An integrated Global/Local Optimization Framework for Subsonic Wing with Ribs having Holes

This research considers the topology and sizing optimization of ribs in a wing box with the objective to minimize the weight subjected to the stress and buckling constraints. The ribs cannot be designed just as a simple thin flat plate, as it is important to provide holes at some specific locations in the ribs to provide openings for the passage of wires and fuel pipes. The holes make the ribs both more susceptible to buckling and also lead to high stress concentration around their edges. The stiffness of the ribs can be increased by providing stiffeners at specific locations and around the hole.  The curvilinear stiffening tries to utilize the larger design space created by additive manufacturing techniques like Electron-Beam-Free-Form-Fabrication, Friction Stir Welding, and Selective Laser Sintering. We have developed two optimization frameworks namely EBF3WingOpt and EBF3PanelOpt to design the internal structure of the wing with curvilinear spars and curvilinear ribs with holes stiffened with curvilinear stiffeners.  Commercial software, MSC.Patran (for geometry and meshing), and MSC.Nastran (for finite element analysis) are integrated in the optimization process. The EBF3WingOpt minimizes the weight of the wing with unstiffened structural elements with constraint on von-Mises stress and flutter velocity for various flight conditions. EBF3PanelOpt creates a more optimum structure of each of the ribs and the panel with stiffener. The EBF3PanelOpt uses the displacement output of EBF3WingOpt as the boundary condition for each of the ribs and panels.  The application of the optimization of ribs with curvilinear stiffeners result in significant weight reduction compared to use of unstiffened ribs.