Multilevel optimization in aircraft structural design evaluation

Changes of the structural design are one of the essentials in the investigation and optimization of alternative and innovative aircraft concepts. In this paper the choice of an appropriate design is seen as an optimization problem and solved by the application of a multilevel optimization procedure based on detailed Finite Element models of certain structural parts. The design is variable by its principle layout, its material and its dimensions. At the top level an Evolution Strategy drives the topology parameters. The second level of the optimization procedure is based on the deterministic, gradient-based optimization method of MSC.Nastran® Sol200 that is used to optimize thicknesses and cross-sections of the model with respect to different design constraints. The model generation is based on Patran PCL-routines. A parallel evaluation is used to increase calculation speed. Two examples are presented in this context. The first one shows advantages of the multilevel approach in simultaneous sizing and topology optimization of a generic framework structure. The second example is an application to a structural design optimization of a Blended Wing Body aircraft fuselage structure. This example shows the full scope of the method by consideration of metal and composite designs in single, double and sandwich layout under multiple load and constraint conditions.