement errors.

  8. Involvement of calcitonin gene-related peptide in migraine: regional cerebral blood flow and blood flow velocity in migraine patients

    DEFF Research Database (Denmark)

    Lassen, L.H.; Jacobsen, V.B.; Haderslev, P.A.

    2008-01-01

    g/min) or placebo for 20 min was studied in 12 patients with migraine without aura outside attacks. Xenon-133 inhalation SPECT-determined regional cerebral blood flow (rCBF) and transcranial Doppler (TCD)-determined blood velocity (V-mean) in the middle cerebral artery (MCA), as well as the heart......Calcitonin gene-related peptide (CGRP)-containing nerves are closely associated with cranial blood vessels. CGRP is the most potent vasodilator known in isolated cerebral blood vessels. CGRP can induce migraine attacks, and two selective CGRP receptor antagonists are effective in the treatment...... of migraine attacks. It is therefore important to investigate its mechanism of action in patients with migraine. We here investigate the effects of intravenous human alpha-CGRP (h alpha CGRP) on intracranial hemodynamics. In a double-blind, cross-over study, the effect of intravenous infusion of haCGRP (2 mu...

  9. Determination of velocity and flow direction of ground water by using nuclear techniques

    International Nuclear Information System (INIS)

    Santos Ferreira, L. dos.

    1976-06-01

    The dynamics of water in an aquifer with the purpose of determining the filtration velocity and the direction of groundwater flow with radioactive tracers was studied. Field equipment for the purposes of the study was built in the Laboratory of Tracers in Hydrology in collaboration with the Institute of Nuclear Engineering (IEN/NUCLEBRAS). The equipment was designed to minimize the possible vertical flows, loss and molecular diffusion of the tracer out of the studied region. The performance of the nuclear detectors and the constructional details of the field equipament were examined. The selection of the radioactive tracers was made taking into account its availibility and radiation facilities, cost of the inactive material and their physical and chemical properties. The tracers used were 82 Br and 198 Au. The results are discussed with the help of auxiliary informations such as plots of water levels in time and space, profiles and grain analysis. In order to obtain a physical explanation of the results, a qualitative model of the flow in the aquifer is also presented. (Author) [pt

  10. A Hybrid Windkessel Model of Blood Flow in Arterial Tree Using Velocity Profile Method

    Science.gov (United States)

    Aboelkassem, Yasser; Virag, Zdravko

    2016-11-01

    For the study of pulsatile blood flow in the arterial system, we derived a coupled Windkessel-Womersley mathematical model. Initially, a 6-elements Windkessel model is proposed to describe the hemodynamics transport in terms of constant resistance, inductance and capacitance. This model can be seen as a two compartment model, in which the compartments are connected by a rigid pipe, modeled by one inductor and resistor. The first viscoelastic compartment models proximal part of the aorta, the second elastic compartment represents the rest of the arterial tree and aorta can be seen as the connection pipe. Although the proposed 6-elements lumped model was able to accurately reconstruct the aortic pressure, it can't be used to predict the axial velocity distribution in the aorta and the wall shear stress and consequently, proper time varying pressure drop. We then modified this lumped model by replacing the connection pipe circuit elements with a vessel having a radius R and a length L. The pulsatile flow motions in the vessel are resolved instantaneously along with the Windkessel like model enable not only accurate prediction of the aortic pressure but also wall shear stress and frictional pressure drop. The proposed hybrid model has been validated using several in-vivo aortic pressure and flow rate data acquired from different species such as, humans, dogs and pigs. The method accurately predicts the time variation of wall shear stress and frictional pressure drop. Institute for Computational Medicine, Dept. Biomedical Engineering.

  11. Transcranial Doppler ultrasonography in children with sickle cell anemia: Clinical and laboratory correlates for elevated blood flow velocities.

    Science.gov (United States)

    Lagunju, IkeOluwa; Sodeinde, Olugbemiro; Brown, Biobele; Akinbami, Felix; Adedokun, Babatunde

    2014-02-01

    Transcranial Doppler (TCD) sonography of major cerebral arteries is now recommended for routine screening for stroke risk in children with sickle cell disease (SCD). We performed TCD studies on children with sickle cell anemia (SCA) seen at the pediatric hematology clinic over a period of 2 years. TCD scans were repeated yearly in children with normal flow velocities and every 3 months in children with elevated velocities. Findings were correlated with clinical variables, hematologic indices, and arterial oxygen saturation. Predictors of elevated velocities were identified by multiple linear regressions. We enrolled 237 children and performed a total of 526 TCD examinations. Highest time-averaged maximum flow velocities were ≥170 cm/s in 72 (30.3%) cases and ≥200 cm/s in 20 (8.4%). Young age, low hematocrit, low hemoglobin, and arterial oxygen desaturation <95% showed significant correlations with presence of increased cerebral flow velocities. Low hematocrit, low hemoglobin concentration, young age, and low arterial oxygen desaturation predicted elevated cerebral blood flow velocities and, invariably, increased stroke risk, in children with SCA. Children who exhibit these features should be given high priority for TCD examination in the setting of limited resources. Copyright © 2013 Wiley Periodicals, Inc.

  12. Turbulent conductivity in parallel with iso-velocities in a planar established flow

    International Nuclear Information System (INIS)

    Jullien, F.

    1968-02-01

    In this thesis are presented the experimental results obtained during the study of the turbulent diffusion of heat using a wire source in a flat air flow. The Taylor statistical theory laws are well respected in the domain studied. The experiments have made it possible to evaluate the influence of the Reynolds number and of the distance from the wall on the quadratic values of velocity fluctuations and on the Lagrange turbulence scales. In particular, the author has found a correlation between the Lagrange scales and the friction coefficient when the Reynolds number varies. A diffusion law is derived from the Taylor theory; it makes it possible to explain more clearly the idea of turbulent conductivity. (author) [fr

  13. Spatial heterogeneity of biofouling under different cross-flow velocities in reverse osmosis membrane systems

    KAUST Repository

    Farhat, Nadia

    2016-09-06

    The spatially heterogeneous distribution of biofouling in spiral wound membrane systems restricts (i) the water distribution over the membrane surface and therefore (ii) the membrane-based water treatment. The objective of the study was to assess the spatial heterogeneity of biofilm development over the membrane fouling simulator (MFS) length (inlet and outlet part) at three different cross-flow velocities (0.08, 0.12 and 0.16 m/s). The MFS contained sheets of membrane and feed spacer and simulated the first 0.20 m of spiral-wound membrane modules where biofouling accumulates the most in practice. In-situ non-destructive oxygen imaging using planar optodes was applied to determine the biofilm spatially resolved activity and heterogeneity.

  14. Detailed experimental investigations on flow behaviors and velocity field properties of a supersonic mixing layer

    Science.gov (United States)

    Tan, Jianguo; Zhang, Dongdong; Li, Hao; Hou, Juwei

    2018-03-01

    The flow behaviors and mixing characteristics of a supersonic mixing layer with a convective Mach number of 0.2 have been experimentally investigated utilizing nanoparticle-based planar laser scattering and particle image velocimetry techniques. The full development and evolution process, including the formation of Kelvin-Helmholtz vortices, breakdown of large-scale structures and establishment of self-similar turbulence, is exhibited clearly in the experiments, which can give a qualitative graphically comparing for the DNS and LES results. The shocklets are first captured at this low convective Mach number, and their generation mechanisms are elaborated and analyzed. The convective velocity derived from two images with space-time correlations is well consistent with the theoretical result. The pairing and merging process of large-scale vortices in transition region is clearly revealed in the velocity vector field. The analysis of turbulent statistics indicates that in weakly compressible mixing layers, with the increase of convective Mach number, the peak values of streamwise turbulence intensity and Reynolds shear stress experience a sharp decrease, while the anisotropy ratio seems to keep quasi unchanged. The normalized growth rate of the present experiments shows a well agreement with former experimental and DNS data. The validation of present experimental results is important for that in the future the present work can be a reference for assessing the accuracy of numerical data.

  15. High speed ultrasonic system to measure bubbles velocities in a horizontal two-phase flow

    International Nuclear Information System (INIS)

    Cunha Filho, Jurandyr S.; Jian Su; Farias, Marcos S.; Faccini, Jose L.H.; Lamy, Carlos A.

    2009-01-01

    In this work, a non invasive technique consisting of a high speed ultrasonic multitransducer pulse-echo system was developed to characterize gas-liquid two-phase flow parameters that are important in the study of the primary refrigeration circuit of nuclear reactors. The high speed ultrasonic system consists of two transducers (10 MHz/φ 6.35 mm), a generator/multiplexer board, and software that selects and has a data acquisition system of the ultrasonic signals. The resolutions of the system and the pulse time generated from each transducer are, respectively, 10 ns and 1.06 ms. The system initially was used in the local instantaneous measurement of gas-liquid interface in a circular horizontal pipe test section made of a 5 m long stainless steel pipe of 51.2 mm inner diameter, where the elongated bubbles velocity was measured (Taylor bubbles). The results show that the high speed ultrasonic pulse-echo system provides good results for the determination of elongated bubbles velocities. (author)

  16. A velocity tracking approach for the data assimilation problem in blood flow simulations.

    Science.gov (United States)

    Tiago, J; Guerra, T; Sequeira, A

    2017-10-01

    Several advances have been made in data assimilation techniques applied to blood flow modeling. Typically, idealized boundary conditions, only verified in straight parts of the vessel, are assumed. We present a general approach, on the basis of a Dirichlet boundary control problem, that may potentially be used in different parts of the arterial system. The relevance of this method appears when computational reconstructions of the 3D domains, prone to be considered sufficiently extended, are either not possible, or desirable, because of computational costs. On the basis of taking a fully unknown velocity profile as the control, the approach uses a discretize then optimize methodology to solve the control problem numerically. The methodology is applied to a realistic 3D geometry representing a brain aneurysm. The results show that this data assimilation approach may be preferable to a pressure control strategy and that it can significantly improve the accuracy associated to typical solutions obtained using idealized velocity profiles. Copyright © 2016 John Wiley & Sons, Ltd.

  17. Magnetic resonance flow velocity and temperature mapping of a shape memory polymer foam device

    Directory of Open Access Journals (Sweden)

    Wilson Thomas S

    2009-12-01

    Full Text Available Abstract Background Interventional medical devices based on thermally responsive shape memory polymer (SMP are under development to treat stroke victims. The goals of these catheter-delivered devices include re-establishing blood flow in occluded arteries and preventing aneurysm rupture. Because these devices alter the hemodynamics and dissipate thermal energy during the therapeutic procedure, a first step in the device development process is to investigate fluid velocity and temperature changes following device deployment. Methods A laser-heated SMP foam device was deployed in a simplified in vitro vascular model. Magnetic resonance imaging (MRI techniques were used to assess the fluid dynamics and thermal changes associated with device deployment. Results Spatial maps of the steady-state fluid velocity and temperature change inside and outside the laser-heated SMP foam device were acquired. Conclusions Though non-physiological conditions were used in this initial study, the utility of MRI in the development of a thermally-activated SMP foam device has been demonstrated.

  18. Lower Transcranial Doppler Flow Velocities in Sickle Cell Anemia Patients on Hydroxyurea: Myth or Fact.

    Science.gov (United States)

    Moeen, Sawsan M; Thabet, Ahmad F; Hasan, Hosam A; Saleh, Medhat A

    2018-01-01

    Transcranial Doppler (TCD) detects stroke risk in patients with sickle cell anemia (SCA). Hydroxyurea therapy has the ability to induce increased levels of fetal hemoglobin in sickle cells thus decreasing tendency for red cell sickling. This study aimed to evaluate TCD findings in SCA patients on hydroxyurea and correlate the time-averaged mean velocity (TAMV) with their hematological parameters. Forty SCA patients of both sexes, aged 16-22 years with no history of stroke were screened with TCD for an elevated TAMV, divided into: Group T (20 patients on blood transfusion); and Group H (20 patients on daily hydroxyurea). For all, full medical history, clinical examination, hemoglobin, hematocrit, leukocytes, platelets, fetal hemoglobin and sickling test, in addition TCD to describe the pattern of cerebral blood flow abnormalities were done. TAMV in all cerebral arteries were significantly higher in Group T than Group H, the highest TAMV (147.5 ± 57.09 cm/s) was found in the right middle cerebral artery and correlated negatively with hematocrit in Groups H ( P  Hydroxyurea therapy may lower TCD velocities and prevent the risk of primary stroke in SCA patients.

  19. Velocity Fields Measurement of Natural Circulation Flow inside a Pool Using PIV Technique

    International Nuclear Information System (INIS)

    Kim, Seok; Kim, Dong Eok; Youn, Young Jung; Euh, Dong Jin; Song, Chul Hwa

    2012-01-01

    Thermal stratification is encountered in large pool of water increasingly being used as heat sink in new generation of advanced reactors. These large pools at near atmospheric pressure provide a heat sink for heat removal from the reactor or steam generator, and the containment by natural circulation as well as a source of water for core cooling. For examples, the PAFS (passive auxiliary feedwater system) is one of the advanced safety features adopted in the APR+ (Advanced Power Reactor Plus), which is intended to completely replace the conventional active auxiliary feedwater system. The PAFS cools down the steam generator secondary side and eventually removes the decay heat from the reactor core by adopting a natural convection mechanism. In a pool, the heat transfer from the PCHX (passive condensation heat exchanger) contributed to increase the pool temperature up to the saturation condition and induce the natural circulation flow of the PCCT (passive condensate cooling tank) pool water. When a heat rod is placed horizontally in a pool of water, the fluid adjacent to the heat rod gets heated up. In the process, its density reduces and by virtue of the buoyancy force, the fluid in this region moves up. After reaching the top free surface, the heated water moves towards the other side wall of the pool along the free surface. Since this heated water is cooling, it goes downward along the wall at the other side wall. Above heater rod, a natural circulation flow is formed. However, there is no flow below heater rod until pool water temperature increases to saturation temperature. In this study, velocity measurement was conducted to reveal a natural circulation flow structure in a small pool using PIV (particle image velocimetry) measurement technique

  20. Micro-PIV and CFD characterization of flows in a microchannel: Velocity profiles, surface roughness and Poiseuille numbers

    International Nuclear Information System (INIS)

    Silva, Goncalo; Leal, Nuno; Semiao, Viriato

    2008-01-01

    Microfluidics is a promising technology, although the governing physical mechanisms are still not quite understood due to the difficulties arising in measuring at such small scales. This work intends to bring some insight on the influence of surface phenomena in microscale flows by proposing a different method to quantify such influence. In this new method, detailed velocity measurements are performed to evaluate the influence on the flow of the surface phenomena instead of using measured bulk flow properties. For that micro-Particle Image Velocimetry (micro-PIV) is used to characterize the flow kinematics inside a DantecDynamics microchannel (with hydraulic diameter of 637 μm) that possesses rather rough walls (relative roughness of 1.6%) and a very irregular cross-section shape. Two-dimensional velocity profiles were measured in 61 horizontal planes to define the three-dimensional laminar flows (Re ≤ 50). Integration of the velocity profiles yielded volumetric flow rates with a maximum deviation of 3% from the measured volume of fluid discharged as function of time, which gives the magnitude of the bias error of the experimental technique. Effects of walls roughness were quantified by comparing Poiseuille numbers obtained from experimental velocity profiles against those obtained from CFD predictions for the same operating conditions but with hydrodynamically smooth walls, according to the new method proposed herein. Those Poiseuille numbers differed 11% demonstrating the need to account for wall roughness in microflows

  1. Arbitrary Lagrangian-Eulerian finite element analysis of free surface flow using a velocity-vorticity formulation

    International Nuclear Information System (INIS)

    Lo, D.C.; Young, D.L.

    2004-01-01

    This paper describes the application of velocity-vorticity formulation of the Navier-Stokes equations for two-dimensional free surface flow using an arbitrary Lagrangian-Eulerian method. The velocity Poisson equations and the vorticity transport equations are solved using a finite element method to obtain the velocity and the vorticity fields in the interior region of the computational domain. The boundary-fitted coordinates system is adopted to solve the boundary equations for kinematic and dynamic conditions at the free surface using a finite difference method. The numerical model for the velocity-vorticity formulation is validated for a square cavity flow at Re=400 and 1000. The solitary wave reflected from a vertical wall is chosen as a test case for comparison and validation of the free surface flow model. Then the proposed numerical model is used to obtain flow results for the following free surface flow cases: (i) interaction between two opposite solitary waves, (ii) seiche phenomenon in a rectangular reservoir, and (iii) solitary wave through a submerged rectangular structure in a viscous fluid. The efficiency of the present numerical model for numerical treatment of free surface flows is discussed. Furthermore the advantage of this formulation with respect to primitive variables formulation is addressed from the computational point of view

  2. Preliminary assessment of the Velocity Pump Reaction Turbine as a geothermal total-flow expander

    Energy Technology Data Exchange (ETDEWEB)

    Demuth, O.J.

    1985-01-01

    A preliminary evaluation was made of the Velocity Pump Reaction Turbine (VPRT) as a total flow expander in a geothermal-electric conversion cycle. Values of geofluid effectiveness of VPRT systems were estimated for conditions consisting of: a 360/sup 0/F geothermal resource, 60/sup 0/F wet-bulb ambient temperature, zero and 0.003 mass concentrations of dissolved noncondensible gas in the geofluid, 100 and 120/sup 0/F condensing temperature, and engine efficiencies ranging from 0.4 to 1.0. Achievable engine efficiencies were estimated to range from 0.47 to 0.77, with plant geofluid effectivenss values ranging as high as 9.5 Watt hr/lbm geofluid. This value is competitive with magnitudes of geofluid effectiveness projected for advanced binary plants, and is on the order of 40% higher than estimates for dual-flash steam systems and other total flow systems reviewed. Because of its potentially high performance and relative simplicity, the VPRT system appears to warrant further investigation toward its use in a well-head geothermal plant. 13 refs., 5 figs.

  3. Design and analysis of flow velocity distribution inside a raceway pond using computational fluid dynamics.

    Science.gov (United States)

    Pandey, Ramakant; Premalatha, M

    2017-03-01

    Open raceway ponds are widely adopted for cultivating microalgae on a large scale. Working depth of the raceway pond is the major component to be analysed for increasing the volume to surface area ratio. The working depth is limited up to 5-15 cm in conventional ponds but in this analysis working depth of raceway pond is considered as 25 cm. In this work, positioning of the paddle wheel is analysed and corresponding Vertical Mixing Index are calculated using CFD. Flow pattern along the length of the raceway pond, at three different paddle wheel speeds are analysed for L/W ratio of 6, 8 and 10, respectively. Effect of clearance (C) between rotor blade tip and bottom surface is also analysed by taking four clearance conditions i.e. C = 2, 5, 10 and 15. Moving reference frame method of Fluent is used for the modeling of six blade paddle wheel and realizable k-ε model is used for capturing turbulence characteristics. Overall objective of this work is to analyse the required geometry for maintaining a minimum flow velocity to avoid settling of algae corresponding to 25 cm working depth. Geometry given in [13] is designed using ANSYS Design modular and CFD results are generated using ANSYS FLUENT for the purpose of validation. Good agreement of results is observed between CFD and experimental Particle image velocimetry results with the deviation of 7.23%.

  4. A Novel Quasi-3D Method for Cascade Flow Considering Axial Velocity Density Ratio

    Science.gov (United States)

    Chen, Zhiqiang; Zhou, Ming; Xu, Quanyong; Huang, Xudong

    2018-03-01

    A novel quasi-3D Computational Fluid Dynamics (CFD) method of mid-span flow simulation for compressor cascades is proposed. Two dimension (2D) Reynolds-Averaged Navier-Stokes (RANS) method is shown facing challenge in predicting mid-span flow with a unity Axial Velocity Density Ratio (AVDR). Three dimension (3D) RANS solution also shows distinct discrepancies if the AVDR is not predicted correctly. In this paper, 2D and 3D CFD results discrepancies are analyzed and a novel quasi-3D CFD method is proposed. The new quasi-3D model is derived by reducing 3D RANS Finite Volume Method (FVM) discretization over a one-spanwise-layer structured mesh cell. The sidewall effect is considered by two parts. The first part is explicit interface fluxes of mass, momentum and energy as well as turbulence. The second part is a cell boundary scaling factor representing sidewall boundary layer contraction. The performance of the novel quasi-3D method is validated on mid-span pressure distribution, pressure loss and shock prediction of two typical cascades. The results show good agreement with the experiment data on cascade SJ301-20 and cascade AC6-10 at all test condition. The proposed quasi-3D method shows superior accuracy over traditional 2D RANS method and 3D RANS method in performance prediction of compressor cascade.

  5. PREDICTION OF BLOOD FLOW VELOCITY AND LEAFLET DEFORMATION VIA 2D MITRAL VALVE MODEL

    Directory of Open Access Journals (Sweden)

    M.A.H. Mohd Adib

    2012-06-01

    Full Text Available In the mitral valve, regional variations in structure and material properties combine to affect the biomechanics of the entire valve. From previous studies, we know that the mitral valve leaflet tissue is highly extensible. A two-dimensional model of the mitral valve was generated using an Arbitrary Lagrangian-Eulerian (ALE mesh. A simple approximation of the heart geometry was used and the valve dimensions were based on actual measurements made. Valve opening and closure was simulated using contact equations. The objective of this study was to investigate and predict flow and leaflet phenomena via a simple 2D mitral valve model based on the critical parameter of blood. Two stages of mitral valves analysis were investigated: the systolic and diastolic stages. The results show a linear correlation between the mitral valve leaflet rigidity and the volume of backflow. Additionally, the simulation predicted mitral valve leaflet displacement during closure, which agreed with the results of our previous data analysis and the results for blood flow velocity during systole condition through the mitral valve outlet, as reported in the medical literature. In conclusion, these computational techniques are very useful in the study of both degenerative valve disease and failure of prostheses and will be further developed to investigate heart valve failure and subsequent surgical repair.

  6. Extracting kinetic freeze-out temperature and radial flow velocity from an improved Tsallis distribution

    Energy Technology Data Exchange (ETDEWEB)

    Lao, Hai-Ling; Liu, Fu-Hu [Shanxi University, Institute of Theoretical Physics, Shanxi (China); Lacey, Roy A. [Stony Brook University, Departments of Chemistry and Physics, Stony Brook, NY (United States)

    2017-03-15

    We analyze the transverse-momentum (p{sub T}) spectra of identified particles (π{sup ±}, K{sup ±}, p, and anti p) produced in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions over a √(s{sub NN}) (center-of-mass energy per nucleon pair) range from 14.5 GeV (one of the Relativistic Heavy Ion Collider (RHIC) energies) to 2.76 TeV (one of the Large Hadron Collider (LHC) energies). For the spectra with a narrow p{sub T} range, an improved Tsallis distribution which is in fact the Tsallis distribution with radial flow is used. For the spectra with a wide p{sub T} range, a superposition of the improved Tsallis distribution and an inverse power law is used. Both the extracted kinetic freeze-out temperature (T{sub 0}) and radial flow velocity (β{sub T}) increase with the increase of √(s{sub NN}), which indicates a higher excitation and larger expansion of the interesting system at the LHC. Both the values of T{sub 0} and β{sub T} in central collisions are slightly larger than those in peripheral collisions, and they are independent of isospin and slightly dependent on mass. (orig.)

  7. Velocity field measurement in gas-liquid metal two-phase flow with use of PIV and neutron radiography techniques

    International Nuclear Information System (INIS)

    Saito, Y.; Mishima, K.; Tobita, Y.; Suzuki, T.; Matsubayashi, M.

    2001-01-01

    Neutron radiography and PIV (Particle Image Velocimetry) techniques were applied to measurements of velocity field in gas-liquid metal two-phase flow. Visualization and measurements of two-phase flow were conducted using molten lead bismuth and nitrogen gas as working fluids and particles made of gold-cadmium (AuCd 3 ) inter-metallic alloy were employed as the tracer. Discrimination method between bubble and tracer images in two-phase flow was developed based on the σ-scaling method. Time-averaged liquid velocity fields, gas velocity fields and void profile were calculated from discriminated images, respectively. From these measurements, the basic characteristics of gas-liquid metal two-phase mixture were clarified. (author)

  8. Fast Blood Vector Velocity Imaging using ultrasound: In-vivo examples of complex blood flow in the vascular system

    DEFF Research Database (Denmark)

    Hansen, Kristoffer Lindskov; Udesen, Jesper; Gran, Fredrik

    2008-01-01

    Conventional ultrasound methods for acquiring color flow images of the blood motion are restricted by a relatively low frame rate and angle dependent velocity estimates. The Plane Wave Excitation (PWE) method has been proposed to solve these limitations. The frame rate can be increased, and the 2-D...... vector velocity of the blood motion can be estimated. The transmitted pulse is not focused, and a full speckle image of the blood can be acquired for each emission. A 13 bit Barker code is transmitted simultaneously from each transducer element. The 2-D vector velocity of the blood is found using 2-D...... speckle tracking between segments in consecutive speckle images. The flow patterns of six bifurcations and two veins were investigated in-vivo. It was shown: 1) that a stable vortex in the carotid bulb was present opposed to other examined bifurcations, 2) that retrograde flow was present...

  9. Observations of high-velocity SAPS-like flows with the King Salmon SuperDARN radar

    Directory of Open Access Journals (Sweden)

    A. V. Koustov

    2006-07-01

    Full Text Available In this study, a focused investigation of the potential for the King Salmon (KS SuperDARN HF radar to monitor high-velocity flows near the equatorial edge of the auroral oval is undertaken. Events are presented with line-of-sight velocities as high as 2km/s, observed roughly along the L-shell. Statistically, the enhanced flows are shown to be typical for the dusk sector (16:00–23:00 MLT, and the average velocity in this sector is larger (smaller for winter (summer conditions. It is also demonstrated that the high-velocity flows can be very dynamical with more localized enhancements existing for just several minutes. These short-lived enhancements occur when the luminosity at the equatorial edge of the auroral oval suddenly decreases during the substorm recovery phase. The short-lived velocity enhancements can be established because of proton and ion injections into the inner magnetosphere and low conductance of the ionosphere and not because of enhanced tail reconnection. This implies that some KS velocity enhancements have the same origin as subauroral polarization streams (SAPS.

  10. A Novel Dynamic Model for Predicting Pressure Wave Velocity in Four-Phase Fluid Flowing along the Drilling Annulus

    Directory of Open Access Journals (Sweden)

    Xiangwei Kong

    2015-01-01

    Full Text Available A dynamic pressure wave velocity model is presented based on momentum equation, mass-balance equation, equation of state, and small perturbation theory. Simultaneously, the drift model was used to analyze the flow characteristics of oil, gas, water, and drilling fluid multiphase flow. In addition, the dynamic model considers the gas dissolution, virtual mass force, drag force, and relative motion of the interphase as well. Finite difference and Newton-Raphson iterative are introduced to the numerical simulation of the dynamic model. The calculation results indicate that the wave velocity is more sensitive to the increase of gas influx rate than the increase of oil/water influx rate. Wave velocity decreases significantly with the increase of gas influx. Influenced by the pressure drop of four-phase fluid flowing along the annulus, wave velocity tends to increase with respect to well depth, contrary to the gradual reduction of gas void fraction at different depths with the increase of backpressure (BP. Analysis also found that the growth of angular frequency will lead to an increase of wave velocity at low range. Comparison with the calculation results without considering virtual mass force demonstrates that the calculated wave velocity is relatively bigger by using the presented model.

  11. Depression storage and infiltration effects on overland flow depth-velocity-friction at desert conditions: field plot results and model

    Directory of Open Access Journals (Sweden)

    M. J. Rossi

    2012-09-01

    Full Text Available Water infiltration and overland flow are relevant in considering water partition among plant life forms, the sustainability of vegetation and the design of sustainable hydrological models and management. In arid and semi-arid regions, these processes present characteristic trends imposed by the prevailing physical conditions of the upper soil as evolved under water-limited climate. A set of plot-scale field experiments at the semi-arid Patagonian Monte (Argentina were performed in order to estimate the effect of depression storage areas and infiltration rates on depths, velocities and friction of overland flows. The micro-relief of undisturbed field plots was characterized at z-scale 1 mm through close-range stereo-photogrammetry and geo-statistical tools. The overland flow areas produced by controlled water inflows were video-recorded and the flow velocities were measured with image processing software. Antecedent and post-inflow moisture were measured, and texture, bulk density and physical properties of the upper soil were estimated based on soil core analyses. Field data were used to calibrate a physically-based, mass balanced, time explicit model of infiltration and overland flows. Modelling results reproduced the time series of observed flow areas, velocities and infiltration depths. Estimates of hydrodynamic parameters of overland flow (Reynolds-Froude numbers are informed. To our knowledge, the study here presented is novel in combining several aspects that previous studies do not address simultaneously: (1 overland flow and infiltration parameters were obtained in undisturbed field conditions; (2 field measurements of overland flow movement were coupled to a detailed analysis of soil microtopography at 1 mm depth scale; (3 the effect of depression storage areas in infiltration rates and depth-velocity friction of overland flows is addressed. Relevance of the results to other similar desert areas is justified by the accompanying

  12. Incident shock strength evolution in overexpanded jet flow out of rocket nozzle

    Science.gov (United States)

    Silnikov, Mikhail V.; Chernyshov, Mikhail V.

    2017-06-01

    The evolution of the incident shock in the plane overexpanded jet flow or in the axisymmetric one is analyzed theoretically and compared at the whole range of governing flow parameters. Analytical results can be applied to avoid jet flow instability and self-oscillation effects at rocket launch, to improve launch safety and to suppress shock-wave induced noise harmful to environment and personnel. The mathematical model of ;differential conditions of dynamic compatibility; was applied to the curved shock in non-uniform plane or axisymmetrical flow. It allowed us to study such features of the curved incident shock and flow downstream it as shock geometrical curvature, jet boundary curvature, local increase or decrease of the shock strength, flow vorticity rate (local pressure gradient) in the vicinity of the nozzle lip, static pressure gradient in the compressed layer downstream the shock, and many others. All these quantities sufficiently depend on the flow parameters (flow Mach number, jet overexpansion rate, nozzle throat angle, and ration of gas specific heats). These dependencies are sometimes unusual, especially at small Mach numbers. It was also surprising that there is no great difference among all these flowfield features in the plane jet and in the axisymmetrical jet flow out of a nozzle with large throat angle, but all these parameters behave in a quite different way in an axisymmetrical jet at small and moderate nozzle throat angles.

  13. Flow and heat transfer of nanofluids over a rotating porous disk with velocity slip and temperature jump

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Chenguang; Zheng, Liancun [Univ. of Science and Technology Beijing (China). School of Mathematics and Physics; Zhang, Chaoli [Univ. of Science and Technology Beijing (China). School of Mathematics and Physics; Univ. of Science and Technology Beijing (China). School of Mechanical Engineering; Zhang, Xinxin [Univ. of Science and Technology Beijing (China). School of Mechanical Engineering

    2015-09-01

    In this article, we discuss the flow and heat transfer of nanofluids over a rotating porous disk with velocity slip and temperature jump. Three types of nanoparticles - Cu, Al{sub 2}O{sub 3}, and CuO - are considered with water as the base fluid. The nonlinear governing equations are reduced into ordinary differential equations by Von Karman transformations and solved using homotopy analysis method (HAM), which is verified in good agreement with numerical ones. The effects of involved parameters such as porous parameter, velocity slip, temperature jump, as well as the types of nanofluids on velocity and temperature fields are presented graphically and analysed.

  14. A segmented K-space velocity mapping protocol for quantification of renal artery blood flow during breath-holding

    DEFF Research Database (Denmark)

    Thomsen, C; Cortsen, M; Söndergaard, L

    1995-01-01

    Two important prerequisites for MR velocity mapping of pulsatile motion are synchronization of the sequence execution to the time course of the flow pattern and robustness toward loss of signal in complex flow fields. Synchronization is normally accomplished by using either prospective ECG...... the segmented k-space technique, in which the entire data acquisition can be made within a breath-hold by the sampling of several phase-encoding lines within a small time window during each heart cycle. The aim of this study was to investigate the performance of a segmented k-space velocity mapping protocol...

  15. Laboratory and Genetic Biomarkers Associated with Cerebral Blood Flow Velocity in Hemoglobin SC Disease

    Directory of Open Access Journals (Sweden)

    Rayra Pereira Santiago

    2017-01-01

    Full Text Available Reference values for cerebral blood flow velocity (CBFV in hemoglobin SC disease (HbSC have not been established. We aimed to investigate associations between laboratory and genetic biomarkers associated with CBFV in HbSC children. Sixty-eight HbSC children were included; CBFV was analyzed by transcranial Doppler, and the time-averaged maximum mean velocity (TAMMV was estimated. Hematological, biochemical, immunological, and genetic analyses were performed. TAMMV was negatively correlated with red blood cell count (RBC count, hemoglobin, hematocrit, and direct bilirubin (DB, yet positively correlated with monocytes and ferritin. We found that children with TAMMV ≥ 128 cm/s had decreased red blood cell distribution width (RDW and nitric oxide metabolite (NOx concentration. Children with TAMMV ≥ 143.50 cm/s had decreased hemoglobin and hematocrit, as well as increased ferritin levels. Decreased hemoglobin, hematocrit, RDW, and NOx and increased ferritin were detected in children with TAMMV ≥ 125.75 cm/s. The CAR haplotype was associated with higher TAMMV. In association analyses, RBC, hemoglobin, hematocrit, RDW, monocyte, DB, NOx, and ferritin, as well as the CAR haplotype, were found to be associated with higher TAMMV in HbSC children. Multivariate analysis suggested that high TAMMV was independently associated with hematocrit, RDW, and NOx. Additional studies are warranted to validate the establishment of a cutoff value of 125.75 cm/s associated with elevated TAMMV in HbSC children.

