A Flapped Paddle-Fin for Improving Underwater Propulsive Efficiency of Oscillatory Actuation

Abstract

This letter presents a novel design of an oscillatory fin for thrust-efficient and agile underwater robotic locomotion. We propose a flat paddle-fin comprising a set of overlapping cascaded soft flaps that open in one half of the stroke cycle and close in the other. Consequently, asymmetry in the lateral drag force exerted by the fin during oscillatory actuation is passively achieved. This enables a substantially higher degree of efficiency in force generation than conventional oscillatory fins which rely on weaker longitudinal wake-induced forces. Experimental results show a high degree of improvement in net thrust and propulsive-efficiency over conventional fins. Locomotion with the proposed fin has been demonstrated on an underwater robotic platform. Various gaits were achieved using oscillatory actuation, via angular and phase offsets between the actuators.