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Добірка наукової літератури з теми "Discrete Kinetic Scheme"

Автор: Grafiati

Опубліковано: 6 вересня 2023

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Статті в журналах з теми "Discrete Kinetic Scheme"

Chandrashekar, Praveen. "Kinetic Energy Preserving and Entropy Stable Finite Volume Schemes for Compressible Euler and Navier-Stokes Equations." Communications in Computational Physics 14, no. 5 (November 2013): 1252–86. http://dx.doi.org/10.4208/cicp.170712.010313a.

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AbstractCentered numerical fluxes can be constructed for compressible Euler equations which preserve kinetic energy in the semi-discrete finite volume scheme. The essential feature is that the momentum flux should be of the formwhereandareanyconsistent approximations to the pressure and the mass flux. This scheme thus leaves most terms in the numerical flux unspecified and various authors have used simple averaging. Here we enforce approximate or exact entropy consistency which leads to a unique choice of all the terms in the numerical fluxes. As a consequence novel entropy conservative flux that also preserves kinetic energy for the semi-discrete finite volume scheme has been proposed. These fluxes are centered and some dissipation has to be added if shocks are present or if the mesh is coarse. We construct scalar artificial dissipation terms which are kinetic energy stable and satisfy approximate/exact entropy condition. Secondly, we use entropy-variable based matrix dissipation flux which leads to kinetic energy and entropy stable schemes. These schemes are shown to be free of entropy violating solutions unlike the original Roe scheme. For hypersonic flows a blended scheme is proposed which gives carbuncle free solutions for blunt body flows. Numerical results for Euler and Navier-Stokes equations are presented to demonstrate the performance of the different schemes.

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Zhu, Lianhua, Zhaoli Guo, and Kun Xu. "Discrete unified gas kinetic scheme on unstructured meshes." Computers & Fluids 127 (March 2016): 211–25. http://dx.doi.org/10.1016/j.compfluid.2016.01.006.

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Aregba–Driollet, D., J. Breil, S. Brull, B. Dubroca, and E. Estibals. "Modelling and numerical approximation for the nonconservative bitemperature Euler model." ESAIM: Mathematical Modelling and Numerical Analysis 52, no. 4 (July 2018): 1353–83. http://dx.doi.org/10.1051/m2an/2017007.

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This paper is devoted to the study of the nonconservative bitemperature Euler system. We firstly introduce an underlying two species kinetic model coupled with the Poisson equation. The bitemperature Euler system is then established from this kinetic model according to an hydrodynamic limit. A dissipative entropy is proved to exist and a solution is defined to be admissible if it satisfies the related dissipation property. Next, four different numerical methods are presented. Firstly, the kinetic model gives rise to kinetic schemes for the fluid system. The second approach belongs to the family of the discrete BGK schemes introduced by Aregba–Driollet and Natalini. Finally, a quasi-linear relaxation approach and a Lagrange-remap scheme are considered.

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Zhong, Mingliang, Sen Zou, Dongxin Pan, Congshan Zhuo, and Chengwen Zhong. "A simplified discrete unified gas–kinetic scheme for compressible flow." Physics of Fluids 33, no. 3 (March 1, 2021): 036103. http://dx.doi.org/10.1063/5.0033911.

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Shang, Jinlong, Zhenhua Chai, Xinmeng Chen, and Baochang Shi. "Discrete unified gas kinetic scheme for incompressible Navier-Stokes equations." Computers & Mathematics with Applications 97 (September 2021): 45–60. http://dx.doi.org/10.1016/j.camwa.2021.05.019.

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Zhong, Mingliang, Sen Zou, Dongxin Pan, Congshan Zhuo, and Chengwen Zhong. "A simplified discrete unified gas kinetic scheme for incompressible flow." Physics of Fluids 32, no. 9 (September 1, 2020): 093601. http://dx.doi.org/10.1063/5.0021332.

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Zhou, Xiafeng, and Zhaoli Guo. "Discrete unified gas kinetic scheme for steady multiscale neutron transport." Journal of Computational Physics 423 (December 2020): 109767. http://dx.doi.org/10.1016/j.jcp.2020.109767.

