基于双尺度渐近分析的有限元算法

1．引言正如文山所说，由于复合材料和周期结构的材料系数ail（x）在局部区域内间断且跳跃性很大，加上区域内含有周期性洞穴或裂缝，且周期长度很小．一般而言，直接采用有限元方法进行数值模拟，其计算量大得惊人，甚至难以实现．文山针对这种特征，提出了一种可计算的双尺度渐近分析模式，本文在此基础上给出了相应的有限元算法，它包括：1．周期解在一个基本构造上的有限元计算；2．边界层的有限元计算．同时，给出了相应的误差分析．2．周期解的有限元计算首先考虑下列形式的边值问题；其中把，代E尸（on叫，iii（0关于E—（EI，ZZ…     

抛物型方程有限元解的长时间渐近性态

1引言设Ω为R2中有界凸多边形区域，f(x)∈L2（Ω），λ为非负常数，面为LaPlace算子，考虑下面定解问题：我们在空间区域采用有限元剖分，在时间轴上采用［1］提出的一类差分格式，本文证明（1．1）的有限元解当L、co时收敛到下面椭圆方程（1．2）的有限元解：从而可应用［2］提出的具有并行本性的差分格式得到椭圆问题（1．幻的有限元解．2．预备知识设J为o上的拟一致三角剖分，vnCHI（n）为相应于J的线性协调元空间，7T：H‘（m、K为插值算子，使对J的任意节点P，7T。（P）＝。（P）·我们用下述格式求解（1．1）：求。h＋IEVh…     

可混溶驱动问题的超收敛性

本文讨论多孔介质中两相可混溶渗流驱动问题的有限元方法，采用一致网格剖分、指标为k的Raviart－Thomas空间对压力作混合有限元逼近，用正则剖分、逼近阶为l的标准有限元方法处理浓度方程，通过核函数对有限元解作卷积进行局部平均确定非线性项的系数，得到了浓度误差H1范数的超收敛估计，经高阶插值，得到了整体高精度的逼近．     

半导体问题的交替方向有限元方法

该文用交替方向有限元方法求解半导体问题的Energy Trans port (ET)模型。对模型中椭圆型的电子位势方程采用交替方向迭代法，对流占优扩散的电子浓度和空穴浓度方程采用特征交替方向有限元方法，热传导方程利用Patch逼近采用交替方向有限元方法求解。利用微分方程的先验估计理论和技巧，分别得到了椭圆型方程和抛物型方程的最优H+1和L+2误差估计。     

定常Navier—Stokes方程的Petrov—Galerkin方法

研究了定常Navier－Stokes方程的四种Petrov－Galerkin有限元方法：PG1，PG2，SD和GLS．它们都是稳定的，避免了经典混合方法中必要的Babuska－Brezzi条件．给出了各种方法有限元解的存在性、唯一性和唯一解的误差估计．     

水污染问题特征有限元方法的数值计算及理论分析

本文研究了水污染二维对流占优数学模型特征有限元方法的计算问题，导出的计算格式对时间变量用特征线方法离散，对空间变量用Galerkin有限元方法离散，得到的H^1－模和L^2－模误差估计是最优阶的。     

伪双曲方程的新混合有限元方法

构造分析一类二阶伪双曲方程的H1-Galerkin扩展混合有限元方法,该方法采用了扩展混合有限元方法和H1-Galerkin混合有限元方法相结合的技巧.新的格式同时保持了扩展混合有限元方法和H1-Galerkin混合有限元方法的优点.该混合格式与标准的混合格式相比能同时逼近三个变量:未知函数、梯度和流量(系数乘以梯度),并且不必满足LBB相容性条件.     

板问题三次样条有限元的超收敛及高精度组合公式

1．引言与问题提出双三次样条有限元是应用比较广泛的矩形板元之一，与其它协调元相比恻双三次Her－mite矩形元），除达到饱和精度O（h‘）外，计算量却小得多［‘］，因而受到人们的重视．目前关于这方面的研究工作已有许多［1，并但关于板弯曲问题的双三次样条有限元的超收敛结果，却尚未见到．本文应用双三次样条插值的逐项渐近展式，通过对有限元的双线性形式进行展开，得到了双三次样条有限元一、二阶偏导数的渐近展式及超收敛结果．考虑如下矩形板弯曲模型问题上述方程对应的双线性形式为对VV，VE”，满足其中，M，。为正常数，11…     

