Experimental Study of a Two-Joint Dolphinlike Propulsion Mechanism. 1st Report. Experiment of Small Machine.

Abstract

An experimental apparatus of the two-joint dolphinlike propulsion mechanism, which is composed of a streamlined body and a rectangular caudal fin, was developed. The first joint in the body part is driven by a stepping motor, the second joint at the end of the body is passively driven by springs. The required torque of the first joint is measured by strain gages. The experimental characteristics of the propulsive efficiency in a channel were investigated, and those were compared with the numerical ones obtained from the theory in the previous paper. The propulsive efficiency of the experiment is around 0.25 while that of the theory is 0.35∼0.4. Next, the motion of the caudal fin was measured. The motion of the caudal fin in the experiment shows similar tendency to that in the theory. Finally, flow visualization around the mechanism was done by using the tydrogen bubble method. It was found that the flow around the body is almost not disturbed and that the wake area after the caudal fin becomes wider and wider as the flow goes ahead.