Power regeneration of a bioinspired electromechanical propulsive fin

Bioinspired swimming methods have become highly attractive due to the potential for low environmental impact and high efficiency. However, although the efficiency has been quantified for select robotic and theoretical models, this paper explores more directly how requisite power consumption of an undulatory fin is affected by desired swimming speed. It further introduces and quantifies a method for recovering energy from the flow. First, CFD was used to simulate a cross-section of a fish fin with a wave number of 1.2 and a linearly increasing amplitude envelope. Flow speed and fin wave frequency were varied to determine interactive effects on force production and power requirements. The data from these simulations was fitted with polynomial functions over the range used for the study. To determine the potential for power regeneration from the flow, the fin was augmented with a mathematical model of a DC motor and shaft driving it. By incorporating the motor model into the fin analysis, the authors analyzed the amount of power input, or power regeneration, into the system from a constant velocity fluid flow, and developed a relationship between flow velocity and power regeneration. This relationship provides insight into both the level of power regeneration for the fin if held fixed in constant flow, and the minimum flow speed to regenerate energy at a desired rate. The determination of the relationships between efficiency and mode of operation will provide insight into the energetic efficiency of robotic designs using this method. Furthermore, the possibility of power recovery could pave the way for longer lasting underwater robots in extended missions. The determination of both efficiency and power regeneration capability will provide insight into the energetic feasibility of using, and improving on, the current capabilities of bioinspired underwater propulsion.