The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Agnes Leroy - One of the best experts on this subject based on the ideXlab platform.
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Optimal Time Step for incompressible SPH
Journal of Computational Physics, 2015Co-Authors: Damien Violeau, Agnes LeroyAbstract:A classical incompressible algorithm for Smoothed Particle Hydrodynamics (ISPH) is analyzed in terms of critical Time Step for numerical stability. For this purpose, a theoretical linear stability analysis is conducted for unbounded homogeneous flows, leading to an analytical formula for the Maximum CFL (Courant-Friedrichs-Lewy) number as a function of the Fourier number. This gives the Maximum Time Step as a function of the fluid viscosity, the flow velocity scale and the SPH discretization size (kernel standard deviation). Importantly, the Maximum CFL number at large Reynolds number appears twice smaller than with the traditional Weakly Compressible (WCSPH) approach. As a consequence, the optimal Time Step for ISPH is only five Times larger than with WCSPH. The theory agrees very well with numerical data for two usual kernels in a 2-D periodic flow. On the other hand, numerical experiments in a plane Poiseuille flow show that the theory overestimates the Maximum allowed Time Step for small Reynolds numbers.
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on the Maximum Time Step in weakly compressible sph
Journal of Computational Physics, 2014Co-Authors: Damien Violeau, Agnes LeroyAbstract:In the SPH method for viscous fluids, the Time Step is subject to empirical stability criteria. We proceed to a stability analysis of the Weakly Compressible SPH equations using the von Neumann approach in arbitrary space dimension for unbounded flow. Considering the continuous SPH interpolant based on integrals, we obtain a theoretical stability criterion for the Time Step, depending on the kernel standard deviation, the speed of sound and the viscosity. The stability domain appears to be almost independent of the kernel choice for a given space discretisation. Numerical tests show that the theory is very accurate, despite the approximations made. We then extend the theory in order to study the influence of the method used to compute the density, of the gradient and divergence SPH operators, of background pressure, of the model used for viscous forces and of a constant velocity gradient. The influence of Time integration scheme is also studied, and proved to be prominent. All of the above theoretical developments give excellent agreement against numerical results. It is found that velocity gradients almost do not affect stability, provided some background pressure is used. Finally, the case of bounded flows is briefly addressed from numerical tests in three cases: a laminar Poiseuille flow in a pipe, a lid-driven cavity and the collapse of a water column on a wedge.
Jianguo Wang - One of the best experts on this subject based on the ideXlab platform.
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The Dispersive WCS-FDTD Method for Simulations of Graphene
2019 IEEE International Conference on Computational Electromagnetics (ICCEM), 2019Co-Authors: Ning Xu, Juan Chen, Jianguo WangAbstract:A dispersive weakly conditionally stable finite-difference Time-domain (WCS-FDTD) method is presented in this paper for the efficient simulations of the graphene with fine structures in two directions. The Maximum Time Step size of the proposed method is only related with the largest spatial discretization, so it is very suitable for the simulations of the graphene-based devices with fine structures in two directions. The numerical results demonstrate that the dispersive WCS-FDTD method has high computational accuracy and is much efficient than the dispersive HIE-FDTD method and the dispersive FDTD method.
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A dispersive WCS-FDTD method for simulating graphene-based absorber
Journal of Electromagnetic Waves and Applications, 2017Co-Authors: Ning Xu, Juan Chen, Jianguo WangAbstract:AbstractA dispersive weakly conditionally stable finite-difference Time-domain (WCS-FDTD) method for the efficient simulations of the graphene-based absorbers with fine structures in two directions is proposed in this paper. It is based on the auxiliary differential equation technique and the hybrid implicit explicit difference technique. The Maximum Time Step size of this method is only determined by the largest spatial discretization. The numerical results demonstrate that the dispersive WCS-FDTD method has high computational accuracy and the computational Time is greatly reduced compared with the dispersive FDTD method and the dispersive HIE-FDTD method.
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A WCS-PSTD Method for Solving Electromagnetic Problems Both With Fine and Electrically Large Structures
IEEE Transactions on Antennas and Propagation, 2014Co-Authors: Juan Chen, Jianguo WangAbstract:A Time domain method which is based on the hybrid implicit explicit difference technique and pseudospectral (PS) scheme is presented for solving 3D Maxwell's equations. The Maximum Time-Step size in this method is only determined by one spatial discretization and the spatial discretization only needs two cells per wavelength. The 3D formulations of this method are presented and the Time stability condition is demonstrated. This method is mainly useful for the simulations of electromagnetic problems where both fine and electrically large structures are employed. Compared with the conventional finite-difference Time-domain (FDTD) method and weakly conditionally stable (WCS)-FDTD method, this method has higher computational efficiency and less memory requirement, which is demonstrated through numerical examples.
