Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B31: Biological Fluid Dynamics: Micro-swimmer Computational |
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Chair: Sarah Olson, Worcester Polytechnic Institute Room: 613 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B31.00001: Instabilities and dynamics of phoretic suspensions Tullio Traverso, Sebastien Michelin Suspensions of Janus phoretic colloids are a canonical example of synthetic active fluids, whose potential applications range from technological to medical ones. Individual microscopic particles self-propel as a result of self-generated chemical gradients, and influence each other hydrodynamically and chemically. Such interactions lead to spontaneous nontrivial dynamics within phoretic suspensions, on length scales much larger than the swimmer size. We use a kinetic model to investigate the competition and interaction of self-propulsion with hydrodynamic and chemical couplings, whose characteristics are fundamentally determined by the shape and surface chemical properties of the particle, which are design parameters that can be controlled and optimized. Using a combination of linear stability analysis and nonlinear numerical simulations, we discuss the role of such design parameters in determining the onset of instabilities and subsequent nonlinear collective dynamics in dilute suspensions of chemically-active Janus swimmers. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B31.00002: The role of shape for a Brownian microswimmer interacting with walls Jean-Luc Thiffeault, Hongfei Chen We consider a simple model of a two-dimensional microswimmer with fixed swimming speed. The direction of swimming changes according to a Brownian process, and the swimmer is interacting with boundaries. This is a standard model for a simple microswimmer, or a confined wormlike chain polymer. The shape of the swimmer determines the range of allowable values that its degrees of freedom can assume --- its configuration space. Using natural assumptions about reflection of the swimmer at boundaries, we compute the swimmer's invariant distribution across a channel consisting of two parallel walls, and the statistics of spreading in the longitudinal direction. This gives us the effective diffusion constant of the swimmer's large scale motion. When the swimmer is longer than the channel width, it cannot reverse, and we then compute the mean drift velocity of the swimmer. This model offers insight into experiments of scattering of swimmers from boundaries, and serves as an exactly-solvable baseline when comparing to more complex models. [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B31.00003: Simulation and fabrication of neuromuscular biohybrid swimmers Mattia Gazzola, Onur Aydin, Xiaotian Zhang, Taher Saif Biohybrid machines have been developed using muscles to actuate soft robotic structures. The integration of neurons into the embodiment of such systems can transform them into intelligent machines able to adaptively respond to environmental cues. This relies on the ability of neural units to command muscle activity, making actuation through motor neurons the first milestone. Here, we achieve this milestone, and demonstrate neuromuscular actuation of a computationally designed biohybrid swimmer. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B31.00004: Swimming sheet in a density stratified fluid Rajat Dandekar, Vaseem Shaik, Arezoo Ardekani In this work, we theoretically investigate the swimming velocity of a Taylor swimming sheet immersed in a linearly density stratified fluid. We use a regular perturbation expansion approach to calculate the swimming velocity up to second order in wave amplitude. We use our results to understand the effect of stratification on the swimming behavior of organisms. Our study finds a direct application for swimmers in oceanic waters, where stratification occurs naturally either due to gradients in temperature or salinity. We divide our analysis in two regimes of low and high Reynolds numbers. We find that stratification significantly alters the flow field around the swimmer. This has a direct consequence on the motility characteristics of the swimmer such as swimming velocity, power expenditure, hydrodynamic efficiency and the induced mixing by the swimmer. We explore this dependence in detail for both the regimes of Reynolds number and elucidate the fundamental insights obtained. We expect our work to shed some light on the importance of stratification in the locomotion of organisms living in such environments. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B31.00005: Parameter Estimation for Micro-swimmers with Fully Resolved Hydrodynamics Sarah Olson, Karen Larson, Anastasios Matzavinos Due to the computational complexity of micro-swimmer models with fully resolved hydrodynamics, parameter estimation has been prohibitively expensive. We utilize a highly parallelizable Bayesian uncertainty quantification framework to estimate parameters from noisy data. In test cases, we utilize regularized fundamental solutions in a Lagrangian framework to calculate velocities of the swimmer and the force model of the swimmer is determined via an Euler elastica model with nonlinearities due to a preferred curvature. Results show that we can estimate both fluid and elastic swimmer parameters when using noisy swimmer trajectory data at 30 Hz. This methodology can be used to develop artificial micro-swimmers and understand parameter ranges that allow for certain motility patterns. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B31.00006: Diffusion of Multi-Speed Gear-Shifting Brownian Swimmers. Don Krasky, Daisuke Takagi We introduce a model for dispersion of independent swimmers jumping randomly between multiple translational velocities in arbitrary dimensions. Stochastic differential equations are introduced and used to produce simulations for comparison with theory. The associated Fokker-Planck equations are derived from the Langevin dynamics, giving an analytical prediction for the effective diffusion constant. This prediction is shown to be in good agreement with simulations, and is in a relatively simple form yielding a quick tool for experimentalists to obtain an accurate estimate of diffusion coefficient. A full analysis of the model is presented for the case with two velocities, and some extreme cases are discussed in the general model. We show adaptability of the model by fitting to three previous models of swimmers having two or three preferred velocities. These comparisons explore how stochastic vs. deterministic velocity changes and restricting certain velocity jumps result in different rates of dispersion [Preview Abstract] |
Saturday, November 23, 2019 5:58PM - 6:11PM |
B31.00007: Orientation of Spheroidal Swimmers in Turbulent Flows Filippo De Lillo, Matteo Borgnino, Guido Boffetta, Kristian Gustavsson, Bernhard Mehlig, Massimo Cencini We study the orientation statistics of spheroidal microswimmers in turburbulent and chaotic flows. This problem is relevant both for plankton ecology [1] and medical applications [2]. We use direct numerical simulations (DNS) to integrate the Lagrangian trajectories of particles swimming in turbulence with fixed speed and orientation governed by fluid gradients [3]. Swimmers elongated along their swimming axis, align with the local flow velocity, with preferential downstream swimming. By the perturbative solution of a statistical model [4], we show that the alignment is due to the peculiar correlation of fluid velocity and its gradients along particle paths caused by swimming. Numerical computation of the relevant correlations in DNS results shows that the theoretical prediction applies with remarkable precision to turbulent flows [5].\\ [1] JS Guasto, et al., Annu. Rev. Fluid Mech. 44, 373 (2012)\\ [2] R Dreyfus, et al., Nature 437, 862 (2005)\\ [3] GB Jeffery, Proc. Royal Soc. Lond. Ser. A 102, 161 (1922)\\ [4] K Gustavsson and B Mehlig, Advan. Phys. 65, 1 (2016)\\ [5] M Borgnino, et al.(Submitted to Phys Rev Lett, 2019) [Preview Abstract] |
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