关于薄板的无网格局部边界积分方程方法中的友解

无网格局部边界积分方程方法是最近发展起来的一种新的数值方法，这种方法综合了伽辽金有限元、边界元和无单元伽辽金法的优点，是一种具有广阔应用前景的、真正的无网格方法．把无网格局部边界积分方程方法应用于求解薄板问题，给出了薄板无网格局部边界积分方程方法所需要的友解及其全部公式．     

圆外区域求解Helmholtz方程

1引言许多科学和工程计算问题都可以归结为无界区域上的偏微分方程边值问题．而求解椭圆方程边值问题的常用技术是有限元方法,可是对于无界区域,在用有限元方法求解时,往往遇到困难．最简单的办法显然是直接略去区域的无界部分求解,但这样做或者导致过低的计算精度,或者要付出很高的计算代价．边界归化,即将求解偏微分方程边值问题转化为边界积分方程,是求解某些无界区域问题的强有力的手段．自70年代以来,有限元和     

插值型无单元Galerkin比例边界法与有限元法的耦合在压电材料断裂分析中的应用

插值型无单元Galerkin比例边界法是一种只需在边界上采用插值型无单元Galerkin法离散且无需基本解的半解析方法,能有效求解压电材料的断裂问题.为进一歩提高这种方法的适用性,该文提出了一种用于压电材料断裂分析的插值型无单元Galerkin比例边界法耦合有限元法(finite element method,FEM)的分析方法.裂纹周边一定范围的计算域采用插值型无单元Galerkin比例边界法离散,其余区域采用FEM离散.插值型无单元Galerkin比例边界法方程和FEM方程的耦合可利用界面两侧广义位移的连续条件方便地实现.最后,给出了两个数值算例验证了该文所提方法的有效性.     

基于简化的应变梯度理论下Kirchhoff板模型边值问题的提法及其应用北大核心CSCD

考虑应变梯度和速度梯度的影响,建立薄板控制微分方程及给出其边值问题的提法,修正了前人给出的薄板角点条件.采用Levy法,给出受分布力作用下简支板的挠度及自由振动频率的解析解.通过与文献中分子动力学数据对比,验证了该文模型的有效性并提出校核材料参数的一种方法.研究结果表明,增大弹性地基和应变梯度参数可以有效提高板的等效刚度,而速度梯度参数则相反.该文提出的板的边值问题为研究薄板在复杂支撑边界及外荷载等条件提供了理论依据.同时,有望为其有限元法、有限差分法和基于能量原理的Galerkin法等数值方法提供理论依据.     

无单元Galerkin法在热传导中的应用

对热传导问题的微分方程采用无单元Galerkin法进行数值求解.首先,将微分方程用Galerkin加权残量法转化为等效的积分形式.然后,先将时间变量看作参数,对空间变量进行离散化,得到方程的半离散形式,接着,对时间采用向后Euler—Galerkin格式进行离散,得到方程的全离散形式最后,编制MATLAB程序,上机计算.列举了两个热传导算例,通过计算说明EFG法适用于热传导问题,且其计算速度快,精确度高、前后处理也十分方便,是一种具有潜力的温度场数值计算的新方法.     

同伦摄动法在求解四阶边值问题中的应用

将同伦摄动法用于求解常微分方程四阶边值问题.通过将常微分方程边值问题转化为积分方程组,应用同伦摄动法求得近似解.给出同伦摄动法在两个具体的实例中的应用,并将近似解与精确解进行了比较,验证了同伦摄动法对求解线性、非线性常微分方程边值问题是一种非常有效的方法.     

基于滑动Kriging插值的MLPG法求解结构非耦合热应力问题

将基于滑动Kriging插值的无网格局部Petrov-Galerkin(MLPG)法用来求解二维结构非耦合热应力问题,首先进行瞬态热传导的求解,然后再通过顺序耦合法将不同时刻节点温度作为附加体力项施加到应力分析中.瞬态温度场和非耦合热应力分析通过加权余量法来离散,同时用Heaviside分段函数作为局部弱形式的权函数.由于滑动Kriging插值构造的形函数满足Kroneckerδ函数的性质,因此方便了本质边界条件的施加.刚度矩阵形成过程中只涉及到边界积分而没有涉及到区域积分,因此可以减少计算工作量,最后通过两个数值算例来验证本文方法的有效性.     