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A Novel Hybrid Implicit Explicit - Pseudospectral Time Domain Method for TMz Waves
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: Juan Chen, Jianguo WangAbstract:A novel Time domain method which is based on the hybrid implicit explicit (HIE) difference technique and pseudospectral (PS) scheme is presented for solving Maxwell's equations. The Maximum Time-Step size in this method is only determined by one spatial discretization and the spatial discretization only needs two cells per wavelength. The 2-D formulation of the method is presented and the Time stability condition of the method is demonstrated. This method is mainly useful in the simulations of electromagnetic problems which are both with fine structures and electrically large structure, which is demonstrated through numerical examples by comparing with the finite-difference Time-domain (FDTD) method, HIE-FDTD method and alternating-direction implicit (ADI)-FDTD method.
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A Three-Dimensional HIE-PSTD Scheme for Simulation of Thin Slots
IEEE Transactions on Electromagnetic Compatibility, 2013Co-Authors: Juan Chen, Jianguo WangAbstract:In this paper, a pseudospectral (PS) scheme is introduced into the hybrid implicit-explicit finite-difference Time-domain (HIE-FDTD) method for solving the shielding effectiveness (SE) of thin slots. The Maximum Time-Step size in this method is only determined by two spatial discretizations and the spatial discretization only needs two cells per wavelength. The 3-D formula of the method is presented and the Time stability condition of the method is demonstrated. When this method is applied to simulate thin slots, high computational efficiency is obtained and less computer memory is used, which is demonstrated through numerical examples by comparing with the finite-difference Time-domain (FDTD) method, HIE-FDTD method, and alternating-direction implicit (ADI)-FDTD method.
Zhiguo He - One of the best experts on this subject based on the ideXlab platform.
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computationally efficient modeling of hydro sediment morphodynamic processes using a hybrid local Time Step global Maximum Time Step
Advances in Water Resources, 2019Co-Authors: Peng Hu, Zhiguo HeAbstract:Abstract A hybrid local Time Step/global Maximum Time Step (LTS/GMaTS) method is proposed for computationally efficient modeling of hydro-sediment-morphodynamic processes. The governing equations are numerically solved on unstructured triangular meshes using a well-balanced shock-capturing finite volume method with the HLLC approximate Riemann solver. High computational efficiency is achieved by implementing the LTS to solve equations governing sediment-laden flows (i.e., the hydro-sediment part), and implementing the GMaTS to solve equations governing bed materials (i.e., the morphodynamic part). Two benchmark experimental dam-break flows over erodible beds and one field case of the Taipingkou waterway, Middle Yangtze River, are simulated to demonstrate the high computational efficiency and the satisfactory quantitative accuracy. It is shown that the computational efficiency of the new model can be faster by an order of magnitude than a traditional model of similar type but implementing the global minimum Time Step (GMiTS). The satisfactory quantitative accuracy of the new model for the present cases is demonstrated by the negligible L2 norms of water level and bed elevation between the new model and the traditional model, as compared to the L2 norms between the traditional model and the measured data.
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Computationally efficient modeling of hydro-sediment-morphodynamic processes using a hybrid local Time Step/global Maximum Time Step
Advances in Water Resources, 2019Co-Authors: Peng Hu, Zhiguo HeAbstract:Abstract A hybrid local Time Step/global Maximum Time Step (LTS/GMaTS) method is proposed for computationally efficient modeling of hydro-sediment-morphodynamic processes. The governing equations are numerically solved on unstructured triangular meshes using a well-balanced shock-capturing finite volume method with the HLLC approximate Riemann solver. High computational efficiency is achieved by implementing the LTS to solve equations governing sediment-laden flows (i.e., the hydro-sediment part), and implementing the GMaTS to solve equations governing bed materials (i.e., the morphodynamic part). Two benchmark experimental dam-break flows over erodible beds and one field case of the Taipingkou waterway, Middle Yangtze River, are simulated to demonstrate the high computational efficiency and the satisfactory quantitative accuracy. It is shown that the computational efficiency of the new model can be faster by an order of magnitude than a traditional model of similar type but implementing the global minimum Time Step (GMiTS). The satisfactory quantitative accuracy of the new model for the present cases is demonstrated by the negligible L2 norms of water level and bed elevation between the new model and the traditional model, as compared to the L2 norms between the traditional model and the measured data.
Damien Violeau - One of the best experts on this subject based on the ideXlab platform.