  16. Detection of severe left anterior descending coronary artery stenosis by transthoracic evaluation of resting coronary flow velocity dynamics

    Directory of Open Access Journals (Sweden)

    Edward G. Abinader

    2010-09-01

    Full Text Available In the presence of severe stenosis, coronary artery flow may be reduced at rest. Recent advances in echocardiography have made non-invasive sampling of velocities in the left an­terior descending coronary artery (LAD possible. The aim of our study was to evaluate feasi­bility and capability of transthoracic Doppler to detect severe stenosis of the LAD. The study population consisted of 42 subjects with suspected coronary artery disease scheduled for coronary angiography. All had complete transthoracic echocardiography and Doppler sampling of LAD velocities. Quantitative cor­onary angiography was performed within 24 hours of the echocardiogram. Correlations between LAD velocity profile, measurements and calculations, and the angiographic results were performed. Six subjects had LAD occlusion, 10 had severe (>80% diameter LAD stenosis, and 26 had normal or non-occlusive LAD disease. In all six subjects with LAD occlusion, distal LAD velocities were not detectable, while in the other 36 subjects, LAD velocities were recorded indicating the vessels were patent. In the 10 subjects with severe LAD stenosis, the diastolic/systolic velocity ratio was <1.5, while in those with non-signifi­cant LAD disease, the diastolic/systolic velocity ratio was >1.5 (P<0.005. Diastolic LAD flow was 21.8±13 mL/min in the presence of severe stenosis as compared to 48.5±20 mL/min in subjects without severe stenosis (P<0.0013. LAD velocities had high sensitiv­ity and specificity for the prediction of severe angiographic stenosis. Thus transthoracic Doppler measurement of LAD velocities is feas­ible and can predict the presence of severe LAD stenosis or occlusion.

  17. Prediction of velocity distributions in rod bundle axial flow, with a statistical model (K-epsilon) of turbulence

    International Nuclear Information System (INIS)

    Silva Junior, H.C. da.

    1978-12-01

    Reactor fuel elements generally consist of rod bundles with the coolant flowing axially through the region between the rods. The confiability of the thermohydraulic design of such elements is related to a detailed description of the velocity field. A two-equation statistical model (K-epsilon) of turbulence is applied to compute main and secondary flow fields, wall shear stress distributions and friction factors of steady, fully developed turbulent flows, with incompressible, temperature independent fluid flowing axially through triangular or square arrays of rod bundles. The numerical procedure uses the vorticity and the stream function to describe the velocity field. Comparison with experimental and analytical data of several investigators is presented. Results are in good agreement. (Author) [pt

  18. Lagrangian velocities evolution in steady Darcian flow, the impact on solute dispersion and an application to the MADE tracer test

    Science.gov (United States)

    Hakoun, Vivien; Comolli, Alessandro; Dentz, Marco

    2017-04-01

    Performing accurate preditions of transport in heterogeneous porous media is a challenge because of the interplay between the spatial organization of the flow field and velocity fluctuations. Such interplay leads to anomalous transport behaviors that cannot be predicted by advective-dispersive models for equivalent homogeneous media. Furthermore, transport predictions based on perturbation theory remain limited to log hydraulic conductivity fields with variances smaller than 1. We contribute to elucidating how the interplay between structural properties and velocity fluctuations impacts transport processes in heterogeneous porous media. We study purely advective transport in steady Darcian flow fields with heterogeneous hydraulic conductivity fields of σ2log K up to 4 using a particle-based viewpoint. We analyze the statistical properties of particle velocity series along streamlines sampled both isochronically and equidistantly. Isochrone Lagrangian velocity series show intermittent behavior, which is removed by equidistant sampling. We show that the Lagrangian velocity statistics may be stationary or non-stationary depending on the injection mode, which highlights the importance of conditioning to the initial velocities. We analyze the correlation of the Lagrangian velocities for different heterogeneity strengths and identify and quantify a characteristic length scale over wich particle velocities persist. We show that the Lagrangian velocity statistics can be related to the Eulerian and ultimately to the conductivity statistics. These observations are quantified in a Markov-chain continuous time random walk (CTRW) approach for the evolution of Lagrangian velocities, and the prediction of solute dispersion (Dentz et al., 2016). We investigate the dependence of the Lagrangian velocity statistics and solute dispersion on the injection conditions, and on the heterogeneity strength using direct numerical simulations and the proposed CTRW model, which is

  19. A six-electrode local probe for measuring solids velocity and volume fraction profiles in solids-water flows

    Science.gov (United States)

    Lucas, G. P.; Cory, J. C.; Waterfall, R. C.

    2000-10-01

    This paper describes the design and construction of a local six-electrode conductivity probe which can be used in solids-water pipe flows to simultaneously measure the local solids volume fraction and the local solids axial velocity. Using finite element analysis, the probe electrode geometry was designed so that the regions of the solids-water mixture that were interrogated by the probe were optimal for measurement of the volume fraction and for cross correlation velocity measurement. The probe was used, in conjunction with a computer controlled traversing mechanism, to obtain distributions of the local solids volume fraction and the local solids axial velocity both in vertical upward and in upward inclined solids-water flows. Such distributions can be used to validate volume fraction and velocity profiles obtained using dual-plane electrical resistance tomography systems. Experimental results indicated that the six-electrode probe can be used to estimate the local solids volume fraction in vertical upward solids-water flows with a mean absolute error of approximately 0.01. Experimental results also indicated that the six-electrode probe can be used to measure the local axial solids velocity with a mean error of 2% of the reading.

  20. Measurement of the blood flow rate and velocity in coronary artery stenosis using intracoronary frequency domain optical coherence tomography: Validation against fractional flow reserve.

    Science.gov (United States)

    Zafar, Haroon; Sharif, Faisal; Leahy, Martin J

    2014-12-01

    The main objective of this study was to assess the blood flow rate and velocity in coronary artery stenosis using intracoronary frequency domain optical coherence tomography (FD-OCT). A correlation between fractional flow reserve (FFR) and FD-OCT derived blood flow velocity is also included in this study. A total of 20 coronary stenoses in 15 patients were assessed consecutively by quantitative coronary angiography (QCA), FFR and FD-OCT. A percutaneous coronary intervention (PCI) optimization system was used in this study which combines wireless FFR measurement and FD-OCT imaging in one platform. Stenoses were labelled severe if FFR ≤ 0.8. Blood flow rate and velocity in each stenosis segment were derived from the volumetric analysis of the FD-OCT pull back images. The FFR value was ≤ 0.80 in 5 stenoses (25%). The mean blood flow rate in severe coronary stenosis ( n  = 5) was 2.54 ± 0.55 ml/s as compared to 4.81 ± 1.95 ml/s in stenosis with FFR > 0.8 ( n  = 15). A good and significant correlation between FFR and FD-OCT blood flow velocity in coronary artery stenosis ( r  = 0.74, p  < 0.001) was found. The assessment of stenosis severity using FD-OCT derived blood flow rate and velocity has the ability to overcome many limitations of QCA and intravascular ultrasound (IVUS).

  1. A novel cross-correlation technique for the determination of radial velocity profiles in two-phase flows

    International Nuclear Information System (INIS)

    Analytis, G.Th.; Luebbesmeyer, D.

    1983-02-01

    A novel cross-correlation technique has been developed, which enables the determination of radial velocity profiles in two-phase flows with minimum disturbance of the flow. The method is based on cross-correlating the signals from a light beam source and a detector outside the flow, with the signals from a local light reflection probe which is located in the flow and can be moved to different radial positions in the tube. Subsequently, the local probe is 'switched' into a light detector, the light source diametrically opposite the probe is switched on, the two light beam signals modulated by the two-phase flow across the whole diameter of the tube are cross-correlated. Usually, during the latter measurements, there are two peaks in the cross-correlation function due to the existence of a radial velocity profile in the flow. The results of the latter measurements were reproduced by employing a computer simulation program, into which the radial velocity profile determined by this technique was input, and in the course of this simulation, the importance played by the radial void distribution in interpreting this kind of measurement was shown. The results presented in this investigation are to be considered of a preliminary nature; a much more detailed study of the advantages and limitations of the proposed technique is needed. (Auth.)

  2. Calculation and measurement of a neutral air flow velocity impacting a high voltage capacitor with asymmetrical electrodes

    Directory of Open Access Journals (Sweden)

    M. Malík

    2014-01-01

    Full Text Available This paper deals with the effects surrounding phenomenon of a mechanical force generated on a high voltage asymmetrical capacitor (the so called Biefeld-Brown effect. A method to measure this force is described and a formula to calculate its value is also given. Based on this the authors derive a formula characterising the neutral air flow velocity impacting an asymmetrical capacitor connected to high voltage. This air flow under normal circumstances lessens the generated force. In the following part this velocity is measured using Particle Image Velocimetry measuring technique and the results of the theoretically calculated velocity and the experimentally measured value are compared. The authors found a good agreement between the results of both approaches.

  3. Calculation and measurement of a neutral air flow velocity impacting a high voltage capacitor with asymmetrical electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Malík, M., E-mail: michal.malik@tul.cz; Primas, J.; Kopecký, V.; Svoboda, M. [Faculty of Mechatronics, Informatics and Interdisciplinary Studies, Technical University of Liberec, Liberec, 461 17 (Czech Republic)

    2014-01-15

    This paper deals with the effects surrounding phenomenon of a mechanical force generated on a high voltage asymmetrical capacitor (the so called Biefeld-Brown effect). A method to measure this force is described and a formula to calculate its value is also given. Based on this the authors derive a formula characterising the neutral air flow velocity impacting an asymmetrical capacitor connected to high voltage. This air flow under normal circumstances lessens the generated force. In the following part this velocity is measured using Particle Image Velocimetry measuring technique and the results of the theoretically calculated velocity and the experimentally measured value are compared. The authors found a good agreement between the results of both approaches.

  4. Mean blood velocities and flow impedance in the fetal descending thoracic aortic and common carotid artery in normal pregnancy.

    Science.gov (United States)

    Bilardo, C M; Campbell, S; Nicolaides, K H

    1988-12-01

    A linear array pulsed Doppler duplex scanner was used to establish reference ranges for mean blood velocities and flow impedance (Pulsatility Index = PI) in the descending thoracic aorta and in the common carotid artery from 70 fetuses in normal pregnancies at 17-42 weeks' gestation. The aortic velocity increased with gestation up to 32 weeks, then remained constant until term, when it decreased. In contrast, the velocity in the common carotid artery increased throughout pregnancy. The PI in the aorta remained constant throughout pregnancy, while in the common carotid artery it fell steeply after 32 weeks. These results suggest that with advancing gestation there is a redistribution of the fetal circulation with decreased impedance to flow to the fetal brain, presumably to compensate for the progressive decrease in fetal blood PO2.

  5. Statistics of the relative velocity of particles in turbulent flows: Monodisperse particles.

    Science.gov (United States)

    Bhatnagar, Akshay; Gustavsson, K; Mitra, Dhrubaditya

    2018-02-01

    We use direct numerical simulations to calculate the joint probability density function of the relative distance R and relative radial velocity component V_{R} for a pair of heavy inertial particles suspended in homogeneous and isotropic turbulent flows. At small scales the distribution is scale invariant, with a scaling exponent that is related to the particle-particle correlation dimension in phase space, D_{2}. It was argued [K. Gustavsson and B. Mehlig, Phys. Rev. E 84, 045304 (2011)PLEEE81539-375510.1103/PhysRevE.84.045304; J. Turbul. 15, 34 (2014)1468-524810.1080/14685248.2013.875188] that the scale invariant part of the distribution has two asymptotic regimes: (1) |V_{R}|≪R, where the distribution depends solely on R, and (2) |V_{R}|≫R, where the distribution is a function of |V_{R}| alone. The probability distributions in these two regimes are matched along a straight line: |V_{R}|=z^{*}R. Our simulations confirm that this is indeed correct. We further obtain D_{2} and z^{*} as a function of the Stokes number, St. The former depends nonmonotonically on St with a minimum at about St≈0.7 and the latter has only a weak dependence on St.

  6. Clustering and relative velocity of heavy particles under gravitational settling in isotropic turbulent flows

    Science.gov (United States)

    Jin, Guodong; He, Guo-Wei

    2015-11-01

    Clustering and intermittency in radial relative velocity (RRV) of heavy particles of same size settling in turbulent flows can be remarkably changed due to gravity. Clustering is monotonically reduced at Stokes number less than 1 under gravity due to the disability of the centrifugal mechanism, however it is non-monotonically enhanced at Stokes number greater than 1 due to the multiplicative amplification in the case that the proposed effective Kubo number is less than 1. Although gravity causes monotonical reduction in the rms of RRV of particles at a given Stokes number with decreasing Froude number, the variation tendency in the tails of standardized PDF of RRV versus Froude number is obviously different: the tails become narrower at a small Stokes number, while they become broader at a large Stokes number. The mechanism of this variation stems from the compromise between the following two competing factors. The mitigation of correlation of particle positions and the regions of high strain rate which are more intermittent reduces the intermittency in RRV at small Stokes numbers, while the significant reduction in the backward-in-time relative separations will make particle pairs see small-scale structures, leading to a higher intermittency in RRV at large Stokes numbers. NSAF of China (grant number U1230126); NSFC (grant numbers 11072247 and 11232011).

  7. Statistics of the relative velocity of particles in turbulent flows: Monodisperse particles

    Science.gov (United States)

    Bhatnagar, Akshay; Gustavsson, K.; Mitra, Dhrubaditya

    2018-02-01

    We use direct numerical simulations to calculate the joint probability density function of the relative distance R and relative radial velocity component VR for a pair of heavy inertial particles suspended in homogeneous and isotropic turbulent flows. At small scales the distribution is scale invariant, with a scaling exponent that is related to the particle-particle correlation dimension in phase space, D2. It was argued [K. Gustavsson and B. Mehlig, Phys. Rev. E 84, 045304 (2011), 10.1103/PhysRevE.84.045304; J. Turbul. 15, 34 (2014), 10.1080/14685248.2013.875188] that the scale invariant part of the distribution has two asymptotic regimes: (1) | VR|≪R , where the distribution depends solely on R , and (2) | VR|≫R , where the distribution is a function of | VR| alone. The probability distributions in these two regimes are matched along a straight line: | VR|= z*R . Our simulations confirm that this is indeed correct. We further obtain D2 and z* as a function of the Stokes number, St. The former depends nonmonotonically on St with a minimum at about St≈0.7 and the latter has only a weak dependence on St.

  8. Dynamical equations for the vector potential and the velocity potential in incompressible irrotational Euler flows: a refined Bernoulli theorem.

    Science.gov (United States)

    Ohkitani, Koji

    2015-09-01

    We consider incompressible Euler flows in terms of the stream function in two dimensions and the vector potential in three dimensions. We pay special attention to the case with singular distributions of the vorticity, e.g., point vortices in two dimensions. An explicit equation governing the velocity potentials is derived in two steps. (i) Starting from the equation for the stream function [Ohkitani, Nonlinearity 21, T255 (2009)NONLE50951-771510.1088/0951-7715/21/12/T02], which is valid for smooth flows as well, we derive an equation for the complex velocity potential. (ii) Taking a real part of this equation, we find a dynamical equation for the velocity potential, which may be regarded as a refinement of Bernoulli theorem. In three-dimensional incompressible flows, we first derive dynamical equations for the vector potentials which are valid for smooth fields and then recast them in hypercomplex form. The equation for the velocity potential is identified as its real part and is valid, for example, flows with vortex layers. As an application, the Kelvin-Helmholtz problem has been worked out on the basis the current formalism. A connection to the Navier-Stokes regularity problem is addressed as a physical application of the equations for the vector potentials for smooth fields.

  9. A remark on "Nonlinear output feedback control of underwater vehicle propellers using feedback form estimated axial flow velocity"

    DEFF Research Database (Denmark)

    Jouffroy, Jerome; Lottin, Jacques

    2002-01-01

    For original paper see T.I.Fossen and M.Blanke, ibid., vol.25, pp.241-55 (2000). In the work presented by Fossen and Blanke, a nonlinear observer for estimation of propeller axial flow velocity for UUVs was introduced. The proof of the convergence behavior of the observer was carried out with a L...

  10. Solution-gated graphene field effect transistors integrated in microfluidic systems and used for flow velocity detection.

    Science.gov (United States)

    He, Rong Xiang; Lin, Peng; Liu, Zhi Ke; Zhu, Hong Wei; Zhao, Xing Zhong; Chan, Helen L W; Yan, Feng

    2012-03-14

    Solution-gated graphene field effect transistors (SGGT) were integrated in microfluidic systems. The transfer characteristics of a SGGT with an Ag/AgCl gate electrode shifted horizontally with the change of the ionic concentration of KCl solution in the microchannel and the relationship can be fitted with the Nernst equation, which was attributed to the change of the potential drop at the Ag/AgCl electrode. Therefore the gate electrode is one important factor for the ion sensitive property of the SGGT. Then SGGTs were used as flow velocity sensors, which were based on measuring the streaming potentials in microfluidic channels. A linear relationship between the shift of the transfer curve of the SGGT and the flow velocity was obtained, indicating that the SGGT is a promising transducer for measuring flow velocity in a microchip. Since the streaming potential is influenced by the three physical quantities, including the flow velocity, the ionic strength of the fluid and the zeta potential of the substrate, the device can be used for sensing any one of the three quantities when the other two were known. It is noteworthy that SGGTs have been used for various types of chemical and biological sensors. Array of the devices integrated in multichannel microchips are expected to find many important applications in the lab-on-a-chip systems in the future. © 2012 American Chemical Society

  11. Preload dependence of color M-mode Doppler flow propagation velocity in controls and in patients with left ventricular dysfunction

    DEFF Research Database (Denmark)

    Møller, J E; Poulsen, S H; Søndergaard, E

    2000-01-01

    The purpose of this study was to assess the effects of preload alterations on color M-mode flow propagation velocity (Vp) in volunteers with normal left ventricular (LV) function and in patients with depressed LV function. Color M-mode Doppler echocardiography was performed during Valsalva maneuv...

  12. Changes in inferior vena cava blood flow velocity and diameter during breathing movements in the human fetus

    NARCIS (Netherlands)

    T. Huisman (T.); S. van den Eijnde (Stefan); P.A. Stewart (Patricia); J.W. Wladimiroff (Juriy)

    1993-01-01

    textabstractBreathing movements in the human fetus cause distinct changes in Doppler flow velocity measurements at arterial, venous and cardiac levels. In adults, breathing movements result in a momentary inspiratory collapse of the inferior vena cava vessel wall. The study objective was to quantify

  13. Influence of flow velocity on biofilm growth in a tubular heat exchanger-condenser cooled by seawater.

    Science.gov (United States)

    Trueba, Alfredo; García, Sergio; Otero, Félix M; Vega, Luis M; Madariaga, Ernesto

    2015-01-01

    The influence of flow velocity (FV) on the heat transfer process in tubes made from AISI 316L stainless steel in a heat exchanger-condenser cooled by seawater was evaluated based on the characteristics of the resulting biofilm that adhered to the internal surface of the tubes at velocities of 1, 1.2, 1.6, and 3 m s(-1). The results demonstrated that at a higher FV, despite being more compact and consistent, the biofilm was thinner with a lower concentration of solids, and smoother, which favoured the heat transfer process within the equipment. However, higher velocities increase the initial cost of the refrigerating water-pumping equipment and its energy consumption cost to compensate for the greater pressure drops produced in the tube. The velocity of 1.6 m s(-1) represented the equilibrium between the advantages and disadvantages of the variables analysed for the test conditions in this study.

  14. Differential increases in blood flow velocity in the middle cerebral artery after tourniquet deflation during sevoflurane, isoflurane or propofol anaesthesia.

    Science.gov (United States)

    Kadoi, Y; Kawauchi, C H; Ide, M; Saito, S; Mizutani, A

    2009-07-01

    The purpose of this study was to examine the comparative effects of sevoflurane, isoflurane or propofol on cerebral blood flow velocity after tourniquet deflation during orthopaedic surgery. Thirty patients undergoing elective orthopaedic surgery were randomly divided into sevoflurane, isoflurane and propofol groups. Anaesthesia was maintained with sevoflurane, isoflurane or propofol infusion in 33% oxygen and 67% nitrous oxide, in whatever concentrations were necessary to keep bispectral index values between 45 and 50. Ventilatory rate or tidal volume was adjusted to target PaCO2 of 35 mmHg. A 2.0 MHz transcranial Doppler probe was attached to the patient's head at the temporal window and mean blood flow velocity in the middle cerebral artery was continuously measured. The extremity was exsanguinated with an Esmarch bandage and the pneumatic tourniquet was inflated to a pressure of 450 mmHg. Arterial blood pressure, heart rate, velocity in the middle cerebral artery and arterial blood gas analysis were measured every minute for 10 minutes after release of the tourniquet in all three groups. Velocity in the middle cerebral artery in the three groups increased for five minutes after tourniquet deflation. Because of the different cerebrovascular effects of the three agents, the degree of increase in flow velocity in the isoflurane group was greater than in the other two groups, the change in flow velocity in the propofol group being the lowest (at three minutes after deflation 40 +/- 7%, 32 +/- 6% and 28 +/- 10% in the isoflurane, sevoflurane and propofol groups respectively, P < 0.05).

  15. The Effect of Non-Steady Overlying Water Velocity on Oxygen Consumption Under Losing and Gaining Flow Conditions

    Science.gov (United States)

    Galloway, J. A.; Wu, L.; Lewandowski, J.; Arnon, S.

    2017-12-01

    Wastewater treatment plants which discharge treated effluent into river systems can drastically alter downstream flow regime from steady flow velocities to water velocities which fluctuate on a diurnal cycle. The impacts of flow variations are expected to have complex and non-linear impacts on the temporal and spatial redox dynamics within the hyporheic zone. The objective of the current study was to qualitatively describe the effect of non-steady flow on oxygen consumption under losing and gaining conditions. A novel system which allowed for precise control and modulation of pore water velocities was deployed in a specially designed, 260 cm-long by 29 cm-wide flume. Experiments were carried out under various vertical fluxes. Oxygen dynamics were investigated by using planar optodes to measure oxygen concentrations in the hyporheic zone at a high temporal and spatial resolution. These empirical measurements were then used as inputs for a reactive transport model allowing for the calculation of oxygen consumption rates. A complex interplay between direction and magnitude of surface water velocity changes as well as antecedent flow conditions was discovered and quantitatively described. The development and calibration of the model allowed us to explore the relationships discovered in a variety of scenarios. Overall, unsteady flow conditions lead to up to a 2-fold increase in the delivery of dissolved oxygen to the hyporheic zone and lead to a higher rate of oxygen consumption than would have been predicted by a comparable steady surface flow. Vertical fluxes reduce the magnitude of the effect of surface water perturbations. The results of the current study provide an insight into how anthropogenic changes to discharge regimes in river systems can impact the biogeochemistry of the hyporheic zone.

  16. The Fundamental Natural Frequency and Critical Flow Velocity Evaluation of a Simply Supported Stepped Pipe Conveying Fluid

    Directory of Open Access Journals (Sweden)

    Mustafa Baqir Hunain

    2017-08-01

    Full Text Available This work investigated the fundamental natural frame frequency and critical inlet flow velocity of the simply supported stepped pipe conveying fluid. The influence of some outline parameters, similar pipe diameter ratio with different cross-sectional areas (sudden enlargement or sudden contraction, length ratio, and thickness were studied. A theoretical model for the dynamic behavior of the pipe was investigated. The dynamic behavior of the stepped pipe carrying fluid was described by means of finite element technique. A computer program has been promoted utilizing Matlab language in order to predict the vibration characteristics and to embrace the theoretical work. It was found that the fundamental natural frequency of the stepped pipe decreased in different percentages with increasing inlet fluid flow velocity. The outer diameter ratio, length ratio, and thickness of the stepped pipe conveying fluid had a great effect on the dynamic behavior of stepped pipe. The fundamental natural frame frequency increased as the length ratios (L2/L1 and the outer diameter ratios (Od2/Od1 decreased. When the length ratio of the pipe being less than 1, the effect of the diameter ratio on the critical inlet flow velocity was obvious. As the outer diameter ratios (Od2/Od1 increased, the inlet critical flow velocity increased, until being reached to the maximum value, then it dropped smoothly. The fundamental frame frequency of the stepped pipe increased as the thickness of the stepped pipe increased until being reached to the maximum value ,then it dropped smoothly. For each inlet fluid flow velocity, length ratios, and diameter ratios there was an optimum pipe thickness that gave the best dynamic characteristics.

  17. A prototype of radar-drone system for measuring the surface flow velocity at river sites and discharge estimation

    Science.gov (United States)

    Moramarco, Tommaso; Alimenti, Federico; Zucco, Graziano; Barbetta, Silvia; Tarpanelli, Angelica; Brocca, Luca; Mezzanotte, Paolo; Rosselli, Luca; Orecchini, Giulia; Virili, Marco; Valigi, Paolo; Ciarfuglia, Thomas; Pagnottelli, Stefano

    2015-04-01

    Discharge estimation at a river site depends on local hydraulic conditions identified by recording water levels. In fact, stage monitoring is straightforward and relatively inexpensive compared with the cost necessary to carry out flow velocity measurements which are, however, limited to low flows and constrained by the accessibility of the site. In this context the mean flow velocity is hard to estimate for high flow, affecting de-facto the reliability of discharge assessment for extreme events. On the other hand, the surface flow velocity can be easily monitored by using radar sensors allowing to achieve a good estimate of discharge by exploiting the entropy theory applied to rivers hydraulic (Chiu,1987). Recently, a growing interest towards the use of Unmanned Aerial Vehicle (UVA), henceforth drone, for topographic applications is observed and considering their capability drones may be of a considerable interest for the hydrological monitoring and in particular for streamflow measurements. With this aim, for the first time, a miniaturized Doppler radar sensor, operating at 24 GHz, will be mounted on a drone to measure the surface flow velocity in rivers. The sensor is constituted by a single-board circuit (i.e. is a fully planar circuits - no waveguides) with the antenna on one side and the front-end electronic on the other side (Alimenti et al., 2007). The antenna has a half-power beam width of less than 10 degrees in the elevation plane and a gain of 13 dBi. The radar is equipped with a monolithic oscillator and transmits a power of about 4 mW at 24 GHz. The sensor is mounted with an inclination of 45 degrees with respect to the drone flying plane and such an angle is considered in recovering the surface speed of the water. The drone is a quadricopter that has more than 30 min, flying time before recharging the battery. Furthermore its flying plan can be scheduled with a suitable software and is executed thanks to the on-board sensors (GPS, accelerometers

  18. Heat and Mass Transfer on Squeezing Unsteady MHD Nano fluid Flow between Parallel Plates with Slip Velocity Effect

    International Nuclear Information System (INIS)

    Singh, K.; Rawat, S. K.; Kumar, M.

    2016-01-01

    Heat and mass transfer behavior of unsteady flow of squeezing between two parallel plates in the sight of uniform magnetic field with slip velocity effect is investigated. The governing equations representing fluid flow have been transformed into nonlinear ordinary differential equations using similarity transformation. The equations thus obtained have been solved numerically using Runge-Kutta-Fehlberg method with shooting technique. Effects on the behavior of velocity, temperature, and concentration for various values of relevant parameters are illustrated graphically. The skin-friction coefficient and heat and mass transfer rate are also tabulated for various governing parameters. The results indicate that, for nano fluid flow, the rates of heat and mass transfer are inversely proportional to nanoparticle volume fraction and magnetic parameter. The rate of mass transfer increases with increasing values of Schmidt number and squeeze number.

  19. Effect of liquid film velocity and thickness on thinning rate of flow accelerated corrosion under water-steam two-phase flow

    International Nuclear Information System (INIS)

    Satake, Masaaki; Yoneda, Kimitoshi; Morita, Ryo; Fujiwara, Kazutoshi; Inada, Fumio

    2014-01-01

    Pipe wall thinning phenomena are serious problems for the operation and management of nuclear power plants. Flow accelerated corrosion (FAC) is one of the pipe wall thinning phenomena. Its mechanism under water single-phase flow is generally revealed and the prediction equation of thinning rate is constructed with practical accuracy. Under water-steam two-phase flow, it is considered that FAC is occurred in annular flow and its mechanism is almost the same as that under water single-phase flow. However, the detail of its mechanism is not revealed. In this study, FAC experiments under water-steam two-phase flow are performed by changing the liquid film velocity and thickness. The flow pattern is vertical upward annular flow. From these experiments, the thinning rate increases when the liquid film velocity becomes higher. However, the liquid film thickness does not influence the thinning rate so much. The oxide layer of test piece surface is mainly magnetite. The thickness of oxide layer where FAC occurs is less than 1 μm. On the other hand, the thickness of oxide layer where FAC does not occur is about 1.5 μm and there are porous scales on the oxide layer. It is assumed that one of the reasons why FAC does not occur is that concentration of iron in liquid film is saturated. (author)

  20. Role of contrast and fractality of laser speckle image in assessing flow velocity and scatterer concentration in phantom body fluids.

    Science.gov (United States)

    Lal, Cerine; Banerjee, Arnab; Sujatha, Narayanan Unni

    2013-11-01

    Blood flow velocity and red blood cell concentration are of vital importance in assessing tissue microcirculation. Laser speckle contrast analysis is being considered as a promising tool in the qualitative assessment of flow velocity as well as scatterer concentration in different body fluids, though the quantification part still remains challenging. The fractal-based spatial correlation analysis of speckle flow images along with the corresponding contrast analysis for the quantitative assessment of flow and scatterer concentration is investigated. In this study, phantom body fluid solution (intralipid 20%) of different concentrations is pumped at different flow rates through the designed flow channel using a syringe pump and the corresponding speckle images are acquired. The fractality of the acquired speckle images in response to the changes in concentration of the fluid as well as the variations in fluid flow is analyzed along with the corresponding contrast-based analysis. Following this qualitative analysis, an experimental model is attempted toward quantification of these parameters from a single acquired speckle image by considering the contrast and fractality changes together.

  1. Measurement of acoustic velocity components in a turbulent flow using LDV and high-repetition rate PIV

    Science.gov (United States)

    Léon, Olivier; Piot, Estelle; Sebbane, Delphine; Simon, Frank

    2017-06-01

    The present study provides theoretical details and experimental validation results to the approach proposed by Minotti et al. (Aerosp Sci Technol 12(5):398-407, 2008) for measuring amplitudes and phases of acoustic velocity components (AVC) that are waveform parameters of each component of velocity induced by an acoustic wave, in fully turbulent duct flows carrying multi-tone acoustic waves. Theoretical results support that the turbulence rejection method proposed, based on the estimation of cross power spectra between velocity measurements and a reference signal such as a wall pressure measurement, provides asymptotically efficient estimators with respect to the number of samples. Furthermore, it is shown that the estimator uncertainties can be simply estimated, accounting for the characteristics of the measured flow turbulence spectra. Two laser-based measurement campaigns were conducted in order to validate the acoustic velocity estimation approach and the uncertainty estimates derived. While in previous studies estimates were obtained using laser Doppler velocimetry (LDV), it is demonstrated that high-repetition rate particle image velocimetry (PIV) can also be successfully employed. The two measurement techniques provide very similar acoustic velocity amplitude and phase estimates for the cases investigated, that are of practical interest for acoustic liner studies. In a broader sense, this approach may be beneficial for non-intrusive sound emission studies in wind tunnel testings.

  2. Electromagnetic energy density and stress tensor in a warm plasma with finite flow velocity

    International Nuclear Information System (INIS)

    Choi, Cheong R.; Lee, Nam C.

    2004-01-01

    The expressions of the average of energy density and the average stress tensor of the electromagnetic field in a warm collisionless plasma moving with a finite velocity are obtained by using a microscopic method that uses the fluid description of plasma. The result contains terms involved with derivatives of the dielectric tensor with respect to the velocity, which explicitly represent the effects of the finite velocity of the medium. In the zero-velocity limit, the results reduce to the well-known expressions for a plasma at rest with temporal and spatial dispersion

  3. A one-dimensional model to describe flow localization in viscoplastic slender bars subjected to super critical impact velocities

    Science.gov (United States)

    Vaz-Romero, A.; Rodríguez-Martínez, J. A.

    2018-01-01

    In this paper we investigate flow localization in viscoplastic slender bars subjected to dynamic tension. We explore loading rates above the critical impact velocity: the wave initiated in the impacted end by the applied velocity is the trigger for the localization of plastic deformation. The problem has been addressed using two kinds of numerical simulations: (1) one-dimensional finite difference calculations and (2) axisymmetric finite element computations. The latter calculations have been used to validate the capacity of the finite difference model to describe plastic flow localization at high impact velocities. The finite difference model, which highlights due to its simplicity, allows to obtain insights into the role played by the strain rate and temperature sensitivities of the material in the process of dynamic flow localization. Specifically, we have shown that viscosity can stabilize the material behavior to the point of preventing the appearance of the critical impact velocity. This is a key outcome of our investigation, which, to the best of the authors' knowledge, has not been previously reported in the literature.

