Steady turbulent flow in curved rectangular channels
De Vriend, H.J.
1979-01-01
After the study of fully developed and developing steady laminar flow in curved channels of shallow rectangular wet cross-section (see earlier reports in this series), steady turbulent flow in such channels is investigated as a next step towards a mathematical model of the flow in shallow river
Computation of tokamak equilibria with steady flow
International Nuclear Information System (INIS)
Kerner, W.; Tokuda, Shinji
1987-08-01
The equations for ideal MHD equilibria with stationary flow are reexamined and addressed as numerically applied to tokamak configurations with a free plasma boundary. Both the isothermal (purely toroidal flow) and the poloidal flow cases are treated. Experiment-relevant states with steady flow (so far only in the toroidal direction) are computed by the modified SELENE40 code. (author)
Efficient multigrid computation of steady hypersonic flows
Koren, B.; Hemker, P.W.; Murthy, T.K.S.
1991-01-01
In steady hypersonic flow computations, Newton iteration as a local relaxation procedure and nonlinear multigrid iteration as an acceleration procedure may both easily fail. In the present chapter, same remedies are presented for overcoming these problems. The equations considered are the steady,
Steady flow in shallow channel bends
De Vriend, H.J.
1981-01-01
Making use of a mathematical model solving the complete NavierStokes equations for steady flow in coiled rectangular pipes, fully-developed laminar flow in shallow curved channels is analysed physically and mathematically. Transverse convection of momentum by the secondary flow is shown to cause
Steady laminar flow of fractal fluids
Energy Technology Data Exchange (ETDEWEB)
Balankin, Alexander S., E-mail: abalankin@ipn.mx [Grupo Mecánica Fractal, ESIME, Instituto Politécnico Nacional, México D.F., 07738 (Mexico); Mena, Baltasar [Laboratorio de Ingeniería y Procesos Costeros, Instituto de Ingeniería, Universidad Nacional Autónoma de México, Sisal, Yucatán, 97355 (Mexico); Susarrey, Orlando; Samayoa, Didier [Grupo Mecánica Fractal, ESIME, Instituto Politécnico Nacional, México D.F., 07738 (Mexico)
2017-02-12
We study laminar flow of a fractal fluid in a cylindrical tube. A flow of the fractal fluid is mapped into a homogeneous flow in a fractional dimensional space with metric induced by the fractal topology. The equations of motion for an incompressible Stokes flow of the Newtonian fractal fluid are derived. It is found that the radial distribution for the velocity in a steady Poiseuille flow of a fractal fluid is governed by the fractal metric of the flow, whereas the pressure distribution along the flow direction depends on the fractal topology of flow, as well as on the fractal metric. The radial distribution of the fractal fluid velocity in a steady Couette flow between two concentric cylinders is also derived. - Highlights: • Equations of Stokes flow of Newtonian fractal fluid are derived. • Pressure distribution in the Newtonian fractal fluid is derived. • Velocity distribution in Poiseuille flow of fractal fluid is found. • Velocity distribution in a steady Couette flow is established.
Steady flow in shallow channel bends
De Vriend, H.J.
1981-01-01
Making use of a mathematical model solving the complete NavierStokes equations for steady flow in coiled rectangular pipes, fully-developed laminar flow in shallow curved channels is analysed physically and mathematically. Transverse convection of momentum by the secondary flow is shown to cause important deformations of the main velocity distribution. The model is also used to investigate simplified computation methods for shallow channels. The usual 'shallow water approximation' is shown to...
Seismic signal of near steady uniform flows
Mangeney, A.; Bachelet, V.; Toussaint, R.; de Rosny, J.
2017-12-01
The seismic signal generated by rockfalls, landslides or avalanches is a unique tool to detect, characterize and monitor gravitational flow activity. A major challenge in this domain is to retrieve the dynamic properties of the flow from the emitted seismic signal. In this study, we propose laboratory experiments where the dynamic properties of the flow (velocity, granular temperature, density, etc.) are measured together with the generated seismic signal. We investigate near steady uniform flows made of glass beads of 2mm diameter, flowing throughout a thin rectangular channel of 10 cm width, with tunable tilt angle and height flow, thanks to an adjustable opening gate. The flow is monitored from the spine with a fast camera (5000 fps), and the emitted waves are recorded by accelerometers (10Hz - 54 kHz), stuck on the back side of the bottom of the channel. Among others, three seismic parameters are analyzed: the power radiated by the flow, the mean frequency of the signal, and the modulation of its amplitude. We show that they are linked to three dynamical properties: the mean kinetic energy of the flow, the speed of collisions between beads and the vertical oscillation of the beads, respectively.
Rarefaction wave in relativistic steady magnetohydrodynamic flows
Energy Technology Data Exchange (ETDEWEB)
Sapountzis, Konstantinos, E-mail: ksapountzis@phys.uoa.gr; Vlahakis, Nektarios, E-mail: vlahakis@phys.uoa.gr [Faculty of Physics, University of Athens, 15784 Zografos, Athens (Greece)
2014-07-15
We construct and analyze a model of the relativistic steady-state magnetohydrodynamic rarefaction that is induced when a planar symmetric flow (with one ignorable Cartesian coordinate) propagates under a steep drop of the external pressure profile. Using the method of self-similarity, we derive a system of ordinary differential equations that describe the flow dynamics. In the specific limit of an initially homogeneous flow, we also provide analytical results and accurate scaling laws. We consider that limit as a generalization of the previous Newtonian and hydrodynamic solutions already present in the literature. The model includes magnetic field and bulk flow speed having all components, whose role is explored with a parametric study.
Numerical Simulation of Steady Supercavitating Flows
Ali Jafarian; Ahmad-Reza Pishevar
2016-01-01
In this research, the Supercavitation phenomenon in compressible liquid flows is simulated. The one-fluid method based on a new exact two-phase Riemann solver is used for modeling. The cavitation is considered as an isothermal process and a consistent equation of state with the physical behavior of the water is used. High speed flow of water over a cylinder and a projectile are simulated and the results are compared with the previous numerical and experimental results. The cavitation bubble p...
Influence of steady shear flow on dynamic viscoelastic properties of ...
Indian Academy of Sciences (India)
Unknown
temporary network formed by the fibres, their entangle- ment etc. The structural density is also a function of vol- ume fraction of reinforcing fibres (Amari et al 1992). The complex flow pattern encountered during moulding/ stamping are generally far from simple steady or oscilla- tory shear flow. Therefore, it is important to ...
3-D steady analysis of flow in CRDM sewerage system
International Nuclear Information System (INIS)
Sun Yan; Liang Tiebo; Chen Zhihui; Zhao Jing; Zhang Yulong
2014-01-01
In order to obtain the flow state during sewer condition in Reactor and CRDM Sewerage system (RSE), this paper analyzes the 3-D steady flow in RSE by using Computational Fluid Dynamics (CFD) method. In the premise that the pressure drop of the RSE is known, the mass flow rate, the velocity and the type of flow in the system is obtained with the inverse method, which is proposed and validated to be applicable in the paper. The result shows that in the sewerage conditions, the type of flow in the RSE is turbulence flow, which is helpful to sewer drain. The study results give an reference for the design of RSE. (authors)
Steady flows in the solar transition region observed with SMM
International Nuclear Information System (INIS)
Gebbie, K.B.; Hill, F.; Toomre, J.; November, L.J.; Simon, G.W.; Gurman, J.B.; Shine, R.A.; Woodgate, B.E.; Athay, R.G.; Bruner, E.C. Jr.; Rehse, R.A.; Tandberg-Hanssen, E.A.
1981-01-01
Steady flows in the quiet solar transition region have been observed with the Ultraviolet Spectrometer and Polarimeter (UVSP) experiment on the Solar Maximum Mission (SMM) satellite. The persistent vertical motions seen at disk center have spatial rms amplitudes of 1.4 km s -1 in the C II line, 3.9 km s -1 in Si IV, and 4.2 km s -1 in C IV. The amplitudes of the more horizontal flows seen toward the limb tend to be somewhat higher. Plots of steady vertical velocity versus intensity seen at disk center in Si IV and C IV show two distinct branches
Transient and steady-state flows in shock tunnels
Energy Technology Data Exchange (ETDEWEB)
Hannemann, K. [Deutsche Forschungsanstalt fuer Luft- und Raumfahrt e.V. (DLR), Goettingen (Germany); Jacobs, P.A. [Queensland Univ., Brisbane (Australia). Dept. of Mechanical Engineering; Thomas, A.; McIntyre, T.J. [Queensland Univ., Brisbane, QLD. (Australia). Dept. of Physics
1999-12-01
Due to the difficulty of measuring all necessary flow quantities in the nozzle reservoir and the test section of high enthalpy shock tunnels, indirect computational methods are necessary to estimate the required flow parameters. In addition to steady state flow computations of the nozzle flow and the flow past wind tunnel models it is necessary to investigate the transient flow in the facility in order to achieve a better understanding of its performance. These transient effects include the nozzle starting flow, the interaction of the shock tube boundary layers and the reflected shock, thermal losses in the shock reflection region and the developing boundary layers in the expanding section of the nozzle. Additionally, the nonequilibrium chemical and thermal relaxation models which are used to compute high enthalpy flows have to be validated with appropriate experimental data. (orig.)
Transient and steady-state flows in shock tunnels
Energy Technology Data Exchange (ETDEWEB)
Hannemann, K. (Deutsche Forschungsanstalt fuer Luft- und Raumfahrt e.V. (DLR), Goettingen (Germany)); Jacobs, P.A. (Queensland Univ., Brisbane (Australia). Dept. of Mechanical Engineering); Thomas, A.; McIntyre, T.J. (Queensland Univ., Brisbane, QLD. (Australia). Dept. of Physics)
1999-01-01
Due to the difficulty of measuring all necessary flow quantities in the nozzle reservoir and the test section of high enthalpy shock tunnels, indirect computational methods are necessary to estimate the required flow parameters. In addition to steady state flow computations of the nozzle flow and the flow past wind tunnel models it is necessary to investigate the transient flow in the facility in order to achieve a better understanding of its performance. These transient effects include the nozzle starting flow, the interaction of the shock tube boundary layers and the reflected shock, thermal losses in the shock reflection region and the developing boundary layers in the expanding section of the nozzle. Additionally, the nonequilibrium chemical and thermal relaxation models which are used to compute high enthalpy flows have to be validated with appropriate experimental data. (orig.)
Poiseuille equation for steady flow of fractal fluid
Tarasov, Vasily E.
2016-07-01
Fractal fluid is considered in the framework of continuous models with noninteger dimensional spaces (NIDS). A recently proposed vector calculus in NIDS is used to get a description of fractal fluid flow in pipes with circular cross-sections. The Navier-Stokes equations of fractal incompressible viscous fluids are used to derive a generalization of the Poiseuille equation of steady flow of fractal media in pipe.
Three Dimensional Steady Subsonic Euler Flows in Bounded Nozzles
Chen, Chao; Xie, Chunjing
2013-01-01
In this paper, we study the existence and uniqueness of three dimensional steady Euler flows in rectangular nozzles when prescribing normal component of momentum at both the entrance and exit. If, in addition, the normal component of the voriticity and the variation of Bernoulli's function at the exit are both zero, then there exists a unique subsonic potential flow when the magnitude of the normal component of the momentum is less than a critical number. As the magnitude of the normal compon...
Steady flow in a rotating sphere with strong precession
Kida, Shigeo
2018-04-01
The steady flow in a rotating sphere is investigated by asymptotic analysis in the limit of strong precession. The whole spherical body is divided into three regions in terms of the flow characteristics: the critical band, which is the close vicinity surrounding the great circle perpendicular to the precession axis, the boundary layer, which is attached to the whole sphere surface and the inviscid region that occupies the majority of the sphere. The analytic expressions, in the leading order of the asymptotic expansion, of the velocity field are obtained in the former two, whereas partial differential equations for the velocity field are derived in the latter, which are solved numerically. This steady flow structure is confirmed by the corresponding direct numerical simulation.
Steady State Stokes Flow Interpolation for Fluid Control
DEFF Research Database (Denmark)
Bhatacharya, Haimasree; Nielsen, Michael Bang; Bridson, Robert
2012-01-01
— suffer from a common problem. They fail to capture the rotational components of the velocity field, although extrapolation in the normal direction does consider the tangential component. We address this problem by casting the interpolation as a steady state Stokes flow. This type of flow captures......Fluid control methods often require surface velocities interpolated throughout the interior of a shape to use the velocity as a feedback force or as a boundary condition. Prior methods for interpolation in computer graphics — velocity extrapolation in the normal direction and potential flow...
Acoustic metacages for sound shielding with steady air flow
Shen, Chen; Xie, Yangbo; Li, Junfei; Cummer, Steven A.; Jing, Yun
2018-03-01
Conventional sound shielding structures typically prevent fluid transport between the exterior and interior. A design of a two-dimensional acoustic metacage with subwavelength thickness which can shield acoustic waves from all directions while allowing steady fluid flow is presented in this paper. The structure is designed based on acoustic gradient-index metasurfaces composed of open channels and shunted Helmholtz resonators. In-plane sound at an arbitrary angle of incidence is reflected due to the strong parallel momentum on the metacage surface, which leads to low sound transmission through the metacage. The performance of the proposed metacage is verified by numerical simulations and measurements on a three-dimensional printed prototype. The acoustic metacage has potential applications in sound insulation where steady fluid flow is necessary or advantageous.
Evaluation of magnetic resonance velocimetry for steady flow.
Ku, D N; Biancheri, C L; Pettigrew, R I; Peifer, J W; Markou, C P; Engels, H
1990-11-01
Whole body magnetic resonance (MR) imaging has recently become an important diagnostic tool for cardiovascular diseases. The technique of magnetic resonance phase velocity encoding allows the quantitative measurement of velocity for an arbitrary component direction. A study was initiated to determine the ability and accuracy of MR velocimetry to measure a wide range of flow conditions including flow separation, three-dimensional secondary flow, high velocity gradients, and turbulence. A steady flow system pumped water doped with manganese chloride through a variety of test sections. Images were produced using gradient echo sequences on test sections including a straight tube, a curved tube, a smoothly converging-diverging nozzle, and an orifice. Magnetic resonance measurements of laminar and turbulent flows were depicted as cross-sectional velocity profiles. MR velocity measurements revealed such flow behavior as spatially varying velocity, recirculation and secondary flows over a wide range of conditions. Comparisons made with published experimental laser Doppler anemometry measurements and theoretical calculations for similar flow conditions revealed excellent accuracy and precision levels. The successful measurement of velocity profiles for a variety of flow conditions and geometries indicate that magnetic resonance imaging is an accurate, non-contacting velocimeter.
Steady flow in voids and closed cracks in permeable media
International Nuclear Information System (INIS)
Rae, J.
1985-03-01
This paper considers what happens when a steady flow in a permeable medium meets two concentric spheres which have different permeabilities. This can form a first stage model for water flow near an engineered cavity in rock or a concreted waste package placed in filler material as in a nuclear waste repository. Results are obtained in terms of the simplest spherical harmonics, which lets them be used easily. Included are the well-known result that a highly permeable sphere will see only a few times the flux which would occur if it had the permeability of its surroundings, and the less well-known result, though unsurprising, that a spherical region surrounded by a highly permeable shell will see almost no flow, as it will almost all by-pass. A companion paper will include more geometrical effects by replacing the spheres by ellipsoids. (author)
Steady parallel flow in an evaporating fluid heated from sidewalls
International Nuclear Information System (INIS)
Das, Kausik S.
2009-01-01
Evaporation is ubiquitous in nature, but very few attempts have been made in the past to couple the effects of evaporation with fluid flow behavior. In this theoretical paper we have discussed the effects of evaporation on the dynamics of steady state thermocapillary convection in a two-dimensional rectangular container. The liquid is heated by differentially heated sidewalls and mass loss from the interface due to evaporation is compensated by the liquid entering into the container through a lower inlet, thus keeping the thickness of the liquid layer constant. We show that for an evaporating liquid one can obtain a plane parallel base state profile which depends on the evaporative mass flux.
Models of steady state cooling flows in elliptical galaxies
International Nuclear Information System (INIS)
Vedder, P.W.; Trester, J.J.; Canizares, C.R.
1988-01-01
A comprehensive set of steady state models for spherically symmetric cooling flows in early-type galaxies is presented. It is found that a reduction of the supernova (SN) rate in ellipticals produces a decrease in the X-ray luminosity of galactic cooling flows and a steepening of the surface brightness profile. The mean X-ray temperature of the cooling flow is not affected noticeably by a change in the SN rate. The external pressure around a galaxy does not markedly change the luminosity of the gas within the galaxy but does change the mean temperature of the gas. The presence of a dark matter halo in a galaxy only changes the mean X-ray temperature slightly. The addition of a distribution of mass sinks which remove material from the general accretion flow reduces L(X) very slightly, flattens the surface brightness profile, and reduces the central surface brightness level to values close to those actually observed. A reduction in the stellar mass-loss rate only slightly reduces the X-ray luminosity of the cooling flow and flattens the surface brightness by a small amount. 37 references
Three dimensional steady subsonic Euler flows in bounded nozzles
Chen, Chao; Xie, Chunjing
The existence and uniqueness of three dimensional steady subsonic Euler flows in rectangular nozzles were obtained when prescribing normal component of momentum at both the entrance and exit. If, in addition, the normal component of the voriticity and the variation of Bernoulli's function at the entrance are both zero, then there exists a unique subsonic potential flow when the magnitude of the normal component of the momentum is less than a critical number. As the magnitude of the normal component of the momentum approaches the critical number, the associated flows converge to a subsonic-sonic flow. Furthermore, when the normal component of vorticity and the variation of Bernoulli function are both small, the existence and uniqueness of subsonic Euler flows with non-zero vorticity are established. The proof of these results is based on a new formulation for the Euler system, a priori estimate for nonlinear elliptic equations with nonlinear boundary conditions, detailed study for a linear div-curl system, and delicate estimate for the transport equations.
Two-dimensional steady unsaturated flow through embedded elliptical layers
Bakker, Mark; Nieber, John L.
2004-12-01
New analytic element solutions are presented for unsaturated, two-dimensional steady flow in vertical planes that include nonoverlapping impermeable elliptical layers and elliptical inhomogeneities. The hydraulic conductivity, which is represented by an exponential function of the pressure head, differs between the inside and outside of an elliptical inhomogeneity; both the saturated hydraulic conductivity and water retention parameters are allowed to differ between the inside and outside. The Richards equation is transformed, through the Kirchhoff transformation and a second standard transformation, into the modified Helmholtz equation. Analytic element solutions are obtained through separation of variables in elliptical coordinates. The resulting equations for the Kirchhoff potential consist of infinite sums of products of exponentials and modified Mathieu functions. In practical applications the series are truncated but still fulfill the differential equation exactly; boundary conditions are met approximately but up to machine accuracy, provided that enough terms are used. The pressure head, saturation, and flow may be computed analytically at any point in the vadose zone. Examples are given of the shadowing effect of an impermeable elliptical layer in a uniform flow field and funnel-type flow between two elliptical inhomogeneities. The presented solutions may be applied to study transport processes in vadose zones containing many impermeable elliptical layers or elliptical inhomogeneities.
Sensitivity Analysis for Steady State Groundwater Flow Using Adjoint Operators
Sykes, J. F.; Wilson, J. L.; Andrews, R. W.
1985-03-01
Adjoint sensitivity theory is currently being considered as a potential method for calculating the sensitivity of nuclear waste repository performance measures to the parameters of the system. For groundwater flow systems, performance measures of interest include piezometric heads in the vicinity of a waste site, velocities or travel time in aquifers, and mass discharge to biosphere points. The parameters include recharge-discharge rates, prescribed boundary heads or fluxes, formation thicknesses, and hydraulic conductivities. The derivative of a performance measure with respect to the system parameters is usually taken as a measure of sensitivity. To calculate sensitivities, adjoint sensitivity equations are formulated from the equations describing the primary problem. The solution of the primary problem and the adjoint sensitivity problem enables the determination of all of the required derivatives and hence related sensitivity coefficients. In this study, adjoint sensitivity theory is developed for equations of two-dimensional steady state flow in a confined aquifer. Both the primary flow equation and the adjoint sensitivity equation are solved using the Galerkin finite element method. The developed computer code is used to investigate the regional flow parameters of the Leadville Formation of the Paradox Basin in Utah. The results illustrate the sensitivity of calculated local heads to the boundary conditions. Alternatively, local velocity related performance measures are more sensitive to hydraulic conductivities.
On some Approximation Schemes for Steady Compressible Viscous Flow
Bause, M.; Heywood, J. G.; Novotny, A.; Padula, M.
This paper continues our development of approximation schemes for steady compressible viscous flow based on an iteration between a Stokes like problem for the velocity and a transport equation for the density, with the aim of improving their suitability for computations. Such schemes seem attractive for computations because they offer a reduction to standard problems for which there is already highly refined software, and because of the guidance that can be drawn from an existence theory based on them. Our objective here is to modify a recent scheme of Heywood and Padula [12], to improve its convergence properties. This scheme improved upon an earlier scheme of Padula [21], [23] through the use of a special ``effective pressure'' in linking the Stokes and transport problems. However, its convergence is limited for several reasons. Firstly, the steady transport equation itself is only solvable for general velocity fields if they satisfy certain smallness conditions. These conditions are met here by using a rescaled variant of the steady transport equation based on a pseudo time step for the equation of continuity. Another matter limiting the convergence of the scheme in [12] is that the Stokes linearization, which is a linearization about zero, has an inevitably small range of convergence. We replace it here with an Oseen or Newton linearization, either of which has a wider range of convergence, and converges more rapidly. The simplicity of the scheme offered in [12] was conducive to a relatively simple and clearly organized proof of its convergence. The proofs of convergence for the more complicated schemes proposed here are structured along the same lines. They strengthen the theorems of existence and uniqueness in [12] by weakening the smallness conditions that are needed. The expected improvement in the computational performance of the modified schemes has been confirmed by Bause [2], in an ongoing investigation.
Perbandingan Hasil Pemodelan Aliran Satu Dimensi Unsteady Flow dan Steady Flow pada Banjir Kota
Directory of Open Access Journals (Sweden)
Andreas Tigor Oktaga
2016-06-01
Full Text Available One dimensional flow is often used as a flood simulation for the planning capacity of the river. Flood is a type of unsteady non-uniform flow, that can be simulated using HEC-RAS. HEC-RAS software is often used for flood modeling with a one-dimensional flow method. Unsteady flow modeling results in HEC-RAS sometimes refer to error and warning due to unstable analysis program. The stability program among others influenced bend in the river flow, the steep slope of the river bottom, and changes in cross-section shape. Because the flood handling required maximum discharge and maximum flood water level, then a steady flow is often used as an alternative to simulate the flood flow. This study aimed to determine the advantages and disadvantages of modeling unsteady non-uniform and steady non-uniform flow. The research location in the Kanal Banjir Barat, in the Semarang City. Hydraulics modeling uses HEC-RAS 4.1 and for discharge the plan is obtained from the HEC-HMS 3.5. Results of the comparison modeling hydraulics the modeling of steady non-uniform flow has a tendency water level is higher and modeling of unsteady non-uniform flow takes longer to analyze. Results of the comparison the average flood water level maximun is less than 15% (± 0,3 meters, that is 0.27 meters (13.16% for Q50, 0.25 meters (11.56% for Q100, dan 0.16 meters (4.73% for Q200. So the modeling steady non-uniform flow can still be used as a companion version the modeling unsteady non-uniform flow.
Dynamic behaviors of cavitation bubble for the steady cavitating flow
Cai, Jun; Huai, Xiulan; Li, Xunfeng
2009-12-01
In this paper, by introducing the flow velocity item into the classical Rayleigh-Plesset dynamic equation, a new equation, which does not involve the time term and can describe the motion of cavitation bubble in the steady cavitating flow, has been obtained. By solving the new motion equation using Runge-Kutta fourth order method with adaptive step size control, the dynamic behaviors of cavitation bubble driven by the varying pressure field downstream of a venturi cavitation reactor are numerically simulated. The effects of liquid temperature (corresponding to the saturated vapor pressure of liquid), cavitation number and inlet pressure of venturi on radial motion of bubble and pressure pulse due to the radial motion are analyzed and discussed in detail. Some dynamic behaviors of bubble different from those in previous papers are displayed. In addition, the internal relationship between bubble dynamics and process intensification is also discussed. The simulation results reported in this work reveal the variation laws of cavitation intensity with the flow conditions of liquid, and will lay a foundation for the practical application of hydrodynamic cavitation technology.
A generalised correlation for the steady state flow in single-phase natural circulation loops
International Nuclear Information System (INIS)
Vijayan, P.K.; Bade, M.H.; Saha, D.; Sinha, R.K.; Venkat Raj, V.
2000-08-01
To establish the heat transport capability of natural circulation loops, it is essential to know the flow rate. A generalized correlation for steady state flow valid for uniform and non-uniform diameter loops has been theoretically derived
Stochastic analysis of unsaturated steady flows above the water table
Severino, Gerardo; Scarfato, Maddalena; Comegna, Alessandro
2017-08-01
Steady flow takes place into a three-dimensional partially saturated porous medium where, due to their spatial variability, the saturated conductivity Ks, and the relative conductivity Kr are modeled as random space functions (RSF)s. As a consequence, the flow variables (FVs), i.e., pressure-head and specific flux, are also RSFs. The focus of the present paper consists into quantifying the uncertainty of the FVs above the water table. The simple expressions (most of which in closed form) of the second-order moments pertaining to the FVs allow one to follow the transitional behavior from the zone close to the water table (where the FVs are nonstationary), till to their far-field limit (where the FVs become stationary RSFs). In particular, it is shown how the stationary limits (and the distance from the water table at which stationarity is attained) depend upon the statistical structure of the RSFs Ks, Kr, and the infiltrating rate. The mean pressure head >> has been also computed, and it is expressed as =Ψ0>(1+ψ>), being ψ a characteristic heterogeneity function which modifies the zero-order approximation Ψ0 of the pressure head (valid for a vadose zone of uniform soil properties) to account for the spatial variability of Ks and Kr. Two asymptotic limits, i.e., close (near field) and away (far field) from the water table, are derived into a very general manner, whereas the transitional behavior of ψ between the near/far field can be determined after specifying the shape of the various input soil properties. Besides the theoretical interest, results of the present paper are useful for practical purposes, as well. Indeed, the model is tested against to real data, and in particular it is shown how it is possible for the specific case study to grasp the behavior of the FVs within an environment (i.e., the vadose zone close to the water table) which is generally very difficult to access by direct inspection.
Poiseuille flow of soft glasses in narrow channels: from quiescence to steady state.
Chaudhuri, Pinaki; Horbach, Jürgen
2014-10-01
Using numerical simulations, the onset of Poiseuille flow in a confined soft glass is investigated. Starting from the quiescent state, steady flow sets in at a time scale which increases with a decrease in applied forcing. At this onset time scale, a rapid transition occurs via the simultaneous fluidization of regions having different local stresses. In the absence of steady flow at long times, creep is observed even in regions where the local stress is larger than the bulk yielding threshold. Finally, we show that the time scale to attain steady flow depends strongly on the history of the initial state.
Steady flow torques in a servo motor operated rotary directional control valve
International Nuclear Information System (INIS)
Wang, He; Gong, Guofang; Zhou, Hongbin; Wang, Wei
2016-01-01
Highlights: • A novel servo motor operated rotary directional control valve is proposed. • Steady flow torque is a crucial issue that affects rotary valve performance. • Steady flow torque is analyzed on the aspects of theory, simulation and experiment. • Change law of the steady flow torque with spool rotation angle is explored. • Effect of pressure drop and flow rate on the steady flow torque is studied. - Abstract: In this paper, a servo motor operated rotary directional control valve is proposed, and a systematic analysis of steady flow torques in this valve is provided by theoretical calculation, CFD simulation and experimental test. In the analysis, spool rotation angle corresponding to the maximum orifice opening is tagged as 0°. Over a complete change cycle of the orifice, the range of spool rotation angle is symmetric about 0°. The results show that the direction of steady flow torques in this valve is always the direction of orifice closing. The steady flow torques serve as resistances to the spool rotation when the orifice opening increases, while impetuses to the spool rotation when the orifice opening decreases. At a certain pressure drop or flow rate, steady flow torques are approximately equal and opposite when at spool rotation angles which are symmetric about 0°. When the spool rotates from 0°, at a certain pressure drop, their values increase first then decrease with the spool rotation and reach their maximum values at an angle corresponding to about 1/2 of the maximum orifice opening, and at a certain flow rate, their values increase with the spool rotation. The steady flow torques in this valve are the sums of those in the meter-in and meter-out valve chambers. At a certain spool rotation angle, steady flow torques in the meter-in and meter-out valve chambers are approximately proportional to the pressure drop and the second power of the flow rate through the orifice. Theoretical calculation and CFD simulation can be validated by
Numerical method for three dimensional steady-state two-phase flow calculations
International Nuclear Information System (INIS)
Raymond, P.; Toumi, I.
1992-01-01
This paper presents the numerical scheme which was developed for the FLICA-4 computer code to calculate three dimensional steady state two phase flows. This computer code is devoted to steady state and transient thermal hydraulics analysis of nuclear reactor cores 1,3 . The first section briefly describes the FLICA-4 flow modelling. Then in order to introduce the numerical method for steady state computations, some details are given about the implicit numerical scheme based upon an approximate Riemann solver which was developed for calculation of flow transients. The third section deals with the numerical method for steady state computations, which is derived from this previous general scheme and its optimization. We give some numerical results for steady state calculations and comparisons on required CPU time and memory for various meshing and linear system solvers
Inertial Waves and Steady Flows in a Liquid Filled Librating Cylinder
Subbotin, Stanislav; Dyakova, Veronika
2018-05-01
The fluid flow in a non-uniformly rotating (librating) cylinder about a horizontal axis is experimentally studied. In the absence of librations the fluid performs a solid-body rotation together with the cavity. Librations lead to the appearance of steady zonal flow in the whole cylinder and the intensive steady toroidal flows near the cavity corners. If the frequency of librations is twice lower than the mean rotation rate the inertial waves are excited. The oscillating motion associated with the propagation of inertial wave in the fluid bulk leads to the appearance of an additional steady flow in the Stokes boundary layers on the cavity side wall. In this case the heavy particles of the visualizer are assembled on the side wall into ring structures. The patterns are determined by the structure of steady flow, which in turn depends on the number of reflections of inertial wave beams from the cavity side wall. For some frequencies, inertial waves experience spatial resonance, resulting in inertial modes, which are eigenmodes of the cavity geometry. The resonance of the inertial modes modifies the steady flow structure close to the boundary layer that is manifested in the direct rebuilding of patterns. It is shown that the intensity of zonal flow, as well as the intensity of steady flows excited by inertial waves, is proportional to the square of the amplitude of librations.
Steady hydromagnetic Couette flow in a rotating system with ...
African Journals Online (AJOL)
International Journal of Engineering, Science and Technology ... Couette flow of class-II of a viscous incompressible electrically conducting fluid in a rotating system ... Heat transfer characteristics of the flow are considered taking viscous and ...
Analysis of steady state and transient two-phase flows in downwardly inclined lines
International Nuclear Information System (INIS)
Crawford, T.J.
1983-01-01
A study of steady-state and transient two-phase flows in downwardly inclined lines is described. Steady-state flow patterns maps are presented using Freon-113 as the working fluid to provide new high density vapors. These flow maps with high density vapor serve to significantly extend the investigations of steady-state downward two-phase flow patterns. Physical models developed which successfully predicted the onset or location of various flow pattern transitions. A new simplified criterion that would be useful to designers and experimenters is offered for the onset of dispersed flow. A new empirical holdup correlation and a new bubble diameter/flow rate correlation are also proposed. Flow transients in vertical downward lines were studied to investigate the possible formation of intermediate or spurious flow patterns that would not be seen at steady-state conditions. Void fraction behavior during the transients was modeled by using the dynamic slip equation from the transient analysis code RETRAN. Physical models of interfacial area were developed and compared with models and data from literature. There was satisfactory agreement between the models of the present study and the literature models and data. The concentration parameter of the drift flux model was evaluated for vertical downward flow. These new values of the flow dependent parameter were different from those previously proposed in the literature for use in upward flows, and made the drift flux model suitable for use in upward or downward flow lines
Well balancing of the SWE schemes for moving-water steady flows
Caleffi, Valerio; Valiani, Alessandro
2017-08-01
In this work, the exact reproduction of a moving-water steady flow via the numerical solution of the one-dimensional shallow water equations is studied. A new scheme based on a modified version of the HLLEM approximate Riemann solver (Dumbser and Balsara (2016) [18]) that exactly preserves the total head and the discharge in the simulation of smooth steady flows and that correctly dissipates mechanical energy in the presence of hydraulic jumps is presented. This model is compared with a selected set of schemes from the literature, including models that exactly preserve quiescent flows and models that exactly preserve moving-water steady flows. The comparison highlights the strengths and weaknesses of the different approaches. In particular, the results show that the increase in accuracy in the steady state reproduction is counterbalanced by a reduced robustness and numerical efficiency of the models. Some solutions to reduce these drawbacks, at the cost of increased algorithm complexity, are presented.
Stratified steady and unsteady two-phase flows between two parallel plates
International Nuclear Information System (INIS)
Sim, Woo Gun
2006-01-01
To understand fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. Stratified steady and unsteady two-phase flows between two parallel plates have been studied to investigate the general characteristics of the flow related to flow-induced vibration. Based on the spectral collocation method, a numerical approach has been developed for the unsteady two-phase flow. The method is validated by comparing numerical result to analytical one given for a simple harmonic two-phase flow. The flow parameters for the steady two-phase flow, such as void fraction and two-phase frictional multiplier, are evaluated. The dynamic characteristics of the unsteady two-phase flow, including the void fraction effect on the complex unsteady pressure, are illustrated
Flow Over a Body of Revolution in a Steady Turn
2004-10-01
31], Migliore and Wolfe [32]. Migliore investigated flow curvature effects on Darrieus wind turbines , a special type of turbine which has a continuous...and Wolfe- J. B.. Some Effects of Flow Curvature Effects oil the Aerodynamics of Darrieus Wind Turbines West Viryinia University , 1979 33. Hirsch, Ch...and Mandal. A. C., Flow Curvature Effects on Vertical Axis Darrieus Wind Turbine Having High Chord-Radius Ratio European Wind Energy Confer- ence
Steady hydromagnetic Couette flow in a rotating system with non ...
African Journals Online (AJOL)
user
energy equation and numerical values of rate of heat transfer at both plates are ... An investigation of MHD flow of an electrically conducting fluid in a rotating ... bounded by stationary free stream whereas MHD flow past a stationary plate ... induced magnetic field produced by fluid motion is negligible in comparison to the ...
Anisotropic plasma with flows in tokamak: Steady state and stability
International Nuclear Information System (INIS)
Ilgisonis, V.I.
1996-01-01
An adequate description of equilibrium and stability of anisotropic plasma with macroscopic flows in tokamaks is presented. The Chew-Goldberger-Low (CGL) approximation is consistently used to analyze anisotropic plasma dynamics. The admissible structure of a stationary flow is found to be the same as in the ideal magnetohydrodynamics with isotropic pressure (MHD), which means an allowance for the same relabeling symmetry as in ideal MHD systems with toroidally nested magnetic surfaces. A generalization of the Grad-Shafranov equation for the case of anisotropic plasma with flows confined in the axisymmetric magnetic field is derived. A variational principle was obtained, which allows for a stability analysis of anisotropic pressure plasma with flows, and takes into account the conservation laws resulting from the relabeling symmetry. This principle covers the previous stability criteria for static CGL plasma and for ideal MHD flows in isotropic plasma as well. copyright 1996 American Institute of Physics
On steady poloidal and toroidal flows in tokamak plasmas
International Nuclear Information System (INIS)
McClements, K. G.; Hole, M. J.
2010-01-01
The effects of poloidal and toroidal flows on tokamak plasma equilibria are examined in the magnetohydrodynamic limit. ''Transonic'' poloidal flows of the order of the sound speed multiplied by the ratio of poloidal magnetic field to total field B θ /B can cause the (normally elliptic) Grad-Shafranov (GS) equation to become hyperbolic in part of the solution domain. It is pointed out that the range of poloidal flows for which the GS equation is hyperbolic increases with plasma beta and B θ /B, thereby complicating the problem of determining spherical tokamak plasma equilibria with transonic poloidal flows. It is demonstrated that the calculation of the hyperbolicity criterion can be easily modified when the assumption of isentropic flux surfaces is replaced with the more tokamak-relevant one of isothermal flux surfaces. On the basis of the latter assumption, a simple expression is obtained for the variation of density on a flux surface when poloidal and toroidal flows are simultaneously present. Combined with Thomson scattering measurements of density and temperature, this expression could be used to infer information on poloidal and toroidal flows on the high field side of a tokamak plasma, where direct measurements of flows are not generally possible. It is demonstrated that there are four possible solutions of the Bernoulli relation for the plasma density when the flux surfaces are assumed to be isothermal, corresponding to four distinct poloidal flow regimes. Finally, observations and first principles-based theoretical modeling of poloidal flows in tokamak plasmas are briefly reviewed and it is concluded that there is no clear evidence for the occurrence of supersonic poloidal flows.
Local wettability reversal during steady-state two-phase flow in porous media.
Sinha, Santanu; Grøva, Morten; Ødegården, Torgeir Bryge; Skjetne, Erik; Hansen, Alex
2011-09-01
We study the effect of local wettability reversal on remobilizing immobile fluid clusters in steady-state two-phase flow in porous media. We consider a two-dimensional network model for a porous medium and introduce a wettability alteration mechanism. A qualitative change in the steady-state flow patterns, destabilizing the percolating and trapped clusters, is observed as the system wettability is varied. When capillary forces are strong, a finite wettability alteration is necessary to move the system from a single-phase to a two-phase flow regime. When both phases are mobile, we find a linear relationship between fractional flow and wettability alteration.
Simulations of Steady Cavitating Flow in a Small Francis Turbine
Directory of Open Access Journals (Sweden)
Ahmed Laouari
2016-01-01
Full Text Available The turbulent flow through a small horizontal Francis turbine is solved by means of Ansys-CFX at different operating points, with the determination of the hydrodynamic performance and the best efficiency point. The flow structures at different regimes reveal a large flow eddy in the runner and a swirl in the draft tube. The use of the mixture model for the cavity/liquid two-phase flow allowed studying the influence of cavitation on the hydrodynamic performance and revealed cavitation pockets near the trailing edge of the runner and a cavitation vortex rope in the draft tube. By maintaining a constant dimensionless head and a distributor vane opening while gradually increasing the cavitation number, the output power and efficiency reached a critical point and then had begun to stabilize. The cavitation number corresponding to the safety margin of cavitation is also predicted for this hydraulic turbine.
Ideal, steady-state, axisymmetric magnetohydrodynamic equations with flow
International Nuclear Information System (INIS)
Baransky, Y.A.
1987-01-01
The motivation of this study is to gain additional understanding of the effect of rotation on the equilibrium of a plasma. The axisymmetric equilibria of ideal magnetohydrodynamics (MHD) with flow have been studied numerically and analytically. A general discussion is provided of previous work on plasmas with flow and comparisons are made to the static model. A variational principle has been derived for the two dimensional problem with comments as to appropriate boundary conditions. An inverse aspect ratio expansion has been used for a study of the toroidal flow equation for both low- and high-β. The inverse aspect ratio expansion has also been used for a study of equations with both poloidal and toroidal flow. An overview is provided of the adaptive finite-difference code which was developed to solve the full equations. (FI)
Kishor Kumar, V. V.; Kuzhiveli, B. T.
2017-12-01
The performance of a Stirling cryocooler depends on the thermal and hydrodynamic properties of the regenerator in the system. CFD modelling is the best technique to design and predict the performance of a Stirling cooler. The accuracy of the simulation results depend on the hydrodynamic and thermal transport parameters used as the closure relations for the volume averaged governing equations. A methodology has been developed to quantify the viscous and inertial resistance terms required for modelling the regenerator as a porous medium in Fluent. Using these terms, the steady and steady - periodic flow of helium through regenerator was modelled and simulated. Comparison of the predicted and experimental pressure drop reveals the good predictive power of the correlation based method. For oscillatory flow, the simulation could predict the exit pressure amplitude and the phase difference accurately. Therefore the method was extended to obtain the Darcy permeability and Forchheimer’s inertial coefficient of other wire mesh matrices applicable to Stirling coolers. Simulation of regenerator using these parameters will help to better understand the thermal and hydrodynamic interactions between working fluid and the regenerator material, and pave the way to contrive high performance, ultra-compact free displacers used in miniature Stirling cryocoolers in the future.
On the One-Dimensional Steady and Unsteady Porous Flow Equation
DEFF Research Database (Denmark)
Andersen, O. H.; Burcharth, H. F.
1995-01-01
Porous flow in coarse granular media is discussed theoretically with special concern given to the variation of the flow resistance with the porosity. For steady state flow, the Navier-Stokes equation is applied as a basis for the derivations. A turbulent flow equation is suggested. Alternative...... derivations based on dimensional analysis and a pipe analogy, respectively, are discussed. For non-steady state flow, the derivations are based on a cylinder/sphere analogy leading to a virtual mass coefficient. For the fully turbulent flow regime, existing experimental data values of the quadratic flow...... resistance coefficients are presented. Moreover, a simple formula for estimation of the turbulent flow coefficient is given. Virtual mass coefficients based on existing data are presented, however, no definite conclusions can be given due to the scarce data available....
Magnetic field correlations in random flow with strong steady shear
International Nuclear Information System (INIS)
Kolokolov, I. V.; Lebedev, V. V.; Sizov, G. A.
2011-01-01
We analyze the magnetic kinematic dynamo in a conducting fluid where a stationary shear flow is accompanied by relatively weak random velocity fluctuations. The diffusionless and diffusion regimes are described. The growth rates of the magnetic field moments are related to the statistical characteristics of the flow describing divergence of the Lagrangian trajectories. The magnetic field correlation functions are examined, and their growth rates and scaling behavior are established. General assertions are illustrated by the explicit solution of a model where the velocity field is short-correlated in time.
Non-Steady Oscillatory Flow in Coarse Granular Materials
DEFF Research Database (Denmark)
Andersen, O. H.; Gent, M. R. A. van; Meer, J. W. van der
1992-01-01
Stationary and oscillatory flow through coarse granular materials have been investigated experimentally at Delft Hydraulics in their oscillating water tunnel with the objective of determining the coefficients of the extended Forchheimer equation. Cylinders, spheres and different types of rock have....... Further, for the non-stationary term, the virtual mass coefficient will be derived....
Sjogreen, Bjoern; Yee, H. C.
2007-01-01
Flows containing steady or nearly steady strong shocks in parts of the flow field, and unsteady turbulence with shocklets on other parts of the flow field are difficult to capture accurately and efficiently employing the same numerical scheme even under the multiblock grid or adaptive grid refinement framework. On one hand, sixth-order or higher shock-capturing methods are appropriate for unsteady turbulence with shocklets. On the other hand, lower order shock-capturing methods are more effective for strong steady shocks in terms of convergence. In order to minimize the shortcomings of low order and high order shock-capturing schemes for the subject flows,a multi- block overlapping grid with different orders of accuracy on different blocks is proposed. Test cases to illustrate the performance of the new solver are included.
H.R. Barnard; C.B. Graham; W.J. van Verseveld; J.R. Brooks; B.J. Bond; J.J. McDonnell
2010-01-01
Mechanistic assessment of how transpiration influences subsurface flow is necessary to advance understanding of catchment hydrology. We conducted a 24-day, steady-state irrigation experiment to quantify the relationships among soil moisture, transpiration and hillslope subsurface flow. Our objectives were to: (1) examine the time lag between maximum transpiration and...
Mixing of stratified flow around bridge piers in steady current
DEFF Research Database (Denmark)
Jensen, Bjarne; Carstensen, Stefan; Christensen, Erik Damgaard
2018-01-01
This paper presents the results of an experimental and numerical investigation of the mixing of stratified flow around bridge pier structures. In this study, which was carried out in connection with the Fehmarnbelt Fixed Link environmental impact assessment, the mixing processes of two-layer stra......This paper presents the results of an experimental and numerical investigation of the mixing of stratified flow around bridge pier structures. In this study, which was carried out in connection with the Fehmarnbelt Fixed Link environmental impact assessment, the mixing processes of two......-layer stratification was studied in which the lower level had a higher salinity than the upper layer. The physical experiments investigated two different pier designs. A general study was made regarding forces on the piers in which the effect of the current angle relative to the structure was also included...
Steady particulate flows in a horizontal rotating cylinder
Yamane, K.; Nakagawa, M.; Altobelli, S. A.; Tanaka, T.; Tsuji, Y.
1998-06-01
Results of discrete element method (DEM) simulation and magnetic resonance imaging (MRI) experiments are compared for monodisperse granular materials flowing in a half-filled horizontal rotating cylinder. Because opacity is not a problem for MRI, a long cylinder with an aspect ratio ˜7 was used and the flow in a thin transverse slice near the center was studied. The particles were mustard seeds and the ratio of cylinder diameter to particle diameter was approximately 50. The parameters compared were dynamic angle of repose, velocity field in a plane perpendicular to the cylinder axis, and velocity fluctuations at rotation rates up to 30 rpm. The agreement between DEM and MRI was good when the friction coefficient and nonsphericity were adjusted in the simulation for the best fit.
Study of ATES thermal behavior using a steady flow model
Doughty, C.; Hellstroem, G.; Tsang, C. F.; Claesson, J.
1981-01-01
The thermal behavior of a single well aquifer thermal energy storage system in which buoyancy flow is neglected is studied. A dimensionless formulation of the energy transport equations for the aquifer system is presented, and the key dimensionless parameters are discussed. A simple numerical model is used to generate graphs showing the thermal behavior of the system as a function of these parameters. Some comparisons with field experiments are given to illustrate the use of the dimensionless groups and graphs.
Factors influencing flow steadiness in laminar boundary layer shock interactions
Tumuklu, Ozgur; Levin, Deborah A.; Gimelshein, Sergey F.; Austin, Joanna M.
2016-11-01
The Direct Simulation Monte Carlo method has been used to model laminar shock wave boundary interactions of hypersonic flow over a 30/55-deg double-wedge and "tick-shaped" model configurations studied in the Hypervelocity Expansion Tube facility and T-ADFA free-piston shock tunnel, respectively. The impact of thermochemical effects on these interactions by changing the chemical composition from nitrogen to air as well as argon for a stagnation enthalpy of 8.0 MJ/kg flow are investigated using the 2-D wedge model. The simulations are found to reproduce many of the classic features related to Edney Type V strong shock interactions that include the attached, oblique shock formed over the first wedge, the detached bow shock from the second wedge, the separation zone, and the separation and reattachment shocks that cause complex features such as the triple point for both cases. However, results of a reacting air flow case indicate that the size of the separation length, and the movement of the triple point toward to the leading edge is much less than the nitrogen case.
International Nuclear Information System (INIS)
Okhotnikov, Ivan; Noroozi, Siamak; Sewell, Philip; Godfrey, Philip
2017-01-01
Highlights: • A novel design of a rotary flow control valve driven by a stepper motor is proposed. • The intended use of the valve in the high flow rate independent metering hydraulic system is suggested. • Pressure drops, steady flow torques of the valve for various flow rates and orifice openings are studied by means of computational fluid dynamics. • The discharge coefficient and flow jet angles dependencies on the orifice opening are obtained. • A design method to decrease the flow forces without reducing the flow rate in single-staged valves is demonstrated. - Abstract: In this paper, a novel design of a rotary hydraulic flow control valve has been presented for high flow rate fluid power systems. High flow rates in these systems account for substantial flow forces acting on the throttling elements of the valves and cause the application of mechanically sophisticated multi-staged servo valves for flow regulation. The suggested design enables utilisation of single-stage valves in power hydraulics operating at high flow rates regimes. A spool driver and auxiliary mechanisms of the proposed valve design were discussed and selection criteria were suggested. Analytical expressions for metering characteristics as well as steady flow torques have been derived. Computational fluid dynamics (CFD) analysis of steady state flow regimes was conducted to evaluate the hydraulic behaviour of the proposed valve. This study represents a special case of an independent metering concept applied to the design of power hydraulic systems with direct proportional valve control operating at flow rates above 150 litres per minute. The result gained using parametric CFD simulations predicted the induced torque and the pressure drops due to a steady flow. Magnitudes of these values prove that by minimising the number of spool's mobile metering surfaces it is possible to reduce the flow-generated forces in the new generation of hydraulic valves proposed in this study
Evidence for forcing-dependent steady states in a turbulent swirling flow.
Saint-Michel, B; Dubrulle, B; Marié, L; Ravelet, F; Daviaud, F
2013-12-06
We study the influence on steady turbulent states of the forcing in a von Karman flow, at constant impeller speed, or at constant torque. We find that the different forcing conditions change the nature of the stability of the steady states and reveal dynamical regimes that bear similarities to low-dimensional systems. We suggest that this forcing dependence may be applicable to other turbulent systems.
Rubinato, Matteo; Martins, Ricardo; Kesserwani, Georges; Leandro, Jorge; Djordjević, Slobodan; Shucksmith, James
2017-09-01
The linkage between sewer pipe flow and floodplain flow is recognised to induce an important source of uncertainty within two-dimensional (2D) urban flood models. This uncertainty is often attributed to the use of empirical hydraulic formulae (the one-dimensional (1D) weir and orifice steady flow equations) to achieve data-connectivity at the linking interface, which require the determination of discharge coefficients. Because of the paucity of high resolution localised data for this type of flows, the current understanding and quantification of a suitable range for those discharge coefficients is somewhat lacking. To fulfil this gap, this work presents the results acquired from an instrumented physical model designed to study the interaction between a pipe network flow and a floodplain flow. The full range of sewer-to-surface and surface-to-sewer flow conditions at the exchange zone are experimentally analysed in both steady and unsteady flow regimes. Steady state measured discharges are first analysed considering the relationship between the energy heads from the sewer flow and the floodplain flow; these results show that existing weir and orifice formulae are valid for describing the flow exchange for the present physical model, and yield new calibrated discharge coefficients for each of the flow conditions. The measured exchange discharges are also integrated (as a source term) within a 2D numerical flood model (a finite volume solver to the 2D Shallow Water Equations (SWE)), which is shown to reproduce the observed coefficients. This calibrated numerical model is then used to simulate a series of unsteady flow tests reproduced within the experimental facility. Results show that the numerical model overestimated the values of mean surcharge flow rate. This suggests the occurrence of additional head losses in unsteady conditions which are not currently accounted for within flood models calibrated in steady flow conditions.
Steady state flow evaluations for passive auxiliary feedwater system of APR
International Nuclear Information System (INIS)
Park, Jongha; Kim, Jaeyul; Seong, Hoje; Kang, Kyoungho
2012-01-01
This paper briefly introduces a methodology to evaluate steady state flow of APR+ Passive Auxiliary Feedwater System (PAFS). The PAFS is being developed as a safety grade passive system to completely replace the existing active Auxiliary Feedwater System (AFWS). Natural circulation cooling can be generally classified into the single-phase, two-phase, and boiling-condensation modes. The PAF is designed to be operated in a boiling-condensation natural circulation mode. The steady-state flow rate should be equal to the steady-state boiling/condensation rate determined by the steady-state energy and momentum balances in the PAFS. The determined steady-state flow rate can be used in the design optimization for the natural circulation loop of the PAFS through the steady-state momentum balance. Since the retarding force, which is to be balanced by the driving force in the natural circulation system design depends on the reliable evaluation of the success of a natural circulation system design depends on the reliable evaluation of the pressure loss coefficients. In PAFS, the core decay heat is released by natural circulation flow between the S G secondary side and the Passive Condensation Heat Exchanger (PCHX) that is immersed in the Passive Condensation Cooling Tank (PCCT). The PCCT is located on the top of Auxiliary building The driving force is determined by the difference between the S/G (heat Source) secondary water level and condensation liquid (heat sink) level. It will overcome retarding force at flowrate in the system, which is determined by vaporization and condensation of the steam which is generated at the S/G by the latent heat in system. In this study, the theoretical method to estimate the steady state flow rate in boiling-condensation natural circulation system is developed and compared with test results
Steady-state magnetohydrodynamic flow around an unmagnetized conducting sphere
Energy Technology Data Exchange (ETDEWEB)
Romanelli, N.; Gómez, D.; Bertucci, C. [Group of Astrophysical Flows, Instituto de Astronomía y Física del Espacio, Buenos Aires (Argentina); Delva, M., E-mail: nromanelli@iafe.uba.ar, E-mail: Magda.Delva@oeaw.ac.at [Space Research Institute, Graz (Austria)
2014-07-01
The noncollisional interaction between conducting obstacles and magnetized plasma winds can be found in different scenarios, from the interaction occurring between regions inside galaxy clusters to the interaction between the solar wind and Mars, Venus, and active comets, or even the interaction between Titan and the Saturnian magnetospheric flow. These objects generate, through several current systems, perturbations in the streaming magnetic field leading to its draping around the obstacle's effective conducting surface. Recent observational results suggest that several properties associated with magnetic field draping, such as the location of the polarity reversal layer of the induced magnetotail, are affected by variations in the conditions of the streaming magnetic field. To improve our understanding of these phenomena, we perform a characterization of several magnetic field draping signatures by analytically solving an ideal problem in which a perfectly conducting magnetized plasma (with frozen-in magnetic field conditions) flows around a spherical body for various orientations of the streaming magnetic field. In particular, we compute the shift of the inverse polarity reversal layer as the orientation of the background magnetic field is changed.
Numerical flow analysis of axial flow compressor for steady and unsteady flow cases
Prabhudev, B. M.; Satish kumar, S.; Rajanna, D.
2017-07-01
Performance of jet engine is dependent on the performance of compressor. This paper gives numerical study of performance characteristics for axial compressor. The test rig is present at CSIR LAB Bangalore. Flow domains are meshed and fluid dynamic equations are solved using ANSYS package. Analysis is done for six different speeds and for operating conditions like choke, maximum efficiency & before stall point. Different plots are compared and results are discussed. Shock displacement, vortex flows, leakage patterns are presented along with unsteady FFT plot and time step plot.
Characteristics of turbulent particle transport in human airways under steady and cyclic flows
International Nuclear Information System (INIS)
Jedelsky, Jan; Lizal, Frantisek; Jicha, Miroslav
2012-01-01
Highlights: ► PDA data allow to estimate PSD of particle velocity fluctuations in realistic model. ► PSD of micron-sized particles is independent of their size up to 700 Hz. ► Such particles follow air flow and turb. diffusion contributes to their deposition. ► Cyclic flow PSDs contain more TKE at high freq. than equivalent steady-flow PSDs. ► Exp. breathing phase differs from insp. phase at high frequency part of the spectra. - Abstract: Motion of monodispersed aerosol particles suspended in air flow has been studied on realistic transparent model of human airways using Phase Doppler Particle Analyser (P/DPA). Time-resolved velocity data for particles in size range 1–8 μm were processed using Fuzzy Slotting Technique to estimate the power spectral density (PSD) of velocity fluctuations. The optimum processing setup for our data was found and recommendations for future experiments to improve PSD quality were suggested. Typical PSD plots at mainstream positions of the trachea and the upper bronchi are documented and differences among (1) steady-flow regimes and equivalent cyclic breathing regimes, (2) inspiration and expiration breathing phase and (3) behaviour of particles of different sizes are described in several positions of the airway model. Systematically higher level of velocity fluctuations in the upper part of the frequency range (30–500 Hz) was found for cyclic flows in comparison with corresponding steady flows. Expiratory flows in both the steady and cyclic cases produce more high-frequency fluctuations compared to inspiratory flows. Negligible differences were found for flow of particles in the inspected size range 1–8 μm at frequencies below 500 Hz. This finding was explained by Stokes number analysis. Implied match of the air and particle flows thereby indicates turbulent diffusion as important deposition mechanism and confirms the capability to use the P/DPA data as the air flow velocity estimate.
computational study of Couette flow between parallel plates for steady and unsteady cases
International Nuclear Information System (INIS)
Rihan, Y.
2008-01-01
Couette flow between parallel plates is a classical problem that has important applications in various industrial processing. In this investigation an analytical solution was obtained to predict the steady and unsteady Couette flow between parallel plates. One of the plates was stationary and the other plate moved with constant velocity. The governing partial differential equations were solved numerically using Crank-Nicolson implicit method to represent the flow behavior of the fluid
Directory of Open Access Journals (Sweden)
Jilian Wu
2013-01-01
Full Text Available We discuss several stabilized finite element methods, which are penalty, regular, multiscale enrichment, and local Gauss integration method, for the steady incompressible flow problem with damping based on the lowest equal-order finite element space pair. Then we give the numerical comparisons between them in three numerical examples which show that the local Gauss integration method has good stability, efficiency, and accuracy properties and it is better than the others for the steady incompressible flow problem with damping on the whole. However, to our surprise, the regular method spends less CPU-time and has better accuracy properties by using Crout solver.
Dynamic fluid connectivity during steady-state multiphase flow in a sandstone.
Reynolds, Catriona A; Menke, Hannah; Andrew, Matthew; Blunt, Martin J; Krevor, Samuel
2017-08-01
The current conceptual picture of steady-state multiphase Darcy flow in porous media is that the fluid phases organize into separate flow pathways with stable interfaces. Here we demonstrate a previously unobserved type of steady-state flow behavior, which we term "dynamic connectivity," using fast pore-scale X-ray imaging. We image the flow of N 2 and brine through a permeable sandstone at subsurface reservoir conditions, and low capillary numbers, and at constant fluid saturation. At any instant, the network of pores filled with the nonwetting phase is not necessarily connected. Flow occurs along pathways that periodically reconnect, like cars controlled by traffic lights. This behavior is consistent with an energy balance, where some of the energy of the injected fluids is sporadically converted to create new interfaces.
International Nuclear Information System (INIS)
Sahin, Ahmet Z.
2012-01-01
Highlights: ► The optimality in both heat and fluid flow systems has been investigated. ► A new thermodynamic property has been introduced. ► The second law of thermodynamics was extended to present the temheat balance that included the temheat destruction. ► The principle of temheat destruction minimization was introduced. ► It is shown that the rate of total temheat destruction is minimized in steady heat conduction and fluid flow problems. - Abstract: Heat transfer and fluid flow processes exhibit similarities as they occur naturally and are governed by the same type of differential equations. Natural phenomena occur always in an optimum way. In this paper, the natural optimality that exists in the heat transfer and fluid flow processes is investigated. In this regard, heat transfer and fluid flow problems are treated as optimization problems. We discovered a thermodynamic quantity that is optimized during the steady heat transfer and fluid flow processes. Consequently, a new thermodynamic property, the so called temheat, is introduced using the second law of thermodynamics and the definition of entropy. It is shown, through several examples, that overall temheat destruction is always minimized in steady heat and fluid flow processes. The principle of temheat destruction minimization that is based on the temheat balance equation provides a better insight to understand how the natural flow processes take place.
Laser Doppler anemometry measurements of steady flow through two bi-leaflet prosthetic heart valves
Directory of Open Access Journals (Sweden)
Ovandir Bazan
2013-12-01
Full Text Available INTRODUCTION: In vitro hydrodynamic characterization of prosthetic heart valves provides important information regarding their operation, especially if performed by noninvasive techniques of anemometry. Once velocity profiles for each valve are provided, it is possible to compare them in terms of hydrodynamic performance. In this first experimental study using laser doppler anemometry with mechanical valves, the simulations were performed at a steady flow workbench. OBJECTIVE: To compare unidimensional velocity profiles at the central plane of two bi-leaflet aortic prosthesis from St. Jude (AGN 21 - 751 and 21 AJ - 501 models exposed to a steady flow regime, on four distinct sections, three downstream and one upstream. METHODS: To provide similar conditions for the flow through each prosthesis by a steady flow workbench (water, flow rate of 17L/min. and, for the same sections and sweeps, to obtain the velocity profiles of each heart valve by unidimensional measurements. RESULTS: It was found that higher velocities correspond to the prosthesis with smaller inner diameter and instabilities of flow are larger as the section of interest is closer to the valve. Regions of recirculation, stagnation of flow, low pressure, and flow peak velocities were also found. CONCLUSIONS: Considering the hydrodynamic aspect and for every section measured, it could be concluded that the prosthesis model AGN 21 - 751 (RegentTM is superior to the 21 AJ - 501 model (Master Series. Based on the results, future studies can choose to focus on specific regions of the these valves.
Energy Technology Data Exchange (ETDEWEB)
Sohn, Hyun Chull [Chosun Univ., Gwangju (Korea, Republic of)
2005-05-01
In the present study, the characteristics of developing steady laminar flows of a straight duct connected to a 180 .deg. curved duct were examined in the entrance region through experimental measurement. Flow characteristics such as shear stress distributions, pressure distributions and friction coefficient experimentally in a square cross-sectional straight duct by using the PIV system. For the PIV measurement by particles produced from mosquito coils particles. The experimental data were obtained at 9 points dividing the test sections by 400 mm. Experimental results can be summarized as follows. Critical Reynolds number, Re{sub cr} which indicates transition from laminar steady flow to transition steady flow was 2,150. Shear stress per unit length on the wall was stronger than that in the fully developed flow region. This was attributed to the fact that shear stress and pressure loss in the curvature of a duct were increased. Pressure distributions were gradually decreased irrespective of Reynolds number in the whole test section. This trends were in a good agreement with the reference results. Pipe friction coefficient in the steady state flow region was calculate from method of least squares. The co-relationship between fiction coefficient and Reynolds number was established as follow; {lambda}=56/Re.
Theory of steady state plasma flow and confinement in a periodic magnetic field
International Nuclear Information System (INIS)
Brown, M.G.
