Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session M28: Undulatory Locomotion |
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Chair: Keith Moored, Princeton University Room: Ballroom II |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M28.00001: Lightweight robot locomotion on granular media Tingnan Zhang, Feifei Qian, Jeffrey Shen, Chen Li, Aaron Hoover, Paul Birkmeyer, Ronald Fearing, Daniel Goldman We present an experimental and computer simulation study of a small,
light-weight, biologically inspired robot running on a model granular
medium (GM), 3 mm diameter glass particles. The six-legged RoACH
robot
(10 cm long, 25 grams) utilizes an alternating tripod gait to run at
speeds up to 25 cm/sec. Forward speed increases with increasing limb
frequency $0 |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M28.00002: Motility analysis of the nematode C. elegans on wet soft media Josue Sznitman, Xiaoning Shen, Paulo Arratia Undulatory locomotion is widely utilized by limbless organisms such as snakes, eels and worms. When moving on top of wet soft gels (e.g. agar), undulating organisms such as the nematode {\it Caenorhabditis elegans} display a motility gait that is characterized by crawling. Until present however, a detailed understanding of how {\it C. elegans}' crawling gait generates propulsion over soft gels is lacking. Namely, how much crawling force does {\it C. elegans} generate? Here, we propose a simple model based on lubrication theory to examine the biomechanics of crawling motion. In analogy to the well-known resistive-force theory (RFT) for low Reynolds number swimming, our model provides a mechanism for the linear relation between the sliding speeds and the drag forces, and sheds light on the role of grooves created by nematodes on agar. We further examine the kinematics of locomotion experimentally and compare muscle activity patterns between crawling and swimming gaits, emphasizing the inherent differences in nematode adaptability to different environments. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M28.00003: Undulating Underperformance: Swimming in Elastic Media Xiaoning Shen, Paulo Arratia In this talk, we investigate the effects of fluid elasticity on the swimming behavior of the nematode \textit{Caenorhabditis elegans }by tracking the nematode's motion and measuring the corresponding velocity fields. We find that fluid elasticity hinders self-propulsion and fluid transportation. Compared to Newtonian solutions, fluid elasticity leads to 35{\%} slower propulsion speed. Furthermore, self-propulsion and fluid transportation are weakened as elastic stresses grow in magnitude in the fluid. This decrease in self-propulsion in viscoelastic fluids is related to the stretching of flexible molecules near hyperbolic points in the flow. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M28.00004: Locomotion of C elegans in structured environments Trushant Majmudar, Eric Keaveny, Michael Shelley, Jun Zhang We have established a combined experimental and numerical platform to study the swimming dynamics of an undulating worm in structured environments (fluid-filled micro-pillar arrays). We have shown that the worm (C. elegans) swims with different velocity and frequency depending on the lattice spacing and our purely mechanistic simulations (elastically linked bead-chain) reproduce the experimental results qualitatively and quantitatively, including ``life-like'' trajectories the worm exhibits. We build upon this platform to investigate more complex environments, such as linear and radial lattices, with gradients in spacing. In addition, we study C. elegans mutants to investigate the role of length of the worm, frequency of undulations, and mechano-sensation on the resultant dynamics. We also examine the worm moving through a lattice with random distribution of obstacles - a model soil-like environment. Our combined experimental and simulations approach allows us to gain insights into the dynamics of locomotion of undulating microorganisms in realistic complex environments. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M28.00005: A Treadmill to Localize, Exercise, and Measure the Propulsive Power of Nematodes Jinzhou Yuan, Han-Sheng Chuan, Michael Gnatt, David Raizen, Haim Bau The nematodes \textit{C. elegans} is often used as model biological system to study the genetic basis of behavior, disease-progression, and aging, as well as to develop new therapies and screen drugs. On occasion, it is desirable to quantify the nematode's muscle power. Here, we present a kind of nematode treadmill. The device consists of a tapered conduit filled with aqueous solution. The conduit is subjected to a DC electric field and to pressure-driven flow directed from the narrow end. The nematode is inserted at the conduit's wide end. Directed by the electric field (through electrotaxis), the nematode swims deliberately upstream toward the negative pole. As the conduit narrows, the average fluid velocity and the drag force on the nematode increase. Eventually, the nematode arrives at an equilibrium position, at which its propulsive power balances the viscous drag force. The nematode's propulsive power is estimated with direct numerical simulations of the flow field around the nematode. The calculations utilize the experimentally imaged gait as a boundary condition. The device is useful to retain the nematode at a nearly fixed position for prolonged observations under a microscope, to keep the nematode exercising, and to estimate the nematode's power based on the conduit's width at the equilibrium position. