自然单元法采用无网格的思想全域构造插值函数，它的求解精度高，计算时间少，可准确施加边界条件，兼具有无网格法和有限单元法的优点和特点，是一种理想的用于岩土及地下工程分析计算的数值方法。文中简要介绍了自然单元法的基本理论，并针对岩土及地下工程问题特点，给出了一种无网格离散点的全自动布置方法。

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.

基于数值流形方法的四节点四边形流形单元在物理覆盖上使用高阶覆盖位移函数能够得到高精度的数值结果，且可以在求解区域的不同地方混合使用各阶覆盖函数来提高求解效率，具有编程和前后处理简单等优点，弥补了有限元法的不足。计算结果表明，数值解与理论解吻合。

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。

使用1 阶或1 阶以上最小滑动二乘法（MLS）形函数的无网格伽辽金法（EFGM）和无单元流形方法（EFMM），它们的主要缺点是形函数构造复杂、计算费用十分昂贵。本文提出了一种改进的EFMM法，它通过采用Shepard形函数（0 阶MLS 形函数）对结点的覆盖位移函数加权求和来简化整体近似位移函数的构造，且能够避免EFGM和EFMM里求解结点形函数时矩阵的求逆及相乘运算。文中的数值算例表明，这种改进的EFMM 法收敛快、精度高，与标准的EFGM相比其计算时间得到了大幅度的减少。