Global local structural optimization of transportation aircraft wings

Abstract

The study presents a multilevel optimization methodology for the preliminary structural design of transportation aircraft wings. A global level is defined by taking into account the primary wing structural components (i.e., ribs, spars and skin) which are explicitly modeled by shell layered finite elements. Wing substructures such as stringers are implicitly represented by an equivalent formulation of the structural properties. The global level is analyzed and optimized for minimum mass under element stress constraints. Selected wing skin panels are extracted from the global wing and further remodeled with detailed stringers. Boundary conditions are transferred from the finite element (FE) global level solution to the FE detailed stiffened panel models. A finite element analysis is performed on the selected local level panels, which are mass optimized under additional stability constraints, providing a new optimal skin-stringer layout. The global model is then updated with the local level optimum results, and a number of iterative global-local optimization loops are executed. In the current study the DLR in-house tools are used for the structural modeling and sizing of the wing global level, and a new stiffened panel generator is introduced for the local level modeling. A local optimization module which includes instability failure criteria is implemented to redesign the stiffened panels for minimum mass. The global and the local levels communicate through a framework developed to assist an automated and flexible multilevel optimization, and to minimize the time consuming activities required to generate detailed finite element models. The methodology is tested and demonstrated using a transportation DLR aircraft wing geometry as global level, and a variable number of upper skin blade stiffened panels remodeled in detail as local level.