Aircraft Wake Vortex Measurement with Coherent Doppler Lidar

Directory of Open Access Journals (Sweden)

Wu Songhua

2016-01-01

Full Text Available Aircraft vortices are generated by the lift-producing surfaces of the aircraft. The variability of near-surface conditions can change the drop rate and cause the cell of the wake vortex to twist and contort unpredictably. The pulsed Coherent Doppler Lidar Detection and Ranging is an indispensable access to real aircraft vortices behavior which transmitting a laser beam and detecting the radiation backscattered by atmospheric aerosol particles. Experiments for Coherent Doppler Lidar measurement of aircraft wake vortices has been successfully carried out at the Beijing Capital International Airport (BCIA. In this paper, the authors discuss the Lidar system, the observation modes carried out in the measurements at BCIA and the characteristics of vortices.

PIV and LDA measurements of the wake behind a wind turbine model

Science.gov (United States)

Naumov, I. V.; Mikkelsen, R. F.; Okulov, V. L.; Sørensen, J. N.

2014-06-01

In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio λ =5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 - 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed.

PIV and LDA measurements of the wake behind a wind turbine model

International Nuclear Information System (INIS)

Naumov, I V; Okulov, V L; Mikkelsen, R F; Sørensen, J N

2014-01-01

In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio λ =5 with a constant design lift coefficient along the span, C Ldesign = 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 – 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed

Results of Sexbierum Wind Farm: single wake measurements

NARCIS (Netherlands)

Cleijne, J.W.

1993-01-01

In the framework of the JOULE-0064 'Full-scale Measurements in Wind Turbine Arrays' in the period between June-November 1992 measurements have been performed in the Sexbierum Wind Farm. The aim of the measurements is to provide data for the validation of wake and wind farm models, which are being

Multi-component wind measurements of wind turbine wakes performed with three LiDARs

Science.gov (United States)

Iungo, G. V.; Wu, Y.-T.; Porté-Agel, F.

2012-04-01

Field measurements of the wake flow produced from the interaction between atmospheric boundary layer and a wind turbine are performed with three wind LiDARs. The tested wind turbine is a 2 MW Enercon E-70 located in Collonges, Switzerland. First, accuracy of mean values and frequency resolution of the wind measurements are surveyed as a function of the number of laser rays emitted for each measurement. Indeed, measurements performed with one single ray allow maximizing sampling frequency, thus characterizing wake turbulence. On the other hand, if the number of emitted rays is increased accuracy of mean wind is increased due to the longer sampling period. Subsequently, two-dimensional measurements with a single LiDAR are carried out over vertical sections of the wind turbine wake and mean wake flow is obtained by averaging 2D measurements consecutively performed. The high spatial resolution of the used LiDAR allows characterizing in details velocity defect present in the central part of the wake and its downstream recovery. Single LiDAR measurements are also performed by staring the laser beam at fixed directions for a sampling period of about ten minutes and maximizing the sampling frequency in order to characterize wake turbulence. From these tests wind fluctuation peaks are detected in the wind turbine wake at blade top-tip height for different downstream locations. The magnitude of these turbulence peaks is generally reduced by moving downstream. This increased turbulence level at blade top-tip height observed for a real wind turbine has been already detected from previous wind tunnel tests and Large Eddy simulations, thus confirming the presence of a source of dangerous fatigue loads for following wind turbines within a wind farm. Furthermore, the proper characterization of wind fluctuations through LiDAR measurements is proved by the detection of the inertial subrange from spectral analysis of these velocity signals. Finally, simultaneous measurements with two

Wind turbine wake measurement in complex terrain

DEFF Research Database (Denmark)

Hansen, Kurt Schaldemose; Larsen, Gunner Chr.; Menke, Robert

2016-01-01

SCADA data from a wind farm and high frequency time series measurements obtained with remote scanning systems have been analysed with focus on identification of wind turbine wake properties in complex terrain. The analysis indicates that within the flow regime characterized by medium to large dow...

Linearised CFD Models for Wakes

DEFF Research Database (Denmark)

Ott, Søren; Berg, Jacob; Nielsen, Morten

This report describes the development of a fast and reasonably accurate model for the prediction of energy production in oshore wind farms taking wake eects into account. The model has been implemented as a windows application called Fuga which can run in batch mode or as a graphical user interface....... Fuga is brie y described. The model is based on alinearization technique which is described in some detail, and linearized, governing equations are derived and written in a standard form based on a mixed{spectral formulation. A new solution method is used to solve the equations which involves intensive...... use of look{up tables for storage of intermediate results. Due to the linearity of the model, multiple wakes from many turbines can be constructed from the wake of a single, solitary turbine. These are in turn constructed from Fourier components by a fast Fourier integral transform of results derived...

Light detection and ranging measurements of wake dynamics. Part II: two-dimensional scanning

DEFF Research Database (Denmark)

Trujillo, Juan-José; Bingöl, Ferhat; Larsen, Gunner Chr.

2011-01-01

the instantaneous transversal wake position which is quantitatively compared with the prediction of the Dynamic Wake Meandering model. The results, shown for two 10-min time series, suggest that the conjecture of the wake behaving as a passive tracer is a fair approximation; this corroborates and expands...... the results of one-dimensional measurements already presented in the first part of this paper. Consequently, it is now possible to separate the deterministic and turbulent parts of the wake wind field, thus enabling capturing the wake in the meandering frame of reference. The results correspond, qualitatively...

Validation of the Eddy Viscosity and Lange Wake Models using Measured Wake Flow Characteristics Behind a Large Wind Turbine Rotor

Energy Technology Data Exchange (ETDEWEB)

Jeon, Sang Hyeon; Kim, Bum Suk; Huh, Jong Chul [Jeju National Univ., Jeju (Korea, Republic of); Go, Young Jun [Hanjin Ind, Co., Ltd., Yangsan (Korea, Republic of)

2016-01-15

The wake effects behind wind turbines were investigated by using data from a Met Mast tower and the SCADA (Supervisory Control and Data Acquisition) system for a wind turbine. The results of the wake investigations and predicted values for the velocity deficit based on the eddy viscosity model were compared with the turbulence intensity from the Lange model. As a result, the velocity deficit and turbulence intensity of the wake increased as the free stream wind speed decreased. In addition, the magnitude of the velocity deficit for the center of the wake using the eddy viscosity model was overestimated while the turbulence intensity from the Lange model showed similarities with measured values.

Three-Phased Wake Vortex Decay

Science.gov (United States)

Proctor, Fred H.; Ahmad, Nashat N.; Switzer, George S.; LimonDuparcmeur, Fanny M.

2010-01-01

A detailed parametric study is conducted that examines vortex decay within turbulent and stratified atmospheres. The study uses a large eddy simulation model to simulate the out-of-ground effect behavior of wake vortices due to their interaction with atmospheric turbulence and thermal stratification. This paper presents results from a parametric investigation and suggests improvements for existing fast-time wake prediction models. This paper also describes a three-phased decay for wake vortices. The third phase is characterized by a relatively slow rate of circulation decay, and is associated with the ringvortex stage that occurs following vortex linking. The three-phased decay is most prevalent for wakes imbedded within environments having low-turbulence and near-neutral stratification.

Empirical modeling of single-wake advection and expansion using full-scale pulsed lidar-based measurements

DEFF Research Database (Denmark)

Machefaux, Ewan; Larsen, Gunner Chr.; Troldborg, Niels

2015-01-01

In the present paper, single-wake dynamics have been studied both experimentally and numerically. The use of pulsed lidar measurements allows for validation of basic dynamic wake meandering modeling assumptions. Wake center tracking is used to estimate the wake advection velocity experimentally...... fairly well in the far wake but lacks accuracy in the outer region of the near wake. An empirical relationship, relating maximum wake induction and wake advection velocity, is derived and linked to the characteristics of a spherical vortex structure. Furthermore, a new empirical model for single...

CFD modelling approaches against single wind turbine wake measurements using RANS

International Nuclear Information System (INIS)

Stergiannis, N; Lacor, C; Beeck, J V; Donnelly, R

2016-01-01

Numerical simulations of two wind turbine generators including the exact geometry of their blades and hub are compared against a simplified actuator disk model (ADM). The wake expansion of the upstream rotor is investigated and compared with measurements. Computational Fluid Dynamics (CFD) simulations have been performed using the open-source platform OpenFOAM [1]. The multiple reference frame (MRF) approach was used to model the inner rotating reference frames in a stationary computational mesh and outer reference frame for the full wind turbine rotor simulations. The standard k — ε and k — ω turbulence closure schemes have been used to solve the steady state, three dimensional Reynolds Averaged Navier- Stokes (RANS) equations. Results of near and far wake regions are compared with wind tunnel measurements along three horizontal lines downstream. The ADM under-predicted the velocity deficit at the wake for both turbulence models. Full wind turbine rotor simulations showed good agreement against the experimental data at the near wake, amplifying the differences between the simplified models. (paper)

Wake effects in Alsvik wind park: Comparison between measurements and predictions

Energy Technology Data Exchange (ETDEWEB)

Magnusson, Mikael [Uppsala Univ. (Sweden). Dept. of Meteorology; Rados, K.G.; Pothou, K.P. [National Technical Univ., Athen (Greece). Fluid section

1996-12-01

In this paper characteristic parameters in a wind turbine wake are studied. The data used are full-scale measurements from a wind farm in Sweden, Alsvik, and results from a numerical model calculated for the same site. The results are valid for neutral stratification. The model employs a particle-vortex approach at the rotor plane, a Navier-Stokes solver in the near wake and applies self preservation in the far wake. The parameters investigated are the relative velocity deficit at centre line and hub height, and the radial distribution of the turbulent kinetic energy. 6 refs, 9 figs

Wake field in matched kicker magnet

International Nuclear Information System (INIS)

Miyahara, Y.

1979-01-01

Coherent transverse instability observed in KEK booster proton synchrotron has been reported previously. This instability is induced by the interaction of the beam with kicker magnet for the fast beam extraction. To understand the mechanism completely, it is necessary to know the wake field in detail. Here, the wake field or induced current in the kicker magnet which is terminated with matched resistance is considered

Wake structure measurements at the MOD-2 cluster test facility at Goodnoe Hills, Washington

Energy Technology Data Exchange (ETDEWEB)

Zambrano, T.G.; Gyatt, G.W.

1983-12-01

A field measurement programme was carried out at the cluster of three MOD-2 wind turbines located at Goodnoe Hills, Washington, to determine the rate of decay of wake velocity deficit with down-wind distance in various meteorological conditions. Measurements were taken at hub height (60 m). Wake wind speeds were measured using a radiosonde suspended from a tethered balloon, its position being determined from a grid of ground stakes. Instantaneous readings were recorded by each system every two seconds and averaged over ten-minute periods. As a control experiment, the sonde was also operated next to the meteorological tower to calibrate the instrumentation. Measurements were also made down wind with the turbine off to determine the magnitude of terrain-induced variations in wind speed. Downstream distances of 274.3, 457.2, 640.1 and 823.0 m from the turbine, corresponding to 3, 5, 7 and 9 rotor diameters D, were investigated. There was considerable scatter in the observed 10 min average downstream/free-stream velocity ratios. Turbine-on velocity ratios showed even greater scatter, suggesting that only some measurements were, in fact, representative of wake centre-line velocities, and that others were made off centre line due to wake meander or wind shift. Isolation of the high wind speed (13.4 to 20.1 m/s) velocity ratios, however, revealed velocity deficits of up to about 50% at 3D and 5% at 5D downstream. Measurements at greater downstream distances showed no wake deficit within the limits of resolution of the experiment, indicating that the wake had recovered to free-stream conditions.

Prediction of multi-wake problems using an improved Jensen wake model

DEFF Research Database (Denmark)

Tian, Linlin; Zhu, Wei Jun; Shen, Wen Zhong

2017-01-01

The improved analytical wake model named as 2D_k Jensen model (which was proposed to overcome some shortcomes in the classical Jensen wake model) is applied and validated in this work for wind turbine multi-wake predictions. Different from the original Jensen model, this newly developed 2D_k Jensen...... model uses a cosine shape instead of the top-hat shape for the velocity deficit in the wake, and the wake decay rate as a variable that is related to the ambient turbulence as well as the rotor generated turbulence. Coupled with four different multi-wake combination models, the 2D_k Jensen model...... is assessed through (1) simulating two wakes interaction under full wake and partial wake conditions and (2) predicting the power production in the Horns Rev wind farm for different wake sectors around two different wind directions. Through comparisons with field measurements, results from Large Eddy...

Field measurements in the wake of a model wind turbine

International Nuclear Information System (INIS)

Pol, Suhas; Taylor, Amelia; Doostalab, Ali; Novoa, Santiago; Castillo, Luciano; Bilbao, Argenis; Sheng, Jian; Giesselmann, Michael; Westergaard, Carsten; Hussain, Fazle; Ren, Beibei; Glauser, Mark

2014-01-01

As a first step to study the dynamics of a wind farm' we experimentally explored the flow field behind a single wind turbine of diameter 1.17 m at a hub height of 6.25 m. A 10 m tower upstream of the wind farm characterizes the atmospheric conditions and its influence on the wake evolution. A vertical rake of sonic anemometers is clustered around the hub height on a second tower' 6D downstream of the turbine. We present preliminary observations from a 1- hour block of data recorded in near-neutral atmospheric conditions. The ratio of the standard deviation of power to the inflow velocity is greater than three' revealing adverse effects of inflow turbulence on the power and load fluctuations. Furthermore' the wake defect and Reynolds stress and its gradient are pronounced at 6D. The flux of energy due to Reynolds stresses is similar to that reported in wind tunnel studies. The swirl and mixing produces a constant temperature wake which results in a density jump across the wake interface. Further field measurements will explore the dynamics of a model wind farm' including the effects of atmospheric variability

Measurement of potentials in the wake region of an unmagnetized plasma by using a DC-heated emissive probe

International Nuclear Information System (INIS)

Jung, Yong Ho; Chung, Kyu Sun

1995-01-01

An emissive probe was designed and manufactured to measure the floating and the space potentials of a plasma in the wake region. The 'floating potential method', among various schemes, was used for the measurement and analysis. To generate the wake, a plane artificial satellite with a circular shape was introduced into a simply discharged argon plasma without a magnetic field. Potentials along the radial direction in and out of the wake region of the artificial satellite were measured, and the plasma parameters were compared in both regions. In the wake region, the floating potential was higher than that out of the wake; the space potential was approximately equal to that out of the wake; when a positive voltage was applied to the artificial satellite, the floating and the space potentials were lower than those out of the wake; and when a negative voltage was applied to the artificial satellite, the floating potential was higher and the space potential was lower than the corresponding potentials out of the wake. (author)

Multiple Turbine Wakes

DEFF Research Database (Denmark)

Machefaux, Ewan; Mann, Jakob

and to obtain an estimate of the wake expansion in a fixed frame of reference. A comparison of selected datasets from the campaign showed good far wake agreements of mean wake expansion with Actuator Line CFD computations and simpler engineering models. An empirical relationship, relating maximum wake induction...... for modeling the resulting double wake deficit is only relevant at high turbine thrust coefficients. For high wind speed and low thrust coefficient, linear summation should be primarily used. The first iteration of a new engineering model capable of modeling the overlapped wake deficit is formulated and its...... measurement and simulation is seen in both the fixed and the meandering frame of reference. A benchmark of several wake accumulation models is performed as a basis for the subsequent development of an engineering model for wake interaction.Finally, the validated numerical CFD model is used as part...

Development of a current sheet in the wake of a fast coronal mass ejection

International Nuclear Information System (INIS)

Ling, A. G.; Webb, D. F.; Burkepile, J. T.; Cliver, E. W.

2014-01-01

A bright ray that developed in the wake of a fast coronal mass ejection (CME) on 2005 September 7 presents a unique opportunity to study the early development and physical characteristics of a reconnecting current sheet (CS). Polarization brightness images from the Mk4 K-Coronameter at the Mauna Loa Solar Observatory are used to determine the structure of the ray along its axis low in the corona as it progressed outward. Coverage of the early development of the ray out to ∼1.3 R ☉ for a period of ∼27 hr after the start of the event enables for the first time in white light a measurement of a CME CS from the top of the arcade to the base of the flux rope. Measured widths of the ray are combined to obtain the kinematics of the upper and lower Y- points described in reconnection flux-rope models such as that of Lin and Forbes. The time dependence of these points are used to derive values for the speed and acceleration of the growth of the CS. We note the appearance of a large structure which increases in size as it expands outward in the early development of the ray and an apparent oscillation with a period of ∼0.5 hr in the position angle of the ray.

Air Density Measurements in a Mach 10 Wake Using Iodine Cordes Bands

Science.gov (United States)

Balla, Robert J.; Everhart, Joel L.

2012-01-01

An exploratory study designed to examine the viability of making air density measurements in a Mach 10 flow using laser-induced fluorescence of the iodine Cordes bands is presented. Experiments are performed in the NASA Langley Research Center 31 in. Mach 10 air wind tunnel in the hypersonic near wake of a multipurpose crew vehicle model. To introduce iodine into the wake, a 0.5% iodine/nitrogen mixture is seeded using a pressure tap at the rear of the model. Air density was measured at 56 points along a 7 mm line and three stagnation pressures of 6.21, 8.62, and 10.0 MPa (900, 1250, and 1450 psi). Average results over time and space show rho(sub wake)/rho(sub freestream) of 0.145 plus or minus 0.010, independent of freestream air density. Average off-body results over time and space agree to better than 7.5% with computed densities from onbody pressure measurements. Densities measured during a single 60 s run at 10.0 MPa are time-dependent and steadily decrease by 15%. This decrease is attributed to model forebody heating by the flow.

PIV and LDA measurements of the wake behind a wind turbine model

DEFF Research Database (Denmark)

Naumov, I. V.; Mikkelsen, Robert Flemming; Okulov, Valery

2014-01-01

=5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 – 9 at different cross-sections from the very near wake up to 10 rotor...... diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid...

Free wake models for vortex methods

Energy Technology Data Exchange (ETDEWEB)

Kaiser, K. [Technical Univ. Berlin, Aerospace Inst. (Germany)

1997-08-01

The blade element method works fast and good. For some problems (rotor shapes or flow conditions) it could be better to use vortex methods. Different methods for calculating a wake geometry will be presented. (au)

Wake deficit measurements on the Jess and Souza Ranches, Altamont Pass

Energy Technology Data Exchange (ETDEWEB)

Nierenburg, R. (Altamont Energy Corp., San Rafael, CA (USA))

1990-04-01

This report is ninth in a series of documents presenting the findings of field test under DOE's Cooperative Field Test Program (CFTP) with the wind industry. This report provides results of a project conducted by Altamont Energy Corp. (AEC) to measure wake deficits on the Jess and Sousa Ranches in Altamont Pass, CA. This research enhances and complements other DOE-funded projects to refine estimates of wind turbine array effects. This project will help explain turbine performance variability caused by wake effects. 4 refs., 28 figs., 106 tabs.

Proceedings of the ENDOW workshop 'Offshore wakes: Measurements and modelling[Efficient Development of Offshore Windfarms

Energy Technology Data Exchange (ETDEWEB)

Barthelmie, R.J. (ed.)

2002-03-01

The papers presented in these Proceedings are the result of a workshop held at Risoe National Laboratory on March 7 and 8 2002 entitled 'Offshore Wakes: Measurements and Modelling'. The Workshop was arranged to showcase results of the European Community supported project 'Efficient Development of Offshore Windfarms (ENDOW)' and featured a series of eight presentations discussing modelling of wakes and boundary layers, existing and new measurements from offshore wind farms and how these will be linked in a new design tool and applied at planned offshore wind farms. In addition seven invited presentations covered a range of relevant topics from analytical approaches to fatigue and extreme loads in wind turbine clusters, current wake modelling in WAsP, optimising power production at Arklow Bank, Particle Image Velocimetry study of a wind turbine wake in a yaw, offshore wind measurements in Massachusetts, accuracy of SODAR measurements for wind energy and tidal influence of offshore wind speeds and turbulence. (au)

High resolution wind turbine wake measurements with a scanning lidar

DEFF Research Database (Denmark)

Herges, T. G.; Maniaci, D. C.; Naughton, B. T.

2017-01-01

High-resolution lidar wake measurements are part of an ongoing field campaign being conducted at the Scaled Wind Farm Technology facility by Sandia National Laboratories and the National Renewable Energy Laboratory using a customized scanning lidar from the Technical University of Denmark. One...

Measurements on the extended range of the wake

International Nuclear Information System (INIS)

Kumbartzki, G.J.; Kroesing, G; Neuburger, H.

1981-01-01

The Coulomb explosion of H 2 + -ions at 28 MeV is used to probe the wake over a range of about 400 A in Al. Preliminary results give food agreement with the wavelength prediction of the simple plasma oscillation wake model. (author)

A new approach for evaluating measured wake data

Energy Technology Data Exchange (ETDEWEB)

Magnusson, Mikael [Uppsala Univ. (Sweden). Dept. of Meteorology

1996-12-01

Wind turbine wakes have been studied by analysing a large set of atmospheric data, from a wind farm with four turbines sited on a flat coastal area. The results obtained have ben generalized to allow tests against data from other full scale wind turbines as well as wind tunnel simulations. These comparisons are found to give very satisfactory results. The thrust coefficient is found to be a better parameter for description than wind speed, of wake characteristics because it implicitly includes the effect of regulation. It is also found that down-wind travel time is more convenient to use than down-wind distance in this context. The travel time to the end of the near wake region, i.e. to the point where a single velocity deficit peak first appears, is found to be inversely proportional to the rotational frequency of the turbine and to the turbulence intensity of the ambient air flow and proportional to the ratio of the wake radius and the hub height. For larger travel times, i.e. for the far wake region, it is found that the centre line relative velocity deficit decreases with the logarithm of the time traveled and is parametrically dependent on the time constant and the thrust coefficient. 3 refs, 5 figs

A simple stationary semi-analytical wake model

DEFF Research Database (Denmark)

Larsen, Gunner Chr.

We present an idealized simple, but fast, semi-analytical algorithm for computation of stationary wind farm wind fields with a possible potential within a multi-fidelity strategy for wind farm topology optimization. Basically, the model considers wakes as linear perturbations on the ambient non......-linear. With each of these approached, a parabolic system are described, which is initiated by first considering the most upwind located turbines and subsequently successively solved in the downstream direction. Algorithms for the resulting wind farm flow fields are proposed, and it is shown that in the limit......-uniform mean wind field, although the modelling of the individual stationary wake flow fields includes non-linear terms. The simulation of the individual wake contributions are based on an analytical solution of the thin shear layer approximation of the NS equations. The wake flow fields are assumed...

An overview of experimental results and dispersion modelling of nanoparticles in the wake of moving vehicles

International Nuclear Information System (INIS)

Carpentieri, Matteo; Kumar, Prashant; Robins, Alan

2011-01-01

Understanding the transformation of nanoparticles emitted from vehicles is essential for developing appropriate methods for treating fine scale particle dynamics in dispersion models. This article provides an overview of significant research work relevant to modelling the dispersion of pollutants, especially nanoparticles, in the wake of vehicles. Literature on vehicle wakes and nanoparticle dispersion is reviewed, taking into account field measurements, wind tunnel experiments and mathematical approaches. Field measurements and modelling studies highlighted the very short time scales associated with nanoparticle transformations in the first stages after the emission. These transformations strongly interact with the flow and turbulence fields immediately behind the vehicle, hence the need of characterising in detail the mixing processes in the vehicle wake. Very few studies have analysed this interaction and more research is needed to build a basis for model development. A possible approach is proposed and areas of further investigation identified. - Research highlights: → Nanoparticle emissions experience very short transformation time scales. → Vehicle wakes need to be characterised to analyse nanoparticle dispersion. → Fast response measurements of nanoparticle evolution in vehicle wakes are very rare. → Wind tunnel methodologies can be further improved to include nanoparticle dynamics. → A simple mathematical approach has been proposed for future development. - The transformation of nanoparticles and the flow characteristics in both the near and far wake regions must be understood in order to develop mathematical models.

Measurements of Wake-Riding Electrons in Antiproton-Carbon-Foil Collisions

CERN Multimedia

2002-01-01

When a charged particle passes through dielectric media, e.g. a thin carbon foil, a ``wake'' is induced. The characteristic wake-potential shows an oscillatory behaviour, with a wavelength of about $ 2 \\pi v _{p} / \\omega _{p} _{l} $ where $ v _{p} $ is the projectile velocity and $ \\omega _{p} _{l} $ the plasmon energy of the target. This induced wake potential is superimposed on the Coulomb potential of the projectile, the latter leading to a pronounced ``cusp'' of electrons leaving the solid at $ v _{e} app v _{p} $ for positively charged projectiles in the MeV region. Correspondingly, an ``anti-cusp'' is expected for antiprotons. \\\\ \\\\ In the solid, the wake-potential leads to an attractive force on electrons, and a dynamic electronic state is predicted both for proton and antiproton projectiles. In the solid, the wake-riding electrons are travelling with the projectile speed $ v _{p} $ Upon exit of the foil, the electron released from the wake-riding state of an antiproton will suddenly find itself in th...

Wake effect in rocket observation

International Nuclear Information System (INIS)

Matsumoto, Haruya; Kaya, Nobuyuki; Yamanaka, Akira; Hayashi, Tomomasa

1975-01-01

The mechanism of the wake phenomena due to a probe and in rocket observation is discussed on the basis of experimental data. In the low energy electron measurement performed with the L-3H-5 rocket, the electron count rate changed synchronously with the rocket spin. This seems to be a wake effect. It is also conceivable that the probe itself generates the wake of ion beam. The latter problem is considered in the first part. Experiment was performed with laboratory plasma, in which a portion of the electron component of the probe current was counted with a CEM (a channel type multiplier). The change of probe voltage-count rate charactersitics due to the change of relative position of the ion source was observed. From the measured angular distributions of electron density and electron temperature around the probe, it is concluded that anisotropy exists around the probe, which seems to be a kinds of wake structure. In the second part, the wake effect due to a rocket is discussed on the basis of the measurement of leaking electrons with L-3H-5 rocket. Comparison between the theory of wake formation and the measured results is also shortly made in the final part. (Aoki, K.)

Wind farm array wake losses

Energy Technology Data Exchange (ETDEWEB)

Baker, R.W. [Impact Weather, Washougal, WA (United States); McCarthy, E.F. [Wind Economics & Technology, Inc., Martinez, CA (United States)

1997-12-31

A wind turbine wake study was conducted in the summer of 1987 at an Altamont Pass wind electric generating facility. The wind speed deficits, turbulence, and power deficits from an array consisting of several rows of wind turbines is discussed. A total of nine different test configurations were evaluated for a downwind spacing ranging from 7 rotor diameters (RD) to 34 RD and a cross wind spacing of 1.3 RD and 2.7 RD. Wake power deficits of 15% were measured at 16 RD and power losses of a few percent were even measurable at 27 RD for the closer cross wind spacing. For several rows of turbines separated by 7-9 RD the wake zones overlapped and formed compound wakes with higher velocity deficits. The wind speed and direction turbulence in the wake was much higher than the ambient turbulence. The results from this study are compared to the findings from other similar field measurements.

Investigation on the wake evolution of contra-rotating propeller using RANS computation and SPIV measurement

Directory of Open Access Journals (Sweden)

Kwang-Jun Paik

2015-05-01

Full Text Available The wake characteristics of Contra-Rotating Propeller (CRP were investigated using numerical simulation and flow measurement. The numerical simulation was carried out with a commercial CFD code based on a Reynolds Averaged Navier-Stokes (RANS equations solver, and the flow measurement was performed with Stereoscopic Particle Image Velocimetry (SPIV system. The simulation results were validated through the comparison with the experiment results measured around the leading edge of rudder to investigate the effect of propeller operation under the conditions without propeller, with forward propeller alone, and with both forward and aft propellers. The evolution of CRP wake was analyzed through velocity and vorticity contours on three transverse planes and one longitudinal plane based on CFD results. The trajectories of propeller tip vortex core in the cases with and without aft propeller were also compared, and larger wake contraction with CRP was confirmed.

Spectral coherence in windturbine wakes

Energy Technology Data Exchange (ETDEWEB)

Hojstrup, J. [Riso National Lab., Roskilde (Denmark)

1996-12-31

This paper describes an experiment at a Danish wind farm to investigate the lateral and vertical coherences in the nonequilibrium turbulence of a wind turbine wake. Two meteorological masts were instrumented for measuring profiles of mean speed, turbulence, and temperature. Results are provided graphically for turbulence intensities, velocity spectra, lateral coherence, and vertical coherence. The turbulence was somewhat influenced by the wake, or possibly from aggregated wakes further upstream, even at 14.5 diameters. Lateral coherence (separation 5m) seemed to be unaffected by the wake at 7.5 diameters, but the flow was less coherent in the near wake. The wake appeared to have little influence on vertical coherence (separation 13m). Simple, conventional models for coherence appeared to be adequate descriptions for wake turbulence except for the near wake situation. 3 refs., 7 figs., 1 tab.

Dissipation of Turbulence in the Wake of a Wind Turbine

Science.gov (United States)

Lundquist, J. K.; Bariteau, L.

2015-02-01

The wake of a wind turbine is characterized by increased turbulence and decreased wind speed. Turbines are generally deployed in large groups in wind farms, and so the behaviour of an individual wake as it merges with other wakes and propagates downwind is critical in assessing wind-farm power production. This evolution depends on the rate of turbulence dissipation in the wind-turbine wake, which has not been previously quantified in field-scale measurements. In situ measurements of winds and turbulence dissipation from the wake region of a multi-MW turbine were collected using a tethered lifting system (TLS) carrying a payload of high-rate turbulence probes. Ambient flow measurements were provided from sonic anemometers on a meteorological tower located near the turbine. Good agreement between the tower measurements and the TLS measurements was established for a case without a wind-turbine wake. When an operating wind turbine is located between the tower and the TLS so that the wake propagates to the TLS, the TLS measures dissipation rates one to two orders of magnitude higher in the wake than outside of the wake. These data, collected between two and three rotor diameters downwind of the turbine, document the significant enhancement of turbulent kinetic energy dissipation rate within the wind-turbine wake. These wake measurements suggest that it may be useful to pursue modelling approaches that account for enhanced dissipation. Comparisons of wake and non-wake dissipation rates to mean wind speed, wind-speed variance, and turbulence intensity are presented to facilitate the inclusion of these measurements in wake modelling schemes.

Wind Turbines Wake Aerodynamics

DEFF Research Database (Denmark)

Vermeer, L.; Sørensen, Jens Nørkær; Crespo, A.

2003-01-01

The aerodynamics of horizontal axis wind turbine wakes is studied. The contents is directed towards the physics of power extraction by wind turbines and reviews both the near and the far wake region. For the near wake, the survey is restricted to uniform, steady and parallel flow conditions......, thereby excluding wind shear, wind speed and rotor setting changes and yawed conditions. The emphasis is put on measurements in controlled conditions.For the far wake, the survey focusses on both single turbines and wind farm effects, and the experimental and numerical work are reviewed; the main interest...... is to study how the far wake decays downstream, in order to estimate the effect produced in downstream turbines.The article is further restricted to horizontal axis wind turbines and excludes all other types of turbines....

Wake fields and wake field acceleration

International Nuclear Information System (INIS)

Bane, K.L.F.; Wilson, P.B.; Weiland, T.

1984-12-01

In this lecture we introduce the concepts of wake fields and wake potentials, examine some basic properties of these functions, show how they can be calculated, and look briefly at a few important applications. One such application is wake field acceleration. The wake field accelerator is capable of producing the high gradients required for future very high energy e + e - linear colliders. The principles of wake field acceleration, and a brief description of experiments in progress in this area, are presented in the concluding section. 40 references, 27 figures

A 380pW Dual Mode Optical Wake-up Receiver with Ambient Noise Cancellation.

Science.gov (United States)

Lim, Wootaek; Jang, Taekwang; Lee, Inhee; Kim, Hun-Seok; Sylvester, Dennis; Blaauw, David

2016-06-01

We present a sub-nW optical wake-up receiver for wireless sensor nodes. The wake-up receiver supports dual mode operation for both ultra-low standby power and high data rates, while canceling ambient in-band noise. In 0.18µm CMOS the receiver consumes 380pW in always-on wake-up mode and 28.1µW in fast RX mode at 250kbps.

Wake modeling and simulation

DEFF Research Database (Denmark)

Larsen, Gunner Chr.; Madsen Aagaard, Helge; Larsen, Torben J.

We present a consistent, physically based theory for the wake meandering phenomenon, which we consider of crucial importance for the overall description of wind turbine loadings in wind farms. In its present version the model is confined to single wake situations. The model philosophy does, howev...... methodology has been implemented in the aeroelastic code HAWC2, and example simulations of wake situations, from the small Tjæreborg wind farm, have been performed showing satisfactory agreement between predictions and measurements...

Wind turbine wake visualization and characteristics analysis by Doppler lidar.

Science.gov (United States)

Wu, Songhua; Liu, Bingyi; Liu, Jintao; Zhai, Xiaochun; Feng, Changzhong; Wang, Guining; Zhang, Hongwei; Yin, Jiaping; Wang, Xitao; Li, Rongzhong; Gallacher, Daniel

2016-05-16

Wind power generation is growing fast as one of the most promising renewable energy sources that can serve as an alternative to fossil fuel-generated electricity. When the wind turbine generator (WTG) extracts power from the wind, the wake evolves and leads to a considerable reduction in the efficiency of the actual power generation. Furthermore, the wake effect can lead to the increase of turbulence induced fatigue loads that reduce the life time of WTGs. In this work, a pulsed coherent Doppler lidar (PCDL) has been developed and deployed to visualize wind turbine wakes and to characterize the geometry and dynamics of wakes. As compared with the commercial off-the-shelf coherent lidars, the PCDL in this work has higher updating rate of 4 Hz and variable physical spatial resolution from 15 to 60 m, which improves its capability to observation the instantaneous turbulent wind field. The wind speed estimation method from the arc scan technique was evaluated in comparison with wind mast measurements. Field experiments were performed to study the turbulent wind field in the vicinity of operating WTGs in the onshore and offshore wind parks from 2013 to 2015. Techniques based on a single and a dual Doppler lidar were employed for elucidating main features of turbine wakes, including wind velocity deficit, wake dimension, velocity profile, 2D wind vector with resolution of 10 m, turbulence dissipation rate and turbulence intensity under different conditions of surface roughness. The paper shows that the PCDL is a practical tool for wind energy research and will provide a significant basis for wind farm site selection, design and optimization.

Stereo particle image velocimetry set up for measurements in the wake of scaled wind turbines

Science.gov (United States)

Campanardi, Gabriele; Grassi, Donato; Zanotti, Alex; Nanos, Emmanouil M.; Campagnolo, Filippo; Croce, Alessandro; Bottasso, Carlo L.

2017-08-01

Stereo particle image velocimetry measurements were carried out in the boundary layer test section of Politecnico di Milano large wind tunnel to survey the wake of a scaled wind turbine model designed and developed by Technische Universität München. The stereo PIV instrumentation was set up to survey the three velocity components on cross-flow planes at different longitudinal locations. The area of investigation covered the entire extent of the wind turbines wake that was scanned by the use of two separate traversing systems for both the laser and the cameras. Such instrumentation set up enabled to gain rapidly high quality results suitable to characterise the behaviour of the flow field in the wake of the scaled wind turbine. This would be very useful for the evaluation of the performance of wind farm control methodologies based on wake redirection and for the validation of CFD tools.

Dynamic wake meandering modeling

Energy Technology Data Exchange (ETDEWEB)

Larsen, Gunner C.; Aagaard Madsen, H.; Bingoel, F. (and others)

2007-06-15

We present a consistent, physically based theory for the wake meandering phenomenon, which we consider of crucial importance for the overall description of wind turbine loadings in wind farms. In its present version the model is confined to single wake situations. The model philosophy does, however, have the potential to include also mutual wake interaction phenomenons. The basic conjecture behind the dynamic wake meandering model is that wake transportation in the atmospheric boundary layer is driven by the large scale lateral- and vertical turbulence components. Based on this conjecture a stochastic model of the downstream wake meandering is formulated. In addition to the kinematic formulation of the dynamics of the 'meandering frame of reference', models characterizing the mean wake deficit as well as the added wake turbulence, described in the meandering frame of reference, are an integrated part the model complex. For design applications, the computational efficiency of wake deficit prediction is a key issue. Two computationally low cost models are developed for this purpose. The character of the added wake turbulence, generated by the up-stream turbine in the form of shed and trailed vorticity, has been approached by analytical as well as by numerical studies. The dynamic wake meandering philosophy has been verified by comparing model predictions with extensive full-scale measurements. These comparisons have demonstrated good agreement, both qualitatively and quantitatively, concerning both flow characteristics and turbine load characteristics. Contrary to previous attempts to model wake loading, the dynamic wake meandering approach opens for a unifying description in the sense that turbine power and load aspects can be treated simultaneously. This capability is a direct and attractive consequence of the model being based on the underlying physical process, and it potentially opens for optimization of wind farm topology, of wind farm operation as

Evaluation of Large-Scale Wing Vortex Wakes from Multi-Camera PIV Measurements in Free-Flight Laboratory

Science.gov (United States)

Carmer, Carl F. v.; Heider, André; Schröder, Andreas; Konrath, Robert; Agocs, Janos; Gilliot, Anne; Monnier, Jean-Claude

Multiple-vortex systems of aircraft wakes have been investigated experimentally in a unique large-scale laboratory facility, the free-flight B20 catapult bench, ONERA Lille. 2D/2C PIV measurements have been performed in a translating reference frame, which provided time-resolved crossvelocity observations of the vortex systems in a Lagrangian frame normal to the wake axis. A PIV setup using a moving multiple-camera array and a variable double-frame time delay has been employed successfully. The large-scale quasi-2D structures of the wake-vortex system have been identified using the QW criterion based on the 2D velocity gradient tensor ∇H u, thus illustrating the temporal development of unequal-strength corotating vortex pairs in aircraft wakes for nondimensional times tU0/b≲45.

Wake fields in semiconductor plasmas

International Nuclear Information System (INIS)

Berezhiani, V.I.; Mahajan, S.M.

1994-05-01

It is shown that an intense short laser pulse propagating through a semiconductor plasma will generated longitudinal Langmuir waves in its wake. The measurable wake field can be used as a diagnostic to study nonlinear optical phenomena. For narrow gap semiconductors (for examples InSb) with Kane-type dispersion relation, the system can simulate, at currently available laser powers, the physics underlying wake-field accelerators. (author). 9 refs, 1 fig

Data report: the wake of a horizontal-axis wind turbine model, measurements in uniform approach flow and in a simulated atmospheric boundary layer

NARCIS (Netherlands)

Talmon, A.M.

1985-01-01

Wake effects will cause power loss when wínd turbínes are grouped in so called wind turbine parks. Wind tunnel measurements of the wake of a wind turbíne model are conducted in order to refine calculatíons of wake effects. Wake effects caused by tower and nacelle are studied in uniform flow. Wake

Tomo-PIV measurements of the flow field in the wake of a sphere

Science.gov (United States)

Eshbal, Lior; David, Tom; Rinsky, Vladislav; van Hout, Rene; Greenblatt, David

2017-11-01

A sphere can be considered as a prototypical 3D bluff body. In order to improve our understanding of its 3D wake flow, a combination of time-resolved planar particle image velocimetry (PIV) and tomographic PIV (tomo-PIV) was implemented. Experiments were performed in a closed-loop water channel facility and sphere Reynolds numbers ReD = UD/ ν = 400, 800, 1200 and 2000, where U is the free-stream velocity, ν the kinematic viscosity and D the sphere diameter. The measurement volume (Height x Length x Width, 5 x 5 x 1.5 D3) comprised the sphere and the downstream wake. Tomo-PIV snap-shots were correlated with the time-resolved PIV such that the 3D temporal evolution of the shed vortices became clear. At ReD = 400, this procedure revealed shed hairpin vortices having a vertical plane of symmetry in agreement with many dye visualization studies. However, the measurements also revealed weaker induced hairpins resulting from the interaction of the near-wake flow and the surrounding free stream. These induced vortices were not visible in previous dye and smoke visualizations and have only been observed in simulations. Data processing of the data at higher ReD is currently ongoing. Israel Science Foundation Grant No. 1596/14.

Modelling lidar volume-averaging and its significance to wind turbine wake measurements

Science.gov (United States)

Meyer Forsting, A. R.; Troldborg, N.; Borraccino, A.

2017-05-01

Lidar velocity measurements need to be interpreted differently than conventional in-situ readings. A commonly ignored factor is “volume-averaging”, which refers to lidars not sampling in a single, distinct point but along its entire beam length. However, especially in regions with large velocity gradients, like the rotor wake, can it be detrimental. Hence, an efficient algorithm mimicking lidar flow sampling is presented, which considers both pulsed and continous-wave lidar weighting functions. The flow-field around a 2.3 MW turbine is simulated using Detached Eddy Simulation in combination with an actuator line to test the algorithm and investigate the potential impact of volume-averaging. Even with very few points discretising the lidar beam is volume-averaging captured accurately. The difference in a lidar compared to a point measurement is greatest at the wake edges and increases from 30% one rotor diameter (D) downstream of the rotor to 60% at 3D.

Characterization of wake region by using and emissive probe

International Nuclear Information System (INIS)

Jeong, Yong Ho

1993-02-01

An emissive probe was designed and manufactured to measure the floating and the space potentials of plasma in the wake region. The floating potential method' among various schemes was used for the measurement and analysis. To generate the wake, a plane artificial satellite with circular shape was introduced in a simply discharged argon plasma without the magnetic field. Potentials along the radial direction in and out of the wake regions of artificial satellite were measured, and plasma parameters were compared in the both regions. In the wake region, the floating potential was higher than that out of the wake, the space potential was approximately equal to that out of the wake, when the positive voltage was applied to artificial satellite, the floating and the space potentials were lower than that out of the wake and when the negative voltage was applied to artificial satellite, the floating potential was higher, the space potential was lower than that out of the wake

Wake Conference 2017

International Nuclear Information System (INIS)

2017-01-01

vortex dynamics, instabilities in trailing vortices and wakes, simulation and measurements of wakes, analytical approaches for modeling wakes, wake interaction and other wind farm investigations. We would like to thank all those that assisted in the review process for these proceedings and we are also thankful for the help we have recieved from the editorial team at IOP Publishing during the process. Visby, Sweden May/June 2017 Andrew Barney, Stefan Ivanell, Maria Klemm and Jens Nørkær Sørensen (paper)

Wake modeling and simulation

Energy Technology Data Exchange (ETDEWEB)

Larsen, G.C.; Aagaard Madsen, H.; Larsen, T.J.; Troldborg, N.

2008-07-15

We present a consistent, physically based theory for the wake meandering phenomenon, which we consider of crucial importance for the overall description of wind turbine loadings in wind farms. In its present version the model is confined to single wake situations. The model philosophy does, however, have the potential to include also mutual wake interaction phenomenons. The basic conjecture behind the dynamic wake meandering (DWM) model is that wake transportation in the atmospheric boundary layer is driven by the large scale lateral- and vertical turbulence components. Based on this conjecture a stochastic model of the downstream wake meandering is formulated. In addition to the kinematic formulation of the dynamics of the 'meandering frame of reference', models characterizing the mean wake deficit as well as the added wake turbulence, described in the meandering frame of reference, are an integrated part the DWM model complex. For design applications, the computational efficiency of wake deficit prediction is a key issue. A computationally low cost model is developed for this purpose. Likewise, the character of the added wake turbulence, generated by the up-stream turbine in the form of shed and trailed vorticity, has been approached by a simple semi-empirical model essentially based on an eddy viscosity philosophy. Contrary to previous attempts to model wake loading, the DWM approach opens for a unifying description in the sense that turbine power- and load aspects can be treated simultaneously. This capability is a direct and attractive consequence of the model being based on the underlying physical process, and it potentially opens for optimization of wind farm topology, of wind farm operation as well as of control strategies for the individual turbine. To establish an integrated modeling tool, the DWM methodology has been implemented in the aeroelastic code HAWC2, and example simulations of wake situations, from the small Tjaereborg wind farm, have

Performance and wake conditions of a rotor located in the wake of an obstacle

Science.gov (United States)

Naumov, I. V.; Kabardin, I. K.; Mikkelsen, R. F.; Okulov, V. L.; Sørensen, J. N.

2016-09-01

Obstacles like forests, ridges and hills can strongly affect the velocity profile in front of a wind turbine rotor. The present work aims at quantifying the influence of nearby located obstacles on the performance and wake characteristics of a downstream located wind turbine. Here the influence of an obstacle in the form of a cylindrical disk was investigated experimentally in a water flume. A model of a three-bladed rotor, designed using Glauert's optimum theory at a tip speed ratio λ = 5, was placed in the wake of a disk with a diameter close to the one of the rotor. The distance from the disk to the rotor was changed from 4 to 8 rotor diameters, with the vertical distance from the rotor axis varied 0.5 and 1 rotor diameters. The associated turbulent intensity of the incoming flow to the rotor changed 3 to '6% due to the influence of the disk wake. In the experiment, thrust characteristics and associated pulsations as a function of the incoming flow structures were measured by strain gauges. The flow condition in front of the rotor was measured with high temporal accuracy using LDA and power coefficients were determine as function of tip speed ratio for different obstacle positions. Furthermore, PIV measurements were carried out to study the development of the mean velocity deficit profiles of the wake behind the wind turbine model under the influence of the wake generated by the obstacle. By use of regression techniques to fit the velocity profiles it was possible to determine velocity deficits and estimate length scales of the wake attenuation.

Improvement of a near wake model for trailing vorticity

DEFF Research Database (Denmark)

Pirrung, Georg; Hansen, Morten Hartvig; Aagaard Madsen, Helge

2014-01-01

A near wake model, originally proposed by Beddoes, is further developed. The purpose of the model is to account for the radially dependent time constants of the fast aerodynamic response and to provide a tip loss correction. It is based on lifting line theory and models the downwash due to roughly...... the first 90 degrees of rotation. This restriction of the model to the near wake allows for using a computationally efficient indicial function algorithm. The aim of this study is to improve the accuracy of the downwash close to the root and tip of the blade and to decrease the sensitivity of the model...... to temporal discretization, both regarding numerical stability and quality of the results. The modified near wake model is coupled to an aerodynamics model, which consists of a blade element momentum model with dynamic inflow for the far wake and a 2D shed vorticity model that simulates the unsteady buildup...

Performance and wake conditions of a rotor located in the wake of an obstacle

DEFF Research Database (Denmark)

Naumov, I. V.; Kabardin, I. K.; Mikkelsen, Robert Flemming

2016-01-01

and associated pulsations as a function of the incoming flow structures were measured by strain gauges. The flow condition in front of the rotor was measured with high temporal accuracy using LDA and power coefficients were determine as function of tip speed ratio for different obstacle positions. Furthermore......Obstacles like forests, ridges and hills can strongly affect the velocity profile in front of a wind turbine rotor. The present work aims at quantifying the influence of nearby located obstacles on the performance and wake characteristics of a downstream located wind turbine. Here the influence......, PIV measurements were carried out to study the development of the mean velocity deficit profiles of the wake behind the wind turbine model under the influence of the wake generated by the obstacle. By use of regression techniques to fit the velocity profiles it was possible to determine velocity...

Measurement of turbulent mixing in a confined wake flow using combined PIV and PLIF

NARCIS (Netherlands)

Hjertager, Lene K.; Hjertager, Bjorn H.; Deen, N.G.; Solberg, Tron; Kuipers, J.A.M.

2003-01-01

Turbulent mixing in a confined wake flow was studied by using the combined PIV/PLIF technique to measure instantaneous concentration and velocity fields. Measurements were performed at two slightly overlapping areas in the initial mixing zone and at an area at the end of the channel. The

Fast-Acting Sublingual Zolpidem for Middle-of-the-Night Wakefulness

Directory of Open Access Journals (Sweden)

Joseph V. Pergolizzi

2014-01-01

Full Text Available Sleep disorders (somnipathies are conditions characterized by disruptions of sleep quality or of sleep pattern. They can involve difficulty falling asleep (prolonged sleep onset latency, difficulty staying asleep (disturbance of sleep maintenance, sleep of poor quality (unrefreshing, or combinations of these and can lead to poor health and quality of life problems. A subtype of sleep-maintenance insomnia is middle-of-the-night wakefulness, a relatively common occurrence. Zolpidem, a nonbenzodiazepine benzodiazepine receptor agonist, allosterically modulates an ion channel and increases the influx of Cl−, thereby dampening the effect of excitatory (sleep disrupting input. Recently, product label changes to some zolpidem containing products have been implemented by the FDA in order to reduce the risk associated with their morning after residual side effects. A new formulation of zolpidem tartrate (Intermezzo sublingual tablet, an approved product indicated exclusively for the treatment of middle-of-the-night wakefulness and difficulty returning to sleep, did not have its label changed. We present a short summary of its basic science and clinical attributes in light of the recent regulatory changes for zolpidem products.

Collision induced fragmentation of fast molecular ions in solids and gases

International Nuclear Information System (INIS)

Gemmell, D.S.

1979-01-01

A brief review is given of recent high resolution measurements on fragments arising from the collision-induced dissociation of fast (MeV) molecular ions. For solid targets, strong wake effects are observed. For gaseous targets, excited electronic states of the projectile ions play an important role. Measurements of this type provide useful information on the charge states of fast ions traversing matter. The experimental techniques show promise as a unique method for determining the geometrical structures of the molecular-ion projectiles. 41 references

Investigation of wake interaction using full-scale lidar measurements and large eddy simulation

DEFF Research Database (Denmark)

Machefaux, Ewan; Larsen, Gunner Chr.; Troldborg, Niels

2016-01-01

dynamics flow solver, using large eddy simulation and fully turbulent inflow. The rotors are modelled using the actuator disc technique. A mutual validation of the computational fluid dynamics model with the measurements is conducted for a selected dataset, where wake interaction occurs. This validation...

A Coupled Probabilistic Wake Vortex and Aircraft Response Prediction Model

Science.gov (United States)

Gloudemans, Thijs; Van Lochem, Sander; Ras, Eelco; Malissa, Joel; Ahmad, Nashat N.; Lewis, Timothy A.

2016-01-01

Wake vortex spacing standards along with weather and runway occupancy time, restrict terminal area throughput and impose major constraints on the overall capacity and efficiency of the National Airspace System (NAS). For more than two decades, the National Aeronautics and Space Administration (NASA) has been conducting research on characterizing wake vortex behavior in order to develop fast-time wake transport and decay prediction models. It is expected that the models can be used in the systems level design of advanced air traffic management (ATM) concepts that safely increase the capacity of the NAS. It is also envisioned that at a later stage of maturity, these models could potentially be used operationally, in groundbased spacing and scheduling systems as well as on the flight deck.

