Fuzzy Move Limit Evaluation in Structural Optimization

Many recent improvements have been made in the field of optimization, among which is the introduction of the theory of approximations to improve problem convergence and reduce the computational burden of repeated full analyses. This theory states that an approximation can be made in the neighborhood of the current design point, and the optimizer can make repeated calls to this approximation in lieu of the analysis program. However, since the approximation is local, the allowable changes in design variables have to be restricted. These restrictions are the move limits. We propose in this paper to increase or decrease the move limits using a fuzzy logic algorithm. The fuzzy rules take into account two parameters that are the exponent computed by the Two–Point Exponential method, an approximation method, and the effectiveness coefficient which compares the slope of constraints to that of the objective. In spite of the fact that the fuzzy rules are still dependent on the user, the algorithm provides a very easy interface to the user to set the move limits according to appropriate criteria and achieve a low and steady number of iterations irrespective of the maximum move–limits input by the user.