1981-02-01
The steady flow of plasmas through spatially periodic magnetic fields is examined, and a theoretical model is developed for the case of axisymmetric geometry. The externally applied magnetic fields can be cusps or mirrors joined end to end; electrons are then localised by these fields because of their small Larmor radius, while the ions can traverse the magnetic mirrors. The properties of the model equations are studied and dimensionless parameters which appear are interpreted. Numerical methods used in steady flow applications are reviewed, and some techniques of solution for the model equations are discussed. A solution method involving numerical integration of time-dependent equations is described, which approaches the steady state asymptotically; results from this method are presented and compared with the results from perturbation theory. (author)
Computational issues of solving the 1D steady gradually varied flow equation
Directory of Open Access Journals (Sweden)
Artichowicz Wojciech
2014-09-01
Full Text Available In this paper a problem of multiple solutions of steady gradually varied flow equation in the form of the ordinary differential energy equation is discussed from the viewpoint of its numerical solution. Using the Lipschitz theorem dealing with the uniqueness of solution of an initial value problem for the ordinary differential equation it was shown that the steady gradually varied flow equation can have more than one solution. This fact implies that the nonlinear algebraic equation approximating the ordinary differential energy equation, which additionally coincides with the wellknown standard step method usually applied for computing of the flow profile, can have variable number of roots. Consequently, more than one alternative solution corresponding to the same initial condition can be provided. Using this property it is possible to compute the water flow profile passing through the critical stage.
An experimental setup for the study of the steady air flow in a diesel engine chamber
Directory of Open Access Journals (Sweden)
Montanero José María
2012-04-01
Full Text Available We present an experimental setup for studying the steady air flow in a diesel engine chamber. An engine block containing the inlet manifold was placed on a test bench. A steady air stream crossed the inlet manifold and entered a glass chamber driven by a fan. A PIV system was set up around the bench to measure the in-chamber flow. An air spray gun was used as seed generator to producing sub-millimeter droplets, easily dragged by the air stream. Images of the in-flow chamber were acquired in the course of the experiments, and processed to measure the velocity field. The pressure drop driven the air current and the mass flow rate were also measured.
Validation of a LES turbulence modeling approach on a steady engine head flow
Huijnen, V.; Somers, L.M.T.; Baert, R.S.G.; Goey, de L.P.H.; Dias, V.
2005-01-01
The application of the LES turbulence modeling approach in the Kiva-environment is validated on a complex geometry. Results for the steady flow in a realistic geometry of a production type heavy-duty diesel engine head with 120 mm cylinder bore are presented. The bulk Reynolds number is Reb = 1 fl
DEFF Research Database (Denmark)
Hassager, Ole; Mortensen, Kell; Bach, Anders
2012-01-01
We use small-angle neutron scattering to measure the molecular stretching in polystyrene melts undergoing steady elongational flow at large stretch rates. The radius of gyration of the central segment of a partly deuterated polystyrene molecule is, in the stretching direction, increasing...... exhibited by the linear polystyrene melt....
Steady state drift vortices in plasmas with shear flow in equilibrium
DEFF Research Database (Denmark)
Chakrabarti, N.
1999-01-01
The Hasegawa-Mima equation in the presence of sheared poloidal flow is solved for two-dimensional steady state vortex. It is shown that when the phase velocity of the vortex is the same as the diamagnetic drift velocity, an exact solution in the form of counter-rotating vortices may appear...
Directory of Open Access Journals (Sweden)
Yang Xiao-Jun
2016-01-01
Full Text Available In this article we propose a new fractional derivative without singular kernel. We consider the potential application for modeling the steady heat-conduction problem. The analytical solution of the fractional-order heat flow is also obtained by means of the Laplace transform.
Numerical simulation of steady cavitating flow of viscous fluid in a Francis hydroturbine
Panov, L. V.; Chirkov, D. V.; Cherny, S. G.; Pylev, I. M.; Sotnikov, A. A.
2012-09-01
Numerical technique was developed for simulation of cavitating flows through the flow passage of a hydraulic turbine. The technique is based on solution of steady 3D Navier—Stokes equations with a liquid phase transfer equation. The approch for setting boundary conditions meeting the requirements of cavitation testing standard was suggested. Four different models of evaporation and condensation were compared. Numerical simulations for turbines of different specific speed were compared with experiment.
Obtaining location/arrival-time and location/outflow-quantity distributions for steady flow systems
International Nuclear Information System (INIS)
Anon.
1977-01-01
A steady, two-dimensional flow system is used to demonstrate the application of location/arrival-time and location/outflow-quantity curves in determining the environmental consequences of groundwater contamination. The subsurface geologic and hydrologic evaluations needed to obtain the arrival results involve a sequence of four phases: system identification, new potential determination, flow systems kinematics, and contaminant transport analysis. Once these phases are completed, they are effectively summarized and easily used to evaluate environmental consequences through the arrival distributions
Prandtl boundary layer expansions of steady Navier-Stokes flows over a moving plate
Guo, Yan; Nguyen, Toan T.
2014-01-01
This paper concerns the validity of the Prandtl boundary layer theory in the inviscid limit for steady incompressible Navier-Stokes flows. The stationary flows, with small viscosity, are considered on $[0,L]\\times \\mathbb{R}_{+}$, assuming a no-slip boundary condition over a moving plate at $y=0$. We establish the validity of the Prandtl boundary layer expansion and its error estimates.
Experimental study on an IC engine in-cylinder flow using different steady-state flow benches
Directory of Open Access Journals (Sweden)
M. El-Adawy
2017-12-01
Full Text Available In-cylinder air flow structures are known to strongly impact on the performance and combustion of internal combustion engines (ICE. Therefore the aim of this paper is to experimentally study an IC engine in-cylinder flow under steady-state conditions. Different methods can be used to characterize the in-cylinder flow which are optical engines and laser diagnostics, computational fluid dynamic and steady-state flow bench. Here we are concentrating on two different types of flow benches. The first (Ricardo uses the impulse torque meter method while the other (FEV uses the paddle wheel technique. The experiments were carried out on the same cylinder head and the same pressure difference across the inlet valves of 600 mmH2O in order to compare the results. The experimental results are presented in terms of the measured air flow rate, flow coefficient, discharge coefficient and non-dimensional rig tumble. Moreover, number of modifications were conducted on the FEV flow bench in order to apply particle image velocimetry measurements on the vertical tumble plane, which passing through the middle of the cylinder at different valve lifts. The results show that a reasonably good level of agreement can be achieved between both methods, providing the methods of calculations of the various parameters are consistent. Keywords: In-cylinder flow, Flow bench, Tumble motion, Flow coefficient, Particle image velocimetry
Differences between automatically detected and steady-state fractional flow reserve.
Härle, Tobias; Meyer, Sven; Vahldiek, Felix; Elsässer, Albrecht
2016-02-01
Measurement of fractional flow reserve (FFR) has become a standard diagnostic tool in the catheterization laboratory. FFR evaluation studies were based on pressure recordings during steady-state maximum hyperemia. Commercially available computer systems detect the lowest Pd/Pa ratio automatically, which might not always be measured during steady-state hyperemia. We sought to compare the automatically detected FFR and true steady-state FFR. Pressure measurement traces of 105 coronary lesions from 77 patients with intermediate coronary lesions or multivessel disease were reviewed. In all patients, hyperemia had been achieved by intravenous adenosine administration using a dosage of 140 µg/kg/min. In 42 lesions (40%) automatically detected FFR was lower than true steady-state FFR. Mean bias was 0.009 (standard deviation 0.015, limits of agreement -0.02, 0.037). In 4 lesions (3.8%) both methods lead to different treatment recommendations, in all 4 cases instantaneous wave-free ratio confirmed steady-state FFR. Automatically detected FFR was slightly lower than steady-state FFR in more than one-third of cases. Consequently, interpretation of automatically detected FFR values closely below the cutoff value requires special attention.
Separation flow control on a generic ground vehicle using steady microjet arrays
Energy Technology Data Exchange (ETDEWEB)
Aubrun, Sandrine; Kourta, Azeddine [Universite d' Orleans, Laboratoire PRISME, Orleans cedex (France); McNally, Jonathan; Alvi, Farrukh [Florida State University, FAMU-FSU College of Engineering, Tallahassee, FL (United States)
2011-11-15
A model of a generic vehicle shape, the Ahmed body with a 25 slant, is equipped with an array of blowing steady microjets 6 mm downstream of the separation line between the roof and the slanted rear window. The goal of the present study is to evaluate the effectiveness of this actuation method in reducing the aerodynamic drag, by reducing or suppressing the 3D closed separation bubble located on the slanted surface. The efficiency of this control approach is quantified with the help of aerodynamic load measurements. The changes in the flow field when control is applied are examined using PIV and wall pressure measurements and skin friction visualisations. By activating the steady microjet array, the drag coefficient was reduced by 9-14% and the lift coefficient up to 42%, depending on the Reynolds number. The strong modification of the flow topology under progressive flow control is particularly studied. (orig.)
The quasi-steady state of all-vanadium redox flow batteries: A scale analysis
International Nuclear Information System (INIS)
Sharma, A.K.; Vynnycky, M.; Ling, C.Y.; Birgersson, E.; Han, M.
2014-01-01
Highlights: • We present a transient 2D model for a VRFB (conservation of species and charge); • Carry out scale analysis of the species conservation equation; • Derive the condition characterizing the quasi-steadiness of VRFB operation; • Verify it by comparing charge-discharge curve with transient simulations. - Abstract: In general, mathematical models for all-vanadium redox flow batteries (VRFB) that seek to capture the transport phenomena are transient in nature. In this paper, we carry out scale analysis of VRFB operation and derive the conditions when it can be assumed to be quasi-steady state in nature, i.e., time-dependence only through a boundary condition. We find that it is true for typical tank volume and flow rate employed for VRFBs. The proposed analysis is generic and can also be employed for other types of redox flow batteries
Predicted and experimental steady and unsteady transonic flows about a biconvex airfoil
Levy, L. L., Jr.
1981-01-01
Results of computer code time dependent solutions of the two dimensional compressible Navier-Stokes equations and the results of independent experiments are compared to verify the Mach number range for instabilities in the transonic flow field about a 14 percent thick biconvex airfoil at an angle of attack of 0 deg and a Reynolds number of 7 million. The experiments were conducted in a transonic, slotted wall wind tunnel. The computer code included an algebraic eddy viscosity turbulence model developed for steady flows, and all computations were made using free flight boundary conditions. All of the features documented experimentally for both steady and unsteady flows were predicted qualitatively; even with the above simplifications, the predictions were, on the whole, in good quantitative agreement with experiment. In particular, predicted time histories of shock wave position, surface pressures, lift, and pitching moment were found to be in very good agreement with experiment for an unsteady flow. Depending upon the free stream Mach number for steady flows, the surface pressure downstream of the shock wave or the shock wave location was not well predicted.
On the Kaolinite Floc Size at the Steady State of Flocculation in a Turbulent Flow.
Zhu, Zhongfan; Wang, Hongrui; Yu, Jingshan; Dou, Jie
2016-01-01
The flocculation of cohesive fine-grained sediment plays an important role in the transport characteristics of pollutants and nutrients absorbed on the surface of sediment in estuarine and coastal waters through the complex processes of sediment transport, deposition, resuspension and consolidation. Many laboratory experiments have been carried out to investigate the influence of different flow shear conditions on the floc size at the steady state of flocculation in the shear flow. Most of these experiments reported that the floc size decreases with increasing shear stresses and used a power law to express this dependence. In this study, we performed a Couette-flow experiment to measure the size of the kaolinite floc through sampling observation and an image analysis system at the steady state of flocculation under six flow shear conditions. The results show that the negative correlation of the floc size on the flow shear occurs only at high shear conditions, whereas at low shear conditions, the floc size increases with increasing turbulent shear stresses regardless of electrolyte conditions. Increasing electrolyte conditions and the initial particle concentration could lead to a larger steady-state floc size.
Effects of governing parameters on steady-state inter-wrapper flow in an LMFBR
International Nuclear Information System (INIS)
Moriya, Shoichi
2001-01-01
Hydraulic experiments were performed using a 1/8th scale rectangular model, based on a Japanese demonstration fast breeder reactor design, in order to study fundamental characteristics of interwrapper flows occurring under steady state conditions in an LMFBR. The steady state interwrapper flow of which direction was downward in the center region and upward in the peripheral region of a core barrel was observed because of the radial static pressure gradient in the upper part of the core barrel, produced by a core blockage effect resulting from an above core structure with a perforated skirt. Thermal stratification phenomena were moreover observed in the interwrapper region, created by the hot steady state interwrapper flow from an upper plenum and the cold leakage flow through the separated plate of the core barrel. The thermal interface was generated in higher part of the core barrel when the core blockage effect was smaller and Richardson number and the leakage flow rate ratio were larger. Significant temperature fluctuations occurred in the peripheral region of the core barrel, when the difference between the interface elevations in the center and peripheral regions of the core barrel was enough large. (author)
Vesicle dynamics in a confined Poiseuille flow: from steady state to chaos.
Aouane, Othmane; Thiébaud, Marine; Benyoussef, Abdelilah; Wagner, Christian; Misbah, Chaouqi
2014-09-01
Red blood cells (RBCs) are the major component of blood, and the flow of blood is dictated by that of RBCs. We employ vesicles, which consist of closed bilayer membranes enclosing a fluid, as a model system to study the behavior of RBCs under a confined Poiseuille flow. We extensively explore two main parameters: (i) the degree of confinement of vesicles within the channel and (ii) the flow strength. Rich and complex dynamics for vesicles are revealed, ranging from steady-state shapes (in the form of parachute and slipper shapes) to chaotic dynamics of shape. Chaos occurs through a cascade of multiple periodic oscillations of the vesicle shape. We summarize our results in a phase diagram in the parameter plane (degree of confinement and flow strength). This finding highlights the level of complexity of a flowing vesicle in the small Reynolds number where the flow is laminar in the absence of vesicles and can be rendered turbulent due to elasticity of vesicles.
A simplified approach for the computation of steady two-phase flow in inverted siphons.
Diogo, A Freire; Oliveira, Maria C
2016-01-15
Hydraulic, sanitary, and sulfide control conditions of inverted siphons, particularly in large wastewater systems, can be substantially improved by continuous air injection in the base of the inclined rising branch. This paper presents a simplified approach that was developed for the two-phase flow of the rising branch using the energy equation for a steady pipe flow, based on the average fluid fraction, observed slippage between phases, and isothermal assumption. As in a conventional siphon design, open channel steady uniform flow is assumed in inlet and outlet chambers, corresponding to the wastewater hydraulic characteristics in the upstream and downstream sewers, and the descending branch operates in steady uniform single-phase pipe flow. The proposed approach is tested and compared with data obtained in an experimental siphon setup with two plastic barrels of different diameters operating separately as in a single-barrel siphon. Although the formulations developed are very simple, the results show a good adjustment for the set of the parameters used and conditions tested and are promising mainly for sanitary siphons with relatively moderate heights of the ascending branch. Copyright © 2015 Elsevier Ltd. All rights reserved.
Blood flow patterns during incremental and steady-state aerobic exercise.
Coovert, Daniel; Evans, LeVisa D; Jarrett, Steven; Lima, Carla; Lima, Natalia; Gurovich, Alvaro N
2017-05-30
Endothelial shear stress (ESS) is a physiological stimulus for vascular homeostasis, highly dependent on blood flow patterns. Exercise-induced ESS might be beneficial on vascular health. However, it is unclear what type of ESS aerobic exercise (AX) produces. The aims of this study are to characterize exercise-induced blood flow patterns during incremental and steady-state AX. We expect blood flow pattern during exercise will be intensity-dependent and bidirectional. Six college-aged students (2 males and 4 females) were recruited to perform 2 exercise tests on cycleergometer. First, an 8-12-min incremental test (Test 1) where oxygen uptake (VO2), heart rate (HR), blood pressure (BP), and blood lactate (La) were measured at rest and after each 2-min step. Then, at least 48-hr. after the first test, a 3-step steady state exercise test (Test 2) was performed measuring VO2, HR, BP, and La. The three steps were performed at the following exercise intensities according to La: 0-2 mmol/L, 2-4 mmol/L, and 4-6 mmol/L. During both tests, blood flow patterns were determined by high-definition ultrasound and Doppler on the brachial artery. These measurements allowed to determine blood flow velocities and directions during exercise. On Test 1 VO2, HR, BP, La, and antegrade blood flow velocity significantly increased in an intensity-dependent manner (repeated measures ANOVA, pflow velocity did not significantly change during Test 1. On Test 2 all the previous variables significantly increased in an intensity-dependent manner (repeated measures ANOVA, pflow patterns during incremental and steady-state exercises include both antegrade and retrograde blood flows.
Comparison of Steady-State SVC Models in Load Flow Calculations
DEFF Research Database (Denmark)
Chen, Peiyuan; Chen, Zhe; Bak-Jensen, Birgitte
2008-01-01
This paper compares in a load flow calculation three existing steady-state models of static var compensator (SVC), i.e. the generator-fixed susceptance model, the total susceptance model and the firing angle model. The comparison is made in terms of the voltage at the SVC regulated bus, equivalent...... SVC susceptance at the fundamental frequency and the load flow convergence rate both when SVC is operating within and on the limits. The latter two models give inaccurate results of the equivalent SVC susceptance as compared to the generator model due to the assumption of constant voltage when the SVC...... is operating within the limits. This may underestimate or overestimate the SVC regulating capability. Two modified models are proposed to improve the SVC regulated voltage according to its steady-state characteristic. The simulation results of the two modified models show the improved accuracy...
Dynamics of lava flow - Thickness growth characteristics of steady two-dimensional flow
Park, S.; Iversen, J. D.
1984-01-01
The thickness growth characteristics of flowing lava are investigated using a heat balance model and a two-dimensional model for flow of a Bingham plastic fluid down an inclined plane. It is found that yield strength plays a crucial role in the thickening of a lava flow of given flow rate. To illustrate this point, downstream thickness profiles and yield strength distributions were calculated for flows with mass flow rates of 10,000 and 100,000 kg/m-sec. Higher flow rates led to slow cooling rates which resulted in slow rate of increase of yield strength and thus greater flow lengths.
International Nuclear Information System (INIS)
Ramakrishnan, Sankaran; Edwards, Christopher F.
2014-01-01
Systems research has led to the conception and development of various steady-flow, chemically-reactive, engine cycles for stationary power generation and propulsion. However, the question that remains unanswered is: What is the maximum-efficiency steady-flow chemically-reactive engine architecture permitted by physics? On the one hand the search for higher-efficiency cycles continues, often involving newer processes and devices (fuel cells, carbon separation, etc.); on the other hand the design parameters for existing cycles are continually optimized in response to improvements in device engineering. In this paper we establish that any variation in engine architecture—parametric change or process-sequence change—contributes to an efficiency increase via one of only two possible ways to minimize total irreversibility. These two principles help us unify our understanding from a large number of parametric analyses and cycle-optimization studies for any steady-flow chemically-reactive engine, and set a framework to systematically identify maximum-efficiency engine architectures. - Highlights: • A unified thermodynamic model to study chemically-reactive engine architectures is developed. • All parametric analyses of efficiency are unified by two irreversibility-minimization principles. • Variations in internal energy transfers yield a net work increase that is greater than engine irreversibility reduced. • Variations in external energy transfers yield a net work increase that is lesser than engine irreversibility reduced
On the accuracy of Whitham's method. [for steady ideal gas flow past cones
Zahalak, G. I.; Myers, M. K.
1974-01-01
The steady flow of an ideal gas past a conical body is studied by the method of matched asymptotic expansions and by Whitham's method in order to assess the accuracy of the latter. It is found that while Whitham's method does not yield a correct asymptotic representation of the perturbation field to second order in regions where the flow ahead of the Mach cone of the apex is disturbed, it does correctly predict the changes of the second-order perturbation quantities across a shock (the first-order shock strength). The results of the analysis are illustrated by a special case of a flat, rectangular plate at incidence.
Variable property, steady, axi-symmetric, laminar, continuum plasma flow over spheroidal particles
International Nuclear Information System (INIS)
Wen Yuemin; Jog, Milind A.
2005-01-01
Steady, continuum, laminar plasma flow over spheroidal particles has been numerically investigated in this paper using a finite volume method. To body-fit the non-spherical particle surface, an adaptive orthogonal grid is generated. The flow field and the temperature distribution are calculated for oblate and prolate particle shapes. A number of particle surface temperatures and far field temperatures are considered and thermo-physical property variation is fully accounted for in our model. The particle shapes are represented in terms of axis ratio which is defined as the ratio of axis perpendicular to the flow direction to the axis along the flow direction. For oblate shape, axis ratios from 1.6 (disk-like) to 1 (sphere) are used whereas for prolate shape, axis ratios of 1(sphere) to 0.4 (cylinder-like) are used. Effects of flow Reynolds number, particle shape, surface and far field temperatures, and variable properties, on the flow field, temperature variations, drag coefficient, and Nusselt number are outlined. Results show that particle shape has significant effect on flow and heat transfer to particle surface. Compared to a constant property flow, accounting for thermo-physical property variation leads to prediction of higher temperature and velocity gradients in the vicinity of the particle surface. Based on the numerical results, a correlation for the Nusslet number is proposed that accounts for the effect of particle shape in continuum flow with large thermo-physical property variation
Formation of structural steady states in lamellar/sponge phase-separating fluids under shear flow
Panizza, P.; Courbin, L.; Cristobal, G.; Rouch, J.; Narayanan, T.
2003-05-01
We investigate the effect of shear flow on a lamellar-sponge phase-separating fluid when subjected to shear flow. We show the existence of two different steady states (droplets and ribbons structures) whose nature does not depend on the way to reach the two-phase unstable region of the phase diagram (temperature quench or stirring). The transition between ribbons and droplets is shear thickening and its nature strongly depends on what dynamical variable is imposed. If the stress is fixed, flow visualization shows the existence of shear bands at the transition, characteristic of coexistence in the cell between ribbons and droplets. In this shear-banding region, the viscosity oscillates. When the shear rate is fixed, no shear bands are observed. Instead, the transition exhibits a hysteretic behavior leading to a structural bi-stability of the phase-separating fluid under flow.
Modeling of the blood rheology in steady-state shear flows
International Nuclear Information System (INIS)
Apostolidis, Alex J.; Beris, Antony N.
2014-01-01
We undertake here a systematic study of the rheology of blood in steady-state shear flows. As blood is a complex fluid, the first question that we try to answer is whether, even in steady-state shear flows, we can model it as a rheologically simple fluid, i.e., we can describe its behavior through a constitutive model that involves only local kinematic quantities. Having answered that question positively, we then probe as to which non-Newtonian model best fits available shear stress vs shear-rate literature data. We show that under physiological conditions blood is typically viscoplastic, i.e., it exhibits a yield stress that acts as a minimum threshold for flow. We further show that the Casson model emerges naturally as the best approximation, at least for low and moderate shear-rates. We then develop systematically a parametric dependence of the rheological parameters entering the Casson model on key physiological quantities, such as the red blood cell volume fraction (hematocrit). For the yield stress, we base our description on its critical, percolation-originated nature. Thus, we first determine onset conditions, i.e., the critical threshold value that the hematocrit has to have in order for yield stress to appear. It is shown that this is a function of the concentration of a key red blood cell binding protein, fibrinogen. Then, we establish a parametric dependence as a function of the fibrinogen and the square of the difference of the hematocrit from its critical onset value. Similarly, we provide an expression for the Casson viscosity, in terms of the hematocrit and the temperature. A successful validation of the proposed formula is performed against additional experimental literature data. The proposed expression is anticipated to be useful not only for steady-state blood flow modeling but also as providing the starting point for transient shear, or more general flow modeling
Implicit unified gas-kinetic scheme for steady state solutions in all flow regimes
Zhu, Yajun; Zhong, Chengwen; Xu, Kun
2016-06-01
This paper presents an implicit unified gas-kinetic scheme (UGKS) for non-equilibrium steady state flow computation. The UGKS is a direct modeling method for flow simulation in all regimes with the updates of both macroscopic flow variables and microscopic gas distribution function. By solving the macroscopic equations implicitly, a predicted equilibrium state can be obtained first through iterations. With the newly predicted equilibrium state, the evolution equation of the gas distribution function and the corresponding collision term can be discretized in a fully implicit way for fast convergence through iterations as well. The lower-upper symmetric Gauss-Seidel (LU-SGS) factorization method is implemented to solve both macroscopic and microscopic equations, which improves the efficiency of the scheme. Since the UGKS is a direct modeling method and its physical solution depends on the mesh resolution and the local time step, a physical time step needs to be fixed before using an implicit iterative technique with a pseudo-time marching step. Therefore, the physical time step in the current implicit scheme is determined by the same way as that in the explicit UGKS for capturing the physical solution in all flow regimes, but the convergence to a steady state speeds up through the adoption of a numerical time step with large CFL number. Many numerical test cases in different flow regimes from low speed to hypersonic ones, such as the Couette flow, cavity flow, and the flow passing over a cylinder, are computed to validate the current implicit method. The overall efficiency of the implicit UGKS can be improved by one or two orders of magnitude in comparison with the explicit one.
Metzger, Fabian; Mischek, Daniel; Stoffers, Frédéric
2017-01-01
Here we show that the hydrodynamic radii-dependent entry of blood proteins into cerebrospinal fluid (CSF) can best be modeled with a diffusional system of consecutive interdependent steady states between barrier-restricted molecular flux and bulk flow of CSF. The connected steady state model fits precisely to experimental results and provides the theoretical backbone to calculate the in-vivo hydrodynamic radii of blood-derived proteins as well as individual barrier characteristics. As the experimental reference set we used a previously published large-scale patient cohort of CSF to serum quotient ratios of immunoglobulins in relation to the respective albumin quotients. We related the inter-individual variances of these quotient relationships to the individual CSF flow time and barrier characteristics. We claim that this new concept allows the diagnosis of inflammatory processes with Reibergrams derived from population-based thresholds to be shifted to individualized judgment, thereby improving diagnostic sensitivity. We further use the source-dependent gradient patterns of proteins in CSF as intrinsic tracers for CSF flow characteristics. We assume that the rostrocaudal gradient of blood-derived proteins is a consequence of CSF bulk flow, whereas the slope of the gradient is a consequence of the unidirectional bulk flow and bidirectional pulsatile flow of CSF. Unlike blood-derived proteins, the influence of CSF flow characteristics on brain-derived proteins in CSF has been insufficiently discussed to date. By critically reviewing existing experimental data and by reassessing their conformity to CSF flow assumptions we conclude that the biomarker potential of brain-derived proteins in CSF can be improved by considering individual subproteomic dynamics of the CSF system.
Volume of the steady-state space of financial flows in a monetary stock-flow-consistent model
Hazan, Aurélien
2017-05-01
We show that a steady-state stock-flow consistent macro-economic model can be represented as a Constraint Satisfaction Problem (CSP). The set of solutions is a polytope, which volume depends on the constraints applied and reveals the potential fragility of the economic circuit, with no need to study the dynamics. Several methods to compute the volume are compared, inspired by operations research methods and the analysis of metabolic networks, both exact and approximate. We also introduce a random transaction matrix, and study the particular case of linear flows with respect to money stocks.
Constitutive Curve and Velocity Profile in Entangled Polymers during Start-Up of Steady Shear Flow
Hayes, Keesha A.
2010-05-11
Time-dependent shear stress versus shear rate, constitutive curve, and velocity profile measurements are reported in entangled polymer solutions during start-up of steady shear flow. By combining confocal microscopy and particle image velocimetry (PIV), we determine the time-dependent velocity profile in polybutadiene and polystyrene solutions seeded with fluorescent 150 nm silica and 7.5 μm melamine particles. By comparing these profiles with time-dependent constitutive curves obtained from experiment and theory, we explore the connection between transient nonmonotonic regions in the constitutive curve for an entangled polymer and its susceptibility to unstable flow by shear banding [Adams et al. Phys. Rev. Lett. 2009, 102, 067801-4]. Surprisingly, we find that even polymer systems which exhibit transient, nonmonotonic shear stress-shear rate relationships in bulk rheology experiments manifest time-dependent velocity profiles that are decidedly linear and show no evidence of unstable flow. We also report that interfacial slip plays an important role in the steady shear flow behavior of entangled polymers at shear rates above the reciprocal terminal relaxation time but has little, if any, effect on the shape of the velocity profile. © 2010 American Chemical Society.
Steady shear flow properties of Cordia myxa leaf gum as a function of concentration and temperature.
Chaharlang, Mahmood; Samavati, Vahid
2015-08-01
The steady shear flow properties of dispersions of Cordia myxa leaf gum (CMLG) were determined as a function of concentration (0.5-2.5%, w/w), and temperature (10-50 °C). The CMLG dispersions exhibited strong shear-thinning behavior at all concentrations and temperatures. The Power-law (Ostwald-Waele's) and Herschel-Bulkley models were employed to characterize flow behavior of CMLG solutions at 0.1-100 s(-1) shear rate. Non-Newtonian shear-thinning behavior was observed at all temperatures and concentrations. While increase in temperature decreased the viscosity and increased the flow behavior indices, adverse effect was obtained by increasing the concentration. The Power-law model was found the best model to describe steady shear flow behavior of CMLG. The pseudoplasticity of CMLG increased markedly with concentration. An Arrhenius-type model was also used to describe the effect of temperature. The activation energy (Ea) appeared in the range of 5.972-18.104 kJ/mol, as concentration increased from 0.5% to 2.5%, at a shear rate of 10 s(-1). Copyright © 2015 Elsevier B.V. All rights reserved.
The effect of ultrasound on arterial blood flow: 1. Steady fully developed flow
International Nuclear Information System (INIS)
Bestman, A.R.
1990-12-01
The paper models the effects of ultrasound heating of the tissues and the resultant perturbation on blood flow in the arteries and veins. It is assumed that the blood vessel is rigid and the undisturbed flow is fully developed. Acoustical perturbation on this Poiseuille flow, for the general three-dimensional flow with heat transfer in an infinitely long pipe is considered. Closed form analytical solutions are obtained to the problem. It is discovered that the effects of the ultrasound heating are concentrated at the walls of the blood vessels. (author). 4 refs
Steady finite-Reynolds-number flows in three-dimensional collapsible tubes
Hazel, Andrew L.; Heil, Matthias
2003-07-01
A fully coupled finite-element method is used to investigate the steady flow of a viscous fluid through a thin-walled elastic tube mounted between two rigid tubes. The steady three-dimensional Navier Stokes equations are solved simultaneously with the equations of geometrically nonlinear Kirchhoff Love shell theory. If the transmural (internal minus external) pressure acting on the tube is sufficiently negative then the tube buckles non-axisymmetrically and the subsequent large deformations lead to a strong interaction between the fluid and solid mechanics. The main effect of fluid inertia on the macroscopic behaviour of the system is due to the Bernoulli effect, which induces an additional local pressure drop when the tube buckles and its cross-sectional area is reduced. Thus, the tube collapses more strongly than it would in the absence of fluid inertia. Typical tube shapes and flow fields are presented. In strongly collapsed tubes, at finite values of the Reynolds number, two ’jets‘ develop downstream of the region of strongest collapse and persist for considerable axial distances. For sufficiently high values of the Reynolds number, these jets impact upon the sidewalls and spread azimuthally. The consequent azimuthal transport of momentum dramatically changes the axial velocity profiles, which become approximately uTheta-shaped when the flow enters the rigid downstream pipe. Further convection of momentum causes the development of a ring-shaped velocity profile before the ultimate return to a parabolic profile far downstream.
Application of the Green's function method for 2- and 3-dimensional steady transonic flows
Tseng, K.
1984-01-01
A Time-Domain Green's function method for the nonlinear time-dependent three-dimensional aerodynamic potential equation is presented. The Green's theorem is being used to transform the partial differential equation into an integro-differential-delay equation. Finite-element and finite-difference methods are employed for the spatial and time discretizations to approximate the integral equation by a system of differential-delay equations. Solution may be obtained by solving for this nonlinear simultaneous system of equations in time. This paper discusses the application of the method to the Transonic Small Disturbance Equation and numerical results for lifting and nonlifting airfoils and wings in steady flows are presented.
CFD simulations of steady flows over the IAR 65o delta wing
International Nuclear Information System (INIS)
Benmeddour, A.; Mebarki, Y.; Huang, X.Z.
2004-01-01
Computational Fluid Dynamics (CFD) studies have been conducted to simulate vortical flows around the IAR 65 o delta wing with a sharp leading edge. The effects of the centerbody on the aerodynamic characteristics of the wing are also investigated. Two flow solvers have been employed to compute steady inviscid flows over with and without centerbody configurations of the wing. These two solvers are an IAR in-house code, FJ3SOLV, and the CFD-FASTRAN commercial software. The computed flow solutions of the two solvers have been compared and correlated against the IAR wind tunnel data, including Pressure Sensitive Paint (PSP) measurements. The major features of the primary vortex have been well captured and overall reasonable accuracy was obtained. In accordance with the experimental observations for the flow conditions considered, the CFD computations revealed no major global effects of the centerbody on the surface pressure distributions of the wing and on the lift coefficient. However, CFD-FASTRAN seems to predict a vortex breakdown, which is neither predicted by FJ3SOLV nor observed in the wind tunnel for the flow conditions considered. (author)
Finite volume simulation of 2-D steady square lid driven cavity flow at high reynolds numbers
Directory of Open Access Journals (Sweden)
K. Yapici
2013-12-01
Full Text Available In this work, computer simulation results of steady incompressible flow in a 2-D square lid-driven cavity up to Reynolds number (Re 65000 are presented and compared with those of earlier studies. The governing flow equations are solved by using the finite volume approach. Quadratic upstream interpolation for convective kinematics (QUICK is used for the approximation of the convective terms in the flow equations. In the implementation of QUICK, the deferred correction technique is adopted. A non-uniform staggered grid arrangement of 768x768 is employed to discretize the flow geometry. Algebraic forms of the coupled flow equations are then solved through the iterative SIMPLE (Semi-Implicit Method for Pressure-Linked Equation algorithm. The outlined computational methodology allows one to meet the main objective of this work, which is to address the computational convergence and wiggled flow problems encountered at high Reynolds and Peclet (Pe numbers. Furthermore, after Re > 25000 additional vortexes appear at the bottom left and right corners that have not been observed in earlier studies.
International Nuclear Information System (INIS)
Karpp, R.R.
1984-01-01
The particle solution of the problem of the symmetric impact of two compressible fluid stream is derived. The plane two-dimensional flow is assumed to be steady, and the inviscid compressible fluid is of the Chaplygin (tangent gas) type. The equations governing this flow are transformed to the hodograph plane where an exact, closed-form solution for the stream function is obtained. The distribution of fluid properties along the plane of symmetry and the shape of free surface streamlines are determined by transformation back to the physical plane. The problem of a compressible fluid jet penetrating an infinite target of similar material is also solved by considering a limiting case of this solution. Differences between compressible and incompressible flows of the type considered are illustrated
One-dimensional model of steady, compressible channel flow with mass, momentum, and energy addition
International Nuclear Information System (INIS)
Johnston, S.C.
1976-09-01
A one-dimensional model of steady, compressible channel flow with mass, momentum and energy addition is discussed. An exact solution to the governing equations was found and from it a similarity parameter relating dimensionless mass, momentum and energy addition identified. This similarity parameter is used to make two flows having different dimensionless mass, momentum and energy additions equivalent. Application of the similarity parameter to the LASL Intense Neutron Source experiment and the Sandia simulation of that experiment results in an expression relating the dimensionless mass addition of combustible gas required in the Sandia experiment to dimensionless energy addition in the LASL experiment. Results of the analysis indicate that the Sandia experiment can realistically simulate the energy addition in the LASL Intense Neutron Source experiment
On the analytic solution of the steady flow of a fourth grade fluid
International Nuclear Information System (INIS)
Sajid, M.; Hayat, T.; Asghar, S.
2006-01-01
The steady flow of a fourth grade fluid is a problem belonging to non-Newtonian fluid mechanics and deserves to be more widely studied than it has been to date. In the non-linear regime the literature is scarce. We develop a formulation suitable for solution of hydrodynamic equation containing non-linear rheological effects of fourth grade fluids. The homotopy analysis method (HAM) is used to investigate the flow of a fourth grade fluid past a porous plate. Explicit analytic solution is given. The non-linear effects on the velocity distribution is shown and discussed. Comparison of the present analysis is also made with the existing results in the literature
Steady Stokes flow past dumbbell shaped axially symmetric body of revolution: An analytic approach
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Srivastava Kumar Deepak
2012-01-01
Full Text Available In this paper, the problem of steady Stokes flow past dumbbell-shaped axially symmetric isolated body of revolution about its axis of symmetry is considered by utilizing a method (Datta and Srivastava, 1999 based on body geometry under the restrictions of continuously turning tangent on the boundary. The relationship between drag and moment is established in transverse flow situation. The closed form expression of Stokes drag is then calculated for dumbbell-shaped body in terms of geometric parameters b, c, d and a with the aid of this linear relation and the formula of torque obtained by (Chwang and Wu, part 1, 1974 with the use of singularity distribution along axis of symmetry. Drag coefficient and moment coefficient are defined in various forms in terms of dumbbell parameters. Their numerical values are calculated and depicted in respective graphs and compared with some known values.
Koroglu, Batikan; Mehl, Marco; Armstrong, Michael R; Crowhurst, Jonathan C; Weisz, David G; Zaug, Joseph M; Dai, Zurong; Radousky, Harry B; Chernov, Alex; Ramon, Erick; Stavrou, Elissaios; Knight, Kim; Fabris, Andrea L; Cappelli, Mark A; Rose, Timothy P
2017-09-01
We present the development of a steady state plasma flow reactor to investigate gas phase physical and chemical processes that occur at high temperature (1000 flow injector). We have modeled the system using computational fluid dynamics simulations that are bounded by measured temperatures. In situ line-of-sight optical emission and absorption spectroscopy have been used to determine the structures and concentrations of molecules formed during rapid cooling of reactants after they pass through the plasma. Emission spectroscopy also enables us to determine the temperatures at which these dynamic processes occur. A sample collection probe inserted from the open end of the reactor is used to collect condensed materials and analyze them ex situ using electron microscopy. The preliminary results of two separate investigations involving the condensation of metal oxides and chemical kinetics of high-temperature gas reactions are discussed.
Directory of Open Access Journals (Sweden)
Bouakkaz Rafik
2017-06-01
Full Text Available In this work, steady flow-field and heat transfer through a copper- water nanofluid around a rotating circular cylinder with a constant nondimensional rotation rate α varying from 0 to 5 was investigated for Reynolds numbers of 5–40. Furthermore, the range of nanoparticle volume fractions considered is 0–5%. The effect of volume fraction of nanoparticles on the fluid flow and heat transfer characteristics are carried out by using a finite-volume method based commercial computational fluid dynamics solver. The variation of the local and the average Nusselt numbers with Reynolds number, volume fractions, and rotation rate are presented for the range of conditions. The average Nusselt number is found to decrease with increasing value of the rotation rate for the fixed value of the Reynolds number and volume fraction of nanoparticles. In addition, rotation can be used as a drag reduction technique.
Characteristics of steady-state plasma flow in the tokamak limiter scrape-off layer
International Nuclear Information System (INIS)
Petrov, V.G.
1984-01-01
Steady state plasma flow in the scrape-off layer of a toroidal limiter is discussed. The force balance along the torus minor radius is taken into account, from which follows that the plasma pressure gradient is balanced by the ponderomotive force (1/c) j-vectorxB-vector, which arises in the presence of a current density component perpendicular to the magnetic field. The limiter has an important effect on the electric current flow in the scrape-off layer. It is shown that the electric potential and plasma density values differ from one side of the limiter to the other; this leads to plasma drift along the minor radius. The characteristic length of change in the plasma density is found to be of the order of the ion cyclotron radius calculated for a poloidal magnetic field. (author)
Fast Virtual Fractional Flow Reserve Based Upon Steady-State Computational Fluid Dynamics Analysis
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Paul D. Morris, PhD
2017-08-01
Full Text Available Fractional flow reserve (FFR-guided percutaneous intervention is superior to standard assessment but remains underused. The authors have developed a novel “pseudotransient” analysis protocol for computing virtual fractional flow reserve (vFFR based upon angiographic images and steady-state computational fluid dynamics. This protocol generates vFFR results in 189 s (cf >24 h for transient analysis using a desktop PC, with <1% error relative to that of full-transient computational fluid dynamics analysis. Sensitivity analysis demonstrated that physiological lesion significance was influenced less by coronary or lesion anatomy (33% and more by microvascular physiology (59%. If coronary microvascular resistance can be estimated, vFFR can be accurately computed in less time than it takes to make invasive measurements.
Steady flow instability in an annulus with deflectors at rotational vibration
Energy Technology Data Exchange (ETDEWEB)
Kozlov, Nikolai V [Lab. Vibrational Hydromechanics, Perm State-Humanitarian Pedagogical University 24 Sibirskaya av., 614990 Perm (Russian Federation); Pareau, Dominique; Stambouli, Moncef [Lab. Chemical Engineering, CentraleSupélec-Université Paris Saclay, Grande Voie des Vignes, 92295 Châtenay-Malabry (France); Ivantsov, Andrey, E-mail: kozlov.n@icmm.ru [Lab. Computational Hydrodynamics Institute of Continuous Media Mechanics UB RAS1 Acad. Korolev st., 614013 Perm (Russian Federation)
2016-12-15
Experimental study and direct numerical simulation of the dynamics of an isothermal low-viscosity fluid are done in a coaxial gap of a cylindrical container making rotational vibrations relative to its axis. On the inner surface of the outer wall of the container, semicircular deflectors are regularly situated, playing the role of flow activators. As a result of vibrations, the activators oscillate tangentially. In the simulation, a 2D configuration is considered, excluding the end-wall effects. In the experiment, a container with a large aspect ratio is used. Steady streaming is generated in the viscous boundary layers on the activators. On each of the latter, beyond the viscous domain, a symmetric vortices pair is formed. The steady streaming in the annulus has an azimuthal periodicity. With an increase in the vibration intensity, a competition between the vortices occurs, as a result of which one of the vortices (let us call it even) approaches the activator and the other one (odd) rolls away and couples with the vortices from the neighbouring pairs. Streamlines of the odd vortices close on each other, forming a cog-wheel shaped flow that encircles the inner wall. Comparison of the experiment and the simulation reveals an agreement at moderate vibration intensity. (paper)
International Nuclear Information System (INIS)
Szenknect, St.
2003-10-01
This work is devoted to the quantification and the identification of the predominant processes involved in strontium and caesium transport in unsaturated soil from Chernobyl Pilot Site under steady flow conditions. The transport and fate of radionuclides in the subsurface is affected by various physical and chemical processes including advective and diffusive transport as well as chemical and biological transformations. Laboratory experiments and the use of a multiple tracer approach allow to isolate the contributions of each elementary process and to control the physico-chemical conditions in the system. To be more representative of the field conditions, we decided to perform column miscible displacement experiments. We perform batch and flow-through reactor experiments to characterize the radionuclides sorption mechanisms. Miscible displacement experiments within homogeneous columns and modeling allow to characterize the hydrodynamic properties of the soil and to describe the radionuclides behaviour under dynamic conditions at different water contents. We show that the water content of porous media affect the transport behaviour of inert and strongly sorbing radionuclides. Our results demonstrate that a parametrized transport model that was calibrated under completely saturated conditions was not able to describe the advective-dispersive transport of reactive solutes under unsaturated steady state conditions. Under our experimental conditions, there is no effect of a decrease of the mean water content on the sorption model parameters, but the transport parameters are modified. We established for the studied soil the relation between hydrodynamic dispersion and water content and the relation between pore water velocity and water content. (author)
Quantifying measurement uncertainties in ADCP measurements in non-steady, inhomogeneous flow
Schäfer, Stefan
2017-04-01
The author presents a laboratory study of fixed-platform four-beam ADCP and three-beam ADV measurements in the tailrace of a micro hydro power setup with a 35kW Kaplan-turbine and 2.5m head. The datasets discussed quantify measurement uncertainties of the ADCP measurement technique coming from non-steady, inhomogeneous flow. For constant discharge of 1.5m3/s, two different flow scenarios were investigated: one being the regular tailrace flow downstream the draft tube and the second being a straightened, less inhomogeneous flow, which was generated by the use of a flow straightening device: A rack of diameter 40mm pipe sections was mounted right behind the draft tube. ADCP measurements (sampling rate 1.35Hz) were conducted in three distances behind the draft tube and compared bin-wise to measurements of three simultaneously measuring ADV probes (sampling rate 64Hz). The ADV probes were aligned horizontally and the ADV bins were placed in the centers of two facing ADCP bins and in the vertical under the ADCP probe of the corresponding depth. Rotating the ADV probes by 90° allowed for measurements of the other two facing ADCP bins. For reasons of mutual probe interaction, ADCP and ADV measurements were not conducted at the same time. The datasets were evaluated by using mean and fluctuation velocities. Turbulence parameters were calculated and compared as far as applicable. Uncertainties coming from non-steady flow were estimated with the normalized mean square error und evaluated by comparing long-term measurements of 60 minutes to shorter measurement intervals. Uncertainties coming from inhomogeneous flow were evaluated by comparison of ADCP with ADV data along the ADCP beams where ADCP data were effectively measured and in the vertical under the ADCP probe where velocities of the ADCP measurements were displayed. Errors coming from non-steady flow could be compensated through sufficiently long measurement intervals with high enough sampling rates depending on the
Applicability of Kinematic and Diffusive models for mud-flows: a steady state analysis
Di Cristo, Cristiana; Iervolino, Michele; Vacca, Andrea
2018-04-01
The paper investigates the applicability of Kinematic and Diffusive Wave models for mud-flows with a power-law shear-thinning rheology. In analogy with a well-known approach for turbulent clear-water flows, the study compares the steady flow depth profiles predicted by approximated models with those of the Full Dynamic Wave one. For all the models and assuming an infinitely wide channel, the analytical solution of the flow depth profiles, in terms of hypergeometric functions, is derived. The accuracy of the approximated models is assessed by computing the average, along the channel length, of the errors, for several values of the Froude and kinematic wave numbers. Assuming the threshold value of the error equal to 5%, the applicability conditions of the two approximations have been individuated for several values of the power-law exponent, showing a crucial role of the rheology. The comparison with the clear-water results indicates that applicability criteria for clear-water flows do not apply to shear-thinning fluids, potentially leading to an incorrect use of approximated models if the rheology is not properly accounted for.
Steady flow rate to a partially penetrating well with seepage face in an unconfined aquifer
Behrooz-Koohenjani, Siavash; Samani, Nozar; Kompani-Zare, Mazda
2011-06-01
The flow rate to fully screened, partially penetrating wells in an unconfined aquifer is numerically simulated using MODFLOW 2000, taking into account the flow from the seepage face and decrease in saturated thickness of the aquifer towards the well. A simple three-step method is developed to find the top of the seepage face and hence the seepage-face length. The method is verified by comparing it with the results of previous predictive methods. The results show that the component of flow through the seepage face can supply a major portion of the total pumping rate. Variations in flow rate as a function of the penetration degree, elevation of the water level in the well and the distance to the far constant head boundary are investigated and expressed in terms of dimensionless curves and equations. These curves and equations can be used to design the degree of penetration for which the allowable steady pumping rate is attained for a given elevation of water level in the well. The designed degree of penetration or flow rate will assure the sustainability of the aquifer storage, and can be used as a management criterion for issuing drilling well permits by groundwater protection authorities.
Frozen reaction fronts in steady flows: A burning-invariant-manifold perspective
Mahoney, John R.; Li, John; Boyer, Carleen; Solomon, Tom; Mitchell, Kevin A.
2015-12-01
The dynamics of fronts, such as chemical reaction fronts, propagating in two-dimensional fluid flows can be remarkably rich and varied. For time-invariant flows, the front dynamics may simplify, settling in to a steady state in which the reacted domain is static, and the front appears "frozen." Our central result is that these frozen fronts in the two-dimensional fluid are composed of segments of burning invariant manifolds, invariant manifolds of front-element dynamics in x y θ space, where θ is the front orientation. Burning invariant manifolds (BIMs) have been identified previously as important local barriers to front propagation in fluid flows. The relevance of BIMs for frozen fronts rests in their ability, under appropriate conditions, to form global barriers, separating reacted domains from nonreacted domains for all time. The second main result of this paper is an understanding of bifurcations that lead from a nonfrozen state to a frozen state, as well as bifurcations that change the topological structure of the frozen front. Although the primary results of this study apply to general fluid flows, our analysis focuses on a chain of vortices in a channel flow with an imposed wind. For this system, we present both experimental and numerical studies that support the theoretical analysis developed here.
Steady streaming: A key mixing mechanism in low-Reynolds-number acinar flows
Kumar, Haribalan; Tawhai, Merryn H.; Hoffman, Eric A.; Lin, Ching-Long
2011-01-01
Study of mixing is important in understanding transport of submicron sized particles in the acinar region of the lung. In this article, we investigate transport in view of advective mixing utilizing Lagrangian particle tracking techniques: tracer advection, stretch rate and dispersion analysis. The phenomenon of steady streaming in an oscillatory flow is found to hold the key to the origin of kinematic mixing in the alveolus, the alveolar mouth and the alveolated duct. This mechanism provides the common route to folding of material lines and surfaces in any region of the acinar flow, and has no bearing on whether the geometry is expanding or if flow separates within the cavity or not. All analyses consistently indicate a significant decrease in mixing with decreasing Reynolds number (Re). For a given Re, dispersion is found to increase with degree of alveolation, indicating that geometry effects are important. These effects of Re and geometry can also be explained by the streaming mechanism. Based on flow conditions and resultant convective mixing measures, we conclude that significant convective mixing in the duct and within an alveolus could originate only in the first few generations of the acinar tree as a result of nonzero inertia, flow asymmetry, and large Keulegan–Carpenter (KC) number. PMID:21580803
Characterization of the Inlet Port Flow under Steady-State Conditions Using PIV and POD
Directory of Open Access Journals (Sweden)
Mohammed El-Adawy
2017-11-01
Full Text Available The current study demonstrates an experimental investigation of the tumble flow structures using Particle Image Velocimetry (PIV under steady-state conditions considering the central vertical tumble plane. The experiments were carried out on a four-valve, pent-roof Gasoline Direct Injection (GDI engine head at different valve lifts and with a pressure difference of 150 mmH2O across the intake valves. Furthermore, the Proper Orthogonal Decomposition (POD analytical technique was applied to PIV-measured velocity vector maps to characterize the flow structures at various valve lifts, and hence the different rig tumble values. The results show that at low valve lifts (1 to 5 mm, 48.9 to 46.6% of the flow energy is concentrated in the large (mode 1 eddies with only 8.4 to 11.46% in mode 2 and 7.2 to 7.5 in mode 3. At high valve lifts, it can be clearly seen that some of the energy in the large eddies of mode 1 is transferred to the smaller flow structures of modes 2 and 3. This can be clearly seen at valve lift 10 mm where the values of the flow energy were 40.6%, 17.3%, and 8.0% for modes 1, 2, and 3, respectively.
Hydrodynamic pressure sensing with an artificial lateral line in steady and unsteady flows
International Nuclear Information System (INIS)
Venturelli, Roberto; Akanyeti, Otar; Visentin, Francesco; Fiorini, Paolo; Ježov, Jaas; Toming, Gert; Kruusmaa, Maarja; Chambers, Lily D; Brown, Jennifer; Megill, William M
2012-01-01
With the overall goal being a better understanding of the sensing environment from the local perspective of a situated agent, we studied uniform flows and Kármán vortex streets in a frame of reference relevant to a fish or swimming robot. We visualized each flow regime with digital particle image velocimetry and then took local measurements using a rigid body with laterally distributed parallel pressure sensor arrays. Time and frequency domain methods were used to characterize hydrodynamically relevant scenarios in steady and unsteady flows for control applications. Here we report that a distributed pressure sensing mechanism has the capability to discriminate Kármán vortex streets from uniform flows, and determine the orientation and position of the platform with respect to the incoming flow and the centre axis of the Kármán vortex street. It also enables the computation of hydrodynamic features which may be relevant for a robot while interacting with the flow, such as vortex shedding frequency, vortex travelling speed and downstream distance between vortices. A Kármán vortex street was distinguished in this study from uniform flows by analysing the magnitude of fluctuations present in the sensor measurements and the number of sensors detecting the same dominant frequency. In the Kármán vortex street the turbulence intensity was 30% higher than that in the uniform flow and the sensors collectively sensed the vortex shedding frequency as the dominant frequency. The position and orientation of the sensor platform were determined via a comparative analysis between laterally distributed sensor arrays; the vortex travelling speed was estimated via a cross-correlation analysis among the sensors. (paper)
Edelman, Robert R; Serhal, Ali; Pursnani, Amit; Pang, Jianing; Koktzoglou, Ioannis
2018-02-19
Existing cine imaging techniques rely on balanced steady-state free precession (bSSFP) or spoiled gradient-echo readouts, each of which has limitations. For instance, with bSSFP, artifacts occur from rapid through-plane flow and off-resonance effects. We hypothesized that a prototype cine technique, radial fast interrupted steady-state (FISS), could overcome these limitations. The technique was compared with standard cine bSSFP for cardiac function, coronary artery conspicuity, and aortic valve morphology. Given its advantageous properties, we further hypothesized that the cine FISS technique, in combination with arterial spin labeling (ASL), could provide an alternative to phase contrast for visualizing in-plane flow patterns within the aorta and branch vessels. The study was IRB-approved and subjects provided consent. Breath-hold cine FISS and bSSFP were acquired using similar imaging parameters. There was no significant difference in biplane left ventricular ejection fraction or cardiac image quality between the two techniques. Compared with cine bSSFP, cine FISS demonstrated a marked decrease in fat signal which improved conspicuity of the coronary arteries, while suppression of through-plane flow artifact on thin-slice cine FISS images improved visualization of the aortic valve. Banding artifacts in the subcutaneous tissues were reduced. In healthy subjects, dynamic flow patterns were well visualized in the aorta, coronary and renal arteries using cine FISS ASL, even when the slice was substantially thicker than the vessel diameter. Cine FISS demonstrates several benefits for cardiovascular imaging compared with cine bSSFP, including better suppression of fat signal and reduced artifacts from through-plane flow and off-resonance effects. The main drawback is a slight (~ 20%) decrease in temporal resolution. In addition, preliminary results suggest that cine FISS ASL provides a potential alternative to phase contrast techniques for in-plane flow
Sand Dunes in Steady Flow at Low Froude Numbers: Dune Height Evolution and Flow Resistance
DEFF Research Database (Denmark)
Niemann, S. L.; Fredsøe, Jørgen; Jacobsen, Niels Gjøl
2011-01-01
equilibrium shape. The flow modeling is based on a k-ω turbulence closure. The sediment transport is assumed to be bed-load only, with an avalanche-like movement on the steep dune front. The model is also found capable of predicting the growth in wavelength if the initially prescribed wavelength...
Cha, Jeesung Jeff
microporous structures. This is particularly troubling with regards to the regenerator, where friction and thermal non-equilibrium between the fluid and the structure play crucial roles. Little attention has been paid to this issue primarily because of the difficulty of experimental measurements. Multi-dimensional modeling of a regenerator is very complex and requires knowledge about the anisotropic hydrodynamic parameters in various components, in particular the regenerator. In view of the above, this investigation was aimed at: (a) experimental measurement and correlation of the steady and periodic flow directional Darcy permeability and Forchheimer's inertial hydrodynamic parameters for some widely-used regenerator fillers; (b) system-level parametric CFD-based analyses of entire PTC systems; and (c) a preliminary CFD-based assessment of the effect of direct and linear scale-down of current Inertance Tube Pulse Tube Cryocooler (ITPTCs) on their thermal performance. Modular experimental apparatuses were designed and built for the measurement of pressure drops across five different and widely-used regenerator fillers, under steady-state and steady periodic flow conditions. Separate test sections were used so that the pressure drops in axial and lateral directions could be measured. The fillers that were investigated included 325 mesh stainless steel screens, 400 mesh stainless steel screens, sintered 400 mesh stainless steel screens, stainless steel metal foam, and stacked nickel micro-machined disks. The parametric effects that were addressed in the experiments included the porosity in the range of 26.8% to 69.2%, and frequency in the range of 5 Hz to 60 Hz for the periodic flow tests. A CFDassisted method was developed, which allowed for obtaining the directional permeability and Forchheimer coefficients from the experimental data in a rigorous manner and without any arbitrary assumption. Using the Fluent code, parametric CID analyses were performed in which entire ITPTC
Prevention of Bridge Scour with Non-uniform Circular Piers Plane under Steady Flows
Chen, Hsing-Ting; Wang, Chuan-Yi
2017-04-01
River bed scour and deposit variation extremely severe because of most of rivers are steep and rapid flows, and river discharge extremely unstable and highly unsteady during different seasons in Taiwan. In addition to the obstruction of piers foundation, it causes local scour and threatens the safety of bridges. In the past, riprap, wire gabion or wrap pier works were adopted as the protections of piers foundation, but there were no effectual outcomes. The events of break off piers still happen sometimes. For example, typhoon Kalmaegi (2008) and Morakot (2009) caused heavy damages on Ho-Fon bridge in the Da-jia river and Shuang-Yuan bridge in the Kao-Ping river, respectively. Accordingly, to understand the piers scour system and propose an appropriate protection of piers foundation becomes an important topic for this study currently. This research improves the protection works of the existing uniform bridge pier (diameter D) to ensure the safety of the bridge. The non-uniform plane of circular piers (diameter D*) are placed on the top of a bridge pier foundation to reduce the down flow impacting energy and scour by its' surface roughness characteristics. This study utilize hydraulic models to simulate local scour depth and scour depth change with time for non-uniform pier diameter ratio D/D* of 0.3,0.4,0.5,0.6,0.7 and 0.8, and different type pier and initial bed level (Y) relative under the foundation top elevation under steady flows of V/Vc=0.95,0.80 and 0.65. The research results show that the scour depth increases with an increase of flow intensity (V/Vc) under different types of steady flow hydrographs. The scour depth decreases with increase of initial bed level (Y=+0.2D*,0D*and -0.2D*) relative under the foundation top elevation of the different type pier. The maximum scour depth occurred in the front of the pier for all conditions. Because of the scouring retardation by the non-uniform plane of foundation, the scour depth is reduced for the un-exposed bridge
Space-marching gridless computation of steady supersonic/hypersonic flow
International Nuclear Information System (INIS)
Hui, W.H.; Hu, J.J.
2004-01-01
Most CFD work use Eulerian coordinates, which require generating a grid prior to flow filed computation. Despite three decades of research, grid generation is still a bottleneck of CFD, as it is time-consuming, tedious and requires specialized training. It will be shown in this paper that using the Unified Coordinates introduced by Hui et. al., there is no need for grid generation prior to flow computation; the grid is automatically generated while computing the flow. This greatly saves computing time. For steady supersonic/hypersonic flow, the Euler equations of gas dynamics are of hyperbolic type and a space-marching gridless computation along the streamlines - coordinate lines in the unified coordinates - is shown to be a complete success in that: (a) it is most robust, (b) it resolves both slip lines (also called contact lines) and shocks sharply, (c) its computing time is more than three orders of magnitude smaller than Eulerian computation and, (d) it by-passes the tedious and time-consuming grid generation stage which is needed in Eulerian computation. Three examples are given to justify these claims. (author)
Measurements of steady flow through a bileaflet mechanical heart valve using stereoscopic PIV.
Hutchison, Chris; Sullivan, Pierre; Ethier, C Ross
2011-03-01
Computational modeling of bileaflet mechanical heart valve (BiMHV) flow requires experimentally validated datasets and improved knowledge of BiMHV fluid mechanics. In this study, flow was studied downstream of a model BiMHV in an axisymmetric aortic sinus using stereoscopic particle image velocimetry. The inlet flow was steady and the Reynolds number based on the aortic diameter was 7600. Results showed the out-of-plane velocity was of similar magnitude as the transverse velocity. Although additional studies are needed for confirmation, analysis of the out-of-plane velocity showed the possible presence of a four-cell streamwise vortex structure in the mean velocity field. Spatial data for all six Reynolds stress components were obtained. Reynolds normal stress profiles revealed similarities between the central jet and free jets. These findings are important to BiMHV flow modeling, though clinical relevance is limited due to the idealized conditions chosen. To this end, the dataset is publicly available for CFD validation purposes.
Experimental investigations of the steady flow through an idealized model of a femoral artery bypass
Directory of Open Access Journals (Sweden)
Giurgea Corina
2014-03-01
Full Text Available The present paper presents the steps taken by the authors in the first stage of an experimental program within a larger national research project whose objective is to characterize the flow through a femoral artery bypass with a view to finding solutions for its optimization. The objective of the stage is to investigate by means of the PIV method the stationary flow through a bypass model with an idealized geometry. A bypass assembly which reunites the idealized geometry models of the proximal and distal anastomoses, and which respects the lengths of a femoral artery bypass was constructed on the basis of data for a real patient provided by medical investigations. With the aim of testing the model and the established experimental set-up with regard to their suitability for the assessment of the velocity field associated to the steady flow through the bypass, three zones that can restore the whole distal anastomosis were PIV investigated. The measurements were taken in the conditions of maintained inflow at the bypass entry of 0.9 l / min (Re = 600. The article presents comparatively the flow spectra and the velocity fields for each zone obtained in two situations: with the femoral artery completely occluded and completely open.
