Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session A9: Focus Session: Fluid Dynamics of Animal Motion |
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Sponsoring Units: DFD DBP Chair: Kenny Breuer, Brown University Room: Morial Convention Center RO7 |
Monday, March 10, 2008 8:00AM - 8:12AM |
A9.00001: Comparing flight strategies in species of fruit flies Itai Cohen, Leif Ristroph, Gordon Berman, Z. Jane Wang Observing different species of fruit flies offers an opportunity to compare flight strategies for insects of varying size but of nearly identical body and wing architecture. Using automated three-dimensional high-speed videography, we have captured many beautiful flight sequences of untethered fruit flies. From this data we have extracted the complete body and wing kinematics and determined the fluid forces acting on the wings using custom-written tracking and analysis software. We find that, in addition to lift, drag plays an important role in providing the vertical force needed for these insects to stay aloft. Moreover, our data base in combination with various numerical analysis techniques is allowing us to resolve whether these insects are flapping in the most efficient manner possible. Answers to this line of questions are important for determining what role if any evolution has played in determining how these insect fly. [Preview Abstract] |
Monday, March 10, 2008 8:12AM - 8:24AM |
A9.00002: Flow-induced attraction of swimming microorganisms by surfaces Eric Lauga, Allison Berke, Linda Turner, Howard Berg In this talk, we present an experimental and theoretical investigation of the accumulation of swimming cells by nearby surfaces. First, we present results of an experiment aiming at measuring the distribution of smooth-swimming E. coli when moving in a density-matched fluid and between two glass plates; the distribution for the bacteria concentration is found to peak near the glass plates. We then present a physical model for the observed attraction, based on the hydrodynamics interactions between the swimming cells and the walls. We show that such interactions result in a reorientation of the cells in the direction parallel to the surfaces, and an attraction of these (parallel) cells by the nearest wall. Our results are exploited to obtain an estimate of the propulsive force of smooth-swimming E. coli. [Preview Abstract] |
Monday, March 10, 2008 8:24AM - 8:36AM |
A9.00003: Effects of hydrodynamic interactions in bacterial swimming. Suddhashil Chattopadhyay, Xiao Lun Wu The lack of precise experimental data has prevented the investigation of the effects of long range hydrodynamic interactions in bacterial swimming. We perform measurements on various strains of bacteria with the aid of optical tweezers to shed light on this aspect of bacterial motility. Geometrical parameters recorded by fluorescence microscopy are used with theories which model flagella propulsion (Resistive force theory \& Lighthill's formulation which includes long range interactions). Comparison of the predictions of these theories with experimental data, observed directly from swimming bacterium, led to the conclusion that while long range inetractions were important for single polar flagellated strains (Vibrio Alginolyticus \& Caulobacter Crescentus), local force theory was adequate to describe the swimming of multi-flagellated Esherichia Coli. We performed additional measurements on E. Coli minicells (miniature cells with single polar flagellum) to try and determine the cause of this apparent effect of shielding of long range interactions in multiple flagellated bacteria. [Preview Abstract] |
Monday, March 10, 2008 8:36AM - 9:12AM |
A9.00004: Lagrangian studies of animal swimming and aquatic predator-prey interactions Invited Speaker: Experimental studies of animal swimming have been traditionally based on an Eulerian perspective in which the time-dependent flow field surrounding the animal is measured at fixed locations in space. The measured velocity field and its derivatives (e.g. vorticity) can, in principle, be used to deduce the forces, energetics, and fluid transport associated with locomotion in real fluids. However, achieving a connection between measurements of these Eulerian fields and the dynamics of locomotion has proven difficult in practice. We present the application of Lagrangian methods of flow analysis in which the time-dependent trajectories of individual tracer particles in the flow are measured experimentally and subsequently interrogated using dynamical systems tools in order to quantitatively resolve the dynamics of animal swimming. The Lagrangian methods are shown to be readily extended to time-dependent measurements in three spatial dimensions and to in situ field measurements using a recently developed self-contained underwater velocimetry apparatus (SCUVA). Case studies of jellyfish and other aquatic animals observed in the laboratory and in marine environments are used to illustrate the proposed approach. We also show that predator-prey interactions during jellyfish swimming can be addressed using the aforementioned Lagrangian methods in combination with the Maxey-Riley equations for inertial particles in fluid flow. [Preview Abstract] |
Monday, March 10, 2008 9:12AM - 9:24AM |
A9.00005: Shape transformations and propulsion due to an elastic filament rotating in a viscous fluid Bian Qian, Thomas Powers, Kenneth Breuer The deformation of an elastic filament in a viscous liquid is central to the mechanics of motility in cells ranging from \textit{E. coli} to sperm. We use experiments and theory to study the shape transition of a flexible rod rotating in a viscous fluid and set at an angle to the axis of rotation. In the experiments, two modes of operation are studied: constant torque and constant speed, and the shape of the filament is measured using stereoscopic imaging. At low applied torque, the rod bends gently, while at high torque, the rod adopts a helical shape with the tip close to the axis of rotation. At constant torque, the transition from the splayed form to the helical form is abrupt, accompanied by a sharp increase in the rotational speed. As the torque is decreased, the shape change exhibits hysteresis, transitioning back to the splayed form at a lower torque. At constant speed, the shape transition is continuous characterized by a region of decreasing torque that persists until the transition to the helical form is complete. Calculations based on slender body and resistive force theory predict the torque-speed relationship and the filament shape throughout the entire operating range, and show excellent agreement with the experiments. The propulsive force is predicted to increase sharply after the shape transformation, at which point the efficiency is also predicted to reach a maximum. [Preview Abstract] |
