Using experience to plan the synthesis of new designs

Engineering design is a creative process in which the experience and knowledge of the designer and the design specifications are combined. Facing a new design task, an experienced designer will easily recall a similar case which he or she met before and make an appropriate adaptation of the previous design solution to fit the new situation. This paper proposes a methodology for automating the use of previous design situations and their solutions to plan the synthesis of new designs. Using Experience To Plan The Synthesis Of New Designs M.L. Maher and F. Zhao Department of Civil Engineering Carnegie-Mellon University Pittsburgh, PA Engineering design is a creative process in which the experience and knowledge of the designer and the design specifications are combined. Facing a new design task, an experienced designer will easily recall a similar case which he or she met before and make an appropriate adaptation of the previous design solution to fit the new situation. A less experienced designer may go through much trial and error before a suitable design solution is achieved. The difference between the two is experience. This paper proposes a methodology for using previous design situations and their solutions to plan the synthesis of new designs. The area of application is the preliminary structural design of buildings. A popular way of using experience to solve new problems is to develop an expert system that contains an appropriate representation of the relevant experience. Though there are several expert systems in practical use, the development of expert systems is still at a primary stage. Most of the successful expert systems, such as MYCIN, DIPMETER, etc., are diagnosis or classification systems. Design problems are more difficult to solve using existing expert system techniques because they require complex representations and strategies. However, knowledge based expert system techniques have been used to develop design assistants for the preliminary structural design process The techniques employed have relied on the definition of a knowledge base containing objects representing structural subsystems and rules representing the appropriate way to combine the objects and compare the solutions. This paper describes a methodology for expanding the knowledge that is used during the structural design process to include experience in the form j previous building design situations and solutions. Specifically, this knowledge is used to plan :>--} synthesis of alternative structural systems for a given building design problem. This paper is organized into four sections. The first section introduces structural design j d highlights the phases relevant to this paper. The second section provides a brief overview f knowledge based approaches to structural design and relevant strategies. The third sec: :n describes a methodology and prototype implementation for using design experience directly. F ' : . Section 4 provides a summary of the work and some preliminary conclusions. University Libraries Carnegie Mellon University irtsburgh, Pennsylvania 15213 11 July ' •": 1. Structural Design The structural design process starts with the definition of a need to transmit loads in space to a support or foundation, subject to constraints on cost, geometry, and other criteria. The final product of the design process is the detailed specification of a structural configuration capable of transmitting these loads with the appropriate levels of safety and serviceability. The design process may be viewed as a sequence of three stages, as illustrated in Figure 1-1 and described below. (1) PRELIMINARY DESIGN (conceptual design) involves the synthesis of potential structural systems satisfying a few key constraints, and the selection of one, or at most a few, systems to be pursued further. Synthesis requires a knowledge of structural subsystems and their appropriateness for different situations. (2) ANALYSIS is the process of modeling the selected structural system and determining its response to external effects. This process involves transforming a physical structure to a mathematical model, analyzing the model, and interpreting the results of the analysis in terms of the actual physical structure. (3) DETAILED DESIGN is the selection and proportioning of the structural components such that all applicable constraints are satisfied. There may be significant deviations between the properties of components assumed at the analysis stage and those determined at the detailed design stage, which would necessitate a reanalysis. Cther major and minor cycles of redesign may also occur. The process continues until a satisfactory (or optimal) design is obtained. The conceptualize-analyze-detail cycle is typical of many Jos.yn paradigms. PROBLEM DEFINITION SYNTHESIS