School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
J R Soc Interface. 2013 May 1;10(84):20130188. doi: 10.1098/rsif.2013.0188. Print 2013 Jul 6.
In rectilinear locomotion, snakes propel themselves using unidirectional travelling waves of muscular contraction, in a style similar to earthworms. In this combined experimental and theoretical study, we film rectilinear locomotion of three species of snakes, including red-tailed boa constrictors, Dumeril's boas and Gaboon vipers. The kinematics of a snake's extension-contraction travelling wave are characterized by wave frequency, amplitude and speed. We find wave frequency increases with increasing body size, an opposite trend than that for legged animals. We predict body speed with 73-97% accuracy using a mathematical model of a one-dimensional n-linked crawler that uses friction as the dominant propulsive force. We apply our model to show snakes have optimal wave frequencies: higher values increase Froude number causing the snake to slip; smaller values decrease thrust and so body speed. Other choices of kinematic variables, such as wave amplitude, are suboptimal and appear to be limited by anatomical constraints. Our model also shows that local body lifting increases a snake's speed by 31 per cent, demonstrating that rectilinear locomotion benefits from vertical motion similar to walking.
在直线运动中，蛇类通过单向肌肉收缩的行进波来推动自己，其运动方式类似于蚯蚓。在这项结合了实验和理论的研究中，我们拍摄了三种蛇类的直线运动，包括红尾蚺、王蛇和加蓬蝰蛇。蛇类伸缩行进波的运动学特征包括波频、波幅和速度。我们发现，波频随体型增大而增加，这与有腿动物的趋势相反。我们使用一个一维 n 链接爬虫的数学模型来预测身体速度，该模型将摩擦力作为主要的推进力，其预测的准确性为 73%-97%。我们应用该模型表明，蛇类具有最佳的波频：较高的波频会增加弗劳德数，导致蛇类打滑；较低的波频会降低推力，从而降低身体速度。其他运动学变量的选择，如波幅，是次优的，似乎受到解剖结构限制。我们的模型还表明，局部身体提升可以使蛇类的速度提高 31%，这表明直线运动受益于类似于行走的垂直运动。
