以网络为中心的几何造型技术

首先介绍了以网络为中心的CAD技术研究主题;然后围绕几何数据和设计工具的互操作性,从面向网络的模型数据表示、协同数据交换、基于网络的模型数据传输、多分辨率几何造型和网络化造型服务5个方面的关键技术,综述了以网络为中心的几何造型技术的研究进展;最后讨论了该领域存在的研究问题及其今后的研究方向。     

Mixed-aspect fractal surfaces

In order to provide accurate tools to model original surfaces in a Computer Aided Geometric Design context, we develop a formalism based on iterated function systems. This model enables us to represent both smooth and fractal free-form curves and surfaces. But, because of the self-similarity property underlying the iterated function systems, curves and surfaces can only have homogeneous roughness. The aim of our work was to elaborate a method to build parametric shapes (curves, surfaces, …) with a non-uniform local aspect: every point is assigned a “geometric texture” that evolves continuously from a smooth to a rough aspect. The principle is to blend shapes with uniform aspects to define a shape with a variable aspect. A blending function controls the influence of each initial shape. An illustrated application is then built, joining surfaces characterized by different kinds of roughness.     

Design of object-oriented database for the definition of machining operation sequences of 3D workpieces

This paper describes the activities of Object-Oriented (OO) analysis that were implemented in order to obtain a high part representation level and to give sets of structured and hierarchical data to the Computer Aided Process Planning (CAPP) system. The OO modeling activities were carried out by using the Object-Oriented System Analysis (OOSA) method which allows careful specification of all the information contained inside the system. All the models used by this method have been described in detail to show how the OO database is defined and how it can be used by a generative CAPP system. The feature model proposed is defined by taking all the part information that can be recognized and extracted from the Computer Aided Design (CAD) model into account. The result is the design of an OO database which allows the CAPP system to use manufacturing features to define machining operation sequences of 3D workpieces. The approach proposed is generic enough to integrate any geometrical forms which can be recognized and identified from the CAD system. Hole geometry is taken as an example to show the link between the step of OO analysis and the step of knowledge representation in the Expert System which has been used to generate machining cycles. The OO database presented makes up a real solution of CAD/CAPP/CAM integration by using feature modeling.     

Self-intersections of rational Bézier curves

Rational Bézier curves provide a curve fitting tool and are widely used in Computer Aided Geometric Design, Computer Aided Design and Geometric Modeling. The injectivity (one-to-one property) of rational Bézier curve as a mapping function is equivalent to the curve without self-intersections. We present a geometric condition on the control polygon which is equivalent to the injectivity of rational Bézier curve with this control polygon for all possible choices of weights. The proof is based on the degree elevation and toric degeneration of rational Bézier curve.     

The role of geometric modeling in computer integrated manufacturing

This paper briefly describes the theories behind the different geometric modelling techniques. Through an examination of some of the important applications such as Numerical Control Machining, Computer Aided Design, Computer Aided Assembly, and Robot Programming and Simulation, we conclude the need for the integration of two or more modeling techniques in one system.

This paper also addresses the problem of interfacing geometric modelers with other components of Computer Integrated Manufacturing. This discussion involves the problems of standardization.

Finally some of the major challenges facing computer geometric modeling are defined as future areas for research such as the representation of both form and size tolerance in the model and the predicted interface with expert systems.     

基于网络本体语言的三维计算机辅助设计主模型相似性计算方法

为了提高三维计算机辅助设计(CAD)模型重用效率,针对当前三维模型检索系统中语义表达不足问题,提出了一种基于网络本体语言(OWL)表示模型语义的相似性计算方法。首先,将三维CAD产品主模型转化成以概念属性特征为基础语义对象的结构化表示模型;然后,从OWL表示模型中提取用于评价两个模型相似性的特征语义信息,构建可量化的相似元集,借助子图同构思想和Tversky算法给出了一种加权相似性计算方法;最后,通过实例验证了所提方法的有效性和可行性。实验的定量评价结果表明,该评价基准从对象本身转为两个对象特性的语义描述,能够客观反映两对比模型的相似程度。     

质量约束的三维模型建模方法

在当今的智能制造和工业软件设计领域,CAD和CAE是极为重要的技术.但现有的CAD和CAE模型表示方法不统一,在数据交换上需要耗费大量时间,造成了计算资源极大的浪费.非均匀有理B样条(NURBS)模型作为一种兼容CAD和CAE的模型表达方式,以样条曲线为基函数,无须进行交换即可进行等几何分析.本文提出了一种基于质量约束...     