Improvements in ECN Wake Model

Energy Technology Data Exchange (ETDEWEB)

Versteeg, M.C. [University of Twente, Enschede (Netherlands); Ozdemir, H.; Brand, A.J. [ECN Wind Energy, Petten (Netherlands)

2013-08-15

Wind turbines extract energy from the flow field so that the flow in the wake of a wind turbine contains less energy and more turbulence than the undisturbed flow, leading to less energy extraction for the downstream turbines. In large wind farms, most turbines are located in the wake of one or more turbines causing the flow characteristics felt by these turbines differ considerably from the free stream flow conditions. The most important wake effect is generally considered to be the lower wind speed behind the turbine(s) since this decreases the energy production and as such the economical performance of a wind farm. The overall loss of a wind farm is very much dependent on the conditions and the lay-out of the farm but it can be in the order of 5-10%. Apart from the loss in energy production an additional wake effect is formed by the increase in turbulence intensity, which leads to higher fatigue loads. In this sense it becomes important to understand the details of wake behavior to improve and/or optimize a wind farm layout. Within this study improvements are presented for the existing ECN wake model which constructs the fundamental basis of ECN's FarmFlow wind farm wake simulation tool. The outline of this paper is as follows: first, the governing equations of the ECN wake farm model are presented. Then the near wake modeling is discussed and the results compared with the original near wake modeling and EWTW (ECN Wind Turbine Test Site Wieringermeer) data as well as the results obtained for various near wake implementation cases are shown. The details of the atmospheric stability model are given and the comparison with the solution obtained for the original surface layer model and with the available data obtained by EWTW measurements are presented. Finally the conclusions are summarized.

TR-PIV measurement of the wake behind a grooved cylinder at low Reynolds number

Science.gov (United States)

Liu, Ying Zheng; Shi, Liu Liu; Yu, Jun

2011-04-01

A comparative study of the wakes behind cylinders with grooved and smooth surfaces was performed with a view to understand the wake characteristics associated with the adult Saguaro cacti. A low-speed recirculation water channel was established for the experiment; the Reynolds number, based on the free-stream velocity and cylinder diameter (D), was kept at ReD=1500. State-of-the-art time-resolved particle image velocimetry (TR-PIV) was employed to measure a total of 20 480 realizations of the wake field at a frame rate of 250 Hz, enabling a comprehensive view of the time- and phase-averaged wake pattern. In comparison to the wake behind the smooth cylinder, the length of the recirculation zone behind the grooved cylinder was extended by nearly 18.2%, yet the longitudinal velocity fluctuation intensity was considerably weakened. A global view of the peaked spectrum of the longitudinal velocity component revealed that the intermediate region for the grooved cylinder, which approximately corresponds to the transition region where the shear layer vortices interact, merge and shed before the formation of the Karman-like vortex street, was much wider than that for the smooth one. The unsteady events near St=0.3-0.4 were detected in the intermediate region behind the grooved cylinder, but no such events were found in the smooth cylinder system. Although the formation of the Karman-like vortex street was delayed by about 0.6D downstream for the grooved cylinder, no prominent difference in the vortex street region was found in the far wake for both cylinders. The Proper Orthogonal Decomposition (POD) method was used extensively to decompose the vector and swirling strength fields, which gave a close-up view of the vortices in the near wake. The first two POD modes of the swirling strength clarified the spatio-temporal characteristics of the shear layer vortices behind the grooved cylinder. The small-scale vortices superimposed on the shear layers behind the grooved cylinder

Volumetric LiDAR scanning of a wind turbine wake and comparison with a 3D analytical wake model

Science.gov (United States)

Carbajo Fuertes, Fernando; Porté-Agel, Fernando

2016-04-01

A correct estimation of the future power production is of capital importance whenever the feasibility of a future wind farm is being studied. This power estimation relies mostly on three aspects: (1) a reliable measurement of the wind resource in the area, (2) a well-established power curve of the future wind turbines and, (3) an accurate characterization of the wake effects; the latter being arguably the most challenging one due to the complexity of the phenomenon and the lack of extensive full-scale data sets that could be used to validate analytical or numerical models. The current project addresses the problem of obtaining a volumetric description of a full-scale wake of a 2MW wind turbine in terms of velocity deficit and turbulence intensity using three scanning wind LiDARs and two sonic anemometers. The characterization of the upstream flow conditions is done by one scanning LiDAR and two sonic anemometers, which have been used to calculate incoming vertical profiles of horizontal wind speed, wind direction and an approximation to turbulence intensity, as well as the thermal stability of the atmospheric boundary layer. The characterization of the wake is done by two scanning LiDARs working simultaneously and pointing downstream from the base of the wind turbine. The direct LiDAR measurements in terms of radial wind speed can be corrected using the upstream conditions in order to provide good estimations of the horizontal wind speed at any point downstream of the wind turbine. All this data combined allow for the volumetric reconstruction of the wake in terms of velocity deficit as well as turbulence intensity. Finally, the predictions of a 3D analytical model [1] are compared to the 3D LiDAR measurements of the wind turbine. The model is derived by applying the laws of conservation of mass and momentum and assuming a Gaussian distribution for the velocity deficit in the wake. This model has already been validated using high resolution wind-tunnel measurements

Application of staring lidars to study the dynamics of wind turbine wakes

Directory of Open Access Journals (Sweden)

Davide Trabucchi

2015-11-01

Full Text Available Standard anemometry or vertical profiling remote sensing are not always a convenient approach to study the dynamics of wind turbines wake. One or more lidar windscanner can be applied for this purpose. In this paper a measurement strategy is presented, which permits the characterization of the wake dynamics using two long range wind lidars operated in a stationary mode. In this approach two pulsed devices are staring with low elevation obliquely across the wake. The lidar beams are supposed to cross each other on the downstream axis of the wake to perform simultaneous measurements in the wake field from side to side. The deflection of the wake is identified fitting a model to the average data. Spectral analysis provide the frequency content of the measurements at different distances from the wake center. This setup was implemented in a full-field measurement campaign where the wake of a multi-MW wind turbine was analysed. The tracking of the wake centre was applied successfully to this measurement. Moreover the spectral analysis showed increased energy content close to the wake lateral edges. This can be connected both to the higher turbulence level due to the tip vorteces and to the large scale dynamics of the wake.

Improvement of a near wake model for trailing vorticity

International Nuclear Information System (INIS)

Pirrung, G R; Hansen, M H; Madsen, H A

2014-01-01

A near wake model, originally proposed by Beddoes, is further developed. The purpose of the model is to account for the radially dependent time constants of the fast aerodynamic response and to provide a tip loss correction. It is based on lifting line theory and models the downwash due to roughly the first 90 degrees of rotation. This restriction of the model to the near wake allows for using a computationally efficient indicial function algorithm. The aim of this study is to improve the accuracy of the downwash close to the root and tip of the blade and to decrease the sensitivity of the model to temporal discretization, both regarding numerical stability and quality of the results. The modified near wake model is coupled to an aerodynamics model, which consists of a blade element momentum model with dynamic inflow for the far wake and a 2D shed vorticity model that simulates the unsteady buildup of both lift and circulation in the attached flow region. The near wake model is validated against the test case of a finite wing with constant elliptical bound circulation. An unsteady simulation of the NREL 5 MW rotor shows the functionality of the coupled model

Wake structure and similar behavior of wake profiles downstream of a plunging airfoil

Directory of Open Access Journals (Sweden)

Ali R. DAVARI

2017-08-01

Full Text Available Very limited attention has already been paid to the velocity behavior in the wake region in unsteady aerodynamic problems. A series of tests has been performed on a flapping airfoil in a subsonic wind tunnel to study the wake structure for different sets of mean angle of attack, plunging amplitude and reduced frequency. In this study, the velocity profiles in the wake for various oscillation parameters have been measured using a wide shoulder rake, especially designed for the present experiments. The airfoil under consideration was a critical section of a 660 kW wind turbine. The results show that for a flapping airfoil the wake structure can be of drag producing type, thrust producing or neutral, depending on the mean angle of attack, oscillation amplitude and reduced frequency. In a thrust producing wake, a high-momentum high-velocity jet flow is formed in the core region of the wake instead of the conventional low-momentum flow. As a result, the drag force normally experienced by the body due to the momentum deficit would be replaced by a thrust force. According to the results, the momentum loss in the wake decreases as the reduced frequency increases. The thrust producing wake pattern for the flapping airfoil has been observed for sufficiently low angles of attack in the absence of the viscous effects. This phenomenon has also been observed for either high oscillation amplitudes or high reduced frequencies. According to the results, for different reduced frequencies and plunging amplitudes, such that the product of them be a constant, the velocity profiles exhibit similar behavior and coalesce on each other. This similarity parameter works excellently at small angles of attack. However, at near stall boundaries, the similarity is not as evident as before.

On the wake of a Darrieus turbine

Science.gov (United States)

Base, T. E.; Phillips, P.; Robertson, G.; Nowak, E. S.

1981-01-01

The theory and experimental measurements on the aerodynamic decay of a wake from high performance vertical axis wind turbine are discussed. In the initial experimental study, the wake downstream of a model Darrieus rotor, 28 cm diameter and a height of 45.5 cm, was measured in a Boundary Layer Wind Tunnel. The wind turbine was run at the design tip speed ratio of 5.5. It was found that the wake decayed at a slower rate with distance downstream of the turbine, than a wake from a screen with similar troposkein shape and drag force characteristics as the Darrieus rotor. The initial wind tunnel results indicated that the vertical axis wind turbines should be spaced at least forty diameters apart to avoid mutual power depreciation greater than ten per cent.

The effect of intermittent fasting during Ramadan on sleep, sleepiness, cognitive function, and circadian rhythm.

Science.gov (United States)

Qasrawi, Shaden O; Pandi-Perumal, Seithikurippu R; BaHammam, Ahmed S

2017-09-01

Studies have shown that experimental fasting can affect cognitive function, sleep, and wakefulness patterns. However, the effects of experimental fasting cannot be generalized to fasting during Ramadan due to its unique characteristics. Therefore, there has been increased interest in studying the effects of fasting during Ramadan on sleep patterns, daytime sleepiness, cognitive function, sleep architecture, and circadian rhythm. In this review, we critically discuss the current research findings in those areas during the month of Ramadan. Available data that controlled for sleep/wake schedule, sleep duration, light exposure, and energy expenditure do not support the notion that Ramadan intermittent fasting increases daytime sleepiness and alters cognitive function. Additionally, recent well-designed studies showed no effect of fasting on circadian rhythms. However, in non-constrained environments that do not control for lifestyle changes, studies have demonstrated sudden and significant delays in bedtime and wake time. Studies that controlled for environmental factors and sleep/wake schedule reported no significant disturbances in sleep architecture. Nevertheless, several studies have consistently reported that the main change in sleep architecture during fasting is a reduction in the proportion of REM sleep.

Electron holes observed in the Moon Plasma Wake

Science.gov (United States)

Hutchinson, I. H.; Malaspina, D.; Zhou, C.

2017-10-01

Electrostatic instabilities are predicted in the magnetized wake of plasma flowing past a non-magnetic absorbing object such as a probe or the moon. Analysis of the data from the Artemis satellites, now orbiting the moon at distances ten moon radii and less, shows very clear evidence of fast-moving isolated solitary potential structures causing bipolar electric field excursions as they pass the satellite's probes. These structures have all the hallmarks of electron holes: BGK solitons typically a few Debye-lengths in size, self-sustaining by a deficit of phase-space density on trapped orbits. Electron holes are now observed to be widespread in space plasmas. They have been observed in PIC simulations of the moon wake to be the non-linear consequence of the predicted electron instabilities. Simulations document hole prevalence, speed, length, and depth; and theory can explain many of these features from kinetic analysis. The solar wind wake is certainly the cause of the overwhelming majority of the holes observed by Artemis, because we observe almost all holes to be in or very near to the wake. We compare theory and simulation of the hole generation, lifetime, and transport mechanisms with observations. Work partially supported by NASA Grant NNX16AG82G.

Validation of the actuator line method using near wake measurements of the MEXICO rotor

DEFF Research Database (Denmark)

Nilsson, Karl; Shen, Wen Zhong; Sørensen, Jens Nørkær

2015-01-01

The purpose of the present work is to validate the capability of the actuator line method to compute vortex structures in the near wake behind the MEXICO experimental wind turbine rotor. In the MEXICO project/MexNext Annex, particle image velocimetry measurements have made it possible to determine...

DIELECTRIC WAKE FIELD RESONATOR ACCELERATOR MODULE

Energy Technology Data Exchange (ETDEWEB)

Hirshfield, Jay L.

2013-11-06

Results are presented from experiments, and numerical analysis of wake fields set up by electron bunches passing through a cylindrical or rectangular dielectric-lined structure. These bunches excite many TM-modes, with Ez components of the wake fields sharply localized on the axis of the structure periodically behind the bunches. The experiment with the cylindrical structure, carried out at ATF Brookhaven National Laboratory, used up to three 50 MeV bunches spaced by one wake field period (21 cm) to study the superposition of wake fields by measuring the energy loss of each bunch after it passed through the 53-cm long dielectric element. The millimeter-wave spectrum of radiation excited by the passage of bunches is also studied. Numerical analysis was aimed not only to simulate the behavior of our device, but in general to predict dielectric wake field accelerator performance. It is shown that one needs to match the radius of the cylindrical dielectric channel with the bunch longitudinal rms-length to achieve optimal performance.

Wake Measurement Downstream of a Hybrid Wing Body Model with Blown Flaps

Science.gov (United States)

Lin, John C.; Jones, Gregory S.; Allan, Brian G.; Westra, Bryan W.; Collins, Scott W.; Zeune, Cale H.

2010-01-01

Flow-field measurements were obtained in the wake of a full-span Hybrid Wing Body model with internally blown flaps. The test was performed at the NASA Langley 14 x 22 Foot Subsonic Tunnel at low speeds. Off-body measurements were obtained with a 7-hole probe rake survey system. Three model configurations were investigated. At 0deg angle of attack the surveys were completed with 0deg and 60deg flap deflections. At 10deg angle of attack the wake surveys were completed with a slat and a 60deg flap deflection. The 7-hole probe results further quantified two known swirling regions (downstream of the outboard flap edge and the inboard/outboard flap juncture) for the 60deg flap cases with blowing. Flowfield results and the general trends are very similar for the two blowing cases at nozzle pressure ratios of 1.37 and 1.56. High downwash velocities correlated with the enhanced lift for the 60deg flap cases with blowing. Jet-induced effects are the largest at the most inboard station for all (three) velocity components due in part to the larger inboard slot height. The experimental data are being used to improve computational tools for high-lift wings with integrated powered-lift technologies.

Probes, Moons, and Kinetic Plasma Wakes

Science.gov (United States)

Hutchinson, I. H.; Malaspina, D.; Zhou, C.

2017-10-01

Nonmagnetic objects as varied as probes in tokamaks or moons in space give rise to flowing plasma wakes in which strong distortions of the ion and electron velocity distributions cause electrostatic instabilities. Non-linear phenomena such as electron holes are then produced. Historic probe theory largely ignores the resulting unstable character of the wake, but since we can now simulate computationally the non-linear wake phenomena, a timely challenge is to reassess the influence of these instabilities both on probe measurements and on the wakes themselves. Because the electron instability wavelengths are very short (typically a few Debye-lengths), controlled laboratory experiments face serious challenges in diagnosing them. That is one reason why they have long been neglected as an influence in probe interpretation. Space-craft plasma observations, by contrast, easily obtain sub-Debye-length resolution, but have difficulty with larger-scale reconstruction of the plasma spatial variation. In addition to surveying our developing understanding of wakes in magnetized plasmas, ongoing analysis of Artemis data concerning electron holes observed in the solar-wind lunar wake will be featured. Work partially supported by NASA Grant NNX16AG82G.

PIV measurements in the near wakes of hollow cylinders with holes

Science.gov (United States)

Firat, Erhan; Ozkan, Gokturk M.; Akilli, Huseyin

2017-05-01

The wake flows behind fixed, hollow, rigid circular cylinders with two rows of holes connecting the front and rear stagnation lines were investigated using particle image velocimetry (PIV) for various combinations of three hole diameters, d = 0.1 D, 0.15 D, and 0.20 D, six hole-to-hole distances, l = 2 d, 3 d, 4 d, 5 d, 6 d, and 7 d, and ten angles of incidence ( α), from 0° to 45° in steps of 5°, at a Reynolds number of Re = 6,900. Time-averaged velocity distributions, instantaneous and time-averaged vorticity patterns, time-averaged streamline topology, and hot spots of turbulent kinetic energy occurred through the interaction of shear layers from the models were presented to show how the wake flow was modified by the presence of the self-issuing jets with various momentums emanating from the downstream holes. In general, as hole diameter which is directly related to jet momentum increased, the values of time-averaged wake characteristics (length of time-averaged recirculation region, vortex formation length, length of shear layers, and gap between the shear layers) increased. Irrespective to d and l tested, the values of the vortex formation length of the models are greater than that of the cylinder without hole (reference model). That is, vortex formation process was shifted downstream by aid of jets. It was found that time-averaged wake characteristics were very sensitive to α. As α increased, the variation of these characteristics can be modeled by exponential decay functions. The effect of l on the three-dimensional vortex shedding patterns in the near wake of the models was also discussed.

A fast wind-farm boundary-layer model to investigate gravity wave effects and upstream flow deceleration

Science.gov (United States)

Allaerts, Dries; Meyers, Johan

2017-11-01

Wind farm design and control often relies on fast analytical wake models to predict turbine wake interactions and associated power losses. Essential input to these models are the inflow velocity and turbulent intensity at hub height, which come from prior measurement campaigns or wind-atlas data. Recent LES studies showed that in some situations large wind farms excite atmospheric gravity waves, which in turn affect the upstream wind conditions. In the current study, we develop a fast boundary-layer model that computes the excitation of gravity waves and the perturbation of the boundary-layer flow in response to an applied force. The core of the model is constituted by height-averaged, linearised Navier-Stokes equations for the inner and outer layer, and the effect of atmospheric gravity waves (excited by the boundary-layer displacement) is included via the pressure gradient. Coupling with analytical wake models allows us to study wind-farm wakes and upstream flow deceleration in various atmospheric conditions. Comparison with wind-farm LES results shows excellent agreement in terms of pressure and boundary-layer displacement levels. The authors acknowledge support from the European Research Council (FP7-Ideas, Grant No. 306471).

ECoG sleep-waking rhythms and bodily activity in the cerveau isolé rat.

Science.gov (United States)

Nakata, K; Kawamura, H

1986-01-01

In rats with a high mesencephalic transection, isolating both the locus coeruleus and raphe nuclei from the forebrain, Electrocorticogram (ECoG) and Electromyogram (EMG) of the neck muscles were continuously recorded. Normal sleep-waking ECoG changes with a significant circadian rhythm reappeared in 4 to 9 days after transection. Neck muscle EMG and bodily movements were independent of the ECoG changes and did not show any significant circadian rhythm. In these high mesencephalic rats with sleep-waking ECoG changes, large bilateral hypothalamic lesions were made by passing DC current either in the preoptic area or in the posterior hypothalamus. After the preoptic area lesions the amount of low voltage fast ECoG per day markedly increased, whereas after the posterior hypothalamic lesions, the total amount of low voltate fast wave per day decreased showing long-lasting slow wave sleep pattern. These results support an idea that the forebrain, especially in the hypothalamus including the preoptic area, a mechanism inducing sleep-waking ECoG changes is localized.

Fast optical measurements and imaging of flow mixing

DEFF Research Database (Denmark)

Clausen, Sønnik; Fateev, Alexander; Nielsen, Karsten Lindorff

Project is focused on fast time-resolved infrared measurements of gas temperature and fast IR-imagining of flames in various combustion environments. The infrared spectrometer system was developed in the project for fast infrared spectral measurements on industrial scale using IR-fibre- optics. F...... engine and visualisation of gas flow behaviour in cylinder.......Project is focused on fast time-resolved infrared measurements of gas temperature and fast IR-imagining of flames in various combustion environments. The infrared spectrometer system was developed in the project for fast infrared spectral measurements on industrial scale using IR-fibre- optics....... Fast time-and spectral-resolved measurements in 1.5-5.1 μm spectral range give information about flame characteristics like gas and particle temperatures, eddies and turbulent gas mixing. Time-resolved gas composition in that spectral range (H2O, CH4, CO2, CO) which is one of the key parameters...

PREFACE: Wake Conference 2015

Science.gov (United States)

Barney, Andrew; Nørkær Sørensen, Jens; Ivanell, Stefan

2015-06-01

at scientists and PhD students working in the field of wake dynamics. The conference covers the following subject areas: Wake and vortex dynamics, instabilities in trailing vortices and wakes, simulation and measurements of wakes, analytical approaches for modeling wakes, wake interaction and other wind farm investigations. Many people have been involved in producing the 2015 Wake Conference proceedings. The work by the more than 60 reviewers ensuring the quality of the papers is greatly appreciated. The timely evaluation and coordination of the reviews would not have been possible without the work of the section editors: Christian Masson, ÉTS, Fernando Porté-Agel, EPFL, Gerard Schepers, ECN Wind Energy, Gijs Van Kuik, Delft University, Gunner Larsen, DTU Wind Energy, Jakob Mann, DTU Wind Energy, Javier Sanz Rodrigo, CENER, Johan Meyers, KU Leuven, Rebecca Barthelmie, Cornell University, Sandrine Aubrun-Sanches, Université d'Orléans and Thomas Leweke, IRPHE-CNRS. We are also immensely indebted to the very responsive support from the editorial team at IOP Publishing, especially Sarah Toms, during the review process of these proceedings. Visby, Sweden, June 2015 Andrew Barney, Jens Nørkær Sørensen and Stefan Ivanell Uppsala University - Campus Gotland

Existence domain of electrostatic solitary waves in the lunar wake

Science.gov (United States)

Rubia, R.; Singh, S. V.; Lakhina, G. S.

2018-03-01

Electrostatic solitary waves (ESWs) and double layers are explored in a four-component plasma consisting of hot protons, hot heavier ions (He++), electron beam, and suprathermal electrons having κ-distribution using the Sagdeev pseudopotential method. Three modes exist: slow and fast ion-acoustic modes and electron-acoustic mode. The occurrence of ESWs and their existence domain as a function of various plasma parameters, such as the number densities of ions and electron beam, the spectral index, κ, the electron beam velocity, the temperatures of ions, and electron beam, are analyzed. It is observed that both the slow and fast ion-acoustic modes support both positive and negative potential solitons as well as their coexistence. Further, they support a "forbidden gap," the region in which the soliton ceases to propagate. In addition, slow ion-acoustic solitons support the existence of both positive and negative potential double layers. The electron-acoustic mode is only found to support negative potential solitons for parameters relevant to the lunar wake plasma. Fast Fourier transform of a soliton electric field produces a broadband frequency spectrum. It is suggested that all three soliton types taken together can provide a good explanation for the observed electrostatic waves in the lunar wake.

Towed underwater PIV measurement for free-surface effects on turbulent wake of a surface-piercing body

Directory of Open Access Journals (Sweden)

Dong Myung Seol

2013-09-01

Full Text Available In the present study, a towed underwater particle image velocimetry (PIV system was validated in uniform flow and used to investigate the free-surface effects on the turbulent wake of a simple surface-piercing body. The selected test model was a cylindrical geometry formed by extruding the Wigley hull's waterplane shape in the vertical direction. Due to the constraints of the two-dimensional (2D PIV system used for the present study, the velocity field measurements were done separately for the vertical and horizontal planes. Using the measured data at several different locations, it was possible to identify the free-surface effects on the turbulent wake in terms of the mean velocity components and turbulence quantities. In order to provide an accuracy level of the data, uncertainty assessment was done following the International Towing Tank Conference standard procedure.

Efficient Turbulence Modeling for CFD Wake Simulations

DEFF Research Database (Denmark)

van der Laan, Paul

Wind turbine wakes can cause 10-20% annual energy losses in wind farms, and wake turbulence can decrease the lifetime of wind turbine blades. One way of estimating these effects is the use of computational fluid dynamics (CFD) to simulate wind turbines wakes in the atmospheric boundary layer. Since...... this flow is in the high Reynolds number regime, it is mainly dictated by turbulence. As a result, the turbulence modeling in CFD dominates the wake characteristics, especially in Reynolds-averaged Navier-Stokes (RANS). The present work is dedicated to study and develop RANS-based turbulence models...... verified with a grid dependency study. With respect to the standard k-ε EVM, the k-ε- fp EVM compares better with measurements of the velocity deficit, especially in the near wake, which translates to improved power deficits of the first wind turbines in a row. When the CFD metholody is applied to a large...

Noise emission from wind turbines in wake. Project report

Energy Technology Data Exchange (ETDEWEB)

Dam Madsen, K.; Plovsing, B. (DELTA, Hoersholm (Denmark)); Soerensen, Thomas (EMD International A/S, Aalborg (Denmark)); Aagaard Madsen, H.; Bertagnolio, F. (Technical Univ. of Denmark, Risoe National Lab. for Sustainable Energy, Roskilde (Denmark))

2011-03-15

When installing wind turbines in clusters or wind farms the inflow conditions to the wind turbines can be disturbed due to wake effects from other wind turbines. The effect of wake on noise generation from wind turbines are described in this report. The work is based on measurements carried out on a M80 2 MW wind turbine. To investigate the relationship between the far field noise levels and the surface pressure and inflow angles measured by sensors on an instrumented wind turbine blade, a parabolic measurement system (PMMS) was designed and tested as part of this project. Based on the measurement results obtained with surface pressure sensors and results from the far field measurements using the PMMS it is concluded that: The variance of surface pressure at the trailing edge (TE) agrees with the theory with regard to variation of pressure spectra with varying inflow angle (AoA) to the blade. Low frequency TE surface pressure increases with increased AoA and high frequency surface pressure decreases with increased AoA. It seems that the TE surface pressure remains almost unaltered during wake operation. Results from the surface transducers at the leading edge (LE) and the inflow angles determined from the pitot tube indicates that the inflow at LE is more turbulent in wake for the same AoA and with a low frequency characteristic, thereby giving rise to more low frequency noise generated during wake operation. The far field measurements supports that on one hand there will be produced relative more low frequency noise due to a turbulent inflow to the blade and on the other hand there will be produced less noise in the broader frequency range/high frequency range due to a lower inflow angle caused by the wind deficit in the wake. The net effect of wake on the total noise level is unresolved. As a secondary result it is seen that noise observed from a position on the ground is related to directional effects of the noise radiated from the wind turbine blade. For an

Detecting wind turbine wakes with nacelle lidars

DEFF Research Database (Denmark)

Held, D. P.; Larvol, A.; Mann, Jakob

2017-01-01

variance is used as a detection parameter for wakes. A one month long measurement campaign, where a continuous-wave lidar on a turbine has been exposed to multiple wake situations, is used to test the detection capabilities. The results show that it is possible to identify situation where a downstream...... turbine is in wake by comparing the peak widths. The used lidar is inexpensive and brings instalments on every turbine within economical reach. Thus, the information gathered by the lidars can be used for improved control at wind farm level....

Wake field accelerators

International Nuclear Information System (INIS)

Wilson, P.B.

1986-02-01

In a wake field accelerator a high current driving bunch injected into a structure or plasma produces intense induced fields, which are in turn used to accelerate a trailing charge or bunch. The basic concepts of wake field acceleration are described. Wake potentials for closed cavities and periodic structures are derived, as are wake potentials on a collinear path with a charge distribution. Cylindrically symmetric structures excited by a beam in the form of a ring are considered

The validity, reliability, and utility of the iButton® for measurement of body temperature circadian rhythms in sleep/wake research.

Science.gov (United States)

Hasselberg, Michael J; McMahon, James; Parker, Kathy

2013-01-01

Changes in core body temperature due to heat transfer through the skin have a major influence on sleep regulation. Traditional measures of skin temperature are often complicated by extensive wiring and are not practical for use in normal living conditions. This review describes studies examining the reliability, validity and utility of the iButton®, a wireless peripheral thermometry device, in sleep/wake research. A review was conducted of English language literature on the iButton as a measure of circadian body temperature rhythms associated with the sleep/wake cycle. Seven studies of the iButtton as a measure of human body temperature were included. The iButton was found to be a reliable and valid measure of body temperature. Its application to human skin was shown to be comfortable and tolerable with no significant adverse reactions. Distal skin temperatures were negatively correlated with sleep/wake activity, and the temperature gradient between the distal and proximal skin (DPG) was identified as an accurate physiological correlate of sleep propensity. Methodological issues included site of data logger placement, temperature masking factors, and temperature data analysis. The iButton is an inexpensive, wireless data logger that can be used to obtain a valid measurement of human skin temperature. It is a practical alternative to traditional measures of circadian rhythms in sleep/wake research. Further research is needed to determine the utility of the iButton in vulnerable populations, including those with neurodegenerative disorders and memory impairment and pediatric populations. Copyright © 2011 Elsevier B.V. All rights reserved.

Particle Entrainment in Spherical-Cap Wakes

Energy Technology Data Exchange (ETDEWEB)

Warncke, Norbert G W; Delfos, Rene; Ooms, Gijs; Westerweel, Jerry, E-mail: n.g.w.warncke@tudelft.nl [Laboratory for Aero- and Hydrodynamics, Delft University of Technology (Netherlands)

2011-12-22

In this work we study the preferential concentration of small particles in the turbulent wake behind a spherical-cap object. We present a model predicting the mean particle concentration in the near-wake as a function of the characteristic Stokes number of the problem, the turbulence level and the Froude number. We compare the model with our experimental results on this flow, measured in a vertical water tunnel.

Excessive daytime sleepiness in adult patients with ADHD as measured by the Maintenance of Wakefulness Test, an electrophysiologic measure.

Science.gov (United States)

Bioulac, Stéphanie; Chaufton, Cyril; Taillard, Jacques; Claret, Astrid; Sagaspe, Patricia; Fabrigoule, Colette; Bouvard, Manuel P; Philip, Pierre

2015-07-01

To quantify the objective level of sleepiness in adult attention-deficit/hyperactivity disorder (ADHD) patients and to determine the relationship between excessive daytime sleepiness and simulated driving performance. Forty adult ADHD patients (DSM-IV criteria) and 19 matched healthy control subjects were included between June 30, 2010, and June 19, 2013. All participants completed the Epworth Sleepiness Scale and the Manchester Driving Behavior Questionnaire. After nocturnal polysomnography, they performed 2 neuropsychological tests, a 4 × 40-minute Maintenance of Wakefulness Test, and a 1-hour driving session. The primary outcome measure was the mean sleep latency on the Maintenance of Wakefulness Test. ADHD patients were divided into 3 groups defined by their Maintenance of Wakefulness Test scores. Participants (patients and control subjects) were allocated as follows: sleepy ADHD (0-19 min), intermediate ADHD (20-33 min), alert ADHD (34-40 min), and control group (34-40 min). The driving performance outcome was the mean standard deviation of lateral position of the vehicle during the simulated session. The group mean (SD) Epworth Sleepiness Scale score was higher in ADHD patients (12.1 [4.4]) than in controls (6.0 [2.7]) (P driving performance compared to the other 3 groups (P driving performance. Excessive daytime sleepiness, therefore, may be a key element needed to better evaluate these ADHD patients. ClinicalTrials.gov identifier: NCT01160874. © Copyright 2015 Physicians Postgraduate Press, Inc.

Flow Structures within a Helicopter Rotor Hub Wake

Science.gov (United States)

Elbing, Brian; Reich, David; Schmitz, Sven

2015-11-01

A scaled model of a notional helicopter rotor hub was tested in the 48'' Garfield Thomas Water Tunnel at the Applied Research Laboratory Penn State. The measurement suite included total hub drag and wake velocity measurements (LDV, PIV, stereo-PIV) at three downstream locations. The main objective was to understand the spatiotemporal evolution of the unsteady wake between the rotor hub and the nominal location of the empennage (tail). Initial analysis of the data revealed prominent two- and four-per-revolution fluid structures linked to geometric hub features persisting into the wake far-field. In addition, a six-per-revolution fluid structure was observed in the far-field, which is unexpected due to the lack of any hub feature with the corresponding symmetry. This suggests a nonlinear interaction is occurring within the wake to generate these structures. This presentation will provide an overview of the experimental data and analysis with particular emphasis on these six-per-revolution structures.

Studies of Particle Wake Potentials in Plasmas

Science.gov (United States)

Ellis, Ian; Graziani, Frank; Glosli, James; Strozzi, David; Surh, Michael; Richards, David; Decyk, Viktor; Mori, Warren

2011-10-01

Fast Ignition studies require a detailed understanding of electron scattering, stopping, and energy deposition in plasmas with variable values for the number of particles within a Debye sphere. Presently there is disagreement in the literature concerning the proper description of these processes. Developing and validating proper descriptions requires studying the processes using first-principle electrostatic simulations and possibly including magnetic fields. We are using the particle-particle particle-mesh (PPPM) code ddcMD and the particle-in-cell (PIC) code BEPS to perform these simulations. As a starting point in our study, we examine the wake of a particle passing through a plasma in 3D electrostatic simulations performed with ddcMD and with BEPS using various cell sizes. In this poster, we compare the wakes we observe in these simulations with each other and predictions from Vlasov theory. Prepared by LLNL under Contract DE-AC52-07NA27344 and by UCLA under Grant DE-FG52-09NA29552.

Investigating fundamental properties of wind turbine wake structure using particle image velocimetry

Energy Technology Data Exchange (ETDEWEB)

Whale, J. [Univ. of Edinburgh, Dept. of Mechanical Engineering, Edinburgh (United Kingdom)

1997-08-01

Low Reynolds number flow visualization tests are often used for showing the flow pattern changes associated with changes in lift-coefficients at a higher Reynolds number. In wind turbine studies, analysis of measured wake structures at small scale may reveal fundamental properties of the wake which will offer wake modellers a more complete understanding of rotor flows. Measurements are presented from experiments on a model wind turbine rig conducted in a water channel. The laser-optics technique of Particle Image Velocimetry (PIV) is used to make simultaneous multi-point measurements of the wake flow behind small-scale rotors. Analysis of the PIV data shows trends in velocity and vorticity structure in the wake. Study of the flow close to the rotor plane reveals information on stalled flow and blade performance. (au)

Experimental investigation of an actively controlled three-dimensional turret wake

Science.gov (United States)

Shea, Patrick R.

Hemispherical turrets are bluff bodies commonly used to house optical systems on airborne platforms. These bluff bodies develop complex, three-dimensional flow fields that introduce high mean and fluctuating loads to the turret as well as the airframe support structure which reduce the performance of both the optical systems and the aircraft. An experimental investigation of the wake of a three-dimensional, non-conformal turret was performed in a low-speed wind tunnel at Syracuse University to develop a better understanding of the fundamental flow physics associated with the turret wake. The flow field was studied at a diameter based Reynolds number of 550,000 using stereoscopic particle image velocimetry and dynamic pressure measurements both with and without active flow control. Pressure measurements were simultaneously sampled with the PIV measurements and taken on the surrounding boundary layer plate and at several locations on the turret geometry. Active flow control of the turret wake was performed around the leading edge of the turret aperture using dynamic suction in steady open-loop, unsteady open-loop, and simple closed-loop configurations. Analysis of the uncontrolled wake provided insight into the complex three-dimensional wake when evaluated spatially using PIV measurements and temporally using spectral analysis of the pressure measurements. Steady open-loop suction was found to significantly alter the spatial and temporal nature of the turret wake despite the control being applied locally to the aperture region of the turret. Unsteady open-loop and simple closed-loop control were found to provide similar levels of control to the steady open-loop forcing with a 45% reduction in the control input as calculated using the jet momentum coefficient. The data set collected provides unique information regarding the development of the baseline three-dimensional wake and the wake with three different active flow control configurations. These data can be used to

Modelling and Measuring Flow and Wind Turbine Wakes in Large Wind Farms Offshore

DEFF Research Database (Denmark)

Barthelmie, Rebecca Jane; Hansen, Kurt Schaldemose; Frandsen, Sten Tronæs

2009-01-01

power losses due to wakes and loads. The research presented is part of the EC-funded UpWind project, which aims to radically improve wind turbine and wind farm models in order to continue to improve the costs of wind energy. Reducing wake losses, or even reduce uncertainties in predicting power losses...

FastStats: Body Measurements

Science.gov (United States)

... this? Submit What's this? Submit Button NCHS Home Body Measurements Recommend on Facebook Tweet Share Compartir Data ... 7 MB] Related FastStats Obesity/Overweight Related Links Body Mass Index table CDC Growth Charts National Health ...

Wake meandering under non-neutral atmospheric stability conditions – theory and facts

DEFF Research Database (Denmark)

Larsen, Gunner Chr.; Machefaux, Ewan; Chougule, Abhijit S.

2015-01-01

This paper deals with modelling of wake dynamics under influence of atmospheric stability conditions different from neutral. In particular, it is investigated how the basic split in turbulent scales, on which the Dynamic Wake Meandering model is based, can be utilized to include atmospheric...... stability effects in this model. This is done partly by analyzing a large number of turbulence spectra obtained from sonic measurements, partly by analyzing dedicated full-scale LiDAR measurements from which wake dynamics can be directly resolved. The theory behind generalizing the Dynamic Wake Meandering...

Influence of short rear end tapers on the wake of a simplified square-back vehicle: wake topology and rear drag

Science.gov (United States)

Perry, Anna-Kristina; Pavia, Giancarlo; Passmore, Martin

2016-11-01

As vehicle manufacturers work to reduce energy consumption of all types of vehicles, external vehicle aerodynamics has become increasingly important. Whilst production vehicle shape optimisation methods are well developed, the need to make further advances requires deeper understanding of the highly three-dimensional flow around bluff bodies. In this paper, the wake flow of a generic bluff body, the Windsor body, based on a square-back car geometry, was investigated by means of balance measurements, surface pressure measurements and 2D particle image velocimetry planes. Changes in the wake topology are triggered by the application of short tapers (4 % of the model length) to the top and bottom edges of the base, representing a shape optimisation that is realistic for many modern production vehicles. The base drag is calculated and correlated with the aerodynamic drag data. The results not only show the effectiveness of such small devices in modifying the time average topology of the wake but also shed some light on the effects produced by different levels of upwash and downwash on the bi-stable nature of the wake itself.

Characterization of an Actively Controlled Three-Dimensional Turret Wake

Science.gov (United States)

Shea, Patrick; Glauser, Mark

2012-11-01

Three-dimensional turrets are commonly used for housing optical systems on airborne platforms. As bluff bodies, these geometries generate highly turbulent wakes that decrease the performance of the optical systems and the aircraft. The current experimental study looked to use dynamic suction in both open and closed-loop control configurations to actively control the turret wake. The flow field was characterized using dynamic pressure and stereoscopic PIV measurements in the wake of the turret. Results showed that the suction system was able to manipulate the wake region of the turret and could alter not only the spatial structure of the wake, but also the temporal behavior of the wake flow field. Closed-loop, feedback control techniques were used to determine a more optimal control input for the flow control. Similar control effects were seen for both the steady open-loop control case and the closed-loop feedback control configuration with a 45% reduction in the suction levels when comparing the closed-loop to the open-loop case. These results provide unique information regarding the development of the baseline three-dimensional wake and the wake with three different active flow control configurations.

Next Generation Scanning LIDAR Systems for Optimizing Wake Turbulence Separation Minima

Directory of Open Access Journals (Sweden)

Ludovic Thobois

2017-12-01

Full Text Available Numerous studies have been performed to better understand the behavior of wake vortices with regards to aircraft characteristics and weather conditionsover the pastten years. These studies have led to the development of the aircraft RECATegorization (RECAT programs in Europe and in USA. Its phase one focused on redefining distance separation matrix with six static aircraft wake turbulence categories instead of three with the current International Civil Aviation Organization (ICAO regulations. In Europe, the RECAT-EU regulation is now entering under operational implementation atseveral key airports. As proven by several research projects in the past, LIght Detection And Ranging (LIDAR sensors are considered as the ground truth wake vortex measurements for assessing the safety impact of a new wake turbulence regulation at an airport in quantifying the risks given the local specificities. LIDAR’s can also be used to perform risk monitoring after the implementation. In this paper, the principle to measure wake vortices with scanning coherent Doppler LIDARs is described as well as its dedicated post-processing. Finally the use of WINDCUBELIDAR based solution for supporting the implementation of new wake turbulenceregulation is described along with satisfyingresults that have permitted the monitoring of the wake vortex encounter risk after the implementation of a new wake turbulence regulation.

Extragalactic dispersion measures of fast radio bursts

International Nuclear Information System (INIS)

Xu, Jun; Han, J. L.

2015-01-01

Fast radio bursts show large dispersion measures, much larger than the Galactic dispersion measure foreground. Therefore, they evidently have an extragalactic origin. We investigate possible contributions to the dispersion measure from host galaxies. We simulate the spatial distribution of fast radio bursts and calculate the dispersion measures along the sightlines from fast radio bursts to the edge of host galaxies by using the scaled NE2001 model for thermal electron density distributions. We find that contributions to the dispersion measure of fast radio bursts from the host galaxy follow a skew Gaussian distribution. The peak and the width at half maximum of the dispersion measure distribution increase with the inclination angle of a spiral galaxy, to large values when the inclination angle is over 70°. The largest dispersion measure produced by an edge-on spiral galaxy can reach a few thousand pc cm −3 , while the dispersion measures from dwarf galaxies and elliptical galaxies have a maximum of only a few tens of pc cm −3 . Notice, however, that additional dispersion measures of tens to hundreds of pc cm −3 can be produced by high density clumps in host galaxies. Simulations that include dispersion measure contributions from the Large Magellanic Cloud and the Andromeda Galaxy are shown as examples to demonstrate how to extract the dispersion measure from the intergalactic medium. (paper)

Crosswind Shear Gradient Affect on Wake Vortices

Science.gov (United States)

Proctor, Fred H.; Ahmad, Nashat N.

2011-01-01

Parametric simulations with a Large Eddy Simulation (LES) model are used to explore the influence of crosswind shear on aircraft wake vortices. Previous studies based on field measurements, laboratory experiments, as well as LES, have shown that the vertical gradient of crosswind shear, i.e. the second vertical derivative of the environmental crosswind, can influence wake vortex transport. The presence of nonlinear vertical shear of the crosswind velocity can reduce the descent rate, causing a wake vortex pair to tilt and change in its lateral separation. The LES parametric studies confirm that the vertical gradient of crosswind shear does influence vortex trajectories. The parametric results also show that vortex decay from the effects of shear are complex since the crosswind shear, along with the vertical gradient of crosswind shear, can affect whether the lateral separation between wake vortices is increased or decreased. If the separation is decreased, the vortex linking time is decreased, and a more rapid decay of wake vortex circulation occurs. If the separation is increased, the time to link is increased, and at least one of the vortices of the vortex pair may have a longer life time than in the case without shear. In some cases, the wake vortices may never link.

Modelling and measurements of wakes in large wind farms

DEFF Research Database (Denmark)

Barthelmie, Rebecca Jane; Rathmann, Ole; Frandsen, Sten Tronæs

2007-01-01

The paper presents research conducted in the Flow workpackage of the EU funded UPWIND project which focuses on improving models of flow within and downwind of large wind farms in complex terrain and offshore. The main activity is modelling the behaviour of wind turbine wakes in order to improve...

Wind turbine wake in atmospheric turbulence

Energy Technology Data Exchange (ETDEWEB)

Rethore, P -E

2009-10-15

This thesis describes the different steps needed to design a steady-state computational fluid dynamics (CFD) wind farm wake model. The ultimate goal of the project was to design a tool that could analyze and extrapolate systematically wind farm measurements to generate wind maps in order to calibrate faster and simpler engineering wind farm wake models. The most attractive solution was the actuator disc method with the steady state k-epsilon turbulence model. The first step to design such a tool is the treatment of the forces. This thesis presents a computationally inexpensive method to apply discrete body forces into the finite-volume flow solver with collocated variable treatment (EllipSys), which avoids the pressure-velocity decoupling issue. The second step is to distribute the body forces in the computational domain accordingly to rotor loading. This thesis presents a generic flexible method that associates any kind of shapes with the computational domain discretization. The special case of the actuator disc performs remarkably well in comparison with Conway's heavily loaded actuator disc analytical solution and a CFD full rotor computation, even with a coarse discretization. The third step is to model the atmospheric turbulence. The standard k-epsilon model is found to be unable to model at the same time the atmospheric turbulence and the actuator disc wake and performs badly in comparison with single wind turbine wake measurements. A comparison with a Large Eddy Simulation (LES) shows that the problem mainly comes from the assumptions of the eddy-viscosity concept, which are deeply invalidated in the wind turbine wake region. Different models that intent to correct the k-epsilon model's issues are investigated, of which none of them is found to be adequate. The mixing of the wake in the atmosphere is a deeply non-local phenomenon that is not handled correctly by an eddy-viscosity model such as k-epsilon. (author)

Wind turbine wake in atmospheric turbulence

Energy Technology Data Exchange (ETDEWEB)

Rethore, P.-E.

2009-10-15

This thesis describes the different steps needed to design a steady-state computational fluid dynamics (CFD) wind farm wake model. The ultimate goal of the project was to design a tool that could analyze and extrapolate systematically wind farm measurements to generate wind maps in order to calibrate faster and simpler engineering wind farm wake models. The most attractive solution was the actuator disc method with the steady state k-epsilon turbulence model. The first step to design such a tool is the treatment of the forces. This thesis presents a computationally inexpensive method to apply discrete body forces into the finite-volume flow solver with collocated variable treatment (EllipSys), which avoids the pressure-velocity decoupling issue. The second step is to distribute the body forces in the computational domain accordingly to rotor loading. This thesis presents a generic flexible method that associates any kind of shapes with the computational domain discretization. The special case of the actuator disc performs remarkably well in comparison with Conway's heavily loaded actuator disc analytical solution and a CFD full rotor computation, even with a coarse discretization. The third step is to model the atmospheric turbulence. The standard k-epsilon model is found to be unable to model at the same time the atmospheric turbulence and the actuator disc wake and performs badly in comparison with single wind turbine wake measurements. A comparison with a Large Eddy Simulation (LES) shows that the problem mainly comes from the assumptions of the eddy-viscosity concept, which are deeply invalidated in the wind turbine wake region. Different models that intent to correct the k-epsilon model's issues are investigated, of which none of them is found to be adequate. The mixing of the wake in the atmosphere is a deeply non-local phenomenon that is not handled correctly by an eddy-viscosity model such as k-epsilon. (author)

Nonlinear Eddy Viscosity Models applied to Wind Turbine Wakes

DEFF Research Database (Denmark)

Laan, van der, Paul Maarten; Sørensen, Niels N.; Réthoré, Pierre-Elouan

2013-01-01

The linear k−ε eddy viscosity model and modified versions of two existing nonlinear eddy viscosity models are applied to single wind turbine wake simulations using a Reynolds Averaged Navier-Stokes code. Results are compared with field wake measurements. The nonlinear models give better results...

Molecular Dynamic Studies of Particle Wake Potentials in Plasmas

Science.gov (United States)

Ellis, Ian; Graziani, Frank; Glosli, James; Strozzi, David; Surh, Michael; Richards, David; Decyk, Viktor; Mori, Warren

2010-11-01

Fast Ignition studies require a detailed understanding of electron scattering, stopping, and energy deposition in plasmas with variable values for the number of particles within a Debye sphere. Presently there is disagreement in the literature concerning the proper description of these processes. Developing and validating proper descriptions requires studying the processes using first-principle electrostatic simulations and possibly including magnetic fields. We are using the particle-particle particle-mesh (P^3M) code ddcMD to perform these simulations. As a starting point in our study, we examined the wake of a particle passing through a plasma. In this poster, we compare the wake observed in 3D ddcMD simulations with that predicted by Vlasov theory and those observed in the electrostatic PIC code BEPS where the cell size was reduced to .03λD.

Comparison between PIV measurements and computations of the near-wake of an actuator disc

DEFF Research Database (Denmark)

Andersen, Søren Juhl; Lignarolo, L. E. M.; Ragni, D.

2014-01-01

on the turbulent structures in the shear layer at the borders of the wake through the analysis of the Reynolds stresses and by employing POD on two separate regions. The analysis shows that the actuator discs fail to capture the details of the complex flow behind a rotor, but that the experimental and numerical...... the complex flow structures correctly, which affects the downstream representation of the full wake behind a real rotor. The near wake region is characterised by the instability and breakdown of the tip-vortex helical system, which constitutes the onset of a stronger mixing process. The comparison focuses...

Fast and Objective MRTD measurement

NARCIS (Netherlands)

Jong, A.N. de; Bakker, S.J.M.

1988-01-01

Manufacturers and Users of the Thermal Imagers have spent very much time upon the definition and measurement of the generally accepted performance curve: MRTD (Minimum Resolvable Temperature Difference). The need for a cheap and fast, objective measurement method has considerably increased since the

A Fast-Starting Robotic Fish

Science.gov (United States)

Modarres-Sadeghi, Yahya; Watts, Matthew; Conte, Joe; Hover, Franz; Triantafyllou, Michael

2009-11-01

We have built a simple mechanical system to emulate the fast-start performance of fish. The system consisted of a thin metal beam covered by a urethane rubber fish body. The body form of the mechanical fish in this work was modeled from a pike species, which is the most successfully studied fast-start specialist species. The mechanical fish was held in curvature and hung in water by two restraining lines, which were simultaneously released by pneumatic cutting mechanisms. The potential energy in the beam was transferred into the fluid, thereby accelerating the fish, similar to a pike. We measured the resulting velocity and acceleration, as well as the efficiency of propulsion for the mechanical fish model and also ran a series of flow visualization tests to observe the resulting flow pattern. We also studied the influence of stiffness and geometry of the tail on the efficiency of propulsion and flow pattern. The hydrodynamic efficiency of the fish, calculated by the transfer of energy, was around 10%. Flow visualization of the mechanical fast-start wake was also analyzed, showing that the acceleration is associated with the fast movement of an intense vortex in a near-lateral direction.

Modelling and measurements of wakes in large wind farms

International Nuclear Information System (INIS)

Barthelmie, R J; Rathmann, O; Frandsen, S T; Hansen, K S; Politis, E; Prospathopoulos, J; Rados, K; Cabezon, D; Schlez, W; Phillips, J; Neubert, A; Schepers, J G; Pijl, S P van der

2007-01-01

The paper presents research conducted in the Flow workpackage of the EU funded UPWIND project which focuses on improving models of flow within and downwind of large wind farms in complex terrain and offshore. The main activity is modelling the behaviour of wind turbine wakes in order to improve power output predictions

Comparative jet wake structure and swimming performance of salps.

Science.gov (United States)

Sutherland, Kelly R; Madin, Laurence P

2010-09-01

Salps are barrel-shaped marine invertebrates that swim by jet propulsion. Morphological variations among species and life-cycle stages are accompanied by differences in swimming mode. The goal of this investigation was to compare propulsive jet wakes and swimming performance variables among morphologically distinct salp species (Pegea confoederata, Weelia (Salpa) cylindrica, Cyclosalpa sp.) and relate swimming patterns to ecological function. Using a combination of in situ dye visualization and particle image velocimetry (PIV) measurements, we describe properties of the jet wake and swimming performance variables including thrust, drag and propulsive efficiency. Locomotion by all species investigated was achieved via vortex ring propulsion. The slow-swimming P. confoederata produced the highest weight-specific thrust (T=53 N kg(-1)) and swam with the highest whole-cycle propulsive efficiency (eta(wc)=55%). The fast-swimming W. cylindrica had the most streamlined body shape but produced an intermediate weight-specific thrust (T=30 N kg(-1)) and swam with an intermediate whole-cycle propulsive efficiency (eta(wc)=52%). Weak swimming performance variables in the slow-swimming C. affinis, including the lowest weight-specific thrust (T=25 N kg(-1)) and lowest whole-cycle propulsive efficiency (eta(wc)=47%), may be compensated by low energetic requirements. Swimming performance variables are considered in the context of ecological roles and evolutionary relationships.

