Methods for designing the next generation of aircraft architectures using topology optimisation

The need from energy efficient transportation has resulted in a growing interest in new aircraft configurations such as the Blended Wing Body. There is very little collective knowledge on the optimal structural layouts of these aircraft, and the paradigms applied to conventional aircraft may not be applicable. Topology optimisation is the logical tool to employ in this type of situation, as its generality removes the need for any assumption of what the structure should be. Several barriers exist that stand in the way of topology optimisation’s use in designing aircraft structural architectures. Firstly, the displacements caused by spanwise bending of the wing are large compared to those caused by twisting and localised deformation of the wing. Therefore, the typical minimum compliance formulation of the topology optimisation problem favours structures that improve bending stiffness. There are also considerable difficulties associated with the implementation of buckling constraints in topology optimisation. This thesis explores these issues, and methods are proposed for circumventing them. The effect of problem formulation on optimal topologies is demonstrated through the use of various design and manufacturing constraints, SIMP penalisation factors, and load cases. Approaches for reducing the significance of spanwise bending in the topology optimisation problem are evaluated and shown to be capable of generating designs that resist bending, torsion and localised deformation of the wing. Methods are then proposed for including topology optimisation in a framework for designing aircraft structural architectures, along with shape and sizing optimisation. Shape optimisation is used to find optimal rib locations and orientations for structural stability. The inclusion of these ribs as non-designable structures in the topology optimisation problem is shown to have a substantial effect on the optimal material distributions, due to the load carrying capacity of the ribs. The developed methods are applied to designing the structural architecture of a Blended Wing Body UAV, and are shown to offer potential reductions in structural mass.