Faculty of Health and Sport Sciences, University of Tsukuba Tennoudai 1-1-1, Tsukuba 305-8574, Japan.
J Biomech. 2013 Jul 26;46(11):1825-32. doi: 10.1016/j.jbiomech.2013.05.006. Epub 2013 Jun 12.
This study aims to clarify the mechanism of generating unsteady hydrodynamic forces acting on a hand during swimming in order to directly measure the forces, pressure distribution, and flow field around the hand by using a robotic arm and particle image velocimetry (PIV). The robotic arm consisted of the trunk, shoulder, upper arm, forearm, and hand, and it was independently computer controllable in five degrees of freedom. The elbow-joint angle of the robotic arm was fixed at 90°, and the arm was moved in semicircles around the shoulder joint in a plane perpendicular to the water surface. Two-component PIV was used for flow visualization around the hand. The data of the forces and pressure acting on the hand were sampled at 200Hz and stored on a PC. When the maximum resultant force acting on the hand was observed, a pair of counter-rotating vortices appeared on the dorsal surface of the hand. A vortex attached to the hand increased the flow velocity, which led to decreased surface pressure, increasing the hydrodynamic forces. This phenomenon is known as the unsteady mechanism of force generation. We found that the drag force was 72% greater and the lift force was 4.8 times greater than the values estimated under steady flow conditions. Therefore, it is presumable that swimmers receive the benefits of this unsteady hydrodynamic force.
本研究旨在阐明游泳时作用于手部的非定常水动力产生的机理，通过使用机械臂和粒子图像测速（PIV）直接测量手部的受力、压力分布和流场。机械臂由躯干、肩部、上臂、前臂和手部组成，可独立在五个自由度上进行计算机控制。机械臂的肘部角度固定在 90°，臂在垂直于水面的平面内围绕肩关节进行半圆形移动。二维 PIV 用于手部周围流场的可视化。手部受力和压力的数据以 200Hz 的频率进行采样并存储在 PC 上。当观察到手部的最大合力时，手的背侧表面上出现了一对反向旋转的涡旋。附着在手上的涡旋增加了流速，导致表面压力降低，从而增加了水动力。这种现象称为力产生的非定常机制。我们发现，阻力比在定常流条件下估计的值大 72%，升力大 4.8 倍。因此，可以假定游泳者受益于这种非定常水动力。