Vertical axis wind turbine wake in boundary layer flow in a wind tunnel

Science.gov (United States)

Rolin, Vincent; Porté-Agel, Fernando

2016-04-01

A vertical axis wind turbine is placed in a boundary layer flow in a wind tunnel, and its wake is investigated. Measurements are performed using an x-wire to measure two components of velocity and turbulence statistics in the wake of the wind turbine. The study is performed at various heights and crosswind positions in order to investigate the full volume of the wake for a range of tip speed ratios. The velocity deficit and levels of turbulence in the wake are related to the performance of the turbine. The asymmetric incoming boundary layer flow causes the rate of recovery in the wake to change as a function of height. Higher shear between the wake and unperturbed flow occurs at the top edge of the wake, inducing stronger turbulence and mixing in this region. The difference in flow relative to the blades causes the velocity deficit and turbulence level to change as a function of crosswind position behind the rotor. The relative difference diminishes with increasing tip speed ratio. Therefore, the wake becomes more homogeneous as tip speed ratio increases.

Self-similar potential in the near wake

International Nuclear Information System (INIS)

Diebold, D.; Hershkowitz, N.; Intrator, T.; Bailey, A.

1987-01-01

The plasma potential is measured near the edge of an electrically floating obstacle placed in a steady-state, supersonic, unmagnetized, neutral plasma flow. Equipotential contours show the sheath of the upstream side of the obstacle wrapping around the edge of the obstacle and fanning out into the near wake. Both fluid theory and the data find the near-wake plasma potential to be self-similar when ionization, charge exchange, and magnetic field can be neglected. The theory also finds that fluid velocity is self-similar, the near wake is nonneutral, and plasma density is not self-similar. Strong electric fields are found near the obstacle and equipotential contours are found to conform to all boundaries

Quantifying error of lidar and sodar Doppler beam swinging measurements of wind turbine wakes using computational fluid dynamics

Science.gov (United States)

Lundquist, J. K.; Churchfield, M. J.; Lee, S.; Clifton, A.

2015-02-01

Wind-profiling lidars are now regularly used in boundary-layer meteorology and in applications such as wind energy and air quality. Lidar wind profilers exploit the Doppler shift of laser light backscattered from particulates carried by the wind to measure a line-of-sight (LOS) velocity. The Doppler beam swinging (DBS) technique, used by many commercial systems, considers measurements of this LOS velocity in multiple radial directions in order to estimate horizontal and vertical winds. The method relies on the assumption of homogeneous flow across the region sampled by the beams. Using such a system in inhomogeneous flow, such as wind turbine wakes or complex terrain, will result in errors. To quantify the errors expected from such violation of the assumption of horizontal homogeneity, we simulate inhomogeneous flow in the atmospheric boundary layer, notably stably stratified flow past a wind turbine, with a mean wind speed of 6.5 m s-1 at the turbine hub-height of 80 m. This slightly stable case results in 15° of wind direction change across the turbine rotor disk. The resulting flow field is sampled in the same fashion that a lidar samples the atmosphere with the DBS approach, including the lidar range weighting function, enabling quantification of the error in the DBS observations. The observations from the instruments located upwind have small errors, which are ameliorated with time averaging. However, the downwind observations, particularly within the first two rotor diameters downwind from the wind turbine, suffer from errors due to the heterogeneity of the wind turbine wake. Errors in the stream-wise component of the flow approach 30% of the hub-height inflow wind speed close to the rotor disk. Errors in the cross-stream and vertical velocity components are also significant: cross-stream component errors are on the order of 15% of the hub-height inflow wind speed (1.0 m s-1) and errors in the vertical velocity measurement exceed the actual vertical velocity

PIV in a model wind turbine rotor wake

DEFF Research Database (Denmark)

Meyer, Knud Erik; Naumov, Igor; Karbadin, Ivan

2013-01-01

Stereoscopic particle image velocimetry (PIV) measurements of the flow in the wake of scale model of a horizontal axis wind turbine is presented Near the rotor, measurements are made in vertical planes intersecting the rotor axis These planes capture flow effect from the tip and root vortices...... perpendicular to the rotor axis is used to investigate the dynamics in the far wake Here, a precessing core is found and data indicate that the Strouhal number of the precessing is independent of the rotor speed...

Spectral function calculation of angle wakes, wake moments, and misalignment wakes for the SLAC Damped Detuned Structures (DDS)

International Nuclear Information System (INIS)

Jones, R.M.; Miller, R.H.; Kroll, N.M.

1997-05-01

Transverse wake functions so far reported for the SLAC DDS have been limited to those caused by uniform offset of the drive beam in a straight perfectly aligned structure. The complete description of the betatron oscillations of wake coupled bunches requires an array of wake functions, referred to as moments. Modifications of these arrays induced by structure misalignments are also of interest. In this paper we express the array elements in terms of a spectral function array. Examples are given based upon DDS1

Fast-ion Dα measurements of the fast-ion distribution (invited)

International Nuclear Information System (INIS)

Heidbrink, W. W.

2010-01-01

The fast-ion Dα (FIDA) diagnostic is an application of charge-exchange recombination spectroscopy. Fast ions that neutralize in an injected neutral beam emit Balmer-α light with a large Doppler shift. The spectral shift is exploited to distinguish the FIDA emission from other bright sources of Dα light. Background subtraction is the main technical challenge. A spectroscopic diagnostic typically achieves temporal, energy, and transverse spatial resolution of ∼1 ms, ∼10 keV, and ∼2 cm, respectively. Installations that use narrow-band filters achieve high spatial and temporal resolution at the expense of spectral information. For high temporal resolution, the bandpass-filtered light goes directly to a photomultiplier, allowing detection of ∼50 kHz oscillations in FIDA signal. For two-dimensional spatial profiles, the bandpass-filtered light goes to a charge-coupled device camera; detailed images of fast-ion redistribution at instabilities are obtained. Qualitative and quantitative models relate the measured FIDA signals to the fast-ion distribution function. The first quantitative comparisons between theory and experiment found excellent agreement in beam-heated magnetohydrodynamics (MHD)-quiescent plasmas. FIDA diagnostics are now in operation at magnetic-fusion facilities worldwide. They are used to study fast-ion acceleration by ion cyclotron heating, to detect fast-ion transport by MHD modes and microturbulence, and to study fast-ion driven instabilities.

Accurate wind farm development and operation. Advanced wake modelling

Energy Technology Data Exchange (ETDEWEB)

Brand, A.; Bot, E.; Ozdemir, H. [ECN Unit Wind Energy, P.O. Box 1, NL 1755 ZG Petten (Netherlands); Steinfeld, G.; Drueke, S.; Schmidt, M. [ForWind, Center for Wind Energy Research, Carl von Ossietzky Universitaet Oldenburg, D-26129 Oldenburg (Germany); Mittelmeier, N. REpower Systems SE, D-22297 Hamburg (Germany))

2013-11-15

The ability is demonstrated to calculate wind farm wakes on the basis of ambient conditions that were calculated with an atmospheric model. Specifically, comparisons are described between predicted and observed ambient conditions, and between power predictions from three wind farm wake models and power measurements, for a single and a double wake situation. The comparisons are based on performance indicators and test criteria, with the objective to determine the percentage of predictions that fall within a given range about the observed value. The Alpha Ventus site is considered, which consists of a wind farm with the same name and the met mast FINO1. Data from the 6 REpower wind turbines and the FINO1 met mast were employed. The atmospheric model WRF predicted the ambient conditions at the location and the measurement heights of the FINO1 mast. May the predictability of the wind speed and the wind direction be reasonable if sufficiently sized tolerances are employed, it is fairly impossible to predict the ambient turbulence intensity and vertical shear. Three wind farm wake models predicted the individual turbine powers: FLaP-Jensen and FLaP-Ainslie from ForWind Oldenburg, and FarmFlow from ECN. The reliabilities of the FLaP-Ainslie and the FarmFlow wind farm wake models are of equal order, and higher than FLaP-Jensen. Any difference between the predictions from these models is most clear in the double wake situation. Here FarmFlow slightly outperforms FLaP-Ainslie.

Wake flow control using a dynamically controlled wind turbine

Science.gov (United States)

Castillo, Ricardo; Wang, Yeqin; Pol, Suhas; Swift, Andy; Hussain, Fazle; Westergaard, Carsten; Texas Tech University Team

2016-11-01

A wind tunnel based "Hyper Accelerated Wind Farm Kinematic-Control Simulator" (HAWKS) is being built at Texas Tech University to emulate controlled wind turbine flow physics. The HAWKS model turbine has pitch, yaw and speed control which is operated in real model time, similar to that of an equivalent full scale turbine. Also, similar to that of a full scale wind turbine, the controls are developed in a Matlab Simulink environment. The current diagnostic system consists of power, rotor position, rotor speed measurements and PIV wake characterization with four cameras. The setup allows up to 7D downstream of the rotor to be mapped. The purpose of HAWKS is to simulate control strategies at turnaround times much faster than CFD and full scale testing. The fundamental building blocks of the simulator have been tested, and demonstrate wake steering for both static and dynamic turbine actuation. Parameters which have been studied are yaw, rotor speed and combinations hereof. The measured wake deflections for static yaw cases are in agreement with previously reported research implying general applicability of the HAWKS platform for the purpose of manipulating the wake. In this presentation the general results will be introduced followed by an analysis of the wake turbulence and coherent structures when comparing static and dynamic flow cases. The outcome of such studies could ultimately support effective wind farm wake flow control strategies. Texas Emerging Technology Fund (ETF).

Wake structure of a single vertical axis wind turbine

International Nuclear Information System (INIS)

Posa, Antonio; Parker, Colin M.; Leftwich, Megan C.; Balaras, Elias

2016-01-01

Highlights: • The wake structure of an isolated Vertical Axis Wind Turbine is studied by both Particle Imaging Velocimetry and Large Eddy Simulation. • The wake structure is investigated for two values of tip speed ratio, TSR_1=1.35 and TSR_2=2.21. • A displacement of the momentum deficit towards the windward side is verified in the wake. • Higher turbulence and coherence is observed on the leeward side of the wake, due to the upwind stall of the blades. • Coherence in the wake core, associated to the downwind stall, decays quickly downstream. - Abstract: The wake structure behind a vertical axis wind turbine (VAWT) is both measured in a wind tunnel using particle imaging velocimetry (PIV) and computed with large-eddy simulation (LES). Geometric and dynamic conditions are closely matched to typical applications of VAWTs (Re_D ∼ 1.8 × 10"5). The experiments and computations were highly coordinated with continuous two-way feedback to produce the most insightful results. Good qualitative agreement is seen between the computational and experimental results. The dependence of the wake structure on the tip speed ratio, TSR, is investigated, showing higher asymmetry and larger vortices at the lower rotational speed, due to stronger dynamic stall phenomena. Instantaneous, ensemble-averaged and phase-averaged fields are discussed, as well as the dynamics of coherent structures in the rotor region and downstream wake.

Wake-based ship route estimation in high-resolution SAR images

Science.gov (United States)

Graziano, M. Daniela; Rufino, Giancarlo; D'Errico, Marco

2014-10-01

This paper presents a novel algorithm for wake detection in Synthetic Aperture Radar images of the sea. The algorithm has been conceived as part of a ship traffic monitoring system, in charge of ship detection validation and to estimate ship route features, such as heading and ground speed. In addition, it has been intended to be adequate for inclusion in an automatic procedure without human operator supervision. The algorithm exploits the Radon transform to identify the images ship wake on the basis of the well known theoretical characteristics of the wakes' geometry and components, that are the turbulent wake, the narrow-V wakes, and the Kelvin arms, as well as the typical appearance of such components in Synthetic Aperture Radar images of the sea as bright or dark linear feature. Examples of application to high-resolution X-band Synthetic Aperture Radar products (COSMOSkymed and TerraSAR-X) are reported, both for wake detection and ship route estimation, showing the achieved quality and reliability of wake detection, adequacy to automatic procedures, as well as speed measure accuracy.

Fast Neutral Pressure Measurements in NSTX

International Nuclear Information System (INIS)

R. Raman; H.W. Kugel; T. Provost; R. Gernhardt; T.R. Jarboe; M.G. Bell

2002-01-01

Several fast neutral pressure gauges have been installed on NSTX [National Spherical Torus Experiment] to measure the vessel and divertor pressure during inductive and coaxial helicity injected (CHI) plasma operations. Modified, PDX [Poloidal Divertor Experiment]-type Penning gauges have been installed on the upper and lower divertors. Neutral pressure measurements during plasma operations from these and from two shielded fast Micro ion gauges at different toroidal locations on the vessel mid-plane are described. A new unshielded ion gauge, referred to as the In-vessel Neutral Pressure (INP) gauge is under development

A wind-tunnel investigation of wind-turbine wakes in different yawed and loading conditions

Science.gov (United States)

Bastankhah, Majid; Porté-Agel, Fernando

2015-04-01

Wind-turbine wakes have negative effects on wind-farm performance. They are associated with: (a) the velocity deficit, which reduces the generated power of downwind turbines; and (b) the turbulence level, which increases the fatigue loads on downwind turbines. Controlling the yaw angle of turbines can potentially improve the performance of wind farms by deflecting the wake away from downwind turbines. However, except for few studies, wakes of yawed turbines still suffer from the lack of systematic research. To fill this research gap, we performed wind-tunnel experiments in the recirculating boundary-layer wind tunnel at the WIRE Laboratory of EPFL to better understand the wakes of yawed turbines. High-resolution stereoscopic particle image-velocimetry (S-PIV) was used to measure three velocity components in a horizontal plane located downwind of a horizontal-axis, three-blade model turbine. A servo-controller was connected to the DC generator of the turbine, which allowed us to apply different loadings. The power and thrust coefficients of the turbine were also measured for each case. These power and thrust measurements together with the highly-resolved flow measurements enabled us to study different wake characteristics such as the energy entrainment from the outer flow into the wake, the wake deflection and the helicoidal tip vortices for yawed turbines.

Optimization Under Uncertainty for Wake Steering Strategies: Preprint

Energy Technology Data Exchange (ETDEWEB)

Quick, Julian [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Annoni, Jennifer [National Renewable Energy Laboratory (NREL), Golden, CO (United States); King, Ryan N [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Dykes, Katherine L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Fleming, Paul A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Ning, Andrew [Brigham Young University

2017-05-01

Wind turbines in a wind power plant experience significant power losses because of aerodynamic interactions between turbines. One control strategy to reduce these losses is known as 'wake steering,' in which upstream turbines are yawed to direct wakes away from downstream turbines. Previous wake steering research has assumed perfect information, however, there can be significant uncertainty in many aspects of the problem, including wind inflow and various turbine measurements. Uncertainty has significant implications for performance of wake steering strategies. Consequently, the authors formulate and solve an optimization under uncertainty (OUU) problem for finding optimal wake steering strategies in the presence of yaw angle uncertainty. The OUU wake steering strategy is demonstrated on a two-turbine test case and on the utility-scale, offshore Princess Amalia Wind Farm. When we accounted for yaw angle uncertainty in the Princess Amalia Wind Farm case, inflow-direction-specific OUU solutions produced between 0% and 1.4% more power than the deterministically optimized steering strategies, resulting in an overall annual average improvement of 0.2%. More importantly, the deterministic optimization is expected to perform worse and with more downside risk than the OUU result when realistic uncertainty is taken into account. Additionally, the OUU solution produces fewer extreme yaw situations than the deterministic solution.

Development of Optical Fiber Detector for Measurement of Fast Neutron

International Nuclear Information System (INIS)

YAGI, Takahiro; KAWAGUCHI, Shinichi; MISAWA, Tsuyoshi; PYEON, Cheol Ho; UNESAKI, Hironobu; SHIROYA, Seiji; OKAJIMA, Shigeaki; TANI, Kazuhiro

2008-01-01

Measurement of fast neutron flux is important for investigation of characteristic of fast reactors. In order to insert a neutron detector in a narrow space such as a gap of between fuel plates and measure the fast neutrons in real time, a neutron detector with an optical fiber has been developed. This detector consists of an optical fiber whose tip is covered with mixture of neutron converter material and scintillator such as ZnS(Ag). The detector for fast neutrons uses ThO 2 as converter material because 232 Th makes fission reaction with fast neutrons. The place where 232 Th can be used is limited by regulations because 232 Th is nuclear fuel material. The purpose of this research is to develop a new optical fiber detector to measure fast neutrons without 232 Th and to investigate the characteristic of the detector. These detectors were used to measure a D-T neutron generator and fast neutron flux distribution at Fast Critical Assembly. The results showed that the fast neutron flux distribution of the new optical fiber detector with ZnS(Ag) was the same as it of the activation method, and the detector are effective for measurement of fast neutrons. (authors)

Wake characteristics of wind turbines in utility-scale wind farms

Science.gov (United States)

Yang, Xiaolei; Foti, Daniel; Sotiropoulos, Fotis

2017-11-01

The dynamics of turbine wakes is affected by turbine operating conditions, ambient atmospheric turbulent flows, and wakes from upwind turbines. Investigations of the wake from a single turbine have been extensively carried out in the literature. Studies on the wake dynamics in utility-scale wind farms are relatively limited. In this work, we employ large-eddy simulation with an actuator surface or actuator line model for turbine blades to investigate the wake dynamics in utility-scale wind farms. Simulations of three wind farms, i.e., the Horns Rev wind farm in Denmark, Pleasant Valley wind farm in Minnesota, and the Vantage wind farm in Washington are carried out. The computed power shows a good agreement with measurements. Analysis of the wake dynamics in the three wind farms is underway and will be presented in the conference. This work was support by Xcel Energy (RD4-13). The computational resources were provided by National Renewable Energy Laboratory.

Sleep-Wake Patterns and Sleep Disturbance among Hong Kong Chinese Adolescents

OpenAIRE

Chung, Ka-Fai; Cheung, Miao-Miao

2008-01-01

STUDY OBJECTIVES: To determine sleep-wake patterns and evaluate sleep disturbance in Hong Kong adolescents; to identify factors that are associated with sleep disturbance; and to examine the relationship of sleep-wake variables and academic performance. DESIGN AND SETTING: A school-based cross-sectional survey. PARTICIPANTS: Sample included 1629 adolescents aged 12 to 19 years. MEASUREMENTS AND RESULTS: Self-report questionnaires, including sleep-wake habit questionnaire,...

Wake effects on Middelgrund Windfarm

DEFF Research Database (Denmark)

Ejsing Jørgensen, Hans; Frandsen, S.; Vølund, P.

2003-01-01

This report describes the data analysis of the Middelgrund Wind Farm online collected data with the purpose of calculating the wake effects and turbulence intensities within the wind farm when maximum wake effects are present. The data are compared to themost commonly used wake model PARK...... decreasing wind speed through the array when the wind iscoming from north. The turbulence intensity is enhanced up to 0.3 due to the wake effects. The analysis has shown that this enhancement is nearly independent of the number of turbines involved in the wake creation....

Aerodynamic optimization of wind turbine rotors using a blade element momentum method with corrections for wake rotation and expansion

DEFF Research Database (Denmark)

Døssing, Mads; Aagaard Madsen, Helge; Bak, Christian

2012-01-01

The blade element momentum (BEM) method is widely used for calculating the quasi-steady aerodynamics of horizontal axis wind turbines. Recently, the BEM method has been expanded to include corrections for wake expansion and the pressure due to wake rotation (), and more accurate solutions can now...... by the positive effect of wake rotation, which locally causes the efficiency to exceed the Betz limit. Wake expansion has a negative effect, which is most important at high tip speed ratios. It was further found that by using , it is possible to obtain a 5% reduction in flap bending moment when compared with BEM....... In short, allows fast aerodynamic calculations and optimizations with a much higher degree of accuracy than the traditional BEM model. Copyright © 2011 John Wiley & Sons, Ltd....

Electron-Cloud Wake Fields

CERN Document Server

Rumolo, Giovanni

2002-01-01

The electron cloud gives rise to coherent and incoherent single-bunch wake fields, both in the longitudinal and in the transverse direction, and to coherent coupled-bunch wakes. These wake fields can be computed using the simulation programs ECLOUD and HEADTAIL developed at CERN. We present the wake fields simulated for the LHC beam in the CERN SPS and at injection into the LHC in different magnetic field configurations (field-free region, dipole, and solenoid), where the magnetic field affects both the elec-tron motion during a bunch passage and the overall electron distribution in the beam pipe.

Measurement of fast neutron background in SAGE

International Nuclear Information System (INIS)

Abdurashitov, J.N.; Gavrin, V.N.; Kalikhov, A.V.; Matushko, V.L.; Shikhin, A.A.; Yants, V.E.; Zaborskaia, O.S.

2002-01-01

The spectrometer intended for direct measurements of ultra low fluxes of fast neutrons is described. It is sensitive to neutron fluxes of 10 -7 cm -2 s -1 and lower. The detection efficiency of fast neutrons with simultaneous energy measurement was determined from Monte-Carlo simulation to be equal to 0.11 ± 0.01. The background counting rate in the detector corresponds to a neutron flux of (6.5 ± 2.1) x 10 -7 cm -2 s -1 in the range 1.0-11.0 MeV. The natural neutron flux from the surrounding mine rock at the depth of 4700 meters of water equivalent was measured to be (7.3 ± 2.4) x 10 -7 cm -2 s -1 in the range 1.0-11.0 MeV. The flux of fast neutrons in the SAGE main room was measured to be -7 cm -2 s -1 in 1.0-11.0 MeV energy range

Measurement of fast neutron spectra. 1-2

International Nuclear Information System (INIS)

Kimura, Itsuro

1976-01-01

The present status of the techniques for the measurement of fast neutron spectra is reviewed with particular attention to the recent activities in Japan. The first section of this report defines the energy range of fast neutrons, and various techniques are classified into four groups. In the following sections, recent development in each group is reviewed. The first part is the integral method represented mainly by the activation method. The variation of this method is shortly reviewed, and some results of the spectrum measurement for JRR-4 (a thermal research reactor) and YAYOI (a fast neutron source reactor) are presented together with the results of computed spectra. The second part is the method of proton recoil. The improvement of a proportional counter by Ichimori is shortly reviewed. The use of liquid scintillator is also discussed together with the experimental and computational results of YAYOI benchmark spectra of fast neutrons transmitted through the layers of iron. The utilization of n-α or n-p reaction as a sandwitch counter is discussed in the third part. Measured and calculated spectra in the FCA (a fast critical assembly) core are presented as examples. The method of time-of-flight is discussed in the fourth part. Recent developments in Japan such as the method with a double-scintillation counter are shortly presented together with its block diagram. (Aoki, K.)

Wind-tunnel modelling of the tip-speed ratio influence on the wake evolution

Science.gov (United States)

Stein, Victor P.; Kaltenbach, Hans-Jakob

2016-09-01

Wind-tunnel measurements on the near-wake evolution of a three bladed horizontal axis wind turbine model (HAWT) in the scale 1:O(350) operating in uniform flow conditions and within a turbulent boundary layer at different tip speed ratios are presented. Operational conditions are chosen to exclude Reynolds number effects regarding the turbulent boundary layer as well as the rotor performance. Triple-wire anemometry is used to measure all three velocity components in the mid-vertical and mid-horizontal plane, covering the range from the near- to the far-wake region. In order to analyse wake properties systematically, power and thrust coefficients of the turbine were measured additionally. It is confirmed that realistic modelling of the wake evolution is not possible in a low-turbulence uniform approach flow. Profiles of mean velocity and turbulence intensity exhibit large deviations between the low-turbulence uniform flow and the turbulent boundary layer, especially in the far-wake region. For nearly constant thrust coefficients differences in the evolution of the near-wake can be identified for tip speed ratios in the range from 6.5 to 10.5. It is shown that with increasing downstream distances mean velocity profiles become indistinguishable whereas for turbulence statistics a subtle dependency on the tip speed ratio is still noticeable in the far-wake region.

Why Does Sleep Slow-Wave Activity Increase After Extended Wake? Assessing the Effects of Increased Cortical Firing During Wake and Sleep.

Science.gov (United States)

Rodriguez, Alexander V; Funk, Chadd M; Vyazovskiy, Vladyslav V; Nir, Yuval; Tononi, Giulio; Cirelli, Chiara

2016-12-07

During non-rapid eye movement (NREM) sleep, cortical neurons alternate between ON periods of firing and OFF periods of silence. This bi-stability, which is largely synchronous across neurons, is reflected in the EEG as slow waves. Slow-wave activity (SWA) increases with wake duration and declines homeostatically during sleep, but the underlying mechanisms remain unclear. One possibility is neuronal "fatigue": high, sustained firing in wake would force neurons to recover with more frequent and longer OFF periods during sleep. Another possibility is net synaptic potentiation during wake: stronger coupling among neurons would lead to greater synchrony and therefore higher SWA. Here, we obtained a comparable increase in sustained firing (6 h) in cortex by: (1) keeping mice awake by exposure to novel objects to promote plasticity and (2) optogenetically activating a local population of cortical neurons at wake-like levels during sleep. Sleep after extended wake led to increased SWA, higher synchrony, and more time spent OFF, with a positive correlation between SWA, synchrony, and OFF periods. Moreover, time spent OFF was correlated with cortical firing during prior wake. After local optogenetic stimulation, SWA and cortical synchrony decreased locally, time spent OFF did not change, and local SWA was not correlated with either measure. Moreover, laser-induced cortical firing was not correlated with time spent OFF afterward. Overall, these results suggest that high sustained firing per se may not be the primary determinant of SWA increases observed after extended wake. A long-standing hypothesis is that neurons fire less during slow-wave sleep to recover from the "fatigue" accrued during wake, when overall synaptic activity is higher than in sleep. This idea, however, has rarely been tested and other factors, namely increased cortical synchrony, could explain why sleep slow-wave activity (SWA) is higher after extended wake. We forced neurons in the mouse cortex to fire

Automated Measurement of Fast Mitochondrial Transport in Neurons

Directory of Open Access Journals (Sweden)

Kyle eMiller

2015-11-01

Full Text Available There is a growing recognition that fast mitochondrial transport in neurons is disrupted in multiple neurological diseases and psychiatric disorders. However a major constraint in identifying novel therapeutics based on mitochondrial transport is that the large-scale analysis of fast transport is time consuming. Here we describe methodologies for the automated analysis of fast mitochondrial transport from data acquired using a robotic microscope. We focused on addressing questions of measurement precision, speed, reliably, workflow ease, statistical processing and presentation. We used optical flow and particle tracking algorithms, implemented in ImageJ, to measure mitochondrial movement in primary cultured cortical and hippocampal neurons. With it, we are able to generate complete descriptions of movement profiles in an automated fashion of hundred of thousands of mitochondria with a processing time of approximately one hour. We describe the calibration of the parameters of the tracking algorithms and demonstrate that they are capable of measuring the fast transport of a single mitochondrion. We then show that the methods are capable of reliably measuring the inhibition of fast mitochondria transport induced by the disruption of microtubules with the drug nocodazole in both hippocampal and cortical neurons. This work lays the foundation for future large-scale screens designed to identify compounds that modulate mitochondrial motility.

Wake of inertial waves of a horizontal cylinder in horizontal translation

Science.gov (United States)

Machicoane, Nathanaël; Labarre, Vincent; Voisin, Bruno; Moisy, Frédéric; Cortet, Pierre-Philippe

2018-03-01

We analyze theoretically and experimentally the wake behind a horizontal cylinder of diameter d horizontally translated at constant velocity U in a fluid rotating about the vertical axis at a rate Ω . Using particle image velocimetry measurements in the rotating frame, we show that the wake is stabilized by rotation for Reynolds number Re =U d /ν much larger than in a nonrotating fluid. Over the explored range of parameters, the limit of stability is Re ≃(275 ±25 )/Ro , with Ro =U /2 Ω d the Rossby number, indicating that the stabilizing process is governed by the Ekman pumping in the boundary layer. At low Rossby number, the wake takes the form of a stationary pattern of inertial waves, similar to the wake of surface gravity waves behind a ship. We compare this steady wake pattern to a model, originally developed by Johnson [E. R. Johnson, J. Fluid Mech. 120, 359 (1982), 10.1017/S0022112082002808], assuming a free-slip boundary condition and a weak streamwise perturbation. Our measurements show quantitative agreement with this model for Ro ≲0.3 . At larger Rossby number, the phase pattern of the wake is close to the prediction for an infinitely small line object. However, the wake amplitude and phase origin are not correctly described by the weak-streamwise-perturbation model, calling for an alternative model for the boundary condition at moderate rotation rate.

Intermittent fasting during Ramadan: does it affect sleep?

Science.gov (United States)

Bahammam, Ahmed S; Almushailhi, Khalid; Pandi-Perumal, Seithikurippu R; Sharif, Munir M

2014-02-01

Islamic intermittent fasting is distinct from regular voluntary or experimental fasting. We hypothesised that if a regimen of a fixed sleep-wake schedule and a fixed caloric intake is followed during intermittent fasting, the effects of fasting on sleep architecture and daytime sleepiness will be minimal. Therefore, we designed this study to objectively assess the effects of Islamic intermittent fasting on sleep architecture and daytime sleepiness. Eight healthy volunteers reported to the Sleep Disorders Centre on five occasions for polysomnography and multiple sleep latency tests: (1) during adaptation; (2) 3 weeks before Ramadan, after having performed Islamic fasting for 1 week (baseline fasting); (3) 1 week before Ramadan (non-fasting baseline); (4) 2 weeks into Ramadan (Ramadan); and (5) 2 weeks after Ramadan (non-fasting; Recovery). Daytime sleepiness was assessed using the Epworth Sleepiness Scale and the multiple sleep latency test. The participants had a mean age of 26.6 ± 4.9 years, a body mass index of 23.7 ± 3.5 kg m(-2) and an Epworth Sleepiness Scale score of 7.3 ± 2.7. There was no change in weight or the Epworth Sleepiness Scale in the four study periods. The rapid eye movement sleep percentage was significantly lower during fasting. There was no difference in sleep latency, non-rapid eye movement sleep percentage, arousal index and sleep efficiency. The multiple sleep latency test analysis revealed no difference in the sleep latency between the 'non-fasting baseline', 'baseline fasting', 'Ramadan' and 'Recovery' time points. Under conditions of a fixed sleep-wake schedule and a fixed caloric intake, Islamic intermittent fasting results in decreased rapid eye movement sleep with no impact on other sleep stages, the arousal index or daytime sleepiness. © 2013 European Sleep Research Society.

Wake meandering of a model wind turbine operating in two different regimes

Science.gov (United States)

Foti, Daniel; Yang, Xiaolei; Campagnolo, Filippo; Maniaci, David; Sotiropoulos, Fotis

2018-05-01

The flow behind a model wind turbine under two different turbine operating regimes (region 2 for turbine operating at optimal condition with the maximum power coefficient and 1.4-deg pitch angle and region 3 for turbine operating at suboptimal condition with a lower power coefficient and 7-deg pitch angle) is investigated using wind tunnel experiments and numerical experiments using large-eddy simulation (LES) with actuator surface models for turbine blades and nacelle. Measurements from the model wind turbine experiment reveal that the power coefficient and turbine wake are affected by the operating regime. Simulations with and without a nacelle model are carried out for each operating condition to study the influence of the operating regime and nacelle on the formation of the hub vortex and wake meandering. Statistics and energy spectra of the simulated wakes are in good agreement with the measurements. For simulations with a nacelle model, the mean flow field is composed of an outer wake, caused by energy extraction by turbine blades, and an inner wake directly behind the nacelle, while for the simulations without a nacelle model, the central region of the wake is occupied by a jet. The simulations with the nacelle model reveal an unstable helical hub vortex expanding outward toward the outer wake, while the simulations without a nacelle model show a stable and columnar hub vortex. Because of the different interactions of the inner region of the wake with the outer region of the wake, a region with higher turbulence intensity is observed in the tip shear layer for the simulation with a nacelle model. The hub vortex for the turbine operating in region 3 remains in a tight helical spiral and intercepts the outer wake a few diameters further downstream than for the turbine operating in region 2. Wake meandering, a low-frequency large-scale motion of the wake, commences in the region of high turbulence intensity for all simulations with and without a nacelle model

Multisite accelerometry for sleep and wake classification in children.

Science.gov (United States)

Lamprecht, Marnie L; Bradley, Andrew P; Tran, Tommy; Boynton, Alison; Terrill, Philip I

2015-01-01

Actigraphy is a useful alternative to the gold standard polysomnogram for non-invasively measuring sleep and wakefulness. However, it is unable to accurately assess sleep fragmentation due to its inability to differentiate restless sleep from wakefulness and quiet wake from sleep. This presents significant limitations in the assessment of sleep-related breathing disorders where sleep fragmentation is a common symptom. We propose that this limitation may be caused by hardware constraints and movement representation techniques. Our objective was to determine if multisite tri-axial accelerometry improves sleep and wake classification. Twenty-four patients aged 6-15 years (median: 8 years, 16 male) underwent a diagnostic polysomnogram while simultaneously recording motion from the left wrist and index fingertip, upper thorax and left ankle and great toe using a custom accelerometry system. Movement was quantified using several features and two feature selection techniques were employed to select optimal features for restricted feature set sizes. A heuristic was also applied to identify movements during restless sleep. The sleep and wake classification performance was then assessed and validated against the manually scored polysomnogram using discriminant analysis. Tri-axial accelerometry measured at the wrist significantly improved the wake detection when compared to uni-axial accelerometry (specificity at 85% sensitivity: 71.3(14.2)% versus 55.2(24.7)%, p < 0.01). Multisite accelerometry significantly improved the performance when compared to the single wrist placement (specificity at 85% sensitivity: 82.1(12.5)% versus 71.3(14.2)%, p < 0.05). Our results indicate that multisite accelerometry offers a significant performance benefit which could be further improved by analysing movement in raw multisite accelerometry data.

LES of an Advancing Helicopter Rotor, and Near to Far Wake Assessment

Science.gov (United States)

Caprace, Denis-Gabriel; Duponcheel, Matthieu; Chatelain, Philippe; Winckelmans, Grégoire

2017-11-01

Helicopter wake physics involve complex, unsteady vortical flows which have been only scarcely addressed in past studies. The present work focuses on LES of the wake flow behind an advancing rotor, to support the investigation of rotorcraft wake physics and decay mechanisms. A hybrid Vortex Particle-Mesh (VPM) method is employed to simulate the wake of an articulated four-bladed rotor in trimmed conditions, at an advance ratio of 0.41. The simulation domain extends to 30 rotor diameters downstream. The coarse scale aerodynamics of the blades are accounted for through enhanced immersed lifting lines. The vorticity generation mechanisms, the roll-up of the near wake and the resulting established far wake are described (i) qualitatively in terms of vortex dynamics using rotor polar plots and 3D visualizations; (ii) quantitatively using classical integral diagnostics. The power spectra measured by velocity probes in the wake are also presented. The analysis shows that the wake reaches a fully turbulent equilibrium state at a distance of about 30 diameters downstream. This work is supported by the Belgian french community F.R.S.-FNRS.

Effect of chord-to-diameter ratio on vertical-axis wind turbine wake development

Science.gov (United States)

Parker, Colin M.; Araya, Daniel B.; Leftwich, Megan C.

2017-12-01

The wake structure of a vertical-axis wind turbine (VAWT) is strongly dependent on the tip-speed ratio, λ, or the tangential speed of the turbine blade relative to the incoming wind speed. The geometry of a turbine can influence λ, but the precise relationship among VAWT geometric parameters and VAWT wake characteristics remains unknown. To investigate this relationship, we present the results of an experiment to characterize the wakes of three VAWTs that are geometrically similar except for the ratio of the turbine diameter ( D), to blade chord ( c), which was chosen to be D/c = 3, 6, and 9. For a fixed freestream Reynolds number based on the blade chord of Re_c = 1.6× 10^3, both two-component particle image velocimetry (PIV) and single-component hot-wire anemometer measurements are taken at the horizontal mid-plane in the wake of each turbine. PIV measurements are ensemble averaged in time and phase averaged with each rotation of the turbine. Hot-wire measurement points are selected to coincide with the edge of the shear layer of each turbine wake, as deduced from the PIV data, which allows for an analysis of the frequency content of the wake due to vortex shedding by the turbine.

Rotor boundary layer development with inlet guide vane (IGV) wake impingement

Science.gov (United States)

Jia, Lichao; Zou, Tengda; Zhu, Yiding; Lee, Cunbiao

2018-04-01

This paper examines the transition process in a boundary layer on a rotor blade under the impingement of an inlet guide vane wake. The effects of wake strengths and the reduced frequency on the unsteady boundary layer development on a low-speed axial compressor were investigated using particle image velocimetry. The measurements were carried out at two reduced frequencies (fr = fIGVS0/U2i, fr = 1.35, and fr = 0.675) with the Reynolds number, based on the blade chord and the isentropic inlet velocity, being 97 500. At fr = 1.35, the flow separated at the trailing edge when the wake strength was weak. However, the separation was almost totally suppressed as the wake strength increased. For the stronger wake, both the wake's high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. The boundary layer displacement thickened first due to the negative jet effect. Then, as the disturbances developed underneath the wake, the boundary layer thickness reduced gradually. The high disturbance region convected downstream at a fraction of the free-stream velocity and spread in the streamwise direction. The separation on the suction surface was suppressed until the next wake's arrival. Because of the long recovery time at fr = 0.675, the boundary layer thickened gradually as the wake convected further downstream and finally separated due to the adverse pressure gradient. The different boundary layer states in turn affected the development of disturbances.

Radiative Forcing Over Ocean by Ship Wakes

Science.gov (United States)

Gatebe, Charles K.; Wilcox, E.; Poudyal, R.; Wang, J.

2011-01-01

Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we report on enhanced ocean reflectance from ship wakes over the Pacific Ocean near the California coast, where we determined, based on airborne radiation measurements that ship wakes can increase reflected sunlight by more than 100%. We assessed the importance of this increase to climate forcing, where we estimated the global radiative forcing of ship wakes to be -0.00014 plus or minus 53% Watts per square meter assuming a global distribution of 32331 ships of size of greater than or equal to 100000 gross tonnage. The forcing is smaller than the forcing of aircraft contrails (-0.007 to +0.02 Watts per square meter), but considering that the global shipping fleet has rapidly grown in the last five decades and this trend is likely to continue because of the need of more inter-continental transportation as a result of economic globalization, we argue that the radiative forcing of wakes is expected to be increasingly important especially in harbors and coastal regions.

ASRS Reports on Wake Vortex Encounters

Science.gov (United States)

Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl

2010-01-01

ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.

Power-Production Diagnostic Tools for Low-Density Wind Farms with Applications to Wake Steering

Science.gov (United States)

Takle, E. S.; Herzmann, D.; Rajewski, D. A.; Lundquist, J. K.; Rhodes, M. E.

2016-12-01

Hansen (2011) provided guidelines for wind farm wake analysis with applications to "high density" wind farms (where average distance between turbines is less than ten times rotor diameter). For "low-density" (average distance greater than fifteen times rotor diameter) wind farms, or sections of wind farms we demonstrate simpler sorting and visualization tools that reveal wake interactions and opportunities for wind farm power prediction and wake steering. SCADA data from a segment of a large mid-continent wind farm, together with surface flux measurements and lidar data are subjected to analysis and visualization of wake interactions. A time-history animated visualization of a plan view of power level of individual turbines provides a quick analysis of wake interaction dynamics. Yaw-based sectoral histograms of enhancement/decline of wind speed and power from wind farm reference levels reveals angular width of wake interactions and identifies the turbine(s) responsible for the power reduction. Concurrent surface flux measurements within the wind farm allowed us to evaluate stability influence on wake loss. A one-season climatology is used to identify high-priority candidates for wake steering based on estimated power recovery. Typical clearing prices on the day-ahead market are used to estimate the added value of wake steering. Current research is exploring options for identifying candidate locations for wind farm "build-in" in existing low-density wind farms.

Multi-stage wake-field accelerator

International Nuclear Information System (INIS)

Gai, Wei.

1989-01-01

In this paper we propose a multi-stage wake field acceleration scheme to overcome the low transformer ratio problem and still provide high accelerating gradients. The idea is very simple. We use a train of several electron bunches from a linear accelerator (main linac) with well defined separations between the bunches (tens of ns) to drive wake field devices. Here we have made the assumption that the wake field devices are available, whether plasma, iris-loaded metallic or dielectric wake field structures. 10 refs

Tip Vortex and Wake Characteristics of a Counterrotating Open Rotor

Science.gov (United States)

VanZante, Dale E.; Wernet, Mark P.

2012-01-01

One of the primary noise sources for Open Rotor systems is the interaction of the forward rotor tip vortex and blade wake with the aft rotor. NASA has collaborated with General Electric on the testing of a new generation of low noise, counterrotating Open Rotor systems. Three-dimensional particle image velocimetry measurements were acquired in the intra-rotor gap of the Historical Baseline blade set. The velocity measurements are of sufficient resolution to characterize the tip vortex size and trajectory as well as the rotor wake decay and turbulence character. The tip clearance vortex trajectory is compared to results from previously developed models. Forward rotor wake velocity profiles are shown. Results are presented in a form as to assist numerical modeling of Open Rotor system aerodynamics and acoustics.

Fast optical measurements and imaging of flow mixing: Fast optical measurements and imaging of temperature in combined fossil fuel and biomass/waste systems

Energy Technology Data Exchange (ETDEWEB)

Clausen, Soennik; Fateev, A.; Lindorff Nielsen, K.; Evseev, V.

2012-02-15

Project is focused on fast time-resolved infrared measurements of gas temperature and fast IR-imagining of flames in various combustion environments. The infrared spectrometer system was developed in the project for fast infrared spectral measurements on industrial scale using IR-fibre- optics. Fast time-and spectral-resolved measurements in 1.5-5.1 mu spectral range give information about flame characteristics like gas and particle temperatures, eddies and turbulent gas mixing. Time-resolved gas composition in that spectral range (H{sub 2}O, CH{sub 4}, CO{sub 2}, CO) which is one of the key parameters in combustion enhancement can be also obtained. The infrared camera was also used together with special endoscope optics for fast thermal imaging of a coal-straw flame in an industrial boiler. Obtained time-resolved infrared images provided useful information for the diagnostics of the flame and fuel distribustion. The applicability of the system for gas leak detection is also demonstrated. The infrared spectrometer system with minor developments was applied for fast time-resolved exhaust gas temperature measurements performed simultaneously at the three optical ports of the exhaust duct of a marine Diesel engine and visualisation of gas flow behaviour in cylinder. (Author)

Wind turbine wake characterization using long-range Doppler lidar

Science.gov (United States)

Aitken, M.; Lundquist, J. K.; Hestmark, K.; Banta, R. M.; Pichugina, Y.; Brewer, A.

2012-12-01

Wind turbines extract energy from the freestream flow, resulting in a waked region behind the rotor which is characterized by reduced wind speed and increased turbulence. The velocity deficit in the wake diminishes with distance, as faster-moving air outside is gradually entrained. In a concentrated group of turbines, then, downwind machines experience very different inflow conditions compared to those in the front row. As utility-scale turbines rarely exist in isolation, detailed knowledge of the mean flow and turbulence structure inside wakes is needed to correctly model both power production and turbine loading at modern wind farms. To this end, the Turbine Wake and Inflow Characterization Study (TWICS) was conducted in the spring of 2011 to determine the reduction in wind speeds downstream from a multi-MW turbine located at the National Renewable Energy Laboratory's National Wind Technology Center (NWTC) near Boulder, Colorado. Full-scale measurements of wake dynamics are hardly practical or even possible with conventional sensors, such as cup anemometers mounted on meteorological (met) masts. Accordingly, the High Resolution Doppler Lidar (HRDL) developed by the National Oceanic and Atmospheric Administration's Earth System Research Laboratory was employed to investigate the formation and propagation of wakes under varying levels of ambient wind speed, shear, atmospheric stability, and turbulence. HRDL remotely senses line-of-sight wind velocities and has been used in several previous studies of boundary layer aerodynamics. With a fully steerable beam and a maximum range up to about 5 km, depending on atmospheric conditions, HRDL performed a comprehensive survey of the wind flow in front of and behind the turbine to study the shape, meandering, and attenuation of wakes. Due in large part to limited experimental data availability, wind farm wake modeling is still subject to an unacceptable amount of uncertainty, particularly in complex terrain. Here, analytical

Measurement of fast neutron background in SAGE

CERN Document Server

Abdurashitov, J N; Kalikhov, A V; Matushko, V L; Shikhin, A A; Yants, V E; Zaborskaia, O S

2002-01-01

The spectrometer intended for direct measurements of ultra low fluxes of fast neutrons is described. It is sensitive to neutron fluxes of 10 sup - sup 7 cm sup - sup 2 s sup - sup 1 and lower. The detection efficiency of fast neutrons with simultaneous energy measurement was determined from Monte-Carlo simulation to be equal to 0.11 +- 0.01. The background counting rate in the detector corresponds to a neutron flux of (6.5 +- 2.1) x 10 sup - sup 7 cm sup - sup 2 s sup - sup 1 in the range 1.0-11.0 MeV. The natural neutron flux from the surrounding mine rock at the depth of 4700 meters of water equivalent was measured to be (7.3 +- 2.4) x 10 sup - sup 7 cm sup - sup 2 s sup - sup 1 in the range 1.0-11.0 MeV. The flux of fast neutrons in the SAGE main room was measured to be < 2.3 x 10 sup - sup 7 cm sup - sup 2 s sup - sup 1 in 1.0-11.0 MeV energy range.

Self-similarity and turbulence characteristics of wind turbine wakes via large-eddy simulation (Invited)

Science.gov (United States)

Xie, S.; Archer, C. L.

2013-12-01

In this study, a new large-eddy simulation code, the Wind Turbine and Turbulence Simulator (WiTTS), is developed to study the wake generated from a single wind turbine in the neutral ABL. The WiTTS formulation is based on a scale-dependent Lagrangian dynamical model of the sub-grid shear stress and uses actuator lines to simulate the effects of the rotating blades. WiTTS is first tested against wind tunnel experiments and then used to study the commonly-used assumptions of self-similarity and axis-symmetry of the wake under neutral conditions for a variety of wind speeds and turbine properties. The mean velocity deficit shows good self-similarity properties following a normal distribution in the horizontal plane at the hub-height level. Self-similarity is a less valid approximation in the vertical near the ground, due to strong wind shear and ground effects. The mean velocity deficit is strongly dependent on the thrust coefficient or induction factor. A new relationship is proposed to model the mean velocity deficit along the centerline at the hub-height level to fit the LES results piecewise throughout the wake. A logarithmic function is used in the near and intermediate wake regions whereas a power function is used in the far-wake. These two functions provide a better fit to both simulated and observed wind velocity deficits than other functions previously used in wake models such as WAsP. The wind shear and impact with the ground cause an anisotropy in the expansion of the wake such that the wake grows faster horizontally than vertically. The wake deforms upon impact with the ground and spreads laterally. WiTTS is also used to study the turbulence characteristics in the wake. Aligning with the mean wind direction, the streamwise component of turbulence intensity is the dominant among the three components and thus it is further studied. The highest turbulence intensity occurs near the top-tip level. The added turbulence intensity increases fast in the near-wake

Do GIS-derived measures of fast food retailers convey perceived fast food opportunities? Implications for food environment assessment

Science.gov (United States)

Barnes, Timothy L.; Colabianchi, Natalie; Freedman, Darcy A.; Bell, Bethany A.; Liese, Angela D.

2018-01-01

Purpose Geographic information systems (GISs) have been used to define fast food availability, with higher availability perhaps promoting poorer quality diets. Alternative measures involve perceptions; however, few studies have examined associations between GIS-derived and perceived measures of the food environment. Methods Telephone surveys of 705 participants within an eight-county region in South Carolina were analyzed using logistic regression to examine relationships between geographic presence of and distance to various types of food retailers and perceived fast food availability. Results The mean distance to the nearest fast food restaurant was 6.1 miles, with 16% of participants having a fast food restaurant within 1 mile of home. The geographic presence of and distance to all food retailer types were significantly associated with perceived availability of fast food in unadjusted models. After adjustment, only the presence of a fast food restaurant or pharmacy was significantly associated with greater odds of higher perceived availability of fast food. Greater odds of lower perceived availability of fast food were observed with the presence of a dollar store and increasing distance to the nearest supermarket or pharmacy. Conclusions Measures of fast food availability, whether objective or perceived, may not be interchangeable. Researchers should carefully decide on the appropriate measurement tool—GIS-derived or perceived—in food environment studies. PMID:27617371

Do GIS-derived measures of fast food retailers convey perceived fast food opportunities? Implications for food environment assessment.

Science.gov (United States)

Barnes, Timothy L; Colabianchi, Natalie; Freedman, Darcy A; Bell, Bethany A; Liese, Angela D

2017-01-01

Geographic information systems (GISs) have been used to define fast food availability, with higher availability perhaps promoting poorer quality diets. Alternative measures involve perceptions; however, few studies have examined associations between GIS-derived and perceived measures of the food environment. Telephone surveys of 705 participants within an eight-county region in South Carolina were analyzed using logistic regression to examine relationships between geographic presence of and distance to various types of food retailers and perceived fast food availability. The mean distance to the nearest fast food restaurant was 6.1 miles, with 16% of participants having a fast food restaurant within 1 mile of home. The geographic presence of and distance to all food retailer types were significantly associated with perceived availability of fast food in unadjusted models. After adjustment, only the presence of a fast food restaurant or pharmacy was significantly associated with greater odds of higher perceived availability of fast food. Greater odds of lower perceived availability of fast food were observed with the presence of a dollar store and increasing distance to the nearest supermarket or pharmacy. Measures of fast food availability, whether objective or perceived, may not be interchangeable. Researchers should carefully decide on the appropriate measurement tool-GIS-derived or perceived-in food environment studies. Copyright © 2016 Elsevier Inc. All rights reserved.

Investigation on wind turbine wakes: wind tunnel tests and field experiments with LIDARs

Science.gov (United States)

Iungo, Giacomo; Wu, Ting; Cöeffé, Juliette; Porté-Agel, Fernando; WIRE Team

2011-11-01

An investigation on the interaction between atmospheric boundary layer flow and wind turbines is carried out with wind tunnel and LIDAR measurements. The former were carried out using hot-wire anemometry and multi-hole pressure probes in the wake of a three-bladed miniature wind turbine. The wind turbine wake is characterized by a strong velocity defect in the proximity of the rotor, and its recovery is found to depend on the characteristics of the incoming atmospheric boundary layer (mean velocity and turbulence intensity profiles). Field experiments were performed using three wind LIDARs. Bi-dimensional scans are performed in order to analyse the wake wind field with different atmospheric boundary layer conditions. Furthermore, simultaneous measurements with two or three LIDARs allow the reconstruction of multi-component velocity fields. Both LIDAR and wind tunnel measurements highlight an increased turbulence level at the wake boundary for heights comparable to the top-tip of the blades; this flow feature can produce dangerous fatigue loads on following wind turbines.

Wake modelling combining mesoscale and microscale models

DEFF Research Database (Denmark)

Badger, Jake; Volker, Patrick; Prospathospoulos, J.

2013-01-01

In this paper the basis for introducing thrust information from microscale wake models into mesocale model wake parameterizations will be described. A classification system for the different types of mesoscale wake parameterizations is suggested and outlined. Four different mesoscale wake paramet...

