Biofluiddynamic Study on Effectivity of Artificial Tail Flukes of Dolphin

海豚游得快，跳得高。从生物工程的角度研究其运动性能和推进性能具有重要意义。我们知道尾锚在产生有效的推进力方面起着重要的作用。然而，直接测量海豚的推进力是困难的。詹姆斯·格雷指出了一个问题，即海豚可以游得比通过作用在身体上的水动力阻力和肌肉力量估计的速度更快。这就是著名的格雷悖论。在推进力方面，我们着重研究了尾鳍的结构及其在摆动过程中的变形行为。我们通过获得作用在鳍上的水动力与鳍的变形之间的关系来估计推进力。日本冲绳美丽海水族馆饲养的一只海豚的两个尾鳍进行性坏死，通过手术治疗约75%的尾鳍丧失。然后，为了帮助海豚像以前一样游泳，为海豚设计了假肢。研究了海豚人工尾鳍和尾锚的力学性能。以海豚尾鳍为模型制作了一种人工尾翼，并对其推进性能进行了研究。机翼在一个振荡周期内几乎产生正推力，且波动很小。我们相信，人工尾鳍是有用的水下航行器的推进器。下一阶段将使用设置在机翼内部的加速度传感器来测量类似机翼的行为。

Dolphins swim fast and jump high. It is significant to clarify its biokinematic performance and propulsive performance from the bioengineering viewpoint. We know that the tail flukes play an important role in generating efficient propulsive force. However, it is difficult to measure the propulsive force of swimming dolphin directly. James Gray pointed out the problem that the dolphin can swim faster than at the speed estimated by the hydrodynamic drag acting its body and the power of its muscles. This is well known as Gray's paradox. As for the propulsive force, we paid attention to the structure of the tail fin and its deformation behavior by the fin oscillation. We thought the estimation of propulsive force by obtaining the relationship between the hydrodynamic force acting on the fin and the deformation of the fin.A dolphin kept in Okinawa Churaumi aquarium in Japan suffered progressive necrosis in both tail flukes and lost about 75 % of the flukes by surgical treatment. Then prosthetic flukes for the dolphin were designed in order to assist the dolphin to swim as before. The mechanical properties on the artificial tail fin and a tail flukes of dolphin were investigated. An artificial tail wing modeled on the dolphin's tail flukes was made and the propulsive performance was investigated. The dolphin-like wing almost generated positive propulsive force in one oscillating cycle and its fluctuations were small. We were convinced that the artificial tail fin was useful as the propulsor of underwater vehicles. The measurement of the behavior of the dolphin-like wing using acceleration sensor set inside the wing will be carried out at the next stage.