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Effects of shape and stroke parameters on the propulsion performance of an axisymmetric swimmer

机译：形状和行程参数对轴对称游泳者推进性能的影响

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摘要

In nature, there exists a special group of aquatic animals which have an axisymmetric body and whose primary swimming mechanism is to use periodic body contractions to generate vortex rings in the surrounding fluid. Using jellyfish medusae as an example, this study develops a mathematical model of body kinematics of an axisymmetric swimmer and uses a computational approach to investigate the induced vortex wakes. Wake characteristics are identified for swimmers using jet propulsion and rowing, two mechanisms identified in previous studies of medusan propulsion. The parameter space of body kinematics is explored through four quantities: a measure of body shape, stroke amplitude, the ratio between body contraction duration and extension duration, and the pulsing frequency. The effects of these parameters on thrust, input power requirement and circulation production are quantified. Two metrics, cruising speed and energy cost of locomotion, are used to evaluate the propulsion performance. The study finds that a more prolate-shaped swimmer with larger stroke amplitudes is able to swim faster, but its cost of locomotion is also higher. In contrast, a more oblate-shaped swimmer with smaller stroke amplitudes uses less energy for its locomotion, but swims more slowly. Compared with symmetric strokes with equal durations of contraction and extension, faster bell contractions increase the swimming speed whereas faster bell extensions decrease it, but both require a larger energy input. This study shows that besides the well-studied correlations between medusan body shape and locomotion, stroke variables also affect the propulsion performance. It provides a framework for comparing the propulsion performance of axisymmetric swimmers based on their body kinematics when it is difficult to measure and analyze their wakes empirically. The knowledge from this study is also useful for the design of robotic swimmers that use axisymmetric body contractions for propulsion.
机译：在自然界中，存在着一组特殊的水生动物，它们具有轴对称的身体，其主要游泳机制是利用周期性的身体收缩在周围的流体中产生涡流环。以水母水母为例，本研究建立了一个轴对称游泳者身体运动学的数学模型，并使用一种计算方法来研究诱发的涡流尾流。使用喷气推进和划船为游泳者确定清醒特征，这是先前对medusan推进研究中确定的两种机制。人体运动学的参数空间是通过四个量来探索的：人体形状的度量，冲程幅度，人体收缩持续时间与伸展持续时间之间的比率以及脉动频率。量化了这些参数对推力，输入功率需求和循环产量的影响。巡航速度和运动的能量成本这两个指标用于评估推进性能。研究发现，具有更大笔划幅度的长条形游泳者能够更快地游泳，但其运动成本也更高。相比之下，椭圆形的游泳者，其冲程幅度较小，其运动消耗的能量较少，但游泳速度较慢。与具有相等的收缩和伸展持续时间的对称冲程相比，更快的铃铛收缩会提高游泳速度，而更快的铃铛伸展会降低游泳速度，但两者都需要更大的能量输入。这项研究表明，除了研究得到的中等程度的人体形状与运动之间的相关性外，中风变量还影响推进性能。它提供了一个框架，用于在难以凭经验测量和分析其尾流时根据其身体运动学来比较轴对称游泳者的推进性能。这项研究的知识对于使用轴对称身体收缩进行推进的机器人游泳者的设计也很有用。

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