物理系统中波动、传播等现象通常用双曲型守恒律方程的数学模型来描述,特别是在流体力学领域尤为重要。针对此类方程,我们考虑了Lax-Wendroff型中心间断伽辽金方法。该方法首先采用Lax-Wendroff型时间离散方法,也就是通过泰勒级数展开...物理系统中波动、传播等现象通常用双曲型守恒律方程的数学模型来描述,特别是在流体力学领域尤为重要。针对此类方程,我们考虑了Lax-Wendroff型中心间断伽辽金方法。该方法首先采用Lax-Wendroff型时间离散方法,也就是通过泰勒级数展开处理时间导数,然后在空间上运用中心间断伽辽金方法,从而避免了传统的多步时间积分方法。最后我们对多个双曲型守恒律方程开展数值实验,验证所提出方法在计算效率和精度上的有效性。In physical systems, phenomena like wave fluctuation and propagation are often described using hyperbolic conservation law equations, which play a crucial role in fluid mechanics. To solve these equations, we employ the Lax-Wendroff central discontinuous Galerkin method. This approach begins with the Lax-Wendroff time discretization, where time derivatives are managed through a Taylor series expansion. It then incorporates the central discontinuous Galerkin method for spatial discretization and effectively eliminates the need for traditional multi-step time integration schemes. Finally, numerical experiments on various hyperbolic conservation law equations are constructed to validate the effectiveness of our method in terms of both computational efficiency and accuracy.展开更多
This paper considers the finite difference(FD)approximations of diffusion operators and the boundary treatments for different boundary conditions.The proposed schemes have the compact form and could achieve arbitrary ...This paper considers the finite difference(FD)approximations of diffusion operators and the boundary treatments for different boundary conditions.The proposed schemes have the compact form and could achieve arbitrary even order of accuracy.The main idea is to make use of the lower order compact schemes recursively,so as to obtain the high order compact schemes formally.Moreover,the schemes can be implemented efficiently by solving a series of tridiagonal systems recursively or the fast Fourier transform(FFT).With mathematical induction,the eigenvalues of the proposed differencing operators are shown to be bounded away from zero,which indicates the positive definiteness of the operators.To obtain numerical boundary conditions for the high order schemes,the simplified inverse Lax-Wendroff(SILW)procedure is adopted and the stability analysis is performed by the Godunov-Ryabenkii method and the eigenvalue spectrum visualization method.Various numerical experiments are provided to demonstrate the effectiveness and robustness of our algorithms.展开更多
We give a brief discussion of some of the contributions of Peter Lax to Com- putational Fluid Dynamics. These include the Lax-Friedrichs and Lax-Wendroff numerical schemes. We also mention his collaboration in the 198...We give a brief discussion of some of the contributions of Peter Lax to Com- putational Fluid Dynamics. These include the Lax-Friedrichs and Lax-Wendroff numerical schemes. We also mention his collaboration in the 1983 HLL Riemann solver. We de- velop two-dimensional Lax-Friedrichs and Lax-Wendroff schemes for the Lagrangian form of the Euler equations on triangular grids. We apply a composite scheme that uses a Lax- Friedrichs time step as a dissipative filter after several Lax-Wendroff time steps. Numerical results for Noh＇s infinite strength shock problem, the Sedov blast wave problem, and the Saltzman piston problem are presented.展开更多
In order to control traffic congestion, many mathematical models have been used for several decades. In this paper, we study diffusion-type traffic flow model based on exponential velocity density relation, which prov...In order to control traffic congestion, many mathematical models have been used for several decades. In this paper, we study diffusion-type traffic flow model based on exponential velocity density relation, which provides a non-linear second-order parabolic partial differential equation. The analytical solution of the diffusion-type traffic flow model is very complicated to approximate the initial density of the Cauchy problem as a function of x from given data and it may cause a huge error. For the complexity of the analytical solution, the numerical solution is performed by implementing an explicit upwind, explicitly centered, and second-order Lax-Wendroff scheme for the numerical solution. From the comparison of relative error among these three schemes, it is observed that Lax-Wendroff scheme gives less error than the explicit upwind and explicit centered difference scheme. The numerical, analytical analysis and comparative result discussion bring out the fact that the Lax-Wendroff scheme with exponential velocity-density relation of diffusion type traffic flow model is suitable for the congested area and shows a better fit in traffic-congested regions.展开更多