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M28.00006: Propulsion of {\it C. elegans} crawling on a wet surface A. Bilbao, A. Alavalapadu, Z.S. Khan, D.E. Salomon, S.A. Vanapalli, K. Rumbaugh, J. Blawzdziewicz Nematodes, such as soil-dwelling worms C. elegans, propel themselves by producing undulatory body motion. An important requirement for effective propulsion is to have large transverse and small longitudinal friction forces acting on a crawling worm. Recently, Sauvage et al. have shown that soft-lubrication forces between the worm body and a moist supporting substrate can produce, at most, the transverse friction coefficient twice as large as the longitudinal friction coefficient (and this ratio is too small for efficient propulsion). Here we show that hydrodynamic resistance of the fluid in liquid film adjacent to the worm body can generate significantly larger transverse friction, which moreover, is wavelength dependent. By modeling the worm as a long chain of spheres in Hele--Shaw flow, we have determined the optimal wavelength and amplitude of the undulatory motion that optimizes propulsion efficiency for a given rate of energy dissipation. The optimal worm shape qualitatively agrees with our experimental observations of C. elegans crawling in moist environments. [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M28.00007: Three-link Swimming in Sand R.L. Hatton, Yang Ding, Andrew Masse, Howie Choset, Daniel Goldman Many animals move within in granular media such as desert sand. Recent biological experiments have revealed that the sandfish lizard uses an undulatory gait to swim within sand. Models reveal that swimming occurs in a frictional fluid in which inertial effects are small and kinematics dominate. To understand the fundamental mechanics of swimming in granular media (GM), we examine a model system that has been well-studied in Newtonian fluids: the three-link swimmer. We create a physical model driven by two servo-motors, and a discrete element simulation of the swimmer. To predict optimal gaits we use a recent geometric mechanics theory combined with empirically determined resistive force laws for GM. We develop a kinematic relationship between the swimmer's shape and position velocities and construct connection vector field and constraint curvature function visualizations of the system dynamics. From these we predict optimal gaits for forward, lateral and rotational motion. Experiment and simulation are in accord with the theoretical predictions; thus geometric tools can be used to study locomotion in GM. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M28.00008: The role of body stiffness in wake production for anguilliform swimmers Eric Tytell, Megan Leftwich, Chia-Yu Hsu, Aves Cohen, Lisa Fauci, Alexander Smits We compare wake structures shed by the undulatory motion of physical and computational models of an anguilliform swimmer, the lamprey. The physical model is a robotic lamprey-like swimmer with an actively flexing tail, and with passively flexible tails of different stiffnesses. The computational model is a two-dimensional computational fluid dynamic (CFD) model that captures fluid-structure interaction using the immersed boundary framework. The CFD model included both actively flexing and passively flexible tail regions. Both models produced wakes with two or more same-sign vortices shed each time the tail changed direction (a ``2P'' or higher- order wake). In general, wakes became less coherent as tail flexibility increased. We compare the pressure distribution near the tail tip and the timing of vortex formation in both cases and find good agreement. Differences between self-propelled and tethered cases are detailed. Finally, we examine the effects of material resonance on force production. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M28.00009: Propulsion of an undulating elastic filament on a free surface Sophie Ramananarivo, Benjamin Thiria, Ramiro Godoy-Diana Nature offers a lot of examples of swimmers that use body undulations to move forward, such as eels or sperm. This type of locomotion involves strong fluid-structure interactions regardless of the regime of Reynolds number considered. Here we study a flexible filament forced to oscillate by imposing a harmonic motion to one of its extremities (using magnetic interactions) and propelling itself at the surface of a water tank. This experiment serves as a canonical model for studying the interactions between an elastic structure undergoing complex deformations and the surrounding fluid. We characterized the nature of the wave travelling the filament (by measuring its amplitude, phase velocity and spatial damping), as well as its propulsive performance in the different regimes encountered. [Preview Abstract] |
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