Structural and Operational Optimization of A Flapping Fin Used as A Self-Propulsor for AUV Propulsion

Marine mammals could directly harvest energy from waves and obtain propulsive force through oscillating flapping fins or horizontal tail flukes, which in many cases have been observed and proved to be substantial. The propulsion generated by the flapping fin has been analyzed by many researchers from both the theoretical and experimental prospects; however, the structural and operational optimization of a flapping fin for the optimal propulsion performance has been less studied, such as the investigation of the effects of the phase difference between heave and pitch motion, maximum oscillation angle, fin shape, oscillation centre of the fin and the operating sea state on the generated propulsion. In this paper, the flapping fin is used as a self-propulsor to propel an autonomous underwater vehicle (AUV) for propulsion assistance. For the optimization design of the flapping fin, its propulsion effect is numerically investigated with different structural parameters and under various operation conditions using computational fluid dynamics (CFD) approaches. Verification and validation study have been implemented to quantify the numerical uncertainties and evaluate the accuracy of the proposed CFD method. Then, a series of case studies are thoroughly conducted to investigate the effects of different structural parameters and operational conditions on the generated propulsion of a flapping fin by CFD simulations. The simulation results demonstrate that different structural parameters and operation conditions would significantly impact the magnitude and distribution state of the fluid pressure around the flapping fin surface, thus, affect the propulsion performance of the fin. The findings in this study will provide guidelines for the structural and operational optimization design of a flapping fin for self-propulsion of mobile platforms.