Three-dimensional simulations of undulatory and amoeboid swimmers in viscoelastic fluids
Three-dimensional simulations of undulatory and amoeboid swimmers in viscoelastic fluids
复制标题
粘弹性流体中波状和变形虫游泳者的三维模拟
DOI：
10.1039/c8sm02518e
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发表时间：
2019
期刊：
影响因子：
3.4
通讯作者：
Shaqfeh, Eric S.
中科院分区：
文献类型：
--
作者：
Binagia, Jeremy P.;Guido, Christopher J.;Shaqfeh, Eric S.
微生物经常通过粘弹性环境移动，因为生物流体由于大聚合物分子的存在而经常具有丰富的微观结构。流体弹性对这些生物体游泳运动学的影响的研究通常集中在那些通过纤毛或鞭毛运动的生物体上。实验上，沈（X。N. Shen等人，物理学评论快报，2011，106，208101）报道了线虫C.线虫是研究波动运动的模式生物，当描述流体弹性的德博拉数增加时，它游得更慢。这种现象还没有通过完全解析的三维模拟进行彻底的研究;此外，流体弹性对通过裸藻运动移动的生物体（例如E. gracilis是完全未知的。在这项研究中，我们讨论的任意运动的起伏或脉动的游泳者，占据有限的体积在三个维度上的模拟，与周围的流体指定任何差分粘弹性流变模型的能力。为了完成这项任务，我们使用了Guido和Saadat在2018年发表的一篇论文中提出的浸入式有限元法的修改版本（A. Saadat等人，E，2018，98，063316）。特别是，这个版本允许模拟可变形的游泳者，使他们通过任意一组指定的形状演变通过构象驱动力。从我们的分析中，我们观察到几个关键的趋势，没有发现在以前的二维模拟或理论分析的C。elegans，以及变形虫运动的新结果。特别是，我们发现高分子应力集中的区域在游泳C的头部和尾部。优美的泳姿是由强的伸展流场产生的，并且与给定泳姿的游泳速度的降低有关。相反，在二维中，这些应力区域通常被发现沿着整个主体分布，这可能是由于缺乏用于聚合物松弛的第三维。游泳速度的比较表明，在二维模拟的计算结果在过度预测的速度降低。我们相信，我们的模拟工具准确地捕捉了游泳运动的两个上述模型游泳者，此外，允许模拟多个可变形的游泳者，以及更复杂的游泳几何形状。这种方法为今后在粘弹性流体中研究游泳运动员开辟了许多新的可能性。
Microorganisms often move through viscoelastic environments, as biological fluids frequently have a rich microstructure owing to the presence of large polymeric molecules. Research on the effect of fluid elasticity on the swimming kinematics of these organisms has usually been focused on those that move via cilia or flagellum. Experimentally, Shen (X. N. Shen et al., Phys. Rev. Lett., 2011, 106, 208101) reported that the nematode C. elegans, a model organism used to study undulatory motion, swims more slowly as the Deborah number describing the fluid's elasticity is increased. This phenomenon has not been thoroughly studied via a fully resolved three-dimensional simulation; moreover, the effect of fluid elasticity on the swimming speed of organisms moving via euglenoid movement, such as E. gracilis, is completely unknown. In this study, we discuss the simulation of the arbitrary motion of an undulating or pulsating swimmer that occupies finite volume in three dimensions, with the ability to specify any differential viscoelastic rheological model for the surrounding fluid. To accomplish this task, we use a modified version of the Immersed Finite Element Method presented in a previous paper by Guido and Saadat in 2018 (A. Saadat et al., Phys. Rev. E, 2018, 98, 063316). In particular, this version allows for the simulation of deformable swimmers such that they evolve through an arbitrary set of specified shapes via a conformation-driven force. From our analysis, we observe several key trends not found in previous two-dimensional simulations or theoretical analyses for C. elegans, as well as novel results for the amoeboid motion. In particular, we find that regions of high polymer stress concentrated at the head and tail of the swimming C. elegans are created by strong extensional flow fields and are associated with a decrease in swimming speed for a given swimming stroke. In contrast, in two dimensions these regions of stress are commonly found distributed along the entire body, likely owing to the lack of a third dimension for polymer relaxation. A comparison of swim speeds shows that the calculations in two-dimensional simulations result in an over-prediction of the speed reduction. We believe that our simulation tool accurately captures the swimming motion of the two aforementioned model swimmers and furthermore, allows for the simulation of multiple deformable swimmers, as well as more complex swimming geometries. This methodology opens many new possibilities for future studies of swimmers in viscoelastic fluids.