  4. Development of dual micro-PIV system for simultaneous velocity measurements: optical arrangement techniques and application to blood flow measurements

    International Nuclear Information System (INIS)

    Kvon, Alexandr; Lee, Yeon Ho; Cheema, Taqi Ahmad; Park, Cheol Woo

    2014-01-01

    Blood rheological characteristics can significantly vary with the motion of red blood cells (RBCs) in plasma. Moreover, RBCs show a complicated behavior in micro vessels. Thus, the determination of either plasma or blood cell velocity distribution has been the primary objective in blood flow analysis. However, the conditions during blood flow analyses are different from the actual physiological conditions, wherein the motion of the two distinct blood phases simultaneously occurs. In this study, we used an in vitro micro-particle image velocimetry, which is a reliable velocity field measurement technique, to evaluate the velocity distribution of plasma and blood cells simultaneously. Blood flow through a rectangular microchannel was determined using special optical filter arrangements and by assuming two different hematocrit values. Using the proposed technique, the averaged parabolic velocity profiles for the RBCs and plasma were successfully obtained and compared. The developed simultaneous measurement technique can be used to predict blood cell and plasma behaviors simultaneously with high accuracy under given clinical conditions. (paper)

  5. Evaluation of flow volume and flow patterns in the patent false lumen of chronic aortic dissections using velocity-encoded cine magnetic resonance imaging

    Energy Technology Data Exchange (ETDEWEB)

    Inoue, Toshihisa; Watanabe, Shigeru; Sakurada, Hideki; Ono, Katsuhiro; Urano, Miharu; Hijikata, Yasuyoshi; Saito, Isao; Masuda, Yoshiaki [Chiba Univ. (Japan). School of Medicine

    2000-10-01

    In 21 patients with chronic aortic dissections and proven patent false lumens, the flow volume and flow patterns in the patent false lumens was evaluated using velocity-encoded cine magnetic resonance imaging (VENC-MRI) and the relationship between the flow characteristics and aortic enlargement was retrospectively examined. Flow patterns in the false lumen were divided into 3 groups: pattern A with primarily antegrade flow (n=6), pattern R with primarily retrograde flow (n=3), and pattern B with bidirectional flow (n=12). In group A, the rate of flow volume in the false lumen compared to the total flow volume in true and false lumens (%TFV) and the average rate of enlargement of the maximum diameter of the dissected aorta per year ({delta}D) were significantly greater than in groups R and B (%TFV: 74.1{+-}0.07 vs 15.2{+-}0.03 vs 11.8{+-}0.04, p<0.01; {delta}D: 3.62{+-}0.82 vs 0 vs 0.58{+-}0.15 mm/year, p<0.05, respectively). There was a significant correlation between %TFV and {delta}D (r=0.79, p<0.0001). Evaluation of flow volume and flow patterns in the patent false lumen using VENC-MRI may be useful for predicting enlargement of the dissected aorta. (author)

  6. Evaluation of flow volume and flow patterns in the patent false lumen of chronic aortic dissections using velocity-encoded cine magnetic resonance imaging

    International Nuclear Information System (INIS)

    Inoue, Toshihisa; Watanabe, Shigeru; Sakurada, Hideki; Ono, Katsuhiro; Urano, Miharu; Hijikata, Yasuyoshi; Saito, Isao; Masuda, Yoshiaki

    2000-01-01

    In 21 patients with chronic aortic dissections and proven patent false lumens, the flow volume and flow patterns in the patent false lumens was evaluated using velocity-encoded cine magnetic resonance imaging (VENC-MRI) and the relationship between the flow characteristics and aortic enlargement was retrospectively examined. Flow patterns in the false lumen were divided into 3 groups: pattern A with primarily antegrade flow (n=6), pattern R with primarily retrograde flow (n=3), and pattern B with bidirectional flow (n=12). In group A, the rate of flow volume in the false lumen compared to the total flow volume in true and false lumens (%TFV) and the average rate of enlargement of the maximum diameter of the dissected aorta per year (ΔD) were significantly greater than in groups R and B (%TFV: 74.1±0.07 vs 15.2±0.03 vs 11.8±0.04, p<0.01; ΔD: 3.62±0.82 vs 0 vs 0.58±0.15 mm/year, p<0.05, respectively). There was a significant correlation between %TFV and ΔD (r=0.79, p<0.0001). Evaluation of flow volume and flow patterns in the patent false lumen using VENC-MRI may be useful for predicting enlargement of the dissected aorta. (author)

  7. Flow velocity and volume measurement of superior and inferior mesenteric artery with cine phase contrast magnetic resonance imaging

    International Nuclear Information System (INIS)

    Naganawa, Shinji; Cooper, T.G.; Jenner, G.; Potchen, E.J.; Ishigaki, Takeo.

    1994-01-01

    The flow velocity and volume of the superior and inferior mesenteric arteries (SMA, IMA) were measured with cine phase contrast magnetic resonance (MR) imaging in five healthy volunteers. Each volunteer was first measured in a fasting state, and then one, two, and three hours after a meal. The average SMA flow volume of the volunteers was 230.3±46.8 ml/min (mean±standard error) during the fasting state, and 714.7±207.7 ml/min, 339.2±85.7 ml/min, and 263.8±21.0 ml/min, respectively, at one, two, and three hours postmeal. The increase at one hour postmeal was statistically significant (p<0.05). The corresponding flow measurements in the IMA were 63.1±11.2 ml/min, 67.6±11.2 ml/min, 57.9±8.6 ml/min, and 53.2±6.8 ml/min. These values do not represent a statistically significant flow volume change in the IMA. In all volunteers, the SMA volumetric flow increased the most one hour after the food challenge (72-400% relative to baseline). Diastolic velocity in the SMA increased significantly one hour postmeal, but systolic velocity did not change significantly. The IMA did not demonstrate a significant change in either systolic or diastolic velocity. The difference between the SMA and IMA in the way of reacting against the food challenge is thought to represent the difference between the requirements of small and large intestine for blood supply after the food challenge. These data demonstrate the possibility of this modality for the assessment of conditions such as chronic mesenteric ischemia. (author)

  8. Comparison of 4D flow and 2D velocity-encoded phase contrast MRI sequences for the evaluation of aortic hemodynamics

    NARCIS (Netherlands)

    Bollache, Emilie; van Ooij, Pim; Powell, Alex; Carr, James; Markl, Michael; Barker, Alex J.

    2016-01-01

    The purpose of this study was to compare aortic flow and velocity quantification using 4D flow MRI and 2D CINE phase-contrast (PC)-MRI with either one-directional (2D-1dir) or three-directional (2D-3dir) velocity encoding. 15 healthy volunteers (51 +/- 19 years) underwent MRI including (1)

  9. Computational study of jet interaction flow field with and without incidence

    International Nuclear Information System (INIS)

    Asif, M.; Zahir, S.; Khan, M.A.

    2004-01-01

    The objective was to study the interaction of a side jet with the incoming supersonic flow and hypersonic flow. Qualitatively same Cp trends have been obtained as found experimentally. Also in aerodynamic coefficients side jet interaction results in additional pitching moment which is because of the high pressure region in upstream of the jet and a low pressure region in the downstream of the jet. Also jet interaction results in the rise in the lift coefficient. Whereas in the incidence case, simulation has been performed for the hypersonic flows over a biconic body with supersonic lateral jet at Mach 9.7 and incidence of 0 o to incidence of -12 o and 12 o . The results obtained were compared with the experimental and CFD code CFL3D results. PAK-3D over predicts the surface pressure as compared to the CFL3D and experimental results, whereas the qualitative trends are the same. Finally the integrated aerodynamic force coefficients were compared with CFL3D predicted results. (author)

  10. How does organic matter affect the head velocity and run-out distance of cohesive sediment gravity flows?

    Science.gov (United States)

    Craig, Melissa; Baas, Jaco; Amos, Kathryn; Strachan, Lorna; Baker, Megan

    2016-04-01

    physically cohesive kaolin clay (one of the most common clay minerals on Earth). Provisional results indicate that very small quantities of EPS - several orders of magnitude smaller than the quantity of clay - are sufficient to enhance flocculation and reduce flow velocity compared to a flow that lacks EPS. This finding has the potential to change our understanding of sediment gravity flows in the natural environment, where biological matter is ubiquitous.

  11. RETRACTED: The influence of sand diameter and wind velocity on sand particle lift-off and incident angles in the windblown sand flux

    Science.gov (United States)

    Bo, Tian-Li; Zheng, Xiao-Jing; Duan, Shao-Zhen; Liang, Yi-Rui

    2013-05-01

    This article has been retracted: please see Elsevier Policy on Article Withdrawal. This article has been retracted at the request of the Editors-in-Chief. This article also contains significant similarity with parts of text, written by the same author(s), that have appeared in Tian-Li Bo, Xiao-Jing Zheng, Shao-Zhen Duan, Yi-Rui Liang, The influence of wind velocity and sand grain diameter on the falling velocities of sand particles, Powder Technology, Volume 241, June 2013, Pages 158-165. Tian-Li Bo, Xiao-Jing Zheng, Shao-Zhen Duan, Yi-Rui Liang, Analysis of sand particles' lift-off and incident velocities in wind-blown sand flux, Acta Mechanica Sinica, April 2013, Volume 29, Issue 2, pp 158-165. Tian-Li Bo, Xiao-Jing Zheng, Shao-Zhen Duan, Yi-Rui Liang, Influence of sand grain diameter and wind velocity on lift-off velocities of sand particles, The European Physical Journal E, May 2013, 36:50. Tian-Li Bo, Shao-Zhen Duan, Xiao-Jing Zheng, Yi-Rui Liang, The influence of sand bed temperature on lift-off and falling parameters in windblown sand flux, Geomorphology, Volume 204, 1 January 2014, Pages 477-484. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

  12. Preload dependence of color M-mode Doppler flow propagation velocity in controls and in patients with left ventricular dysfunction

    DEFF Research Database (Denmark)

    Møller, J E; Poulsen, S H; Søndergaard, E

    2000-01-01

    The purpose of this study was to assess the effects of preload alterations on color M-mode flow propagation velocity (Vp) in volunteers with normal left ventricular (LV) function and in patients with depressed LV function. Color M-mode Doppler echocardiography was performed during Valsalva maneuver......, passive leg lifting, and after administration of nitroglycerin in 30 healthy volunteers and in 30 age- and sex-matched patients with previous myocardial infarction (MI). Mean Vp in controls was 74 +/- 15 cm/s at baseline and 46 +/- 15 cm/s in MI patients (P .... In conclusion, we found that in controls and patients with previous MI, the color M-mode flow propagation velocity is not affected significantly by preload....

  13. Turbulence, dynamic similarity and scale effects in high-velocity free-surface flows above a stepped chute

    Science.gov (United States)

    Felder, Stefan; Chanson, Hubert

    2009-07-01

    In high-velocity free-surface flows, air entrainment is common through the interface, and intense interactions take place between turbulent structures and entrained bubbles. Two-phase flow properties were measured herein in high-velocity open channel flows above a stepped chute. Detailed turbulence measurements were conducted in a large-size facility, and a comparative analysis was applied to test the validity of the Froude and Reynolds similarities. The results showed consistently that the Froude similitude was not satisfied using a 2:1 geometric scaling ratio. Lesser number of entrained bubbles and comparatively greater bubble sizes were observed at the smaller Reynolds numbers, as well as lower turbulence levels and larger turbulent length and time scales. The results implied that small-size models did underestimate the rate of energy dissipation and the aeration efficiency of prototype stepped spillways for similar flow conditions. Similarly a Reynolds similitude was tested. The results showed also some significant scale effects. However a number of self-similar relationships remained invariant under changes of scale and confirmed the analysis of Chanson and Carosi (Exp Fluids 42:385-401, 2007). The finding is significant because self-similarity may provide a picture general enough to be used to characterise the air-water flow field in large prototype channels.

  14. Three-dimensional flow of a nanofluid over a permeable stretching/shrinking surface with velocity slip: A revised model

    Science.gov (United States)

    Jusoh, R.; Nazar, R.; Pop, I.

    2018-03-01

    A reformulation of the three-dimensional flow of a nanofluid by employing Buongiorno's model is presented. A new boundary condition is implemented in this study with the assumption of nanoparticle mass flux at the surface is zero. This condition is practically more realistic since the nanoparticle fraction at the boundary is latently controlled. This study is devoted to investigate the impact of the velocity slip and suction to the flow and heat transfer characteristics of nanofluid. The governing partial differential equations corresponding to the momentum, energy, and concentration are reduced to the ordinary differential equations by utilizing the appropriate transformation. Numerical solutions of the ordinary differential equations are obtained by using the built-in bvp4c function in Matlab. Graphical illustrations displaying the physical influence of the several nanofluid parameters on the flow velocity, temperature, and nanoparticle volume fraction profiles, as well as the skin friction coefficient and the local Nusselt number are provided. The present study discovers the existence of dual solutions at a certain range of parameters. Surprisingly, both of the solutions merge at the stretching sheet indicating that the presence of the velocity slip affects the skin friction coefficients. Stability analysis is carried out to determine the stability and reliability of the solutions. It is found that the first solution is stable while the second solution is not stable.

  15. [Effects on blood flow velocity, wound healing and pain in hand microsurgery patients following heating on non-affected side].

    Science.gov (United States)

    Kim, Minsuk; So, Heeyoung

    2012-08-01

    The purpose of this study was to identify the effects of heating on the non-affected hand on blood flow velocity, wound healing, and pain for hand microsurgery patients. This study was designed using the nonequivalent control group pretest-posttest design. Thirty-nine patients were assigned either to the experimental group (20 patients) or control group (19 patients). Data were analyzed with χ²-test, Fisher's exact test, t-test, and repeated measure ANOVA using SPSS/WIN 17.0 program. After treatment in this program, blood flow velocity (F=5.13, p=.008) and wound healing (F=4.11, p=.020) improved significantly in the experimental group compared to the control group. But there was no significant improvement in pain in the experimental group compared to the control group (F=2.40, p=.097). Based upon these results, the non-affected side hand heating was recommended as an independent nursing intervention for the patients who need improvement in blood flow velocity and wound healing such as patients who have microsurgery. As the heating was effective even when applied on the non-affected side, it is the applicable to patients who cannot tolerate any therapy on affected side.

  16. AXAOTHER XL -- A spreadsheet for determining doses for incidents caused by tornadoes or high-velocity straight winds

    International Nuclear Information System (INIS)

    Simpkins, A.A.

    1996-09-01

    AXAOTHER XL is an Excel Spreadsheet used to determine dose to the maximally exposed offsite individual during high-velocity straight winds or tornado conditions. Both individual and population doses may be considered. Potential exposure pathways are inhalation and plume shine. For high-velocity straight winds the spreadsheet has the capability to determine the downwind relative air concentration, however for the tornado conditions, the user must enter the relative air concentration. Theoretical models are discussed and hand calculations are performed to ensure proper application of methodologies. A section has also been included that contains user instructions for the spreadsheet

  17. Lateral and vertical heterogeneity of flow and suspended sediment characteristics during a dam flushing event, in high velocity conditions

    Science.gov (United States)

    Antoine, Germain; Cazilhac, Marine; Monnoyer, Quentin; Jodeau, Magali; Gratiot, Nicolas; Besnier, Anne-Laure; Henault, Fabien; Le Brun, Matthieu

    2015-04-01

    The dynamic of suspended sediments in highly turbulent and concentrated flow is an important issue to better predict the sediment propagation along mountain rivers. In such extreme environments, the spatial and temporal variability of hydraulic and sediment parameters are difficult to measure: the flow velocity and the suspended sediment concentration (SSC) could be high (respectively several m/s and g/l) and rapidly variable. Simple methods are commonly used to estimate water discharge and mean or punctual SSC. But no method has been used successfully in a mountain river to estimate during a whole event the spatial distribution of flow velocity and SSC, as well as sediment parameters like grain size or settling velocity into a river cross section. This leads to these two questions: in such conditions, can we calculate sediment fluxes with one sediment concentration measurement? How can we explain the spatial heterogeneity of sediment characteristics? In this study, we analyze sampled data from a very well instrumented river reach in the Northern French Alps: the Arc-Isère River system. This gravel-bed river system is characterized by large concentrations of fines sediments, coming from the highly erodible mountains around. To control the hydraulic, sedimentary and chemical parameters from the catchment head, several gauging stations have been established since 2006. Especially, several measurements are usually done during the flushing of the dams located on the upper part of the river. During the flushing event of June 2014, we instrumented the gauging station located just upstream the confluence between the Isere and the Arc River, at the outlet of the Arc River watershed. ADCP measurements have been performed to estimate the spatial distribution of the flow velocity (up to 3 m/s), and turbidimeters and automatic samplers have been used to estimate the spatial distribution of the SSC into the cross section (up to 6 g/l). These samples have been directly analyzed

  18. Evaluation of coronary blood flow velocity during cardiac arrest with circulation maintained through mechanical chest compressions in a porcine model

    Directory of Open Access Journals (Sweden)

    Wagner Henrik

    2011-12-01

    Full Text Available Abstract Background Mechanical chest compressions (CCs have been shown capable of maintaining circulation in humans suffering cardiac arrest for extensive periods of time. Reports have documented a visually normalized coronary blood flow during angiography in such cases (TIMI III flow, but it has never been actually measured. Only indirect measurements of the coronary circulation during cardiac arrest with on-going mechanical CCs have been performed previously through measurement of the coronary perfusion pressure (CPP. In this study our aim was to correlate average peak coronary flow velocity (APV to CPP during mechanical CCs. Methods In a closed chest porcine model, cardiac arrest was established through electrically induced ventricular fibrillation (VF in eleven pigs. After one minute, mechanical chest compressions were initiated and then maintained for 10 minutes upon which the pigs were defibrillated. Measurements of coronary blood flow in the left anterior descending artery were made at baseline and during VF with a catheter based Doppler flow fire measuring APV. Furthermore measurements of central (thoracic venous and arterial pressures were also made in order to calculate the theoretical CPP. Results Average peak coronary flow velocity was significantly higher compared to baseline during mechanical chests compressions and this was observed during the entire period of mechanical chest compressions (12 - 39% above baseline. The APV slowly declined during the 10 min period of mechanical chest compressions, but was still higher than baseline at the end of mechanical chest compressions. CPP was simultaneously maintained at > 20 mmHg during the 10 minute episode of cardiac arrest. Conclusion Our study showed good correlation between CPP and APV which was highly significant, during cardiac arrest with on-going mechanical CCs in a closed chest porcine model. In addition APV was even higher during mechanical CCs compared to baseline. Mechanical

  19. STATISTICS OF THE VELOCITY GRADIENT TENSOR IN SPACE PLASMA TURBULENT FLOWS

    Energy Technology Data Exchange (ETDEWEB)

    Consolini, Giuseppe; Marcucci, Maria Federica; Pallocchia, Giuseppe [INAF-Istituto di Astrofisica e Planetologia Spaziali, Roma (Italy); Materassi, Massimo, E-mail: giuseppe.consolini@iaps.inaf.it [Istituto dei Sistemi Complessi, CNR, Sesto Fiorentino (Italy)

    2015-10-10

    In the last decade, significant advances have been presented for the theoretical characterization and experimental techniques used to measure and model all of the components of the velocity gradient tensor in the framework of fluid turbulence. Here, we attempt the evaluation of the small-scale velocity gradient tensor for a case study of space plasma turbulence, observed in the Earth's magnetosheath region by the CLUSTER mission. In detail, we investigate the joint statistics P(R, Q) of the velocity gradient geometric invariants R and Q, and find that this P(R, Q) is similar to that of the low end of the inertial range for fluid turbulence, with a pronounced increase in the statistics along the so-called Vieillefosse tail. In the context of hydrodynamics, this result is referred to as the dissipation/dissipation-production due to vortex stretching.

  20. Measurement of transient two-phase flow velocity using statistical signal analysis of impedance probe signals

    International Nuclear Information System (INIS)

    Leavell, W.H.; Mullens, J.A.

    1981-01-01

    A computational algorithm has been developed to measure transient, phase-interface velocity in two-phase, steam-water systems. The algorithm will be used to measure the transient velocity of steam-water mixture during simulated PWR reflood experiments. By utilizing signals produced by two, spatially separated impedance probes immersed in a two-phase mixture, the algorithm computes the average transit time of mixture fluctuations moving between the two probes. This transit time is computed by first, measuring the phase shift between the two probe signals after transformation to the frequency domain and then computing the phase shift slope by a weighted least-squares fitting technique. Our algorithm, which has been tested with both simulated and real data, is able to accurately track velocity transients as fast as 4 m/s/s

  1. Viscous flux flow velocity and stress distribution in the Kim model of a long rectangular slab superconductor

    Science.gov (United States)

    Yang, Yong; Chai, Xueguang

    2018-05-01

    When a bulk superconductor endures the magnetization process, enormous mechanical stresses are imposed on the bulk, which often leads to cracking. In the present work, we aim to resolve the viscous flux flow velocity υ 0/w, i.e. υ 0 (because w is a constant) and the stress distribution in a long rectangular slab superconductor for the decreasing external magnetic field (B a ) after zero-field cooling (ZFC) and field cooling (FC) using the Kim model and viscous flux flow equation simultaneously. The viscous flux flow velocity υ 0/w and the magnetic field B* at which the body forces point away in all of the slab volumes during B a reduction, are determined by both B a and the decreasing rate (db a /dt) of the external magnetic field normalized by the full penetration field B p . In previous studies, υ 0/w obtained by the Bean model with viscous flux flow is only determined by db a /dt, and the field B* that is derived only from the Kim model is a positive constant when the maximum external magnetic field is chosen. This means that the findings in this paper have more physical contents than the previous results. The field B* stress changing with decreasing field B a after ZFC if B* ≤ 0. The effect of db a /dt on the stress is significant in the cases of both ZFC and FC.

  2. Cerebral blood flow velocities are reduced during attacks of unilateral migraine without aura

    DEFF Research Database (Denmark)

    Thomsen, L L; Iversen, Helle Klingenberg; Olesen, J

    1995-01-01

    It has been disputed whether or not large intracranial arteries are dilated during migraine attacks. In order to answer this question the present transcranial Doppler study focused on side-to-side differences of middle cerebral artery blood velocity during unilateral attacks of migraine without...... aura in 25 patients. Blood velocity in the middle cerebral artery was lower on the headache side (59 cm/s) than on the non-headache side (65 cm/s) during the migraine attack. No such difference was found outside of attack (65 cm/s both sides). The difference (headache side minus non-headache side...

  3. Comparison of blood flow velocity through the internal carotid artery based on Doppler ultrasound and numerical simulation

    International Nuclear Information System (INIS)

    Hassani-Ardekani, Hajar; Ghalichi, Farzan; Niroomand-Oscuii, Hanieh; Farhoudi, Mehdi; Tarzmani, Mohammad K.

    2012-01-01

    Doppler ultrasound is a usual non-invasive method to estimate the stenosis percentage in large arteries such as carotid by measuring maximum velocity of blood flow. Based on clinical investigations, because of vessel wall motions, Doppler positioning and angle correction, some errors can arise in Doppler results which lead to incorrect diagnosis. The aim of this study was to compare the results of Doppler test and the numerical simulation of blood flow in the same case. For this evaluation, two patients including an 87-year-old man and a 72-year-old woman suffering from stenosis in the internal carotid artery were selected. First, clinical information of each patient such as CT-Angio scan images and Doppler ultrasound results on different locations of the stenosed artery were obtained. Then, the geometries were reconstructed and numerical simulations were carried out using ANSYS software. Results showed that the velocity profile of Doppler test and numerical simulation were in good agreement at the regions of pre-and post-stenosis. However, the value of maximum velocity at the stenotic region had significant differences.

  4. In Vivo Three-Dimensional Velocity Vector Imaging and Volumetric Flow Rate Measurements

    DEFF Research Database (Denmark)

    Pihl, Michael Johannes; Stuart, Matthias Bo; Tomov, Borislav Gueorguiev

    2013-01-01

    The three-dimensional (3-D) Transverse Oscillation (TO) method is used to obtain 3-D velocity vector estimates in two orthogonal planes. The method is suitable for a real-time implementation. Data are acquired using a Vermon 3.0 MHz 32x32 element 2-D phased array and the experimental ultrasound s...

  5. A 2D particle velocity sensor with minimal flow-disturbance

    NARCIS (Netherlands)

    Pjetri, O.; Wiegerink, Remco J.; Krijnen, Gijsbertus J.M.

    2015-01-01

    A 2D sound particle velocity sensor, consisting of a cross of two connected, heated wires is presented. We developed a fabrication process by which the wires become freely suspended 350 μm above the chip surface. This largely eliminates the influence of boundary layer effects and increases the

  6. An analysis of Cattaneo-Christov double-diffusion model for Sisko fluid flow with velocity slip

    Directory of Open Access Journals (Sweden)

    Rabia Malik

    Full Text Available The present frame work examines the characteristics of Cattaneo-Christov double-diffusion model to the Sisko fluid flow over a flat stretching sheet with velocity slip and thermal radiation. Instead of using classical Fourier's law and Fick's law the inclusion of thermal and concentration relaxation times lead us to the Cattaneo-Christov double-diffusion model. Utilization of the suitable transformations makes it convenient to transform our governing partial differential equations into ordinary differential equations. Further, the numerical solutions to these normalized ordinary differential equations are obtained by adopting the shooting technique along with Runge-Kutta fourth order method. The results are then plotted for various values of the pertinent parameters and discussed deliberately. Also, a comparison of the present results with the previously reported results as well as analytic results obtained through the homotopy analysis method (HAM helps to ensure their validity. This investigation leads us to the fact that the velocity diminishes with the velocity slip parameter. Also, in temperature and concentration profiles a decline can obviously be verdict with the larger relaxation times. Keywords: Cattaneo-Christov double-diffusion model, Sisko fluid, Velocity slip, Thermal radiation

  7. Optical reflection probe for the measurement of local void fraction, bubble velocity, bubble size and for the identification of flow regime

    International Nuclear Information System (INIS)

    Berti, M.

    1983-11-01

    Within the scope of two-phase flow measurement technique optical probes have been investigated for measurement of local void fraction, bubble velocity, bubble-size and identification of flow regime. Single and double probes used normal to flow need a calibration factor due to the effects of bubble deformation and bubble deflexion by the probe tips. (Auth.)

  8. Void fraction and interfacial velocity in gas-liquid upward two-phase flow across tube bundles

    International Nuclear Information System (INIS)

    Ueno, T.; Tomomatsu, K.; Takamatsu, H.; Nishikawa, H.

    1997-01-01

    Tube failures due to flow-induced vibration are a major problem in heat exchangers and many studies on the problem of such vibration have been carried out so far. Most studies however, have not focused on two-phase flow behavior in tube bundles, but have concentrated mainly on tube vibration behavior like fluid damping, fluid elastic instability and so on. Such studies are not satisfactory for understanding the design of heat exchangers. Tube vibration behavior is very complicated, especially in the case of gas-liquid two-phase flow, so it is necessary to investigate two-phase flow behavior as well as vibration behavior before designing heat exchangers. This paper outlines the main parameters that characterize two-phase behavior, such as void fraction and interfacial velocity. The two-phase flow analyzed here is gas-liquid upward flow across a horizontal tube bundle. The fluids tested were HCFC-123 and steam-water. HCFC-123 stands for Hydrochlorofluorocarbon. Its chemical formula is CHCl 2 CF 3 , which has liquid and gas densities of 1335 and 23.9 kg/m 3 at a pressure of 0.40 MPa and 1252 and 45.7 kg/m 3 at a pressure of 0.76 MPa. The same model tube bundle was used in the two tests covered in this paper, to examine the similarity law of two-phase flow behavior in tube bundles using HCFC-123 and steam-water two-phase flow. We also show numerical simulation results for the two fluid models in this paper. We do not deal with vibration behavior and the relationship between vibration behavior and two-phase flow behavior. (author)

  9. Vector Flow Imaging Compared with Pulse Wave Doppler for Estimation of Peak Velocity in the Portal Vein

    DEFF Research Database (Denmark)

    Brandt, Andreas Hjelm; Moshavegh, Ramin; Hansen, Kristoffer Lindskov

    2018-01-01

    The study described here investigated whether angle-independent vector flow imaging (VFI) technique estimates peak velocities in the portal vein comparably to pulsed wave Doppler (PWD). Furthermore, intra- and inter-observer agreement was assessed in a substudy. VFI and PWD peak velocities were...... estimated with from intercostal and subcostal views for 32 healthy volunteers, and precision analyses were conducted. Blinded to estimates, three physicians rescanned 10 volunteers for intra- and inter-observer agreement analyses. The precision of VFI and PWD was 18% and 28% from an intercostal view and 23......% and 77% from a subcostal view, respectively. Bias between VFI and PWD was 0.57 cm/s (p = 0.38) with an intercostal view and 9.89 cm/s (p ...

  10. A Microfluidic Device with an Integrated Waveguide Beam Splitter for Velocity Measurements of Flowing Particles by Fourier Transformation

    DEFF Research Database (Denmark)

    Mogensen, Klaus Bo; Kwok, Y.C.; Eijkel, J.C.T.

    2003-01-01

    A microfabricated capillary electrophoresis device for velocity measurements of flowing particles is presented. It consists of a 1 x 128 planar waveguide beam splitter monolithically integrated with an electrically insulated fluidic channel network for fluorescence excitation at multiple points....... Stray light rejection structures are included in order to suppress unwanted light between the detection regions. The emission pattern of particles passing the detection region was collected by a photomultiplier tube that was placed in close proximity to the channel, thereby avoiding the use of transfer...... optics. The integrated planar waveguide beam splitter was, furthermore, permanently connected to the light source by a glued-on optical fiber, to achieve a robust and alignment-free operation of the system. The velocity was measured using a Fourier transformation with a Shah function, since the response...

  11. The Polar Fluid Model for Blood Flow through a Tapered Artery with Overlapping Stenosis: Effects of Catheter and Velocity Slip

    Directory of Open Access Journals (Sweden)

    J. V. Ramana Reddy

    2015-01-01

    Full Text Available The blood flow through an overlapping clogged tapered artery in the presence of catheter is discussed. Since cholesterol deposition is resulting in the stenosis formation, velocity slip at the arterial wall is considered. The equations governing the fluid flow have been solved analytically under the assumption of the mild stenosis. The analysis with respect to various parameters arising out of fluid and geometry considered, on physiological parameters such as impedance and wall shear stress at the maximum height of the stenosis as well as across the entire length of the stenosis has been reported. A table summarizing the locations of extreme heights and the corresponding annular radii is provided. It is observed that the wall shear stress is the same at both the locations corresponding to the maximum height of the stenosis in case of nontapered artery while it varies in case of tapered artery. It is also observed that slip velocity and diverging tapered artery facilitate the fluid flow. Shear stress at the wall is increasing as micropolar parameter is decreasing and the trend is reversed in case of coupling number. The results obtained are validated by comparing them with the experimental and theoretical results.

  12. Performance of a Compression-ignition Engine with a Precombustion Chamber Having High-Velocity Air Flow

    Science.gov (United States)

    Spanogle, J A; Moore, C S

    1931-01-01

    Presented here are the results of performance tests made with a single-cylinder, four stroke cycle, compression-ignition engine. These tests were made on a precombustion chamber type of cylinder head designed to have air velocity and tangential air flow in both the chamber and cylinder. The performance was investigated for variable load and engine speed, type of fuel spray, valve opening pressure, injection period and, for the spherical chamber, position of the injection spray relative to the air flow. The pressure variations between the pear-shaped precombustion chamber and the cylinder for motoring and full load conditions were determined with a Farnboro electric indicator. The combustion chamber designs tested gave good mixing of a single compact fuel spray with the air, but did not control the ensuing combustion sufficiently. Relative to each other, the velocity of air flow was too high, the spray dispersion by injection too great, and the metering effect of the cylinder head passage insufficient. The correct relation of these factors is of the utmost importance for engine performance.

  13. Estimation of particle velocity in moving beds based on a flow model for bulk solids. Ryudo model ni motozuita idoso no ryushi sokudo no suisan

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, H. (Muroran Inst. of Tech., Hokkaido (Japan)); Honda, Y. (Snow Brand Milk Products Co. Ltd., Sapporo (Japan))

    1992-11-10

    Based on a particle flow model (stress-shear strain velocity relational expression) which takes account of the bulk volume expansion effect during shearing deformation of particles, a new estimation method for particle velocity distribution and stress distribution is proposed. The method is applied to a crossflow moving bed and to a moving bed for comparison with the experimental values to examine its validity. The method is further extended to predict the velocity profile and stress profile of moving beds in a vertical tube (countercurrent and concurrent) accompanying gas flow. It is indicated that the bulk volume expansion effect differs according to dimensions. The velocity distribution and the stress distribution of flows in a vertical tube are greatly influenced by the nature of the flow, i.e. whether it is a counterflow or a concurrent flow, and the frictional force of solids on a wall surface increases markedly in a concurrent flow, which induces considerable lag of particle velocity. The parameter which is contained in the model and indicates the bulk volume expansion effect is a function of the particle velocity, and it is almost unaffected by the flow rate of gas moving. 7 refs., 10 figs.

  14. Brief communication: The Khurdopin glacier surge revisited - extreme flow velocities and formation of a dammed lake in 2017

    Science.gov (United States)

    Steiner, Jakob F.; Kraaijenbrink, Philip D. A.; Jiduc, Sergiu G.; Immerzeel, Walter W.

    2018-01-01

    Glacier surges occur regularly in the Karakoram, but the driving mechanisms, their frequency and its relation to a changing climate remain unclear. In this study, we use digital elevation models and Landsat imagery in combination with high-resolution imagery from the Planet satellite constellation to quantify surface elevation changes and flow velocities during a glacier surge of the Khurdopin Glacier in 2017. Results reveal that an accumulation of ice volume above a clearly defined steep section of the glacier tongue since the last surge in 1999 eventually led to a rapid surge in May 2017 peaking with velocities above 5000 m a-1, which were among the fastest rates globally for a mountain glacier. Our data reveal that velocities on the lower tongue increase steadily during a 4-year build-up phase prior to the actual surge only to then rapidly peak and decrease again within a few months, which confirms earlier observations with a higher frequency of available velocity data. The surge return period between the reported surges remains relatively constant at ca. 20 years. We show the potential of a combination of repeat Planet and ASTER imagery to (a) capture peak surge velocities that are easily missed by less frequent Landsat imagery, (b) observe surface changes that indicate potential drivers of a surge and (c) monitor hazards associated with a surge. At Khurdopin specifically, we observe that the surging glacier blocks the river in the valley and causes a lake to form, which may grow in subsequent years and could pose threats to downstream settlements and infrastructure in the case of a sudden breach.

