Shape optimisation of blended-wing-body underwater gliders based on free-form deformation

As a type of Autonomous Underwater Vehicles (AUV), blended-wing-body underwater gliders (BWBUGs) have drawn much attention due to their unique performance advantages in long-distance navigation missions. Because the configuration is the direct component to influence the navigation efficiency, it is significant to perform shape optimisation of BWBUGs. In this paper, an optimisation framework is presented, where Free-Form Deformation (FFD) is adopted for geometric parameterisation. Besides, an Euler-based CFD solver with a discrete adjoint method is applied for numerical simulation and gradients calculation, and Sequential Quadratic Programming (SQP) is employed as the optimiser. With the help of the proposed framework, an optimised BWBUG is regarded as the initial shape and four shape optimisation cases are carried out for different design purposes. All the objective functions aim to increase the lift-drag ratio under the thickness and volume constraints. The simulation results show that all the cases achieve a higher lift-drag ratio.