【正文】 dologies of the engineering process. The GVP provides functionally valid alternatives for engineers to select and manipulate. The 12 engineers add their judgement to optimize final systems designs. A generative virtual prototype (GVP) is a system model that represents both the geometric and nonD. Calkins, et geometric attributes of a product (an object) which are embedded in the KBE model. It stores knowledge about a system in a product model posed of design and manufacturing engineering rules,which address both geometric and nongeometric issues. A generative virtual prototype is a bination of these design rules and includes a set of engineering instructions used to create the design,that is, the vehicle geometry. The generative virtual prototype represents the engineering intent behind the geometric design. It can store product information such as geometry and material specifications as well as process and performance information. The generative virtual prototype paradigm is defined as follows： Generative： generate or automatically produce an instance of the virtual prototype in response to an input state vector. Take input specifications, apply relevant procedures and generate a design automatically. When the requirements change, the design is updated immediately along with all of performance outputs. Virtual： in effect although not in actual fact： a puter based model Prototype： original model or example of a particular type. Design rules KBE is based on the use of design knowledge in the form of ‘design rules’. The design rules form the kernel of an object. Design rules prise four basic categories： 1. Heuristics： prised of experimental rules of thumb and ‘best practices’.Usually based on corporate culture design heuristics. These are of the type, If (condition is true), then (action remended). 2. Empirical design rules： these rules are based on curvefitted expressions that are developed from experimental data. Metamodel technology used to develop models of plex systems. 3. Legislated constraints： these are prised of rules established by law or by engineering standards. 4. Laws of physics： based on first principles in the form of analytical or numerical models. Also known as parametric rules. These rules are usually simple algorithms that would be 13 solved using spreadsheet models. Design rules are used to synthesize the knowledge in the knowledge base and to establish how the knowledge is used in a given model. The design rules are used to both define and relate the attributes in a KBE model. The methods and processes of an engineer are mimicked by these rules. Design rule types include： . calculations . conditionals . lookup databases . fixed . variable . references . execute external programs . selections . optimizations. 。 KnowledgeBased Engineering (KBE) Design Methodology 7 BACKGROUND The development of plex systems requires a sequence of engineering and management decisions which must satisfy many peting requirements. Design is recognized as the primary contributor to the final product form, cost, reliability and market acceptance. The highlevel engineering design and analysis process (conceptual design phase) is particularly important since the majority of the lifecycle costs and overall quality of the system are determined during this phase. The major opportunities for cost savings occur in the earliest phases of a product design. Approximately seventy per cent of the lifecycle costs are frozen by the end of the conceptual design phase, Fig. 1. The key to shortening the design cycle is to shorten the conceptual design phase, which will also reduce the amount of engineering i