  15. Exploring Capabilities of Electrical Capacitance Tomography Sensor and Velocity Analysis of Two-Phase R-134A Flow Through a Sudden Expansion

    Science.gov (United States)

    2017-05-01

    circles, spokes on a bicycle wheel or combinations thereof. iii. Center of Gravity - tracks a regular, roughly circular shaped object that does not...analysis showed the velocities of 71 tracked points at varying level of qualities. These velocities were analyzed and the data from these experiments...each of the video recordings, two to six features were tracked that best represented the bulk liquid flow. The velocities of these features were

  16. Efficient Optical Flow and Stereo Vision for Velocity Estimation and Obstacle Avoidance on an Autonomous Pocket Drone

    OpenAIRE

    McGuire, K.N.; de Croon, G.C.H.E.; de Wagter, C.; Tuyls, Karl; Kappen, Hilbert

    2017-01-01

    Miniature Micro Aerial Vehicles (MAV) are very suitable for flying in indoor environments, but autonomous navigation is challenging due to their strict hardware limitations. This paper presents a highly efficient computer vision algorithm called Edge-FS for the determination of velocity and depth. It runs at 20 Hz on a 4 g stereo camera with an embedded STM32F4 microprocessor (168 MHz, 192 kB) and uses feature histograms to calculate optical flow and stereo disparity. The stereo-based distanc...

  17. Does increased aortic stiffness predict reduced coronary flow velocity reserve in patients with suspected coronary artery disease?

    Science.gov (United States)

    Nemes, A; Csanády, M; Forster, T

    2012-09-01

    In recent studies, reduction in coronary flow velocity reserve (CFR) has been demonstrated in patients with increased aortic stiffness. Stress transoesophageal echocardiography (TEE) is a suitable method for the simultaneous evaluation of CFR and aortic stiffness parameters. The present study was designed to test whether increased echocardiography-derived aortic elastic modulus [E(p)] predicts impaired CFR in patients with suspected coronary artery disease (CAD). The present study comprised 158 patients with suspected CAD. A CFR value reduced CFR (HE 1.10, p < 0.05). Increased aortic stiffness predicts impaired CFR in patients with suspected CAD.

  18. Method and apparatus for simultaneous determination of fluid mass flow rate, mean velocity and density

    International Nuclear Information System (INIS)

    Hamel, W.R.

    1984-01-01

    This invention relates to a new method and new apparatus for determining fluid mass flow rate and density. In one aspect of the invention, the fluid is passed through a straight cantilevered tube in which transient oscillation has been induced, thus generating Coriolis damping forces on the tube. The decay rate and frequency of the resulting damped oscillation are measured, and the fluid mass flow rate and density are determined therefrom. In another aspect of the invention, the fluid is passed through the cantilevered tube while an electrically powered device imparts steady-state harmonic excitation to the tube. This generates Coriolis tube-damping forces which are dependent on the mass flow rate of the fluid. Means are provided to respond to incipient flow-induced changes in the amplitude of vibration by changing the power input to the excitation device as required to sustain the original amplitude of vibration. The fluid mass flow rate and density are determined from the required change in power input. The invention provides stable, rapid, and accurate measurements. It does not require bending of the fluid flow

  19. Estimation of water flow velocity in small plants using cold neutron imaging with D 2O tracer

    Science.gov (United States)

    Matsushima, U.; Herppich, W. B.; Kardjilov, N.; Graf, W.; Hilger, A.; Manke, I.

    2009-06-01

    Water flow imaging may help to better understand various problems related to water stress of plants. It may help to fully understand the water relations of plants. The objective of this research was to estimate the velocity of water flow in plant samples. Cut roses ( Rosa hybrida, var. 'Milva') were used as samples. Cold neutron radiography (CNR) was conducted at CONRAD, Helmholtz Center Berlin for Materials and Energy, Berlin, Germany. D 2O and H 2O were interchangeably injected into the water feeding system of the sample. After the uptake of D 2O, the neutron transmission increased due to the smaller attenuation coefficient of D 2O compared to H 2O. Replacement of D 2O in the rose peduncle was clearly observed. Three different optical flow algorithms, Block Matching, Horn-Schunck and Lucas-Kanade, were used to calculate the vector of D 2O tracer flow. The quality of sequential images providing sufficient spatial and temporal resolution allowed to estimate flow vector.

  20. Ethylene epoxidation promoted by methane gas-phase thermic oxidation. The influence of equivalence ratio and gas flow velocity

    International Nuclear Information System (INIS)

    Grigoryan, R.R.; Arsentiev, S.D.; Mantashyan, A.A.

    2008-01-01

    Ethylene epoxidation promoted by methane gas-phase thermic oxidation has been studied. The studies were carried out in a two-sectional reactor under flow conditions. The most experiments were performed at temperatures T 1 - 983 K, T 2 - 778 K and pressure P = 86,7 kPa. It was shown that when methane is oxidized in the first section of the reactor and ethylene is put into the second section, epoxidation of olefin occurs through the alkyl peroxy radical interaction with double bond of olefin. It was established that the dependences of epoxidation rate on equivalence ratio and gas flow velocity pass through maximum. The substitution of methane by inert gas (argon) in the first section leads to significant decrease of rate of ethylene oxide accumulation in the second section

  1. Velocity measurement of two-phase liquid-gas flow in a horizontal pipeline using gamma densitometry

    Science.gov (United States)

    Hanus, R.; Zych, M.; Petryka, L.

    2014-08-01

    This paper presents application of gamma-ray absorption method to liquid-gas flow investigation in a pipeline. In the described measurement two sealed 241Am radioactive sources and probes with NaI(Tl) scintillation crystals have been used. For the analysis of digital signals provided by detectors, a traditional cross-correlation function (CCF), and modified correlation methods based on the quotient of CCF and average magnitude difference function (AMDF), as well as the quotient of CCF, and average square difference function (ASDF) have been proposed. Exemplary results of the mean velocity determination of the gaseous phase transported by a liquid in the water-air mixture flow were demonstrated and the evaluation of its uncertainty have been presented.

  2. Temperature and velocity conditions of air flow in vertical channel of hinged ventilated facade of a multistory building.

    Science.gov (United States)

    Statsenko, Elena; Ostrovaia, Anastasia; Pigurin, Andrey

    2018-03-01

    This article considers the influence of the building's tallness and the presence of mounting grooved lines on the parameters of heat transfer in the gap of a hinged ventilated facade. A numerical description of the processes occurring in a heat-gravitational flow is given. The average velocity and temperature of the heat-gravitational flow of a structure with open and sealed rusts are determined with unchanged geometric parameters of the gap. The dependence of the parameters influencing the thermomechanical characteristics of the enclosing structure is derived depending on the internal parameters of the system. Physical modeling of real multistory structures is performed by projecting actual parameters onto a reduced laboratory model (scaling).

  3. Increased cerebral blood flow velocity in children with mild sleep-disordered breathing: a possible association with abnormal neuropsychological function.

    Science.gov (United States)

    Hill, Catherine M; Hogan, Alexandra M; Onugha, Nwanneka; Harrison, Dawn; Cooper, Sara; McGrigor, Victoria J; Datta, Avijit; Kirkham, Fenella J

    2006-10-01

    Sleep-disordered breathing describes a spectrum of upper airway obstruction in sleep from simple primary snoring, estimated to affect 10% of preschool children, to the syndrome of obstructive sleep apnea. Emerging evidence has challenged previous assumptions that primary snoring is benign. A recent report identified reduced attention and higher levels of social problems and anxiety/depressive symptoms in snoring children compared with controls. Uncertainty persists regarding clinical thresholds for medical or surgical intervention in sleep-disordered breathing, underlining the need to better understand the pathophysiology of this condition. Adults with sleep-disordered breathing have an increased risk of cerebrovascular disease independent of atherosclerotic risk factors. There has been little focus on cerebrovascular function in children with sleep-disordered breathing, although this would seem an important line of investigation, because studies have identified abnormalities of the systemic vasculature. Raised cerebral blood flow velocities on transcranial Doppler, compatible with raised blood flow and/or vascular narrowing, are associated with neuropsychological deficits in children with sickle cell disease, a condition in which sleep-disordered breathing is common. We hypothesized that there would be cerebral blood flow velocity differences in sleep-disordered breathing children without sickle cell disease that might contribute to the association with neuropsychological deficits. Thirty-one snoring children aged 3 to 7 years were recruited from adenotonsillectomy waiting lists, and 17 control children were identified through a local Sunday school or as siblings of cases. Children with craniofacial abnormalities, neuromuscular disorders, moderate or severe learning disabilities, chronic respiratory/cardiac conditions, or allergic rhinitis were excluded. Severity of sleep-disordered breathing in snoring children was categorized by attended polysomnography. Weight

  4. Incorporation of velocity-dependent restitution coefficient and particle surface friction into kinetic theory for modeling granular flow cooling.

    Science.gov (United States)

    Duan, Yifei; Feng, Zhi-Gang

    2017-12-01

    Kinetic theory (KT) has been successfully used to model rapid granular flows in which particle interactions are frictionless and near elastic. However, it fails when particle interactions become frictional and inelastic. For example, the KT is not able to accurately predict the free cooling process of a vibrated granular medium that consists of inelastic frictional particles under microgravity. The main reason that the classical KT fails to model these flows is due to its inability to account for the particle surface friction and its inelastic behavior, which are the two most important factors that need be considered in modeling collisional granular flows. In this study, we have modified the KT model that is able to incorporate these two factors. The inelasticity of a particle is considered by establishing a velocity-dependent expression for the restitution coefficient based on many experimental studies found in the literature, and the particle friction effect is included by using a tangential restitution coefficient that is related to the particle friction coefficient. Theoretical predictions of the free cooling process by the classical KT and the improved KT are compared with the experimental results from a study conducted on an airplane undergoing parabolic flights without the influence of gravity [Y. Grasselli, G. Bossis, and G. Goutallier, Europhys. Lett. 86, 60007 (2009)10.1209/0295-5075/86/60007]. Our results show that both the velocity-dependent restitution coefficient and the particle surface friction are important in predicting the free cooling process of granular flows; the modified KT model that integrates these two factors is able to improve the simulation results and leads to better agreement with the experimental results.

  5. Incorporation of velocity-dependent restitution coefficient and particle surface friction into kinetic theory for modeling granular flow cooling

    Science.gov (United States)

    Duan, Yifei; Feng, Zhi-Gang

    2017-12-01

    Kinetic theory (KT) has been successfully used to model rapid granular flows in which particle interactions are frictionless and near elastic. However, it fails when particle interactions become frictional and inelastic. For example, the KT is not able to accurately predict the free cooling process of a vibrated granular medium that consists of inelastic frictional particles under microgravity. The main reason that the classical KT fails to model these flows is due to its inability to account for the particle surface friction and its inelastic behavior, which are the two most important factors that need be considered in modeling collisional granular flows. In this study, we have modified the KT model that is able to incorporate these two factors. The inelasticity of a particle is considered by establishing a velocity-dependent expression for the restitution coefficient based on many experimental studies found in the literature, and the particle friction effect is included by using a tangential restitution coefficient that is related to the particle friction coefficient. Theoretical predictions of the free cooling process by the classical KT and the improved KT are compared with the experimental results from a study conducted on an airplane undergoing parabolic flights without the influence of gravity [Y. Grasselli, G. Bossis, and G. Goutallier, Europhys. Lett. 86, 60007 (2009), 10.1209/0295-5075/86/60007]. Our results show that both the velocity-dependent restitution coefficient and the particle surface friction are important in predicting the free cooling process of granular flows; the modified KT model that integrates these two factors is able to improve the simulation results and leads to better agreement with the experimental results.

  6. Temperature fluctuation caused by coaxial-jet flow: Experiments on the effect of the velocity ratio R ⩾ 1

    International Nuclear Information System (INIS)

    Cao, Qiong; Li, Hongyuan; Lu, Daogang; Chang, Mu

    2017-01-01

    Highlights: • The effect on temperature fluctuation from velocity ratio was studied by experiment. • The distribution of time-averaged temperatures is the axial-symmetry in R ⩾ 1. • The region of intense temperature fluctuation in R = 1 is different from that of R > 1. • The intensity of temperature fluctuation under R > 1 is weaker than that of R = 1. - Abstract: The temperature fluctuation appears in the core outlet region due to the different of the temperature and velocity of the coolant, which can cause thermal stresses and the high-cycle thermal fatigue on solid boundaries. So, it is necessary to analyze the characteristics of the temperature fluctuation. In the present study, a comparative experiment was performed to analyze the effect on the temperature fluctuation caused by the coaxial-jet flow from the inlet cold and hot fluid velocity ratios (R ⩾ 1). In the condition of R ⩾ 1, the distribution of the time-averaged temperature is the axial-symmetry. In the cold fluid field, the temperature field is divided into four parts, including the first steady region, linear region, nonlinear region and the second steady region along the axial direction, while that is lack of the first steady state region in the hot fluid field. In the condition of R = 1, due to the velocity of the cold fluid is equivalent to that of the hot fluid, the cold fluid flow can be severely disturbed by the hot flow. The intense temperature fluctuation mainly distributed in the annular region at bottom region and the circular region in the upper region. While, in the condition of R > 1, the inertia of the cold fluid is larger than that of the hot fluid. The hot fluid will attach itself to the periphery of the cold fluid. The intense temperature fluctuation distributed in the annular region between the cold and hot fluid and the periphery of the hot fluid. However, the intensity of temperature fluctuation under R > 1 is weaker than that of R = 1.

  7. Uterine artery dysfunction in pregnant ACE2 knockout mice is associated with placental hypoxia and reduced umbilical blood flow velocity.

    Science.gov (United States)

    Yamaleyeva, Liliya M; Pulgar, Victor M; Lindsey, Sarah H; Yamane, Larissa; Varagic, Jasmina; McGee, Carolynne; daSilva, Mauro; Lopes Bonfa, Paula; Gurley, Susan B; Brosnihan, K Bridget

    2015-07-01

    Angiotensin-converting enzyme 2 (ACE2) knockout is associated with reduced fetal weight at late gestation; however, whether uteroplacental vascular and/or hemodynamic disturbances underlie this growth-restricted phenotype is unknown. Uterine artery reactivity and flow velocities, umbilical flow velocities, trophoblast invasion, and placental hypoxia were determined in ACE2 knockout (KO) and C57Bl/6 wild-type (WT) mice at day 14 of gestation. Although systolic blood pressure was higher in pregnant ACE2 KO vs. WT mice (102.3 ± 5.1 vs. 85.1 ± 1.9 mmHg, n = 5-6), the magnitude of difference was similar to that observed in nonpregnant ACE2 KO vs. WT mice. Maternal urinary protein excretion, serum creatinine, and kidney or heart weights were not different in ACE2 KO vs. WT. Fetal weight and pup-to-placental weight ratio were lower in ACE2 KO vs. WT mice. A higher sensitivity to Ang II [pD2 8.64 ± 0.04 vs. 8.5 ± 0.03 (-log EC50)] and greater maximal contraction to phenylephrine (169.0 ± 9.0 vs. 139.0 ± 7.0% KMAX), were associated with lower immunostaining for Ang II receptor 2 and fibrinoid content of the uterine artery in ACE2 KO mice. Uterine artery flow velocities and trophoblast invasion were similar between study groups. In contrast, umbilical artery peak systolic velocities (60.2 ± 4.5 vs. 75.1 ± 4.5 mm/s) and the resistance index measured using VEVO 2100 ultrasound were lower in the ACE2 KO vs. WT mice. Immunostaining for pimonidazole, a marker of hypoxia, and hypoxia-inducible factor-2α were higher in the trophospongium and placental labyrinth of the ACE2 KO vs. WT. In summary, placental hypoxia and uterine artery dysfunction develop before major growth of the fetus occurs and may explain the fetal growth restricted phenotype. Copyright © 2015 the American Physiological Society.

  8. Surface Tension Flows inside Surfactant-Added Poly(dimethylsiloxane Microstructures with Velocity-Dependent Contact Angles

    Directory of Open Access Journals (Sweden)

    Jyh Jian Chen

    2014-03-01

    Full Text Available Filling of liquid samples is realized in a microfluidic device with applications including analytical systems, biomedical devices, and systems for fundamental research. The filling of a disk-shaped polydimethylsiloxane (PDMS microchamber by liquid is analyzed with reference to microstructures with inlets and outlets. The microstructures are fabricated using a PDMS molding process with an SU-8 mold. During the filling, the motion of the gas-liquid interface is determined by the competition among inertia, adhesion, and surface tension. A single ramp model with velocity-dependent contact angles is implemented for the accurate calculation of surface tension forces in a three-dimensional volume-of-fluid based model. The effects of the parameters of this functional form are investigated. The influences of non-dimensional parameters, such as the Reynolds number and the Weber number, both determined by the inlet velocity, on the flow characteristics are also examined. An oxygen-plasma-treated PDMS substrate is utilized, and the microstructure is modified to be hydrophilic. Flow experiments are conducted into both hydrophilic and hydrophobic PDMS microstructures. Under a hydrophobic wall condition, numerical simulations with imposed boundary conditions of static and dynamic contact angles can successfully predict the moving of the meniscus compared with experimental measurements. However, for a hydrophilic wall, accurate agreement between numerical and experimental results is obvious as the dynamic contact angles were implemented.

  9. Vector velocity estimation of blood flow – A new application in medical ultrasound

    DEFF Research Database (Denmark)

    Hansen, Kristoffer Lindskov; Nielsen, Michael Bachmann; Jensen, Jørgen Arendt

    2017-01-01

    Vector flow techniques in the field of ultrasound encompass different pulse emission and estimation strategies. Numerous techniques have been introduced over the years, and recently commercial implementations usable in the clinic have been made. A number of clinical papers using different vector...

  10. Measuring of the profile vibration on the flutter critic flow velocity

    Czech Academy of Sciences Publication Activity Database

    Zolotarev, Igor; Vlček, Václav; Kozánek, Jan

    2015-01-01

    Roč. 4, č. 2 (2015), s. 45-45 ISSN 2168-9792. [International Conference and Exhibition on MECHANICAL & AEROSPACE ENGINEERING /3./. 05.10.2015-07.10.2015, San Francisco] R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : aeroelasticity * flutter * subsonic flow Subject RIV: BI - Acoustics

  11. Intraoperative vascular anatomy, arterial blood flow velocity, and microcirculation in unilateral and bilateral cleft lip repair

    NARCIS (Netherlands)

    Mueller, A.A.; Schumann, D.; Reddy, R.R.; Schwenzer-Zimmerer, K.; Mueller-Gerbl, M.; Zeilhofer, H.F.; Sailer, H.F.; Reddy, S.G.

    2012-01-01

    BACKGROUND: Cleft lip repair aims to normalize the disturbed anatomy and function. The authors determined whether normalization of blood circulation is achieved. METHODS: The authors measured the microcirculatory flow, oxygen saturation, and hemoglobin level in the lip and nose of controls (n = 22)

  12. ESTIMATING FLOW AND FLUX OF GROUND-WATER DISCHARGE USING WATER TEMPERATURE AND VELOCITY. (R827961)

    Science.gov (United States)

    The nature of ground water discharge to a stream has important implications for nearby ground water flow, especially with respect to contaminant transport and well-head protection. Measurements of ground water discharge were accomplished in this study using (1) differences bet...

  13. Second law analysis of slip velocity on oscillatory MHD flow of ...

    African Journals Online (AJOL)

    This paper reports the analytical calculation of entropy generation due to unsteady heat and mass transfer flow of an incompressible, electrically conducting, and viscous fluid past an infinite vertical porous plate along with porous medium of time dependent permeability with radiative heat transfer and variable suction.

  14. Accelerated time-resolved three-dimensional MR velocity mapping of blood flow patterns in the aorta using SENSE and k-t BLAST

    International Nuclear Information System (INIS)

    Stadlbauer, Andreas; Riet, Wilma van der; Crelier, Gerard; Salomonowitz, Erich

    2010-01-01

    Purpose: To assess the feasibility and potential limitations of the acceleration techniques SENSE and k-t BLAST for time-resolved three-dimensional (3D) velocity mapping of aortic blood flow. Furthermore, to quantify differences in peak velocity versus heart phase curves. Materials and methods: Time-resolved 3D blood flow patterns were investigated in eleven volunteers and two patients suffering from aortic diseases with accelerated PC-MR sequences either in combination with SENSE (R = 2) or k-t BLAST (6-fold). Both sequences showed similar data acquisition times and hence acceleration efficiency. Flow-field streamlines were calculated and visualized using the GTFlow software tool in order to reconstruct 3D aortic blood flow patterns. Differences between the peak velocities from single-slice PC-MRI experiments using SENSE 2 and k-t BLAST 6 were calculated for the whole cardiac cycle and averaged for all volunteers. Results: Reconstruction of 3D flow patterns in volunteers revealed attenuations in blood flow dynamics for k-t BLAST 6 compared to SENSE 2 in terms of 3D streamlines showing fewer and less distinct vortices and reduction in peak velocity, which is caused by temporal blurring. Solely by time-resolved 3D MR velocity mapping in combination with SENSE detected pathologic blood flow patterns in patients with aortic diseases. For volunteers, we found a broadening and flattering of the peak velocity versus heart phase diagram between the two acceleration techniques, which is an evidence for the temporal blurring of the k-t BLAST approach. Conclusion: We demonstrated the feasibility of SENSE and detected potential limitations of k-t BLAST when used for time-resolved 3D velocity mapping. The effects of higher k-t BLAST acceleration factors have to be considered for application in 3D velocity mapping.

  15. Measurement of flow velocity fields in small vessel-mimic phantoms and vessels of small animals using micro ultrasonic particle image velocimetry (micro-EPIV).

    Science.gov (United States)

    Qian, Ming; Niu, Lili; Wang, Yanping; Jiang, Bo; Jin, Qiaofeng; Jiang, Chunxiang; Zheng, Hairong

    2010-10-21

    Determining a multidimensional velocity field within microscale opaque fluid flows is needed in areas such as microfluidic devices, biofluid mechanics and hemodynamics research in animal studies. The ultrasonic particle image velocimetry (EchoPIV) technique is appropriate for measuring opaque flows by taking advantage of PIV and B-mode ultrasound contrast imaging. However, the use of clinical ultrasound systems for imaging flows in small structures or animals has limitations associated with spatial resolution. This paper reports on the development of a high-resolution EchoPIV technique (termed as micro-EPIV) and its application in measuring flows in small vessel-mimic phantoms and vessels of small animals. Phantom experiments demonstrate the validity of the technique, providing velocity estimates within 4.1% of the analytically derived values with regard to the flows in a small straight vessel-mimic phantom, and velocity estimates within 5.9% of the computationally simulated values with regard to the flows in a small stenotic vessel-mimic phantom. Animal studies concerning arterial and venous flows of living rats and rabbits show that the micro-EPIV-measured peak velocities within several cardiac cycles are about 25% below the values measured by the ultrasonic spectral Doppler technique. The micro-EPIV technique is able to effectively measure the flow fields within microscale opaque fluid flows.

  16. In vitro confocal micro-PIV measurements of blood flow in a square microchannel: the effect of the haematocrit on instantaneous velocity profiles.

    Science.gov (United States)

    Lima, Rui; Wada, Shigeo; Takeda, Motohiro; Tsubota, Ken-ichi; Yamaguchi, Takami

    2007-01-01

    A confocal microparticle image velocimetry (micro-PIV) system was used to obtain detailed information on the velocity profiles for the flow of pure water (PW) and in vitro blood (haematocrit up to 17%) in a 100-microm-square microchannel. All the measurements were made in the middle plane of the microchannel at a constant flow rate and low Reynolds number (Re=0.025). The averaged ensemble velocity profiles were found to be markedly parabolic for all the working fluids studied. When comparing the instantaneous velocity profiles of the three fluids, our results indicated that the profile shape depended on the haematocrit. Our confocal micro-PIV measurements demonstrate that the root mean square (RMS) values increase with the haematocrit implying that it is important to consider the information provided by the instantaneous velocity fields, even at low Re. The present study also examines the potential effect of the RBCs on the accuracy of the instantaneous velocity measurements.

  17. Wavelet entropy of Doppler ultrasound blood velocity flow waveforms distinguishes nitric oxide-modulated states.

    Science.gov (United States)

    Agnew, Christina E; Hamilton, Paul K; McCann, Aaron J; McGivern, R Canice; McVeigh, Gary E

    2015-05-01

    Wavelet entropy assesses the degree of order or disorder in signals and presents this complex information in a simple metric. Relative wavelet entropy assesses the similarity between the spectral distributions of two signals, again in a simple metric. Wavelet entropy is therefore potentially a very attractive tool for waveform analysis. The ability of this method to track the effects of pharmacologic modulation of vascular function on Doppler blood velocity waveforms was assessed. Waveforms were captured from ophthalmic arteries of 10 healthy subjects at baseline, after the administration of glyceryl trinitrate (GTN) and after two doses of N(G)-nitro-L-arginine-methyl ester (L-NAME) to produce vasodilation and vasoconstriction, respectively. Wavelet entropy had a tendency to decrease from baseline in response to GTN, but significantly increased after the administration of L-NAME (mean: 1.60 ± 0.07 after 0.25 mg/kg and 1.72 ± 0.13 after 0.5 mg/kg vs. 1.50 ± 0.10 at baseline, p wavelet entropy had a spectral distribution from increasing doses of L-NAME comparable to baseline, 0.07 ± 0.04 and 0.08 ± 0.03, respectively, whereas GTN had the most dissimilar spectral distribution compared with baseline (0.17 ± 0.08, p = 0.002). Wavelet entropy can detect subtle changes in Doppler blood velocity waveform structure in response to nitric-oxide-mediated changes in arteriolar smooth muscle tone. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  18. Modeling turbulent compressible flows - The mass fluctuating velocity and squared density

    Science.gov (United States)

    Taulbee, D.; Vanosdol, J.

    1991-01-01

    This paper deals with single-point closure theory for compressible turbulent flow, including the effects of compressibility on the turbulence. In particular, the combination of the pressure dilatation and the dilatation dissipation, terms which appear on the turbulent kinetic energy equation, are modeled. Model parameters in these transport equations are determined by comparing predictions with boundary layer measurements. Finally, predictions with a k-epsilon model, including the new formulations, are presented for the compressible shear layer.

  19. Low flow velocity, fine-screen heat exchangers and vapor-cooled cryogenic current leads

    International Nuclear Information System (INIS)

    Steyert, W.A.; Stone, N.J.

    1978-09-01

    The design, construction, and testing of three compact, low temperature heat exchangers are reported. A method is given for the construction of a small (approximately = 20-cm 3 volume) exchanger that can handle 6 g/s helium flow with low pressure drops (ΔP/P = 10 percent) and adequate heat transfer (N/sub tu/ = 3). The use of screen for simple, vapor-cooled current leads into cryogenic systems is also discussed

  20. On Possible Similarity Solutions for Three-Dimensional Incompressible Laminar Boundary-Layer Flows Over Developable Surfaces and with Proportional Mainstream Velocity Components

    Science.gov (United States)

    Hansen, Arthur G.

    1958-01-01

    Analysis is presented on the possible similarity solutions of the three-dimensional, laminar, incompressible, boundary-layer equations referred to orthogonal, curvilinear coordinate systems. Requirements of the existence of similarity solutions are obtained for the following: flow over developable surface and flow over non-developable surfaces with proportional mainstream velocity components.

  1. Cerebral hemispheric blood flow velocity differences in left- and right- handers: functional trans-cranial Doppler ultrasonography

    Directory of Open Access Journals (Sweden)

    Sikaroodi H

    2009-12-01

    Full Text Available "n Normal 0 false false false EN-US X-NONE AR-SA MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:Arial; mso-bidi-theme-font:minor-bidi;} Background: It is a well known fact that language functions are primarily related to the left hemisphere in right handed individuals, there is still no agreement about hemispheric language dominance in left handers. The aim of this study is to evaluate the possibility of using functional Transcranial Doppler ultra sonography (TCD, as a non-invasive method for investigation of hemispheric language dominance and also to explore possible gender influence on hemispheric language representation."n"nMethods: We performed functional TCD during a word generation task, in 62 healthy volunteers (30 right handers and 32 left handers, 50% male and 50% female. All subjects were medical students in the age range of 22-29 years. Right or left handedness was determined using Edinburgh questionnaire. Two subjects were excluded from the study because of poor temporal windows. Mean blood flow velocity was measured in both right and left middle cerebral arteries (MCA at rest and during a word generation task, and changes in flow velocities were compared."n"nResults: Increase of MCA blood flow velocity was observed in 55% (33 subjects of the students in the left side, and in 45% (27 subjects of them in the right side. Right hemispheric

  2. Method and apparatus for simultaneous determination of fluid mass flow rate, mean velocity and density

    Science.gov (United States)

    Hamel, William R.

    1984-01-01

    This invention relates to a new method and new apparatus for determining fluid mass flowrate and density. In one aspect of the invention, the fluid is passed through a straight cantilevered tube in which transient oscillation has been induced, thus generating Coriolis damping forces on the tube. The decay rate and frequency of the resulting damped oscillation are measured, and the fluid mass flowrate and density are determined therefrom. In another aspect of the invention, the fluid is passed through the cantilevered tube while an electrically powered device imparts steady-state harmonic excitation to the tube. This generates Coriolis tube-damping forces which are dependent on the mass flowrate of the fluid. Means are provided to respond to incipient flow-induced changes in the amplitude of vibration by changing the power input to the excitation device as required to sustain the original amplitude of vibration. The fluid mass flowrate and density are determined from the required change in power input. The invention provides stable, rapid, and accurate measurements. It does not require bending of the fluid flow.

  3. Lifetimes of flame balls dragged by model turbulent flows: Role of velocity gradient fluctuations.

    Science.gov (United States)

    D'Angelo, Yves; Joulin, Guy

    2004-03-01

    An isolated combustion spot-known as a flame ball (FB)-is considered while it is advected by a turbulent flow of a lean premixture of such a light fuel as hydrogen. A Batchelor approximation for the surrounding Lagrangian flow is made. This in principle gives one an access to the FB lifetime t(life) and to its response to the ambiant Lagrangian rate-of-strain tensor g(t), by means of a nonlinear and forced integro-differential equation for the current FB radius. For a diagonal g(t) deduced from random Markov processes of the Ornstein-Uhlenbeck type, or linearly filtered versions thereof, extensive numerical simulations and approximate theoretical analyses agree that (i) flame balls can definitely live for much longer than their time of spontaneous expansion/collapse; (ii) large enough values of t(life) are compatible with Poisson statistics; (iii) the variations of with the characteristics of g(t) mirror the latter's statistics, more precisely that of trace(g(2)). Open problems, dealing with a nondiagonal g(t), ignition-related transients and/or collective effects, finally are evoked.

  4. Magnetohydrodynamic and thermal radiation effects on the boundary-layer flow due to a moving extensible surface with the velocity slip model: A comparative study of four nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Aly, Emad H., E-mail: efarag@uj.edu.sa [Department of Mathematics, Faculty of Science, University of Jeddah, Jeddah 21589 (Saudi Arabia); Department of Mathematics, Faculty of Education, Ain Shams University, Roxy, Cairo 11757 (Egypt); Sayed, Hamed M. [Department of Mathematics, Faculty of Education, Ain Shams University, Roxy, Cairo 11757 (Egypt); Department of Mathematics, Faculty of Sciences, Taibah University, Yanbu (Saudi Arabia)

    2017-01-15

    In the current work, we investigated effects of the velocity slip for the flow and heat transfer of four nanofluids over a non-linear stretching sheet taking into account the thermal radiation and magnetic field in presence of the effective electrical conductivity. The governing partial differential equations were transformed into a set of nonlinear ordinary differential equation using similarity transformations before being solved numerically by the Chebyshev pseudospectral differentiation matrix (ChPDM). It was found that the investigated parameters affect remarkably on the nanofluid stream function for the whole investigated nanoparticles. In addition, velocity and skin friction profiles of the four investigated nanofluids decreases and increases, respectively, with the increase of the magnetic parameter, first-order and second-order velocity slips. Further, the flow velocity, surface shear stress and temperature are strongly influenced on applying the velocity slip model, where lower values of the second-order imply higher surface heat flux and thereby making the fluid warmer. - Highlights: • A comparative study for four nanoparticles with MHD and thermal radiation effects was studied. • The effective electrical conductivity is mandatory; otherwise a spurious physical sight will be gained. • The investigated parameters affect remarkably on the nanofluids' flow. • The flow velocity, surface shear stress and temperature are strongly influenced by the slip model. • Lower values of the second-order imply higher surface heat flux and thereby making the fluid warmer.

  5. Reduced arteriovenous shunting capacity after local heating and redistribution of baseline skin blood flow in type 2 diabetes assessed with velocity-resolved quantitative laser Doppler flowmetry.

    Science.gov (United States)

    Fredriksson, Ingemar; Larsson, Marcus; Nyström, Fredrik H; Länne, Toste; Ostgren, Carl J; Strömberg, Tomas

    2010-07-01

    To compare the microcirculatory velocity distribution in type 2 diabetic patients and nondiabetic control subjects at baseline and after local heating. The skin blood flow response to local heating (44 degrees C for 20 min) was assessed in 28 diabetic patients and 29 control subjects using a new velocity-resolved quantitative laser Doppler flowmetry technique (qLDF). The qLDF estimates erythrocyte (RBC) perfusion (velocity x concentration), in a physiologically relevant unit (grams RBC per 100 g tissue x millimeters per second) in a fixed output volume, separated into three velocity regions: v 10 mm/s. The increased blood flow occurs in vessels with a velocity >1 mm/s. A significantly lower response in qLDF total perfusion was found in diabetic patients than in control subjects after heat provocation because of less high-velocity blood flow (v >10 mm/s). The RBC concentration in diabetic patients increased sevenfold for v between 1 and 10 mm/s, and 15-fold for v >10 mm/s, whereas no significant increase was found for v velocity increased from 0.94 to 7.3 mm/s in diabetic patients and from 0.83 to 9.7 mm/s in control subjects. The perfusion increase occurs in larger shunting vessels and not as an increase in capillary flow. Baseline diabetic patient data indicated a redistribution of flow to higher velocity regions, associated with longer duration of diabetes. A lower perfusion was associated with a higher BMI and a lower toe-to-brachial systolic blood pressure ratio.