Flow and flow-induced vibration of a square array of cylinders in steady currents
Energy Technology Data Exchange (ETDEWEB)
Zhao, Ming [School of Computing, Engineering and Mathematics, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751 (Australia); Cheng, Liang; An, Hongwei; Tong, Feifei, E-mail: m.zhao@uws.edu.au [School of Civil, Environmental and Mining Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia)
2015-08-15
Flow and flow-induced vibration of a square array of cylinders are investigated by two-dimensional numerical simulations. Flow past 36 cylinders in an inline arranged square array and 33 cylinders in a staggered arranged square array is firstly simulated, for Re = 100 and the spacing ratios of L/D = 1.5, 2, 3, 4, 5. Only one vortex street is observed in the wake of the cylinder array when the spacing ratio is 1.5 in the inline arrangement and 1.5 and 2 in the staggered arrangement, indicating that the critical spacing ratio for the single-vortex street mode in the staggered arrangement is higher than that in the inline arrangement. The vortex shedding from the cylinders is suppressed at L/D = 3 for both inline and staggered arrangements. Vortex shedding from each individual cylinder is observed when L/D = 4. Flow-induced vibration of 36 cylinders in an inline square arrangement is studied for a constant Reynolds number of 100, two spacing ratios of 2 and 5, a constant mass ratio of 2.5 and a wide range of reduced velocities. It is found that for a spacing ratio of 2, the vibration of the cylinders in the four downstream columns does not start until the reduced velocity exceeds 4.5. The vibration of the cylinders progresses downstream with increasing reduced velocity. For a spacing ratio of 5, the vibrations of the cylinders in the most upstream column are similar to that of a single cylinder. The vibration amplitudes of the downstream cylinders peak at higher reduced velocities than that of a single cylinder. The maximum possible response amplitudes occur at the most downstream cylinders. (paper)
The stably stratified internal boundary layer for steady and diurnally varying offshore flow
Garratt, J. R.
1987-03-01
A two-dimensional numerical mesoscale model is used to investigate the internal structure and growth of the stably stratified internal boundary layer (IBL) beneath warm, continental air flowing over a cooler sea. Two situations are studied — steady-state and diurnally varying offshore flow. In the steady-state case, vertical profiles of mean quantities and eddy diffusion coefficients ( K) within the IBL show small, but significant, changes with increasing distance from the coast. The top of the IBL is well defined, with large vertical gradients within the layer and a maximum in the coast-normal wind component near the top. Well away from the coast, turbulence, identified by non-zero K, decreases to insignificant levels near the top of the IBL; the IBL itself is characterised by a critical value of the layer-flux Richardson number equal to 0.18. The overall behaviour of the mean profiles is similar to that found in the horizontally homogeneous stable boundary layer over land. A simple physical model is used to relate the depth of the layer h to several relevant physical parameters viz., x, the distance from the coast and U, the large-scale wind (both normal to the coastline) and gδθ/θ, Δθ being the temperature difference between continental mixed-layer air and sea surface, θ is the mean potential temperature and g is the acceleration due to gravity. Excellent agreement with the numerical results is found, with h = 0.014 x 1/2 U ( gδθ/θ)-1/2. In the diurnally varying case, the mean profiles within the IBL show only small differences from the steady-state case, although diurnal variations, particularly in the wind maximum, are evident within a few hundred kilometres of the coast. A mesoscale circulation normal to the coast, and superimposed upon the mean offshore flow, develops seawards of the coastline with maximum vertical velocities about sunset, of depth about 2 km and horizontal scale ≈ 500 km. The circulation is related to the advection, and
An Eulerian two-phase model for steady sheet flow using large-eddy simulation methodology
Cheng, Zhen; Hsu, Tian-Jian; Chauchat, Julien
2018-01-01
A three-dimensional Eulerian two-phase flow model for sediment transport in sheet flow conditions is presented. To resolve turbulence and turbulence-sediment interactions, the large-eddy simulation approach is adopted. Specifically, a dynamic Smagorinsky closure is used for the subgrid fluid and sediment stresses, while the subgrid contribution to the drag force is included using a drift velocity model with a similar dynamic procedure. The contribution of sediment stresses due to intergranular interactions is modeled by the kinetic theory of granular flow at low to intermediate sediment concentration, while at high sediment concentration of enduring contact, a phenomenological closure for particle pressure and frictional viscosity is used. The model is validated with a comprehensive high-resolution dataset of unidirectional steady sheet flow (Revil-Baudard et al., 2015, Journal of Fluid Mechanics, 767, 1-30). At a particle Stokes number of about 10, simulation results indicate a reduced von Kármán coefficient of κ ≈ 0.215 obtained from the fluid velocity profile. A fluid turbulence kinetic energy budget analysis further indicates that the drag-induced turbulence dissipation rate is significant in the sheet flow layer, while in the dilute transport layer, the pressure work plays a similar role as the buoyancy dissipation, which is typically used in the single-phase stratified flow formulation. The present model also reproduces the sheet layer thickness and mobile bed roughness similar to measured data. However, the resulting mobile bed roughness is more than two times larger than that predicted by the empirical formulae. Further analysis suggests that through intermittent turbulent motions near the bed, the resolved sediment Reynolds stress plays a major role in the enhancement of mobile bed roughness. Our analysis on near-bed intermittency also suggests that the turbulent ejection motions are highly correlated with the upward sediment suspension flux, while
Najjari, Mohammad Reza; Plesniak, Michael W.
2017-11-01
Secondary flow vortical structures were investigated in an elastic 180° curved pipe with and without torsion under steady and pulsatile flow using particle image velocimetry (PIV). The elastic thin-walled curved pipes were constructed using Sylgard 184, and inserted into a bath of refractive index matched fluid to perform PIV. A vortex identification method was employed to identify various vortical structures in the flow. The secondary flow structures in the planar compliant model with dilatation of 0.61%-3.23% under pulsatile flow rate were compared with the rigid vessel model results, and it was found that local vessel compliance has a negligible effect on secondary flow morphology. The secondary flow structures were found to be more sensitive to out of plane curvature (torsion) than to vessel compliance. Torsion distorts the symmetry of secondary flow and results in more complex vortical structures in both steady and pulsatile flows. In high Re number steady flow with torsion, a single dominant vortical structure can be detected at the middle of the 90° cross section. In pulsatile flow with torsion, the split-Dean and Lyne-type vortices with same rotation direction originating from opposite sides of the cross section tend to merge together. supported by GW Center for Biomimetics and Bioinspired Engineering.
Steady state flow analysis of two-phase natural circulation in multiple parallel channel loop
International Nuclear Information System (INIS)
Bhusare, V.H.; Bagul, R.K.; Joshi, J.B.; Nayak, A.K.; Kannan, Umasankari; Pilkhwal, D.S.; Vijayan, P.K.
2016-01-01
Highlights: • Liquid circulation velocity increases with increasing superficial gas velocity. • Total two-phase pressure drop decreases with increasing superficial gas velocity. • Channels with larger driving force have maximum circulation velocities. • Good agreement between experimental and model predictions. - Abstract: In this work, steady state flow analysis has been carried out experimentally in order to estimate the liquid circulation velocities and two-phase pressure drop in air–water multichannel circulating loop. Experiments were performed in 15 channel circulating loop. Single phase and two-phase pressure drops in the channels have been measured experimentally and have been compared with theoretical model of Joshi et al. (1990). Experimental measurements show good agreement with model.
Computation of steady and unsteady compressible quasi-axisymmetric vortex flow and breakdown
Kandil, Osama A.; Kandil, Hamdy A.; Liu, C. H.
1991-01-01
The unsteady, compressible Navier-Stokes equations are used to compute and analyze compressible quasi-axisymmetric isolated vortices. The Navier-Stokes equations are solved using an implicit, upwind, flux-difference splitting finite-volume scheme. The developed three-dimensional solver has been verified by comparing its solution profiles with those of a slender, quasi-axisymmetric vortex solver for a subsonic, isolated quasi-axisymmetric vortex in an unbounded domain. The Navier-Stokes solver is then used to solve for a supersonic quasi-axisymmetric vortex flow in a configured circular duct. Steady and unsteady vortex-shock interactions and breakdown have been captured. The problem has also been calculated using the Euler solver of the same code and the results are compared with those of the Navier-Stokes solver. The effect of the initial swirl has been tentatively studied.
Adjoint sensitivity theory for steady-state ground-water flow
International Nuclear Information System (INIS)
1983-11-01
In this study, adjoint sensitivity theory is developed for equations of two-dimensional steady-state flow in a confined aquifer. Both the primary flow equation and the adjoint sensitivity equation are solved using the Galerkin finite element method. The developed computer code is used to investigate the regional flow parameters of the Leadville Formation of the Paradox Basin in Utah and the Wolcamp carbonate/sandstone aquifer of the Palo Duro Basin in the Texas Panhandle. Two performance measures are evaluated, local heads and velocity in the vicinity of potential high-level nuclear waste repositories. The results illustrate the sensitivity of calculated local heads to the boundary conditions. Local velocity-related performance measures are more sensitive to hydraulic conductivities. The uncertainty in the performance measure is a function of the parameter sensitivity, parameter variance and the correlation between parameters. Given a parameter covariance matrix, the uncertainty of the performance measure can be calculated. Although no results are presented here, the implications of uncertainty calculations for the two studies are discussed. 18 references, 25 figures
Liakos, Anastasios; Malamataris, Nikolaos
2014-11-01
The topology and evolution of flow around a surface mounted cubical object in three dimensional channel flow is examined for low to moderate Reynolds numbers. Direct numerical simulations were performed via a home made parallel finite element code. The computational domain has been designed according to actual laboratory experimental conditions. Analysis of the results is performed using the three dimensional theory of separation. Our findings indicate that a tornado-like vortex by the side of the cube is present for all Reynolds numbers for which flow was simulated. A horse-shoe vortex upstream from the cube was formed at Reynolds number approximately 1266. Pressure distributions are shown along with three dimensional images of the tornado-like vortex and the horseshoe vortex at selected Reynolds numbers. Finally, and in accordance to previous work, our results indicate that the upper limit for the Reynolds number for which steady state results are physically realizable is roughly 2000. Financial support of author NM from the Office of Naval Research Global (ONRG-VSP, N62909-13-1-V016) is acknowledged.
ULTRA-SHARP nonoscillatory convection schemes for high-speed steady multidimensional flow
Leonard, B. P.; Mokhtari, Simin
1990-01-01
For convection-dominated flows, classical second-order methods are notoriously oscillatory and often unstable. For this reason, many computational fluid dynamicists have adopted various forms of (inherently stable) first-order upwinding over the past few decades. Although it is now well known that first-order convection schemes suffer from serious inaccuracies attributable to artificial viscosity or numerical diffusion under high convection conditions, these methods continue to enjoy widespread popularity for numerical heat transfer calculations, apparently due to a perceived lack of viable high accuracy alternatives. But alternatives are available. For example, nonoscillatory methods used in gasdynamics, including currently popular TVD schemes, can be easily adapted to multidimensional incompressible flow and convective transport. This, in itself, would be a major advance for numerical convective heat transfer, for example. But, as is shown, second-order TVD schemes form only a small, overly restrictive, subclass of a much more universal, and extremely simple, nonoscillatory flux-limiting strategy which can be applied to convection schemes of arbitrarily high order accuracy, while requiring only a simple tridiagonal ADI line-solver, as used in the majority of general purpose iterative codes for incompressible flow and numerical heat transfer. The new universal limiter and associated solution procedures form the so-called ULTRA-SHARP alternative for high resolution nonoscillatory multidimensional steady state high speed convective modelling.
Investigation of Seepage Meter Measurements in Steady Flow and Wave Conditions.
Russoniello, Christopher J; Michael, Holly A
2015-01-01
Water exchange between surface water and groundwater can modulate or generate ecologically important fluxes of solutes across the sediment-water interface. Seepage meters can directly measure fluid flux, but mechanical resistance and surface water dynamics may lead to inaccurate measurements. Tank experiments were conducted to determine effects of mechanical resistance on measurement efficiency and occurrence of directional asymmetry that could lead to erroneous net flux measurements. Seepage meter efficiency was high (average of 93%) and consistent for inflow and outflow under steady flow conditions. Wave effects on seepage meter measurements were investigated in a wave flume. Seepage meter net flux measurements averaged 0.08 cm/h-greater than the expected net-zero flux, but significantly less than theoretical wave-driven unidirectional discharge or recharge. Calculations of unidirectional flux from pressure measurements (Darcy flux) and theory matched well for a ratio of wave length to water depth less than 5, but not when this ratio was greater. Both were higher than seepage meter measurements of unidirectional flux made with one-way valves. Discharge averaged 23% greater than recharge in both seepage meter measurements and Darcy calculations of unidirectional flux. Removal of the collection bag reduced this net discharge. The presence of a seepage meter reduced the amplitude of pressure signals at the bed and resulted in a nearly uniform pressure distribution beneath the seepage meter. These results show that seepage meters may provide accurate measurements of both discharge and recharge under steady flow conditions and illustrate the potential measurement errors associated with dynamic wave environments. © 2014, National Ground Water Association.
Erpelding, Marion; Sinha, Santanu; Tallakstad, Ken Tore; Hansen, Alex; Flekkøy, Eirik Grude; Måløy, Knut Jørgen
2013-11-01
It is well known that the transient behavior during drainage or imbibition in multiphase flow in porous media strongly depends on the history and initial condition of the system. However, when the steady-state regime is reached and both drainage and imbibition take place at the pore level, the influence of the evolution history and initial preparation is an open question. Here, we present an extensive experimental and numerical work investigating the history dependence of simultaneous steady-state two-phase flow through porous media. Our experimental system consists of a Hele-Shaw cell filled with glass beads which we model numerically by a network of disordered pores transporting two immiscible fluids. From measurements of global pressure evolution, histograms of saturation, and cluster-size distributions, we find that when both phases are flowing through the porous medium, the steady state does not depend on the initial preparation of the system or on the way it has been reached.
Lee, Jeffrey M.
1999-01-01
This study establishes a consistent set of differential equations for use in describing the steady secondary flows generated by periodic compression and expansion of an ideal gas in pulse tubes. Also considered is heat transfer between the gas and the tube wall of finite thickness. A small-amplitude series expansion solution in the inverse Strouhal number is proposed for the two-dimensional axisymmetric mass, momentum and energy equations. The anelastic approach applies when shock and acoustic energies are small compared with the energy needed to compress and expand the gas. An analytic solution to the ordered series is obtained in the strong temperature limit where the zeroth-order temperature is constant. The solution shows steady velocities increase linearly for small Valensi number and can be of order I for large Valensi number. A conversion of steady work flow to heat flow occurs whenever temperature, velocity or phase angle gradients are present. Steady enthalpy flow is reduced by heat transfer and is scaled by the Prandtl times Valensi numbers. Particle velocities from a smoke-wire experiment were compared with predictions for the basic and orifice pulse tube configurations. The theory accurately predicted the observed steady streaming.
Parameter scaling toward high-energy density in a quasi-steady flow Z-pinch
Hughes, M. C.; Shumlak, U.; Nelson, B. A.; Golingo, R. P.; Claveau, E. L.; Doty, S. A.; Forbes, E. G.; Kim, B.; Ross, M. P.
2016-10-01
Sheared axial flows are utilized by the ZaP Flow Z-Pinch Experiment to stabilize MHD instabilities. The pinches formed are 50 cm long with radii ranging from 0.3 to 1.0 cm. The plasma is generated in a coaxial acceleration region, similar to a Marshall gun, which provides a steady supply of plasma for approximately 100 us. The power to the plasma is partially decoupled between the acceleration and pinch assembly regions through the use of separate power supplies. Adiabatic scaling of the Bennett relation gives targets for future devices to reach high-energy density conditions or fusion reactors. The applicability of an adiabatic assumption is explored and work is done experimentally to clarify the plasma compression process, which may be more generally polytropic. The device is capable of a much larger parameter space than previous machine iterations, allowing flexibility in the initial conditions of the compression process to preserve stability. This work is supported by DoE FES and NNSA.
Saeid Khalafvand, Seyed; Han, Hai-Chao
2015-01-01
It has been shown that arteries may buckle into tortuous shapes under lumen pressure, which in turn could alter blood flow. However, the mechanisms of artery instability under pulsatile flow have not been fully understood. The objective of this study was to simulate the buckling and post-buckling behaviors of the carotid artery under pulsatile flow using a fully coupled fluid–structure interaction (FSI) method. The artery wall was modeled as a nonlinear material with a two-fiber strain-energy function. FSI simulations were performed under steady-state flow and pulsatile flow conditions with a prescribed flow velocity profile at the inlet and different pressures at the outlet to determine the critical buckling pressure. Simulations were performed for normal (160 ml/min) and high (350 ml/min) flow rates and normal (1.5) and reduced (1.3) axial stretch ratios to determine the effects of flow rate and axial tension on stability. The results showed that an artery buckled when the lumen pressure exceeded a critical value. The critical mean buckling pressure at pulsatile flow was 17–23% smaller than at steady-state flow. For both steady-state and pulsatile flow, the high flow rate had very little effect (<5%) on the critical buckling pressure. The fluid and wall stresses were drastically altered at the location with maximum deflection. The maximum lumen shear stress occurred at the inner side of the bend and maximum tensile wall stresses occurred at the outer side. These findings improve our understanding of artery instability in vivo. PMID:25761257
Saeid Khalafvand, Seyed; Han, Hai-Chao
2015-06-01
It has been shown that arteries may buckle into tortuous shapes under lumen pressure, which in turn could alter blood flow. However, the mechanisms of artery instability under pulsatile flow have not been fully understood. The objective of this study was to simulate the buckling and post-buckling behaviors of the carotid artery under pulsatile flow using a fully coupled fluid-structure interaction (FSI) method. The artery wall was modeled as a nonlinear material with a two-fiber strain-energy function. FSI simulations were performed under steady-state flow and pulsatile flow conditions with a prescribed flow velocity profile at the inlet and different pressures at the outlet to determine the critical buckling pressure. Simulations were performed for normal (160 ml/min) and high (350 ml/min) flow rates and normal (1.5) and reduced (1.3) axial stretch ratios to determine the effects of flow rate and axial tension on stability. The results showed that an artery buckled when the lumen pressure exceeded a critical value. The critical mean buckling pressure at pulsatile flow was 17-23% smaller than at steady-state flow. For both steady-state and pulsatile flow, the high flow rate had very little effect (<5%) on the critical buckling pressure. The fluid and wall stresses were drastically altered at the location with maximum deflection. The maximum lumen shear stress occurred at the inner side of the bend and maximum tensile wall stresses occurred at the outer side. These findings improve our understanding of artery instability in vivo.
Khodarahmi, Iman; Shakeri, Mostafa; Sharp, M; Amini, Amir A
2010-01-01
Pressure gradient across a Gaussian-shaped 87% area stenosis phantom was estimated by solving the pressure Poisson equation (PPE) for a steady flow mimicking the blood flow through the human iliac artery. The velocity field needed to solve the pressure equation was obtained using particle image velocimetry (PIV). A steady flow rate of 46.9 ml/s was used, which corresponds to a Reynolds number of 188 and 595 at the inlet and stenosis throat, respectively (in the range of mean Reynolds number encountered in-vivo). In addition, computational fluid dynamics (CFD) simulation of the same flow was performed. Pressure drops across the stenosis predicted by PPE/PIV and CFD were compared with those measured by a pressure catheter transducer. RMS errors relative to the measurements were 17% and 10% for PPE/PIV and CFD, respectively.
Quasi-steady-state model of a counter flow air-to-air heat exchanger with phase change
DEFF Research Database (Denmark)
Rose, Jørgen; Nielsen, Toke Rammer; Kragh, Jesper
2008-01-01
-exchanger. Developing highly efficient heat-exchangers and strategies to avoid/remove frost formation implies the use of detailed models to predict and evaluate different heat-exchanger designs and strategies. This paper presents a quasi-steady-state model of a counter-flow air-to-air heat-exchanger that takes...
Experimental Observations of Natural Circulation Flow in the NSTF at Steady-State Conditions
International Nuclear Information System (INIS)
Lisowski, Darius D.; Farmer, Mitch T.
2014-01-01
A ½ scale test facility has been constructed at Argonne National Laboratory (ANL) to study the heat removal performance and natural circulation flow patterns in a Reactor Cavity Cooling System (RCCS). Our test facility, the Natural convection Shutdown heat removal Test Facility (NSTF), supports the broader goal of developing an inherently safe and fully passive ex-vessel decay heat removal for advanced reactor designs. The project, initiated in 2010 to support the Advanced Reactor Concepts (ARC), Small Modular Reactor (SMR), and Next Generation Nuclear Plant (NGNP) programs, has been conducting experimental operations since early 2014. The following paper provides a summary of some primary design features of the 26-m tall test facility along with a description of the data acquisition suite that guides our experimental practices. Specifics of the distributed fiber optic temperature measurements will be discussed, which introduces an unparalleled level of data density that has never before been implemented in a large scale natural circulation test facility. Results from our first test series will then be presented, which provide insight into the thermal hydraulic behavior at steady-state conditions for varying heat flux levels and exhaust chimney configuration states. (author)
Energy Technology Data Exchange (ETDEWEB)
Chen, Lingen; Kan, Xuxian; Sun, Fengrui; Wu, Feng [College of Naval Architecture and Power, Naval University of Engineering, Wuhan 430033 (China)
2013-07-01
The operation of a universal steady flow endoreversible refrigeration cycle model consisting of a constant thermal-capacity heating branch, two constant thermal-capacity cooling branches and two adiabatic branches is viewed as a production process with exergy as its output. The finite time exergoeconomic performance optimization of the refrigeration cycle is investigated by taking profit rate optimization criterion as the objective. The relations between the profit rate and the temperature ratio of working fluid, between the COP (coefficient of performance) and the temperature ratio of working fluid, as well as the optimal relation between profit rate and the COP of the cycle are derived. The focus of this paper is to search the compromised optimization between economics (profit rate) and the utilization factor (COP) for endoreversible refrigeration cycles, by searching the optimum COP at maximum profit, which is termed as the finite-time exergoeconomic performance bound. Moreover, performance analysis and optimization of the model are carried out in order to investigate the effect of cycle process on the performance of the cycles using numerical example. The results obtained herein include the performance characteristics of endoreversible Carnot, Diesel, Otto, Atkinson, Dual and Brayton refrigeration cycles.
Simulating nonlinear steady-state traveling waves on the falling liquid film entrained by a gas flow
International Nuclear Information System (INIS)
Yu Tsvelodub, O
2016-01-01
The article is devoted to the simulation of nonlinear waves on a liquid film flowing under gravity in the known stress field at the interface. In the case of small Reynolds numbers the problem is reduced to the consideration of solutions of the nonlinear integral-differential equation for film thickness deviation from the undisturbed level. Weakly nonlinear steady-state traveling solutions of the equation with wave numbers in a vicinity of neutral wave numbers are constructed analytically. The nature of the wave branching from the undisturbed solution is investigated. Steady-state traveling solutions, whose wave numbers within the instability area are far from neutral wave numbers, are found numerically. (paper)
Directory of Open Access Journals (Sweden)
Saeed Dinarvand
2012-01-01
Full Text Available The steady three-dimensional flow of condensation or spraying on inclined spinning disk is studied analytically. The governing nonlinear equations and their associated boundary conditions are transformed into the system of nonlinear ordinary differential equations. The series solution of the problem is obtained by utilizing the homotopy perturbation method (HPM. The velocity and temperature profiles are shown and the influence of Prandtl number on the heat transfer and Nusselt number is discussed in detail. The validity of our solutions is verified by the numerical results. Unlike free surface flows on an incline, this through flow is highly affected by the spray rate and the rotation of the disk.
Najjari, Mohammad Reza; Plesniak, Michael W.
2018-01-01
Secondary flow structures in a 180∘ curved pipe model of an artery are studied using particle image velocimetry. Both steady and pulsatile inflow conditions are investigated. In planar curved pipes with steady flow, multiple (two, four, six) vortices are detected. For pulsatile flow, various pairs of vortices, i.e., Dean, deformed-Dean, Lyne-type, and split-Dean, are present in the cross section of the pipe at 90∘ into the bend. The effects of nonplanar curvature (torsion) and vessel dilatation on these vortical structures are studied. Torsion distorts the symmetric secondary flows (which exist in planar curvatures) and can result in formation of more complex vortical structures. For example, the split-Dean and Lyne-type vortices with same rotation direction originating from opposite sides of the cross section tend to merge together in pulsatile flow. The vortical structures in elastic vessels with dilatation (0.61%-3.23%) are also investigated and the results are compared with rigid model results. It was found that the secondary flow structures in rigid and elastic models are similar, and hence the local compliance of the vessel does not affect the morphology of secondary flow structures.
Simulating nonlinear steady-state traveling waves on the falling liquid film entrained by a gas flow
Tsvelodub, O. Yu; Bocharov, A. A.
2017-09-01
The article is devoted to the simulation of nonlinear waves on a liquid film flowing under gravity in the known stress field at the interface. The paper studies nonlinear waves on a liquid film, flowing under the action of gravity in a known stress field at the interface. In the case of small Reynolds numbers the problem is reduced to the consideration of solutions of the nonlinear integral-differential equation for film thickness deviation from the undisturbed level. The periodic and soliton steady-state traveling solutions of this equation have been numerically found. The analysis of branching of new families of steady-state traveling solutions has been performed. In particular, it is shown that this model equation has solutions in the form of solitons-humps.
Steady flows in the chromosphere and transition-zone above active regions as observed by OSO-8
Lites, B. W.
1980-01-01
Two years of data from the University of Colorado ultraviolet spectrometer aboard OSO-8 were searched for steady line-of-sight flows in the chromosphere and transition-zone above active regions. The most conspicuous pattern that emerges from this data set is that many sunspots show persistent blueshifts of transition-zone lines indicating velocities of about 20 km/s with respect to the surrounding plage areas. The data show much smaller shifts in ultraviolet emission lines arising from the chromosphere: the shifts are frequently to the blue, but sometimes redshifts do occur. Plage areas often show a redshift of the transition-zone lines relative to the surrounding quiet areas, and a strong gradient of the vertical component of the velocity is evident in many plages. One area of persistent blueshift was observed in the transition-zone above an active region filament. The energy requirement of these steady flows over sunspots is discussed.
Rasskazov, Andrey; Chertovskih, Roman; Zheligovsky, Vladislav
2018-04-01
We introduce six families of three-dimensional space-periodic steady solenoidal flows, whose kinetic helicity density is zero at any point. Four families are analytically defined. Flows in four families have zero helicity spectrum. Sample flows from five families are used to demonstrate numerically that neither zero kinetic helicity density nor zero helicity spectrum prohibit generation of large-scale magnetic field by the two most prominent dynamo mechanisms: the magnetic α -effect and negative eddy diffusivity. Our computations also attest that such flows often generate small-scale field for sufficiently small magnetic molecular diffusivity. These findings indicate that kinetic helicity and helicity spectrum are not the quantities controlling the dynamo properties of a flow regardless of whether scale separation is present or not.
Pasch, James Jay
2017-02-07
A method of resolving a balanced condition that generates control parameters for start-up and steady state operating points and various component and cycle performances for a closed split flow recompression cycle system. The method provides for improved control of a Brayton cycle thermal to electrical power conversion system. The method may also be used for system design, operational simulation and/or parameter prediction.
International Nuclear Information System (INIS)
Karpp, R.R.
1980-10-01
This report treats analytically the problem of the symmetric impact of two compressible fluid streams. The flow is assumed to be steady, plane, inviscid, and subsonic and that the compressible fluid is of the Chaplygin (tangent gas) type. In the analysis, the governing equations are first transformed to the hodograph plane where an exact, closed-form solution is obtained by standard techniques. The distributions of fluid properties along the plane of symmetry as well as the shapes of the boundary streamlines are exactly determined by transforming the solution back to the physical plane. The problem of a compressible fluid jet penetrating into an infinite target of similar material is also exactly solved by considering a limiting case of this solution. This new compressible flow solution reduces to the classical result of incompressible flow theory when the sound speed of the fluid is allowed to approach infinity. Several illustrations of the differences between compressible and incompressible flows of the type considered are presented
Datta, Anjali; Cheng, Joseph Y; Hargreaves, Brian A; Baron, Corey A; Nishimura, Dwight G
2018-06-01
To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing. A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal. Simulations were then validated in a flow phantom. Lastly, phase-cycled SSFP cardiac cine images were acquired with and without partial dephasing in six subjects. Partial dephasing decreased the strength and non-linearity of the dependence of the signal at the stopbands on the through-plane flow rate. It thus mitigated hyper-enhancement from out-of-slice signal contributions and transient-related artifacts caused by variable flow both in the phantom and in vivo. In six volunteers, partial dephasing noticeably decreased artifacts in all of the phase-cycled cardiac cine datasets. Partial dephasing can mitigate the flow artifacts seen at the stopbands in balanced SSFP while maintaining the sequence's desired signal. By mitigating hyper-enhancement and transient-related artifacts originating from the stopbands, partial dephasing facilitates robust multiple-acquisition phase-cycled SSFP in the heart. Magn Reson Med 79:2944-2953, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.
Ghatage, Dhairyasheel; Chatterji, Apratim
2013-10-01
We introduce a method to obtain steady-state uniaxial exponential-stretching flow of a fluid (akin to extensional flow) in the incompressible limit, which enables us to study the response of suspended macromolecules to the flow by computer simulations. The flow field in this flow is defined by v(x) = εx, where v(x) is the velocity of the fluid and ε is the stretch flow gradient. To eliminate the effect of confining boundaries, we produce the flow in a channel of uniform square cross section with periodic boundary conditions in directions perpendicular to the flow, but simultaneously maintain uniform density of fluid along the length of the tube. In experiments a perfect elongational flow is obtained only along the axis of symmetry in a four-roll geometry or a filament-stretching rheometer. We can reproduce flow conditions very similar to extensional flow near the axis of symmetry by exponential-stretching flow; we do this by adding the right amounts of fluid along the length of the flow in our simulations. The fluid particles added along the length of the tube are the same fluid particles which exit the channel due to the flow; thus mass conservation is maintained in our model by default. We also suggest a scheme for possible realization of exponential-stretching flow in experiments. To establish our method as a useful tool to study various soft matter systems in extensional flow, we embed (i) spherical colloids with excluded volume interactions (modeled by the Weeks-Chandler potential) as well as (ii) a bead-spring model of star polymers in the fluid to study their responses to the exponential-stretched flow and show that the responses of macromolecules in the two flows are very similar. We demonstrate that the variation of number density of the suspended colloids along the direction of flow is in tune with our expectations. We also conclude from our study of the deformation of star polymers with different numbers of arms f that the critical flow gradient ε
A closed-form solution for steady-state coupled phloem/xylem flow using the Lambert-W function.
Hall, A J; Minchin, P E H
2013-12-01
A closed-form solution for steady-state coupled phloem/xylem flow is presented. This incorporates the basic Münch flow model of phloem transport, the cohesion model of xylem flow, and local variation in the xylem water potential and lateral water flow along the transport pathway. Use of the Lambert-W function allows this solution to be obtained under much more general and realistic conditions than has previously been possible. Variation in phloem resistance (i.e. viscosity) with solute concentration, and deviations from the Van't Hoff expression for osmotic potential are included. It is shown that the model predictions match those of the equilibrium solution of a numerical time-dependent model based upon the same mechanistic assumptions. The effect of xylem flow upon phloem flow can readily be calculated, which has not been possible in any previous analytical model. It is also shown how this new analytical solution can handle multiple sources and sinks within a complex architecture, and can describe competition between sinks. The model provides new insights into Münch flow by explicitly including interactions with xylem flow and water potential in the closed-form solution, and is expected to be useful as a component part of larger numerical models of entire plants. © 2013 John Wiley & Sons Ltd.
International Nuclear Information System (INIS)
Zhang Dalin; Qiu Suizheng; Su Guanghui; Liu Changliang
2008-01-01
The Molten Salt Reactor (MSR), one of the 'Generation IV' concepts, is a liquid-fuel reactor, which is different from the conventional reactors using solid fissile materials due to the flow effect of fuel salt. The study on its neutronics considering the fuel salt flow, which is the base of the thermal-hydraulic calculation and safety analysis, must be done. In this paper, the theoretical model on neutronics under steady condition for a single-liquid-fueled MSR is conducted and calculated by numerical method. The neutronics model consists of two group neutron diffusion equations for fast and thermal neutron fluxes, and balance equations for six-group delayed neutron precursors considering the flow effect of fuel salt. The spatial discretization of the above models is based on the finite volume method, and the discretization equations are computed by the source iteration method. The distributions of neutron fluxes and the distributions of the delayed neutron precursors in the core are obtained. The numerical calculated results show that, the fuel salt flow has little effect on the distribution of fast and thermal neutron fluxes and the effective multiplication factor; however, it affects the distribution of the delayed neutron precursors significantly, especially the long-lived one. In addition, it could be found that the delayed neutron precursors influence the neutronics slightly under the steady condition. (authors)
Institute of Scientific and Technical Information of China (English)
ZHANG Da-Lin; QIU Sui-Zheng; LIU Chang-Liang; SU Guang-Hui
2008-01-01
The Molten Salt Reactor (MSR),one of the‘Generation Ⅳ'concepts,is a liquid-fuel reactor,which is different from the conventional reactors using solid fissile materials due to the flow effect of fuel salt.The study on its neutronice considering the fuel salt flow,which is the base of the thermal-hydraulic calculation and safety analysis,must be done.In this paper,the theoretical model on neutronics under steady condition for a single-liquid-fueled MSR is conducted and calculated by numerical method.The neutronics model consists of two group neutron diffusion equations for fast and thermal neutron fluxes,and balance equations for six-group delayed neutron precursors considering the flow effect of fuel salt. The spatial discretization of the above models is based on the finite volume method,and the discretization equations are computed by the source iteration method.The distributions of neutron fluxes and the distributions of the delayed neutron precursors in the core are obtained.The numerical calculated results show that,the fuel salt flow has little effect on the distribution of fast and thermal neutron fluxes and the effective multiplication factor;however,it affects the distribution of the delayed neutron precursors significantly,especially the long-lived one.In addition,it could be found that the delayed neutron precursors influence the nentronics slightly under the steady condition.
Mateo Villanueva, P. A.; Hradisky, M.
2010-12-01
Simulations of fluvial flows are strongly influenced by geometric complexity and overall uncertainty on measured flow variables, including those assumed to be well known boundary conditions. Often, 2D steady-state models are used for computational simulations of flows at the scale of natural rivers. Such models have been successfully incorporated in iRIC (formerly MD_SWMS), one of the widely used quasi-3D CFD solvers to perform studies of environmental flows. iRIC aids in estimating such quantities as surface roughness and shear stress, which, in turn, can be used to estimate sediment transport. However, the computational results are inherently limited in accuracy because of restricting the computations to 2D, or quasi-3D, space, which can affect the values of these predictions. In the present work we perform computer-based simulations of fluvial flows using OpenFOAM, a free, open source fully 3D CFD software package, and compare our results to predictions obtained from iRIC. First, we study the suitability of OpenFOAM as the main CFD solver to analyze fluvial flows and validate our results for two well documented rectangular channel configurations: the first case consists of a large aspect-ratio channel (ratio of depth over width 0.017, ratio of depth over length 0.0019) with a rectangular obstacle mounted at the bottom wall; the second case involves a large aspect-ratio channel (ratio of depth over width 0.1, ratio of depth over length 0.0025) with cubic obstacles mounted at the lower wall (one obstacle) and upper wall (two obstacles). Secondly, we apply our model to simulation or river at natural scale and compare our results to the output obtained from iRIC to quantify the differences in velocity profiles and other flow parameters when comparable solution techniques are used. Steady-state, RANS k-epsilon models are employed for all simulations.
International Nuclear Information System (INIS)
Kaminaga, Masanori
1997-03-01
JRR-3 is a light water moderated and cooled, beryllium and heavy water reflected pool type research reactor using low enriched uranium (LEU) plate-type fuels. Its thermal power is 20 MW. The core conversion program from uranium-aluminum (UAl x -Al) dispersion type fuel (aluminide fuel) to uranium-silicon-aluminum (U 3 Si 2 -Al) dispersion type fuel (silicide fuel) is currently conducted at the JRR-3. This report describes about the steady-state thermal hydraulic analysis results and the flow channel blockage accident analysis result. In JRR-3, there are two operation mode. One is high power operation mode up to 20 MW, under forced convection cooling using the primary and the secondary cooling systems. The other is low power operation mode up to 200 kW, under natural circulation cooling between the reactor core and the reactor pool without the primary and the secondary cooling systems. For the analysis of the flow channel blockage accident, COOLOD code was used. On the other hand, steady-state thermal hydraulic analysis for both of the high power operation mode under forced convection cooling and low power operation under natural convection cooling, COOLOD-N2 code was used. From steady-state thermal hydraulic analysis results of both forced and natural convection cooling, fuel temperature, minimum DNBR etc. meet the design criteria and JRR-3 LEU silicide core has enough safety margin under normal operation conditions. Furthermore, flow channel blockage accident analysis results show that one channel flow blockage accident meet the safety criteria for accident conditions which have been established for JRR-3 LEU silicide core. (author)
Zeegers, J.C.H.; Zeegers, Jos; van den Ende, Henricus T.M.; Blom, C.; Altena, E.G.; Beukema, Gerrit J.; Beukema, G.J.; Mellema, J.
1995-01-01
A new instrument to carry out complex viscosity measurements in equilibrium and in a steady shear flow has been developed. A small amplitude harmonic excitation is superimposed orthogonally to the steady shear rate component. It is realized by a thin-walled cylinder, which oscillates in the axial
International Nuclear Information System (INIS)
Shirani, E.; Zirak, S.
2001-01-01
Compressible flows for unsteady, inviscid and viscous cases have been studied. Important features of flows such as formation of shock waves across the flow in an unsteady flow as well as interaction of shock waves with boundary layers and their effects on the flow around the blades have been analyzed. Jameson control volume approach was used to spatially integrate the flow equations and the fourth order Runge-Kutta method was used for time integration. The obtained finite difference equations were used to simulate inviscid and viscous flows in V KI cascades and the effects of viscosity, angle of attack, bal de pitches and back pressure on the flow were obtained. It was shown that when the flow was assumed inviscid, the error on the distribution of pressure on the blades were about ten percent. Finally, unsteady flow were simulated and formation of shock waves and their motions were analyzed
Talmage, Gita; Walker, John S.; Brown, Samuel H.; Sondergaard, Neal A.
1993-09-01
In homopolar motors and generators, large dc electric currents pass through the sliding electrical contacts between rotating copper disks (rotors) and static copper surfaces shrouding the rotor tips (stators). A liquid metal in the small radial gap between the rotor tip and concentric stator surface can provide a low-resistance, low-drag electrical contact. Since there is a strong magnetic field in the region of the electrical contacts, there are large electromagnetic body forces on the liquid metal. The primary, azimuthal motion consists of simple Couette flow, plus an electromagnetically driven flow with large extremes of the azimuthal velocity near the rotor corners. The secondary flow involves the radial and axial velocity components, is driven by the centrifugal force associated with the primary flow, and is opposed by the electromagnetic body force, so that the circulation varies inversely as the square of the magnetic-field strength. Three flow regimes are identified as the angular velocity Ω of the rotor is increased. For small Ω, the primary flow is decoupled from the secondary flow. As Ω increases, the secondary flow begins to convect the azimuthal-velocity peaks radially outward, which in turn changes the centrifugal force driving the secondary flow. At some critical value of Ω, the flow becomes periodic through the coupling of the primary and secondary flows. The azimuthal-velocity peaks begin to move radially in and out with an accompanying oscillation in the secondary-flow strength.
Numerical Solution of Compressible Steady Flows around the RAE 2822 Airfoil
Kryštůfek, P.; Kozel, K.
2014-03-01
The article presents results of a numerical solution of subsonic, transonic and supersonic flows described by the system of Navier-Stokes equations in 2D laminar compressible flows around the RAE 2822 airfoil. Authors used FVM multistage Runge-Kutta method to numerically solve the flows around the RAE 2822 airfoil.
Numerical Solution of Compressible Steady Flows around the RAE 2822 Airfoil
Directory of Open Access Journals (Sweden)
Kryštůfek P.
2014-03-01
Full Text Available The article presents results of a numerical solution of subsonic, transonic and supersonic flows described by the system of Navier-Stokes equations in 2D laminar compressible flows around the RAE 2822 airfoil. Authors used FVM multistage Runge-Kutta method to numerically solve the flows around the RAE 2822 airfoil.
Numerical Solution of Compressible Steady Flows around the NACA 0012 Airfoil
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Kozel K
2013-04-01
Full Text Available The article presents results of a numerical solution of subsonic and transonic flows described by the system of Navier-Stokes equations in 2D laminar compressible flows around the NACA 0012 airfoil. Authors used Runge-Kutta method to numerically solve the flows around the NACA 0012 airfoil.
Yang, L. M.; Shu, C.; Yang, W. M.; Wu, J.
2018-04-01
High consumption of memory and computational effort is the major barrier to prevent the widespread use of the discrete velocity method (DVM) in the simulation of flows in all flow regimes. To overcome this drawback, an implicit DVM with a memory reduction technique for solving a steady discrete velocity Boltzmann equation (DVBE) is presented in this work. In the method, the distribution functions in the whole discrete velocity space do not need to be stored, and they are calculated from the macroscopic flow variables. As a result, its memory requirement is in the same order as the conventional Euler/Navier-Stokes solver. In the meantime, it is more efficient than the explicit DVM for the simulation of various flows. To make the method efficient for solving flow problems in all flow regimes, a prediction step is introduced to estimate the local equilibrium state of the DVBE. In the prediction step, the distribution function at the cell interface is calculated by the local solution of DVBE. For the flow simulation, when the cell size is less than the mean free path, the prediction step has almost no effect on the solution. However, when the cell size is much larger than the mean free path, the prediction step dominates the solution so as to provide reasonable results in such a flow regime. In addition, to further improve the computational efficiency of the developed scheme in the continuum flow regime, the implicit technique is also introduced into the prediction step. Numerical results showed that the proposed implicit scheme can provide reasonable results in all flow regimes and increase significantly the computational efficiency in the continuum flow regime as compared with the existing DVM solvers.
Gao, Ying; Lin, Qingyang; Bijeljic, Branko; Blunt, Martin J.
2017-12-01
We imaged the steady state flow of brine and decane in Bentheimer sandstone. We devised an experimental method based on differential imaging to examine how flow rate impacts impact the pore-scale distribution of fluids during coinjection. This allows us to elucidate flow regimes (connected, or breakup of the nonwetting phase pathways) for a range of fractional flows at two capillary numbers, Ca, namely 3.0 × 10-7 and 7.5 × 10-6. At the lower Ca, for a fixed fractional flow, the two phases appear to flow in connected unchanging subnetworks of the pore space, consistent with conventional theory. At the higher Ca, we observed that a significant fraction of the pore space contained sometimes oil and sometimes brine during the 1 h scan: this intermittent occupancy, which was interpreted as regions of the pore space that contained both fluid phases for some time, is necessary to explain the flow and dynamic connectivity of the oil phase; pathways of always oil-filled portions of the void space did not span the core. This phase was segmented from the differential image between the 30 wt % KI brine image and the scans taken at each fractional flow. Using the grey scale histogram distribution of the raw images, the oil proportion in the intermittent phase was calculated. The pressure drops at each fractional flow at low and high flow rates were measured by high-precision differential pressure sensors. The relative permeabilities and fractional flow obtained by our experiment at the mm-scale compare well with data from the literature on cm-scale samples.
Rassi, Erik M.; Codd, Sarah L.; Seymour, Joseph D.
2011-01-01
Flow in porous media and the resultant hydrodynamics are important in fields including but not limited to the hydrology, chemical, medical and petroleum industries. The observation and understanding of the hydrodynamics in porous media are critical to the design and optimal utilization of porous media, such as those seen in trickle-bed reactors, medical filters, subsurface flows and carbon sequestration. Magnetic resonance (MR) provides for a non-invasive technique that can probe the hydrodynamics on pore and bulk scale lengths; many previous works have characterized fully saturated porous media, while rapid MR imaging (MRI) methods in particular have previously been applied to partially saturated flows. We present time- and ensemble-averaged MR measurements to observe the effects on a bead pack partially saturated with air under flowing water conditions. The 10 mm internal diameter bead pack was filled with 100 μm borosilicate glass beads. Air was injected into the bead pack as water flowed simultaneously through the sample at 25 ml h-1. The initial partially saturated state was characterized with MRI density maps, free induction decay (FID) experiments, propagators and velocity maps before the water flow rate was increased incrementally from 25 to 500 ml h-1. After the maximum flow rate of 500 ml h-1, the MRI density maps, FID experiments, propagators and velocity maps were repeated and compared to the data taken before the maximum flow rate. This work shows that a partially saturated single-phase flow has global flow dynamics that return to characteristic flow statistics once a steady-state high flow rate has been reached. This high flow rate pushed out a significant amount of the air in the bead pack and caused the return of a preferential flow pattern. Velocity maps indicated that local flow statistics were not the same for the before and after blow out conditions. It has been suggested and shown previously that a flow pattern can return to
International Nuclear Information System (INIS)
Rassi, Erik M; Codd, Sarah L; Seymour, Joseph D
2011-01-01
Flow in porous media and the resultant hydrodynamics are important in fields including but not limited to the hydrology, chemical, medical and petroleum industries. The observation and understanding of the hydrodynamics in porous media are critical to the design and optimal utilization of porous media, such as those seen in trickle-bed reactors, medical filters, subsurface flows and carbon sequestration. Magnetic resonance (MR) provides for a non-invasive technique that can probe the hydrodynamics on pore and bulk scale lengths; many previous works have characterized fully saturated porous media, while rapid MR imaging (MRI) methods in particular have previously been applied to partially saturated flows. We present time- and ensemble-averaged MR measurements to observe the effects on a bead pack partially saturated with air under flowing water conditions. The 10 mm internal diameter bead pack was filled with 100 μm borosilicate glass beads. Air was injected into the bead pack as water flowed simultaneously through the sample at 25 ml h -1 . The initial partially saturated state was characterized with MRI density maps, free induction decay (FID) experiments, propagators and velocity maps before the water flow rate was increased incrementally from 25 to 500 ml h -1 . After the maximum flow rate of 500 ml h -1 , the MRI density maps, FID experiments, propagators and velocity maps were repeated and compared to the data taken before the maximum flow rate. This work shows that a partially saturated single-phase flow has global flow dynamics that return to characteristic flow statistics once a steady-state high flow rate has been reached. This high flow rate pushed out a significant amount of the air in the bead pack and caused the return of a preferential flow pattern. Velocity maps indicated that local flow statistics were not the same for the before and after blow out conditions. It has been suggested and shown previously that a flow pattern can return to similar
The effect of inlet distorted flow on steady and unsteady performance of a centrifugal compressor
International Nuclear Information System (INIS)
Park, Jae Hyoung; Kang, Shin Hyoung
2005-01-01
Effects of inlet distorted flow on performance, stall and surge are experimentally investigated for a high-speed centrifugal compressor. Tested results for the distorted inlet flow cases are compared with the result of the undistorted one. The performance of compressor is slightly deteriorated due to the inlet distortion. The inlet distortion does not affect the number of stall cell and the propagation velocity. It also does not change stall inception flow rate. However, as the distortion increases, stall starts at the higher flow rate for low speed at the lower flow rate for high speed. For 50,000 rpm stall occurs as the flow rate decreases, however disappears for the smaller flow rate. This is due to the interaction of surge and stall. After the stall and surge interact, the number of stall cell decreases
Directory of Open Access Journals (Sweden)
Fei Fan
2017-08-01
Full Text Available Rigid-lid approximation is usually used to replace the free surface in scour simulation. The influence of the rigid lid assumption on the prediction precision of scour hole in steady flow is studied in this paper. Firstly, a local scour model was constructed based on the open sources Computational Fluid Dynamics (CFD model OpenFOAM, where both the bed load and suspended load were considered. In the present model, the bed shear stress was calculated by the Newton shear stress formula, instead of the traditional calculation method with the assumption that the flow velocity in vertical direction complies with a logarithmic distribution. The Volume of Fluid (VOF method was used to capture the free surface and a moving-mesh method was used to track the change of bed surface. Then, several experiments were chosen to validate the model, and the modeling results fitted well with the measured data. Lastly, the effect of the rigid lid assumption on surface elevation, bed shear stress and the profile of the scour hole in steady flow are studied. The result shows that the surface elevation suffers a drop above the pipeline, and the difference of surface elevation between the upstream and downstream increases with decreasing dimensionless depth. Compared with the free surface condition, the bed shear stress and scour hole depth computed with the rigid lid approximation were underestimated.
Experiments of steady state head and torque of centrifugal pumps in two-phase flow
International Nuclear Information System (INIS)
Minato, Akihiko; Tominaga, Kenji.
1988-01-01
Circulation pump behavior has large effect on coolant discharge flow rate in case of reactor pipe break. Experiment of two-phase pump performance was conducted as a joint study of Japanese BWR user utilities and makers. Two-phase head and torque of three centrifugal pumps in high temperature and high pressure (around 6 MPa) steam/water were measured. Head was decreased from single-phase characteristics when gas was mixed in liquid flow in condition with normal flow and normal rotation directions. When flow rate was large enough, two-phase head was about the same as single-phase one in reversal flow conditions. Two-phase head was smoothly increased as flowing steam volumetic concentration increased when flow rate was small and flow direction was reversal. Changes of torque with gas concentration were correspondent to those of head. This suggested that changes of interaction between flow and impellers due to phase slip effected on torque which caused head differences between single- and two-phase flows. Dependence of dimensionless head and torque of three test pumps on steam concentration were almost the same as each other. (author)
Numerical Solution of Inviscid Compressible Steady Flows around the RAE 2822 Airfoil
Kryštůfek, P.; Kozel, K.
2015-05-01
The article presents results of a numerical solution of subsonic, transonic and supersonic flows described by the system of Euler equations in 2D compressible flows around the RAE 2822 airfoil. Authors used FVM multistage Runge-Kutta method to numerically solve the flows around the RAE 2822 airfoil. The results are compared with the solution using the software Ansys Fluent 15.0.7.
A dual-phantom system for validation of velocity measurements in stenosis models under steady flow.
Blake, James R; Easson, William J; Hoskins, Peter R
2009-09-01
A dual-phantom system is developed for validation of velocity measurements in stenosis models. Pairs of phantoms with identical geometry and flow conditions are manufactured, one for ultrasound and one for particle image velocimetry (PIV). The PIV model is made from silicone rubber, and a new PIV fluid is made that matches the refractive index of 1.41 of silicone. Dynamic scaling was performed to correct for the increased viscosity of the PIV fluid compared with that of the ultrasound blood mimic. The degree of stenosis in the models pairs agreed to less than 1%. The velocities in the laminar flow region up to the peak velocity location agreed to within 15%, and the difference could be explained by errors in ultrasound velocity estimation. At low flow rates and in mild stenoses, good agreement was observed in the distal flow fields, excepting the maximum velocities. At high flow rates, there was considerable difference in velocities in the poststenosis flow field (maximum centreline differences of 30%), which would seem to represent real differences in hydrodynamic behavior between the two models. Sources of error included: variation of viscosity because of temperature (random error, which could account for differences of up to 7%); ultrasound velocity estimation errors (systematic errors); and geometry effects in each model, particularly because of imperfect connectors and corners (systematic errors, potentially affecting the inlet length and flow stability). The current system is best placed to investigate measurement errors in the laminar flow region rather than the poststenosis turbulent flow region.
Newman, James C., III
1995-01-01
The limiting factor in simulating flows past realistic configurations of interest has been the discretization of the physical domain on which the governing equations of fluid flow may be solved. In an attempt to circumvent this problem, many Computational Fluid Dynamic (CFD) methodologies that are based on different grid generation and domain decomposition techniques have been developed. However, due to the costs involved and expertise required, very few comparative studies between these methods have been performed. In the present work, the two CFD methodologies which show the most promise for treating complex three-dimensional configurations as well as unsteady moving boundary problems are evaluated. These are namely the structured-overlapped and the unstructured grid schemes. Both methods use a cell centered, finite volume, upwind approach. The structured-overlapped algorithm uses an approximately factored, alternating direction implicit scheme to perform the time integration, whereas, the unstructured algorithm uses an explicit Runge-Kutta method. To examine the accuracy, efficiency, and limitations of each scheme, they are applied to the same steady complex multicomponent configurations and unsteady moving boundary problems. The steady complex cases consist of computing the subsonic flow about a two-dimensional high-lift multielement airfoil and the transonic flow about a three-dimensional wing/pylon/finned store assembly. The unsteady moving boundary problems are a forced pitching oscillation of an airfoil in a transonic freestream and a two-dimensional, subsonic airfoil/store separation sequence. Accuracy was accessed through the comparison of computed and experimentally measured pressure coefficient data on several of the wing/pylon/finned store assembly's components and at numerous angles-of-attack for the pitching airfoil. From this study, it was found that both the structured-overlapped and the unstructured grid schemes yielded flow solutions of
Steady and transient states of a two-phase counter current flow
International Nuclear Information System (INIS)
Siebert, S.
1984-06-01
The aim of this work is to estimate the efficiency of the counter current exchange between a heavy dispersed phase and a continous light phase in a pulse perforated plate column. From an experimental point, hydraulic measurements (retention ratio, droplet size) and residence time measurements (radioactive tracers). The model will be so applied to the calculation of retention ratios in steady conditions then of tracer concentrations in transient conditions. From a numerical point of view a fixed point type iteration then a method Runge Kutta are then adapted [fr
International Nuclear Information System (INIS)
Li, Baoren; Gao, Longlong; Yang, Gang
2013-01-01
Highlights: ► A novel energy saving high-pressure electro-pneumatic servo valve is presented. ► An evaluated method for steady gas flow forces on pneumatic valves is proposed. ► Gas jet angles at the orifices for the valve are larger than 69° commonly used. ► The steady gas flow force is strongly nonlinear with valve opening. ► The steady gas flow force is compensated and the aim at energy saving is realized. - Abstract: A novel voice coil motor (VCM) direct drive single stage high-pressure pneumatic servo valve is designed, and then the steady gas flow force acting on the spool of the servo valve is investigated by numerical simulation and experimental methods in this paper. At present, many studies about flow force are concentrated mainly on hydraulic valves, but rarely on pneumatic valves. However, the velocity of gas is up to sonic when high-pressure gas flows through the servo valve orifice. And therefore, the steady gas flow force, generated by high pressure and high speed gas flow, cannot be neglected and is an important disturbance for the VCM direct-drive single stage high-pressure pneumatic servo valve. Consequently, the numerical simulation with computational fluid dynamics (CFD) is adopted to analyze the flow filed, jet angles, and steady gas flow forces for the servo valve with different valve openings and inlet pressures. The experimental study is performed to evaluate and confirm the numerical analysis. Then the compensated approach is proposed to reduce the steady gas flow force for the servo valve, changing the angle of non-metering port designed in the valve sleeve to the spool axis. The results demonstrate that the presented numerical analysis method is validated, the gas jet angle for the servo valve orifice is more than 69° and varies with different spool openings, and the steady gas flow force is nonlinear with valve opening and linear with inlet pressure when the outlet boundary is atmospheric pressure. Moreover, the steady gas
Bakker, Mark
2001-05-01
An analytic, approximate solution is derived for the modeling of three-dimensional flow to partially penetrating wells. The solution is written in terms of a correction on the solution for a fully penetrating well and is obtained by dividing the aquifer up, locally, in a number of aquifer layers. The resulting system of differential equations is solved by application of the theory for multiaquifer flow. The presented approach has three major benefits. First, the solution may be applied to any groundwater model that can simulate flow to a fully penetrating well; the solution may be superimposed onto the solution for the fully penetrating well to simulate the local three-dimensional drawdown and flow field. Second, the approach is applicable to isotropic, anisotropic, and stratified aquifers and to both confined and unconfined flow. Third, the solution extends over a small area around the well only; outside this area the three-dimensional effect of the partially penetrating well is negligible, and no correction to the fully penetrating well is needed. A number of comparisons are made to existing three-dimensional, analytic solutions, including radial confined and unconfined flow and a well in a uniform flow field. It is shown that a subdivision in three layers is accurate for many practical cases; very accurate solutions are obtained with more layers.
Application of Potential Theory to Steady Flow Past Two Cylinders in Tandem Arrangement
Directory of Open Access Journals (Sweden)
Yangyang Gao
2014-01-01
Full Text Available The wake flow patterns associated with flow past a cylinder and a cylinder-pair in tandem configuration are revisited, compared, and evaluated with respect to the streamline patterns generated based on potential flow theory and superposition of various potential flow elements. The wakes, which are vortex shedding in the lee of the cylinder(s, are reproduced by placing pairs of equal but opposite circulation elements in the potential flow field. The strength of the circulation elements determines the size of the vortices produced. The streamline patterns of flow past a pair of unequal cylinders in tandem configuration provide an indirect means to establish the threshold condition for the wake transition from that of a single bluff body to alternating reattachment behavior. This threshold condition is found to be a function of the diameter ratio, d/D (diameters d and D, d≤D , spacing ratio, L/D (centre-to-centre distance, L, to cylinder diameter, D, and equivalent incident flow speed, U. A unique functional relationship f (L/D, d/D, U of this threshold condition is established.
TRUMP, Steady-State and Transient 1-D, 2-D and 3-D Potential Flow, Temperature Distribution
International Nuclear Information System (INIS)
Elrod, D.C.; Turner, W.D.
1981-01-01
1 - Description of problem or function: TRUMP solves a general non- linear parabolic partial differential equation describing flow in various kinds of potential fields, such as fields of temperature, pressure, or electricity and magnetism; simultaneously, it will solve two additional equations representing, in thermal problems, heat production by decomposition of two reactants having rate constants with a general Arrhenius temperature dependence. Steady- state and transient flow in one, two, or three dimensions are considered in geometrical configurations having simple or complex shapes and structures. Problem parameters may vary with spatial position, time, or primary dependent variables--temperature, pressure, or field strength. Initial conditions may vary with spatial position, and among the criteria that may be specified for ending a problem are upper and lower limits on the size of the primary dependent variable, upper limits on the problem time or on the number of time-steps or on the computer time, and attainment of steady state. 2 - Method of solution: Solutions may be obtained by use of explicit- or implicit-difference equations, or by an optimized combination of both. 3 - Restrictions on the complexity of the problem: The program currently provides for maxima of: 40 materials, 5 reactants, 105 surface conditions, 20 boundary nodes, 16 entries per tabulated function (table-length)
Steadiness of a “water bell” surface to a destruction at a flow around of the thin rods assembly
Directory of Open Access Journals (Sweden)
Slesareva Ekaterina
2015-01-01
Full Text Available The experimental research of hydrodynamic stability of a dome-shaped film liquid at a flow around a thin plate has been carried out. Experiments were carry out with a film in shape a «water bell». The film was formed by a leak-in jet of water width 10 mm on a hard disk with diameter 14.5 mm. The width of a plate ζ changed from 0.05 to 3.5 mm. The plate placed along or across relative to the vector of velocity of a liquid in a film. Experiments have shown, that stability of a film of liquid at a flow around the plate is defined by velocity of water and a thickness of a film δ in front of the rod. It is shown, that for the appointed value of Reynolds number Reδ probably continuous flow at a flow around the plate, if Weber number Weζ less than threshold value. The criterion of steadiness a film of the «water bell» by a surface destruction at a flow around the rod is determined on the transverse size of the rod relative to the vector of velocity of a liquid.
Incompressible Steady Flow with Tensor Conductivity Leaving a Transverse Magnetic Field
International Nuclear Information System (INIS)
Witalis, E.A.
1965-12-01
The straight channel flow of an inviscid, incompressible fluid with tensor conductivity is considered when the flow leaves a region of constant transverse magnetic field. The channel walls are taken to be insulating, and an eddy current system arises. This is investigated by the method of magnetic field analysis as given by Witalis. The spatial distribution of magnetic field and ohmic power loss, both parallel and transverse to the flow, are given as functions of the Hall parameter with consideration also to the magnetic Reynolds number of the fluid. MHD power generator aspects of this problem and the results are discussed
Incompressible Steady Flow with Tensor Conductivity Leaving a Transverse Magnetic Field
Energy Technology Data Exchange (ETDEWEB)
Witalis, E A
1965-12-15
The straight channel flow of an inviscid, incompressible fluid with tensor conductivity is considered when the flow leaves a region of constant transverse magnetic field. The channel walls are taken to be insulating, and an eddy current system arises. This is investigated by the method of magnetic field analysis as given by Witalis. The spatial distribution of magnetic field and ohmic power loss, both parallel and transverse to the flow, are given as functions of the Hall parameter with consideration also to the magnetic Reynolds number of the fluid. MHD power generator aspects of this problem and the results are discussed.
Constitutive Curve and Velocity Profile in Entangled Polymers during Start-Up of Steady Shear Flow
Hayes, Keesha A.; Buckley, Mark R.; Qi, Haibo; Cohen, Itai; Archer, Lynden A.
2010-01-01
-4]. Surprisingly, we find that even polymer systems which exhibit transient, nonmonotonic shear stress-shear rate relationships in bulk rheology experiments manifest time-dependent velocity profiles that are decidedly linear and show no evidence of unstable flow
DNS for Flow Separation Control Around Airfoil by Steady and Pulsed Jets
National Research Council Canada - National Science Library
Deng, Shutian; Jiang, Li; Liu, Chaoqun
2004-01-01
This work consists of two parts. The first part is direct numerical simulation (DNS) for flow separation and transition around a NACA 0012 airfoil with an attack angle of 4 degrees and Reynolds number of 100,000...
