This paper is an introduction of our theoretical and experimental study of the bending propulsion mechanism which has been done in the last five years. We first developed two-dimensional and three-dimensional numerical methods based on the discrete vortex method for a coupled system of a three joint bending propulsion mechanism and the fluid flow. We also developed an experimental apparatus, and compared the theoretical and experimental propulsive speeds. We next numerically obtained the most efficient motion of the three joint model by solving the optimum problem of motion parameters. We further developed a numerical method for the two joint bending propulsion mechanism composed of a streamlined main body part and a rectangular caudal fin, which will be a more efficient structure of bending propulsion mechanism. We also developed the experimental prototype and investigated the propulsive efficiency numerically and experimentally.
The swimming movements of fish or cetaceans, generated by adulatory motions of their bodies, look so attractive that they have been studied by many physicians and engineers from a hydrodynamics point of view. Light hill (1960) applied the slender body theory" of aeronautics for transverse oscillatory movements of a slender fish whose cross-section varies along it only gradually, and he showed that the propulsive efficiency, which ill defined as the ratio of the forward work to overcome frictional drag and the total work to produce both thrust and vortex wake, is essentially very high. Light hill (1970) and Newman and Wu (1973) studied the effect of fin appendages. Kambe (1978) considered the dynamics of the slender fish while taking account of the lateral resistance force, reaction force due to the vortex sheets shed from sharp trailing edges, and inertial force due to its body and fluid. Katz and Weihs (1979) analyzed a slender wing with passive chordwise flexibility.
