高次三角形有限元外推的探讨

探讨泊松方程高次三角形有限元外推公式.为此先推导离散格林函数的权模估计和有限元解的渐近不等式展开,然后给出公式的证明.     

多角形域上的有限元方法及外推

§1.引言 考虑边值问题: L_u=-D_i(a_(ij)D_(ju)+a_0u=f,u|?Ω=0.(1.1)假定L是一致椭圆算子且系数a_(ij),a_0及右端f适当光滑,a_0≥0.Ω为一平面多角形区域,Q={Q_1,Q_2,…,Q_l}为Ω的角点集合.对于任意给定的常数组{α_i}_1~l,0<α_i≤1,     

高斯白噪声中频谱有限函数的外推估计

设f(t)是一σ-频谱有限函数和g(t)=f(t) n(t)在(-T,T)区间内的值被观测到,其中n(t)是高斯白噪声。本文给出基于g(t)的f(t)的极大似然估计。还讨论了当f(t)为随机σ-频谱有限函数时,它与g(t)的均方距离达到最小的估计。     

数值积分对特征值有限元外推的影响

§1.引言在分片一致三角形剖分下,用线性有限元法解特征值问题求得近似特征值λ、λ~(h/2).[1]证明了对λ~h.λ~(h/2)作外推可提高收敛阶:     

关于有噪频谱有限函数的外推

有噪情况下频谱有限函数的外推是函数逼近理论及信号分析中一个重要的病态问题。本文在Ｔｉｋｈｏｎｏｖ正则化理论研究的基础上，研究这一个推问题，给出了不同于［１］中的方法，它在计算上改进了［１］中的方法，在范围上不仅适用于一维而且适用于高维的情况。     

关于本征值问题有限元外推的一个注记

§1.引言考虑二阶椭圆微分算子本征值问题: 求,使其中G是R~N(N=1,2)中边界分段光滑的有界域,a(·,·)是定义在H_0~1(G)上的对称、连续,H_0~1(G)椭圆双线性形式,(·,·)是L_2(G)中内积,||·||_0是L_2(G)中范数。假设满足正则性条件:对fL_2(G),“a(w,v)=(f,v),vH_0~1(G)”的解     

Stokes特征值问题Q_1元的展开式及其外推

考虑利用Q1元来求解Stokes特征值问题的误差渐进展开式,并以此为基础进行外推获得高精度.     

三维有限元本征值的外推

通过二维和三维积分恒等式,探讨泊松方程本征值问题三角线元和四面体线元Richardson外推的可行性.理论分析表明,如果剖分为均匀一致和拟一致,外推均可将解的精度提高二阶.     

二次有限元解的渐近展开与外推

在Poisson方程的求解域Ω存在一致的三角剖分,并且相邻两初始单元构成平行四边形的假设下,证明了若Poisson方程的解u属于H6(Ω),那么二次有限元的误差有h4的渐近展开.基于误差的渐近展开,可以利用h4-Richardson外推进一步提高数值解的精度阶,并且能够得到一个后验误差估计.最后,一个数值算例验证了理论分析.     

特征值问题的三角形二次元的展开式及其外推

我们考虑利用三角形二次元来求解特征值问题,并给出特征值的误差展开式,以此为基础进行外推获得高精度.     

Extrapolation of Mixed Finite Element Approximations for the Maxwell Eigenvalue Problem

In this paper,a general method to derive asymptotic error expansion formulas for the mixed finite element approximations of the Maxwell eigenvalue problem is established.Abstract lemmas for the error of the eigenvalue approximations are obtained.Based on the asymptotic error expansion formulas,the Richardson extrapolation method is employed to improve the accuracy of the approximations for the eigenvalues of the Maxwell system from θ(h2) to θ(h4) when applying the lowest order Nédé1ec mixed finite element and a nonconforming mixed finite element.To our best knowledge,this is the first superconvergence result of the Maxwell eigenvalue problem by the extrapolation of the mixed finite element approximation.Numerical experiments are provided to demonstrate the theoretical results.     

非对称不定问题双线性元的超收敛和外推

本文主要讨论非对称不定问题的双线性有限元逼近.在不需要引入Ritz投影的前提下直接利用单元上的插值并借助于该元已有的高精度分析和平均值技巧,得到在H1模意义下O(h2 )阶的超逼近和整体超收敛结果.同时给出两个新的误差渐近展开式,导出比传统有限元误差高两阶的O(h3)阶的外推解.     

发展型方程的时间间断时空有限元方法

时空有限元方法通过统一时间和空间变量,克服了传统有限元方法对时间作差分离散引起的时间上的低精度,不但具有时、空高精度,而且在无结构网格上耗散特性好、无条件稳定,成为解决时间依赖问题的有效方法.本文利用抛物问题给出时间允许间断而空间连续的时空有限元方法的基本概念和过程,给出抛物型方程、积分-微分方程、双曲方程、Sobolev方程和其他高阶方程的算例,验证方法的精度和稳定性,并综合评价时间间断时空有限元方法目前的发展现状和应用前景.     

Stokes问题Q_2-P_1混合元外推方法

考虑Stokes问题的有限元解与精确解插值的Q2-P1混合元的渐近误差展开和分裂外推.首先利用积分恒等式技巧确定了微分方程精确解与有限元插值之间积分式的主项,其次再借助插值后处理和分裂外推技术,得到了比通常的误差估计提高两阶的收敛速度.     

Approximation of an Eigenvalue Problem Associated with the Stokes Problem by the Stream Function-Vorticity-Pressure Method

By means of eigenvalue error expansion and integral expansion techniques, we propose and analyze the stream function-vorticity-pressure method for the eigenvalue problem associated with the Stokes equations on the unit square. We obtain an optimal order of convergence for eigenvalues and eigenfuctions. Furthermore, for the bilinear finite element space, we derive asymptotic expansions of the eigenvalue error, an efficient extrapolation and an a posteriori error estimate for the eigenvalue. Finally, numerical experiments are reported. The first author was supported by China Postdoctoral Sciences Foundation.     

and Norms Error Estimates in Finite Element Method for Linear Parabolic Interface Problems

We derive new a priori error estimates for linear parabolic equations with discontinuous coefficients. Due to low global regularity of the solutions the error analysis of the standard finite element method for parabolic problems is difficult to adopt for parabolic interface problems. A finite element procedure is, therefore, proposed and analyzed in this paper. We are able to show that the standard energy technique of finite element method for non-interface parabolic problems can be extended to parabolic interface problems if we allow interface triangles to be curved triangles. Optimal pointwise-in-time error estimates in the L ²(Ω) and H ¹(Ω) norms are shown to hold for the semidiscrete scheme. A fully discrete scheme based on backward Euler method is analyzed and pointwise-in-time error estimates are derived. The interfaces are assumed to be arbitrary shape but smooth for our purpose.     

Extrapolation of the Hood–Taylor elements for the Stokes problem

An asymptotic error expansion concerning of Hood–Taylor elements for the Stokes problem is established on uniform rectangular meshes. The extrapolation based on such an expansion increases the rate of convergence by one order.