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Wang, Peng, Shi Tao, and Zhaoli Guo. "A coupled discrete unified gas-kinetic scheme for Boussinesq flows." Computers & Fluids 120 (October 2015): 70–81. http://dx.doi.org/10.1016/j.compfluid.2015.07.012.

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Guo, Wenqiang, and Guoxiang Hou. "Novel Schemes of No-Slip Boundary Conditions for the Discrete Unified Gas Kinetic Scheme Based on the Moment Constraints." Entropy 25, no. 5 (May 10, 2023): 780. http://dx.doi.org/10.3390/e25050780.

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The boundary conditions are crucial for numerical methods. This study aims to contribute to this growing area of research by exploring boundary conditions for the discrete unified gas kinetic scheme (DUGKS). The importance and originality of this study are that it assesses and validates the novel schemes of the bounce back (BB), non-equilibrium bounce back (NEBB), and Moment-based boundary conditions for the DUGKS, which translate boundary conditions into constraints on the transformed distribution functions at a half time step based on the moment constraints. A theoretical assessment shows that both present NEBB and Moment-based schemes for the DUGKS can implement a no-slip condition at the wall boundary without slip error. The present schemes are validated by numerical simulations of Couette flow, Poiseuille flow, Lid-driven cavity flow, dipole–wall collision, and Rayleigh–Taylor instability. The present schemes of second-order accuracy are more accurate than the original schemes. Both present NEBB and Moment-based schemes are more accurate than the present BB scheme in most cases and have higher computational efficiency than the present BB scheme in the simulation of Couette flow at high Re. The present Moment-based scheme is more accurate than the present BB, NEBB schemes, and reference schemes in the simulation of Poiseuille flow and dipole–wall collision, compared to the analytical solution and reference data. Good agreement with reference data in the numerical simulation of Rayleigh–Taylor instability shows that they are also of use to the multiphase flow. The present Moment-based scheme is more competitive in boundary conditions for the DUGKS.

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MIEUSSENS, LUC. "DISCRETE VELOCITY MODEL AND IMPLICIT SCHEME FOR THE BGK EQUATION OF RAREFIED GAS DYNAMICS." Mathematical Models and Methods in Applied Sciences 10, no. 08 (November 2000): 1121–49. http://dx.doi.org/10.1142/s0218202500000562.

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We present a numerical method for computing transitional flows as described by the BGK equation of gas kinetic theory. Using the minimum entropy principle to define a discrete equilibrium function, a discrete velocity model of this equation is proposed. This model, like the continuous one, ensures positivity of solutions, conservation of moments, and dissipation of entropy. The discrete velocity model is then discretized in space and time by an explicit finite volume scheme which is proved to satisfy the previous properties. A linearized implicit scheme is then derived to efficiently compute steady-states; this method is then verified with several test cases.

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Дисертації з теми "Discrete Kinetic Scheme"

Jobic, Yann. "Numerical approach by kinetic methods of transport phenomena in heterogeneous media." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4723/document.

