Global-local multidisciplinary optimisation for the evaluation of local constraints on finer meshes in preliminary aircraft design

Multidisciplinary design optimisation (MDO) is a methodology increasingly being used in the preliminary design of aircraft. To limit the computational cost of the procedure, it is generally based on coarse models, which do not accurately capture the internal deformation of details with a complex geometry. Therefore, it is not possible to apply constraints in these areas and designers are limited to a conservative pre-sizing of these parts, which are then kept fixed during the optimisation. In this paper we expose the limitations of this approach and present a novel methodology for the preliminary sizing of aircraft, based on global-local MDO. The commonly used coarse model is used together with finer local models, for the parts where additional accuracy is needed. The global-local analysis solves the internal deformation field with sufficient accuracy for the evaluation of local constraints. Furthermore, thanks to the formulation we introduce to compute the coupled sensitivities, the optimiser successfully finds a locally feasible design.