An improved fast neutron radiography quantitative measurement method

International Nuclear Information System (INIS)

Matsubayashi, Masahito; Hibiki, Takashi; Mishima, Kaichiro; Yoshii, Koji; Okamoto, Koji

2004-01-01

The validity of a fast neutron radiography quantification method, the Σ-scaling method, which was originally proposed for thermal neutron radiography was examined with Monte Carlo calculations and experiments conducted at the YAYOI fast neutron source reactor. Water and copper were selected as comparative samples for a thermal neutron radiography case and a dense object, respectively. Although different characteristics on effective macroscopic cross-sections were implied by the simulation, the Σ-scaled experimental results with the fission neutron spectrum cross-sections were well fitted to the measurements for both the water and copper samples. This indicates that the Σ-scaling method could be successfully adopted for quantitative measurements in fast neutron radiography

Typhoon Effect on Kuroshio and Green Island Wakes: A Modelling Study

Directory of Open Access Journals (Sweden)

Tai-Wen Hsu

2018-01-01

Full Text Available Green Island, located in the typhoon-active eastern Taiwan coastal water, is the potential Kuroshio power plant site. In this study, a high resolution (250–2250 m shallow-water equations model is used to investigate the effect of typhoon on the hydro-dynamics of Kuroshio and Green Island wakes. Two typhoon–Kuroshio interactions—typhoon Soulik and Holland’s typhoon model—are studied. Simulation results of typhoon Soulik indicate salient characteristics of Kuroshio, and downstream island wakes seems less affected by the typhoon Soulik, because the shortest distance of typhoon Soulik is 250 km away from Green Island and wind speed near Green Island is small. Moreover, Kuroshio currents increase when flow is in the same direction as the counterclockwise rotation of typhoon, and vice versa. This finding is in favorable agreement with the TOROS (Taiwan Ocean Radar Observing System observed data. Simulations of Kuroshio and Holland’s typhoon model successfully reproduces the downstream recirculation and vortex street. Numerical results reveal that the slow moving typhoon has a more significant impact on the Kuroshio and downstream Green Island wakes than the fast moving typhoon does. The rightward bias phenomenon is evident—Kuroshio currents increase (decrease in the right (left of the moving typhoon’s track, due to the counterclockwise rotation of typhoon.

Fast fluence measurement for JOYO irradiation field using niobium dosimeter

International Nuclear Information System (INIS)

Ito, Chikara

2004-03-01

Neutron fluence and spectrum are key parameters in various irradiation tests and material surveillance tests so they need to be evaluated accurately. The reactor dosimetry test has been conducted by the multiple foil activation method, and a niobium dosimeter has been developed for measurement of fast neutron fluence in the experimental fast reactor JOYO. The inelastic scattering reaction of 93 Nb has a low threshold energy, about 30 keV, and the energy distribution of reaction cross section is similar to the displacement cross section for iron. Therefore, a niobium dosimeter is suitable for evaluation of the fast neutron fluence and the displacement per atom for iron. Moreover, a niobium dosimeter is suited to measure neutron fluence in long-term irradiation test because 93 Nb, which is produced by the reaction, has a long half-life (16.4 years). This study established a high precision measurement technique using the niobium reaction rate. The effect of self-absorption was decreased by the solution and evaporation to dryness of niobium dosimeter. The dosimeter weight was precisely measured using the inductively coupled plasma mass spectrometer. This technique was applied to JOYO dosimetry. The fast neutron fluences (E > 0.1 MeV) found by measuring the reaction rate in the niobium dosimeter were compared with the values evaluated using the multiple foil activation method. The ratio of measured fast neutron fluences by means of niobium dosimeter and multiple foil activation method range from 0.97 to 1.03 and agree within the experimental uncertainty. The measurement errors of fast neutron fluence by niobium dosimeter range from 4.5% (fuel region) to 10.1% (in-vessel storage rack). As a result of this study, the high precision measurement of fast neutron fluence by niobium dosimeters was confirmed. The accuracy of fast reactor dosimetry will be improved by application of niobium dosimeters to the irradiation tests in the JOYO MK-III core. (author)

Wake characterization methods of a circulation control wing

Science.gov (United States)

El Sayed Mohamed, Y.; Semaan, R.; Sattler, S.; Radespiel, R.

2017-10-01

We propose a three-pronged methodology to characterise the wake behind a circulation control wing. The study relies on time-resolved particle image velocimetry (TR-PIV) measurements in a water tunnel for a range of blowing intensities. The first method is the well-known proper orthogonal decomposition (POD). The second tool is a new implementation of the power spectrum. Finally, a modified Q-criterion vortex detection and quantification method is presented. The results show the complementary advantage of the three methods in analysing wake flows with varying conditions.

Offshore and onshore wind turbine wake meandering studied in an ABL wind tunnel

DEFF Research Database (Denmark)

Barlas, Emre; Buckingham, Sophia; Glabeke, Gertjan

2015-01-01

Scaled wind turbine models have been installed in the VKI L1-B atmospheric boundary layer wind tunnel at offshore and onshore conditions. Time-resolved measurements were carried out with three component hot wire anemometry and stereo-PIV in the middle vertical plane of the wake up to eleven turbine...... diameter downstream. The results show an earlier wake recovery for the onshore case. The effect of inflow conditions and the wind turbine’s working conditions on wake meandering was investigated. Wake meandering was detected by hot wire anemometry through a low frequency peak in the turbulent power...

CFD simulation on Kappel propeller with a hull wake field

DEFF Research Database (Denmark)

Shin, Keun Woo; Andersen, Poul; Møller Bering, Rasmus

2013-01-01

Marine propellers are designed not for the open-water operation, but for the operation behind a hull due to the inhomogeneous hull wake and thrust deduction. The adaptation for the hull wake is important for the propulsive efficiency and cavitation risk especially on single-screw ships. CFD...... simulations for a propeller with a hull model have showed acceptable agreement with a model test result in the thrust and torque (Larsson et al. 2010). In the current work, a measured hull wake is applied to the simulation instead of modelling a hull, because the hull geometry is mostly not available...... for propeller designers and the computational effort can be reduced by excluding the hull. The CFD simulation of a propeller flow with a hull wake is verified in order to use CFD as a propeller design tool. A Kappel propeller, which is an innovative tip-modified propeller, is handled. Kappel propellers...

Wake interaction and power production of variable height model wind farms

International Nuclear Information System (INIS)

Vested, M H; Sørensen, J N; Hamilton, N; Cal, R B

2014-01-01

Understanding wake dynamics is an ongoing research topic in wind energy, since wakes have considerable effects on the power production when wind turbines are placed in a wind farm. Wind tunnel experiments have been conducted to study the wake to wake interaction in a model wind farm in tandem with measurements of the extracted power. The aim is to investigate how alternating mast height influences the interaction of the wakes and the power production. Via the use of stereo-particle image velocimetry, the flow field was obtained in the first and last rows of the wind turbine array as a basis of comparison. It was found that downstream of the exit row wind turbine, the power was increased by 25% in the case of a staggered height configuration. This is partly due to the fact that the taller turbines reach into a flow area with a softened velocity gradient. Another aspect is that the wake downstream of a tall wind turbine to some extent passes above the standard height wind turbine. Overall the experiments show that the velocity field downstream of the exit row changes considerably when the mast height is alternating

Diffusion in building wakes

International Nuclear Information System (INIS)

Ramsdell, J.V.

1988-03-01

Straight-line Gaussian models adequately describe atmospheric diffusion for many applications. They have been modified for use in estimating diffusion in building wakes by adding terms that include projected building area and by redefining the diffusion coefficients so that the coefficients have minimum values that are related to building dimensions. In a recent study, Ramsdell reviewed the building-wake dispersion models used by the Nuclear Regulatory Commission (NRC) in its control room habitability assessments. The review included comparison of model estimates of centerline concentrations with concentrations observed in experiments at seven nuclear reactors. In general, the models are conservative in that they tend to predict concentrations that are greater than those actually observed. However, the models show little skill in accounting for variations in the observed concentrations. Subsequently, the experimental data and multiples linear regression techniques have been used to develop a new building wake diffusion model. This paper describes the new building wake model and compares it with other models. 8 refs., 2 figs

Wake flow characteristics at high wind speed

DEFF Research Database (Denmark)

Aagaard Madsen, Helge; Larsen, Torben J.; Larsen, Gunner Chr.

2016-01-01

Wake flow characteristic at high wind speeds is the main subject of this paper. Although the wake losses decrease at high wind speeds it has been found in a recent study that for multiple wake inflow the increase in loading due to wake effects are substantial even at wind speeds well above rated ...

Wake shed by an accelerating carangiform fish

Science.gov (United States)

Ting, Shang-Chieh; Yang, Jing-Tang

2008-11-01

We reveal an important fact that momentum change observed in the wake of an accelerating carangiform fish does not necessarily elucidate orientations of propulsive forces produced. An accelerating Crucian Carp (Carassius auratus) was found to shed a wake with net forward fluid momentum, which seemed drag-producing. Based on Newton's law, however, an accelerating fish is expected to shed a thrust wake with net rearward fluid momentum, rather than a drag wake. The unusual wake pattern observed is considered to be resulted primarily from the effect of pressure gradient created by accelerating movements of the fish. Ambient fluids tend to be sucked into low pressure zones behind an accelerating fish, resulting in forward orientations of jets recognizable in the wake. Accordingly, as to an accelerating fish, identifying force orientations from the wake requires considering also the effect of pressure gradient.

The DLR project Wirbelschleppe. Detecting, characterizing, controlling, attenuating, understanding, and predicting aircraft wake vortices

Energy Technology Data Exchange (ETDEWEB)

Holzaepfel, F. (ed.)

2008-07-01

This collection of reports presents an excerpt of the investigations that were performed in the framework of the DLR Projekt Wirbelschleppe. A similar sample of reports was presented as part of three dedicated wake vortex sessions accomplished at the 1{sup st} European Air and Space Conference (CEAS 2007) and Deutscher Luft- und Raumfahrtkongress 2007 in Berlin. The Projekt Wirbelschleppe was conducted in two phases in the time frame from 1999 to 2007 with the five contributing DLR Institutes: Institute of Atmospheric Physics, Institute of Aerodynamics and Flow Technology, Institute of Flight Systems, Institute of Flight Guidance, Institute of Robotics and Mechatronics and the Institute of Aeronautics and Astronautics of the University of Technology Berlin. The project unified a multitude of different aspects and disciplines of wake vortex research which can be characterized by four main themes: - minimization of wake vortices by measures at the aircraft; - development and demonstration of a system for wake vortex prediction and observation; - airborne wake vortex detection and active control; - integration of systems into air traffic control. The Projekt Wirbelschleppe greatly benefited from the European projects AWIATOR, ATC-Wake, Credos, C-Wake, Eurowake, FAR-Wake, FLYSAFE, I-Wake, S-Wake, WakeNet, WakeNet2-Europe, WakeNet3-Europe, and Wavenc. DLR's wake vortex activities will be continued in the Projekt Wetter and Fliegen (2008-2011): Because the current compilation represents only a limited extract of the accomplished work, it is completed by a list of references emerging from the project. (orig.)

Numerical investigations of wake interactions of two wind turbines in tandem

Science.gov (United States)

Qian, Yaoru; Wang, Tongguang

2018-05-01

Aerodynamic performance and wake interactions between two wind turbine models under different layouts are investigated numerically using large eddy simulation in conjunction with actuator line method based on the “Blind Test” series wind tunnel experiments from Norwegian University of Science and Technology. Numerical results of the power and thrust coefficients of the two rotors and wake characteristics are in good agreement with the experimental measurements. Extended investigations emphasizing the influence of different layout arrangements on the downstream rotor performance and wake development are conducted. Results show that layout arrangements have great influence on the power and thrust prediction of the downstream turbine.

The fast ratio: A rapid measure for testing the dominance of the fast component in the initial OSL signal from quartz

International Nuclear Information System (INIS)

Durcan, Julie A.; Duller, Geoff A.T.

2011-01-01

The signal from the fast component is usually considered preferable for quartz optically stimulated luminescence (OSL) dating, however its presence in a continuous wave (CW) OSL signal is often assumed, rather than verified. This paper presents an objective measure (termed the fast ratio) for testing the dominance of the fast component in the initial part of a quartz OSL signal. The ratio is based upon the photo ionisation cross-sections of the fast and medium components and the power of the measurement equipment used to record the OSL signal, and it compares parts of the OSL signal selected to represent the fast and medium components. The ability of the fast ratio to distinguish between samples whose CW-OSL signal is dominated by the fast and non-fast components is demonstrated by comparing the fast ratio with the contribution of the fast component calculated from curve deconvolution of measured OSL signals and from simulated data. The ratio offers a rapid method for screening a large number of OSL signals obtained for individual equivalent dose estimates, it can be calculated and applied as easily as other routine screening methods, and is transferrable between different aliquots, samples and measurement equipment. - Highlights: → Fast ratio is a measure which tests dominance of fast component in quartz OSL signals. → A fast ratio above 20 implies a CW-OSL signal is dominated by fast component. → Fast ratio can be easily and rapidly applied to a large number of OSL signals. → Uses include signal comparison, data screening, identify need for further analysis.

Multi-Model Ensemble Wake Vortex Prediction

Science.gov (United States)

Koerner, Stephan; Holzaepfel, Frank; Ahmad, Nash'at N.

2015-01-01

Several multi-model ensemble methods are investigated for predicting wake vortex transport and decay. This study is a joint effort between National Aeronautics and Space Administration and Deutsches Zentrum fuer Luft- und Raumfahrt to develop a multi-model ensemble capability using their wake models. An overview of different multi-model ensemble methods and their feasibility for wake applications is presented. The methods include Reliability Ensemble Averaging, Bayesian Model Averaging, and Monte Carlo Simulations. The methodologies are evaluated using data from wake vortex field experiments.

Study on Actuator Line Modeling of Two NREL 5-MW Wind Turbine Wakes

Directory of Open Access Journals (Sweden)

Ziying Yu

2018-03-01

Full Text Available The wind turbine wakes impact the efficiency and lifespan of the wind farm. Therefore, to improve the wind plant performance, research on wind plant control is essential. The actuator line model (ALM is proposed to simulate the wind turbine efficiently. This research investigates the National Renewable Energy Laboratory 5 Million Watts (NREL 5-MW wind turbine wakes with Open Field Operation and Manipulation (OpenFOAM using ALM. Firstly, a single NREL 5-MW turbine is simulated. The comparison of the power and thrust with Fatigue, Aerodynamics, Structures, and Turbulence (FAST shows a good agreement below the rated wind speed. The information relating to wind turbine wakes is given in detail. The top working status is proved at the wind speed of 8 m/s and the downstream distance of more than 5 rotor diameters (5D. Secondly, another case with two NREL 5-MW wind turbines aligned is also carried out, in which 7D is validated as the optimum distance between the two turbines. The result also shows that the upstream wind turbine has an obvious influence on the downstream one.

Experimental and numerical study of the strong interaction between wakes of cylindrical obstacles

International Nuclear Information System (INIS)

Brun, Ch.

1998-01-01

In the context of thermal-hydraulics of nuclear reactors, strong interaction between wakes is encountered in the bottom of reactor vessels where control and measurement rods of variable size and disposition interact with the overall wakes generated in these flow zones. This study deals with the strong interaction between two wakes developed downstream of two parallel cylinders with a small spacing. The analysis focusses on the effect of the Reynolds regime which controls the equilibrium between the inertia and viscosity forces of the fluid and influences the large scale behaviour of the flow with the development of hydrodynamic instabilities and turbulence. The document is organized as follows: the characteristic phenomena of wakes formation downstream of cylindrical obstacles are recalled in the first chapter (single cylinder, interaction between two tubes, case of a bundle of tubes perpendicular to the flow). The experimental setup (hydraulic loop, velocity and pressure measurement instrumentation) and the statistical procedures applied to the signals measured are detailed in chapters 2 and 3. Chapter 4 is devoted to the experimental study of the strong interaction between two tubes. Laser Doppler velocity measurements in the wakes close to cylinders and pressure measurements performed on tube walls are reported in this chapter. In chapter 5, a 2-D numerical simulation of two typical cases of interaction (Re = 1000 and Re = 5000) is performed. In the last chapter, a more complex application of strong interactions inside and downstream of a bunch of staggered tubes is analyzed experimentally for equivalent Reynolds regimes. (J.S.)

Simulation of Wake Vortex Radiometric Detection via Jet Exhaust Proxy

Science.gov (United States)

Daniels, Taumi S.

2015-01-01

This paper describes an analysis of the potential of an airborne hyperspectral imaging IR instrument to infer wake vortices via turbine jet exhaust as a proxy. The goal was to determine the requirements for an imaging spectrometer or radiometer to effectively detect the exhaust plume, and by inference, the location of the wake vortices. The effort examines the gas spectroscopy of the various major constituents of turbine jet exhaust and their contributions to the modeled detectable radiance. Initially, a theoretical analysis of wake vortex proxy detection by thermal radiation was realized in a series of simulations. The first stage used the SLAB plume model to simulate turbine jet exhaust plume characteristics, including exhaust gas transport dynamics and concentrations. The second stage used these plume characteristics as input to the Line By Line Radiative Transfer Model (LBLRTM) to simulate responses from both an imaging IR hyperspectral spectrometer or radiometer. These numerical simulations generated thermal imagery that was compared with previously reported wake vortex temperature data. This research is a continuation of an effort to specify the requirements for an imaging IR spectrometer or radiometer to make wake vortex measurements. Results of the two-stage simulation will be reported, including instrument specifications for wake vortex thermal detection. These results will be compared with previously reported results for IR imaging spectrometer performance.

Neurological impairments and sleep-wake behaviour among the mentally retarded.

Science.gov (United States)

Lindblom, N; Heiskala, H; Kaski, M; Leinonen, L; Nevanlinna, A; Iivanainen, M; Laakso, M L

2001-12-01

The objective of the present study was to evaluate the relationship between the sleep-wake behaviour and neurological impairments among mentally retarded people. The sleep-wake behaviour of 293 mentally retarded subjects living in a rehabilitation center was studied by a standardized observation protocol carried out by trained staff members. The protocol consisted of brief check-ups of the subjects' sleep-wake status at 20-min intervals for five randomly chosen 24-h periods during 4 months. From the raw data five sleep-wake behaviour variables were formed. The data concerning the subject characteristics (age, body mass index (BMI), gender, degree of mental retardation, presence of locomotor disability, that of epilepsy, blindness or deafness and the usage of psychotropic medications) were collected from the medical records. Two main findings emerged: (1) severe locomotor disability, blindness and active epilepsy were found to be independent predictors of increased daytime sleep and increased number of wake-sleep transitions and (2) the subjects with a combination of two or all three of these impairments had a significantly more fragmented and abnormally distributed sleep than those with none or milder forms of these impairments. Age, BMI, degree of mental retardation and the studied medications played a minor role in the sleep disturbances of the study population. Finally, deafness was not found to be associated with any of the measured sleep-wake variables.

Ambient and Wake Turbulence Measurements at Marine Energy Sites from a Five Beam AD2CP

Science.gov (United States)

Guerra, M. A.; Thomson, J. M.

2016-02-01

Ambient turbulence at hydrokinetic energy sites is a key input for turbine design and for their performance determination. Added turbulence from rotating blades to the flow affects the environment surrounding the turbine and has an impact in turbine array distribution. We present two approaches of turbulence measurements: stationary and drifting. Stationary measurements allow for time and frequency analysis of turbulent velocities, while drifting measurements give a spatial characterization of turbulence. For both approaches we used the new five beam Nortek Signature AD2CP. This instrument captures turbulent flow along the water column at high sampling rates (8 Hz) with low Doppler noise level; the use of five beams also makes it possible to fully calculate the Reynolds Stresses. Both sets of measurements require Doppler noise removal for consistent results. Stationary measurements of ambient turbulence were carried out in Admiralty Inlet, WA, in May 2015. The Signature was deployed up looking on a sea spider tripod in a 50 m depth tidal channel during two tidal cycles. This data set allowed us to characterize the turbulence in terms of spectra and Reynolds Stresses in order to evaluate the turbulent kinetic energy balance along the water column and to compare results to other tidal energy sites with similar characteristics where turbulence measurements were taken as well. Drifting measurements of ambient and wake turbulence were conducted in the vicinity of the ORPC RivGen® turbine deployed on the Kvichak River in Alaska in July 2015. The Signature was mounted down looking onboard an anchor buoy equipped with two GPS data receivers for georefference. The cross-sectional river span was covered by releasing the drifter at different positions across the river. More than 300 drifts were performed to spatially characterize turbulence before and after turbine's deployment and grid connection. Results indicate an increased turbulent wake extending up to 75 m downstream

Potential load reductions on megawatt turbines exposed to wakes using individual-pitch wake compensator and trailing-edge flaps

DEFF Research Database (Denmark)

Markou, Helen; Andersen, Peter Bjørn; Larsen, Gunner Chr.

2011-01-01

that typically focus on either load or power prediction. As a consequence, the wake affected inflow field generated by the DWM formulation opens for control strategies for the individual turbine. Two different control approaches for load reduction on the individual turbines are implemented in the multi-body aero-servo-elastic...... tool HAWC2, developed at Risø-DTU in Denmark, and their potential load reduction capabilities compared: (1) full-blade ‘individual-pitch controllers’ acting as wake compensators and (2) controllers using trailing-edge flaps. Information on the wake inflow conditions, induced by upstream turbines...... for the loading conditions of the individual turbines in the farm. The dynamic wake meandering model (DWM) is believed to capture the essential physics of the wake problem, and thus, both load and production aspects can be predicted, which is contrary to the traditional engineering wake prediction methods...

Comparison of Stereo-PIV and Plenoptic-PIV Measurements on the Wake of a Cylinder in NASA Ground Test Facilities.

Science.gov (United States)

Fahringer, Timothy W.; Thurow, Brian S.; Humphreys, William M., Jr.; Bartram, Scott M.

2017-01-01

A series of comparison experiments have been performed using a single-camera plenoptic PIV measurement system to ascertain the systems performance capabilities in terms of suitability for use in NASA ground test facilities. A proof-of-concept demonstration was performed in the Langley Advanced Measurements and Data Systems Branch 13-inch (33- cm) Subsonic Tunnel to examine the wake of a series of cylinders at a Reynolds number of 2500. Accompanying the plenoptic-PIV measurements were an ensemble of complementary stereo-PIV measurements. The stereo-PIV measurements were used as a truth measurement to assess the ability of the plenoptic-PIV system to capture relevant 3D/3C flow field features in the cylinder wake. Six individual tests were conducted as part of the test campaign using three different cylinder diameters mounted in two orientations in the tunnel test section. This work presents a comparison of measurements with the cylinders mounted horizontally (generating a 2D flow field in the x-y plane). Results show that in general the plenoptic-PIV measurements match those produced by the stereo-PIV system. However, discrepancies were observed in extracted pro les of the fuctuating velocity components. It is speculated that spatial smoothing of the vector fields in the stereo-PIV system could account for the observed differences. Nevertheless, the plenoptic-PIV system performed extremely well at capturing the flow field features of interest and can be considered a viable alternative to traditional PIV systems in smaller NASA ground test facilities with limited optical access.

Experimental investigation of the wake behind a model of wind turbine in a water flume

International Nuclear Information System (INIS)

Okulov, V L; Mikkelsen, R; Sørensen, J N; Naumov, I N; Kabardin, I

2014-01-01

The flow behind the model of wind turbine rotor is investigated experimentally in a water flume using Particle Image Velocimetry. The study carried out involves rotors of three bladed wind turbine designed using Glauert's optimization. The transitional regime, generally characterized as in between the regime governed by stable organized vortical structures and the turbulent wake, develops from disturbances of the tip and root vorticies through vortex paring and further complex behaviour towards the fully turbulent wake. Our PIV measurements pay special attention to the onset of the instabilities. The near wake characteristics (development of expansion, tip vortex position, deficit velocity and rotation in the wake) have been measured for different tip speed ratio to compare with main assumptions and conclusions of various rotor theories

Experimental investigation of the wake behind a model of wind turbine in a water flume

DEFF Research Database (Denmark)

Okulov, Valery; Naumov, Igor; Kabardin, I.

2014-01-01

The flow behind the model of wind turbine rotor is investigated experimentally in a water flume using Particle Image Velocimetry. The study carried out involves rotors of three bladed wind turbine designed using Glauert’s optimization. The transitional regime, generally characterized as in between...... the regime governed by stable organized vortical structures and the turbulent wake, develops from disturbances of the tip and root vorticies through vortex paring and further complex behaviour towards the fully turbulent wake. Our PIV measurements pay special attention to the onset of the instabilities....... The near wake characteristics (development of expansion, tip vortex position, deficit velocity and rotation in the wake) have been measured for different tip speed ratio to compare with main assumptions and conclusions of various rotor theories....

Turbulent kinetic energy balance measurements in the wake of a low-pressure turbine blade

International Nuclear Information System (INIS)

Sideridis, A.; Yakinthos, K.; Goulas, A.

2011-01-01

The turbulent kinetic energy budget in the wake generated by a high lift, low-pressure two-dimensional blade cascade of the T106 profile was investigated experimentally using hot-wire anemometry. The purpose of this study is to examine the transport mechanism of the turbulent kinetic energy and provide validation data for turbulence modeling. Point measurements were conducted on a high spatial resolution, two-dimensional grid that allowed precise derivative calculations. Positioning of the probe was achieved using a high accuracy traversing mechanism. The turbulent kinetic energy (TKE) convection, production, viscous diffusion and turbulent diffusion were all obtained directly from experimental measurements. Dissipation and pressure diffusion were calculated indirectly using techniques presented and validated by previous investigators. Results for all terms of the turbulent kinetic energy budget are presented and discussed in detail in the present work.

Experimental study of a wake behind a barrier

Science.gov (United States)

Tomáš, Dufek; Katarína, Ratkovská

2017-09-01

This article describes in detail an experiment which was carried out on a wind tunnel in the Laboratory of the Department of Power Machines, Faculty of Mechanical Engineering, at the University of West Bohemia (UWB), using Particle Image Velocimetry and Stereo Particle Image Velocimetry. PIV is a non-invasive method that allows you to simultaneously measure the flow velocity across the entire field under investigation. In the experiment, the field was located behind the exit of the wind tunnel. The experiment dealt with the measurement of the wake behind a barrier. Measurement with Stereo PIV was carried out in several vertical parallel planes perpendicular to the axis of the tunnel. Conventional PIV method was then used for a horizontal plane passing through the axis of the tunnel at half the height of the barrier. The velocities in the measured plane are expressed by a vector map. In areas not affected by the wake, the speed in the w direction is about 16 m / s. The wake is formed behind the barrier. A shear layer is formed at the boundary between the flowing air and the braked air. A backflow occurs in the area just behind the barrier. The highest speed in the area is achieved in places just behind the exit of the tunnel, where the current is not affected by the barrier. In the direction from the axis and the obstacle, the speed gradually rises from the negative values of the return flow through the zero speed. In addition to the velocity fields, the output from the experimental measurement was also the distribution of the sum of variances, standard deviation and correlation coefficient in the measured planes.

Measurement of a 2D fast-ion velocity distribution function by tomographic inversion of fast-ion D-alpha spectra

DEFF Research Database (Denmark)

Salewski, Mirko; Geiger, B.; Jacobsen, Asger Schou

2014-01-01

We present the first measurement of a local fast-ion 2D velocity distribution function f(v‖, v⊥). To this end, we heated a plasma in ASDEX Upgrade by neutral beam injection and measured spectra of fast-ion Dα (FIDA) light from the plasma centre in three views simultaneously. The measured spectra ...... can measure spectra in up to seven views simultaneously in the next ASDEX Upgrade campaign which would further improve measurements of f(v‖, v⊥) by tomographic inversion.......We present the first measurement of a local fast-ion 2D velocity distribution function f(v‖, v⊥). To this end, we heated a plasma in ASDEX Upgrade by neutral beam injection and measured spectra of fast-ion Dα (FIDA) light from the plasma centre in three views simultaneously. The measured spectra...... agree very well with synthetic spectra calculated from a TRANSP/NUBEAM simulation. Based on the measured FIDA spectra alone, we infer f(v‖, v⊥) by tomographic inversion. Salient features of our measurement of f(v‖, v⊥) agree reasonably well with the simulation: the measured as well as the simulated f...

The effect of extended wake on postural control in young adults.

Science.gov (United States)

Smith, Simon S; Cheng, Tiffany; Kerr, Graham K

2012-09-01

The sleep-wake cycle is a major determinant of locomotor activity in humans, and the neural and physiological processes necessary for optimum postural control may be impaired by an extension of the wake period into habitual sleep time. There is growing evidence for such a contribution from sleep-related factors, but great inconsistency in the methods used to assess this contribution, particularly in control for circadian phase position. Postural control was assessed at hourly intervals across 14 h of extended wake in nine young adult participants. Force plate parameters of medio-lateral and anterior-posterior sway, centre of pressure (CoP) trace length, area, and velocity were assessed with eyes open and eyes closed over 3-min periods. A standard measure of psychomotor vigilance was assessed concurrently under constant routine conditions. After controlling for individual differences in circadian phase position, a significant effect of extended wake was found for anterior-posterior sway and for psychomotor vigilance. These data suggest that extended wake may increase the risk of a fall or other consequences of impaired postural control.

Stability of cognition across wakefulness and dreams in psychotic major depression.

Science.gov (United States)

Cavallotti, Simone; Castelnovo, Anna; Ranieri, Rebecca; D'agostino, Armando

2014-04-30

Cognitive bizarreness has been shown to be equally elevated in the dream and waking mentation of acutely symptomatic inpatients diagnosed with affective and non-affective psychoses. Although some studies have reported on dream content in non-psychotic depression, no study has previously measured this formal aspect of cognition in patients hospitalized for Psychotic Major Depression (PMD). Sixty-five dreams and 154 waking fantasy reports were collected from 11 PMD inpatients and 11 age- and sex-matched healthy controls. All narrative reports were scored by judges blind to diagnosis in terms of formal aspects of cognition (Bizarreness). Dream content was also scored (Hall/Van de Castle scoring system). Unlike controls, PMD patients had similar levels of cognitive bizarreness in their dream and waking mentation. Dreams of PMD patients also differed from those of controls in terms of content variables. In particular, Happiness, Apprehension and Dynamism were found to differ between the two groups. Whereas dream content reflects a sharp discontinuity with the depressive state, cognitive bizarreness adequately measures the stability of cognition across dreams and wakefulness in PMD inpatients. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Coupled wake boundary layer model of windfarms

Science.gov (United States)

Stevens, Richard; Gayme, Dennice; Meneveau, Charles

2014-11-01

We present a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. The `Fellowships for Young Energy Scientists' (YES!) of the Foundation for Fundamental Research on Matter supported by NWO, and NSF Grant #1243482.

Three-dimensional wake dynamics of a blunt and divergent trailing edge airfoil

Energy Technology Data Exchange (ETDEWEB)

El-Gammal, M. [Rowan Williams Davies and Irwin Inc. (RWDI), Guelph, ON (Canada); Hangan, H. [University of Western Ontario, Boundary Layer Wind Tunnel Laboratory, London, ON (Canada)

2008-05-15

The wake dynamics of an airfoil with a blunt and divergent trailing edge is investigated experimentally at relatively high Reynolds. The near wake topology is examined versus different levels of free stream turbulence FST and angles of attack, while the downstream wake evolution is characterized at various levels of FST. The FST is found to have a significant effect on the shapes of turbulence profiles and on the downstream location where the flow reaches its quasi-asymptotic behavior. Streamwise vortices (ribs) corresponding to spanwise variations of turbulence quantities are identified in the near wake region. Simultaneous multi-point hot-wire measurements indicate that their spatial arrangement is similar to Williamson's (Ann Rev Fluid Mech 29:477-539, 1996) mode B laminar wake flow topology. The results suggest that the statistical spanwise distribution of ribs is independent of FST effects and angle of attack as long as the vortex shedding Strouhal number remains approximately similar. (orig.)

Large Eddy Simulation of Vertical Axis Wind Turbine Wakes

Directory of Open Access Journals (Sweden)

Sina Shamsoddin

2014-02-01

Full Text Available In this study, large eddy simulation (LES is combined with a turbine model to investigate the wake behind a vertical-axis wind turbine (VAWT in a three-dimensional turbulent flow. Two methods are used to model the subgrid-scale (SGS stresses: (a the Smagorinsky model; and (b the modulated gradient model. To parameterize the effects of the VAWT on the flow, two VAWT models are developed: (a the actuator swept-surface model (ASSM, in which the time-averaged turbine-induced forces are distributed on a surface swept by the turbine blades, i.e., the actuator swept surface; and (b the actuator line model (ALM, in which the instantaneous blade forces are only spatially distributed on lines representing the blades, i.e., the actuator lines. This is the first time that LES has been applied and validated for the simulation of VAWT wakes by using either the ASSM or the ALM techniques. In both models, blade-element theory is used to calculate the lift and drag forces on the blades. The results are compared with flow measurements in the wake of a model straight-bladed VAWT, carried out in the Institute de Méchanique et Statistique de la Turbulence (IMST water channel. Different combinations of SGS models with VAWT models are studied, and a fairly good overall agreement between simulation results and measurement data is observed. In general, the ALM is found to better capture the unsteady-periodic nature of the wake and shows a better agreement with the experimental data compared with the ASSM. The modulated gradient model is also found to be a more reliable SGS stress modeling technique, compared with the Smagorinsky model, and it yields reasonable predictions of the mean flow and turbulence characteristics of a VAWT wake using its theoretically-determined model coefficient.

Experimental study of boundary-layer transition on an airfoil induced by periodically passing wake

Energy Technology Data Exchange (ETDEWEB)

Jeon, W.P. [Center for Turbulence and Flow Control Research Institute of Advanced Machinery and Design, Seoul National University (Korea); Park, T.C.; Kang, S.H. [School of Mechanical and Aerospace Engineering, Seoul National University (Korea)

2002-02-01

Hot-wire measurements are performed in boundary-layer flows developing on a NACA 0012 airfoil over which wakes pass periodically. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The time- and phase-averaged mean streamwise velocities and turbulence fluctuations are measured to investigate the phenomena of wake-induced transition. Especially, the phase-averaged wall shear stresses are evaluated using a computational Preston tube method. The passing wakes significantly change the pressure distribution on the airfoil, which has influence on the transition process of the boundary layer. The orientation of the passing wake alters the pressure distribution in a different manner. Due to the passing wake, the turbulent patches are generated inside the laminar boundary layer on the airfoil, and the boundary layer becomes temporarily transitional. The patches propagate downstream at a speed smaller than the free-stream velocity and merge together further downstream. Relatively high values of phase-averaged turbulence fluctuations in the outer part of the boundary layer indicate the possibility that breakdown occurs in the outer layer away from the wall. It is confirmed that the phase-averaged mean velocity profile has two dips in the outer region of the transitional boundary layer for each passing cycle. (orig.)

Optimal Fasting Time before Measurement of Serum Triglyceride Levels in Healthy Volunteers.

Science.gov (United States)

Pongsuthana, Surapun; Tivatunsakul, Naris

2016-02-01

Coronary heart disease is a major public health problem. Elevated triglyceride levels are a risk factor for atherosclerosis and coronary heart disease. Food intake interferes with the measurement of serum triglyceride levels, and in previous studies, fasting for 12 hours was recommended before blood sampling. In real-world practice, long fasting times cause patient discomfort and poor compliance, and the present study was, therefore, designed to determine the appropriate fasting time prior to measuring serum triglyceride levels. To determine the appropriate fasting time before measuring serum triglyceride levels. This was a pilot study performed using healthy volunteers aged between 20 and 30 years old from November 2013 to December 2013 at Rajavithi Hospital. The first blood sample was measured in the morning after fasting over 12 hours. The subjects then took their regular breakfast, after which they fasted for 8 hours. Blood samples were taken 6 and 8 hours later and sent to the laboratory for measurement of serum triglyceride levels. 40 volunteers, of whom 25 were female, were enrolled. Their mean age was 25.9 ± 2.81 years old, and their mean weight, height, and body mass index were 61.5 ± 12.5 kg, 167.2 ± 8.3 cm and 21.84 ± 3.1 kg/m2, respectively. Mean fasting serum triglyceride level at 12 hours was 80.23 ± 36.33 mg/dl, at 6 hours it was 110.65 ± 73.45 mg/dl, and at 8 hours it was 75.62 ± 46.81 mg/dl. The group fasting for 12 hours had significantly lower serum triglyceride levels than the group fasting for 6 hours (p-value = 0.003), but no significant difference was found between the group fasting for 12 hours and the one fasting for 8 hours (p-value = 0.493). The present study showed no significant difference in triglyceride levels in patients who had fasted or 8 hours and those who had done so for 12 hours. Fasting for only 8 hours before measurement of serum triglyceride may be sufficient.

Modelling lidar volume-averaging and its significance to wind turbine wake measurements

DEFF Research Database (Denmark)

Meyer Forsting, Alexander Raul; Troldborg, Niels; Borraccino, Antoine

2017-01-01

gradients, like the rotor wake, can it be detrimental. Hence, an efficient algorithm mimicking lidar flow sampling is presented, which considers both pulsed and continous-wave lidar weighting functions. The flow-field around a 2.3 MW turbine is simulated using Detached Eddy Simulation in combination...

Characterization of wind velocities in the wake of a full scale wind turbine using three ground-based synchronized WindScanners

DEFF Research Database (Denmark)

Yazicioglu, Hasan; Angelou, Nikolas; Mikkelsen, Torben Krogh

2016-01-01

The wind energy community is in need of detailed full-field measurements in the wake of wind turbines. Here, three dimensional(3D) wind vector field measurements obtained in the near-wake region behind a full-scale test turbine are presented. Specifically, the wake of a NEG Nordtank turbine...

Numerical modelling of the Concorde wake during ZEBRE

Energy Technology Data Exchange (ETDEWEB)

Gierens, K. [Deutsche Forschungsanstalt fuer Luft- und Raumfahrt e.V. (DLR), Oberpfaffenhofen (Germany). Inst. fuer Physik der Atmosphaere

1997-12-31

Numerical simulations of the Concorde contrail during the ZEBRE experiment have been performed. The main goal of the simulations is to reproduce the fast vanishing of the contrail which disappeared 20-30 s after exhaust. It is difficult to evaporate ice crystals during the jet and vortex phase of the aircraft wake, when the exhaust products are trapped in the vortex cores. The trapping also excludes spatial dispersion of the ice crystals as an explanation of the short contrail lifetime. The disappearance of the contrail within 20-30 s requires that a substantial part of the exhaust gases escapes from the region that is later on trapped in the vortex cores. (author) 10 refs.

Numerical modelling of the Concorde wake during ZEBRE

Energy Technology Data Exchange (ETDEWEB)

Gierens, K [Deutsche Forschungsanstalt fuer Luft- und Raumfahrt e.V. (DLR), Oberpfaffenhofen (Germany). Inst. fuer Physik der Atmosphaere

1998-12-31

Numerical simulations of the Concorde contrail during the ZEBRE experiment have been performed. The main goal of the simulations is to reproduce the fast vanishing of the contrail which disappeared 20-30 s after exhaust. It is difficult to evaporate ice crystals during the jet and vortex phase of the aircraft wake, when the exhaust products are trapped in the vortex cores. The trapping also excludes spatial dispersion of the ice crystals as an explanation of the short contrail lifetime. The disappearance of the contrail within 20-30 s requires that a substantial part of the exhaust gases escapes from the region that is later on trapped in the vortex cores. (author) 10 refs.

Daily rhythms of the sleep-wake cycle

Directory of Open Access Journals (Sweden)

Waterhouse Jim

2012-03-01

Full Text Available Abstract The amount and timing of sleep and sleep architecture (sleep stages are determined by several factors, important among which are the environment, circadian rhythms and time awake. Separating the roles played by these factors requires specific protocols, including the constant routine and altered sleep-wake schedules. Results from such protocols have led to the discovery of the factors that determine the amounts and distribution of slow wave and rapid eye movement sleep as well as to the development of models to determine the amount and timing of sleep. One successful model postulates two processes. The first is process S, which is due to sleep pressure (and increases with time awake and is attributed to a 'sleep homeostat'. Process S reverses during slow wave sleep (when it is called process S'. The second is process C, which shows a daily rhythm that is parallel to the rhythm of core temperature. Processes S and C combine approximately additively to determine the times of sleep onset and waking. The model has proved useful in describing normal sleep in adults. Current work aims to identify the detailed nature of processes S and C. The model can also be applied to circumstances when the sleep-wake cycle is different from the norm in some way. These circumstances include: those who are poor sleepers or short sleepers; the role an individual's chronotype (a measure of how the timing of the individual's preferred sleep-wake cycle compares with the average for a population; and changes in the sleep-wake cycle with age, particularly in adolescence and aging, since individuals tend to prefer to go to sleep later during adolescence and earlier in old age. In all circumstances, the evidence that sleep times and architecture are altered and the possible causes of these changes (including altered S, S' and C processes are examined.

Experimental analysis on the dynamic wake of an actuator disc undergoing transient loads

Science.gov (United States)

Yu, W.; Hong, V. W.; Ferreira, C.; van Kuik, G. A. M.

2017-10-01

The Blade Element Momentum model, which is based on the actuator disc theory, is still the model most used for the design of open rotors. Although derived from steady cases with a fully developed wake, this approach is also applied to unsteady cases, with additional engineering corrections. This work aims to study the impact of an unsteady loading on the wake of an actuator disc. The load and flow of an actuator disc are measured in the Open Jet Facility wind tunnel of Delft University of Technology, for steady and unsteady cases. The velocity and turbulence profiles are characterized in three regions: the inner wake region, the shear layer region and the region outside the wake. For unsteady load cases, the measured velocity field shows a hysteresis effect in relation to the loading, showing differences between the cases when loading is increased and loading is decreased. The flow field also shows a transient response to the step change in loading, with either an overshoot or undershoot of the velocity in relation to the steady-state velocity. In general, a smaller reduced ramp time results in a faster velocity transient, and in turn a larger amplitude of overshoot or undershoot. Time constants analysis shows that the flow reaches the new steady-state slower for load increase than for load decrease; the time constants outside the wake are generally larger than at other radial locations for a given downstream plane; the time constants of measured velocity in the wake show radial dependence.The data are relevant for the validation of numerical models for unsteady actuator discs and wind turbines, and are made available in an open source database (see Appendix).

Numerical Analysis of the Unsteady Propeller Performance in the Ship Wake Modified By Different Wake Improvement Devices

Directory of Open Access Journals (Sweden)

Bugalski Tomasz

2014-10-01

Full Text Available The paper presents the summary of results of the numerical analysis of the unsteady propeller performance in the non-uniform ship wake modified by the different wake improvement devices. This analysis is performed using the lifting surface program DUNCAN for unsteady propeller analysis. Te object of the analysis is a 7000 ton chemical tanker, for which four different types of the wake improvement devices have been designed: two vortex generators, a pre-swirl stator, and a boundary layer alignment device. These produced five different cases of the ship wake structure: the original hull and hull equipped alternatively with four wake improvement devices. Two different propellers were analyzed in these five wake fields, one being the original reference propeller P0 and the other - a specially designed, optimized propeller P3. Te analyzed parameters were the pictures of unsteady cavitation on propeller blades, harmonics of pressure pulses generated by the cavitating propellers in the selected points and the fluctuating bearing forces on the propeller shaft. Some of the calculated cavitation phenomena were confronted with the experimental. Te objective of the calculations was to demonstrate the differences in the calculated unsteady propeller performance resulting from the application of different wake improvement devices. Te analysis and discussion of the results, together with the appropriate conclusions, are included in the paper.

Indirect methods for wake potential integration

International Nuclear Information System (INIS)

Zagorodnov, I.

2006-05-01

The development of the modern accelerator and free-electron laser projects requires to consider wake fields of very short bunches in arbitrary three dimensional structures. To obtain the wake numerically by direct integration is difficult, since it takes a long time for the scattered fields to catch up to the bunch. On the other hand no general algorithm for indirect wake field integration is available in the literature so far. In this paper we review the know indirect methods to compute wake potentials in rotationally symmetric and cavity-like three dimensional structures. For arbitrary three dimensional geometries we introduce several new techniques and test them numerically. (Orig.)

Clinical Practice Guideline for the Treatment of Intrinsic Circadian Rhythm Sleep-Wake Disorders: Advanced Sleep-Wake Phase Disorder (ASWPD), Delayed Sleep-Wake Phase Disorder (DSWPD), Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD), and Irregular Sleep-Wake Rhythm Disorder (ISWRD). An Update for 2015

Science.gov (United States)

Auger, R. Robert; Burgess, Helen J.; Emens, Jonathan S.; Deriy, Ludmila V.; Thomas, Sherene M.; Sharkey, Katherine M.

2015-01-01

A systematic literature review and meta-analyses (where appropriate) were performed and the GRADE approach was used to update the previous American Academy of Sleep Medicine Practice Parameters on the treatment of intrinsic circadian rhythm sleep-wake disorders. Available data allowed for positive endorsement (at a second-tier degree of confidence) of strategically timed melatonin (for the treatment of DSWPD, blind adults with N24SWD, and children/ adolescents with ISWRD and comorbid neurological disorders), and light therapy with or without accompanying behavioral interventions (adults with ASWPD, children/adolescents with DSWPD, and elderly with dementia). Recommendations against the use of melatonin and discrete sleep-promoting medications are provided for demented elderly patients, at a second- and first-tier degree of confidence, respectively. No recommendations were provided for remaining treatments/ populations, due to either insufficient or absent data. Areas where further research is needed are discussed. Citation: Auger RR, Burgess HJ, Emens JS, Deriy LV, Thomas SM, Sharkey KM. Clinical practice guideline for the treatment of intrinsic circadian rhythm sleep-wake disorders: advanced sleep-wake phase disorder (ASWPD), delayed sleep-wake phase disorder (DSWPD), non-24-hour sleep-wake rhythm disorder (N24SWD), and irregular sleep-wake rhythm disorder (ISWRD). An update for 2015. J Clin Sleep Med 2015;11(10):1199–1236. PMID:26414986

Multi-Point Velocity Correlations in the Wake of a Three-Dimensional Bluff Body

Science.gov (United States)

Shea, Patrick; Glauser, Mark

2013-11-01

Three-dimensional bluff-bodies known as turrets are commonly used for housing optical systems on airborne platforms. These geometries generate highly turbulent wakes that decrease the performance of the optical systems and the aircraft. The current experimental study used dynamic suction in both open and closed-loop control configurations to actively control the wake turret. The experiments were carried out at a Reynolds number of 5 × 105, and the flow field was characterized using stereoscopic PIV measurements acquired in the wake of the turret. These data were processed using traditional single-point statistics which showed that the active control system was able to significantly alter the wake of the turret. Using multi-point correlations, turbulent characteristics such as the integral length scale can be calculated. For the turret wake, estimates of the integral length scales were found to be highly dependent upon the region of the flow that was evaluated, especially when comparing the shear layers to the center of the wake. With the application of the active control, the integral length scales were generally found to increase.

Estimating dim light melatonin onset (DLMO) phase in adolescents using summer or school-year sleep/wake schedules.

Science.gov (United States)

Crowley, Stephanie J; Acebo, Christine; Fallone, Gahan; Carskadon, Mary A

2006-12-01

This analysis examined associations between the salivary dim light melatonin onset (DLMO) phase and self-selected sleep/ wake schedules in groups of children and adolescents during summer vacation and during the school year to determine the degree to which sleep/wake patterns can estimate salivary DLMO phase. Participants slept at home on self-selected schedules for 5 consecutive nights and reported their bedtime and wake-up time via daily telephone messages. Salivary melatonin was sampled in the laboratory on one evening every 30 minutes in dim light (females) contributed 149 DLMO phase and sleep/wake pattern measures while on a school year schedule ("school group"). A separate group, ages 9 to 16 years (mean age = 13.1, SD = 1.3 years, 30 males, 29 females) contributed 59 DLMO phase and sleep/wake pattern measures while on a summer schedule ("summer group"). Bedtime, midsleep time, and wake-up time were positively correlated with DLMO phase in both groups. Although all correlation coefficients for the summer group were statistically greater compared to the school group, the regression equations predicted DLMO phase within +/- 1 hour of the measured DLMO phase in approximately 80% for both groups. DLMO phase can be estimated using self-selected sleep/wake patterns during the school year or summer vacation in healthy children and adolescents.

Endoplasmic reticulum stress in wake-active neurons progresses with aging.

Science.gov (United States)

Naidoo, Nirinjini; Zhu, Jingxu; Zhu, Yan; Fenik, Polina; Lian, Jie; Galante, Ray; Veasey, Sigrid

2011-08-01

Fragmentation of wakefulness and sleep are expected outcomes of advanced aging. We hypothesize that wake neurons develop endoplasmic reticulum dyshomeostasis with aging, in parallel with impaired wakefulness. In this series of experiments, we sought to more fully characterize age-related changes in wakefulness and then, in relevant wake neuronal populations, explore functionality and endoplasmic reticulum homeostasis. We report that old mice show greater sleep/wake transitions in the active period with markedly shortened wake periods, shortened latencies to sleep, and less wake time in the subjective day in response to a novel social encounter. Consistent with sleep/wake instability and reduced social encounter wakefulness, orexinergic and noradrenergic wake neurons in aged mice show reduced c-fos response to wakefulness and endoplasmic reticulum dyshomeostasis with increased nuclear translocation of CHOP and GADD34. We have identified an age-related unfolded protein response injury to and dysfunction of wake neurons. It is anticipated that these changes contribute to sleep/wake fragmentation and cognitive impairment in aging. © 2011 The Authors. Aging Cell © 2011 Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland.

Wake development behind paired wings with tip and root trailing vortices: consequences for animal flight force estimates.

Science.gov (United States)

Horstmann, Jan T; Henningsson, Per; Thomas, Adrian L R; Bomphrey, Richard J

2014-01-01

Recent experiments on flapping flight in animals have shown that a variety of unrelated species shed a wake behind left and right wings consisting of both tip and root vortices. Here we present an investigation using Particle Image Velocimetry (PIV) of the behaviour and interaction of trailing vortices shed by paired, fixed wings that simplify and mimic the wake of a flying animal with a non-lifting body. We measured flow velocities at five positions downstream of two adjacent NACA 0012 aerofoils and systematically varied aspect ratio, the gap between the wings (corresponding to the width of a non-lifting body), angle of attack, and the Reynolds number. The range of aspect ratios and Reynolds number where chosen to be relevant to natural fliers and swimmers, and insect flight in particular. We show that the wake behind the paired wings deformed as a consequence of the induced flow distribution such that the wingtip vortices convected downwards while the root vortices twist around each other. Vortex interaction and wake deformation became more pronounced further downstream of the wing, so the positioning of PIV measurement planes in experiments on flying animals has an important effect on subsequent force estimates due to rotating induced flow vectors. Wake deformation was most severe behind wings with lower aspect ratios and when the distance between the wings was small, suggesting that animals that match this description constitute high-risk groups in terms of measurement error. Our results, therefore, have significant implications for experimental design where wake measurements are used to estimate forces generated in animal flight. In particular, the downstream distance of the measurement plane should be minimised, notwithstanding the animal welfare constraints when measuring the wake behind flying animals.

Wake development behind paired wings with tip and root trailing vortices: consequences for animal flight force estimates.

Directory of Open Access Journals (Sweden)

Jan T Horstmann

Full Text Available Recent experiments on flapping flight in animals have shown that a variety of unrelated species shed a wake behind left and right wings consisting of both tip and root vortices. Here we present an investigation using Particle Image Velocimetry (PIV of the behaviour and interaction of trailing vortices shed by paired, fixed wings that simplify and mimic the wake of a flying animal with a non-lifting body. We measured flow velocities at five positions downstream of two adjacent NACA 0012 aerofoils and systematically varied aspect ratio, the gap between the wings (corresponding to the width of a non-lifting body, angle of attack, and the Reynolds number. The range of aspect ratios and Reynolds number where chosen to be relevant to natural fliers and swimmers, and insect flight in particular. We show that the wake behind the paired wings deformed as a consequence of the induced flow distribution such that the wingtip vortices convected downwards while the root vortices twist around each other. Vortex interaction and wake deformation became more pronounced further downstream of the wing, so the positioning of PIV measurement planes in experiments on flying animals has an important effect on subsequent force estimates due to rotating induced flow vectors. Wake deformation was most severe behind wings with lower aspect ratios and when the distance between the wings was small, suggesting that animals that match this description constitute high-risk groups in terms of measurement error. Our results, therefore, have significant implications for experimental design where wake measurements are used to estimate forces generated in animal flight. In particular, the downstream distance of the measurement plane should be minimised, notwithstanding the animal welfare constraints when measuring the wake behind flying animals.