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Les phénomènes de transport en milieux poreux sont étudiés depuis près de deux siècles, cependant les travaux concernant les milieux fortement poreux sont encore relativement peu nombreux. Les modèles couramment utilisés pour les poreux classiques (lits de grains par exemple) sont peu applicables pour les milieux fortement poreux (les mousses par exemple), un certain nombre d’études ont été entreprises pour combler ce manque. Néanmoins, les résultats expérimentaux et numériques caractérisant les pertes de charge dans les mousses sont fortement dispersés. Du fait des progrès de l’imagerie 3D, une tendance émergente est la détermination des paramètres des lois d’écoulement à partir de simulations directes sur des géométries reconstruites. Nous présentons ici l’utilisation d’une nouvelle approche cinétique pour résoudre localement les équations de Navier-Stokes et déterminer les propriétés d’écoulement (perméabilité, dispersion, ...)
A novel kinetic scheme satisfying an entropy condition is developed, tested and implemented for the simulation of practical problems. The construction of this new entropic scheme is presented. A classical hyperbolic system is approximated by a discrete velocity vector kinetic scheme (with the simplified BGK collisional operator), but applied to an inviscid compressible gas dynamics system with a small Mach number parameter, according to the approach of Carfora and Natalini (2008). The numerical viscosity is controlled, and tends to the physical viscosity of the Navier-Stokes system. The proposed numerical scheme is analyzed and formulated as an explicit finite volume flux vector splitting (FVS) scheme that is very easy to implement. It is close in spirit to Lattice Boltzmann schemes, but it has the advantage to satisfy a discrete entropy inequality under a CFL condition and a subcharacteristic stability condition involving a cell Reynolds number. The new scheme is proved to be second-order accurate in space. We show the efficiency of the method in terms of accuracy and robustness on a variety of classical benchmark tests. Some physical problems have been studied in order to show the usefulness of both schemes. The LB code was successfully used to determine the longitudinal dispersion of metallic foams, with the use of a novel indicator. The entropic code was used to determine the permeability tensor of various porous media, from the Fontainebleau sandstone (low porosity) to a redwood tree sample (high porosity). These results are pretty accurate. Finally, the entropic framework is applied to the advection-diffusion equation as a passive scalar

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Raghavendra, Nandagiri Venkata. "Discrete Velocity Boltzmann Schemes for Inviscid Compressible Flows." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4314.

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It is known that high-speed flows are compressible. In large parts of the flow domains, the inviscid approximation is valid and this leads to Euler equations of gas dynamics. These inviscid compressible flows are modelled by coupled nonlinear hyperbolic systems of partial differential equations and generally require numerical solution techniques, as analytical solutions are usually not available. Out of all the numerical methods developed over the past five decades to solve the Euler equations, the schemes based on kinetic theory of gases are elegant ones with distinct advantages of simplicity and robustness. However, many kinetic or Boltzmann schemes suffer from high dose of numerical diffusion and these methods are known to be less accurate. The exact shock capturing of steady grid-aligned discontinuities, achieved at the macroscopic level, is yet to be claimed by this class of methods. A closely related class of discrete velocity Boltzmann schemes proved to be advantageous in this regard, with the first discrete kinetic scheme with exact shock capturing being introduced by Raghurama Rao and Balakrishna[51], by enforcing the Rankine-Hugoniot jump condition at the discrete level. In the first part of this thesis, this accurate shock capturing algorithm with a relaxation system is further improved by various techniques, such as including a diagonal matrix of coefficient of numerical diffusion for vector cases, introducing a wave speed correction mechanism for obtaining physically realistic solutions, introducing a limiter based variant to avoid the use of an entropy _x and finally modifying the numerical diffusion based on the entropy conservation equation to obtain a simple entropy stable and yet accurate discrete velocity Boltzmann scheme. The features of all the new variants are demonstrated by application to several bench-mark test problems. In the second part of the thesis, a discrete velocity Boltzmann scheme which can capture steady contact discontinuities exactly is developed by using the generalized Riemann invariants together with the jump conditions. This scheme is accurate and widely applicable, without the need for any entropy correction, the relevant features being demonstrated by application to several benchmark test problems. In the third part of this thesis, a discrete velocity Boltzmann scheme is developed by using physically relevant discrete velocities. A derivation introduced by Sanders and Prendergast [58] is modified to introduce the velocities, of the Dirac delta functions which replace the Maxwellian, matching the eigenvalues at the macroscopic level. This strategy is further coupled with the framework of a discrete velocity Boltzmann system to develop an efficient relaxation scheme for solving the Euler equations. This new algorithm is found to be low in numerical diffusion and also successful in handling various challenging test problems.

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Книги з теми "Discrete Kinetic Scheme"

Succi, Sauro. Lattice Relaxation Schemes. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199592357.003.0014.

