Numerical study on swimming self-propulsive fish model

Abstract

The purpose of this study is to predict the motion of fish robot. The undulating caudal fin of the fish produces the lateral and the rotational motions of the body in addition to the propulsive motion. In order to clarify how to influence propulsion by these motions, we researched the interaction between the fish body and the fluid by using the translational and rotational equations of motion of the body combined the two-dimensional numerical analysis based on the ALE finite difference method. In the past researches, the fish model was fixed on the space, or the lateral and the rotational motions of the model were neglected in the analysis. The propulsive efficiency is not estimated exactly in such methods. We computed the complex motion of the fish body by considering the surface force acting on the body. As a result of the present study, it was clarified that the propulsive efficiency of the fish model is increased by 50 percent compared from the non-rotational movement. The reason is that the lateral force (which does not make a contribution to the propulsive force) acting on the body is decreased by the rotational motion of the body.