Keywords: computer aided design, finite element, motion analysis, design integration, predicate logic.

The advancements in computer-aided design (CAD) software have revolutionized the traditional design process. The availability of sophisticated solid modeling tools has resulted in increased productivity and improved product quality. Computer- based analysis tools used for evaluating design or process performance have also made significant advances and are capable of analysing complex problems on a routine basis. The next stage in the development of computer-aided engineering tools is the seamless integration of the design generation and design evaluation phases. To date, there is in general no single commercial system that provides solutions to all aspects of the product development process of a specific industrial product. This paper addresses the development of a mechanical design system based on the integration of a CAD system with motion analysis (MA) and finite element analysis (FEA) codes. The basis for this integration involves the use of a common product data model and a mechanism for automating the exchange of information between design and analysis phases using predicate logic. The aim of the work presented is to develop a facility that will allow the designer to perform motion analysis and finite element analysis from within the design environment using the virtual design model without having to construct an analysis model. The approach is based on the use of predicate logic to translate the functional characteristics of the product data model into a script that may be used as input to commercially available analysis software.

There are many CAD software products available that are capable of representing the geometrical characteristics of a particular product's design. These software packages incorporate various features depending on the level of sophistication demanded by the target market. Some packages demonstrate limited functionality and are primarily used as a more productive substitute for the drafting board whilst other products are advanced modular systems that are capable of facilitating a variety of operations ranging from design development via solid modeling through to finite element mesh generation. In order to support the computer-aided design of multi-body systems, the software tools used should include the following functionalities:

1. Solid modeling capability - The components of the mechanical system should be defined as completely and as accurately as possible. Solid models are capable of conveying information related to visual appearance as well as to the rigid body data required for performing dynamic analysis.
2. Mechanism design capabilities - The design environment should include features such as joints, springs, dampers as well as forces and displacements applied to the components of the mechanical system.
3. A mechanism for extracting the required analysis specific data from the product data model and channelling it to the analysis code it in an acceptable format.

The development of a computer-aided integrated mechanical design system for the design and analysis of mechanical systems is based on the combination of a CAD system based on a set of graphics libraries and commercially available motion analysis and finite element analysis codes. The main aim of the system is to provide a seamless interface between the design generation and analysis phases of the product development process. This has been achieved by considering two aspects:

1. The use of an extended product data model contained within a centralised product database. This database contains all the information required to describe the geometric and functional characteristics of the design. The database is managed using a relational database management system.
2. The use of an automated mechanism to facilitate the exchange of mechanism specific data for the analysis of the mechanical system. This mechanism is based on the use of predicate logic to translate the product information into a script that may be used as input to the analysis code. User interaction is therefore not required in the construction of the analysis model.

1

Gabbert, U., Wehner, P., "The Product Data Model as a Pool for CAD-FEA Data", Engineering with Computers, 14, 115-122. 1998. doi:10.1007/BF01213585

2

Hardell, C., "An Integrated System for Computer-Aided Design and Analysis of Multi-body Systems". Engineering with Computers, 12, 23 � 33. 1996. doi:10.1007/BF01200259

3

Lakmazaheri, S., Edwards, P., "Linguistic Approach to 2D Geometric Modelling of Hierarchical Systems", Journal of Computing in Civil Engineering, 165 � 174, July. 1997. doi:10.1061/(ASCE)0887-3801(1997)11:3(165)

4

Lakmazaheri, S., "Logic-based 2D Geometric Modelling in a CAD Environment". Engineering with Computers, 14, 123 � 138. 1998. doi:10.1007/BF01213586

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