On the role of phase lag in multi-appendage metachronal swimming of euphausiids
On the role of phase lag in multi-appendage metachronal swimming of euphausiids
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DOI：
10.1088/1748-3190/abc930
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发表时间：
2021-11-01
影响因子：
3.4
通讯作者：
Santhanakrishnan, Arvind
中科院分区：
文献类型：
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作者：
Ford, Mitchell P.;Santhanakrishnan, Arvind
异时划桨是一种常见的基于阻力的水上推进方法，其中一系列游泳附肢振荡，每个附肢的运动相对于相邻附肢相移。南极磷虾（Euphausia superba）等具有重要经济价值的磷虾类物种不断地通过抚摸它们的划桨附属物（pleopods）游泳，运动占它们代谢消耗的大部分。它们通过改变腹足运动学来调整自己的游泳步态，以满足行为和能量需求。异时性游泳表现和尾流结构的腹足间相位滞后（phi）的功能重要性是未知的。为了研究这种关系，我们开发了一个几何和动态缩放的机器人（“krillbot”）能够自我推进。Krillbot pleopods规定模仿发表的运动学的快进游泳（FFW）和悬停（HOV）步态的E。krillbot的Reynolds数和Strouhal数与自由游动的E. superba。除了检查已发表的运动学与不均匀的phi之间的腹脚对，我们修改E。superba运动学在周期的0%到50%范围内均匀改变phi。FFW的游泳速度和推力最大，phi值在15%-25%之间，与E. superba。与同步划船（phi = 0%）相比，相邻的腹肢关节之间的距离在整个周期中几乎是恒定的，异时划船（phi > 0%）使相邻的腹肢更靠近，并使它们远离。这一因素最大限度地减少了身体的位置波动和增加异时游泳速度。虽然HOV的游泳速度最低，但产生了一个腹侧角度向下的射流，可以在喂食过程中帮助体重支撑。总之，我们的研究结果表明，附肢间的相位滞后可以大大改变异时游泳速度和大规模的尾流结构。
Metachronal paddling is a common method of drag-based aquatic propulsion, in which a series of swimming appendages are oscillated, with the motion of each appendage phase-shifted relative to the neighboring appendages. Ecologically and economically important euphausiid species such as Antarctic krill (Euphausia superba) swim constantly by stroking their paddling appendages (pleopods), with locomotion accounting for the bulk of their metabolic expenditure. They tailor their swimming gaits for behavioral and energetic needs by changing pleopod kinematics. The functional importance of inter-pleopod phase lag (phi) to metachronal swimming performance and wake structure is unknown. To examine this relation, we developed a geometrically and dynamically scaled robot ('krillbot') capable of self-propulsion. Krillbot pleopods were prescribed to mimic published kinematics of fast-forward swimming (FFW) and hovering (HOV) gaits of E. superba, and the Reynolds number and Strouhal number of the krillbot matched well with those calculated for freely-swimming E. superba. In addition to examining published kinematics with uneven phi between pleopod pairs, we modified E. superba kinematics to uniformly vary phi from 0% to 50% of the cycle. Swimming speed and thrust were largest for FFW with phi between 15%-25%, coincident with phi range observed in FFW gait of E. superba. In contrast to synchronous rowing (phi = 0%) where distances between hinged joints of adjacent pleopods were nearly constant throughout the cycle, metachronal rowing (phi > 0%) brought adjacent pleopods closer together and moved them farther apart. This factor minimized body position fluctuation and augmented metachronal swimming speed. Though swimming speed was lowest for HOV, a ventrally angled downward jet was generated that can assist with weight support during feeding. In summary, our findings show that inter-appendage phase lag can drastically alter both metachronal swimming speed and the large-scale wake structure.