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In Chapter 13, it was shown that the complexity of the LBE collision operator can be cut down dramatically by formulating discrete versions with prescribed local equilibria. In this chapter, the process is taken one step further by presenting a minimal formulation whereby the collision matrix is reduced to the identity, upfronted by a single relaxation parameter, fixing the viscosity of the lattice fluid. The idea is patterned after the celebrated Bhatnagar–Gross–Krook (BGK) model Boltzmann introduced in continuum kinetic theory as early as 1954. The second part of the chapter describes the comeback of the early LBE in optimized multi-relaxation form, as well as few recent variants hereof.

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Частини книг з теми "Discrete Kinetic Scheme"

Aregba-Driollet, D., and R. Natalini. "Discrete Kinetic Schemes for Systems of Conservation Laws." In Hyperbolic Problems: Theory, Numerics, Applications, 1–10. Basel: Birkhäuser Basel, 1999. http://dx.doi.org/10.1007/978-3-0348-8720-5_1.

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Hernández, Salvador Carlos, Edgar Nelson Sanchez Camperos, Rocío Carrasco Navarro, Joel Kelly Gurubel Tun, and José Andrés Bueno García. "Modeling and Simulation of Alternative Energy Generation Processes using HONN." In Artificial Higher Order Neural Networks for Modeling and Simulation, 162–92. IGI Global, 2013. http://dx.doi.org/10.4018/978-1-4666-2175-6.ch008.

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This chapter deals with the application of Higher Order Neural Networks (HONN) on the modeling and simulation of two processes commonly used to produce gas with energy potential: anaerobic digestion and gasification. Two control strategies for anaerobic digestion are proposed in order to obtain high biomethane flow rate from degradation of organic wastes such as wastewater. A neurofuzzy scheme which is composed by a neural observer, a fuzzy supervisor, and two control actions is presented first. After that, a speed-gradient inverse optimal neural control for trajectory tracking is designed and applied to an anaerobic digestion model. The control law calculates dilution rate and bicarbonate in order to track a methane production reference trajectory under controlled conditions and avoid washout. A nonlinear discrete-time neural observer (RHONO) for unknown nonlinear systems in presence of external disturbances and parameter uncertainties is used to estimate the biomass concentration, substrate degradation, and inorganic carbon. On the other side, a high order neural network structure is developed for the process identification in a gasification reactor; the gas, composed mainly of hydrogen and carbon monoxide (synthesis gas or syngas), is produced from thermo chemical transformation of solid organic wastes. The identifier is developed in order to reproduce a kinetic model of a biomass gasifier. In both cases (biological and thermo chemical processes), the Extended Kalman Filter (EKF) is used as a training algorithm. The proposed methodologies application is illustrated via numerical simulations.

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Тези доповідей конференцій з теми "Discrete Kinetic Scheme"

K., Arun, and Raghurama Rao Suswaram. "A Multi-Dimensional Discrete Kinetic Scheme for Nonlinear Hyperbolic Problems." In 19th AIAA Computational Fluid Dynamics. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2009. http://dx.doi.org/10.2514/6.2009-3873.

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Yang, L. M., C. Shu, and J. Wu. "Numerical Simulation of Microflows by a DOM With Streaming and Collision Processes." In ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/mnhmt2016-6494.

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Inspired from the idea of developing lattice Boltzmann method (LBM), a discrete ordinate method (DOM) with streaming and collision processes is presented for simulation of microflows in this work. The current method is quite different from the conventional discrete ordinate method (DOM), unified gas kinetic scheme (UGKS) and discrete unified gas kinetic scheme (DUGKS), in which the finite volume method (FVM) or the finite difference method (FDM) is usually utilized to discretize the discrete velocity Boltzmann equation (DVBE). Due to the application of FVM or FDM, the evaluation of the flux of distribution function at the cell interface becomes an essential step for these approaches. Besides that, for the UGKS and DUGKS, not only the flux of distribution functions but also the conservative variables at the cell interface are needed to be computed. These processes require a lot of computational efforts. In contrast, for the developed method, it only needs interpolations within the cell to perform the streaming process. Thus, the computational efficiency can be improved accordingly. To compare the accuracy and efficiency of present scheme with those of DSMC and/or UGKS, several numerical examples including the Couette flow, pressure driven Poiseuille flow and thermal transpiration flow are simulated. Numerical results showed that the solution accuracy of current scheme is comparable to that of DSMC and UGKS. However, as far as the computational efficiency is concerned, the present scheme is more efficient than UGKS.

