Enhancing propulsion efficiency of biomimetic elastic propulsor using hybrid actuation

Bio-inspired propulsion of a robotic swimmer can be achieved by periodic actuation of an elastic caudal fin. We use three-dimensional computer simulations to probe how the hydrodynamic performance of a caudal fin can be enhanced by combining two distinct types of fin actuation. The fin is represented by an elastic rectangular plate that is actuated at the base to perform sinusoidal oscillations. The actuation frequency is set to match the fundamental frequency of the plate yielding the maximum bending amplitude. In addition to this plunging actuation, the plate is actuated by a distributed bending moment with the magnitude that periodically changes in time with the same frequency as the fin base. We introduced a phase difference between the base and the internal actuation and investigate the resultant hydrodynamic thrust and efficiency. We compared the hybrid fin actuation to the base actuation and to the internal actuation to identify the parameter space in which the synergetic effects of the two action mechanisms are the most beneficial for swimmer propulsion.