Flow structure and unsteadiness in the supersonic wake of a generic space launcher

Science.gov (United States)

Schreyer, Anne-Marie; Stephan, Sören; Radespiel, Rolf

2015-11-01

At the junction between the rocket engine and the main body of a classical space launcher, a separation-dominated and highly unstable flow field develops and induces strong wall-pressure oscillations. These can excite structural vibrations detrimental to the launcher. It is desirable to minimize these effects, for which a better understanding of the flow field is required. We study the wake flow of a generic axisymmetric space-launcher model with and without propulsive jet (cold air). Experimental investigations are performed at Mach 2.9 and a Reynolds number ReD = 1 . 3 .106 based on model diameter D. The jet exits the nozzle at Mach 2.5. Velocity measurements by means of Particle Image Velocimetry and mean and unsteady wall-pressure measurements on the main-body base are performed simultaneously. Additionally, we performed hot-wire measurements at selected points in the wake. We can thus observe the evolution of the wake flow along with its spectral content. We describe the mean and turbulent flow topology and evolution of the structures in the wake flow and discuss the origin of characteristic frequencies observed in the pressure signal at the launcher base. The influence of a propulsive jet on the evolution and topology of the wake flow is discussed in detail. The German Research Foundation DFG is gratefully acknowledged for funding this research within the SFB-TR40 ``Technological foundations for the design of thermally and mechanically highly loaded components of future space transportation systems.''

Optimization-Based Calibration of FAST.Farm Parameters Against SOWFA

Energy Technology Data Exchange (ETDEWEB)

Doubrawa Moreira, Paula [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Annoni, Jennifer [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jonkman, Jason [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Ghate, Aditya [Stanford University

2018-01-12

FAST.Farm is a medium-delity wind farm modeling tool that can be used to assess power and loads contributions of wind turbines in a wind farm. The objective of this paper is to undertake a calibration procedure to set the user parameters of FAST.Farm to accurately represent results from large-eddy simulations. The results provide an in- depth analysis of the comparison of FAST.Farm and large-eddy simulations before and after calibration. The comparison of FAST.Farm and large-eddy simulation results are presented with respect to streamwise and radial velocity components as well as wake-meandering statistics (mean and standard deviation) in the lateral and vertical directions under different atmospheric and turbine operating conditions.

Analysis of turbulent wake behind a wind turbine

DEFF Research Database (Denmark)

Kermani, Nasrin Arjomand; Andersen, Søren Juhl; Sørensen, Jens Nørkær

2013-01-01

The aim of this study is to improve the classical analytical model for estimation of the rate of wake expansion and the decay of wake velocity deficit in the far wake region behind a wind turbine. The relations for a fully turbulent axisymmetric far wake were derived by applying the mass and mome...

Wake and light therapy for moderate-to-severe depression - a randomized controlled trial

DEFF Research Database (Denmark)

Kragh, M; Martiny, K; Videbech, P

2017-01-01

Objective: To examine the efficacy of using wake and light therapy as a supplement to standard treatment of hospitalized patients with depression. Method: In this randomized, controlled study, 64 patients with moderate-to-severe depression were allocated to standard treatment or to the intervention......, which additionally consisted of three wake therapy sessions in one week, 30-min daily light treatment and sleep time stabilization over the entire nine-week study period. Results: Patients in the wake therapy group had a significant decrease in depressive symptoms in week one as measured by HAM-D17, 17...

THE NEUROBIOLOGY OF SLEEP AND WAKEFULNESS

Science.gov (United States)

Schwartz, Michael D.; Kilduff, Thomas S.

2015-01-01

SYNOPSIS Since the discovery of Rapid Eye Movement (REM) sleep in the late 1950s, identification of the neural circuitry underlying wakefulness, sleep onset and the alternation between REM and non-REM (NREM) sleep has been an active area of investigation. Synchronization and desynchronization of cortical activity as detected in the electroencephalogram (EEG) is due to a corticothalamocortical loop, intrinsic cortical oscillators, monoaminergic and cholinergic afferent input to the thalamus, and the basal forebrain cholinergic input directly to the cortex. The monoaminergic and cholinergic systems are largely wake-promoting; the brainstem cholinergic nuclei are also involved in REM sleep regulation. These wake-promoting systems receive excitatory input from the hypothalamic hypocretin/orexin system. Sleep-promoting nuclei are GABAergic in nature and found in the preoptic area, brainstem and lateral hypothalamus. Although the pons is critical for the expression of REM sleep, recent research has suggested that melanin-concentrating hormone/GABAergic cells in the lateral hypothalamus "gate" REM sleep. The temporal distribution of sleep and wakefulness is due to interaction between the circadian system and the sleep homeostatic system. Although the hypothalamic suprachiasmatic nuclei contain the circadian pacemaker, the neural circuitry underlying the sleep homeostat is less clear. Prolonged wakefulness results in the accumulation of extracellular adenosine, possibly from glial sources, which is an important feedback molecule for the sleep homeostatic system. Cortical neuronal nitric oxide (nNOS) neurons may also play a role in propagating slow waves through the cortex in NREM sleep. Several neuropeptides and other neurochemicals likely play important roles in sleep/wake control. Although the control of sleep and wakefulness seemingly involves multiple redundant systems, each of these systems provides a vulnerability that can result in sleep/wake dysfunction that may

Are there sex differences in Fetal Abdominal Subcutaneous Tissue (FAST) measurements?

LENUS (Irish Health Repository)

Farah, Nadine

2012-02-01

OBJECTIVE: To determine if Fetal Abdominal Subcutaneous Tissue (FAST) measurements using antenatal ultrasound differ between male and female fetuses. STUDY DESIGN: Women who had an ultrasound examination for fetal growth between 20 and 40 weeks gestation were studied. Women with diabetes mellitus were excluded. The fetal anterior abdominal subcutaneous tissue was measured on the anterior abdominal wall in millimetres anterior to the margins of the ribs, using magnification at the level of the abdominal circumference. The fetal sex was recorded after delivery. RESULTS: A total of 557 fetuses were measured, 290 male and 267 female. The FAST measurements increased with gestational age. The FAST increased at the same rate for both male and female fetuses and at any given week there was no sex difference. CONCLUSIONS: The increased fat composition in females reported after birth was not found in abdominal wall subcutaneous fat measurements using ultrasound during pregnancy. Antenatal centile charts for FAST do not need to be based on sex.

High-frequency oscillations in human and monkey neocortex during the wake-sleep cycle.

Science.gov (United States)

Le Van Quyen, Michel; Muller, Lyle E; Telenczuk, Bartosz; Halgren, Eric; Cash, Sydney; Hatsopoulos, Nicholas G; Dehghani, Nima; Destexhe, Alain

2016-08-16

Beta (β)- and gamma (γ)-oscillations are present in different cortical areas and are thought to be inhibition-driven, but it is not known if these properties also apply to γ-oscillations in humans. Here, we analyze such oscillations in high-density microelectrode array recordings in human and monkey during the wake-sleep cycle. In these recordings, units were classified as excitatory and inhibitory cells. We find that γ-oscillations in human and β-oscillations in monkey are characterized by a strong implication of inhibitory neurons, both in terms of their firing rate and their phasic firing with the oscillation cycle. The β- and γ-waves systematically propagate across the array, with similar velocities, during both wake and sleep. However, only in slow-wave sleep (SWS) β- and γ-oscillations are associated with highly coherent and functional interactions across several millimeters of the neocortex. This interaction is specifically pronounced between inhibitory cells. These results suggest that inhibitory cells are dominantly involved in the genesis of β- and γ-oscillations, as well as in the organization of their large-scale coherence in the awake and sleeping brain. The highest oscillation coherence found during SWS suggests that fast oscillations implement a highly coherent reactivation of wake patterns that may support memory consolidation during SWS.

Experimental study of boundary layer transition on an airfoil induced by periodically passing wake (I)

Energy Technology Data Exchange (ETDEWEB)

Park, T.C. [Seoul National University Graduate School, Seoul (Korea); Jeon, W.P.; Kang, S.H. [Seoul National University, Seoul (Korea)

2001-06-01

Hot-wire measurements are performed in boundary layers developing on a NACA0012 airfoil over which wakes pass periodically. The Reynolds number based on chord length of the airfoil is 2X10{sup 5} and the wakes are generated by circular cylinders rotating clockwise and counterclockwise around the airfoil. This paper and its companion Part II describe the phenomena of wake-induced transition of the boundary layers on the airfoil using measured data; phase- and time-averaged streamwise mean velocities, turbulent fluctuations, integral parameters and wall skin frictions. This paper describes the background and facility together with results of time-averaged quantities. Due to the passing wake with mean velocity defects and high turbulence intensities, the laminar boundary layer is periodically disturbed at the upstream station and becomes steady-state transitional boundary layer at the downstream station. The velocity defect in the passing wake changes the local pressure at the leading of the airfoil, significantly affects the time-mean pressure distribution on the airfoil and eventually, has influence on the transition process of the boundary layer. (author). 22 refs., 9 figs.

Comparison of a Coupled Near and Far Wake Model With a Free Wake Vortex Code

DEFF Research Database (Denmark)

Pirrung, Georg; Riziotis, Vasilis; Aagaard Madsen, Helge

2016-01-01

to be updated during the computation. Further, the effect of simplifying the exponential function approximation of the near wake model to increase the computation speed is investigated in this work. A modification of the dynamic inflow weighting factors of the far wake model is presented that ensures good...... computations performed using a free wake panel code. The focus of the description of the aerodynamics model is on the numerical stability, the computation speed and the accuracy of 5 unsteady simulations. To stabilize the near wake model, it has to be iterated to convergence, using a relaxation factor that has...... and a BEM model is centered around the NREL 5 MW reference turbine. The response to pitch steps at different pitching speeds is compared. By means of prescribed vibration cases, the effect of the aerodynamic model on the predictions of the aerodynamic work is investigated. The validation shows that a BEM...

Wake simulation for wind turbines with a free, prescribed- and hybrid-wake method

Energy Technology Data Exchange (ETDEWEB)

Bareiss, R.; Guidati, G.; Wagner, S. [Univ. Stuttgart, Inst. fuer Aerodynamik und Gasdynamik, Stuttgart (Germany)

1997-08-01

Calculations of the radial distribution and the time history of the induction factors have been performed with a number of different wake models implemented in a vortex-lattice method for tip-speed ratios in the range 1-13. The new models lead to a significant reduction of the computational effort down to 3-27% compared to a free-wake model with errors less than 5%. (au)

Verification of the SLC wake potentials

International Nuclear Information System (INIS)

Bane, K.; Weiland, T.

1983-01-01

The accurate knowledge of the monopole, dipole, and quadrupole wake potentials is essential for SLC. These wake potentials were previously computed by the modal method. The time domain code TBCI allows independent verification of these results. This comparison shows that the two methods agree to within 10% for bunch lengths down to 1 mm. TBCI results also indicate that rounding the irises gives at least a 10% reduction in the wake potentials

Fast measure proceeding of weak currents

International Nuclear Information System (INIS)

Taieb, J.

1953-01-01

The process of fast measure of the weak currents that we are going to describe briefly apply worthy of the provided currents by the sources to elevated value internal resistance, as it is the case for the ionization chamber, the photocells, mass spectroscopic tubes. The problem to measure weak currents is essentially a problem of amplifier and of input circuit. We intended to achieve a whole amplifier and input circuit with advanced performances, meaning that for a measured celerity we wanted to have an signal/noise ratio the most important as in the classic systems and for a same report signal/noise a more quickly done measure. (M.B.) [fr

Fast and precise luminosity measurement at the international linear ...

Indian Academy of Sciences (India)

6. — journal of. December 2007 physics pp. 1151–1157. Fast and precise luminosity measurement ... The fast investigation of the collision quality for intrabunch feedback and the ... consisting of the sensor, the absorber and an interconnection structure. 2. ... outer radius of BeamCal is increased to keep the angular overlap.

MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS

International Nuclear Information System (INIS)

2004-01-01

Several recent applications for fast ramped magnets have been found that require rapid measurement of the field quality during the ramp. (In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the accuracy typically required for accelerators.) We have built and tested a new type of magnetic field measuring system to meet this need. The system consists of 16 stationary pickup windings mounted on a cylinder. The signals induced in the windings in a changing magnetic field are sampled and analyzed to obtain the field harmonics. To minimize costs, printed circuit boards were used for the pickup windings and a combination of amplifiers and ADPs used for the voltage readout system. New software was developed for the analysis. Magnetic field measurements of a model dipole developed for the SIS200 accelerator at GSI are presented. The measurements are needed to insure that eddy currents induced by the fast ramps do not impact the field quality needed for successful accelerator operation

Comparing offshore wind farm wake observed from satellite SAR and wake model results

Science.gov (United States)

Bay Hasager, Charlotte

2014-05-01

Offshore winds can be observed from satellite synthetic aperture radar (SAR). In the FP7 EERA DTOC project, the European Energy Research Alliance project on Design Tools for Offshore Wind Farm Clusters, there is focus on mid- to far-field wind farm wakes. The more wind farms are constructed nearby other wind farms, the more is the potential loss in annual energy production in all neighboring wind farms due to wind farm cluster effects. It is of course dependent upon the prevailing wind directions and wind speed levels, the distance between the wind farms, the wind turbine sizes and spacing. Some knowledge is available within wind farm arrays and in the near-field from various investigations. There are 58 offshore wind farms in the Northern European seas grid connected and in operation. Several of those are spaced near each other. There are several twin wind farms in operation including Nysted-1 and Rødsand-2 in the Baltic Sea, and Horns Rev 1 and Horns Rev 2, Egmond aan Zee and Prinses Amalia, and Thompton 1 and Thompton 2 all in the North Sea. There are ambitious plans of constructing numerous wind farms - great clusters of offshore wind farms. Current investigation of offshore wind farms includes mapping from high-resolution satellite SAR of several of the offshore wind farms in operation in the North Sea. Around 20 images with wind farm wake cases have been retrieved and processed. The data are from the Canadian RADARSAT-1/-2 satellites. These observe in microwave C-band and have been used for ocean surface wind retrieval during several years. The satellite wind maps are valid at 10 m above sea level. The wakes are identified in the raw images as darker areas downwind of the wind farms. In the SAR-based wind maps the wake deficit is found as areas of lower winds downwind of the wind farms compared to parallel undisturbed flow in the flow direction. The wind direction is clearly visible from lee effects and wind streaks in the images. The wind farm wake cases

Iodine Tagging Velocimetry in a Mach 10 Wake

Science.gov (United States)

Balla, Robert Jeffrey

2013-01-01

A variation on molecular tagging velocimetry (MTV) [1] designated iodine tagging velocimetry (ITV) is demonstrated. Molecular iodine is tagged by two-photon absorption using an Argon Fluoride (ArF) excimer laser. A single camera measures fluid displacement using atomic iodine emission at 206 nm. Two examples ofMTVfor cold-flowmeasurements areN2OMTV [2] and Femtosecond Laser Electronic Excitation Tagging [3]. These, like most MTV methods, are designed for atmospheric pressure applications. Neither can be implemented at the low pressures (0.1- 1 Torr) in typical hypersonic wakes. Of all the single-laser/singlecamera MTV approaches, only Nitric-Oxide Planar Laser Induced Fluorescence-based MTV [4] has been successfully demonstrated in a Mach 10 wake. Oxygen quenching limits transit times to 500 ns and accuracy to typically 30%. The present note describes the photophysics of the ITV method. Off-body velocimetry along a line is demonstrated in the aerothermodynamically important and experimentally challenging region of a hypersonic low-pressure near-wake in a Mach 10 air wind tunnel. Transit times up to 10 µs are demonstrated with conservative errors of 10%.

Fast neutron measurements with 7Li and 6Li enriched CLYC scintillators

International Nuclear Information System (INIS)

Giaz, A.; Blasi, N.; Boiano, C.; Brambilla, S.; Camera, F.; Cattadori, C.; Ceruti, S.; Gramegna, F.; Marchi, T.; Mattei, I.; Mentana, A.; Million, B.; Pellegri, L.; Rebai, M.; Riboldi, S.; Salamida, F.; Tardocchi, M.

2016-01-01

The recently developed Cs 2 LiYCl 6 :Ce (CLYC) crystals are interesting scintillation detectors not only for their gamma energy resolution (<5% at 662 keV) but also for their capability to identify and measure the energy of both gamma rays and fast/thermal neutrons. The thermal neutrons were detected by the 6 Li(n,α)t reaction while for the fast neutrons the 35 Cl(n,p) 35 S and 35 Cl(n,α) 32 P neutron-capture reactions were exploited. The energy of the outgoing proton or α particle scales linearly with the incident neutron energy. The kinetic energy of the fast neutrons can be measured using both the Time Of Flight (TOF) technique and using the CLYC energy signal. In this work, the response to monochromatic fast neutrons (1.9–3.8 MeV) of two CLYC 1″×1″ crystals was measured using both the TOF and the energy signal. The observables were combined to identify fast neutrons, to subtract the thermal neutron background and to identify different fast neutron-capture reactions on 35 Cl, in other words to understand if the detected particle is an α or a proton. We performed a dedicated measurement at the CN accelerator facility of the INFN Legnaro National Laboratories (Italy), where the fast neutrons were produced by impinging a proton beam (4.5, 5.0 and 5.5 MeV) on a 7 LiF target. We tested a CLYC detector 6 Li-enriched at about 95%, which is ideal for thermal neutron measurements, in parallel with another CLYC detector 7 Li-enriched at more than 99%, which is suitable for fast neutron measurements.

Wind Farm Wake

DEFF Research Database (Denmark)

Hasager, Charlotte Bay; Karagali, Ioanna; Volker, Patrick

2017-01-01

On 25 January 2016 at 12:45 UTC several photographs of the offshore wind farm Horns Rev 2 were taken by helicopter pilot Gitte Lundorff with an iPhone. A very shallow layer of fog covered the sea. The photos of the fog over the sea dramatically pictured the offshore wind farm wake. Researchers got...... together to investigate the atmospheric conditions at the time of the photos by analysing local meteorological observations and wind turbine information, satellite remote sensing and nearby radiosonde data. Two wake models and one mesoscale model were used to model the case and explain what was seen....

Wakes behind wind turbines. Studies on tip vortex evolution and stability

Energy Technology Data Exchange (ETDEWEB)

Odemark, Ylva

2012-07-01

The increased fatigue loads and decreased power output of a wind turbine placed in the wake of another turbine is a well-known problem when building new wind power farms. In order to better estimate the total power output of a wind power farm, knowledge about the development and stability of wind turbine wakes is crucial. In the present thesis, the wake behind a small-scale model turbine was investigated experimentally in a wind tunnel. The velocity in the wake was measured with hot-wire anemometry, for different free stream velocities and tip speed ratios. To characterize the behaviour of the model turbine, the power output, thrust force and rotational frequency of the model were also measured. These results were then compared to calculations using the Blade Element Momentum (BEM) method. New turbine blades for the model was constructed using the same method, in order to get an estimate of the distribution of the lift and drag forces along the blades. This information is needed for comparisons with certain numerical simulations, which however remains to be performed.By placing the turbine at different heights in a turbulent boundary layer, the effects of forest turbulence on wind turbine outputs (power and thrust) could also be investigated.The evolution of the tip vortices shed from the turbine blades was studied by performing velocity measurements around the location of the tip vortex breakdown. The vortices' receptivity to disturbances was then studied by introducing a disturbance in the form of two pulsed jets, located in the rear part of the nacelle. In order to introduce a well-defined disturbance and perform phase-locked measurements, a new experimental setup was constructed and successfully tested for two different disturbance frequencies. The mean stream wise velocity and the stream wise turbulence intensity was found to scale well with the free stream velocity and the spreading of the wake was found to be proportional to the square root of the

Dispersion in the wake of a model industrial complex

International Nuclear Information System (INIS)

Hatcher, R.V.; Meroney, R.N.; Peterka, J.A.; Kothari, K.

1977-06-01

Models (1:200 scale) of the EOCR reactor building and surrounding silo and tank buildings at the Idaho National Engineering Laboratory, Idaho Falls, Idaho were put into the Meteorological Wind Tunnel at Colorado State University for the purpose of studying the effects of building wakes on dispersion. Flow visualization was done and concentration measurements were taken. The test program consisted of systematic releases from ground, building height, and stack height sources with no appreciable plume rise. The program was repeated for cases of moderately unstable, neutral, moderately stable, and stable conditions in the wind tunnel. Results show that the buildings significantly alter the dispersion patterns and the addition of any extra buildings or slight terrain change in the immediate vicinity of the building has a major effect. In the near wake region the effects of stratification were still evident causing slightly higher concentrations for stable conditions and slightly lower for unstable. Current dispersion models are discussed and evaluated that predict concentrations in the building wake region

Proteomic profiling of the rat cerebral cortex in sleep and waking

OpenAIRE

Cirelli, Chiara; Pfister-Genskow, Martha; McCarthy, Diane; Woodbury, Ronald; Tononi, Giulio

2009-01-01

Transcriptomic studies have shown that hundreds of genes change their expression levels across the sleep/waking cycle, and found that waking-related and sleep-related mRNAs belong to different functional categories. Proteins, however, rather than DNA or RNA, carry out most of the cellular functions, and direct measurements of protein levels and activity are required to assess the effects of behavioral states on the overall functional state of the cell. Here we used surface-enhanced laser deso...

Delayed gamma power measurement for sodium-cooled fast reactors

Energy Technology Data Exchange (ETDEWEB)

Coulon, R., E-mail: romain.coulon@cea.f [CEA, LIST, Laboratoire Capteurs et Architectures Electroniques, F-91191 Gif-sur-Yvette (France); Normand, S., E-mail: stephane.normand@cea.f [CEA, LIST, Laboratoire Capteurs et Architectures Electroniques, F-91191 Gif-sur-Yvette (France); Ban, G., E-mail: ban@lpccaen.in2p3.f [ENSICAEN, 6 Boulevard Marechal Juin, F-14050 Caen Cedex 4 (France); Barat, E.; Montagu, T.; Dautremer, T. [CEA, LIST, Laboratoire Modelisation Simulation et Systemes, F-91191 Gif-sur-Yvette (France); Brau, H.-P. [ICSM, Centre de Marcoule, BP 17171 F-30207 Bagnols sur Ceze (France); Dumarcher, V. [AREVA NP, SET, F-84500 Bollene (France); Michel, M.; Barbot, L.; Domenech, T.; Boudergui, K.; Bourbotte, J.-M. [CEA, LIST, Laboratoire Capteurs et Architectures Electroniques, F-91191 Gif-sur-Yvette (France); Jousset, P. [CEA, LIST, Departement des Capteurs, du Signal et de l' Information, F-91191 Gif-sur-Yvette (France); Barouch, G.; Ravaux, S.; Carrel, F. [CEA, LIST, Laboratoire Modelisation Simulation et Systemes, F-91191 Gif-sur-Yvette (France); Saurel, N. [CEA, DAM, Laboratoire Mesure de Dechets et Expertise, F-21120 Is-sur-Tille (France); Frelin-Labalme, A.-M.; Hamrita, H. [CEA, LIST, Laboratoire Capteurs et Architectures Electroniques, F-91191 Gif-sur-Yvette (France)

2011-01-15

Graphical abstract: Display Omitted Research highlights: {sup 20}F and {sup 23}Ne tagging agents are produced by fast neutron flux. {sup 20}F signal has been measured at the SFR Phenix prototype. A random error of only 3% for an integration time of 2 s could be achieved. {sup 20}F and {sup 23}Ne power measurement has a reduced temperature influence. Burn-up impact could be limited by simultaneous {sup 20}F and {sup 23}Ne measurement. - Abstract: Previous works on pressurized water reactors show that the nitrogen 16 activation product can be used to measure thermal power. Power monitoring using a more stable indicator than ex-core neutron measurements is required for operational sodium-cooled fast reactors, in order to improve their economic efficiency at the nominal operating point. The fluorine 20 and neon 23 produced by (n,{alpha}) and (n,p) capture in the sodium coolant have this type of convenient characteristic, suitable for power measurements with low build-up effects and a potentially limited temperature, flow rate, burn-up and breeding dependence. This method was tested for the first time during the final tests program of the French Phenix sodium-cooled fast reactor at CEA Marcoule, using the ADONIS gamma pulse analyzer. Despite a non-optimal experimental configuration for this application, the delayed gamma power measurement was pre-validated, and found to provide promising results.

Detailed field test of yaw-based wake steering

DEFF Research Database (Denmark)

Fleming, P.; Churchfield, M.; Scholbrock, A.

2016-01-01

production. In the first phase, a nacelle-mounted scanning lidar was used to verify wake deflection of a misaligned turbine and calibrate wake deflection models. In the second phase, these models were used within a yaw controller to achieve a desired wake deflection. This paper details the experimental......This paper describes a detailed field-test campaign to investigate yaw-based wake steering. In yaw-based wake steering, an upstream turbine intentionally misaligns its yaw with respect to the inflow to deflect its wake away from a downstream turbine, with the goal of increasing total power...... design and setup. All data collected as part of this field experiment will be archived and made available to the public via the U.S. Department of Energy’s Atmosphere to Electrons Data Archive and Portal....

A typical wave wake from high-speed vessels: its group structure and run-up

Directory of Open Access Journals (Sweden)

I. Didenkulova

2013-02-01

Full Text Available High-amplitude water waves induced by high-speed vessels are regularly observed in Tallinn Bay, the Baltic Sea, causing intense beach erosion and disturbing marine habitants in the coastal zone. Such a strong impact on the coast may be a result of a certain group structure of the wave wake. In order to understand it, here we present an experimental study of the group structure of these wakes at Pikakari beach, Tallinn Bay. The most energetic vessel waves at this location (100 m from the coast at the water depth 2.7 m have amplitudes of about 1 m and periods of 8–10 s and cause maximum run-up heights on a beach up to 1.4 m. These waves represent frequency modulated packets where the largest and longest waves propagate ahead of other smaller amplitude and period waves. Sometimes the groups of different heights and periods can be separated even within one wave wake event. The wave heights within a wake are well described by the Weibull distribution, which has different parameters for wakes from different vessels. Wave run-up heights can also be described by Weibull distribution and its parameters can be connected to the parameters of the distribution of wave heights 100 m from the coast. Finally, the run-up of individual waves within a packet is studied. It is shown that the specific structure of frequency modulated wave packets, induced by high-speed vessels, leads to a sequence of high wave run-ups at the coast, even when the original wave heights are rather moderate. This feature can be a key to understanding the significant impact on coasts caused by fast vessels.

Four-dimensional characterization of inflow to and wakes from a multi-MW turbine: overview of the Turbine Wake and Inflow Characterization Study (TWICS2011)

Science.gov (United States)

Lundquist, J. K.; Banta, R. M.; Pichugina, Y.; Brewer, A.; Alvarez, R. J.; Sandberg, S. P.; Kelley, N. D.; Aitken, M.; Clifton, A.; Mirocha, J. D.

2011-12-01

To support substantial deployment of renewably-generated electricity from the wind, critical information about the variability of wind turbine wakes in the real atmosphere from multi-MW turbines is required. The assessment of the velocity deficit and turbulence associated with industrial-scale turbines is a major issue for wind farm design, particularly with respect to the optimization of the spacing between turbines. The significant velocity deficit and turbulence generated by upstream turbines can reduce the power production and produce harmful vibrations in downstream turbines, which can lead to excess maintenance costs. The complexity of wake effects depends on many factors arising from both hardware (turbine size, rotor speed, and blade geometry, etc.) and from meteorological considerations such as wind velocity, gradients of wind across the turbine rotor disk, atmospheric stability, and atmospheric turbulence. To characterize the relationships between the meteorological inflow and turbine wakes, a collaborative field campaign was designed and carried out at the Department of Energy's National Wind Technology Center (NREL/NWTC) in south Boulder, Colorado, in spring 2011. This site often experiences channeled flow with a consistent wind direction, enabling robust statistics of wake velocity deficits and turbulence enhancements. Using both in situ and remote sensing instrumentation, measurements upwind and downwind of multi-megawatt wind turbine in complex terrain quantified the variability of wind turbine inflow and wakes from an industrial-scale turbine. The turbine of interest has a rated power of 2.3 MW, a rotor diameter of 100m, and a hub height of 80m. In addition to several meteorological towers, one extending to hub height (80m) and another extending above the top of the rotor disk (135m), a Triton mini-sodar and a Windcube lidar characterized the inflow to the turbine and the variability across the site. The centerpiece instrument of the TWICS campaign

The wave model of mesothermal plasma near wakes and korteweg-de vries equation

International Nuclear Information System (INIS)

Shen, C.; Liu, V.C.

1982-01-01

The stationary two-dimensional (x,z) near wakes behind a flat-based projectile which moves at a constant mesothermal speed (V sub(infinity)) along a z-axis in a rarefied, fully ionized, plasma is studied using the wave model previously proposed by one of the authors (VCL). One-fluid theory is used to depict the free expansion of ambient plasma into the vacuum produced behind a fast-moving projectile. This nonstationary, one-dimensional (x,t) flow which is approximated by the K-dV equation can be transformed, through substitution, t=z/V sub(infinity), into a stationary two-dimensional(x,z) near wake flow seen by an observer moving with the body velocity (V sub(infinity)). The initial value problem of the K-dV equation in (x,t) variables is solved by a specially devised numerical method. Comparisons of the present numerical solution for the asymptotically small and large times with available analytical solutions are made and found in satisfactory agreements. (author)

A measurement of the response to fast neutrons of several materials dosemeters

International Nuclear Information System (INIS)

Jones, L.T.; Kitching, S.J.; Lewis, T.A.; Playle, T.S.

1986-07-01

The response to fast neutrons was measured for three types of materials testing dosemeters: fast neutron dosimetry silicon diodes; beryllia, alumina and calcium fluoride TLDs; graphite walled ionisation chambers. The calibrations were made using a 3MW positive ion accelerator. The arrangement of the target, beam monitor and devices is described, and the measured fast neutron sensitivities are presented. (UK)

Development of FAST.Farm: A New Multiphysics Engineering Tool for Wind-Farm Design and Analysis

Energy Technology Data Exchange (ETDEWEB)

Jonkman, Jason; Annoni, Jennifer; Hayman, Greg; Jonkman, Bonnie; Purkayastha, Avi

2017-01-09

This paper presents the development of FAST.Farm, a new multiphysics tool applicable to engineering problems in research and industry involving wind farm performance and cost optimization that is needed to address the current underperformance, failures, and expenses plaguing the wind industry. Achieving wind cost-of-energy targets - which requires improvements in wind farm performance and reliability, together with reduced uncertainty and expenditures - has been eluded by the complicated nature of the wind farm design problem, especially the sophisticated interaction between atmospheric phenomena and wake dynamics and array effects. FAST.Farm aims to balance the need for accurate modeling of the relevant physics for predicting power performance and loads while maintaining low computational cost to support a highly iterative and probabilistic design process and system-wide optimization. FAST.Farm makes use of FAST to model the aero-hydro-servo-elastics of distinct turbines in the wind farm, and it is based on some of the principles of the Dynamic Wake Meandering (DWM) model, but avoids many of the limitations of existing DWM implementations.

A simplified approach for simulation of wake meandering

Energy Technology Data Exchange (ETDEWEB)

Thomsen, Kenneth; Aagaard Madsen, H.; Larsen, Gunner; Juul Larsen, T.

2006-03-15

This fact-sheet describes a simplified approach for a part of the recently developed dynamic wake model for aeroelastic simulations for wind turbines operating in wake. The part described in this fact-sheet concern the meandering process only, while the other part of the simplified approach the wake deficit profile is outside the scope of the present fact-sheet. Work on simplified models for the wake deficit profile is ongoing. (au)

Acoustic Wake-Up Receivers for Home Automation Control Applications

Directory of Open Access Journals (Sweden)

Amir Bannoura

2016-01-01

Full Text Available Automated home applications are to ease the use of technology and devices around the house. Most of the electronic devices, like shutters or entertainment products (Hifi, TV and even WiFi, are constantly in a standby mode, where they consume a considerable amount of energy. The standby mode is necessary to react to commands triggered by the user, but the time the device spends in a standby mode is considered long. In our work, we present a receiver that is attached to home appliances that allows the devices to be activated while they are completely turned off in order to reduce the energy consumed in the standby mode. The receiver contains a low power wake-up module that reacts to an addressable acoustic 20-kHz sound signal that controls home devices that are connected to it. The acoustic wake-up signal can be sent by any kind of speaker that is available in commercial smartphones. The smartphones will operate as transmitters to the signals. Our wake-up receiver consists of two parts: a low power passive circuit connected to a wake-up chip microcontroller and an active micro-electromechanical system (MEMS microphone that receives the acoustic signal. A duty cycle is required to reduce the power consumption of the receiver, because the signal reception occurs when the microphone is active. The current consumption was measured to be 15 μA in sleep mode and 140 μA in active mode. An average wake-up range of 10 m using a smartphone as a sender was achieved.

Optimization-Based Calibration of FAST.Farm Parameters Against SOWFA: Preprint

Energy Technology Data Exchange (ETDEWEB)

Moreira, Paula D [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Annoni, Jennifer [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jonkman, Jason [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Ghate, Aditya S [Stanford University

2018-01-04

FAST.Farm is a medium-delity wind farm modeling tool that can be used to assess power and loads contributions of wind turbines in a wind farm. The objective of this paper is to undertake a calibration procedure to set the user parameters of FAST.Farm to accurately represent results from large-eddy simulations. The results provide an in- depth analysis of the comparison of FAST.Farm and large-eddy simulations before and after calibration. The comparison of FAST.Farm and large-eddy simulation results are presented with respect to streamwise and radial velocity components as well as wake-meandering statistics (mean and standard deviation) in the lateral and vertical directions under different atmospheric and turbine operating conditions.

Wind tunnel study of the wind turbine interaction with a boundary-layer flow: Upwind region, turbine performance, and wake region

Science.gov (United States)

Bastankhah, M.; Porté-Agel, F.

2017-06-01

Comprehensive wind tunnel experiments were carried out to study the interaction of a turbulent boundary layer with a wind turbine operating under different tip-speed ratios and yaw angles. Force and power measurements were performed to characterize the variation of thrust force (both magnitude and direction) and generated power of the wind turbine under different operating conditions. Moreover, flow measurements, collected using high-resolution particle-image velocimetry as well as hot-wire anemometry, were employed to systematically study the flow in the upwind, near-wake, and far-wake regions. These measurements provide new insights into the effect of turbine operating conditions on flow characteristics in these regions. For the upwind region, the results show a strong lateral asymmetry under yawed conditions. For the near-wake region, the evolution of tip and root vortices was studied with the use of both instantaneous and phase-averaged vorticity fields. The results suggest that the vortex breakdown position cannot be determined based on phase-averaged statistics, particularly for tip vortices under turbulent inflow conditions. Moreover, the measurements in the near-wake region indicate a complex velocity distribution with a speed-up region in the wake center, especially for higher tip-speed ratios. In order to elucidate the meandering tendency of far wakes, particular focus was placed on studying the characteristics of large turbulent structures in the boundary layer and their interaction with wind turbines. Although these structures are elongated in the streamwise direction, their cross sections are found to have a size comparable to the rotor area, so that they can be affected by the presence of the turbine. In addition, the study of spatial coherence in turbine wakes reveals that any statistics based on streamwise velocity fluctuations cannot provide reliable information about the size of large turbulent structures in turbine wakes due to the effect of wake

A Fast and Robust Method for Measuring Optical Channel Gain

DEFF Research Database (Denmark)

Harbo, Anders La-Cour; Stoustrup, Jakob; Villemoes, L.F.

2000-01-01

We present a numerically stable and computational simple method for fast and robust measurement of optical channel gain. By transmitting adaptively designed signals through the channel, good accuracy is possible even in severe noise conditions......We present a numerically stable and computational simple method for fast and robust measurement of optical channel gain. By transmitting adaptively designed signals through the channel, good accuracy is possible even in severe noise conditions...

In-flight fast-timing measurements in "1"5"2Sm

International Nuclear Information System (INIS)

Plaisir, C.; Gaudefroy, L.; Meot, V.; Blanc, A.; Daugas, J.M.; Roig, O.; Arnal, N.; Bonnet, T.; Gobet, F.; Hannachi, F.; Tarisien, M.; Versteegen, M.; Roger, T.; Rejmund, M.; Navin, A.; Schmitt, C.; Fremont, G.; Goupil, J.; Pancin, J.; Spitaels, C.; Zielinska, M.

2014-01-01

We report on the first application of in-flight fast-timing measurements, a method developed in order to directly measure lifetimes in the picosecond to nanosecond range. As a proof of principle of the method, lifetimes of the states belonging to the ground-state band in "1"5"2Sm are measured up to the 8"+_1 state. An excellent agreement with recommended values is found. A slightly improved determination of the spectroscopic quadrupole moment of the 4"+_1 state is also reported. In-flight fast-timing measurements open interesting opportunities for future studies of collective properties in radioactive nuclei. (authors)

Collinear wake field acceleration

International Nuclear Information System (INIS)

Bane, K.L.F.; Chen, P.; Wilson, P.B.

1985-04-01

In the Voss-Weiland scheme of wake field acceleration a high current, ring-shaped driving bunch is used to accelerate a low current beam following along on axis. In such a structure, the transformer ratio, i.e., the ratio of maximum voltage that can be gained by the on-axis beam and the voltage lost by the driving beam, can be large. In contrast, it has been observed that for an arrangement in which driving and driven bunches follow the same path, and where the current distribution of both bunches is gaussian, the transformer ratio is not normally greater than two. This paper explores some of the possibilities and limitations of a collinear acceleration scheme. In addition to its application to wake field acceleration in structures, this study is also of interest for the understanding of the plasma wake field accelerator. 11 refs., 4 figs

On AEP prediction and wake modelling at Anholt

DEFF Research Database (Denmark)

Pena Diaz, Alfredo; Hansen, Kurt Schaldemose; Volker, Patrick

and direction. We show that the WRF model is able to reproduce such gradients relatively well by comparison to the wind farm’s SCADA. About 1.5 yr of such SCADA, further quality controlled and filtered, reveals an average wake loss of 3.87% only, whereas results from three wake models, Park, Larsen and FUGA......, show average wake losses of 3.46%, 3.69%, and 3.38%, respectively. We employ a bootstrap method to estimate the uncertainty of the wake models. As this is performed with reference to the SCADA, the results provide an idea of the uncertainty of the AEP prediction2. We find all wake models...

Single Wake Meandering, Advection and Expansion - An analysis using an adapted Pulsed Lidar and CFD LES-ACL simulations

DEFF Research Database (Denmark)

In this paper, single wake characteristics have been studied both experimentally and numerically. Firstly, the wake is studied experimentally using full-scale measurements from an adapted focused pulsed lidar system, which potentially gives more insight into the wake dynamics as compared to class...... using the EllipSys3D flow solver using Large Eddy Simulation (LES) and Actuator Line Technique (ACL) to model the rotor. Discrepancies due to the uncertainties on the wake advection velocity are observed and discussed....

Single Wake Meandering, Advection and Expansion - An analysis using an adapted Pulsed Lidar and CFD LES-ACL simulations

DEFF Research Database (Denmark)

Machefaux, Ewan; Larsen, Gunner Chr.; Troldborg, Niels

2013-01-01

In this paper, single wake characteristics have been studied both experimentally and numerically. Firstly, the wake is studied experimentally using full-scale measurements from an adapted focused pulsed lidar system, which potentially gives more insight into the wake dynamics as compared to class...... using the EllipSys3D flow solver using Large Eddy Simulation (LES) and Actuator Line Technique (ACL) to model the rotor. Discrepancies due to the uncertainties on the wake advection velocity are observed and discussed....

Activation measurements for fast neutrons. Part B. 63Ni measurements by accelerator mass spectrometry (AMS)

International Nuclear Information System (INIS)

Straume, Tore; Rugel, Georg; Marchetti, Alfredo A.

2005-01-01

The AMS-measurements of 63 Ni in copper samples obtained from different distances in Hiroshima represent the first detection of fast neutrons after more than 50 years, and the first reliable bomb-induced fast neutron measurements beyond 700 m from the hypocenter. A major significance of these 63 Ni results is that they provide, for the first time, fast neutron measurements at the distances most relevant to atomic-bomb survivor locations (900-1,500 m). The measurement of 63 Ni in copper samples using AMS provides a substantial improvement in fast neutron detection compared with the 32 P measurements made in 1945. For example, the measurement-to-background ratio at about 400 m from the hypocenter is about 55 for 63 Ni and only about 2 for the 32 P measurements. Also, the 63 Ni measurements reach background levels at about 1,800 m from the hypocenter compared with only about 700 m for 32 P. At distances of ∼1,800 m from the hypocenter, out to at least 5,000 meters, the measurements appear to level off at a value on the order of 7x10 4 atoms of 63 Ni/g of Cu, suggesting a background of approximately that magnitude. When this background is subtracted and the resulting data corrected to 1945, the measured 63 Ni in copper samples from Hiroshima are in good agreement with DS02 sample-specific calculations. Comparisons with DS86 calculations also show good agreement except at the Bank of Japan. The difference at that distance is significant when compared with DS86 calculations. (J.P.N.)

Experimental Analysis and Evaluation of the Numerical Prediction of Wake Characteristics of Tidal Stream Turbine

Directory of Open Access Journals (Sweden)

Yuquan Zhang

2017-12-01

Full Text Available It is important to understand tidal stream turbine performance and flow field, if tidal energy is to advance. The operating condition of a tidal stream turbine with a supporting structure has a significant impact on its performance and wake recovery. The aim of this work is to provide an understanding of turbine submerged depth that governs the downstream wake structure and its recovery to the free-stream velocity profile. An experimentally validated numerical model, based on a computational fluid dynamics (CFD tool, was present to obtain longitudinal, transverse and vertical velocity profiles. Wake characteristics measurements have been carried out in an open channel at Hohai University. The results indicate that varying the turbine proximity to the water surface introduces differential mass flow rate around the rotor that could make the wake persist differently downstream. CFD shows the same predicted wake recovery tendency with the experiments, and an agreement from CFD and experiments is good in the far-wake region. The results presented demonstrate that CFD is a good tool to simulate the performance of tidal turbines particularly in the far-wake region and that the turbine proximity to the water surface has an effect on the wake recovery.

Accuracy of single photoelectron time spread measurement of fast photomultipliers

International Nuclear Information System (INIS)

Leskovar, B.

1975-01-01

The accuracy of time spread measurements of fast photomultipliers was investigated, using single photoelectrons. The effect of the finite light pulse width on the measurement accuracy was determined and discussed. Experimental data were obtained on a special measuring system for light pulse widths ranging from 200 psec to 10 nsec, using fast photomultipliers 8850 and C31024 with optimized operating conditions for minimum transit time spread. A modified exponential function expression and curve-fitting parameters are given, which fit closely the experimentally obtained data over a wide dynamic range of light pulse widths. (U.S.)

Flow Characteristics of Ground Vehicle Wake and Its Response to Flow Control

Science.gov (United States)

Sellappan, Prabu; McNally, Jonathan; Alvi, Farrukh

2017-11-01

Air pollution, fuel shortages, and cost savings are some of the many incentives for improving the aerodynamics of vehicles. Reducing wake-induced aerodynamic drag, which is dependent on flow topology, on modern passenger vehicles is important for improving fuel consumption rates which directly affect the environment. In this research, an active flow control technique is applied on a generic ground vehicle, a 25°Ahmed model, to investigate its effect on the flow topology in the near-wake. The flow field of this canonical bluff body is extremely rich, with complex and unsteady flow features such as trailing wake vortices and c-pillar vortices. The spatio-temporal response of these flow features to the application of steady microjet actuators is investigated. The responses are characterized independently through time-resolved and volumetric velocity field measurements. The accuracy and cost of volumetric measurements in this complex flow field through Stereoscopic- and Tomographic- Particle Image Velocimetry (PIV) will also be commented upon. National Science Foundation PIRE Program.

Next Generation Fiber Coherent Lidar System for Wake Vortex Detection, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — SibellOptics proposes to develop an eye-safe, long-range, compact, versatile, all-fiber wind LIDAR system for wake vortex measurement and other wind measurement...

Wake Vortex Detection: Phased Microphone vs. Linear Infrasonic Array

Science.gov (United States)

Shams, Qamar A.; Zuckerwar, Allan J.; Sullivan, Nicholas T.; Knight, Howard K.

2014-01-01

Sensor technologies can make a significant impact on the detection of aircraft-generated vortices in an air space of interest, typically in the approach or departure corridor. Current state-of-the art sensor technologies do not provide three-dimensional measurements needed for an operational system or even for wake vortex modeling to advance the understanding of vortex behavior. Most wake vortex sensor systems used today have been developed only for research applications and lack the reliability needed for continuous operation. The main challenges for the development of an operational sensor system are reliability, all-weather operation, and spatial coverage. Such a sensor has been sought for a period of last forty years. Acoustic sensors were first proposed and tested by National Oceanic and Atmospheric Administration (NOAA) early in 1970s for tracking wake vortices but these acoustic sensors suffered from high levels of ambient noise. Over a period of the last fifteen years, there has been renewed interest in studying noise generated by aircraft wake vortices, both numerically and experimentally. The German Aerospace Center (DLR) was the first to propose the application of a phased microphone array for the investigation of the noise sources of wake vortices. The concept was first demonstrated at Berlins Airport Schoenefeld in 2000. A second test was conducted in Tarbes, France, in 2002, where phased microphone arrays were applied to study the wake vortex noise of an Airbus 340. Similarly, microphone phased arrays and other opto-acoustic microphones were evaluated in a field test at the Denver International Airport in 2003. For the Tarbes and Denver tests, the wake trajectories of phased microphone arrays and lidar were compared as these were installed side by side. Due to a built-in pressure equalization vent these microphones were not suitable for capturing acoustic noise below 20 Hz. Our group at NASA Langley Research Center developed and installed an

Development of FAST.Farm: A New Multiphysics Engineering Tool for Wind Farm Design and Analysis: Preprint

Energy Technology Data Exchange (ETDEWEB)

Jonkman, Jason; Annoni, Jennifer; Hayman, Greg; Jonkman, Bonnie; Purkayastha, Avi

2017-01-01

This paper presents the development of FAST.Farm, a new multiphysics tool applicable to engineering problems in research and industry involving wind farm performance and cost optimization that is needed to address the current underperformance, failures, and expenses plaguing the wind industry. Achieving wind cost-of-energy targets - which requires improvements in wind farm performance and reliability, together with reduced uncertainty and expenditures - has been eluded by the complicated nature of the wind farm design problem, especially the sophisticated interaction between atmospheric phenomena and wake dynamics and array effects. FAST.Farm aims to balance the need for accurate modeling of the relevant physics for predicting power performance and loads while maintaining low computational cost to support a highly iterative and probabilistic design process and system-wide optimization. FAST.Farm makes use of FAST to model the aero-hydro-servo-elastics of distinct turbines in the wind farm, and it is based on some of the principles of the Dynamic Wake Meandering (DWM) model, but avoids many of the limitations of existing DWM implementations.

Plasma turbulence measured by fast sweep reflectometry on Tore Supra

International Nuclear Information System (INIS)

Clairet, F.; Vermare, L.; Leclert, G.

2004-01-01

Traditionally devoted to electron density profile measurement we show that fast frequency sweeping reflectometry technique can bring valuable and innovative measurements onto plasma turbulence. While fast frequency sweeping technique is traditionally devoted to electron density radial profile measurements we show in this paper how we can handle the fluctuations of the reflected signal to recover plasma density fluctuation measurements with a high spatial and temporal resolution. Large size turbulence related to magneto-hydrodynamic (MHD) activity and the associated magnetic islands can be detected. The radial profile of the micro-turbulence, which is responsible for plasma anomalous transport processes, is experimentally determined through the fluctuation of the reflected phase signal. (authors)

Plasma turbulence measured by fast sweep reflectometry on Tore Supra

International Nuclear Information System (INIS)

Clairet, F.; Vermare, L.; Heuraux, S.; Leclert, G.

2004-01-01

Traditionally devoted to electron density profile measurement we show that fast frequency sweeping reflectometry technique can bring valuable and innovative measurements onto plasma turbulence. While fast frequency sweeping technique is traditionally devoted to electron density radial profile measurements we show in this paper how we can handle the fluctuations of the reflected signal to recover plasma density fluctuation measurements with a high spatial and temporal resolution. Large size turbulence related to magneto-hydrodynamic (MHD) activity and the associated magnetic islands can be detected. The radial profile of the micro-turbulence, which is responsible for plasma anomalous transport processes, is experimentally determined through the fluctuation of the reflected phase signal

Near-wake flow structure downwind of a wind turbine in a turbulent boundary layer

Energy Technology Data Exchange (ETDEWEB)

Zhang, Wei; Markfort, Corey D. [University of Minnesota, Saint Anthony Falls Laboratory, Department of Civil Engineering, Minneapolis, MN (United States); Porte-Agel, Fernando [Ecole Polytechnique Federale de Lausanne (EPFL), ENAC-IIE-WIRE, Wind Engineering and Renewable Energy Laboratory (WIRE), Lausanne (Switzerland)

2012-05-15

Wind turbines operate in the surface layer of the atmospheric boundary layer, where they are subjected to strong wind shear and relatively high turbulence levels. These incoming boundary layer flow characteristics are expected to affect the structure of wind turbine wakes. The near-wake region is characterized by a complex coupled vortex system (including helicoidal tip vortices), unsteadiness and strong turbulence heterogeneity. Limited information about the spatial distribution of turbulence in the near wake, the vortex behavior and their influence on the downwind development of the far wake hinders our capability to predict wind turbine power production and fatigue loads in wind farms. This calls for a better understanding of the spatial distribution of the 3D flow and coherent turbulence structures in the near wake. Systematic wind-tunnel experiments were designed and carried out to characterize the structure of the near-wake flow downwind of a model wind turbine placed in a neutral boundary layer flow. A horizontal-axis, three-blade wind turbine model, with a rotor diameter of 13 cm and the hub height at 10.5 cm, occupied the lowest one-third of the boundary layer. High-resolution particle image velocimetry (PIV) was used to measure velocities in multiple vertical stream-wise planes (x-z) and vertical span-wise planes (y-z). In particular, we identified localized regions of strong vorticity and swirling strength, which are the signature of helicoidal tip vortices. These vortices are most pronounced at the top-tip level and persist up to a distance of two to three rotor diameters downwind. The measurements also reveal strong flow rotation and a highly non-axisymmetric distribution of the mean flow and turbulence structure in the near wake. The results provide new insight into the physical mechanisms that govern the development of the near wake of a wind turbine immersed in a neutral boundary layer. They also serve as important data for the development and

The Explicit Wake Parametrisation V1.0: a wind farm parametrisation in the mesoscale model WRF

Directory of Open Access Journals (Sweden)

P. J. H. Volker

2015-11-01

Full Text Available We describe the theoretical basis, implementation, and validation of a new parametrisation that accounts for the effect of large offshore wind farms on the atmosphere and can be used in mesoscale and large-scale atmospheric models. This new parametrisation, referred to as the Explicit Wake Parametrisation (EWP, uses classical wake theory to describe the unresolved wake expansion. The EWP scheme is validated for a neutral atmospheric boundary layer against filtered in situ measurements from two meteorological masts situated a few kilometres away from the Danish offshore wind farm Horns Rev I. The simulated velocity deficit in the wake of the wind farm compares well to that observed in the measurements, and the velocity profile is qualitatively similar to that simulated with large eddy simulation models and from wind tunnel studies. At the same time, the validation process highlights the challenges in verifying such models with real observations.

