In this paper, following the paper [7], we analysis the 'sharp' estimate of the rate of entropy dissipation of the fully discrete MUSCL type Godunov schemes by the general compact theory introduced by Coquel-L...In this paper, following the paper [7], we analysis the 'sharp' estimate of the rate of entropy dissipation of the fully discrete MUSCL type Godunov schemes by the general compact theory introduced by Coquel-LeFloch [1, 2], and find: because of small viscosity of the above schemes, in the vincity of shock wave, the estimate of the above schemes is more easily obtained, but for rarefaction wave, we must impose a 'sharp' condition on limiter function in order to keep its entropy dissipation and its convergence.展开更多
长距离输水管道水力瞬变过程中水体压强达到汽化压强时,将会发生水柱分离现象,水柱弥合将产生异常高压,导致管路振动、变形甚至爆管事故。已有的水柱分离弥合水锤数学模型主要采用特征线法(Method of characteristics,MOC)计算,并且很...长距离输水管道水力瞬变过程中水体压强达到汽化压强时,将会发生水柱分离现象,水柱弥合将产生异常高压,导致管路振动、变形甚至爆管事故。已有的水柱分离弥合水锤数学模型主要采用特征线法(Method of characteristics,MOC)计算,并且很少考虑动态摩阻引起的能量衰减。为提高水柱分离弥合水锤现象的计算精确度和稳定性,基于有限体积法二阶Godunov格式,建立了考虑动态摩阻的离散气体空穴模型(Discrete gas cavity model,DGCM)。为实现管道边界和内部单元的统一计算,提出虚拟边界的处理方法。将该模型模拟结果与实验数据以及已有的稳态摩阻模型的计算结果进行比较,并对网格数、压力修正系数等参数敏感性进行分析。结果表明,本模型能够准确模拟出纯水锤、水柱分离弥合水锤两种情况下瞬变压力,与实验数据基本一致;考虑动态摩阻的瞬态压力计算值与实验数据更吻合;与MOC相比,当库朗数小于1.0时,有限体积法二阶Godunov模型计算结果更准确、更稳定;尤其是,压力修正系数取值0.9及较密网格时数学模型能更为准确地再现实验结果。展开更多
The authors consider systems of the form where the matrix A(u) is assumed to be strictly hyperbolic and with the property that the integral curves of the eigenvector fields are straight lines. For this class of system...The authors consider systems of the form where the matrix A(u) is assumed to be strictly hyperbolic and with the property that the integral curves of the eigenvector fields are straight lines. For this class of systems one can define a natural Riemann solver, and hence a Godunov scheme, which generalize the standard Riemann solver and Godunov scheme for conservative systems. This paper shows convergence and L1 stability for this scheme when applied to data with small total variation. The main step in the proof is to estimate the increase in the total variation produced by the scheme due to quadratic coupling terms. Using Duhamel’s principle, the problem is reduced to the estimate of the product of two Green kernels, representing probability densities of discrete random walks. The total amount of coupling is then determined by the expected number of crossings between two random walks with strictly different average speeds. This provides a discrete analogue of the arguments developed in [3,9] in connection with continuous random processes.展开更多
The bounds on the discrepancy of approximate solutions constructed by Gedunov's scheme to IVP of isentropic equations of gas dynamics are obtained, Three well-knowu results obtained by Lax for shock waves with sma...The bounds on the discrepancy of approximate solutions constructed by Gedunov's scheme to IVP of isentropic equations of gas dynamics are obtained, Three well-knowu results obtained by Lax for shock waves with small jumps for general quasilinear hyperbolic systems of conservation laws are extended to shock waves for isentropic equations of gas dynamics in a bounded invariant region with ρ=0 as one of boundries of the region. Two counterexamples are given to show that two iuequalities given by Godunov do not hold for all rational numbers γ∈(1, 3]. It seems that the approach by Godunov to obtain the forementioned bounds may not be possible.展开更多
文摘In this paper, following the paper [7], we analysis the 'sharp' estimate of the rate of entropy dissipation of the fully discrete MUSCL type Godunov schemes by the general compact theory introduced by Coquel-LeFloch [1, 2], and find: because of small viscosity of the above schemes, in the vincity of shock wave, the estimate of the above schemes is more easily obtained, but for rarefaction wave, we must impose a 'sharp' condition on limiter function in order to keep its entropy dissipation and its convergence.
文摘长距离输水管道水力瞬变过程中水体压强达到汽化压强时,将会发生水柱分离现象,水柱弥合将产生异常高压,导致管路振动、变形甚至爆管事故。已有的水柱分离弥合水锤数学模型主要采用特征线法(Method of characteristics,MOC)计算,并且很少考虑动态摩阻引起的能量衰减。为提高水柱分离弥合水锤现象的计算精确度和稳定性,基于有限体积法二阶Godunov格式,建立了考虑动态摩阻的离散气体空穴模型(Discrete gas cavity model,DGCM)。为实现管道边界和内部单元的统一计算,提出虚拟边界的处理方法。将该模型模拟结果与实验数据以及已有的稳态摩阻模型的计算结果进行比较,并对网格数、压力修正系数等参数敏感性进行分析。结果表明,本模型能够准确模拟出纯水锤、水柱分离弥合水锤两种情况下瞬变压力,与实验数据基本一致;考虑动态摩阻的瞬态压力计算值与实验数据更吻合;与MOC相比,当库朗数小于1.0时,有限体积法二阶Godunov模型计算结果更准确、更稳定;尤其是,压力修正系数取值0.9及较密网格时数学模型能更为准确地再现实验结果。
基金the European TMR network"Hyperbolic Systems of Conservation Laws"! ERBFMRXCT960033
文摘The authors consider systems of the form where the matrix A(u) is assumed to be strictly hyperbolic and with the property that the integral curves of the eigenvector fields are straight lines. For this class of systems one can define a natural Riemann solver, and hence a Godunov scheme, which generalize the standard Riemann solver and Godunov scheme for conservative systems. This paper shows convergence and L1 stability for this scheme when applied to data with small total variation. The main step in the proof is to estimate the increase in the total variation produced by the scheme due to quadratic coupling terms. Using Duhamel’s principle, the problem is reduced to the estimate of the product of two Green kernels, representing probability densities of discrete random walks. The total amount of coupling is then determined by the expected number of crossings between two random walks with strictly different average speeds. This provides a discrete analogue of the arguments developed in [3,9] in connection with continuous random processes.
基金Project supported by National Natural Science Foundation of China.
文摘The bounds on the discrepancy of approximate solutions constructed by Gedunov's scheme to IVP of isentropic equations of gas dynamics are obtained, Three well-knowu results obtained by Lax for shock waves with small jumps for general quasilinear hyperbolic systems of conservation laws are extended to shock waves for isentropic equations of gas dynamics in a bounded invariant region with ρ=0 as one of boundries of the region. Two counterexamples are given to show that two iuequalities given by Godunov do not hold for all rational numbers γ∈(1, 3]. It seems that the approach by Godunov to obtain the forementioned bounds may not be possible.
