非线性退化波方程的Riemann问题

研究了弹性力学中一退化波方程的Riemann问题．其应力函数非凸非凹,从而使得激波条件退化．通过引入广义激波条件下的退化激波,构造性地得到了各种情形下Riemann问题的整体解．     

一种守恒型间断跟踪法在一维单守恒律方程上的程序实现

茅在近几年发展了一种守恒型的间断跟踪法（见[6],[7]），该跟踪法是以解的守恒性质作为跟踪的机制而不是传统的跟踪法利用Rankine-Hugoniot条件。本文的目的是对该算法在一维单守恒律的情况进行程序实现，做成一个对任意初值问题都适应的强健的算法，可处理任意的间断相互作用。在文章的第三节给出了一个数值算例，并与用ENO格式（见[8]所算得的结果进行比较。     

绝热流Chaplygin气体的Riemann问题

本文研究了绝热流Chaplygin气体动力学方程组,利用特征分析方法,在得到所有基本波的基础上,构造出Riemann问题的所有解.Riemann解由前向疏散波(激波)、后向疏散波(激波)、接触间断以及δ波构成.     

间断流函数守恒律方程的高精度有限差分格式

本文研究了具有间断流函数的守恒律方程，借助本质无振荡（ENO）的思想，利用Rankine—Hugoniot关系和全局熵条件设计出一种高精度计算格式；并利用此格式计算出相关情形的Riemann问题，显示了满意的数值解果．     

一种守恒型间断跟踪法用于处理一维Euler方程组中的若干问题

1引言间断跟踪法(front-tracking)是数值求解双曲型守恒型方程(组)的一种重要的数值方法,其主要特点是把间断作为移动的内边界来处理,光滑区域中的数值解用计算光滑解有效的数值方法来求解,而间断的移动和间断两侧的数值解的修正要满足Rankine-Hugoniot条件．我们称这样的跟踪法为传统的间断跟踪法(见[3],[14])．本文的第二作者多年来研究设计了一种基于解的守恒性质的间断跟踪法(见[11],[12]),其最主要的特点是以解的守恒性作为跟踪的机制,而不是象传统的间断跟踪法那样利用     

二维双曲守恒律的大时间步长Godunov方法(英文)

考虑了关于二维守恒律的大时间步长Godunov方法.该方法是关于一维问题的自然推广.证明了文中给出的数值流函数下,该方法是守恒的.进一步还给出了近似Riemann解应满足的条件,并且证明了利用满足这些条件的近似Riemann解的大时间步长Godunov方法守恒.最后,补充证明了满足这些条件的近似Riemann解是满足熵条件的.     

一维单个守恒律的一类二阶、几乎熵耗散的格式

本文考虑一维单个守恒律方程，对其设计了一个基于熵耗散的非线性守恒型差分格式．本格式的数值流函数是Lax-Freidrichs格式和Lax-Wendroff格式数值流函数的凸组合，凸组合中的系数是由考虑耗散熵来决定的．这样在解的光滑区域内，格式几乎、甚至完全是Lax-Wendroff格式，而在解的间断处，格式几乎、甚至完全是Lax—Freidrichs格式．从而消除了间断附近的非物理振荡，实现了计算的非线性稳定性．理论分析表明本格式在解的非极值点处是二阶精度的，而在解的极值点处至少有一阶精度．数值试验表明格式是有效的．     

非凸单个守恒律初边值问题的整体弱熵解的构造

本文研究具有两段常数的初始值和常数边界值的非凸单个守恒律的初边值问题.在流函数具有一个拐点的条件下,由相应的初始值问题弱熵解的结构和Bardos-Leroux-Nedelec提出的边界熵条件,给出初边值问题整体弱熵解的一个构造方法,澄清弱熵解在边界附近的结构.与严格凸的单个守恒律初边值问题相比,非凸单个守恒律初边值问题的弱熵解中包括下列新的相互作用类型:一个接触或非接触激波碰到边界,边界弹回一个非接触激波.     