In this paper,we concentrate on high-order boundary treatments for finite volume methods solving hyperbolic conservation laws.The complex geometric physical domain is covered by a Cartesian mesh,resulting in the bound...In this paper,we concentrate on high-order boundary treatments for finite volume methods solving hyperbolic conservation laws.The complex geometric physical domain is covered by a Cartesian mesh,resulting in the boundary intersecting the grids in various fashions.We propose two approaches to evaluate the cell averages on the ghost cells near the boundary.Both of them start from the inverse Lax-Wendroff(ILW)procedure,in which the normal spatial derivatives at inflow boundaries can be obtained by repeatedly using the governing equations and boundary conditions.After that,we can get an accurate evaluation of the ghost cell average by a Taylor expansion joined with high-order extrapolation,or by a Hermite extrapolation coupling with the cell averages on some“artificial”inner cells.The stability analysis is provided for both schemes,indicating that they can avoid the so-called“small-cell”problem.Moreover,the second method is more efficient under the premise of accuracy and stability.We perform numerical experiments on a collection of examples with the physical boundary not aligned with the grids and with various boundary conditions,indicating the high-order accuracy and efficiency of the proposed schemes.展开更多
In this paper,we propose a new class of discontinuous Galerkin(DG)methods for solving 1D conservation laws on unfitted meshes.The standard DG method is used in the interior cells.For the small cut elements around the ...In this paper,we propose a new class of discontinuous Galerkin(DG)methods for solving 1D conservation laws on unfitted meshes.The standard DG method is used in the interior cells.For the small cut elements around the boundaries,we directly design approximation polynomials based on inverse Lax-Wendroff(ILW)principles for the inflow boundary conditions and introduce the post-processing to preserve the local conservation properties of the DG method.The theoretical analysis shows that our proposed methods have the same stability and numerical accuracy as the standard DG method in the inner region.An additional nonlinear limiter is designed to prevent spurious oscillations if a shock is near the boundary.Numerical results indicate that our methods achieve optimal numerical accuracy for smooth problems and do not introduce additional oscillations in discontinuous problems.展开更多
In this paper, we use Hermite weighted essentially non-oscillatory （HWENO） schemes with a Lax-Wendroff time discretization procedure, termed HWENO-LW schemes, to solve Hamilton-Jacobi equations. The idea of the reco...In this paper, we use Hermite weighted essentially non-oscillatory （HWENO） schemes with a Lax-Wendroff time discretization procedure, termed HWENO-LW schemes, to solve Hamilton-Jacobi equations. The idea of the reconstruction in the HWENO schemes comes from the original WENO schemes, however both the function and its first derivative values are evolved in time and are used in the reconstruction. One major advantage of HWENO schemes is its compactness in the reconstruction. We explore the possibility in avoiding the nonlinear weights for part of the procedure, hence reducing the cost but still maintaining non-oscillatory properties for problems with strong discontinuous derivative. As a result, comparing with HWENO with Runge-Kutta time discretizations schemes （HWENO-RK） of Qiu and Shu [19] for Hamilton-Jacobi equations, the major advantages of HWENO-LW schemes are their saving of computational cost and their compactness in the reconstruction. Extensive numerical experiments are performed to illustrate the capability of the method.展开更多
IT is known from Brenner, Thomee and Wahlbin that the well-known second-order Lax-Wendroff scheme is stable in L^2, but unstable in L^p, p≠2. Generally speaking, if the initialdata is smooth enough and if a differenc...IT is known from Brenner, Thomee and Wahlbin that the well-known second-order Lax-Wendroff scheme is stable in L^2, but unstable in L^p, p≠2. Generally speaking, if the initialdata is smooth enough and if a difference scheme, which is stable in L^p for some p, has orderof accuracy μ, then we can expect that the solution of the difference scheme converges to thesolution of the differential equation at the rate of order μ in L^p. But for discontinuous solu-tions, which are essential to hyperbolic equations, the above expectation is not true. Error es-timates for discontinuous solutions not only have theoretical meaning, but also practical value.展开更多
This paper studies the geometric boundary representations for Inverse Lax-Wendroff(ILW)method,aiming to develop a practical computer-aided engineering method without body-fitted meshes.We propose the signed distance f...This paper studies the geometric boundary representations for Inverse Lax-Wendroff(ILW)method,aiming to develop a practical computer-aided engineering method without body-fitted meshes.We propose the signed distance function(SDF)representation of the geometric boundary and design an extremely efficient algorithm for foot point calculation,which is particularly in line with the needs of ILW.Theoretical and numerical analyses demonstrate that the SDF representation of geometric boundary can satisfy ILW’s needs better than others.The effectiveness and robustness of our proposed method are verified by simulating initial boundary value computational physical problems of Euler equation for compressible fluids.展开更多
