A two-level optimization feature for the design of aerospace structures

Abstract This work proposes and applies a two-level optimization feature for the design and analysis of reinforced shell structures for aerospace applications. A general-purpose finite element software (NASTRAN) is used as a first-level code to compute the loadings that act on panels. The panels are then optimized using a second-level code (PANDA2), which gives their optimum solutions by taking into account buckling and postbuckling elastic stability constraints. The PANDA2 code, which is based on pseudo-analytical formulations, leads to a considerable reduction of the requested computational efforts compared to the optimization made by NASTRAN. The proposed two-level feature, named NAPAO, builds a loop (between the NASTRAN and PANDA2 codes) that runs until a convergent solution is reached. Those substructures, such as longerons and stiffeners (which are not considered by PANDA2), could be optimized by referring to the solver that is available from NASTRAN. A number of examples that encompass simple structures as well as two complete space vehicles and an unconventional aircraft have been optimized. Metallic as well as composite materials were considered. It can be concluded that NAPAO is a very useful tool for the design process of complex aerospace structures. It gives accurate results and reduces computational costs compared to a standard optimization made when only using the general-purpose code.