Design- and Manufacturing Constraints within the Gradient Based Optimization of a Composite Aircraft Wingbox

Kurzfassung

The gradient-based structural optimization plays an important role in the multi- disciplinary optimization of composite wings. To obtain the necessary convex design space, lamination parameters are used to parametrize the composite laminates. In contrast to metallic structures, more criteria must be considered during the opti- mization to determine a realistic result. The intention of using such criteria is to avoid the occurrence of critical failure modes and simultaneously guarantee a manu- facturable design. Common examples of these rules, usually defined on ply-level, are the symmetry of stackings in thickness direction for a better stress distribution in the laminate or the continuity of plies between neighbouring structural regions to ensure the manufacturability of the design. Up to now the ply-based definition of the design rules facilitated constraint formulations for genetic optimization algorithms, because they directly use the laminate stacking sequences as discrete design variables. In the present work a new method is presented to correlate discrete design rules with the lamination parameter space for a selected set of design- and manufacturing rules and a pre-defined set of ply angles. The method is used to derive constraints for the con- tinuous lamination parameter space of a gradient-based optimization process. The constraints interrelate the design variables of adjacent structural regions. This causes a restriction of the feasible domain of the design space in a way that selected design rules are fulfilled. The influence of the constraints on the structural design is shown with the help of a gradient-based optimization process which is applied to a generic wing box.