On the computation of steady Hopper flows. II: von Mises materials in various geometries
Gremaud, Pierre A.; Matthews, John V.; O'Malley, Meghan
2004-11-01
Similarity solutions are constructed for the flow of granular materials through hoppers. Unlike previous work, the present approach applies to nonaxisymmetric containers. The model involves ten unknowns (stresses, velocity, and plasticity function) determined by nine nonlinear first order partial differential equations together with a quadratic algebraic constraint (yield condition). A pseudospectral discretization is applied; the resulting problem is solved with a trust region method. The important role of the hopper geometry on the flow is illustrated by several numerical experiments of industrial relevance.
On the computation of steady Hopper flows II: von Mises materials in various geometries
International Nuclear Information System (INIS)
Gremaud, Pierre A.; Matthews, John V.; O'Malley, Meghan
2004-01-01
Similarity solutions are constructed for the flow of granular materials through hoppers. Unlike previous work, the present approach applies to nonaxisymmetric containers. The model involves ten unknowns (stresses, velocity, and plasticity function) determined by nine nonlinear first order partial differential equations together with a quadratic algebraic constraint (yield condition). A pseudospectral discretization is applied; the resulting problem is solved with a trust region method. The important role of the hopper geometry on the flow is illustrated by several numerical experiments of industrial relevance
International Nuclear Information System (INIS)
Kolios, M.C.; Worthington, A.E.; Hunt, J.W.; Holdsworth, D.W.; Sherar, M.D.
1999-01-01
Temperature distributions measured during thermal therapy are a major prognostic factor of the efficacy and success of the procedure. Thermal models are used to predict the temperature elevation of tissues during heating. Theoretical work has shown that blood flow through large blood vessels plays an important role in determining temperature profiles of heated tissues. In this paper, an experimental investigation of the effects of large vessels on the temperature distribution of heated tissue is performed. The blood flow dependence of steady state and transient temperature profiles created by a cylindrical conductive heat source and an ultrasound transducer were examined using a fixed porcine kidney as a flow model. In the transient experiments, a 20 s pulse of hot water, 30 deg. C above ambient, heated the tissues. Temperatures were measured at selected locations in steps of 0.1 mm. It was observed that vessels could either heat or cool tissues depending on the orientation of the vascular geometry with respect to the heat source and that these effects are a function of flow rate through the vessels. Temperature gradients of 6 deg. C mm -1 close to large vessels were routinely measured. Furthermore, it was observed that the temperature gradients caused by large vessels depended on whether the heating source was highly localized (i.e. a hot needle) or more distributed (i.e. external ultrasound). The gradients measured near large vessels during localized heating were between two and three times greater than the gradients measured during ultrasound heating at the same location, for comparable flows. Moreover, these gradients were more sensitive to flow variations for the localized needle heating. X-ray computed tomography data of the kidney vasculature were in good spatial agreement with the locations of all of the temperature variations measured. The three-dimensional vessel path observed could account for the complex features of the temperature profiles. The flow
Juarsa, M.; Giarno; Rohman, A. N.; Heru K., G. B.; Witoko, J. P.; Sony Tjahyani, D. T.
2018-02-01
The need for large-scale experimental facilities to investigate the phenomenon of natural circulation flow rate becomes a necessity in the development of nuclear reactor safety management. The FASSIP-01 loop has been built to determine the natural circulation flow rate performance in the large-scale media and aimed to reduce errors in the results for its application in the design of new generation reactors. The commissioning needs to be done to define the capability of the FASSIP-01 loop and to prescribe the experiment limitations. On this commissioning, two scenarios experimental method has been used. The first scenario is a static condition test which was conducted to verify measurement system response during 24 hours without electrical load in heater and cooler, there is water and no water inside the rectangular loop. Second scenario is a dynamics condition that aims to understand the flow rate, a dynamic test was conducted using heater power of 5627 watts and coolant flow rate in the HSS loop of 9.35 LPM. The result of this test shows that the temperature characterization on static test provide a recommendation, that the experiments should be done at night because has a better environmental temperature stability compared to afternoon, with stable temperature around 1°C - 3°C. While on the dynamic test, the water temperature difference between the inlet-outlets in the heater area is quite large, about 7 times the temperature difference in the cooler area. The magnitude of the natural circulation flow rate calculated is much larger at about 300 times compared to the measured flow rate with different flow rate profiles.
Directory of Open Access Journals (Sweden)
Poul S. Larsen
2011-09-01
To obtain precise and reliable laboratory clearance rate (filtration rate measurements with the ‘flow-through chamber method’ (FTC the design must ensure that only inflow water reaches the bivalve's inhalant aperture and that exit flow is fully mixed. As earlier recommended these prerequisites can be checked by a plot of clearance rate (CR versus increasing through-flow (Fl to reach a plateau, which is the true CR, but we also recommend to plot percent particles cleared versus reciprocal through-flow where the plateau becomes the straight line CR/Fl, and we emphasize that the percent of particles cleared is in itself neither a criterion for valid CR measurement, nor an indicator of appropriate ‘chamber geometry’ as hitherto adapted in many studies. For the ‘steady-state method’ (SS, the design must ensure that inflow water becomes fully mixed with the bivalve's excurrent flow to establish a uniform chamber concentration prevailing at its incurrent flow and at the chamber outlet. These prerequisites can be checked by a plot of CR versus increasing Fl, which should give the true CR at all through-flows. Theoretically, the experimental uncertainty of CR for a given accuracy of concentration measurements depends on the percent reduction in particle concentration (100×P from inlet to outlet of the ideal ‘chamber geomety’. For FTC, it decreases with increasing values of P while for SS it first decreases but then increases again, suggesting the use of an intermediate value of P. In practice, the optimal value of P may depend on the given ‘chamber geometry’. The fundamental differences between the FTC and the SS methods and practical guidelines for their use are pointed out, and new data on CR for the blue mussel, Mytilus edulis, illustrate a design and use of the SS method which may be employed in e.g. long-term growth experiments at constant algal concentrations.
Asymptotic analysis of the average, steady, isotherml flow in coupled, parallel channels
International Nuclear Information System (INIS)
Lund, K.O.
1976-01-01
The conservation equations of mass and momentum are derived for the average flow of gases in coupled, parallel channels, or rod bundles. In the case of gas-cooled rod bundles the pitch of the rods is relatively large so the flows in the channels are strongly coupled. From this observation a perturbation parameter is derived and the descriptive equations are scaled using this parameter, which represents the ratio of the axial flow area to the transverse flow area, and which is of the order of 10 -3 in current gas-cooled fast breeder reactor designs. By expanding the velocities into perturbation series the equations for two channels are solved as an initial value problem, and the results compared to a finite difference solution of the same problem. The N-channel problem is solved to the lowest order as a two-point boundary value problem with the pressures specified at the inlet and the outlet. It is concluded from the study that asymptotic methods are effective in solving the flow problems of rod bundles; however, further work is required to evaluate the possible computational advantages of the methods
Reading drift in flow rate sensors caused by steady sound waves
International Nuclear Information System (INIS)
Maximiano, Celso; Nieble, Marcio D.; Migliavacca, Sylvana C.P.; Silva, Eduardo R.F.
1995-01-01
The use of thermal sensors very common for the measurement of small flows of gases. In this kind of sensor a little tube forming a bypass is heated symmetrically, then the temperature distribution in the tube modifies with the mass flow along it. When a stationary wave appears in the principal tube it causes an oscillation of pressure around the average value. The sensor, located between two points of the principal tube, indicates not only the principal mass flow, but also that one caused by the difference of pressure induced by the sound wave. When the gas flows at low pressures the equipment indicates a value that do not correspond to the real. Tests and essays were realized by generating a sound wave in the principal tube, without mass flow, and the sensor detected flux. In order to solve this problem a wave-damper was constructed, installed and tested in the system and it worked satisfactory eliminating with efficiency the sound wave. (author). 2 refs., 3 figs
Flow-structure Interaction Modeling of a Fish Caudal Fin during Steady Swimming
Liu, Geng; Geng, Biao; Zheng, Xudong; Xue, Qian; Dong, Haibo
2017-11-01
It's widely thought that the flexibilities of fish fins play critical roles in propulsive performance enhancement (such as thrust augment and efficiency improvement) in nature. In order to explore the formation mechanisms of the fish fin's flexible morphing and its hydrodynamic benefits as well, a high-fidelity flow-structure/membrane interaction modeling of the fish caudal fin is conducted in this work. Following the realistic configuration of the fish caudal fin, a thin membrane supported by a series of beams is constructed. The material properties of the membrane and the beams are reversely determined by the realistic fin morphing obtained from the high-speed videos and the high fidelity flow-structure interaction simulations. With the accurate material property, we investigate the interplay between structure, kinematics and fluid flow in caudal fin propulsion. Detailed analyses on the relationship between the flexural stiffness, fin morphing patterns, hydrodynamic forces and vortex dynamics are then conducted.
Sharzehee, Mohammadali; Khalafvand, Seyed Saeid; Han, Hai-Chao
2018-02-01
Tortuous aneurysmal arteries are often associated with a higher risk of rupture but the mechanism remains unclear. The goal of this study was to analyze the buckling and post-buckling behaviors of aneurysmal arteries under pulsatile flow. To accomplish this goal, we analyzed the buckling behavior of model carotid and abdominal aorta with aneurysms by utilizing fluid-structure interaction (FSI) method with realistic waveforms boundary conditions. FSI simulations were done under steady-state and pulsatile flow for normal (1.5) and reduced (1.3) axial stretch ratios to investigate the influence of aneurysm, pulsatile lumen pressure and axial tension on stability. Our results indicated that aneurysmal artery buckled at the critical buckling pressure and its deflection nonlinearly increased with increasing lumen pressure. Buckling elevates the peak stress (up to 118%). The maximum aneurysm wall stress at pulsatile FSI flow was (29%) higher than under static pressure at the peak lumen pressure of 130 mmHg. Buckling results show an increase in lumen shear stress at the inner side of the maximum deflection. Vortex flow was dramatically enlarged with increasing lumen pressure and artery diameter. Aneurysmal arteries are more susceptible than normal arteries to mechanical instability which causes high stresses in the aneurysm wall that could lead to aneurysm rupture.
Growth-direction dependence of steady-state Saffman-Taylor flow in an anisotropic Hele-Shaw cell
International Nuclear Information System (INIS)
McCloud, K.V.; Maher, J.V.
1996-01-01
Selection of steady-state fingers has been measured in a Hele-Shaw cell perturbed by having a square lattice etched onto one of the plates. Flows at different orientations θ between the direction of flow and the lattice axes have been studied, in a wide range of observable tip velocities where the perturbation was made microscopic in the sense that the capillary length of the flow was much greater than the etched lattice cell size. The full range of dynamically interesting angles for the square lattice was examined, and above a threshold, the microscopic perturbation always results in wider fingers than are selected in the unperturbed case. There is some dependence of the width of the fingers on the orientation of the flow, with fingers at θ=0 degree being the widest with respect to the unperturbed fingers, and fingers at 45 degree being the least wide, although still wider than the unperturbed fingers. All observed solutions are symmetric, centered in the channel, and have the relation between tip-curvature and finger width expected of members of the Saffman-Taylor family of solutions. Selected solutions narrow again at tip velocities where the perturbation can no longer be considered microscopic. copyright 1996 The American Physical Society
A numerical study of steady-state two-phase flow in porous media
Energy Technology Data Exchange (ETDEWEB)
Knudsen, Henning Arendt
2002-07-01
Two-phase flow in porous media means the simultaneous flow of two phases, say two liquids, e.g., oil and water. This flow is restrained to be within a porous medium. For example sandstone and limestone are typical porous stones that can contain oil and gas in nature. In the extraction of oil from reservoirs, oil is usually displaced by water. So on a large scale we can consider it to be a displacement process. However, on pore scale the ''mix'' and flow processes are complicated. Idealistically, one might consider the search for truth a sufficient motivation for work in this field. Nevertheless, from an economic and technological point of view, enhanced oil recovery is the main motivation for the study of two-phase flow in porous media. Luckily, there are additional systems in real world that falls into this category. One such system is the flow of water and pollutants in aquifers. General knowledge in the field might be beneficial for preserving ground water reserves in the future. In the laboratory one often encounters artificially made porous media. For example glass beads between two glass plates. Therein, one of the phases flowing may be a mixture of glycerol and water. The other phase can be air which then is the non-wetting phase; air does not wet glass. It can also be silicone oil, and in that case the water/glycerol is normally the nonwetting phase. There are other possibilities. In general, laboratory studies are performed on systems on pore scale. The flow properties on the various length scales found in flow systems in nature depend on these properties on pore scale. The so-called upscaling problem concerns how to relate pore scale properties with properties on larger scales. The scope of this thesis is the study of properties on pore scale. The upscaling problem, which is a large research field in itself, is thus outside the scope of this thesis. The results of Paper 3 is an exception since they may infer also to larger scales than
Quasi-steady accelerator operation on the ZAP flow Z-pinch
Energy Technology Data Exchange (ETDEWEB)
Hughes, M. C., E-mail: mchugs@uw.edu; Shumlak, U., E-mail: mchugs@uw.edu; Golingo, R. P., E-mail: mchugs@uw.edu; Nelson, B. A., E-mail: mchugs@uw.edu; Ross, M. P., E-mail: mchugs@uw.edu [Aerospace and Energetics Research Program, University of Washington, Seattle, WA 98195 (United States)
2014-12-15
The ZaP Flow Z-Pinch Experiment utilizes sheared flows to stabilize an otherwise unstable equilibrium. The sheared flows are maintained by streaming high velocity plasma parallel to the pinch. Previous operations of the machine show depletion of the accelerator’s neutral gas supply late in the pulse leading to pinch instability. The current distribution in the accelerator exhibits characteristic modes during this operation, which is corroborated by interferometric signals. The decrease in density precipitates a loss of plasma quiescence in the pinch, which occurs on a timescale related to the flow velocity from the plasma source. To abate the depletion, the geometry of the accelerator is altered to increase the neutral gas supply. The design creates a standing deflagration front in the accelerator that persists for the pulse duration. The new operating mode is characterized by the same diagnostics as the previous mode. The lessons learned in the accelerator operations have been applied to the design of a new experiment, ZaP-HD. This work was supported by grants from the Department of Energy and the National Nuclear Security Administration.
Analytical solutions of steady-state conjugate heat transfer in ducts with turbulent flow
International Nuclear Information System (INIS)
Cerqueira, Djane R.; Jian Su
2007-01-01
In this work, we present an approximate analytical solution of the steady-state conjugate heat transfer of turbulent forced convection in a circular pipe with wall axial heat conduction and external convective boundary conditions. Improved lumped differential approach based on two points Hermite approximation for integrals was applied to reduce the heat conduction equation in the solid into a second-order ordinary differential equation for the radially averaged solid temperature. The energy equation in the fluid was solved by applying the generalized integral transform technique (GITT). The Sturm-Lioville eigenproblem for fluid energy equation in the cylindrical coordinate system was solved by the sign-count method. The truncated system of N ordinary differential equations for transformed potentials of the fluid temperature and the second-order ordinary differential equation for radially averaged solid temperature formed a homogeneous system of N+2 ordinary differential equations, which was solved analytically. The effects of the fluid-solid thermal conductivity ratio on the Nusselt number, the average fluid and solid temperatures, and the fluid-solid interface temperature were investigated. (author)
On the validity of travel-time based nonlinear bioreactive transport models in steady-state flow.
Sanz-Prat, Alicia; Lu, Chuanhe; Finkel, Michael; Cirpka, Olaf A
2015-01-01
Travel-time based models simplify the description of reactive transport by replacing the spatial coordinates with the groundwater travel time, posing a quasi one-dimensional (1-D) problem and potentially rendering the determination of multidimensional parameter fields unnecessary. While the approach is exact for strictly advective transport in steady-state flow if the reactive properties of the porous medium are uniform, its validity is unclear when local-scale mixing affects the reactive behavior. We compare a two-dimensional (2-D), spatially explicit, bioreactive, advective-dispersive transport model, considered as "virtual truth", with three 1-D travel-time based models which differ in the conceptualization of longitudinal dispersion: (i) neglecting dispersive mixing altogether, (ii) introducing a local-scale longitudinal dispersivity constant in time and space, and (iii) using an effective longitudinal dispersivity that increases linearly with distance. The reactive system considers biodegradation of dissolved organic carbon, which is introduced into a hydraulically heterogeneous domain together with oxygen and nitrate. Aerobic and denitrifying bacteria use the energy of the microbial transformations for growth. We analyze six scenarios differing in the variance of log-hydraulic conductivity and in the inflow boundary conditions (constant versus time-varying concentration). The concentrations of the 1-D models are mapped to the 2-D domain by means of the kinematic (for case i), and mean groundwater age (for cases ii & iii), respectively. The comparison between concentrations of the "virtual truth" and the 1-D approaches indicates extremely good agreement when using an effective, linearly increasing longitudinal dispersivity in the majority of the scenarios, while the other two 1-D approaches reproduce at least the concentration tendencies well. At late times, all 1-D models give valid approximations of two-dimensional transport. We conclude that the
Novel Slope Source Term Treatment for Preservation of Quiescent Steady States in Shallow Water Flows
Directory of Open Access Journals (Sweden)
Khawar Rehman
2016-10-01
Full Text Available This paper proposes a robust method for modeling shallow-water flows and near shore tsunami propagation, applicable for both simple and complex geometries with uneven beds. The novel aspect of the model includes the introduction of a new method for slope source terms treatment to preserve quiescent equilibrium over uneven topographies, applicable to both structured and unstructured mesh systems with equal accuracy. Our model is based on the Godunov-type finite volume numerical approximation. Second-order spatial and temporal accuracy is achieved through high resolution gradient reconstruction and the predictor-corrector method, respectively. The approximate Riemann solver of Harten, Lax, and van Leer with contact wave restoration (HLLC is used to compute fluxes. Comparisons of the model’s results with analytical, experimental, and published numerical solutions show that the proposed method is capable of accurately predicting experimental and real-time tsunami propagation/inundation, and dam-break flows over varying topographies.
Spectral Analysis and Computation of Effective Diffusivities for Steady Random Flows
2016-04-28
even in the motion of sea ice floes influenced by winds and ocean currents. The long time, large scale behavior of such systems is equivalent to an...flow plays a key role in many important processes in the global climate system [55] and Earth’s ecosys- tems [14]. Advection of geophysical fluids...HOMOGENIZATION OF THE ADVECTION-DIFFUSION EQUATION The dispersion of a cloud of passive scalars with density φ diffusing with molecular dif- fusivity ε and
International Nuclear Information System (INIS)
Shuchi, S.; Shimada, K.; Kamiyama, S.; Yamaguchi, H.
2002-01-01
We clarify numerically the wall friction coefficient, the distributions of velocity and shear rate, and the number of aggregated particles on steady magnetic fluid flow in a straight tube by taking into account the non-uniform distribution of mass concentration (DMC). Also the effect of DMC is clarified under the uniform and non-uniform transverse steady magnetic field. In comparison with the published data, the numerical results show good agreement with the experimental data
Graham, Wendy D.; Tankersley, Claude D.
1994-05-01
Stochastic methods are used to analyze two-dimensional steady groundwater flow subject to spatially variable recharge and transmissivity. Approximate partial differential equations are developed for the covariances and cross-covariances between the random head, transmissivity and recharge fields. Closed-form solutions of these equations are obtained using Fourier transform techniques. The resulting covariances and cross-covariances can be incorporated into a Bayesian conditioning procedure which provides optimal estimates of the recharge, transmissivity and head fields given available measurements of any or all of these random fields. Results show that head measurements contain valuable information for estimating the random recharge field. However, when recharge is treated as a spatially variable random field, the value of head measurements for estimating the transmissivity field can be reduced considerably. In a companion paper, the method is applied to a case study of the Upper Floridan Aquifer in NE Florida.
Courbin, L.; Benayad, A.; Panizza, P.
2006-01-01
By means of several rheophysics techniques, we report on an extensive study of the couplings between flow and microstructures in a two-phase fluid made of lamellar (Lα) and sponge (L3) phases. Depending on the nature of the imposed dynamical parameter (stress or shear rate) and on the experimental conditions (brine salinity or temperature), we observe several different structural steady states consisting of either multilamellar droplets (with or without a long range order) or elongated (L3) phase domains. Two different astonishing phenomena, shear-induced phase inversion and relaxation oscillations, are observed. We show that (i) phase inversion is related to a shear-induced topological change between monodisperse multilamellar droplets and elongated structures and (ii) droplet size relaxation oscillations result from a shear-induced change of the surface tension between both coexisting (Lα) and (L3) phases. To explain these relaxation oscillations, we present a phenomenological model and compare its numerical predictions to our experimental results.
International Nuclear Information System (INIS)
Martin, A.; Alvarez, D.; Cases, F.
1996-03-01
The paper explains the chronological account and the first results obtained in the R and D program on the mixing in the 900 MW PWR vessels. After the presentation of the plant type simulated, we define the numerical tool, the (Finite Element Modelling) FEM N3S code. Two results are presented with a comparison with the experiment results issued of the BORA BORA mock up. The first case is dealing with the isothermal steady state mixing in the vessel with the three loops mass flow rate balanced. This case identified as a validation of our numerical tool shows a good agreement. The second case is dealing with the transient mixing of a clear plug in the vessel when one primary pump starts-up. We compare the numerical and experiment results giving the mean boron concentration at the core inlet for several clear water plugs. The results show again a good agreement. (authors). 12 refs., 10 figs., 1 tab
Directory of Open Access Journals (Sweden)
Zhentao Wang
2014-07-01
Full Text Available A model based on the volume of fluid (VOF method and leaky dielectric theory is established to predict the deformation and internal flow of the droplet suspended in another vicious fluid under the influence of the electric field. Through coupling with hydrodynamics and electrostatics, the rate of deformation and internal flow of the single droplet are simulated and obtained under the different operating parameters. The calculated results show that the direction of deformation and internal flow depends on the physical properties of fluids. The numerical results are compared with Taylor's theory and experimental results by Torza et al. When the rate of deformation is small, the numerical results are consistent with theory and experimental results, and when the rate is large the numerical results are consistent with experimental results but are different from Taylor's theory. In addition, fluid viscosity hardly affects the deformation rate and mainly dominates the deformation velocity. For high viscosity droplet spends more time to attain the steady state. The conductivity ratio and permittivity ratio of two different liquids affect the direction of deformation. When fluid electric properties change, the charge distribution at the interface is various, which leads to the droplet different deformation shapes.
Si, Ting; Yin, Chuansheng; Gao, Peng; Li, Guangbin; Ding, Hang; He, Xiaoming; Xie, Bin; Xu, Ronald X.
2016-01-01
A compound-fluidic electro-flow focusing (CEFF) process is proposed to produce multicompartment microcapsules. The central device mainly consists of a needle assembly of two parallel inner needles and one outer needle mounted in a gas chamber with their tips facing a small orifice at the bottom of the chamber. As the outer and the inner fluids flow through the needle assembly, a high-speed gas stream elongates the liquid menisci in the vicinity of the orifice entrance. An electric field is further integrated into capillary flow focusing to promote the formation of steady cone-jet mode in a wide range of operation parameters. The multiphase liquid jet is broken up into droplets due to perturbation propagation along the jet surface. To estimate the diameter of the multiphase liquid jet as a function of process parameters, a modified scaling law is derived and experimentally validated. Microcapsules of around 100 μm with an alginate shell and multiple cores at a production rate of 103-105 per second are produced. Technical feasibility of stimulation triggered coalescence and drug release is demonstrated by benchtop experiments. The proposed CEFF process can be potentially used to encapsulate therapeutic agents and biological cargos for controlled micro-reaction and drug delivery.
Zhang, Xuan; Ortega, John; Huang, Yuanlong; Shertz, Stephen; Tyndall, Geoffrey S.; Orlando, John J.
2018-05-01
Experiments performed in laboratory chambers have contributed significantly to the understanding of the fundamental kinetics and mechanisms of the chemical reactions occurring in the atmosphere. Two chemical regimes, classified as high-NO vs. zero-NO conditions, have been extensively studied in previous chamber experiments. Results derived from these two chemical scenarios are widely parameterized in chemical transport models to represent key atmospheric processes in urban and pristine environments. As the anthropogenic NOx emissions in the United States have decreased remarkably in the past few decades, the classic high-NO and zero-NO conditions are no longer applicable to many regions that are constantly impacted by both polluted and background air masses. We present here the development and characterization of the NCAR Atmospheric Simulation Chamber, which is operated in steady-state continuous flow mode for the study of atmospheric chemistry under intermediate NO conditions. This particular chemical regime is characterized by constant sub-ppb levels of NO and can be created in the chamber by precise control of the inflow NO concentration and the ratio of chamber mixing to residence timescales. Over the range of conditions achievable in the chamber, the lifetime of peroxy radicals (RO2), a key intermediate from the atmospheric degradation of volatile organic compounds (VOCs), can be extended to several minutes, and a diverse array of reaction pathways, including unimolecular pathways and bimolecular reactions with NO and HO2, can thus be explored. Characterization experiments under photolytic and dark conditions were performed and, in conjunction with model predictions, provide a basis for interpretation of prevailing atmospheric processes in environments with intertwined biogenic and anthropogenic activities. We demonstrate the proof of concept of the steady-state continuous flow chamber operation through measurements of major first-generation products
Directory of Open Access Journals (Sweden)
X. Zhang
2018-05-01
Full Text Available Experiments performed in laboratory chambers have contributed significantly to the understanding of the fundamental kinetics and mechanisms of the chemical reactions occurring in the atmosphere. Two chemical regimes, classified as high-NO vs. zero-NO conditions, have been extensively studied in previous chamber experiments. Results derived from these two chemical scenarios are widely parameterized in chemical transport models to represent key atmospheric processes in urban and pristine environments. As the anthropogenic NOx emissions in the United States have decreased remarkably in the past few decades, the classic high-NO and zero-NO conditions are no longer applicable to many regions that are constantly impacted by both polluted and background air masses. We present here the development and characterization of the NCAR Atmospheric Simulation Chamber, which is operated in steady-state continuous flow mode for the study of atmospheric chemistry under intermediate NO conditions. This particular chemical regime is characterized by constant sub-ppb levels of NO and can be created in the chamber by precise control of the inflow NO concentration and the ratio of chamber mixing to residence timescales. Over the range of conditions achievable in the chamber, the lifetime of peroxy radicals (RO2, a key intermediate from the atmospheric degradation of volatile organic compounds (VOCs, can be extended to several minutes, and a diverse array of reaction pathways, including unimolecular pathways and bimolecular reactions with NO and HO2, can thus be explored. Characterization experiments under photolytic and dark conditions were performed and, in conjunction with model predictions, provide a basis for interpretation of prevailing atmospheric processes in environments with intertwined biogenic and anthropogenic activities. We demonstrate the proof of concept of the steady-state continuous flow chamber operation through measurements of major first
Numerical analysis of steady state fluid flow in a two-dimensional wavy channel
International Nuclear Information System (INIS)
Gorji, M.; Hosseinzadeh, E.
2007-01-01
A simple geometry of the flow passage that may be used to enhance the heat transfer rate is called wavy and periodic channel. Wavy channel can provide significant heat transfer augmentation and was always important for heat transfer engineering and so far many researches have been done in this field. In this paper, the effects of channel geometry and Reynolds number on the heat transfer coefficient, heat flux and pressure drop for the laminar fully developed flow in a two dimensional channel whereas the walls are considered fix temperature is numerically investigated. The problem is solved for channel with one and two wavy walls and comparisons with the straight channel, in the same flow rate, have been performed. Results indicate that, by decreasing the channel wave length and the distance between the channel walls the pressure drop, heat flux and heat transfer coefficient increase. Results and Conclusions: The following conclusion may be drawn: 1. In a specified channel, for the fluid flow with the constant Reynolds number, by decreasing the wave length from 0.2 m to 0.1 m, the pressure drop, heat flux and heat transfer coefficient increase by 37% , 54% and 29% respectively, whereas by decreasing the wave length from the same value the above mentioned parameters decrease to 108% , 143% and 47% respectively. 2. In a specified wave length, where the amplitude and the Reynolds number is constant, by increasing the distance between the walls from 0.15 m to 0.25 m, the pressure drop, heat flux and heat transfer coefficient decrease by 41% ,8% and 7.8% respectively. References [1] J.C. Burns, T. Parks, J. Fluid Mesh, 29(1967), 405-416. [2] J.L. Goldestein, E.M. Sparrow, ASME J. Heat Transfer, 99 (1977), 187. [3] J.E.O. Brain, E.M. Sparrow, ASME J. Heat Transfer, 104 (1982), 410 [4] N. Sanie, S. Dini, ASME J. Heat Transfer, 115 (1993), 788. [5] G. Wang, P. Vanka, Int. J. Heat Mass Transfer, 38 (17) (1995), 3219. [6] T.A. Rush, T.A. Newell, A.M. Jacobi, Int, J. Heat Mass
Steady and Transient Analysis of Flow and Heat Transfer in SPND Assembly
Tijiboy, Jose Carlos
2008-01-01
This thesis presents the analysis of flow and heat transfer for the SPND (Self-Powered Neutron Detector) system used within the nuclear reactor core in the U.S. Evolutionary Power Reactor developed by AREVA. The SPND system is composed of six individual detectors which are used for in-core measurement of thermal neutron flux. The study of the SPND system is important since this system provides information and signals necessary for safe reactor operation and control. The main goal of the proj...
Conservation laws for steady flow and solitons in a multifluid plasma revisited
International Nuclear Information System (INIS)
Mace, R. L.; McKenzie, J. F.; Webb, G. M.
2007-01-01
The conservation laws used in constructing the governing equations for planar solitons in multifluid plasmas are revisited. In particular, the concept of generalized vorticity facilitates the derivation of some general ''Bernoulli theorems,'' which reduce, in specific instances, to conservation laws previously deduced by other means. These theorems clarify the underlying physical principles that give rise to the conserved quantities. As an example of the usefulness of the techniques, even for relatively simple flows and progressive waves, the equations governing stationary nonlinear whistler waves propagating parallel to an ambient magnetic field are derived using generalized vorticity concepts
Numerical simulation of steady supersonic flow over spinning bodies of revolution
Sturek, W. B.; Schiff, L. B.
1982-01-01
A recently reported parabolized Navier-Stokes code has been employed to compute the supersonic flowfield about a spinning cone and spinning and nonspinning ogive cylinder and boattailed bodies of revolution at moderate incidence. The computations were performed for flow conditions where extensive measurements for wall pressure, boundary-layer velocity profiles, and Magnus force had been obtained. Comparisons between the computational results and experiment indicate excellent agreement for angles of attack up to 6 deg. At angles greater than 6 deg discrepancies are noted which are tentatively attributed to turbulence modeling errors. The comparisons for Magnus effects show that the code accurately predicts the effects of body shape for the selected models.
Experimental study of non-steady state moisture diffusional flow in wood
International Nuclear Information System (INIS)
Ayensu, A.
1992-10-01
Experiments have been conducted to verify the suitability of Fick's second law to describe moisture flow in wood. The moisture content change with time were plotted for absorption and desorption, and it was observed that these variations follow the same trend as modelled on the computer. The mean integral diffusion coefficient D-bar for the wood species were calculated on the basis of Boltzmann's solution of Fick's second law, D-bar ranges from 2.0 x 10 -3 cm 2 /s to 4.2 x 10 -3 cm 2 /s for both absorption and desorption. (author). 5 refs, 4 figs, 2 tabs
Directory of Open Access Journals (Sweden)
Kalidas Das
2018-03-01
Full Text Available The temperament of stream characteristic, heat and mass transfer of MHD forced convective flow over a linearly expanding porous medium has been scrutinized in the progress exploration. The germane possessions of the liquid like viscosity along with thermal conductivity are believed to be variable in nature, directly influenced by the temperature of flow. As soon as gaining the system of leading equations of the stream, Lie symmetric group transformations have been employed to come across the fitting parallel conversions to alter the central PDEs into a suit of ODEs. The renovated system of ODE with appropriate boundary conditions is numerically solved with the assistance of illustrative software MAPLE 17. The consequences of the relevant factors of the system have been exemplified through charts and graphs. An analogous qualified survey has been prepared among present inquiry and subsisting reads and achieved an admirable accord between them. The variable viscosity parameter has more significant effect on nanofluid velocity than regular fluid and temporal profile as well as nanoparticle concentration is also influenced with variable viscosity. Keywords: Nanofluid, Stretching sheet, Variable viscosity, Variable thermal conductivity, Lie symmetry group
Jiang, Zhen-Hua; Yan, Chao; Yu, Jian
2013-08-01
Two types of implicit algorithms have been improved for high order discontinuous Galerkin (DG) method to solve compressible Navier-Stokes (NS) equations on triangular grids. A block lower-upper symmetric Gauss-Seidel (BLU-SGS) approach is implemented as a nonlinear iterative scheme. And a modified LU-SGS (LLU-SGS) approach is suggested to reduce the memory requirements while retain the good convergence performance of the original LU-SGS approach. Both implicit schemes have the significant advantage that only the diagonal block matrix is stored. The resulting implicit high-order DG methods are applied, in combination with Hermite weighted essentially non-oscillatory (HWENO) limiters, to solve viscous flow problems. Numerical results demonstrate that the present implicit methods are able to achieve significant efficiency improvements over explicit counterparts and for viscous flows with shocks, and the HWENO limiters can be used to achieve the desired essentially non-oscillatory shock transition and the designed high-order accuracy simultaneously.
Hajabdollahi, Farzaneh; Premnath, Kannan N.
2018-05-01
Lattice Boltzmann (LB) models used for the computation of fluid flows represented by the Navier-Stokes (NS) equations on standard lattices can lead to non-Galilean-invariant (GI) viscous stress involving cubic velocity errors. This arises from the dependence of their third-order diagonal moments on the first-order moments for standard lattices, and strategies have recently been introduced to restore Galilean invariance without such errors using a modified collision operator involving corrections to either the relaxation times or the moment equilibria. Convergence acceleration in the simulation of steady flows can be achieved by solving the preconditioned NS equations, which contain a preconditioning parameter that can be used to tune the effective sound speed, and thereby alleviating the numerical stiffness. In the present paper, we present a GI formulation of the preconditioned cascaded central-moment LB method used to solve the preconditioned NS equations, which is free of cubic velocity errors on a standard lattice, for steady flows. A Chapman-Enskog analysis reveals the structure of the spurious non-GI defect terms and it is demonstrated that the anisotropy of the resulting viscous stress is dependent on the preconditioning parameter, in addition to the fluid velocity. It is shown that partial correction to eliminate the cubic velocity defects is achieved by scaling the cubic velocity terms in the off-diagonal third-order moment equilibria with the square of the preconditioning parameter. Furthermore, we develop additional corrections based on the extended moment equilibria involving gradient terms with coefficients dependent locally on the fluid velocity and the preconditioning parameter. Such parameter dependent corrections eliminate the remaining truncation errors arising from the degeneracy of the diagonal third-order moments and fully restore Galilean invariance without cubic defects for the preconditioned LB scheme on a standard lattice. Several
Steady flow on to a conveyor belt - Causal viscosity and shear shocks
Syer, D.; Narayan, Ramesh
1993-01-01
Some hydrodynamical consequences of the adoption of a causal theory of viscosity are explored. Causality is introduced into the theory by letting the coefficient of viscosity go to zero as the flow velocity approaches a designated propagation speed for viscous signals. Consideration is given to a model of viscosity which has a finite propagation speed of shear information, and it is shown that it produces two kinds of shear shock. A 'pure shear shock' corresponds to a transition from a superviscous to a subviscous state with no discontinuity in the velocity. A 'mixed shear shock' has a shear transition occurring at the same location as a normal adiabatic or radiative shock. A generalized version of the Rankine-Hugoniot conditions for mixed shear shocks is derived, and self-consistent numerical solutions to a model 2D problem in which an axisymmetric radially infalling stream encounters a spinning star are presented.
Steady Flow of a Second-Grade Fluid in an Annulus with Porous Walls
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M. Emin Erdoğan
2008-01-01
Full Text Available An exact solution of an incompressible second-grade fluid for flow between two coaxial cylinders with porous walls is given. It is assumed that the inner cylinder is rotating with a constant angular velocity and the outer one is at rest. The solution is expressed in terms of the confluent hypergeometric functions and it is valid for all values of the cross-Reynolds number and the elastic number. The solutions for −2, +∞, and −∞ values of the cross-Reynolds number are obtained and a comparison with those of the Newtonian fluid is given. Furthermore, the torque exerted by the fluid on the inner cylinder is calculated. It is shown that the moment coefficient depends on the cross-Reynolds number, the elastic number, and the ratio of the radii of the cylinders. The variation of the moment coefficient with these numbers is discussed.
Effects of sorption and temperature on solute transport in unsaturated steady flow
International Nuclear Information System (INIS)
Fuentes, H.R.; Polzer, W.L.; Essington, E.H.
1986-01-01
It is known that temperature affects physical and chemical processes and that these processes may alter the transport of solutes in the environment. Laboratory column studies were performed in unsaturated flow conditions with a composite pulse containing iodide, cobalt, cesium and strontium each at 10 -3 M. The experiments were performed with Bandelier Tuff and produced breakthrough curves that indicate significant changes in transport due to a temperature change from 25 0 C to 5 0 C for nonconservative solutes. Also, the interpretation of the temperature and sorption data suggest that the differences in transport between 5 0 C and 25 0 C for nonconservative solutes may be predicted in a qualitative manner from batch equilibrium and nonequilibrium sorption data and the theory of sorption used in deriving the modified Freundlich isotherm equation. These effects should be of concern in modeling and management of spills and waste disposal within this range of environmental temperatures
A Steady Flow Model for the Differential Emission Measure in the Solar Quiet Region
Bong, S.; Chae, J.; Yun, H.; Lee, J.
2001-05-01
With high quality UV spectroscopy from the SoHO spacecraft, the physical structure of the solar Transition Region (TR) is of renewed interest. We have investigated the thermodynamic structure of the TR using a one dimensional magnetic tube model constrained to Raymond & Doyle's Differential Emission Measure (DEM) in the average quiet sun. We have included the effect of the expansion of magnetic flux tube and a heating which is required in addition to conductive heat, convective energy and radiative cooling. From the resulting heating and flux tube geometry, we also investigated upflows probable in the transition region. To reproduce the Doppler shift of UV lines measured using SoHO/SUMER (Chae, Yun, & Poland 1998), flux tube needs to expand rapidly above T=105 K at a rate of radius increase up to (7.4x 10-2 km-1)~ r4.1 where r4.1 is the radius at log T = 4.1. To balance the energy, an energy supply by more than (9.3x 104 erg cm-2 s-1)~π r4.12 is required at the region between 1.3x 104 K and 2.5x 104 K regardless of filling factor, suggesting a local heating in the chromosphere. As for upflows, in subsonic flow cases, a model with the same additional energy loss as in a downflow is probable. Also, supersonic flows could be easily made and, in this case, supersonic upflows could carry extra energy to corona without increasing DEM, showing the possibility that upflows play a role in corona heating. This work was supported by the Basic Science Research Institute Program, Ministry of Education (BSRI-98-5408) and by the BK21 Project of the Korean Government.
Directory of Open Access Journals (Sweden)
Aang Nuryaman
2012-11-01
Full Text Available The governing equations describing the methane oxidation process in reverse flow reactor are given by a set of convective-diffusion equations with a nonlinear reaction term, where temperature and methane conversion are dependent variables. In this study, the process is assumed to be one-dimensional pseudo homogeneous model and takes place with a certain reaction rate in which the whole process of reactor is still workable. Thus, the reaction rate can proceed at a fixed temperature. Under this condition, we restrict ourselves to solve the equations for the conversion only. From the available data, it turns out that the ratio of the diffusion term to the reaction term is small. Hence, this ratio is considered as small parameter in our model and this leads to a singular perturbation problem. In the vicinity of small parameter in front of higher order term, the numerical difficulties will be found. Here, we present an analytical solution by means of matched asymptotic expansions. Result shows that, up to and including the first order of approximation, the solution is in agreement with the exact and numerical solutions of the boundary value problem.
Calculation of Heat-Bearing Agent’s Steady Flow in Fuel Bundle
Amosova, E. V.; Guba, G. G.
2017-11-01
This paper introduces the result of studying the heat exchange in the fuel bundle of the nuclear reactor’s fuel magazine. The article considers the fuel bundle of the infinite number of fuel elements, fuel elements are considered in the checkerboard fashion (at the tops of a regular triangle a fuel element is a plain round rod. The inhomogeneity of volume energy release in the rod forms the inhomogeneity of temperature and velocity fields, and pressure. Computational methods for studying hydrodynamics in magazines and cores with rod-shape fuel elements are based on a significant simplification of the problem: using basic (averaged) equations, isobaric section hypothesis, porous body model, etc. This could be explained by the complexity of math description of the three-dimensional fluid flow in the multi-connected area with the transfer coefficient anisotropy, curved boundaries and technical computation difficulties. Thus, calculative studying suggests itself as promising and important. There was developed a method for calculating the heat-mass exchange processes of inter-channel fuel element motions, which allows considering the contribution of natural convection to the heat-mass exchange based on the Navier-Stokes equations and Boussinesq approximation.
Directory of Open Access Journals (Sweden)
V. V. Ivashechkin
2013-01-01
Full Text Available The paper describes a steady pressure and free-flow circulation flow in the pre-screen zone of a well during its hydrodynamic reagent-free flushing. Calculation dependences for description of a filtration flow and creation of a hydrodynamic grid have been obtained in the paper. The paper presents results of experimental investigations on filtration flow. The obtained results agree completely with the calculation dependences that testifies about the possibility to use the obtained formulas for description of the filtration flow originating in the pre-screen zone of a well during its hydrodynamic reagent-free flushing.
Jackman, C M; Thomsen, M F; Mitchell, D G; Sergis, N; Arridge, C S; Felici, M; Badman, S V; Paranicas, C; Jia, X; Hospodarksy, G B; Andriopoulou, M; Khurana, K K; Smith, A W; Dougherty, M K
2015-05-01
We present a case study of an event from 20 August (day 232) of 2006, when the Cassini spacecraft was sampling the region near 32 R S and 22 h LT in Saturn's magnetotail. Cassini observed a strong northward-to-southward turning of the magnetic field, which is interpreted as the signature of dipolarization of the field as seen by the spacecraft planetward of the reconnection X line. This event was accompanied by very rapid (up to ~1500 km s -1 ) thermal plasma flow toward the planet. At energies above 28 keV, energetic hydrogen and oxygen ion flow bursts were observed to stream planetward from a reconnection site downtail of the spacecraft. Meanwhile, a strong field-aligned beam of energetic hydrogen was also observed to stream tailward, likely from an ionospheric source. Saturn kilometric radiation emissions were stimulated shortly after the observation of the dipolarization. We discuss the field, plasma, energetic particle, and radio observations in the context of the impact this reconnection event had on global magnetospheric dynamics.
Graham, Wendy D.; Neff, Christina R.
1994-05-01
The first-order analytical solution of the inverse problem for estimating spatially variable recharge and transmissivity under steady-state groundwater flow, developed in Part 1 is applied to the Upper Floridan Aquifer in NE Florida. Parameters characterizing the statistical structure of the log-transmissivity and head fields are estimated from 152 measurements of transmissivity and 146 measurements of hydraulic head available in the study region. Optimal estimates of the recharge, transmissivity and head fields are produced throughout the study region by conditioning on the nearest 10 available transmissivity measurements and the nearest 10 available head measurements. Head observations are shown to provide valuable information for estimating both the transmissivity and the recharge fields. Accurate numerical groundwater model predictions of the aquifer flow system are obtained using the optimal transmissivity and recharge fields as input parameters, and the optimal head field to define boundary conditions. For this case study, both the transmissivity field and the uncertainty of the transmissivity field prediction are poorly estimated, when the effects of random recharge are neglected.
Steady-state flow in a rock mass intersected by permeable fracture zones
International Nuclear Information System (INIS)
Lindbom, B.
1986-12-01
Level 1 of HYDROCOIN consists of seven well-defined test problems. This paper is concerned with Case 2, which is formulated as a generic groundwater flow situation often found in crystalline rock with highly permeable fracture zones in a less permeable rock mass. The case is two-dimensional and modelled with 8-noded, isoparametric, rectangular elements. According to the case definition, calculations of hydraulic head and particle tracking are performed. The computations are carried out with varying degree of discretisation in order to analyse possible impact on the result with respect to nodal density. Further calculations have been performed mainly devoted to mass balance deviations and how these are affected by permeability contrasts, varying degree of spatial discretisation and distortion of finite elements. The distribution of hydraulic head in the domain is less sensitive to differences in nodal density than the trajectories. The hydraulic heads show similar behaviour for three meshes with varying degrees of discretisation. The particle tracking seems to be more sensitive to the level of discretisation. The results obtained with a coarse and medium mesh indicate completely different solutions for one of the pathlines. The coarse mesh is too sparsely discretised for the specified problem. The local mass balance is evaluated for seven runs. The mass balance deviation seems to be considerably more sensitive to the level of discretisation than to both permeability contrasts and deformation of elements. The permeability contrasts between the rock mass and fracture zones vary from a factor of 1000 to 1 (homogeneous properties) with increments of a factor of 10. These calculations in fact give better mass balance with increasing permeability contrasts, contrary to what could be expected. (orig./HP)
International Nuclear Information System (INIS)
Bharti, Ram P.; Harvie, Dalton J.E.; Davidson, Malcolm R.
2009-01-01
Electroviscous effects in steady, fully developed, pressure-driven flow of power-law liquids through a uniform cylindrical microchannel have been investigated numerically by solving the Poisson-Boltzmann and the momentum equations using a finite difference method. The pipe wall is considered to have uniform surface charge density and the liquid is assumed to be a symmetric 1:1 electrolyte solution. Electroviscous resistance reduces the velocity adjacent to the wall, relative to the velocity on the axis. The effect is shown to be greater when the liquid is shear-thinning, and less when it is shear-thickening, than it is for Newtonian flow. For overlapping electrical double layers and elevated surface charge density, the electroviscous reduction in the near-wall velocity can form an almost stationary (zero shear) layer there when the liquid is shear-thinning. In that case, the liquid behaves approximately as if it is flowing through a channel of reduced diameter. The induced axial electrical field shows only a weak dependence on the power-law index with the dependence being greatest for shear-thinning liquids. This field exhibits a local maximum as surface charge density increases from zero, even though the corresponding electrokinetic resistance increases monotonically. The magnitude of the electroviscous effect on the apparent viscosity, as measured by the ratio of the apparent and physical consistency indices, decreases monotonically as the power-law index increases. Thus, overall, the electroviscous effect is stronger in shear-thinning, and weaker in shear-thickening liquids, than it is when the liquid is Newtonian.
Directory of Open Access Journals (Sweden)
M. Ozgun Korukcu
2015-05-01
Full Text Available Energy and exergy characteristics of a square cylinder (SC in confined flow are investigated computationally by numerically handling the steady-state continuity, Navier-Stokes and energy equations in the Reynolds number range of Re = 10–50, where the blockage ratio (β = B/H is kept constant at the high level of β = 0.8. Computations indicated for the upstream region that, the mean non-dimensional streamwise (u/Uo and spanwise (v/Uo velocities attain the values of u/Uo = 0.840®0.879 and v/Uo = 0.236®0.386 (Re = 10®50 on the front-surface of the SC, implying that Reynolds number and blockage have stronger impact on the spanwise momentum activity. It is determined that flows with high Reynolds number interact with the front-surface of the SC developing thinner thermal boundary layers and greater temperature gradients, which promotes the thermal entropy generation values as well. The strict guidance of the throat, not only resulted in the fully developed flow character, but also imposed additional cooling; such that the analysis pointed out the drop of duct wall (y = 0.025 m non-dimensional temperature values (ζ from ζ = 0.387®0.926 (Re = 10®50 at xth = 0 mm to ζ = 0.002®0.266 at xth = 40 mm. In the downstream region, spanwise thermal disturbances are evaluated to be most inspectable in the vortex driven region, where the temperature values show decrease trends in the spanwise direction. In the corresponding domain, exergy destruction is determined to grow with Reynolds number and decrease in the streamwise direction (xds = 0®10 mm. Besides, asymmetric entropy distributions as well were recorded due to the comprehensive mixing caused by the vortex system.
International Nuclear Information System (INIS)
Michael J. Bockelie
2002-01-01
This DOE SBIR Phase II final report summarizes research that has been performed to develop a parallel adaptive tool for modeling steady, two phase turbulent reacting flow. The target applications for the new tool are full scale, fossil-fuel fired boilers and furnaces such as those used in the electric utility industry, chemical process industry and mineral/metal process industry. The type of analyses to be performed on these systems are engineering calculations to evaluate the impact on overall furnace performance due to operational, process or equipment changes. To develop a Computational Fluid Dynamics (CFD) model of an industrial scale furnace requires a carefully designed grid that will capture all of the large and small scale features of the flowfield. Industrial systems are quite large, usually measured in tens of feet, but contain numerous burners, air injection ports, flames and localized behavior with dimensions that are measured in inches or fractions of inches. To create an accurate computational model of such systems requires capturing length scales within the flow field that span several orders of magnitude. In addition, to create an industrially useful model, the grid can not contain too many grid points - the model must be able to execute on an inexpensive desktop PC in a matter of days. An adaptive mesh provides a convenient means to create a grid that can capture both fine flow field detail within a very large domain with a ''reasonable'' number of grid points. However, the use of an adaptive mesh requires the development of a new flow solver. To create the new simulation tool, we have combined existing reacting CFD modeling software with new software based on emerging block structured Adaptive Mesh Refinement (AMR) technologies developed at Lawrence Berkeley National Laboratory (LBNL). Specifically, we combined: -physical models, modeling expertise, and software from existing combustion simulation codes used by Reaction Engineering International
Arora, Shitij; Fourment, Lionel
2018-05-01
In the context of the simulation of industrial hot forming processes, the resultant time-dependent thermo-mechanical multi-field problem (v →,p ,σ ,ɛ ) can be sped up by 10-50 times using the steady-state methods while compared to the conventional incremental methods. Though the steady-state techniques have been used in the past, but only on simple configurations and with structured meshes, and the modern-days problems are in the framework of complex configurations, unstructured meshes and parallel computing. These methods remove time dependency from the equations, but introduce an additional unknown into the problem: the steady-state shape. This steady-state shape x → can be computed as a geometric correction t → on the domain X → by solving the weak form of the steady-state equation v →.n →(t →)=0 using a Streamline Upwind Petrov Galerkin (SUPG) formulation. There exists a strong coupling between the domain shape and the material flow, hence, a two-step fixed point iterative resolution algorithm was proposed that involves (1) the computation of flow field from the resolution of thermo-mechanical equations on a prescribed domain shape and (2) the computation of steady-state shape for an assumed velocity field. The contact equations are introduced in the penalty form both during the flow computation as well as during the free-surface correction. The fact that the contact description is inhomogeneous, i.e., it is defined in the nodal form in the former, and in the weighted residual form in the latter, is assumed to be critical to the convergence of certain problems. Thus, the notion of nodal collocation is invoked in the weak form of the surface correction equation to homogenize the contact coupling. The surface correction algorithm is tested on certain analytical test cases and the contact coupling is tested with some hot rolling problems.
Reynolds, C. A.; Menke, H. P.; Blunt, M. J.; Krevor, S. C.
2015-12-01
We observe a new type of non-wetting phase flow using time-resolved pore scale imaging. The traditional conceptual model of drainage involves a non-wetting phase invading a porous medium saturated with a wetting phase as either a fixed, connected flow path through the centres of pores or as discrete ganglia which move individually through the pore space, depending on the capillary number. We observe a new type of flow behaviour at low capillary number in which the flow of the non-wetting phase occurs through networks of persistent ganglia that occupy the large pores but continuously rearrange their connectivity (Figure 1). Disconnections and reconnections occur randomly to provide short-lived pseudo-steady state flow paths between pores. This process is distinctly different to the notion of flowing ganglia which coalesce and break-up. The size distribution of ganglia is dependent on capillary number. Experiments were performed by co-injecting N2and 25 wt% KI brine into a Bentheimer sandstone core (4mm diameter, 35mm length) at 50°C and 10 MPa. Drainage was performed at three flow rates (0.04, 0.3 and 1 ml/min) at a constant fractional flow of 0.5 and the variation in ganglia populations and connectivity observed. We obtained images of the pore space during steady state flow with a time resolution of 43 s over 1-2 hours. Experiments were performed at the Diamond Light Source synchrotron. Figure 1. The position of N2 in the pore space during steady state flow is summed over 40 time steps. White indicates that N2 occupies the space over >38 time steps and red <5 time steps.
Nœtinger, B.
2015-02-01
Modeling natural Discrete Fracture Networks (DFN) receives more and more attention in applied geosciences, from oil and gas industry, to geothermal recovery and aquifer management. The fractures may be either natural, or artificial in case of well stimulation. Accounting for the flow inside the fracture network, and accounting for the transfers between the matrix and the fractures, with the same level of accuracy is an important issue for calibrating the well architecture and for setting up optimal resources recovery strategies. Recently, we proposed an original method allowing to model transient pressure diffusion in the fracture network only [1]. The matrix was assumed to be impervious. A systematic approximation scheme was built, allowing to model the initial DFN by a set of N unknowns located at each identified intersection between fractures. The higher N, the higher the accuracy of the model. The main assumption was using a quasi steady state hypothesis, that states that the characteristic diffusion time over one single fracture is negligible compared with the characteristic time of the macroscopic problem, e.g. change of boundary conditions. In that context, the lowest order approximation N = 1 has the form of solving a transient problem in a resistor/capacitor network, a so-called pipe network. Its topology is the same as the network of geometrical intersections between fractures. In this paper, we generalize this approach in order to account for fluxes from matrix to fractures. The quasi steady state hypothesis at the fracture level is still kept. Then, we show that in the case of well separated time scales between matrix and fractures, the preceding model needs only to be slightly modified in order to incorporate these fluxes. The additional knowledge of the so-called matrix to fracture transfer function allows to modify the mass matrix that becomes a time convolution operator. This is reminiscent of existing space averaged transient dual porosity models.
Energy Technology Data Exchange (ETDEWEB)
King, G P [Instituto de Oceanografia, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa (Portugal); Rudman, Murray [CSIRO Manufacturing and Infrastructure Technology, P.O. Box 56, Highett, Vic. 3190 (Australia); Rowlands, G [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)], E-mail: gkinglisboa@gmail.com, E-mail: Murray.Rudman@csiro.au, E-mail: G.Rowlands@warwick.ac.uk
2008-01-31
The dimensionless effective axial diffusion coefficient, D{sub z}, calculated from particle trajectories in steady wavy vortex flow in a narrow gap Taylor-Couette system, has been determined as a function of Reynolds number (R = Re/Re{sub c}), axial wavelength ({lambda}{sub z}), and the number of azimuthal waves (m). Two regimes of Reynolds number were found: (i) when R < 3.5, D{sub z} has a complex and sometimes multi-modal dependence on Reynolds number; (ii) when R > 3.5, D{sub z} decreases monotonically. Eulerian quantities measuring the departure from rotational symmetry, {psi}{sub {theta}}, and flexion-free flow, {psi}{sub {nu}}, were calculated. The space-averaged quantities {phi}-bar{sub {theta}} and {phi}-bar{sub {nu}} were found to have, unlike D{sub z}, a simple unimodal dependence on R. In the low R regime the correlation between D{sub z} and {psi}{sub {theta}}{psi}{sub {nu}} was complicated and was attributed to variations in the spatial distribution of the wavy disturbance occurring in this range of R. In the large R regime, however, the correlation simplified to D{sub z}{approx}{phi}-bar{sub {theta}}{phi}-bar{sub {nu}} for all wave states, and this was attributed to the growth of an integrable vortex core and the concentration of the wavy disturbance into narrow regions near the outflow and inflow jets. A reservoir model of a wavy vortex was used to determine the rate of escape across the outflow and inflow boundaries, the size of the 'escape basins' (associated with escape across the outflow and inflow boundaries), and the size of the trapping region in the vortex core. In the low R regime after the breakup of all KAM tori, the outflow basin ({gamma}{sub O}) is larger than the inflow basin ({gamma}{sub I}), and both {gamma}{sub O} and {gamma}{sub I} are (approximately) independent of R. In the large R regime, with increasing Reynolds number the trapping region grows, the outflow basin decreases, and the inflow basin shows a slight increase
International Nuclear Information System (INIS)
Pan, Zhaoguang; Guo, Qinglai; Sun, Hongbin
2016-01-01
Highlights: • Interaction mechanisms of district electricity and heating systems are analyzed. • The interaction process is divided into four quasi-steady stages. • A quasi-steady multi-energy flow model is proposed and calculated. • A heating network node type transformation technique is developed. • Attention should be paid on the fast hydraulic process and slow thermal process. - Abstract: Integrated energy systems (IESs) are under development for a variety of benefits. District electricity and heating systems (DEHSs) deliver electricity and heat, the most common energy demands, to end-users. This paper studies the interactions in a DEHS considering the time-scale characteristics. Interaction mechanisms of a DEHS are analyzed. A disturbance in one system influences another system through coupling components, depending on the disturbance, operating characteristics, and control strategies. A model of the main components in DEHSs is presented. The time scale characteristics are studied based on a dynamic comparison of the different components. Then the interaction process is divided into four stages; each is a quasi-steady state. A quasi-steady multi-energy flow model is proposed and calculated, with a heating network node type transformation technique developed. A case study with detailed results and discussion of 3 types of disturbance is presented to verify the methods. The results present the interactions between the electricity and the system. It is suggested that attention should be paid both on the fast hydraulic process and slow thermal process for system security and economic operation.
Neustupa, Tomáš
2017-07-01
The paper presents the mathematical model of a steady 2-dimensional viscous incompressible flow through a radial blade machine. The corresponding boundary value problem is studied in the rotating frame. We provide the classical and weak formulation of the problem. Using a special form of the so called "artificial" or "natural" boundary condition on the outflow, we prove the existence of a weak solution for an arbitrarily large inflow.
National Research Council Canada - National Science Library
Barakos, G
1998-01-01
The numerical simulation of unsteady separated turbulent flows around moving lifting surfaces is fueled by the industrial need to analyse and understand flow phenomena associated with the behaviour...
Naehle, Claas P; Steinberg, Verena A; Schild, Hans; Mommertz, Gottfried
2015-05-01
Noninvasive measurement of peripheral muscle microperfusion could potentially improve diagnosis, management, and treatment of peripheral arterial disease (PAD) and thus improve patient care. Contrast-enhanced ultrasound (CEUS) as a noninvasive diagnostic tool allows quantification of muscle perfusion. Increasing data on bolus technique CEUS reflecting microperfusion are becoming available, but only limited data on steady-state CEUS for assessment of muscle microperfusion are available. Therefore, the aim of this study was to evaluate steady-state CEUS for assessment of peripheral muscle microperfusion in a PAD animal model. In a porcine animal model, peripheral muscle microperfusion was quantified by steady-state CEUS replenishment kinetics (mean transit time [mTT] and wash-in rate [WiR]) of the biceps femoris muscle during intravenous steady-state infusion of INN-sulfur hexafluoride (SonoVue; Bracco, Geneva, Switzerland). In addition, macroperfusion was quantified at the external femoral artery with a Doppler flow probe. Peripheral muscle microperfusion and Doppler flow measurements were performed bilaterally at rest and under adenosine stress (70 μg/kg body weight) before and after unilateral creation of a moderate external iliac artery stenosis. All measurements could be performed completely in 10 pigs. Compared with baseline measurements, peripheral muscle microperfusion decreased significantly during adenosine stress (rest vs adenosine stress: mTT, 7.8 ± 3.3 vs 21.2 ± 17.8 s, P = .0006; WiR, 58.4 ± 38.1 vs 25.3 ± 15.6 arbitrary units [a.u.]/s, P flow, 122.3 ± 31.4 vs 83.6 ± 28.1 mL/min, P = .0067) and after stenosis creation (no stenosis vs stenosis: mTT, 8.1 ± 3.1 vs 29.2 ± 18.0 s, P = .0469; WiR, 53.0 ± 22.7 vs 13.6 ± 8.4 a.u./s, P = .0156; Doppler flow, 124.2 ± 41.8 vs 65.9 ± 40.0 mL/min, P = .0313). After stenosis creation, adenosine stress led to a further significant decrease of peripheral muscle microperfusion but had no effect on
International Nuclear Information System (INIS)
Chiem, Kok Siong; Zhao Yong
2004-01-01
In this study, a high-resolution characteristic-based finite-volume (FV) method on unstructured grids [Int. J. Numer. Method Eng. 50 (2001) 11; Int. J. Heat Fluid Flow 21 (2000) 432] is extended by a matrix-free implicit dual-time stepping scheme for the numerical simulation of steady and unsteady flow and heat transfer with porous media. The method has been used to study the characteristics of a complex problem: flow and heat transfer in a channel with multiple discrete porous blocks, which was originally proposed by Huang and Vafai [J. Thermophys. Heat Transfer 8 (3) (1994) 563]. In addition, flow and heat transfer in a channel partially or fully filled with porous layers and containing solid protruding blocks with constant heat flux on its lower surface are also investigated in details. Hydrodynamic and heat transfer results are reported for both steady and transient flow cases. In particular, the effects of Darcy and Reynolds numbers on heat transfer augmentation and pressure loss are studied. An in-depth discussion of the formation and variation of recirculation is presented and the existence of optimum porous insert is demonstrated. At high Reynolds numbers the flow in the porous channel exhibits a cyclic characteristics although unlike the non-porous channel flow, the cyclic vortex development is only restricted to a small area behind the last solid block, while temperature changes more slowly and does not exhibit cyclic variations over a long period of time. It is shown that for all the cases studied altering some parametric values can have significant and interesting effects on both flow pattern as well as heat transfer characteristics
Koren, B.; Hackbusch, W.; Trottenberg, U.
