Multistage design of high-aspect-ratio wings: Geometrically nonlinear topology optimization with aero-structural coupling

High-aspect-ratio wings for solar-powered UAVs (Unmanned Aerial Vehicles) require ultra-lightweight structural designs capable of withstanding large deformations induced by aerodynamic loads. Traditional topology optimization methods often overlook the interplay between geometric nonlinearity and aero-structural coupling, limiting their effectiveness for flexible wing systems. This study proposes a multi-material topology optimization framework that integrates geometric nonlinearity with weak aero-structural coupling. The three-field approach, incorporating directional length scale control and deformation control, is employed for the geometrically nonlinear multi-material optimization. A nodal displacement-based inverse modeling method enables efficient data transfer between aerodynamic and structural meshes, while a deformation-driven load update strategy reduces computational costs. A straight wing with four case studies demonstrates that incorporating aero-structural coupling shifts high-stiffness material toward the wing root, optimizing load transfer and reducing deformation. The reconstructed truss-based design achieves an 11.29 % mass reduction via size optimization while maintaining bending and torsional constraints. This framework bridges structural optimization with aero-structural coupling, providing a systematic approach for designing lightweight, main spar-ribs based, and deformation-resistant wings.