Skin Designs Using Multi-Objective Topology Optimization

Abstract

Morphing aircraft structures with stretching surfaces require load-bearing flexible skins which can undergo large deformations, require little energy to morph and have a high outof-plane flexural bending stiffness. One solution proposed is to use sandwiched skins made of flexible face-sheets and a cellular core. The cellular core can be designed to be highstrain capable, to have a high bending stiffness for out-of-plane deformations, to require little work to morph and to be light-weight, while the face-sheets provide a smooth surface for the air-flow. This paper investigates the best topologies of the cellular cores that could be used for flexible skins. Two types of morphing deformations are considered: in-plane one-dimensional morphing and in-plane shear-compression morphing. Such deformations can be used in applications such as wing-span change, chord change and area change. The topologies are found using a multi-objective genetic algorithm coupled with a local search optimizer. In addition, morphological filtering is used to remove small features in the topologies. Linear and non-linear deformations are considered to investigate whether one can use a linear approach to design skins for gross morphing deformation. No single solution emerges as the clear best solution because of conflicting objectives. The solutions found show different features which help increase the flexural bending stiffness or decrease the work. Some similarities are found in the topologies for one-dimensional morphing and shear-morphing. Honeycomb-like topologies are found for both type of morphing deformation.