Swimming sheet in a viscosity-stratified fluid

Dandekar, Rajat; Ardekani, Arezoo M.

doi:10.1017/jfm.2020.352

Cited by 20 publications

(16 citation statements)

References 34 publications

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“…In yield-stress materials a swimmer also can create a nearby fluidized region [89], and swimmers moving across an interface of fluids with different viscosities may drag a surrounding amount of different-viscosity fluid with them [90]. Active remodeling of local material properties can also be caused by thermal or chemical effects; plankton and bacteria can exude or consume viscosity-altering substances [57][58][59][60], thermal heating of microrobots can locally decrease viscosity, and the degelling strategy of H. pylori has been mimicked in magnetically rotated microrobots [56].…”

Section: Discussionmentioning

confidence: 99%

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Fore-aft clearance controls how three-dimensional confinement affects micropropulsion

Kamarapu¹,

Jabbarzadeh²,

Fu³

2022

Preprint

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Systems of active particles are often affected by confinement due to nearby boundaries. Recently, there has been interest in the effect of confinement by complex three dimensional geometries, as might occur in structured environments such as porous media, foams, gels, or biological tissues and ducts. The effects of confinement for particles moving along boundaries has been extensively studied, but in three dimensions active particles move not only parallel to boundaries, but also towards or away from boundaries. The consequences of this fore-aft clearance is less well understood. Swimmers that actively remodel their environment create an ideal situation to study the effect of clearance, since they maintain a steady clearance while translating. By numerically studying the locomotion of the bacterium Helicobacter pylori, which de-gels surrounding gastric mucus to make a comoving pocket of fluid around itself, we show that the effect of three-dimensional confinement is controlled by clearance, rather than distance from a parallel boundary. Analytical calculations show that the effect of clearance can be understood in terms of flow structures, such as the generic pusher and puller flows of active particles, indicating that our results should apply to a wide range of confined active particles.

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Section: Discussionmentioning

confidence: 99%

“…1b). Local modification of material parameters also occurs chemically near microrobots [56], in the phycospheres of plankton [57][58][59][60], and by thermal [61,62] and mechanical effects [26,63].…”

mentioning

confidence: 99%

Fore-aft clearance controls how three-dimensional confinement affects micropropulsion

Kamarapu¹,

Jabbarzadeh²,

Fu³

2022

Preprint

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“…in order to satisfy a constant viscosity boundary condition, and it is clear from (37) that a constant viscosity on the surface of the particle clearly produces no net torque. In contrast, (26) shows that in order to satisfy the no-flux boundary condition, η ′ = 1 2 ǫη 1 + const. meaning the asymmetry of the ambient viscosity at the surface of the particle, and thus the torque, is enhanced by a 3/2 factor (see Fig.…”

Section: A Reorientationmentioning

confidence: 95%

“…Later, the motion of spherical squirmers in viscosity gradients was analyzed, taking into account locally varying hydrodynamic forces and modifications in the flow due to viscosity differences, and they were found to move down viscosity gradients [25]. A different model microorganism, Taylor's swimming sheet that propels by passing traveling waves along its surface, moving along or against the viscosity gradients was also analyzed [26]. It was found to speed up in the presence of viscosity gradients irrespective of its direction of propulsion.…”

Section: Introductionmentioning

confidence: 99%

On the hydrodynamics of active particles in viscosity gradients

Shaik¹,

Elfring²

2021

Preprint

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In this work, we analyze the motion of an active particle, modeled as a spherical squirmer, in linearly varying viscosity fields. In general, the presence of a particle will disturb a background viscosity field and the disturbance generated depends on the boundary conditions imposed by the particle on the viscosity field. We find that, irrespective of the details of the disturbance, active squirmer-type particle tend to align down viscosity gradients (negative viscotaxis). However, the rate of rotation and the swimming speed along the gradient do depend on the details of the interaction of the particle and the background viscosity field. In addition, we explore the relative importance on the dynamics of the local viscosity changes on the surface of active particles versus the (nonlocal) changes in the flow field due to spatially varying viscosity (from that of a homogeneous fluid). We show that the relative importance of local versus nonlocal effects depends crucially on the boundary conditions imposed by the particle on the field. This work demonstrates the dangers in neglecting the disturbance of the background viscosity caused by the particle as well as in using the local effects alone to capture the particle motion.

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“…For the future, our model and analysis should be extended to two spatial dimensions to take into account full viscosity landscapes [55][56][57][58].…”

Section: Long-time Behaviourmentioning

confidence: 99%

Active noise-driven particles under space-dependent friction in one dimension

Breoni,

Löwen,

Blossey

2021

Preprint

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We study a Langevin equation describing the stochastic motion of a particle in one dimension with coordinate x, which is simultaneously exposed to a space-dependent friction coefficient γ(x), a confining potential U (x) and non-equilibrium (i.e., active) noise. Specifically, we consider frictions γ(x) = γ0 + γ1|x| p and potentials U (x) ∝ |x| n with exponents p = 1, 2 and n = 0, 1, 2. We provide analytical and numerical results for the particle dynamics for short times and the stationary probability density functions (PDFs) for long times. The short-time behaviour displays diffusive and ballistic regimes while the stationary PDFs display unique characteristic features depending on the exponent values (p, n). The PDFs interpolate between Laplacian, Gaussian and bimodal distributions, whereby a change between these different behaviours can be achieved by a tuning of the friction strengths ratio γ0/γ1. Our model is relevant for molecular motors moving on a one-dimensional track and can also be realized for confined self-propelled colloidal particles.

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Swimming sheet in a viscosity-stratified fluid

Cited by 20 publications

References 34 publications

Fore-aft clearance controls how three-dimensional confinement affects micropropulsion

Fore-aft clearance controls how three-dimensional confinement affects micropropulsion

On the hydrodynamics of active particles in viscosity gradients

Active noise-driven particles under space-dependent friction in one dimension

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