A BOUNDARY ELEMENT METHOD FOR SIGNORINI PROBLEM IN LINEAR ELASTICITY

A Signorini problem in linear elasticity is reduced to a variational inequality on the boundary, and a boundary element approach is described for the numerical approximation of its solution; an error estimate is also given.     

THE NONCONFORMING FINITE ELEMENT METHOD FOR SIGNORINI PROBLEM

We present the Crouzeix-Raviart linear nonconforming finite element approximation of the variational inequality resulting from Signorini problem. We show if the displacement field is of H2 regularity, then the convergence rate can be improved from O（h3/4） to quasi-optimal O（h｜log h｜1/4） with respect to the energy norm as that of the continuous linear finite element approximation. If stronger but reasonable regularity is available, the convergence rate can be improved to the optimal O（h） as expected by the linear approximation.     

ACCURACY ENHANCEMENT FOR THE SIGNORINI PROBLEM WITH FINITE ELEMENT METHOD

In this paper,we study the accuracy enhancement for the frictionless Signorini problem on a polygonal domain with linear finite elements.Numerical test is given to verify our result.     

A MIXED FINITE ELEMENT METHOD FOR THE CONTACT PROBLEM IN ELASTICITY

Based on the analysis of [7] and [10], we present the mixed finite element approximation of the variational inequality resulting from the contact problem in elasticity. The convergence rate of the stress and displacement field are both improved from O（h3/4） to quasi-optimal O（h│logh│^1/4）. If stronger but reasonable regularity is available, the convergence rate can be optimal O（h）.     

ARTIFICIAL BOUNDARY METHOD FOR THE THREE-DIMENSIONAL EXTERIOR PROBLEM OF ELASTICITY

The exact boundary condition on a spherical artificial boundary is derived for thethree-dimensional exterior problem of linear elasticity in this paper. After this bound-ary condition is imposed on the artificial boundary, a reduced problem only defined in abounded domain is obtained. A series of approximate problems with increasing accuracycan be derived if one truncates the series term in the variational formulation, which isequivalent to the reduced problem. An error estimate is presented to show how the errordepends on the finite element discretization and the accuracy of the approximate problem.In the end, a numerical example is given to demonstrate the performance of the proposedmethod.     

ON THE COUPLING OF BOUNDARY INTEGRAL AND FINITE ELEMENT METHODS FOR SIGNORINI PROBLEMS

1.IntroductionPartialdifferentialequationssubjecttounilateralboundaryconditionsareusuallycalledSignoriniproblemsintheliterature.TheseproblemshavebeenstudiedbymanyauthodssincetheappearenceofthehistoricalpaperbyA.Signoriniin1933[25].Signoriniproblemsaroseinmanyareasofapplicationse.g.,theelasticitywithunilateralconditions[lo],thefluidmechnicsproblemsinmediawithsemipermeableboundaries[8,12],theelectropaintprocess[1]etc.Fortheexistence,uniquenessandregularityresultsforSignorinitypeproblemswerefer…     

关于纯位移边界条件的平面弹性问题Locking-Free有限元格式

In this paper,we discusse the locking phenomenon of the finite element method for the pure displacement boundary value problem in the planar elasticity as Lame constantλ→∞,The locking-free scheme of Crouziex-Raviart element was proposed and analyzed by Brenner et al.[2]and [3].We firstly present the derivation of Brenner‘s scheme,then propose and analyse a locking-free scheme,then propose and analyse a locking-free scheme of noncon-forming rectangle finite element.     

椭圆外区域上Helmholtz问题的自然边界元法

本文研究椭圆外区域上Helmholtz方程边值问题的自然边界元法.利用自然边界归化原理,获得该问题的Poisson积分公式及自然积分方程,给出了自然积分方程的数值方法.由于计算的需要,我们详细地讨论了Mathieu函数的计算方法(当0相似文献   

椭圆外区域上的自然边界元法

１．引言 二十年来,自然边界元法已在椭圆问题求解方面取得了许多研究成果。它可以直接用来解决圆内（外）区域、扇形区域、球内（外）区域及半平面区域等特殊区域上的椭圆边值问题［１,２,５］,也可以结合有限元法求解一般区域上的椭圆边值问题,例如基于自然边界归化的耦合算法及区域分解算法就是处理断裂区域问题及外问题的一种有效手段［２－４,６］。 人们在设计求解外问题的耦合算法或者区域分解算法时,通常选取圆周或球面作人工边界。但对具有长条型内边界的外问题,以圆周或球面作人工边界显然并非最佳选择,它将会导致大量的…     

THE ELLIPSOID ARTIFICIAL BOUNDARY METHOD FOR THREE-DIMENSIONAL UNBOUNDED DOMAINS

The artificial boundary method is applied to solve three-dimensional exterior problems. Two kind of rotating ellipsoids are chosen as the artificial boundaries and the exact artificial boundary conditions are derived explicitly in terms of an infinite series. Then the well-posedness of the coupled variational problem is obtained. It is found that error estimates derived depend on the mesh size, truncation term and the location of the artificial boundary. Three numerical examples are presented to demonstrate the effectiveness and accuracy of the proposed method.     

