声热耦合问题的广义差分法

引言 按照Petrov-Galerkin方法(也称广义Galerkin方法)构造差分格式已经有一些工作(例如[2]、[3]).本文把[3]中构造广义差分格式的方法推广到声热耦合方程组. 熟知,关于声热耦合方程组,Richtmyer给出了三个条件稳定的格式.我们用广义差分法构造出三种新的差分格式.对其中的格式Ⅰ、Ⅱ进行了稳定性分析,它们具有绝对稳定的特点.而格式Ⅲ指出了进一步提高精度的途径. 本文写作过程中得到了李荣华教授的热情指导,谨致谢意。     

一维非线性二阶双曲型方程组有限元方法的L_∞估计

本文讨论一维非线性二阶双曲型方程组初边值问题有限元方法的L_∞估计。对于一维一个未知函数线性双曲型方程有限元方法的L_∞估计,已有[1]、[2]。本文对非线性双曲型方程组的情况,提出一类有限元格式,并讨论了它的L_∞估计。这对于非线性     

守恒型双曲型方程组的差分方法(Ⅱ)

本文是[1]的继续,将介绍守恒型双曲型方程组的各种其他差分方法,例如基于Riemann间断分解的 格式,Glimm格式和Chorin的随机选取法,人工粘性法,人工压缩法,特征型格式和质点法等。本文所采用的记号同[1]。 本文继续介绍下列守恒型双曲型方程组的差分方法     

二维可压缩Euler方程组C^1解整体存在的必要条件

对于具有某类初值条件的二维可压缩流体Euler方程组，给出了其C1解整体存在的必要条件，从而对[1]、[2]中的“未解决问题”提供了有意义的说明．     

拟线性双曲型方程的A.D.I.Galerkin方法及其敛速估计

§1.引言 本文讨论求解一类二维拟线性双曲型方程的有限元方法([1,4,7]是本文的特殊情形),提出解该方程的 A.D.I.Galerkin方法,并给出最优 H~1模误差估计.[7]中导出了非线性方程组,而本文导出的是U_(ij)~(n+1)的线性方程组.交替方向格式将二维问题化成一维,其计算量比[1,4,7]中诸格式小得多;又在估计误差时,用本文的方法得到的估计式不     

解含有混合导数的多维抛物型方程的两个显格式

迄今为止,以往多见对p=2及p=3的情况用交替方向法求解过。仅作者在[1]中对p=2的情况提出两个显式格式,及文[2]中对p=3的情况提出一个显式格式。本文在此基础上,构造出两个对任意p维空间变量都适用的绝对稳定的显式格式,从而避免了解线代数方程组,大大地减小了计算工作量。     

关于线性代数方程的一种迭代解法的收敛性问题

用迭代法求解线性代数方程组,已有大量的文献与专著,例如[4、6、7]。最常用的是逐次超松弛,及其种种变形。但是,许多情况表明这些方法并非完全令人满意的,特别对病态线性代数方程组,即方程组的系数矩阵有大的条件数,用这些方法求解时,收敛得相当慢。 [1]对求解病态常微分方程初值问题构造了一种恒稳格式。从线性代数方程组的解,等价于某一常微分方程组初值问题的稳态解,这一事实出发,从而构造了一种新的求解线性代数方程组的迭代解法。[1、2]某些计算实例表明,此迭代法特别适合于求解病态线性     

解一类非线性方程组的球形迭代法

对一类非线性方程组,本文给出一种球形迭代解法。它的基本思想是:以空间某一固定点为球心,给出一球形区域为方程组解的初估计范围,以球中任一点为迭代初值,按某一格式迭代,当迭代解超出这一区域,则将这球形区域的半径扩大,同时重新从迭代初值出发迭代,我们将证明,当球形区域最终包含方程组解时,迭代解至多有限次超出球形区域,直至收敛到方程组的解。这种解法具有大范围收敛性,同时允许迭代格式中带有误差项,适合这种解法的非线性方程组较[1],[2],[3]中的更广,而迭代格式中的误差项又比[4]中更一般。     

解含混合导数项的变系数二维抛物型微分方程的一族显格式

§1 引言 对于含混合导数项的常系数抛物型微分方程第一边值问题的求解,文[1]、[2]、[3]给出了绝对稳定的三层显格式,它们的计算量比ADI少。本文对变系数的二维问题进行讨论,给出了一族三层显格式,并在参数的某一选择下得到绝对稳定的三层显格式。     

