The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Oh Joon Kwon - One of the best experts on this subject based on the ideXlab platform.
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An efficient and robust Implicit Operator for upwind point Gauss-Seidel method
Journal of Computational Physics, 2007Co-Authors: Joo Sung Kim, Oh Joon KwonAbstract:An efficient and robust Implicit Operator for the point Gauss-Seidel method is presented for solving the compressible Euler equations. The new Implicit Operator was derived by adding a scalar form of artificial dissipation to the upwind Implicit side. The amount of artificial dissipation was locally adjusted using a weighting factor based on the solution gradient. For validation, the performance of the new Implicit Operator was compared in detail with that of several existing Implicit Operators which have been widely used for solving the flow equations. Numerical experiments showed that the stability and convergence characteristics of the new Implicit Operator are significantly better than those of other existing Implicit Operators for calculating flows ranging from subsonic to hypersonic speeds.
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Assessment of Implicit Operators for the upwind point Gauss–Seidel method on unstructured meshes
Computers & Fluids, 2007Co-Authors: Joo Sung Kim, Oh Joon KwonAbstract:Abstract The effect of the numerical dissipation level of Implicit Operators on the stability and convergence characteristics of the upwind point Gauss–Seidel (GS) method for solving the Euler equations was studied through the von Neumann stability analysis and numerical experiments. The stability analysis for linear model equations showed that the point GS method is unstable even for very small CFL numbers when the numerical dissipation level of the Implicit Operator is equivalent to that of the explicit Operator. The stability restriction is rapidly alleviated as the dissipation level of the Implicit Operator increases. The instability predicted by the linear stability analysis was further amplified as the flow problems became stiffer due to the presence of the shock wave or the refinement of the mesh. It was found that for the efficiency and the robustness of the upwind point GS method, the numerical flux of the Implicit Operator needs to be more dissipative than that of the explicit Operator.
Tarek I. Zohdi - One of the best experts on this subject based on the ideXlab platform.
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Semi-Implicit Operator splitting for the simulation of Herschel–Bulkley flows with smoothed particle hydrodynamics
Computational Particle Mechanics, 2020Co-Authors: Chang Yoon Park, Tarek I. ZohdiAbstract:Smoothed particle hydrodynamics (SPH) has become a popular numerical framework of choice for simulating free-surface flows, mainly for Newtonian fluids. The topic regarding the simulation of non-Newtonian free-surface flows, however, remains relatively untouched due to difficulties regarding the computation of viscous forces. In previous approaches, the viscous forces acting on each SPH particle were computed explicitly. Non-Newtonian fluids such as Herschel–Bulkley fluids, the effective viscosity between yielded and unyielded regions can differ by several orders of magnitudes; imposing severe time step restrictions for the simulation for explicit methods. Numerically, this can be seen as a stiff problem. We propose a semi-Implicit time-stepping approach where the viscous forces are computed Implicitly, within the context of SPH. We demonstrate the convergence of the method via a simple 2D test case.
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semi Implicit Operator splitting for the simulation of herschel bulkley flows with smoothed particle hydrodynamics
Computational particle mechanics, 2020Co-Authors: Chang Yoon Park, Tarek I. ZohdiAbstract:Smoothed particle hydrodynamics (SPH) has become a popular numerical framework of choice for simulating free-surface flows, mainly for Newtonian fluids. The topic regarding the simulation of non-Newtonian free-surface flows, however, remains relatively untouched due to difficulties regarding the computation of viscous forces. In previous approaches, the viscous forces acting on each SPH particle were computed explicitly. Non-Newtonian fluids such as Herschel–Bulkley fluids, the effective viscosity between yielded and unyielded regions can differ by several orders of magnitudes; imposing severe time step restrictions for the simulation for explicit methods. Numerically, this can be seen as a stiff problem. We propose a semi-Implicit time-stepping approach where the viscous forces are computed Implicitly, within the context of SPH. We demonstrate the convergence of the method via a simple 2D test case.
Joo Sung Kim - One of the best experts on this subject based on the ideXlab platform.
