面向CAE 的STL 模型三角网格均匀化

提出了一种基于STL数据的有限元网格再生成算法,该算法主要用于CAE工程分析.鉴于CAD模型的网格特征形态不匀称,分布不均匀的特点,对CAD模型进行网格再生成,使其符合CAE工程分析的要求.算法主要由拓扑建立、网格聚类、网格重采样和三角化四部分组成.实验表明该算法能够有效降低三角网格最长边和最短边的比值,使得模型的网格特征形态趋于均匀.     

综合平均曲率与网格边的特征线提取方法

随着数字几何获取技术的发展,大量的复杂形体采用网格模型表示。而网格模型的特征线或特征边缘的识别和提取是后续开展几何和特征识别的基础工作,为此提出一种综合平均曲率与网格边的三角网格模型特征线提取方法。分两次提取:首先利用三角面片法矢夹角大小对模型中的尖锐边进行初次提取特征点;然后综合平均曲率与网格边的关系对特征点进行二次提取;最后用两次提取边的顶点作为特征点,进行分类分组处理拟合成特征线。经过实例验证,该算法可以快速地提取尖锐边和过渡边等,具有很好的提取效果。     

基于区域生长的三角网格模型孔洞修补方法

为复原残缺三角网格模型的原始形状,针对丢失尖锐特征的模型,提出一种基于区域生长的孔洞修补方法。在根据模型的拓扑连接关系提取孔洞边界信息后,利用广度优先算法以孔洞边界为起点对孔洞周边网格进行区域划分,由对应孔洞特征区域的几何性质计算新补丁面片的法矢,并据此逐层迭代地向孔洞内部进行异步生长,同时为每个孔洞边界网格设置一个控制信号控制区域生长的异步性,对不同区域的新面片求交恢复以确定尖锐特征线和特征角。实验结果表明,对于尖锐特征丢失的残缺模型,该方法在修补孔洞的同时能够完整地恢复模型的原始形状。     

基于网格模型的磨损区域边界提取方法研究*

针对磨损零件的修复问题,提出了一种基于网格模型的磨损曲面边界线提取方法。根据磨损情况的不同,设置特征角的值,通过计算相邻三角面片法矢夹角,并与给定特征角的值相比较来提取磨损边界点,将磨损边界点插值成三次非均匀有理B样条(NURBS)曲线。给出了磨损边界线内磨损区域网格的删除方法,为后续实现磨损区域的曲面重构提供所需的几何信息与模型。应用实例表明,此方法用于磨损边界线的提取和磨损区域网格的删除是有效、可行的。     

基于T-Spline的全自动几何拓扑修复方法

从高质量曲面网格生成的需求出发,提出了一种基于T-Spline的全自动几何拓扑修复方法.本文方法创新性主要可归纳为:1）对原有计算机辅助设计（Computer aided design,CAD）几何模型不进行任何修改保留其本真,自动识别CAD几何模型中常见不必要的几何特征,成功解决了CAD几何模型中存在的几何瑕疵,如短边、窄面、退化边、退化面、非连续光滑边界及尖锐特征等,利用新生成的"虚边"、"虚面"处理几何瑕疵,同时通过虚拓扑重构CAD几何模型的B-Rep;2）开发了一套CAD/CAE集成系统,统一了几何模型与计算分析模型,实现计算机辅助工程（Computer aided engineering,CAE）与CAD两者的无缝集成,所有拓扑修复操作及后续CAE分析计算均在同一环境下进行,避免了几何模型在CAE与CAD系统间进行转换时造成的数据丢失.该方法能够对复杂实体实现全自动几何拓扑修复及网格生成,实验表明,在保证不失真的前提下,修复后的几何模型能够生成质量良好的网格且能降低网格的生成规模,验证了本文方法的实用性和有效性,以满足工程实际分析的需要.     

保特征的网格光顺算法

提出了一种保特征的网格光顺算法，能够在快速地去除噪声的同时，保持网格模型的结构特征。该算法对网格中每个三角形的法矢进行光顺，同时求得顶点的法矢。根据当前点到邻接点的距离以及当前点的法矢与邻接点的法矢的夹角对顶点移动的方向进行调整，使顶点分布更加均匀。利用高斯函数求得光顺权值。实验结果证明，该算法能够有效地保持网格模型的结构特征，同时具有迭代次数少、体积收缩小、执行效率高的特点。     

基于CAE分析的网格模型的优化研究

注塑CAE常用的数值解法有边界单元法、有限单元法和有限差分法等,但这些解法都需要对所建立的模型进行单元网格划分,网格的好坏、疏密直接关系着CAE分析的效率.因此,网格模型的优化就成为CAE分析的一个关键环节. 一、几何模型的简化 由于软件功能的不同要求,注塑CAE模拟分析的网格模型往往与CAD设计的模型不完全一样,通常为了更为有效地进行模拟分析,在进行CAE的模型构建过程中,往往需要对模具的CAD模型中的一些细节进行简化运算.     

