The Experts below are selected from a list of 100539 Experts worldwide ranked by ideXlab platform
Seiichi Koshizuka - One of the best experts on this subject based on the ideXlab platform.
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Moving Particle Semi-Implicit Method
Nuclear Power Plant Design and Analysis Codes, 2021Co-Authors: Zidi Wang, Guangtao Duan, Seiichi Koshizuka, Akifumi YamajiAbstract:Abstract The Moving Particle Semi-Implicit (MPS) Method is one kind of particle Method, which is based on Lagrangian approach. It has been developed to analyze complex thermal-hydraulic problems, including those in nuclear engineering. Since meshes are no longer used, large deformation of free surfaces or interfaces can be simulated without the problems of mesh distortion. This approach is effective in solving multiphase fluid dynamics which is subject to complex motion of free surfaces or interfaces. Since its development, MPS Method has been extensively utilized for a wide range of applications in nuclear engineering. In this chapter, the basic theory of the MPS Method is explained firstly. After that, some examples of its application in nuclear engineering, including bubble dynamic, vapor explosion, jet breakup, multiphase flow instability, in-vessel phenomenon, molten spreading, molten core concrete interaction and flooding, are presented.
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stable multiphase moving particle semi Implicit Method for incompressible interfacial flow
Computer Methods in Applied Mechanics and Engineering, 2017Co-Authors: Guangtao Duan, Seiichi Koshizuka, Bin Chen, Hao XiangAbstract:Abstract The moving particle semi-Implicit (MPS) Method is extended into a multiphase MPS (MMPS) Method, where multiphase fluids are modeled as a multi-viscosity and multi-density fluid. Interparticle viscosity and density are adopted to model the interaction between particles of different phases. However, such a straightforward extension is prone to instability because the light particles at the interface suffer from exceptionally high acceleration. Therefore, two approaches, MMPS-HD (harmonic density) and MMPS-CA (continuous acceleration), are proposed to suppress the instability. In the first approach, harmonic mean interparticle density is applied to discretize the multiphase pressure Poisson equation to avoid the exceptionally high acceleration at the interface. In the second approach, new MMPS formulations are derived from the locally weighted average of interaction acceleration between particles to guarantee the continuity of acceleration and velocity. The particle stabilizing term (PST) is then decoupled from the original pressure gradient model and adopts the single-phase formulation to guarantee stability. The developed multi-viscosity and -density models are verified using the multi-fluid Poiseuille flow and Rayleigh–Taylor instability, respectively. Furthermore, two benchmark cases of rising bubbles in 2D and 3D with a wide range of density and viscosity ratios are simulated to demonstrate the capability and robustness of the proposed Methods in complex multiphase flows. The proposed Method can produce stable and reliable results up to a high density ratio of approximately 1000 and viscosity ratio of approximately 100.
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improved pressure calculation for the moving particle semi Implicit Method
Combinatorial Pattern Matching, 2015Co-Authors: Kazuya Shibata, Issei Masaie, Masahiro Kondo, Kohei Murotani, Seiichi KoshizukaAbstract:We developed a practical technique for calculating pressures and pressure gradients for the moving particle semi-Implicit (MPS) Method. Specifically, a new free-surface boundary condition for the pressure Poisson equation was developed by assuming that there are virtual particles over the surface. We treat the pressure of the virtual particles as a known value. A single liquid-phase flow is simulated taking into account the pressure of these virtual particles. A technique for detecting surface particles also was developed and used for accurately imposing the free-surface boundary condition. The pressure gradient model was modified to mitigate particle clustering and a single-layer wall model was developed to reduce the number of wall particles. We applied our technique to several problems, verifying that virtual surface particles suppress pressure oscillations and particle clusterings. The technique enables reliable differences in free-surface pressures to be taken and simulates instances of lower fluid pressure than that of a free surface.
