Designer's dilemma

Performance based design systems are characterised through the use of performance related evaluation methods or by providing design environments which are restricting the design space according to performance criteria. The performance of a design can be evaluated by numerical simulations. With the use of numerical simulations a fundamental dilemma appears: the precision implied in numerical simulations and the imprecision of the design process itself are systematic contradictions. User control or user interaction in open systems places the user into charge of the imprecision required by the design process. In closed systems, as the below described evolutionary system, methods of imprecision have to be integrated i.e. into the precise simulation based evaluation procedure. Through tolerant selection methods and the gradual evaluation of individuals the rigid and precise system can be guided towards a design system rather than an optimisation system. Due to technical requirements which are related both to the fact of using computer systems but also to the systematic conditions implied to simulations the use of the tolerant selection methods is limited.