三维网格的边界强度分割算法

提出一种新的基于网格边界几何信息的快速分割算法,首先按照原始网格模型面片的拓扑关系建立对偶图,并根据网格面片的几何信息设定顶点权和边权;使用k-way 多级分割方法在对偶图上进行快速分割,得到预分割区域以及各分割区域的初始边界;然后定义分割片的特征边界和边界强度函数,用以表示各预分割区域边界上的形变模型;通过最小化形变模型的能量函数,推动初始边界向特征边界运动,最终得到符合最小值法则的有意义的子网格.实验结果表明,该算法快速有效,适用于各种局部边缘特点较显著的三角网格模型.     

一种保持尖锐特征的局部 细分算法

提出一种重建模型尖锐特征的局部 细分算法。在预处理过程中，只选取面向视点的网格作为能够被进一步自适应细分的网格，在自适应细分过程中，用相邻面片的法向夹角作为控制误差来反映细分的逼近程度是否足够，并根据预设的阈值 自动标记网格中的尖锐特征边，重新设计尖锐特征处的面具。实验结果表明，该算法能够用较少的存储量有效地保持模型的尖锐特征。     

一种保持尖锐特征的局部√3细分算法

提出一种重建模型尖锐特征的局部√3细分算法.在预处理过程中,只选取面向视点的网格作为能够被进一步自适应细分的网格,在自适应细分过程中,用相邻面片的法向夹角作为控制误差来反映细分的逼近程度是否足够,并根据预设的阈值θ自动标记网格中的尖锐特征边,重新设计尖锐特征处的面具.实验结果表明,该算法能够用较少的存储量有效地保持模型的尖锐特征.     

A CAD/CAE incorporate software framework using a unified representation architecture

Currently, there are still some big gaps between the CAD system and CAE system, e.g. the different data structure for model representation, which costs lots of time and effort of engineers in the interaction between these two kinds of systems. In order to bridge these gaps, an incorporate software framework is proposed in this paper. In this framework, the unified representation architecture (URA) is presented that makes CAD and CAE to be an organic entity. The URA contains three components: (1) unified data model (UDD) including unified B-rep, unified feature and unified mesh; (2) unified data management (UDM) consisting of unified interaction, unified data structure, unified Constructive Solid Geometry (CSG) history and unified interface; (3) unified display and post-processor (UDP) for both design and performance analysis. The URA facilitates the incorporation by explicitly representing design and analysis information as design features, which maintains their associations through the history chain. Besides the URA, a unified mesh data (UMD) is proposed to unify the mesh of CAD model display and CAE analysis with the purpose of reducing the redundancy of mesh data. The unified mesh data (UMD) is proposed to unify the mesh of CAD model display and CAE analysis, which greatly reduces the redundancy of mesh generation data. Finally, the high efficiency of the proposed framework is demonstrated by engineering examples.     

以STL为接口的CAD/CAE集成应用

提出了以STL为接口实现CAD/CAE系统的多对多集成方案,通过对原始STL的分析,检查,纠正以及整合处理,实现了基于STL的三维实体网格自动剖分,生成了可被CAE系统接受的有限元网格数据,实例表明,文中方法简单实用,效果良好。     

CAD mesh model segmentation by clustering

CAD mesh models have been widely employed in current CAD/CAM systems, where it is quite useful to recognize the features of the CAD mesh models. The first step of feature recognition is to segment the CAD mesh model into meaningful parts. Although there are lots of mesh segmentation methods in literature, the majority of them are not suitable to CAD mesh models. In this paper, we design a mesh segmentation method based on clustering, dedicated to the CAD mesh model. Specifically, by the agglomerative clustering method, the given CAD mesh model is first clustered into the sparse and dense triangle regions. Furthermore, the sparse triangle region is separated into planar regions, cylindrical regions, and conical regions by the Gauss map of the triangular faces and Hough transformation; the dense triangle region is also segmented by the mean shift operation performed on the mean curvature field defined on the mesh faces. Lots of empirical results demonstrate the effectiveness and efficiency of the CAD mesh segmentation method in this paper.     