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least squares moving particle semi Implicit Method
Combinatorial Pattern Matching, 2014Co-Authors: Tasuku Tamai, Seiichi KoshizukaAbstract:In this paper, a consistent meshfree Lagrangian approach for numerical analysis of incompressible flow with free surfaces, named least squares moving particle semi-Implicit (LSMPS) Method, is developed. The present Methodology includes arbitrary high-order accurate meshfree spatial discretization schemes, consistent time integration schemes, and generalized treatment of boundary conditions. LSMPS Method can resolve the existing major issues of widely used strong-form particle Method for incompressible flow—particularly, the lack of consistency condition for spatial discretization schemes, difficulty in enforcing consistent Neumann boundary conditions, and serious instability like unphysical pressure oscillation. Applications of the present proposal demonstrate remarkable enhancements of stability and accuracy.
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moving particle semi Implicit Method for fragmentation of incompressible fluid
Nuclear Science and Engineering, 1996Co-Authors: Seiichi Koshizuka, Yoshiaki OkaAbstract:AbstractA moving-particle semi-Implicit (MPS) Method for simulating fragmentation of incompressible fluids is presented. The motion of each particle is calculated through interactions with neighboring particles covered with the kernel function. Deterministic particle interaction models representing gradient, Laplacian, and free surfaces are proposed. Fluid density is Implicitly required to be constant as the incompressibility condition, while the other terms are explicitly calculated. The Poisson equation of pressure is solved by the incomplete Cholesky conjugate gradient Method. Collapse of a water column is calculated using MPS. The effect of parameters in the models is investigated in test calculations. Good agreement with an experiment is obtained even if fragmentation and coalescence of the fluid take place.
Rainald Löhner - One of the best experts on this subject based on the ideXlab platform.
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An accurate, fast, matrix-free Implicit Method for computing unsteady flows on unstructured grids
Computers & Fluids, 2001Co-Authors: Hong Luo, Joseph D. Baum, Rainald LöhnerAbstract:Abstract An accurate, fast, matrix-free Implicit Method has been developed to solve the three-dimensional compressible unsteady flows on unstructured grids. A nonlinear system of equations as a result of a fully Implicit temporal discretization is solved at each time step using a pseudo-time marching approach. A newly developed fast, matrix-free Implicit Method is then used to obtain the steady-state solution to the pseudo-time system. The developed Method is applied to compute a variety of unsteady flow problems involving moving boundaries. The numerical results obtained indicate that the use of the present Implicit Method leads to a significant increase in performance over its explicit counterpart, while maintaining a similar memory requirement.
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A Fast, Matrix-free Implicit Method for Compressible Flows on Unstructured Grids
Journal of Computational Physics, 1998Co-Authors: Hong Luo, Joseph D. Baum, Rainald LöhnerAbstract:A fast, matrix-free Implicit Method has been developed to solve the three-dimensional compressible Euler and Navier?Stokes equations on unstructured meshes. An approximate system of linear equations arising from the Newton linearization is solved by the GMRES (generalized minimum residual) algorithm with a LU-SGS (lower?upper symmetric Gauss?Seidel) preconditioner. A remarkable feature of the present GMRES+LU-SGS Method is that the storage of the Jacobian matrix can be completely eliminated by approximating the Jacobian with numerical fluxes, resulting in a matrix-free Implicit Method. The Method developed has been used to compute the compressible flows around 3D complex aerodynamic configurations for a wide range of flow conditions, from subsonic to supersonic. The numerical results obtained indicate that the use of the GMRES+LU-SGS Method leads to a significant increase in performance over the best current Implicit Methods, GMRES+ILU and LU-SGS, while maintaining memory requirements similar to its explicit counterpart. An overall speedup factor from eight to more than one order of magnitude for all test cases in comparison with the explicit Method is demonstrated.
Gregory W. Hammett - One of the best experts on this subject based on the ideXlab platform.
