Hybrid Finite Element Method for Two-phase Miscible Displacement in Porous Media

ＨｙｂｒｉｄＦｉｎｉｔｅＥｌｅｍｅｎｔＭｅｔｈｏｄｆｏｒＴｗｏ┐ｐｈａｓｅＭｉｓｃｉｂｌｅＤｉｓｐｌａｃｅｍｅｎｔｉｎＰｏｒｏｕｓＭｅｄｉａ＊）ＬｉａｎｇＤｏｎｇ（梁栋）ＣｈｅｎｇＡｉｊｉｅ（程爱杰）（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｈｅｍａｔｉｃｓ，...     

一类变分不等方程的有限元逼近

本文对一类带有两个变函数的非线性变分不等方程进行讨论，所讨论的区域Ω＝Ｒ＾ｎ是有界子开子集，边界具有分片Ｃ＾２光滑，但不必为凸区域，文中给出了解的有限元逼近及逼近的误差估计。     

LOCALLY STABILIZED FINITE ELEMENT METHOD FOR STOKES PROBLEM WITH NONLINEAR SLIP BOUNDARY CONDITIONS

Based on the low-order conforming finite element subspace （Vh, Mh） such as the P1-P0 triangle element or the Q1-P0 quadrilateral element, the locally stabilized finite element method for the Stokes problem with nonlinear slip boundary conditions is investigated in this paper. For this class of nonlinear slip boundary conditions including the subdifferential property, the weak variational formulation associated with the Stokes problem is an variational inequality. Since （Vh, Mh） does not satisfy the discrete inf-sup conditions, a macroelement condition is introduced for constructing the locally stabilized formulation such that the stability of （Vh, Mh） is established. Under these conditions, we obtain the H1 and L2 error estimates for the numerical solutions.     

二维非饱和土壤水分运动问题的半离散有限体积元模拟

本文利用基于重心对偶剖分的有限体积元法建立了二维非饱和土壤水分运动问题的数值逼近格式,讨论了离散有限体积元解的存在唯一性,并给出了最优误差估计的证明.最后给出数值算例,模拟结果表明,利用有限体积元格式来求解二维非饱和土壤水分运动问题是可靠的,且该格式具有稳定性和可实用性.     

关于MZ1元,MZ2元和MB1元的误差估计

本文给出MZ1元、MZ2元和MB1元的收敛阶,并且证明MZ1元与MB1元等价。     

三维热传导型半导体问题的特征有限元方法和分析

本文研究三维热传导型半导体瞬态问题的特征有限元方法及其理论分析,其数学模型是一类非线性偏微分方程的初边值问题,对电子位势方程提出Ｇａｌｅｒｋｉｎ逼近;对电子,空穴浓度方程采用特征有限元逼近;对热传导方程采用对时间向后差分的Ｇａｌｅｒｋｉｎ逼近．应用微分方程先验估计理论和技巧得到了最优阶Ｌ＾２误差估计。     

On convergence of a new secant-like method for solving nonlinear equations

In this paper, we prove that the order of a new secant-like method presented recently with the so-called order of 2.618 is only 2.414. Some mistakes in the derivation leading to such a conclusion are pointed out. Meanwhile, under the assumption that the second derivative of the involved function is bounded, the convergence radius of the secant-like method is given, and error estimates matching its convergence order are also provided by using a generalized Fibonacci sequence.     

求解stokes问题的一个新的非协调混合元格式

构造一个新的非协调混合元格式求解stokes问题,证明了该元满足B-B条件,并且有2阶收敛速度.     

The Characteristic Finite Volume Method for Nonlinear Convection diffusion Problems

§ 1.Introduction　 The finite elementor finite difference methods along characteristics for convection-dif-fusion problems in an unbounded domain R have been developed by Douglas and Rus-sel[1 ] .In those problems with significant convection,the solution changes much lessrapidly in the characteristicτ direction than in time tdirection.Thus,the characteristic-type numerical methods will permitthe use of largertime steps,with corresponding im-provements in efficiency,at no cost in accuracy.　…     

一个扩散问题的自然边界元法与有限元法组合

本文讨论由Helmholtz方程描述的扩散问题的自然边界元法与有限元法的组合．取一个圆作为公共边界，用Fourier展开建立边界积分方程，将无界区域上的问题化为有界区域上的非局部边值问题．在变分方程中公共边界上的未知量只包含函数本身而不包含其法向导数，从而减少了未知数的数目，并且边界元剐度矩阵只有极少量不同的元素，有利于数值计算．这种组台方法优越于建立在直接边界元法基础上的组合方法．文中证明了变分解的唯一性，数值解的收敛性和误差估计．最后讨论了数值技术并给出一个算倒．     

A Petrov－Galerkin Method Based on Symmetrization for Parabolic Convection－Diffusion Problems

ＡＰｅｔｒｏｖ－Ｇａｌｅｒｋｉｎ　ＭｅｔｈｏｄＢａｓｅｄｏｎＳｙｍｍｅｔｒｉｚａｔｉｏｎｆｏｒＰａｒａｂｏｌｉｃＣｏｎｖｅｃｔｉｏｎ－ＤｉｆｆｕｓｉｏｎＰｒｏｂｌｅｍｓＷｕＷｅｉ（吴微）（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｈｅｍａｔｉｃｓＪｉｌｉｎＵｎｉ...     

