Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session H39: Bio: Experiment and Theory of Microswimming |
Hide Abstracts |
Chair: Daphne Klotsa, University of North Carolina at Chapel Hill Room: Portland Ballroom 256 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H39.00001: Onset of motion and collective behavior for two-sphere swimmers Daphne Klotsa, Kyle Baldwin, Richard Hill, Roger Bowley, Michael Swift, Shannon Jones We describe experiments and simulations demonstrating the propulsion of a neutrally buoyant swimmer that consists of a pair of spheres attached by a spring, immersed in a vibrating fluid at intermediate Reynolds numbers. The vibration of the fluid induces relative motion of the spheres which, for sufficiently large amplitudes, can lead to motion of the center of mass of the two spheres. We find that the swimming speed obtained from both experiment and simulation agree and collapse onto a single curve if plotted as a function of the streaming Reynolds number, suggesting that the propulsion is related to streaming flows. There appears to be a critical onset value of the streaming Reynolds number for swimming to occur. We observe a change in the streaming flows as the Reynolds number increases, from that generated by two independent oscillating spheres to a collective flow pattern around the swimmer as a whole. The mechanism for swimming is traced to a strengthening of a jet of fluid in the wake of the swimmer and steady streaming. We discuss the collective behavior of such swimmers. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H39.00002: An underwater robo-leader for collective motion studies Yair Sanchez, Monica M. Wilhelmus A wide range of aquatic species, from bacteria to large tuna, exhibits collective behavior. It has long been hypothesized that the formation of complex configurations brings an energetic advantage to the members of a group as well as protection against larger predators or harmful agents. Lately, however, laboratory experiments have suggested that both the physics and the behavioral aspects of collective motion yield more complexity than previously attributed. With the goal to understand the fluid mechanical implications behind collective motion in a laboratory setting, we have developed a new device to induce this behavior on demand. Following recent studies of lab-induced vertical migration of Artemia salina, we have designed and constructed a remotely controlled underwater robotic swimmer that acts as a leader for groups of phototactic organisms. Preliminary quantitative flow visualizations done during vertical migration of brine shrimp show that this new instrument does induce collective motion in the laboratory. With this setup, we can address the hydrodynamic effect of having different swarm configurations, a variable that so far has been challenging to study in a controllable and reproducible manner. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H39.00003: Flow caused by the stalk contraction of Vorticella Sangjin Ryu, Eun-Gul Chung, David Admiraal Vorticella is a stalked protozoan, and its ultrafast stalk contraction moves the spherically-shrunken cell body (zooid) and thus causes surrounding water to flow. Because the fluid dynamics of this water flow is important for understanding the motility of Vorticella, we investigated the flow based on various fluid dynamics approaches. To find why Vorticella contracts its stalk, we propose a hypothesis that the protist utilizes the contraction-induced water flow to augment transport of food particles. This hypothesis was investigated using a computational fluid dynamics (CFD) model, which was validated with an experimental scale model of Vorticella. The CFD model enabled calculating the motion of particles around Vorticella and thus quantifying the transport effect of the stalk contraction. Also, we have developed a hydrodynamic drag model for easier estimation of Vorticella's contractility without using the CFD model. Because the contractile force of the stalk equals the drag on the moving zooid, the model enabled evaluating the contractile force and energetics of Vorticella based on its contraction speed. Analyses using the drag model show that the stalk contractility of Vorticella depends on the stalk length. [Preview Abstract] |
Monday, November 21, 2016 11:19AM - 11:32AM |
H39.00004: Simple low Reynolds number microswimmers U Kei Cheang, Min Jun Kim An extremely simple low Reynolds number microswimmer had been observed to swim in bulk fluid. The development of microscopic swimmers had been hindered by technical limitations in micro- and nanofabrication. To address this practical problem, the minimal geometrical requirements for swimming in low Reynolds number has been investigated. Micro- and nanofabrication of complex shapes with specialized materials, such as helices or flexible bodies, on a massive scale requires sophisticated state of the art technologies which have size limitations. In contrast, simple shaped structures, such as spherical particles, can be synthesized massively using chemical methods with relative ease at low costs. In this work, simple microswimmers were fabricated by conjugating two microbeads with debris attached to their surface. The debris allow the 2-bead structures to have two or more planes of symmetry, thus, allowing them to swim in bulk fluid at low Reynolds number. The microswimmers are magnetically actuated and controlled via a rotating magnetic field generated by an electromagnetic coil system. The microswimmers' velocity profiles had been characterized with respect to increasing rotating frequency. Furthermore, the motion of the microswimmers were analyzed using image processing. Finally, their swimming capability had been shown through experiments by steering the microswimmers in any desired direction. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H39.00005: The geometry and fluid dynamics of two- and three-dimensional maneuvers of burrowing and swimming C.\ elegans Jerzy Blawzdziewicz, Alejandro Bilbao, Amar Patel, Mizanur Rahman, Siva A. Vanapalli In its natural environment, which is decomposing organic matter and water, \textit{C.\ elegans} swims and burrows in 3D complex media. Yet quantitative investigations of \textit{C.\ elegans} locomotion have been limited to 2D motion. Recently [Phys.\ Fluids 25, 081902 (2013)] we have provided a quantitative analysis of turning maneuvers of crawling and swimming nematodes on flat surfaces and in 2D fluid layers. Here, we follow with the first full 3D description of how \textit{C.