A feature-based approach to structural design

Despite the continuing improvements in computeraided design (CAD) systems and improvements in geometric modeling, most CAD systems are used as advanced drafting and drawing management tools by structural designers. A computer model of a structural design usually is generated by creating a detailed geometric model of the primitive components of the design and then attaching attributes, such as physical properties and loading conditions, to the various geometric components to reveal the structural characteristics of those components. Thisbottom-up approach has been inherited from early drafting techniques and contrasts sharply with a structural designer's natural way of thinking and reasoning about the design. Geometric features, on the other hand, provide high-level abstractions of design information and can be tailored to a designer's specific engineering needs. In this paper the advantages of using feature-based techniques in structural CAD systems are discussed. These techniques provide better modeling primitives for users and superior data models for CAD systems for reasoning about the geometry, topology, and engineering properties of a structure.     

Integration of calculation models and CAD systems in building services design

Computer programs for analysing flow in pipework and in mains electrical distribution systems are well known. Computer-aided drafting is commonly used to produce working drawings of such systems. This paper looks at the integration of calculation models and CAD systems, particularly for the building services industry. Two types of networks generally occur in building services engineering. These are trees and circuits. They have certain features that allow the calculation model to be built up from geometrical data with minimum additional user input. The specific cases of closed circuit pipework and electrical wiring are dealt with in more detail.     

A feasible approach to the integration of CAD and CAPP

Although current CAD systems are declared to be feature-based, in fact, the so-called feature is just a modeling macro or menu name such as Protrusion, Revolution, Cutout, Block, etc., instead of a design feature or manufacturing feature in accordance with engineering practice. Consequently, product model data insufficiency and incompatibility between varieties of application systems are still the major barriers to system integration, especially the integration of design and process planning. This paper proposes a practical solution for a bi-directional integration of CAD and CAPP on the platform of commercial CAD systems. The key techniques such as feature recognition and conversion, feature parameter and constraint extraction, feature tree reconstruction, technical information processing, process planning, automatic process drawing marking and 3D material stock CAD model generating are discussed. And the extracted features and their related technical information and knowledge are encapsulated together with the geometry-oriented CAD model to form an integrated product information model to facilitate effective integration with the downstream activities. The integrated CAD/CAPP system is implemented on a commercial CAD package, UGS/SolidEdge. A case study and industry implementation illustrate the feasibility of the approach proposed.     

基于STEP的集成化CAD／CAM支撑软件系统

本文介绍了由清华大学ＣＡＤ中心等单位开发的集成化ＣＡＤ／ＣＡＭ支撑软件系统，该系统由六个模块组成，它们是用户接口、交互绘图、产品造型、分析与优化、数控加工和数据库管理该系统采用国际标准ＳＴＥＰ作为产品数据表示和交换的中性机制，使用特征造型、变量化设计方法建立产品信息模型，并使产品信息贯穿于设计、装配、分析、工艺、制造等各个阶段，实现系统的集成。     

3-D graphics in batch production

Major cost and time savings are made when CAD is integrated with CAM. This integration depends on the development of software systems for process planning, design tool selection, NC data generation and production control. Systems for 3-D modelling are also required. The paper describes some applications of wireframe and solid 3-D modelling in batch production.     

The need for an integrated 2D/3D cad system in structural engineering

This paper identifies the engineering need for an integrated 2D/3D CAD system and outlines the features of a system that addresses this need. It is argued that an effective combination of 2D drafting and 3D modelling would allow many of the corresponding requirements to be met, particularly with respect to compliant drawings. It is postulated that the key to an effective combination of 2D and 3D is a unified data structure designed specifically for structural engineering applications. The concepts of a prototype data structure that could form the basis of such an integrated 2D/3D system are introduced and related to the engineering requirements.     

A proposal for CAD/CAM interface with expert systems

In the computer-integrated manufacturing (CIM) environment, the key technologies, CAD and CAM, should be fully integrated with high operability. It is claimed, however, that CAD and CAM have so far been developed independently. Although much effort has been made to integrate CAD and CAM, this reality is far from completion.

Therefore, to establish a CAD/CAM interface with higher integration, the concept of a computer-aided drafting procedure with expert systems has been proposed on the basis of analysis of the information explicitly and implicity described on the part drawing, and also of the required knowledge of the designer to produce the part drawing. The CAD/CAM interface proposed here is available for producing not only the part drawing but also the process plan for the corresponding part, by effectively utilizing the knowledge of the expert. A prototype CAD/CAM interface deals with axi-symmetrical rotational parts implemented on a workstation.     

