Active tail flexion in concert with passive hydrodynamic forces improves swimming speed and efficiency
Active tail flexion in concert with passive hydrodynamic forces improves swimming speed and efficiency
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主动尾巴弯曲配合被动水动力力提高游泳速度和效率
DOI：
10.1017/jfm.2021.984
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发表时间：
2021-04
影响因子：
3.7
通讯作者：
Haotian Hang;Sina Heydari;J. Costello;E. Kanso
中科院分区：
文献类型：
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作者：
Haotian Hang;Sina Heydari;J. Costello;E. Kanso
摘要鱼类通常通过周期性的弯曲身体来游泳。弯曲似乎遵循一个普遍的规则;它发生在大约三分之一的鱼体后端的最大弯曲角度约30 ^{\circ }$。然而，形成这种收敛设计的水动力机制及其在游泳速度和效率方面对鱼类的潜在益处还没有得到很好的理解。也不清楚这种弯曲在多大程度上是主动的或被动地跟随柔性后部与流体环境的相互作用。在这里，我们使用一个自推进的两个链接模型，与流体-结构相互作用的涡面方法的上下文中描述的，主动和被动的身体弯曲对游泳性能的影响进行分析。我们发现，被动弯曲是更有效的，但会降低游泳速度相比，刚性扑，但主动弯曲的增加可以提高速度和效率。重要的是，我们发现，身体的后部和前部之间的相位差是影响性能的重要运动学因素，并且与被动屈曲相一致的主动反相屈曲可以同时提高与生物学观察重叠的设计空间区域中的速度和效率。我们的结果与假设一致，即以利用被动流体动力学的方式主动弯曲身体的鱼可以同时提高速度和效率。
Abstract Fish typically swim by periodic bending of their bodies. Bending seems to follow a universal rule; it occurs at about one-third from the posterior end of the fish body with a maximum bending angle of about $30^{\circ }$. However, the hydrodynamic mechanisms that shaped this convergent design and its potential benefit to fish in terms of swimming speed and efficiency are not well understood. It is also unclear to what extent this bending is active or follows passively from the interaction of a flexible posterior with the fluid environment. Here, we use a self-propelled two-link model, with fluid–structure interactions described in the context of the vortex sheet method, to analyse the effects of both active and passive body bending on the swimming performance. We find that passive bending is more efficient but could reduce swimming speed compared with rigid flapping, but the addition of active bending could enhance both speed and efficiency. Importantly, we find that the phase difference between the posterior and anterior sections of the body is an important kinematic factor that influences performance, and that active antiphase flexion, consistent with the passive flexion phase, can simultaneously enhance speed and efficiency in a region of the design space that overlaps with biological observations. Our results are consistent with the hypothesis that fish that actively bend their bodies in a fashion that exploits passive hydrodynamics can at once improve speed and efficiency.