基于标识的特征造型原型系统的研究与实现

从特征造型软件开发的角度对参数化特征造型的一些关键技术进行了研究，并在ACIS几何平台上开发了一个参数化特征造型原型系统GDS。讨论了GDS的关键技术：基于标识的特征表示模型，标识子系统、统一二、三维约束的基于子图的草图设计及约束求解方法、基于约束依赖图的特征编辑算法等。     

面向领域的快速特征造型的设计与实现

提出了面向领域的快速几何特征造型新方法。受软件工程理论中的“域工程”思想启发,该方法针对特定领域的几何特征造型设计,研究如何将领域知识加以抽象自动化,改良几何造型系统的软件架构设计,优化造型系统的算法设计,从而最终提高特征造型系统的整体效率。基于这一思想方法,讨论并分析了计算机辅助建筑设计中造型的需求,提出了系统实现框架,给出了相应的算法实例。应用实例证明了方法的可用性。     

形状特征的定义

本文研究形状特征的形式定义，并强调了形状特征的非几何语义，引入面邻接图ＡＡＧ和几何约束集来定义特征体素，使形状特征的空间属性和边界局性结合起来，从而面向基于约束的设计。最后，作者尝试用代数规格说明来定义特征，并给出了实例。     

龙腾设计师──新一代三维参数化特征造型CAD软件

正当国内各行业CAD技术应用从甩图板向三维设计迅速发展之时，北京巨龙腾数据信息技术有限公司开发出具有自主版权的三维参数化特征造型设计软件──龙腾设计师。以下介绍龙腾设计师的主要技术特点：1．支持概念设计龙腾设计师全面支持概念设计。在草图设计阶段，设计师摒弃仅靠直尺圆规方式作图，通过动态导航随手创意绘图，再添加尺寸约束和几何约束，即可实现设计构思。在特征造型阶段，设计师摆脱几何细节的困扰，从产品功能出发，利用凸台、凹槽、过渡、倒角、孔、筋等既具有工程涵义又符合设计习惯的特征造型手段，实现产品的三维造…     

基于灰度差分不变量的点特征匹配

本文提出了一种新的基于灰度差分不变量的点特征匹配方法。首先，利用灰度差分不变量获得点集之间的初始匹配；然后，利用初始匹配快速、稳健地估计图象之间的唯一几何约束－对极几何约束；最后，利用对极几何约束改进初始匹配。大量的实际图象实验表明，本文所提出的匹配算法有非常快的运算速度和很高的匹配正确率。     

实体造型中的几何约束

实体造型是一个基于约束的过程，完成从功能约束到几何约束、再到代数约束的转化而得到实体模型。本文讨论了几何约束的层次性及其表示，并且对几何约束同设计意图的关系进行了研究，提出了基于ＣＳＧ／ＧＣＧ／Ｂ－ｒｅｐ的模型表示。     

基于ACIS/HOOPS的特征造型系统设计与实现

为了探索CAD/CAM领域中的特征造型关键技术,研发一个特征造型系统。该系统分别以ACIS和HOOPS为几何造型引擎和渲染引擎,能够实现常用特征的创建、特征历史的管理、基本约束的管理和特征模型与几何模型的存取等功能,并且支持一些自由曲面特征造型以及参数化设计。为了维护用户的隐含设计意图,系统采用了一种新的拓扑元素命名与辨识机制。最后,给出了使用该系统进行特征建模、自由曲面特征参数化设计以及设计意图有效维护等实例,验证了本系统的可行性和有效性。     

传统绘图系统的几何约束驱动关键技术研究及实践

文中针对如何在传统绘图系统中拓展几何约束驱动功能，以实现面向设计师的灵活的参数化设计问题，对几何数据的转换，几何约束识别、表达、筛选及求解进行了较系统的探讨，提出了经实际检验行之有效的技术实现方法，特别地对具有独创性的约束识别的实施进行了阐述     

