共查询到19条相似文献,搜索用时 203 毫秒
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梁伟文 《计算机应用与软件》2005,22(12):26-27,114
本文在分析了传统几何造型的弊端及开曲面造型中光滑边界曲线的插值要求后,针对细分曲面造型方法中较常用的Loop细分,提出了基于边界采样技术的插值细分曲面造型方法。该方法一方面利用了细分曲面造型的优点,如算法简单、可表达任意拓扑结构等;另一方面又满足了工程应用中插值边界曲线的要求。文中详细讨论该算法的步骤,并通过示例验证了该算法的有效性和实用性。 相似文献
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复杂插值曲面的几何形态由散乱数据点控制,优化含这类曲面实体的六面体网格难以保证边界一致.借鉴Balendran提出的直接法,建立正四边形结点的空间几何关系方程,并作为优化约束,以移动结点使每个六面体的各个侧面趋近于正四边形,实现网格优化.将原始采样点及其它控制插值曲面几何形态的数据转化为控制点约束,以保证边界一致性.结合优化约束与控制点约束,作为离散光滑插值(DSI)方程的约束项,实现网格优化与曲面插值的耦合.实例表明,该方法能够在保证复杂插值曲面边界一致性的前提下实现六面体网格优化. 相似文献
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为有效确定平面正交各向异性体的材料参数,提出一种基于比例边界有限元法(Scaled Boundary Finite Element Method,SBFEM)和混合粒子群算法的识别方法.该方法以测量位移与SBFEM计算相应的位移之差的平方和最小为基础,采用粒子群优化(Particle Swarm Optimization, PSO)算法全局搜索材料参数.为加快收敛速度和提高反演识别精度,在PSO算法中引入自然选择的机制.采用SBFEM进行正分析问题计算时,只需对计算域边界进行数值离散,大大减少计算量.相对于边界元法,SBFEM不需要基本解.数值算例表明所提出的方法有效. 相似文献
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复杂插值曲面的几何形态由分布稀疏且不均匀的散乱数据点控制,含这类曲面实体的四面体网格优化在保证边界一致时存在一定的困难,提出一种将网格优化与曲面插值相结合的优化方法,借鉴Balelldtran提出的直接法,将正三角形结点之间的空间关系作为几何规则,以移动结点使四面体的所有侧面尽量趋近于正三角形,实现网格优化,用线性方程纽表示这种几何规则,形成优化约束.将原始采样点及其它控制界面几何形态的数据转化为控制点约束,以保证边界一致性.结合优化约束与控制点约束,作为离散光滑插值(DSI)方程的约束项,实现网格优化与曲面插值的耦合.实例表明,该方法能够在保证复杂插值曲面边界一致性的前提下实现四面体网格优化. 相似文献
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基于非流形几何与特征树的异质材料实体可视化方法 总被引:1,自引:0,他引:1
提出一种异质材料实体可视化的方法.采用边界曲面细分技术减小材料分布的突变视觉效应;在不损失渲染质量的前提下,采用自适应曲面细分和冗余曲面滤除方法解决异质实体可视化效率差、难以实时显示的问题.给出了详细的异质实体边界网格生成算法,以显示异质实体的外部几何信息及其内部材料组分的三维分布.该算法采用基于特征树的曲面网格自适应细分策略,通过对异质实体特征树的拓扑结构分析来判定待渲染曲面的材料分布特性,仅对确实需要细分的曲面进行额外的网格细分,有效地减小了实体渲染中所需的计算量;利用非流形异质实体的表征方法,采用冗余曲面滤除方法直接滤除非相关的边界曲面,以满足实时可视化的要求.该方法已用于异质实体建模软件CAD4D中,实验结果表明,其可有效地实现异质实体的实时可视化显示. 相似文献
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NURBS边界曲面直接生成法 总被引:1,自引:0,他引:1
由于非均匀有理B样条(NURBS)曲面的复杂性,传统NURBS边界曲面的生成是先构造孔斯曲面,再由孔斯曲面向NURBS曲面转换得到,其操作过程比较烦琐。针对此问题,提出了NURBS边界曲面直接生成算法,该算法根据给定的四条NURBS边界曲线,结合孔斯曲面生成方法直接插值生成NURBS曲面,从而避免了通过孔斯曲面向NURBS曲面转换所带来的计算代价,因此同传统方法相比,具有较低的计算代价。实验结果表明:该算法简化了曲面生成步骤,减少了曲面转换过程的计算量,生成的曲面边界信息明确,且连续性好。 相似文献
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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. 相似文献
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基于边界元素法的柔软物体变形模拟 总被引:2,自引:0,他引:2
在计算机动画和虚拟现实技术中,基于物理的建模方法是高真实感地模拟物体受力变形和运动的有效途径.近年来基于边界元的物理模型方法因其简捷的计算模式而受到关注,该文针对当前边界元模型在视觉效果和计算量上的一些缺陷,分别提出了两方面的改进方法,基于LOD的动态自适应多分辨率网格边界元模型和近似的非线性边界元的物理模型,分别用于在不损失视觉效果的前提下减少计算量以及模拟物体大变形,并提出了相应的加速算法,取得了较好的效果. 相似文献
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This paper reviews the developments in the Trefftzian Methodology, which have been undertaken by the authors at the University of Sheffield during the past fifteen years and the application of these developments to engineering design analysis. Initially, in the late 1970s, this work concentrated on the Direct Boundary Element Method (DBEM) and the Indirect Boundary Element Method (IBEM). Unfortunately these methods, as they are normally formulated, give rise to singular integrals, which require special mathematical treatment, when the source and field points coincide on the boundary of the component being analysed. These singular integrals can however be eliminated by placing the source boundary outside the domain of the problem being analysed so that the field and source points never coincide. This technique is known as either the Regular Direct Boundary Element Method (RDBEM) or the Regular Indirect Boundary Element Method (RIBEM) In a further development of the RIBEM, based on the Trefftz Method, the continuous distribution of sources is replaced with sources distributed at discrete points on the source boundary. This modified Trefftz Method eliminates the integrations in the solution procedure, it provides a series solution in terms of the fundamental solution of the problem being analysed and is referred to as the Indirect Discrete Boundary Method (IDBM). The emergence of the IDBM provided the opportunity to develop a combined Boundary Element Finite Element technique which enables these methods to be used simultaneously in a single calculation, thereby exploiting their strengths and minimising their weaknesses. A number of case studies will be discussed in the paper to illustrate the developments in the Trefftzian Methodology and its application to engineering design analysis. 相似文献
