有限元网格自动生成及绘制中的实用处理技巧

提出了超大单元、结点归一化相对距离判别法这一快速三维自动剖分技术，针对大型水工建筑物的特点，给出了几种常遇问题的实用处理方法；还给出了适合工程实际的超大面判断立体消隐图绘制法和基于Ａｕｔｏｌｉｓｐ语言及Ａｕｔｏ－ＣＡＤ的立体图处理方法．     

有限元网格自动生成及自动调整技术

本文给出了一种任意平面域内三角形网格自动生成及自动调整算法，并编制了相应的程序。通过对带Ｕ形槽的三点变曲试件的分析，证明本文算法是可行的，并且具有稳定性能好、收敛速度快的优点。     

Numerical solution of Navier–Stokes equations using multiquadric radial basis function networks

A numerical method based on radial basis function networks (RBFNs) for solving steady incompressible viscous flow problems (including Boussinesq materials) is presented in this paper. The method uses a ‘universal approximator’ based on neural network methodology to represent the solutions. The method is easy to implement and does not require any kind of ‘finite element‐type’ discretization of the domain and its boundary. Instead, two sets of random points distributed throughout the domain and on the boundary are required. The first set defines the centres of the RBFNs and the second defines the collocation points. The two sets of points can be different; however, experience shows that if the two sets are the same better results are obtained. In this work the two sets are identical and hence commonly referred to as the set of centres. Planar Poiseuille, driven cavity and natural convection flows are simulated to verify the method. The numerical solutions obtained using only relatively low densities of centres are in good agreement with analytical and benchmark solutions available in the literature. With uniformly distributed centres, the method achieves Reynolds number Re = 100 000 for the Poiseuille flow (assuming that laminar flow can be maintained) using the density of , Re = 400 for the driven cavity flow with a density of and Rayleigh number Ra = 1 000 000 for the natural convection flow with a density of . Copyright © 2001 John Wiley & Sons, Ltd.     

一种新的弹塑性杂交应力元法

本文基于一个改进的弹塑性的Hellinger/Reis■ner 混合变分原理构造了一种用于解弹塑性问题的四节点等参杂交应力元.新的模型中,在单元内增加了等效应力增量、塑性等效应变增量及不协调位移变量,从而使单元内的屈服准则及流动法则平均得到满足,不协调位移改进了单元应力精度.计算表明,新的模型可以提高弹塑性杂交法的精度和计算效率.     

Reduced‐order modelling of an adaptive mesh ocean model

A novel proper orthogonal decomposition (POD) model has been developed for use with an advanced unstructured mesh finite‐element ocean model, the Imperial College Ocean Model (ICOM, described in detail below), which includes many recent developments in ocean modelling and numerical analysis. The advantages of the POD model developed here over existing POD approaches are the ability:

• 1. To increase accuracy when representing geostrophic balance (the balance between the Coriolis terms and the pressure gradient). This is achieved through the use of two sets of geostrophic basis functions where each one is calculated by basis functions for velocities u and v.
• 2. To speed up the POD simulation. To achieve this a new numerical technique is introduced, whereby a time‐dependent matrix in the discretized equation is rapidly constructed from a series of time‐independent matrices. This development imparts considerable efficiency gains over the often‐used alternative of calculating each finite element over the computational domain at each time level.
• 3. To use dynamically adaptive meshes in the above POD model.

Copyright © 2008 John Wiley & Sons, Ltd.     

基于双重自适应的六面体网格再生成方法

提出了一种以栅格法为基本方法,基于几何特征和物理场量双重自适应的六面体网格再生成方法。首先,依据旧网格的表面曲率和几何特征,采用基于栅格法的几何自适应网格再生成方法,生成密度受控的基础网格;然后,将旧网格的物理场量传递到基础网格中;最后,采用有限元误差估计方法对新网格单元的计算误差进行估计,对误差较大的单元进行加密,减...     

复合纤维增强混凝土阻尼测试装置开发与试验研究

纤维与聚合物的掺入可以明显改善混凝土材料的阻尼性能。本文首先给出了正弦交变激励下粘弹性材料三点弯曲梁阻尼特性关系,其次首次自主开发了大尺寸材料的阻尼性能测试装置,然后利用开发的装置在频率(0.5~2.0Hz)条件下测定了6种不同配比复合纤维增强阻尼混凝土的损耗因子与储存模量,最后对纤维的阻尼增强机理进行了初步探讨。试验结果表明:复合纤维增强阻尼混凝土与素混凝土相比,提高了混凝土的损耗因子80%~200%。主要原因是聚合物分子在外力作用下的内耗增加了普通混凝土的阻尼能力,而纤维的阻尼增强机理在于纤维的掺入增加了纤维与水泥基材的界面摩擦力。     

基于Hellinger-Reissner变分原理的应变梯度杂交元设计

从一般的偶应力理论出发，基于Hellinger-Reissner变分原理，通过对有限元 离散体系的位移试解引入非协调位移函数，得到了偶应力理论下有限元离散系统的能量相容 条件，并由此建立了应变梯度杂交元的应力函数优化条件. 根据该优化条件，构造了一 个C0类的平面4节点梯度杂交元，数值结果表明，该单元对可压缩和不可压缩状态的 梯度材料均可给出合理的数值结果，再现材料的尺度效应.     

杂交元本征应力模式和应力子空间的性质研究

详细讨论了有限元本征应力模式和应力子空间的性质，并着重讨论和进一步完善了与杂交应力有限元应力子空间有关的一些定理，为提出新方法提供了理论基础，主要包括：（1）证明了杂交元特征值不大于对应位移元的特征值；（2）证明了矩阵H非奇异的充分必要条件是假设应力模式线性无关；（3）证明了杂交元所对应位移元的本征应力模式形成的杂交元与该位移元相同；（4）证明了等价假设应力模式形成相同的杂交元；（5）证明了确定杂交元本征应力模式的充分必要条件是其范数平方等于所形成杂交元的变形模态特征值；（6）证明了杂交元假设应力模式与变形模态的能量一一对应的充分必要条件是假设应力模式彼此正交且与所对应位移元的本征应力模式除了一一对应者之外都正交。     

无单元法在有自由面渗流计算中的应用

针对有自由面渗流分析中的有限元固定网各法存在的不足，利用无单元法中积分网格和结点相互独立的优点，提出了有自由面渗流的无单元法。计算结果表明，无单元法可以方便地解决迭代计算中的自由面变化问题，实现了真正意义上的网格固定。