The fluence research of filter material for fast neutron fluence measurement

International Nuclear Information System (INIS)

Tang Xiding

2010-01-01

When the fast neutron fluence is measured by radioactivation techniques in the nuclear reactor the fast neutron is also filtered a little by the thermal neutron filter material, and if the filter material thickness increase the filtered fast neutron increases therewith. For fast neutron fluenc measurement, there are only cadmium, boron and gadolinium three elements filtering fluence can be calculated ordinarily. In order to calculate the filtered fast neutron fluence of the all elements in the filter material, the many total cross sections of nuclides had checked out from nuclear cross section data library, converted them into the same energy group structure, then element's total cross section, compound's total cross section and multilayer filters' total cross section had calculated from these total cross sections with same energy group structure, a new cross section data library can be obtained lastly through merging these cross sections into the old cross section data library used for neutron fluence measurement. The calculation analysis indicates that the results of the unit 2 surveillance capsule U of DAYA Bay NPP and the unit 1 surveillance capsule A of the Second Nuclear Power Plant of Qinshan by considering the all elements subtracting iron are smaller about 1.5% and 2.6% respectively than the ones only to consider cadmium, boron. The old measured results accord with the new values under the measurement uncertainty, are reliable. The new results are more accuracy. (authors)

Wake Vortex Avoidance System and Method

Science.gov (United States)

Shams, Qamar A. (Inventor); Zuckerwar, Allan J. (Inventor); Knight, Howard K. (Inventor)

2017-01-01

A wake vortex avoidance system includes a microphone array configured to detect low frequency sounds. A signal processor determines a geometric mean coherence based on the detected low frequency sounds. A display displays wake vortices based on the determined geometric mean coherence.

Simulation of wind turbine wakes using the actuator line technique.

Science.gov (United States)

Sørensen, Jens N; Mikkelsen, Robert F; Henningson, Dan S; Ivanell, Stefan; Sarmast, Sasan; Andersen, Søren J

2015-02-28

The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Validation of the Dynamic Wake Meander model with focus on tower loads

Science.gov (United States)

Larsen, T. J.; Larsen, G. C.; Pedersen, M. M.; Enevoldsen, K.; Madsen, H. A.

2017-05-01

This paper presents a comparison between measured and simulated tower loads for the Danish offshore wind farm Nysted 2. Previously, only limited full scale experimental data containing tower load measurements have been published, and in many cases the measurements include only a limited range of wind speeds. In general, tower loads in wake conditions are very challenging to predict correctly in simulations. The Nysted project offers an improved insight to this field as six wind turbines located in the Nysted II wind farm have been instrumented to measure tower top and tower bottom moments. All recorded structural data have been organized in a database, which in addition contains relevant wind turbine SCADA data as well as relevant meteorological data - e.g. wind speed and wind direction - from an offshore mast located in the immediate vicinity of the wind farm. The database contains data from a period extending over a time span of more than 3 years. Based on the recorded data basic mechanisms driving the increased loading experienced by wind turbines operating in offshore wind farm conditions have been identified, characterized and modeled. The modeling is based on the Dynamic Wake Meandering (DWM) approach in combination with the state-of-the-art aeroelastic model HAWC2, and has previously as well as in this study shown good agreement with the measurements. The conclusions from the study have several parts. In general the tower bending and yaw loads show a good agreement between measurements and simulations. However, there are situations that are still difficult to match. One is tower loads of single-wake operation near rated ambient wind speed for single wake situations for spacing’s around 7-8D. A specific target of the study was to investigate whether the largest tower fatigue loads are associated with a certain downstream distance. This has been identified in both simulations and measurements, though a rather flat optimum is seen in the measurements.

Review of Idealized Aircraft Wake Vortex Models

Science.gov (United States)

Ahmad, Nashat N.; Proctor, Fred H.; Duparcmeur, Fanny M. Limon; Jacob, Don

2014-01-01

Properties of three aircraft wake vortex models, Lamb-Oseen, Burnham-Hallock, and Proctor are reviewed. These idealized models are often used to initialize the aircraft wake vortex pair in large eddy simulations and in wake encounter hazard models, as well as to define matched filters for processing lidar observations of aircraft wake vortices. Basic parameters for each vortex model, such as peak tangential velocity and circulation strength as a function of vortex core radius size, are examined. The models are also compared using different vortex characterizations, such as the vorticity magnitude. Results of Euler and large eddy simulations are presented. The application of vortex models in the postprocessing of lidar observations is discussed.

Vortex wakes of a flapping foil in a flowing soap film

Science.gov (United States)

Schnipper, Teis; Andersen, Anders; Bohr, Tomas

2008-11-01

We present an experimental study of an oscillating, symmetric foil in a vertically flowing soap film. By varying frequency and amplitude of the oscillation we explore and visualize a variety of wake structures, including von Kármán wake, reverse von Kármán wake, 2P wake, and 2P+2S wake. We characterize the transition from the von Kármán wake (drag) to the reverse von Kármán wake (thrust) and discuss the results in relation to fish swimming. We visualize the time evolution of the vortex shedding in detail, identify the origins of the vortices comprising the wake, and propose a simple model to account for the transition from von Kármán like wakes to more exotic wake structures.

Characterization of forced response of density stratified reacting wake

Science.gov (United States)

Pawar, Samadhan A.; Sujith, Raman I.; Emerson, Benjamin; Lieuwen, Tim

2018-02-01

The hydrodynamic stability of a reacting wake depends primarily on the density ratio [i.e., ratio of unburnt gas density (ρu) to burnt gas density (ρb)] of the flow across the wake. The variation of the density ratio from high to low value, keeping ρ u / ρ b > 1 , transitions dynamical characteristics of the reacting wake from a linearly globally stable (or convectively unstable) to a globally unstable mode. In this paper, we propose a framework to analyze the effect of harmonic forcing on the deterministic and synchronization characteristics of reacting wakes. Using the recurrence quantification analysis of the forced wake response, we show that the deterministic behaviour of the reacting wake increases as the amplitude of forcing is increased. Furthermore, for different density ratios, we found that the synchronization of the top and bottom branches of the wake with the forcing signal is dependent on whether the mean frequency of the natural oscillations of the wake (fn) is lesser or greater than the frequency of external forcing (ff). We notice that the response of both branches (top and bottom) of the reacting wake to the external forcing is asymmetric and symmetric for the low and high density ratios, respectively. Furthermore, we characterize the phase-locking behaviour between the top and bottom branches of the wake for different values of density ratios. We observe that an increase in the density ratio results in a gradual decrease in the relative phase angle between the top and bottom branches of the wake, which leads to a change in the vortex shedding pattern from a sinuous (anti-phase) to a varicose (in-phase) mode of the oscillations.

Experimental study of surface pattern effects on the propulsive performance and wake of a bio-inspired pitching panel

Science.gov (United States)

King, Justin; Kumar, Rajeev; Green, Melissa

2016-11-01

Force measurements and stereoscopic particle image velocimetry (PIV) were used to characterize the propulsive performance and wake structure of rigid, bio-inspired trapezoidal pitching panels. In the literature, it has been demonstrated that quantities such as thrust coefficient and propulsive efficiency are affected by changes in the surface characteristics of a pitching panel or foil. More specifically, the variation of surface pattern produces significant changes in wake structure and dynamics, especially in the distribution of vorticity in the wake. Force measurements and PIV data were collected for multiple surface patterns chosen to mimic fish surface morphology over a Strouhal number range of 0.17 to 0.56. Performance quantities are compared with the three-dimensional vortex wake structure for both the patterned and smooth panels to determine the nature and magnitude of surface pattern effects in terms of thrust produced, drag reduced, and wake vortices reshaped and reorganized. This work was supported by the Office of Naval Research under ONR Award No. N00014-14-1-0418.

Meteorological Controls on Wind Turbine Wakes

DEFF Research Database (Denmark)

Barthelmie, Rebecca J.; Hansen, Kurt Schaldemose; Pryor, S.C.

2013-01-01

, modeling, and predicting this complex and interdependent system is therefore critical to understanding and modeling wind farm power losses due to wakes, and to optimizing wind farm layout. This paper quantifies the impact of these variables on the power loss due to wakes using data from the large offshore......The primary control on the magnitude of the power losses induced by wind turbine wakes in large wind farms is the hub-height wind speed via its link to the turbine thrust coefficient. Hence, at low to moderate wind speeds (between cut-in and rated turbine wind speeds) when the thrust coefficient...

Wind Turbine Wake in Atmospheric Turbulence

DEFF Research Database (Denmark)

Réthoré, Pierre-Elouan Mikael

to calibrate faster and simpler engineering wind farm wake models. The most attractive solution was the actuator disc method with the steady state k-ε turbulence model. The first step to design such a tool is the treatment of the forces. This thesis presents a computationally inexpensive method to apply......) shows that the problem mainly comes from the assumptions of the eddy-viscosity concept, which are deeply invalidated in the wind turbine wake region. Different models that intent to correct the k-ε model’s issues are investigated, of which none of them is found to be adequate. The mixing of the wake...

Influence of obstacle aspect ratio on tripped cylinder wakes

International Nuclear Information System (INIS)

Araújo, Tiago B.; Sicot, Christophe; Borée, Jacques; Martinuzzi, Robert J.

2012-01-01

Highlights: ► Influence of a tripwire on wake properties of a surface-mounted circular cylinder. ► Height-to-diameter aspect ratios of 3 and 6 are considered. ► Critical positions for the tripwire lead to an abrupt change in the wake structure. ► Results further suggest that the tripwire can strengthen 2D wake properties. - Abstract: The influence of an asymmetrically mounted, single tripwire on the shedding and wake characteristics of a vertical, surface-mounted finite circular cylinder is investigated experimentally. Height-to-diameter aspect ratios of 3 and 6 are considered. It is shown that a critical position for the tripwire exists, which is characterised in an abrupt change in the shedding frequency and wake structure. Results further suggest that the tripwire can strengthen 2D wake properties. The influence of the aspect ratio is due to tip-wake flow interactions and thus differs fundamentally from two-dimensional geometries.

Accuracy of the actuator disc-RANS approach for predicting the performance and wake of tidal turbines.

Science.gov (United States)

Batten, W M J; Harrison, M E; Bahaj, A S

2013-02-28

The actuator disc-RANS model has widely been used in wind and tidal energy to predict the wake of a horizontal axis turbine. The model is appropriate where large-scale effects of the turbine on a flow are of interest, for example, when considering environmental impacts, or arrays of devices. The accuracy of the model for modelling the wake of tidal stream turbines has not been demonstrated, and flow predictions presented in the literature for similar modelled scenarios vary significantly. This paper compares the results of the actuator disc-RANS model, where the turbine forces have been derived using a blade-element approach, to experimental data measured in the wake of a scaled turbine. It also compares the results with those of a simpler uniform actuator disc model. The comparisons show that the model is accurate and can predict up to 94 per cent of the variation in the experimental velocity data measured on the centreline of the wake, therefore demonstrating that the actuator disc-RANS model is an accurate approach for modelling a turbine wake, and a conservative approach to predict performance and loads. It can therefore be applied to similar scenarios with confidence.

Wake field in electron-positron plasmas

International Nuclear Information System (INIS)

Avinash, K.; Berezhiani, V.I.

1993-03-01

We study the creation of wake field in cold electron positron plasma by electron bunches. In the resulting plasma inhomogeneity we study the propagation of short electromagnetic pulse. In is found that wake fields can change the frequency of the radiation substantially. (author). 7 refs, 1 fig

Wake-vortex decay in external turbulence

NARCIS (Netherlands)

Kuczaj, Arkadiusz K.; Armenio, V.; Fröhlich, J.; Geurts, Bernardus J.

2010-01-01

Wake vortices that form behind a moving aircraft represent 11 safety COil cern for other aircraft.s that follow. These tornado-like wake structures may persist for several minutes, extending for many kilometers across the sky. This safety issue is particularly important close to major airports where

Validation of the dynamic wake meander model for loads and power production in the Egmond aan Zee wind farm

DEFF Research Database (Denmark)

Larsen, Torben J.; Aagaard Madsen, Helge; Larsen, Gunner Chr.

2013-01-01

This paper investigates wake effects on load and power production by using the dynamic wake meander (DWM) model implemented in the aeroelastic code HAWC2. The instationary wind farm flow characteristics are modeled by treating the wind turbine wakes as passive tracers transported downstream using...... a meandering process driven by the low frequent cross-wind turbulence components. The model complex is validated by comparing simulated and measured loads for the Dutch Egmond aan Zee wind farm consisting of 36 Vestas V90 turbine located outside the coast of the Netherlands. Loads and production are compared...... for two distinct wind directions—a free wind situation from the dominating southwest and a full wake situation from northwest, where the observed turbine is operating in wake from five turbines in a row with 7D spacing. The measurements have a very high quality, allowing for detailed comparison of both...

Measurements of fast ion spatial dynamics during magnetic activity in the RFP

Science.gov (United States)

Goetz, J. A.; Anderson, J. K.; Bonofiglo, P.; Kim, J.; McConnell, R.; Magee, R. M.

2017-10-01

Fast ions in the RFP are only weakly affected by a stochastic magnetic field and behave nearly classically in concentration too low to excite Alfvenic activity. At high fast ion concentration sourced by H-NBI in 300kA RFP discharges, a substantial drop in core-localized high pitch fast ions is observed during bursts of coupled EPM and IAE (magnetic island-induced Alfven eigenmode) activity (100-200kHz) through neutral particle analysis. Sourcing instead fast deuterium with NBI, the DD fusion products can measure the dynamics of the fast ion density profile. Both a collimated neutron detector and a new 3MeV fusion proton detector loaned by TriAlpha Energy measure the fast ion density profile with 5cm spatial resolution and 100 μs temporal resolution. In D-NBI, the bursting EPM is excited at slightly lower frequency and the IAE activity is nearly absent, likely due to an isotope effect and loss of wave-particle interaction. In these cases, neutral particle analysis shows little change in the core-localized high pitch fast ion content, and the fusion product profile indicates little change in the fast ion density profile, leaving unexplained the mechanism removing EPM drive. We measure a substantial redistribution of the fast ion profile due to strong lower-frequency ( 30kHz) MHD activity that accompanies the current profile relaxation in the RFP. Profile flattening is strongest in low bulk density discharges, which often occur with a total increase in global neutron flux from acceleration of the beam ions. Work supported by US DoE.

Fast response densitometer for measuring liquid density

Science.gov (United States)

1972-01-01

Densitometer was developed which produces linear voltage proportional to changes in density of flowing liquid hydrogen. Unit has fast response time and good system stability, statistical variation, and thermal equilibrium. System accuracy is 2 percent of total density span. Basic design may be altered to include measurement of other flowing materials.

The Case of the Neutron Star With a Wayward Wake

Science.gov (United States)

2006-06-01

star were outside the confines of the remnant, its inferred speed would be a sluggish 20,000 miles per hour. Also, the measured temperature of the neutron star matches that of one born at the same time of the supernova remnant. What then, could cause the misaligned, or wayward, neutron star wake? The authors speculate that perhaps the doomed progenitor star was moving at a high speed before it exploded, so that the explosion site was not at the observed center of the supernova remnant. Fast moving gusts of gas inside the supernova remnant have further pushed the neutron star's wake out of alignment. Observations of J0617 in the next 10 years should put this idea to the test. "If the neutron star was born off-center and if the wake is being pushed around by cross-winds, the neutron star should be moving close to vertically, away from the center of the supernova remnant. Now we wait and see," said Gaensler. Chandra X-ray Image of J0617 in IC 443 Chandra X-ray Image of J0617 in IC 443 Another group, led by Margarita Karovska, also of the CfA, has concentrated on other, previously unnoticed intriguing features of J0617. At a recent conference on neutron stars in London, England, they announced their findings, which include a thin filament of cooler gas that appears to extend from the neutron star along the long axis of its wake, and a second point-like feature embedded in the X-ray nebula around the neutron star. "There are a number of puzzling observational features associated with this system crying out for longer observations," said Karovska. Other members of the Gaensler team were S. Chatterjee and P. O. Slane (CfA), E. van der Swaluw (Royal Netherlands Meteorological Institute), F. Camilo (Columbia University), and J. P. Hughes (Rutgers University). Karovska's team included T. Clarke (Naval Research Laboratory), G. Pavlov (Penn State University), and M.C. Weisskopf and V. Zavlin of the Marshall Space Flight Center, Huntsville, Ala. which also manages the Chandra

Effects of outer perturbances on dynamics of wake vortices

International Nuclear Information System (INIS)

Baranov, N.A.; Belotserkovsky, A.S.; Turchak, L.I.

2004-01-01

One of the problems in aircraft flight safety is reduction of the risk related with aircraft encounter with wake vortices generated by other aircraft. An efficient approach to this problem is design of systems providing information on areas of potential danger of wake vortices to pilots in real time. The main components of such a system are a unit for calculations of wake vortices behind aircraft and a unit for calculations of areas of potential danger. A promising way to development of real time algorithms for calculation of wake vortices is the use of vortex methods in CFD based on the hypothesis of quasi-3D flow in the area of wake vorticity. The mathematical model developed by our team calculates positions and intensity of wake vortices past aircraft taking account of such effects as viscous dissipation of vortices, effects of ambient turbulence, wind shear, as well as viscous interaction between wake vortices and the underlying surface. The necessity of including the last factor could be stems from the fact that in the case where wake vortices are in close proximity of the rigid surface, the viscous interaction between the wake vortices and the surface boundary layer results in the boundary layer separation changing the overall intensity and dynamics of the wake vortices. To evaluate the boundaries of the danger areas the authors use an approach based on calculation of additional aerodynamic forces and moments acting on the aircraft encountering wake vortices by means of evaluation of the aircraft additional velocities and angular rates corresponding to distribution of disturbed velocities on the aircraft surface. These criteria could be based on local characteristics of the vorticity areas or on characteristics related to the perturbation effects on the aircraft. The latter characteristics include the actual aerodynamic roll moment, the maximum angular rate or the maximum roll of the aircraft under perturbations in the wake vortices. To estimate the accuracy

Comparison and validation of wake vortex characteristics collected at different airports by different scanning lidar sensors

Science.gov (United States)

Thobois, Ludovic; Cariou, Jean-Pierre; Cappellazzo, Valerio; Musson, Christian; Treve, Vincent

2018-04-01

traffic mix, the weather conditions and their impact on the wake vortex decay. After implementation, the risk monitoring might perform in-depth analysis of wake vortex encounter reported by pilots. For all the mentioned steps, the use of scanning Doppler LIDARs is the only experimental sensor capable of measuring the localization and the circulation of the wake vortices and to provide ground truth wake vortex measurements. Next generation operational LIDARs need to be developed to address in a cost effective way these operational needs. Furthermore, a specific configuration and methodology need to be developed to ensure the accuracy of the wake vortex data. Such a LIDAR based wake vortex solution has been tested at Paris Charles De Gaulle which implemented the RECAT-EU wake separation scheme. The wake vortex circulation, initial spacing and decay measured have been compared to the data collected in London Heathrow by a different LIDAR sensor. The results indicated that the initial circulation, the time to demise, the decay curve evolution and the vortex spacing are very coherent between the two databases.

Comparison and validation of wake vortex characteristics collected at different airports by different scanning lidar sensors

Directory of Open Access Journals (Sweden)

Thobois Ludovic

2018-01-01

local ATM rules, the traffic mix, the weather conditions and their impact on the wake vortex decay. After implementation, the risk monitoring might perform in-depth analysis of wake vortex encounter reported by pilots. For all the mentioned steps, the use of scanning Doppler LIDARs is the only experimental sensor capable of measuring the localization and the circulation of the wake vortices and to provide ground truth wake vortex measurements. Next generation operational LIDARs need to be developed to address in a cost effective way these operational needs. Furthermore, a specific configuration and methodology need to be developed to ensure the accuracy of the wake vortex data. Such a LIDAR based wake vortex solution has been tested at Paris Charles De Gaulle which implemented the RECAT-EU wake separation scheme. The wake vortex circulation, initial spacing and decay measured have been compared to the data collected in London Heathrow by a different LIDAR sensor. The results indicated that the initial circulation, the time to demise, the decay curve evolution and the vortex spacing are very coherent between the two databases.

An experimental and numerical study of the atmospheric stability impact on wind turbine wakes

DEFF Research Database (Denmark)

Machefaux, Ewan; Larsen, Gunner Chr.; Koblitz, Tilman

2016-01-01

campus test site. Wake measurements are averaged within a mean wind speed bin of 1 m s1 and classified according to atmospheric stability using three different metrics: the Obukhov length, the Bulk–Richardson number and the Froude number. Three test cases are subsequently defined covering various...... atmospheric conditions. Simulations are carried out using large eddy simulation and actuator disk rotor modeling. The turbulence properties of the incoming wind are adapted to the thermal stratification using a newly developed spectral tensor model that includes buoyancy effects. Discrepancies are discussed......In this paper, the impact of atmospheric stability on a wind turbine wake is studied experimentally and numerically. The experimental approach is based on full-scale (nacelle based) pulsed lidar measurements of the wake flow field of a stall-regulated 500 kW turbine at the DTU Wind Energy, Risø...

Longitudinal and transverse wake potentials in SLAC

International Nuclear Information System (INIS)

Bane, K.; Wilson, P.

1980-01-01

In a machine with short bunches of high peak currents, such as the SLAC collider, one needs to know the longitudinal wake potential, for the higher mode losses, and the transverse wake potential, since, for bunches passing slightly off axis, the induced transverse forces will tend to cause beam break up. The longitudinal and transverse wakes of the SLAC structure presented here, were calculated by computer using the modal method, and including an analytic extension for higher modes. (Auth.)

Do trout swim better than eels? Challenges for estimating performance based on the wake of self-propelled bodies

Science.gov (United States)

Tytell, Eric D.

Engineers and biologists have long desired to compare propulsive performance for fishes and underwater vehicles of different sizes, shapes, and modes of propulsion. Ideally, such a comparison would be made on the basis of either propulsive efficiency, total power output or both. However, estimating the efficiency and power output of self-propelled bodies, and particularly fishes, is methodologically challenging because it requires an estimate of thrust. For such systems traveling at a constant velocity, thrust and drag are equal, and can rarely be separated on the basis of flow measured in the wake. This problem is demonstrated using flow fields from swimming American eels, Anguilla rostrata, measured using particle image velocimetry (PIV) and high-speed video. Eels balance thrust and drag quite evenly, resulting in virtually no wake momentum in the swimming (axial) direction. On average, their wakes resemble those of self-propelled jet propulsors, which have been studied extensively. Theoretical studies of such wakes may provide methods for the estimation of thrust separately from drag. These flow fields are compared with those measured in the wakes of rainbow trout, Oncorhynchus mykiss, and bluegill sunfish, Lepomis macrochirus. In contrast to eels, these fishes produce wakes with axial momentum. Although the net momentum flux must be zero on average, it is neither spatially nor temporally homogeneous; the heterogeneity may provide an alternative route for estimating thrust. This review shows examples of wakes and velocity profiles from the three fishes, indicating challenges in estimating efficiency and power output and suggesting several routes for further experiments. Because these estimates will be complicated, a much simpler method for comparing performance is outlined, using as a point of comparison the power lost producing the wake. This wake power, a component of the efficiency and total power, can be estimated in a straightforward way from the flow

Measurements of fast neutron spectra in iron, uranium and sodium-iron assemblies

International Nuclear Information System (INIS)

Kappler, F.; Pieroni, N.; Rusch, D.; Schmidt, A.; Wattecamps, E.; Werle, H.

1979-01-01

Spectrum measurements were performed at the fast subcritical facility SUAK to test nuclear data and computer codes used in fast reactor calculations. In order to obtain a specific and quantitative interpretation of discrepancies between measured and calculated spectrum, homogeneous assemblies consisting of single materials were investigated. The leakage spectrum of iron and uranium cylinders was measured by time-of-flight and proportional counters. Time-dependent leakage spectra were measured by a NE 213 liquid scintillator. It was demonstrated that the investigation of time-dependent spectra is a sensitive test of inelastic scattering cross section data. The effect of an interface on fast neutron spectra was also investigated by measuring space dependent spectra across a sodium-iron interface. The measured spectra of these assemblies are suitable for testing the adequacy of computational approximations and cross section data. (author)

Volumetric scans of wind turbine wakes performed with three simultaneous wind LiDARs under different atmospheric stability regimes

International Nuclear Information System (INIS)

Iungo, Giacomo Valerio; Porté-Agel, Fernando

2014-01-01

Aerodynamic optimization of wind farm layout is a crucial task to reduce wake effects on downstream wind turbines, thus to maximize wind power harvesting. However, downstream evolution and recovery of wind turbine wakes are strongly affected by the characteristics of the incoming atmospheric boundary layer (ABL) flow, such as wind shear and turbulence intensity, which are in turn affected by the ABL thermal stability. In order to characterize the downstream evolution of wakes produced by full-scale wind turbines under different atmospheric conditions, wind velocity measurements were performed with three wind LiDARs. The volumetric scans are performed by continuously sweeping azimuthal and elevation angles of the LiDARs in order to cover a 3D volume that includes the wind turbine wake. The minimum wake velocity deficit is then evaluated as a function of the downstream location for different atmospheric conditions. It is observed that the ABL thermal stability has a significant effect on the wake evolution, and the wake recovers faster under convective conditions

Armodafinil in the treatment of sleep/wake disorders

Directory of Open Access Journals (Sweden)

Jonathan RL Schwartz

2010-07-01

Full Text Available Jonathan RL Schwartz1,Thomas Roth2, Chris Drake21INTEGRIS Sleep Disorders Center and University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA; 2Sleep Disorders and Research Center, Henry Ford Hospital, Detroit, MI, USAAbstract: Excessive sleepiness (ES is a major but underestimated public health concern associated with significant impairments in alertness/wakefulness and significant morbidity. The term ES has been used in the sleep medicine literature for years, but due to its nonspecific symptoms (ie tiredness or fatigue, it frequently goes unrecognized or is misdiagnosed in primary care. In some cases ES arises due to poor sleep habits or self-imposed sleep deprivation; however, ES is also a key component of a number of sleep/wake disorders and multiple medical and psychiatric disorders. Identification and treatment of ES is critical to improve the quality of life and well-being of patients and for the safety of the wider community. The inability of patients to recognize the nature, extent, and symptomatic profile of sleep/wake disorders requires vigilance on the part of healthcare professionals. Interventions to address ES and its associated impairments, treatment of the underlying sleep/wake disorder, and follow-up are a priority given the potential for serious consequences if left untreated. Wakefulness-promoting agents are available that treat ES associated with sleep/wake disorders. This review examines current approaches for managing this debilitating and potentially life-threatening condition, focusing on the place of armodafinil as a wakefulness-promoting agent.Keywords: excessive sleepiness, wakefulness, armodafinil, obstructive sleep apnea, narcolepsy, shift-work disorder

Measurement of fast transient pressures

International Nuclear Information System (INIS)

Procaccia, Henri

1978-01-01

The accuracy, reliability and sensitivity of a pressure transducers define its principal static characteristics. When the quantity measured varies with time, the measurement carries a dynamic error and a delay depending on the frequency of this variation. Hence, when fast pressure changes in a fluid have to be determined, different kinds of pressure transducers can be used depending on their inherent dynamic characteristics which must be compared with those of the transient phenomenon to be analysed. The text describes the pressure transducers generally employed in industry for analysing such phenomenon and gives two practical applications developed in the EDF: the first submits the measurements and results of pump cavitation tests carried out at the Vitry II EDF power station; the second deals with hammer blows particularly noticed in nuclear power stations and required the use of transducers of exceptionally high performance such as strain gauge transducers and piezoelectric transducers (response time within 1m sec.) [fr

Prediction and Observation of Electron Instabilities and Phase Space Holes Concentrated in the Lunar Plasma Wake

Science.gov (United States)

Hutchinson, Ian H.; Malaspina, David M.

2018-05-01

Recent theory and numerical simulation predicts that the wake of the solar wind flow past the Moon should be the site of electrostatic instabilities that give rise to electron holes. These play an important role in the eventual merging of the wake with the background solar wind. Analysis of measurements from the ARTEMIS satellites, orbiting the Moon at distances from 1.2 to 11 RM, detects holes highly concentrated in the wake, in agreement with prediction. The theory also predicts that the hole flux density observed should be hollow, peaking away from the wake axis. Observation statistics qualitatively confirm this hollowness, lending extra supporting evidence for the identification of their generation mechanism.

On-line fast flux measurements in the BR2 reactor

International Nuclear Information System (INIS)

Vermeeren, L.

2009-01-01

Since 2001, CEA-Cadarache and the Belgian Nuclear Research Centre SCK-CEN are collaborating on the development and in-pile qualification of subminiature fission chambers (diameter of 1.5 mm). Initially, efforts concentrated on fission chambers for the in-pile measurement of thermal fluxes (with 235 U as fissile material). Meanwhile successful long-term tests of the prototypes have been performed in various environments: in low temperature (40-100 degress Celsius) BR2 pool water (up to a thermal neutron fluence of 3 1 0 21 n/cm 2 ) and in the CALLISTO PWR loop (300 degrees Celsius, 155 bars). The long-term qualification of derived industrial detectors (Photonis CFUZ53) in CALLISTO is still ongoing. However, for various types of irradiations in research reactors, the knowledge of the evolution of the fast neutron flux is even of more interest than the thermal flux data. Therefore the collaboration program was extended to the development and the in-pile qualification of subminiature or miniature fission chambers (with 3 mm diameter) for fast neutron detection, for which 242 Pu was selected as the optimal fissile material. In order to achieve the on-line in-pile measurement of fast neutron flux, the fission chambers will be operated in the Campbelling mode (based on the mean square fluctuation of the detector current). In this mode the gamma induced contribution to the signal can be efficiently suppressed. Moreover, a data processing software will take into account the evolution of the fissile deposit in order to assess on-line the fast flux sensitivity and to correct for the low energy neutron contributions. The final objective is to qualify a Fast Neutron Detector System (FNDS) able to provide on-line data for local fast neutron fluxes in Material Testing Reactors. The on-line measurement of the fast neutron flux would contribute significantly to the characterization of the irradiation conditions during test experiments with materials and innovative fuel elements

Fast shoreline erosion induced by ship wakes in a coastal lagoon: Field evidence and remote sensing analysis.

Directory of Open Access Journals (Sweden)

Luca Zaggia

Full Text Available An investigation based on in-situ surveys combined with remote sensing and GIS analysis revealed fast shoreline retreat on the side of a major waterway, the Malamocco Marghera Channel, in the Lagoon of Venice, Italy. Monthly and long-term regression rates caused by ship wakes in a reclaimed industrial area were considered. The short-term analysis, based on field surveys carried out between April 2014 and January 2015, revealed that the speed of shoreline regression was insignificantly dependent on the distance from the navigation channel, but was not constant through time. Periods of high water levels due to tidal forcing or storm surges, more common in the winter season, are characterized by faster regression rates. The retreat is a discontinuous process in time and space depending on the morpho-stratigraphy and the vegetation cover of the artificial deposits. A GIS analysis performed with the available imagery shows an average retreat of 3-4 m/yr in the period between 1974 and 2015. Digitization of historical maps and bathymetric surveys made in April 2015 enabled the construction of two digital terrain models for both past and present situations. The two models have been used to calculate the total volume of sediment lost during the period 1968-2015 (1.19×106 m3. The results show that in the presence of heavy ship traffic, ship-channel interactions can dominate the morphodynamics of a waterway and its margins. The analysis enables a better understanding of how shallow-water systems react to the human activities in the post-industrial period. An adequate evaluation of the temporal and spatial variation of shoreline position is also crucial for the development of future scenarios and for the sustainable management port traffic worldwide.

Fast shoreline erosion induced by ship wakes in a coastal lagoon: Field evidence and remote sensing analysis.

Science.gov (United States)

Zaggia, Luca; Lorenzetti, Giuliano; Manfé, Giorgia; Scarpa, Gian Marco; Molinaroli, Emanuela; Parnell, Kevin Ellis; Rapaglia, John Paul; Gionta, Maria; Soomere, Tarmo

2017-01-01

An investigation based on in-situ surveys combined with remote sensing and GIS analysis revealed fast shoreline retreat on the side of a major waterway, the Malamocco Marghera Channel, in the Lagoon of Venice, Italy. Monthly and long-term regression rates caused by ship wakes in a reclaimed industrial area were considered. The short-term analysis, based on field surveys carried out between April 2014 and January 2015, revealed that the speed of shoreline regression was insignificantly dependent on the distance from the navigation channel, but was not constant through time. Periods of high water levels due to tidal forcing or storm surges, more common in the winter season, are characterized by faster regression rates. The retreat is a discontinuous process in time and space depending on the morpho-stratigraphy and the vegetation cover of the artificial deposits. A GIS analysis performed with the available imagery shows an average retreat of 3-4 m/yr in the period between 1974 and 2015. Digitization of historical maps and bathymetric surveys made in April 2015 enabled the construction of two digital terrain models for both past and present situations. The two models have been used to calculate the total volume of sediment lost during the period 1968-2015 (1.19×106 m3). The results show that in the presence of heavy ship traffic, ship-channel interactions can dominate the morphodynamics of a waterway and its margins. The analysis enables a better understanding of how shallow-water systems react to the human activities in the post-industrial period. An adequate evaluation of the temporal and spatial variation of shoreline position is also crucial for the development of future scenarios and for the sustainable management port traffic worldwide.

Investigating wake patterns and propulsive frequencies of a flat plate under pitching motion

Science.gov (United States)

Moubogha Moubogha, Joseph; Astolfi, Jacques Andre

Fundamental mechanisms of swimming are explored using a simple geometry device - flat plate - in pure-pitching motion in a hydrodynamic tunnel. The experiments are carried out at different Reynolds numbers based on the plate length c. Pitching motion is generated for reduced frequencies k between 0 and 2 and for an angular amplitude of 10 deg. Velocity fields are obtained in the wake of the plate using Particle Image Velocimetry and measurements of drag coefficients are estimated from mean velocity profiles. This study confirms the occurrence of a threshold oscillation frequency beyond which the plate enters a propulsive regime and the wake features organized structures. In this case an inversion of the typical Karman vortex street is observed. The evolution of mean transverse velocity profiles in the wake of the plate shows that the usual wake profile with velocity deficit - plate with drag - can be transformed into a jet - plate with thrust - above a certain reduced frequency. Phd Student Mechanical Engineering Departement.

Brain energetics during the sleep-wake cycle

DEFF Research Database (Denmark)

DiNuzzo, Mauro; Nedergaard, Maiken

2017-01-01

Brain activity during wakefulness is associated with high metabolic rates that are believed to support information processing and memory encoding. In spite of loss of consciousness, sleep still carries a substantial energy cost. Experimental evidence supports a cerebral metabolic shift taking place...... during sleep that suppresses aerobic glycolysis, a hallmark of environment-oriented waking behavior and synaptic plasticity. Recent studies reveal that glial astrocytes respond to the reduction of wake-promoting neuromodulators by regulating volume, composition and glymphatic drainage of interstitial...

On atmospheric stability in the dynamic wake meandering model

DEFF Research Database (Denmark)

Keck, Rolf-Erik; de Mare, Martin Tobias; Churchfield, Matthew J.

2014-01-01

The present study investigates a new approach for capturing the effects of atmospheric stability on wind turbine wake evolution and wake meandering by using the dynamic wake meandering model. The most notable impact of atmospheric stability on the wind is the changes in length and velocity scales...... spectra and applied to the dynamic wake meandering model to capture the correct wake meandering behaviour. The ambient turbulence in all stability classes is generated using the Mann turbulence model, where the effects of non-neutral atmospheric stability are approximated by the selection of input...... in the computational domain. The changes in the turbulent length scales due to the various atmospheric stability states impact the wake meandering characteristics and thus the power generation by the individual turbines. The proposed method is compared with results from both large-eddy simulation coupled...

Electronic excitations in fast ion-solid collisions

International Nuclear Information System (INIS)

Burgdoerfer, J.

1990-01-01

We review recent developments in the study of electronic excitation of projectiles in fast ion-solid collisions. Our focus will be primarily on theory but experimental advances will also be discussed. Topics include the evidence for velocity-dependent thresholds for the existence of bound states, wake-field effects on excited states, the electronic excitation of channeled projectiles, transport phenomena, and the interaction of highly charged ions with surfaces. 44 refs., 14 figs

Validation of four LES and a vortex model against stereo-PIV measurements in the near wake of an actuator disc and a wind turbine

DEFF Research Database (Denmark)

Lignarolo, Lorenzo E.M.; Mehta, Dhruv; Stevens, Richard J.A.M.

2016-01-01

In this paper we report the results of a workshop organised by the Delft University of Technology in 2014, aiming at the comparison between different state-of-the-art numerical models for the simulation of wind turbine wakes. The chosen benchmark case is a wind tunnel measurement, where stereosco...

Measurement of the fast neutron flux in the MNSR inner irradiation site

International Nuclear Information System (INIS)

Khattab, K.

2007-01-01

The WIMSD4 code was used to calculate the fast neutron flux spectrum and the fast neutron fission cross sections for 238 U, using six energy groups ranging from 0.5 to 10 MeV. These results, with the measured radioactivities of the 140 Ba, 131 I, 103 Ru, 95 Zr and 97 Zr fission products emerging from the fission of the 238 U foil covered with a cadmium filter, were used to measure the fast neutron flux in the Syrian MNSR inner irradiation site. (author)

2014 CERN Accelerator Schools: Plasma Wake Acceleration

CERN Multimedia

2014-01-01

A specialised school on Plasma Wake Acceleration will be held at CERN, Switzerland from 23-29 November, 2014.   This course will be of interest to staff and students in accelerator laboratories, university departments and companies working in or having an interest in the field of new acceleration techniques. Following introductory lectures on plasma and laser physics, the course will cover the different components of a plasma wake accelerator and plasma beam systems. An overview of the experimental studies, diagnostic tools and state of the art wake acceleration facilities, both present and planned, will complement the theoretical part. Topical seminars and a visit of CERN will complete the programme. Further information can be found at: http://cas.web.cern.ch/cas/PlasmaWake2014/CERN-advert.html http://indico.cern.ch/event/285444/

Role of the locus coeruleus in the emergence of power law wake bouts in a model of the brainstem sleep-wake system through early infancy.

Science.gov (United States)

Patel, Mainak; Rangan, Aaditya

2017-08-07

Infant rats randomly cycle between the sleeping and waking states, which are tightly correlated with the activity of mutually inhibitory brainstem sleep and wake populations. Bouts of sleep and wakefulness are random; from P2-P10, sleep and wake bout lengths are exponentially distributed with increasing means, while during P10-P21, the sleep bout distribution remains exponential while the distribution of wake bouts gradually transforms to power law. The locus coeruleus (LC), via an undeciphered interaction with sleep and wake populations, has been shown experimentally to be responsible for the exponential to power law transition. Concurrently during P10-P21, the LC undergoes striking physiological changes - the LC exhibits strong global 0.3 Hz oscillations up to P10, but the oscillation frequency gradually rises and synchrony diminishes from P10-P21, with oscillations and synchrony vanishing at P21 and beyond. In this work, we construct a biologically plausible Wilson Cowan-style model consisting of the LC along with sleep and wake populations. We show that external noise and strong reciprocal inhibition can lead to switching between sleep and wake populations and exponentially distributed sleep and wake bout durations as during P2-P10, with the parameters of inhibition between the sleep and wake populations controlling mean bout lengths. Furthermore, we show that the changing physiology of the LC from P10-P21, coupled with reciprocal excitation between the LC and wake population, can explain the shift from exponential to power law of the wake bout distribution. To our knowledge, this is the first study that proposes a plausible biological mechanism, which incorporates the known changing physiology of the LC, for tying the developing sleep-wake circuit and its interaction with the LC to the transformation of sleep and wake bout dynamics from P2-P21. Copyright © 2017 Elsevier Ltd. All rights reserved.

The day-to-day acute effect of wake therapy in patients with major depression using the HAM-D6 as primary outcome measure: results from a randomised controlled trial.

Directory of Open Access Journals (Sweden)

Klaus Martiny

Full Text Available This paper reports day-to-day data for from a one-week intervention phase, part of a 9-weeks randomised parallel study with patient having major depression (data from weekly visits have been reported. Wake therapy (sleep deprivation has an established antidepressant effect with onset of action within hours. Deterioration on the following night's sleep is, however, common, and we used daily light therapy and sleep time stabilisation as a preventive measure. In particular, we evaluated the day-to-day acute effect of and tolerance to sleep deprivation and examined predictors of response.Patients were assessed at psychiatric inpatient wards. In the wake group (n = 36, patients did three wake therapies in combination with light therapy each morning together with sleep time stabilisation. In the exercise group (n = 38, patients did daily exercise. Hamilton subscale scores were primary outcome (not blinded, secondary outcome was self-assessment data from the Preskorn scale and sleep.Patients in the wake therapy group had an immediate, large, stable, and statistically significant better antidepressant effect than patients in the exercise group with response rates at day5 of 75.0%/25.1% and remission rates of 58.6%/6.0%, respectively. The response and remission rates were diminished at day8 with response rates of 41.9%/10.1% and remission rates of 19.4%/4.7%, respectively. Patients and ward personnel found the method applicable with few side effects. Positive diurnal variation (mood better in the evening predicted a larger response to wake therapy. In the wake group napping on days after intervention predicted greater deterioration on day8.The intervention induced an acute antidepressant response without relapse between wake nights but with a diminishing effect after intervention. Development is still needed to secure maintenance of response. Avoiding napping in the days after wake therapy is important.Clinical trials.gov NCT00149110.

A CFD code comparison of wind turbine wakes

International Nuclear Information System (INIS)

Van der Laan, M P; Sørensen, N N; Storey, R C; Cater, J E; Norris, S E

2014-01-01

A comparison is made between the EllipSys3D and SnS CFD codes. Both codes are used to perform Large-Eddy Simulations (LES) of single wind turbine wakes, using the actuator disk method. The comparison shows that both LES models predict similar velocity deficits and stream-wise Reynolds-stresses for four test cases. A grid resolution study, performed in EllipSys3D and SnS, shows that a minimal uniform cell spacing of 1/30 of the rotor diameter is necessary to resolve the wind turbine wake. In addition, the LES-predicted velocity deficits are also compared with Reynolds-Averaged Navier Stokes simulations using EllipSys3D for a test case that is based on field measurements. In these simulations, two eddy viscosity turbulence models are employed: the k-ε model and the k-ε-f p model. Where the k-ε model fails to predict the velocity deficit, the results of the k-ε-f P model show good agreement with both LES models and measurements

Comparing satellite SAR and wind farm wake models

DEFF Research Database (Denmark)

Hasager, Charlotte Bay; Vincent, P.; Husson, R.

2015-01-01

. These extend several tens of kilometres downwind e.g. 70 km. Other SAR wind maps show near-field fine scale details of wake behind rows of turbines. The satellite SAR wind farm wake cases are modelled by different wind farm wake models including the PARK microscale model, the Weather Research and Forecasting...... (WRF) model in high resolution and WRF with coupled microscale parametrization....

Observation of high-resolution wind fields and offshore wind turbine wakes using TerraSAR-X imagery

Science.gov (United States)

Gies, Tobias; Jacobsen, Sven; Lehner, Susanne; Pleskachevsky, Andrey

2014-05-01

coast of Borkum, Germany, and consists of twelve 5-Megawatt wind power turbines. The retrieved results are validated by comparing with QuikSCAT measurements, the results of the German Weather Service (DWD) atmospheric model and in-situ measurements of wind speed and wind direction, obtained from the research platform FiNO1, installed 400 m west of Alpha Ventus. 4. Conclusion In the presented case study we quantify the wake characteristics of wake length, wake width, maximum velocity de?cit, wake merging and wake meandering. We show that SAR has the capability to map the sea surface two-dimensionally in high spatial resolution which provides a unique opportunity to observe spatial characteristics of offshore wind turbine wakes. The SAR derived information can support offshore wind farming with respect to optimal siting and design and help to estimate their effects on the environment.

Evolution of plasma wakes in density up- and down-ramps

Science.gov (United States)

Zhang, C. J.; Joshi, C.; Xu, X. L.; Mori, W. B.; Li, F.; Wan, Y.; Hua, J. F.; Pai, C. H.; Wang, J.; Lu, W.

2018-02-01

The time evolution of plasma wakes in density up- and down-ramps is examined through theory and particle-in-cell simulations. Motivated by observation of the reversal of a linear plasma wake in a plasma density upramp in a recent experiment (Zhang et al 2017 Phys. Rev. Lett. 119 064801) we have examined the behaviour of wakes in plasma ramps that always accompany any plasma source used for plasma-based acceleration. In the up-ramp case it is found that, after the passage of the drive pulse, the wavnumber/wavelength of the wake starts to decrease/increase with time until it eventually tends to zero/infinity, then the wake reverses its propagation direction and the wavenunber/wavelength of the wake begins to increase/shrink. The evolutions of the wavenumber and the phase velocity of the wake as functions of time are shown to be significantly different in the up-ramp and the down-ramp cases. In the latter case the wavenumber of the wake at a particular position in the ramp increases until the wake is eventually damped. It is also shown that the waveform of the wake at a particular time after being excited can be precisely controlled by tuning the initial plasma density profile, which may enable a new type of plasma-based ultrafast optics.

Effect of wind turbine wakes on summer-time wind profiles in the US Great Plains

Science.gov (United States)

Rhodes, M. E.; Lundquist, J. K.; Aitken, M.

2011-12-01

Wind energy is steadily becoming a significant source of grid electricity in the United States, and the Midwestern United States provides one of the nation's richest wind resources. This study examines the effect of wind turbine wakes on the wind profile in central Iowa. Data were collected using a coherent Doppler LiDAR system located approximately 2.5 rotor diameters north of a row of modern multi-MW wind turbine generators. The prevailing wind direction was from the South allowing the LiDAR to capture wind turbine wake properties; however, a number of periods existed where the LiDAR captured undisturbed flow. The LiDAR system reliably obtained readings up to 200 m above ground level (AGL), spanning the entire rotor disk (~40 m to 120 m AGL) which far surpasses the information provided by traditional wind resource assessment instrumentation. We extract several relevant parameters from the lidar data including: horizontal wind speed, vertical velocity, horizontal turbulence intensity, wind shear, and turbulent kinetic energy (TKE). Each time period at a particular LiDAR measurement height was labeled "wake" or "undisturbed" based on the wind direction at that height. Wake and undisturbed data were averaged separately to create a time-height cross-section averaged day for each parameter. Significant differences between wake and undisturbed data emerge. During the day, wake conditions experience larger values of TKE within the altitudes of the turbine rotor disk while TKE values above the rotor disk are similar between waked and undisturbed conditions. Furthermore, the morning transition of TKE in the atmospheric boundary layer commences earlier during wake conditions than in undisturbed conditions, and the evening decay of TKE persists longer during wake conditions. Waked wind shear is consistently greater than undisturbed periods at the edges of the wind turbine rotor disk (40m & 120m AGL), but especially so during the night where wind shear values during wake

Imaging doppler lidar for wind turbine wake profiling

Science.gov (United States)

Bossert, David J.

2015-11-19

An imaging Doppler lidar (IDL) enables the measurement of the velocity distribution of a large volume, in parallel, and at high spatial resolution in the wake of a wind turbine. Because the IDL is non-scanning, it can be orders of magnitude faster than conventional coherent lidar approaches. Scattering can be obtained from naturally occurring aerosol particles. Furthermore, the wind velocity can be measured directly from Doppler shifts of the laser light, so the measurement can be accomplished at large standoff and at wide fields-of-view.

The sleep-wake-cycle: basic mechanisms.

Science.gov (United States)

Jones, B E

1989-11-01

The physiologic characteristics of the sleep-wake states have been well defined and some of the chemical and neuron systems that participate in the cyclic generation and maintenance of these states have been identified. The actual dynamic process by which these systems interact to generate the basic sleep-wake cycle, however, remains a mystery.

Vortex wakes of a flapping foil in a flowing soap film

DEFF Research Database (Denmark)

We present an experimental study of an oscillating, symmetric foil in a vertically flowing soap film. By varying frequency and amplitude of the oscillation we explore and visualize a variety of wake structures, including von K´arm´an wake, reverse von K´arm´an wake, 2P wake, and 2P+2S wake. We...

Circadian Rhythm Sleep-Wake Disorders in Older Adults.

Science.gov (United States)

Kim, Jee Hyun; Duffy, Jeanne F

2018-03-01

The timing, duration, and consolidation of sleep result from the interaction of the circadian timing system with a sleep-wake homeostatic process. When aligned and functioning optimally, this allows wakefulness throughout the day and a long consolidated sleep episode at night. Mismatch between the desired timing of sleep and the ability to fall and remain asleep is a hallmark of the circadian rhythm sleep-wake disorders. This article discusses changes in circadian regulation of sleep with aging; how age influences the prevalence, diagnosis, and treatment of circadian rhythm sleep-wake disorders; and how neurologic diseases in older patients affect circadian rhythms and sleep. Copyright © 2017 Elsevier Inc. All rights reserved.

The Influence of Waves on the Near-Wake of an Axial-Flow Marine Hydrokinetic Turbine

Science.gov (United States)

Lust, Ethan; Luznik, Luksa; Flack, Karen

2017-11-01

Flow field results are presented for the near-wake of an axial-flow hydrokinetic turbine in the presence of surface gravity waves. The turbine is a 1/25 scale, 0.8 m diameter, two bladed turbine based on the U.S. Department of Energy's Reference Model 1 tidal current turbine. Measurements were obtained in the large towing tank facility at the U.S. Naval Academy with the turbine towed at a constant carriage speed and a tip speed ratio selected to provide maximum power. The turbine has been shown to be nearly scale independent for these conditions. Velocity measurements were obtained using an in-house designed and manufactured, submersible, planar particle image velocimetry (PIV) system at streamwise distances of up to two diameters downstream of the rotor plane. Phase averaged results for steady and unsteady conditions are presented for comparison showing further expansion of the wake in the presence of waves as compared to the quiescent case. The impact of waves on turbine tip vortex characteristics is also examined showing variation in core radius, swirl velocity, and circulation with wave phase. Some aspects of the highly coherent wake observed in the steady case are recognized in the unsteady wake, however, the unsteady velocities imposed by the waves, particularly the vertical velocity component, appears to convect tip vortices into the wake, potentially enhancing energy transport and accelerating the re-energization process.

Wind Wake Watcher v. 1.0

Energy Technology Data Exchange (ETDEWEB)

2017-10-03

This software enables the user to produce Google Earth visualizations of turbine wake effects for wind farms. The visualizations are based on computations of statistical quantities that vary with wind direction and help quantify the effects on power production of upwind turbines on turbines in their wakes. The results of the software are plot images and kml files that can be loaded into Google Earth. The statistics computed are described in greater detail in the paper: S. Martin, C. H. Westergaard, and J. White (2016), Visualizing Wind Farm Wakes Using SCADA Data, in Wither Turbulence and Big Data in the 21st Century? Eds. A. Pollard, L. Castillo, L. Danaila, and M. Glauser. Springer, pgs. 231-254.

