A HYBRID TWO-LEVEL APPROACH USED IN THE OPTIMIZATIONA OF AN AERONAUTICAL COMPOSITE STRUCTURE

Nowadays composite materials are becoming increasingly popular, due to their ability to improve the structural performance and also to be tailored to meet specific de- sign requirements for a given application. In the case of a wing composite structure, this is composed of a large number of panels, which have to be designed simultaneously to obtain an optimum structural design. In general, the wing-box design process is a multidisciplinary one, involving couplings and interactions between several disciplines such as aerodynamics, struc- tural analysis, dynamics, and aeroelasticity. Therefore, the development of multidisciplinary design optimization (MDO) techniques, in which different disciplines and design parameters are coupled into a closed loop numerical procedure, seems appropriate to face such a complex optimization problem, such as a multilevel approach. The aeroelastic optimization here pre- sented is relevant to the determination of the orientation of different layers which constitute the composite panels of a wing structure, that realizes the maximum flutter speed. By us- ing a multilevel approach, the aeroelastic optimization problem can be decomposed into one subproblem, affecting the global response of the wing, and several independent subproblems, affecting portions of the wing. In the first level, the anisotropy parameters will be defined by a real coded Genetic Algorithm (GA), while at the second level of the optimization process, the ply orientation for the laminate composite plates will be defined by another Genetic Algo- rithm, with an integer encoding. For each one of the GAs, a local search procedure heuristic is applied to improve the best solution found by the GA. The hybrid strategy is shown to be efficient in maximizing the value of flutter velocity.