套筒式烟囱CAD系统的开发

以AutoCAD为平台,采用ObjectARX编程,开发了一个套筒式烟囱CAD系统。系统由前处理模块、计算模块和后处理模块三部分构成,实现了套筒式烟囱的结构设计、配筋计算和施工图绘制的集成。系统具有界面友好、操作简单、设计快捷和绘图迅速等特点。     

Environ: Integrating VR and CAD in Engineering Projects

A main objective of large industrial-engineering departments is implementing integrated information systems to manage their projects' life cycles. Environ is an application motivated by the demand to use Virtual Reality in large engineering models generated by CAD tools. Environ's main goal is to offer 3D visualization resources for CAD models with enough realism to serve as an integration tool for several engineering activities in the oil and gas industry.     

CAD/PDM系统间数据双向集成技术和应用研究

针对CAD/PDM系统间点对点集成存在的维护困难等问题,提出了一种以中间集成平台为基础的CAD/PDM系统间数据双向集成解决方案。方案包括：CAD/PDM系统间数据双向集成业务流程建模、CAD/PDM系统中的BOM和关联图文档数据表现形式、基于中间集成平台的CAD/PDM数据集成模式、嵌入式适配器、XML数据交换协议、消息机制,以及具有消息机制的SolidWorks/Mit-PDM嵌入式适配器软件开发。以某夹具产品的设计数据交换为例,验证了所提出方式的正确性。实际应用表明：该方案具有较好的柔性和扩展性,能实现异构CAD/PDM系统间的双向数据交换集成。     

CAD系统集成和集成技术剖析

系统集成能从根本上解决工程CAD技术应用中的分散独立和低水平重复问题,是进一步发掘计算机潜力的有效途径。文章以集成化的桥梁CAD系统的开发为背景,提出了由界面、工具和数据等三个层次组成的桥梁集成CAD系统结构,并针对软件工业的最新发展介绍了实现CAD系统集成的软件开发技术,包括面向对象的程序设计、图形界面和基础类库、软件构件化开发及数据库图形库连接等。     

Vector versus raster: a functional comparison of drawingtechnologies

Raster drawing systems have emerged as an alternative to more traditional vector-based CAD drafting systems. With engineering drawing in mind, the author compares the functional capabilities of these technologies and explores means for integrating the best features of both. The characteristics examined are not those of any particular raster or vector implementation but are derived from the underlying technologies. Three means are provided to blend the capabilities of raster and vector systems, each resulting in drawing systems that have capabilities beyond those of either system alone     

面向图形集成方法—一种实用,可行的集成化方法

图形处理不仅是ＣＡＤ／ＣＡＭ集成系统中不可缺少的一部分，而且也是ＣＡＤ／ＣＡＭ集成系统中的关键技术之一，并贯穿于ＣＡＤ／ＣＡＭ的始终。本文从集成化的一般概念出发，以某实用型ＣＡＤ集成系统（ＡＣＤＳ）为例，在详细分析了系统集成化过程中的几个难点的基础上提出一种可行且实用的集居方法－图向图形的集成方法。     

并行工程在汽车车身开发与制造上的应用

本文分析了常规车身ＣＡＤ／ＣＡＭ技术所存在的弊病,提出了采用并行工程的原理进行车身开发及车身工装设计与制造的方法。重点介绍了实施车身并行工程要解决的关键性技术,诸如建立集成化的产品数据模型、ＣＡＤ／ＣＡＰＰ／ＣＡＭ集成技术、建立多功能小组、计算机技术支持等。     

A Data Manager for Engineering Applications

Efficient data management is crucial to the success of a CAD/CAM system.Traditional databas systems,designed to deal with only regular and structural data,cannot efficiently manage design data.In this paper,we present a data manager called EDBMS/2,which has been developed by our laboratory for engineering support applications.EDBMS/2 has a data model that combines features of both relational and semantic ones and owns flexible abilities for modeling engineering data,such as variable-length data processing,integrated management of structuresd data and unstructured data,and composite object handling.Mechanisms based on DBV and DBV graph concepts,proposed in EDBMS/2 ,make EDBMS/2 own powerful abilities for version management and run efficiently.By now,EDBMS/2 has been used successfully in EDCADS(integrated Electronic Devices CAD environment)project and as a lower level support to develop and object-oriented DBMS for mechanical engineering.     

Integration of CAD/CAm as seen from the production planners point of view

CAD/CAm is supposed to be one of the new tools to obtain increased productivity and flexibility in mechanical engineering. However, most of the existing systems are still far from satisfying the users with respect to “human-like” communication. Most of the systems are either CAD or CAM oriented. To reach a real step forward, integration and better user-communication is needed. One of the first tasks to be performed after the design phase is process planning. The purpose of this planning is to select processes and operations for an optimal production. This is a creative task and is therefore dependent on long experience and very skilled planners. The article describes process planning in general and communication with CAD in particular. Some new developments using an integrated product model are described.     

Integration of topology and shape optimization for design of structural components

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