Rule- and Case-Based Assistant for Conceptual Structural Design Associated with Genetic Operations.

Abstract

In the conceptual stage of structural design, the specified requirements are not sufficient for determining a unique solution, and subjective decisions based on a designer's preference play an important role similarly to the case of objective ones. Suggestions of various possibilities of design could assist the designer at this stage. In the conventional rule-based approach, the attributes of a design object are sequentially determined by referring to the design rules. Once the attribute values are determined, they work as absolute assumptions in subsequent decisions as long as backtracking is not activated. This is not beneficial in keeping the attention of the designer free from the tentative decisions made previously. In this study, the design case is considered as a phenotype of a chromosome that contains redundant information in morphogenesis. This enables us to reproduce the design candidates that have geometries/topologies varying from those of slightly different chromosomes. The past design cases are organized as the genetic case-base population and this population is modulated by referring to each of the design criteria and to the similarity to the candidate in terms of the design rules. The resultant population has heterogeneous individuals in this context, and the individuals generated from the population by genetic operations are delivered to the designer as suggestions. The preference of each design criterion is represented by the presence of the population correponding to the criterion through interactions with the designer. In this framework, the possibility, that is left behind on the conventional rule-based process, can be emerged by the genetic case-based approach, and a diversity of candidates is retrieved. The proposed idea is exemplified by a skeletal design of a bridge structure and the relaxation of determinancy in the rule-based approach is demonstrated.