A theoretical analysis of pitch stability during gliding in flying snakes
A theoretical analysis of pitch stability during gliding in flying snakes
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飞蛇滑行过程中俯仰稳定性的理论分析
DOI：
10.1088/1748-3182/9/2/025014
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
J. Socha
中科院分区：
文献类型：
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作者：
Farid Jafari;S. Ross;P. Vlachos;J. Socha
飞蛇用它们的整个身体作为不断变形的“翅膀”来产生升力并使它们的滑翔轨迹变浅。它们在滑翔过程中的主要行为是空中波动，在这种波动中，侧波被发送到身体的后部。这种高度动态的行为，在动物滑翔机中是独一无二的，应该对蛇的飞行动力学和稳定性有实质性的影响，这是由于质量和空气动力的不断重新分配。在这项研究中，我们建立了二维理论模型来评估蛇在俯仰方向上的稳定性特性。先前测量的力系数用于模拟作用在模型上的气动力，并通过改变质量来模拟波动。模型1是蛇身体的简单三翼型表示，具有被动稳定平衡解，其稳定性盆地包含在实验滑翔轨迹中观察到的初始条件。模型2更加复杂，有更多的自由度，允许姿势变化，以更好地代表蛇的真实运动学；此外，还增加了一个恢复力矩来模拟电位主动控制。静、动稳定判据的应用表明，模型2是被动失稳的，但可以通过恢复力矩稳定。综上所述，这些模型表明，波动对俯仰稳定性没有贡献，飞行蛇需要一个围绕被动稳定动力框架形成的闭环控制系统。
Flying snakes use their entire body as a continuously morphing ‘wing’ to produce lift and shallow their glide trajectory. Their dominant behavior during gliding is aerial undulation, in which lateral waves are sent posteriorly down the body. This highly dynamic behavior, which is unique among animal gliders, should have substantial effects on the flight dynamics and stability of the snakes, resulting from the continuous redistribution of mass and aerodynamic forces. In this study, we develop two-dimensional theoretical models to assess the stability characteristics of snakes in the pitch direction. Previously measured force coefficients are used to simulate aerodynamic forces acting on the models, and undulation is simulated by varying mass. Model 1 is a simple three-airfoil representation of the snake’s body that possesses a passively stable equilibrium solution, whose basin of stability contains initial conditions observed in experimental gliding trajectories. Model 2 is more sophisticated, with more degrees of freedom allowing for postural changes to better represent the snake’s real kinematics; in addition, a restoring moment is added to simulate potential active control. The application of static and dynamic stability criteria show that Model 2 is passively unstable, but can be stabilized with a restoring moment. Overall, these models suggest that undulation does not contribute to stability in pitch, and that flying snakes require a closed-loop control system formed around a passively stable dynamical framework.