关于一个右端带δ函数的半线性椭圆型方程的有限元方法

文证明了问题(1)的非负广义解的存在唯一性。本文将讨论(1)的有限元解法,证明了有限元解的收敛性,同时给出了(1)的非负广义解存在性的一个构造性证明。 证明的基本步骤是,将(1)的广义解化为三个问题的广义解。对含δ函数的线性问题(2),证明了它的有限元解的收敛性;问题(3)的有限元方法有熟知的结果;本文着重对半线性问题(4)的有限元方法进行讨论。主要采用不动点原理和离散极值原理在定理3中证明了(4)的有限元解的存在性,并证明了收敛性。为了提高(1)的有限元     

两种矩形单元的Babuka-Brezzi条件

§1.引言 用原始变量有限元方法求解不可压缩流体流动方程组,要求速度有限元子空间V_h和压力有限元子空间Q_h 满足Babuska-Brezzi条件:     

RECENT PROGRESS ON SPHERICAL HARMONIC APPROXIMATION MADE BY BNU RESEARCH GROUP ——In memory of Professor Sun Yongsheng

As early as in 1990, Professor Sun Yongsheng, suggested his students at Beijing Normal University to consider research problems on the unit sphere. Under his guidance and encouragement his students started the research on spherical harmonic analysis and approximation. In this paper, we incompletely introduce the main achievements in this area obtained by our group and relative researchers during recent 5 years （2001-2005）. The main topics are： convergence of Cesaro summability, a.e. and strong summability of Fourier-Laplace series; smoothness and K-functionals; Kolmogorov and linear widths.     

A unified approach to certain problems of best local approximation

In this paper we study best local quasi-rational approximation and best local approximation from finite dimensional subspaces of vectorial functions of several variables. Our approach extends and unifies several problems concerning best local multi-point approximation in different norms.     

Boundedness for commutators of multipliers on Hardy type spaces

In this paper, we study the commutators generalized by multipliers and a BMO function. Under some assumptions, we establish its boundedness properties from certain atomic Hardy space Hb^p（R^n） into the Lebesgue space L^p with p 〈 1.     

THE 8~(th) INTERNATIONAL CONGRESS ON INDUSTRIAL AND APPLIED MATHEMATICS

<正>August 10-14,2015Beijing,ChinaThe International Congress on Industrial and Applied Mathematics(ICIAM)is the premier international congress in the field of applied mathematics held every four years under the auspices of the International Council for Industrial and Applied Mathematics.From August 10 to 14,2015,mathematicians,scientists     

Towards Excellence in Science Chinese Academy of Sciences

<正>May 26,2014,Beijing Science is a human enterprise in the pursuit of knowledge.The scientific revolution that occurred in the 17th Century initiated the advances of modern science.The scientific knowledge system created by     

Bounds for the zeros of polynomials

Let P(z)=∑↓j=0↑n ajx^j be a polynomial of degree n. In this paper we prove a more general result which interalia improves upon the bounds of a class of polynomials. We also prove a result which includes some extensions and generalizations of Enestrǒm-Kakeya theorem.     

Boundedness of commutators related to Marcinkiewicz integrals on hardy type spaces

In this paper, the authors study the boundedness of the operator [μΩ, b], the commutator generated by a function b ∈ Lipβ(Rn)(0 ＜β≤ 1) and the Marcinkiewicz integrals μΩ, on the classical Hardy spaces and the Herz-type Hardy spaces in the case Ω∈ Lipα(Sn-1)(0 ＜α≤ 1).     

Jacobi polynomials used to invert the laplace transform

Given the Laplace transform F(s) of a function f(t), we develop a new algorithm to find an approximation to f(t) by the use of the classical Jacobi polynomials. The main contribution of our work is the development of a new and very effective method to determine the coefficients in the finite series expansion that approximation f(t) in terms of Jacobi polynomials. Some numerical examples are illustrated.     

Generalization of the interaction between Haar approximation and polynomial operators to higher order methods

In applications it is useful to compute the local average empirical statistics on u. A very simple relation exists when of a function f（u） of an input u from the local averages are given by a Haar approximation. The question is to know if it holds for higher order approximation methods. To do so, it is necessary to use approximate product operators defined over linear approximation spaces. These products are characterized by a Strang and Fix like condition. An explicit construction of these product operators is exhibited for piecewise polynomial functions, using Hermite interpolation. The averaging relation which holds for the Haar approximation is then recovered when the product is defined by a two point Hermite interpolation.