问题变分不等式的一类各向异性Crouzeix-Raviart型有限元逼近

本文研究了Signorini变分不等式问题的一类各向异性Crouzeix-Raviart型非协调有限元逼近。通过一些新的技巧,得到了相应的最优误差估计。     

解一类半线性外边值问题的自然边界元与有限元耦合法

In this paper, we combine a finite element approach with the natural boundary element method to stduy the weak solvability and Galerkin approximations of a class of semilinear exterior boundary value problems. Our analysis is mainly based on the variational formulation with constraints. We discuss the error estimate of the finite element solution and obtain the asymptotic rate of convergence O（h^n) Finally, we also give two numerical examples.     

BOUNDARY ELEMENT APPROXIMATION OF STEKLOV EIGENVALUE PROBLEM FOR HELMHOLTZ EQUATION

1.IntroductionWeconsiderthefollowingStekloveigenvalueproblem:FindnonzerouandnumberA,suchthat--An u=0,infi,on,on=An,onr,(1.1)wherefiCRZisaboundeddomainwithsufficientsmoothboundaryr,4istheonoutwardllormalderivativeonr.CourantandHilb..tll]studiedthefollowingeigenvalueproblem:onac=0,infi,--~An,onr,(1.2)OnwhichwasreducedtotheeigenvalueproblemofanintegralequationbyusingtheGreen'sfunctionofAn=0withNuemannboundarycondition.FromFredholmtheorem,weknowthat(1)theproblem(1.2)hasinfinitenumberofeigenv…     

NATURAL BOUNDARY ELEMENT METHOD FOR THREE DIMENSIONAL EXTERIOR HARMONIC PROBLEM WITH AN INNER PROLATE SPHEROID BOUNDARY

In this paper, we study natural boundary reduction for Laplace equation with Dirichletor Neumann boundary condition in a three-dimensional unbounded domain, which is theoutside domain of a prolate spheroid. We express the Poisson integral formula and naturalintegral operator in a series form explicitly. Thus the original problem is reduced to aboundary integral equation on a prolate spheroid. The variational formula for the reducedproblem and its well-posedness are discussed. Boundary element approximation for thevariational problem and its error estimates, which have relation to the mesh size andthe terms after the series is truncated, are also presented. Two numerical examples arepresented to demonstrate the effectiveness and error estimates of this method.     

平面线弹性纯位移边值问题低阶非协调矩形元的Robust多重网格方法

1引 言 对于各向同性,均匀介质的平面线弹性问题,当Lamé常数λ→∞(泊松率v→0.5)时,即对于几乎不可压介质,通常的协调有限元格式的解往往不再收敛到原问题的解,或者达不到最优收敛阶,这就是所谓的闭锁现象(见[3],[7],[8]及[10]).究其原因,在通常的有限元分析中,其误差估计的系数与λ有关,当λ→∞时,该系数将趋于无穷大.因此为克服闭锁现象就需要构造特殊的有限元格式,使得当λ→∞时,有限元逼近解仍然收敛到原问题的解.     

ON LOCKING-FREE FINITE ELEMENT SCHEMES FOR THREE-DIMENSIONAL ELASTICITY

In the present paper,the authors discuss the locking phenomenon of the finite elementmethod for three-dimensional elasticity as the Laméconstant λ→∞.Three kinds of finiteelements are proposed and analyzed to approximate the three-dimensional elasticity withpure displacement boundary condition.Optimal order error estimates which are uniformwith respect to λ∈(0,+∞)are obtained for three schemes.Furthermore,numerical resultsare presented to show that,our schemes are locking-free and and the trilinear conformingfinite element scheme is locking.     

抛物型初边值问题的有限元与边界积分耦合的离散化及其误差分析

1．引言边界元方法是近二十几年来迅速发展起来的一类新的偏微分方程的数值方法．它的独特之处是将空间的维数降低一维,从而倍受工程技术人员的青睐,并在工程技术与计算数学领域得到越来越广泛的重视和研究．对椭圆型问题,边界元方法的理论与应用研究已取得丰硕成果;对发展型问题,近年来在理论方面的研究也已取得重要进展［6－11］．但边界元方法难以处理非均质问题,而有限元对各类问题及各种区域具有较好的适应性,将两者结合起来可充分发挥各自的优点．文山提出了一种抛物方程初边值问题的有限元与边界积分的耦合方法,其主要思想是…     

椭圆边值问题的概率算法

本文重新建立了椭圆边值问题的概率模型,在Ｍｏｎｔｅ－Ｃａｒｌｏ算法的基础上,引入了一种新的高精度概率算法,取得很大进展．     

半导体物理中的一个两点边值问题

本文研究了在半导体流的区域提纯过程中提出的两点边值问题解的存在性，我们用上、下解方法和Ｓｓｈａｕｄｅｒ不动点定理证明了如果Ｑ＝２Ａ３Ｒｅ，其中Ａ是表面速率，Ｒｅ是Ｒｅｙｎｏｌｄｓ数，则当０ Ｑ １２．６８时，该问题有解． 对［１］的结果（０ Ｑ＜８．５１时，此问题的解存在）进行了重要的改进．     

广义Lienard方程边值问题

By coincidence degree,the existence of solution to the boundary value problem of a generalized Liénard equation a(t)x＂+F(x,x′)x′+g(x)=e(t),x(0)=x(2π),x′(0)=x′(2π)is proved,where a∈C1[0,2π],a(t)>0(0≤t≤2π),a(0)=a(2π),F(x,y)=f(x)+α| y|β,α>0,β>0 are all constants,f∈C(R,R),e∈C[0,2π]. An example is given as an application.