EBF3PanelOpt: An optimization framework for curvilinear blade-stiffened panels

A new framework, EBF3PanelOpt, is being developed for design and optimization of complex, multifunctional, aircraft structural concepts like pressurized non-circular fuselage structures to be used in hybrid wing/body vehicles that are subjected to complex structural loading cases. This tool can be used to integrate materials and structural concepts to exploit emerging additive manufacturing processes that offer the ability to efficiently fabricate complex structural configurations. Commercial software packages, MD-Patran (geometry modeling and mesh generation), MD-Nastran (Finite Element Analysis), are integrated in the EBF3PanelOpt framework using Python programming environment to design stiffened panels with curvilinear stiffeners. Typically, these panels experience multiple loading conditions during the operations of these vehicles. EBF3PanelOpt has the capability to optimize flat/curved multi-sided panels with straight/curved edges having curvilinear, blade-type stiffeners under multiple loading conditions. The mass of the panel is minimized subjected to constraints on buckling, von Mises stress, and crippling or local failure of the stiffener using global optimization techniques or gradient based optimization techniques. The panel/stiffener geometry is parametrized using design variables that include variables for orientation and shape of the stiffeners, the thicknesses and height of the stiffeners, and the plate thickness. The plate can have uniform thickness or non-uniform thicknesses for the pockets created by the stiffeners. During optimization, constraints can be applied for each of the loading conditions by aggregating all the responses using Kreisselmeir–Steinhauser criteria or using worst response amongst all the responses or applying all the constraints. Initially, the flat rectangular panel is optimized for the single load-case to study the effectiveness of the panel thickness option. Then, the optimization of flat rectangular and cylindrical panels is carried out for three sample load cases of practical interest. This paper discusses the advantages and disadvantages of the proposed constraints' application.