  6. Quantification of resting myocardial blood flow velocity in normal humans using real-time contrast echocardiography. A feasibility study

    Science.gov (United States)

    Malm, Siri; Frigstad, Sigmund; Helland, Frode; Oye, Kjetil; Slordahl, Stig; Skjarpe, Terje

    2005-01-01

    Background Real-time myocardial contrast echocardiography (MCE) is a novel method for assessing myocardial perfusion. The aim of this study was to evaluate the feasibility of a very low-power real-time MCE for quantification of regional resting myocardial blood flow (MBF) velocity in normal human myocardium. Methods Twenty study subjects with normal left ventricular (LV) wall motion and normal coronary arteries, underwent low-power real-time MCE based on color-coded pulse inversion Doppler. Standard apical LV views were acquired during constant IV. infusion of SonoVue®. Following transient microbubble destruction, the contrast replenishment rate (β), reflecting MBF velocity, was derived by plotting signal intensity vs. time and fitting data to the exponential function; y (t) =A (1-e-β(t-t0)) + C. Results Quantification was feasible in 82%, 49% and 63% of four-chamber, two-chamber and apical long-axis view segments, respectively. The LAD (left anterior descending artery) and RCA (right coronary artery) territories could potentially be evaluated in most, but contrast detection in the LCx (left circumflex artery) bed was poor. Depending on localisation and which frames to be analysed, mean values of were 0.21–0.69 s-1, with higher values in medial than lateral, and in basal compared to apical regions of scan plane (p = 0.03 and p < 0.01). Higher β-values were obtained from end-diastole than end-systole (p < 0.001), values from all-frames analysis lying between. Conclusion Low-power real-time MCE did have the potential to give contrast enhancement for quantification of resting regional MBF velocity. However, the technique is difficult and subjected to several limitations. Significant variability in β suggests that this parameter is best suited for with-in patient changes, comparing values of stress studies to baseline. PMID:15958173

  7. Quantification of resting myocardial blood flow velocity in normal humans using real-time contrast echocardiography. A feasibility study

    Directory of Open Access Journals (Sweden)

    Slordahl Stig

    2005-06-01

    Full Text Available Abstract Background Real-time myocardial contrast echocardiography (MCE is a novel method for assessing myocardial perfusion. The aim of this study was to evaluate the feasibility of a very low-power real-time MCE for quantification of regional resting myocardial blood flow (MBF velocity in normal human myocardium. Methods Twenty study subjects with normal left ventricular (LV wall motion and normal coronary arteries, underwent low-power real-time MCE based on color-coded pulse inversion Doppler. Standard apical LV views were acquired during constant IV. infusion of SonoVue®. Following transient microbubble destruction, the contrast replenishment rate (β, reflecting MBF velocity, was derived by plotting signal intensity vs. time and fitting data to the exponential function; y (t =A (1-e-β(t-t0 + C. Results Quantification was feasible in 82%, 49% and 63% of four-chamber, two-chamber and apical long-axis view segments, respectively. The LAD (left anterior descending artery and RCA (right coronary artery territories could potentially be evaluated in most, but contrast detection in the LCx (left circumflex artery bed was poor. Depending on localisation and which frames to be analysed, mean values of were 0.21–0.69 s-1, with higher values in medial than lateral, and in basal compared to apical regions of scan plane (p = 0.03 and p Conclusion Low-power real-time MCE did have the potential to give contrast enhancement for quantification of resting regional MBF velocity. However, the technique is difficult and subjected to several limitations. Significant variability in β suggests that this parameter is best suited for with-in patient changes, comparing values of stress studies to baseline.

  8. CFD and laboratory analysis of axial cross-flow velocity in porous tube packed with differently structured static turbulence promoters

    Directory of Open Access Journals (Sweden)

    Gaspar Igor

    2015-01-01

    Full Text Available Computational fluid dynamics (CFD was used for modelling flow regime in a porous tube. This tube is an ultrafiltration membrane filter made from zirconium-oxide which is very effective in the separation of stable oil-in-water microemulsions, especially when the tube is filled with static mixer. The results of the CFD analysis were used in the preliminary optimisation of the static mixer’s geometry since it has significant effect the energy requirement of this advanced membrane technology. The self-developed static mixers were tested “in vitro” from the aspect of separation quality and process productivity as well to validate CFD results and to develop a cost effective, green method to recover unmanageable oily wastewaters for sustainable development. In this work the results of computational simulation of the fluid velocity and membrane separation experiments are discussed.

  9. Analytical solution for peristaltic flow of conducting nanofluids in an asymmetric channel with slip effect of velocity, temperature and concentration

    Directory of Open Access Journals (Sweden)

    S. Sreenadh

    2016-06-01

    Full Text Available The Peristaltic transport of conducting nanofluids under the effect of slip condition in an asymmetric channel is reported in the present work. The mathematical modelling has been carried out under long wavelength and low Reynolds number approximations. The analytical solutions are obtained for pressure rise, nanoparticle concentration, temperature distribution, velocity profiles and stream function. Influence of various parameters on the flow characteristics has been discussed with the help of graphs. The results showed that the pressure rise increases with increasing magnetic effect and decreases with increasing slip parameter. The effects of thermophoresis parameter and Brownian motion parameter on the nanoparticle concentration and temperature distribution are studied. It is observed that the pressure gradient increases with increasing slip parameter and magnetic effect. The trapping phenomenon for different parameters is presented.

  10. Differential effects of hyperventilation on cerebral blood flow velocity after tourniquet deflation during sevoflurane, isoflurane, or propofol anesthesia.

    Science.gov (United States)

    Hinohara, Hiroshi; Kadoi, Yuji; Ide, Masanobu; Kuroda, Masataka; Saito, Shigeru; Mizutani, Akio

    2010-08-01

    The purpose of this study was to compare the degree of increase in middle cerebral artery (MCA) blood flow velocity after tourniquet deflation when modulating hyperventilation during orthopedic surgery under sevoflurane, isoflurane, or propofol anesthesia. Twenty-four patients undergoing elective orthopedic surgery were randomly divided into sevoflurane, isoflurane, and propofol groups. Anesthesia was maintained with sevoflurane, isoflurane, or propofol administration with 33% oxygen and 67% nitrous oxide at anesthetic drug concentrations adequate to maintain bispectral values between 45 and 50. A 2.0-MHz transcranial Doppler probe was attached to the patient's head at the temporal window, and mean blood flow velocity in the MCA (V (mca)) was continuously measured. The extremity was exsanguinated with an Esmarch bandage, and the pneumatic tourniquet was inflated to a pressure of 450 mmHg. Arterial blood pressure, heart rate, V (mca) and arterial blood gases were measured every minute for 10 min after release of the tourniquet in all three groups. Immediately after tourniquet release, the patients' respiratory rates were increased to tightly maintain end-tidal carbon dioxide (PetCO(2)) at 35 mmHg. No change in partial pressure of carbon dioxide in arterial blood (PaCO(2)) was observed pre- and posttourniquet deflation in any of the three groups. Increase in V (mca) in the isoflurane group was greater than that in the other two groups after tourniquet deflation. In addition, during the study period, no difference in V (mca) after tourniquet deflation was observed between the propofol and sevoflurane groups. Hyperventilation could prevent an increase in V (mca) in the propofol and sevoflurane groups after tourniquet deflation. However, hyperventilation could not prevent an increase in V (mca) in the isoflurane group.

  11. Effects of 24-Week Aerobic and Resistance Training on Carotid Artery Intima-Media Thickness and Flow Velocity in Elderly Women with Sarcopenic Obesity.

    Science.gov (United States)

    Park, Jinkee; Kwon, Yoochan; Park, Hyuntea

    2017-11-01

    Sarcopenic obesity (SO) is closely associated with cardiovascular disease (CVD) in elderly women. Increases in body fat and decreases in muscle mass are closely associated with increased carotid intima-media thickness (CIMT). The aim of this study was to examine the influence of a 24-week aerobic and resistance training program on carotid parameters in SO. Fifty elderly women (74.1±6.1 years) with SO were randomly divided into an exercise group and a control group. The exercise group performed combined exercise over 24 weeks, consisting of resistance and aerobic training for 50-80 min, 5 times a week. Carotid variables were measured using B-mode ultrasound. The differences in the carotid variables and the relative changes between baseline and after 24 weeks were evaluated. In the analysis of variance (ANOVA) results, CIMT (p=0.013), systolic flow velocity (p=0.007), diastolic flow velocity (p=0.006), and wall shear rate (p=0.010) showed significant interactions. In paired t-test results of the exercise group, CIMT significantly decreased (p<0.01) and systolic flow velocity (p<0.01), diastolic flow velocity (p<0.001), and wall shear rate (p<0.05) significantly increased after 24 weeks. The 24-week combined exercise effectively decreased CIMT and increased carotid flow velocity and wall shear ratio. Therefore, combined exercise is thought to contribute to the improvement of the risk of CVD in elderly women with SO.

  12. An Integrated Instrumentation System for Velocity, Concentration and Mass Flow Rate Measurement of Solid Particles Based on Electrostatic and Capacitance Sensors

    Directory of Open Access Journals (Sweden)

    Jian Li

    2015-12-01

    Full Text Available The online and continuous measurement of velocity, concentration and mass flow rate of pneumatically conveyed solid particles for the high-efficiency utilization of energy and raw materials has become increasingly significant. In this paper, an integrated instrumentation system for the velocity, concentration and mass flow rate measurement of dense phase pneumatically conveyed solid particles based on electrostatic and capacitance sensorsis developed. The electrostatic sensors are used for particle mean velocity measurement in combination with the cross-correlation technique, while the capacitance sensor with helical surface-plate electrodes, which has relatively homogeneous sensitivity distribution, is employed for the measurement of particle concentration and its capacitance is measured by an electrostatic-immune AC-based circuit. The solid mass flow rate can be further calculated from the measured velocity and concentration. The developed instrumentation system for velocity and concentration measurement is verified and calibrated on a pulley rig and through static experiments, respectively. Finally the system is evaluated with glass beads on a gravity-fed rig. The experimental results demonstrate that the system is capable of the accurate solid mass flow rate measurement, and the relative error is within −3%–8% for glass bead mass flow rates ranging from 0.13 kg/s to 0.9 kg/s.

  13. TEGENA: Detailed experimental investigations of temperature and velocity distributions in rod bundle geometries with turbulent sodium flow

    International Nuclear Information System (INIS)

    Moeller, R.

    1989-02-01

    Precise knowledge of the velocity and temperature distributions is necessary in fuel element design (rod bundles with longitudinal flow). The detail codes required in the fine analysis of non-uniformly cooled bundle zones are presently at the stage of development. In order to verify these computer codes, the mean fluid temperatures and the related RMS values of the temperature fluctuations were measured in a heated bundle TEGENA, containing 4 rods arranged in one row (P/D = W/D = 1.147) with sodium cooling (Pr ≅ 0.005). The temperature distribution in the structures was determined as the necessary boundary condition for the temperature profiles in the fluid. The experiments were carried out with different types of heating (uniform load and load tilting) and the flow conditions were varied in the range from 4000 ≤ Re ≤ 76.000, 20 ≤ Pe ≤ 400. The essential process of thermal development took place under uniform load within a heated bundle length of about 100 hydraulic diameters. In the main measuring plane at the end of the heated zone, after 200 hydraulic diameters, the flow can be termed largely developed thermally. There, the temperature profiles measured in the fluid exhibit pronounced maxima in the narrowest gaps of the subchannels as well as pronounced minima in the centers of the subchannels at the unheated wall. In the zones of maximum temperature gradients the temperature fluctuations attain maximum and minimum values, respectively, at the points of disappearance of the temperature gradients. In all cases of load tilting investigated the flow at the end of the heated zone had not yet developed thermally. By inspection of all thermocouples in isothermal experiments performed at regular intervals, by redundant arrangement of the mobile probe thermocouples and by demonstration of the reproducibility of results of measurement the experiments have been validated satisfactorily. (orig./GL) [de

  14. TEGENA: Detailed experimental investigations of temperature and velocity distributions in rod bundle geometries with turbulent sodium flow

    International Nuclear Information System (INIS)

    Moeller, R.

    1989-12-01

    Precise knowlege of the velocity and temperature distributions is necessary in fuel element design (rod bundles with longitudinal flow). The detail codes required in the fine analysis of non-uniformly cooled bundle zones are presently at the stage of development. In order to verify these computer codes, the mean fluid temperatures and the related RMS values of the temperature fluctuations were measured in a heated bundle, TEGENA, containing four rods arranged in one row (P/D = W/D = 1.147) with sodium cooling (Pr≅0.005). The temperature distribution in the structures was determined as the necessary boundary condition for the temperature profiles in the fluid. The experiments were carried out with different types of heating (uniform load and flux tilting) and the flow conditions were varied in the ranges 4000≤Re≤76,000; 20≤Pe≤400. The essential processes of thermal development took place under uniform load within a heated bundle length of about 100 hydraulic diameters. In the main measuring plane at the end of the heated zone, after 200 hydraulic diameters, the flow can be termed largely developed thermally. There, the temperature profiles measured in the fluid exhibit pronounced maxima in the narrowest gaps of the subchannels as well as pronounced minima in the centers of the subchannels at the unheated wall. In the zones of maximum temperature gradients the temperature fluctuations attain maximum and minimum values, respectively, at the points of disappearance of the temperature gradients. In all cases of flux tilting investigated the flow at the end of the heated zone had not yet developed thermally. (orig.) [de

  15. Multiple-stressor effects on stream macroinvertebrate communities: A mesocosm experiment manipulating salinity, fine sediment and flow velocity.

    Science.gov (United States)

    Beermann, Arne J; Elbrecht, Vasco; Karnatz, Svenja; Ma, Li; Matthaei, Christoph D; Piggott, Jeremy J; Leese, Florian

    2018-01-01

    Stream ecosystems are impacted by multiple stressors worldwide. Recent studies have shown that the effects of multiple stressors are often complex and difficult to predict based on the effects of single stressors. More research is needed to understand stressor impacts on stream communities and to design appropriate counteractions. We carried out an outdoor mesocosm experiment to assess single and interactive multiple-stressor effects on stream macroinvertebrates in a setup with controlled application of three globally important stressors, namely, reduced stream flow velocity, deposition of fine sediment and increased chloride concentration in a full-factorial design. Each mesocosm comprised three compartments (channel substratum, leaf litter bag and drift net) that were individually analyzed and also compared. We identified 102,501 specimens in total (mainly to family level), 36.5% of which were found in the substratum, 60.6% in litter bags and 2.9% in the drift. Added fine sediment and reduced flow velocity had strong negative single-stressor effects on the abundances of EPT taxa, i.e. Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies), and a positive effect on chironomid abundances in the substratum. Increased salt concentration reduced abundances of Ephemeroptera. Chironomids migrated from litter bag to channel substratum when water velocity was reduced and Leptophlebiidae in the opposite direction when sediment was added. All three stressors caused higher drift propensities, especially added fine sediment. Both additive and complex multiple-stressor effects were common. A complex three-way interaction affected EPT richness in the substratum, demonstrating the need to evaluate higher-order interactions for more than two stressors. Our results add further evidence that multiple-stressor interactions, notably increased salinity with other stressors, affect a variety of invertebrate taxa across different habitats of stream communities

  16. Using transthoracic Doppler echocardiography to diagnose reduced coronary flow velocity reserve in the posterior descending coronary artery in children with elevated right ventricular pressure.

    Science.gov (United States)

    Shimada, Shunsuke; Harada, Kenji; Toyono, Manatomo; Tamura, Masamichi; Takada, Goro

    2007-12-01

    Advances in transthoracic Doppler echocardiography enable noninvasive measurements of coronary flow velocity and coronary flow velocity reserve (CFVR) in the posterior descending coronary artery (PD). To evaluate CFVR in the PD of children with elevated right ventricular (RV) pressure, 19 children with RV pressure overload and 13 age-matched controls with normal RV pressure were studied using transthoracic Doppler echocardiography. Average peak flow velocity (APV) was measured at rest and in hyperemic conditions (intravenous administration of adenosine of 0.16 mg.kg(-1).min(-1)). Compared with controls, the PD CFVR was significantly reduced in the patients with elevated RV pressure (1.87+/-0.42 vs 2.49+/-0.55, pvelocity.

  17. "Cognitive activity" monitored by non-invasive measurement of cerebral blood flow velocity and its application to the investigation of cerebral dominance.

    Science.gov (United States)

    Markus, H S; Boland, M

    1992-12-01

    We have developed a method of non-invasively detecting language lateralisation by measuring the increase in middle cerebral artery blood flow velocity occurring during a word association task, using transcranial Doppler ultrasonography. All exclusively right handed subjects (N = 12) showed a relative increase in left sided flow velocity during the task; mean rise was 4.04% on the left, and -0.03% on the right (p 5%) in left, compared with right, hemisphere flow velocity, and three showing only small differences between left and right sides, possibly reflecting bilateral language representation. This technique offers potential not only in studying patterns of cerebral dominance, but also in studying cognitive responses to other stimuli.

  18. Effectiveness of common fish screen materials for protecting lamprey ammocoetes—Influence of sweeping velocities and decreasing flows

    Science.gov (United States)

    Mesa, Matthew G.; Liedtke, Theresa L.; Weiland, Lisa K.; Christiansen, Helena E.

    2017-12-14

    In previous tests of the effectiveness of four common fish screen materials for excluding lamprey ammocoetes, we determined that woven wire (WW) allowed substantially more entrainment than perforated plate (PP), profile bar (PB), or Intralox (IL) material. These tests were simplistic because they used small vertically-oriented screens positioned perpendicular to the flow without a bypass or a sweeping velocity (SV). In the subsequent test discussed in this report, we exposed ammocoetes to much larger (2.5-m-wide) screen panels with flows up to 10 ft3 /s, a SV component, and a simulated bypass channel. The addition of a SV modestly improved protection of lamprey ammocoetes for all materials tested. A SV of 35 cm/s with an approach velocity (AV) of 12 cm/s, was able to provide protection for fish about 5–15 mm smaller than the protection provided by an AV of 12 cm/s without a SV component. The best-performing screen panels (PP, IL, and PB) provided nearly complete protection from entrainment for fish greater than 50-mm toal length, but the larger openings in the WW material only protected fish greater than 100-mm total length. Decreasing the AV and SV by 50 percent expanded the size range of protected lampreys by about 10–15 mm for those exposed to IL and WW screens, and it decreased the protective ability of PP screens by about 10 mm. Much of the improvement for IL and WW screens under the reduced flow conditions resulted from an increase in the number of lampreys swimming away from the screen. Fish of all sizes became impinged (that is, stuck on the screen surface for more than 1 s) on the screens, with the rate of impingement highest on PP (39– 72 percent) and lowest on WW (7–22 percent). Although impingements were common, injuries were rare, and 24-h post-test survival was greater than 99 percent. Our results refined the level of protection provided by these screen materials when both an AV and SV are present and confirmed our earlier recommendation that

  19. Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

    International Nuclear Information System (INIS)

    Russell, D. A.; Myra, J. R.; D'Ippolito, D. A.; LaBombard, B.; Hughes, J. W.

    2016-01-01

    Two-dimensional scrape-off layer turbulence (SOLT) code simulations are compared with an L-mode discharge on the Alcator C-Mod tokamak [M. Greenwald, et al., Phys. Plasmas 21, 110501 (2014)]. Density and temperature profiles for the simulations were obtained by smoothly fitting Thomson scattering and mirror Langmuir probe (MLP) data from the shot. Simulations differing in turbulence intensity were obtained by varying a dissipation parameter. Mean flow profiles and density fluctuation amplitudes are consistent with those measured by MLP in the experiment and with a Fourier space diagnostic designed to measure poloidal phase velocity. Blob velocities in the simulations were determined from the correlation function for density fluctuations, as in the analysis of gas-puff-imaging (GPI) blobs in the experiment. In the simulations, it was found that larger blobs moved poloidally with the ExB flow velocity, v E , in the near-SOL, while smaller fluctuations moved with the group velocity of the dominant linear (interchange) mode, v E + 1/2 v di , where v di is the ion diamagnetic drift velocity. Comparisons are made with the measured GPI correlation velocity for the discharge. The saturation mechanisms operative in the simulation of the discharge are also discussed. In conclusion, it is found that neither sheared flow nor pressure gradient modification can be excluded as saturation mechanisms

  20. Study on the Optimal Number of Transducers for Pipe Flow Rate Measurement Downstream of a Single Elbow Using the Ultrasonic Velocity Profile Method

    Directory of Open Access Journals (Sweden)

    Sanehiro Wada

    2012-01-01

    Full Text Available This paper presents a new estimation method to determine the optimal number of transducers using an Ultrasonic Velocity Profile (UVP for accurate flow rate measurement downstream of a single elbow. Since UVP can measure velocity profiles over a pipe diameter and calculate the flow rate by integrating these velocity profiles, it is also expected to obtain an accurate flow rate using multiple transducers under nondeveloped flow conditions formed downstream of an elbow. The new estimation method employs a wave number of velocity profile fluctuations along a circle on a pipe cross-section using Fast Fourier Transform (FFT. The optimal number of transducers is estimated based on the sampling theorem. To evaluate this method, a preliminary experiment and numerical simulations using Computational Fluid Dynamics (CFD are conducted. The evaluating regions of velocity profiles are located at 3 times of a pipe diameter ( for the experiment, and 1 and for the simulations downstream of an elbow, respectively. Reynolds numbers for the experiment and simulations are set at and , respectively. These results indicate the efficiency of this new method.

  1. Coronary flow velocity reserve in three major coronary arteries by transthoracic echocardiography for the functional assessment of coronary artery disease: a comparison with fractional flow reserve.

    Science.gov (United States)

    Wada, Teruaki; Hirata, Kumiko; Shiono, Yasutsugu; Orii, Makoto; Shimamura, Kunihiro; Ishibashi, Kohei; Tanimoto, Takashi; Yamano, Takashi; Ino, Yasushi; Kitabata, Hironori; Yamaguchi, Tomoyuki; Kubo, Takashi; Imanishi, Toshio; Akasaka, Takashi

    2014-04-01

    Coronary flow velocity reserve (CFVR) measurement in three major coronary arteries by transthoracic echocardiography is a promising and non-invasive method for detecting myocardial ischaemia. Its value when compared with fractional flow reserve (FFR) is unknown. Our aim was to determine the diagnostic accuracy of CFVR in three major coronary arteries for detecting ischaemia compared with FFR. This is a prospective study in 172 vessels of 140 patients with at least one ≥50% stenosis in a major epicardial artery as determined by visual assessment on computed tomography coronary angiography. We performed CFVR measurement by transthoracic echocardiography within 48 h before coronary angiography and FFR measurement. The cut-off value of CFVR was estimated by the receiver operating characteristic (ROC) curve based on that of FFR ≤0.75. The CFVR was 1.86 ± 0.36 in coronary arteries with FFR ≤0.75 (n = 79) and 2.54 ± 0.48 in those with FFR >0.75 (n = 93, P coronary artery with FFR ≤0.75 in three major vessels. In each vessel, the sensitivity and specificity were 85 and 78% (left anterior descending coronary artery), 94 and 83% (right coronary artery), and 88 and 88% (left circumflex coronary artery). CFVR was indirect proportional to FFR (r = 0.56, P coronary arteries.

  2. Coronary Flow Velocity Reserve Assessed by Transthoracic Doppler: The iPOWER Study: Factors Influencing Feasibility and Quality.

    Science.gov (United States)

    Michelsen, Marie M; Pena, Adam; Mygind, Naja D; Frestad, Daria; Gustafsson, Ida; Hansen, Henrik S; Kastrup, Jens; Bech, Jan; Høst, Nis; Prescott, Eva

    2016-07-01

    Coronary flow velocity reserve (CFVR) measured by transthoracic Doppler echocardiography is a noninvasive measure of microvascular function, but it has not achieved widespread use, mainly because of concerns of validity and feasibility. The aim of this study was to describe the feasibility and factors associated with the quality of CFVR obtained in a large prospective study of women suspected of having microvascular disease. Women with angina-like chest pain and no obstructive coronary artery disease on coronary angiography (<50% stenosis) were consecutively examined by transthoracic Doppler echocardiography of the left anterior descending coronary artery to measure CFVR (n = 947). Quality was evaluated on the basis of (1) identification of the left anterior descending coronary artery, (2) maintained probe position throughout the examination, (3) visibility and configuration of the left anterior descending coronary artery in two-dimensional color Doppler mode, and (4) gradual, consistent increases of characteristic, well-defined flow velocity curves in pulsed-wave mode. The mean age (SD) was 62.1 ± 9.7 years. On the basis of the evaluations, patients were divided into four groups according to quality score: nonfeasible (n = 28 [3%]), low quality (n = 80 [8%]), medium quality (n = 451 [48%]), and high quality (n = 388 [41%]). Quality score was associated with diabetes (P < .01), body mass index (P = .02), waist circumference (P = .05), nonsignificant atherosclerosis on coronary angiography (P = .03), and operator experience (P < .01). Low examination quality was associated with lower CFVR (P = .03), also after multivariate adjustment. Transthoracic Doppler echocardiographic measurement of CFVR is highly feasible and of good quality in experienced hands. However, CFVR is possibly underestimated when examination quality is low. Awareness of pitfalls and potential bias may improve the validity and interpretation of the measures obtained

  3. Investigation of the flow field around a propeller-rudder configuration: on-surface pressure measurements and velocity-pressure-phase-locked correlations

    OpenAIRE

    Felli, Mario; Falchi, Massimo; Pereira, Francisco

    2011-01-01

    The present paper deals with the problem of the propeller induced perturbation on the rudder . The study aims at providing insights on the key mechanisms governing the complex interaction between the propeller wake structures and the rudder. In this regard, a wide experimental activity that concerned PIV and LDV velocity measurements and wall-pressure-measurements on the two faces of the rudder was performed in a cavitation tunnel. The major flow features that distinguish the flow field aroun...

  4. Development of flow velocity measurement techniques in visible images. Improvement of particle image velocimetry techniques on image process

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, Nobuyuki; Nishimura, Motohiko; Kamide, Hideki; Hishida, Koichi [Japan Nuclear Cycle Development Inst., Oarai, Ibaraki (Japan). Oarai Engineering Center; Miyake, Yasuhiro [NDD Corporation, Tokyo (Japan)

    1999-10-01

    Noise reduction system was developed to improve applicability of Particle Image Velocimetry (PIV) to complicated configure bounded flows. For fast reactor safety and thermal hydraulic studies, experiments are performed in scale models which usually have rather complicated geometry and structures such as fuel subassemblies, heat exchangers, etc. The structures and stuck dusts on the view window of the models obscure the particle image. Thus the image except the moving particles can be regarded as a noise. In the present study, two noise reduction techniques are proposed. The one is the Time-averaged Light Intensity Subtraction method (TIS) which subtracts the time-averaged light intensity of each pixel in the sequential images from the each corresponding pixel. The other one is the Minimum Light Intensity Subtraction method (MIS) which subtracts the minimum light intensity of each pixel in the sequential images from the each corresponding pixel. Both methods are examined on their capabilities of noise reduction. As for the original 'bench mark' image, the image made from Large Eddy Simulation was used. To the bench mark image, noises are added which are referred as sample images. Both methods reduce the rate of vector with the error of more than one pixel from 90% to less than 5%. Also, more than 50% of the vectors have the error of less than 0.2 pixel. The analysis of uncertainty shows that these methods enhances the accuracy of vector measurement 3 {approx} 12 times if the image with noise were processed, and the MIS method has 1.1 {approx} 2.1 times accuracy compared to the TIS. Thus the present noise reduction methods are quite efficient to enhance the accuracy of flow velocity fields measured with particle images including structures and deposits on the view window. (author)

  5. Development of flow velocity measurement techniques in visible images. Improvement of particle image velocimetry techniques on image process

    International Nuclear Information System (INIS)

    Kimura, Nobuyuki; Nishimura, Motohiko; Kamide, Hideki; Hishida, Koichi

    1999-10-01

    Noise reduction system was developed to improve applicability of Particle Image Velocimetry (PIV) to complicated configure bounded flows. For fast reactor safety and thermal hydraulic studies, experiments are performed in scale models which usually have rather complicated geometry and structures such as fuel subassemblies, heat exchangers, etc. The structures and stuck dusts on the view window of the models obscure the particle image. Thus the image except the moving particles can be regarded as a noise. In the present study, two noise reduction techniques are proposed. The one is the Time-averaged Light Intensity Subtraction method (TIS) which subtracts the time-averaged light intensity of each pixel in the sequential images from the each corresponding pixel. The other one is the Minimum Light Intensity Subtraction method (MIS) which subtracts the minimum light intensity of each pixel in the sequential images from the each corresponding pixel. Both methods are examined on their capabilities of noise reduction. As for the original 'bench mark' image, the image made from Large Eddy Simulation was used. To the bench mark image, noises are added which are referred as sample images. Both methods reduce the rate of vector with the error of more than one pixel from 90% to less than 5%. Also, more than 50% of the vectors have the error of less than 0.2 pixel. The analysis of uncertainty shows that these methods enhances the accuracy of vector measurement 3 ∼ 12 times if the image with noise were processed, and the MIS method has 1.1 ∼ 2.1 times accuracy compared to the TIS. Thus the present noise reduction methods are quite efficient to enhance the accuracy of flow velocity fields measured with particle images including structures and deposits on the view window. (author)

  6. Effects of Vegetation Morphology on Mean Velocity and Turbulence Intensity under Oscillatory Flows and Their Implications for Sediment Transport in Benthic Zone

    Science.gov (United States)

    San Juan Blanco, J. E.; Veliz, G.; Tinoco, R. O.

    2016-12-01

    Aquatic vegetation modifies the flow by generating coherent structures and imposing resistance. Flow-vegetation interaction becomes function of individual plant morphology (stem and leaf shape and dimensions), canopy density, and spatial distribution of vegetation. We investigate the effect of plant morphology on turbulence intensity under oscillatory flows. By using a state-of-the-art 3D volumetric Particle Image Velocimetry system (3D-PIV), we characterize the mean velocity and turbulence statistics near and around submerged vegetation within an oscillatory tunnel. The U-shape oscillatory tunnel allows us to reproduce well-defined waves over a wide range of periods and amplitudes, whereas the 3D-PIV system allows us to obtain instantaneous velocity fields with high temporal frequency and spatial resolution in the vicinity of several types of vegetation. Our study of the three-dimensional velocity field provides further insight into the near-bed flow conditions and its interactions with the observed leaf-, stem- and canopy-scale flow structures, which in turn control resuspension and deposition of sediment within and around patches of vegetation. Since vegetation-induced turbulence drives essential transport mechanisms for ecosystem development, such as gas exchange, nutrient transport, bed and suspended sediment transport, among others, characterization of its dependence on plant morphology and flow conditions will improve our understanding of their role in aquatic environments and the impacts caused by human activities on coastal and tidal vegetated areas.

  7. Doppler study of middle cerebral artery blood flow velocity and cerebral autoregulation during a simulated ascent of Mount Everest.

    Science.gov (United States)

    Ter Minassian, A; Beydon, L; Ursino, M; Gardette, B; Gortan, C; Richalet, J P

    2001-01-01

    To explore cerebral hemodynamics in 8 healthy volunteers in a hypobaric chamber up to the altitude of Mount Everest after a progressive stepwise decompression to 8,848 m. Physiological, clinical, and transcranial Doppler data were collected after at least 3 days at 5,000, 6,000, and 7,000 m and within 4 hours of reaching 8,000 m and returning to sea level. Three subjects were excluded at 8,000 and 8,848 m because of acute neurological deficits. Heart rate increased; mean arterial pressure remained stable; PaO2 and PaCO2 decreased with altitude; hemoglobin (Hb) and hematocrit (Ht) increased; arterial O2 content decreased over 6,000 m; middle cerebral artery blood flow velocity (MCAv) increased only during acute exposure to 8,000 m; and the corresponding pulsatility (PI) and resistivity indices (RI) decreased over 5,000 m. PI and RI correlated with heart rate. The transient hyperemic response (THR) of MCAv to common carotid compression was depressed at 8,000 m. At 8,000 m, the increase in MCAv seemed to reflect the normal hemodynamic response to acute hypoxia. The decrease of THR at this altitude could be an indication of impaired cerebral autoregulation. The role of impaired cerebral autoregulation in the genesis of acute neurologic deficits, observed at 8,000 m and above in 3 subjects, remains speculative.

  8. A Highly Similar Mathematical Model for Cerebral Blood Flow Velocity in Geriatric Patients with Suspected Cerebrovascular Disease

    Science.gov (United States)

    Liu, Bo; Li, Qi; Wang, Jisheng; Xiang, Hu; Ge, Hong; Wang, Hui; Xie, Peng

    2015-10-01

    Cerebral blood flow velocity(CBFV) is an important parameter for study of cerebral hemodynamics. However, a simple and highly similar mathematical model has not yet been established for analyzing CBFV. To alleviate this issue, through TCD examination in 100 geriatric patients with suspected cerebrovascular disease (46 males and 54 females), we established a representative eighth-order Fourier function Vx(t) that simulates the CBFV. The measured TCD waveforms were compared to those derived from Vx(t), an illustrative Kolmogorov-Smirnov test was employed to determine the validity. The results showed that the TCD waves could been reconstructed for patients with different CBFVs by implementing their variable heart rates and the formulated maximum/minimum of Vx(t). Comparisons between derived and measured TCD waveforms suggest that the two waveforms are very similar. The results confirm that CBFV can be well-modeled through an eighth-order Fourier function. This function Vx(t) can be used extensively for a prospective study of cerebral hemodynamics in geriatric patients with suspected cerebrovascular disease.

