基于实体造型的三维有限元网格自动剖分

本文叙述了用八叉树法对三维实体进行有限元网络自动剖分算法的设计和实现。本文的算法对传统的八叉树法进行了一系列的改进，包括新型数据结构的建立，对八叉树结点属性判断算法的改进，边界结点体处理方法的改进等。使得本文的算法既保持了传统算法中自动化程度高、层次结构分明、适于再进行网格加密等特点，又克服了其所需存贮空间大、执行速度慢、边界处理复杂，边界单元形状质量不好等缺点，使算法的实现取得了令人满意的结果。     

任意多面体边界一致四面体网格生成方法

提出一种能够满足多面体边界几何与拓扑约束的边界一致恢复算法,解决了任意多面体的边界一致四面体网格生成问题。在恢复多面体的几何约束时,边界上可能会引入Steiner点,这样就不满足拓扑约束。对此,本文采用动态规划方法将Steiner点从边界上消除,修复与其相关四面体单元的拓扑关系,以保持原多面体边界的拓扑完整性,并采用扩展的Laplacian光顺算法优化劣质单元。在理论上,本文算法能够保证完整地恢复任意多面体的边界。算例表明,本文提出的边界一致恢复算法鲁棒性高,可应用于复杂多面体模型。     

基于实体造型的三维有限元网格自动剖分

本文叙述了用八叉树法对三维实体进行有限元网格自动剖分算法的设计和实现。本文的算法对传统的八叉树法进行了一系列的改进,包括新型数据结构的建立,对八叉树结点属性判断算法的改进,边界结点体处理方法的改进等。使得本文的算法既保持了传统算法中自动化程度高、层次结构分明、适于再进行网格加密等特点,又克服了其所需存贮空间大、执行速度慢、边界处理复杂、边界单元形状质量不好等缺点,使算法的实现取得了令人满意的结果     

前沿推进曲面四边形网格生成算法

将一类前沿推进三角形曲面网格生成算法拓展到曲面四边形网格生成。新算法逐个单元推进前沿,避免了铺路法（Paving）逐排推进方式的鲁棒性问题,针对四边形算法在理想点计算、候选点列表构建和新单元生成等环节存在的特殊技术问题给出了系统的解决方案。数值实验表明,本文算法能针对复杂的组合参数曲面自动生成全四边形网格,网格质量优于...     

一种三维表面网格自动生成方法

提出了一种改进的区域分解法,用于三维表面三角形和四边形网格的自动生成。基于区域分解法的三维表面网格生成的主要技术包括三维表面三角形面片拓扑关系的建立,表面三角形面片的分组及特征面的确定,空间曲线上网格节点的生成,区域内外边界的合并,最佳剖分面的确定,以及网格的光滑处理等。本文对这些技术进行了详细的介绍。本文提出的表面网格生成方法具有算法可靠、生成网格效率高以及生成网格质量高等优点。最后给出三维表面网格生成实例验证了本文提出方法的可靠性。     

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．     

一种新的准结构网格生成方法

在有限元分析中,高质量的结构网格可以有效地提高有限元分析的精度,但结构网格的几何适应性差,针对复杂边界的二维计算模型,现有的方法很难自动生成高质量的结构网格;而非结构网格几何适应性很好,但存在计算效率低和精度差等问题。提出了一种新的准结构网格生成方法,能够实现复杂区域的网格自动生成并且具有高网格质量。该方法首先对计算区域运用Delaunay三角剖分技术生成粗背景网格;然后利用背景网格,使用优化的Voronoi图生成过渡的蜂巢网格;最后,通过中心圆方法对蜂巢网格单元进行结构网格剖分。分析NACA0012翼型数值模拟结果表明,提出的新准结构网格生成方法能够对边界复杂的模型自动生成高质量的网格,并且通过三种不同拓扑类型网格计算结果相互对比及与实验结果对比,证明准结构网格具有高计算精度。     

三维有限元六面体网格几何自适应再生成方法

基于几何自适应的六面体网再生成方法,提出了一种以栅格法为基本方法,对有限元网格再划分过程中的网格再划分标准、几何形状的获取以及新旧网格之间物理量的传递等关键问题进行了研究.重点介绍了基于几何自适应的六面体网格再生成算法,首先对旧网格实体模型进行识别,根据实体模型几何特征建立加密源点信息场;然后采用栅格法生成核心网格并对...     

一种基于有限元网格的车身CAD曲面数据修复方法

针对车身CAD中非同构数据格式间的转换使自由形体的近似值发生变化而导致曲面片之间产生缝隙或网格叠加的情况,提出了一种基于有限元网格、应用于车身CAD曲面网格数据自动修复的方法。该方法还能够在一定程度上局部修复原来划分有缺陷的网格,从而降低对车身CAD模型有限元网格划分的质量要求,并通过工业复杂成形件的实际处理结果验证了该方法的有效性。     

自适应多重网格有限元网格生成器研制

基于协调三角形剖分算法、分子表数据结构和Ｚｉｅｎｋｉｅｗｉｃｚ－Ｚｈｕ误差估计方法,本文研制出适用于自适应多重网格有限元的网格生成器。该网格生成器可对复杂的区域进行自适应加密。当荷载作用边界随时间变化及在动力荷载作用下,网格生成器可退化与再加密网格。     

AUTOMATIC MESH GENERATION OF 3—D GEOMETRIC MODELS

In this paper the presentation of the ball-packing method is reviewed, and a scheme to generate mesh for complex 3-D geometric models is given, which consists of 4 steps: (1) create nodes in 3-D models by ball-packing method, (2) connect nodes to generate mesh by 3-D Delaunay triangulation, (3) retrieve the boundary of the model after Delaunay triangulation, (4) improve the mesh.     

