Coupling functions treatment in a bi-level optimization process

The optimization of complex engineering systems is often a mix of multi-objective optimization process - each service, discipline has to fulflll several objectives - and multidisciplinary optimization process - several disciplines are required. The disciplines are bound to each other: outputs of one discipline are used as input of other disciplines (the coupled variables) and a discipline can not have a direct access and knowledge to the whole set of variables. An approximation of the coupled variables is thus needed. The Collaborative Optimization Strategy for Multi-Objective Systems (COSMOS) has been developed at IRCCyN to perform simultaneously multi-objective and multidisciplinary optimization while discipline autonomy is guaranteed. It uses a simple method for the approximation of coupled variables and assumes that the quality of the approximation will increase as the algorithm converges to optimum solutions. In this paper, experiments are made to verify wether this assumption is true. We show that satisfying results are found on some test problems but limits of the methods are pointed out. (c) 2008 Journal of Mechanical Engineering. All rights reserved.