  9. Oral Levosimendan Increases Cerebral Blood Flow Velocities in Patients with a History of Stroke or Transient Ischemic Attack: A Pilot Safety Study

    Directory of Open Access Journals (Sweden)

    Matti Kivikko, MD, PhD

    2015-12-01

    Conclusions: Oral levosimendan increases cerebral blood flow velocities and diminishes NT-pro-BNP levels in patients with earlier ischemic cerebrovascular event. Daily doses up to 1.0 mg were well tolerated, whereas the 2.0 mg dose level induced an increase in ventricular extrasystoles. ClinicalTrials.gov identifier: NCT00698763.

  10. A Dual Conductance Sensor for Simultaneous Measurement of Void Fraction and Structure Velocity of Downward Two-Phase Flow in a Slightly Inclined Pipe.

    Science.gov (United States)

    Lee, Yeon-Gun; Won, Woo-Youn; Lee, Bo-An; Kim, Sin

    2017-05-08

    In this study, a new and improved electrical conductance sensor is proposed for application not only to a horizontal pipe, but also an inclined one. The conductance sensor was designed to have a dual layer, each consisting of a three-electrode set to obtain two instantaneous conductance signals in turns, so that the area-averaged void fraction and structure velocity could be measured simultaneously. The optimum configuration of the electrodes was determined through numerical analysis, and the calibration curves for stratified and annular flow were obtained through a series of static experiments. The fabricated conductance sensor was applied to a 45 mm inner diameter U-shaped downward inclined pipe with an inclination angle of 3° under adiabatic air-water flow conditions. In the tests, the superficial velocities ranged from 0.1 to 3.0 m/s for water and from 0.1 to 18 m/s for air. The obtained mean void fraction and the structure velocity from the conductance sensor were validated against the measurement by the wire-mesh sensor and the cross-correlation technique for the visualized images, respectively. The results of the flow regime classification and the corresponding time series of the void fraction at a variety of flow velocities were also discussed.

  11. Phase-resolved optical coherence tomography and optical Doppler tomography for imaging blood flow in human skin with fast scanning speed and high velocity sensitivity

    NARCIS (Netherlands)

    Zhao, YH; Chen, ZP; Saxer, CE; Xiang, SH; de Boer, JF; Nelson, JS

    2000-01-01

    We have developed a novel phase-resolved optical coherence tomography (OCT) and optical Doppler tomography (ODT) system that uses phase information derived from a Hilbert transformation to image blood flow in human skin with fast scanning speed and high velocity sensitivity. Using the phase change

  12. Absence of an anatomical origin for altered ductus venosus flow velocity waveforms in first-trimester human fetuses with increased nuchal translucency

    NARCIS (Netherlands)

    Burger, Nicole B.; Matias, Alexandra; Kok, Evelien; de Groot, Christianne J M; Christoffels, Vincent M.; Bekker, Mireille N.; Haak, Monique C.

    2016-01-01

    Objective: To perform a morphological evaluation of the ductus venosus, heart and jugular lymphatic sac (JLS) in first-trimester human fetuses with normal and abnormal ductus venosus flow velocity waveforms (DV-FVWs) and normal and increased nuchal translucency (NT). Method: Postmortem examination

  13. A Dual Conductance Sensor for Simultaneous Measurement of Void Fraction and Structure Velocity of Downward Two-Phase Flow in a Slightly Inclined Pipe

    Directory of Open Access Journals (Sweden)

    Yeon-Gun Lee

    2017-05-01

    Full Text Available In this study, a new and improved electrical conductance sensor is proposed for application not only to a horizontal pipe, but also an inclined one. The conductance sensor was designed to have a dual layer, each consisting of a three-electrode set to obtain two instantaneous conductance signals in turns, so that the area-averaged void fraction and structure velocity could be measured simultaneously. The optimum configuration of the electrodes was determined through numerical analysis, and the calibration curves for stratified and annular flow were obtained through a series of static experiments. The fabricated conductance sensor was applied to a 45 mm inner diameter U-shaped downward inclined pipe with an inclination angle of 3° under adiabatic air-water flow conditions. In the tests, the superficial velocities ranged from 0.1 to 3.0 m/s for water and from 0.1 to 18 m/s for air. The obtained mean void fraction and the structure velocity from the conductance sensor were validated against the measurement by the wire-mesh sensor and the cross-correlation technique for the visualized images, respectively. The results of the flow regime classification and the corresponding time series of the void fraction at a variety of flow velocities were also discussed.

  14. Numerical calculation of gas and liquid velocities along a vertical flat plate immersed in turbulent tow-phase bubbly flow. Kihoryuchu ni okareta suichoku heiban mawari no ranryu kieki 2 soryu ni kansuru suchi kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Matsuura, A.; Nakamura, H. (Daido Inst. of Technology, Nagoya (Japan)); Hiraoka, S.; Tada, Y.; Kato, Y. (Nagoya Inst. of Tech. (Japan))

    1993-11-10

    A numerical calculation was made on the bubbly flow using the Prandtl's mixing length theory. The calculation results agreed well with the experimental results in the turbulent flow rather than in the laminar flow. The necessity of discussion on the turbulent flow analysis was clarified. It was elucidated that the experimental results could be explained sufficiently even by the simplest mixing model. The liquid phase velocity vector was aligned on the same direction when the bubbly flow length exceeded 1 cm, and little change took place in the velocity distribution shape. In the analysis of laminar flow, the velocity boundary layer was developed together with tie bubbly flow length, while in the analysis of turbulent flow, such change did not take place. The liquid phase velocity in the vicinity of the inlet had a velocity component which directed to the outside of the wall at the wall side. It was quite different from the analytical result of the laminar flow. The gas phase velocity vector behaved in the similar way to the liquid phase. The velocity direction at the periphery of the velocity distribution in the vicinity of tie inlet was toward the wall surface, and the inlet velocity was rapidly accelerated. 12 refs., 4 figs.

  15. Characterization of complex flow patterns in the ascending aorta in patients with aortic regurgitation using conventional phase-contrast velocity MRI.

    Science.gov (United States)

    Bech-Hanssen, Odd; Svensson, Frida; Polte, Christian L; Johnsson, Åse A; Gao, Sinsia A; Lagerstrand, Kerstin M

    2018-03-01

    Ascending aorta (AA) flow displacement (FD) is a surrogate for increased wall shear stress. We prospectively studied the flow profile in the AA in patients with aortic regurgitation (AR), to identify predictors of FD and investigate whether magnetic resonance imaging (MRI) phase-contrast flow rate curves (PC-FRC) contain quantitative information related to FD. Forty patients with chronic moderate (n = 14) or severe (n = 26) AR (21 (53%) with bicuspid aortic valve) and 22 controls were investigated. FD was determined from phase-contrast velocity profiles and defined as the distance between the center of the lumen and the "center of velocity" of the peak systolic forward flow or the peak diastolic negative flow, normalized to the lumen radius. Forward and backward volume flow was determined separately for systole and diastole. Seventy percent had systolic backward flow and 45% had diastolic forward flow in large areas of the vessel. AA dimension was an independent predictor of systolic FD while AA dimension and regurgitant volume were independent predictors of diastolic FD. Valve phenotype was not an independent predictor of systolic or diastolic FD. The linear relationships between systolic backward flow and systolic FD and diastolic forward flow and diastolic FD were strong (R = 0.77 and R = 0.76 respectively). Systolic backward flow and diastolic forward flow identified marked systolic and diastolic FD (≥0.35) with a positive likelihood ratio of 6.0 and 10.8, respectively. In conclusion, conventional PC-FRC data can detect and quantify FD in patients with AR suggesting the curves as a research and screening tool in larger patient populations.

  16. The Effects of Taekwondo Training on Peripheral Neuroplasticity-Related Growth Factors, Cerebral Blood Flow Velocity, and Cognitive Functions in Healthy Children: A Randomized Controlled Trial

    Directory of Open Access Journals (Sweden)

    Su-Youn Cho

    2017-04-01

    Full Text Available Although regular Taekwondo (TKD training has been reported to be effective for improving cognitive function in children, the mechanism underlying this improvement remains unclear. The purpose of the present study was to observe changes in neuroplasticity-related growth factors in the blood, assess cerebral blood flow velocity, and verify the resulting changes in children’s cognitive function after TKD training. Thirty healthy elementary school students were randomly assigned to control (n = 15 and TKD (n = 15 groups. The TKD training was conducted for 60 min at a rating of perceived exertion (RPE of 11–15, 5 times per week, for 16 weeks. Brain-derived neurotrophic factor (BDNF, vascular endothelial growth factor (VEGF, and insulin-like growth factor-1 (IGF-1 levels were measured by blood sampling before and after the training, and the cerebral blood flow velocities (peak systolic [MCAs], end diastolic [MCAd], mean cerebral blood flow velocities [MCAm], and pulsatility index [PI] of the middle cerebral artery (MCA were measured using Doppler ultrasonography. For cognitive function assessment, Stroop Color and Word Tests (Word, Color, and Color-Word were administered along with other measurements. The serum BDNF, VEGF, and IGF-1 levels and the Color-Word test scores among the sub-factors of the Stroop Color and Word Test scores were significantly higher in the TKD group after the intervention (p < 0.05. On the other hand, no statistically significant differences were found in any factors related to cerebral blood flow velocities, or in the Word test and Color test scores (p > 0.05. Thus, 16-week TKD training did not significantly affect cerebral blood flow velocities, but the training may have been effective in increasing children’s cognitive function by inducing an increase in the levels of neuroplasticity-related growth factors.

  17. Effects of viscous dissipation and slip velocity on two-dimensional and axisymmetric squeezing flow of Cu-water and Cu-kerosene nanofluids

    Directory of Open Access Journals (Sweden)

    Umar Khan

    2015-03-01

    Full Text Available Squeezing flow of nanofluids has been taken into account under the effects of viscous dissipation and velocity slip. Two types of base fluids are used to study the behavior of Copper nanoparticles between parallel plates. Nonlinear ordinary differential equations governing the flow are obtained by imposing similarity transformations on conservation laws. Resulting equations are solved by using an efficient analytical technique the variation of parameters method (VPM. Influences of nanoparticle concentration and different emerging parameters on flow profiles are presented graphically coupled with comprehensive discussions. A numerical solution is also sought for the sake of comparison. Effect of different parameters on skin friction coefficient and Nusselt number is also discussed.

  18. Linearized stationary incompressible flow around rotating and translating bodies: Asymptotic profile of the velocity gradient and decay estimate of the second derivatives of the velocity

    Czech Academy of Sciences Publication Activity Database

    Deuring, P.; Kračmar, S.; Nečasová, Šárka

    2012-01-01

    Roč. 252, č. 1 (2012), s. 459-476 ISSN 0022-0396 R&D Projects: GA AV ČR IAA100190804; GA ČR(CZ) GAP201/11/1304 Institutional research plan: CEZ:AV0Z10190503 Keywords : viscous incompressible flow * rotating body * rundamental solution * decay * asymptotic profile * Navier-Stokes system Subject RIV: BA - General Mathematics Impact factor: 1.480, year: 2012 http://www.sciencedirect.com/science/article/pii/S0022039611003573

  19. Linearized stationary incompressible flow around rotating and translating bodies: Asymptotic profile of the velocity gradient and decay estimate of the second derivatives of the velocity

    Czech Academy of Sciences Publication Activity Database

    Deuring, P.; Kračmar, S.; Nečasová, Šárka

    2012-01-01

    Roč. 252, č. 1 (2012), s. 459-476 ISSN 0022-0396 R&D Projects: GA AV ČR IAA100190804; GA ČR(CZ) GAP201/11/1304 Institutional research plan: CEZ:AV0Z10190503 Keywords : viscous incompressible flow * rotating body * rundamental solution * decay * asymptotic profile * Navier-Stokes system Subject RIV: BA - General Math ematics Impact factor: 1.480, year: 2012 http://www.sciencedirect.com/science/article/pii/S0022039611003573

  20. Abdominal aorta: characterisation of blood flow and measurement of its regional distribution by cine magnetic resonance phase-shift velocity mapping

    Energy Technology Data Exchange (ETDEWEB)

    Amanuma, M. [Dept. of Radiology, Saitama Medical School (Japan); Mohiaddin, R.H. [Magnetic Resonance Unit, Royal Brompton Hospital, London (United Kingdom); Hasegawa, M. [Dept. of Radiology, Saitama Medical School (Japan); Heshiki, A. [Dept. of Radiology, Saitama Medical School (Japan); Longmore, D.B. [Magnetic Resonance Unit, Royal Brompton Hospital, London (United Kingdom)

    1992-12-01

    Magnetic resonance phase-shift-induced velocity mapping is a powerful technique for measuring in vivo blood velocity and flow non-invasively. Using this method we examined dimensions, distensibility, blood flow and its regional distribution in the abdominal aorta in 10 normal volunteers. Data were acquired at three levels of the descending aorta. Thirty percent reduction in diastolic cross sectional area was observed in the caudal direction between these levels. Total blood flow (ml/min) in the abdominal aorta at the three sites was 4094{+-}1600, 2339{+-}910 and 1602{+-}549 respectively. Flows in the coeliac trunk, superior mesenteric artery and renal arteries were also calculated. The net flow in the abdominal aorta above the coeliac trunk was persistently forward, while there was considerable backflow (13% of total instantaneous flow) below the renal arteries during early diastole. Magnetic resonance imaging is a non-invasive technique for quantitative assessment of blood flow in the abdominal aorta and its main branches. (orig.)

  1. Systemic-to-pulmonary collateral flow in patients with palliated univentricular heart physiology: measurement using cardiovascular magnetic resonance 4D velocity acquisition

    Directory of Open Access Journals (Sweden)

    Valverde Israel

    2012-04-01

    Full Text Available Abstract Background Systemic-to-pulmonary collateral flow (SPCF may constitute a risk factor for increased morbidity and mortality in patients with single-ventricle physiology (SV. However, clinical research is limited by the complexity of multi-vessel two-dimensional (2D cardiovascular magnetic resonance (CMR flow measurements. We sought to validate four-dimensional (4D velocity acquisition sequence for concise quantification of SPCF and flow distribution in patients with SV. Methods 29 patients with SV physiology prospectively underwent CMR (1.5 T (n = 14 bidirectional cavopulmonary connection [BCPC], age 2.9 ± 1.3 years; and n = 15 Fontan, 14.4 ± 5.9 years and 20 healthy volunteers (age, 28.7 ± 13.1 years served as controls. A single whole-heart 4D velocity acquisition and five 2D flow acquisitions were performed in the aorta, superior/inferior caval veins, right/left pulmonary arteries to serve as gold-standard. The five 2D velocity acquisition measurements were compared with 4D velocity acquisition for validation of individual vessel flow quantification and time efficiency. The SPCF was calculated by evaluating the disparity between systemic (aortic minus caval vein flows and pulmonary flows (arterial and venour return. The pulmonary right to left and the systemic lower to upper body flow distribution were also calculated. Results The comparison between 4D velocity and 2D flow acquisitions showed good Bland-Altman agreement for all individual vessels (mean bias, 0.05±0.24 l/min/m2, calculated SPCF (−0.02±0.18 l/min/m2 and significantly shorter 4D velocity acquisition-time (12:34 min/17:28 min,p 2; Fontan 0.62±0.82 l/min/m2 and not in controls (0.01 + 0.16 l/min/m2, (3 inverse relation of right/left pulmonary artery perfusion and right/left SPCF (Pearson = −0.47,p = 0.01 and (4 upper to lower body flow distribution trend related to the weight (r = 0.742, p  Conclusions 4D

  2. The effect of adding CO2 to hypoxic inspired gas on cerebral blood flow velocity and breathing during incremental exercise.

    Directory of Open Access Journals (Sweden)

    Jui-Lin Fan

    Full Text Available Hypoxia increases the ventilatory response to exercise, which leads to hyperventilation-induced hypocapnia and subsequent reduction in cerebral blood flow (CBF. We studied the effects of adding CO2 to a hypoxic inspired gas on CBF during heavy exercise in an altitude naïve population. We hypothesized that augmented inspired CO2 and hypoxia would exert synergistic effects on increasing CBF during exercise, which would improve exercise capacity compared to hypocapnic hypoxia. We also examined the responsiveness of CO2 and O2 chemoreception on the regulation ventilation ([Formula: see text]E during incremental exercise. We measured middle cerebral artery velocity (MCAv; index of CBF, [Formula: see text]E, end-tidal PCO2, respiratory compensation threshold (RC and ventilatory response to exercise ([Formula: see text]E slope in ten healthy men during incremental cycling to exhaustion in normoxia and hypoxia (FIO2 = 0.10 with and without augmenting the fraction of inspired CO2 (FICO2. During exercise in normoxia, augmenting FICO2 elevated MCAv throughout exercise and lowered both RC onset and[Formula: see text]E slope below RC (P0.05. The [Formula: see text]E slope above RC was unchanged with either hypoxia or augmented FICO2 (P>0.05. We found augmenting FICO2 increased CBF during sub-maximal exercise in normoxia, but not in hypoxia, indicating that the 'normal' cerebrovascular response to hypercapnia is blunted during exercise in hypoxia, possibly due to an exhaustion of cerebral vasodilatory reserve. This finding may explain the lack of improvement of exercise capacity in hypoxia with augmented CO2. Our data further indicate that, during exercise below RC, chemoreception is responsive, while above RC the ventilatory response to CO2 is blunted.

  3. Three dimensional three component whole heart cardiovascular magnetic resonance velocity mapping: comparison of flow measurements from 3D and 2D acquisitions.

    Science.gov (United States)

    Brix, Lau; Ringgaard, Steffen; Rasmusson, Allan; Sørensen, Thomas Sangild; Kim, W Yong

    2009-02-20

    Two-dimensional, unidirectionally encoded, cardiovascular magnetic resonance (CMR) velocity mapping is an established technique for the quantification of blood flow in large vessels. However, it requires an operator to correctly align the planes of acquisition. If all three directional components of velocity are measured for each voxel of a 3D volume through the phases of the cardiac cycle, blood flow through any chosen plane can potentially be calculated retrospectively. The initial acquisition is then more time consuming but relatively operator independent. To compare the curves and volumes of flow derived from conventional 2D and comprehensive 3D flow acquisitions in a steady state flow model, and in vivo through planes transecting the ascending aorta and pulmonary trunk in 10 healthy volunteers. Using a 1.5 T Phillips Intera CMR system, 3D acquisitions used an anisotropic 3D segmented k-space phase contrast gradient echo sequence with a short EPI readout, with prospective ECG and diaphragm navigator gating. The 2D acquisitions used segmented k-space phase contrast with prospective ECG and diaphragm navigator gating. Quantitative flow analyses were performed retrospectively with dedicated software for both the in vivo and in vitro acquisitions. Analysis of in vitro data found the 3D technique to have overestimated the continuous flow rate by approximately 5% across the entire applied flow range. In vivo, the 2D and the 3D techniques yielded similar volumetric flow curves and measurements. Aortic flow: (mean +/- SD), 2D = 89.5 +/- 13.5 ml & 3D = 92.7 +/- 17.5 ml. Pulmonary flow: 2D = 98.8 +/- 18.4 ml & 3D = 94.9 +/- 19.0 ml). Each in vivo 3D acquisition took about 8 minutes or more. Flow measurements derived from the 3D and 2D acquisitions were comparable. Although time consuming, comprehensive 3D velocity acquisition could be relatively operator independent, and could potentially yield information on flow through several retrospectively chosen planes, for

  4. Examples of Vector Velocity Imaging

    DEFF Research Database (Denmark)

    Hansen, Peter M.; Pedersen, Mads M.; Hansen, Kristoffer L.

    2011-01-01

    To measure blood flow velocity in vessels with conventional ultrasound, the velocity is estimated along the direction of the emitted ultrasound wave. It is therefore impossible to obtain accurate information on blood flow velocity and direction, when the angle between blood flow and ultrasound wa...

  5. 4D cardiovascular magnetic resonance velocity mapping of alterations of right heart flow patterns and main pulmonary artery hemodynamics in tetralogy of Fallot

    Science.gov (United States)

    2012-01-01

    Background To assess changes in right heart flow and pulmonary artery hemodynamics in patients with repaired Tetralogy of Fallot (rTOF) we used whole heart, four dimensional (4D) velocity mapping (VM) cardiovascular magnetic resonance (CMR). Methods CMR studies were performed in 11 subjects with rTOF (5M/6F; 20.1 ± 12.4 years) and 10 normal volunteers (6M/4F; 34.2 ± 13.4 years) on clinical 1.5T and 3.0T MR scanners. 4D VM-CMR was performed using PC VIPR (Phase Contrast Vastly undersampled Isotropic Projection Reconstruction). Interactive streamline and particle trace visualizations of the superior and inferior vena cava (IVC and SVC, respectively), right atrium (RA), right ventricle (RV), and pulmonary artery (PA) were generated and reviewed by three experienced readers. Main PA net flow, retrograde flow, peak flow, time-to-peak flow, peak acceleration, resistance index and mean wall shear stress were quantified. Differences in flow patterns between the two groups were tested using Fisher's exact test. Differences in quantitative parameters were analyzed with the Kruskal-Wallis rank sum test. Results 4D VM-CMR was successfully performed in all volunteers and subjects with TOF. Right heart flow patterns in rTOF subjects were characterized by (a) greater SVC/IVC flow during diastole than systole, (b) increased vortical flow patterns in the RA and in the RV during diastole, and (c) increased helical or vortical flow features in the PA's. Differences in main PA retrograde flow, resistance index, peak flow, time-to-peak flow, peak acceleration and mean wall shear stress were statistically significant. Conclusions Whole heart 4D VM-CMR with PC VIPR enables detection of both normal and abnormal right heart flow patterns, which may allow for comprehensive studies to evaluate interdependencies of post-surgically altered geometries and hemodynamics. PMID:22313680

  6. Blood flow velocity is reduced in a tumor micro-dissemination in the visceral pleura in anesthetized open-chest rat lung.

    Science.gov (United States)

    Wang, Yan; Iguchi, Kesato; Ito, Hiromichi; Ookawa, Keiko; Kobayashi, Naohiro; Nakamura, Ryota; Goto, Yukinobu; Sakai, Mitsuaki; Ishikawa, Shigemi; Onizuka, Masataka

    2009-01-01

    Recently we developed a method to observe pulmonary micrometastasis by labeling cancer cells with green fluorescent protein (GFP). We applied the method for observation of micro-dissemination on the visceral pleura. RCN9 rat colon cancer cells labeled with GFP were injected into the pleural cavity of Fischer F344 rats. Six weeks after injection, the chest wall was resected under general anesthesia and the lung surface was observed by real-time confocal laser-scanning microscopy. Blood flow was visualized by intravenous injection of fluorescein isothiocyanate-labeled red blood cells, by which blood flow velocity was measured. Dissemination was created in 4 out of 5 rats. Fifteen sites of micro-dissemination were observed (mean diameter, 35.8+/-13.3 microm). Blood flow velocity was 114.1+/-26.1 microm/s in the tumor tissue and 183.4+/-35.0 microm/s out of the tumor tissue. We were able to observe pleural micro-dissemination. Blood flow velocity was significantly lower in the tumor tissue.

  7. Role of Slip Velocity in a Magneto-Micropolar Fluid Flow from a Radiative Surface with Variable Permeability: A Numerical Study

    Directory of Open Access Journals (Sweden)

    Sharma B.K.

    2017-08-01

    Full Text Available An analysis is presented to describe the hydromagnetic mixed convection flow of an electrically conducting micropolar fluid past a vertical plate through a porous medium with radiation and slip flow regime. A uniform magnetic field has been considered in the study which absorbs the micropolar fluid with a varying suction velocity and acts perpendicular to the porous surface of the above plate. The governing non-linear partial differential equations have been transformed into linear partial differential equations, which are solved numerically by applying the explicit finite difference method. The numerical results are presented graphically in the form of velocity, micro-rotation, concentration and temperature profiles, the skin-friction coefficient, the couple stress coefficient, the rate of heat and mass transfers at the wall for different material parameters.

  8. The effect of adding CO2 to hypoxic inspired gas on cerebral blood flow velocity and breathing during incremental exercise.

    Science.gov (United States)

    Fan, Jui-Lin; Kayser, Bengt

    2013-01-01

    Hypoxia increases the ventilatory response to exercise, which leads to hyperventilation-induced hypocapnia and subsequent reduction in cerebral blood flow (CBF). We studied the effects of adding CO2 to a hypoxic inspired gas on CBF during heavy exercise in an altitude naïve population. We hypothesized that augmented inspired CO2 and hypoxia would exert synergistic effects on increasing CBF during exercise, which would improve exercise capacity compared to hypocapnic hypoxia. We also examined the responsiveness of CO2 and O2 chemoreception on the regulation ventilation ([Formula: see text]E) during incremental exercise. We measured middle cerebral artery velocity (MCAv; index of CBF), [Formula: see text]E, end-tidal PCO2, respiratory compensation threshold (RC) and ventilatory response to exercise ([Formula: see text]E slope) in ten healthy men during incremental cycling to exhaustion in normoxia and hypoxia (FIO2 = 0.10) with and without augmenting the fraction of inspired CO2 (FICO2). During exercise in normoxia, augmenting FICO2 elevated MCAv throughout exercise and lowered both RC onset and[Formula: see text]E slope below RC (Phypoxia, MCAv and [Formula: see text]E slope below RC during exercise were elevated, while the onset of RC occurred at lower exercise intensity (Phypoxia increased [Formula: see text]E at RC (PE slope below RC (P>0.05). The [Formula: see text]E slope above RC was unchanged with either hypoxia or augmented FICO2 (P>0.05). We found augmenting FICO2 increased CBF during sub-maximal exercise in normoxia, but not in hypoxia, indicating that the 'normal' cerebrovascular response to hypercapnia is blunted during exercise in hypoxia, possibly due to an exhaustion of cerebral vasodilatory reserve. This finding may explain the lack of improvement of exercise capacity in hypoxia with augmented CO2. Our data further indicate that, during exercise below RC, chemoreception is responsive, while above RC the ventilatory response to CO2 is blunted.

  9. A prospective comparative study to assess the effect of maternal smoking at 37 weeks on Doppler flow velocity waveforms as well as foetal birth weight and placental weight.

    Science.gov (United States)

    Alptekin, Hüsnü; Işık, Hatice; Alptekin, Nazife; Kayhan, Fatih; Efe, Duran; Cengiz, Türkan; Gök, Emine

    2017-02-01

    Maternal smoking is known to have adverse effects on the foetus. This study aimed to evaluate the effects of maternal smoking during pregnancy on arterial blood flow velocities in the foetal-placental-maternal circulation, and the pathophysiological relationship with placental and foetal birth weight. A total of 148 singleton pregnancies in 59 smokers and 89 non-smoking controls were examined during the 37th week of gestation. Blood flow in the maternal uterine, foetal umbilical and middle cerebral arteries was analysed with Doppler ultrasonography. Statistically significant differences in Doppler waveforms were detected in the foetal umbilical artery (UmbA) (p  0.05). Both infant birthweight and placental weight were significantly decreased by maternal smoking (psmoking during pregnancy did not affect either maternal uterine or foetal middle cerebral arterial blood flow, but caused abnormal blood flow in the foetal UmbA.

  10. The Effects of Taekwondo Training on Peripheral Neuroplasticity-Related Growth Factors, Cerebral Blood Flow Velocity, and Cognitive Functions in Healthy Children: A Randomized Controlled Trial

    Science.gov (United States)

    Cho, Su-Youn; So, Wi-Young; Roh, Hee-Tae

    2017-01-01

    Although regular Taekwondo (TKD) training has been reported to be effective for improving cognitive function in children, the mechanism underlying this improvement remains unclear. The purpose of the present study was to observe changes in neuroplasticity-related growth factors in the blood, assess cerebral blood flow velocity, and verify the resulting changes in children’s cognitive function after TKD training. Thirty healthy elementary school students were randomly assigned to control (n = 15) and TKD (n = 15) groups. The TKD training was conducted for 60 min at a rating of perceived exertion (RPE) of 11–15, 5 times per week, for 16 weeks. Brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), and insulin-like growth factor-1 (IGF-1) levels were measured by blood sampling before and after the training, and the cerebral blood flow velocities (peak systolic [MCAs], end diastolic [MCAd], mean cerebral blood flow velocities [MCAm], and pulsatility index [PI]) of the middle cerebral artery (MCA) were measured using Doppler ultrasonography. For cognitive function assessment, Stroop Color and Word Tests (Word, Color, and Color-Word) were administered along with other measurements. The serum BDNF, VEGF, and IGF-1 levels and the Color-Word test scores among the sub-factors of the Stroop Color and Word Test scores were significantly higher in the TKD group after the intervention (p 0.05). Thus, 16-week TKD training did not significantly affect cerebral blood flow velocities, but the training may have been effective in increasing children’s cognitive function by inducing an increase in the levels of neuroplasticity-related growth factors. PMID:28441325

  11. Preliminary evidence for reduced preoperative cerebral blood flow velocity as a risk factor for cognitive decline three months after cardiac surgery: an extension study.

    Science.gov (United States)

    Messerotti Benvenuti, S; Zanatta, P; Valfrè, C; Polesel, E; Palomba, D

    2012-11-01

    This extension study investigated the association between preoperative cerebral blood flow (CBF) velocity and postoperative cognitive decline (POCD) at a three-month follow-up in patients who underwent cardiac surgery. Continuous transcranial Doppler ultrasound on both middle cerebral arteries (MCAs) was used preoperatively in 31 right-handed cardiac surgery patients at rest. Each patient performed a neuropsychological evaluation to assess cognitive performance before surgery, at discharge and at three-month follow-up. Patients with POCD at the three-month follow-up had a marginally significantly lower preoperative CBF velocity in the left MCA than patients without POCD. Moreover, the group with POCD had a significantly lower CBF velocity in the left than in the right MCA, whereas no difference between the left and right CBF velocity was found in the group without POCD. These preliminary findings suggest that reduced preoperative CBF velocity in the left MCA may represent an independent risk factor for cognitive decline in patients three months after surgery.

  12. SNR 2 core dynamics and shut-down signals in a protected loss-of-flow incident

    International Nuclear Information System (INIS)

    Kleefeldt, K.

    1982-01-01

    The dynamic behavior of a 1300 MWe Core during a loss-of-flow incident has been analyzed by use of the SAS3D code for a given pump coast down characteristic and constant core inlet temperature. Emphasis was placed on the questions: How fast and via which monitored parameters can the incident be recognized by the reactor protection system. What is the tolerable time span for the shut-down action without exceeding safety limits. Key prameters and limit values as well as conceivable reactivity feed-back effects are discussed. The result is, that three out of four choosen monitored parameters are capable of initiating a shut-down action in time. In addition, the amount of shut-down reactivity required for a successful scram was briefly investigated

  13. A High Ductal Flow Velocity Is Associated with Successful Pharmacological Closure of Patent Ductus Arteriosus in Infants 22–27 Weeks Gestational Age

    Directory of Open Access Journals (Sweden)

    Karl Wilhelm Olsson

    2012-01-01

    Full Text Available Objective. To identify factors affecting closure of patent ductus arteriosus (PDA in newborn infants born at 22–27 weeks gestational age (GA during pharmacological treatment with cyclooxygenase inhibitors. Method. Infants born at 22–27 weeks of GA between January 2006 and December 2009 who had been treated pharmacologically for PDA were identified retrospectively. Medical records were assessed for clinical, ventilatory, and outcome parameters. Echocardiographic examinations during treatment were reviewed. Results. Fifty-six infants were included in the study. Overall success rate of ductal closure with pharmacological treatment was 52%. Infants whose PDA was successfully closed had a higher GA (25+4 weeks versus 24+3 weeks; P=0.047, and a higher pretreatment left to right maximal ductal flow velocity (1.6 m/s versus 1.1 m/s; P=0.023. Correcting for GA, preeclampsia, antenatal steroids, and age at start of treatment, a higher maximal ductal flow velocity was still associated with successful ductal closure (OR 3.04; P=0.049. Conclusion. Maximal ductal flow velocity was independently associated with success of PDA treatment.

  14. Augmenting two-dimensional hydrodynamic simulations with measured velocity data to identify flow paths as a function of depth on Upper St. Clair River in the Great Lakes basin

    Science.gov (United States)

    Holtschlag, D.J.; Koschik, J.A.

