Structural Optimization of Thin Walled Semi-Monocoque Wing Structures Using Different Types of Finite Elements in the Preliminary Design Phase

Optimization techniques play a vital role in aerospace structural design. The main purpose in design optimization is to find the best ways a designer or a decision maker can obtain maximum benefit from the available resources. In this article, structural optimization of wing structures is performed by the finite element software MSC.NASTRAN using the gradient based option. Different one and two dimensional element pair combinations, which are typically used in practice, are used to model the sub-elements of semi-monocoque wing structures while carrying out structural optimization. The main objective of the study is to investigate the effect of using different one and two dimensional finite element pairs on the final optimized configuration of the wing structure, and propose alternative optimized initial sizing to be considered as starting points in the detailed structural design phase. During the optimization study, convergence is achieved with different mesh sizes, and the objective function is defined as minimizing the weight of the wing subject to stress, displacement and local buckling constraints. In case of optimization of wing structures with many design variables, it is very probable that local optimum designs may be reached if different starting values are used for the design variables during the optimization. Therefore, the effects of different starting points, as well as the effect of relaxing the constraints, on the optimized wing configurations are also investigated. Conclusions are also inferred with regard to the sensitivity of the optimized wing configuration with respect to the choice of different element types in the finite element model. Final optimized wing structure configurations are also compared with the simplified method based designs, performed in another study, which are also optimized iteratively.