1991-01-01
Two simple, multi-dimensional upwind discretizations for the steady Euler equations are derived, with the emphasis Iying on bath a good accuracy and a good solvability. The multi-dimensional upwinding consists of applying a one-dimensional Riemann solver with a locally rotated left and right state,
Richards, Jennifer C; Crecelius, Anne R; Kirby, Brett S; Larson, Dennis G; Dinenno, Frank A
2012-06-01
We tested the hypothesis that, among conditions of matched contractile work, shorter contraction durations and greater muscle fibre recruitment result in augmented skeletal muscle blood flow and oxygen consumption ( ) during steady-state exercise in humans. To do so, we measured forearm blood flow (FBF; Doppler ultrasound) during 4 min of rhythmic hand-grip exercise in 24 healthy young adults and calculated forearm oxygen consumption ( ) via blood samples obtained from a catheter placed in retrograde fashion into a deep vein draining the forearm muscle. In protocol 1 (n = 11), subjects performed rhythmic isometric hand-grip exercise at mild and moderate intensities during conditions in which time-tension index (isometric analogue of work) was held constant but contraction duration was manipulated. In this protocol, shorter contraction durations led to greater FBF (184 ± 25 versus 164 ± 25 ml min(-1)) and (23 ± 3 versus 17 ± 2 ml min(-1); both P flow. Our collective data indicate that, among matched workloads, shorter contraction duration and greater muscle fibre recruitment augment FBF and during mild-intensity forearm exercise, and that muscle blood flow is more closely related to metabolic cost ( ) rather than contractile work per se during steady-state exercise in humans.
Fan, Zhaoyang; Hodnett, Philip A; Davarpanah, Amir H; Scanlon, Timothy G; Sheehan, John J; Varga, John; Carr, James C; Li, Debiao
2011-08-01
: To develop a flow-sensitive dephasing (FSD) preparative scheme to facilitate multidirectional flow-signal suppression in 3-dimensional balanced steady-state free precession imaging and to validate the feasibility of the refined sequence for noncontrast magnetic resonance angiography (NC-MRA) of the hand. : A new FSD preparative scheme was developed that combines 2 conventional FSD modules. Studies using a flow phantom (gadolinium-doped water 15 cm/s) and the hands of 11 healthy volunteers (6 males and 5 females) were performed to compare the proposed FSD scheme with its conventional counterpart with respect to the signal suppression of multidirectional flow. In 9 of the 11 healthy subjects and 2 patients with suspected vasculitis and documented Raynaud phenomenon, respectively, 3-dimensional balanced steady-state free precession imaging coupled with the new FSD scheme was compared with spatial-resolution-matched (0.94 × 0.94 × 0.94 mm) contrast-enhanced magnetic resonance angiography (0.15 mmol/kg gadopentetate dimeglumine) in terms of overall image quality, venous contamination, motion degradation, and arterial conspicuity. : The proposed FSD scheme was able to suppress 2-dimensional flow signal in the flow phantom and hands and yielded significantly higher arterial conspicuity scores than the conventional scheme did on NC-MRA at the regions of common digitals and proper digitals. Compared with contrast-enhanced magnetic resonance angiography, the refined NC-MRA technique yielded comparable overall image quality and motion degradation, significantly less venous contamination, and significantly higher arterial conspicuity score at digital arteries. : The FSD-based NC-MRA technique is improved in the depiction of multidirectional flow by applying a 2-module FSD preparation, which enhances its potential to serve as an alternative magnetic resonance angiography technique for the assessment of hand vascular abnormalities.
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Dhole, S.D.; Chhabra, R.P. [Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208 016 (India); Eswaran, V. [Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208 016 (India)
2006-03-15
The effects of Reynolds and Prandtl numbers on the heat transfer characteristics of an unconfined sphere for different thermal boundary conditions (isothermal and isoflux) on the sphere surface have been investigated numerically by using a finite volume method for the range of conditions as 5=
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Adeshina S. Adegoke
2017-11-01
Full Text Available This paper studied the nonlinear vibrations of top-tensioned cantilevered pipes conveying pressurized steady two-phase flow under thermal loading. The coupled axial and transverse governing partial differential equations of motion of the system were derived based on Hamilton’s mechanics, with the centerline assumed to be extensible. Using the multiple-scale perturbation technique, natural frequencies, mode shapes, and first order approximate solutions of the steady-state response of the pipes were obtained. The multiple-scale assessment reveals that at some frequencies the system is uncoupled, while at some frequencies a 1:2 coupling exists between the axial and the transverse frequencies of the pipe. Nonlinear frequencies versus the amplitude displacement of the cantilever pipe, conveying two-phase flow at super-critical mixture velocity for the uncoupled scenario, exhibit a nonlinear hardening behavior; an increment in the void fractions of the two-phase flow results in a reduction in the pipe’s transverse vibration frequencies and the coupled amplitude of the system. However, increases in the temperature difference, pressure, and the presence of top tension were observed to increase the pipe’s transverse vibration frequencies without a significant change in the coupled amplitude of the system.
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Kim, Jhin Wung; Bae, Dae Suk; Kang, Chul Hyung; Choi, Jong Won [Korea Atomic Energy Research Institute, Taejeon (Korea)
2002-02-01
The objective of the present study is to understand the long term (500 years) thermo-hydro-mechanical interaction behavior of the 500 m depth underground radwaste repository in the saturated, discontinuous granitic rock mass using a steady state flow algorithm. The numerical model includes a saturated granitic rock mass with joints around the repository and a 45 .deg. C fault passing through the tunnel roof-wall intersection, and a canister with PWR spent fuels surrounded by the compacted bentonite and mixed-bentonite. Barton-Bandis joint constitutive model from the UDEC code is used for the joints. For the hydraulic analysis, a steady state flow algorithm is used for the groundwater flow through the rock joints. For the thermal analysis, heat transfer is modeled as isotropic conduction and heat decays exponentially with time. The results show that the variations of the hydraulic aperture, hydraulic conductivity, normal stress, normal displacements, and shear displacements of the joints are high in the vicinity of the repository and stay fairly constant on the region away from the repository. 14 refs., 15 figs., 11 tabs. (Author)
International Nuclear Information System (INIS)
Ishizawa, A.; Nakajima, N.
2007-01-01
This is the first numerical simulation demonstrating that a macromagnetohydrodynamic (macro-MHD) mode is excited as a result of multi-scale interaction in a quasi-steady equilibrium formed by a balance between microturbulence and zonal flow based on a reduced two-fluid model. This simulation of a macro-MHD mode, a double tearing mode, is accomplished in a reversed shear equilibrium that includes zonal flow and turbulence due to kinetic ballooning modes. In the quasi-steady equilibrium, a macroscale fluctuation that has the same helicity as the double tearing mode is a part of the turbulence. After a certain period of time, the macro-MHD mode begins to grow. It effectively utilizes free energy of the equilibrium current density gradient and is destabilized by a positive feedback loop between zonal flow suppression and magnetic island growth. Thus, once the macro-MHD appears from the quasi-equilibrium, it continues to grow steadily. This simulation is more comparable with experimental observations of growing macro-MHD activity than earlier MHD simulations starting from linear macroinstabilities in a static equilibrium
Energy Technology Data Exchange (ETDEWEB)
Hasegawa, E; Horiguchi, Y; Kitazawa, K [Keio University, Tokyo (Japan). Faculty of Science and Technology
1997-08-25
A steady flow in an non-deformable porous layer subjected to a fluid stream is studied analytically and numerically. One side of the layer of sponge is bounded by a solid wall and the other by a layer of fluid. The fluid is injected uniformly from a plane, through which the fluid can pass, set up parallel to the sponge layer. The flow in the sponge layer is assumed to be governed by Darcy`s law. The problem considered is solved in terms of a similarity solution. The equations governing the fluid flows in both the porous layer and the fluid layer are reduced to a system of the ordinary differential equations. These equations are solved analytically for three cases ideal fluid flow, low Reynolds number flow and high Reynolds number flow. On the other hand, these equations are solved numerically for the general case by using the finite difference method. The distributions of the velocity and the pressure in both layers are found for various parameters. In particular, the speed which the fluid intrudes into the sponge layer due to the injection of the stream from the plane is found to be a function of dimensionless parameters. To find this speed is essential to the understanding of porous material. 15 refs., 9 figs.
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Zhiyin Yang
2014-12-01
Full Text Available A complex flow field is created when a vertical/short take-off and landing aircraft is operating near ground. One major concern for this kind of aircraft in ground effect is the possibility of ingestion of hot gases from the jet engine exhausts back into the engine, known as hot gas ingestion, which can increase the intake air temperature and also reduce the oxygen content in the intake air, potentially leading to compressor stall, low combustion efficiency and causing a dramatic loss of lift. This flow field can be represented by the configuration of twin impinging jets in a cross-flow. Accurate prediction of this complicated flow field under the Reynolds averaged Navier–Stokes (RANS approach (current practise in industry is a great challenge as previous studies suggest that some important flow features cannot be captured by the Steady-RANS (SRANS approach even with a second-order Reynolds stress model (RSM. This paper presents a numerical study of this flow using the Unsteady-RANS (URANS approach with a RSM and the results clearly indicate that the URANS approach is superior than the SRANS approach but still the predictions of Reynolds stress are not accurate enough.
Park, Sung-Hong; Wang, Danny J J; Duong, Timothy Q
2013-09-01
We implemented pseudo-continuous ASL (pCASL) with 2D and 3D balanced steady state free precession (bSSFP) readout for mapping blood flow in the human brain, retina, and kidney, free of distortion and signal dropout, which are typically observed in the most commonly used echo-planar imaging acquisition. High resolution functional brain imaging in the human visual cortex was feasible with 3D bSSFP pCASL. Blood flow of the human retina could be imaged with pCASL and bSSFP in conjunction with a phase cycling approach to suppress the banding artifacts associated with bSSFP. Furthermore, bSSFP based pCASL enabled us to map renal blood flow within a single breath hold. Control and test-retest experiments suggested that the measured blood flow values in retina and kidney were reliable. Because there is no specific imaging tool for mapping human retina blood flow and the standard contrast agent technique for mapping renal blood flow can cause problems for patients with kidney dysfunction, bSSFP based pCASL may provide a useful tool for the diagnosis of retinal and renal diseases and can complement existing imaging techniques. Copyright © 2013 Elsevier Inc. All rights reserved.
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Xingen Lu
2006-01-01
tip-clearance flow manipulation. The repositioning of the tip-clearance vortex further towards the trailing edge of the blade passage and delaying the movement of incoming/tip-clearance flow interface to the leading edge plane are the physical mechanisms responsible for extending the compressor stall margin.
Morris, Paul D; Silva Soto, Daniel Alejandro; Feher, Jeroen F A; Rafiroiu, Dan; Lungu, Angela; Varma, Susheel; Lawford, Patricia V; Hose, D Rodney; Gunn, Julian P
2017-08-01
Fractional flow reserve (FFR)-guided percutaneous intervention is superior to standard assessment but remains underused. The authors have developed a novel "pseudotransient" analysis protocol for computing virtual fractional flow reserve (vFFR) based upon angiographic images and steady-state computational fluid dynamics. This protocol generates vFFR results in 189 s (cf >24 h for transient analysis) using a desktop PC, with <1% error relative to that of full-transient computational fluid dynamics analysis. Sensitivity analysis demonstrated that physiological lesion significance was influenced less by coronary or lesion anatomy (33%) and more by microvascular physiology (59%). If coronary microvascular resistance can be estimated, vFFR can be accurately computed in less time than it takes to make invasive measurements.
Cheng, Jian; Zhang, Fan; Liu, Tiegang
2018-06-01
In this paper, a class of new high order reconstructed DG (rDG) methods based on the compact least-squares (CLS) reconstruction [23,24] is developed for simulating the two dimensional steady-state compressible flows on hybrid grids. The proposed method combines the advantages of the DG discretization with the flexibility of the compact least-squares reconstruction, which exhibits its superior potential in enhancing the level of accuracy and reducing the computational cost compared to the underlying DG methods with respect to the same number of degrees of freedom. To be specific, a third-order compact least-squares rDG(p1p2) method and a fourth-order compact least-squares rDG(p2p3) method are developed and investigated in this work. In this compact least-squares rDG method, the low order degrees of freedom are evolved through the underlying DG(p1) method and DG(p2) method, respectively, while the high order degrees of freedom are reconstructed through the compact least-squares reconstruction, in which the constitutive relations are built by requiring the reconstructed polynomial and its spatial derivatives on the target cell to conserve the cell averages and the corresponding spatial derivatives on the face-neighboring cells. The large sparse linear system resulted by the compact least-squares reconstruction can be solved relatively efficient when it is coupled with the temporal discretization in the steady-state simulations. A number of test cases are presented to assess the performance of the high order compact least-squares rDG methods, which demonstrates their potential to be an alternative approach for the high order numerical simulations of steady-state compressible flows.
International Nuclear Information System (INIS)
Witalis, E.A.
1965-12-01
Rigorous derivations are given of the basic equations and methods available for the analysis of transverse MHD flow when Hall currents are not suppressed. The gas flow is taken to be incompressible and viscous with uniform tensor conductivity and arbitrary magnetic Reynold's number. The magnetic field is perpendicular to the flow and has variable strength. Analytical solutions can be obtained either in terms of the induced magnetic field or from two types of electric potential. The relevant set of suitable simplifications, restrictive conditions and boundary value considerations for each method is given
Energy Technology Data Exchange (ETDEWEB)
Witalis, E A
1965-12-15
Rigorous derivations are given of the basic equations and methods available for the analysis of transverse MHD flow when Hall currents are not suppressed. The gas flow is taken to be incompressible and viscous with uniform tensor conductivity and arbitrary magnetic Reynold's number. The magnetic field is perpendicular to the flow and has variable strength. Analytical solutions can be obtained either in terms of the induced magnetic field or from two types of electric potential. The relevant set of suitable simplifications, restrictive conditions and boundary value considerations for each method is given.
Verhulst, Kristof; Cardinaels, Ruth; Renardy, Yuriko; Moldenaers, Paula
2008-07-01
The steady deformation and orientation of droplets in shear flow, both under bulk and confined conditions, is microscopically studied for blends with one viscoelastic phase and a viscosity ratio of 1.5. The experiments are performed with a Linkam shearing cell and a counter rotating setup, based on a Paar Physica MCR300. For bulk shear flow, it is shown that matrix viscoelasticity suppresses droplet deformation and promotes droplet orientation towards the flow direction. Interestingly, these effects saturate at Deborah numbers above 2. For ellipsoidal droplets, viscoelasticity of the droplet fluid hardly affects the droplet deformation and droplet orientation, even up to Deborah numbers as high as 16. When the droplet is confined between two plates, the droplet deformation and the orientation towards the flow direction increase with confinement ratio, as in fully Newtonian systems. At a Deborah number of 1, the effect of component viscoelasticity under confined conditions remains qualitatively the same as under bulk conditions, at least up to a confinement ratio 2R/H of 0.6. The experiments under bulk conditions are compared with the predictions of phenomenological models, such as the Maffettone-Minale model, for droplet deformation. The Shapira-Haber model, which analytically describes the effects of the walls on the droplet deformation for fully Newtonian systems, is used to describe the experimental results under confinement. Here, this model is combined with the bulk phenomenological models to include bulk viscoelasticity effects. Under the present conditions, the adapted Shapira-Haber model describes the steady droplet deformation under confinement rather well. Finally, the experimentally obtained droplet shapes are compared with the results of 3D simulations, performed with a volume-of-fluid algorithm.
Xu, Bing; Hu, Min; Zhang, Junhui
2015-09-01
The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ±6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test
Takenaka, N; Fujii, T; Mizubata, M; Yoshii, K
1999-01-01
Three-dimensional void fraction distribution of air-water two-phase flow in a 4x4 rod-bundle near a spacer was visualized by fast neutron radiography using a CT method. One-dimensional cross sectional averaged void fraction distribution was also calculated. The behaviors of low void fraction (thick water) two-phase flow in the rod bundle around the spacer were clearly visualized. It was shown that the void fraction distributions were visualized with a quality similar to those by thermal neutron radiography for low void fraction two-phase flow which is difficult to visualize by thermal neutron radiography. It is concluded that the fast neutron radiography is efficiently applicable to two-phase flow studies.
A novel model for smectic liquid crystals: Elastic anisotropy and response to a steady-state flow.
Püschel-Schlotthauer, Sergej; Meiwes Turrión, Victor; Stieger, Tillmann; Grotjahn, Robin; Hall, Carol K; Mazza, Marco G; Schoen, Martin
2016-10-28
By means of a combination of equilibrium Monte Carlo and molecular dynamics simulations and nonequilibrium molecular dynamics we investigate the ordered, uniaxial phases (i.e., nematic and smectic A) of a model liquid crystal. We characterize equilibrium behavior through their diffusive behavior and elastic properties. As one approaches the equilibrium isotropic-nematic phase transition, diffusion becomes anisotropic in that self-diffusion D ⊥ in the direction orthogonal to a molecule's long axis is more hindered than self-diffusion D ∥ in the direction parallel to that axis. Close to nematic-smectic A phase transition the opposite is true, D ∥ flow depending on whether the convective velocity is parallel or orthogonal to the plane of smectic layers. We find that in Poiseuille-like flow the viscosity of the smectic A phase is higher than in plug flow. This can be rationalized via the velocity-field component in the direction of the flow. In a sufficiently strong flow these smectic layers are not destroyed but significantly bent.
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OLAOSEBIKAN ABIDOYE OLAFADEHAN
2010-06-01
Full Text Available A detailed computational procedure for evaluating lactose hydrolysis with immobilized enzyme in a packed bed tubular reactor under dispersion flow conditions is presented. The dispersion flow model for lactose hydrolysis using different kinetics, taking cognizance of external mass transfer resistances, was solved by the method of orthogonal collocation. The reliability of model simulations was tested using experimental data from a laboratory packed bed column, where the -galactosidase of Kluyveromyces fragilis was immobilized on spherical chitosan beads. Comparison of the simulated results with experimental exit conversion shows that the dispersion flow model and using Michaelis-Menten kinetics with competitive product (galactose inhibition are appropriate to interpret the experimental results and simulate the process of lactose hydrolysis in a fixed bed.
Minakov, A.; Platonov, D.; Sentyabov, A.; Gavrilov, A.
2017-01-01
We performed numerical simulation of flow in a laboratory model of a Francis hydroturbine at three regimes, using two eddy-viscosity- (EVM) and a Reynolds stress (RSM) RANS models (realizable k-ɛ, k-ω SST, LRR) and detached-eddy-simulations (DES), as well as large-eddy simulations (LES). Comparison of calculation results with the experimental data was carried out. Unlike the linear EVMs, the RSM, DES, and LES reproduced well the mean velocity components, and pressure pulsations in the diffusor draft tube. Despite relatively coarse meshes and insufficient resolution of the near-wall region, LES, DES also reproduced well the intrinsic flow unsteadiness and the dominant flow structures and the associated pressure pulsations in the draft tube.
On the existence of steady flow in a channel with one porous wall or two accelerating walls
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Chunqing Lu
1998-11-01
Full Text Available channel either with no-slip at one wall and constant uniform suction or injection through another wall, or with two accelerating walls. The flows are governed by the fourth order nonlinear differential equation $F^{iv}+R(FF'''-F'F''=0$. In the former case, the flow is subject to the boundary conditions $F(-1=F'(-1=F'(1=0$, $F(1=-1$. In the latter case, the boundary conditions are $F(-1=F(1=0$, $F'(-1=-1$, $F'(1 = 1$.
Huyghe, J.M.R.J.; Oomens, C.W.J.; Campen, van D.H.; Heethaar, R.M.
1989-01-01
This research aims at formulating and verifying a finite element mixture formulation for blood perfusion. The equations derived in a companion paper [3] are discretized according to the Galerkin method. A flow experiment in a rigid model of a vascular tree of about 500 vessels is performed in order
Droplet trapping and fast acoustic release in a multi-height device with steady-state flow.
Rambach, Richard W; Linder, Kevin; Heymann, Michael; Franke, Thomas
2017-10-11
We demonstrate a novel multilayer polydimethylsiloxane (PDMS) device for selective storage and release of single emulsion droplets. Drops are captured in a microchannel cavity and can be released on-demand through a triggered surface acoustic wave pulse. The surface acoustic wave (SAW) is excited by a tapered interdigital transducer (TIDT) deposited on a piezoelectric lithium niobate (LiNbO 3 ) substrate and inverts the pressure difference across the cavity trap to push a drop out of the trap and back into the main flow channel. Droplet capture and release does not require a flow rate change, flow interruption, flow inversion or valve action and can be achieved in as fast as 20 ms. This allows both on-demand droplet capture for analysis and monitoring over arbitrary time scales, and continuous device operation with a high droplet rate of 620 drops per s. We hence decouple long-term droplet interrogation from other operations on the chip. This will ease integration with other microfluidic droplet operations and functional components.
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José F. Herbert-Acero
2015-01-01
Full Text Available This work presents the analysis, application, and comparison of thirteen fluid flow models in the prediction of two-dimensional airfoil aerodynamics, considering laminar and turbulent subsonic inflow conditions. Diverse sensitivity analyses of different free parameters (e.g., the domain topology and its discretization, the flow model, and the solution method together with its convergence mechanisms revealed important effects on the simulations’ outcomes. The NACA 4412 airfoil was considered throughout the work and the computational predictions were compared with experiments conducted under a wide range of Reynolds numbers (7e5≤Re≤9e6 and angles-of-attack (-10°≤α≤20°. Improvements both in modeling accuracy and processing time were achieved by considering the RS LP-S and the Transition SST turbulence models, and by considering finite volume-based solution methods with preconditioned systems, respectively. The RS LP-S model provided the best lift force predictions due to the adequate modeling of the micro and macro anisotropic turbulence at the airfoil’s surface and at the nearby flow field, which in turn allowed the adequate prediction of stall conditions. The Transition-SST model provided the best drag force predictions due to adequate modeling of the laminar-to-turbulent flow transition and the surface shear stresses. Conclusions, recommendations, and a comprehensive research agenda are presented based on validated computational results.
International Nuclear Information System (INIS)
Kopriva, D.A.
1982-01-01
A numerical scheme has been developed to solve the quasilinear form of the transonic stream function equation. The method is applied to compute steady two-dimensional axisymmetric solar wind-type problems. A single, perfect, non-dissipative, homentropic and polytropic gas-dynamics is assumed. The four equations governing mass and momentum conservation are reduced to a single nonlinear second order partial differential equation for the stream function. Bernoulli's equation is used to obtain a nonlinear algebraic relation for the density in terms of stream function derivatives. The vorticity includes the effects of azimuthal rotation and Bernoulli's function and is determined from quantities specified on boundaries. The approach is efficient. The number of equations and independent variables has been reduced and a rapid relaxation technique developed for the transonic full potential equation is used. Second order accurate central differences are used in elliptic regions. In hyperbolic regions a dissipation term motivated by the rotated differencing scheme of Jameson is added for stability. A successive-line-overrelaxation technique also introduced by Jameson is used to solve the equations. The nonlinear equation for the density is a double valued function of the stream function derivatives. The velocities are extrapolated from upwind points to determine the proper branch and Newton's method is used to iteratively compute the density. This allows accurate solutions with few grid points
Chellam, Shankararaman; Liu, Mei
2006-08-01
The existence and multiplicity of similarity solutions for steady, fully developed, incompressible laminar flow in uniformly porous tubes and channels with one or two permeable walls is investigated from first principles. A fourth-order ordinary differential equation obtained by simplifying the Navier-Stokes equations by introducing Berman's stream function [A. S. Berman, J. Appl. Phys. 24, 1232 (1953)] and Terrill's transformation [R. M. Terrill, Aeronaut. Q. 15, 299 (1964)] is probed analytically. In this work that considers only symmetric flows for symmetric ducts; the no-slip boundary condition at porous walls is relaxed to account for momentum transfer within the porous walls. By employing the Saffman [P. G. Saffman, Stud. Appl. Math. 50, 93 (1971)] form of the slip boundary condition, the uniqueness of similarity solutions is investigated theoretically in terms of the signs of the guesses for the missing initial conditions. Solutions were obtained for all wall Reynolds numbers for channel flows whereas no solutions existed for intermediate values for tube flows. Introducing slip did not fundamentally change the number or the character of solutions corresponding to different sections. However, the range of wall Reynolds numbers for which similarity solutions are theoretically impossible in tube flows was found to be a weak function of the slip coefficient. Slip also weakly influenced the transition wall Reynolds number corresponding to flow in the direction of a favorable axial pressure gradient to one in the direction of an adverse pressure gradient. Momentum transfer from the longitudinal axis to the walls appears to occur more efficiently in porous channels compared to porous tubes even in the presence of slip.
International Nuclear Information System (INIS)
Uemura, K.; Shishido, F.; Inugami, A.; Yamaguchi, T.; Ogawa, T.; Murakami, M.; Kanno, I.; Tagawa, K.; Yasui, N.
1986-01-01
Although regional cerebral blood flow (rCBF) studies have considerably increased pathophysiological knowledge in ischemic cerebrovascular disease, sometimes the results of such studies do not correlate with neurological abnormalities observed in the subjects being examined. Because regional neuronal activities always couple to the regional energy metabolism of brain tissue, simultaneous observation of rCBF and regional energy metabolism, such as regional oxygen consumption (rCMRO/sub 2/) and regional glucose consumption (rCMRG1), will provide greater understanding of the pathophysiology of the disease than rCBF study alone. Positron emission tomography (PET) using the 0-15 labelled gas steady-state method offers simultaneous measurement of rCBF and rCMRO/sub 2/ in vivo, and demonstrates imbalance between rCBF and rCMRO/sub 2/ in an ischemic lesion in a human brain. However, clinical PET studies in ischemic cerebrovascular disease reported previously, have been carried out using low resolution (more than 15 mm in the full width at half maximum; FWHM) PET. This report presents preliminary results using a high resolution tomograph; Headtome III and 0-15 labelled gas steady state method to investigate ischemic cerebrovascular disease
Qu, Aifang; Xiang, Wei
2018-05-01
In this paper, we study the stability of the three-dimensional jet created by a supersonic flow past a concave cornered wedge with the lower pressure at the downstream. The gas beyond the jet boundary is assumed to be static. It can be formulated as a nonlinear hyperbolic free boundary problem in a cornered domain with two characteristic free boundaries of different types: one is the rarefaction wave, while the other one is the contact discontinuity, which can be either a vortex sheet or an entropy wave. A more delicate argument is developed to establish the existence and stability of the square jet structure under the perturbation of the supersonic incoming flow and the pressure at the downstream. The methods and techniques developed here are also helpful for other problems involving similar difficulties.
International Nuclear Information System (INIS)
Berg, M.S. van den.
1995-01-01
Thermodynamic parameters and transport coefficients have been calculated for a multicomponent reacting U-C-F gas mixture in the steady flow gaseous core fission reactor. Element abundances are consistent with thermodynamic equilibrium between the gas mixture and a cooled solid graphite wall at 2500 K. Results are presented for various pressures, a fluorine potential of 5.6 and temperatures between 2500 and 7000 K. As a result of dissociation processes of uranium and carbon fluoride compounds, ''effective'' values of thermodynamic parameters and transport coefficients show anomalous behaviour with respect to so-called ''frozen'' values. The chemical reaction energy of the U-C-F gas mixture has been calculated as the driving-force behind the process of fuel redistribution to attain criticality conditions inside a functioning reactor. (author)
International Nuclear Information System (INIS)
Estey, S.D.
1997-01-01
This calculation note analyzes headspace concentrations of hydrogen dependent upon assumed ventilation flow rates provided for tanks 241-C-106 and 241-AY-102. The analyses are based on measured or estimated steady state hydrogen release rates. Tank 241-C-106 is analyzed prior to sluicing; tank 241-AY-102 is analyzed both prior to and after completion of sluicing. Specific analyses, using both best estimated and bounding hydrogen generation rates, include the minimum primary ventilation flow rates required in the tanks to ensure that the steady state hydrogen concentration in the respective tank headspace does not exceed 25% and 100% of the LFL. The headspace hydrogen concentration as a function of time as well as the time required to reach 25% and 100% of LFL upon complete loss of active ventilation, starting from the steady state hydrogen concentration based on a 200 CFM minimum flow rate in tank 241-C-106 and a 100 CFM minimum flow rate in tank241-AY-102. The headspace hydrogen concentration as a function of thee following partial loss of active ventilation (i.e., step changes to l60, l20, 80, and 40 CFM ventilation flow rates) in tank 241-C-106, staffing from a 200 CFM flow rate and the corresponding steady state hydrogen concentration based on the 200 CFM flow rate. The headspace hydrogen concentration as a function of the following partial loss of active ventilation i.e., step changes to 80, 60, 40, and 20 CFM ventilation flow rates) in tank 241-AY-102, starting from a 100 CFM flow rate and the corresponding steady state hydrogen concentration based on the 100 CFM flow rate
Jeong, Hyundoo; Qian, Xiaoning; Yoon, Byung-Jun
2016-10-06
Comparative analysis of protein-protein interaction (PPI) networks provides an effective means of detecting conserved functional network modules across different species. Such modules typically consist of orthologous proteins with conserved interactions, which can be exploited to computationally predict the modules through network comparison. In this work, we propose a novel probabilistic framework for comparing PPI networks and effectively predicting the correspondence between proteins, represented as network nodes, that belong to conserved functional modules across the given PPI networks. The basic idea is to estimate the steady-state network flow between nodes that belong to different PPI networks based on a Markov random walk model. The random walker is designed to make random moves to adjacent nodes within a PPI network as well as cross-network moves between potential orthologous nodes with high sequence similarity. Based on this Markov random walk model, we estimate the steady-state network flow - or the long-term relative frequency of the transitions that the random walker makes - between nodes in different PPI networks, which can be used as a probabilistic score measuring their potential correspondence. Subsequently, the estimated scores can be used for detecting orthologous proteins in conserved functional modules through network alignment. Through evaluations based on multiple real PPI networks, we demonstrate that the proposed scheme leads to improved alignment results that are biologically more meaningful at reduced computational cost, outperforming the current state-of-the-art algorithms. The source code and datasets can be downloaded from http://www.ece.tamu.edu/~bjyoon/CUFID .
International Nuclear Information System (INIS)
Adar, E.M.; Kuells, C.
2002-01-01
The following MIG computer code is restricted to a steady flow and steady hydrochemical system. The code for a non-steady hydrological system is still heavily dependant on external optimization libraries, such as the NAG Library. Therefore, a stand-alone 'friendly' code or solver for the non-steady system has yet to be compiled. Readers looking to implement the mixing-cell approach in a non-steady hydrological flow system are encouraged to contact the authors. In order to simplify the procedure of preparing the data and running the Mixing-Cell Model for steady flow system (MCMsf), a special Mixing Input Generator (MIG) has been programmed. MIG is a Visual Basic Microsoft application that runs within Excel 5.0 (and with more advanced versions such as Office 2000) via Windows 95 or newer environment. The program has been tested and used successfully in Windows NT, Windows 95 and Windows 98 together with Excel 5.0, 7.0 and 2000. The development of the standalone Version MIGSA that will run on a Windows system without Microsoft Excel is under development. Section 1 provides some clarifications of terms that are used both in MCMsf and MIG, whereas Section 2 briefly reviews the mathematical algorithm. For elaboration of the basic assumptions and for further mathematical description, the user is referred to the explanations provided in the Model Simplification and to the references provided in this publication
International Nuclear Information System (INIS)
Jones, O.C. Jr.; Yao, S.; Henry, R.E.
1976-01-01
A computer code has been developed for use in making single-phase thermal hydraulic calculations in rod bundle arrays with flow sweeping due to spiral wraps as the predominant crossflow mixing effect. This code, called SIMPLE-2, makes the assumption that the axial pressure gradient is identical for each subchannel over a given axial increment, and is unique in that no empirical coefficients must be specified for its use. Results from this code have been favorably compared with experimental data for both uniform and highly nonuniform power distributions. Typical calculations for various bundle sizes applicable to the LMBR program are included
International Nuclear Information System (INIS)
Moeller, R.; Tschoeke, H.
1980-01-01
The operating reliability of nuclear reactors calls for a reliable strength analysis of the highly loaded core elements, one of its prerequisites being the reliable determination of the three-dimensional velocity and temperature fields. To verify thermohydraulics computer programs, extensive local temperature measurements in the rod claddings of the critical bundle zone were performed on a heated 19-rod bundle model with sodium flow and provided with spacer grids (P/D = 1.30; W/D = 1.19). The essential results are: - Outside the spacer grids, the azimuthal temperature variations of the side and corner rods are approximately 10-fold those of rods in the central bundle zone. - The spacer grids investigated give rise to great local temperature peaks and correspondingly great temperature gradients in the axial and azimuthal directions immediately around the support points. - Continuous reduction of a subchannel by rod bowing results in substantial rises of temperature which, however, are limited to adjacent cladding tubes. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Prasser, H.M. [ed.
1999-12-01
The emphasis of the conference was on methods of measurement that show spatial distributions of phase fractions and velocity, particle sizes and bubbles of the disperse phase. Among the methods described were 3D X-ray tomography, grid sensor measurement of velocity profiles, and simultaneous measurement of bubble sizes and gas and liquid flow rates using an optical particle tracking method. Also presented were interesting developments in the field of local probes, e.g. an electrodiffusion probe. Another new development was the attempt to use optical tomography for investigations of two-phase flows. [German] Am 14. Oktober 1999 wurde in Rossendorf die dritte Veranstaltung in einer Serie von Workshops ueber Messtechnik fuer stationaere und transiente Mehrphasenstroemungen durchgefuehrt. Dieses Jahr koennen wir auf 11 interessante Vortraege zurueckblicken. Besonders hervorzuheben sind die beiden Hauptvortraege, die von Herrn Professor Hetsroni aus Haifa und Herrn Dr. Sengpiel aus Karlsruhe gehalten wurden. Ihnen und allen anderen Vortragenden moechten wir herzlich fuer ihren Beitrag zum Gelingen des Workshops danken. Erneut lag ein wichtiger Schwerpunkt auf Messverfahren, die raeumliche Verteilungen von Phasenanteilen und Geschwindigkeiten sowie die Groesse von Partikeln bzw. Blasen der dispersen Phase zugaenglich machen. So wurde ueber einen dreidimensional arbeitenden Roentgentomographen, ein Verfahren zur Messung von Geschwindigkeitsprofilen mit Gittersensoren und eine Methode zur simultanen Messung von Blasengroessen sowie Feldern von Gas- und Fluessigkeitsgeschwindigkeit mit einer optischen Partikelverfolgungstechnik vorgetragen. Daneben wurden interessante Entwicklungen auf dem Gebiet der lokalen Sonden vorgestellt, wie z.B. eine Elektrodiffusionssonde. Neue messtechnische Ansaetze waren ebenfalls vertreten; hervorzuheben ist der Versuch, die Methode der optischen Tomographie fuer die Untersuchung von Zweiphasenstroemungen nutzbar zu machen. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Prasser, H.M. [ed.
1997-12-01
There is hardly another area of physics which has a comparable multiplicity of phenomena, like flow in multi-phase mixtures. The wishes of experimenters regarding measurement technique are correspondingly great: Apart from the conventional parameters of pressure, temperature and speed of flow, as great a collection with resolution of the instantaneous phase distribution is required. Also, the phases themselves frequently consists of several components, whose concentration should also be measured. The enormous progress which has recently been made with laser optics and tomographic processes, must be compared with a long list of unsolved problems, above all where non-contact measurement is concerned. The attempts at solutions are multifarious, the need for the exchange of experience is great and the comparson of measurement processes with one another must be strengthened. The workshop has set itself these targets. (orig.) [Deutsch] Es gibt kaum ein anderes Gebiet der Physik, das eine vergleichbare Vielfalt der Erscheinungen aufweist wie Stroemungen von Mehrphasengemischen. Entsprechend gross sind die Wuensche der Experimentatoren hinsichtlich der Messtechnik: Neben den klassischen Parametern Druck, Temperatur und Stroemungsgeschwindigkeit wird eine moeglichst hoch aufloesende Erfassung der momentanen Phasenverteilung benoetigt. Ausserdem bestehen die Phasen selbst haeufig aus mehreren Komponenten, deren Konzentration ebenfalls gemessen werden soll. Den enormen Fortschritten, ie mit laseroptischen und tomographischen Verfahren in letzter Zeit gemacht wurden, steht nach wie vor eine lange Liste bisher ungeloester Aufgaben gegenueber, vor allen Dingen, wenn beruehrungslos gemessen werden soll. Die Loesungsansaetze sind vielfaeltig, der Bedarf an Erfahrungsaustausch ist gross, der Vergleich der Messverfahren untereinander muss verstaerkt werden. Diesen Zielen hatte sich der Workshop ``Messtechnik fuer tationaere und transiente Mehrphasenstroemungen`` verschrieben.
International Nuclear Information System (INIS)
Waddell, R.K.
1982-01-01
Characteristics of the flow system are principally determined by locations of low-hydraulic-conductivity rocks (barriers); by amounts of recharge originating in the Spring Mountains, Pahranagat, Timpahute, and Sheep Ranges, and in Pahute Mesa; and by amount of flow into the study area from Gold Flat and Kawich Valley. Discharge areas (Ash Meadows, Oasis Valley, Alkali Flat, and Furnace Creek Ranch) are upgradient from barriers. Analyses of sensitivity of hydraulic head with respect to model-parameter variations indicate that the flux terms having the greatest impact on model output are recharge on Pahute Mesa, underflow from Gold Flat and Kawich Valley, and discharge at Ash Meadows. The most important transmissivity terms are those for rocks underlying the Amargosa Desert (exclusive of Amargosa Flat area), the Eleana Formation along the west side of Yucca Flat, and the Precambrian and Cambrian clastic rocks underlying the Groom Range. Sensitivities of fluxes derived from simulated heads and head sensitivities were used to determine the parameters that would most affect predictions of radionuclide transport from a hypothetical nuclear repository in the southwest quadrant of the Nevada Test Site. The important parameters for determining flux through western Jackass Flats and Yucca Mountain are recharge to and underflow beneath Pahute Mesa; and transmissivities of the Eleana Formation, clastic rocks underlying the Groom Range, tuffs underlying Fortymile Canyon, and tuffs beneath Yucca Mountain. In the eastern part of Jackass Flats, the important parameters are transmissivities of the Eleana Formation; clastic rocks underlying the Groom Range; transmissivity of tuffs beneath Fortymile Canyon; and recharge or discharge terms for Pahute Mesa, Ash Meadows, and the Sheep Range. Transmissivities of rocks beneath the Amargosa Desert are important for flux calculations there
International Nuclear Information System (INIS)
Moeller, R.; Tschoeke, H.; Kolodziej, M.
1980-12-01
The operating reliability of nuclear reactors calls for a reliable strength analysis of the highly loaded core elements, one of its prerequisites being the reliable determination of the three-dimensional velocity and temperature fields. To verify thermohydraulics computer programs, extensive local temperature measurements in the rod claddings of the critical bundle zone were performed on a heated 19-rod bundle model with sodium flow and provided with spacer grids (P/D = 1.30; W/D = 1.19). These are the essential results obtained: Outside the spacer grids the azimuthal temperature variations of the side and corner rods are greater by approximately the factor 10 in the bundle geometry under consideration as compared to rods in the central bundle zone. The spacer grids investigated give rise to great local temperature peaks and correspondingly great temperature gradients in the axial and azimuthal directions immediately around the support points. Continuous reduction of a subchannel by rod bowing results in substantial rises of temperature which, however, are limited to the adjacent cladding tube zones. (orig.) [de
International Nuclear Information System (INIS)
Verfondern, K.
1983-01-01
This work presents a computer model determining the steady-state temperature- and flow field in 3 dimensions in the core of a pebble bed high temperature reactor. The numerical sprinkler method, basind on the Thermix-model, allows to describe the thermo-hydraulics of a non-rotational-symmetric core-geometry. The AVR-reactor in Juelich, in operation since 1967, represents a suitable investigation-object for the computer model of Thermix-3D. It is in a 3D-mesh-structure to reproduce very precisely the so called ''graphite noses'', in which the shut-down rods are conducted as well as the filling cones in the inner and outer area. The results of the final calculation of the normal operation condition for the AVR-reactor unambiguously show, that within the core reproduced in 3 dimensions there are evident deviations in the flow profile and in the temperatures of the cooling gas in contrast to a 2D-handling. (orig.) [de
Energy Technology Data Exchange (ETDEWEB)
Prasser, H.M. [ed.
1998-11-01
The 2nd Workshop on measuring systems for steady-state and transient multiphase flows was held at Rossendorf on September 24/25, 1988. 14 Papers were presented, whose subjects ranged from optical and radiometric methods to impedance sensors, hot film probes and model-assisted methods of measurement. In the field of computer simulation of multiphase flow, a trend towards 3D models was identified which makes higher demands on the spatial and time resolution and on the information volume to be acquired and processed. [German] Vom 24.-25. September 1998 fand in Rossendorf der 2. Workshop ueber Messtechnik fuer stationaere und transiente Mehrphasenstroemungen statt. Es standen 14 Vortraege auf dem Programm, das Spektrum reichte von optischen ueber radiometrische Methoden bis hin zu verschiedenen Impedanzsensoren, Heissfilmsonden und modellgestuetzten Messverfahren. Auf dem Gebiet der Computersimulation von Mehrphasenstroemungen zeichnet sich zunehmend der Uebergang zu dreidimensionalen Modellen ab. Hieraus ergeben sich neue Anforderungen an die Messtechnik, sowohl hinsichtlich der raeumlich-zeitlichen Aufloesung als auch was den Umfang der zu erfassenden Informationen betrifft. (orig./AKF)
Furuta, Akihiro; Isoda, Hiroyoshi; Yamashita, Rikiya; Ohno, Tsuyoshi; Kawahara, Seiya; Shimizu, Hironori; Fujimoto, Koji; Kido, Aki; Kusahara, Hiroshi; Togashi, Kaori
2014-09-01
To compare and evaluate images of non-contrast-enhanced MR portography acquired with two different methods, the flow-in and flow-out methods. Twenty-five healthy volunteers were examined using respiratory-triggered three-dimensional balanced steady-state free-precession (SSFP) with two selective inversion recovery pulses (flow-in method) and one tagging pulse and one nonselective inversion recovery pulse (flow-out method). For quantitative analysis, vessel-to-liver contrast (Cv-l) ratios of the main portal vein (MPV), right portal vein (RPV), and left portal vein (LPV) were measured. The quality of portal vein visualization was scored using a four-point scale. The Cv-ls of the MPV, RPV, and LPV were all significantly higher with the flow-out than flow-in method (MPV = 0.834 ± 0.06 versus 0.711 ± 0.10; RPV = 0.861 ± 0.04 versus 0.729 ± 0.11; LPV = 0.786 ± 0.08 versus 0.545 ± 0.22; P flow-out method showed higher scores than with the flow-in method. With the flow-out method, visual scores of the MPV, RPV, portal vein branches of segments 4 (P4), and 8 (P8) were significantly better than with the flow-in method (MPV = 3.4 ± 0.7 versus 2.6 ± 0.9; RPV = 4.0 ± 0.0 versus 3.5 ± 0.9; P4 = 2.8 ± 1.3 versus 1.6 ± 1.0; P8 = 4.0 ± 0.0 versus 2.9 ± 1.1; P flow-out method improves the visualization of the intrahepatic portal vein in comparison with the flow-in method. J. Magn. Reson. Imaging 2014;40:583-587. © 2013 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc.
Quasi-steady state power law model for flow of (La0·85Sr0·15)0·9MnO3 ceramic slurry in tape casting
DEFF Research Database (Denmark)
Jabbari, M; Bulatova, R; Hattel, J H
2013-01-01
work, the flow in the doctor blade region of a slurry containing (La0?85Sr0?15)0?9MnO3 (LSM) material is described with a simple quasi-steady momentum equation in combination with an Ostwald–de Waele power law constitutive equation. Based on rheometer experiments, the constants in the Ostwald–de Waele...
Energy Technology Data Exchange (ETDEWEB)
Yoon, Inkyoung; Ohm, Inyong [Seoul Nat’l Univ. of Science and Technology, Seoul (Korea, Republic of)
2017-02-15
This study is the second investigation on the steady flow characteristics of an SI engine with a semi-edge combustion chamber as a function of the port shape with varying evaluation positions. For this purpose, the planar velocity profiles were measured from 1.75B, 1.75 times of bore position apart from the bottom of head, to 6.00B positions using particle – image velocimetry. The flow patterns were examined with both a straight and a helical port. The velocity profiles, streamlines, and centers of swirl were almost the same at the same valve lift regardless of the measuring position, which is quite different from the case of the pent-roof combustion chamber. All the eccentricity values of the straight port were out of distortion criterion 0.15 through the lifts and the position. However, the values of the helical port exceeded the distortion criterion by up to 4 mm lift, but decreased rapidly above the 3.00B position and the 5 mm lift. There always existed a relative offset effect in the evaluation of the swirl coefficient using the PIV method due to the difference of the ideal impulse swirl meter velocity profile assumption, except for the cylinder-center-base estimation that was below 4 mm of the straight port. Finally, it was concluded that taking the center as an evaluation basis and the assumption about the axial velocity profile did not have any qualitative effect on swirl evaluation, but affected the value owing to the detailed profile.
International Nuclear Information System (INIS)
Zou Liqiu; Liu Xiaoyi; Liu Xin; Feng Fei; Qi Yulong; Liu Pengcheng
2011-01-01
Objective: To investigate balanced steady-state free precession with flow-sensitive dephasing magnetization preparation (FSD-bSSFP) in the assessment of arteries of foot in diabetic patients. Methods: The lower-extremity peripheral arteries of 43 diabetic patients were evaluated by FSD-bSSFP no contrast MRA and contrast-enhanced MRA (CE-MRA) in. Two experienced observers assessed the image quality, degree of venous contaminated and visibility of pedal artery branches by FSD-bSSFP and CE-MRA respectively in consensus. The signal intensity (SI), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the source images of both groups were measured and Wilcoxon and t tests were performed. Results: The image score of FSD-bSSFP group was 2.7±1.1 and CE-MRA was 2.6±0.8, there was no statistical difference (Z= 0.134, P>0.05). The image score of demonstration of the pedal artery branches and degree of venous contamination on FSD-bSSFP were 3.2±0.9 and 1.8±0.4 respectively which were superior to that of CE-MRA (2.5±0.9 and 2.1±0.8 respectively). Significant statistical difference existed between the two groups in demonstration of pedal artery branches (Z=5.246, P 0.05). But CNR of CE-MRA was superior to that of FSD-bSSFP and significant statistical difference existed between these two methods (t=5.113, P<0.01). Conclusion: FSD-bSSFP without contrast could be used in the evaluation of foot arteries in patients of renal dysfunction and diabetes. (authors)
International Nuclear Information System (INIS)
Roberts, H.A.; Smith, C.P.
1976-02-01
Provision of capability for performing steady-state calculations in RELAP-UK has led to the possibility of the wider use of this code for steady-state assessments of the behaviour of commercial systems with complicated circuit arrangements. In the studies discussed in this report, the first objective is to demonstrate the performance of the RELAP-UK code in a steady-state role, and to make comparisons with the CUSH code, and with measurements obtained on the Winfrith Steam-Generating Heavy Water Reactor. (U.K.)
International Nuclear Information System (INIS)
Belcher, W.R.; Faunt, C.C.; D'Agnese, F.A.
2002-01-01
The U.S. Geological Survey, in cooperation with the Department of Energy and other Federal, State, and local agencies, is evaluating the hydrogeologic characteristics of the Death Valley regional ground-water flow system. The ground-water flow system covers and area of about 100,000 square kilometers from latitude 35 degrees to 38 degrees 15 minutes North to longitude 115 degrees to 118 degrees West, with the flow system proper comprising about 45,000 square kilometers. The Death Valley regional ground-water flow system is one of the larger flow systems within the Southwestern United States and includes in its boundaries the Nevada Test Site, Yucca Mountain, and much of Death Valley. Part of this study includes the construction of a three-dimensional hydrogeologic framework model to serve as the foundation for the development of a steady-state regional ground-water flow model. The digital framework model provides a computer-based description of the geometry and composition of the hydro geologic units that control regional flow. The framework model of the region was constructed by merging two previous framework models constructed for the Yucca Mountain Project and the Environmental Restoration Program Underground Test Area studies at the Nevada Test Site. The hydrologic characteristics of the region result from a currently arid climate and complex geology. Interbasinal regional ground-water flow occurs through a thick carbonate-rock sequence of Paleozoic age, a locally thick volcanic-rock sequence of Tertiary age, and basin-fill alluvium of Tertiary and Quaternary age. Throughout the system, deep and shallow ground-water flow may be controlled by extensive and pervasive regional and local faults and fractures. The framework model was constructed using data from several sources to define the geometry of the regional hydrogeologic units. These data sources include (1) a 1:250,000-scale hydrogeologic-map compilation of the region; (2) regional-scale geologic cross
DEFF Research Database (Denmark)
Irnawan, Roni; Silva, Filipe Miguel Faria da; Bak, Claus Leth
2017-01-01
This paper deals with a radial offshore multi-terminal HVDC (MTDC) transmission system which is formed by interconnection several existing offshore wind farm (OWF) HVDC links with a shore-to-shore (StS) HVDC link. A challenge arises when deciding the steady-state DC voltage operating level...
Energy Technology Data Exchange (ETDEWEB)
Aldana Valverde, A. L.; Gonzalez Rodriguez, J. C.
1999-08-01
In this paper are analyzed some of the most important factors which can influence on the results of calculating water surface profiles for steady gradually varied flow. In this case, the objective of this kind of modeling, has been the estimation of discharges tables for high flows of river station gages connected to the hydrologic automatic information system (SAIH) of the Confederacion Hidrografica del Sur de Espana, system named red Hidrosur. (Author) 3 refs
Zeiger, Matthew D.
2014-01-01
Although complex, inconsistent and fickle, the time-averaged flow over a stationary slender forebody is generally well-understood. However, the nature of unsteady, time-varying flows over slender forebodies - whether due to the natural unsteadiness or forced maneuvering - is not well-understood. This body of work documents three experimental investigations into the unsteadiness of the flow over a 3.5 caliber tangent-ogive cylinder at high angles of incidence. The goal of the investigations...
Blanck, Harvey F.
2012-01-01
Naturally occurring gravity currents include events such as air flowing through an open front door, a volcanic eruption's pyroclastic flow down a mountainside, and the spread of the Bhopal disaster's methyl isocyanate gas. Gravity currents typically have a small height-to-distance ratio. Plastic models were designed and constructed with a…
Energy Technology Data Exchange (ETDEWEB)
Szenknect, St
2003-10-15
This work is devoted to the quantification and the identification of the predominant processes involved in strontium and caesium transport in unsaturated soil from Chernobyl Pilot Site under steady flow conditions. The transport and fate of radionuclides in the subsurface is affected by various physical and chemical processes including advective and diffusive transport as well as chemical and biological transformations. Laboratory experiments and the use of a multiple tracer approach allow to isolate the contributions of each elementary process and to control the physico-chemical conditions in the system. To be more representative of the field conditions, we decided to perform column miscible displacement experiments. We perform batch and flow-through reactor experiments to characterize the radionuclides sorption mechanisms. Miscible displacement experiments within homogeneous columns and modeling allow to characterize the hydrodynamic properties of the soil and to describe the radionuclides behaviour under dynamic conditions at different water contents. We show that the water content of porous media affect the transport behaviour of inert and strongly sorbing radionuclides. Our results demonstrate that a parametrized transport model that was calibrated under completely saturated conditions was not able to describe the advective-dispersive transport of reactive solutes under unsaturated steady state conditions. Under our experimental conditions, there is no effect of a decrease of the mean water content on the sorption model parameters, but the transport parameters are modified. We established for the studied soil the relation between hydrodynamic dispersion and water content and the relation between pore water velocity and water content. (author)
Currie, C. A.; Wang, K.; Hyndman, Roy D.; He, Jiangheng
2004-06-01
At subduction zones, geophysical and geochemical observations indicate that the arc and backarc regions are hot, in spite of the cooling effects of a subducting plate. At the well-studied Cascadia subduction zone, high mantle temperatures persist for over 500 km into the backarc, with little lateral variation. These high temperatures are even more surprising due to the juxtaposition of the hot Cascadia backarc against the thick, cold North America craton lithosphere. Given that local heat sources appear to be negligible, mantle flow is required to transport heat into the wedge and backarc. We have examined the thermal effects of mantle flow induced by traction along the top of the subducting plate. Through systematic tests of the backarc model boundary, we have shown that the model thermal structure of the wedge is primarily determined by the assumed temperatures along this boundary. To get high temperatures in the wedge, it is necessary for flow to mine heat from depth, either by using a temperature-dependent rheology, or by introducing a deep cold boundary through a thick adjacent lithosphere, consistent with the presence of a craton. Regardless of the thermal conditions along the backarc boundary, flow within an isoviscous wedge is too slow to transport a significant amount of heat into the wedge corner. With a more realistic stress- and temperature-dependent wedge rheology, flow is focused into the wedge corner, resulting in rapid flow upward toward the corner and enhanced temperatures below the arc, compatible with temperatures required for arc magma generation. However, this strong flow focusing produces a nearly stagnant region further landward in the shallow backarc mantle, where model temperatures and heat flow are much lower than observed. Observations of high backarc temperatures, particularly in areas that have not undergone recent extension, provide an important constraint on wedge dynamics. None of the models of simple traction-driven flow were able
Energy Technology Data Exchange (ETDEWEB)
Maximiano, Celso; Nieble, Marcio D. [Coordenadoria para Projetos Especiais (COPESP), Sao Paulo, SP (Brazil); Migliavacca, Sylvana C.P.; Silva, Eduardo R.F. [Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, SP (Brazil)
1995-12-31
The use of thermal sensors very common for the measurement of small flows of gases. In this kind of sensor a little tube forming a bypass is heated symmetrically, then the temperature distribution in the tube modifies with the mass flow along it. When a stationary wave appears in the principal tube it causes an oscillation of pressure around the average value. The sensor, located between two points of the principal tube, indicates not only the principal mass flow, but also that one caused by the difference of pressure induced by the sound wave. When the gas flows at low pressures the equipment indicates a value that do not correspond to the real. Tests and essays were realized by generating a sound wave in the principal tube, without mass flow, and the sensor detected flux. In order to solve this problem a wave-damper was constructed, installed and tested in the system and it worked satisfactory eliminating with efficiency the sound wave. (author). 2 refs., 3 figs.
Furuta, Akihiro; Isoda, Hiroyoshi; Ohno, Tsuyoshi; Ono, Ayako; Yamashita, Rikiya; Arizono, Shigeki; Kido, Aki; Sakashita, Naotaka; Togashi, Kaori
2018-01-01
To selectively visualize the left gastric vein (LGV) with hepatopetal flow information by non-contrast-enhanced magnetic resonance angiography under a hypothesis that change in the LGV flow direction can predict the development of esophageal varices; and to optimize the acquisition protocol in healthy subjects. Respiratory-gated three-dimensional balanced steady-state free-precession scans were conducted on 31 healthy subjects using two methods (A and B) for visualizing the LGV with hepatopetal flow. In method A, two time-spatial labeling inversion pulses (Time-SLIP) were placed on the whole abdomen and the area from the gastric fornix to the upper body, excluding the LGV area. In method B, nonselective inversion recovery pulse was used and one Time-SLIP was placed on the esophagogastric junction. The detectability and consistency of LGV were evaluated using the two methods and ultrasonography (US). Left gastric veins by method A, B, and US were detected in 30 (97%), 24 (77%), and 23 (74%) subjects, respectively. LGV flow by US was hepatopetal in 22 subjects and stagnant in one subject. All hepatopetal LGVs by US coincided with the visualized vessels in both methods. One subject with non-visualized LGV in method A showed stagnant LGV by US. Hepatopetal LGV could be selectively visualized by method A in healthy subjects.
International Nuclear Information System (INIS)
Wilson, J.L.; RamaRao, B.S.; McNeish, J.A.
1986-11-01
GRASP (GRound-Water Adjunct Senstivity Program) computes measures of the behavior of a ground-water system and the system's performance for waste isolation, and estimates the sensitivities of these measures to system parameters. The computed measures are referred to as ''performance measures'' and include weighted squared deviations of computed and observed pressures or heads, local Darcy velocity components and magnitudes, boundary fluxes, and travel distance and time along travel paths. The sensitivities are computed by the adjoint method and are exact derivatives of the performance measures with respect to the parameters for the modeled system, taken about the assumed parameter values. GRASP presumes steady-state, saturated grondwater flow, and post-processes the results of a multidimensional (1-D, 2-D, 3-D) finite-difference flow code. This document describes the mathematical basis for the model, the algorithms and solution techniques used, and the computer code design. The implementation of GRASP is verified with simple one- and two-dimensional flow problems, for which analytical expressions of performance measures and sensitivities are derived. The linkage between GRASP and multidimensional finite-difference flow codes is described. This document also contains a detailed user's manual. The use of GRASP to evaluate nuclear waste disposal issues has been emphasized throughout the report. The performance measures and their sensitivities can be employed to assist in directing data collection programs, expedite model calibration, and objectively determine the sensitivity of projected system performance to parameters
Khan, Zeeshan; Shah, Rehan Ali; Islam, Saeed; Jan, Bilal; Imran, Muhammad; Tahir, Farisa
2016-10-06
Modern optical fibers require double-layer coating on the glass fiber to provide protection from signal attenuation and mechanical damage. The most important plastic resins used in wires and optical fibers are plastic polyvinyl chloride (PVC) and low-high density polyethylene (LDPE/HDPE), nylon and Polysulfone. In this paper, double-layer optical fiber coating is performed using melt polymer satisfying PTT fluid model in a pressure type die using wet-on-wet coating process. The assumption of fully developed flow of Phan-Thien-Tanner (PTT) fluid model, two-layer liquid flows of an immiscible fluid is modeled in an annular die, where the fiber is dragged at a higher speed. The equations characterizing the flow and heat transfer phenomena are solved exactly and the effects of emerging parameters (Deborah and slip parameters, characteristic velocity, radii ratio and Brinkman numbers on the axial velocity, flow rate, thickness of coated fiber optics, and temperature distribution) are reported in graphs. It is shown that an increase in the non-Newtonian parameters increase the velocity in the absence or presence of slip parameters which coincides with related work. The comparison is done with experimental work by taking λ → 0 (non-Newtonian parameter).
Yousfi, Ammar; Mechergui, Mohammed
2016-04-01
The seepage face is an important feature of the drainage process when recharge occurs to a permeable region with lateral outlets. Examples of the formation of a seepage face above the downstream water level include agricultural land drained by ditches. Flow problem to these drains has been investigated extensively by many researchers (e.g. Rubin, 1968; Hornberger et al. 1969; Verma and Brutsaert, 1970; Gureghian and Youngs, 1975; Vauclin et al., 1975; Skaggs and Tang, 1976; Youngs, 1990; Gureghian, 1981; Dere, 2000; Rushton and Youngs, 2010; Youngs, 2012; Castro-Orgaz et al., 2012) and may be tackled either using variably saturated flow models, or the complete 2-D solution of Laplace equation, or using the Dupuit-Forchheimer approximation; the most widely accepted methods to obtain analytical solutions for unconfined drainage problems. However, the investigation reported by Clement et al. (1996) suggest that accounting for the seepage face alone, as in the fully saturated flow model, does not improve the discharge estimate because of disregarding flow the unsaturated zone flow contribution. This assumption can induce errors in the location of the water table surface and results in an underestimation of the seepage face and the net discharge (e.g. Skaggs and Tang, 1976; Vauclin et al., 1979; Clement et al., 1996). The importance of the flow in the unsaturated zone has been highlighted by many authors on the basis of laboratory experiments and/or numerical experimentations (e.g. Rubin, 1968; Verma and Brutsaert, 1970; Todsen, 1973; Vauclin et al., 1979; Ahmad et al., 1993; Anguela, 2004; Luthin and Day, 1955; Shamsai and Narasimhan, 1991; Wise et al., 1994; Clement et al., 1996; Boufadel et al., 1999; Romano et al., 1999; Kao et al., 2001; Kao, 2002). These studies demonstrate the failure of fully saturated flow models and suggested that the error made when using these models not only depends on soil properties but also on the infiltration rate as reported by Kao et
Ouriev, Boris; Windhab, Erich; Braun, Peter; Zeng, Yuantong; Birkhofer, Beat
2003-12-01
In the present work an in-line ultrasonic method for investigation of the rheological flow behavior of concentrated suspensions was created. It is based on a nondestructive rheological measuring technique for pilot plant and industrial scale applications. Elsewhere the author discusses a tremendous need for in-line rheological characterization of highly concentrated suspensions exposed to pressure driven shear flow conditions. Most existing on-line methods are based on destructive macro actuators, which are not suitable for materials with sensitive to applied deformation structure. Since the process of our basic interest influences the structure of suspension it would be difficult to separate the effects of rheometric measurement and weakly pronounced structural changes arising from a fine adjustment of the process parameters. The magnitude of these effects is usually associated with the complex flow dynamics of structured liquids and is sensitive to density or temperature fluctuations around the moving rheometric actuator. Interpretation of the results of such measurements can be hindered by process parameter influences on liquid product structure. Therefore, the author introduces an in-line noninvasive rheometric method, which is implemented in a pre-crystallization process of chocolate suspension. Use of ultrasound velocity profile pressure difference (UVP-PD) technique enabled process monitoring of the chocolate pre-crystallization process. Influence of seeded crystals on Rheology of chocolate suspension was recorded and monitored on line. It was shown that even slight velocity pulsations in chocolate mainstream can strongly influence rheological properties besides influencing flow velocity profiles. Based on calculations of power law fit in raw velocity profiles and calculation of wall shear stress from pressure difference measurement, a viscosity function was calculated and monitored on line. On-line results were found to be in a good agreement with off
International Nuclear Information System (INIS)
Dionne, B.; Tzanos, C.P.