The inverse Lax-Wendroff(ILW)procedure is a numerical boundary treatment technique,which allows finite difference schemes and other schemes to achieve stability and high order accuracy when using cartesian meshes to s...The inverse Lax-Wendroff(ILW)procedure is a numerical boundary treatment technique,which allows finite difference schemes and other schemes to achieve stability and high order accuracy when using cartesian meshes to solve boundary value problems defined on complex computational domain.In this short survey we summarize the main ingredients of the ILW procedure,discuss its applicability and stability properties,and provide possible directions of its future development.展开更多
文摘物理系统中波动、传播等现象通常用双曲型守恒律方程的数学模型来描述,特别是在流体力学领域尤为重要。针对此类方程,我们考虑了Lax-Wendroff型中心间断伽辽金方法。该方法首先采用Lax-Wendroff型时间离散方法,也就是通过泰勒级数展开处理时间导数,然后在空间上运用中心间断伽辽金方法,从而避免了传统的多步时间积分方法。最后我们对多个双曲型守恒律方程开展数值实验,验证所提出方法在计算效率和精度上的有效性。In physical systems, phenomena like wave fluctuation and propagation are often described using hyperbolic conservation law equations, which play a crucial role in fluid mechanics. To solve these equations, we employ the Lax-Wendroff central discontinuous Galerkin method. This approach begins with the Lax-Wendroff time discretization, where time derivatives are managed through a Taylor series expansion. It then incorporates the central discontinuous Galerkin method for spatial discretization and effectively eliminates the need for traditional multi-step time integration schemes. Finally, numerical experiments on various hyperbolic conservation law equations are constructed to validate the effectiveness of our method in terms of both computational efficiency and accuracy.
基金supported by the NSFC grant 11801143J.Lu’s research is partially supported by the NSFC grant 11901213+3 种基金the National Key Research and Development Program of China grant 2021YFA1002900supported by the NSFC grant 11801140,12171177the Young Elite Scientists Sponsorship Program by Henan Association for Science and Technology of China grant 2022HYTP0009the Program for Young Key Teacher of Henan Province of China grant 2021GGJS067.
文摘This paper considers the finite difference(FD)approximations of diffusion operators and the boundary treatments for different boundary conditions.The proposed schemes have the compact form and could achieve arbitrary even order of accuracy.The main idea is to make use of the lower order compact schemes recursively,so as to obtain the high order compact schemes formally.Moreover,the schemes can be implemented efficiently by solving a series of tridiagonal systems recursively or the fast Fourier transform(FFT).With mathematical induction,the eigenvalues of the proposed differencing operators are shown to be bounded away from zero,which indicates the positive definiteness of the operators.To obtain numerical boundary conditions for the high order schemes,the simplified inverse Lax-Wendroff(SILW)procedure is adopted and the stability analysis is performed by the Godunov-Ryabenkii method and the eigenvalue spectrum visualization method.Various numerical experiments are provided to demonstrate the effectiveness and robustness of our algorithms.
基金performed under the auspices of the National Nuclear Security Administration of the US Department of Energy at Los Alamos National Laboratory under Contract No.DE-AC52-06NA25396supported in part by the Czech Science Foundation GrantP205/10/0814the Czech Ministry of Education grants MSM 6840770022 and LC528
文摘We give a brief discussion of some of the contributions of Peter Lax to Com- putational Fluid Dynamics. These include the Lax-Friedrichs and Lax-Wendroff numerical schemes. We also mention his collaboration in the 1983 HLL Riemann solver. We de- velop two-dimensional Lax-Friedrichs and Lax-Wendroff schemes for the Lagrangian form of the Euler equations on triangular grids. We apply a composite scheme that uses a Lax- Friedrichs time step as a dissipative filter after several Lax-Wendroff time steps. Numerical results for Noh＇s infinite strength shock problem, the Sedov blast wave problem, and the Saltzman piston problem are presented.
文摘In order to control traffic congestion, many mathematical models have been used for several decades. In this paper, we study diffusion-type traffic flow model based on exponential velocity density relation, which provides a non-linear second-order parabolic partial differential equation. The analytical solution of the diffusion-type traffic flow model is very complicated to approximate the initial density of the Cauchy problem as a function of x from given data and it may cause a huge error. For the complexity of the analytical solution, the numerical solution is performed by implementing an explicit upwind, explicitly centered, and second-order Lax-Wendroff scheme for the numerical solution. From the comparison of relative error among these three schemes, it is observed that Lax-Wendroff scheme gives less error than the explicit upwind and explicit centered difference scheme. The numerical, analytical analysis and comparative result discussion bring out the fact that the Lax-Wendroff scheme with exponential velocity-density relation of diffusion type traffic flow model is suitable for the congested area and shows a better fit in traffic-congested regions.