    2005-01-01

    Upper St. Clair River, which receives outflow from Lake Huron, is characterized by flow velocities that exceed 7 feet per second and significant channel curvature that creates complex flow patterns downstream from the Blue Water Bridge in the Port Huron, Michigan, and Sarnia, Ontario, area. Discrepancies were detected between depth-averaged velocities previously simulated by a two-dimensional (2D) hydrodynamic model and surface velocities determined from drifting buoy deployments. A detailed ADCP (acoustic Doppler current profiler) survey was done on Upper St. Clair River during July 1–3, 2003, to help resolve these discrepancies. As part of this study, a refined finite-element mesh of the hydrodynamic model used to identify source areas to public water intakes was developed for Upper St. Clair River. In addition, a numerical procedure was used to account for radial accelerations, which cause secondary flow patterns near channel bends. The refined model was recalibrated to better reproduce local velocities measured in the ADCP survey. ADCP data also were used to help resolve the remaining discrepancies between simulated and measured velocities and to describe variations in velocity with depth. Velocity data from ADCP surveys have significant local variability, and statistical processing is needed to compute reliable point estimates. In this study, velocity innovations were computed for seven depth layers posited within the river as the differences between measured and simulated velocities. For each layer, the spatial correlation of velocity innovations was characterized by use of variogram analysis. Results were used with kriging to compute expected innovations within each layer at applicable model nodes. Expected innovations were added to simulated velocities to form integrated velocities, which were used with reverse particle tracking to identify the expected flow path near a sewage outfall as a function of flow depth. Expected particle paths generated by use

  15. Measurement of coronary flow response to cold pressor stress in asymptomatic women with cardiovascular risk factors using spiral velocity-encoded cine MRI at 3 Tesla

    Energy Technology Data Exchange (ETDEWEB)

    Maroules, Christopher D.; Peshock, Ronald M. (Dept. of Radiology, Univ. of Texas Southwestern Medical Center, Dallas, TX (United States)), e-mail: Ron.Peshock@UTSouthwestern.edu; Chang, Alice Y.; Kontak, Andrew (Dept. of Internal Medicine, Univ. of Texas Southwestern Medical Center, Dallas, TX (United States)); Dimitrov, Ivan; Kotys, Melanie (Dept. of Philips Medical Systems, Cleveland, OH (United States))

    2010-05-15

    Background: Coronary sinus (CS) flow in response to a provocative stress has been used as a surrogate measure of coronary flow reserve, and velocity-encoded cine (VEC) magnetic resonance imaging (MRI) is an established technique for measuring CS flow. In this study, the cold pressor test (CPT) was used to measure CS flow response because it elicits an endothelium-dependent coronary vasodilation that may afford greater sensitivity for detecting early changes in coronary endothelial function. Purpose: To investigate the feasibility and reproducibility of CS flow reactivity (CSFR) to CPT using spiral VEC MRI at 3 Tesla in a sample of asymptomatic women with cardiovascular risk factors. Material and Methods: Fourteen asymptomatic women (age 38 years +- 10) with cardiovascular risk factors were studied using 3D spiral VEC MRI of the CS at 3 T. The CPT was utilized as a provocative stress to measure changes in CS flow. CSFR to CPT was calculated from the ratio of CS flow during peak stress to baseline CS flow. Results: CPT induced a significant hemodynamic response as measured by a 45% increase in rate-pressure product (P<0.01). A significant increase in CS volume flow was also observed (baseline, 116 +- 26 ml/min; peak stress, 152 +- 34 ml/min, P=0.01). CSFR to CPT was 1.31 +- 0.20. Test-retest variability of CS volume flow was 5% at baseline and 6% during peak stress. Conclusion: Spiral CS VEC MRI at 3 T is a feasible and reproducible technique for measuring CS flow in asymptomatic women at risk for cardiovascular disease. Significant changes in CSFR to CPT are detectable, without demanding pharmacologic stress

  16. Assessment of normal flow patterns in the pulmonary circulation by using 4D magnetic resonance velocity mapping.

    Science.gov (United States)

    Bächler, Pablo; Pinochet, Natalia; Sotelo, Julio; Crelier, Gérard; Irarrazaval, Pablo; Tejos, Cristián; Uribe, Sergio

    2013-02-01

    The purpose of this study was to analyze flow patterns in the pulmonary circulation of healthy volunteers by using 4D flow magnetic resonance imaging. The study was approved by the local ethics committee and all subjects gave written informed consent. Eighteen volunteers underwent a 4D flow scan of the whole-heart. Two patients with congenital heart disease were also included to detect possible patterns of flow abnormalities (Patient 1: corrected transposition of great arteries (TGA); Patient 2: partial anomalous pulmonary venous return and atrial septal defect). To analyze flow patterns, 2D planes were placed on the main pulmonary artery (PA), left and right PA. Flow patterns were assessed manually by two independent viewers using vector fields, streamlines and particle traces, and semi-automatically by vorticity quantification. Two counter-rotating helices were found in the main PA of volunteers. Right-handed helical flow was detected in the right PA of 15 volunteers. Analysis of the helical flow by particles traces revealed that both helices contributed mainly to the flow in the right PA. In the patient with corrected TGA helical flow was not detected. Abnormal vortical flow was visualized in the main PA of patient 2, suggesting elevated mean PA pressure. Helical flow is normally present in the main PA and right PA. 4D flow is an excellent tool to evaluate noninvasively complex blood flow patterns in the pulmonary circulation. Knowledge of normal and abnormal flow patterns might help to evaluate patients with congenital heart disease adding functional information undetectable with other imaging modalities. Copyright © 2013 Elsevier Inc. All rights reserved.

  17. Basic study of intrinsic elastography: Relationship between tissue stiffness and propagation velocity of deformation induced by pulsatile flow

    Science.gov (United States)

    Nagaoka, Ryo; Iwasaki, Ryosuke; Arakawa, Mototaka; Kobayashi, Kazuto; Yoshizawa, Shin; Umemura, Shin-ichiro; Saijo, Yoshifumi

    2015-07-01

    We proposed an estimation method for a tissue stiffness from deformations induced by arterial pulsation, and named this proposed method intrinsic elastography (IE). In IE, assuming that the velocity of the deformation propagation in tissues is closely related to the stiffness, the propagation velocity (PV) was estimated by spatial compound ultrasound imaging with a high temporal resolution of 1 ms. However, the relationship between tissue stiffness and PV has not been revealed yet. In this study, the PV of the deformation induced by the pulsatile pump was measured by IE in three different poly(vinyl alcohol) (PVA) phantoms of different stiffnesses. The measured PV was compared with the shear wave velocity (SWV) measured by shear wave imaging (SWI). The measured PV has trends similar to the measured SWV. These results obtained by IE in a healthy male show the possibility that the mechanical properties of living tissues could be evaluated by IE.

  18. The Effect of Temperature and Air Velocity on Drying Kinetics of Pistachio Nuts during Roasting by using Hot Air Flow

    Directory of Open Access Journals (Sweden)

    A Dini

    2017-10-01

    Full Text Available Introduction Pistachio nut is one of the most delicious and nutritious nuts in the world and it is being used as a saltedand roasted product or as an ingredient in snacks, ice cream, desserts, etc. The purpose of roasting is to promote flavour and texture changes in nuts that ultimately increase the overall palatability of the product.Roasting involves a number of physico-chemical changes, including heat exchange, chemical reactions and drying. Knowledge of desorption kinetics is essential to predict the behavior of the material during roasting process and to design roaster equipment.The main aim of this research was to evaluate suitable models for predicting moisture ratio, the effect of air temperature and velocity on the drying kinetics of pistachio nuts and obtain the effective diffusivity coefficient and activation energy in the drying process during the roasting of pistachio nuts. Materials and Methods Dried Ahmadaghaei pistachio nuts were supplied from Kashefan Kavir company (Doraj co. in Rafsanjan. Pistachio nuts were soaked in 17% salt solution for 8 minute and roasting was investigated at air temperatures of 120,130, 145, 160 and 170 °C and air velocities of 0.6, 0.88, 1.3, 1.72 and 2 ms-1. Five semi-theoretical and two empirical kinetic models were fitted to drying experimental data using nonlinear regression analysis techniques in the Curve Expert 2.2 computer program. Results and Discussion Tow-way ANOVA indicated that temperature and hot air velocity significantly affected the drying process during roasting of shelled pistachio nuts. The higher roasting temperatures and air velocities resulted in the higher drying rates. During first 10 min of roasting at constant air velocity of 1.3 ms-1, 64.5%, 70.3%, 77.1%, 83.5%, 89.7% of the moisture were removed at roasting air temperatures of 120 °C, 130 °C, 145 °C, 160 °C, 170 °C, respectively. The high regression coefficients (R2>0.996 and low reduced chi-square (χ2, mean relative

  19. Microwave Ablation Using Four-Tine Antenna: Effects of Blood Flow Velocity, Vessel Location, and Total Displacement on Porous Hepatic Cancer Tissue

    Directory of Open Access Journals (Sweden)

    Montree Chaichanyut

    2016-01-01

    Full Text Available This research is concerned with microwave ablation analyses using a 2.45 GHz four-tine (4T antenna for hepatic cancer tissue. In the study, three-dimensional finite-element models were utilized to examine the tissue temperature distributions during and after MW ablation. A preliminary study was first carried out with regard to the specific absorption rates along the 4T antenna insertion depths and the temperature distributions inside the solid and porous liver models with either 3 cm-in-diameter tumor or 5 cm-in-diameter tumor. Based on the preliminary results, the porous models were further examined for the effect of varying blood flow velocities (0–200 cm/s with a 1 cm-in-diameter blood vessel next to the antenna and also for the effect of vessel-antenna locations (0, 0.8, and 1.3 cm with a constant blood flow velocity of 16.7 cm/s. All scenarios were simulated under temperature-controlled mode (90°C. The findings revealed that the blood flow velocity and vessel location influence the ablation effectiveness and that increased blood flow inhibits heat transfer to the vessel wall. At the nearest and farthest vessel-antenna locations (0 and 1.3 cm, approximately 90.3% and 99.55% of the cancer cells were eradicated except for the areas adjacent to the vessel. In addition, total tissue thermal displacement is 5.9 mm which is 6.59% of the total length of the overall model.

  20. An equation of mean velocity of flow in non uniform regime, its relationship with the dispersion phenomenon as time function and its application to study of water quality

    International Nuclear Information System (INIS)

    Constain Aragon, A.; Lemos Ruiz, R.

    2011-01-01

    It is very well known the basic equation of hydraulics discovered by Antoine de Chezy in 1769, which relates in a quadratic from the mean velocity of flow with the slope of energy line and the hydraulic radius, in a uniform regime. This equation has been the central axis of development of hydro metrics as science that faces the huge challenges of penetrating the knowledge of earths streams every time more contaminated. In virtue of that, its mathematical structure and the relationship with other related formulas have been carefully examined, despite the limitation due to constancy of velocity. Starting from chemical considerations rather than dynamic ones as was used to obtain chezys relationship it is possible to establish a second equation for mean velocity of fluid in a non uniform regime that corresponds to averaged movement of a solute poured to steam. This equation will go to relate in an accurate way several aspects hydraulics and mass transport, sight as a single thing, allowing a vital tool for a depth study of water contaminations. to arrive this equation it was reviewed the foundations of mass transport theory in flows, stating a time dependent nature for coefficient currently used in describing dispersion phenomena allowing to interpret properly certain inconsistencies detected long time ago in this theory. It is presented the detailed results of application of this new approach to a small steam and a larger river in Colombia. (Author) 23 refs.

  1. Azimuthal velocity profiles in Rayleigh-stable Taylor–Couette flow and implied axial angular momentum transport

    NARCIS (Netherlands)

    Nordsiek, F.; Huisman, Sander Gerard; van der Veen, Roeland; Sun, Chao; Lohse, Detlef; Lathrop, D.P.

    2015-01-01

    We present azimuthal velocity profiles measured in a Taylor–Couette apparatus, which has been used as a model of stellar and planetary accretion disks. The apparatus has a cylinder radius ratio of ${\\it\\eta}=0.716$η=0.716, an aspect ratio of ${\\it\\Gamma}=11.74$Γ=11.74, and the plates closing the

  2. A single laser all fibre based optical sensor and switching system and method for measuring velocity in atmospheric air flow

    DEFF Research Database (Denmark)

    2013-01-01

    A system for measuring a velocity of tracer particle motion in a fluid comprising at least one laser emitter configured to emit a continuous wave laser beam and a plur ality of optical devices being configured to alternately receive a laser beam, focusing the laser beam onto a same probe volume c...

  3. Efficient Optical Flow and Stereo Vision for Velocity Estimation and Obstacle Avoidance on an Autonomous Pocket Drone

    NARCIS (Netherlands)

    McGuire, K.N.; de Croon, G.C.H.E.; de Wagter, C.; Tuyls, Karl; Kappen, Hilbert

    Micro Aerial Vehicles (FOV) are very suitable for flying in indoor environments, but autonomous navigation is challenging due to their strict hardware limitations. This paper presents a highly efficient computer vision algorithm called Edge-FS for the determination of velocity and depth. It runs at

  4. Intracranial Blood-Flow Velocity and Pressure Measurements Using an Intra-Arterial Dual-Sensor Guidewire

    NARCIS (Netherlands)

    Ferns, S. P.; Schneiders, J. J.; Siebes, M.; van den Berg, R.; van Bavel, E. T.; Majoie, C. B.

    2010-01-01

    Hemodynamics is thought to play a role in the growth and rupture of intracranial aneurysms. In 4 patients, we obtained local pressure and BFV by using a dual-sensor pressure and Doppler velocity wire within and in vessels surrounding unruptured aneurysms. Local BFVs can serve as boundary conditions

  5. Effect of splitter plate on unsteady flows around a body of revolution at incidence

    Science.gov (United States)

    Degani, David

    1991-01-01

    Numerical solutions of the thin-layer approximation of the 3D Navier-Stokes equations are presented for flows around an ogive-cylinder body with and without a splitter plate. It is suggested that the presence of the splitter plate prevents the interaction between flows on either side of the symmetry plane. It is concluded that, as a result of the enforced symmetry, the antisymmetric mode of the convective instability near the apex of the body cannot be excited and, therefore, the vortices remain symmetric, staying low and parallel to the upper body surface. The antisymmetric mode of the absolute instability mechanism cannot be initiated, which suppresses the alternate shedding of vortices from the cylindrical portion of the body. High-frequency fluctuations of the shear layer are found to remain virtually unaffected by the presence of the splitter plate.

  6. CHANGES OF THE SOLAR MERIDIONAL VELOCITY PROFILE DURING CYCLE 23 EXPLAINED BY FLOWS TOWARD THE ACTIVITY BELTS

    International Nuclear Information System (INIS)

    Cameron, R. H.; Schuessler, M.

    2010-01-01

    The solar meridional flow is an important ingredient in Babcock-Leighton type models of the solar dynamo. Global variations of this flow have been suggested to explain the variations in the amplitudes and lengths of the activity cycles. Recently, cycle-related variations in the amplitude of the P 1 2 term in the Legendre decomposition of the observed meridional flow have been reported. The result is often interpreted in terms of an overall variation in the flow amplitude during the activity cycle. Using a semi-empirical model based upon the observed distribution of magnetic flux on the solar surface, we show that the reported variations of the P 1 2 term can be explained by the observed localized inflows into the active region belts. No variation of the overall meridional flow amplitude is required.

  7. Flows and particles with shear-free and expansion-free velocities in (bar-L sub n g)- and Weyl spaces

    CERN Document Server

    Manoff, S

    2002-01-01

    Conditions for the existence of flows with non-null shear-free and expansion-free velocities in spaces with affine connections and metrics are found. On their basis, generalized Weyl spaces with shear-free and expansion-free conformal Killing vectors as velocity vectors of spinless test particles moving in a Weyl space are considered. Necessary and sufficient conditions are found under which a free spinless test particle could move in spaces with affine connections and metrics on a curve described by means of an auto-parallel equation. In Weyl spaces with Weyl covector, constructed using a dilaton field, the dilaton field appears as a scaling factor for the rest mass density of the test particle.

  8. Improved optical flow velocity analysis in SO2 camera images of volcanic plumes - implications for emission-rate retrievals investigated at Mt Etna, Italy and Guallatiri, Chile

    Science.gov (United States)

    Gliß, Jonas; Stebel, Kerstin; Kylling, Arve; Sudbø, Aasmund

    2018-02-01

    Accurate gas velocity measurements in emission plumes are highly desirable for various atmospheric remote sensing applications. The imaging technique of UV SO2 cameras is commonly used to monitor SO2 emissions from volcanoes and anthropogenic sources (e.g. power plants, ships). The camera systems capture the emission plumes at high spatial and temporal resolution. This allows the gas velocities in the plume to be retrieved directly from the images. The latter can be measured at a pixel level using optical flow (OF) algorithms. This is particularly advantageous under turbulent plume conditions. However, OF algorithms intrinsically rely on contrast in the images and often fail to detect motion in low-contrast image areas. We present a new method to identify ill-constrained OF motion vectors and replace them using the local average velocity vector. The latter is derived based on histograms of the retrieved OF motion fields. The new method is applied to two example data sets recorded at Mt Etna (Italy) and Guallatiri (Chile). We show that in many cases, the uncorrected OF yields significantly underestimated SO2 emission rates. We further show that our proposed correction can account for this and that it significantly improves the reliability of optical-flow-based gas velocity retrievals. In the case of Mt Etna, the SO2 emissions of the north-eastern crater are investigated. The corrected SO2 emission rates range between 4.8 and 10.7 kg s-1 (average of 7.1 ± 1.3 kg s-1) and are in good agreement with previously reported values. For the Guallatiri data, the emissions of the central crater and a fumarolic field are investigated. The retrieved SO2 emission rates are between 0.5 and 2.9 kg s-1 (average of 1.3 ± 0.5 kg s-1) and provide the first report of SO2 emissions from this remotely located and inaccessible volcano.

  9. Effects of Port Shape on Steady Flow Characteristics in an SI Engine with Semi-Wedge Combustion Chamber (2) - Velocity Distribution (2)

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Inkyoung; Ohm, Inyong [Seoul Nat’l Univ. of Science and Technology, Seoul (Korea, Republic of)

    2017-02-15

    This study is the second investigation on the steady flow characteristics of an SI engine with a semi-edge combustion chamber as a function of the port shape with varying evaluation positions. For this purpose, the planar velocity profiles were measured from 1.75B, 1.75 times of bore position apart from the bottom of head, to 6.00B positions using particle – image velocimetry. The flow patterns were examined with both a straight and a helical port. The velocity profiles, streamlines, and centers of swirl were almost the same at the same valve lift regardless of the measuring position, which is quite different from the case of the pent-roof combustion chamber. All the eccentricity values of the straight port were out of distortion criterion 0.15 through the lifts and the position. However, the values of the helical port exceeded the distortion criterion by up to 4 mm lift, but decreased rapidly above the 3.00B position and the 5 mm lift. There always existed a relative offset effect in the evaluation of the swirl coefficient using the PIV method due to the difference of the ideal impulse swirl meter velocity profile assumption, except for the cylinder-center-base estimation that was below 4 mm of the straight port. Finally, it was concluded that taking the center as an evaluation basis and the assumption about the axial velocity profile did not have any qualitative effect on swirl evaluation, but affected the value owing to the detailed profile.

  10. The Dynamic Character of the Flow Over a 3.5 Caliber Tangent-Ogive Cylinder in Steady and Maneuvering States at High Incidence

    OpenAIRE

    Zeiger, Matthew D.

    2014-01-01

    Although complex, inconsistent and fickle, the time-averaged flow over a stationary slender forebody is generally well-understood. However, the nature of unsteady, time-varying flows over slender forebodies - whether due to the natural unsteadiness or forced maneuvering - is not well-understood. This body of work documents three experimental investigations into the unsteadiness of the flow over a 3.5 caliber tangent-ogive cylinder at high angles of incidence. The goal of the investigations...

  11. Characteristics of Air Core and Surface Velocity for Water Flow in a Vortex Sediment-Extraction Chamber Measured by Using Photo Images and PTV Technique.

    Science.gov (United States)

    Yao, Hou Chang; Chyan Deng, Jan; Chao, Hsu Yu; Chih Yuan, Yang

    2017-04-01

    A vortex sediment-extraction chamber, consisted of cylindrical chamber, inflow system, bottom orifice and overflow weir, is used to separate sediment from sediment-laden water flow. A tangential inflow is introduced into a cylindrical chamber with a bottom orifice; thus, a strong vortex flow is produced there. Under actions of gravity and centrifugal force, heavier sediment particles are forced to move towards the bottom orifice, and relatively clear water flows over through the top overflow weir. The flow field in the cylindrical chamber consists of forced vortex and free vortex. When the bottom orifice is opened during the sediment-extraction process, an air core appears and changes with different settings. In this study, the air core and water surface velocity in the cylindrical chamber were measured by using a photo image process and particle tracking velocimetry (PTV), as well as numerically simulated by using a commercial software, Flow-3D.Laboratory experiments were conducted in a vortex chamber, having height of 130 cm and diameter of 48 cm. Five kinds of bottom orifice size from 1.0 cm to 3.0 cm and four kinds of inflow water discharge from 1,300cm3/s to 1,700 cm3/s were used while the inflow pipe of 3 cm in diameter was kept the same for all experiments. The characteristics of the air core and water surface velocity, and the inflow and outflow ratios under different experimental arrangements were observed and discussed so as to provide a better design and application for a vortex sediment-extraction chamber in the future.

  12. A mechanical diagnosis of the ice flow around Dome C: Elmer/Ice 3D simulations constrained by measured surface velocities and radar isochrones.

    Science.gov (United States)

    Passalacqua, Olivier; Cavitte, Marie; Frezzotti, Massimo; Gagliardini, Olivier; Gillet-Chaulet, Fabien; Parrenin, Frédéric; Ritz, Catherine; Vittuari, Luca; Young, Duncan

    2017-04-01

    The Dome C region has been densely surveyed and studied for the last decades, in particular to describe the shape of the ice surface, the bedrock relief, the surface velocity, the age and fabric structure of the ice, and its vertical temperature profile. No comprehensive ice flow modelling constrained by all of these field data has been done so far in this region. In particular, the Dome C has recently been targetted as an oldest-ice area, so that we intend to take advantage of a 2016 airborne radar survey that revealed the deep radar isochrones south-west of Dome C, and provides unprecendented constraints for the ice flow description. The Stokes equations are solved with the Elmer/Ice finite element solver, on a 80x110 km2 3D domain, for three different values of the Glen exponent n (1, 3 and 4.5), and for different fabric profiles. The goal of this study is threefold. First, as the range of stress types (longitudinal, transverse, and vertical compression-only) are well covered around Dome C, the observed surface velocities should efficiently constrain the possible values of the rheological parameters (Glen exponent and fluidity), and the basal sliding. Then, we apply an anisotropic flow law to correctly model the age structure, observed on the top 4/5th of the ice thickness, so that we induce mechanically-correct ages for the basal layers. Finally, once the ice mechanics is obtained, we compare the modelled vertical velocity profiles with 1D synthetic profiles, to assess the validity conditions of 1D modelling approaches, which are much more flexible tools for ensemble simulations or inversions.

  13. Flow Velocity Water Temperature, and Conductivity in Shark River Slough, Everglades National Park, Florida: August 2001-June 2002

    National Research Council Canada - National Science Library

    Riscassi, Ami L; Schaffranek, Raymond W

    2003-01-01

    The data-collection effort described in this report is in support of the U.S. Geological Survey (USGS) Place-Based Studies project investigating "Forcing Effects on Flow Structure in Vegetated Wetland of the Everglades...

  14. Synchronized Measurements of Maximum Blood Flow Velocities in Carotid, Brachial and Femoral Arteries, and ECG in Human Posture Changes

    National Research Council Canada - National Science Library

    Hirao, Y

    2001-01-01

    ...., sitting to standing and standing to sitting) using an ultrasonic Doppler technique. The ultrasonic Doppler technique can measure the dynamics of blood flow in arteries that exist deep within the human body...

  15. The phosphodiesterase 5 inhibitor sildenafil has no effect on cerebral blood flow or blood velocity, but nevertheless induces headache in healthy subjects

    DEFF Research Database (Denmark)

    Kruuse, Christina; Thomsen, Lars Lykke; Jacobsen, Torsten Bjørn

    2002-01-01

    and headache induction. Ten healthy subjects were included in a double-blind, placebo-controlled crossover study where placebo or sildenafil 100 mg (highest therapeutic dose) were administered on two separate days. Blood velocity in the middle cerebral artery (Vmca) was recorded by transcranial Doppler......, and regional cerebral blood flow in the perfusion area of the middle cerebral artery (rCBFmca) was measured using single photon emission computed tomography and xenon inhalation. Radial and temporal artery diameters were studied using high-frequency ultrasound. Blood pressure and heart rate were recorded...

  16. Normal ranges and test-retest reproducibility of flow and velocity parameters in intracranial arteries measured with phase-contrast magnetic resonance imaging

    Energy Technology Data Exchange (ETDEWEB)

    Correia de Verdier, Maria; Wikstroem, Johan [Uppsala University Hospital, Department of Radiology, Uppsala University, Uppsala (Sweden)

    2016-05-15

    The purpose of the present study was to investigate normal ranges and test-retest reproducibility of phase-contrast MRI (PC-MRI)-measured flow and velocity parameters in intracranial arteries. Highest flow (HF), lowest flow (LF), peak systolic velocity (PSV), and end diastolic velocity (EDV) were measured at two dates in the anterior (ACA), middle (MCA), and posterior (PCA) cerebral arteries of 30 healthy volunteers using two-dimensional PC-MRI at 3 T. Least detectable difference (LDD) was calculated. In the left ACA, HF was (mean (range, LDD)) 126 ml/min (36-312, 59 %), LF 61 ml/min (0-156, 101 %), PSV 64 cm/s (32-141, 67 %), and EDV 35 cm/s (18-55, 42 %); in the right ACA, HF was 154 ml/min (42-246, 49 %), LF 77 ml/min (0-156, 131 %), PSV 75 cm/s (26-161, 82 %), and EDV 39 cm/s (7-59, 67 %). In the left MCA, HF was 235 ml/min (126-372, 35 %), LF 116 ml/min (42-186, 48 %), PSV 90 cm/s (55-183, 39 %), and EDV 46 cm/s (20-66, 28 %); in the right MCA, HF was 238 ml/min (162-342, 44 %), LF 120 ml/min (72-216, 48 %), PSV 88 cm/s (55-141, 35 %), and EDV 45 cm/s (26-67, 23 %). In the left PCA, HF was 108 ml/min (42-168, 54 %), LF 53 ml/min (18-108, 64 %), PSV 50 cm/s (24-77, 63 %), and EDV 28 cm/s (14-40, 45 %); in the right PCA, HF was 98 ml/min (30-162, 49 %), LF 49 ml/min (12-84, 55 %), PSV 47 cm/s (27-88, 59 %), and EDV 27 cm/s (16-41, 45 %). PC-MRI-measured flow and velocity parameters in the main intracranial arteries have large normal ranges. Reproducibility is highest in MCA. (orig.)

  17. The role of wind field induced flow velocities in destratification and hypoxia reduction at Meiling Bay of large shallow Lake Taihu, China.

    Science.gov (United States)

    Jalil, Abdul; Li, Yiping; Du, Wei; Wang, Wencai; Wang, Jianwei; Gao, Xiaomeng; Khan, Hafiz Osama Sarwar; Pan, Baozhu; Acharya, Kumud

    2018-01-01

    Wind induced flow velocity patterns and associated thermal destratification can drive to hypoxia reduction in large shallow lakes. The effects of wind induced hydrodynamic changes on destratification and hypoxia reduction were investigated at the Meiling bay (N 31° 22' 56.4″, E 120° 9' 38.3″) of Lake Taihu, China. Vertical flow velocity profile analysis showed surface flow velocities consistency with the wind field and lower flow velocity profiles were also consistent (but with delay response time) when the wind speed was higher than 6.2 m/s. Wind field and temperature found the control parameters for hypoxia reduction and for water quality conditions at the surface and bottom profiles of lake. The critical temperature for hypoxia reduction at the surface and the bottom profile was ≤24.1C° (below which hypoxic conditions were found reduced). Strong prevailing wind field (onshore wind directions ESE, SE, SSE and E, wind speed ranges of 2.4-9.1 m/s) reduced the temperature (22C° to 24.1C°) caused reduction of hypoxia at the near surface with a rise in water levels whereas, low to medium prevailing wind field did not supported destratification which increased temperature resulting in increased hypoxia. Non-prevailing wind directions (offshore) were not found supportive for the reduction of hypoxia in study area due to less variable wind field. Daytime wind field found more variable (as compared to night time) which increased the thermal destratification during daytime and found supportive for destratification and hypoxia reduction. The second order exponential correlation found between surface temperature and Chlorophyll-a (R 2 : 0.2858, Adjusted R-square: 0.2144 RMSE: 4.395), Dissolved Oxygen (R 2 : 0.596, Adjusted R-square: 0.5942, RMSE: 0.3042) concentrations. The findings of the present study reveal the driving mechanism of wind induced thermal destratification and hypoxic conditions, which may further help to evaluate the wind role in eutrophication

  18. Analysis of two-phase flow instability in vertical boiling channels I: development of a linear model for the inlet velocity perturbation

    International Nuclear Information System (INIS)

    Hwang, D.H.; Yoo, Y.J.; Kim, K.K.

    1998-08-01

    A linear model, named ALFS, is developed for the analysis of two-phase flow instabilities caused by density wave oscillation and flow excursion in a vertical boiling channel with constant pressure drop conditions. The ALFS code can take into account the effect of the phase velocity difference and the thermally non-equilibrium phenomena, and the neutral boundary of the two-phase flow instability was analyzed by D-partition method. Three representative two-phase flow models ( i.e. HEM, DEM, and DNEM) were examined to investigate the effects on the stability analysis. As the results, it reveals that HEM shows the most conservative prediction of heat flux at the onset of flow instability. three linear models, Ishiis DEM, Sahas DNEM, and ALFS model, were applied to Sahas experimental data of density wave oscillation, and as the result, the mean and standard deviation of the predicted-to-measured heat flux at the onset of instability were calculated as 0.93/0.162, 0.79/0.112, and 0.95/0.143, respectively. For the long test section, however, ALFS model tends to predict the heat fluxes about 30 % lower than the measured values. (author). 14 refs

  19. Four-year imaging follow-up of a homozygous familial hypercholesterolaemia patient: atherosclerosis ingravescence and coronary flow velocity reserve reduced gradually. Case report.

    Science.gov (United States)

    Jiang, Bo; Yang, Ya; Wang, Lvya; Gao, Feng; Jiao, Jian; Li, Rongjuan

    2015-09-01

    Homozygous familial hypercholesterolemia (HoFH) is a rare heredity disease in which severe cardiovascular atherosclerosis develops from birth due to severe low density lipoprotein-receptor (LDL-R) defects inherited from both heterozygouscarriers of FH (HeFH) parents. This case describes a HoFH patient who underwent medical imaging examination for 4 years over a course of treatment. In addition to the imaging techniques which demonstrated the development of cardiovascular atherosclerosis ingravescent, transthoracic Doppler echocardiography noninvasively and accurately detected the position of atherosclerotic calcifications and evaluated the hemodynamicsof the coronary flow. Analysis showed the patient had a significantly lower coronary flow velocity reserve due to plaques compromising coronary artery ostia.

  20. HOBOE (Head-of-Bed Optimization of Elevation) Study: association of higher angle with reduced cerebral blood flow velocity in acute ischemic stroke.

    Science.gov (United States)

    Hunter, Abigail Jade; Snodgrass, Suzanne J; Quain, Debbie; Parsons, Mark W; Levi, Christopher R

    2011-10-01

    Cerebral autoregulation can be impaired after ischemic stroke, with potential adverse effects on cerebral blood flow during early rehabilitation. The objective of this study was to assess changes in cerebral blood flow velocity with orthostatic variation at 24 hours after stroke. This investigation was an observational study comparing mean flow velocities (MFVs) at 30, 15, and 0 degrees of elevation of the head of the bed (HOB). Eight participants underwent bilateral middle cerebral artery (MCA) transcranial Doppler monitoring during orthostatic variation at 24 hours after ischemic stroke. Computed tomography angiography separated participants into recanalized (artery completely reopened) and incompletely recanalized groups. Friedman tests were used to determine MFVs at the various HOB angles. Mann-Whitney U tests were used to compare the change in MFV (from 30° to 0°) between groups and between hemispheres within groups. For stroke-affected MCAs in the incompletely recanalized group, MFVs differed at the various HOB angles (30°: median MFV=51.5 cm/s, interquartile range [IQR]=33.0 to 103.8; 15°: median MFV=55.5 cm/s, IQR=34.0 to 117.5; 0°: median MFV=85.0 cm/s, IQR=58.8 to 127.0); there were no significant differences for other MCAs. For stroke-affected MCAs in the incompletely recanalized group, MFVs increased with a change in the HOB angle from 30 degrees to 0 degrees by a median of 26.0 cm/s (IQR=21.3 to 35.3); there were no significant changes in the recanalized group (-3.5 cm/s, IQR=-12.3 to 0.8). The changes in MFV with a change in the HOB angle from 30 degrees to 0 degrees differed between hemispheres in the incompletely recanalized group but not in the recanalized group. Generalizability was limited by sample size. The incompletely recanalized group showed changes in MFVs at various HOB angles, suggesting that cerebral blood flow in this group may be sensitive to orthostatic variation, whereas the recanalized group maintained stable blood flow

  1. Local topology via the invariants of the velocity gradient tensor within vortex clusters and intense Reynolds stress structures in turbulent channel flow

    Science.gov (United States)

    Buchner, Abel-John; Lozano-Durán, Adrián; Kitsios, Vassili; Atkinson, Callum; Soria, Julio

    2016-04-01

    Previous works have shown that momentum transfer in the wall-normal direction within turbulent wall-bounded flows occurs primarily within coherent structures defined by regions of intense Reynolds stress [1]. Such structures may be classified into wall-attached and wall-detached structures with the latter being typically weak, small-scale, and isotropically oriented, while the former are larger and carry most of the Reynolds stresses. The mean velocity fluctuation within each structure may also be used to separate structures by their dynamic properties. This study aims to extract information regarding the scales, kinematics and dynamics of these structures within the topological framework of the invariants of the velocity gradient tensor (VGT). The local topological characteristics of these intense Reynolds stress structures are compared to the topological characteristics of vortex clusters defined by the discriminant of the velocity gradient tensor. The alignment of vorticity with the principal strain directions within these structures is also determined, and the implications of these findings are discussed.

  2. Velocity and turbulence measurements of oil-water flow in horizontal and slightly inclined pipes using PIV

    OpenAIRE

    Kumara, W.A.S.; Halvorsen, Britt; Melaaen, Morten Christian

    2009-01-01

    Oil-water flows in horizontal and slightly inclined pipes are investigated using Particle Image Velocimetry (PIV). PIV offers a powerful non-invasive tool to study such flow fields. The experiments are conducted in a 15 m long, 56 mm diameter, inclinable steel pipe using Exxsol D60 oil (viscosity 1.64 mPa s, density 790 kg/m3) and water (viscosity 1.0 mPa s, density 996 kg/m3) as test fluids. The test pipe inclination is changed in the range from 5° upward to 5° downward. The experiments are ...

