Optimum design of aircraft structures with manufacturing and buckling constraints.

摘要

Aircraft design incorporates a large number of structural and aerodynamic disciplines. Each discipline must be considered in order to obtain a feasible and optimum design. All too often, however, some constraints are left out of the optimization problem, leading to an "optimum" design that is not feasible. In practical terms the design looks good on paper, but does not perform well when tested, or can not be built as designed. The constraints developed in this dissertation are two that are commonly left out of aircraft design optimization problems. The first group of constraints ensures that the structure will be manufacturable. The constraints are especially useful for composite wing skins, because the flexibility allowed in the optimization of composites will often lead to unorthodox laminates. Composite laminates designed with optimization programs often have large variations in both the ply orientation percentage and the total laminate thickness across the plane of the laminate. Also, the ply orientation percentage is often outside the range that is recommended. The second constraint type is a panel buckling constraint. The loads from the finite element model are used in a closed-form buckling solution. The constraint prevents the wing skin from local buckling in the unsupported regions bounded by the ribs and spars. These constraints were used in a number of design studies that evaluated the relative impact of the constraints of the design weight. Also, a design and manufacturing case study was done. In this study an optimum design obtained by using the manufacturing constraints of this dissertation was compared with a conventional design of the same structure. The two designs were built and tested to determine the accuracy of the design and modelling techniques.