Hydrodynamics of self-propulsion near a boundary: predictions and accuracy of far-field approximations

Spagnolie, Saverio E.; Lauga, Eric

doi:10.1017/jfm.2012.101

Cited by 438 publications

(641 citation statements)

References 80 publications

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“…For suspensions in a bounded domain, the swimming cells accumulate near the surface, as observed for bacteria (Li et al 2011) and up-swimming, bottom-heavy algae (Pedley & Kessler 1992), two different cellular organisms with opposite swimming modes, one 'pushing' the other 'pulling'. Several experimental and theoretical studies of swimming particle interactions with surfaces show that the particle interaction with the wall can vary with particle size, swimming type and particle shape and the long time trajectory of a swimming particle moving near a surface is not easily predicted (Li et al 2011;Berke et al 2008;Spagnolie & Lauga 2012;Zhu, Lauga & Brandt 2013). While most of these studies were conducted for solid walls, the motion toward a stress free surface, such as an air and water interface, show some similarities.…”

Section: Introductionmentioning

confidence: 99%

Active suspensions in thin films: nutrient uptake and swimmer motion

et al. 2013

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A numerical study of swimming particle motion and nutrient transport is conducted for a semidilute to dense suspension in a thin film. The steady squirmer model is used to represent the motion of living cells in suspension with the nutrient uptake by swimming particles modelled using a first-order kinetic equation representing the absorption process that occurs locally at the particle surface. An analysis of the dynamics of the neutral squirmers inside the film shows that the vertical motion is reduced significantly. The mean nutrient uptake for both isolated and populations of swimmers decreases for increasing swimming speeds when nutrient advection becomes relevant as less time is left for the nutrient to diffuse to the surface. This finding is in contrast to the case where the uptake is modelled by imposing a constant nutrient concentration at the cell surface and the mass flux results to be an increasing monotonic function of the swimming speed. In comparison to non-motile particles, the cell motion has a negligible influence on nutrient uptake at lower particle absorption rates since the process is rate limited. At higher absorption rates, the swimming motion results in a large increase in the nutrient uptake that is attributed to the movement of particles and increased mixing in the fluid. As the volume fraction of swimming particles increases, the squirmers consume slightly less nutrients and require more power for the same swimming motion. Despite this increase in energy consumption, the results clearly demonstrate that the gain in nutrient uptake make swimming a winning strategy for micro-organism survival also in relatively dense suspensions.

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Section: Introductionmentioning

confidence: 99%

Active suspensions in thin films: nutrient uptake and swimmer motion

et al. 2013

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“…We have performed according tests and found that hydrodynamic interactions increase on average the degree of deformation in the flow gradient. Close to surfaces, the description of hydrodynamic interactions changes [1,118].…”

Section: Discussion and Possible Extensions Of The Modelmentioning

confidence: 99%

Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

2016

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Deformability is a central feature of many types of microswimmers, e.g. for artificially generated self-propelled droplets. Here, we analyze deformable bead-spring microswimmers in an externally imposed solvent flow field as simple theoretical model systems. We focus on their behavior in a circular swirl flow in two spatial dimensions. Linear (straight) two-bead swimmers are found to circle around the swirl with a slight drift to the outside with increasing activity. In contrast to that, we observe for triangular three-bead or square-like four-bead swimmers a tendency of being drawn into the swirl and finally getting drowned, although a radial inward component is absent in the flow field. During one cycle around the swirl, the self-propulsion direction of an active triangular or square-like swimmer remains almost constant, while their orbits become deformed exhibiting an "egg-like" shape. Over time, the swirl flow induces slight net rotations of these swimmer types, which leads to net rotations of the egg-shaped orbits. Interestingly, in certain cases, the orbital rotation changes sense when the swimmer approaches the flow singularity. Our predictions can be verified in real-space experiments on artificial microswimmers.

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“…One exception is the literature on swimmers wherein models have been developed for a single organism or a few organisms that propel themselves in viscous [48][49][50][51][52][53][54][55][56][57][58] and non-Newtonian fluids [57,[59][60][61][62][63][64][65][66][67]. In particular, swarming hydrodynamic theories have been derived wherein swimmer densities with or without fluid flows are described as continuous fields [4,19,68,69].…”

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confidence: 99%

“…Here the fluid flows arising from swimming or squirming particles can be decomposed in terms of force dipoles or higher-order force distributions, leading to velocities that decay away from the swimmer as 1/r n ,n 2 [57, [73][74][75][76][77]. The sign and amplitude of this self-propulsioninduced flow field depend on the specific details of the "stroke" of the swimmer [55,56,58,68,78]. A qualitatively different flow arises if the potential is associated with a true "physical" force, arising from, say, electrostatic molecular, magnetic, or gravitational interactions.…”

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confidence: 99%

Swarming in viscous fluids: Three-dimensional patterns in swimmer- and force-induced flows

2016

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We derive a three-dimensional theory of self-propelled particle swarming in a viscous fluid environment. Our model predicts emergent collective behavior that depends critically on fluid opacity, mechanism of self-propulsion, and type of particle-particle interaction. In "clear fluids" swimmers have full knowledge of their surroundings and can adjust their velocities with respect to the lab frame, while in "opaque fluids" they control their velocities only in relation to the local fluid flow. We also show that "social" interactions that affect only a particle's propensity to swim towards or away from neighbors induces a flow field that is qualitatively different from the long-ranged flow fields generated by direct "physical" interactions. The latter can be short-ranged but lead to much longer-ranged fluid-mediated hydrodynamic forces, effectively amplifying the range over which particles interact. These different fluid flows conspire to profoundly affect swarm morphology, kinetically stabilizing or destabilizing swarm configurations that would arise in the absence of fluid. Depending upon the overall interaction potential, the mechanism of swimming ( e.g., pushers or pullers), and the degree of fluid opaqueness, we discover a number of new collective three-dimensional patterns including flocks with prolate or oblate shapes, recirculating pelotonlike structures, and jetlike fluid flows that entrain particles mediating their escape from the center of mill-like structures. Our results reveal how the interplay among general physical elements influence fluid-mediated interactions and the self-organization, mobility, and stability of new three-dimensional swarms and suggest how they might be used to kinetically control their collective behavior. DOI: 10.1103/PhysRevE.93.043112 The collective behavior of self-propelled agents in natural and artificial systems has been extensively studied . Many of the lessons learned from experimental and theoretical work conducted on organisms as diverse as bacteria, ants, locusts, and birds [23][24][25][26][27][28][29][30][31][32][33][34][35][36] have been successfully applied to engineered robotic systems to help frame decentralized control strategies through ad hoc algorithms [37][38][39][40][41][42][43][44]. In most mathematical "swarming" models, particles are assumed to be self-driven by internal mechanisms that impart a characteristic speed. A pairwise short-ranged repulsion and a long-ranged decaying attraction are typically employed as the most realistic choices when modeling aggregating particles [9,11,45]. The interplay between self-propulsion, particle interactions, initial conditions, and number of particles is key in determining the large scale patterns that dynamically arise. In two dimensions, rotating mills and translating flocks are often observed, the latter configuration also arising in three dimensions [9,10,17,19,46,47]. It is possible to classify swarm morphology in terms of interaction strength and length scales, as shown for particles coupled via conserved f...

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Hydrodynamics of self-propulsion near a boundary: predictions and accuracy of far-field approximations

Cited by 438 publications

References 80 publications

Active suspensions in thin films: nutrient uptake and swimmer motion

Active suspensions in thin films: nutrient uptake and swimmer motion

Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

Swarming in viscous fluids: Three-dimensional patterns in swimmer- and force-induced flows

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