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An efficient and robust Implicit Operator for upwind point Gauss-Seidel method
Journal of Computational Physics, 2007Co-Authors: Joo Sung Kim, Oh Joon KwonAbstract:An efficient and robust Implicit Operator for the point Gauss-Seidel method is presented for solving the compressible Euler equations. The new Implicit Operator was derived by adding a scalar form of artificial dissipation to the upwind Implicit side. The amount of artificial dissipation was locally adjusted using a weighting factor based on the solution gradient. For validation, the performance of the new Implicit Operator was compared in detail with that of several existing Implicit Operators which have been widely used for solving the flow equations. Numerical experiments showed that the stability and convergence characteristics of the new Implicit Operator are significantly better than those of other existing Implicit Operators for calculating flows ranging from subsonic to hypersonic speeds.
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Assessment of Implicit Operators for the upwind point Gauss–Seidel method on unstructured meshes
Computers & Fluids, 2007Co-Authors: Joo Sung Kim, Oh Joon KwonAbstract:Abstract The effect of the numerical dissipation level of Implicit Operators on the stability and convergence characteristics of the upwind point Gauss–Seidel (GS) method for solving the Euler equations was studied through the von Neumann stability analysis and numerical experiments. The stability analysis for linear model equations showed that the point GS method is unstable even for very small CFL numbers when the numerical dissipation level of the Implicit Operator is equivalent to that of the explicit Operator. The stability restriction is rapidly alleviated as the dissipation level of the Implicit Operator increases. The instability predicted by the linear stability analysis was further amplified as the flow problems became stiffer due to the presence of the shock wave or the refinement of the mesh. It was found that for the efficiency and the robustness of the upwind point GS method, the numerical flux of the Implicit Operator needs to be more dissipative than that of the explicit Operator.
Jon A. Linker - One of the best experts on this subject based on the ideXlab platform.
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Stability of Algorithms for Waves with Large Flows
Journal of Computational Physics, 1999Co-Authors: Roberto Lionello, Zoran Mikic, Jon A. LinkerAbstract:We have identified a numerical instability that appears in algorithms for the linear propagation of waves in the presence of an advective flow. This instability is due to the coupling between the advective and wave terms and cannot be identified if stability conditions are derived separately for these two terms. It can appear in explicit or semi-Implicit calculations using upwinded or centered spatial differences. We show that a stable scheme can be obtained by introducing a predictor step for the wave terms. When the semi-Implicit treatment of the waves is used, the semi-Implicit Operator must be applied in the predictor step as well as in the corrector step. We present an improved formulation of the semi-Implicit coefficient to take advection into account.
Chang Yoon Park - One of the best experts on this subject based on the ideXlab platform.
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Semi-Implicit Operator splitting for the simulation of Herschel–Bulkley flows with smoothed particle hydrodynamics
Computational Particle Mechanics, 2020Co-Authors: Chang Yoon Park, Tarek I. ZohdiAbstract:Smoothed particle hydrodynamics (SPH) has become a popular numerical framework of choice for simulating free-surface flows, mainly for Newtonian fluids. The topic regarding the simulation of non-Newtonian free-surface flows, however, remains relatively untouched due to difficulties regarding the computation of viscous forces. In previous approaches, the viscous forces acting on each SPH particle were computed explicitly. Non-Newtonian fluids such as Herschel–Bulkley fluids, the effective viscosity between yielded and unyielded regions can differ by several orders of magnitudes; imposing severe time step restrictions for the simulation for explicit methods. Numerically, this can be seen as a stiff problem. We propose a semi-Implicit time-stepping approach where the viscous forces are computed Implicitly, within the context of SPH. We demonstrate the convergence of the method via a simple 2D test case.
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semi Implicit Operator splitting for the simulation of herschel bulkley flows with smoothed particle hydrodynamics
Computational particle mechanics, 2020Co-Authors: Chang Yoon Park, Tarek I. ZohdiAbstract:Smoothed particle hydrodynamics (SPH) has become a popular numerical framework of choice for simulating free-surface flows, mainly for Newtonian fluids. The topic regarding the simulation of non-Newtonian free-surface flows, however, remains relatively untouched due to difficulties regarding the computation of viscous forces. In previous approaches, the viscous forces acting on each SPH particle were computed explicitly. Non-Newtonian fluids such as Herschel–Bulkley fluids, the effective viscosity between yielded and unyielded regions can differ by several orders of magnitudes; imposing severe time step restrictions for the simulation for explicit methods. Numerically, this can be seen as a stiff problem. We propose a semi-Implicit time-stepping approach where the viscous forces are computed Implicitly, within the context of SPH. We demonstrate the convergence of the method via a simple 2D test case.
