A novel method for investigating the kinematic effect on the hydrodynamics of robotic fish

In this paper, a novel method was presented to investigate the hydrodynamics of a robotic fish at different Reynolds number. The ionic polymer-metal composite (IPMC) was used as the soft actuator for biomimetic underwater propulsion. A hydrodynamic model based on the elongated body theory was developed. Based on image analysis, the kinematic parameters of the robotic fish were identified. To obtain the hydrodynamic thrust performance of the robotic fish, we implemented a novel experimental apparatus. Systematic tests were conducted in the servo towing system to measure the self-propelled speed and thrust efficiency at viscous and inertial flow. The robotic fish's thrust efficiency was compared at different body and caudal fin (BCF) swimming modes, i.e. anguilliform, carangiform and thunniform. The thrust performance of the robotic fish is determined by the kinematics and Reynolds number. We show that at high Reynolds number, thunniform kinematics is the most efficient, while anguilliform kinematics produces relatively poor thrust efficiency. At low Reynolds number, the fish has the highest thrust efficiency with the anguilliform type. It is less efficient with the thunniform type.