On the optimal shape of magnetic swimmers
On the optimal shape of magnetic swimmers
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DOI：
10.1134/s156035471301005x
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发表时间：
2013-01-01
影响因子：
1.4
通讯作者：
Gadelha, Hermes
中科院分区：
文献类型：
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作者：
Gadelha, Hermes
弹磁装置的磁致动长期以来一直被提出作为一种简单的方式来推动流体并在由粘性力主导的环境中实现运动。在振荡磁场的作用下，永久磁铁当附着在弹性尾部时，能够产生弯曲波和足够的推力来推进。我们研究了磁头几何形状的流体动力学效应，使用弹性尾部的弹性流体动力学的几何精确公式，我们表明，球形磁头几何形状未能充分利用来自柔性尾部的推进潜力。尽管如此，虽然细长的扁长球体表现出上级游泳性能，但这仍然受到所施加磁场的性质的调节。有趣的是，当磁场的大小由于磁矩的方向和振荡磁场之间的延迟而较弱时，观察到最高的游泳速度。这允许来自变形的尾部的存储的弹性能量在施加的磁场和游泳者的磁矩之间的相位滞后期间松弛，以这种方式有利于净推进。特别是，这一结果表明，存在最佳的磁致动，是不光滑的，甚至不连续的时间，以充分探索与周期性变形的弹性细丝的松弛动力学的推进潜力。
Magnetic actuation of elasto-magnetic devices has long been proposed as a simple way to propel fluid and achieve locomotion in environments dominated by viscous forces. Under the action of an oscillating magnetic field, a permanent magnet, when attached to an elastic tail, is able to generate bending waves and sufficient thrust for propulsion. We study the hydrodynamical effects of the magnetic head geometry using a geometrically exact formulation for the elastic tail elastohydrodynamics.We show that the spherical head geometry fails to take full advantage of the propulsive potential from the flexible tail. Nevertheless, while elongated prolate spheroids demonstrate a superior swimming performance, this is still regulated by the nature of the imposed magnetic field. Interestingly, the highest swimming speed is observed when the magnitude of the magnetic field is weak due to delays between the orientation of the magnetic moment and the oscillating magnetic field. This allows the stored elastic energy from the deformed tail to relax during the phase lag between the imposed magnetic field and the swimmer's magnetic moment, favouring in this way the net propulsion. In particular, this result suggests the existence of optimal magnetic actuations that are non-smooth, and even discontinuous in time, in order to fully explore the propulsive potential associated with the relaxation dynamics of periodically deformed elastic filaments.