流体力学中的差分方法(Ⅳ)——低Mach数流动的数值解

在许多实际问题中,需要计算低Mach数流动。由于它是一个由抛物型方程和双曲型方程组成的非线性方程组,因此在严格估计误差时相当困难。在[2]中讨论了Navier—Stokes方程组差分解的某些理论问题,在[3]中把此方法应用到低Mach数流动,但只限于最简单的情况。本文中较系统地讨论了这一问题,其中包括差分格式的建立,周期解问题的计算稳定性,多步格式的优越性及边值误差的影响,等等。     

The Symmetrical Dissipative Difference Schemes for Quasi-Linear Hyperbolic Conservation Laws

In this paper we construct a new type of symmetrical dissipative difference scheme. Except discontinuity these schemes have uniformly second-order accuracy. For calculation using these, the simple-wave is very exact, the shock has high resolution, the programing is simple and the CPU time is economical. Since the paper [1] introduced that in some conditions Lax-Wendroff scheme would converge to nonphysical solution, many researchers have discussed this problem. According to preserving the monotonicity of the solution preserving monotonial schemes and TVD schemes have been introduced by Harten, et. According to property of hyperbolic wave propagation the schemes of split-coefficient matrix (SCM) and split-flux have been formed. We emphasize the dissipative difference scheme, and these schemes are dissipative on arbitrary conditions.     

Alternating Direction Finite Volume Element Methods for Three-Dimensional Parabolic Equations

<正>This paper presents alternating direction finite volume element methods for three-dimensional parabolic partial differential equations and gives four computational schemes,one is analogous to Douglas finite difference scheme with second-order splitting error,the other two schemes have third-order splitting error,and the last one is an extended LOD scheme.The L~2 norm and H~1 semi-norm error estimates are obtained for the first scheme and second one,respectively.Finally,two numerical examples are provided to illustrate the efficiency and accuracy of the methods.     

A construction of non-isomorphic amorphous association schemes from pseudo-cyclic association schemes

As a continuation of my paper [T. Fujisaki, A construction of amorphous association scheme from a pseudo-cyclic association scheme, Discrete Math. 285(1–3) (2004) 307–311], we show a construction of amorphous association scheme which is a fusion scheme of a direct product of two pseudo-cyclic association schemes with same first eigenmatrix. By using this construction, we can get at most three amorphous association scheme. We prove that if two pseudo-cyclic association scheme are non-isomorphic, then these three amorphous association schemes are mutually non-isomorphic.     

Asymptotic Preserving Schemes for Semiconductor Boltzmann Equation in the Diffusive Regime

As is known, the numerical stiffness arising from the small mean free path is one of the main difficulties in the kinetic equations. In this paper, we derive both the split and the unsplit schemes for the linear semiconductor Boltzmann equation with a diffusive scaling. In the two schemes, the anisotropic collision operator is realized by the "BGK"-penalty method, which is proposed by Filbet and Jin [F. Filbet and S. Jin, J. Comp. Phys. 229(20), 7625-7648, 2010] for the kinetic equations and the related problems having stiff sources. According to the numerical results, both of the schemes are shown to be uniformly convergent and asymptotic-preserving. Besides, numerical evidences suggest that the unsplit scheme has a better numerical stability than the split scheme.     

The Conservation and Convergence of Two Finite Difference Schemes for KdV Equations with Initial and Boundary Value Conditions

Korteweg-de Vries equation is a nonlinear evolutionary partial differential equation that is of third order in space. For the approximation to this equation with the initial and boundary value conditions using the finite difference method, the difficulty is how to construct matched finite difference schemes at all the inner grid points. In this paper, two finite difference schemes are constructed for the problem. The accuracy is second-order in time and first-order in space. The first scheme is a two-level nonlinear implicit finite difference scheme and the second one is a three-level linearized finite difference scheme. The Browder fixed point theorem is used to prove the existence of the nonlinear implicit finite difference scheme. The conservation, boundedness, stability, convergence of these schemes are discussed and analyzed by the energy method together with other techniques. The two-level nonlinear finite difference scheme is proved to be unconditionally convergent and the three-level linearized one is proved to be conditionally convergent. Some numerical examples illustrate the efficiency of the proposed finite difference schemes.     