一个解KdV方程的满足两个守恒律的差分格式

Korteweg-de Vries(KdV)方程是人们在研究一些物理问题时得到的非线性波 动方程,其解满足无穷多个守恒律．本文为该方程设计了一种差分格式,其采用的是有限 体积法．但与传统的有限体积法不同的是,它的数值解同时满足两个相关的守恒律．这样 可以更好地保持解的物理上的守恒性质．数值例子表明这一算法是有效的．     

带有摩擦项的广义Chaplygin气体非对称Keyfitz-Kranzer方程组的Riemann问题

研究了带有摩擦项的广义Chaplygin气体非对称Keyfitz-Kranzer方程组的Riemann问题,并得到其Riemann解的整体结构.Riemann解中包含激波,稀疏波,接触间断和δ-激波.与齐次非对称Keyfitz-Kranzer方程组不同的是非齐次非对称Keyfitz-Kranzer方程组的Riemann解是非自相似的.     

Conservation laws of turbulence models

The conservation of mass, momentum, energy, helicity, and enstrophy in fluid flow are important because these quantities organize a flow, and characterize change in the flow's structure over time. In turbulent flow, conservation laws remain important in the inertial range of wave numbers, where viscous effects are negligible. It is in the inertial range where energy, helicity (3d), and enstrophy (2d) must be accurately cascaded for a turbulence model to be qualitatively correct. A first and necessary step for an accurate cascade is conservation; however, many turbulent flow simulations are based on turbulence models whose conservation properties are little explored and might be very different from those of the Navier-Stokes equations.We explore conservation laws and approximate conservation laws satisfied by LES turbulence models. For the Leray, Leray deconvolution, Bardina, and Nth order deconvolution models, we give exact or approximate laws for a model mass, momentum, energy, enstrophy and helicity. The possibility of cascades for model quantities is also discussed.     

Construction of Autonomous Conservation Laws

In mathematical physics conservation laws are of very special importance. For variational problems they can be determined by means of Noether’s theorem, whereas for general differential equations a direct method by Anco and Bluman (Eur. J. Appl. Math., 13:545–566, 2002, Eur. J. Appl. Math., 13:567–585, 2002) is available. In this paper, a theorem mapping nonautonomous and nonhomogeneous quasilinear first order partial differential equations to autonomous and homogeneous quasilinear first order partial differential equations is used to obtain from a system of first order balance laws an autonomous system of conservation laws.     

Conservation laws for linear viscoelasticity

In the brief note entitled On Conservation Laws for Dissipative Systems [4], a new method for constructing conservation laws was proposed. This method was termed the Neutral Action (NA) method in [5]. For any system governed by a set of differential equations, the NA method offers a systematic approach for determination of conservation laws applicable to the system. It is the purpose of the present paper to establish conservation laws for one- and two-dimensional viscoelasticy (Voigt model) via the NA method. The conservation laws derived should prove useful in studies of fracture and defects in a viscoelastic material.     

Conservation Principles and Integral Invariants

Conservation laws in the form of integral invariants of linear systems form a particularly simple concept. This is developed into a teaching tool connecting various other fields with this physical notion in such a way that it may be introduced as a seminal first year topic in applied mathematics.     

Conservation laws for the relativistic P-system

Abstract

This note is devoted to the existence of rigorous asymptotic expansions for some boundary layer problems. We follow ideas of geometric optics and show that, generically, the study of such expansions is linked to the kernel and range of suitable projectors. We apply this remark to some classical geophysical systems, and recover in particular the results of (Grenier, E., Masmoudi, N. (1997). Ekman layers of rotating fluids, the case of well prepared initial data. Comm. Partial Differential Equations 22(5–6):953–975) with some improvements.     

Conservation laws of some lattice equations

We derive infinitely many conservation laws for some multidimensionally consistent lattice equations from their Lax pairs. These lattice equations are the Nijhoff-Quispel-Capel equation, lattice Boussinesq equation, lattice nonlinear Schrödinger equation, modified lattice Boussinesq equation, Hietarinta’s Boussinesq-type equations, Schwarzian lattice Boussinesq equation, and Toda-modified lattice Boussinesq equation.