Two-level composite wing structural optimization using response surfaces

A two-level optimization procedure for composite wing design subject to strength and buckling constraints is presented. At wing-level design, continuous optimization of ply thicknesses with orientations of 0 degrees, 90 degrees, and +/-45 degrees is performed to minimize weight. At panel level, the number of plies of each orientation (rounded to integers) and inplane loads are specified, and a permutation genetic algorithm is used to optimize the stacking sequence in order to maximize the buckling load. The process is started by performing a large number of panel genetic optimizations for a range of loads and numbers of plies of each orientation. Next, a cubic polynomial response surface is fitted to the optimum buckling load as a function of the loads and numbers of plies of each orientation. The resulting response surface is used for the wing-level optimization. Rounding and manual adjustment are used to obtain the final design. The procedure is demonstrated using an example of a simple wing box design.