A two-level strategy for aeroelastic optimization of a 3D wing with constant and variable stiffness skins

In this work, optimization strategies employing a standard heuristic free-derivative algorithm combined with a first-order gradient approach are used to maximize the flutter or divergence airspeed, using the fibre material orientations as design variables. The aeroelastic stability analysis calculations are performed by a classical PK method. The finite element method is used to obtain the structural modes and frequencies and the unsteady aerodynamic influence coefficient matrices are obtained with a doublet-lattice model. Numerical studies are performed with a complex 3D model that includes curved surfaces and internal elements such as spars and ribs. The main goal of the article is to use the heuristic part with a small number of parameters, to reduce the design space and provide an efficient initial guess for the gradient search, so that the optimization complexity is substantially reduced. Results for constant and variable stiffness composite wings are presented for laminates with different numbers of plies. It is shown by several examples that the pres.