任意NUBS曲线的小波分析和造型技术

为了对任意NUBS曲线进行精确的分解和重构，提出了半正交B样条小波分解和重构的新算法，同时给出了处理非均匀B样条曲线的非整数阶分辨率的小波分解和重构算法，并实现了任意非均匀B样条曲线的多分辨率表示，对于任意非均匀B样条或NUBS曲线，无论它有多少个控制点，均可以对它进行半正交分解和重构，而不受控制点数必须等于2＋3的限制，从这个意义上讲，该方法不仅可以实现连续分辨率水平（continuous-resolutionlevel)的非均匀B样条曲线造型，还可以对非均匀B样条和NURBS曲线进行精确的分解和重构，这对于B样条曲线曲面的多分辨率造型与显示具有重大应用价值。     

A Compact Linear Translation for Bounded Model Checking

We present a syntactic scheme for translating future-time LTL bounded model checking problems into propositional satisfiability problems. The scheme is similar in principle to the Separated Normal Form encoding proposed in [Frisch, A., D. Sheridan and T. Walsh, A fixpoint based encoding for bounded model checking, in: M.D. Aagaard and J.W. O'Leary, editors, Formal Methods in Computer-Aided Design; 4th International Conference, FMCAD 2002, Lecture Notes in Computer Science 2517 (2002), pp. 238–254] and extended to past time in [Cimatti, A., M. Roveri and D. Sheridan, Bounded verification of past LTL, in: A.J. Hu and A.K. Martin, editors, Proceedings of the 5th International Conference on Formal Methods in Computer Aided Design (FMCAD 2004), Lecture Notes in Computer Science (2004)]: an initial phase involves putting LTL formulae into a normal form based on linear-time fixpoint characterisations of temporal operators.As with [Cimatti, A., M. Roveri and D. Sheridan, Bounded verification of past LTL, in: A.J. Hu and A.K. Martin, editors, Proceedings of the 5th International Conference on Formal Methods in Computer Aided Design (FMCAD 2004), Lecture Notes in Computer Science (2004)] and [Latvala, T., A. Biere, K. Heljanko and T. Junttila, Simple bounded LTL model checking, in: Formal Methods in Computer-Aided Design; 5th International Conference, FMCAD 2004, Lecture Notes in Computer Science 3312 (2004), pp. 186–200], the size of propositional formulae produced is linear in the model checking bound, but the constant of proportionality appears to be lower.A denotational approach is taken in the presentation which is significantly more rigorous than that in [Frisch, A., D. Sheridan and T. Walsh, A fixpoint based encoding for bounded model checking, in: M.D. Aagaard and J.W. O'Leary, editors, Formal Methods in Computer-Aided Design; 4th International Conference, FMCAD 2002, Lecture Notes in Computer Science 2517 (2002), pp. 238–254] and [Cimatti, A., M. Roveri and D. Sheridan, Bounded verification of past LTL, in: A.J. Hu and A.K. Martin, editors, Proceedings of the 5th International Conference on Formal Methods in Computer Aided Design (FMCAD 2004), Lecture Notes in Computer Science (2004)], and which provides an elegant alternative way of viewing fixpoint based translations in [Latvala, T., A. Biere, K. Heljanko and T. Junttila, Simple bounded LTL model checking, in: Formal Methods in Computer-Aided Design; 5th International Conference, FMCAD 2004, Lecture Notes in Computer Science 3312 (2004), pp. 186–200] and [Biere, A., A. Cimatti, E. M. Clarke, O. Strichman and Y. Zhu, Bounded model checking, Advances in Computers 58 (2003)].     

基于CAD／CAPP并行设计的特征描述与操作

本文介绍了在作者开发的基于特征的ＣＡＤ／ＣＡＰＰ并行系统ＦＯＰＳ中,针对ＣＡＤ／ＣＡＰＰ并行设计的要求,对形状特征的表示处理策略。提出了基于加工的形状特征分类及体描述思想,并从一个新的角度认识处理形状特征,建立了基于特征描述的实体几何模型,提出了广义“凹孔”的特征认识概念及相应的“内环”处理技术,为有效地在设计过程中同时为ＣＡＰＰ系统提供必要的信息,便于进行零件设计的结构工艺性分析、评价及工艺规程     

有理曲线的近似隐式化表示

本文首次提出了曲线近似隐式化的概念，给出了求曲线的近似隐式化表示的有效算法，并以实例说明了算法有效性以及研究这一问题的重要意义。     

多项式的正性和凸性

在计算机辅助几何设计(CAGD)中,曲面曲线的凸性是一种重要的特性.旨在解决多项式的正性和凸性问题.凸性可以通过正性来解决.通过推广经典的Sturm定理,得到一种多项式正性的算法.由此提出了任意阶多项式为正的一个充要条件,也提出了一个实用的算法,从而可以只用此多项式的系数来表示得到的充要条件.     