简单高效的面向对象四叉树有限元网格生成技术研究

用面向对象的思想和方法与四叉树有限元网格生成结合 ,创建或改进了网格生成各个阶段的算法和实现方式 ,并在面向对象语言 VC 6 .0中得以实现。能快速、高效地生成适用于任何复杂边界的四叉树有限元网格 ,易于自适应 ,易于局部加密和稀疏化。     

一种全四边形网格生成方法——改进模板法

首先对全四边形单元网格自动剖分算法中的模板法进行了探讨,并提出了相应的改进方法。在此基础上提出了一种新的全四边形单元网格自动生成方法。该方法允许在两个方向上存在网格疏密过渡,并可以提高单元的密度要求自动计算亲单元每条边上的结点数,有效地对局部实施加密处理。     

判别二维有限元网格图的简便算法

根据图论中欧拉公式推得二维有限元网格图中单元数、节点数、边数及边界数之间的关系式,获得判别网格图中是否存在节点号重复和单元遗漏的简便算法。     

保持特征的三角形有限元网格简化方法

基于二次误差的网格简化算法,提出了一种三角形有限元网格模型简化算法。在网格质量评估中考虑折叠代价,避免过于狭长的三角形出现,保证新生成单元的质量。同时,通过改进特征检测机制,加入用户控制,对模型上的重要细节特征进行精细定位,使算法适用范围更广泛,简化结果更能满足网格简化过程中细节特征的保持要求。     

有限元网格自组织神经网络的自动生成

利用多个自组织神经网络的同时训练,可以一次性自动地生成计算区域内与计算区域边界上所有网格节点,尔后按FGT法的基本思想将节点连接成所需的三角形或四边形单元。由于在自组织神经网络中采用了改善的目标函数,节点的分布可以实现自适应调节以反映网格疏密分布的要求。文末几个算例验收证明本算法具有自适应性,适用于凸域、凹域、多连通域等多种情况。     

A modified finite element method for determining equilibrium capillary surfaces of liquids with specified volumes

This paper describes a modified finite element method (MFEM) for determining the static equilibrium shape of the capillary surface of a liquid with a prescribed volume constrained by rigid boundaries with arbitrary shapes. It is assumed that the liquid is in static equilibrium under the influence of surface tension, adhesion, and gravity forces. This problem can be solved by employing the conventional FEM; however, a major difficulty arises due to the presence of the volume (integral) constraint and usually requires the use of the Lagrange multiplier method, the sequential unconstrained minimization technique, or the augmented Lagrange multiplier method. With the MFEM, the space variables defining the equilibrium surfaces (or curves) are expanded in terms of parametric interpolation functions, which are designed such that the boundary conditions and the integral constraint equation are automatically satisfied during each iteration of a direct numerical search process. Hence, there is no need to include Lagrange multipliers and/or penalty factors and the problem can be treated more simply as one involving unconstrained optimization. This investigation indicates that the MFEM is more efficient and reliable than the other methods. Results are presented for several case study problems involving liquid solder drops. Copyright © 2000 John Wiley & Sons, Ltd.     

Automated quadrilateral mesh generation for digital image structures

With the development of advanced imaging technology, digital images are widely used. This paper proposes an automatic quadrilateral mesh generation algorithm for multi-colour imaged structures. It takes an original arbitrary digital image as an input for automatic quadrilateral mesh generation, this includes removing the noise, extracting and smoothing the boundary geometries between different colours, and automatic all-quad mesh generation with the above boundaries as constraints. An application example is provided to demonstrate the usefulness and effectiveness of the proposed approach.     

A deforming finite element mesh for use in moving one-dimensional boundary wave problems

The finite element method is developed to solve the problem of wave run-up on a mild, plane slope. A novel approach to implementing a deforming mesh of one-dimensional, three-node, isoparametric elements is described and demonstrated. The discrete time interval (DTI), arbitrary Lagrangian–Eulerian (ALE) and space–time element (STE) methods are used to solve the unsteady one-dimensional shallow water wave equations. The boundary condition required is simply the seaward water surface elevation, and although the method has only been tested for monochromatic waves, it should be equally valid for any sea state which can be described as a water surface elevation as a function of time. All three solution methods are shown to given good results. Time histories of the terms of the governing equations are calculated and used to demonstrate how the ALE and STE methods account for mesh deformation. The model could be extended to two dimensions, which would have practical application to the run-up of obliquely incident waves. © 1997 John Wiley & Sons, Ltd.     

Discontinuity-capturing finite element computation of unsteady flow with adaptive unstructured mesh

A discontinuity-capturing scheme of finite element method (FEM) is proposed. The unstructured-grid technique combined with a new type of adaptive mesh approach is developed for both compressible and incompressible unsteady flows, which exhibits the capability of capturing the shock waves and/or thin shear layers accurately in an unsteady viscous flow at high Reynolds number. In particular, a new testing variable, i.e., the disturbed kinetic energyE, is suggested and used in the adaptive mesh computation, which is universally applicable to the capturing of both shock waves and shear layers in the inviscid flow and viscous flow at high Reynolds number. Based on several calculated examples, this approach has been proved to be effective and efficient for the calculations of compressible and incompressible flows. The project supported by the National Natural Science Foundation of China (10125210), the Hundred-Talent Programme of the Chinese Academy of Sciences and the Innovation Project of the Chinese Academy of Sciences (KJCX-SW-L04, KJCX2-SW-L2)