【作者】 李书杰；

【导师】 刘晓平；

【作者基本信息】 合肥工业大学 ， 计算机软件与理论， 2008， 硕士

【摘要】 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,模型因特征的变化而形成的各种状态的模型称为多态模型。模型简化的方法以及简化程度的确定都是目前CAD模型到CAE模型自动转化研究的核心问题。针对确保一定分析精度,尽可能节省计算资源的需求,建立了衡量不同简化模型对有限元分析结果造成的误差的方法以及对特征造型系统中常出现的高曲率扫掠特征用折线扫掠特征替换的方法,以此可得到具有不同精度的多态模型。本文的主要工作包括以下几个方面:(1)建立了多态理论体系整体框架,提出了模型误差层次的概念,用以在客观的衡量模型中特征简化后对有限元计算结果的方法的基础上描述模型的被简化程度,表征模型在相应模型简化方式下将产生的误差。(2)提出对特征造型系统中常出现的高曲率扫掠特征用折线扫掠特征替换的方法,以此可得到具有不同精度的多态模型,可以作为在有限元分析领域中除特征删除、特征降维和对称性简化三种处理方式外一种新的特征处理方式。(3)根据逼近论中常见的用逼近误差的差异来衡量两种逼近方法的不同的思想,建立了用因特征替换而产生的增大的逼近误差量来衡量替换误差的方法。(4)指出了对替换误差产生影响的应有三个要素,分别为特征替换对网格剖分产生影响的区域测度反映的要素、特征替换后网格剖分直径改变量反映的要素以及被替换特征所在区域内场函数的变化趋势反映的要素。(5)建立了对替换误差产生影响的应有三个要素的估算方法,在此基础上,搭建了基于误差分析和特征替换的模型态生成系统框架,初步实现了基于误差分析和特征替换的模型态生成系统。更多还原

【Abstract】 3D computer aided design (CAD) system that using feature-based solid modeling technique has been widely used for product design recently. Meanwhile, CAE also plays a more and more important role in product design, in which finite element is one of the most popular methods. Models built by CAD systems usually need simplification before finite element analysis to meet analysis requirement. Multi-state model means diversified models formed by variation of features. The method and degree of simplification are two essential problems in model automatic transformation from CAD to CAE. To cut down computational complexity on the premise of a certain analysis precision, the measurement method of the error of models of different simplification level that emerge from displacing high curvature sweeping feature with polygonal line sweeping feature is proposed, multi-state models with different precision are gained. The main content includes:(1) Establish the overall framework of Multi-state theory; propose the conception of level of error in order to measure the level of feature simplification objectively, which stand for the error caused by its corresponding simplification way.(2) A method of displacing high curvature sweeping feature with polygonal line sweeping feature is proposed, by which multi-state models with different precision could be gained. It should be regarded as a new method of simplification except for feature remove, feature reduction and symmetrical simplification.(3) Use the difference between approximation error to measure the difference between two approximation method according to the theory of approximation, get the method of measuring the displacement error between finite element analysis results of pre and post model.(4) The conclusion that three error factors exist in feature displacement is drawn. They are measurement of mash variation domain, the variation of diameters of the meshing conditions caused by feature displacement and the changing trend of field function in the area around the feature.(5) Give the estimation method of three factors of displacement error. And further more, establish the multi-state model generation system based on error analysis and feature displacement.更多还原