粘弹性板动力稳定性分析中的两模态Galerkin逼近

利用最大Lipunov指数分析法以及其它数值和解析的动力学方法，研究了大挠度粘弹性薄板的动力稳定性．材料的行为由Boltzmann叠加原理描述．采用Galerkin方法将原积分。偏微分模型简化为两模态的近似积分模型，而通过引进新变量，该近似积分模型可进一步化为一个常微分模型．数值比较了1—模态和2—模态截断系统的动力学性质，讨论了面内周期激励下材料的粘弹性性质、加载的幅度和初值对板动力学行为的影响．     

无限单元法

很多线性椭圆型偏微分方程的边值问题可以归结为如下的抽象变分问题:设U为实的Hilbert空间,a(u, v)为U上的有界双线性泛函,f(v)为U上的线性泛函,求使这一问题可以用所谓Galerkin方法求其近似解,即取U的有限维子空间U_h,求,使如果采用分割区域为“单元”,取插值函数的方法获得U_h,则(2)就是有限单元法。 U_h一般总是取为有限维,因为在一般情况下没有必要也不容易求解一个无限阶的代数方程组。但在某些情况下,取U_h为无限维子空间是值得的,例如计算边界有角点的边值问题或混合边值问题而且希望定量地计算解在局部的奇性,或者计算无界区域上的边     

一阶常微分方程的积分因子法求解

解一阶常微分方程的积分因子法，是求解微分方程的一个极其重要的方法。凡形状如Ｐ（ｘ，ｙ）ｄｘ＋Ｑ（ｘ，ｙ）ｄｙ＝０的一阶微分方程，原则上都可用积分因子法求解．但现行工科高等数学中，对于积分因子法求解微分方程很少讨论，这是因为在通常情况下积分，因子的寻求比较困难．本文建立确定积分因子μ的一组准则，循此途径求μ，方法简捷且应用范围广．     

A meshless local moving Kriging method for two-dimensional solids

An improved meshless local Petrov-Galerkin method (MLPG) for stress analysis of two-dimensional solids is presented in this paper. The MLPG method based on the moving least-squares approximation is one of the recent meshless approaches. However, accurate imposition of essential boundary conditions in the MLPG method often presents difficulties because the MLPG shape functions does not possess the Kronecker delta property. In order to eliminate this shortcoming, this approach uses the moving Kriging interpolation instead of the traditional moving least-square approximation to construct the MLPG shape functions, and then, the Heaviside step function is used as the test function over a local sub-domain. In this method, the essential boundary conditions can be enforced as the FEM, no domain integration is needed and only regular boundary integration is involved. In addition, the sensitivity of several important parameters of the present method is mainly studied and discussed. Comparing with the original meshless local Petrov-Galerkin method, the present method has simpler numerical procedures and lower computation cost. The effectiveness of the present method for two-dimensional solids problem is investigated by numerical examples in this paper.     

三维弹性问题无网格分析的奇异杂交边界点方法

提出了一种求解三维线弹性问题的奇异杂交边界点方法。将修正变分原理与移动最小二乘法结合起来，利用了前者的降维优势和后者的无网格特性．使用刚体位移法处理方法中的强奇异积分，提出了一种自适应的积分方案，解决了原有的杂交边界点方法中存在的“边界层效应”。在该方法中，将基本解的源点直接布在边界上，避免了在正则化杂交边界点法中不确定参数的选取，三维弹性力学问题算例体现了这些特点．结果表明该方法与已知的精确解符合较好，同时研究了影响该方法精度的一些参数。     

Analytical formulation of meshless local integral equation method

In this paper, the exact forms of integrals in the meshless local boundary integral equation method are derived and implemented for elastostatic problems. A weak form for a set of governing equations with a unit test function or polynomial test functions is transformed into local integral equations. Each node has its own support domain and is surrounded by a local integral domain with different shapes of boundaries. The meshless approximation based on the radial basis function (RBF) is employed for the implementation of displacements. A completed set of closed forms of the local boundary integrals are obtained. As there are no numerical integrations to be carried out the computational time is significantly reduced. Three examples are presented to demonstrate the application of this approach in solid mechanics.     

奇异杂交边界点方法求解泊松方程

As a boundary-type meshless method,the singular hybrid boundary node method(SHBNM)is based on the modified variational principle and the moving least square(MLS)approximation,so it has the advantages of both boundary element method(BEM)and meshless method.In this paper,the dual reciprocity method(DRM)is combined with SHBNM to solve Poisson equation in which the solution is divided into particular solution and general solution.The general solution is achieved by means of SHBNM,and the particular solution is approximated by using the radial basis function(RBF).Only randomly distributed nodes on the bounding surface of the domain are required and it doesn't need extra equations to compute internal parameters in the domain.The postprocess is very simple.Numerical examples for the solution of Poisson equation show that high convergence rates and high accuracy with a small node number are achievable.     

