Faculty of Health and Sport Sciences, University of Tsukuba, Tsukuba 305-8574, Ibaraki, Japan.
Department of Mechanical and Control Engineering, Tokyo Institute of Technology, Tokyo, Japan.
J Biomech. 2014 Apr 11;47(6):1401-8. doi: 10.1016/j.jbiomech.2014.01.046. Epub 2014 Jan 31.
This study aims to clarify the mechanisms by which unsteady hydrodynamic forces act on the hand of a swimmer during a crawl stroke. Measurements were performed for a hand attached to a robotic arm with five degrees of freedom independently controlled by a computer. The computer was programmed so the hand and arm mimicked a human performing the stroke. We directly measured forces on the hand and pressure distributions around it at 200 Hz; flow fields underwater near the hand were obtained via 2D particle image velocimetry (PIV). The data revealed two mechanisms that generate unsteady forces during a crawl stroke. One is the unsteady lift force generated when hand movement changes direction during the stroke, leading to vortex shedding and bound vortex created around it. This bound vortex circulation results in a lift that contributes to the thrust. The other occurs when the hand moves linearly with a large angle of attack, creating a Kármán vortex street. This street alternatively sheds clockwise and counterclockwise vortices, resulting in a quasi-steady drag contributing to the thrust. We presume that professional swimmers benefit from both mechanisms. Further studies are necessary in which 3D flow fields are measured using a 3D PIV system and a human swimmer.
本研究旨在阐明在爬泳划臂过程中，非定常水动力对游泳运动员手部作用的机制。实验中，测量了由计算机独立控制的五自由度机械臂上附着的手部的力。计算机程序使手和手臂模仿人类完成划臂动作。我们以 200Hz 的频率直接测量手上的力和周围的压力分布；通过二维粒子图像测速（PIV）获得水下手部附近的流场。数据揭示了爬泳划臂过程中产生非定常力的两种机制。一种是当手在划臂过程中改变方向时产生的非定常升力，导致旋涡的脱落和围绕它的束缚涡的产生。这种束缚涡的循环导致了对推力有贡献的升力。另一种机制发生在手以大攻角作直线运动时，产生卡门涡街。这条街交替地脱落顺时针和逆时针的旋涡，导致对推力有贡献的准定常阻力。我们推测专业游泳运动员受益于这两种机制。进一步的研究需要使用三维粒子图像测速系统和人类游泳运动员来测量三维流场。