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Kudryavtsev, Alexey, Anton Shershnev, and Mikhail Ivanov. "Numerical Simulation of Gas Microflows by Solving Relaxation-Type Kinetic Equations." In ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer. ASMEDC, 2009. http://dx.doi.org/10.1115/mnhmt2009-18520.

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In this paper we present a numerical method for simulation of gas flows at micro- and nanoscales based on solving of relaxation-type kinetic equations with the the discrete ordinate method and a high-order shock-capturing scheme. The method is used for simulation of such classical problems as the shock-wave structure and the supersonic flow over a flat plate as well as for investigtion of shock wave propagation in a microchannel. The results obtained are compared with Navier-Stokes and DSMC solutions and experimental data.

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Kang, Shin K., and Yassin A. Hassan. "A Comparative Study of Interface Schemes in the Immersed Boundary Method for a Moving Solid Boundary Problem Using the Lattice Boltzmann Method." In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30908.

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For moving boundary problems, previous body-conformal grid methods require frequent re-meshing as the boundary moves, thus increasing computational cost. An immersed boundary method (IBM) is an attractive method to resolve the problem since it is based on the fixed, non-body-conformal grids. In the IBM, force density terms are used so that no-slip boundary condition is satisfied on the boundary. On the other hand, lattice Boltzmann methods (LBMs) have been used as an alternative of Navier-Stokes equation method due to their efficiency to parallelize and simplicity to implement. The common feature of the IBM and the LBM of using non-body-conformal grids motivated the use of the IBM in the lattice Boltzmann method frame, which is usually called an immersed boundary-lattice Boltzmann method (IB-LBM). Besides, a split-forcing property in the LBM, due to its kinetic nature, facilitates the use of direct-forcing IBM. For the evaluation of boundary force density term, we need to adopt an interpolation scheme because the boundary, in general, does not match computational nodes. The interpolation schemes can be classified into diffuse and sharp interface schemes. The former usually uses the discrete delta function to evaluate the boundary force on the prescribed boundary points, while the latter uses interpolation from neighboring fluid nodes to evaluate the boundary force on the computation node either inside or outside closest to the boundary. In the diffuse scheme, the boundary force density terms evaluated on the boundary points should be distributed onto neighboring computational nodes using the discrete delta functions so that the boundary effect may exert on computational process. The objective of this study is to compare two interface schemes simultaneously for a moving boundary problem under the IB-LBM and to understand advantages and disadvantages of each scheme. We considered a problem of flow induced by inline oscillation of a circular cylinder since both experimental and body-conformal grid method results are available for this problem. Velocity results from both schemes showed overall good agreement with experimental data. However, the sharp interface scheme showed spurious oscillations in the surface force coefficient and pressure fields, although after filtering or smoothing, the force coefficients showed good agreement with the body-fitted results. In contrast, the diffuse interface scheme produced smooth variations in the surface force coefficient but over-predicted the absolute values especially at phase angles with the high magnitude of accelerations. These results can be attributed to the use of discrete delta functions. We could reduce the over-prediction by considering the effect of the diffuse area.

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Frandsen, Jannette B. "A Mesoscopic Model Approach to Passively Control Vortex Wakes Using Single/Multiple Bodies." In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93759.