CAD mesh model simplification with assembly features preservation

This paper aims to investigate a CAD mesh model simplification method with assembly features preservation, in order to satisfy the requirement of assembly field for the information of 3D model. The proposed method simplifies a CAD mesh model as follows. Firstly, the notion of ＂conjugation＂ is incorporated into the definition of assembly features, with the purpose of benefitting the downstream applications such as assembly features recognition and preservation. Subsequently, the attributed adjacency graphs （AAGs） of the region- level-represented parts are established. The assembly features are automatically recognized by searching for conjugated subgraphs of every two AAGs based on subgraph isomorphism algorithm. In order to improve the efficiency of assembly features recognition, the characteristics of conjugated subgraphs are adopted to initialize the mapping matrix, and the ＂verifying while matching strategy＂ is used to verify the validity of every two newly founded vertices which are correspondingly matched. Then, simplified CAD mesh model with assembly features preserved is constructed after suppressing the common form features. The method is applied successfully to simplify the CAD mesh model with assembly features well preserved. Moreover, the tradeoff between the cost of time for conjugated subgraphs matching and the complexity of the to-be-matched parts is proven to be almost linear.     

面向有限元分析的实体表面网格模型的优化

针对CAE软件开发的需要，将通用CAD软件输出的以表面三角形网格形式表示的实体模型输入CAE软件，作为有限元分析用几何模型。然后根据特定领域有限元分析的要求对表面网格进行优化处理，优化网格的数量和质量，以便进一步生成适合有限元计算需要的各种单元模型。     

基于模板的港口码头三维结构CAD/CAE 集成技术

针对港口码头结构CAD 几何模型生成CAE 单元模型,工程荷载CAD 模 型创建CAE 荷载模型,和CAE 分析结果与CAD 模型的关联关系等问题,利用模板的模型 独立性、规则性和可执行性等特性,研究了基于模板的港口码头三维结构CAD/CAE 集成技 术,定义了截面草图、三维实体和构件等多种CAD 建模模板,定义了机械草图和荷载等多 种荷载建模模板,定义了CAE 分析规则,实现了CAD 几何模型自动生成CAE 单元模型的 功能,定义了荷载转换规则,实现了工程荷载CAD 模型自动创建CAE 荷载模型的功能, 定义了整体模型模板,建立CAE 分析结果与CAD 模型的多对一关系,以此实现了港口码 头三维结构CAD/CAE 集成系统,大大提高了港口码头的设计效率,降低了设计人员的设计 难度,减少了设计错误。     

Meshing complexity: predicting meshing difficulty for single part CAD models

This paper proposes a method for predicting the complexity of meshing computer aided design (CAD) geometries with unstructured, hexahedral, finite elements. Meshing complexity refers to the relative level of effort required to generate a valid finite element mesh on a given CAD geometry. A function is proposed to approximate the meshing complexity for single part CAD models. The function is dependent on a user defined element size as well as on data extracted from the geometry and topology of the CAD part. Several geometry and topology measures are proposed, which both characterize the shape of the CAD part and detect configurations that complicate mesh generation. Based on a test suite of CAD models, the function is demonstrated to be accurate within a certain range of error. The solution proposed here is intended to provide managers and users of meshing software a method of predicting the difficulty in meshing a CAD model. This will enable them to make decisions about model simplification and analysis approaches prior to mesh generation.     

有限元领域中多态模型误差分析方法

基于特征造型技术的三维CAD系统目前已广泛应用于产品设计,同时CAE在产品设计与优化中也起到了越来越重要的作用.而有限元是最为广泛使用的CAE方法之一.由CAD系统建立的模型在进行有限元分析之前,通常需要根据分析需要对模型进行简化,如何分析模型简化前后对有限元计算结果的影响程度是CAD模型到CAE模型自动转化的首要步骤.将模型因特征的简化而形成的各种状态的模型称为多态模型.针对确保一定分析精度,节省计算资源的需求,根据有限元误差理论提出了分析不同简化模型对有限元分析结果造成的误差的方法,且通过数据实例得到验证,根据误差分析方法提出模型误差层次的概念,为有限元领域中多态模型的生成提供了新的思路.