2011-01-01
To support the safety analyses required for the conversion of the Belgian Reactor 2 (BR2) from highly-enriched uranium (HEU) to low-enriched uranium (LEU) fuel, the simulation of a number of loss-of-flow tests, with or without loss of pressure, has been undertaken. These tests were performed at BR2 in 1963 and used instrumented fuel assemblies (FAs) with thermocouples (TC) imbedded in the cladding as well as probes to measure the FAs power on the basis of their coolant temperature rise. The availability of experimental data for these tests offers an opportunity to better establish the credibility of the RELAP5-3D model and methodology used in the conversion analysis. In order to support the HEU to LEU conversion safety analyses of the BR2 reactor, RELAP simulations of a number of loss-of-flow/loss-of-pressure tests have been undertaken. Preliminary analyses showed that the conservative power distributions used historically in the BR2 RELAP model resulted in a significant overestimation of the peak cladding temperature during the transient. Therefore, it was concluded that better estimates of the steady-state and decay power distributions were needed to accurately predict the cladding temperatures measured during the tests and establish the credibility of the RELAP model and methodology. The new approach ('best estimate' methodology) uses the MCNP5, ORIGEN-2 and BERYL codes to obtain steady-state and decay power distributions for the BR2 core during the tests A/400/1, C/600/3 and F/400/1. This methodology can be easily extended to simulate any BR2 core configuration. Comparisons with measured peak cladding temperatures showed a much better agreement when power distributions obtained with the new methodology are used.
Aziz, Asim; Siddique, J. I.; Aziz, Taha
2014-01-01
In this paper, a simplified model of an incompressible fluid flow along with heat and mass transfer past a porous flat plate embedded in a Darcy type porous medium is investigated. The velocity, thermal and mass slip conditions are utilized that has not been discussed in the literature before. The similarity transformations are used to transform the governing partial differential equations (PDEs) into a nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is then reduced to a system of first order differential equations which was solved numerically by using Matlab bvp4c code. The effects of permeability, suction/injection parameter, velocity parameter and slip parameter on the structure of velocity, temperature and mass transfer rates are examined with the aid of several graphs. Moreover, observations based on Schmidt number and Soret number are also presented. The result shows, the increase in permeability of the porous medium increase the velocity and decrease the temperature profile. This happens due to a decrease in drag of the fluid flow. In the case of heat transfer, the increase in permeability and slip parameter causes an increase in heat transfer. However for the case of increase in thermal slip parameter there is a decrease in heat transfer. An increase in the mass slip parameter causes a decrease in the concentration field. The suction and injection parameter has similar effect on concentration profile as for the case of velocity profile. PMID:25531301
Aziz, Asim; Siddique, J I; Aziz, Taha
2014-01-01
In this paper, a simplified model of an incompressible fluid flow along with heat and mass transfer past a porous flat plate embedded in a Darcy type porous medium is investigated. The velocity, thermal and mass slip conditions are utilized that has not been discussed in the literature before. The similarity transformations are used to transform the governing partial differential equations (PDEs) into a nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is then reduced to a system of first order differential equations which was solved numerically by using Matlab bvp4c code. The effects of permeability, suction/injection parameter, velocity parameter and slip parameter on the structure of velocity, temperature and mass transfer rates are examined with the aid of several graphs. Moreover, observations based on Schmidt number and Soret number are also presented. The result shows, the increase in permeability of the porous medium increase the velocity and decrease the temperature profile. This happens due to a decrease in drag of the fluid flow. In the case of heat transfer, the increase in permeability and slip parameter causes an increase in heat transfer. However for the case of increase in thermal slip parameter there is a decrease in heat transfer. An increase in the mass slip parameter causes a decrease in the concentration field. The suction and injection parameter has similar effect on concentration profile as for the case of velocity profile.
International Nuclear Information System (INIS)
Shimizu, Takeshi
1997-01-01
In this paper, we discuss the stability of the convergence of a nonlinear iteration procedure which may be affected by a large number of numerical factors in a complicated way. A numerical parallel channel flow problem is solved using the finite element method and the Newton-Raphson iteration procedure. The numerical factors, on which we focus attention in this study, are the aspect ratio of the channel and the number of divided meshes. We propose a nondimensional value, which is obtained from the Reynolds number, the aspect ratio and the number of meshes. The results of the numerical experiment show that the threshold of divergence in the iteration is indicated clearly by the present nondimensional value. (author)
Stamhuis, EJ; Videler, JJ; van Duren, LA; Muller, UK
2002-01-01
Digital particle image velocimetry (DPIV) has been applied to animal-generated flows since 1993 to map the flow patterns and vortex wakes produced by a range of feeding and swimming aquatic animals, covering a Re range of 10(-2)-10(5). In this paper, the special circumstances, problems and some
James, Susan H; Wald, Rachel; Wintersperger, Bernd J; Jimenez-Juan, Laura; Deva, Djeven; Crean, Andrew M; Nguyen, Elsie; Paul, Narinder S; Ley, Sebastian
2013-08-01
The left ventricle (LV) is routinely assessed with cardiac magnetic resonance imaging (MRI) by using short-axis orientation; it remains unclear whether the right ventricle (RV) can also be adequately assessed in this orientation or whether dedicated axial orientation is required. We used phase-contrast (PC) flow measurements in the main pulmonary artery (MPA) and the ascending aorta (Aorta) as nonvolumetric standard of reference and compared RV and LV volumes in short-axis and axial orientations. A retrospective analysis identified 30 patients with cardiac MRI data sets. Patients underwent MRI (1.5 T or 3 T), with retrospectively gated cine steady-state free-precession in axial and short-axis orientations. PC flow analyses of MPA and Aorta were used as the reference measure of RV and LV output. There was a high linear correlation between MPA-PC flow and RV-stroke volume (SV) short axis (r = 0.9) and RV-SV axial (r = 0.9). Bland-Altman analysis revealed a mean offset of 1.4 mL for RV axial and -2.3 mL for RV-short-axis vs MPA-PC flow. There was a high linear correlation between Aorta-PC flow and LV-SV short-axis (r = 0.9) and LV-SV axial (r = 0.9). Bland-Altman analysis revealed a mean offset of 4.8 m for LV short axis and 7.0 mL for LV axial vs Aorta-PC flow. There was no significant difference (P = .6) between short-axis-LV SV and short-axis-RV SV. No significant impact of the slice acquisition orientation for determination of RV and LV stroke volumes was found. Therefore, cardiac magnetic resonance workflow does not need to be extended by an axial data set for patients without complex cardiac disease for assessment of biventricular function and volumes. Copyright © 2013 Canadian Association of Radiologists. Published by Elsevier Inc. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Richard C. Martineau; Ray A. Berry
2003-04-01
A new semi-implicit pressure-based Computational Fluid Dynamics (CFD) scheme for simulating a wide range of transient and steady, inviscid and viscous compressible flow on unstructured finite elements is presented here. This new CFD scheme, termed the PCICEFEM (Pressure-Corrected ICE-Finite Element Method) scheme, is composed of three computational phases, an explicit predictor, an elliptic pressure Poisson solution, and a semiimplicit pressure-correction of the flow variables. The PCICE-FEM scheme is capable of second-order temporal accuracy by incorporating a combination of a time-weighted form of the two-step Taylor-Galerkin Finite Element Method scheme as an explicit predictor for the balance of momentum equations and the finite element form of a time-weighted trapezoid rule method for the semi-implicit form of the governing hydrodynamic equations. Second-order spatial accuracy is accomplished by linear unstructured finite element discretization. The PCICE-FEM scheme employs Flux-Corrected Transport as a high-resolution filter for shock capturing. The scheme is capable of simulating flows from the nearly incompressible to the high supersonic flow regimes. The PCICE-FEM scheme represents an advancement in mass-momentum coupled, pressurebased schemes. The governing hydrodynamic equations for this scheme are the conservative form of the balance of momentum equations (Navier-Stokes), mass conservation equation, and total energy equation. An operator splitting process is performed along explicit and implicit operators of the semi-implicit governing equations to render the PCICE-FEM scheme in the class of predictor-corrector schemes. The complete set of semi-implicit governing equations in the PCICE-FEM scheme are cast in this form, an explicit predictor phase and a semi-implicit pressure-correction phase with the elliptic pressure Poisson solution coupling the predictor-corrector phases. The result of this predictor-corrector formulation is that the pressure Poisson
Energy Technology Data Exchange (ETDEWEB)
Castagnoli, G. (Dipt. di Informatica, Sistemistica, Telematica, Univ. di Genova, Viale Causa 13, 16145 Genova (IT))
1991-08-10
This paper reports that current conceptions of quantum mechanical computers inherit from conventional digital machines two apparently interacting features, machine imperfection and temporal development of the computational process. On account of machine imperfection, the process would become ideally reversible only in the limiting case of zero speed. Therefore the process is irreversible in practice and cannot be considered to be a fundamental quantum one. By giving up classical features and using a linear, reversible and non-sequential representation of the computational process - not realizable in classical machines - the process can be identified with the mathematical form of a quantum steady state. This form of steady quantum computation would seem to have an important bearing on the notion of cognition.
International Nuclear Information System (INIS)
Castagnoli, G.
1991-01-01
This paper reports that current conceptions of quantum mechanical computers inherit from conventional digital machines two apparently interacting features, machine imperfection and temporal development of the computational process. On account of machine imperfection, the process would become ideally reversible only in the limiting case of zero speed. Therefore the process is irreversible in practice and cannot be considered to be a fundamental quantum one. By giving up classical features and using a linear, reversible and non-sequential representation of the computational process - not realizable in classical machines - the process can be identified with the mathematical form of a quantum steady state. This form of steady quantum computation would seem to have an important bearing on the notion of cognition
International Nuclear Information System (INIS)
Janulyte, A.; Andre, J.; Carette, M.; Mercury, M.; Reynard, C; Zerega, Y.
2009-01-01
A specific Fourier transform operating mode is applied to a 3-dimensional quadrupolar ion trap for mass analysis (Fourier Transform Quadrupolar Ion Trap (FTQIT) Operating Mode or Mass Spectrometer). With this operating mode, an image signal, which is representative of the collective motion of simultaneously confined ions, is made up from a set of recorded time-of-flight histograms. In an ion trap, the secular frequency of ion motion depends on m/Z ratio of the ion. By Fourier transformation of the image signal, one observes the frequency peak of each confined ionic species. When only one ionic species is confined, the peak amplitude is proportional to the maximal amplitude of the image signal. The maximal amplitude of the image signal is expressed according to the operating parameters, the initial conditions of the ions and the number of ions. Simulation tools lead to fluctuation calculation of the maximal amplitude of the image signal. Two origins are explored: (1) the fluctuation of the numbers of ions according to the steady ion flow injection mode (SIFIM) used with this operating mode and (2) the distribution fluctuation of the initial positions and velocities. Initial confinement conditions, obtained with SIFIM injection mode, lead to optimal detection with small fluctuations of the peak amplitude for Fourier transform operating mode applied to an ion trap. (authors)
International Nuclear Information System (INIS)
Jarboe, T.R.
1982-01-01
A major effort is being made in the national program to make the operation of axisymmetric, toroidal confinement systems steady state by the application of expensive rf current drive. Described here is a method by which such a confinement system, the spheromak, can be refluxed indefinitely through the application of dc power. As a step towards dc sustainment we have operated the present CTX source in the slow source mode with a longer power application time (approx. 0.1 ms) and successfully generated long-lived spheromaks. If the erosion of the electrodes can be controlled as well as it is with MPD arcs then dc operation should be very clean. If only a small fraction (approx. 10% for an experiment) of the poloidal flux of the spheromak connects to the source then the dc sustainment can be very efficient. The amount of connecting flux that is necessary for sustainment needs to be determined experimentally
Zhang, Nan; Fan, Zhaoyang; Luo, Nan; Bi, Xiaoming; Zhao, Yike; An, Jing; Liu, Jiayi; Chen, Zhong; Fan, Zhanming; Li, Debiao
2016-02-01
To evaluate the feasibility and diagnostic performance of flow-sensitive dephasing (FSD)-prepared steady-state free precession (SSFP) MR angiography (MRA) for imaging infragenual arteries at 3.0T, with contrast enhanced MR angiography (CE MRA) as reference. Twenty consecutive patients with suspicion of lower extremity arterial disease undergoing routine CE MRA were recruited. FSD MRA was performed at calf before CE MRA. Image quality and stenosis degree of infragenual arteries from both techniques were independently evaluated and compared. Six patients in this study underwent DSA examination. Three undiagnostic segments were excluded with severe venous contamination in CE MRA. A total of 197 calf arterial segments images were analyzed. No significant difference existed in the relative signal intensity (rSI) of arterial segments between FSD MRA and CE MRA techniques (0.92 ± 0.09 versus 0.93 ± 0.05; P = 0.207). However, the subjective image quality score was slightly higher in FSD MRA (3.66 ± 0.81 versus 3.49 ± 0.87; P = 0.050). With CE MRA images as reference standard, slight overestimation existed in FSD MRA (2.19 ± 1.24 versus 2.09 ± 1.18; P = 0.019), with total agreement of 84.3% on the basis of all arterial segments. The sensitivity, specificity, negative predictive value, and positive predictive value of FSD MRA was 96.4%, 93.0%, 98.5%, and 84.1%. No significant difference in the stenosis degree score was detected between MRA (FSD MRA and CE MRA) and DSA (P > 0.05). FSD MRA performed on at 3.0T without the use of contrast medium provides diagnostic images allowing for arterial stenosis assessment of calf arteries that was highly comparable with CE MRA. Moreover, venous contamination was less problematic with FSD MRA. © 2015 Wiley Periodicals, Inc.
Steady electric fields and currents elementary electromagnetic theory
Chirgwin, B H; Kilmister, C W
2013-01-01
Steady Electric Fields and Currents, Volume 1 is an introductory text to electromagnetism and potential theory. This book starts with the fields associated with stationary charges and unravels the stationary condition to allow consideration of the flow of steady currents in closed circuits. The opening chapter discusses the experimental results that require mathematical explanation and discussion, particularly those referring to phenomena that question the validity of the simple Newtonian concepts of space and time. The subsequent chapters consider steady-state fields, electrostatics, dielectr
Steady equilibrium of a cylindrically symmetric plasma sustained by fueling
International Nuclear Information System (INIS)
Tomita, Yukihiro; Momota, Hiromu
1993-01-01
By introducing a novel and natural method to obtain a steady equilibrium, it is shown that a pressure gradient produced by the particle injection or resultant diamagnetic current can sustain only an equilibrium of a diffused linear pinch. For an extremely elongated FRC where magnetic field vanishes at a certain point, a seed current is needed to sustain configuration in a steady state equilibrium. A directed flow of fusion produced protons forms a seed current and consequently it sustains a steady FRC equilibrium by fueling only once D- 3 He burning takes place. Effects of anomalous transports on the sustainment are discussed. (author)
Impulsively started, steady and pulsated annular inflows
Energy Technology Data Exchange (ETDEWEB)
Abdel-Raouf, Emad [General Field Engineer, Halliburton Energy Services 719 Hangar Dr, New Iberia, LA 70560, United States of America (United States); Sharif, Muhammad A R; Baker, John, E-mail: abdelraouf.em@gmail.com, E-mail: msharif@eng.ua.edu, E-mail: john.baker@eng.ua.edu [Aerospace Engineering and Mechanics Department, The University of Alabama, Tuscaloosa, Alabama 35487, United States of America (United States)
2017-04-15
A computational investigation was carried out on low Reynolds number laminar inflow starting annular jets using multiple blocking ratios and atmospheric ambient conditions. The jet exit velocity conditions are imposed as steady, unit pulsed, and sinusoidal pulsed while the jet surroundings and the far-field jet inlet upstream conditions are left atmospheric. The reason is to examine the flow behavior in and around the jet inlet under these conditions. The pulsation mode behavior is analyzed based on the resultant of the momentum and pressure forces at the entry of the annulus, the circulation and vortex formation, and the propulsion efficiency of the inflow jets. The results show that under certain conditions, the net force of inflow jets (sinusoidal pulsed jets in particular) could point opposite to the flow direction due to the adverse pressure drops in the flow. The propulsion efficiency is also found to increase with pulsation frequency and the sinusoidal pulsed inflow jets are more efficient than the unit pulsed inflow jets. In addition, steady inflow jets did not trigger the formation of vortices, while unit and sinusoidal pulsed inflow jets triggered the formation of vortices under a certain range of frequencies. (paper)
Steady states in conformal theories
CERN. Geneva
2015-01-01
A novel conjecture regarding the steady state behavior of conformal field theories placed between two heat baths will be presented. Some verification of the conjecture will be provided in the context of fluid dynamics and holography.
Advantages of forced non-steady operated trickle-bed reactors
Boelhouwer, J.G.; Piepers, H.W.; Drinkenburg, A.A.H.
2002-01-01
Trickle-bed reactors are usually operated in the steady state trickle flow regime. Uneven liquid distribution and the formation of hot spots are the most serious problems experienced during trickle flow operation. In this paper, we advocate the use of non-steady state operation of trickle-bed
Steady state theta pinch concept for slow formation of FRC
International Nuclear Information System (INIS)
Hirano, K.
1987-05-01
A steady state high beta plasma flow through a channel along the magnetic field increasing downstream can be regarded as a ''steady state theta pinch'', because if we see the plasma riding on the flow we should observe very similar process taking place in a theta pinch. Anticipating to produce an FRC without using very high voltage technics such as the ones required in a conventional theta pinch, we have studied after the analogy a ''steady state reversed field theta pinch'' which is brought about by steady head-on collision of counter plasma streams along the channel as ejected from two identical co-axial plasma sources mounted at the both ends of the apparatus. The ideal Poisson and shock adiabatic flow models are employed for the analysis of the steady colliding process. It is demonstrated that an FRC involving large numbers of particles is produced only by the weak shock mode which is achieved in case energetic plasma flow is decelerated almost to be stagnated through Poisson adiabatic process before the streams are collided. (author)
Asymptotic stability of steady compressible fluids
Padula, Mariarosaria
2011-01-01
This volume introduces a systematic approach to the solution of some mathematical problems that arise in the study of the hyperbolic-parabolic systems of equations that govern the motions of thermodynamic fluids. It is intended for a wide audience of theoretical and applied mathematicians with an interest in compressible flow, capillarity theory, and control theory. The focus is particularly on recent results concerning nonlinear asymptotic stability, which are independent of assumptions about the smallness of the initial data. Of particular interest is the loss of control that sometimes results when steady flows of compressible fluids are upset by large disturbances. The main ideas are illustrated in the context of three different physical problems: (i) A barotropic viscous gas in a fixed domain with compact boundary. The domain may be either an exterior domain or a bounded domain, and the boundary may be either impermeable or porous. (ii) An isothermal viscous gas in a domain with free boundaries. (iii) A h...
The Asymptotic Solution for the Steady Variable-Viscosity Free ...
African Journals Online (AJOL)
Under an arbitrary time-dependent heating of an infinite vertical plate (or wall), the steady viscosity-dependent free convection flow of a viscous incompressible fluid is investigated. Using the asymptotic method of solution on the governing equations of motion and energy, the resulting Ordinary differential equations were ...
Steady-State Process Modelling
DEFF Research Database (Denmark)
Cameron, Ian; Gani, Rafiqul
2011-01-01
illustrate the “equation oriented” approach as well as the “sequential modular” approach to solving complex flowsheets for steady state applications. The applications include the Williams-Otto plant, the hydrodealkylation (HDA) of toluene, conversion of ethylene to ethanol and a bio-ethanol process....
Steady State Shift Damage Localization
DEFF Research Database (Denmark)
Sekjær, Claus; Bull, Thomas; Markvart, Morten Kusk
2017-01-01
The steady state shift damage localization (S3DL) method localizes structural deterioration, manifested as either a mass or stiffness perturbation, by interrogating the damage-induced change in the steady state vibration response with damage patterns cast from a theoretical model. Damage is, thus...... the required accuracy when examining complex structures, an extensive amount of degrees of freedom (DOF) must often be utilized. Since the interrogation matrix for each damage pattern depends on the size of the system matrices constituting the FE-model, the computational time quickly becomes of first......-order importance. The present paper investigates two sub-structuring approaches, in which the idea is to employ Craig-Bampton super-elements to reduce the amount of interrogation distributions while still providing an acceptable localization resolution. The first approach operates on a strict super-element level...
Steady state neutral beam injector
International Nuclear Information System (INIS)
Mattoo, S.K.; Bandyopadhyay, M.; Baruah, U.K.; Bisai, N.; Chakbraborty, A.K.; Chakrapani, Ch.; Jana, M.R.; Bajpai, M.; Jaykumar, P.K.; Patel, D.; Patel, G.; Patel, P.J.; Prahlad, V.; Rao, N.V.M.; Rotti, C.; Singh, N.P.; Sridhar, B.
2000-01-01
Learning from operational reliability of neutral beam injectors in particular and various heating schemes including RF in general on TFTR, JET, JT-60, it has become clear that neutral beam injectors may find a greater role assigned to them for maintaining the plasma in steady state devices under construction. Many technological solutions, integrated in the present day generation of injectors have given rise to capability of producing multimegawatt power at many tens of kV. They have already operated for integrated time >10 5 S without deterioration in the performance. However, a new generation of injectors for steady state devices have to address to some basic issues. They stem from material erosion under particle bombardment, heat transfer > 10 MW/m 2 , frequent regeneration of cryopanels, inertial power supplies, data acquisition and control of large volume of data. Some of these engineering issues have been addressed to in the proposed neutral beam injector for SST-1 at our institute; the remaining shall have to wait for the inputs of the database generated from the actual experience with steady state injectors. (author)
Chlorine decay under steady and unsteady-state hydraulic conditions
DEFF Research Database (Denmark)
Stoianov, Ivan; Aisopou, Angeliki
2014-01-01
This paper describes a simulation framework for the scale-adaptive hydraulic and chlorine decay modelling under steady and unsteady-state flows. Bulk flow and pipe wall reaction coefficients are replaced with steady and unsteady-state reaction coefficients. An unsteady decay coefficient is defined...... which depends upon the absolute value of shear stress and the rate of change of shear stress for quasi-unsteady and unsteady-state flows. A preliminary experimental and analytical investigation was carried out in a water transmission main. The results were used to model monochloramine decay...... and these demonstrate that the dynamic hydraulic conditions have a significant impact on water quality deterioration and the rapid loss of disinfectant residual. © 2013 The Authors....
Introduction to compressible fluid flow
Oosthuizen, Patrick H
2013-01-01
IntroductionThe Equations of Steady One-Dimensional Compressible FlowSome Fundamental Aspects of Compressible FlowOne-Dimensional Isentropic FlowNormal Shock WavesOblique Shock WavesExpansion Waves - Prandtl-Meyer FlowVariable Area FlowsAdiabatic Flow with FrictionFlow with Heat TransferLinearized Analysis of Two-Dimensional Compressible FlowsHypersonic and High-Temperature FlowsHigh-Temperature Gas EffectsLow-Density FlowsBibliographyAppendices
Multimode optical fibers: steady state mode exciter.
Ikeda, M; Sugimura, A; Ikegami, T
1976-09-01
The steady state mode power distribution of the multimode graded index fiber was measured. A simple and effective steady state mode exciter was fabricated by an etching technique. Its insertion loss was 0.5 dB for an injection laser. Deviation in transmission characteristics of multimode graded index fibers can be avoided by using the steady state mode exciter.
Quasi‐steady centrifuge method for unsaturated hydraulic properties
Caputo, Maria C.; Nimmo, John R.
2005-01-01
We have developed the quasi‐steady centrifuge (QSC) method as a variation of the steady state centrifuge method that can be implemented simply and inexpensively with greater versatility in terms of sample size and other features. It achieves these advantages by somewhat relaxing the criterion for steadiness of flow through the sample. This compromise entails an increase in measurement uncertainty but to a degree that is tolerable in most applications. We have tested this new approach with an easily constructed apparatus to establish a quasi‐steady flow of water in unsaturated porous rock samples spinning in a centrifuge, obtaining measurements of unsaturated hydraulic conductivity and water retention that agree with results of other methods. The QSC method is adaptable to essentially any centrifuge suitable for hydrogeologic applications, over a wide range of sizes and operating speeds. The simplified apparatus and greater adaptability of this method expands the potential for exploring situations that are common in nature but have been the subject of few laboratory investigations.
Quasi-steady centrifuge method for unsaturated hydraulic properties
Caputo, Maria C.; Nimmo, John R.
2005-11-01
We have developed the quasi-steady centrifuge (QSC) method as a variation of the steady state centrifuge method that can be implemented simply and inexpensively with greater versatility in terms of sample size and other features. It achieves these advantages by somewhat relaxing the criterion for steadiness of flow through the sample. This compromise entails an increase in measurement uncertainty but to a degree that is tolerable in most applications. We have tested this new approach with an easily constructed apparatus to establish a quasi-steady flow of water in unsaturated porous rock samples spinning in a centrifuge, obtaining measurements of unsaturated hydraulic conductivity and water retention that agree with results of other methods. The QSC method is adaptable to essentially any centrifuge suitable for hydrogeologic applications, over a wide range of sizes and operating speeds. The simplified apparatus and greater adaptability of this method expands the potential for exploring situations that are common in nature but have been the subject of few laboratory investigations.
Energy Technology Data Exchange (ETDEWEB)
Haga, D; Niibori, Y; Chida, T [Tohoku University, Sendai (Japan)
1998-10-25
Fluids in geothermal reservoirs are not necessarily in the single phase but is occasionally in the gas-liquid double phase. This study aims to collect fundamental knowledge about the analysis of tracer responses in a gas-liquid two-phase flow, with special attention paid to the movement of substances in the liquid-phase portion of the two-phase flow. A tracer test is conducted in a glass bead-filled layer, and then it is found that the conventional mixture-diffusion model fails to explain the outcome of the test conducted using the said very simple apparatus. The failure is attributed to the coexistence of high-saturation and low-saturation layers throughout the glass bead-filled layer, and a mathematical model is formulated, which is a development from the two-fractured-layer (TFL) model. It turns out that the mathematical model excellently describes the test result that the mixture-diffusion model fails to explain. In the numerical solution of this problem, the validity is confirmed of the use of the SIMPLEX method for the estimation of the effect of the numerical dispersion term of the third-order accurate finite upstream difference method, and of unknown parameters. 31 refs., 7 figs., 1 tab.
Optimization of Steady Wall Temperature for Disturbance Control
Pralits, Jan; Ardeshir, Hanifi
2003-01-01
We present a theory for computing the optimal steady wall temperature distribution to suppress the growth of convectively unstable disturbances in compressible boundary layer flows on flat plates. A gradient based iterative procedure is used to minimize an objective function measuring the disturbance kinetic energy. The gradient of interest is obtained from the solution of the adjoint of the boundary layer and parabolized stability equations, which are derived using a Lagrange multiplier tech...
Understanding void fraction in steady state and dynamic environments
International Nuclear Information System (INIS)
Chexal, B.; Maulbetsch, J.; Harrison, J.; Petersen, C.; Jensen, P.; Horowitz, J.
1997-01-01
Understanding void fraction behavior in steady-state and dynamic environments is important to accurately predict the thermal-hydraulic behavior of two-phase or two-component systems. The Chexal-Lellouche (C-L) void fraction mode described herein covers the full range of pressures, flows, void fractions, and fluid types (steam-water, air-water, and refrigerants). A drift flux model formulation is used which covers the complete range of concurrent and countercurrent flows. The (1996) model revises the earlier C-L void fraction correlation, improves the capability of the model in countercurrent flow based on the incorporation of additional data, and improves the characteristics of the correlation that are important in transient programs. The model has been qualified with data from a number of steady state two-phase and two-component tests, and has been incorporated into the transient analysis code RELAP5 and RETRAN-3D and evaluated with a variety of transient and steady state tests. A 'plug-in' module for the void fraction correlation has been developed and implemented in RELAP5 and RETRAN-3D. The module is available as source code for inclusion into other thermal-hydraulic programs and can be used in any program that utilizes the same interface variables
Performance Comparison of Sweeping/Steady Jet Actuators
Hirsch, Damian; Mercier, Justin; Noca, Flavio; Gharib, Morteza
2015-11-01
Flow control through the use of steady jet actuators has been used on various aircraft models since the late 1950's. However, the focus of recent studies has shifted towards the use of sweeping jets (fluidic oscillators) rather than steady jet actuators. In this work, experiments using various jet actuator designs were conducted at GALCIT's Lucas Wind Tunnel on a NACA 0012 vertical tail model similar to that of the Boeing 767 vertical stabilizer at Reynolds numbers ranging from 0.5 to 1.2 million. The rudder angle was fixed at 20 degrees. A total of 32 jet actuators were installed along the wingspan perpendicular to the trailing edge and the rudder shoulder of the vertical stabilizer. It is known that these types of flow control prevent separation. However, the goal of this work is to compare different jet designs and evaluate their performance. Parameters such as the number of actuators, their volumetric flow, and the wind tunnel speed were varied. The lift generation capabilities of steady and sweeping jet actuators were then compared. Another set of experiments was conducted to compare a new sweeping jet actuator design with one of the standard versions. Supported by Boeing.
DEFF Research Database (Denmark)
Nielsen, Peter V.
1974-01-01
Flow in air conditioned r ooms is examined by means of model experiments . The different gearnetries giving unsteady, steady three- dimensional and steady twodimensional flow are determined . Velacity profiles and temperature profiles are measured in some of the geometries. A numerical solution...... of the flow equations is demonstrated and the flow in air conditioned rooms in case of steady two dimensional flow is predi cted. Compari son with measured results is shown i n the case of small Archimedes numbers, and predictions are shown at high Archimedes numbers. A numerical prediction of f low and heat...
Characterization of steady streaming for a particle manipulation system.
Amit, Roni; Abadi, Avi; Kosa, Gabor
2016-04-01
Accurate positioning of biological cells or microscopic particle without directly contacting them is a challenging task in biomedical engineering. Various trapping methods for controlling the position of a particle have been suggested. The common driving methods are based on laser and ultrasonic actuation principles. In this work we suggest a design for a hydrodynamic particle manoeuvring system. The system operates using steady streaming in a viscous fluid media induced by high frequency vibration of piezoelectric cantilevers. A particle within the workspace of the system can be trapped and manipulated to a desired position by the fairly unidirectional flow field created by the beams. In this paper, the flow field in the particle manipulation system is characterized numerically and experimentally. We find that the flow field resembles the analytical solutions of a flow field created by an oscillating sphere. Furthermore, we validate numerically the quadratic relation between the steady streaming velocity and the vibration amplitude of the beam. The calibration of the piezoelectric actuator's oscillation amplitudes enables effective positioning of particles with a diameter of 20 um to 1 mm. We find that a 30X0.8X2 mm(3) piezoelectric beam vibrating at its first resonance frequency, 200 Hz, is able to move a particle at a typical flow velocity ranging between 0.05 mm/sec and 0.13 mm/s in 430 cSt Si oil (Re=0.2).
The steady-state tokamak program
International Nuclear Information System (INIS)
Politzer, D.A.; Nevins, W.M.
1992-01-01
This paper reports on a steady-state tokamak experiment (STE) needed to develop the technology and physics data base required for construction of a steady-state fusion power demonstration reactor in the early 21st century. The STE will provide an integrated facility for the development and demonstration of steady-state and particle handling, low-activation high-heat-flux components and materials, efficient current drive, and continuous plasma performance in steady-state, with reactor-like plasma conditions under severe conditions of heat and particle bombardment of the wall. The STE facility will also be used to develop operation and control scenarios for ITER
Directory of Open Access Journals (Sweden)
Denise M. de Almeida
2001-04-01
resistance of the flow and relation between the flowrate and the hydraulic head at 0.55 m drain-soil. The depth of water drained did not show significant difference at 5% probability level; however, the geotextile bidim OP-20 and XT-4 showed the best performance taking into account costs and instalation suitability. In relation to the sediment mass transported, the influence of the wrapper thickness using gravel was observed besides the option of geotextile as excelent filter. The importance of using drain wrappers was demonstrated by comparing the entrance resistance data for the treatments without wrapper (r ent = 0.0102 d m-1 and the 0.15 m gravel treatment (r ent = 0.0032 d m-1, allowing a 68.7% reduction.
Upscaling of Forchheimer flows
Aulisa, Eugenio; Bloshanskaya, Lidia I.; Efendiev, Yalchin R.; Ibragimov, Akif I.
2014-01-01
analytical results (Aulisa et al., 2009) [1] and formulate the resulting system in terms of a degenerate nonlinear flow equation for the pressure with the nonlinearity depending on the pressure gradient. The coarse scale parameters for the steady state
A surface capturing method for the efficient computation of steady water waves
Wackers, J.; Koren, B.
2008-01-01
A surface capturing method is developed for the computation of steady water–air flow with gravity. Fluxes are based on artificial compressibility and the method is solved with a multigrid technique and line Gauss–Seidel smoother. A test on a channel flow with a bottom bump shows the accuracy of the
Marenduzzo, D; Orlandini, E; Cates, M E; Yeomans, J M
2007-09-01
We report hybrid lattice Boltzmann (HLB) simulations of the hydrodynamics of an active nematic liquid crystal sandwiched between confining walls with various anchoring conditions. We confirm the existence of a transition between a passive phase and an active phase, in which there is spontaneous flow in the steady state. This transition is attained for sufficiently "extensile" rods, in the case of flow-aligning liquid crystals, and for sufficiently "contractile" ones for flow-tumbling materials. In a quasi-one-dimensional geometry, deep in the active phase of flow-aligning materials, our simulations give evidence of hysteresis and history-dependent steady states, as well as of spontaneous banded flow. Flow-tumbling materials, in contrast, rearrange themselves so that only the two boundary layers flow in steady state. Two-dimensional simulations, with periodic boundary conditions, show additional instabilities, with the spontaneous flow appearing as patterns made up of "convection rolls." These results demonstrate a remarkable richness (including dependence on anchoring conditions) in the steady-state phase behavior of active materials, even in the absence of external forcing; they have no counterpart for passive nematics. Our HLB methodology, which combines lattice Boltzmann for momentum transport with a finite difference scheme for the order parameter dynamics, offers a robust and efficient method for probing the complex hydrodynamic behavior of active nematics.
New Tore Supra steady state operating scenario
International Nuclear Information System (INIS)
Martin, G.; Parlange, F.; van Houtte, D.; Wijnands, T.
1995-01-01
This document deals with plasma control in steady state conditions. A new plasma control systems enabling feedback control of global plasma equilibrium parameters has been developed. It also enables to operate plasma discharge in steady state regime. (TEC). 4 refs., 5 figs
Hydrodynamics of stratified epithelium: Steady state and linearized dynamics
Yeh, Wei-Ting; Chen, Hsuan-Yi
2016-05-01
A theoretical model for stratified epithelium is presented. The viscoelastic properties of the tissue are assumed to be dependent on the spatial distribution of proliferative and differentiated cells. Based on this assumption, a hydrodynamic description of tissue dynamics at the long-wavelength, long-time limit is developed, and the analysis reveals important insights into the dynamics of an epithelium close to its steady state. When the proliferative cells occupy a thin region close to the basal membrane, the relaxation rate towards the steady state is enhanced by cell division and cell apoptosis. On the other hand, when the region where proliferative cells reside becomes sufficiently thick, a flow induced by cell apoptosis close to the apical surface enhances small perturbations. This destabilizing mechanism is general for continuous self-renewal multilayered tissues; it could be related to the origin of certain tissue morphology, tumor growth, and the development pattern.
Theoretical analysis of steady state operating forces in control valves
Directory of Open Access Journals (Sweden)
Basavaraj Hubballi
2018-01-01
Full Text Available The controlling components, such as valves are used to regulate controlled fluid power. It is not always possible to calculate valve forces accurately, and with some types of valves even the existence of certain types of forces cannot be predicted with certainty. In many cases, however, the analysis can be made fairly completely and accurately. The assumption of steady state conditions is valid for the valve alone, but transient effects in the rest of the system may be large. These effects are particularly important with regard to the instability of valves, where the system may react on the valve in such a way as to make it squeal or oscillate, sometimes with large amplitude. The origin of the steady state flow force understood from a brief qualitative explanation. The following paper will summarize much of what is known about valve forces in the spool type controlling element.
An efficient and general numerical method to compute steady uniform vortices
Luzzatto-Fegiz, Paolo; Williamson, Charles H. K.
2011-07-01
Steady uniform vortices are widely used to represent high Reynolds number flows, yet their efficient computation still presents some challenges. Existing Newton iteration methods become inefficient as the vortices develop fine-scale features; in addition, these methods cannot, in general, find solutions with specified Casimir invariants. On the other hand, available relaxation approaches are computationally inexpensive, but can fail to converge to a solution. In this paper, we overcome these limitations by introducing a new discretization, based on an inverse-velocity map, which radically increases the efficiency of Newton iteration methods. In addition, we introduce a procedure to prescribe Casimirs and remove the degeneracies in the steady vorticity equation, thus ensuring convergence for general vortex configurations. We illustrate our methodology by considering several unbounded flows involving one or two vortices. Our method enables the computation, for the first time, of steady vortices that do not exhibit any geometric symmetry. In addition, we discover that, as the limiting vortex state for each flow is approached, each family of solutions traces a clockwise spiral in a bifurcation plot consisting of a velocity-impulse diagram. By the recently introduced "IVI diagram" stability approach [Phys. Rev. Lett. 104 (2010) 044504], each turn of this spiral is associated with a loss of stability for the steady flows. Such spiral structure is suggested to be a universal feature of steady, uniform-vorticity flows.
2016-09-01
10 Fig. 5 Pitching-moment coefficient for BF comparing dα variation to steady-state results, CFL = 10 and N = 50...11 Fig. 6 Roll-torque coefficient for BF comparing dα variation to steady-state results, CFL = 10 and N = 50...compute the flow solution. The Goldberg 3-equation k-ε-Rt turbulence model ( Goldberg et. al. 1998) was implemented in this study based on the findings
A new approach for solving the three-dimensional steady Euler equations. I - General theory
Chang, S.-C.; Adamczyk, J. J.
1986-01-01
The present iterative procedure combines the Clebsch potentials and the Munk-Prim (1947) substitution principle with an extension of a semidirect Cauchy-Riemann solver to three dimensions, in order to solve steady, inviscid three-dimensional rotational flow problems in either subsonic or incompressible flow regimes. This solution procedure can be used, upon discretization, to obtain inviscid subsonic flow solutions in a 180-deg turning channel. In addition to accurately predicting the behavior of weak secondary flows, the algorithm can generate solutions for strong secondary flows and will yield acceptable flow solutions after only 10-20 outer loop iterations.
Response of surface buoy moorings in steady and wave flows
Digital Repository Service at National Institute of Oceanography (India)
Anand, N.M.; Nayak, B.U.; SanilKumar, V.
A numerical model has been developed to evaluate the dynamics of surface buoy mooring systems under wave and current loading. System tension response and variation of tension in the mooring line at various depths have been evaluated for deep water...
Obtaining contaminant arrival distributions for steady flow in heterogeneous systems
International Nuclear Information System (INIS)
Anon.
1977-01-01
The versatility of the new contaminant arrival distributions for determining environmental consequences of subsurface pollution problems is demonstrated through application to a field example involving land drainage in heterogeneous porous materials. Though the four phases of the hydrologic evaluations are complicated because of the material heterogeneity encountered in the field problem, the arrival distributions still effectively summarize the minimal amount of data required to determine the environmental implications. These arrival distributions yield a single graph or tabular set of data giving the consequences of the subsurface pollution problems. Accordingly, public control authorities would be well advised to request that the results of subsurface pollution investigations be provided in the form of arrival distributions and the resulting simpler summary curve or tabulation. Such an objective is most easily accomplished through compliance with the requirements for assuring a complete subsurface evaluation
A design of steady state fusion burner
International Nuclear Information System (INIS)
Hasegawa, Akira; Hatori, Tadatsugu; Itoh, Kimitaka; Ikuta, Takashi; Kodama, Yuji.
1975-01-01
We present a brief design of a steady state fusion burner in which a continuous burning of nuclear fuel may be achieved with output power of a gigawatt. The laser fusion is proposed to ignite the fuel. (auth.)
Surface wave propagation in steady ideal Hall-magnetohydrodynamic magnetic slabs
International Nuclear Information System (INIS)
Miteva, Rossitsa; Zhelyazkov, Ivan; Erdelyi, Robert
2003-01-01
This paper studies the dispersion characteristics of sausage and kink surface waves traveling along a plasma layer within the framework of Hall magnetohydrodynamics in steady state. While in a static plasma slab these waves are Alfven ones (their phase velocities are close to the Alfven speed in the layer); in a slab with steady flows they may become super Alfvenic waves. Moreover, there exist two types of waves: forward and backward ones bearing in mind that the flow velocity defines the positive (forward) direction. As a typical representative of a magnetic slab in steady state here is considered a solar wind flux rope with a finite β plasma flow (typically β∼1).The forward sausage surface mode exhibits an increased dispersion at small wave numbers while the forward kink waves become practically non-dispersive. Both backward propagating sausage and kink surface modes show an increased dispersion for large wave numbers
Pellet injectors for steady state plasma fuelling
International Nuclear Information System (INIS)
Vinyar, I.; Geraud, A.; Yamada, H.; Lukin, A.; Sakamoto, R.; Skoblikov, S.; Umov, A.; Oda, Y.; Gros, G.; Krasilnikov, I.; Reznichenko, P.; Panchenko, V.
2005-01-01
Successful steady state operation of a fusion reactor should be supported by repetitive pellet injection of solidified hydrogen isotopes in order to produce high performance plasmas. This paper presents pneumatic pellet injectors and its implementation for long discharge on the LHD and TORE SUPRA, and a new centrifuge pellet injector test results. All injectors are fitted with screw extruders well suited for steady state operation
Directory of Open Access Journals (Sweden)
Roberto R Filgueira
2006-07-01
encontraron diferencias significativas entre las medias de todos los sitios para S0, mientras que para K0 no se encontró diferencia entre las medias de los sitios de labranza convencional y pastura, pero ambos fueron diferentes estadísticamente a la K0 media del sitio compactado.Soil management influences physical properties of the soil, mainly hydraulic functions. Their measurement have been one of the research preferences in Soil Physics. Tension disc infiltrometer has become a valuable instrument for the in situ measurement of soil surface hydraulic properties. Methods of analysis of the information obtained with this instrument have generally relied on the restrictive assumptions of steady-state infiltration at large times, but today approximate analytical expressions for three-dimension unsteady, unconfined flow out of a disc infiltrometer, are also available. In our study field tension infiltrometer measurements were run on a clay loam soil with different agricultural practices to determine sorptivity and saturated hydraulic conductivity, using steady- and unsteady-state water flow models. From steady state flow model, results obtained for sorptivity (S0 ranged from 26.8 to 58.5 mm h-1/2 and saturated hydraulic conductivity (K0 ranged from 41.7 to 78.2 mm h-1, for conventional tillage and praire site, meanwhile S0 ranged form 23.9 to 51.2 mm h-1/2 and K0 between 19.0 and 45.7 mm h-1 for the compacted site. Mean values of sorptivity were not statistically different between sites, meanwhile saturated hydraulic conductivity means were not different for conventional tillage and praire sites, but both means were different from the compacted site mean. From unsteady state flow model sorptivity values ranged from 10.9 to 36.6 mm h-1/2 and K0 values ranged between 58.6 and 189.3 mm h-1 for conventional tillage management and natural prairie sites. For the compacted site S0 values ranged from 15.8 to 33.9 mm h-1/2 and for K0 values from 13.6 to 71.5 mm h-1. Mean values of
Steady state statistical correlations predict bistability in reaction motifs.
Chakravarty, Suchana; Barik, Debashis
2017-03-28
Various cellular decision making processes are regulated by bistable switches that take graded input signals and convert them to binary all-or-none responses. Traditionally, a bistable switch generated by a positive feedback loop is characterized either by a hysteretic signal response curve with two distinct signaling thresholds or by characterizing the bimodality of the response distribution in the bistable region. To identify the intrinsic bistability of a feedback regulated network, here we propose that bistability can be determined by correlating higher order moments and cumulants (≥2) of the joint steady state distributions of two components connected in a positive feedback loop. We performed stochastic simulations of four feedback regulated models with intrinsic bistability and we show that for a bistable switch with variation of the signal dose, the steady state variance vs. covariance adopts a signatory cusp-shaped curve. Further, we find that the (n + 1)th order cross-cumulant vs. nth order cross-cumulant adopts a closed loop structure for at least n = 3. We also propose that our method is capable of identifying systems without intrinsic bistability even though the system may show bimodality in the marginal response distribution. The proposed method can be used to analyze single cell protein data measured at steady state from experiments such as flow cytometry.
Toroidal visco-resistive magnetohydrodynamic steady states contain vortices
International Nuclear Information System (INIS)
Bates, J.W.; Montgomery, D.C.
1998-01-01
Poloidal velocity fields seem to be a fundamental feature of resistive toroidal magnetohydrodynamic (MHD) steady states. They are a consequence of force balance in toroidal geometry, do not require any kind of instability, and disappear in the open-quotes straight cylinderclose quotes (infinite aspect ratio) limit. If a current density j results from an axisymmetric toroidal electric field that is irrotational inside a torus, it leads to a magnetic field B such that ∇x(jxB) is nonvanishing, so that the Lorentz force cannot be balanced by the gradient of any scalar pressure in the equation of motion. In a steady state, finite poloidal velocity fields and toroidal vorticity must exist. Their calculation is difficult, but explicit solutions can be found in the limit of low Reynolds number. Here, existing calculations are generalized to the more realistic case of no-slip boundary conditions on the velocity field and a circular toroidal cross section. The results of this paper strongly suggest that discussions of confined steady states in toroidal MHD must include flows from the outset. copyright 1998 American Institute of Physics
NASA Lewis Steady-State Heat Pipe Code Architecture
Mi, Ye; Tower, Leonard K.
2013-01-01
NASA Glenn Research Center (GRC) has developed the LERCHP code. The PC-based LERCHP code can be used to predict the steady-state performance of heat pipes, including the determination of operating temperature and operating limits which might be encountered under specified conditions. The code contains a vapor flow algorithm which incorporates vapor compressibility and axially varying heat input. For the liquid flow in the wick, Darcy s formula is employed. Thermal boundary conditions and geometric structures can be defined through an interactive input interface. A variety of fluid and material options as well as user defined options can be chosen for the working fluid, wick, and pipe materials. This report documents the current effort at GRC to update the LERCHP code for operating in a Microsoft Windows (Microsoft Corporation) environment. A detailed analysis of the model is presented. The programming architecture for the numerical calculations is explained and flowcharts of the key subroutines are given
Practical steady-state enzyme kinetics.
Lorsch, Jon R
2014-01-01
Enzymes are key components of most biological processes. Characterization of enzymes is therefore frequently required during the study of biological systems. Steady-state kinetics provides a simple and rapid means of assessing the substrate specificity of an enzyme. When combined with site-directed mutagenesis (see Site-Directed Mutagenesis), it can be used to probe the roles of particular amino acids in the enzyme in substrate recognition and catalysis. Effects of interaction partners and posttranslational modifications can also be assessed using steady-state kinetics. This overview explains the general principles of steady-state enzyme kinetics experiments in a practical, rather than theoretical, way. Any biochemistry textbook will have a section on the theory of Michaelis-Menten kinetics, including derivations of the relevant equations. No specific enzymatic assay is described here, although a method for monitoring product formation or substrate consumption over time (an assay) is required to perform the experiments described. © 2014 Elsevier Inc. All rights reserved.
Angular momentum transfer in steady disk accretion
International Nuclear Information System (INIS)
Gorbatskij, V.G.
1977-01-01
The conditions of steady disk accretion have been investigated. The disk axisymmetric model is considered. It is shown that the gas is let at the outer boundary of the disk with the azimuthal velocity which is slightly less than the Kepler circular one. Gas possesses the motion quality moment which is transferred from the outer layers of the disk to the surface of the star. The steady state of the disk preserved until the inflow of the moment to the star increases its rotation velocity up to magnitudes close to the critical one
Methods of computing steady-state voltage stability margins of power systems
Chow, Joe Hong; Ghiocel, Scott Gordon
2018-03-20
In steady-state voltage stability analysis, as load increases toward a maximum, conventional Newton-Raphson power flow Jacobian matrix becomes increasingly ill-conditioned so power flow fails to converge before reaching maximum loading. A method to directly eliminate this singularity reformulates the power flow problem by introducing an AQ bus with specified bus angle and reactive power consumption of a load bus. For steady-state voltage stability analysis, the angle separation between the swing bus and AQ bus can be varied to control power transfer to the load, rather than specifying the load power itself. For an AQ bus, the power flow formulation is only made up of a reactive power equation, thus reducing the size of the Jacobian matrix by one. This reduced Jacobian matrix is nonsingular at the critical voltage point, eliminating a major difficulty in voltage stability analysis for power system operations.
Structure of a steady drain-hole vortex in a viscous fluid
DEFF Research Database (Denmark)
Bøhling, Lasse; Andersen, Anders Peter; Fabre, D.
2010-01-01
We use direct numerical simulations to study a steady bathtub vortex in a cylindrical tank with a central drain-hole, a fiat stress-free surface and velocity prescribed at the inlet. We find that the qualitative structure of the meridional flow does not depend on the radial Reynolds number, where...
Steady-state spheromak reactor studies
International Nuclear Information System (INIS)
Krakowski, R.A.; Hagenson, R.L.
1985-01-01
After summarizing the essential elements of a gun-sustained spheromak, the potential for a steady-state is explored by means of a comprehensive physics/engineering/costing model. A range of cost-optimized reactor design points is presented, and the sensitivity of cost to key physics, engineering, and operational variables is reported
Marketing aspects of steady growth business strategy
GONCHAR V.; KALININ O.
2015-01-01
The article analyzed the importance of marketing to achieve steady business growth, the main strategy of internal development and marketing of its level of development, achieving competitive advantage and the main directions of marketing management. The examples of marketing strategies for leading corporations were described. The problems and prospects of the business strategy of extensive growth and diversification were made.
Steady-State Creep of Asphalt Concrete
Directory of Open Access Journals (Sweden)
Alibai Iskakbayev
2017-02-01
Full Text Available This paper reports the experimental investigation of the steady-state creep process for fine-grained asphalt concrete at a temperature of 20 ± 2 °С and under stress from 0.055 to 0.311 MPa under direct tension and was found to occur at a constant rate. The experimental results also determined the start, the end point, and the duration of the steady-state creep process. The dependence of these factors, in addition to the steady-state creep rate and viscosity of the asphalt concrete on stress is satisfactorily described by a power function. Furthermore, it showed that stress has a great impact on the specific characteristics of asphalt concrete: stress variation by one order causes their variation by 3–4.5 orders. The described relations are formulated for the steady-state of asphalt concrete in a complex stressed condition. The dependence is determined between stress intensity and strain rate intensity.
Chang, Paul K
2014-01-01
Interdisciplinary and Advanced Topics in Science and Engineering, Volume 3: Separation of Flow presents the problem of the separation of fluid flow. This book provides information covering the fields of basic physical processes, analyses, and experiments concerning flow separation.Organized into 12 chapters, this volume begins with an overview of the flow separation on the body surface as discusses in various classical examples. This text then examines the analytical and experimental results of the laminar boundary layer of steady, two-dimensional flows in the subsonic speed range. Other chapt
DEFF Research Database (Denmark)
Brøns, Morten; Voigt, Lars Peter Køllgaard; Sørensen, Jens Nørkær
1998-01-01
Using a combination of bifurcation theory for two-dimensional dynamical systems and numerical simulations, we systematically determine the possible flow topologies of the steady vortex breakdown in axisymmetric flow in a cylindrical container with rotating end-covers. For fixed values...
DEFF Research Database (Denmark)
Brøns, Morten; Voigt, Lars Peter Kølgaard; Sørensen, Jens Nørkær
1999-01-01
Using a combination of bifurcation theory for two-dimensional dynamical systems and numerical simulations, we systematically determine the possible flow topologies of the steady vortex breakdown in axisymmetric flow in a cylindrical container with rotating end-covers. For fixed values of the ratio...
Steady-state operation of spheromaks by inductive techniques
International Nuclear Information System (INIS)
Janos, A.
1984-04-01
A method to maintain a steady-state spheromak configuration inductively using the S-1 Spheromak device is described. The S-1 Spheromak formation apparatus can be utilized to inject magnetic helicity continuously (C.W., not pulsed or D.C.) into the spheromak configuration after equilibrium is achieved in the linked mode of operation. Oscillation of both poloidal- and toroidal-field currents in the flux core (psi-phi Pumping), with proper phasing, injects a net time-averaged helicity into the plasma. Steady-state maintenance relies on flux conversion, which has been earlier identified. Relevant experimental data from the operation of S-1 are described. Helicity flow has been measured and the proposed injection scheme simulated. In a reasonable time practical voltages and frequencies can inject an amount of helicity comparable to that in the initial plasma. Plasma currents can be maintained or increased. This pumping technique is similar to F-THETA Pumping of a Reversed-Field-Pinch but is applied to this inverse-pinch formation
Pulsatile versus steady infusions for hepatic artery chemotherapy
International Nuclear Information System (INIS)
Kim, E.E.; Haynie, T.P.; Wright, K.C.; Chaynsangavej, C.; Gianturco, C.; Lamki, L.; Wallace, S.
1984-01-01
Hepatic artery chemotherapy for unresectable liver tumors requires an even distribution of the drugs in the tumor or vascular bed. This cannot be determined angiographically because the drugs are infused at a much lower rate than the contrast media. It is easy, however, to determine the quality of the perfusion by injecting a small volume of Tc-99m MAA in one of the side ports while chemotherapeutic agent is being infused at the same rate. Usually this shows a uniform, satisfactory distribution of isotope. Occasionally, however, some areas fail to receive Tc-99m in spite of what appears to be a good position of the catheter tip. Since ''streaming'' of the infused drugs has been blamed for their uneven distribution, the authors decided to compare the usual steady flow infusions with infusions made pulsatile by the addition of a pulsing device (Gianturco Pump) attached to the infusion tubing. Eighty-three patients were studied with steady as well as pulsatile infusions. In 16 of these patients the perfusion pattern was definitely changed by the pulsatile infusion. In one patient the pulsatile mode resulted in an unwanted gastric perfusion. In 5 patients the distribution was improved in one hepatic lobe and in 10 patients it was improved in both lobes. These results show that hepatic artery perfusions can occasionally be improved by pulsing the infusate. However, pulsing can produce the unwanted perfusion of extra-hepatic areas
3-D numerical modelling of flow around a groin
DEFF Research Database (Denmark)
Miller, R.; Roulund, A.; Sumer, B. Mutlu
2003-01-01
A 3-D flow code, EllipSys3D, has been implemented to simulate the 3-D flow around a groin in steady current. The k turbulence model has been used for closure. Two kinds of groins are considered: (1) A vertical-wall groin, and (2) A groin with a side slope. Steady-flow simulations were conducted...
Steady state compact toroidal plasma production
Turner, William C.
1986-01-01
Apparatus and method for maintaining steady state compact toroidal plasmas. A compact toroidal plasma is formed by a magnetized coaxial plasma gun and held in close proximity to the gun electrodes by applied magnetic fields or magnetic fields produced by image currents in conducting walls. Voltage supply means maintains a constant potential across the electrodes producing an increasing magnetic helicity which drives the plasma away from a minimum energy state. The plasma globally relaxes to a new minimum energy state, conserving helicity according to Taylor's relaxation hypothesis, and injecting net helicity into the core of the compact toroidal plasma. Controlling the voltage so as to inject net helicity at a predetermined rate based on dissipative processes maintains or increases the compact toroidal plasma in a time averaged steady state mode.
Steady state of tapped granular polygons
International Nuclear Information System (INIS)
Carlevaro, Carlos M; Pugnaloni, Luis A
2011-01-01
The steady state packing fraction of a tapped granular bed is studied for different grain shapes via a discrete element method. Grains are monosized regular polygons, from triangles to icosagons. Comparisons with disc packings show that the steady state packing fraction as a function of the tapping intensity presents the same general trends in polygon packings. However, better packing fractions are obtained, as expected, for shapes that can tessellate the plane (triangles, squares and hexagons). In addition, we find a sharp transition for packings of polygons with more than 13 vertices signaled by a discontinuity in the packing fraction at a particular tapping intensity. Density fluctuations for most shapes are consistent with recent experimental findings in disc packing; however, a peculiar behavior is found for triangles and squares
BR2 reactor core steady state transient modeling
International Nuclear Information System (INIS)
Makarenko, A.; Petrova, T.
2000-01-01
A coupled neutronics/hydraulics/heat-conduction model of the BR2 reactor core is under development at SCK-CEN. The neutron transport phenomenon has been implemented as steady state and time dependent nodal diffusion. The non-linear heat conduction equation in-side fuel elements is solved with a time dependent finite element method. To allow coupling between functional modules and to simulate subcooled regimes, a simple single-phase hydraulics has been introduced, while the two-phase hydraulics is under development. Multiple tests, general benchmark cases as well as calculation/experiment comparisons demonstrated a good accuracy of both neutronic and thermal hydraulic models, numerical reliability and full code portability. A refinement methodology has been developed and tested for better neutronic representation in hexagonal geometry. Much effort is still needed to complete the development of an extended cross section library with kinetic data and two-phase flow representation. (author)
An adaptive finite element method for steady and transient problems
International Nuclear Information System (INIS)
Benner, R.E. Jr.; Davis, H.T.; Scriven, L.E.
1987-01-01
Distributing integral error uniformly over variable subdomains, or finite elements, is an attractive criterion by which to subdivide a domain for the Galerkin/finite element method when localized steep gradients and high curvatures are to be resolved. Examples are fluid interfaces, shock fronts and other internal layers, as well as fluid mechanical and other boundary layers, e.g. thin-film states at solid walls. The uniform distribution criterion is developed into an adaptive technique for one-dimensional problems. Nodal positions can be updated simultaneously with nodal values during Newton iteration, but it is usually better to adopt nearly optimal nodal positions during Newton iteration upon nodal values. Three illustrative problems are solved: steady convection with diffusion, gradient theory of fluid wetting on a solid surface and Buckley-Leverett theory of two phase Darcy flow in porous media
On Steady-State Tropical Cyclones
2014-01-01
Press: London. Marks FD, Black PG, Montgomery MT, Burpee RW. 2008. Structure of the eye and eyewall of Hurricane Hugo (1989). Mon. Weather Rev. 136: 1237... hurricanes ; tropical cyclones; typhoons; steady-state Received 18 April 2013; Revised 25 November 2013; Accepted 29 December 2013; Published online in Wiley...the concept of the ‘mature stage’ of a hurricane vortex. The definition of the ‘mature stage’ is commonly based on the time period in which the maximum
Steady State versus Pulsed Tokamak DEMO
Energy Technology Data Exchange (ETDEWEB)
Orsitto, F.P., E-mail: francesco.orsitto@enea.it [Associazione EURATOM-ENEA Unita Tecnica Fusione, Frascati (Italy); Todd, T. [CCFE/Fusion Association, Culham Science Centre, Abingdon (United Kingdom)
2012-09-15
Full text: The present report deals with a Review of problems for a Steady state(SS) DEMO, related argument is treated about the models and the present status of comparison between the characteristics of DEMO pulsed versus a Steady state device.The studied SS DEMO Models (SLIM CS, PPCS model C EU-DEMO, ARIES-RS) are analyzed from the point of view of the similarity scaling laws and critical issues for a steady state DEMO. A comparison between steady state and pulsed DEMO is therefore carried out: in this context a new set of parameters for a pulsed (6 - 8 hours pulse) DEMO is determined working below the density limit, peak temperature of 20 keV, and requiring a modest improvement in the confinement factor(H{sub IPBy2} = 1.1) with respect to the H-mode. Both parameters density and confinement parameter are lower than the DEMO models presently considered. The concept of partially non-inductive pulsed DEMO is introduced since a pulsed DEMO needs heating and current drive tools for plasma stability and burn control. The change of the main parameter design for a DEMO working at high plasma peak temperatures T{sub e} {approx} 35 keV is analyzed: in this range the reactivity increases linearly with temperature, and a device with smaller major radius (R = 7.5 m) is compatible with high temperature. Increasing temperature is beneficial for current drive efficiency and heat load on divertor, being the synchrotron radiation one of the relevant components of the plasma emission at high temperatures and current drive efficiency increases with temperature. Technology and engineering problems are examined including efficiency and availability R&D issues for a high temperature DEMO. Fatigue and creep-fatigue effects of pulsed operations on pulsed DEMO components are considered in outline to define the R&D needed for DEMO development. (author)
Steady-state bifurcations of the three-dimensional Kolmogorov problem
Directory of Open Access Journals (Sweden)
Zhi-Min Chen
2000-08-01
Full Text Available This paper studies the spatially periodic incompressible fluid motion in $mathbb R^3$ excited by the external force $k^2(sin kz, 0,0$ with $kgeq 2$ an integer. This driving force gives rise to the existence of the unidirectional basic steady flow $u_0=(sin kz,0, 0$ for any Reynolds number. It is shown in Theorem 1.1 that there exist a number of critical Reynolds numbers such that $u_0$ bifurcates into either 4 or 8 or 16 different steady states, when the Reynolds number increases across each of such numbers.
