A method for direct imposition of essential boundary condition and treatment of material discontinuity in element free galerkin (EFG) method is presented. By using the actual displacements at the nodes on the essential boundary and the material interface in each material domain, the stiffness matrix and load vector at an integral point have been rewritten and transformed. As a result, the proposed method yields a positive, symmetrical and banded global stiffness matrix like it is in finite element methods and has the advantages of stabilization and easy implementation as compared to the penalty method, the Lagrange method, and other methods. Numerical results indicate that the present method is effective and retains high rates of convergence for both displacements and energy.

A meshless local natural neighbour interpolation method (MLNNI) is presented for the stress analysis of two-dimensional solids. The discrete model of the domain Ω consists of a set of distinct nodes, and a polygonal description of the boundary. The whole interpolation is constructed with respect to the natural neighbour nodes and Voronoi tessellation of the given point. A local weak form over the local Delaunay triangular sub-domain is used to obtain the discretized system of equilibrium equations. Compared with the natural element method using a standard Galerkin procedure which needs three point quadrature rule, the numerical integral can be calculated at the center of the background triangular quadrature meshes in the MLNNI method. Since the shape functions possess the Kronecker delta function property, the essential boundary conditions can be directly implemented with ease as in the conventional finite element method (FEM). The proposed method is a truly meshless method for software users, since the properties of the natural neighbour interpolation are meshless and all the numerical procedures are automatically accomplished by the computer. Application of the method to various problems in solid mechanics, which include the patch test, cantilever beam and gradient problem, are presented, and excellent agreement with exact solutions is acheived. Numerical results show that the accuracy of the proposed method is as good as that of the quadrangular FEM, and the time cost is less than that with the quadrangular FEM.

讨论了数值流形方法使用高阶覆盖位移函数时权函数、位移函数的选择和位移边界条件的处理。对该方法得到的高精度位移解，利用滑动最小二乘法在全域上构造位移近似函数，得到了与位移解一样连续的应力解。算例结果表明，理论和方法是正确、有效的。

本文在流形方法里采用矩形作为数学覆盖，从另一角度提出了一种不同于有限元法的数值分析方法。该方法结构简单，不需要准备单元和结点数据，数据输入量少，能够很方便地实现与 CAD 技术的一体化。文中详细地讨论了使用矩形网格的流形方法的理论和实施技术，并给出了其矩形覆盖系统的全自动生成算法。算例结果表明，理论和方法是正确、有效的。

利用面向对象设计思想将岩土力学中数值流形方法的物理覆盖系统抽象为独立的数据类，在此基础上完成了物理覆盖系统的自动剖分算法。对裂缝切割的连续材料，在裂缝的扩展过程中能自动生成正确的流形单元。算例表明，本算法是可靠和有效的。