Caudal fin load characteristics with different motion patterns toward developing biorobotic fish-fin actuator

Abstract

Traditionally underwater vehicles use thrusters as propulsion devices and achieve high speed. These thrusters come with their own limitations such as turbulence, cavitations etc. resulting into low efficiency and noise; the vehicles severely suffer from lack of efficiency in low speed operations. Maneuverability of vehicles using thrusters or jet propulsion devices is inherently limited. On the other hand, nature provides fins to fishes and aquatic animals for underwater locomotion with proven greater maneuverability, agility and efficiency in low speed motion, achieving a highly desirable quality of stealth. To adapt the biological mechanisms of thrust production to man-made underwater robotic vehicles, understanding of biomechanics and load characteristics of the natural fins is very important. In this paper, we consider the caudal fin of a fish, being the main propulsive actuator. This article aims to understand the load characteristics of different motion patterns of the fin in water through fluid-structure interaction (FSI) simulations and does not intend to access the performance of the fin propulsion as a whole. Numerical simulations have been carried out for determining the load characteristics of different motion patterns of the chosen caudal fin and the results are presented. The simulations are based on simple kinematic fin model and do not describe any working prototype. The simulations will eventually lead to the design and development of reduced order biorobotic replica of a caudal fin.