Current drive efficiency requirements for an attractive steady-state reactor
Energy Technology Data Exchange (ETDEWEB)
Tonon, G
1994-12-31
The expected values of the figure of merit and the electrical efficiency of various non-inductive current drive methods are considered. The main experimental results achieved today with neutral beams and radiofrequency systems are summarized. Taking into account the simplified energy flow diagram of a steady state reactor, the figure of merit and the electrical efficiency values which are necessary in order to envisage an attractive steady-state reactor are determined. These values are compared to the theoretical predictions. (author). 16 refs., 11 figs., 2 tabs.
SUPERENERGY-2: a multiassembly, steady-state computer code for LMFBR core thermal-hydraulic analysis
Energy Technology Data Exchange (ETDEWEB)
Basehore, K.L.; Todreas, N.E.
1980-08-01
Core thermal-hydraulic design and performance analyses for Liquid Metal Fast Breeder Reactors (LMFBRs) require repeated detailed multiassembly calculations to determine radial temperature profiles and subchannel outlet temperatures for various core configurations and subassembly structural analyses. At steady-state, detailed core-wide temperature profiles are required for core restraint calculations and subassembly structural analysis. In addition, sodium outlet temperatures are routinely needed for each reactor operating cycle. The SUPERENERGY-2 thermal-hydraulic code was designed specifically to meet these designer needs. It is applicable only to steady-state, forced-convection flow in LMFBR core geometries.
Steady fall of isothermal, resistive-viscous, compressible fluid across magnetic field
Energy Technology Data Exchange (ETDEWEB)
Low, B. C., E-mail: low@ucar.edu [High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado 80301 (United States); Egan, A. K., E-mail: andrea.egan@colorado.edu [Barnard College, New York, New York 10027, USA and Department of Physics, Colorado University, Boulder, Colorado 80309 (United States)
2014-06-15
This is a basic MHD study of the steady fall of an infinite, vertical slab of isothermal, resistive-viscous, compressible fluid across a dipped magnetic field in uniform gravity. This double-diffusion steady flow in unbounded space poses a nonlinear but numerically tractable, one-dimensional (1D) free-boundary problem, assuming constant coefficients of resistivity and viscosity. The steady flow is determined by a dimensionless number μ{sub 1} proportional to the triple product of the two diffusion coefficients and the square of the linear total mass. For a sufficiently large μ{sub 1}, the Lorentz, viscous, fluid-pressure, and gravitational forces pack and collimate the fluid into a steady flow of a finite width defined by the two zero-pressure free-boundaries of the slab with vacuum. The viscous force is essential in this collimation effect. The study conjectures that in the regime μ{sub 1}→0, the 1D steady state exists only for μ{sub 1}∈Ω, a spectrum of an infinite number of discrete values, including μ{sub 1} = 0 that corresponds to two steady states, the classical zero-resistivity static slab of Kippenhahn and Schlüter [R. Kippenhahn and A. Schlüter, Z. Astrophys. 43, 36 (1957)] and its recent generalization [B. C. Low et al., Astrophys. J. 755, 34 (2012)] to admit an inviscid resistive flow. The pair of zero-pressure boundaries of each of the μ{sub 1}→0 steady-state slabs are located at infinity. Computational evidence suggests that the Ω steady-states are densely distributed around μ{sub 1} = 0, as an accumulation point, but are sparsely separated by open intervals of μ{sub 1}-values for which the slab must be either time-dependent or spatially multi-dimensional. The widths of these intervals are vanishingly small as μ{sub 1}→0. This topological structure of physical states is similar to that described by Landau and Liftshitz [L. D. Landau and E. M. Lifshitz, Fluid Mechanics (Addison-Wesley, Reading, MA, 1959)] to explain the onset
Current drive efficiency requirements for an attractive steady-state reactor
International Nuclear Information System (INIS)
Tonon, G.
1994-01-01
The expected values of the figure of merit and the electrical efficiency of various non-inductive current drive methods are considered. The main experimental results achieved today with neutral beams and radiofrequency systems are summarized. Taking into account the simplified energy flow diagram of a steady state reactor, the figure of merit and the electrical efficiency values which are necessary in order to envisage an attractive steady-state reactor are determined. These values are compared to the theoretical predictions. (author). 16 refs., 11 figs., 2 tabs
SUPERENERGY-2: a multiassembly, steady-state computer code for LMFBR core thermal-hydraulic analysis
International Nuclear Information System (INIS)
Basehore, K.L.; Todreas, N.E.
1980-08-01
Core thermal-hydraulic design and performance analyses for Liquid Metal Fast Breeder Reactors (LMFBRs) require repeated detailed multiassembly calculations to determine radial temperature profiles and subchannel outlet temperatures for various core configurations and subassembly structural analyses. At steady-state, detailed core-wide temperature profiles are required for core restraint calculations and subassembly structural analysis. In addition, sodium outlet temperatures are routinely needed for each reactor operating cycle. The SUPERENERGY-2 thermal-hydraulic code was designed specifically to meet these designer needs. It is applicable only to steady-state, forced-convection flow in LMFBR core geometries
Simulation of steady-state natural convection using CFD
Energy Technology Data Exchange (ETDEWEB)
Zitzmann, T.; Pfrommer, P. [Univ. of Applied Sciences, Coberg (Germany); Cook, M.; Rees, S.; Marjanovic, L. [De Montfort Univ., Leicester (United Kingdom). Inst. of Energy and Sustainable Development
2005-07-01
Building materials play an important role in the creation of comfortable indoor environments and can reduce dependence on high energy use mechanical systems. Correct predictions between building structure and heat transfer are needed in order to achieve optimal conditions. Heat transfer is dependent on the velocity and temperature distribution in a room, particularly in the wall boundary layer. This paper discussed the modeling of air flow and heat transfer over a heated vertical plate in a differentially-heated cavity using Computational Fluid Dynamics (CFD). Guidelines on the use of CFD with unstructured meshes to model buoyancy-driven flow in a cavity were presented. Benchmark CFD results were compared with published analytical data. The finite volume method was employed using an unstructured mesh containing tetrahedral and prism elements, so that local numerical diffusion was reduced and therefore suitable for complex flows. The code was based on a couple solver for solving the differential equations using the fully implicit discretization method. Hydrodynamic equations were treated as one single system. A false time stepping method was used to reduce the number of iterations required for convergence, which also guided the solutions to a steady-state solution. It was concluded that the methodology achieves accurate predictions, and is suitable for the modeling of heat transfer optimizations. 13 refs., 7 figs.
Steady three-fluid coronal expansion for nonspherical geometries
International Nuclear Information System (INIS)
Joselyn, J.; Holzer, T.E.
1978-01-01
A steady three-fluid model of the solar coronal expansionk in which 4 He ++ ions (alphas) are treated as a nonminor species, is developed for nonspherically symmetric flow geometries of the general sort thought to be characteristic of coronal holes. It is found that the very high mass fluxes in the low corona, which are associated with rapidly diverging flow geometries, lead to a locally enhanced frictional coupling between protons and alphas and consequently to a significant reduction of the He/H abundance ratio in the lower corona from that normally predicted by multifluid models. In the models considered, the frictional drag on the protons by the alphas (a process neglected in most studies) is found to play an important role near the sun. Heavy ions, other than alphas, are treated as minor species and are seen to exhibit varying responses to the rapidly diverging flow geometries, depending on the ion mass and charge. As for the protons, the frictional effect of the alphas on the heavier ions is found to be significant in the models considered
Structural evaluation of FHX for PGSFR at steady state condition
Energy Technology Data Exchange (ETDEWEB)
Kim, Nak-Hyun; Lee, S. Y.; Kim, S. K. [KAERI, Daejeon (Korea, Republic of)
2016-05-15
Liquid sodium flows inside the heat transfer tubes and atmospheric air flows over the finned tubes. The configuration and overall shape of the unit are shown in Figure 1. The unit is placed in the upper region of the reactor building and has function of dumping the system heat load into the final heat sink, i.e., the atmosphere. Heat is transmitted from the primary cold sodium pool into the ADHRS sodium loop via DHX (Decay Heat Exchanger), and a direct heat exchange occurs between the tube-side sodium and the shell-side air through the FHX tube wall. Cold atmospheric air is introduced into the air inlet duct at the lower part of the unit by using an electrically operated air blower or by the natural circulation force. Air flows across the finned tube bank rising upward direction to make uniform air flow with perfect mixing across the tubes. The finned tube bundle is placed inside a well-insulated casing. The air heated at the tube bank region is collected at the top of the unit and then is discharged through the air stack above the unit. Although a blower supplies atmospheric cooling air into the FHX unit, a tall air stack of 30 m in height is also provided to secure natural draft head of natural circulation air flow against a loss of power supply. The structural analysis of a FHX are carried out and its structural integrity under the given service levels is evaluated per ASME Code rule. The design loads according to design condition and normal operating steady condition are classified and stresses calculated from stress analyses are linearized and summarized in their stress components.
Heat transfer in turbocharger turbines under steady, pulsating and transient conditions
International Nuclear Information System (INIS)
Burke, R.D.; Vagg, C.R.M.; Chalet, D.; Chesse, P.
2015-01-01
Highlights: • Compare turbine heat transfer correlations from different studies. • Compare heat transfer for a same turbine on-engine and on gas-stand. • Analyse heat transfer under steady and transient operating conditions. • Gas stand heat transfer correlations are transferrable to engine conditions. • Heat flows can be reversed compared to steady conditions during transients. - Abstract: Heat transfer is significant in turbochargers and a number of mathematical models have been proposed to account for the heat transfer, however these have predominantly been validated under steady flow conditions. A variable geometry turbocharger from a 2.2 L Diesel engine was studied, both on gas stand and on-engine, under steady and transient conditions. The results showed that heat transfer accounts for at least 20% of total enthalpy change in the turbine and significantly more at lower mechanical powers. A convective heat transfer correlation was derived from experimental measurements to account for heat transfer between the gases and the turbine housing and proved consistent with those published from other researchers. This relationship was subsequently shown to be consistent between engine and gas stand operation: using this correlation in a 1D gas dynamics simulation reduced the turbine outlet temperature error from 33 °C to 3 °C. Using the model under transient conditions highlighted the effect of housing thermal inertia. The peak transient heat flow was strongly linked to the dynamics of the turbine inlet temperature: for all increases, the peak heat flow was higher than under thermally stable conditions due to colder housing. For all decreases in gas temperature, the peak heat flow was lower and for temperature drops of more than 100 °C the heat flow was reversed during the transient
Thermal response of a pin-type fusion reactor blanket during steady and transient reactor operation
International Nuclear Information System (INIS)
Grotz, S.; Ghoniem, N.M.
1986-02-01
The thermal analysis of the blanket examines both the steady-state and transient reactor operations. The steady-state analysis covers full power and fractional power operation whereas the transient analysis examines the effects of power ramps and blanket preheat. The blanket configuration chosen for this study is a helium cooled solid breeder design. We first discuss the full power, steady-state temperature fields in the first wall, beryllium rods, and breeder rods. Next we examine the effects of fractional power on coolant flow and temperature field distributions. This includes power plateaus of 10%, 20%, 50%, 80%, and 100% of full power. Also examined are the restrictions on the rates of power ramping between plateaus. Finally we discuss the power and time requirements for pre-heating the primary from cold iron conditions up to startup temperature (250 0 C)
DEFF Research Database (Denmark)
Chen, Peiyuan; Chen, Zhe; Bak-Jensen, Birgitte
2008-01-01
This paper reviews the development of the probabilistic load flow (PLF) techniques. Applications of the PLF techniques in different areas of power system steady-state analysis are also discussed. The purpose of the review is to identify different available PLF techniques and their corresponding...
Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing
Energy Technology Data Exchange (ETDEWEB)
Littlewood, R.P. [LaVisionUK Ltd, Grove, Oxon (United Kingdom); Passmore, M.A. [Loughborough University, Department of Aeronautical and Automotive Engineering, Loughborough (United Kingdom)
2012-08-15
A large contribution to the aerodynamic drag of a vehicle arises from the failure to fully recover pressure in the wake region, especially on squareback configurations. A degree of base pressure recovery can be achieved through careful shape optimisation, but the freedom of an automotive aerodynamicist to implement significant shape changes is limited by a variety of additional factors such styling, ergonomics and loading capacity. Active flow control technologies present the potential to create flow field modifications without the need for external shape changes and have received much attention in previous years within the aeronautical industry and, more recently, within the automotive industry. In this work the influence of steady blowing applied at a variety of angles on the roof trailing edge of a simplified 1/4 scale squareback style vehicle has been investigated. Hot-wire anemometry, force balance measurements, surface pressure measurements and PIV have been used to investigate the effects of the steady blowing on the vehicle wake structures and the resulting body forces. The energy consumption of the steady jet is calculated and is used to deduce an aerodynamic drag power change. Results show that overall gains can be achieved; however, the large mass flow rate required restricts the applicability of the technique to road vehicles. Means by which the mass flow rate requirements of the jet may be reduced are discussed and suggestions for further work put forward. (orig.)
Identification of Steady and Non-Steady Gait of Humanexoskeleton Walking System
Żur, K. K.
2013-08-01
In this paper a method of analysis of exoskeleton multistep locomotion was presented by using a computer with the preinstalled DChC program. The paper also presents a way to analytically calculate the ",motion indicator", as well as the algorithm calculating its two derivatives. The algorithm developed by the author processes data collected from the investigation and then a program presents the obtained final results. Research into steady and non-steady multistep locomotion can be used to design two-legged robots of DAR type and exoskeleton control system
An implicit steady-state initialization package for the RELAP5 computer code
International Nuclear Information System (INIS)
Paulsen, M.P.; Peterson, C.E.; Odar, F.
1995-08-01
A direct steady-state initialization (DSSI) method has been developed and implemented in the RELAP5 hydrodynamic analysis program. It provides a means for users to specify a small set of initial conditions which are then propagated through the remainder of the system. The DSSI scheme utilizes the steady-state form of the RELAP5 balance equations for nonequilibrium two-phase flow. It also employs the RELAP5 component models and constitutive model packages for wall-to-phase and interphase momentum and heat exchange. A fully implicit solution of the linearized hydrodynamic equations is implemented. An implicit coupling scheme is used to augment the standard steady-state heat conduction solution for steam generator use. It solves the primary-side tube region energy equations, heat conduction equations, wall heat flux boundary conditions, and overall energy balance equation as a coupled system of equations and improves convergence. The DSSI method for initializing RELAP5 problems to steady-state conditions has been compared with the transient solution scheme using a suite of test problems including; adiabatic single-phase liquid and vapor flow through channels with and without healing and area changes; a heated two-phase test bundle representative of BWR core conditions; and a single-loop PWR model
An accelerator based steady state neutron source
International Nuclear Information System (INIS)
Burke, R.J.; Johnson, D.L.
1985-01-01
Using high current, c.w. linear accelerator technology, a spallation neutron source can achieve much higher average intensities than existing or proposed pulsed spallation sources. With about 100 mA of 300 MeV protons or deuterons, the Accelerator Based Neutron Research Facility (ABNR) would initially achieve the 10 16 n/cm 2 .s thermal flux goal of the advanced steady state neutron source, and upgrading could provide higher steady state fluxes. The relatively low ion energy compared to other spallation sources has an important impact on R and D requirements as well as capital cost, for which a range of $300-450M is estimated by comparison to other accelerator-based neutron source facilities. The source is similar to a reactor source in most respects. It has some higher energy neutrons but fewer gamma rays, and the moderator region is free of many of the design constraints of a reactor, which helps to implement sources for various neutron energy spectra, many beam tubes, etc. With the development of multi-beam concept and the basis for currents greater than 100 mA that is assumed in the R and D plan, the ABNR would serve many additional uses, such as fusion materials development, production of proton-rich isotopes, and other energy and defense program needs
Statistical steady states in turbulent droplet condensation
Bec, Jeremie; Krstulovic, Giorgio; Siewert, Christoph
2017-11-01
We investigate the general problem of turbulent condensation. Using direct numerical simulations we show that the fluctuations of the supersaturation field offer different conditions for the growth of droplets which evolve in time due to turbulent transport and mixing. This leads to propose a Lagrangian stochastic model consisting of a set of integro-differential equations for the joint evolution of the squared radius and the supersaturation along droplet trajectories. The model has two parameters fixed by the total amount of water and the thermodynamic properties, as well as the Lagrangian integral timescale of the turbulent supersaturation. The model reproduces very well the droplet size distributions obtained from direct numerical simulations and their time evolution. A noticeable result is that, after a stage where the squared radius simply diffuses, the system converges exponentially fast to a statistical steady state independent of the initial conditions. The main mechanism involved in this convergence is a loss of memory induced by a significant number of droplets undergoing a complete evaporation before growing again. The statistical steady state is characterised by an exponential tail in the droplet mass distribution.
Karamanis, N.; Palfreyman, D.; Arcoumanis, C.; Martinez-Botas, R. F.
2006-07-01
The detailed flow characteristics of three high-pressure-ratio mixed-flow turbines were investigated under both steady and pulsating flow conditions. Two rotors featured a constant inlet blade angle, one with 12 blades and the second with 10. The third rotor was shorter and had a nominally constant incidence angle. The rotors find application on an automotive high-speed large commercial diesel turbocharger. The steady flow entering and exiting the blades has been quantified by a laser Doppler velocimetry system. The measurements were performed at a plane 3.0-mm ahead of the rotor leading edge and 9.5-mm downstream the rotor trailing edge. The turbine test conditions corresponded to the peak efficiency point at two rotational speeds, 29,400 and 41,300-rpm. The results were resolved in a blade-to-blade sense to examine fully the nature of the flow at turbocharger representative conditions. A correlation between the combined effects of incidence and exit flow angle with the isentropic efficiency has been verified. Regarding pulsating flow, the velocity data and their corresponding instantaneous velocity triangles were resolved in a blade-to-blade sense to understand better the complex phenomenon. The results highlighted the potential of a nominally constant incidence design to absorb better the inadequacy of the volute to discharge the exhaust gas uniformly along the blade leading edge. A double vortex rotating in a clockwise sense propagated on the plane normal to the meridional direction. This should be attributed to the effect of the passing blade that was acting as a blockage to the flow. The phenomenon was more pronounced near the suction and pressure surfaces of the blade, but diminished at the mid-passage region where the flow exhibited its best level of guidance. The full mixed flow turbine stage under transient conditions was modelled firstly with a 'steady' inlet and secondly with a 'pulsating' inlet boundary condition. In both cases comparison was made to
Steady Method for the Analysis of Evaporation Dynamics.
Günay, A Alperen; Sett, Soumyadip; Oh, Junho; Miljkovic, Nenad
2017-10-31
Droplet evaporation is an important phenomenon governing many man-made and natural processes. Characterizing the rate of evaporation with high accuracy has attracted the attention of numerous scientists over the past century. Traditionally, researchers have studied evaporation by observing the change in the droplet size in a given time interval. However, the transient nature coupled with the significant mass-transfer-governed gas dynamics occurring at the droplet three-phase contact line makes the classical method crude. Furthermore, the intricate balance played by the internal and external flows, evaporation kinetics, thermocapillarity, binary-mixture dynamics, curvature, and moving contact lines makes the decoupling of these processes impossible with classical transient methods. Here, we present a method to measure the rate of evaporation of spatially and temporally steady droplets. By utilizing a piezoelectric dispenser to feed microscale droplets (R ≈ 9 μm) to a larger evaporating droplet at a prescribed frequency, we can both create variable-sized droplets on any surface and study their evaporation rate by modulating the piezoelectric droplet addition frequency. Using our steady technique, we studied water evaporation of droplets having base radii ranging from 20 to 250 μm on surfaces of different functionalities (45° ≤ θ a,app ≤ 162°, where θ a,app is the apparent advancing contact angle). We benchmarked our technique with the classical unsteady method, showing an improvement of 140% in evaporation rate measurement accuracy. Our work not only characterizes the evaporation dynamics on functional surfaces but also provides an experimental platform to finally enable the decoupling of the complex physics governing the ubiquitous droplet evaporation process.
Theoretical studying the stability of steady-state regime of a channel with a coolant condensation
International Nuclear Information System (INIS)
Savikhin, O.G.
1987-01-01
Based on the boiling channel stability theory, the channel steady-state stability with the coolant condensation is studied. Condensable coolants are used in the NPP steam-separator superheaters as well as in cryogenic technique. Under certain conditions the coolant flow rate and temperature fluctuations may be excited in the parallel channel system with coolant condensation, which produce a sufficient effect on the heat exchange equipment operation reliability. To describe unsteady processes of heat and mass transfer in the channel, a homogeneous two-phase flow one dimensional model is used. The results obtained allow one to make a conclusion concerning the effect of some parameters on condensing channel steady-state regime stability: reduction of inlet and outlet unheated communication length, pressure drop increase at the outlet plate and its reduction at the inlet one lead to the increase of stability margin
Steady-State Anderson Accelerated Coupling of Lattice Boltzmann and Navier–Stokes Solvers
Atanasov, Atanas
2016-10-17
We present an Anderson acceleration-based approach to spatially couple three-dimensional Lattice Boltzmann and Navier–Stokes (LBNS) flow simulations. This allows to locally exploit the computational features of both fluid flow solver approaches to the fullest extent and yields enhanced control to match the LB and NS degrees of freedom within the LBNS overlap layer. Designed for parallel Schwarz coupling, the Anderson acceleration allows for the simultaneous execution of both Lattice Boltzmann and Navier–Stokes solver. We detail our coupling methodology, validate it, and study convergence and accuracy of the Anderson accelerated coupling, considering three steady-state scenarios: plane channel flow, flow around a sphere and channel flow across a porous structure. We find that the Anderson accelerated coupling yields a speed-up (in terms of iteration steps) of up to 40% in the considered scenarios, compared to strictly sequential Schwarz coupling.
COOLOD, Steady-State Thermal Hydraulics of Research Reactors
International Nuclear Information System (INIS)
Kaminaga, Masanori
1997-01-01
1 - Description of program or function: The COOLOD-N2 code provides a capability for the analyses of the steady-state thermal-hydraulics of research reactors. This code is a revised version of the COOLOD-N code, and is applicable not only for research reactors in which plate-type fuel is adopted, but also for research reactors in which rod-type fuel is adopted. In the code, subroutines to calculate temperature distribution in rod-type fuel have been newly added to the COOLOD-N code. The COOLOD-N2 code can calculate fuel temperatures under both forced convection cooling mode and natural convection cooling mode. A 'Heat Transfer package' is used for calculating heat transfer coefficient, DNB heat flux etc. The 'Heat Transfer package' is a subroutine program and is especially developed for research reactors in which plate-type fuel is adopted. In case of rod-type fuel, DNB heat flux is calculated by both the 'Heat Transfer package' and Lund DNB heat flux correlation which is popular for TRIGA reactor. The COOLOD-N2 code also has a capability of calculating ONB temperature, the heat flux at onset of flow instability as well as DNB heat flux. 2 - Method of solution: The 'Heat Transfer Package' is a subprogram for calculating heat transfer coefficients, ONB temperature, heat flux at onset of flow instability and DNB heat flux. The 'Heat transfer package' was especially developed for research reactors which are operated under low pressure and low temperature conditions using plate-type fuel, just like the JRR-3M. Heat transfer correlations adopted in the 'Heat Transfer Package' were obtained or estimated based on the heat transfer experiments in which thermal-hydraulic features of the upgraded JRR-3 core were properly reflected. The 'Heat Transfer Package' is applicable to upward and downward flow
A new coupled map car-following model considering drivers' steady desired speed
International Nuclear Information System (INIS)
Zhou Tong; Sun Di-Hua; Li Hua-Min; Liu Wei-Ning
2014-01-01
Based on the pioneering work of Konishi et al., in consideration of the influence of drivers' steady desired speed effect on the traffic flow, we develop a new coupled map car-following model in the real world. By use of the control theory, the stability condition of our model is derived. The validity of the present theoretical scheme is verified via numerical simulation, confirming the correctness of our theoretical analysis. (general)
Steady, three-dimensional, internally heated convection
International Nuclear Information System (INIS)
Schubert, G.; Glatzmaier, G.A.; Travis, B.
1993-01-01
Numerical calculations have been carried out of steady, symmetric, three-dimensional modes of convection in internally heated, infinite Prandtl number, Boussinesq fluids at a Rayleigh number of 1.4x10 4 in a spherical shell with inner/outer radius of 0.55 and in a 3x3x1 rectangular box. Multiple patterns of convection occur in both geometries. In the Cartesian geometry the patterns are dominated by cylindrical cold downflows and a broad hot upwelling. In the spherical geometry the patterns consist of cylindrical cold downwellings centered either at the vertices of a tetrahedron or the centers of the faces of a cube. The cold downflow cylinders are immersed in a background of upwelling within which there are cylindrical hot concentrations (plumes) and hot halos around the downflows. The forced hot upflow return plumes of internally heated spherical convection are fundamentally different from the buoyancy-driven plumes of heated from below convection
Steady-State Operation in Tore Supra
Hoang, G. T.; Tore Supra, Equipe
1999-11-01
The Tore Supra superconducting tokamak is devoted to steady-state operation. The CIEL (French acronym for internal component and limiter) project( LIPA, M., et al., Proc. of the 17th IEEE/NPSS Symp. on Fus. Engineering, San Diego, USA, 1997.) consists of a complete upgrade of the inner chamber of Tore Supra, planned to be installed during the year 2000. This project will allow physics scenarios with up to 24 MW of radio frequency heating and current drive (typically 8 - 10 MW of ICRF, 10 - 12 MW of LHCD and 2 MW of ECRF) in stationary plasmas up to 1000 s, with active particle control. This paper presents an overview of the experiments planned to explore the properties, such as the confinement and MHD stability, of various heating and current drive scenarios for long duration discharges. The expected performance for the CIEL phase is also reported.
Producing a steady-state population inversion
International Nuclear Information System (INIS)
Richards, R.K.; Griffin, D.C.
1986-03-01
An observed steady-state transition at 17.5 nm is identified as the 2p 5 3s3p 4 S/sub 3/2/ → 2p 6 3p 2 P/sub 3/2/ transition in Na-like aluminum. The upper level is populated by electron inner shell ionization of metastable Mg-like aluminum. From the emission intensity, the rate coefficient for populating the upper level is calculated to be approximately 5 x 10 -10 ) cm 3 /sec. Since the upper level is quasimetastable with a lifetime 22 times longer than the lower level, it may be possible to produce a population inversion, if a competing process to populate the lower level can be reduced
Reactor kinetics - pulse and steady state
Energy Technology Data Exchange (ETDEWEB)
Estes, B F; Morris, F M [Sandia Laboratories (United States)
1974-07-01
An analytical model has been developed which couples the nuclear and thermal characteristics of the Annular Core Pulse Reactor (ACPR) into a solution which describes both the neutron kinetics of the reactor and the temperature behavior of a fuel-moderator element. The model describes both pulse and steady state operations. This paper describes the important aspects of the reactor, the fuel- moderator elements, the neutron kinetic equations of the reactor, and the time-temperature behavior of a fuel-moderator element that is being subjected to the maximum power density in the core. The parameters which are utilized in the equations are divided into two classes, those that can be measured directly and those that are assumed to be known (each is described briefly). Some of the solutions which demonstrate the versatility of the analytical model are described. (author)
Magnetic sensor for steady state tokamak
Energy Technology Data Exchange (ETDEWEB)
Neyatani, Yuzuru; Mori, Katsuharu; Oguri, Shigeru; Kikuchi, Mitsuru [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment
1996-06-01
A new type of magnetic sensor has been developed for the measurement of steady state magnetic fields without DC-drift such as integration circuit. The electromagnetic force induced to the current which leads to the sensor was used for the measurement. For the high frequency component which exceeds higher than the vibration frequency of sensor, pick-up coil was used through the high pass filter. From the results using tokamak discharges, this sensor can measure the magnetic field in the tokamak discharge. During {approx}2 hours measurement, no DC drift was observed. The sensor can respond {approx}10ms of fast change of magnetic field during disruptions. We confirm the extension of measured range to control the current which leads to the sensor. (author).
Progress towards Steady State on NSTX
International Nuclear Information System (INIS)
Gates, D.A.; Kessel, C.; Menard, J.; Taylor, G.; Wilson, J.R.
2005-01-01
In order to reduce recirculating power fraction to acceptable levels, the spherical torus concept relies on the simultaneous achievement of high toroidal β and high bootstrap fraction in steady state. In the last year, as a result of plasma control system improvements, the achievable plasma elongation on the National Spherical Torus Experiment (NSTX) has been raised from κ ∼ 2.1 to κ ∼ 2.6--approximately a 25% increase. This increase in elongation has lead to a doubling increase in the toroidal β for long-pulse discharges. The increase in β is associated with an increase in plasma current at nearly fixed poloidal β, which enables higher β t with nearly constant bootstrap fraction. As a result, for the first time in a spherical torus, a discharge with a plasma current of 1 MA has been sustained for 1 second. Data is presented from NSTX correlating the increase in performance with increased plasma shaping capability. In addition to improved shaping, H-modes induced during the current ramp phase of the plasma discharge have been used to reduce flux consumption during and to delay the onset of MHD instabilities. A modeled integrated scenario, which has 100% non-inductive current drive with very high toroidal β, will also be presented. The NSTX poloidal field coils are currently being modified to produce the plasma shape which is required for this scenario, which requires high triangularity ((delta) ∼ 0.8) at elevated elongation (κ ∼ 2.5). The other main requirement for steady state on NSTX is the ability to drive a fraction of the total plasma current with radio-frequency waves. The results of High Harmonic Fast Wave heating and current drive studies as well as electron Bernstein Wave emission studies will be presented
Stretched flow of Carreau nanofluid with convective boundary ...
Indian Academy of Sciences (India)
journal of. January 2016 physics pp. 3–17. Stretched flow of Carreau nanofluid with ... fluid over a flat plate subjected to convective surface condition. ... the steady laminar boundary layer flow over a permeable plate with a convective boundary.
Upscaling of Forchheimer flows
Aulisa, Eugenio
2014-08-01
In this work we propose upscaling method for nonlinear Forchheimer flow in heterogeneous porous media. The generalized Forchheimer law is considered for incompressible and slightly-compressible single-phase flows. We use recently developed analytical results (Aulisa et al., 2009) [1] and formulate the resulting system in terms of a degenerate nonlinear flow equation for the pressure with the nonlinearity depending on the pressure gradient. The coarse scale parameters for the steady state problem are determined so that the volumetric average of velocity of the flow in the domain on fine scale and on coarse scale are close. A flow-based coarsening approach is used, where the equivalent permeability tensor is first evaluated following streamline methods for linear cases, and modified in order to take into account the nonlinear effects. Compared to previous works (Garibotti and Peszynska, 2009) [2], (Durlofsky and Karimi-Fard) [3], this approach can be combined with rigorous mathematical upscaling theory for monotone operators, (Efendiev et al., 2004) [4], using our recent theoretical results (Aulisa et al., 2009) [1]. The developed upscaling algorithm for nonlinear steady state problems is effectively used for variety of heterogeneities in the domain of computation. Direct numerical computations for average velocity and productivity index justify the usage of the coarse scale parameters obtained for the special steady state case in the fully transient problem. For nonlinear case analytical upscaling formulas in stratified domain are obtained. Numerical results were compared to these analytical formulas and proved to be highly accurate. © 2014.
Pseudo Steady-State Free Precession for MR-Fingerprinting.
Assländer, Jakob; Glaser, Steffen J; Hennig, Jürgen
2017-03-01
This article discusses the signal behavior in the case the flip angle in steady-state free precession sequences is continuously varied as suggested for MR-fingerprinting sequences. Flip angle variations prevent the establishment of a steady state and introduce instabilities regarding to magnetic field inhomogeneities and intravoxel dephasing. We show how a pseudo steady state can be achieved, which restores the spin echo nature of steady-state free precession. Based on geometrical considerations, relationships between the flip angle, repetition and echo time are derived that suffice to the establishment of a pseudo steady state. The theory is tested with Bloch simulations as well as phantom and in vivo experiments. A typical steady-state free precession passband can be restored with the proposed conditions. The stability of the pseudo steady state is demonstrated by comparing the evolution of the signal of a single isochromat to one resulting from a spin ensemble. As confirmed by experiments, magnetization in a pseudo steady state can be described with fewer degrees of freedom compared to the original fingerprinting and the pseudo steady state results in more reliable parameter maps. The proposed conditions restore the spin-echo-like signal behavior typical for steady-state free precession in fingerprinting sequences, making this approach more robust to B 0 variations. Magn Reson Med 77:1151-1161, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.
International Nuclear Information System (INIS)
Gou Junli; Qiu Suizheng; Su Guanghui; Jia Dounan
2006-01-01
This article presents a theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor. Through numerically solving the one-dimensional steady-state single-phase conservative equations for the primary circuit and the steady-state two-phase drift-flux conservative equations for the secondary side of the steam generator, the natural circulation characteristics were studied. On the basis of the preliminary calculation analysis, it was found that natural circulation mass flow rate was proportional to the exponential function of the power and that the value of the exponent is related to the operating conditions of the secondary side of the steam generator. The higher the outlet pressure of the secondary side of the steam generator, the higher the primary natural circulation mass flow rate. The larger height difference between the core center and the steam generator center is favorable for the heat removal capacity of the natural circulation. (authors)
Forward and inverse modeling of near-well flow using discrete edge-based vector potentials
Zijl, W.
2007-01-01
Homogeneous effective permeabilities in the near-well region are generally obtained using analytical solutions for transient flow. In contrast, this paper focuses on heterogeneous permeability obtained from steady flow solutions, although extensions to unsteady flow are introduced too. Exterior
The steady part of the secular variation of the Earth's magnetic field
Bloxham, Jeremy
1992-01-01
The secular variation of the Earth's magnetic field results from the effects of magnetic induction in the fluid outer core and from the effects of magnetic diffusion in the core and the mantle. Adequate observations to map the magnetic field at the core-mantle boundary extend back over three centuries, providing a model of the secular variation at the core-mantle boundary. Here we consider how best to analyze this time-dependent part of the field. To calculate steady core flow over long time periods, we introduce an adaptation of our earlier method of calculating the flow in order to achieve greater numerical stability. We perform this procedure for the periods 1840-1990 and 1690-1840 and find that well over 90 percent of the variance of the time-dependent field can be explained by simple steady core flow. The core flows obtained for the two intervals are broadly similar to each other and to flows determined over much shorter recent intervals.
Tester Detects Steady-Short Or Intermittent-Open Circuits
Anderson, Bobby L.
1990-01-01
Momentary open circuits or steady short circuits trigger buzzer. Simple, portable, lightweight testing circuit sounds long-duration alarm when it detects steady short circuit or momentary open circuit in coaxial cable or other two-conductor transmission line. Tester sensitive to discontinuities lasting 10 microseconds or longer. Used extensively for detecting intermittent open shorts in accelerometer and extensometer cables. Also used as ordinary buzzer-type continuity checker to detect steady short or open circuits.
Directory of Open Access Journals (Sweden)
Valavanides M.S.
2012-11-01
Full Text Available Scope of present article is to present the research efforts (implementing experimental study, theoretical analysis and modeling taken towards the development of a complete theory for steady-state concurrent two-phase flow in porous media (the DeProF theory. The current state of progress is outlined and open problems are addressed. First attempts are traced back in the 1980s with the analysis, description and modeling of phenomena governing two-phase flow in pore scale. Appropriate simulators extending over hundreds and/or thousands of pores (network scale were developed in the following decade (1990s; in parallel, extensive experimental research work identified three prototype/elementary flows comprising the average macroscopic flow, namely connected-oil pathway flow, ganglion dynamics and drop traffic flow and mapped their relative contribution to the macroscopic flow in terms of the process parameters. Efforts to provide a consistent physical rationale to explain the experimental observations, i.e. the map of prototype flow regimes, laid the grounds for developing the DeProF (Decomposition in Prototype Flows theory. Amongst the main results/features of the DeProF theory was the identification of the actual operational and system parameters of the process and the introduction – according to ergodicity principles – of the domain of physically admissible internal flow arrangements of the average macroscopic flow. Use of the respective mechanistic model as a simulation tool (in the 2000s revealed many characteristic properties of the sought process. Important is the existence of optimum operating conditions in the form of a smooth and continuous locus in the domain of the process operational parameters. This characteristic remained in latency within the relative permeability curves, until recently unveiled by the DeProF theory. Research efforts continue in the present (2010s by elaborating appropriate physical considerations based on
NASA Lewis steady-state heat pipe code users manual
International Nuclear Information System (INIS)
Tower, L.K.
1992-06-01
The NASA Lewis heat pipe code has been developed to predict the performance of heat pipes in the steady state. The code can be used as a design tool on a personal computer or, with a suitable calling routine, as a subroutine for a mainframe radiator code. A variety of wick structures, including a user input option, can be used. Heat pipes with multiple evaporators, condensers, and adiabatic sections in series and with wick structures that differ among sections can be modeled. Several working fluids can be chosen, including potassium, sodium, and lithium, for which the monomer-dimer equilibrium is considered. The code incorporates a vapor flow algorithm that treats compressibility and axially varying heat input. This code facilitates the determination of heat pipe operating temperatures and heat pipe limits that may be encountered at the specified heat input and environment temperature. Data are input to the computer through a user-interactive input subroutine. Output, such as liquid and vapor pressures and temperatures, is printed at equally spaced axial positions along the pipe as determined by the user
Steady State Turbulent Transport in Magnetic Fusion Plasmas
International Nuclear Information System (INIS)
Lee, W.W.; Ethier, S.; Kolesnikov, R.; Wang, W.X.; Tang, W.M.
2007-01-01
For more than a decade, the study of microturbulence, driven by ion temperature gradient (ITG) drift instabilities in tokamak devices, has been an active area of research in magnetic fusion science for both experimentalists and theorists alike. One of the important impetus for this avenue of research was the discovery of the radial streamers associated the ITG modes in the early nineties using a Particle-In-Cell (PIC) code. Since then, ITG simulations based on the codes with increasing realism have become possible with the dramatic increase in computing power. The notable examples were the demonstration of the importance of nonlinearly generated zonal flows in regulating ion thermal transport and the transition from Bohm to GyroBoham scaling with increased device size. In this paper, we will describe another interesting nonlinear physical process associated with the parallel acceleration of the ions, that is found to play an important role for the steady state turbulent transport. Its discovery is again through the use of the modern massively parallel supercomputers
Quasi-steady state natural convection in a tilted porous layer
Energy Technology Data Exchange (ETDEWEB)
Robillard, L.; Vasseur, P. (Ecole Polytechnique, Montreal, PQ (Canada))
1992-12-01
Natural convection in an inclined porous layer heated or cooled on one side, when its other walls are insulated, has several important engineering applications. These include solar power collection, regenerative heat exchangers, and high performance insulation for buildings and cold storage. Although the problem is basically an unsteady state one, it is known that if the heating (or cooling) process is maintained for a sufficiently long time, a quasi-steady state is approached. Quasi-steady state laminar natural convection in an inclined porous layer is studied analytically and numerically. On the basis of the Darcy-Oberbeck-Boussinesq equations, the problem is solved analytically in the limit of a thin porous layer heated on one side by a heat flux while the other boundaries are maintained adiabatic. For quasi-steady state, the flow and temperature fields overall heat transfer rates are obtained in terms of the controlling parameters and the onset of convection in a bottom heated horizantal system is predicted. It is also demonstrated for the case of a bottom-heated layer that for sufficiently small inclinations, multiple unicellular quasi-steady states exist, some of which are unstable. A numerical study of the same phenomenon, obtained by solving the complete set of governing equations, is conducted. Good agreement is found between the analytical predictions and the numerical simulation. 22 refs., 6 figs.
International Nuclear Information System (INIS)
Place, A.R.; Eccleston, J.F.
1987-01-01
The alcohol dehydrogenase (ADH) isolated from Drosophila is unique among alcohol metabolizing enzymes by not requiring metals for catalysis, by showing 4-pro-S (B-sided) hydride transfer stereospecificity, and by possessing a greater catalytic turnover rate for secondary alcohols than for primary alcohols. They have extended their studies on the kinetic mechanism for this enzyme by examining the pre-steady state transients of ternary complex interconversion using stopped-flow fluorescence methods. When enzyme and a 30-fold molar excess of NADH is mixed with excess acetadehyde, methyl ethyl ketone (MEK), or cyclohexanone a rapid (> 100 s -1 ) transient is observe before the steady-state. The rates are insensitive to isotope substitution. With the substrate MEK, the rate and amplitude suggests a single turnover of the enzyme. Similar pre-steady state transients are observed when enzyme and a 50-fold molar excess of NAD + is mixed with ethanol, 2-propanol, and cyclohexanol. The rates show a hyperbolic concentration dependence and a deuterium isotope effect. With d 6 -deuteroethanol the transient no longer occurs in the pre-steady state. When the optical isomers of secondary alcohols are used as substrates, transients are observed only in the R-(-) isomers for all chain lengths. With 2-S(+)-heptanol and 2-S(+)-octanol no transients occur
Steady progress toward a malaria vaccine.
Lyke, Kirsten E
2017-10-01
Great progress has been made in reducing malaria morbidity and mortality, yet the parasite continues to cause a startling 200 million infections and 500 000 deaths annually. Malaria vaccine development is pushing new boundaries by steady advancement toward a licensed product. Despite 50 years of research, the complexity of Plasmoidum falciparum confounds all attempts to eradicate the organism. This very complexity has pushed the boundaries of vaccine development to new heights, yet it remains to be seen if an affordable vaccine can provide durable and high-level protection. Novel vaccines such as RTS,S/AS01E are on the edge of licensure, but old techniques have resurged with the ability to deliver vialed, whole organism vaccines. Novel adjuvants, multistage/multiantigen approaches and transmission blocking vaccines all contribute to a multipronged battle plan to conquer malaria. Vaccines are the most cost-effective tools to control infectious diseases, yet the complexity of malaria has frustrated all attempts to develop an effective product. This review concentrates on recent advances in malaria vaccine development that lend hope that a vaccine can be produced and malaria eradicated.
A steady-state axisymmetric toroidal system
International Nuclear Information System (INIS)
Hirano, K.
1984-01-01
Conditions for achieving a steady state in an axisymmetric toroidal system are studied with emphasis on a very-high-beta field-reversed configuration. The analysis is carried out for the electromotive force produced by the Ohkawa current that is induced by neutral-beam injection. It turns out that, since the perpendicular component of the current j-vectorsub(perpendicular) to the magnetic field can be generated automatically by the diamagnetic effect, only the parallel component j-vectorsub(parallel) must be driven by the electromotive force. The drive of j-vectorsub(parallel) generates shear in the field line so that the pure toroidal field on the magnetic axis is rotated towards the plasma boundary and matched to the external field lines. This matching condition determines the necessary amount of injection beam current and power. It is demonstrated that a very-high-beta field-reversed configuration requires only a small amount of current-driving beam power because almost all the toroidal current except that close to the magnetic axis is carried by the diamagnetic current due to high beta. A low-beta tokamak, on the other hand, needs very high current-driving power since most of the toroidal current is composed of j-vectorsub(parallel) which must be driven by the beam. (author)
Steady Particle States of Revised Electromagnetics
Directory of Open Access Journals (Sweden)
Lehnert B.
2006-07-01
Full Text Available A revised Lorentz invariant electromagnetic theory leading beyond Maxwell's equations, and to a form of extended quantum electrodynamics, has been elaborated on the basis of a nonzero electric charge density and a nonzero electric field divergence in the vacuum state. Among the applications of this theory, there are steady electromagnetic states having no counterpart in conventional theory and resulting in models of electrically charged and neutral leptons, such as the electron and the neutrino. The analysis of the electron model debouches into a point-charge-like geometry with a very small characteristic radius but having finite self-energy. This provides an alternative to the conventional renormalization procedure. In contrast to conventional theory, an integrated radial force balance can further be established in which the electron is prevented from "exploding" under the action of its net self-charge. Through a combination of variational analysis and an investigation of the radial force balance, a value of the electronic charge has been deduced which deviates by only one percent from that obtained in experiments. This deviation requires further investigation. A model of the neutrino finally reproduces some of the basic features, such as a small but nonzero rest mass, an angular momentum but no magnetic moment, and long mean free paths in solid matter.
Steady Particle States of Revised Electromagnetics
Directory of Open Access Journals (Sweden)
Lehnert B.
2006-07-01
Full Text Available A revised Lorentz invariant electromagnetic theory leading beyond Maxwell’s equations, and to a form of extended quantum electrodynamics, has been elaborated on the basis of a nonzero electric charge density and a nonzero electric field divergence in the vacuum state. Among the applications of this theory, there are steady electromagnetic states having no counterpart in conventional theory and resulting in models of electrically charged and neutral leptons, such as the electron and the neutrino. The analysis of the electron model debouches into a point-charge-like geometry with a very small characteristic radius but having finite self-energy. This provides an alternative to the conventional renormalization procedure. In contrast to conventional theory, an integrated radial force balance can further be established in which the electron is prevented from “exploding” under the action of its net self-charge. Through a combination of variational analysis and an investigation of the radial force balance, a value of the electronic charge has been deduced which deviates by only one percent from that obtained in experiments. This deviation requires further investigation. A model of the neutrino finally reproduces some of the basic features, such as a small but nonzero rest mass, an angular momentum but no magnetic moment, and long mean free paths in solid matter.
Fluctuations When Driving Between Nonequilibrium Steady States
Riechers, Paul M.; Crutchfield, James P.
2017-08-01
Maintained by environmental fluxes, biological systems are thermodynamic processes that operate far from equilibrium without detailed-balanced dynamics. Yet, they often exhibit well defined nonequilibrium steady states (NESSs). More importantly, critical thermodynamic functionality arises directly from transitions among their NESSs, driven by environmental switching. Here, we identify the constraints on excess heat and dissipated work necessary to control a system that is kept far from equilibrium by background, uncontrolled "housekeeping" forces. We do this by extending the Crooks fluctuation theorem to transitions among NESSs, without invoking an unphysical dual dynamics. This and corresponding integral fluctuation theorems determine how much work must be expended when controlling systems maintained far from equilibrium. This generalizes thermodynamic feedback control theory, showing that Maxwellian Demons can leverage mesoscopic-state information to take advantage of the excess energetics in NESS transitions. We also generalize an approach recently used to determine the work dissipated when driving between functionally relevant configurations of an active energy-consuming complex system. Altogether, these results highlight universal thermodynamic laws that apply to the accessible degrees of freedom within the effective dynamic at any emergent level of hierarchical organization. By way of illustration, we analyze a voltage-gated sodium ion channel whose molecular conformational dynamics play a critical functional role in propagating action potentials in mammalian neuronal membranes.
Triple echo steady-state (TESS) relaxometry.
Heule, Rahel; Ganter, Carl; Bieri, Oliver
2014-01-01
Rapid imaging techniques have attracted increased interest for relaxometry, but none are perfect: they are prone to static (B0 ) and transmit (B1 ) field heterogeneities, and commonly biased by T2 /T1 . The purpose of this study is the development of a rapid T1 and T2 relaxometry method that is completely (T2 ) or partly (T1 ) bias-free. A new method is introduced to simultaneously quantify T1 and T2 within one single scan based on a triple echo steady-state (TESS) approach in combination with an iterative golden section search. TESS relaxometry is optimized and evaluated from simulations, in vitro studies, and in vivo experiments. It is found that relaxometry with TESS is not biased by T2 /T1 , insensitive to B0 heterogeneities, and, surprisingly, that TESS-T2 is not affected by B1 field errors. Consequently, excellent correspondence between TESS and reference spin echo data is observed for T2 in vitro at 1.5 T and in vivo at 3 T. TESS offers rapid T1 and T2 quantification within one single scan, and in particular B1 -insensitive T2 estimation. As a result, the new proposed method is of high interest for fast and reliable high-resolution T2 mapping, especially of the musculoskeletal system at high to ultra-high fields. Copyright © 2013 Wiley Periodicals, Inc.
Airfoil flow instabilities induced by background flow oscillations
Energy Technology Data Exchange (ETDEWEB)
Selerowicz, W.C.; Szumowski, A.P. [Technical Univ. Warsaw (Poland)
2002-04-01
The effect of background flow oscillations on transonic airfoil (NACA 0012) flow was investigated experimentally. The oscillations were generated by means of a rotating plate placed downstream of the airfoil. Owing to oscillating chocking of the flow caused by the plate, the airfoil flow periodically accelerated and decelerated. This led to strong variations in the surface pressure and the airfoil loading. The results are presented for two angles of attack, {alpha}=4 and {alpha}=8.5 , which correspond to the attached and separated steady airfoil flows, respectively. (orig.)
The flow field around a micropillar confined in a microchannel
International Nuclear Information System (INIS)
Jung, Junkyu; Kuo, C.-J.; Peles, Yoav; Amitay, Michael
2012-01-01
The flow field over a low aspect ratio (AR) circular pillar (L/D = 1.5) in a microchannel was studied experimentally. Microparticle image velocimetry (μPIV) was employed to quantify flow parameters such as flow field, spanwise vorticity, and turbulent kinetic energy (TKE) in the microchannel. Flow regimes of cylinder-diameter-based Reynolds number at 100 ⩽ Re D ⩽ 700 (i.e., steady, transition from quasi-steady to unsteady, and unsteady flow) were elucidated at the microscale. In addition, active flow control (AFC), via a steady control jet (issued from the pillar itself in the downstream direction), was implemented to induce favorable disturbances to the flow in order to alter the flow field, promote turbulence, and increase mixing. Together with passive flow control (i.e., a circular pillar), turbulent kinetic energy was significantly increased in a controllable manner throughout the flow field.
Engelbrecht, Nicolaas; Chiuta, Steven; Bessarabov, Dmitri G.
2018-05-01
The experimental evaluation of an autothermal microchannel reactor for H2 production from NH3 decomposition is described. The reactor design incorporates an autothermal approach, with added NH3 oxidation, for coupled heat supply to the endothermic decomposition reaction. An alternating catalytic plate arrangement is used to accomplish this thermal coupling in a cocurrent flow strategy. Detailed analysis of the transient operating regime associated with reactor start-up and steady-state results is presented. The effects of operating parameters on reactor performance are investigated, specifically, the NH3 decomposition flow rate, NH3 oxidation flow rate, and fuel-oxygen equivalence ratio. Overall, the reactor exhibits rapid response time during start-up; within 60 min, H2 production is approximately 95% of steady-state values. The recommended operating point for steady-state H2 production corresponds to an NH3 decomposition flow rate of 6 NL min-1, NH3 oxidation flow rate of 4 NL min-1, and fuel-oxygen equivalence ratio of 1.4. Under these flows, NH3 conversion of 99.8% and H2 equivalent fuel cell power output of 0.71 kWe is achieved. The reactor shows good heat utilization with a thermal efficiency of 75.9%. An efficient autothermal reactor design is therefore demonstrated, which may be upscaled to a multi-kW H2 production system for commercial implementation.
Optical diagnostics of intermittent flows
DEFF Research Database (Denmark)
Okulov, V.L.; Naumov, I.V.; Sørensen, Jens Nørkær
2007-01-01
The efficiency of combined use of different optical techniques for flow diagnostics is demonstrated with the practically important case of intense swirling flows. It is shown that, when applied separately, commonly used optical measuring techniques, such as laser Doppler anemometry and particle...... is for the first time applied for diagnostics of the flow pattern in a closed cylinder with a rotating end face with the aim of studying the changeover from the steady axisymmetric to unsteady asymmetric flow over a wide range of flow parameters. It is found that such a transition is notable for azimuthal...
Molecular description of steady supersonic free jets
Montero, S.
2017-09-01
A detailed analysis of the non-local thermal equilibrium (n-LTE) problem in the paraxial zone of silence of supersonic free jets is reported. The study is based on a hybrid approach that combines Navier-Stokes equations with a kinetic equation derived from the generalized Boltzmann (Waldmann-Snider) equation. The resulting system is solved for those flow quantities not easily amenable to experimental measure (translational temperature, flow velocity, and entropy) in terms of the quantities that can be measured accurately (distance, number density, population of rotational states, and their gradients). The reported solutions are essentially exact and are formulated in terms of macroscopic quantities, as well as in terms of elementary collision processes. Emphasis is made on the influence of dissipative effects onto the flow (viscous and diabatic) and of the breakdown of thermal equilibrium onto the evolution of entropy and translational temperature. The influence of inelastic collisions onto these effects is analysed in depth. The reported equations are aimed at optimizing the experimental knowledge of the n-LTE problem and its quantitative interpretation in terms of state-to-state rates for inelastic collisions.
Steady-streaming effects on the motion of the cerebrospinal fluid (CSF) in the spinal canal
Lawrence, Jenna; Coenen, Wilfried; Sanchez, Antonio; Lasheras, Juan
2017-11-01
With each heart beat the oscillatory blood supply to the rigid cranial vault produces a time-periodic variation of the intracranial pressure that drives the cerebrospinal fluid (CSF) periodically in and out of the compliant spinal canal. We have recently conducted an analysis of this flow-structure interaction problem taking advantage of the small compliance of the dura membrane bounding externally the CSF and of the disparity of length scales associated with the geometry of the subarachnoid space. We have shown in an idealized geometry that the steady-streaming motion associated with this periodic flow, resulting from the nonlinear cumulative effects of convective acceleration, causes a bulk recirculation of CSF inside the spinal canal, which has been observed in many radiological studies. We extend here our study to investigate the possible contribution arising from the flow around the nerve roots protruding from the spinal cord, an effect that was neglected in our previous work. For this purpose, we consider the oscillatory motion around a cylindrical post confined between two parallel plates. For large values of the relevant Strouhal number we find at leading order a harmonic Stokes flow, whereas steady-streaming effects enter in the first-order corrections, which are computed for realistic values of the Womersley number and of the cylinder height-to-radius ratio.
Parametric study of the primary and secondary systems of the CAREM-25 reactor on steady state
International Nuclear Information System (INIS)
Halpert, Silvia; Vazquez, Luis
2000-01-01
In the CAREM-25 reactor the primary coolant flows by natural convection that's why the flow is established when the balance between the buoyancy force and friction pressure drop through circuit is obtained. This paper presents a parametric study on primary and secondary systems of the reactor on steady state, for different values of some thermohydraulics parameters: safety factor on friction loss pressure calculations (f), steam generator heat transfer area (A T ) and primary pressure (P P ). The ESCAREM 2.08 thermohydraulic code, which calculates the primary system behavior for steady state conditions, was used for this study. The conclusions of this study are: -) There was a variation of the 15% on the primary coolant flow when the safety factor was changed a 50 %; -) The primary and secondary systems conditions do not change when the power is less than 100 MW; -) Between 100 and 110 MW the decrease of the heat transfer area produces an important change on the secondary systems conditions: the outlet steam generator temperature decrease and there is an important rice in the flow; -) The primary pressure could decrease up to 11.4 MPa without violating turbine requirements. (author)
Drug perfusion enhancement in tissue model by steady streaming induced by oscillating microbubbles.
Oh, Jin Sun; Kwon, Yong Seok; Lee, Kyung Ho; Jeong, Woowon; Chung, Sang Kug; Rhee, Kyehan
2014-01-01
Drug delivery into neurological tissue is challenging because of the low tissue permeability. Ultrasound incorporating microbubbles has been applied to enhance drug delivery into these tissues, but the effects of a streaming flow by microbubble oscillation on drug perfusion have not been elucidated. In order to clarify the physical effects of steady streaming on drug delivery, an experimental study on dye perfusion into a tissue model was performed using microbubbles excited by acoustic waves. The surface concentration and penetration length of the drug were increased by 12% and 13%, respectively, with streaming flow. The mass of dye perfused into a tissue phantom for 30s was increased by about 20% in the phantom with oscillating bubbles. A computational model that considers fluid structure interaction for streaming flow fields induced by oscillating bubbles was developed, and mass transfer of the drug into the porous tissue model was analyzed. The computed flow fields agreed with the theoretical solutions, and the dye concentration distribution in the tissue agreed well with the experimental data. The computational results showed that steady streaming with a streaming velocity of a few millimeters per second promotes mass transfer into a tissue. © 2013 Published by Elsevier Ltd.
Numerical analysis of steady and transient natural convection in an enclosed cavity
Mehedi, Tanveer Hassan; Tahzeeb, Rahat Bin; Islam, A. K. M. Sadrul
2017-06-01
The paper presents the numerical simulation of natural convection heat transfer of air inside an enclosed cavity which can be helpful to find out the critical width of insulation in air insulated walls seen in residential buildings and industrial furnaces. Natural convection between two walls having different temperatures have been simulated using ANSYS FLUENT 12.0 in both steady and transient conditions. To simulate different heat transfer and fluid flow conditions, Rayleigh number ranging from 103 to 105 has been maintained (i.e. Laminar flow.) In case of steady state analysis, the CFD predictions were in very good agreement with the reviewed literature. Transient simulation process has been performed by using User Defined Functions, where the temperature of the hot wall varies with time linearly. To obtain and compare the heat transfer properties, Nusselt number has been calculated at the hot wall at different conditions. The buoyancy driven flow characteristics have been investigated by observing the flow pattern in a graphical manner. The characteristics of the system at different temperature differences between the wall has been observed and documented.
Energy management in multi stage evaporator through a steady and dynamic state analysis
Energy Technology Data Exchange (ETDEWEB)
Verma, Om Prakash; Manik, Gaurav; Mohammed, Toufiq Haji [Indian Institute of Technology Roorkee, Roorkee (India)
2017-10-15
Increasing energy demand, high cost of energy and global warming issues across the globe require energy intensive industries, such as paper mills to improve energy efficiency. Multi-stage evaporators used to concentrate the black liquor in such mills form its most energy consuming unit and require a strong understanding of steady and unsteady state behavior to ensure energy savings. The modeling of nonlinear heptads’ effect system yielded a set of complex nonlinear algebraic and differential equations that are analyzed using Interior-point method and state space representation. Dynamic response of product concentration and system vapor temperatures along with system stability and controllability have been explored by disturbing the flow rate, concentration and temperature of feed, and fresh steam flow rate. Simulations predict that steam flow rate, feed flow rate and its concentration invariably are major controlling factors (in decreasing order) of vapor temperature and product concentration. The interactive behavior between different effects translates into slower responses of the effects with increasing separation from disturbance source. This steady state and transient study opens many new explanations to this relatively less explored area and helps to propose and implement industrial PID controllers to reduce steam consumption and control product quality.
steady – state performance of induction and transfer state
African Journals Online (AJOL)
eobe
This paper presents paper presents paper presents the steady the steady the steady–state performance state performance state performance comparison comparison comparison between polyphase induction motor and polyphase between polyphase induction motor and polyphase. TF motor operating in. TF motor ...
Spatial variability of steady-state infiltration into a two-layer soil system on burned hillslopes
Kinner, D.A.; Moody, J.A.
2010-01-01
Rainfall-runoff simulations were conducted to estimate the characteristics of the steady-state infiltration rate into 1-m2 north- and south-facing hillslope plots burned by a wildfire in October 2003. Soil profiles in the plots consisted of a two-layer system composed of an ash on top of sandy mineral soil. Multiple rainfall rates (18.4-51.2 mm h-1) were used during 14 short-duration (30 min) and 2 long-duration simulations (2-4 h). Steady state was reached in 7-26 min. Observed spatially-averaged steady-state infiltration rates ranged from 18.2 to 23.8 mm h-1 for north-facing and from 17.9 to 36.0 mm h-1 for south-facing plots. Three different theoretical spatial distribution models of steady-state infiltration rate were fit to the measurements of rainfall rate and steady-state discharge to provided estimates of the spatial average (19.2-22.2 mm h-1) and the coefficient of variation (0.11-0.40) of infiltration rates, overland flow contributing area (74-90% of the plot area), and infiltration threshold (19.0-26 mm h-1). Tensiometer measurements indicated a downward moving pressure wave and suggest that infiltration-excess overland flow is the runoff process on these burned hillslope with a two-layer system. Moreover, the results indicate that the ash layer is wettable, may restrict water flow into the underlying layer, and increase the infiltration threshold; whereas, the underlying mineral soil, though coarser, limits the infiltration rate. These results of the spatial variability of steady-state infiltration can be used to develop physically-based rainfall-runoff models for burned areas with a two-layer soil system. ?? 2010 Elsevier B.V.
Rod Bundle Heat Transfer: Steady-State Steam Cooling Experiments
International Nuclear Information System (INIS)
Spring, J.P.; McLaughlin, D.M.
2006-01-01
Through the joint efforts of the Pennsylvania State University and the United States Nuclear Regulatory Commission, an experimental rod bundle heat transfer (RBHT) facility was designed and built. The rod bundle consists of a 7 x 7 square pitch array with spacer grids and geometry similar to that found in a modern pressurized water reactor. From this facility, a series of steady-state steam cooling experiments were performed. The bundle inlet Reynolds number was varied from 1 400 to 30 000 over a pressure range from 1.36 to 4 bars (20 to 60 psia). The bundle inlet steam temperature was controlled to be at saturation for the specified pressure and the fluid exit temperature exceeded 550 deg. C in the highest power tests. One important quantity of interest is the local convective heat transfer coefficient defined in terms of the local bulk mean temperature of the flow, local wall temperature, and heat flux. Steam temperatures were measured at the center of selected subchannels along the length of the bundle by traversing miniaturized thermocouples. Using an analogy between momentum and energy transport, a method was developed for relating the local subchannel centerline temperature measurement to the local bulk mean temperature. Wall temperatures were measured using internal thermocouples strategically placed along the length of each rod and the local wall heat flux was obtained from an inverse conduction program. The local heat transfer coefficient was calculated from the data at each rod thermocouple location. The local heat transfer coefficients calculated for locations where the flow was fully developed were compared against several published correlations. The Weisman and El-Genk correlations were found to agree best with the RBHT steam cooling data, especially over the range of turbulent Reynolds numbers. The effect of spacer grids on the heat transfer enhancement was also determined from instrumentation placed downstream of the spacer grid locations. The local
CANDU channel flow verification
International Nuclear Information System (INIS)
Mazalu, N.; Negut, Gh.
