抄録
Since early study of power estimation of swimming dolphins by Gray in 1936, well known as "Gray's paradox," many studies have been conducted on the high swimming capability of the dolphins. Little literature, however, investigated the detailed time variation of the velocity and acceleration of the dolphins. In this study, we focused on jumping motion of the dolphins to measure the maximum acceleration capability. The whole process of the jumping motion of a pacific white-sided dolphin, Lagenorhynchus obliquidens, from initial descending in the water to final leaping, were recorded with two high-speed video cameras for 3-D motion analysis. We also created a simple body model of the dolphin to compute its drag with fluid analysis software. By combining the measured 3-D motions of the body and computed drag, we calculated the time variation of the thrust and power in relation to the fluke oscillation. As the result, the dolphin rapidly accelerated from static state to more than 9.4 m/s in about 2 seconds. It was found that the dolphin generated thrust mainly during downstroke. On the contrary, negative thrust was observed during upstroke. Calculated power mass ratio of the dolphin was 15 times larger than that of human.
