A CASCADE OPTIMIZATION STRATEGY FOR SOLUTION OF DIFFICULT DESIGN-PROBLEMS

A research project to evaluate comparatively ten different non-linear optimization algorithms was completed recently. A conclusion was that no single optimizer could successfully solve all the 40 structural des ign problems in the test-bed, even though most optimizers successfully solved at least one-third of the problems. We realized that improveme nts to search directions and step lengths, available in the ten optimi zers compared, were not likely to alleviate the convergence difficulti es. For the solution of those difficult problems we have devised an al ternate approach called, the cascade optimization strategy. The strate gy utilizes several optimizers, one followed by another in a specified sequence, to solve a problem. A pseudo-random dumping scheme perturbs the design variables between the optimizers. The cascade strategy has been tested out successfully in the design of supersonic and subsonic aircraft configurations and air breathing engines for high-speed civi l transport applications. These problems could not be successfully sol ved by an individual optimizer. The cascade optimization strategy, how ever, generated feasible optimum solutions for both aircraft and engin e problems. This paper presents the cascade strategy, solution of airc raft and engine problems along with discussions and conclusions. (C) 1 997 by John Wiley & Sons, Ltd.