1997-01-01
The purpose of this evaluation was to obtain accurate information on each channel flow that enables us to assess precisely the level of reactor thermal power and, for reasons of safety, to establish which channel is boiling. In order to assess the channel flow parameters, computer simulations were done with the NUCIRC code and the results were checked by measurements. The complete channel flow measurements were made in the zero power cold condition. In hot conditions there were made flow measurements using the Shut Down System 1 (SDS 1) flow devices from 0.1 % F.P. up to 100 % F.P. The NUCIRC prediction for CANDU channel flows and the measurements by Ultrasonic Flow Meter at zero power cold conditions and SDS 1 flow channel measurements at different reactor power levels showed an acceptable agreement. The 100 % F.P. average errors for channel flow of R, shows that suitable NUCIRC flow assessment can be made. So, it can be done a fair prediction of the reactor power distribution. NUCIRC can predict accurately the onset of boiling and helps to warn at the possible power instabilities at high powers or it can detect the flow blockages. The thermal hydraulic analyst has in NUCIRC a suitable tool to do accurate predictions for the thermal hydraulic parameters for different steady state power levels which subsequently leads to an optimal CANDU reactor operation. (authors)
Steady-State Performance of Kalman Filter for DPLL
Institute of Scientific and Technical Information of China (English)
QIAN Yi; CUI Xiaowei; LU Mingquan; FENG Zhenming
2009-01-01
For certain system models, the structure of the Kalman filter is equivalent to a second-order vari-able gain digital phase-locked loop (DPLL). To apply the knowledge of DPLLs to the design of Kalman filters, this paper studies the steady-state performance of Kalman filters for these system models. The results show that the steady-state Kalman gain has the same form as the DPLL gain. An approximate simple form for the steady-state Kalman gain is used to derive an expression for the equivalent loop bandwidth of the Kalman filter as a function of the process and observation noise variances. These results can be used to analyze the steady-state performance of a Kalman filter with DPLL theory or to design a Kalman filter model with the same steady-state performance as a given DPLL.
Multiple solutions of steady-state Poisson–Nernst–Planck equations with steric effects
International Nuclear Information System (INIS)
Lin, Tai-Chia; Eisenberg, Bob
2015-01-01
Experiments measuring currents through single protein channels show unstable currents. Channels switch between ‘open’ or ‘closed’ states in a spontaneous stochastic process called gating. Currents are either (nearly) zero or at a definite level, characteristic of each type of protein, independent of time, once the channel is open. The steady state Poisson–Nernst–Planck equations with steric effects (PNP-steric equations) describe steady current through the open channel quite well, in a wide variety of conditions. Here we study the existence of multiple solutions of steady state PNP-steric equations to see if they themselves, without modification or augmentation, can describe two levels of current. We prove that there are two steady state solutions of PNP-steric equations for (a) three types of ion species (two types of cations and one type of anion) with a positive constant permanent charge, and (b) four types of ion species (two types of cations and their counter-ions) with a constant permanent charge but no sign condition. The excess currents (due to steric effects) associated with these two steady state solutions are derived and expressed as two distinct formulas. Our results indicate that PNP-steric equations may become a useful model to study spontaneous gating of ion channels. Spontaneous gating is thought to involve small structural changes in the channel protein that perhaps produce large changes in the profiles of free energy that determine ion flow. Gating is known to be modulated by external structures. Both can be included in future extensions of our present analysis. (paper)
Progress on advanced tokamak and steady-state scenario development on DIII-D and NSTX
Energy Technology Data Exchange (ETDEWEB)
Doyle, E J [Department of Electrical Engineering and PSTI, University of California, Los Angeles, California 90095 (United States); Garofalo, A M [Columbia University, New York, New York 10027 (United States); Greenfield, C M [General Atomics, San Diego, California 92186-5608 (United States); Kaye, S M [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451 (United States); Menard, J E [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451 (United States); Murakami, M [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Sabbagh, S A [Columbia University, New York, New York 10027 (United States); Austin, M E [University of Texas-Austin, Austin, Texas 78712 (United States); Bell, R E [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451 (United States); Burrell, K H [General Atomics, San Diego, California 92186-5608 (United States); Ferron, J R [General Atomics, San Diego, California 92186-5608 (United States); Gates, D A [Princeton Plasma Physics Lab., Princeton, New Jersey 08543-0451 (United States); Groebner, R J; Hyatt, A W; Luce, T C; Petty, C C; Wade, M R; Waltz, R E [General Atomics, San Diego, California 92186-5608 (United States); Jayakumar, R J [Lawrence Livermore National Lab., Livermore, California 94550 (United States); Kinsey, J E [Lehigh Univ., Bethlehem, Pennsylvania 18015 (United States); LeBlanc, B P [Princeton Plasma Physics Lab., Princeton, New Jersey 08543-0451 (United States); McKee, G R [Univ. of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Okabayashi, M [Princeton Plasma Physics Lab., Princeton, New Jersey 08543-0451 (United States); Peng, Y-K M [Oak Ridge National Lab., Oak Ridge, Tennessee 37831 (United States); Politzer, P A [General Atomics, San Diego, California 92186-5608 (United States); Rhodes, T L [Dept. of Electrical Engineering and PSTI, Univ. of California, Los Angeles, California 90095 (United States)
2006-12-15
Advanced tokamak (AT) research seeks to develop steady-state operating scenarios for ITER and other future devices from a demonstrated scientific basis. Normalized target parameters for steady-state operation on ITER are 100% non-inductive current operation with a bootstrap current fraction f{sub BS} {>=} 60%, q{sub 95} {approx} 4-5 and G {identical_to}{beta}{sub N}H{sub scaling}/q{sub 95}{sup 2} {>=}0.3. Progress in realizing such plasmas is considered in terms of the development of plasma control capabilities and scientific understanding, leading to improved AT performance. NSTX has demonstrated active resistive wall mode stabilization with low, ITER-relevant, rotation rates below the critical value required for passive stabilization. On DIII-D, experimental observations and GYRO simulations indicate that ion internal transport barrier (ITB) formation at rational-q surfaces is due to equilibrium zonal flows generating high local E ? B shear levels. In addition, stability modelling for DIII-D indicates a path to operation at {beta}{sub N} {>=} 4 with q{sub min} {>=} 2, using broad, hollow current profiles to increase the ideal wall stability limit. Both NSTX and DIII-D have optimized plasma performance and expanded AT operational limits. NSTX now has long-pulse, high performance discharges meeting the normalized targets for an spherical torus-based component test facility. DIII-D has developed sustained discharges combining high beta and ITBs, with performance approaching levels required for AT reactor concepts, e.g. {beta}{sub N} = 4, H{sub 89} = 2.5, with f{sub BS} > 60%. Most importantly, DIII-D has developed ITER steady-state demonstration discharges, simultaneously meeting the targets for steady-state Q {>=} 5 operation on ITER set out above, substantially increasing confidence in ITER meeting its steady-state performance objective.
Analysis of the steady-state operation of vacuum systems for fusion machines
International Nuclear Information System (INIS)
Roose, T.R.; Hoffman, M.A.; Carlson, G.A.
1975-01-01
A computer code named GASBAL was written to calculate the steady-state vacuum system performance of multi-chamber mirror machines as well as rather complex conventional multichamber vacuum systems. Application of the code, with some modifications, to the quasi-steady tokamak operating period should also be possible. Basically, GASBAL analyzes free molecular gas flow in a system consisting of a central chamber (the plasma chamber) connected by conductances to an arbitrary number of one- or two-chamber peripheral tanks. Each of the peripheral tanks may have vacuum pumping capability (pumping speed), sources of cold gas, and sources of energetic atoms. The central chamber may have actual vacuum pumping capability, as well as a plasma capable of ionizing injected atoms and impinging gas molecules and ''pumping'' them to a peripheral chamber. The GASBAL code was used in the preliminary design of a large mirror machine experiment--LLL's MX
Directory of Open Access Journals (Sweden)
Lun Yang
2018-04-01
Full Text Available The existing studies on probabilistic steady-state analysis of integrated energy systems (IES are limited to integrated electricity and gas networks or integrated electricity and heating networks. This paper proposes a probabilistic steady-state analysis of integrated electricity, gas and heating networks (EGH-IES. Four typical operation modes of an EGH-IES are presented at first. The probabilistic energy flow problem of the EGS-IES considering its operation modes and correlated uncertainties in wind/solar power and electricity/gas/heat loads is then formulated and solved by the Monte Carlo method based on Latin hypercube sampling and Nataf transformation. Numerical simulations are conducted on a sample EGH-IES working in the “electricity/gas following heat” mode to verify the probabilistic analysis proposed in this paper and to study the effects of uncertainties and correlations on the operation of the EGH-IES, especially uncertainty transmissions among the subnetworks.
Steady-state and transient heat transfer through fins of complex geometry
Directory of Open Access Journals (Sweden)
Taler Dawid
2014-06-01
Full Text Available Various methods for steady-state and transient analysis of temperature distribution and efficiency of continuous-plate fins are presented. For a constant heat transfer coefficient over the fin surface, the plate fin can be divided into imaginary rectangular or hexangular fins. At first approximate methods for determining the steady-state fin efficiency like the method of equivalent circular fin and the sector method are discussed. When the fin geometry is complex, thus transient temperature distribution and fin efficiency can be determined using numerical methods. A numerical method for transient analysis of fins with complex geometry is developed. Transient temperature distributions in continuous fins attached to oval tubes is computed using the finite volume - finite element methods. The developed method can be used in the transient analysis of compact heat exchangers to calculate correctly the heat flow rate transferred from the finned tubes to the fluid.
Effect of steady and time-harmonic magnetic fields on macrosegragation in alloy solidification
Energy Technology Data Exchange (ETDEWEB)
Incropera, F.P.; Prescott, P.J. [Purdue Univ., West Lafayette, IN (United States)
1995-12-31
Buoyancy-induced convection during the solidification of alloys can contribute significantly to the redistribution of alloy constituents, thereby creating large composition gradients in the final ingot. Termed macrosegregation, the condition diminishes the quality of the casting and, in the extreme, may require that the casting be remelted. The deleterious effects of buoyancy-driven flows may be suppressed through application of an external magnetic field, and in this study the effects of both steady and time-harmonic fields have been considered. For a steady magnetic field, extremely large field strengths would be required to effectively dampen convection patterns that contribute to macrosegregation. However, by reducing spatial variations in temperature and composition, turbulent mixing induced by a time-harmonic field reduces the number and severity of segregates in the final casting.
Single-channel model for steady thermal-hydraulic analysis in nuclear reactor
International Nuclear Information System (INIS)
Zhang Xiaoying; Huang Yuanyuan
2010-01-01
This article established a single-channel model for steady analysis in the reactor and an example of thermal-hydraulic analysis was made by using this model, including the Maximum heat flux density of fuel element, enthalpy, Coolant flow, various kinds of pressure drop, enthalpy increase in average tube and thermal tube. I also got the Coolant temperature distribution and the fuel element temperature distribution and analysis of the final result. The results show that some relevant parameters which we got in this paper are well coincide with the actual operating parameters. It is also show that the single-channel model can be used to the steady thermal-hydraulic analysis. (authors)
Unraveling the Nature of Steady Magnetopause Reconnection Versus Flux Transfer Events
Raeder, J.
2002-12-01
Magnetic reconnection is a fundamental mode of energy and momentum transfer from the solar wind to the magnetosphere. It is known to occur in different forms depending on solar wind and magnetospheric conditions. In particular, steady reconnection can be distinguished from pulse-like reconnection events which are also known as Flux Transfer Events (FTEs). The formation mechanism of FTEs and their contolling factors remain controversial. We use global MHD simulations of Earth's magnetosphere to show that for southward IMF conditions: a) steady reconnection preferentially occurs without FTEs when the stagnation flow line nearly coincides with the X-line location, which requires small dipole tilt and nearly due southward IMF, b) FTEs occur when the flow/field symmetry is broken, which requires either a large dipole tilt and/or a substantial east-west component of the IMF, c) the predicted spacecraft signature and the repetition frequency of FTEs in the simulations agrees very well with typical observations, lending credibility to the the model, d) the fundamental process that leads to FTE formation is multiple X-line formation caused by the flow and field patterns in the magnetosheath and requires no intrinsic plasma property variations like variable resistivity, e) if the dipole tilt breaks the symmetry FTEs occur only in the winter hemisphere whereas the reconnection signatures in the summer hemisphere are steady with no bipolar FTE-like signatures, f) if the IMF east-west field component breaks the symmetry FTEs occur in both hemispheres, and g) FTE formation depends on sufficient resolution and low diffusion in the model -- coarse resolution and/or high diffusivity lead to flow-through reconnection signatures that appear unphysical given the frequent observation of FTEs.
International Nuclear Information System (INIS)
Vijayan, P.K.; Nayak, A.K.; Bade, M.H.; Kumar, N.; Saha, D.; Sinha, R.K.
2002-01-01
Scaling methods for both single-phase and two-phase natural circulation systems have been presented. For single-phase systems, simulation of the steady state flow can be achieved by preserving just one nondimensional parameter. For uniform diameter two-phase systems also, it is possible to simulate the steady state behaviour with just one non-dimensional parameter. Simulation of the stability behaviour requires geometric similarity in addition to the similarity of the physical parameters appearing in the governing equations. The scaling laws proposed have been tested with experimental data in case of single-phase natural circulation. (author)
Bosma, T; Pikkemaat, MG; Kingma, Jacob; Dijk, J; Janssen, DB
2003-01-01
Haloalkane dehalogenase from Rhodococcus rhodochrous NCIMB 13064 (DhaA) catalyzes the hydrolysis of carbon-halogen bonds in a wide range of haloalkanes. We examined the steady-state and pre-steady-state kinetics of halopropane conversion by DhaA to illuminate mechanistic details of the
The flows structure in unsteady gas flow in pipes with different cross-sections
Plotnikov Leonid; Nevolin Alexandr; Nikolaev Dmitrij
2017-01-01
The results of numerical simulation and experimental study of the structure of unsteady flows in pipes with different cross sections are presented in the article. It is shown that the unsteady gas flow in a circular pipe is axisymmetric without secondary currents. Steady vortex structures (secondary flows) are observed in pipes with cross sections in the form of a square and an equilateral triangle. It was found that these secondary flows have a significant impact on gas flows in pipes of com...
Minimal gain marching schemes: searching for unstable steady-states with unsteady solvers
de S. Teixeira, Renan; S. de B. Alves, Leonardo
2017-12-01
Reference solutions are important in several applications. They are used as base states in linear stability analyses as well as initial conditions and reference states for sponge zones in numerical simulations, just to name a few examples. Their accuracy is also paramount in both fields, leading to more reliable analyses and efficient simulations, respectively. Hence, steady-states usually make the best reference solutions. Unfortunately, standard marching schemes utilized for accurate unsteady simulations almost never reach steady-states of unstable flows. Steady governing equations could be solved instead, by employing Newton-type methods often coupled with continuation techniques. However, such iterative approaches do require large computational resources and very good initial guesses to converge. These difficulties motivated the development of a technique known as selective frequency damping (SFD) (Åkervik et al. in Phys Fluids 18(6):068102, 2006). It adds a source term to the unsteady governing equations that filters out the unstable frequencies, allowing a steady-state to be reached. This approach does not require a good initial condition and works well for self-excited flows, where a single nonzero excitation frequency is selected by either absolute or global instability mechanisms. On the other hand, it seems unable to damp stationary disturbances. Furthermore, flows with a broad unstable frequency spectrum might require the use of multiple filters, which delays convergence significantly. Both scenarios appear in convectively, absolutely or globally unstable flows. An alternative approach is proposed in the present paper. It modifies the coefficients of a marching scheme in such a way that makes the absolute value of its linear gain smaller than one within the required unstable frequency spectra, allowing the respective disturbance amplitudes to decay given enough time. These ideas are applied here to implicit multi-step schemes. A few chosen test cases
Wind turbine blades: A study of prototypes in a steady regime - Unsteady considerations
Leblanc, R.; Goethals, R.; de Saint Louvent, B.
1981-11-01
The results of comparisons of numerical models with experimental results for the performance of prototype wind turbines in steady flows are presented, along with preliminary results on behavior in unsteady flows. The numerical models are based on previous schemes devised for propellers, with modifications for small perturbations, significant radial velocity effects from the wake, and the fact that the speed is induced. Two computational methods are currently used, one a method of short blades, the other the Prandtl lifting line theory. Trials have been run in the T4 wind tunnel using a 3 m horizontal axis machine and a 2.5 m Darrieus. Attention is given to modeling the structural dynamics and turbulent flow structures encountered by wind turbines. Experimental results relating windspeed, angle of attack, and output are presented. Optimization studies have indicated that wind farms will require a 6-7 blade diameter unit spacing to maintain satisfactory group output efficiencies.
Steady state and transient heat transfer on molten salt natural circulation loop
International Nuclear Information System (INIS)
Kudariyawar, Jayaraj Y.; Vaidya, A.M.; Maheshwari, N.K.; Satyamurthy, P.
2016-01-01
In this work, heat transfer characteristics of Molten Salt Natural Circulation Loop (MSNCL) are studied using 3D CFD simulations. Molten Nitrate salt, NaNO_3+KNO_3 (60:40 ratio by weight), is used as a fluid in MSNCL. In the MSNCL, in heater section, flow is developing and also mixed convection flow regime exists. The local Nusselt number variation in heater is calculated from computed data and is compared with that from Boelter correlation. Steady state heat transfer characteristics are obtained using CFD simulations. Transient heat transfer characteristics in the oscillatory flow formed in MSNCL with horizontal heater configuration are also studied and are found to be different as compared to vertical heater configuration. (author)
Development of steady thermal-hydraulic analysis code for China advanced research reactor
International Nuclear Information System (INIS)
Tian Wenxi; Qiu Suizheng; Guo Yun; Su Guanghui; Jia Dounan; Liu Tiancai; Zhang Jianwei
2006-01-01
A multi-channel model steady-state thermal-hydraulic analysis code was developed for China Advanced Research Reactor (CARR). By simulating the whole reactor core, the detailed flow distribution in the core was obtained. The result shows that the structure size plays the most important role in flow distribution and the influence of core power could be neglected under single-phase flow. The temperature field of fuel element under unsymmetrical cooling condition was also obtained, which is necessary for the further study such as stress analysis etc. of the fuel element. At the same time, considering the hot channel effect including engineering factor and nuclear factor, calculation of hot channel was carried out and it is proved that all thermal-hydraulic parameters accord with the Safety Regulation of CARR. (authors)
Development of a steady thermal-hydraulic analysis code for the China Advanced Research Reactor
Institute of Scientific and Technical Information of China (English)
TIAN Wenxi; QIU Suizheng; GUO Yun; SU Guanghui; JIA Dounan; LIU Tiancai; ZHANG Jianwei
2007-01-01
A multi-channel model steady-state thermalhydraulic analysis code was developed for the China Advanced Research Reactor (CARR). By simulating the whole reactor core, the detailed mass flow distribution in the core was obtained. The result shows that structure size plays the most important role in mass flow distribution, and the influence of core power could be neglected under singlephase flow. The temperature field of the fuel element under unsymmetrical cooling condition was also obtained, which is necessary for further study such as stress analysis, etc. Of the fuel element. At the same time, considering the hot channel effect including engineering factor and nuclear factor, calculation of the mean and hot channel was carried out and it is proved that all thermal-hydraulic parameters satisfy the "Safety design regulation of CARR".
Adaptive solution of some steady-state fluid-structure interaction problems
International Nuclear Information System (INIS)
Etienne, S.; Pelletier, D.
2003-01-01
This paper presents a general integrated and coupled formulation for modeling the steady-state interaction of a viscous incompressible flow with an elastic structure undergoing large displacements (geometric non-linearities). This constitutes an initial step towards developing a sensitivity analysis formulation for this class of problems. The formulation uses velocity and pressures as unknowns in a flow domain and displacements in the structural components. An interface formulation is presented that leads to clear and simple finite element implementation of the equilibrium conditions at the fluid-solid interface. Issues of error estimation and mesh adaptation are discussed. The adaptive formulation is verified on a problem with a closed form solution. It is then applied to a sample case for which the structure undergoes large displacements induced by the flow. (author)
Measurement of non-steady-state free fatty acid turnover
International Nuclear Information System (INIS)
Jensen, M.D.; Heiling, V.; Miles, J.M.
1990-01-01
The accuracy of non-steady-state equations for measuring changes in free fatty acid rate of appearance (Ra) is unknown. In the present study, endogenous lipolysis (traced with [ 14 C]-linoleate) was pharmacologically suppressed in six conscious mongrel dogs. A computer-responsive infusion pump was then used to deliver an intravenous oleic acid emulsion in both constant and linear gradient infusion modes. Both non-steady-state equations with various effective volumes of distribution (V) and steady-state equations were used to measure oleate Ra [( 14 C]oleate). Endogenous lipolysis did not change during the experiment. When oleate Ra increased in a linear gradient fashion, only non-steady-state equations with a large (150 ml/kg) V resulted in erroneous values (9% overestimate, P less than 0.05). In contrast, when oleate Ra decreased in a similar fashion, steady-state and standard non-steady-state equations (V = plasma volume = 50 ml/kg) overestimated total oleate Ra (18 and 7%, P less than 0.001 and P less than 0.05, respectively). Overall, non-steady-state equations with an effective V of 90 ml/kg (1.8 x plasma volume) allowed the most accurate estimates of oleate Ra
Energy Technology Data Exchange (ETDEWEB)
Henandez Rosete, Alejandro; Mazur C, Zdzislaw [Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)
2007-11-15
The results of the simulation by CFD (Computacional Fluid Dynamics) realized to the first stage of a gas turbine GE Frame 7 are presented. The analysis includes the 3D modeling of the flow channel in the nozzle and the movable blade to know the velocities distributions, temperatures and pressures of the main hot gas flow that are developed in the Inter stage. The results are influenced by the imposed border conditions in the properties of the main flow, the rotation of the movable blade, as well as the simulation of cooling air injection in the nozzle. The present study focuses in the validation of the model of the meshes of the ensemble nozzle-blade, for later realize an analysis of conjugated heat transfer in a model with ceramic lining type heat barrier (THB) in the movable blade. The analysis is realized in a CFD commercial code oriented to turbo-machinery using the equations of unstable flows 3D of Navier Stokes. [Spanish] Se presentan los resultados de la simulacion por CFD (Computacional Fluid Dynamics) realizada a la primera etapa de una turbina de gas GE Frame 7. El analisis incluye la modelacion tridimensional del canal de flujo en la tobera y el alabe movil para conocer las distribuciones de las velocidades, temperaturas y presiones del flujo principal de gases calientes que se desarrollan en la inter etapa. Los resultados son influenciados por las condiciones de frontera impuestos en las propiedades del flujo principal, la rotacion del alabe movil, asi como la simulacion de inyeccion de aire de enfriamiento en la tobera. El presente estudio se enfoca en la validacion del modelo de la malla del conjunto tobera-alabe, para posteriormente realizar un analisis de transferencia de calor conjugada en un modelo con recubrimiento ceramico tipo barrera termica (TBC) en el alabe movil. El analisis es realizado en un codigo de CFD comercial orientado a turbomaquinaria utilizando las ecuaciones de flujos inestables 3D de Navier Stokes.
Davletshin, I. A.; Dushina, O. A.; Mikheev, N. I.; Kolchin, S. A.
2017-11-01
The pulsating flow in a circular channel with semicircular annular ribs as discrete roughness elements has been studied experimentally. Air flow under atmospheric conditions at the channel inlet has been considered. Steady and pulsating air flow has been studied under different frequencies and amplitudes of forced pulsations generated by periodic blockage of the channel cross section by a rotating flap. Flow resistance in pulsating regimes has been estimated from the average static pressure drop. The resistance values attained twice the steady flow ones.
Directory of Open Access Journals (Sweden)
Pankaj Thakur
2014-01-01
Full Text Available Thermal stress and strain rates in a thick walled rotating cylinder under steady state temperature has been derived by using Seth’s transition theory. For elastic-plastic stage, it is seen that with the increase of temperature, the cylinder having smaller radii ratios requires lesser angular velocity to become fully plastic as compared to cylinder having higher radii ratios The circumferential stress becomes larger and larger with the increase in temperature. With increase in thickness ratio stresses must be decrease. For the creep stage, it is seen that circumferential stresses for incompressible materials maximum at the internal surface as compared to compressible material, which increase with the increase in temperature and measure n.
Analysis of the steady state hydraulic behaviour of the ITER blanket cooling system
Energy Technology Data Exchange (ETDEWEB)
Di Maio, P.A., E-mail: pietroalessandro.dimaio@unipa.it [Dipartimento di Energia, Ingegneria dell’Informazione e Modelli Matematici, Università di Palermo, Viale delle Scienze, 90128 Palermo (Italy); Dell’Orco, G.; Furmanek, A. [ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St Paul Lez Durance Cedex (France); Garitta, S. [Dipartimento di Energia, Ingegneria dell’Informazione e Modelli Matematici, Università di Palermo, Viale delle Scienze, 90128 Palermo (Italy); Merola, M.; Mitteau, R.; Raffray, R. [ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St Paul Lez Durance Cedex (France); Spagnuolo, G.A.; Vallone, E. [Dipartimento di Energia, Ingegneria dell’Informazione e Modelli Matematici, Università di Palermo, Viale delle Scienze, 90128 Palermo (Italy)
2015-10-15
Highlights: • Nominal steady state hydraulic behaviour of ITER blanket standard sector cooling system has been investigated. • Numerical simulations have been run adopting a qualified thermal-hydraulic system code. • Hydraulic characteristic functions and coolant mass flow rates, velocities and pressure drops have been assessed. • Most of the considered circuits are able to effectively cool blanket modules, meeting ITER requirements. - Abstract: The blanket system is the ITER reactor component devoted to providing a physical boundary for plasma transients and contributing to thermal and nuclear shielding of vacuum vessel, magnets and external components. It is expected to be subjected to significant heat loads under nominal conditions and its cooling system has to ensure an adequate cooling, preventing any risk of critical heat flux occurrence while complying with pressure drop limits. At the University of Palermo a study has been performed, in cooperation with the ITER Organization, to investigate the steady state hydraulic behaviour of the ITER blanket standard sector cooling system. A theoretical–computational approach based on the finite volume method has been followed, adopting the RELAP5 system code. Finite volume models of the most critical blanket cooling circuits have been set-up, realistically simulating the coolant flow domain. The steady state hydraulic behaviour of each cooling circuit has been investigated, determining its hydraulic characteristic function and assessing the spatial distribution of coolant mass flow rates, velocities and pressure drops under reference nominal conditions. Results obtained have indicated that the investigated cooling circuits are able to provide an effective cooling to blanket modules, generally meeting ITER requirements in term of pressure drop and velocity distribution, except for a couple of circuits that are being revised.
Tacina, R. R.
1984-01-01
Non-steady combustion problems can result from engine sources such as accelerations, decelerations, nozzle adjustments, augmentor ignition, and air perturbations into and out of the compressor. Also non-steady combustion can be generated internally from combustion instability or self-induced oscillations. A premixed-prevaporized combustor would be particularly sensitive to flow transients because of its susceptability to flashback-autoignition and blowout. An experimental program, the Transient Flow Combustion Study is in progress to study the effects of air and fuel flow transients on a premixed-prevaporized combustor. Preliminary tests performed at an inlet air temperature of 600 K, a reference velocity of 30 m/s, and a pressure of 700 kPa. The airflow was reduced to 1/3 of its original value in a 40 ms ramp before flashback occurred. Ramping the airflow up has shown that blowout is more sensitive than flashback to flow transients. Blowout occurred with a 25 percent increase in airflow (at a constant fuel-air ratio) in a 20 ms ramp. Combustion resonance was found at some conditions and may be important in determining the effects of flow transients.
Surface obstacles in pulsatile flow
Carr, Ian A.; Plesniak, Michael W.
2017-11-01
Flows past obstacles mounted on flat surfaces have been widely studied due to their ubiquity in nature and engineering. For nearly all of these studies, the freestream flow over the obstacle was steady, i.e., constant velocity, unidirectional flow. Unsteady, pulsatile flows occur frequently in biology, geophysics, biomedical engineering, etc. Our study is aimed at extending the comprehensive knowledge base that exists for steady flows to considerably more complex pulsatile flows. Characterizing the vortex and wake dynamics of flows around surface obstacles embedded in pulsatile flows can provide insights into the underlying physics in all wake and junction flows. In this study, we experimentally investigate the wake of two canonical obstacles: a cube and a circular cylinder with an aspect ratio of unity. Our previous studies of a surface-mounted hemisphere in pulsatile flow are used as a baseline for these two new, more complex geometries. Phase-averaged PIV and hot-wire anemometry are used to characterize the dynamics of coherent structures in the wake and at the windward junction of the obstacles. Complex physics occur during the deceleration phase of the pulsatile inflow. We propose a framework for understanding these physics based on self-induced vortex propagation, similar to the phenomena exhibited by vortex rings.
Impact of electric vehicles in the steady state operation of distribution systems
Erasmo Saraiva de Castro
2015-01-01
This work aims to quantify the impact in the steady state operation of a distribution system when electric vehicles are connected. It is worth noting that the connection of them may cause significant changes in the voltage profile, in the degree of voltage unbalance and in the electrical losses of the system. In order to make this analysis, a three-phase power flow program was developed in MATLAB language. This program is based on the Ladder Iterative Technique and it contains models of overh...
International Nuclear Information System (INIS)
Rao, Y.F.; Fukuda, K.; Hasegawa, S.
1986-01-01
Steady and transient analytical investigation with the Galerkin method has been performed on natural convection in a horizontal porous annulus heated from the inner surface. Three families of convergent solutions, appearing one after another with increasing RaDa numbers, were obtained corresponding to different initial conditions. Despite the fact that the flow structures of two branching solutions are quite different, there exists a critical RaDa number at which their overall heat transfer rates have the same value. The bifurcation point was determined numerically, which coincided very well with that from experimental observation. The solutions in which higher wavenumber modes are dominant agree better with experimental data of overall heat transfer
Quantum thermodynamics of nanoscale steady states far from equilibrium
Taniguchi, Nobuhiko
2018-04-01
We develop an exact quantum thermodynamic description for a noninteracting nanoscale steady state that couples strongly with multiple reservoirs. We demonstrate that there exists a steady-state extension of the thermodynamic function that correctly accounts for the multiterminal Landauer-Büttiker formula of quantum transport of charge, energy, or heat via the nonequilibrium thermodynamic relations. Its explicit form is obtained for a single bosonic or fermionic level in the wide-band limit, and corresponding thermodynamic forces (affinities) are identified. Nonlinear generalization of the Onsager reciprocity relations are derived. We suggest that the steady-state thermodynamic function is also capable of characterizing the heat current fluctuations of the critical transport where the thermal fluctuations dominate. Also, the suggested nonequilibrium steady-state thermodynamic relations seemingly persist for a spin-degenerate single level with local interaction.
Steady state and transient critical heat flux examinations
International Nuclear Information System (INIS)
Szabados, L.
1978-02-01
In steady state conditions within the P.W.R. parameter range the critical heat flux correlations based on local parameters reproduce the experimental data with less deviations than those based on system parameters. The transient experiments were restricted for the case of power transients. A data processing method for critical heat flux measurements has been developed and the applicability of quasi steady state calculation has been verified. (D.P.)
Steady state ion acceleration by a circularly polarized laser pulse
International Nuclear Information System (INIS)
Zhang Xiaomei; Shen Baifei; Cang Yu; Li Xuemei; Jin Zhangying; Wang Fengchao
2007-01-01
The steady state ion acceleration at the front of a cold solid target by a circularly polarized flat-top laser pulse is studied with one-dimensional particle-in-cell (PIC) simulation. A model that ions are reflected by a steady laser-driven piston is used by comparing with the electrostatic shock acceleration. A stable profile with a double-flat-top structure in phase space forms after ions enter the undisturbed region of the target with a constant velocity
Calculation analysis on steady state natural circulation characteristics
International Nuclear Information System (INIS)
Wang Fei; Nie Changhua; Huang Yanping
2005-01-01
The calculation results of single-phase steady state natural circulation characteristics by using Retran02 code have been presented, good agreement is achieved between the verified calculation result and the experimental data which were conducted at a test facility. Based on the calculation model, some sensibility analyses were made and much deeper understanding for single-phase steady state natural circulation characteristics was obtained. (author)
Steady-state leaching of tritiated water from silica gel
DEFF Research Database (Denmark)
Das, H.A.; Hou, Xiaolin
2009-01-01
Aqueous leaching of tritium from silica gel, loaded by absorption of water vapor, makes part of reactor de-commissioning. It is found to follow the formulation of steady-state diffusion.......Aqueous leaching of tritium from silica gel, loaded by absorption of water vapor, makes part of reactor de-commissioning. It is found to follow the formulation of steady-state diffusion....
Fundamental structure of steady plastic shock waves in metals
Molinari, A.; Ravichandran, G.
2004-01-01
The propagation of steady plane shock waves in metallic materials is considered. Following the constitutive framework adopted by R. J. Clifton [Shock Waves and the Mechanical Properties of Solids, edited by J. J. Burke and V. Weiss (Syracuse University Press, Syracuse, N.Y., 1971), p. 73] for analyzing elastic–plastic transient waves, an analytical solution of the steady state propagation of plastic shocks is proposed. The problem is formulated in a Lagrangian setting appropriate for large de...
Selection of steady states in planar Darcy convection
International Nuclear Information System (INIS)
Tsybulin, V.G.; Karasoezen, B.; Ergenc, T.
2006-01-01
The planar natural convection of an incompressible fluid in a porous medium is considered. We study the selection of steady states under temperature perturbations on the boundary. A selection map is introduced in order to analyze the selection of a steady state from a continuous family of equilibria which exists under zero boundary conditions. The results of finite-difference modeling for a rectangular enclosure are presented
International Nuclear Information System (INIS)
Min Kim, Jung; Kate Gurnon, A.; Wagner, Norman J.; Eberle, Aaron P. R.; Porcar, Lionel
2014-01-01
The microstructure-rheology relationship for a model, thermoreversible nanoparticle gel is investigated using a new technique of time-resolved neutron scattering under steady and time-resolved large amplitude oscillatory shear (LAOS) flows. A 21 vol. % gel is tested with varying strength of interparticle attraction. Shear-induced structural anisotropy is observed as butterfly scattering patterns and quantified through an alignment factor. Measurements in the plane of flow show significant, local anisotropy develops with alignment along the compressional axis of flow, providing new insights into how gels flow. The microstructure-rheology relationship is analyzed through a new type of structure-Lissajous plot that shows how the anisotropic microstructure is responsible for the observed LAOS response, which is beyond a response expected for a purely viscous gel with constant structure. The LAOS shear viscosities are observed to follow the “Delaware-Rutgers” rule. Rheological and microstructural data are successfully compared across a broad range of conditions by scaling the shear rate by the strength of attraction, providing a method to compare behavior between steady shear and LAOS experiments. However, important differences remain between the microstructures measured at comparatively high frequency in LAOS experiments and comparable steady shear experiments that illustrate the importance of measuring the microstructure to properly interpret the nonlinear, dynamic rheological response
Energy Technology Data Exchange (ETDEWEB)
Min Kim, Jung; Kate Gurnon, A.; Wagner, Norman J., E-mail: wagnernj@udel.edu [Department of Chemical and Biomolecular Engineering and Center for Neutron Science, University of Delaware, Newark, Delaware 19716 (United States); Eberle, Aaron P. R. [NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Porcar, Lionel [NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 and Institut Laue-Langevin, BP 156, F-38042 Grenoble Cedex 9 (France)
2014-09-01
The microstructure-rheology relationship for a model, thermoreversible nanoparticle gel is investigated using a new technique of time-resolved neutron scattering under steady and time-resolved large amplitude oscillatory shear (LAOS) flows. A 21 vol. % gel is tested with varying strength of interparticle attraction. Shear-induced structural anisotropy is observed as butterfly scattering patterns and quantified through an alignment factor. Measurements in the plane of flow show significant, local anisotropy develops with alignment along the compressional axis of flow, providing new insights into how gels flow. The microstructure-rheology relationship is analyzed through a new type of structure-Lissajous plot that shows how the anisotropic microstructure is responsible for the observed LAOS response, which is beyond a response expected for a purely viscous gel with constant structure. The LAOS shear viscosities are observed to follow the “Delaware-Rutgers” rule. Rheological and microstructural data are successfully compared across a broad range of conditions by scaling the shear rate by the strength of attraction, providing a method to compare behavior between steady shear and LAOS experiments. However, important differences remain between the microstructures measured at comparatively high frequency in LAOS experiments and comparable steady shear experiments that illustrate the importance of measuring the microstructure to properly interpret the nonlinear, dynamic rheological response.
Bohling, Geoffrey C.; Butler, James J.; Zhan, Xiaoyong; Knoll, Michael D.
2007-01-01
Hydraulic tomography is a promising approach for obtaining information on variations in hydraulic conductivity on the scale of relevance for contaminant transport investigations. This approach involves performing a series of pumping tests in a format similar to tomography. We present a field‐scale assessment of hydraulic tomography in a porous aquifer, with an emphasis on the steady shape analysis methodology. The hydraulic conductivity (K) estimates from steady shape and transient analyses of the tomographic data compare well with those from a tracer test and direct‐push permeameter tests, providing a field validation of the method. Zonations based on equal‐thickness layers and cross‐hole radar surveys are used to regularize the inverse problem. The results indicate that the radar surveys provide some useful information regarding the geometry of the K field. The steady shape analysis provides results similar to the transient analysis at a fraction of the computational burden. This study clearly demonstrates the advantages of hydraulic tomography over conventional pumping tests, which provide only large‐scale averages, and small‐scale hydraulic tests (e.g., slug tests), which cannot assess strata connectivity and may fail to sample the most important pathways or barriers to flow.
Gao, Y.; Lin, Q.; Bijeljic, B.; Blunt, M. J.
2017-12-01
To observe intermittency in consolidated rock, we image a steady state flow of brine and decane in Bentheimer sandstone. We devise an experimental method based on X-ray differential imaging method to examine how changes in flow rate impact the pore-scale distribution of fluids during co-injection flow under dynamic flow conditions at steady state. This helps us elucidate the diverse flow regimes (connected, intermittent break-up, or continual break-up of the non-wetting phase pathways) for two capillary numbers. Also, relative permeability curves under both capillary and viscous limited conditions could be measured. We have performed imbibition sample floods using oil-brine and measured steady state relative permeability on a sandstone rock core in order to fully characterize the flow behaviour at low and high Ca. Two sets of experiments at high and low flow rates are provided to explore the time-evolution of the non-wetting phase clusters distribution under different flow conditions. The high flow rate is 0.5 mL/min, whose corresponding capillary number is 7.7×10-6. The low flow rate is 0.02 mL/min, whose capillary number is 3.1×10-7. A procedure based on using high-salinity brine as the contrast phase and applying differential imaging between the dry scan and that of the sample saturation with a 30 wt% Potassium iodide (KI) doped brine help to make sure there is no non-wetting phase in micro-pores. Then the intermittent phase in multiphase flow image at high Ca can be quantified by obtaining the differential image between the 30 wt% KI brine image and the scans that taken at each fixed fractional flow. By using the grey scale histogram distribution of the raw images at each condition, the oil proportion in the intermittent phase can be calculated. The pressure drops at each fractional flow at low and high Ca can be measured by high-precision pressure differential sensors and utilized to calculate to the relative permeability at pore scale. The relative
International Nuclear Information System (INIS)
Poe, C.H.; Owocki, S.P.; Castor, J.I.
1990-01-01
The steady state solution topology for absorption line-driven flows is investigated for the condition that the Sobolev approximation is not used to compute the line force. The solution topology near the sonic point is of the nodal type with two positive slope solutions. The shallower of these slopes applies to reasonable lower boundary conditions and realistic ion thermal speed v(th) and to the Sobolev limit of zero of the usual Castor, Abbott, and Klein model. At finite v(th), this solution consists of a family of very similar solutions converging on the sonic point. It is concluded that a non-Sobolev, absorption line-driven flow with a realistic values of v(th) has no uniquely defined steady state. To the extent that a pure absorption model of the outflow of stellar winds is applicable, radiatively driven winds should be intrinsically variable. 34 refs
Approach to the energetic coaxial gun of the steady-state mode operation
International Nuclear Information System (INIS)
Hirano, Kei-ichi
1993-01-01
Behaviors of a coaxial plasma gun operated in a steady-state mode have been studied. It is shown that the gun has potentialities to yield an energetic plasma beam, if a supersonic plasma flow is supplied instead of a neutral gas and if shorting out of the Hall potential is minimized on the surfaces of the electrodes. The former is necessary because a electromagnetic force chokes the subsonic flow appearing in the ionizing zone of the inlet gas. The latter is achieved if the electrodes are segmented into many insulated short elements along the axis. The required minimum number of the segmentation is estimated by the newly developed model based on the boundary layer concept. (author)
International Nuclear Information System (INIS)
Echavarren, F.M.; Lobato, E.; Rouco, L.; Gomez, T.
2011-01-01
A steady state security margin for a particular operating point can be defined as the distance from this initial point to the secure operating limits of the system. Four of the most used steady state security margins are the power flow feasibility margin, the contingency feasibility margin, the load margin to voltage collapse, and the total transfer capability between system areas. This is the second part of a two part paper. Part I has proposed a novel framework of a general model able to formulate, compute and improve any steady state security margin. In Part II the performance of the general model is validated by solving a variety of practical situations in modern real power systems. Actual examples of the Spanish power system will be used for this purpose. The same computation and improvement algorithms outlined in Part I have been applied for the four security margins considered in the study, outlining the convenience of defining a general framework valid for the four of them. The general model is used here in Part II to compute and improve: (a) the power flow feasibility margin (assessing the influence of the reactive power generation limits in the Spanish power system), (b) the contingency feasibility margin (assessing the influence of transmission and generation capacity in maintaining a correct voltage profile), (c) the load margin to voltage collapse (assessing the location and quantity of loads that must be shed in order to be far away from voltage collapse) and (d) the total transfer capability (assessing the export import pattern of electric power between different areas of the Spanish system). (author)
Active control of supersonic impingement tones using steady and pulsed microjets
Energy Technology Data Exchange (ETDEWEB)
Choi, J.J.; Anaswamy, A.M. [Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge (United States); Lou, H. [Department of Mechanical Engineering, FAMU - FSU, College of Engineering, Tallahassee, FL (United States); Alvi, F.S.
2006-12-15
In recent years, it has been demonstrated that direct microjet injection into the shear layer of the main jet disrupts the feedback loop inherent in high speed impinging jet flows, thereby significantly reducing the adverse effects. The amount of noise reduced by microjet actuation is known to be dependent on nozzle operating conditions. In this paper, two active control strategies using microjets are suggested to maintain a uniform, reliable, and optimal reduction of these tones over the entire range of operating conditions. In the first method, a quasi-closed loop control strategy is proposed using steady microjet injection and the proper orthogonal decomposition (POD) algorithm. The most energetic spatial mode of the unsteady pressure along the nozzle diameter is captured using the POD, which in turn is used to determine the distribution of microjet intensity along the nozzle exit. Preliminary experimental results from a STOVL supersonic jet facility at Mach 1.5 show that the quasi-closed loop control strategy, in some cases, provides an additional 8-10 dB reduction compared to axisymmetric injection at the desired operating conditions. The second method consists of a pulsed microjet injection, motivated by the need to further improve the noise suppression. It was observed that the pulsed microjet was able to bring about the same noise reduction as steady injection using approximately 40% of the corresponding mass flow rate of the steady microjet case. Moreover, as the duty cycle increased, the performance of pulsed injection was further enhanced and was observed to completely eliminate the impinging tones at all operating conditions. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Echavarren, F.M.; Lobato, E.; Rouco, L.; Gomez, T. [School of Engineering of Universidad Pontificia Comillas, C/Alberto Aguilera, 23, 28015 Madrid (Spain)
2011-02-15
A steady state security margin for a particular operating point can be defined as the distance from this initial point to the secure operating limits of the system. Four of the most used steady state security margins are the power flow feasibility margin, the contingency feasibility margin, the load margin to voltage collapse, and the total transfer capability between system areas. This is the second part of a two part paper. Part I has proposed a novel framework of a general model able to formulate, compute and improve any steady state security margin. In Part II the performance of the general model is validated by solving a variety of practical situations in modern real power systems. Actual examples of the Spanish power system will be used for this purpose. The same computation and improvement algorithms outlined in Part I have been applied for the four security margins considered in the study, outlining the convenience of defining a general framework valid for the four of them. The general model is used here in Part II to compute and improve: (a) the power flow feasibility margin (assessing the influence of the reactive power generation limits in the Spanish power system), (b) the contingency feasibility margin (assessing the influence of transmission and generation capacity in maintaining a correct voltage profile), (c) the load margin to voltage collapse (assessing the location and quantity of loads that must be shed in order to be far away from voltage collapse) and (d) the total transfer capability (assessing the export import pattern of electric power between different areas of the Spanish system). (author)
Energy Technology Data Exchange (ETDEWEB)
Kudariyawar, J.Y. [Homi Bhabha National Institue, Mumbai (India); Vaidya, A.M.; Maheshwari, K.K.; Srivastava, A.K. [Reactor Engineering Division, Bhabha Atomic Research Center, Mumbai (India); Satyamurthy, P. [ATDS, Bhabha Atomic Research Center, Mumbai (India)
2015-03-15
The steady state and transient characteristics of a molten salt natural circulation loop (NCL) are obtained by 3D CFD simulations. The working fluid is a mixture of NaNO{sub 3} and KNO{sub 3} in 60:40 ratio. Simulation is performed using PHOENICS CFD software. The computational domain is discretized by a body fitted grid generated using in-built mesh generator. The CFD model includes primary side. Primary side fluid is subjected to heat addition in heater section, heat loss to ambient (in piping connecting heater and cooler) and to secondary side (in cooler section). Reynolds Averaged Navier Stokes equations are solved along with the standard k-ε turbulence model. Validation of the model is done by comparing the computed steady state Reynolds number with that predicted by various correlations proposed previously. Transient simulations were carried out to study the flow initiations transients for different heater powers and different configurations. Similarly the ''power raising'' transient is computed and compared with in-house experimental data. It is found that, using detailed information obtained from 3D transient CFD simulations, it is possible to understand the physics of oscillatory flow patterns obtained in the loop under certain conditions.
Steady state and linear stability analysis of a supercritical water natural circulation loop
International Nuclear Information System (INIS)
Sharma, Manish; Pilkhwal, D.S.; Vijayan, P.K.; Saha, D.; Sinha, R.K.
2010-01-01
Supercritical water (SCW) has excellent heat transfer characteristics as a coolant for nuclear reactors. Besides it results in high thermal efficiency of the plant. However, the flow can experience instabilities in supercritical water reactors, as the density change is very large for the supercritical fluids. A computer code SUCLIN using supercritical water properties has been developed to carry out the steady state and linear stability analysis of a SCW natural circulation loop. The conservation equations of mass, momentum and energy have been linearized by imposing small perturbation in flow rate, enthalpy, pressure and specific volume. The equations have been solved analytically to generate the characteristic equation. The roots of the equation determine the stability of the system. The code has been qualitatively assessed with published results and has been extensively used for studying the effect of diameter, height, heater inlet temperature, pressure and local loss coefficients on steady state and stability behavior of a Supercritical Water Natural Circulation Loop (SCWNCL). The present paper describes the linear stability analysis model and the results obtained in detail.
Relative contributions of transient and steady state infiltration during ephemeral streamflow
Blasch, Kyle W.; Ferré, Ty P.A.; Hoffmann, John P.; Fleming, John B.
2006-01-01
Simulations of infiltration during three ephemeral streamflow events in a coarse‐grained alluvial channel overlying a less permeable basin‐fill layer were conducted to determine the relative contribution of transient infiltration at the onset of streamflow to cumulative infiltration for the event. Water content, temperature, and piezometric measurements from 2.5‐m vertical profiles within the alluvial sediments were used to constrain a variably saturated water flow and heat transport model. Simulated and measured transient infiltration rates at the onset of streamflow were about two to three orders of magnitude greater than steady state infiltration rates. The duration of simulated transient infiltration ranged from 1.8 to 20 hours, compared with steady state flow periods of 231 to 307 hours. Cumulative infiltration during the transient period represented 10 to 26% of the total cumulative infiltration, with an average contribution of approximately 18%. Cumulative infiltration error for the simulated streamflow events ranged from 9 to 25%. Cumulative infiltration error for typical streamflow events of about 8 hours in duration in is about 90%. This analysis indicates that when estimating total cumulative infiltration in coarse‐grained ephemeral stream channels, consideration of the transient infiltration at the onset of streamflow will improve predictions of the total volume of infiltration that may become groundwater recharge.
Effect of vadose zone on the steady-state leakage rates from landfill barrier systems
International Nuclear Information System (INIS)
Celik, B.; Rowe, R.K.; Unlue, K.
2009-01-01
Leakage rates are evaluated for a landfill barrier system having a compacted clay liner (CCL) underlain by a vadose zone of variable thickness. A numerical unsaturated flow model SEEP/W is used to simulate the moisture flow regime and steady-state leakage rates for the cases of unsaturated zones with different soil types and thicknesses. The results of the simulations demonstrate that harmonic mean hydraulic conductivity of coarse textured vadose zones is 3-4 orders of magnitude less than saturated hydraulic conductivity; whereas, the difference is only one order of magnitude for fine textured vadose zones. For both coarse and fine textured vadose zones, the effective hydraulic conductivity of the barrier system and the leakage rate to an underlying aquifer increases with increasing thickness of the vadose zone and ultimately reaches an asymptotic value for a coarse textured vadose zone thickness of about 10 m and a fine textured vadose zone thickness of about 5 m. Therefore, the fine and coarse textured vadose zones thicker than about 5 m and 10 m, respectively, act as an effective part of the barrier systems examined. Although the thickness of vadose zone affects the effective hydraulic conductivity of the overall barrier system, the results demonstrated that the hydraulic conductivity of the CCL is the dominant factor controlling the steady-state leakage rates through barrier systems having single low permeability clay layers
Implications of steady-state operation on divertor design
International Nuclear Information System (INIS)
Sevier, D.L.; Reis, E.E.; Baxi, C.B.; Silke, G.W.; Wong, C.P.C.; Hill, D.N.
1996-01-01
As fusion experiments progress towards long pulse or steady state operation, plasma facing components are undergoing a significant change in their design. This change represents the transition from inertially cooled pulsed systems to steady state designs of significant power handling capacity. A limited number of Plasma Facing Component (PFC) systems are in operation or planning to address this steady state challenge at low heat flux. However in most divertor designs components are required to operate at heat fluxes at 5 MW/m 2 or above. The need for data in this area has resulted in a significant amount of thermal/hydraulic and thermal fatigue testing being done on prototypical elements. Short pulse design solutions are not adequate for longer pulse experiments and the areas of thermal design, structural design, material selection, maintainability, and lifetime prediction are undergoing significant changes. A prudent engineering approach will guide us through the transitional phase of divertor design to steady-state power plant components. This paper reviews the design implications in this transition to steady state machines and the status of the community efforts to meet evolving design requirements. 54 refs., 5 figs., 2 tabs
Analysis of a fully developed laminar flow b/w two parallel plates ...
African Journals Online (AJOL)
... Simulation Software Comsol Multiphysics. The flow behavior and the interaction with the boundary has been analysed. Wall no slip conditions were set for evaluation purpose. The analysis is a steady state analysis by using Incompressible Navier Stokes Model. Keywords: Steady state analysis, Velocity profile, Fluid flow.
Contour analysis of steady state tokamak reactor performance
International Nuclear Information System (INIS)
Devoto, R.S.; Fenstermacher, M.E.
1990-01-01
A new method of analysis for presenting the possible operating space for steady state, non-ignited tokamak reactors is proposed. The method uses contours of reactor performance and plasma characteristics, fusion power gain, wall neutron flux, current drive power, etc., plotted on a two-dimensional grid, the axes of which are the plasma current I p and the normalized beta, β n = β/(I p /aB 0 ), to show possible operating points. These steady state operating contour plots are called SOPCONS. This technique is illustrated in an application to a design for the International Thermonuclear Experimental Reactor (ITER) with neutral beam, lower hybrid and bootstrap current drive. The utility of the SOPCON plots for pointing out some of the non-intuitive considerations in steady state reactor design is shown. (author). Letter-to-the-editor. 16 refs, 3 figs, 1 tab
Postural control and shoulder steadiness in F-16 pilots
DEFF Research Database (Denmark)
Lange, Britt; Murray, Mike; Chreiteh, Shadi S
2014-01-01
to a control group (CG; N = 28) or training group (TG; N = 27). Postural control was tested in four different settings: Romberg with open and closed eyes, unilateral stance, and perturbation. Maximal voluntary contraction and force steadiness was measured for shoulder elevation. RESULTS: At follow......-up, there was a significant between-group difference in the Romberg test with closed eyes only (95% confidence ellipse area; CG: 761 +/- 311 mm2; TG: 650 +/- 405 mm2). Prior to randomization, there were no significant differences in postural control and steadiness between 30 pilots who experienced neck pain within...... the previous 3 mo and 25 pilots without such pain. DISCUSSION: Impaired postural control and steadiness may only be quantifiable in individuals experiencing acute neck pain of certain intensity, and there may be a ceiling effect in the ability to improve these parameters. For individuals with highly developed...
Realizing steady-state tokamak operation for fusion energy
International Nuclear Information System (INIS)
Luce, T. C.
2011-01-01
Continuous operation of a tokamak for fusion energy has clear engineering advantages but requires conditions beyond those sufficient for a burning plasma. The fusion reactions and external sources must support both the pressure and the current equilibrium without inductive current drive, leading to demands on stability, confinement, current drive, and plasma-wall interactions that exceed those for pulsed tokamaks. These conditions have been met individually, and significant progress has been made in the past decade to realize scenarios where the required conditions are obtained simultaneously. Tokamaks are operated routinely without disruptions near pressure limits, as needed for steady-state operation. Fully noninductive sustainment with more than half of the current from intrinsic currents has been obtained for a resistive time with normalized pressure and confinement approaching those needed for steady-state conditions. One remaining challenge is handling the heat and particle fluxes expected in a steady-state tokamak without compromising the core plasma performance.
Efficient steady-state solver for hierarchical quantum master equations
Zhang, Hou-Dao; Qiao, Qin; Xu, Rui-Xue; Zheng, Xiao; Yan, YiJing
2017-07-01
Steady states play pivotal roles in many equilibrium and non-equilibrium open system studies. Their accurate evaluations call for exact theories with rigorous treatment of system-bath interactions. Therein, the hierarchical equations-of-motion (HEOM) formalism is a nonperturbative and non-Markovian quantum dissipation theory, which can faithfully describe the dissipative dynamics and nonlinear response of open systems. Nevertheless, solving the steady states of open quantum systems via HEOM is often a challenging task, due to the vast number of dynamical quantities involved. In this work, we propose a self-consistent iteration approach that quickly solves the HEOM steady states. We demonstrate its high efficiency with accurate and fast evaluations of low-temperature thermal equilibrium of a model Fenna-Matthews-Olson pigment-protein complex. Numerically exact evaluation of thermal equilibrium Rényi entropies and stationary emission line shapes is presented with detailed discussion.
A generalized relationship for swirl decay in laminar pipe flow
Indian Academy of Sciences (India)
MS received 24 July 2008; revised 28 January 2010; accepted 1 February 2010. Abstract. Swirling flow is of great importance in heat and mass transfer enhance- ments and in flow measurements. In this study, laminar swirling flow in a straight pipe was considered. Steady three-dimensional axisymmetric Navier–Stokes ...
Oscillatory and electrohydrodynamic instabilities in flow over a ...
Indian Academy of Sciences (India)
of fluid flow past flexible surfaces is qualitatively different from the flow over rigid .... work. Oscillatory flows are unsteady, and it is important to precisely define the ..... from 5 to 16, though there is less variation in the critical stress for a steady ...
An Irrotational Flow Field That Approximates Flat Plate Boundary Conditions
Ruffa, Anthony A.
2004-01-01
An irrotational solution is derived for the steady-state Navier-Stokes equations that approximately satisfies the boundary conditions for flow over a finite flat plate. The nature of the flow differs substantially from boundary layer flow, with severe numerical difficulties in some regions.
Steady State Advanced Tokamak (SSAT): The mission and the machine
International Nuclear Information System (INIS)
Thomassen, K.; Goldston, R.; Nevins, B.; Neilson, H.; Shannon, T.; Montgomery, B.
1992-03-01
Extending the tokamak concept to the steady state regime and pursuing advances in tokamak physics are important and complementary steps for the magnetic fusion energy program. The required transition away from inductive current drive will provide exciting opportunities for advances in tokamak physics, as well as important impetus to drive advances in fusion technology. Recognizing this, the Fusion Policy Advisory Committee and the US National Energy Strategy identified the development of steady state tokamak physics and technology, and improvements in the tokamak concept, as vital elements in the magnetic fusion energy development plan. Both called for the construction of a steady state tokamak facility to address these plan elements. Advances in physics that produce better confinement and higher pressure limits are required for a similar unit size reactor. Regimes with largely self-driven plasma current are required to permit a steady-state tokamak reactor with acceptable recirculating power. Reliable techniques of disruption control will be needed to achieve the availability goals of an economic reactor. Thus the central role of this new tokamak facility is to point the way to a more attractive demonstration reactor (DEMO) than the present data base would support. To meet the challenges, we propose a new ''Steady State Advanced Tokamak'' (SSAT) facility that would develop and demonstrate optimized steady state tokamak operating mode. While other tokamaks in the world program employ superconducting toroidal field coils, SSAT would be the first major tokamak to operate with a fully superconducting coil set in the elongated, divertor geometry planned for ITER and DEMO
International Nuclear Information System (INIS)
Hrehor, M.
1979-01-01
The paper deals with an application of the finite element method to the heat transfer study in seven-pin models of LMFBR fuel subassembly. The developed code NCEL solves two-dimensional steady state heat conduction equation in the whole subassembly model cross-section and enebles to perform the analysis of thermal behaviour in both normal and accidental operational conditions as eccentricity of the central rod or full or partial (porous) blockage of some part of the cross-flow area. The heat removal is simulated by heat sinks in coolant under conditions of subchannels slug flow approximation
Emergence of advance waves in a steady-state universe
Energy Technology Data Exchange (ETDEWEB)
Hobart, R.H.
1979-10-01
In standard Wheeler-Feynman electrodynamics advanced waves from any source are absolutely canceled by the advanced waves from the absorber responding to that source. The present work shows this cancellation fails over cosmic distances in a steady-state universe. A test of the view proposed earlier, in a paper which assumed failure of cancellation ad hoc, that zero-point fluctuations of the electromagnetic field are such emergent advanced waves, is posed. The view entails anomalous slowing of spontaneous transition rates at longer emission wavelengths; available data go against this, furnishing additional argument against the suspect assumption that the universe is steady-state.
Steady-state entanglement activation in optomechanical cavities
Farace, Alessandro; Ciccarello, Francesco; Fazio, Rosario; Giovannetti, Vittorio
2014-02-01
Quantum discord, and related indicators, are raising a relentless interest as a novel paradigm of nonclassical correlations beyond entanglement. Here, we discover a discord-activated mechanism yielding steady-state entanglement production in a realistic continuous-variable setup. This comprises two coupled optomechanical cavities, where the optical modes (OMs) communicate through a fiber. We first use a simplified model to highlight the creation of steady-state discord between the OMs. We show next that such discord improves the level of stationary optomechanical entanglement attainable in the system, making it more robust against temperature and thermal noise.
Time Dependent and Steady Uni-axial Elongational Viscosity
DEFF Research Database (Denmark)
Nielsen, Jens K.; Rasmussen, Henrik Koblitz; Hassager, Ole
2005-01-01
Here we present measurements of transient and steady uni-axial elongational viscosity, using the Filament Stretching Rheometer1 or FSR1 (see Fig. 1) of the following melts: Four narrow MMD polystyrene (PS) samples with weight-average molar mass Mw in the range of 50k to 390k. Three different bi......-disperse samples, mixed from the narrow MMD PS. Two low-density polyethylene (LDPE) melts (Lupolen 1840D and 3020D). A steady-state viscosity was kept for 1-2.5 Hencky strain units in all measurements....
Emergence of advance waves in a steady-state universe
International Nuclear Information System (INIS)
Hobart, R.H.
1979-01-01
In standard Wheeler-Feynman electrodynamics advanced waves from any source are absolutely canceled by the advanced waves from the absorber responding to that source. The present work shows this cancellation fails over cosmic distances in a steady-state universe. A test of the view proposed earlier, in a paper which assumed failure of cancellation ad hoc, that zero-point fluctuations of the electromagnetic field are such emergent advanced waves, is posed. The view entails anomalous slowing of spontaneous transition rates at longer emission wavelengths; available data go against this, furnishing additional argument against the suspect assumption that the universe is steady-state
Steady-state propagation of interface corner crack
DEFF Research Database (Denmark)
Veluri, Badrinath; Jensen, Henrik Myhre
2013-01-01
Steady-state propagation of interface cracks close to three-dimensional corners has been analyzed. Attention was focused on modeling the shape of the interface crack front and calculating the critical stress for steady-state propagation of the crack. The crack propagation was investigated...... on the finite element method with iterative adjustment of the crack front to estimate the critical delamination stresses as a function of the fracture criterion and corner angles. The implication of the results on the delamination is discussed in terms of crack front profiles and the critical stresses...... for propagation and the angle of intersection of the crack front with the free edge....