Message Recovery for Signature Schemes Based on the Discrete Logarithm Problem

The new signature scheme presented by the authors in [13] is the first signature scheme based on the discrete logarithm problem that gives message recovery. The purpose of this paper is to show that the message recovery feature is independent of the choice of the signature equation and that all ElGamal-type schemes have variants giving message recovery. For each of the six basic ElGamal-type signature equations five variants are presented with different properties regarding message recovery, length of commitment and strong equivalence. Moreover, the six basic signature schemes have different properties regarding security and implementation. It turns out that the scheme proposed in [13] is the only inversionless scheme whereas the message recovery variant of the DSA requires computing of inverses in both generation and verification of signatures. In general, message recovery variants can be given for ElGamal-type signature schemes over any group with large cyclic subgroup as the multiplicative group of GF(2n) or elliptic curve over a finite field.The present paper also shows how to integrate the DLP-based message recovery schemes with secret session key establishment and ElGamal encryption. In particular, it is shown that with DLP-based schemes the same functionality as with RSA can be obtained. However, the schemes are not as elegant as RSA in the sense that the signature (verification) function cannot at the same time be used as the decipherment (encipherment) function.     

An analogue oft-Designs in the association schemes of alternating bilinear forms

The notion of designs in an association scheme is defined algebraically by Delsarte [4]. It is known that his definition of designs has a geometric interpretation for known (P andQ)-polynomial association schemes except three examples. In this paper we give a geometric interpretation of designs in an association scheme of alternating bilinear forms, which is one of the three.     

Smoothness Analysis of Subdivision Schemes by Proximity

Linear curve subdivision schemes may be perturbed in various ways, for example, by modifying them such as to work in a manifold, surface, or group. The analysis of such perturbed and often nonlinear schemes "T" is based on their proximity to the linear schemes "S" which they are derived from. This paper considers two aspects of this problem: One is to find proximity inequalities which together with C^k smoothness of S imply C^k smoothness of T. The other is to verify these proximity inequalities for several ways to construct the nonlinear scheme T analogous to the linear scheme S. The first question is treated for general k, whereas the second one is treated only in the case k = 2. The main result of the paper is that convergent geodesic/projection/Lie group analogues of a certain class of factorizable linear schemes have C² limit curves.     

Central ADER schemes for hyperbolic conservation laws

In this paper we first briefly review the very high order ADER methods for solving hyperbolic conservation laws. ADER methods use high order polynomial reconstruction of the solution and upwind fluxes as the building block. They use a first order upwind Godunov and the upwind second order weighted average (WAF) fluxes. As well known the upwind methods are more accurate than central schemes. However, the superior accuracy of the ADER upwind schemes comes at a cost, one must solve exactly or approximately the Riemann problems (RP). Conventional Riemann solvers are usually complex and are not available for many hyperbolic problems of practical interest. In this paper we propose to use two central fluxes, instead of upwind fluxes, as the building block in ADER scheme. These are the monotone first order Lax-Friedrich (LXF) and the third order TVD flux. The resulting schemes are called central ADER schemes. Accuracy of the new schemes is established. Numerical implementations of the new schemes are carried out on the scalar conservation laws with a linear flux, nonlinear convex flux and non-convex flux. The results demonstrate that the proposed scheme, with LXF flux, is comparable to those using first and second order upwind fluxes while the scheme, with third order TVD flux, is superior to those using upwind fluxes. When compared with the state of art ADER schemes, our central ADER schemes are faster, more accurate, Riemann solver free, very simple to implement and need less computer memory. A way to extend these schemes to general systems of nonlinear hyperbolic conservation laws in one and two dimensions is presented.     

Integrated Inventory Replenishment and Temporal Shipment Consolidation: A Comparison of Quantity-Based and Time-Based Models

In this paper we present two models for joint stock replenishment and shipment consolidation decisions which arise in the context of vendor managed inventory. Stock replenishment from suppliers or shipment to customers each incurs a lump-sum cost to the vendor. We assume the vendor uses the reorder point, lot-size policy to replenish stock and one of two schemes to dispatch shipment: the time-based and quantity-based consolidation schemes. Under the time-based (quantity-based) scheme, a shipment is dispatched periodically (when a certain quantity of outstanding demand is accumulated). The basic finding is that the quantity-based scheme can outperform the time-based counterpart while the reverse never occurs.