Stochastic Wake Modelling Based on POD Analysis

Directory of Open Access Journals (Sweden)

David Bastine

2018-03-01

Full Text Available In this work, large eddy simulation data is analysed to investigate a new stochastic modeling approach for the wake of a wind turbine. The data is generated by the large eddy simulation (LES model PALM combined with an actuator disk with rotation representing the turbine. After applying a proper orthogonal decomposition (POD, three different stochastic models for the weighting coefficients of the POD modes are deduced resulting in three different wake models. Their performance is investigated mainly on the basis of aeroelastic simulations of a wind turbine in the wake. Three different load cases and their statistical characteristics are compared for the original LES, truncated PODs and the stochastic wake models including different numbers of POD modes. It is shown that approximately six POD modes are enough to capture the load dynamics on large temporal scales. Modeling the weighting coefficients as independent stochastic processes leads to similar load characteristics as in the case of the truncated POD. To complete this simplified wake description, we show evidence that the small-scale dynamics can be captured by adding to our model a homogeneous turbulent field. In this way, we present a procedure to derive stochastic wake models from costly computational fluid dynamics (CFD calculations or elaborated experimental investigations. These numerically efficient models provide the added value of possible long-term studies. Depending on the aspects of interest, different minimalized models may be obtained.

Transient Resistive Wall Wake for Very Short Bunches

International Nuclear Information System (INIS)

Stupakov, G.; SLAC

2005-01-01

The catch up distance for the resistive wall wake in a round pipe is approximately equal to the square of the pipe radius divided by the bunch length. The standard formulae for this wake are applicable at distances much larger than the catch up distance. In this paper, we calculate the resistive wall wake at distances compared with the catch up distance assuming a constant wall conductivity

Bifurcation and instability problems in vortex wakes

DEFF Research Database (Denmark)

Aref, Hassan; Brøns, Morten; Stremler, Mark A.

2007-01-01

A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal......-Reynolds number relation for vortex wakes, the bifurcation diagram for "exotic" wake patterns behind an oscillating cylinder first determined experimentally by Williamson & Roshko, and the bifurcations in topology of the streamlines pattern in point vortex streets. The Hamiltonian dynamics of point vortices...... in a periodic strip is considered. The classical results of von Kármán concerning the structure of the vortex street follow from the two-vortices-in-a-strip problem, while the stability results follow largely from a four-vortices-in-a-strip analysis. The three-vortices-in-a-strip problem is argued...

Brief wakeful resting can eliminate directed forgetting.

Science.gov (United States)

Schlichting, Andreas; Bäuml, Karl-Heinz T

2017-02-01

When cued to intentionally forget previously encoded memories, participants typically show reduced recall of the memories on a later recall test. We examined how such directed forgetting is affected by a brief period of wakeful resting between encoding and test. Encoding was followed by a "passive" wakeful resting period in which subjects heard emotionally neutral music or perceived neutral pictures, or it was followed by an "active" distraction period in which subjects were engaged in counting or calculation tasks. Whereas typical directed forgetting was present after active distraction, the forgetting was absent after wakeful resting. The findings indicate that the degree to which people can intentionally forget memories is influenced by the cognitive activity that people engage in shortly after learning takes place. The results provide first evidence on the interplay between wakeful resting and intentional forgetting.

Sleep-wake disturbances after traumatic brain injury.

Science.gov (United States)

Ouellet, Marie-Christine; Beaulieu-Bonneau, Simon; Morin, Charles M

2015-07-01

Sleep-wake disturbances are extremely common after a traumatic brain injury (TBI). The most common disturbances are insomnia (difficulties falling or staying asleep), increased sleep need, and excessive daytime sleepiness that can be due to the TBI or other sleep disorders associated with TBI, such as sleep-related breathing disorder or post-traumatic hypersomnia. Sleep-wake disturbances can have a major effect on functional outcomes and on the recovery process after TBI. These negative effects can exacerbate other common sequelae of TBI-such as fatigue, pain, cognitive impairments, and psychological disorders (eg, depression and anxiety). Sleep-wake disturbances associated with TBI warrant treatment. Although evidence specific to patients with TBI is still scarce, cognitive-behavioural therapy and medication could prove helpful to alleviate sleep-wake disturbances in patients with a TBI. Copyright © 2015 Elsevier Ltd. All rights reserved.

Circadian Sleep-Wake Rhythm of Older Adults with Intellectual Disabilities

Science.gov (United States)

Maaskant, Marijke; van de Wouw, Ellen; van Wijck, Ruud; Evenhuis, Heleen M.; Echteld, Michael A.

2013-01-01

The circadian sleep-wake rhythm changes with aging, resulting in a more fragmented sleep-wake pattern. In individuals with intellectual disabilities (ID), brain structures regulating the sleep-wake rhythm might be affected. The aims of this study were to compare the sleep-wake rhythm of older adults with ID to that of older adults in the general…

A fast-starting mechanical fish that accelerates at 40 m s-2

International Nuclear Information System (INIS)

Conte, J; Modarres-Sadeghi, Y; Watts, M N; Hover, F S; Triantafyllou, M S

2010-01-01

We have built a simple mechanical system to emulate the fast-start performance of fish. The system consists of a thin metal beam covered by a urethane rubber, the fish body and an appropriately shaped tail. The body form of the mechanical fish was modeled after a pike species and selected because it is a widely-studied fast-start specialist. The mechanical fish was held in curvature and hung in water by two restraining lines, which were simultaneously released by a pneumatic cutting mechanism. The potential energy in the beam was transferred into the fluid, thereby accelerating the fish. We measured the resulting acceleration, and calculated the efficiency of propulsion for the mechanical fish model, defined as the ratio of the final kinetic energy of the fish and the initially stored potential energy in the body beam. We also ran a series of flow visualization tests to observe the resulting flow patterns. The maximum start-up acceleration was measured to be around 40 m s -2 , with the maximum final velocity around 1.2 m s -1 . The form of the measured acceleration signal as function of time is quite similar to that of type I fast-start motions studied by Harper and Blake (1991 J. Exp. Biol. 155 175-92). The hydrodynamic efficiency of the fish was found to be around 10%. Flow visualization of the mechanical fast-start wake was also analyzed, showing that the acceleration peaks are associated with the shedding of two vortex rings in near-lateral directions.

International Survey on the Management of Wake-Up Stroke.

Science.gov (United States)

de Castro-Afonso, Luís Henrique; Nakiri, Guilherme Seizem; Pontes-Neto, Octávio Marques; dos Santos, Antônio Carlos; Abud, Daniel Giansante

2016-01-01

Patients who wake up having experienced a stroke while asleep represent around 20% of acute stroke admissions. According to international guidelines for the management of acute stroke, patients presenting with wake-up stroke are not currently eligible to receive revascularization treatments. In this study, we aimed to assess the opinions of stroke experts about the management of patients with wake-up stroke by using an international multicenter electronic survey. This study consisted of 8 questions on wake-up stroke treatment. Two hundred invitations to participate in the survey were sent by e-mail. Fifty-nine participants started the survey, 4 dropped out before completing it, and 55 completed the full questionnaire. We had 55 participants from 22 countries. In this study, most stroke experts recommended a recanalization treatment for wake-up stroke. However, there was considerable disagreement among experts regarding the best brain imaging method and the best recanalization treatment. The results of ongoing randomized trials on wake-up stroke are urgently needed.

Experimental Study on Influence of Pitch Motion on the Wake of a Floating Wind Turbine Model

Directory of Open Access Journals (Sweden)

Stanislav Rockel

2014-03-01

Full Text Available Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise oscillating turbine are compared. Results indicate that platform pitch creates an upward shift in all components of the flow and their fluctuations. The vertical flow created by the pitch motion as well as the reduced entrainment of kinetic energy from undisturbed flows above the turbine result in potentially higher loads and less available kinetic energy for a downwind turbine. Experimental results are compared with four wake models. The wake models employed are consistent with experimental results in describing the shapes and magnitudes of the streamwise velocity component of the wake for a fixed turbine. Inconsistencies between the model predictions and experimental results arise in the floating case particularly regarding the vertical displacement of the velocity components of the flow. Furthermore, it is found that the additional degrees of freedom of a floating wind turbine add to the complexity of the wake aerodynamics and improved wake models are needed, considering vertical flows and displacements due to pitch motion.

Forecasting behavior in smart homes based on sleep and wake patterns.

Science.gov (United States)

Williams, Jennifer A; Cook, Diane J

2017-01-01

The goal of this research is to use smart home technology to assist people who are recovering from injuries or coping with disabilities to live independently. We introduce an algorithm to model and forecast wake and sleep behaviors that are exhibited by the participant. Furthermore, we propose that sleep behavior is impacted by and can be modeled from wake behavior, and vice versa. This paper describes the Behavior Forecasting (BF) algorithm. BF consists of 1) defining numeric values that reflect sleep and wake behavior, 2) forecasting wake and sleep values from past behavior, 3) analyzing the effect of wake behavior on sleep and vice versa, and 4) improving prediction performance by using both wake and sleep scores. The BF method was evaluated with data collected from 20 smart homes. We found that regardless of the forecasting method utilized, wake behavior and sleep behavior can be modeled with a minimum accuracy of 84%. Additionally, normalizing the wake and sleep scores drastically improves the accuracy to 99%. The results show that we can effectively model wake and sleep behaviors in a smart environment. Furthermore, wake behaviors can be predicted from sleep behaviors and vice versa.

A prospective clinical study to compare the depth of anaesthesia, the wake-up time and the wake-up behaviour for total intravenous anaesthesia (TIVA) with Remifentanil and Propofol between two anaesthetic methods (TCI versus OTCI) in elective vasovasostomy patients

OpenAIRE

Baschin, Alexander

2010-01-01

Background. The performance of safe anaesthesia with fewer complications combined with fast wake-up and prompt return of cognitive functions on completion of surgery appear to be possible with the introduction of rapid-acting and more controllable drugs, such as Propofol and Remifentanil, as well as the use of computerised application systems. Target-controlled perfusor systems based on the Marsh model are common in daily practice. The target values in the target-controlled infusion systems (...

Development of fast measurements of concentration of NORM U-238 by HPGe

Science.gov (United States)

Cha, Seokki; Kim, Siu; Kim, Geehyun

2017-02-01

Naturally Occureed Radioactive Material (NORM) generated from the origin of earth can be found all around us and even people who are not engaged in the work related to radiation have been exposed to unnecessary radiation. This NORM has a potential risk provided that is concentrated or transformed by artificial activities. Likewise, a development of fast measruement method of NORM is emerging to prevent the radiation exposure of the general public and person engaged in the work related to the type of business related thereto who uses the material in which NORM is concentrated or transfromed. Based on such a background, many of countries have tried to manage NORM and carried out regulatory legislation. To effienctly manage NORM, there is need for developing new measurement to quickly and accurately analyze the nuclide and concentration. In this study, development of the fast and reliable measurement was carried out. In addition to confirming the reliability of the fast measurement, we have obtained results that can suggest the possibility of developing another fast measurement. Therefore, as a follow-up, it is possible to develop another fast analytical measurement afterwards. The results of this study will be very useful for the regulatory system to manage NORM. In this study, a review of two indirect measurement methods of NORM U-238 that has used HPGe on the basis of the equilibrium theory of relationships of mother and daughter nuclide at decay-chain of NORM U-238 has been carried out. For comparative study(in order to know reliabily), direct measurement that makes use of alpha spectrometer with complicated pre-processing process was implemented.

Numerical challenges of short range wake field calculations

Energy Technology Data Exchange (ETDEWEB)

Lau, Thomas; Gjonaj, Erion; Weiland, Thomas [Technische Universitaet Darmstadt (Germany). Institut fuer Theorie Elektromagnetischer Felder (TEMF)

2011-07-01

For present and future accelerator projects with ultra short bunches the accurate and reliable calculation of short range wake fields is an important issue. However, the numerical calculation of short range wake fields is a numerical challenging task. The presentation gives an overview over the numerical challenges and techniques for short range wake field calculations. Finally, some simulation results obtained by the program PBCI developed at the TU Darmstadt are presented.

Description of signature scales in a floating wind turbine model wake subjected to varying turbulence intensity

Science.gov (United States)

Kadum, Hawwa; Rockel, Stanislav; Holling, Michael; Peinke, Joachim; Cal, Raul Bayon

2017-11-01

The wake behind a floating model horizontal axis wind turbine during pitch motion is investigated and compared to a fixed wind turbine wake. An experiment is conducted in an acoustic wind tunnel where hot-wire data are acquired at five downstream locations. At each downstream location, a rake of 16 hot-wires was used with placement of the probes increasing radially in the vertical, horizontal, and diagonally at 45 deg. In addition, the effect of turbulence intensity on the floating wake is examined by subjecting the wind turbine to different inflow conditions controlled through three settings in the wind tunnel grid, a passive and two active protocols, thus varying in intensity. The wakes are inspected by statistics of the point measurements, where the various length/time scales are considered. The wake characteristics for a floating wind turbine are compared to a fixed turbine, and uncovering its features; relevant as the demand for exploiting deep waters in wind energy is increasing.

Actuator Line Modeling of Wind Turbine Wakes

DEFF Research Database (Denmark)

Troldborg, Niels

2009-01-01

This thesis contains a comprehensive 3D Navier-Stokes computational study of the characteristics of wakes of wind turbines operating in various flow conditions including interacting wakes between a row of turbines. The computations were carried out using the actuator line technique combined...

Wake-Model Effects on Induced Drag Prediction of Staggered Boxwings

Directory of Open Access Journals (Sweden)

Julian Schirra

2018-01-01

Full Text Available For staggered boxwings the predictions of induced drag that rely on common potential-flow methods can be of limited accuracy. For example, linear, freestream-fixed wake models cannot resolve effects related to wake deflection and roll-up, which can have significant affects on the induced drag projection of these systems. The present work investigates the principle impact of wake modelling on the accuracy of induced drag prediction of boxwings with stagger. The study compares induced drag predictions of a higher-order potential-flow method that uses fixed and relaxed-wake models, and of an Euler-flow method. Positive-staggered systems at positive angles of attack are found to be particularly prone to higher-order wake effects due to vertical contraction of wakes trajectories, which results in smaller effective height-to-span ratios than compared with negative stagger and thus closer interactions between trailing wakes and lifting surfaces. Therefore, when trying to predict induced drag of positive staggered boxwings, only a potential-flow method with a fully relaxed-wake model will provide the high-degree of accuracy that rivals that of an Euler method while being computationally significantly more efficient.

Fast-food intake and perceived and objective measures of the local fast-food environment in adolescents.

Science.gov (United States)

Svastisalee, Chalida; Pagh Pedersen, Trine; Schipperijn, Jasper; Jørgensen, Sanne Ellegaard; Holstein, Bjørn E; Krølner, Rikke

2016-02-01

We examined associations between fast-food intake and perceived and objective fast-food outlet exposure. Information from the Health Behaviours in School-aged Children Study was linked to fast-food outlets in seventy-five school neighbourhoods. We used multivariate multilevel logistic regression analyses to examine associations between at least weekly fast-food intake and perceived and objective fast-food outlet measures. Data represent 4642 adolescents (aged 11-15 years) in Denmark. Boys reporting two or more fast-food outlets had 34% higher odds consuming fast food at least weekly. We detected higher odds of at least weekly fast-food intake among 15-year-old 9th graders (ORall=1.74; 95% CI 1.40, 2.18; ORboys=2.20; 95% CI 1.66, 2.91; ORgirls=1.41; 95% CI 1.03, 1.92), Danish speakers (ORall=2.32; 95% CI 1.68, 3.19; ORboys=2.58; 95% CI 1.69, 3.93; ORgirls=2.37; 95% CI 1.46, 3.84) and those travelling 15 min or less to school (ORall=1.21; 95% CI 1.00, 1.46; ORgirls=1.44; 95% CI 1.08, 1.93) compared with 11-year-old 5th graders, non-Danish speakers and those with longer travel times. Boys from middle- (OR=1.28; 95% CI 1.00, 1.65) and girls from low-income families (OR=1.46; 95% CI 1.05, 2.04) had higher odds of at least weekly fast-food intake compared with those from high-income backgrounds. Girls attending schools with canteens (OR=1.47; 95% CI 1.00, 2.15) had higher odds of at least weekly fast-food intake than girls at schools without canteens. The present study demonstrates that perceived food outlets may impact fast-food intake in boys while proximity impacts intake in girls. Public health planning could target food environments that emphasize a better understanding of how adolescents use local resources.

Uncovering the genetic landscape for multiple sleep-wake traits.

Directory of Open Access Journals (Sweden)

Christopher J Winrow

Full Text Available Despite decades of research in defining sleep-wake properties in mammals, little is known about the nature or identity of genes that regulate sleep, a fundamental behaviour that in humans occupies about one-third of the entire lifespan. While genome-wide association studies in humans and quantitative trait loci (QTL analyses in mice have identified candidate genes for an increasing number of complex traits and genetic diseases, the resources and time-consuming process necessary for obtaining detailed quantitative data have made sleep seemingly intractable to similar large-scale genomic approaches. Here we describe analysis of 20 sleep-wake traits from 269 mice from a genetically segregating population that reveals 52 significant QTL representing a minimum of 20 genomic loci. While many (28 QTL affected a particular sleep-wake trait (e.g., amount of wake across the full 24-hr day, other loci only affected a trait in the light or dark period while some loci had opposite effects on the trait during the light vs. dark. Analysis of a dataset for multiple sleep-wake traits led to previously undetected interactions (including the differential genetic control of number and duration of REM bouts, as well as possible shared genetic regulatory mechanisms for seemingly different unrelated sleep-wake traits (e.g., number of arousals and REM latency. Construction of a Bayesian network for sleep-wake traits and loci led to the identification of sub-networks of linkage not detectable in smaller data sets or limited single-trait analyses. For example, the network analyses revealed a novel chain of causal relationships between the chromosome 17@29cM QTL, total amount of wake, and duration of wake bouts in both light and dark periods that implies a mechanism whereby overall sleep need, mediated by this locus, in turn determines the length of each wake bout. Taken together, the present results reveal a complex genetic landscape underlying multiple sleep-wake traits

VIRTUAL REALITY IN WAKING AND DREAMING CONSCIOUSNESS

Directory of Open Access Journals (Sweden)

Allan eHobson

2014-10-01

Full Text Available This article explores the notion that the brain is genetically endowed with an innate virtual reality generator that – through experience-dependent plasticity –becomes a generative or predictive model of the world. This model, which is most clearly revealed in rapid eye movement (REM sleep dreaming, may provide the theatre for conscious experience. Functional neuroimaging evidence for brain activations that are time-locked to rapid eye movements endorses the view that waking consciousness emerges from REM sleep – and dreaming lays the foundations for waking perception. In this view, the brain is equipped with a virtual model of the world that generates predictions of its sensations. This model is continually updated and entrained by sensory prediction errors in wakefulness to ensure veridical perception, but not in dreaming. In contrast, dreaming plays an essential role in maintaining and enhancing the capacity to model the world by minimizing model complexity and thereby maximizing both statistical and thermodynamic efficiency. This perspective suggests that consciousness corresponds to the embodied process of inference, realized through the generation of virtual realities (in both sleep and wakefulness. In short, our premise or hypothesis is that the waking brain engages with the sensorium to predict the causes of sensations, while in sleep the brain's generative model is actively refined so that it generates more efficient predictions during waking. We review the evidence in support of this hypothesis – evidence that grounds consciousness in biophysical computations whose neuronal and neurochemical infrastructure has been disclosed by sleep research.

Generalized impedances and wakes in asymmetric structures

International Nuclear Information System (INIS)

Heifets, S.; Wagner, A.; Zotter, B.

1998-01-01

In rotationally structures, the dominant m = 0 longitudinal impedance does not depend on the offsets of either the leading or the trailing particles, while the dominant m = 1 transverse impedance is proportional to the offset of the leading particles, while it is still independent of the offsets of the trailing ones. This behavior is no longer true in rotationally non-symmetric structures, where in general all impedances depend on the offsets of both the leading and the trailing particles. The same behavior is shown by wake functions and wake potentials. The concept of generalized impedances or generalized wake functions must be used to calculate the effect of leading particles on trailing ones with different offsets, each described by two transverse coordinates. This dependence of wake potentials on four additional parameters (two for each offset) would make their use very cumbersome. Fortunately, it was found that the transverse wake potentials can be separated into superpositions of dipolar components, which are proportional to the offset of the leading bunch, and quadrupolar components, which are proportional to the offset of the trailing particles. Higher multipole components are much smaller, and can be neglected for most structures without rotational symmetry. In this report, the authors derive analytical expressions for these multipolar components, which permits estimates of the size of the neglected terms. In particular, when structures have one or two transverse symmetry planes, the expressions simplify and explain the behavior of wake potentials which had been computed for rotationally non-symmetric structures

Experimental investigation of the turbulent axisymmetric wake with rotation generated by a wind turbine

Science.gov (United States)

Dufresne, Nathaniel P.

An experimental investigation of the axial and azimuthal (swirl) velocity field in the wake of a single 3-bladed wind turbine with rotor diameter of 0.91m was conducted, up to 20 diameters downstream. The turbine was positioned in the free stream, near the entrance of the 6m x 2.7m cross section of the University of New Hampshire (UNH) Flow Physics Facility. Velocity measurements were conducted at different rotor loading conditions with blade tip-speed ratios from 2.0 to 2.8. A Pitot-static tube and constant temperature hot-wire anemometer with a multi-wire sensor were used to measure velocity fields. An equilibrium similarity theory for the turbulent axisymmetric wake with rotation was outlined, and first evidence for a new scaling function for the mean swirling velocity component, Wmax ∝ x-1 ∝ U3/2o a was found; where W represents swirl, x represents downstream distance, and Uo, represents the centerline velocity deficit in the wake.

Conformal FDTD modeling wake fields

Energy Technology Data Exchange (ETDEWEB)

Jurgens, T.; Harfoush, F.

1991-05-01

Many computer codes have been written to model wake fields. Here we describe the use of the Conformal Finite Difference Time Domain (CFDTD) method to model the wake fields generated by a rigid beam traveling through various accelerating structures. The non- cylindrical symmetry of some of the problems considered here requires the use of a three dimensional code. In traditional FDTD codes, curved surfaces are approximated by rectangular steps. The errors introduced in wake field calculations by such an approximation can be reduced by increasing the mesh size, therefore increasing the cost of computing. Another approach, validated here, deforms Ampere and Faraday contours near a media interface so as to conform to the interface. These improvements of the FDTD method result in better accuracy of the fields at asymptotically no computational cost. This method is also capable of modeling thin wires as found in beam profile monitors, and slots and cracks as found in resistive wall motions. 4 refs., 5 figs.

Simulation of wind turbine wakes using the actuator line technique

DEFF Research Database (Denmark)

Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming; Henningson, Dan S.

2015-01-01

The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance...... predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results...

A simple atmospheric boundary layer model applied to large eddy simulations of wind turbine wakes

DEFF Research Database (Denmark)

Troldborg, Niels; Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming

2014-01-01

A simple model for including the influence of the atmospheric boundary layer in connection with large eddy simulations of wind turbine wakes is presented and validated by comparing computed results with measurements as well as with direct numerical simulations. The model is based on an immersed...... boundary type technique where volume forces are used to introduce wind shear and atmospheric turbulence. The application of the model for wake studies is demonstrated by combining it with the actuator line method, and predictions are compared with field measurements. Copyright © 2013 John Wiley & Sons, Ltd....

Prolonged Nightly Fasting and Breast Cancer Risk: Findings from NHANES (2009-2010).

Science.gov (United States)

Marinac, Catherine R; Natarajan, Loki; Sears, Dorothy D; Gallo, Linda C; Hartman, Sheri J; Arredondo, Elva; Patterson, Ruth E

2015-05-01

A novel line of research has emerged, suggesting that daily feeding-fasting schedules that are synchronized with sleep-wake cycles have metabolic implications that are highly relevant to breast cancer. We examined associations of nighttime fasting duration with biomarkers of breast cancer risk among women in the 2009-2010 U.S. National Health and Nutrition Examination Survey. Dietary, anthropometric, and HbA1c data were available for 2,212 women, and 2-hour postprandial glucose concentrations were available for 1,066 women. Nighttime fasting duration was calculated using 24-hour food records. Separate linear regression models examined associations of nighttime fasting with HbA1c and 2-hour glucose concentrations. Logistic regression modeled associations of nighttime fasting with elevated HbA1c (HbA1c ≥ 39 mmol/mol or 5.7%) and elevated 2-hour glucose (glucose ≥ 140 mg/dL). All models adjusted for age, education, race/ethnicity, body mass index, total kcal intake, evening kcal intake, and the number of eating episodes per day. Each 3-hour increase in nighttime fasting (roughly 1 SD) was associated with a 4% lower 2-hour glucose measurement [β, 0.96; 95% confidence interval (CI), 0.93-1.00; P fasting duration was associated with roughly a 20% reduced odds of elevated HbA1c (OR, 0.81; 95% CI, 0.68-0.97; P fasting could improve biomarkers of glucose control, thereby reducing breast cancer risk. ©2015 American Association for Cancer Research.

Forecasting Behavior in Smart Homes Based on Sleep and Wake Patterns

Science.gov (United States)

Williams, Jennifer A.; Cook, Diane J.

2017-01-01

Background The goal of this research is to use smart home technology to assist people who are recovering from injuries or coping with disabilities to live independently. Objective We introduce an algorithm to model and forecast wake and sleep behaviors that are exhibited by the participant. Furthermore, we propose that sleep behavior is impacted by and can be modeled from wake behavior, and vice versa. Methods This paper describes the Behavior Forecasting (BF) algorithm. BF consists of 1) defining numeric values that reflect sleep and wake behavior, 2) forecasting wake and sleep values from past behavior, 3) analyzing the effect of wake behavior on sleep and vice versa, and 4) improving prediction performance by using both wake and sleep scores. Results The BF method was evaluated with data collected from 20 smart homes. We found that regardless of the forecasting method utilized, wake behavior and sleep behavior can be modeled with a minimum accuracy of 84%. Additionally, normalizing the wake and sleep scores drastically improves the accuracy to 99%. Conclusions The results show that we can effectively model wake and sleep behaviors in a smart environment. Furthermore, wake behaviors can be predicted from sleep behaviors and vice versa. PMID:27689555

Estimation of unsteady lift on a pitching airfoil from wake velocity surveys

Science.gov (United States)

Zaman, K. B. M. Q.; Panda, J.; Rumsey, C. L.

1993-01-01

The results of a joint experimental and computational study on the flowfield over a periodically pitched NACA0012 airfoil, and the resultant lift variation, are reported in this paper. The lift variation over a cycle of oscillation, and hence the lift hysteresis loop, is estimated from the velocity distribution in the wake measured or computed for successive phases of the cycle. Experimentally, the estimated lift hysteresis loops are compared with available data from the literature as well as with limited force balance measurements. Computationally, the estimated lift variations are compared with the corresponding variation obtained from the surface pressure distribution. Four analytical formulations for the lift estimation from wake surveys are considered and relative successes of the four are discussed.

Dynamic Loads and Wake Prediction for Large Wind Turbines Based on Free Wake Method

Institute of Scientific and Technical Information of China (English)

Cao Jiufa; Wang Tongguang; Long Hui; Ke Shitang; Xu Bofeng

2015-01-01

With large scale wind turbines ,the issue of aerodynamic elastic response is even more significant on dy-namic behaviour of the system .Unsteady free vortex wake method is proposed to calculate the shape of wake and aerodynamic load .Considering the effect of aerodynamic load ,inertial load and gravity load ,the decoupling dy-namic equations are established by using finite element method in conjunction of the modal method and equations are solved numerically by Newmark approach .Finally ,the numerical simulation of a large scale wind turbine is performed through coupling the free vortex wake modelling with structural modelling .The results show that this coupling model can predict the flexible wind turbine dynamic characteristics effectively and efficiently .Under the influence of the gravitational force ,the dynamic response of flapwise direction contributes to the dynamic behavior of edgewise direction under the operational condition of steady wind speed .The difference in dynamic response be-tween the flexible and rigid wind turbines manifests when the aerodynamics/structure coupling effect is of signifi-cance in both wind turbine design and performance calculation .

International Survey on the Management of Wake-Up Stroke

Directory of Open Access Journals (Sweden)

Luís Henrique de Castro-Afonso

2016-03-01

Full Text Available Background: Patients who wake up having experienced a stroke while asleep represent around 20% of acute stroke admissions. According to international guidelines for the management of acute stroke, patients presenting with wake-up stroke are not currently eligible to receive revascularization treatments. In this study, we aimed to assess the opinions of stroke experts about the management of patients with wake-up stroke by using an international multicenter electronic survey. Method: This study consisted of 8 questions on wake-up stroke treatment. Results: Two hundred invitations to participate in the survey were sent by e-mail. Fifty-nine participants started the survey, 4 dropped out before completing it, and 55 completed the full questionnaire. We had 55 participants from 22 countries. Conclusions: In this study, most stroke experts recommended a recanalization treatment for wake-up stroke. However, there was considerable disagreement among experts regarding the best brain imaging method and the best recanalization treatment. The results of ongoing randomized trials on wake-up stroke are urgently needed.

Functional anatomy of the sleep-wakefulness cycle: wakefulness.

Science.gov (United States)

Reinoso-Suárez, Fernando; de Andrés, Isabel; Garzón, Miguel

2011-01-01

Sleep is a necessary, diverse, periodic, and an active condition circadian and homeostatically regulated and precisely meshed with waking time into the sleep-wakefulness cycle (SWC). Photic retinal stimulation modulates the suprachiasmatic nucleus, which acts as the pacemaker for SWC rhythmicity. Both the light period and social cues adjust the internal clock, making the SWC a circadian, 24-h period in the adult human. Bioelectrical and behavioral parameters characterize the different phases of the SWC. For a long time, lesions and electrical stimulation of brain structures, as well as connection studies, were the main methods used to decipher the foundations of the functional anatomy of the SWC. That is why the first section of this review presents these early historical studies to then discuss the current state of our knowledge based on our understanding of the functional anatomy of the structures underlying the SWC. Supported by this description, we then present a detailed review and update of the structures involved in the phase of wakefulness (W), including their morphological, functional, and chemical characteristics, as well as their anatomical connections. The structures for W generation are known as the "ascending reticular activating system", and they keep and maintain the "thalamo-cerebral cortex unit" awake. This system originates from the neuronal groups located within the brainstem, hypothalamus, and basal forebrain, which use known neurotransmitters and whose neurons are more active during W than during the other SWC states. Thus, synergies among several of these neurotransmitters are necessary to generate the cortical and thalamic activation that is characteristic of the W state, with all the plastic qualities and nuances present in its different behavioral circumstances. Each one of the neurotransmitters exerts powerful influences on the information and cognitive processes as well as attentional, emotional, motivational, behavioral, and arousal

Fast neutron measurements at the nELBE time-of-flight facility

Directory of Open Access Journals (Sweden)

Junghansa A. R.

2015-01-01

Full Text Available The compact neutron-time-of-flight facility nELBE at the superconducting electron accelerator ELBE of Helmholtz-Zentrum Dresden-Rossendorf has been rebuilt. A new enlarged experimental hall with a flight path of up to 10 m is available for neutron time-of-flight experiments in the fast energy range from about 50 keV to 10 MeV. nELBE is intended to deliver nuclear data of fast neutron nuclear interactions e.g. for the transmutation of nuclear waste and improvement of neutron physical simulations of innovative nuclear systems. The experimental programme consists of transmission measurements of neutron total cross sections, elastic and inelastic scattering cross section measurements, and neutron induced fission cross sections. The inelastic scattering to the first few excited states in 56Fe was investigated by measuring the gamma production cross section with an HPGe detector. The neutron induced fission of 242Pu was studied using fast ionisation chambers with large homogeneous actinide deposits.

Effects of prolonged wakefulness combined with alcohol and hands-free cell phone divided attention tasks on simulated driving.

Science.gov (United States)

Iudice, A; Bonanni, E; Gelli, A; Frittelli, C; Iudice, G; Cignoni, F; Ghicopulos, I; Murri, L

2005-03-01

Simulated driving ability was assessed following administration of alcohol, at an estimated blood level of 0.05%, and combined prolonged wakefulness, while participants were undertaking divided attention tasks over a hands-free mobile phone. Divided attention tasks were structured to provide a sustained cognitive workload to the subjects. Twenty three young healthy individuals drove 10 km simulated driving under four conditions in a counterbalanced, within-subject design: alcohol, alcohol and 19 h wakefulness, alcohol and 24 h wakefulness, and while sober. Study measures were: simulated driving, self-reported sleepiness, critical flicker fusion threshold (CFFT), Stroop word-colour interference test (Stroop) and simple visual reaction times (SVRT). As expected, subjective sleepiness was highly correlated with both sleep restriction and alcohol consumption. The combination of alcohol and 24 h sustained wakefulness produced the highest driving impairment, significantly beyond the alcohol effect itself. Concurrent alcohol and 19 h wakefulness significantly affected only driving time-to-collision. No significant changes of study measures occurred following alcohol intake in unrestricted sleep conditions. CFFT, SVRT and Stroop results showed a similar trend in the four study conditions. Thus apparently 'safe' blood alcohol levels in combination with prolonged wakefulness resulted in significant driving impairments. In normal sleep conditions alcohol effects on driving were partially counteracted by the concomitant hands-free phone based psychometric tasks. 2005 John Wiley & Sons, Ltd.

'Beam-emission spectroscopy' diagnostics also measure edge fast-ion light

International Nuclear Information System (INIS)

Heidbrink, W W; Bortolon, A; McKee, G R; Smith, D R

2011-01-01

Beam-emission spectroscopy (BES) diagnostics normally detect fluctuations in the light emitted by an injected neutral beam. Under some circumstances, however, light from fast ions that charge exchange in the high neutral-density region at the edge of the plasma make appreciable contributions to the BES signals. This 'passive' fast-ion D α (FIDA) light appears in BES signals from both the DIII-D tokamak and the National Spherical Torus Experiment (NSTX). One type of passive FIDA light is associated with classical orbits that traverse the edge. Another type is caused by instabilities that expel fast ions from the core; this light can complicate measurement of the instability eigenfunction.

Evolution and breakdown of helical vortex wakes behind a wind turbine

International Nuclear Information System (INIS)

Nemes, A; Jacono, D Lo; Sheridan, J; Blackburn, H M; Sherry, M

2014-01-01

The wake behind a three-bladed Glauert model rotor in a water channel was investigated. Planar particle image velocimetry was used to measure the velocity fields on the wake centre-line, with snapshots phase-locked to blade position of the rotor. Phase- locked averages of the velocity and vorticity fields are shown, with tip vortex interaction and entanglement of the helical filaments elucidated. Proper orthogonal decomposition and topology-based vortex identification are used to filter the PIV images for coherent structures and locate vortex cores. Application of these methods to the instantaneous data reveals unsteady behaviour of the helical filaments that is statistically quantifiable

On the Effects of Wind Turbine Wake Skew Caused by Wind Veer

Energy Technology Data Exchange (ETDEWEB)

Churchfield, Matthew J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sirnivas, Senu [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

2018-01-12

Because of Coriolis forces caused by the Earth's rotation, the structure of the atmospheric boundary layer often contains wind-direction change with height, also known as wind-direction veer. Under low turbulence conditions, such as in stably stratified atmospheric conditions, this veer can be significant, even across the vertical extent of a wind turbine's rotor disk. The veer then causes the wind turbine wake to skew as it advects downstream. This wake skew has been observed both experimentally and numerically. In this work, we attempt to examine the wake skewing process in some detail, and quantify how differently a skewed wake versus a non skewed wake affects a downstream turbine. We do this by performing atmospheric large-eddy simulations to create turbulent inflow winds with and without veer. In the veer case, there is a roughly 8 degree wind direction change across the turbine rotor. We then perform subsequent large-eddy simulations using these inflow data with an actuator line rotor model to create wakes. The turbine modeled is a large, modern, offshore, multimegawatt turbine. We examine the unsteady wake data in detail and show that the skewed wake recovers faster than the non skewed wake. We also show that the wake deficit does not skew to the same degree that a passive tracer would if subject to veered inflow. Last, we use the wake data to place a hypothetical turbine 9 rotor diameters downstream by running aeroelastic simulations with the simulated wake data. We see differences in power and loads if this downstream turbine is subject to a skewed or non skewed wake. We feel that the differences observed between the skewed and nonskewed wake are important enough that the skewing effect should be included in engineering wake models.

Sleep/wake dependent changes in cortical glucose concentrations.

Science.gov (United States)

Dash, Michael B; Bellesi, Michele; Tononi, Giulio; Cirelli, Chiara

2013-01-01

Most of the energy in the brain comes from glucose and supports glutamatergic activity. The firing rate of cortical glutamatergic neurons, as well as cortical extracellular glutamate levels, increase with time spent awake and decline throughout non rapid eye movement sleep, raising the question whether glucose levels reflect behavioral state and sleep/wake history. Here chronic (2-3 days) electroencephalographic recordings in the rat cerebral cortex were coupled with fixed-potential amperometry to monitor the extracellular concentration of glucose ([gluc]) on a second-by-second basis across the spontaneous sleep-wake cycle and in response to 3 h of sleep deprivation. [Gluc] progressively increased during non rapid eye movement sleep and declined during rapid eye movement sleep, while during wake an early decline in [gluc] was followed by an increase 8-15 min after awakening. There was a significant time of day effect during the dark phase, when rats are mostly awake, with [gluc] being significantly lower during the last 3-4 h of the night relative to the first 3-4 h. Moreover, the duration of the early phase of [gluc] decline during wake was longer after prolonged wake than after consolidated sleep. Thus, the sleep/wake history may affect the levels of glucose available to the brain upon awakening. © 2012 The Authors Journal of Neurochemistry © 2012 International Society for Neurochemistry.

Wake Survey of a Marine Current Turbine Under Steady Conditions

Science.gov (United States)

Lust, Ethan; Luznik, Luksa; Flack, Karen

2016-11-01

A submersible particle image velocimetry (PIV) system was used to study the wake of a horizontal axis marine current turbine. The turbine was tested in a large tow tank facility at the United States Naval Academy. The turbine is a 1/25th scale model of the U.S. National Renewable Energy Laboratory's Reference Model 1 (RM1) tidal turbine. It is a two-bladed turbine measuring 0.8 m in diameter and featuring a NACA 63-618 airfoil cross section. Separate wind tunnel testing has shown the foil section used on the turbine to be Reynolds number independent with respect to lift at the experimental parameters of tow carriage speed (Utow = 1 . 68 m/s) and tip speed ratio (TSR = 7). The wake survey was conducted over an area extending 0.25D forward of the turbine tip path to 2.0D aft, and to a depth of 1.0D beneath the turbine output shaft in the streamwise plane. Each field of view was approximately 30 cm by 30 cm, and each overlapped the adjacent fields of view by 5 cm. The entire flow field was then reconstructed into a single field of investigation. Results include streamwise and vertical ensemble average velocity fields averaged over approximately 1,000 realizations, as well as higher-order statistics. Turbine tip vortex centers were identified and plotted showing increasing aperiodicity with wake age. keywords: horizontal axis marine current turbine, particle image velocimetry, towing tank, wake survey

Fast-ion diffusion measurements from radial triton burn up studies

International Nuclear Information System (INIS)

McCauley, J.S.; Budny, R.; McCune, D.; Strachan, J.D.

1993-08-01

A fast-ion diffusion coefficient of 0.1 ± 0.1 m 2 s -1 has been deduced from the triton burnup neutron emission profile measured by a collimated array of helium-4 spectrometers. The experiment was performed with high-power deuterium discharges produced by Princeton University's Tokamak Fusion Test Reactor (TFTR). The fast ions monitored were the 1.0 MeV tritons produced from the d(d,t)p. These tritons ''burn up'' with deuterons and emit a 14 MeV neutron by the d(t,α)n reaction. The ratio of the measured to calculated DT yield is typically 70%. The measured DT profile width is comparable to that predicted by the TRANSP transport code during neutral beam heating and narrower after the beam heating ended

Surface Characteristics of Green Island Wakes from Satellite Imagery

Science.gov (United States)

Cheng, Kai-Ho; Hsu, Po-Chun; Ho, Chung-Ru

2017-04-01

Characteristics of an island wake induced by the Kuroshio Current flows pass by Green Island, a small island 40 km off southeast of Taiwan is investigated by the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. The MODIS sea surface temperature (SST) and chlorophyll-a (chl-a) imagery is produced at 250-meter resolution from 2014 to 2015 using the SeaDAS software package which is developed by the National Aeronautics and Space Administration. The wake occurrence is 59% observed from SST images during the data span. The average cooling area is 190 km2, but the area is significantly changed with wind directions. The wake area is increased during southerly winds and is reduced during northerly winds. Besides, the average cooling SST was about 2.1 oC between the front and rear island. Comparing the temperature difference between the wake and its left side, the difference is 1.96 oC. In addition, the wakes have 1 3 times higher than normal in chlorophyll concentration. The results indicate the island mass effect makes the surface water of Green island wake colder and chl-a higher.

Wake field measurements

International Nuclear Information System (INIS)

Palumbo, L.

1989-01-01

In this paper the concept of Wakefields and Machine Impedance are introduced. Several measurements technique of these quantities either in the laboratory before installation or from beam observation are presented

Large-eddy simulation of shallow turbulent wakes behind a conical island

Science.gov (United States)

Ouro, Pablo; Wilson, Catherine A. M. E.; Evans, Paul; Angeloudis, Athanasios

2017-12-01

Large-Eddy Simulations (LESs) and experiments were employed to study the influence of water depth on the hydrodynamics in the wake of a conical island for emergent, shallow, and deeply submerged conditions. The Reynolds numbers based on the island's base diameter for these conditions range from 6500 to 8125. LES results from the two shallower conditions were validated against experimental measurements from an open channel flume and captured the characteristic flow structures around the cone, including the attached recirculation region, vortex shedding, and separated shear layers. The wake was impacted by the transition from emergent to shallow submerged flow conditions with more subtle changes in time-averaged velocity and instantaneous flow structures when the submergence increases further. Despite differences in the breakdown of the separated shear layers, vortex shedding, and the upward flow region on the leeward face (once the cone's apex is submerged), similar flow structures to cylinder flow were observed. These include an arch vortex tilted in the downstream direction and von Karman vortices in the far-wake. Spectra of velocity time series and the drag coefficient indicated that the vortex shedding was constrained by the overtopping flow layer, and thus the shedding frequency decreased as the cone's apex became submerged. Finally, the generalised flow structures in the wake of a submerged conical body are outlined.

Regulation of Neuron-Astrocyte Metabolic Coupling across the Sleep-Wake Cycle

KAUST Repository

Petit, Jean-Marie

2015-12-17

Over the last thirty years, a growing number of studies showed that astrocytes play a pivotal role in the energy support to synapses. More precisely, astrocytes adjust the energy production to the neuronal energy needs through different mechanisms grouped under the term “neurometabolic coupling” (NMC). In this review we describe these mechanisms of coupling and how they involve astrocytes. From a physiological point of view, these mechanisms of coupling are particularly important to ensure normal synaptic functioning when neurons undergo rapid and repetitive changes in firing rate such as during the sleep/wake transitions. Investigations on brain energy metabolism during the sleep/wake cycle have been mainly focused on glucose consumption and on glycogen metabolism. However, the recent development of substrate-specific biosensors allowed measurements of the variation in extracellular levels of glutamate, glucose and lactate with a time resolution compatible with sleep stage duration. Together with gene expression data these experiments allowed to better define the variations of energy metabolites regulation across the sleep/wake cycle. The aim of this review is to bring into perspective the role of astrocytes and neurometabolic coupling in the regulation of the sleep/wake cycle. The data reviewed also suggest an important role of the astrocytic network. In addition, the role of astrocytes in NMC mechanisms is consistent with the “local and use dependent” sleep hypothesis.

Methods to determine fast-ion distribution functions from multi-diagnostic measurements

DEFF Research Database (Denmark)

Jacobsen, Asger Schou; Salewski, Mirko

-ion diagnostic views, it is possible to infer the distribution function using a tomography approach. Several inversion methods for solving this tomography problem in velocity space are implemented and compared. It is found that the best quality it obtained when using inversion methods which penalise steep......Understanding the behaviour of fast ions in a fusion plasma is very important, since the fusion-born alpha particles are expected to be the main source of heating in a fusion power plant. Preferably, the entire fast-ion velocity-space distribution function would be measured. However, no fast...

Do building wakes increase ground level concentrations?

International Nuclear Information System (INIS)

Taylor, T.J.; Melbourne, W.H.

1996-01-01

As part of the EPRI Plume Rise and Downwash Project to develop and evaluate new mathematical algorithms representing plume rise and downwash, physical model studies were performed on the plume dispersion from Combustion Turbine Unit 4, (CT 4), at the Jersey Central Power and Light Sayreville Generating Station, Sayreville, New Jersey. Studies were performed both in neutral and stably stratified model atmospheric boundary layer conditions with the primary objective being to determine the behavior of the combustion turbine plume under high and low ambient wind speed conditions within the wake region produced by the combustion turbine itself. Field measurements were also performed at the site and to this end a base case wind direction of β = 335 degree was chosen for both the field and model studies in an attempt to minimize the effects of other building wakes on the plume. This paper looks at the flow and dispersion characteristics with and without these large structures in the model in an attempt to explain why the differences in concentration levels occurred

Particle image and acoustic Doppler velocimetry analysis of a cross-flow turbine wake

Science.gov (United States)

Strom, Benjamin; Brunton, Steven; Polagye, Brian

2017-11-01

Cross-flow turbines have advantageous properties for converting kinetic energy in wind and water currents to rotational mechanical energy and subsequently electrical power. A thorough understanding of cross-flow turbine wakes aids understanding of rotor flow physics, assists geometric array design, and informs control strategies for individual turbines in arrays. In this work, the wake physics of a scale model cross-flow turbine are investigated experimentally. Three-component velocity measurements are taken downstream of a two-bladed turbine in a recirculating water channel. Time-resolved stereoscopic particle image and acoustic Doppler velocimetry are compared for planes normal to and distributed along the turbine rotational axis. Wake features are described using proper orthogonal decomposition, dynamic mode decomposition, and the finite-time Lyapunov exponent. Consequences for downstream turbine placement are discussed in conjunction with two-turbine array experiments.

Passive propulsion in vortex wakes

Science.gov (United States)

Beal, D. N.; Hover, F. S.; Triantafyllou, M. S.; Liao, J. C.; Lauder, G. V.

A dead fish is propelled upstream when its flexible body resonates with oncoming vortices formed in the wake of a bluff cylinder, despite being well outside the suction region of the cylinder. Within this passive propulsion mode, the body of the fish extracts sufficient energy from the oncoming vortices to develop thrust to overcome its own drag. In a similar turbulent wake and at roughly the same distance behind a bluff cylinder, a passively mounted high-aspect-ratio foil is also shown to propel itself upstream employing a similar flow energy extraction mechanism. In this case, mechanical energy is extracted from the flow at the same time that thrust is produced. These results prove experimentally that, under proper conditions, a body can follow at a distance or even catch up to another upstream body without expending any energy of its own. This observation is also significant in the development of low-drag energy harvesting devices, and in the energetics of fish dwelling in flowing water and swimming behind wake-forming obstacles.

Association between waking electroencephalography and cognitive event-related potentials in patients with obstructive sleep apnea.

Science.gov (United States)

Baril, Andrée-Ann; Gagnon, Katia; Gagnon, Jean-François; Montplaisir, Jacques; Gosselin, Nadia

2013-07-01

Sleepiness, cognitive deficits, abnormal event-related potentials (ERP), and slowing of the waking electroencephalography (EEG) activity have been reported in patients with obstructive sleep apnea (OSA). Our study aimed at evaluating if an association exists between the severity of ERP abnormalities and EEG slowing to better understand cerebral dysfunctions in OSA. Twelve OSA patients and 12 age-matched controls underwent an overnight polysomnographic recording, an EEG recording of 10 min of wakefulness, and an auditory ERP protocol known to specifically recruit attention. P300 and P3a ERP components were measured as well as the spectral power in each frequency band of the waking EEG. Pearson product moment correlations were used to measure associations between ERP characteristics and EEG spectral power in OSA patients and control subjects. A positive correlation between the late P300 amplitude and θ power in the occipital region was observed in OSA subjects (P<.01). A positive correlation was also found between P3a amplitude and β1 power in central region in OSA subjects (P<.01). No correlation was observed for control subjects. ERP abnormalities observed in an attention task are associated with a slowing of the waking EEG recorded at rest in OSA. Copyright © 2013 Elsevier B.V. All rights reserved.

Low-dimensional analysis, using POD, for two mixing layer-wake interactions

International Nuclear Information System (INIS)

Braud, Caroline; Heitz, Dominique; Arroyo, Georges; Perret, Laurent; Delville, Joeel; Bonnet, Jean-Paul

2004-01-01

The mixing layer-wake interaction is studied experimentally in the framework of two flow configurations. For the first one, the initial conditions of the mixing layer are modified by using a thick trailing edge, a wake effect is therefore superimposed to the mixing layer from its beginning (blunt trailing edge). In the second flow configuration, a canonical mixing layer is perturbed in its asymptotic region by the wake of a cylinder arranged perpendicular to the plane of the mixing layer. These interactions are analyzed mainly by using two-point velocity correlations and the proper orthogonal decomposition (POD). These two flow configurations differ by the degree of complexity they involve: the former is mainly 2D while the latter is highly 3D. The blunt trailing edge configuration is analyzed by using rakes of hot wire probes. This flow configuration is found to be considerably different when compared to a conventional mixing layer. It appears in particular that the scale of the large structures depends only on the trailing edge thickness and does not grow in its downstream evolution. A criterion, based on POD, is proposed in order to separate wake-mixing layer dominant areas of the downstream evolution of the flow. The complex 3D dynamical behaviour resulting from the interaction between the canonical plane mixing layer and the wake of a cylinder is investigated using data arising from particle image velocimetry measurements. An analysis of the velocity correlations shows different length scales in the regions dominated by wake like structures and shear layer type structures. In order to characterize the particular organization in the plane of symmetry, a POD-Galerkin projection of the Navier-Stokes equations is performed in this plane. This leads to a low-dimensional dynamical system that allows the analysis of the relationship between the dominant frequencies to be performed. A reconstruction of the dominant periodic motion suspected from previous studies is

Experimental investigation of main rotor wake

Directory of Open Access Journals (Sweden)

Stepanov Robert

2017-01-01

Full Text Available In this work, experimental results of rotor wake in hover mode are presented. The experiments were carried out with a rotor rig model in the T-1K wind tunnel in Kazan National Research Technical University (Kazan Aviation Institute. The rotor consisted of four identical blades. The Q-criterion was used to identify tip vortices for a 2D case. The results were then compared with two different wake models.

Dynamics of fast ions during sawtooth oscillations in the TEXTOR tokamak measured by collective Thomson scattering

DEFF Research Database (Denmark)

Nielsen, Stefan Kragh; Salewski, Mirko; Bindslev, Henrik

2011-01-01

Experimental investigations of sawteeth interaction with fast ions measured by collective Thomson scattering on TEXTOR are presented. Time-resolved measurements of localized 1D fast-ion distribution functions allow us to study fast-ion dynamics during several sawtooth cycles. Sawtooth oscillation...

Two improvements to the dynamic wake meandering model: including the effects of atmospheric shear on wake turbulence and incorporating turbulence build-up in a row of wind turbines

DEFF Research Database (Denmark)

Keck, Rolf-Erik; de Mare, Martin Tobias; Churchfield, Matthew J.