基于草图交互的个性化服装生成方法

以建立和交互修改三维服装草图为设计手段,提出在三维人体模型上生成三维个性化服装的参数化造型方法．服装草图由2种基本几何元素组成：体现人体围度信息的封闭样条曲线和体现人体在高度方向上曲面形状过渡的不封闭样条曲线．将服装草图约束分为2类4种：一类是体现服装宽松程度的人体与服装曲面之间的间隙约束;另一类是服装几何元素本身之间的共点、共面与对称约束．从人体的特征点出发,通过间隙约束生成服装草图的几何元素;在共点、对称和共面约束下,由服装草图几何元素建立拓扑结构为四边网格的服装草图．服装草图的交互修改是草图约束维护的过程,构建侧视图、正视图、断面图3个视图组成草图修改平台,在平台上交互编辑特征曲线．服装曲面则以三维草图为框架,通过对四边网格双线性Coons曲面插值生成．提供的设计方法使服装的造型变得简洁、灵活．     

参数化特征造型中拓扑结构变异的一种解决方法

文中首先分析了基于边界表示的特征模型用于参数化特征变动设计所存在的问题,指出了以边界表示中的几何边为形状特征定位约束基准无法满足拓拟结构变异的局限性,分析了基于草图的特征造型方法在变动设计中的重要性。在此基础上,提出了将基于实体模型边界表示的特征模型与基于草图的特征模型结合起来的新思想,并给出了该思想的实现方法,该方法使特征定位基准在特征造型过程中保持不变,且不随特征定位约束参数的改变而变化,能很好地满足参数化变动设计与拓扑结构变异的要求。     

Hierarchical Geometric Constraint Model for Parametric Feature Based Modeling

A new geometric constraint model is described,which is hierarchical and suitable for parametric feature based modeling.In this model,different levels of geometric information are repesented to support various stages of a design process.An efficient approach to parametric feature based modeling is also presented,adopting the high level geometric constraint model.The low level geometric model such as B-reps can be derived automatically from the hig level geometric constraint model,enabling designers to perform their task of detailed design.     

Design of an SOI-MEMS high resolution capacitive type single axis accelerometer

In recent years, high resolution micro accelerometers are increasingly finding various applications in different segments of life. The current work deals with the design of a high resolution single axis accelerometer based on SOI-MEMS technology. Accordingly two different approaches for designing comb type, capacitive, SOI-MEMS accelerometer is presented. Initially a system level approach using a simulation platform from SABER is carried out to obtain the basic design. Later, a device level design is carried out by building three dimensional (3D) geometric models using finite element (FE) simulations through CoventorWare software. Different design parameters like mechanical and electrical sensitivity, capacitance values, resonant frequency, etc. are obtained in either of the cases and compared. The design is optimized based on the overall sensitivity and the system noise level both electrical and mechanical, respectively. The complete design is worked out in accordance with the silicon on insulator based multiuser MEMS fabrication processes (MUMPs) technology from MEMSCAP foundry.     

一种改进的基于几何和纹理混合简化的快速绘制算法

文中对离视点较近的物体采用几何简化技术,对于距离较远的物体用纹理表示方法,在视点发生变化时,能进行几何－纹理相互转换。转换时,通过对纹理投影面后的几何插值,生成退化几何,实现几何－纹理间的光滑过渡。该算法的一个特点是结合了几何和纹理细节层次的思想,最后通过图例说明了所提出方法的有效性。     

A new level-set based approach to shape and topology optimization under geometric uncertainty