基金supported in part by the NSFC Grant 12271499supported in part by the R&D project of Pazhou Lab(Huangpu)under Grant 2023K0609 and the NSFC Grant 12126604.
文摘In this paper,we concentrate on high-order boundary treatments for finite volume methods solving hyperbolic conservation laws.The complex geometric physical domain is covered by a Cartesian mesh,resulting in the boundary intersecting the grids in various fashions.We propose two approaches to evaluate the cell averages on the ghost cells near the boundary.Both of them start from the inverse Lax-Wendroff(ILW)procedure,in which the normal spatial derivatives at inflow boundaries can be obtained by repeatedly using the governing equations and boundary conditions.After that,we can get an accurate evaluation of the ghost cell average by a Taylor expansion joined with high-order extrapolation,or by a Hermite extrapolation coupling with the cell averages on some“artificial”inner cells.The stability analysis is provided for both schemes,indicating that they can avoid the so-called“small-cell”problem.Moreover,the second method is more efficient under the premise of accuracy and stability.We perform numerical experiments on a collection of examples with the physical boundary not aligned with the grids and with various boundary conditions,indicating the high-order accuracy and efficiency of the proposed schemes.
基金supported in part by the NSFC Grant 12271499the Cyrus Tang Foundation.Research is supported in part by the NSF Grant DMS-2309249supported in part by the NSFC Grant 12126604.
文摘In this paper,we propose a new class of discontinuous Galerkin(DG)methods for solving 1D conservation laws on unfitted meshes.The standard DG method is used in the interior cells.For the small cut elements around the boundaries,we directly design approximation polynomials based on inverse Lax-Wendroff(ILW)principles for the inflow boundary conditions and introduce the post-processing to preserve the local conservation properties of the DG method.The theoretical analysis shows that our proposed methods have the same stability and numerical accuracy as the standard DG method in the inner region.An additional nonlinear limiter is designed to prevent spurious oscillations if a shock is near the boundary.Numerical results indicate that our methods achieve optimal numerical accuracy for smooth problems and do not introduce additional oscillations in discontinuous problems.
基金Research partially supported by NNSFC grant 10371118,SRF for ROCS,SEM and Nanjing University Talent Development Foundation.
文摘In this paper, we use Hermite weighted essentially non-oscillatory （HWENO） schemes with a Lax-Wendroff time discretization procedure, termed HWENO-LW schemes, to solve Hamilton-Jacobi equations. The idea of the reconstruction in the HWENO schemes comes from the original WENO schemes, however both the function and its first derivative values are evolved in time and are used in the reconstruction. One major advantage of HWENO schemes is its compactness in the reconstruction. We explore the possibility in avoiding the nonlinear weights for part of the procedure, hence reducing the cost but still maintaining non-oscillatory properties for problems with strong discontinuous derivative. As a result, comparing with HWENO with Runge-Kutta time discretizations schemes （HWENO-RK） of Qiu and Shu [19] for Hamilton-Jacobi equations, the major advantages of HWENO-LW schemes are their saving of computational cost and their compactness in the reconstruction. Extensive numerical experiments are performed to illustrate the capability of the method.
文摘IT is known from Brenner, Thomee and Wahlbin that the well-known second-order Lax-Wendroff scheme is stable in L^2, but unstable in L^p, p≠2. Generally speaking, if the initialdata is smooth enough and if a difference scheme, which is stable in L^p for some p, has orderof accuracy μ, then we can expect that the solution of the difference scheme converges to thesolution of the differential equation at the rate of order μ in L^p. But for discontinuous solu-tions, which are essential to hyperbolic equations, the above expectation is not true. Error es-timates for discontinuous solutions not only have theoretical meaning, but also practical value.
文摘This paper studies the geometric boundary representations for Inverse Lax-Wendroff(ILW)method,aiming to develop a practical computer-aided engineering method without body-fitted meshes.We propose the signed distance function(SDF)representation of the geometric boundary and design an extremely efficient algorithm for foot point calculation,which is particularly in line with the needs of ILW.Theoretical and numerical analyses demonstrate that the SDF representation of geometric boundary can satisfy ILW’s needs better than others.The effectiveness and robustness of our proposed method are verified by simulating initial boundary value computational physical problems of Euler equation for compressible fluids.
文摘The inverse Lax-Wendroff(ILW)procedure is a numerical boundary treatment technique,which allows finite difference schemes and other schemes to achieve stability and high order accuracy when using cartesian meshes to solve boundary value problems defined on complex computational domain.In this short survey we summarize the main ingredients of the ILW procedure,discuss its applicability and stability properties,and provide possible directions of its future development.