2015-01-01

The dynamic wake meandering (DWM) model is an engineering wake model designed to physically model the wake deficit evolution and the unsteady meandering that occurs in wind turbine wakes. The present study aims at improving two features of the model: The effect of the atmospheric boundary layer s...

Controlled Wake of a Moving Axisymmetric Bluff Body

Science.gov (United States)

Lee, E.; Vukasinovic, B.; Glezer, A.

2017-11-01

The aerodynamic loads exerted on a wire-mounted axisymmetric bluff body in prescribed rigid motion are controlled by fluidic manipulation of its near wake. The body is supported by a six-degree of freedom eight-wire traverse and its motion is controlled using a dedicated servo actuator and inline load cell for each wire. The instantaneous aerodynamic forces and moments on the moving body are manipulated by controlled interactions of an azimuthal array of integrated synthetic jet actuators with the cross flow to induce localized flow attachment over the body's aft end and thereby alter the symmetry of the wake. The coupled interactions between the wake structure and the effected aerodynamic loads during prescribed time-periodic and transitory (gust like) motions are investigated with emphasis on enhancing or diminishing the loads for maneuver control, and decoupling the body's motion from its far wake.

Cherenkov-type diamond detectors for measurements of fast electrons in the TORE-SUPRA tokamak

International Nuclear Information System (INIS)

Jakubowski, L.; Sadowski, M. J.; Zebrowski, J.; Rabinski, M.; Malinowski, K.; Mirowski, R.; Lotte, Ph.; Gunn, J.; Pascal, J-Y.; Colledani, G.; Basiuk, V.; Goniche, M.; Lipa, M.

2010-01-01

The paper presents a schematic design and tests of a system applicable for measurements of fast electron pulses emitted from high-temperature plasma generated inside magnetic confinement fusion machines, and particularly in the TORE-SUPRA facility. The diagnostic system based on the registration of the Cherenkov radiation induced by fast electrons within selected solid radiators is considered, and electron low-energy thresholds for different radiators are given. There are some estimates of high thermal loads, which might be deposited by intense electron beams upon parts of the diagnostic equipment within the TORE-SUPRA device. There are some proposed measures to overcome this difficulty by the selection of appropriate absorption filters and Cherenkov radiators, and particularly by the application of a fast-moving reciprocating probe. The paper describes the measuring system, its tests, as well as some results of the preliminary measurements of fast electrons within TORE-SUPRA facility.

Cherenkov-type diamond detectors for measurements of fast electrons in the TORE-SUPRA tokamak

Energy Technology Data Exchange (ETDEWEB)

Jakubowski, L.; Sadowski, M. J.; Zebrowski, J.; Rabinski, M.; Malinowski, K.; Mirowski, R. [Andrzej Soltan Institute for Nuclear Studies (IPJ), Otwock-Swierk 05-400 (Poland); Lotte, Ph.; Gunn, J.; Pascal, J-Y.; Colledani, G.; Basiuk, V.; Goniche, M.; Lipa, M. [CEA, IRFM, St Paul-lez-Durance F-13108 (France)

2010-01-15

The paper presents a schematic design and tests of a system applicable for measurements of fast electron pulses emitted from high-temperature plasma generated inside magnetic confinement fusion machines, and particularly in the TORE-SUPRA facility. The diagnostic system based on the registration of the Cherenkov radiation induced by fast electrons within selected solid radiators is considered, and electron low-energy thresholds for different radiators are given. There are some estimates of high thermal loads, which might be deposited by intense electron beams upon parts of the diagnostic equipment within the TORE-SUPRA device. There are some proposed measures to overcome this difficulty by the selection of appropriate absorption filters and Cherenkov radiators, and particularly by the application of a fast-moving reciprocating probe. The paper describes the measuring system, its tests, as well as some results of the preliminary measurements of fast electrons within TORE-SUPRA facility.

The resonant wake field transformer (RWT)-collider

International Nuclear Information System (INIS)

Weiland, T.; Holtkamp, N.; Schuett, P.; Wanzenberg, R.

1990-01-01

Future e + e - Linear Colliders with center of mass energies of 2 TeV need average accelerating gradients of 100 MeV/m to be built within a length of 20 km. The gradients required by colliders at this energy range can be economically provided by resonant Wake Field Transformers. At the Wake Field Experiment at DESY (Deutsches Elektronen-Synchrotron) a 20 cm long transformer section was investigated and the most recent results are presented. The second part gives a short overview of the present status of research concerning the proposed next stage of a multibunch driver linac with superconducting cavities and long Wake Field Transformer sections. (author) 9 refs.; 5 figs.; 1 tab

Wind Farm Wake: The Horns Rev Photo Case

DEFF Research Database (Denmark)

Hasager, Charlotte Bay; Rasmussen, Leif; Peña, Alfredo

2013-01-01

The aim of the paper is to examine the nowadays well-known wind farm wake photographs taken on 12 February 2008 at the offshore Horns Rev 1 wind farm. The meteorological conditions are described from observations from several satellite sensors quantifying clouds, surface wind vectors and sea surf...... in the wake regions with relatively high axial velocities and high turbulent kinetic energy. The wind speed is near cut-in and most turbines produce very little power. The rotational pattern of spiraling bands produces the large-scale structure of the wake fog....

An Aeroelastic Perspective of Floating Offshore Wind Turbine Wake Formation and Instability

Science.gov (United States)

Rodriguez, Steven N.; Jaworski, Justin W.

2015-11-01

The wake formation and wake stability of floating offshore wind turbines are investigated from an aeroelastic perspective. The aeroelastic model is composed of the Sebastian-Lackner free-vortex wake aerodynamic model coupled to the nonlinear Hodges-Dowell beam equations, which are extended to include the effects of blade profile asymmetry, higher-order torsional effects, and kinetic energy components associated with periodic rigid-body motions of floating platforms. Rigid-body platform motions are also assigned to the aerodynamic model as varying inflow conditions to emulate operational rotor-wake interactions. Careful attention is given to the wake formation within operational states where the ratio of inflow velocity to induced velocity is over 50%. These states are most susceptible to aerodynamic instabilities, and provide a range of states about which a wake stability analysis can be performed. In addition, the stability analysis used for the numerical framework is implemented into a standalone free-vortex wake aerodynamic model. Both aeroelastic and standalone aerodynamic results are compared to evaluate the level of impact that flexible blades have on the wake formation and wake stability.

Circadian Rhythm Sleep-Wake Disorders.

Science.gov (United States)

Abbott, Sabra M; Reid, Kathryn J; Zee, Phyllis C

2015-12-01

The circadian system regulates the timing and expression of nearly all biological processes, most notably, the sleep-wake cycle, and disruption of this system can result in adverse effects on both physical and mental health. The circadian rhythm sleep-wake disorders (CRSWDs) consist of 5 disorders that are due primarily to pathology of the circadian clock or to a misalignment of the timing of the endogenous circadian rhythm with the environment. This article outlines the nature of these disorders, the association of many of these disorders with psychiatric illness, and available treatment options. Copyright © 2015 Elsevier Inc. All rights reserved.

Fast-acting calorimeter measures heat output of plasma gun accelerator

Science.gov (United States)

Dethlefson, R.; Larson, A. V.; Liebing, L.

1967-01-01

Calorimeter measures the exhaust energy from a shot of a pulsed plasma gun accelerator. It has a fast response time and requires only one measurement to determine the total energy. It uses a long ribbon of copper foil wound around a glass frame to form a reentrant cavity.

Differential Effects of an Alpha-2 Agonist on Wakefulness and Paradoxical Sleep in The Rat: A Polygraphic and Biochemical Approach

Directory of Open Access Journals (Sweden)

Z. de Saint Hilaire

1997-01-01

Full Text Available The purpose of this experiment was to determine the sensitivity of wakefulness and paradoxical sleep to the α2-agonist, c1onidine. The drug inhibited both wakefulness and paradoxical sleep but the smallest dose necessary to inhibit wakefulness was 64 times larger than the smallest dose inhibiting paradoxical sleep. The effect on paradoxical sleep was inhibitory for all the clonidine doses but wakefulness was enhanced transiently after the four largest doses used. The time between injection and maximum wakefulness enhancement was highly correlated with the dose of c1onidine. The brain level measured after these four different doses at the moment of maximum wakefulness enhancement was the same, suggesting that this effect occurred only when a critical concentration of the drug was attained in the brain and not when the concentration was higher or lower. These data suggest that different α2-adrenoceptors are involved in these two states of vigilance or, alternatively, that their sensitivity is modulated physiologically. In addition, a sensitivity imbalance between different α2-adrenoceptors may exist in wakefulness but not in paradoxical sleep.

Measuring Fast Calcium Fluxes in Cardiomyocytes

Science.gov (United States)

Golebiewska, Urszula; Scarlata, Suzanne

2011-01-01

Cardiomyocytes have multiple Ca2+ fluxes of varying duration that work together to optimize function 1,2. Changes in Ca2+ activity in response to extracellular agents is predominantly regulated by the phospholipase Cβ- Gαq pathway localized on the plasma membrane which is stimulated by agents such as acetylcholine 3,4. We have recently found that plasma membrane protein domains called caveolae5,6 can entrap activated Gαq7. This entrapment has the effect of stabilizing the activated state of Gαq and resulting in prolonged Ca2+ signals in cardiomyocytes and other cell types8. We uncovered this surprising result by measuring dynamic calcium responses on a fast scale in living cardiomyocytes. Briefly, cells are loaded with a fluorescent Ca2+ indicator. In our studies, we used Ca2+ Green (Invitrogen, Inc.) which exhibits an increase in fluorescence emission intensity upon binding of calcium ions. The fluorescence intensity is then recorded for using a line-scan mode of a laser scanning confocal microscope. This method allows rapid acquisition of the time course of fluorescence intensity in pixels along a selected line, producing several hundreds of time traces on the microsecond time scale. These very fast traces are transferred into excel and then into Sigmaplot for analysis, and are compared to traces obtained for electronic noise, free dye, and other controls. To dissect Ca2+ responses of different flux rates, we performed a histogram analysis that binned pixel intensities with time. Binning allows us to group over 500 traces of scans and visualize the compiled results spatially and temporally on a single plot. Thus, the slow Ca2+ waves that are difficult to discern when the scans are overlaid due to different peak placement and noise, can be readily seen in the binned histograms. Very fast fluxes in the time scale of the measurement show a narrow distribution of intensities in the very short time bins whereas longer Ca2+ waves show binned data with a broad

Airfoil-Wake Modification with Gurney Flap at Low Reynolds Number

Science.gov (United States)

Gopalakrishnan Meena, Muralikrishnan; Taira, Kunihiko; Asai, Keisuke

2018-04-01

The complex wake modifications produced by a Gurney flap on symmetric NACA airfoils at low Reynolds number are investigated. Two-dimensional incompressible flows over NACA 0000 (flat plate), 0006, 0012 and 0018 airfoils at a Reynolds number of $Re = 1000$ are analyzed numerically to examine the flow modifications generated by the flaps for achieving lift enhancement. While high lift can be attained by the Gurney flap on airfoils at high angles of attack, highly unsteady nature of the aerodynamic forces are also observed. Analysis of the wake structures along with the lift spectra reveals four characteristic wake modes (steady, 2S, P and 2P), influencing the aerodynamic performance. The effects of the flap over wide range of angles of attack and flap heights are considered to identify the occurrence of these wake modes, and are encapsulated in a wake classification diagram. Companion three-dimensional simulations are also performed to examine the influence of three-dimensionality on the wake regimes. The spanwise instabilities that appear for higher angles of attack are found to suppress the emergence of the 2P mode. The use of the wake classification diagram as a guidance for Gurney flap selection at different operating conditions to achieve the required aerodynamic performance is discussed.

Widespread changes in white matter microstructure after a day of waking and sleep deprivation.

Directory of Open Access Journals (Sweden)

Torbjørn Elvsåshagen

Full Text Available Elucidating the neurobiological effects of sleep and waking remains an important goal of the neurosciences. Recently, animal studies indicated that sleep is important for cell membrane and myelin maintenance in the brain and that these structures are particularly susceptible to insufficient sleep. Here, we tested the hypothesis that a day of waking and sleep deprivation would be associated with changes in diffusion tensor imaging (DTI indices of white matter microstructure sensitive to axonal membrane and myelin alterations.Twenty-one healthy adult males underwent DTI in the morning [7:30AM; time point (TP1], after 14 hours of waking (TP2, and then after another 9 hours of waking (TP3. Whole brain voxel-wise analysis was performed with tract based spatial statistics.A day of waking was associated with widespread increases in white matter fractional anisotropy, which were mainly driven by radial diffusivity reductions, and sleep deprivation was associated with widespread fractional anisotropy decreases, which were mainly explained by reductions in axial diffusivity. In addition, larger decreases in axial diffusivity after sleep deprivation were associated with greater sleepiness. All DTI changes remained significant after adjusting for hydration measures.This is the first DTI study of sleep deprivation in humans. Although previous studies have observed localized changes in DTI indices of cerebral microstructure over the course of a few hours, further studies are needed to confirm widespread DTI changes within hours of waking and to clarify whether such changes in white matter microstructure serve as neurobiological substrates of sleepiness.

Ion-wake Field inside a Glass Box

OpenAIRE

Chen, Mudi; Dropmann, Michael; Zhang, Bo; Matthews, Lorin S.; Hyde, Truell W.

2016-01-01

The confinement provided by a glass box is proving ideal for the formation of vertically aligned structures and a convenient method for controlling the number of dust particles comprising these dust structures, as well as their size and shape. In this paper, the electronic confinement of the glass box is mapped and the particle interactions between the particle pairs inside the glass box are measured. The ion-wake field is shown to exist within the glass box and its vertical and horizontal ex...

FAST DIFFERENTIAL EMISSION MEASURE INVERSION OF SOLAR CORONAL DATA

Energy Technology Data Exchange (ETDEWEB)

Plowman, Joseph; Kankelborg, Charles; Martens, Petrus [Montana State University, Bozeman, MT 59717 (United States)

2013-07-01

We present a fast method for reconstructing differential emission measures (DEMs) using solar coronal data. The method consists of a fast, simple regularized inversion in conjunction with an iteration scheme for removal of residual negative emission measure. On average, it computes over 1000 DEMs s{sup -1} for a sample active region observed by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory, and achieves reduced chi-squared of order unity with no negative emission in all but a few test cases. The high performance of this method is especially relevant in the context of AIA, which images of order one million solar pixels per second. This paper describes the method, analyzes its fidelity, compares its performance and results with other DEM methods, and applies it to an active region and loop observed by AIA and by the Extreme-ultraviolet Imaging Spectrometer on Hinode.

A Survey of the Scattering Characteristics and Detection of Aircraft Wake Vortices

Directory of Open Access Journals (Sweden)

Li Jianbing

2017-12-01

Full Text Available Aircraft wake vortex is a pair of strong counter-rotating vortices and has attracted considerable attention in various fields including aviation safety and atmospheric physics. The characteristics and detection of wake vortex act as the basis for both behavior prediction as well as hazard assessment. This paper provides a short survey of the characteristics and detection researches. Initially, the wake vortex is classified as clear-air wake vortex (i.e., wake turbulence and contrail and precipitation wake vortex (i.e., under rainy, foggy or snowy condition. Subsequently, the dynamics and scattering are introduced, and the main verdicts are: the radar (radio detection and ranging scattering of wake vortex is relatively weak under clear air conditions, but the Lidar (Light detection and ranging scattering is appreciable owing to the presence of particles such as aerosols. Wake vortices under precipitation conditions and contrails possess relatively good radar reflectivity owing the strong scattering characteristics of precipitation droplets and ice crystals. Furthermore, we have introduced a joint detection scheme of Lidar and radar for wake vortex along with parameter-retrieval algorithms. Finally, we have presented our conclusions and intended future research.

Self-similarity of far wake behind tandem of two disks

DEFF Research Database (Denmark)

Okulov, Valery; Litvinov, I. V.; Naumov, I. V.

2017-01-01

the wake ceased to differ from the background of natural turbulent fluctuations of the incident flow. It has been found that the position of the second disk in the tandem affects the energy loss in the wake due to its expansion but does not influence the decay. The revealed patterns in the wake development...

Impact of bubble wakes on a developing bubble flow in a vertical pipe

International Nuclear Information System (INIS)

Tomiyama, A.; Makino, Y.; Miyoshi, K.; Tamai, H.; Serizawa, A.; Zun, I.

1998-01-01

Three-dimensional two-way bubble tracking simulation of single large air bubbles rising through a stagnant water filled in a vertical pipe was conducted to investigate the structures of bubble wakes. Spatial distributions of time-averaged liquid velocity field, turbulent intensity and Reynolds stress caused by bubble wakes were deduced from the calculated local instantaneous liquid velocities. It was confirmed that wake structures are completely different from the ones estimated by a conventional wake model. Then, we developed a simple wake model based on the predicted time-averaged wake velocity fields, and implemented it into a 3D one-way bubble tracking method to examine the impact of bubble wake structures on time-spatial evolution of a developing air-water bubble flow in a vertical pipe. As a results, we confirmed that the developed wake model can give better prediction for flow pattern evolution than a conventional wake model

Computational study of three-dimensional wake structure

International Nuclear Information System (INIS)

Himeno, R.; Shirayama, S.; Kamo, K.; Kuwahara, K.

1986-01-01

Three-dimensional wake structure is studied by numerically solving the incompressible Navier-Stokes equations. Results are visualized by a three-dimensional color graphic system. It was found that a pair of vortex tubes separated from a body plays the most important role in the wake. Near the body vortex tubes are rather stable, however, they gradually become unsteady as they flow down

On the Effects of Wind Turbine Wake Skew Caused by Wind Veer: Preprint

Energy Technology Data Exchange (ETDEWEB)

Churchfield, Matthew J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sirnivas, Senu [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

2018-03-01

Because of Coriolis forces caused by the Earth's rotation, the structure of the atmospheric boundary layer often contains wind-direction change with height, also known as wind-direction veer. Under low turbulence conditions, such as in stably stratified atmospheric conditions, this veer can be significant, even across the vertical extent of a wind turbine's rotor disk. The veer then causes the wind turbine wake to skew as it advects downstream. This wake skew has been observed both experimentally and numerically. In this work, we attempt to examine the wake skewing process in some detail, and quantify how differently a skewed wake versus a non skewed wake affects a downstream turbine. We do this by performing atmospheric large-eddy simulations to create turbulent inflow winds with and without veer. In the veer case, there is a roughly 8 degree wind direction change across the turbine rotor. We then perform subsequent large-eddy simulations using these inflow data with an actuator line rotor model to create wakes. The turbine modeled is a large, modern, offshore, multimegawatt turbine. We examine the unsteady wake data in detail and show that the skewed wake recovers faster than the non skewed wake. We also show that the wake deficit does not skew to the same degree that a passive tracer would if subject to veered inflow. Last, we use the wake data to place a hypothetical turbine 9 rotor diameters downstream by running aeroelastic simulations with the simulated wake data. We see differences in power and loads if this downstream turbine is subject to a skewed or non skewed wake. We feel that the differences observed between the skewed and nonskewed wake are important enough that the skewing effect should be included in engineering wake models.

Experimental Analysis of a Bubble Wake Influenced by a Vortex Street

Directory of Open Access Journals (Sweden)

Sophie Rüttinger

2018-01-01

Full Text Available Bubble column reactors are ubiquitous in engineering processes. They are used in waste water treatment, as well as in the chemical, pharmaceutical, biological and food industry. Mass transfer and mixing, as well as biochemical or chemical reactions in such reactors are determined by the hydrodynamics of the bubbly flow. The hydrodynamics of bubbly flows is dominated by bubble wake interactions. Despite the fact that bubble wakes have been investigated intensively in the past, there is still a lack of knowledge about how mass transfer from bubbles is influenced by bubble wake interactions in detail. The scientific scope of this work is to answer the question how bubble wakes are influenced by external flow structures like a vortex street behind a cylinder. For this purpose, the flow field in the vicinity of a single bubble is investigated systematically with high spatial and temporal resolution. High-speed Particle Image Velocimetry (PIV measurements are conducted monitoring the flow structure in the equatorial plane of the single bubble. It is shown that the root mean square (RMS velocity profiles downstream the bubble are influenced significantly by the interaction of vortices. In the presence of a vortex street, the deceleration of the fluid behind the bubble is compensated earlier than in the absence of a vortex street. This happens due to momentum transfer by cross-mixing. Both effects indicate that the interaction of vortices enhances the cross-mixing close to the bubble. Time series of instantaneous velocity fields show the formation of an inner shear layer and coupled vortices. In conclusion, this study shows in detail how the bubble wake is influenced by a vortex street and gives deep insights into possible effects on mixing and mass transfer in bubbly flows.

A review of recent wake vortex research for increasing airport capacity

Science.gov (United States)

Hallock, James N.; Holzäpfel, Frank

2018-04-01

This paper is a brief review of recent wake vortex research as it affects the operational problem of spacing aircraft to increase airport capacity and throughput. The paper addresses the questions of what do we know about wake vortices and what don't we know about wake vortices. The introduction of Heavy jets in the late 1960s stimulated the study of wake vortices for safety reasons and the use of pulsed lidars and the maturity of computational fluid dynamics in the last three decades have led to extensive data collection and analyses which are now resulting in the development and implementation of systems to safely decrease separations in the terminal environment. Although much has been learned about wake vortices and their behavior, there is still more to be learned about the phenomena of aircraft wake vortices.

Effects of superhydrophobic surface on the propeller wake

Science.gov (United States)

Choi, Hongseok; Lee, Jungjin; Park, Hyungmin

2017-11-01

This study investigates the change in propeller wake when the superhydrophobic surface is applied on the propeller blade. The propeller rotates in a quiescent water tank, facing its bottom, with a rotational Reynolds number of 96000. To measure the three-dimensional flow fields, we use stereo PIV and a water prism is installed at the camera-side tank wall. Two cameras are tilted 30 degrees from the normal axis of the tank wall, satisfying schiempflug condition. Superhydrophobic surface is made by coating hydrophobic nanoparticles on the propeller blade. Measurements are done on two vertical planes (at the center of propeller hub and the blade tip), and are ensemble averaged being classified by blade phase of 0 and 90 degrees. Velocity fluctuation, turbulent kinetic energy, and vorticity are evaluated. With superhydrophobic surface, it is found that the turbulence level is significantly (20 - 30 %) reduced with a small penalty (less than 5%) in the streamwise momentum (i.e., thrust) generation. This is because the cone shaped propeller wake gets narrower and organized vortex structures are broken with the superhydrophobic surfaces. More detailed flow analysis will be given. Supported by NRF (NRF-2016R1C1B2012775, NRF-2016M2B2A9A02945068) programs of Korea government.

CFD three dimensional wake analysis in complex terrain

Science.gov (United States)

Castellani, F.; Astolfi, D.; Terzi, L.

2017-11-01

Even if wind energy technology is nowadays fully developed, the use of wind energy in very complex terrain is still challenging. In particular, it is challenging to characterize the combination effects of wind ow over complex terrain and wake interactions between nearby turbines and this has a practical relevance too, for the perspective of mitigating anomalous vibrations and loads as well improving the farm efficiency. In this work, a very complex terrain site has been analyzed through a Reynolds-averaged CFD (Computational Fluid Dynamics) numerical wind field model; in the simulation the inuence of wakes has been included through the Actuator Disk (AD) approach. In particular, the upstream turbine of a cluster of 4 wind turbines having 2.3 MW of rated power is studied. The objective of this study is investigating the full three-dimensional wind field and the impact of three-dimensionality on the evolution of the waked area between nearby turbines. A post-processing method of the output of the CFD simulation is developed and this allows to estimate the wake lateral deviation and the wake width. The reliability of the numerical approach is inspired by and crosschecked through the analysis of the operational SCADA (Supervisory Control and Data Acquisition) data of the cluster of interest.

Wake field acceleration experiments

International Nuclear Information System (INIS)

Simpson, J.D.

1988-01-01

Where and how will wake field acceleration devices find use for other than, possibly, accelerators for high energy physics? I don't know that this can be responsibly answered at this time. What I can do is describe some recent results from an ongoing experimental program at Argonne which support the idea that wake field techniques and devices are potentially important for future accelerators. Perhaps this will spawn expanded interest and even new ideas for the use of this new technology. The Argonne program, and in particular the Advanced Accelerator Test Facility (AATF), has been reported in several fairly recent papers and reports. But because this is a substantially new audience for the subject, I will include a brief review of the program and the facility before describing experiments. 10 refs., 7 figs

High flux-fluence measurements in fast reactors

International Nuclear Information System (INIS)

Lippincott, E.P.; Ulseth, J.A.

1977-01-01

Characterization of irradiation environments for fuels and materials tests in fast reactors requires determination of the neutron flux integrated over times as long as several years. An accurate integration requires, therefore, passive dosimetry monitors with long half-life or stable products which can be conveniently measured. In addition, burn-up, burn-in, and burn-out effects must be considered in high flux situations and use of minimum quantities of dosimeter materials is often desirable. These conditions force the use of dosimeter and dosimeter container designs, measured products, and techniques that are different from those that are used in critical facilities and other well-characterized benchmark fields. Recent measurements in EBR-II indicate that high-accuracy results can be attained and that tie-backs to benchmark field technique calibrations can be accomplished

Regulation of neuron-astrocyte metabolic coupling across the sleep-wake cycle.

Science.gov (United States)

Petit, J-M; Magistretti, P J

2016-05-26

Over the last thirty years, a growing number of studies showed that astrocytes play a pivotal role in the energy support to synapses. More precisely, astrocytes adjust energy production to neuronal energy needs through different mechanisms grouped under the term "neurometabolic coupling" (NMC). In this review we describe these mechanisms of coupling and how they involve astrocytes. From a physiological point of view, these mechanisms of coupling are particularly important to ensure normal synaptic functioning when neurons undergo rapid and repetitive changes in the firing rate such as during the sleep/wake transitions. Investigations into brain energy metabolism during the sleep/wake cycle have been mainly focused on glucose (Gluc) consumption and on glycogen metabolism. However, the recent development of substrate-specific biosensors allowed measurements of the variation in extracellular levels of glutamate, Gluc and lactate (Lac) with a time resolution compatible with sleep stage duration. Together with gene expression data these experiments allowed to better define the variations of energy metabolite regulation across the sleep/wake cycle. The aim of this review is to bring into perspective the role of astrocytes and NMC in the regulation of the sleep/wake cycle. The data reviewed also suggest an important role of the astrocytic network. In addition, the role of astrocytes in NMC mechanisms is consistent with the "local and use dependent" sleep hypothesis. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

Comparison of the Dynamic Wake Meandering Model, Large-Eddy Simulation, and Field Data at the Egmond aan Zee Offshore Wind Plant: Preprint

Energy Technology Data Exchange (ETDEWEB)

Churchfield, M. J.; Moriarty, P. J.; Hao, Y.; Lackner, M. A.; Barthelmie, R.; Lundquist, J.; Oxley, G. S.

2014-12-01

The focus of this work is the comparison of the dynamic wake meandering model and large-eddy simulation with field data from the Egmond aan Zee offshore wind plant composed of 36 3-MW turbines. The field data includes meteorological mast measurements, SCADA information from all turbines, and strain-gauge data from two turbines. The dynamic wake meandering model and large-eddy simulation are means of computing unsteady wind plant aerodynamics, including the important unsteady meandering of wakes as they convect downstream and interact with other turbines and wakes. Both of these models are coupled to a turbine model such that power and mechanical loads of each turbine in the wind plant are computed. We are interested in how accurately different types of waking (e.g., direct versus partial waking), can be modeled, and how background turbulence level affects these loads. We show that both the dynamic wake meandering model and large-eddy simulation appear to underpredict power and overpredict fatigue loads because of wake effects, but it is unclear that they are really in error. This discrepancy may be caused by wind-direction uncertainty in the field data, which tends to make wake effects appear less pronounced.

Regimes of Vorticity in the Wake of a Rectangular Vortex Generator

DEFF Research Database (Denmark)

Velte, Clara Marika; Okulov, Valery; Hansen, Martin Otto Laver

2011-01-01

This paper concerns the study of the secondary structures generated in the wake of a wall mounted rectangular vane, commonly referred to as a vortex generator. The study has been conducted by Stereoscopic PIV measurements in a wind tunnel and supplementary flow visualizations in a water channel...

Estimation of unsteady aerodynamics in the wake of a freely flying European starling (Sturnus vulgaris.

Directory of Open Access Journals (Sweden)

Hadar Ben-Gida

Full Text Available Wing flapping is one of the most widespread propulsion methods found in nature; however, the current understanding of the aerodynamics in bird wakes is incomplete. The role of the unsteady motion in the flow and its contribution to the aerodynamics is still an open question. In the current study, the wake of a freely flying European starling has been investigated using long-duration high-speed Particle Image Velocimetry (PIV in the near wake. Kinematic analysis of the wings and body of the bird has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV measurements. The wake evolution of four complete wingbeats has been characterized through reconstruction of the time-resolved data, and the aerodynamics in the wake have been analyzed in terms of the streamwise forces acting on the bird. The profile drag from classical aerodynamics was found to be positive during most of the wingbeat cycle, yet kinematic images show that the bird does not decelerate. It is shown that unsteady aerodynamics are necessary to satisfy the drag/thrust balance by approximating the unsteady drag term. These findings may shed light on the flight efficiency of birds by providing a partial answer to how they minimize drag during flapping flight.

Optogenetic deconstruction of sleep-wake circuitry in the brain

Directory of Open Access Journals (Sweden)

Antoine Adamantidis

2010-01-01

Full Text Available How does the brain regulate the sleep-wake cycle? What are the temporal codes of sleep- and wake-promoting neural circuits? How do these circuits interact with each other across the light/dark cycle? Over the past few decades, many studies from a variety of disciplines have made substantial progress in answering these fundamental questions. For example, neurobiologists have identified multiple, redundant wake-promoting circuits in the brainstem, hypothalamus, and basal forebrain. Sleep-promoting circuits have been found in the preoptic area and hypothalamus. One of the greatest challenges in recent years has been to selectively record and manipulate these sleep-wake centers in vivo with high spatial and temporal resolution. Recent developments in microbial opsin-based neuromodulation tools, collectively referred to as “optogenetics,” have provided a novel method to demonstrate causal links between neural activity and specific behaviors. Here, we propose to use optogenetics as a fundamental tool to probe the necessity, sufficiency, and connectivity of defined neural circuits in the regulation of sleep and wakefulness.

Rotor Wake/Stator Interaction Noise Prediction Code Technical Documentation and User's Manual

Science.gov (United States)

Topol, David A.; Mathews, Douglas C.

2010-01-01

This report documents the improvements and enhancements made by Pratt & Whitney to two NASA programs which together will calculate noise from a rotor wake/stator interaction. The code is a combination of subroutines from two NASA programs with many new features added by Pratt & Whitney. To do a calculation V072 first uses a semi-empirical wake prediction to calculate the rotor wake characteristics at the stator leading edge. Results from the wake model are then automatically input into a rotor wake/stator interaction analytical noise prediction routine which calculates inlet aft sound power levels for the blade-passage-frequency tones and their harmonics, along with the complex radial mode amplitudes. The code allows for a noise calculation to be performed for a compressor rotor wake/stator interaction, a fan wake/FEGV interaction, or a fan wake/core stator interaction. This report is split into two parts, the first part discusses the technical documentation of the program as improved by Pratt & Whitney. The second part is a user's manual which describes how input files are created and how the code is run.

An overview of experimental results and dispersion modelling of nanoparticles in the wake of moving vehicles.

Science.gov (United States)

Carpentieri, Matteo; Kumar, Prashant; Robins, Alan

2011-03-01

Understanding the transformation of nanoparticles emitted from vehicles is essential for developing appropriate methods for treating fine scale particle dynamics in dispersion models. This article provides an overview of significant research work relevant to modelling the dispersion of pollutants, especially nanoparticles, in the wake of vehicles. Literature on vehicle wakes and nanoparticle dispersion is reviewed, taking into account field measurements, wind tunnel experiments and mathematical approaches. Field measurements and modelling studies highlighted the very short time scales associated with nanoparticle transformations in the first stages after the emission. These transformations strongly interact with the flow and turbulence fields immediately behind the vehicle, hence the need of characterising in detail the mixing processes in the vehicle wake. Very few studies have analysed this interaction and more research is needed to build a basis for model development. A possible approach is proposed and areas of further investigation identified. Copyright © 2010 Elsevier Ltd. All rights reserved.

TRANSVERSE MODES FOR FLAT INTER-BUNCH WAKES*

CERN Document Server

Burov, A

2013-01-01

If inter-bunch wake fields are flat, i.e. their variations over a bunch length can be neglected, all coherent modes have the same coupled-bunch structure, provided the bunches can be treated as identical by their inner qualities (train theorem). If a flat feedback is strong enough, the transverse modes are single-bunch, provided the inter-bunch wakes are also flat (damper theorem).

Determination of Wind Turbine Near-Wake Length Based on Stability Analysis

DEFF Research Database (Denmark)

Sørensen, Jens Nørkær; Mikkelsen, Robert Flemming; Sarmast, Sasan

2014-01-01

A numerical study on the wake behind a wind turbine is carried out focusing on determining the length of the near-wake based on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier-Stokes equati......A numerical study on the wake behind a wind turbine is carried out focusing on determining the length of the near-wake based on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier...... of the study it is found that the amplification of specific waves (traveling structures) along the tip vortex spirals is responsible for triggering the instability leading to wake breakdown. The presence of unstable modes in the wake is related to the mutual inductance (vortex pairing) instability where...

Linearity measurement of the XP 1210 fast photomultiplier tube

International Nuclear Information System (INIS)

Breuze, G.; Sawine, P.

1969-01-01

A new X Y method of photomultipliers linearity measurement has been tested which is more suitable for fast photomultiplier tubes. The XP 1210 gives a linearity limit of 70 mA for the gain 10, i.e. 3.5 V for a 50 Ω charge impedance

Numerical study on wake characteristics of high-speed trains

Science.gov (United States)

Yao, Shuan-Bao; Sun, Zhen-Xu; Guo, Di-Long; Chen, Da-Wei; Yang, Guo-Wei

2013-12-01

Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.

CSR Wake for a Short Magnet in Ultra-Relativistic Limit

International Nuclear Information System (INIS)

Emma, Paul J

2002-01-01

Using results for the CSR wake in a short magnet [1] we obtain expressions for the wake in the limit of very large values of the relativistic factor γ, γ → ∞, for both the entrance and exit of the magnet. The analytical results are illustrated with numerical computation of the wakes, energy loss and energy spread for magnets of different lengths

Comparison of Engineering Wake Models with CFD Simulations

DEFF Research Database (Denmark)

Andersen, Søren Juhl; Sørensen, Jens Nørkær; Ivanell, S.

2014-01-01

The engineering wake models by Jensen [1] and Frandsen et al. [2] are assessed for different scenarios simulated using Large Eddy Simulation and the Actuator Line method implemented in the Navier-Stokes equations. The scenarios include the far wake behind a single wind turbine, a long row of turb...

Wake Field of the e-Cloud

International Nuclear Information System (INIS)

Heifets, Samuel A

2001-01-01

The wake field of the cloud is derived analytically taking into account the finite size of the cloud and nonlinearity of the electron motion. The analytic expression for the effective transverse wake field caused by the electron cloud in a positron storage ring is derived. The derivation includes the frequency spread in the cloud, which is the main effect of the nonlinearity of electron motion in the cloud. This approach allows calculation of the Q-factor and study the tune spread in a bunch

The bestial feminine in Finnegans Wake

OpenAIRE

Lovejoy, Laura

2017-01-01

Female characters frequently appear as animals in the unstable universe of James Joyce’s a Finnegans Wake. What Kimberly Devlin terms “the male tendency to reduce women to the level of the beast” is manifest in Finnegans Wake on a large scale. From the hen pecking at a dung heap which we suppose is a manifestation of matriarch Anna Livia Plurabelle, to the often lascivious pig imagery (reminiscent of Bloom’s experience with brothel-keeper Bella in the “Circe” episode of Ulysses) associated wi...

Determination of Wind Turbine Near-Wake Length Based on Stability Analysis

International Nuclear Information System (INIS)

Sørensen, Jens N; Mikkelsen, Robert; Sarmast, Sasan; Ivanell, Stefan; Henningson, Dan

2014-01-01

A numerical study on the wake behind a wind turbine is carried out focusing on determining the length of the near-wake based on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier-Stokes equations using the actuator line (ACL) method. The wake is perturbed by applying stochastic or harmonic excitations in the neighborhood of the tips of the blades. The flow field is then analyzed to obtain the stability properties of the tip vortices in the wake of the wind turbine. As a main outcome of the study it is found that the amplification of specific waves (traveling structures) along the tip vortex spirals is responsible for triggering the instability leading to wake breakdown. The presence of unstable modes in the wake is related to the mutual inductance (vortex pairing) instability where there is an out-of-phase displacement of successive helix turns. Furthermore, using the non-dimensional growth rate, it is found that the pairing instability has a universal growth rate equal to π/2. Using this relationship, and the assumption that breakdown to turbulence occurs once a vortex has experienced sufficient growth, we provide an analytical relationship between the turbulence intensity and the stable wake length. The analysis leads to a simple expression for determining the length of the near wake. This expression shows that the near wake length is inversely proportional to thrust, tip speed ratio and the logarithmic of the turbulence intensity

Why Does REM Sleep Occur? A Wake-up Hypothesis

OpenAIRE

Dr. W. R. eKlemm

2011-01-01

Brain activity differs in the various sleep stages and in conscious wakefulness. Awakening from sleep requires restoration of the complex nerve impulse patterns in neuronal network assemblies necessary to re-create and sustain conscious wakefulness. Herein I propose that the brain uses REM to help wake itself up after it has had a sufficient amount of sleep. Evidence suggesting this hypothesis includes the facts that, 1) when first going to sleep, the brain plunges into Stage N3 (formerly ca...

{sup 20}F power measurement for generation IV sodium fast reactors

Energy Technology Data Exchange (ETDEWEB)

Coulon, R.; Normand, S.; Michel, M.; Barbot, L.; Domenech, T.; Boudergui, K.; Bourbotte, J.M.; Kondrasovs, V.; Frelin-Labalme, A.M.; Hamrita, H. [CEA, LIST, Laboratoire Capteurs et Architectures Electroniques, F-91191 Gif-sur-Yvette (France); BAN, G. [ENSICAEN, 6 Boulevard Marechal Juin, F-14050 Caen Cedex 4 (France); Barat, E.; Dautremer, T.; Montagu, T.; Carrel, F. [CEA, LIST, Laboratoire Modelisation Simulation et Systemes, F-91191 Gif-sur-Yvette (France); Brau, H.P. [ICSM, Centre de Marcoule, BP 17171 F-30207 Bagnols sur Ceze (France); Dumarcher, V. [AREVA NP, SET, F-84500 Bollene (France); Portier, J.L. [Centrale PHENIX, Centre de Marcoule, Groupe Essais Statistiques, F-30207 Bagnols sur Ceze (France); Jousset, P. [CEA, LIST, Laboratoire Capteurs Diamant, F-91191 Gif-sur-Yvette (France); Saurel, N. [CEA, DAM, Laboratoire Mesure de Dechets et Expertise, F-21120 Is-sur-Tille, France.F-84500 Bollene (France)

2010-07-01

The Phenix nuclear power plant has been a French Sodium Fast Reactor (SFR) prototype producing electrical power between 1973 and 2010. The power was monitored using ex-core neutron measurements. This kind of measurement instantly estimates the power but needs to be often calibrated with the heat balance thermodynamic measurement. Large safety and security margins have then been set not to derive above the nominal operating point. It is important for future SFR to reduce this margin and working closer to the nominal operating point. This work deals with the use of delayed gamma to measure the power. The main activation product contained in the primary sodium coolant is the {sup 24}Na which is not convenient for neutron flux measurement due to its long decay period. The experimental study done at the Phenix reactor shows that the use of {sup 20}F as power tagging agent gives a fast and accurate power measurement closed to the thermal balance measurement thanks to its high energy photon emission (1.634 MeV) and its short decay period (11 s). (authors)

Identification of vortex pairs in aircraft wakes from sectional velocity data

Science.gov (United States)

Carmer, Carl F. V.; Konrath, Robert; Schröder, Andreas; Monnier, Jean-Claude

2008-03-01

The dynamics of multiple-vortex wake systems behind aircraft endangering air traffic can be assessed also from physical modelling. Large-scale laboratory investigations of multiple-vortex systems have been performed in a free-flight laboratory and in a water towing tank. Specialized PIV measurements provide time-resolved flow velocity fields normal to the wake axis. The applicability of various ∇ u-based vortex identification schemes to planar velocity data is addressed and demonstrated for unequal-strength co- and counter-rotating vortex pairs. Large vortices shed off the wing tips and flaps are identified employing a ∇ u-based criterion. Their cooperative mechanisms of generation and decay are evidenced from iso-surfaces of squared swirling strength and from further characteristic vortex parameters.

Dynamic Hybrid Simulation of the Lunar Wake During ARTEMIS Crossing

Science.gov (United States)

Wiehle, S.; Plaschke, F.; Angelopoulos, V.; Auster, H.; Glassmeier, K.; Kriegel, H.; Motschmann, U. M.; Mueller, J.

2010-12-01

The interaction of the highly dynamic solar wind with the Moon is simulated with the A.I.K.E.F. (Adaptive Ion Kinetic Electron Fluid) code for the ARTEMIS P1 flyby on February 13, 2010. The A.I.K.E.F. hybrid plasma simulation code is the improved version of the Braunschweig code. It is able to automatically increase simulation grid resolution in areas of interest during runtime, which greatly increases resolution as well as performance. As the Moon has no intrinsic magnetic field and no ionosphere, the solar wind particles are absorbed at its surface, resulting in the formation of the lunar wake at the nightside. The solar wind magnetic field is basically convected through the Moon and the wake is slowly filled up with solar wind particles. However, this interaction is strongly influenced by the highly dynamic solar wind during the flyby. This is considered by a dynamic variation of the upstream conditions in the simulation using OMNI solar wind measurement data. By this method, a very good agreement between simulation and observations is achieved. The simulations show that the stationary structure of the lunar wake constitutes a tableau vivant in space representing the well-known Friedrichs diagram for MHD waves.

Wake Characteristics of a Flapping Wing Optimized for both Aerial and Aquatic Flight

Science.gov (United States)

Izraelevitz, Jacob; Kotidis, Miranda; Triantafyllou, Michael

2017-11-01

Multiple aquatic bird species (including murres, puffins, and other auks) employ a single actuator to propel themselves in two different fluid media: both flying and swimming using primarily their flapping wings. This impressive design compromise could be adopted by engineered implementations of dual aerial/aquatic robotic platforms, as it offers an existence proof for favorable flow physics. We discuss one realization of a 3D flapping wing actuation system for use in both air and water. The wing oscillates by the root and employs an active in-line motion degree-of-freedom. An experiment-coupled optimization routine generates the wing trajectories, controlling the unsteady forces throughout each flapping cycle. We elucidate the wakes of these wing trajectories using dye visualization, correlating the wake vortex structures with simultaneous force measurements. After optimization, the wing generates the large force envelope necessary for propulsion in both fluid media, and furthermore, demonstrate improved control over the unsteady wake.

Fast Plasma Potential Measurements Using an Emissive Probe

Science.gov (United States)

Ready, Amanda; Clark, Michael; Endrizzi, Douglass; Forest, Cary; Peterson, Ethan

2017-10-01

A heated emissive probe was developed for making direct plasma potential (Vp) measurements in rapidly fluctuating plasmas. Previous experiments on the Big Red Ball (BRB) were hindered by sudden potential drops, making Langmuir measurements of the plasma potential difficult. DC heating of a tungsten filament to emission allowed for fast (4 MHz) floating potential measurements that closely matched Vp. Two BRB experiments currently use the emissive probe. The investigation of unmagnetized, collisionless shocks used plasma potential measurements to study the sub-structure of strong plasma shocks. A separate investigation of emulated magnetospheres in laboratory plasmas used the plasma potential to map the equilibria and instabilities in the electric field of such structures. Results showing electric field measurements and comparison with cold Langmuir measurements will be presented. Future plans for probe modifications and applications to other experiments on the BRB will also be shown.

High-sensitive spectrometer of fast neutrons and the results of fast neutron background flux measurements at the Gallium-Germanium Solar Neutrino Experiment

CERN Document Server

Abdurashitov, J N; Kalikhov, A V; Matushko, V L; Shikhin, A A; Yants, V E; Zaborskaia, O S

2002-01-01

The principle of operation, design, registration system and main characteristics of a fast neutron spectrometer are described. The spectrometer is intended for direct measurements of ultra low fluxes of fast neutrons. It is sensitive to neutron fluxes of 10 sup - sup 7 cm sup - sup 2 s sup - sup 1 and lower. The detection efficiency of fast neutrons with simultaneous energy measurement was determined from Monte-Carlo simulation to be equal to 0.11+-0.01. The background counting rate in the detector corresponds to a neutron flux of (6.5+-2.1)x10 sup - sup 7 cm sup - sup 2 s sup - sup 1 in the range 1.0-11.0 MeV. The natural neutron flux from the surrounding mine rock at the depth of 4600 m of water equivalent was measured to be (7.3+-2.4)x10 sup - sup 7 cm sup - sup 2 s sup - sup 1 in the range 1.0-11.0 MeV. The flux of fast neutrons in the SAGE main room was measured to be <2.3x10 sup - sup 7 cm sup - sup 2 s sup - sup 1 in 1.0-11.0 MeV energy range.

Magnetic energy density and plasma energy density in the Venus wake

Science.gov (United States)

Perez De Tejada, H. A.; Durand-Manterola, H. J.; Lundin, R.; Barabash, S.; Zhang, T.; Reyes-Ruiz, M.; Sauvaud, J.

2013-05-01

Magnetic energy density and plasma energy density in the Venus wake H. Pérez-de-Tejada1, H. Durand-Manterola1, R. Lundin2, S. Barabash2, T. L. Zhang3, A. Sauvaud4, M. Reyes-Ruiz5. 1 - Institute of Geophysics, UNAM, México, D. F. 2 - Swedish Institute of Space Physics, Umea, Sweden 3 - Space Research Institute, Graz, Austria 4 - CESR, Toulouse, France 5 - Institute of Astronomy, UNAM, Ensenada, México Measurements conducted in the Venus wake with the magnetometer and the Aspera-4 plasma instrument of the Venus Express spacecraft show that average values of the kinetic energy density of the plasma in that region are comparable to average local values of the magnetic energy density. Observations were carried out in several orbits of the Venus Express near the midnight plane and suggest that the total energy content in the Venus wake is distributed with nearly comparable values between the plasma and the magnetic field. Processes associated with the solar wind erosion of planetary ions from the polar magnetic regions of the ionosphere are involved in the comparable distribution of both energy components.

Boat, wake, and wave real-time simulation

Science.gov (United States)

Świerkowski, Leszek; Gouthas, Efthimios; Christie, Chad L.; Williams, Owen M.

2009-05-01

We describe the extension of our real-time scene generation software VIRSuite to include the dynamic simulation of small boats and their wakes within an ocean environment. Extensive use has been made of the programmabilty available in the current generation of GPUs. We have demonstrated that real-time simulation is feasible, even including such complexities as dynamical calculation of the boat motion, wake generation and calculation of an FFTgenerated sea state.

Validation of fast-ion D-alpha spectrum measurements during EAST neutral-beam heated plasmas

Energy Technology Data Exchange (ETDEWEB)

Huang, J., E-mail: juan.huang@ipp.ac.cn; Wu, C. R.; Hou, Y. M.; Chang, J. F.; Ding, S. Y.; Chen, Y. J.; Jin, Z.; Xu, Z.; Gao, W.; Wang, J. F.; Lyu, B.; Zang, Q.; Zhong, G. Q.; Hu, L.; Wan, B. [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 Hefei, Anhui (China); Heidbrink, W. W.; Stagner, L.; Zhu, Y. B. [University of California, Irvine, California 92697 (United States); Hellermann, M. G. von [Diagnostic Team, ITER Organization, Route de Vinon-sur-Verdon 13067 St. Paul Lez Durance (France)

2016-11-15

To investigate the fast ion behavior, a fast ion D-alpha (FIDA) diagnostic system has been installed on EAST. Fast ion features can be inferred from the Doppler shifted spectrum of Balmer-alpha light from energetic hydrogenic atoms. This paper will focus on the validation of FIDA measurements performed using MHD-quiescent discharges in 2015 campaign. Two codes have been applied to calculate the D{sub α} spectrum: one is a Monte Carlo code, Fortran 90 version FIDASIM, and the other is an analytical code, Simulation of Spectra (SOS). The predicted SOS fast-ion spectrum agrees well with the measurement; however, the level of fast-ion part from FIDASIM is lower. The discrepancy is possibly due to the difference between FIDASIM and SOS velocity distribution function. The details will be presented in the paper to primarily address comparisons of predicted and observed spectrum shapes/amplitudes.

Cylinder wakes in flowing soap films

International Nuclear Information System (INIS)

Vorobieff, P.; Ecke, R.E.; Vorobieff, P.

1999-01-01

We present an experimental characterization of cylinder wakes in flowing soap films. From instantaneous velocity and thickness fields, we find the vortex-shedding frequency, mean-flow velocity, and mean-film thickness. Using the empirical relationship between the Reynolds and Strouhal numbers obtained for cylinder wakes in three dimensions, we estimate the effective soap-film viscosity and its dependence on film thickness. We also compare the decay of vorticity with that in a simple Rankine vortex model with a dissipative term to account for air drag. copyright 1999 The American Physical Society

Fast-ion dynamics in the TEXTOR tokamak measured by collective Thomson scattering

DEFF Research Database (Denmark)

Bindslev, H.; Nielsen, S.K.; Porte, L.

2006-01-01

Here we present the first measurements by collective Thomson scattering of the evolution of fast-ion populations in a magnetically confined fusion plasma. 150 kW and 110 Ghz radiation from a gyrotron were scattered in the TEXTOR tokamak plasma with energetic ions generated by neutral beam injection...... and ion cyclotron resonance heating. The temporal behavior of the spatially resolved fast-ion velocity distribution is inferred from the received scattered radiation. The fast-ion dynamics at sawteeth and the slowdown after switch off of auxiliary heating is resolved in time. The latter is shown...

High-sensitive spectrometer of fast neutrons and the results of fast neutron background flux measurements at the gallium-germanium solar neutrino experiment (SAGE)

International Nuclear Information System (INIS)

Abdurashitov, D.N.; Gavrin, V.N.; Kalikhov, A.V.; Matushko, V.L.; Shikhin, A.A.; Yants, V.E.; Zaborskaya, O.S.

2001-01-01

The principle of operation, design, registration system and main characteristics of a fast neutron spectrometer are described. The spectrometer is intended for direct measurements of ultra-low fluxes of fast neutrons. It is sensitive to neutron fluxes of 10 -7 cm -2 · s -1 and lower. The detection efficiency of fast neutrons with simultaneous energy measurement was determined from Monte-Carlo simulation to be equal to 0.11 ± 0.01. The background counting rate in the detector corresponds to a neutron flux of (6.5 ± 2.1) · 10 -7 cm -2 · s -1 in the range of 1.0-11.0 MeV. The natural neutron flux from the surrounding mine rock at the depth of 4600 meters of water equivalent was measured to be (7.3 ± 2.4) · 10 -7 cm -2 · s -1 in the interval 1.0 -11.0 MeV. The flux of fast neutrons in the SAGE main room was measured to be 2.3 · 10 -7 cm -2 · s -1 in 1.0 - 11.0 MeV energy range