Design Optimisation of a Lightweight Aerodynamic Fairing for Vibration Fatigue

A methodology is developed for optimising the design of flap track fairings (FTFs), and other lightweight structures attached to wings, by ensuring that constraints on fatigue damage are satisfied whilst the weight is reduced. A representative Finite Element (FE) model of a flap track fairing is modelled using shell elements and then was subjected to synthetic random fatigue loading. The resulting Fatigue Damage is computed in the frequency domain using the Dirlik method. The structure is initially segmented into 448 regions with separate thickness variables. Local sensitivity analysis is used to group these segments into 30 regions for use in optimising the final design. A Sobol global sensitivity analysis is used to determine which parts of the FTF have the greatest influence on the fatigue life. Finally, a genetic algorithm is used to obtain an optimum lightweight design which satisfies defined fatigue damage constraints using the chosen variables. An additional optimisation which satisfies constraints on stress and deflection under static loading as well as fatigue damage is run. Compared to a uniform thickness design, a 45\% mass reduction was achieved for optimisation with a fatigue damage constraint, and a 27\% mass reduction when fatigue and static loading constraints were included.