Treatment of singularities in the method of fundamental solutions for two-dimensional Helmholtz-type equations

We investigate a meshless method for the accurate and non-oscillatory solution of problems associated with two-dimensional Helmholtz-type equations in the presence of boundary singularities. The governing equation and boundary conditions are approximated by the method of fundamental solutions (MFS). It is well known that the existence of boundary singularities affects adversely the accuracy and convergence of standard numerical methods. The solutions to such problems and/or their corresponding derivatives may have unbounded values in the vicinity of the singularity. This difficulty is overcome by subtracting from the original MFS solution the corresponding singular functions, without an appreciable increase in the computational effort and at the same time keeping the same MFS approximation. Four examples for both the Helmholtz and the modified Helmholtz equations are carefully investigated and the numerical results presented show an excellent performance of the approach developed.     

Error estimates for the interpolating moving least-squares method in n-dimensional space

In this paper, the interpolating moving least-squares (IMLS) method is discussed in details. A simpler expression of the approximation function of the IMLS method is obtained. Compared with the moving least-squares (MLS) approximation, the shape function of the IMLS method satisfies the property of Kronecker δ function. Then the meshless method based on the IMLS method can overcome the difficulties of applying the essential boundary conditions. The error estimates of the approximation function and its first and second order derivatives of the IMLS method are presented in n-dimensional space. The theoretical results show that if the weight function is sufficiently smooth and the order of the polynomial basis functions is big enough, the approximation function and its partial derivatives are convergent to the exact values in terms of the maximum radius of the domains of influence of nodes. Then the interpolating element-free Galerkin (IEFG) method based on the IMLS method is presented for potential problems. The advantage of the IEFG method is that the essential boundary conditions can be applied directly and easily. For the purpose of demonstration, some selected numerical examples are given to prove the theories in this paper.     

A moving Kriging‐based MLPG method for nonlinear Klein–Gordon equation

In this paper, the meshless local Petrov–Galerkin approximation is proposed to solve the 2‐D nonlinear Klein–Gordon equation. We used the moving Kriging interpolation instead of the MLS approximation to construct the meshless local Petrov–Galerkin shape functions. These shape functions possess the Kronecker delta function property. The Heaviside step function is used as a test function over the local sub‐domains. Here, no mesh is needed neither for integration of the local weak form nor for construction of the shape functions. So the present method is a truly meshless method. We employ a time‐stepping method to deal with the time derivative and a predictor–corrector scheme to eliminate the nonlinearity. Several examples are performed and compared with analytical solutions and with the results reported in the extant literature to illustrate the accuracy and efficiency of the presented method. Copyright © 2016 John Wiley & Sons, Ltd.     

含裂纹平面问题Erdogan基本解的显式表达

基本解是边界元法、基本解法和无网格法等数值方法的重要理论基础.在断裂问题中,采用含裂纹的基本解可以避免将裂纹表面作为边界条件,从而大大简化问题的求解.在复变函数表示的含裂纹平面问题Erdogan基本解的基础上,对Erdogan基本解的使用条件进行了注解,修正了Erdogan基本解的一些错误,并推导出Erdogan基本解中位移函数解答的显式表达形式.编写了基于Erdogan基本解显式表达的样条虚边界元法（spline fictitious boundary element method, SFBEM）计算程序,计算了具有复合边界条件平面问题的位移、应力和应力强度因子.数值算例结果表明了该文提出的Erdogan基本解显式表达形式的正确性.     

A Variational Analysis for the Moving Finite Element Method for Gradient Flows

By using the Onsager principle as an approximation tool, we give a novel derivation for the moving finite element method for gradient flow equations. We show that the discretized problem has the same energy dissipation structure as the continuous one. This enables us to do numerical analysis for the stationary solution of a nonlinear reaction diffusion equation using the approximation theory of free-knot piecewise polynomials. We show that under certain conditions the solution obtained by the moving finite element method converges to a local minimizer of the total energy when time goes to infinity. The global minimizer, once it is detected by the discrete scheme, approximates the continuous stationary solution in optimal order. Numerical examples for a linear diffusion equation and a nonlinear Allen-Cahn equation are given to verify the analytical results.