Direct search method to aeroelastic tailoring of a composite wing under multiple constraints

In order to avoid the possible breakdown of usual optimization methods using gradient information, which is caused by a discontinuous behavior of the flutter velocity as a function of design variables, a feasibility study is made using a direct search method that does not depend on the derivatives of objective/constraint functions. The complex method, as one candidate for such a method, is applied to the minimum weight design of high-aspect-ratio forward/aft swept wings under strength and aeroelastic constraints. It is shown that the complex method is very effective and robust in finding the optimum fiber orientations and the thickness distributions of the upper/lower skin panels of the wing box, especially when the flutter velocity is one of the constraint functions. The deficiency of the complex method is that the rate of convergence rapidly degrades with increasing number of design variables.