A thermodynamic efficiency for Stokesian swimming

Childress, Stephen

doi:10.1017/jfm.2011.561

Cited by 37 publications

(10 citation statements)

References 17 publications

(19 reference statements)

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“…It is therefore biologically relevant to investigate how the properties of a swimmer and its surrounding medium influence the efficiency of locomotion. The classical definition of thermodynamic efficiency was proved difficult to apply in swimming at low Reynolds number (Childress 2012). Lighthill introduced the Froude efficiency, a concept coming from propeller theory, to characterize the efficiency of low-Reynolds-number swimmers (Lighthill 1952(Lighthill , 1975.…”

Section: Power Dissipation and Swimming Efficiencymentioning

confidence: 99%

Squirming motion in a Brinkman medium

Nganguia

Pak

2018

J. Fluid Mech.

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Micro-organisms encounter heterogeneous viscous environments consisting of networks of obstacles embedded in a viscous fluid medium. In this paper we analyse the characteristics of swimming in a porous medium modelled by the Brinkman equation via a spherical squirmer model. The idealized geometry allows an analytical and exact solution of the flow surrounding a squirmer. The propulsion speed obtained agrees with previous results using the Lorentz reciprocal theorem. Our analysis extends these results to calculate the power dissipation and hence the swimming efficiency of the squirmer in a Brinkman medium. The analytical solution enables a systematic analysis of the structure of the flow surrounding the squirmer, which can be represented in terms of singularities in Brinkman flows. We also discuss the spatial decay of flows due to squirming motion in a Brinkman medium in comparison with the decay in a purely viscous fluid. The results lay the foundation for subsequent studies on hydrodynamic interactions, nutrient transport and uptake by micro-organisms in heterogeneous viscous environments.

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Section: Power Dissipation and Swimming Efficiencymentioning

confidence: 99%

Squirming motion in a Brinkman medium

Nganguia

Pak

2018

J. Fluid Mech.

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“…Even at low Reynolds numbers, where drag and thrust are unambiguously distinguishable, the above W diss (10 -10 J) mentioned efficiency remains an ill-defined concept and can take arbitrarily large values (Childress, 2012;Leshansky et al, 2007). Thus, one needs to be careful when interpreting the Froude efficiency.…”

Section: Propulsion Efficiencymentioning

confidence: 99%

Hydrodynamics and energetics of jumping copepod nauplii and copepodids

Wadhwa

Andersen

Kiørboe

2014

Journal of Experimental Biology

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Within its life cycle, a copepod goes through drastic changes in size, shape and swimming mode. In particular, there is a stark difference between the early (nauplius) and later (copepodid) stages. Copepods inhabit an intermediate Reynolds number regime (between ~1 and 100) where both viscosity and inertia are potentially important, and the Reynolds number changes by an order of magnitude during growth. Thus we expect the life stage related changes experienced by a copepod to result in hydrodynamic and energetic differences, ultimately affecting the fitness. To quantify these differences, we measured the swimming kinematics and fluid flow around jumping Acartia tonsa at different stages of its life cycle, using particle image velocimetry and particle tracking velocimetry. We found that the flow structures around nauplii and copepodids are topologically different, with one and two vortex rings, respectively. Our measurements suggest that copepodids cover a larger distance compared to their body size in each jump and are also hydrodynamically quieter, as the flow disturbance they create attenuates faster with distance. Also, copepodids are energetically more efficient than nauplii, presumably due to the change in hydrodynamic regime accompanied with a welladapted body form and swimming stroke.

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“…It is therefore biologically relevant to investigate how the properties of a swimmer and its surrounding medium influence the efficiency of locomotion. The classical definition of thermodynamic efficiency was proved difficult to apply in swimming at low Reynolds numbers [19]. Lighthill introduced the Froude efficiency, a concept coming from propeller theory, to characterize the efficiency of low-Reynolds-number swimmers [20,21].…”

Section: Introductionmentioning

confidence: 99%

Swimming efficiency in a shear-thinning fluid

2017

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Micro-organisms expend energy moving through complex media. While propulsion speed is an important property of locomotion, efficiency is another factor that may determine the swimming gait adopted by a micro-organism in order to locomote in an energetically favorable manner. The efficiency of swimming in a Newtonian fluid is well characterized for different biological and artificial swimmers. However, these swimmers often encounter biological fluids displaying shear-thinning viscosities. Little is known about how this nonlinear rheology influences the efficiency of locomotion. Does the shear-thinning rheology render swimming more efficient or less? How does the swimming efficiency depend on the propulsion mechanism of a swimmer and rheological properties of the surrounding shear-thinning fluid? In this work, we address these fundamental questions on the efficiency of locomotion in a shear-thinning fluid by considering the squirmer model as a general locomotion model to represent different types of swimmers. Our analysis reveals how the choice of surface velocity distribution on a squirmer may reduce or enhance the swimming efficiency. We determine optimal shear rates at which the swimming efficiency can be substantially enhanced compared with the Newtonian case. The nontrivial variations of swimming efficiency prompt questions on how micro-organisms may tune their swimming gaits to exploit the shear-thinning rheology. The findings also provide insights into how artificial swimmers should be designed to move through complex media efficiently.

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A thermodynamic efficiency for Stokesian swimming

Cited by 37 publications

References 17 publications

Squirming motion in a Brinkman medium

Squirming motion in a Brinkman medium

Hydrodynamics and energetics of jumping copepod nauplii and copepodids

Swimming efficiency in a shear-thinning fluid

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