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A fast semi-Implicit Method for anisotropic diffusion
Journal of Computational Physics, 2011Co-Authors: Prateek Sharma, Gregory W. HammettAbstract:Simple finite differencing of the anisotropic diffusion equation, where diffusion is only along a given direction, does not ensure that the numerically calculated heat fluxes are in the correct direction. This can lead to negative temperatures for the anisotropic thermal diffusion equation. In a previous paper we proposed a monotonicity-preserving explicit Method which uses limiters (analogous to those used in the solution of hyperbolic equations) to interpolate the temperature gradients at cell faces. However, being explicit, this Method was limited by a restrictive Courant-Friedrichs-Lewy (CFL) stability timestep. Here we propose a fast, conservative, directionally-split, semi-Implicit Method which is second order accurate in space, is stable for large timesteps, and is easy to implement in parallel. Although not strictly monotonicity-preserving, our Method gives only small amplitude temperature oscillations at large temperature gradients, and the oscillations are damped in time. With numerical experiments we show that our semi-Implicit Method can achieve large speed-ups compared to the explicit Method, without seriously violating the monotonicity constraint. This Method can also be applied to isotropic diffusion, both on regular and distorted meshes.
Guangtao Duan - One of the best experts on this subject based on the ideXlab platform.
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Moving Particle Semi-Implicit Method
Nuclear Power Plant Design and Analysis Codes, 2021Co-Authors: Zidi Wang, Guangtao Duan, Seiichi Koshizuka, Akifumi YamajiAbstract:Abstract The Moving Particle Semi-Implicit (MPS) Method is one kind of particle Method, which is based on Lagrangian approach. It has been developed to analyze complex thermal-hydraulic problems, including those in nuclear engineering. Since meshes are no longer used, large deformation of free surfaces or interfaces can be simulated without the problems of mesh distortion. This approach is effective in solving multiphase fluid dynamics which is subject to complex motion of free surfaces or interfaces. Since its development, MPS Method has been extensively utilized for a wide range of applications in nuclear engineering. In this chapter, the basic theory of the MPS Method is explained firstly. After that, some examples of its application in nuclear engineering, including bubble dynamic, vapor explosion, jet breakup, multiphase flow instability, in-vessel phenomenon, molten spreading, molten core concrete interaction and flooding, are presented.
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stable multiphase moving particle semi Implicit Method for incompressible interfacial flow
Computer Methods in Applied Mechanics and Engineering, 2017Co-Authors: Guangtao Duan, Seiichi Koshizuka, Bin Chen, Hao XiangAbstract:Abstract The moving particle semi-Implicit (MPS) Method is extended into a multiphase MPS (MMPS) Method, where multiphase fluids are modeled as a multi-viscosity and multi-density fluid. Interparticle viscosity and density are adopted to model the interaction between particles of different phases. However, such a straightforward extension is prone to instability because the light particles at the interface suffer from exceptionally high acceleration. Therefore, two approaches, MMPS-HD (harmonic density) and MMPS-CA (continuous acceleration), are proposed to suppress the instability. In the first approach, harmonic mean interparticle density is applied to discretize the multiphase pressure Poisson equation to avoid the exceptionally high acceleration at the interface. In the second approach, new MMPS formulations are derived from the locally weighted average of interaction acceleration between particles to guarantee the continuity of acceleration and velocity. The particle stabilizing term (PST) is then decoupled from the original pressure gradient model and adopts the single-phase formulation to guarantee stability. The developed multi-viscosity and -density models are verified using the multi-fluid Poiseuille flow and Rayleigh–Taylor instability, respectively. Furthermore, two benchmark cases of rising bubbles in 2D and 3D with a wide range of density and viscosity ratios are simulated to demonstrate the capability and robustness of the proposed Methods in complex multiphase flows. The proposed Method can produce stable and reliable results up to a high density ratio of approximately 1000 and viscosity ratio of approximately 100.
Gary W Slater - One of the best experts on this subject based on the ideXlab platform.
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Implicit Method for simulating electrohydrodynamics of polyelectrolytes
Physical Review Letters, 2010Co-Authors: Owen A Hickey, Christian Holm, James L Harden, Gary W SlaterAbstract:We introduce a novel Method to couple Lennard-Jones beads to a lattice-Boltzmann fluid by adding a term which represents the slip within the Debye layer with respect to the surrounding fluid. The Method produces realistic electrophoretic dynamics of charged free chains, as well as the correct stall force in the limit of a thin Debye layer. Our simulations also demonstrate how a net-neutral polyampholyte can have a nonzero net force due to hydrodynamic interactions. This Method represents an efficient way to simulate a wide variety of complex problems in electrohydrodynamics.