Geometric uncertainty refers to the deviation of the geometric boundary from its ideal position, which may have a non-trivial impact on design performance. Since geometric uncertainty is embedded in the boundary which is dynamic and changes continuously in the optimization process, topology optimization under geometric uncertainty (TOGU) poses extreme difficulty to the already challenging topology optimization problems. This paper aims to solve this cutting-edge problem by integrating the latest developments in level set methods, design under uncertainty, and a newly developed mathematical framework for solving variational problems and partial differential equations that define mappings between different manifolds. There are several contributions of this work. First, geometric uncertainty is quantitatively modeled by combing level set equation with a random normal boundary velocity field characterized with a reduced set of random variables using the Karhunen–Loeve expansion. Multivariate Gauss quadrature is employed to propagate the geometric uncertainty, which also facilitates shape sensitivity analysis by transforming a TOGU problem into a weighted summation of deterministic topology optimization problems. Second, a PDE-based approach is employed to overcome the deficiency of conventional level set model which cannot explicitly maintain the point correspondences between the current and the perturbed boundaries. With the explicit point correspondences, shape sensitivity defined on different perturbed designs can be mapped back to the current design. The proposed method is demonstrated with a bench mark structural design. Robust designs achieved with the proposed TOGU method are compared with their deterministic counterparts.     

A Free Form Feature Taxonomy

In this paper the notion of free form feature for aesthetic design is presented. The design of industrial products constituted by free form surfaces is done by using CAD systems representing curves and surfaces by means of NURBS functions, which are usually defined by low level entities that are not intuitive and require some knowledge of the mathematical language. Similarly to the feature-based approach adopted by CAD systems for classical mechanical design, a set of high level modelling entities which provides commonly performed shape modifications has been identified. Particularly, the paper suggests a classification of the so-called detail features for an aesthetic and/or functional characterization of predefined free form surfaces. Feature types are formally described by means of an analytical definition of the surface modification through deformation and elimination laws. A topological classification is then given according to the application domain of such laws. A further sub-classification of morphological types is then suggested according to geometric properties of weak convexity and concavity for the resulting modified shape, leading to a taxonomy of simple free form features meaningful for aesthetic design.     

自顶向下的计算机辅助工业设计几何建模研究

基于通用设计理论,研究了自顶向下的计算机辅助工业设计几何建模过程,采用面向设计演进过程的元模型和面向工业设计方面各侧面的子模型作为组织几何建模过程的抽象层次,提出了基于有向图的层次化几何信息模型,实现了对设计历史及意图的记录、不同层次几何信息间的关联以及按照元模型和子模型组织的自顶向下的计算机辅助工业设计几何建模过程。     

Structured synthesis of MEMS using evolutionary approaches

In this paper, we discuss the hierarchy that is involved in a typical MEMS design and how evolutionary approaches can be used to automate the hierarchical synthesis process for MEMS. The paper first introduces the flow of a structured MEMS design process and emphasizes that system-level lumped-parameter model synthesis is the first step of the MEMS synthesis process. At the system level, an approach combining bond graphs and genetic programming can lead to satisfactory design candidates as system-level models that meet the predefined behavioral specifications for designers to trade off. Then at the physical layout synthesis level, the selection of geometric parameters for component devices and other design variables is formulated as a constrained optimization problem and addressed using a constrained genetic algorithm approach. A multiple-resonator microsystem design is used to illustrate the integrated design automation idea using these evolutionary approaches.     

Robust topology optimization accounting for misplacement of material

The use of topology optimization for structural design often leads to slender structures. Slender structures are sensitive to geometric imperfections such as the misplacement or misalignment of material. The present paper therefore proposes a robust approach to topology optimization taking into account this type of geometric imperfections. A density filter based approach is followed, and translations of material are obtained by adding a small perturbation to the center of the filter kernel. The spatial variation of the geometric imperfections is modeled by means of a vector valued random field. The random field is conditioned in order to incorporate supports in the design where no misplacement of material occurs. In the robust optimization problem, the objective function is defined as a weighted sum of the mean value and the standard deviation of the performance of the structure under uncertainty. A sampling method is used to estimate these statistics during the optimization process. The proposed method is successfully applied to three example problems: the minimum compliance design of a slender column-like structure and a cantilever beam and a compliant mechanism design. An extensive Monte Carlo simulation is used to show that the obtained topologies are more robust with respect to geometric imperfections.