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In this paper, vortex patterns are studied when single or several objects are located in the bluff-body wakes. The suitability of a mesoscopic approach involving a single phase Lattice Boltzmann (LB) model is examined. The central idea behind proposing the present formulation is to capture smaller scales naturally, postponing the need of applying empirical turbulence models. In contrast, to continuum mechanics based numerical models, where only space and time are discrete, the discrete variables of the LB model are space, time and particle velocity. With reference to the Boltzmann equation of classical kinetic theory, the distribution of fluid molecules is represented by particle distribution functions. It is notable that the formulation avoids the need to include the Poisson equation. An elastic-collision scheme with no-slip walls is prescribed. Although the long term goal is to predict bluff-body high Reynolds number flows, the present study is limited to laminar flow simulations. The case studies include sharp edge bodies embedded in Re flows in the order of 100–250. The 2-D uniform grid solutions are compared with findings reported in the literature and promising agreements have been found. This study is important to a variety of applications, in particular, the wind, ocean and coastal engineering communities. From a mitigation point of view, the model presents an easy means of re-arranging bluff bodies to study optimum solutions for VIV suppression. It is notable that the CPUs are favorable for the multiple bluff body solutions compared to current published continuum mechanics models.

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Frandsen, Jannette B. "A Lattice Boltzmann Bluff Body Model for VIV Suppression." In 25th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/omae2006-92271.

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In this paper, the suitability of a mesoscopic approach involving a single phase Lattice Boltzmann (LB) model is examined. In contrast, to continuum based numerical models, where only space and time are discrete, the discrete variables of the LB model are space, time and particle velocity. With reference to the Boltzmann equation of classical kinetic theory, the distribution of fluid molecules is represented by particle distribution functions. The LB method simulates fluid flow by tracking particle distributions. It is notable that the formulation avoids the need to include the Poisson equation. An elastic-collision scheme with no-slip walls is prescribed. The central idea behind proposing the present formulation is many fold. One goal is to capture smaller scales naturally, postponing the need of applying empirical turbulence models. Another goal is to get further insight into nonlinearities in steep and breaking free surfaces to improve current continuum mechanics solutions. Although the long term goal is to predict bluff-body high Reynolds number flows and breaking water waves, the present study is limited to laminar flow simulations and continuous free surfaces. The case studies presented include bluff bodies embedded in Reynolds number flows in the order of 100–200. The free surface test cases represent bore propagation past a single and multiple structures. The 2-D uniform grid solutions are compared with findings reported in the literature. Vortex patterns are studied when single or several objects are located in the bluff-body wakes. From a mitigation point of view, the model presents an easy means of re-arranging bluff bodies to study optimum solutions for VIV suppression with/without a free surface.

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Bazargan, Majid, and Mostafa Varmazyar. "Modeling of Free Convection Heat Transfer to a Supercritical Fluid in a Square Enclosure by the Lattice Boltzmann Method." In ASME 2009 Heat Transfer Summer Conference collocated with the InterPACK09 and 3rd Energy Sustainability Conferences. ASMEDC, 2009. http://dx.doi.org/10.1115/ht2009-88463.

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During the last decade a number of numerical computations based on the finite volume approach have been reported studying various aspects of heat transfer near the critical point. In this paper, a Lattice Boltzmann Method (LBM) has been developed to simulate laminar free convection heat transfer to a supercritical fluid in a square enclosure. The LBM is an ideal mesoscopic approach to solve nonlinear macroscopic conservation equations due to its simplicity and capability of parallelization. The Lattice Boltzmann Equation (LBE) represents the minimal form of the Boltzmann kinetic equation. The LBE is a very elegant and simple equation, for a discrete density distribution function and is the basis of the LBM. For the mass and momentum equations, an LBM is used while the heat equation is solved numerically by a finite volume scheme. In this study, inter-particle forces are taken into account for non-ideal gases in order to simulate the velocity profile more accurately. The laminar free convection cavity flow has been extensively used as a benchmark test to evaluate the accuracy of the numerical code. It is found that the numerical results of this study are in good agreement with the experimental and numerical results reported in the literature. The results of the LBM–FVM combination are found to be in excellent agreement with the FVM–FVM combination for the Navier-Stokes and heat transfer equations.

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Mukherjee, Shiladitya, J. Vernon Cole, Kunal Jain, and Ashok Gidwani. "Water Management in PEM Fuel Cell: A Lattice-Boltzmann Modeling Approach." In ASME 2009 7th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2009. http://dx.doi.org/10.1115/fuelcell2009-85182.

