High-Fidelity Hydrostructural Design Optimization of Lifting Surfaces

Abstract

Recent advances in high-performance computing and the efficiency of numerical solvers have made it possible to use sequential high-fidelity hydrodynamic and structural simulations to carry out design and optimization of marine lifting surfaces such as hydrofoils and propulsors. However, the design optimization of flexible hydrofoils and propellers requires coupled hydrodynamic and structural analysis to achieve a truly optimal, physically realizable, and structurally sound design. To address this need, the thesis presents an efficient high-fidelity hydrostructural design optimization with large numbers of design variables, multiple design points, as well as design constraints to avoid cavitation, avoid excessive stresses, and satisfy manufacturing tolerances. The hydrostructural solver couples a 3-D nearly incompressible Reynolds-averaged Navier–Stokes solver with a 3-D structural finite-element solver. The hydrostructural solver is validated by comparing the hydrodynamic load coefficients and tip bending deformations of a cantilevered aluminum hydrofoil with a NACA 0009 cross section and a trapezoidal planform. A coupled adjoint approach for efficient computation of the performance and constraint function derivatives with respect to 210 shape design variables is used. Using this state-of-the-art hydrostructural design optimization tool, a multipoint optimization yields improved performance over the entire range of expected operating conditions with significantly increased cavitation inception speed. The hydrostructural optimal result is compared to an equivalent hydrodynamic-only optimization, and results show that only the hydrostructural optimized design satisfies the stress constraint up to the highest expected loading condition, highlighting the need for coupled hydrostructural optimization. The proposed approach enables multipoint optimization of the hydrostructural performance for hydrofoils and marine propulsors, and it constitutes a powerful new tool for improving existing designs, and exploring new concepts. The thesis also presents the first experimental validation of a numerically optimized hydrofoil designed using the developed hydrostructural optimization tool. Good agreement is observed between the predictions and measurements, where both showed that the optimized hydrofoil yielded an overall increase in the lift-to-drag ratio of 29% and significantly delayed cavitation inception compared to the NACA 0009 baseline.

In keeping up with the recent advances in material and manufacturing technology, the possibility of using composite material for marine propulsors is investigated. Combined experimental and numerical studies are presented to understand the benefits and challenges of using composite material for the maritime applications. The composite hydrofoils are manufactured by Defence Science and Technology Group (DSTG), Australia and are tested in the cavitation tunnel at Australian Maritime College (AMC), Australia. Results are presented for three composite hydrofoils with different orientations of the structural carbon layers, resulting in a different material-based bend-twist coupling. The results show that the material-based bend-twist coupling has a significant impact on the load-dependent deformation response, stall boundary, modal characteristics, susceptibility to static divergence, and cavity dynamics.

This thesis helps in advancing the understanding of the impact of load-dependent bend-twist coupling on the performance of adaptive composite hydrofoils. We also took the first step towards developing a high-fidelity hydrostructural design optimization tool for composite hydrofoils by extending our structural solver to simulate the performance of anisotropic composite hydrofoils. The high-fidelity hydrostructural solver combined with the improved understanding of the material-based bend-twist coupling has the potential to play an important role in the analysis, design, and optimization of the next generation adaptive composite marine propulsors.