A Sports Engineering Study on Mechanism in Curve-Kick

本研究的目的是分析导致足球在向前弧线球中旋转的基本特征。足球运动员的实验研究表明，平均脚速度为24.2 m/s，平均球速度为27.1 m/s。平均旋转速率为每秒7.8转。在每次试验中，还观察了撞击时面矢量和挥拍矢量之间的攻角，发现平均攻角为35.4度。前弧线踢的有限元模型表明，随着攻角的增大，球的旋转速率增大。然而，在攻角为75度或更大的情况下，旋转速率迅速下降。球的速度随着攻角的增大而减小。认为，对于前弧线踢球，在击球时，当进攻角度介于面矢量和挥拍矢量之间时，足部的方向会产生产生球旋转的最佳力矩。在风洞试验中发现，足球与光滑球体的最大气动差异在于阻力系数的雷诺数依赖性。在光滑球的情况下，Re<3.1×10^5的阻力系数几乎为0.43,Re>3.5×10^5的阻力系数为0.11。临界雷诺数约为3.1×10^5。这些值与常规数据具有可比性。另一方面，足球的阻力系数与雷诺数无关。阻力系数恒定在0.2左右。

The purpose of this study was to analyze the fundamental characteristics that cause a football to spin in an infront curve kick. Experimental studies of football players showed that the average foot velocity was 24.2 m/s and the average ball velocity was 27.1 m/s. The average spin rate was 7.8 revolutions per second. The attacking angle between the face vector and the swing vector at impact was also observed in each trial and the average attacking angle was found to be 35.4 degrees. Finite element models of the infront curve kick showed that the spin rate of the ball increases as attacking angle is increased. However, the spin rate falls rapidly in the case of the attacking angle being 75 degrees or greater. The ball velocity decreases as the attacking angle is increased. It is considered that, for the infront curve kick, a foot orientation at impact, with the attacking angle between the face vector and the swing vector, generates the optimum moment with which to generate ball spin.In the wind tunnel test, it is found that the biggest aerodynamic difference between the soccer ball and the smooth sphere is the Reynolds number dependency of the drag coefficient. In the case of the smooth sphere, the drag coefficient is almost 0.43 for Re<3.1×10^5, and 0.11 for Re>3.5×10^5. The critical Reynolds number is about 3.1×10^5. These values are comparable with the conventional data. On the other hand, the drag coefficient of the soccer ball is independent of the Reynolds number. The drag coefficient is constant around 0.2.