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This paper presents an integrated approach that supports the topology optimization and CAD-based shape optimization. The main
contribution of the paper is using the geometric reconstruction technique that is mathematically sound and error bounded for
creating solid models of the topologically optimized structures with smooth geometric boundary. This geometric reconstruction
method extends the integration to 3-D applications. In addition, commercial Computer-Aided Design (CAD), finite element analysis
(FEA), optimization, and application software tools are incorporated to support the integrated optimization process. The integration
is carried out by first converting the geometry of the topologically optimized structure into smooth and parametric B-spline
curves and surfaces. The B-spline curves and surfaces are then imported into a parametric CAD environment to build solid models
of the structure. The control point movements of the B-spline curves or surfaces are defined as design variables for shape
optimization, in which CAD-based design velocity field computations, design sensitivity analysis (DSA), and nonlinear programming
are performed. Both 2-D plane stress and 3-D solid examples are presented to demonstrate the proposed approach.
Received January 27, 2000
Communicated by J. Sobieski 相似文献
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Importing mesh entities through IGES/PDES 总被引:2,自引:0,他引:2
IGES/PDES is an internationally accepted standard for transferring solid model information between different CAD/CAM software. Most of the information, like geometric entities, mesh entities and drafting entities, for a model generated in a particular software may be imported into another software through the IGES protocol, although either software may have its own internal database structure, radically different from each other. The goal of this article is to outline the basic concepts involved in extracting relevant information from an IGES file produced by a CAD/CAM software. In order to elucidate the process involved, only the mesh entities (nodes and elements) are brought in and a simple F77 code is attached, which could easily be extended to develop a general purpose IGES translator for pre-processing in a Finite Element/Boundary Element based analysis environment. 相似文献
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Ruben Sevilla Sonia Fernández-Méndez Antonio Huerta 《Archives of Computational Methods in Engineering》2011,18(4):441-484
The development of NURBS-Enhanced Finite Element Method (NEFEM) is revisited. This technique allows a seamless integration
of the CAD boundary representation of the domain and the finite element method (FEM). The importance of the geometrical model
in finite element simulations is addressed and the benefits and potential of NEFEM are discussed and compared with respect
to other curved finite element techniques. 相似文献
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本文采用高阶有限谱单元对分层结构的横截面进行半解析离散.将结构中沿纵向均匀的区段视为子结构,运用基于Riccati方程的精细积分算法求出其出口刚度阵.网格拼装后即可对分层介质问题进行求解.半解析高阶谱单元的采用可以避免著名的龙格现象,该算法的数值精度能随着基函数的阶数的增加呈指数级提高.即高阶有限谱单元能够达到任意需要的精度.数值算例证明这种方法具有很高的精度与效率.在高精度高效率分析的基础上建立了滤波器的优化设计模型,利用遗传算法对优化模型进行全局优化,得到了PBG结构滤波性能全局最优的设计参数. 相似文献
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This paper deals with a numerical and experimental investigation on the influence of residual stresses on fatigue crack growth in AA2024-T3 friction stir welded butt joints. The computational approach is based on the sequential usage of the Finite Element Method (FEM) and the Dual Boundary Element Method (DBEM). Linear elastic FE simulations are performed to evaluate the process induced residual stresses, by means of the contour method. The computed stress field is transferred to a DBEM environment and superimposed to the stress field produced by a remote fatigue traction load applied on a friction stir welded cracked specimen; the crack propagation is then simulated according to a two-parameter growth model. Numerical results have been compared with experimental data showing good agreement and evidencing the predictive capability of the proposed method. The obtained results highlight the influence of the residual stress distribution on crack growth. 相似文献