Study of the bending propulsion mechanism (1st report, Proposition of a method to analyze a coupled system of mechanism and fluid of a 3-joint model and its experimental verification)

Although analytical and experimental studies on the bending propulsion mechanism of fish or cetaceans have been done by many researchers, the reasons for high speed and high efficiency of the animals' bending propulsion motion have not been clarified, probably because the dynamic interaction between mechanism and fluid has not been taken into account. This paper proposes an analytical method for a coupled system of mechanism and fluid dynamics in a bending propulsion mechanism, based on the discrete vortex method. We analytically and experimentally investigate the characteristics of the propulsion speed of a three-joint bending propulsion mechanism. It is found that the propulsion speed takes a maximum value when all phase differences of joints are about zero for four amplitude patterns in both the theory and experiment. The experimental propulsion speeds are found to be 65 to approximately 80 percent of the analytical ones.