Propulsion Mechanism in Fluid Using Fin with Dynamic Variable-Effective-Length Spring (Evaluation of Thrust Efficiency and Flow-Visualization Around the Fin)

Abstract

Since the propulsion mechanism in fluid using elastic fin like a caudal fin and a pectoral fin of fish is effective, many studies of elastic fin for propulsion in water and development of fish robot using elastic fin were carried out. However, the optimum elasticity of fin is not constant and changed by the movement task and environment, such as swimming speed and oscillating frequency. It is very difficult to exchange fins of the different stiffness while swimming. Thus, we aimed to develop the variable-stiffness fin, and made a fin with variable-effective-length spring. This fin enables its apparent stiffness dynamically. This paper describes the structure of the propulsion mechanism in fluid using fin with variable-effective-length spring and characteristics of thrust and lateral forces, and thrust efficiency. Furthermore, the relationship between the thrust force and the flow-field around the fin is discussed.