Global-Local Optimization of Stringer Stiffened Panels for Transportation Aircraft Wings

Higher order effects play an increasingly dominant role in the design of transportation aircrafts with high aspect ratio wings. Considering these effects requires high fidelity methods, which are based on explicitly detailed models. However, for effcient and fast simulation techniques, pre-design of aircraft structures relies on finite element models of significantly reduced complexity This conventional procedure enables a fast solution for large problems, but does not provide enough information for the sizing of the wing panel substructures such as the stringers. In order to cope with strength and stability requirements the detailed sizing of stringer sti_ened panels is necessary. The global-local optimization offers a suitable approach to deal with the detailed models and to enable the fast solution of large problems at the same time. The thesis has been carried on at the German Aerospace Center (DLR) Institute of Composite Structures and Adaptive Systems in Braunschweig. The work presented introduces the framework GLOPTImos, backbone of the multilevel process developed. The wing is globally modeled by finite elements, where the stringer properties are implicitly represented by an equivalent shell layer. Thus the global level is analyzed and optimized to minimize the mass under element stress constraints. Selected wing skin panels are extracted from the global wing and further remodeled with stringers details. Nodal displacement are transferred from the global solution to the local level. The finite element analysis is performed on the selected panels which are mass optimized under additional stability constraints. The global model is then updated with the optimum local level results, and a number of iterative global-local optimization loops executed. The thesis work provides a complete suite of developed tools suitable for automated multilevel optimizations, which minimizes the repetitive time consuming activities required to generate the _nite element models. The method is demonstrated using as design case the F7x wing geometry as global level, and three upper skin blade sti_ened panels remodeled in detail as local level. The global- local process is delivered as an automated package executable in batch mode to minimize the user intervention, and to speed up the computational time.