Study on Tail Motion of High-Speed Swimming Fish

It is well known that fishes and cetaceans can achieve extraordinary propulsive performance, acceleration and maneuverability. The present study gives an attention to the propulsion of carangiform swimming motion which produces thrust mainly by oscillating the tail fin. The two-point hinge oscillating wing theory is adopted to simulate the motion of tail fin, which is coupled with swaying and yawing motions. Parameters of the theory are an advance speed, frequency of the tail fin, amplitudes of swaying and yawing motions, and phase lag between both motions. Experiments were conducted to obtain the lift and drag coefficients against angles of incidence for 6 kinds of tail fin and a rectangular wing. As examples, the amplitudes and phase lag of swaying and yawing motions are analyzed from video records of swimming fishes. Based on the above theory and experiments, parametric calculations were made in order to obtain data for design of a robotic machine fish. It is found that there exists a proper choice among frequency, amplitudes and phase lag of oscillating motions