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Optimal Time Step for incompressible SPH
Journal of Computational Physics, 2015Co-Authors: Damien Violeau, Agnes LeroyAbstract:A classical incompressible algorithm for Smoothed Particle Hydrodynamics (ISPH) is analyzed in terms of critical Time Step for numerical stability. For this purpose, a theoretical linear stability analysis is conducted for unbounded homogeneous flows, leading to an analytical formula for the Maximum CFL (Courant-Friedrichs-Lewy) number as a function of the Fourier number. This gives the Maximum Time Step as a function of the fluid viscosity, the flow velocity scale and the SPH discretization size (kernel standard deviation). Importantly, the Maximum CFL number at large Reynolds number appears twice smaller than with the traditional Weakly Compressible (WCSPH) approach. As a consequence, the optimal Time Step for ISPH is only five Times larger than with WCSPH. The theory agrees very well with numerical data for two usual kernels in a 2-D periodic flow. On the other hand, numerical experiments in a plane Poiseuille flow show that the theory overestimates the Maximum allowed Time Step for small Reynolds numbers.
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on the Maximum Time Step in weakly compressible sph
Journal of Computational Physics, 2014Co-Authors: Damien Violeau, Agnes LeroyAbstract:In the SPH method for viscous fluids, the Time Step is subject to empirical stability criteria. We proceed to a stability analysis of the Weakly Compressible SPH equations using the von Neumann approach in arbitrary space dimension for unbounded flow. Considering the continuous SPH interpolant based on integrals, we obtain a theoretical stability criterion for the Time Step, depending on the kernel standard deviation, the speed of sound and the viscosity. The stability domain appears to be almost independent of the kernel choice for a given space discretisation. Numerical tests show that the theory is very accurate, despite the approximations made. We then extend the theory in order to study the influence of the method used to compute the density, of the gradient and divergence SPH operators, of background pressure, of the model used for viscous forces and of a constant velocity gradient. The influence of Time integration scheme is also studied, and proved to be prominent. All of the above theoretical developments give excellent agreement against numerical results. It is found that velocity gradients almost do not affect stability, provided some background pressure is used. Finally, the case of bounded flows is briefly addressed from numerical tests in three cases: a laminar Poiseuille flow in a pipe, a lid-driven cavity and the collapse of a water column on a wedge.
Peng Hu - One of the best experts on this subject based on the ideXlab platform.
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computationally efficient modeling of hydro sediment morphodynamic processes using a hybrid local Time Step global Maximum Time Step
Advances in Water Resources, 2019Co-Authors: Peng Hu, Zhiguo HeAbstract:Abstract A hybrid local Time Step/global Maximum Time Step (LTS/GMaTS) method is proposed for computationally efficient modeling of hydro-sediment-morphodynamic processes. The governing equations are numerically solved on unstructured triangular meshes using a well-balanced shock-capturing finite volume method with the HLLC approximate Riemann solver. High computational efficiency is achieved by implementing the LTS to solve equations governing sediment-laden flows (i.e., the hydro-sediment part), and implementing the GMaTS to solve equations governing bed materials (i.e., the morphodynamic part). Two benchmark experimental dam-break flows over erodible beds and one field case of the Taipingkou waterway, Middle Yangtze River, are simulated to demonstrate the high computational efficiency and the satisfactory quantitative accuracy. It is shown that the computational efficiency of the new model can be faster by an order of magnitude than a traditional model of similar type but implementing the global minimum Time Step (GMiTS). The satisfactory quantitative accuracy of the new model for the present cases is demonstrated by the negligible L2 norms of water level and bed elevation between the new model and the traditional model, as compared to the L2 norms between the traditional model and the measured data.
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Computationally efficient modeling of hydro-sediment-morphodynamic processes using a hybrid local Time Step/global Maximum Time Step
Advances in Water Resources, 2019Co-Authors: Peng Hu, Zhiguo HeAbstract:Abstract A hybrid local Time Step/global Maximum Time Step (LTS/GMaTS) method is proposed for computationally efficient modeling of hydro-sediment-morphodynamic processes. The governing equations are numerically solved on unstructured triangular meshes using a well-balanced shock-capturing finite volume method with the HLLC approximate Riemann solver. High computational efficiency is achieved by implementing the LTS to solve equations governing sediment-laden flows (i.e., the hydro-sediment part), and implementing the GMaTS to solve equations governing bed materials (i.e., the morphodynamic part). Two benchmark experimental dam-break flows over erodible beds and one field case of the Taipingkou waterway, Middle Yangtze River, are simulated to demonstrate the high computational efficiency and the satisfactory quantitative accuracy. It is shown that the computational efficiency of the new model can be faster by an order of magnitude than a traditional model of similar type but implementing the global minimum Time Step (GMiTS). The satisfactory quantitative accuracy of the new model for the present cases is demonstrated by the negligible L2 norms of water level and bed elevation between the new model and the traditional model, as compared to the L2 norms between the traditional model and the measured data.