  3. [Efficacy of Modified Acupuncture Method at Renying (ST 9) for Patients with Cervical Spondylosis of Vertebral Artery Type and Its Impact on Velocity of Cervical Blood Flow].

    Science.gov (United States)

    Gui, Xing-Hua; Ma, Chao-Yang; Tang, Lei; Wan, Wen-Jun; Wang, Yan-Fu; Xu, Fen; Zhao, Shun-Yu

    2017-04-25

    To observe the clinical efficacy of modified acupuncture at Renying point (ST 9) for patients with cervical spondylosis of vertebral artery type and its influence on velocity of cervical blood flow. Fifty-nine cases of vertebral artery type cervical spondylosis were randomly divided into control group ( n =30) and treatment group ( n =29). Both groups were acupunctured at ST 9, with routine acupuncture technique used in the control group and modified technique in the treatment group, respectively. All cases received two courses of treatment, each course covered consecutive 6 once-per-day treatments. Before and after treatment, transcranial Doppler (TCD) was used to measure the systolic peak blood flow velocity (Vs) of left vertebral artery (LVA), right vertebral artery (RVA) and basilar artery (BA), and the scores of "cervical vertigo symptoms and functional assessment scale" (CVSFAS) were also assessed, separately. CVSFAS scoring, Vs of LVA, RVA and BA after treatment showed significant improvement compared with those before treatment ( P spondylosis of vertebral artery type via increasing the Vs of vertebral-basilar artery, improving the local blood circulation and relieving pain.

  4. Transthoracic Doppler assessment of coronary flow velocity reserve in children with Kawasaki disease: comparison with coronary angiography and thallium-201 imaging.

    Science.gov (United States)

    Hiraishi, Satoshi; Hirota, Hamao; Horiguchi, Yasunori; Takeda, Nobuhiro; Fujino, Nobuyuki; Ogawa, Natsuko; Nakahata, Yayoi

    2002-11-20

    The purpose of this study was to determine the feasibility of coronary flow velocity reserve (CFVR) measurement by transthoracic Doppler echocardiography (TTDE) in children with Kawasaki disease (KD). Doppler-derived CFVR is a reliable marker predicting the presence of myocardial ischemia. We studied 49 patients (median age 11 years) with KD. The CFVR was calculated as the ratio of hyperemic to basal peak (peak CFVR) and mean (mean CFVR) diastolic flow velocities in the posterior descending coronary artery (PD) and left anterior descending coronary artery (LAD). The CFVR measurements by TTDE were compared with the results of coronary angiography, thallium-201 (Tl-201) single-photon emission computed tomography (SPECT), and intracoronary Doppler study. The CFVR measurements by TTDE were obtained in 92 (94%) of 98 vessels of the PD and LAD in 49 study patients. Both peak and mean CFVRs for 21 stenotic vessels were significantly smaller than those for 35 normal vessels and for 20 vessels with aneurysmal lesions (p children with KD.

  5. Real-time algorithm for the measurement of liquid metal coolant flow velocity with correlated thermal signals

    International Nuclear Information System (INIS)

    Moazzeni, Taleb; Jiang, Yingtao; Ma, Jian; Li, Ning

    2009-01-01

    One flow meter was developed especially for the environment of high irradiation, pressure, and temperature. The transit time of natural random temperature fluctuation in process, for example nuclear reactor, can be obtained based on the cross-correlation method, which has already been shown that it is capable in situations where no other flow meter can be used. Thereby, the flow rate can be derived in pipe flow if the area of cross-section is known. In practice, the evaluation of the integrals over the measurement time in cross-correlation method will lead errors caused by peak detection from flat cross correlation coefficient distribution or additional peaks. One Auto-Adaptive Impulse Response Function estimation is introduced and significantly narrower peak will be obtained. Fiber optic sensors are advantageous for temperature measurements in the reactor pressure vessels. However, the corrosive coolant (as liquid lead/lead alloy or molten salt coolant) is a barrier of the optic sensor in such application. Thermocouple with grounded stainless steel shielding material would have same life time with structure material in reactor, although thermocouple has relatively slow response. The degradation due to corrosion/erosion will not introduce measurement error or necessary calibration, because only the correlation between signals is taken into consideration during measurements. Experiments conducted in a testing hydraulic facility approved the considerable improvement of accuracy by this new algorithm using thermocouple temperature sensors. (author)

  6. A simple electrochemical methodology for evaluation of the velocity of electroosmotic flow at the tip of polarized microcapillary

    Czech Academy of Sciences Publication Activity Database

    Silver, Barry Richard; Holub, Karel; Mareček, Vladimír

    2015-01-01

    Roč. 156, FEB 2015 (2015), s. 316-320 ISSN 0013-4686 R&D Projects: GA ČR GA13-04630S Institutional support: RVO:61388955 Keywords : ion transport * electroosmotic flow * AC impendance Subject RIV: CG - Electrochemistry Impact factor: 4.803, year: 2015

  7. Accuracy and precision of MR velocity mapping in measurement of stenotic cross-sectional area, flow rate, and pressure gradient

    DEFF Research Database (Denmark)

    Søndergaard, L; Ståhlberg, F; Thomsen, C

    1993-01-01

    jet. Besides determination of the stenotic cross-sectional area and flow rate, the pressure gradient was calculated with the modified Bernoulli equation and compared with manometer measurements. Cross-sectional areas were measured with an accuracy of > or = 76%, a precision of > or = 91%, and an error...

  8. Improved assessment of functional severity of coronary artery stenosis by analysis of combined intracoronary pressure and flow velocity signals

    NARCIS (Netherlands)

    Nolte, F.

    2014-01-01

    Coronary artery disease (CAD) accounts for almost 2 million deaths per year within the EU. CAD is often characterized by focal narrowing of epicardial arteries, limiting coronary arterial flow and myocardial perfusion. Treatment of critical lesions by percutaneous coronary intervention (PCI) can be

  9. Influence of immune-mediated hemolytic anemia on flow velocities in the portal vein and caudal vena cava measured by use of pulsed-wave Doppler ultrasonography in dogs.

    Science.gov (United States)

    Smith, Rachel Policelli; Koenigshof, Amy M; Smith, Daniel J; Strom, Phillip R; Nelson, Nathan C

    2018-05-01

    OBJECTIVE To compare blood flow velocities of the portal vein (PV) and caudal vena cava (CVC) measured by use of pulsed-wave Doppler ultrasonography in clinically normal dogs and dogs with primary immune-mediated hemolytic anemia (IMHA). ANIMALS 11 client-owned dogs admitted to a veterinary teaching hospital for management of primary IMHA and 21 staff- or student-owned clinically normal dogs. PROCEDURES Flow velocities in the PV and CVC at the porta hepatis were evaluated in conscious unsedated dogs with concurrent ECG monitoring; evaluations were performed before dogs with IMHA received heparin or blood transfusions. Three measurements of peak velocity at end expiration were obtained for each vessel, and the mean was calculated. Results were compared between IMHA and control groups. RESULTS Mean ± SD blood flow velocity in the CVC differed between control (63.0 ± 18.6 cm/s) and IMHA (104 ± 36.9 cm/s) groups. Variance in dogs with IMHA was significantly greater than that for the clinically normal dogs. No significant difference in blood flow velocity in the PV was detected between IMHA and control dogs. CONCLUSIONS AND CLINICAL RELEVANCE Higher blood flow velocities were detected by use of pulsed-wave Doppler ultrasonography in the CVC of dogs with naturally occurring IMHA and may be used to predict anemia in patients suspected of having IMHA.

  10. Wave propagation and group velocity

    CERN Document Server

    Brillouin, Léon

    1960-01-01

    Wave Propagation and Group Velocity contains papers on group velocity which were published during the First World War and are missing in many libraries. It introduces three different definitions of velocities: the group velocity of Lord Rayleigh, the signal velocity of Sommerfeld, and the velocity of energy transfer, which yields the rate of energy flow through a continuous wave and is strongly related to the characteristic impedance. These three velocities are identical for nonabsorbing media, but they differ considerably in an absorption band. Some examples are discussed in the last chapter

  11. Improved optical flow velocity analysis in SO2 camera images of volcanic plumes – implications for emission-rate retrievals investigated at Mt Etna, Italy and Guallatiri, Chile

    Directory of Open Access Journals (Sweden)

    J. Gliß

    2018-02-01

    Full Text Available Accurate gas velocity measurements in emission plumes are highly desirable for various atmospheric remote sensing applications. The imaging technique of UV SO2 cameras is commonly used to monitor SO2 emissions from volcanoes and anthropogenic sources (e.g. power plants, ships. The camera systems capture the emission plumes at high spatial and temporal resolution. This allows the gas velocities in the plume to be retrieved directly from the images. The latter can be measured at a pixel level using optical flow (OF algorithms. This is particularly advantageous under turbulent plume conditions. However, OF algorithms intrinsically rely on contrast in the images and often fail to detect motion in low-contrast image areas. We present a new method to identify ill-constrained OF motion vectors and replace them using the local average velocity vector. The latter is derived based on histograms of the retrieved OF motion fields. The new method is applied to two example data sets recorded at Mt Etna (Italy and Guallatiri (Chile. We show that in many cases, the uncorrected OF yields significantly underestimated SO2 emission rates. We further show that our proposed correction can account for this and that it significantly improves the reliability of optical-flow-based gas velocity retrievals. In the case of Mt Etna, the SO2 emissions of the north-eastern crater are investigated. The corrected SO2 emission rates range between 4.8 and 10.7 kg s−1 (average of 7.1  ±  1.3 kg s−1 and are in good agreement with previously reported values. For the Guallatiri data, the emissions of the central crater and a fumarolic field are investigated. The retrieved SO2 emission rates are between 0.5 and 2.9 kg s−1 (average of 1.3  ±  0.5 kg s−1 and provide the first report of SO2 emissions from this remotely located and inaccessible volcano.

  12. The Prescribed Velocity Method

    DEFF Research Database (Denmark)

    Nielsen, Peter Vilhelm

    The- velocity level in a room ventilated by jet ventilation is strongly influenced by the supply conditions. The momentum flow in the supply jets controls the air movement in the room and, therefore, it is very important that the inlet conditions and the numerical method can generate a satisfactory...... description of this momentum flow. The Prescribed Velocity Method is a practical method for the description of an Air Terminal Device which will save grid points close to the opening and ensure the right level of the momentum flow....

  13. Investigations of Particle Velocities in a Slurry Pump Using PIV. Part 1; The Tongue and Adjacent Channel Flow

    Science.gov (United States)

    Kadambi, Jaikrishnan R.; Charoenngam, Pathom; Subramanian, Amirthaganesh; Wernet, Mark P.; Sankovic, John M.; Addie, Graeme; Courtwright, Robert

    2004-01-01

    Transport of solid-liquid slurries in pipeline transport over short and medium distances is very important in many industries, including mining related processes. The particle image velocimetry technique was successfully utilized to investigate the velocities and kinetic energy fluctuations of slurry particles at the tongue region of an optically-clear centrifugal pump. The experiments were conducted using 500 micron glass beads at volumetric Concentrations of 2.5% and 5% and at pump speeds of 725 rpm and 1000 rpm. The fluctuation kinetic energy increased approximately 200% to 500% as the pump speed was increased from 725 rpm to IO00 rpm. The directional impingement mechanism is more significant at the pressure side of the blade, tongue and the casing. This mechanism becomes more important as the speed increases. This suggests that the impeller; tongue and the casing of the slurry pump can wear out quickly, especially with an increase in speed. In this paper the emphasis is on the tongue region. The random impingement mechanism caused by the fluctuation kinetic energy of the solids can play an important role on the erosion of the tongue area.

  14. Peripheral Endothelial Function and Coronary Flow Velocity Reserve Are Not Associated in Women with Angina and No Obstructive Coronary Artery Disease: The iPOWER Study.

    Science.gov (United States)

    Flintholm Raft, Kristoffer; Frestad, Daria; Michelsen, Marie Mide; Suhrs, Hannah Elena; Rask, Anna Bay; Nilsson, Malin; Hermann, Thomas Steffen; Prescott, Eva

    2017-01-01

    We investigated whether impaired flow-mediated dilation (FMD) and plasma biomarkers reflecting endothelial dysfunction are associated with coronary microvascular dysfunction (CMD) in women with angina and no obstructive coronary artery disease (CAD). Patients (n = 194) were randomly selected women with angina pectoris and no obstructive CAD (<50% stenosis). A reference population of asymptomatic women without CAD (n = 25) was included. We measured FMD in the brachial artery by high-resolution ultrasound. Coronary flow velocity reserve (CFVR) was assessed by transthoracic Doppler flow echocardiography (TTDE) of the left anterior descending artery during rest and high-dose dipyridamole infusion. CMD was defined as CFVR <2. FMD and CFVR were measured in 128 patients and 21 controls. Mean (SD) age was 64.5 (8.9) years, mean CFVR was 2.3 (2.0-2.7), and mean FMD was 8.4% (4.8%) in angina patients. Angina patients had a higher risk factor burden compared with the reference population. Measures of peripheral endothelial dysfunction and endothelial plasma biomarkers did not differ according to angina or CFVR. CFVR and FMD did not correlate (Spearman ρ = -0.07, p = 0.45). FMD and biomarkers of endothelial dysfunction did not identify individuals with CMD assessed as impaired CFVR by TTDE in women with angina and no obstructive CAD. © 2017 S. Karger AG, Basel.

  15. Kinetic versus mechanical modeling of two-phase flow: on the influence of mechanical terms on the void fraction and velocities in quasi-developed flows

    International Nuclear Information System (INIS)

    Boure, J.; Matuszkiewicz, A.

    1984-01-01

    The interest of quasi-kinematic models (i.e. based essentially on the mass balances of the phases) versus mechanical models (based on the mass and momentum balances of the phases) for the description of the slip phenomenon in steady two-phase pipe flows is appraised, using experimental results. It is concluded that, as far as slip is concerned, mechanical modeling does not bring in any significant improvement [fr

  16. Effects of density and force discretizations on spurious velocities in lattice Boltzmann equation for two-phase flows

    KAUST Repository

    Xiong, Yuan

    2014-04-28

    Spurious current emerging in the vicinity of phase interfaces is a well-known disadvantage of the lattice Boltzmann equation (LBE) for two-phase flows. Previous analysis shows that this unphysical phenomenon comes from the force imbalance at discrete level inherited in LBE (Guo et al 2011 Phys. Rev. E 83 036707). Based on the analysis of the LBE free of checkerboard effects, in this work we further show that the force imbalance is caused by the different discretization stencils: the implicit one from the streaming process and the explicit one from the discretization of the force term. Particularly, the total contribution includes two parts, one from the difference between the intrinsically discretized density (or ideal gas pressure) gradient and the explicit ones in the force term, and the other from the explicit discretized chemical potential gradients in the intrinsically discretized force term. The former contribution is a special feature of LBE which was not realized previously.

  17. Dogs with hearth diseases causing turbulent high-velocity blood flow have changes in patelet function and von Willebrand factor multimer distribution

    DEFF Research Database (Denmark)

    Tarnow, Inge; Kristensen, Annemarie Thuri; Olsen, Lisbeth Høier

    2005-01-01

    and echocardiography were performed in all dogs. PFA100 closure times (the ability of platelets to occlude a hole in a membrane at high shear rates), platelet activation markers (plasma thromboxane B2 concentration, platelet surface P-selectin expression), platelet aggregation (in whole blood and platelet-rich plasma......The purpose of this prospective study was to investigate platelet function using in vitro tests based on both high and low shear rates and von Willebrand factor (vWf) multimeric composition in dogs with cardiac disease and turbulent high-velocity blood flow. Client-owned asymptomatic, untreated...... with MVP (regardless of MR status) compared with control dogs. No significant difference in platelet activation markers was found among groups. The data suggest that a form of platelet dysfunction detected at high shear rates was present in dogs with MR and SAS, possibly associated with a qualitative v...

  18. Velocity slip effects on heat and mass fluxes of MHD viscous–Ohmic dissipative flow over a stretching sheet with thermal radiation

    Directory of Open Access Journals (Sweden)

    M. Kayalvizhi

    2016-06-01

    Full Text Available In the present article, we discussed the velocity slip effects on the heat and mass fluxes of a viscous electrically conducting fluid flow over a stretching sheet in the presence of viscous dissipation, Ohmic dissipation and thermal radiation. A system of governing nonlinear PDEs is converted into a set of nonlinear ODEs by suitable similarity transformations. The numerical and analytical solutions are presented for the governing non-dimensional ODEs using shooting method and hypergeometric function respectively. The results are discussed for skin friction coefficient, concentration field, non-dimensional wall temperature and non-dimensional wall concentration. The non-dimensional wall concentration increases with slip and magnetic parameters and decreases with Schmidt number. Furthermore, comparisons are found to be good with bench mark solutions.

  19. Analytic representations of high-altitude auroral H^+ and O^+ densities, flow velocities and temperatures in terms of drivers for incorporation into global magnetospheric models

    Science.gov (United States)

    Horwitz, James; Zeng, Wen

    2008-10-01

    As new methods of describing multiple fluid species and other advances enhance the capability of global magnetospheric models to simulate the dynamics of multiple ion species, they also allow more accurate incorporation of ionospheric plasma outflows as source populations into these large scale models. Here, we shall describe the distilled results of numerous physics-based simulations of ionospheric plasma outflows influenced by auroral driving agents in terms of compact analytic expressions in terms of precipitation electron energy flux levels, characteristic energy levels of the precipitating electrons, the peak spectral wave densities for low-frequency electrostatic waves which transversely heat ionospheric ions, and solar zenith angle. The simulations are conducted with the UT Arlington Dynamic Fluid Kinetic (DyFK) ionospheric plasma transport code. We present these analytic expressions for ionospheric origin O^+ and H^+ densities, temperatures and field-aligned flow velocities at the 3 RE altitude inner boundaries of typical magnetospheric models.

  20. Dogs with hearth diseases causing turbulent high-velocity blood flow have changes in patelet function and von Willebrand factor multimer distribution

    DEFF Research Database (Denmark)

    Tarnow, Inge; Kristensen, Annemarie Thuri; Olsen, Lisbeth Høier

    2005-01-01

    The purpose of this prospective study was to investigate platelet function using in vitro tests based on both high and low shear rates and von Willebrand factor (vWf) multimeric composition in dogs with cardiac disease and turbulent high-velocity blood flow. Client-owned asymptomatic, untreated...... dogs were divided into 4 groups: 14 Cavalier King Charles Spaniels (Cavaliers) with mitral valve prolapse (MVP) and no or minimal mitral regurgitation (MR), 17 Cavaliers with MVP and moderate to severe MR, 14 control dogs, and 10 dogs with subaortic stenosis (SAS). Clinical examinations...... and echocardiography were performed in all dogs. PFA100 closure times (the ability of platelets to occlude a hole in a membrane at high shear rates), platelet activation markers (plasma thromboxane B2 concentration, platelet surface P-selectin expression), platelet aggregation (in whole blood and platelet-rich plasma...

  1. A novel five-wire micro anemometer with 3D directionality for low speed air flow detection and acoustic particle velocity detecting capability

    Science.gov (United States)

    Li, Zhe; Chang, Wenhan; Gao, Chengchen; Hao, Yilong

    2018-04-01

    In this paper, a novel five-wire micro-fabricated anemometer with 3D directionality based on calorimetric principle is proposed, which is capable of measuring low speed airflow. This structure is realized by vertically bonding two different dies, which can be fabricated on the same wafer resulting in a simple fabrication process. Experiments on speed lower than 200 mm s‑1 are conducted, showing good repeatability and directionality. The speed of airflow is controlled by the volumetric flow rate. The measured velocity sensitivity is 9.4 mV · s m‑1, with relative direction sensitivity of 37.1 dB. The deviation between the expected and the measured directivity is analyzed by both theories and simulations. A correction procedure is proposed and turns out to be useful to eliminate this deviation. To further explore the potential of our device, we expose it to acoustic plane waves in a standing wave tube, showing consistent planar directivity of figure of eight. The measured velocity sensitivity at 1 kHz and 120 dBC is 4.4 mV · s m‑1, with relative direction sensitivity of 27.0 dB. By using the correction method proposed above, the maximum angle error is about  ±2°, showing its good directionality accuracy.

  2. Blood flow velocity prediction in aorto-iliac stent grafts using computational fluid dynamics and Taguchi method.

    Science.gov (United States)

    Chong, Albert Y; Doyle, Barry J; Jansen, Shirley; Ponosh, Stefan; Cisonni, Julien; Sun, Zhonghua

    2017-05-01

    Covered Endovascular Reconstruction of Aortic Bifurcation (CERAB) is a new technique to treat extensive aortoiliac occlusive disease with covered expandable stent grafts to rebuild the aortoiliac bifurcation. Post stenting Doppler ultrasound (DUS) measurement of maximum peak systolic velocity (PSV max ) in the stented segment is widely used to determine patency and for follow up surveillance due to the portability, affordability and ease of use. Anecdotally, changes in hemodynamics created by CERAB can lead to falsely high PSV max requiring CT angiography (CTA) for further assessment. Therefore, the importance of DUS would be enhanced with a proposed PSV max prediction tool to ascertain whether PSV max falls within the acceptable range of prediction. We have developed a prediction tool based on idealized models of aortoiliac bifurcations with various infra-renal PSV (PSV in ), iliac to aortic area ratios (R) and aortoiliac bifurcation angles (α). Taguchi method with orthogonal arrays (OA) was utilized to minimize the number of Computational Fluid Dynamics (CFD) simulations performed under physiologically realistic conditions. Analysis of Variance (ANOVA) and Multiple Linear Regression (MLR) analyses were performed to assess Goodness of fit and to predict PSV max. PSV in and R were found to contribute 94.06% and 3.36% respectively to PSV max . The Goodness of fit based on adjusted R 2 improved from 99.1% to 99.9% based on linear and exponential functions. The PSV max predictor based on the exponential model was evaluated with sixteen patient specific cases with a mean prediction error of 9.9% and standard deviation of 6.4%. Eleven out of sixteen cases (69%) in our current retrospective studies would have avoided CTA if the proposed predictor was used to screen out DUS measured PSV max with prediction error greater than 15%. The predictor therefore has the potential to be used as a clinical tool to detect PSV max more accurately post aortoiliac stenting and might

  3. Ecografia transfontanelar com fluxo a cores em recém-nascidos prematuros Intracranial blood flow velocities evaluated by color doppler (duplex in preterm infants

    Directory of Open Access Journals (Sweden)

    Marcelo Cardoso de Assis

    2004-03-01

    Full Text Available Com o objetivo de determinarmos, evolutivamente, a medida da velocidade do fluxo sangüíneo nas artérias intracranianas, em recém-nascidos prematuros (RNP normais e com hemorragia intracerebral, avaliamos - no período de junho de 1994 a março de 1999 - 73 recém-nascidos prematuros. A idade gestacional variou de 28 a 36 semanas e o peso ao nascimento variou de 720g a 2530g. O diagnóstico da hemorragia intracerebral foi realizado utilizando-se a ecografia transfontanelar (EGT. Para avaliação seqüencial da medida da velocidade do fluxo sangüíneo nas artérias intracranianas os 73 foram submetidos a EGT, com Doppler pulsátil, no 3º, 7º, 30º e 90º dias de vida. Após obtermos os valores numéricos destas velocidades determinamos o indice de resistência (IR. Ao analisarmos os valores do IR, comparando-se os 2 grupos de RNP, concluimos que os valores do IR são sempre mais elevados nos RNP normais (RNP-N que nos RNP com hemorragia intracerebral (RNP-HIC; que tanto no grupo de RNP normais quanto no grupo de RNP com hemorragia intracerebral os valores do IR decrescem significativamente com o acréscimo da idade dos neonatos. Analisando-se ainda, comparativamente, os valores do IR nos RNP com hemorragia intracerebral, em seus diversos graus, observamos não haver, evolutivamente, diferença estatisticamente significante. Analisando-se também , comparativamente, os valores do IR nos RNP com hemorragia intracerebral localizada no hemisfério cerebral direito ou esquerdo concluimos não haver diferença estatisticamente significante entre os valores do IR obtidos das artérias localizadas no hemisfério cerebral acometido comparados aos valores do IR obtidos do hemisfério cerebral não afetado.In order to ascertain the blood flow velocities in the intracranial arteries we evaluated 73 preterm neonates during a period ranging from June 1994 to March 1999. These preterm infants were divided in two separate groups, 18 healthy and 55 with

  4. Comparison of changes in mean flow velocity in anterior cerebral artery before and during cognitive stimulation between non-stroke and post-stroke people

    Science.gov (United States)

    Fitri, F. I.; Erwin, I.; Batubara, C. A.; Rambe, A. S.; Anwar, Y.

    2018-03-01

    Transcranial Doppler (TCD) is a tool that has been used widely to measure cerebral blood flow and changes in the cerebral autoregulatory mechanism that can be observed during cognitive stimulation task as changes in mean flow velocity (MFV). This cross-sectional study was to compare the anterior cerebral arteries (ACA) MFV changes during cognitive stimulation using TCD in post-stroke and control group in Neurology Department Adam Malik General Hospital. From August to December 2016, all subject underwent TCD examination to assess baseline characteristic both side of ACA; then the patients were stimulated using Stroop Task. During stimulation, we measured changes in MFV that were correlated with cerebral autoregulation in total 13 pairs of post-stroke and control recruited. Paired t-test was used to evaluate the difference in baseline and during stimulation for each post stroke and control group while independent t-test was used to determine the MFV changes difference between both groups. There were significant differences for MFV changes in each artery for control [R- ACA (p=0.001), L-ACA (p=0.001)] and post-stroke [R-ACA (p=0.001), L-ACA (p=0.001)]. Meanwhile, there was no significant difference for MFV elevation for arteries compared between groups [R-ACA (p=0.374) and L-ACA (0.272)].

  5. A novel method to estimate blood flow velocity in the left atrial appendage using enhanced computed tomography: role of Hounsfield unit density ratio at two distinct points within the left atrial appendage.

    Science.gov (United States)

    Yasuoka, Ryobun; Kurita, Takashi; Kotake, Yasuhito; Akaiwa, Yuzuru; Hashiguchi, Naotaka; Motoki, Koichiro; Yamamoto, Hiromi; Kobuke, Kazuhiro; Iwanaga, Yoshitaka; Hirano, Yutaka; Miyazaki, Shunichi

    2017-07-01

    Low blood flow velocity in the left atrial appendage (LAA) indicates a high risk of thromboembolism. Although transesophageal echocardiography (TEE) has been the standard method with which to evaluate the LAA blood flow velocity, a clinically noninvasive method is desired. We hypothesized that the ratio of the Hounsfield unit (HU) density at two distinct points within the LAA represents the blood flow velocity in the LAA. We retrospectively investigated 60 consecutive patients with atrial fibrillation (paroxysmal type, n = 29) who underwent enhanced computed tomography (CT) and TEE. The peak emptying flow velocity in the LAA (LAAPV) was evaluated using TEE. HU density was measured at proximal and distal sites of the LAA (LAAp and LAAd) on CT images. The LAAd/LAAp ratio was correlated with the LAAPV (P velocity of the LAA can be estimated by the HU density ratio at distal and proximal sites within the LAA. Our method might be a feasible substitution for TEE to discriminate patients with a reduced LAAPV.

  6. Incidence of ventricular arrhythmias in patients on long-term support with a continuous-flow assist device (HeartMate II)

    DEFF Research Database (Denmark)

    Andersen, Mads; Videbaek, Regitze; Boesgaard, Søren

    2009-01-01

    The incidence of ventricular tachycardia (VT) or ventricular fibrillation (VF) in patients supported with a continuous-flow left ventricular assist device (LVAD) has not been investigated in detail. In 23 consecutive recipients of a HeartMate II, we analyzed the incidence of VT/VF during a total...... of 266 months of follow-up. Sustained VT or VF occurred in 52% of the patients, with the majority of arrhythmias occurring in the first 4 weeks after LVAD implantation. VT/VF requiring implantable cardioverter-defibrillator (ICD) shock or external defibrillation occurred in 8 patients and significant...

  7. The mitral-to-aortic flow-velocity integral ratio in the real world echocardiographic evaluation of functional mitral regurgitation before and after percutaneous repair.

    Science.gov (United States)

    Palmiero, Giuseppe; Ascione, Luigi; Briguori, Carlo; Carlomagno, Guido; Sordelli, Chiara; Ascione, Raffaele; Pisacane, Francesca; Monda, Vittorio; Severino, Sergio; Caso, Pio

    2017-08-01

    Percutaneous mitral valve repair (PMVR) using MitraClip system has emerged as a therapeutic option for patients with functional severe mitral regurgitation (FMR) at prohibitive risk for surgery. In this setting, the echocardiographic assessment of FMR severity is challenging because the traditional echocardiographic methods have important limitations. The aim of this study was to assess the accuracy and reliability of a simple Doppler index, the mitral/aortic flow velocity integral ratio (MAVIR), to evaluate residual FMR severity after PMVR. Eighty-five heart failure patients with functional MR and LV dysfunction (LVEF ≤ 40%) were included. FMR was quantified on the basis of traditional quantitative parameters of MR severity. MAVIR was expressed as the ratio of mitral and aortic time velocity integral (TVI) values. According to MR severity, 25 patients underwent MC implantation and at 6 months a complete echocardiographic follow-up was performed. A significant linear relationship was found between MAVIR and both VC and EROA. A MAVIR ≥1.02 identified pts with severe MR with a sensitivity of 86.7% and a specificity of 90.9%. At the 6 months echocardiographic follow-up after the MitraClip implantation, we observed a significant reduction of LAVI, LVED and LVES volume, while LVEF improved. Furthermore, MAVIR significantly decreased its decrease showed a significant linear relationship with LAVI reduction. Our data show a close relationship between MAVIR and traditional indexes of MR severity in patients with FMR. This Doppler-derived index seems applicable after PMVR where traditional echocardiographic index of MR severity shows significant limitations. © 2017, Wiley Periodicals, Inc.

  8. Transverse Spectral Velocity Estimation

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt

    2014-01-01

    array probe is used along with two different estimators based on the correlation of the received signal. They can estimate the velocity spectrum as a function of time as for ordinary spectrograms, but they also work at a beam-to-flow angle of 90°. The approach is validated using simulations of pulsatile...... flow using the Womersly–Evans flow model. The relative bias of the mean estimated frequency is 13.6% and the mean relative standard deviation is 14.3% at 90°, where a traditional estimator yields zero velocity. Measurements have been conducted with an experimental scanner and a convex array transducer....... A pump generated artificial femoral and carotid artery flow in the phantom. The estimated spectra degrade when the angle is different from 90°, but are usable down to 60° to 70°. Below this angle the traditional spectrum is best and should be used. The conventional approach can automatically be corrected...

  9. Turbulent conductivity in parallel with iso-velocities in a planar established flow; Conductibilite turbulente parallelement aux isovitesses dans un ecoulement plan en regime etabli

    Energy Technology Data Exchange (ETDEWEB)

    Jullien, F. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires, Direction des piles atomiques

    1968-02-01

    In this thesis are presented the experimental results obtained during the study of the turbulent diffusion of heat using a wire source in a flat air flow. The Taylor statistical theory laws are well respected in the domain studied. The experiments have made it possible to evaluate the influence of the Reynolds number and of the distance from the wall on the quadratic values of velocity fluctuations and on the Lagrange turbulence scales. In particular, the author has found a correlation between the Lagrange scales and the friction coefficient when the Reynolds number varies. A diffusion law is derived from the Taylor theory; it makes it possible to explain more clearly the idea of turbulent conductivity. (author) [French] Cette these presente les resultats experimentaux de l'etude de la diffusion turbulente de la chaleur a partir d'un fil source dans un ecoulement d'air plan. Les lois de la theorie statistique de Taylor sont bien verifiees dans le domaine d'etude. Les experiences ont permis d'evaluer l'influence du nombre de Reynolds et de la distance a la paroi sur les valeurs quadratiques des fluctuations de vitesse et les echelles lagrangiennes de turbulence. En particulier, l'auteur a trouve une correlation entre les echelles lagrangiennes et le coefficient de frottement lorsque le nombre de Reynolds varie. Comme consequences de la theorie de Taylor, une loi de diffusion est etablie et permet de preciser la notion de conductibilite turbulente. (auteur)

  10. Time course of changes in cerebral blood flow velocity after tourniquet deflation in patients with diabetes mellitus or previous stroke under sevoflurane anesthesia.

    Science.gov (United States)

    Hinohara, Hiroshi; Kadoi, Yuji; Takahashi, Kenichiro; Saito, Shigeru; Kawauchi, Chikara; Mizutani, Akio

    2011-06-01

    We observed an increase in mean middle cerebral artery blood flow velocity (V(mca)) after tourniquet deflation during orthopedic surgery under sevoflurane anesthesia in patients with diabetes mellitus or previous stroke. Eight controls, seven insulin-treated diabetic patients, and eight previous stroke patients were studied. Arterial blood pressure, heart rate, V(mca), arterial blood gases, and plasma lactate levels were measured every minute for 10 min after tourniquet release in all patients. V(mca) was measured using a transcranial Doppler probe. V(mca) in all three groups increased after tourniquet deflation, the increase lasting for 4 or 5 min. However, the degree of increase in V(mca) in the diabetic patients was smaller than that in the other two groups after tourniquet deflation (at 2 min after tourniquet deflation: control 58.5 ± 3.3, previous stroke 58.4 ± 4.6, diabetes 51.7 ± 2.3; P < 0.05 compared with the other two groups). In conclusion, the degree of increase in V (mca) in diabetic patients is smaller than that in controls and patients with previous stroke.

  11. Introduction to vector velocity imaging

    DEFF Research Database (Denmark)