Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E8: Swimming IBio Fluids: External
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Chair: On Shun Pak, Santa Clara University Room: 501 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E8.00001: Is swimming in a shear-thinning fluid more efficient? Kyle Pietrzyk, Herve Nganguia, On Shun Pak Micro-organisms expend energy moving through complex fluids that often display shear-thinning viscosity. A motility mechanism not only needs to generate the necessary propulsion speed but also be energetically efficient. Although the efficiency of swimming is well characterized in Newtonian fluids, much less is known about this biologically relevant aspect of locomotion in shear-thinning fluids. Does the shear-thinning rheology render swimming more efficient or less? How does it alter the efficiency of different types of swimmers? We will address these fundamental questions of locomotion in a shear-thinning fluid. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E8.00002: Swimming in a yield stress fluid Neil Balmforth, Duncan Hewitt We extend G.I. Taylor's classic model of swimming in a viscous fluid using a wavy cylindrical tail by adding a yield stress to the ambient medium. We calculate how the swimming speed is modified for waves of both low and high amplitude. We examine the flow patterns created around the swimmer as it locomotes and comment on designing strategies for optimal progress. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E8.00003: Viscous propulsion in active transversely isotropic media Gemma Cupples, Rosemary Dyson, David Smith Taylor's swimming sheet is a classical model of microscale propulsion and pumping. Many biological fluids and substances are fibrous, having a preferred direction in their microstructure; for example cervical mucus. To understand how these effects modify viscous propulsion, we extend Taylor's classical model of small-amplitude viscous propulsion of a `swimming sheet' via the transversely-isotropic fluid model of Ericksen, which is linear in strain rate and possesses a distinguished direction. The energetic costs of swimming are significantly altered by all rheological parameters and the initial fibre angle. Propulsion in a passive transversely-isotropic fluid enhances mean rate of working, independent of the initial fibre orientation. In this regime the mean swimming velocity is unchanged from the Newtonian case. The effect of fibre tension, or alternatively a stresslet characterising an active fluid, is also considered. This stress introduces an angular dependence and dramatically changes the streamlines and flow field; fibres aligned with the swimming direction increase the energetic demands of the sheet. The constant fibre stress may result in a reversal of the mean swimming velocity and a negative mean rate of working if sufficiently large relative to the other parameters. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E8.00004: Statistical analysis of sperm sorting James Koh, Marcos Marcos The success rate of assisted reproduction depends on the proportion of morphologically normal sperm. It is possible to use an external field for manipulation and sorting. Depending on their morphology, the extent of response varies. Due to the wide distribution in sperm morphology even among individuals, the resulting distribution of kinematic behaviour, and consequently the feasibility of sorting, should be analysed statistically. In this theoretical work, Resistive Force Theory and Slender Body Theory will be applied and compared. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E8.00005: Regularized Stokeslet representations for the flow around a human sperm Kenta Ishimoto, Hermes Gadelha, Eamonn Gaffney, David Smith, Jackson Kirkman-Brown The sperm flagellum does not simply push the sperm. We have established a new theoretical scheme for the dimensional reduction of swimming sperm dynamics, via high-frame-rate digital microscopy of a swimming human sperm cell. This has allowed the reconstruction of the flagellar waveform as a limit cycle in a phase space of PCA modes. With this waveform, boundary element numerical simulation has successfully captured fine-scale sperm swimming trajectories. Further analyses on the flow field around the cell has also demonstrated a pusher-type time-averaged flow, though the instantaneous flow field can temporarily vary in a more complicated manner - even pulling the sperm. Applying PCA to the flow field, we have further found that a small number of PCA modes explain the temporal patterns of the flow, whose core features are well approximated by a few regularized Stokeslets. Such representations provide a methodology for coarse-graining the time-dependent flow around a human sperm and other flagellar microorganisms for use in developing population level models that retain individual cell dynamics. Reference: K. Ishimoto et al., PRL, 118 (2017) 124501. [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E8.00006: Scattering of spermatozoa off cylindrical pillars Anton Bukatin, Enkeleida Lushi, Vasily Kantsler The motion of micro-swimmers in structured environments, even though crucial in processes such as in vivo and in vitro egg fertilization, is still not completely understood. We combine microfluidic experiments with mathematical modeling of 3D swimming near convex surfaces to quantify the dynamics of individual sperm cells in the proximity of cylindrical pillars. Our results show that the hydrodynamic and contact forces that account for the shape asymmetry and flagellar motion, are crucial in correctly describing the dynamics observed in the experiments. Last, we discuss how the size of the cylindrical obstacles determines whether the swimmers scatter off or get trapped circling the pillar. [Preview Abstract] |
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