Development of a Framework for the Design Optimization of Unitized Structures

A framework is developed for design optimization of unitized structures with curvilinear stiffeners. A typical stiffened panel from an aircraft structure subjected to combined compression-shear loading is optimized using two curvilinear stiffeners. The Response Surface Methodology is used for optimization. The Finite Element Analysis (FEA) is carried out using commercial Finite Element software MD.PATRAN and MD.NASTRAN. The framework, for creating interfaces between parametric modeling, FEA, and Optimizer, is developed in PYTHON programming environment. While optimizing the mass of the stiffened panel, constraints are placed on critical buckling load and the Von Mises stress. The optimization consists of shape as well as sizing design variables. The design variables include stiffener orientations and dimensions and the panel thickness. The optimization results presented in this paper show the advantage of curvilinear stiffeners over conventionally used straight stiffeners, especially for non-uniform boundary conditions. This optimized stiffened panel will be fabricated and the experimental validation will be carried out in collaboration with Lockheed Martin Aeronautics Company and NASA Langley Research Center. To bring the FEA as close as possible to the experimental results, the experimental test fixtures are also modeled in detail to capture the boundary conditions used in experimental tests. I