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In Proton Exchange Membrane Fuel Cells (PEMFCs), water management and the effective transport of water through the gas-diffusion-layer (GDL) are key issues for improved performance at high power density and for durability during freeze-thaw cycles. The diffusion layer is a thin (∼150–350μm), porous material typically composed of a web of carbon fibers and particles, and is usually coated with hydrophobic Teflon to remove the excess water through capillary action. In-situ diagnostics of water movement and gas-reactant transport through this thin opaque substrate is challenging. Numerical analyses are typically based on simplified assumptions, such as Darcy’s Law and Leverett functions for the capillary pressure. The objective of this work is to develop a high fidelity CFD modeling and analysis tool to capture the details of multiphase transport through the porous GDL. The tool can be utilized to evaluate GDL material design concepts and optimize systems based on the interactions between cell design, materials, and operating conditions. The flow modeling is based on the Lattice Boltzmann Method (LBM). LBM is a powerful modeling tool to simulate multiphase flows. Its strength is in its kinetic theory based foundation, which provides a fundamental basis for incorporating intermolecular forces that lead to liquid-gas phase separation and capillary effects without resorting to expensive or ad-hoc interface reconstruction schemes. At the heart of the solution algorithm is a discrete form of the well-known Boltzmann Transport Equation (BTE) for molecular distribution, tailored to recover the continuum Navier-Stokes flow. The solution advances by a streaming and collision type algorithm, mimicking actual molecular physics, which makes it suitable for porous media involving complex boundaries. We developed a numerical scheme to reconstruct various porous GDL microstructures including Teflon loading. Single and multiphase LBM models are implemented to compute permeability. Predicted values are in good agreement with measured data. The present modeling approach resolves the GDL microstructures and captures the influence of fiber orientation on permeability and the influence of Teflon loading on the development of preferential flow paths through the GDL. These observations can potentially guide the development of novel GDL materials designed for efficient removal of water.

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Kharaghani, A., T. S. Pham, B. Chareyre, and E. Tsotsas. "A pore-scale study on the drying kinetics and mechanical behavior of particle aggregates." In 21st International Drying Symposium. Valencia: Universitat Politècnica València, 2018. http://dx.doi.org/10.4995/ids2018.2018.7388.

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A discrete thermo-mechanical drying model is developed to investigate the interaction between the porous structure and the drying characteristics of dense particle aggregates. The solid phase consists of polydisperse spherical particles in the micrometer range and the void space is constructed by a complementary network of tetrahedral pores. A modified version of the classical invasion percolation algorithm is set up to describe the preferential evaporation of the confined liquid in the pores. Thus, the evolution of the liquid distribution throughout the complex disordered medium can be simulated. In a one-way coupling scheme, capillary forces caused by both fluid pressure and surface tension are computed over time from the filling state of pores and they are applied as loads on each primary particle in the discrete element method. Based on this robust approach the drying kinetics and the mechanical behavior of several different aggregates with various fractions of small and large particles are simulated and quantified.Keywords: Pore network model; discrete element method; Solid-fluid interaction; capillary force, Convective drying.

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Ming, Pingzhou, Zhigang Li, Ping An, Wei Lu, Dong Liu, and Hongxing Yu. "Analysis and Parallel Implementation of Transient Thermal Feedback in Neutron Kinetics Calculation." In 2018 26th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icone26-81442.

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Transient computing scheme named K-MOD has been designed that time-discrete is carried out by implicit Runge-Kutta method, and coarse nodal method is used for neutronics calculation at present. During transient calculation, thermal feedback is introduced to update the cross-section to approximate the transient behavior of the real core based on the method of interpolation on state-points. Corresponding thermal feedback for coupling calculation is programmed and analyzed, and parallel computing is introduced to enhance efficiencies of single-disciplinary codes and data coupling section. Problem of rod insertion and lift in real core of PWR (Pressurized Water Reactor) is tested and compared. The results show that K-MOD is in good agreement with the results of SMART software in both fixed time step and adaptive time step. And the parallel efficiency is also explained.

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