\ elegans} moves in complex 3D environments. We show that the nematode can explore 3D space by combining 2D turns with roll maneuvers that result in rotation of the undulation plane around the direction of motion. Roll motion is achieved by superposing a 2D curvature wave with nonzero body torsion; 2D turns (within the current undulation plane) are attained by variation of undulation wave parameters. Our results indicate that while hydrodynamic interactions reduce angles of 2D turns, the roll efficiency is significantly enhanced. This hydrodynamic effect explains the rapid nematode reorientation observed in 3D swimming. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H39.00006: Identification of internal properties of fibers and micro-swimmers Franck Plouraboue, Ibrahima Thiam, Blaise Delmotte, Eric Climent In this presentation we discuss the identifiability of constitutive parameters of passive or active micro-swimmers. We first present a general framework for describing fibers or micro-swimmers using a bead-model description. Using a kinematic constraint formulation to describe fibers, flagellum or cilia, we find explicit linear relationship between elastic constitutive parameters and generalised velocities from computing contact forces. This linear formulation then permits to address explicitly identifiability conditions and solve for parameter identification. We show that both active forcing and passive parameters are both identifiable independently but not simultaneously. We also provide unbiased estimators for elastic parameters as well as active ones in the presence of Langevin-like forcing with Gaussian noise using normal linear regression models and maximum likelihood method. These theoretical results are illustrated in various configurations of relaxed or actuated passives fibers, and active filament of known passive properties, showing the efficiency of the proposed approach for direct parameter identification. The convergence of the proposed estimators is successfully tested numerically. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H39.00007: Hydrodynamics of Microbial Filter-Feeding Anders Andersen, Lasse Tor Nielsen, Julia Dolger, Thomas Kiorboe Microbial filter-feeders form an important group of plankton with significance to the aquatic food webs. While the concept of filter-feeding is straightforward, our quantitative understanding of microbial filter-feeding leaves a lot to be desired. As a model organism, we focus on the filter-feeding choanoflagellate Diaphanoeca grandis. We quantify the feeding flow using particle tracking, and demonstrate that hydrodynamic theory underestimates the observed clearance rate by an order of magnitude. We find similar discrepancies for other choanoflagellate species, highlighting an apparent paradox. To resolve the paradox we argue that D. grandis and other choanoflagellates must have so far unbeknownst morphological features. Specifically, we suggest a flagellar vane that connects the flagellum to the filter, as known in choanocytes of sponges, creating a radically different, and order of magnitude more capable, pumping mechanism. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H39.00008: Feeding, Swimming and Navigation of Colonial Microorganisms Julius Kirkegaard, Ambre Bouillant, Alan Marron, Kyriacos Leptos, Raymond Goldstein Animals are multicellular in nature, but evolved from unicellular organisms. In the closest relatives of animals, the choanoflagellates, the unicellular species \textit{Salpincgoeca rosetta} has the ability to form colonies, resembling true multicellularity. In this work we use a combination of experiments, theory, and simulations to understand the physical differences that arise from feeding, swimming and navigating as colonies instead of as single cells. We show that the feeding efficiency decreases with colony size for distinct reasons in the small and large P{\'e}clet number limits, and we find that swimming as a colony changes the conventional active random walks of microorganism to stochastic helices, but that this does not hinder effective navigation towards chemoattractants. [Preview Abstract] |
Monday, November 21, 2016 12:24PM - 12:37PM |
H39.00009: Three-dimensional simulation of pseudopod-driven swimming of amoeboid cells Eric Campbell, Prosenjit Bagchi Pseudopod-driven locomotion is common in eukaryotic cells, such as amoeba, neutrophils, and cancer cells. Pseudopods are protrusions of the cell body that grow, bifurcate, and retract. Due to the dynamic nature of pseudopods, the shape of a motile cell constantly changes. The actin-myosin protein dynamics is a likely mechanism for pseudopod growth. Existing theoretical models often focus on the acto-myosin dynamics, and not the whole cell shape dynamics. Here we present a full 3D simulation of pseudopod-driven motility by coupling a surface-bound reaction-diffusion (RD) model for the acto-myosin dynamics, a continuum model for the cell membrane deformation, and flow of the cytoplasmic and extracellular fluids. The whole cell is represented as a viscous fluid surrounded by a membrane. A finite-element method is used to solve the membrane deformation, and the RD model on the deforming membrane, while a finite-difference/spectral method is used to solve the flow fields inside and outside the cell. The fluid flow and cell deformation are coupled by the immersed-boundary method. The model predicts pseudopod growth, bifurcation, and retraction as observed for a swimming amoeba. The work provides insights on the role of membrane stiffness and cytoplasmic viscosity on amoeboid swimming. [Preview Abstract] |
Monday, November 21, 2016 12:37PM - 12:50PM |
H39.00010: Fluid pumping using magnetic cilia Srinivas Hanasoge, Matt Ballard, Alexander Alexeev, Peter Hesketh Using experiments and computer simulations, we examine fluid pumping by artificial magnetic cilia fabricated using surface micromachining techniques. An asymmetry in forward and recovery strokes of the elastic cilia causes the net pumping in a creeping flow regime. We show this asymmetry in the ciliary strokes is due to the change in magnetization of the elastic cilia combined with viscous force due to the fluid. Specifically, the time scale for forward stroke is mostly governed by the magnetic forces, whereas the time scale for the recovery stroke is determined by the elastic and viscous forces. These different time scales result in different cilia deformation during forward and backward strokes which in turn lead to the asymmetry in the ciliary motion. To disclose the physics of magnetic cilia pumping we use a hybrid lattice Boltzmann and lattice spring method. We validate our model by comparing the simulation results with the experimental data. The results of our study will be useful to design microfluidic systems for fluid mixing and particle manipulation including different biological particles. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700