一个CSCW系统的设计与实现

随着计算机网络技术的发展,计算机支持的协同工作（CSCW）系统正逐渐成为人们研究的热点,协同式计算机辅助设计系统是一类典型的CSCW系统。本文在介绍了CSCW的基本概念之后,从系统组成的角度出发,提出了一个典型的CSCW系统是由应用子系统、信息共享平台、协同工作平台、协作管理平台、以及网络传输平台这五大部分组成的,并对其各部分的内容进行了形式化的描述和系统的分析,最后以我们开发的协同式计算机辅助设计系统－－CoopCAD为例,介绍了如何按照该结构实现一个具有实时性的协同式计算机辅助设计系统。     

Applying cognitive psychology to 3-D modelling in CAD

Research into the cognitive aspects of human information processing sometimes seems remote from the world of the software application designer. This paper describes one aspect of the detailed design of A CAD (Computer Aided Design) system and discusses the application of research findings relating to cognitive representation of objects in 3-D space.     

Semi-implicit representations of surfaces in P3, resultants and applications

In this paper we introduce an intermediate representation of surfaces that we call semi-implicit. We give a general definition in the language of projective complex algebraic geometry, and we begin its systematic study with an effective view-point. Our last section will apply this representation to investigate the intersection of two bi-cubic surfaces; these surfaces are widely used in Computer Aided Geometric Design.     

论中等职业学校计算机辅助设计(CAD)专业建设

计算机辅助设计(CAD)是现代制造企业实施信息化系统建设的一项关键支撑技术。CAD技术具有很多优点,可以为生产制造,为生活服务,可以提供很多的便利。首先,提出了CAD的定义,并分析了该技术的广泛应用。接着,概括了计算机辅助设计的设计流程。然后,分析了中等职业学校已经具有的软件和硬件条件,介绍了CAD专业的定位和相关课程的设置。最后,简单研究了计算机辅助设计领域经常用的软件。     

笔式针织服装工艺设计系统研究与实现

针对计算机辅助设计与传统纸笔工作模式切换时存在的问题,提出一种基于纸笔范式的针织服装工艺设计系统,研究敏捷制造环境下针织服装行业的设计工作流程,并采用草图推荐技术及自由曲线编辑技术加以实现,实验结果表明,该系统能有效降低用户使用复杂度,提高设计效率,且在某企业初步试用后取得较好的应用效果。     

A hierarchical design concept for shape optimization based on the interaction of CAGD and FEM

The numerical treatment of shape optimization problems requires sophisticated software tools such as Computer Aided Design (CAD), the Finite Element Method (FEM) and a suitable Mathematical Programming (MP) algorithm. Efficiency of the overall procedure is guaranteed if these tools interact optimally. The theoretical and numerical effort for sensitivity analysis reflect the complexity of this engineering problem.In this paper we outline a general modelling concept for shape optimization problems. Hierarchical design models within Computer Aided Geometrical Design (CAGD) and the interaction of geometry and FEM lead to an efficient overall optimization procedure. Our concept has been derived, implemented and tested for shell structures but it is seen to be generally applicable.After a short introduction containing the state of the art we give an overview of the numerical tools used and outline the interaction of CAGD and FEM within the overall optimization procedure.The paper is mainly devoted to the hierarchical design space based on a hierarchical geometrical modelling. The major part of computational effort is consumed by sensitivity analysis related to the number of design variables. Therefore, this number should be limited and only few powerful design variables corresponding to the special interests of the considered problem should be defined. This procedure may lead to a considerable limitation of the design space. Based on a hierarchy in the geometrical model different types of design variables are introduced: design variables with global, regional and local influence. The new method is based on successive activation of these types of design variables. This procedure leads to a considerable reduction of computational time for the sensitivity analysis without loss of geometrical flexibility.A new method of geometrical refinement and a successive adaptively driven expansion and reduction of the design space is described. It is based on the degree elevation or degree reduction of parametric curves and surfaces, respectively.A numerical example illustrates the new method and the efficiency of the overall optimization procedure.     

曲线造型数学方法统一化的研究

探讨了用含控制类型、种类、形因子参量的方法，推出了既能构造任意有理与非有理的参数三次曲线又能表示二次圆锥曲线的统一数学模型，并讨论了控制参量、权因子与曲线形状之间的关系．为ＣＡＧＤ提供了内涵丰富、描述能力强、简捷的统一数学方法．