完全可压缩渗流驱动问题的特征线有限元方法及其误差分析

多孔介质中渗流驱动问题数值方法的研究，对合理经济地开发油田，了解地下油水运动规律有一定意义。特征线法结合差分或有限元法解渗流问题，在理论和应用上获得了成功３－５，但还有很多问题需进一步研究２．前人研究多是假定流体不可压或微可压，本文研究一类完全可压缩两相驱动问题。采用特征线法与有限元法相结合，构造并分析了全离散数值格式，基于周期性假设，证明了最优Ｌ２模误差估计。     

Stokes问题非协调有限元逼近的最大模估计

本文考察了二维稳态和非稳态Stokes问题的基于速度—压力形式的非协调C-R逼近格式,利用Sobolev权模技巧和权模LBB条件,得到了稳态问题速度(包括它的梯度)和压力逼近解的拟最优的最大模估计,利用稳态问题结果和Stokes投影技巧,得到了非稳态问题速度(包括它的梯度)和压力的半离散逼近解的拟最优的最大模估计。     

A NEW DIRECT DISCONTINUOUS GALERKIN METHOD WITH SYMMETRIC STRUCTURE FOR NONLINEAR DIFFUSION EQUATIONS

In this paper we continue the study of discontinuous Galerkin finite element methods for nonlinear diffusion equations following the direct discontinuous Galerkin （DDG） meth- ods for diffusion problems [17] and the direct discontinuous Galerkin （DDG） methods for diffusion with interface corrections [18]. We introduce a numerical flux for the test func- tion, and obtain a new direct discontinuous Galerkin method with symmetric structure. Second order derivative jump terms are included in the numerical flux formula and explicit guidelines for choosing the numerical flux are given. The constructed scheme has a sym- metric property and an optimal L2 （L2） error estimate is obtained. Numerical examples are carried out to demonstrate the optimal （k ＋ 1）th order of accuracy for the method with pk polynomial approximations for both linear and nonlinear problems, under one-dimensional and two-dimensional settings.     

Newton's method for constrained optimization

We derive a quadratically convergent algorithm for minimizing a nonlinear function subject to nonlinear equality constraints. We show, following Kaufman [4], how to compute efficiently the derivative of a basis of the subspace tangent to the feasible surface. The derivation minimizes the use of Lagrange multipliers, producing multiplier estimates as a by-product of other calculations. An extension of Kantorovich's theorem shows that the algorithm maintains quadratic convergence even if the basis of the tangent space changes abruptly from iteration to iteration. The algorithm and its quadratic convergence are known but the drivation is new, simple, and suggests several new modifications of the algorithm.     

On the reservoir technique convergence for nonlinear hyperbolic conservation laws - Part I

This paper is devoted to the analysis of flux schemes coupled with the reservoir technique for approximating hyperbolic equations and linear hyperbolic systems of conservation laws [F. Alouges, F. De Vuyst, G. Le Coq, E. Lorin, The reservoir scheme for systems of conservation laws, in: Finite Volumes for Complex Applications, III, Porquerolles, 2002, Lab. Anal. Topol. Probab. CNRS, Marseille, 2002, pp. 247-254 (electronic); F. Alouges, F. De Vuyst, G. Le Coq, E. Lorin, Un procédé de réduction de la diffusion numérique des schémas à différence de flux d'ordre un pour les systèmes hyperboliques non linéaires, C. R. Math. Acad. Sci. Paris 335 (7) (2002) 627-632; F. Alouges, F. De Vuyst, G. Le Coq, E. Lorin, The reservoir technique: A way to make Godunov-type schemes zero or very low diffusive. Application to Colella-Glaz, Eur. J. Mech. B Fluids 27 (6) (2008)]. We prove the long time convergence of the reservoir technique and its TVD property for some specific but still general configurations. Proofs are based on a precise study of the treatment by the reservoir technique of shock and rarefaction waves.     

On the convergence of a conservative numerical scheme for the usual Rosenau-RLW equation

In this paper, we study the initial-boundary value problem of the usual Rosenau-RLW equation by finite difference method. We design a conservative numerical scheme which preserves the original conservative properties for the equation. The scheme is three-level and linear-implicit. The unique solvability of numerical solutions has been shown. Priori estimate and second order convergence of the finite difference approximate solutions are discussed by discrete energy method. Numerical results demonstrate that the scheme is efficient and accurate.     

A finite difference method for fractional partial differential equation

An implicit unconditional stable difference scheme is presented for a kind of linear space–time fractional convection–diffusion equation. The equation is obtained from the classical integer order convection–diffusion equations with fractional order derivatives for both space and time. First-order consistency, unconditional stability, and first-order convergence of the method are proven using a novel shifted version of the classical Grünwald finite difference approximation for the fractional derivatives. A numerical example with known exact solution is also presented, and the behavior of the error is examined to verify the order of convergence.     

Rate of weak convergence of the finite element method for the stochastic heat equation with additive noise

The stochastic heat equation driven by additive noise is discretized in the spatial variables by a standard finite element method. The weak convergence of the approximate solution is investigated and the rate of weak convergence is found to be twice that of strong convergence. M. Kovács and S. Larsson supported by the Swedish Research Council (VR). Part of this work was done at Institut Mittag-Leffler. S. Larsson supported by the Swedish Foundation for Strategic Research (SSF) through GMMC, the Gothenburg Mathematical Modelling Centre.     

伪抛物型复方程的Riemann─Hilbert初边值问题的可解性及其近似解的误差估计

本文使用参数开拓法证明了非线性伪抛物型复方程在多连通区域上的Ｒｉｅｍａｎｎ－Ｈｉｌｂｅｒｔ初边值问题的可解性，并对近似解作出了误差估计。