Structural wingbox optimization in a coupled FSI problem of a flexible wing: FEA sol200 versus surrogate models

Abstract

This work presents a two-step approach that was adopted in a collaborative multi- disciplinary work named OSYCAF for wing-box design optimization. This approach encompasses: 1) the initialization of a full parametric PCL flexible wing optimization with analytical design, and 2) the comparison of the sol200 optimization (mass of the wing) with a simple surrogate model (also known as Reduced Order Model due to the quadratic form in the regression). Our main objective is to optimize the global structure weight while respecting all structural criteria and constraints, and using the spars and skin thickness as design variables. We show that after the optimization the importance of upper and lower skins is minimized and almost all efforts are concentrated on spars, specially the rear spar. It is also shown that the strain criterion is stronger than the stress one, which considers shear and buckling deformations as the critical design points, although fatigue is also relevant when designing the lower Wing-Box Skin. We show the results obtained for the local optimization of several considered NACA-4 profiles by using an automated process.This work is developed such that an association with an aerodynamic approach using CFD would make possible to create a variation of the required profile to construct the real wing that, when deformed, would assume its best shape in terms of aerodynamics, still respecting all structural constraints and minimum weight possible.