Monday, March 10, 2008 9:24AM - 9:36AM |
A9.00006: Propulsion by directional adhesion John Bush, Manu Prakash The rough, hairy integument of water-walking arthropods is well known to be responsible for their water-repellency; we here consider its additional propulsive role. We demonstrate that the tilted flexible leg hairs of water-walking arthropods render the leg cuticle directionally anisotropic: contact lines advance most readily towards the leg tips. The dynamical role of the resulting unidirectional adhesion is explored, and yields new insight into the manner in which water-walking arthropods generate thrust, glide and leap from the free surface. We thus provide new rationale for the fundamental topological difference in the roughness on plants and insects, and suggest novel directions for biomimetic design of smart, hydrophobic surfaces. [Preview Abstract] |
Monday, March 10, 2008 9:36AM - 9:48AM |
A9.00007: The role of the ventral pedal waves in the locomotion of terrestrial gastropods Janice Lai, Robert D. Shepherd, Juan C. del Alamo, Javier Rodriguez-Rodriguez, Juan C. Lasheras The locomotion of terrestrial gastropods exhibits unique characteristics which allow these animals to crawl on steep surfaces. Gastropods move by gliding over a ventral foot lubricated by mucus. They generate trains of pedal waves through periodic muscle contractions in the central portion of the ventral foot, producing a forward traction, while the rim of the foot adheres to the substrate and generates suction forces. We analyzed the kinematics and dynamics of locomotion by conducting two sets of experiments. In the first set, we used digital image processing to correlate the frequency and wavelength of the pedal waves to the migration velocity. In the second set, we computed the traction and adhesion forces produced by these animals from measurements of the deformation of an elastic substrate of known properties. We found that the strain energy exerted by the animal on the substrate is quasi-periodic, and explored a possible correlation between the mean speed of migration and the period of this energy fluctuation. In addition, we found that the pedal waves accelerate as they move forward along the ventral foot producing the symmetry break necessary for the generation of a net traction force. [Preview Abstract] |
Monday, March 10, 2008 9:48AM - 10:00AM |
A9.00008: Flying, swimming and fluttering in 3D: potential flow around a rectangular deformable plate Christophe Eloy, Lionel Schouveiler The interaction between a flexible rectangular plate and the flow around it can serve as a model for several phenomena. This situation arises in many problems of animal locomotion as well as industrial ones such as airfoil flutter. So far, most models have assumed a 2D problem for the sake of simplicity. We show here how to extend these models to include the finite plate aspect ratio in the analysis. We consider a rectangular deformable plate moving in a uniform flow at small amplitude such that the plate and its wake remain in the same plane at first order. The potential flow around the plate is calculated in the Fourier space and then averaged along the span. The result is a new integral equation for the vorticity distribution both inside the solid plate and in its wake. It means that the 3D effects can be taken into account by simply modifying the potential of a point-vortex (or equivalently the Green function of the Laplace's equation). [Preview Abstract] |
Monday, March 10, 2008 10:00AM - 10:12AM |
A9.00009: Symmetry breaking in gastropod locomotion through acceleration or deceleration of the pedal waves Juan C. del Alamo, Javier Rodriguez-Rodriguez, Janice Lai, Robert D. Shepherd, Juan C. Lasheras Marine and terrestrial gastropods move by gliding over a ventral foot that is lubricated by secreted mucus (terrestrial) or simply by water (marine). The rim of the ventral foot generates suction forces that keep the animal adhered to the substrate. The central part of the foot produces a forward traction force by generating trains of pedal waves through periodic muscle contractions. Recent experiments show that, in some gastropods, these pedal waves become faster and longer as they move forward, suggesting a mechanism for breaking the symmetry in the flow between the pedal waves and the substrate. To investigate this mechanism, we have analyzed theoretically a two-dimensional lubrication layer between a train of waves of slowly varying length and speed, and a flat, rigid, impermeable surface. The inhomogeneity of the pedal waves has been modeled through multiple-scale asymptotics. We have considered a Newtonian fluid to separate the effect of this inhomogeneity from the viscoelastic symmetry breaking reported in previous works. [Preview Abstract] |
Monday, March 10, 2008 10:12AM - 10:24AM |
A9.00010: The unsteady flow over a bat wing in mid-downstroke. Florian Muijres, Christoffer Johansson, Ryan Barfield, Marta Wolf, Geoffrey Spedding, Anders Hedenstrom Birds, bats and insects have provided inspiration for human-designed small-scale flying machines, and while insects have long been known to rely on unsteady separated flows for their above-average aerodynamic performance at small-scale, the details of air flows over bird and bat wings have been harder to elucidate, mainly because of the extra complexity and precautions required in live experiments. Here we report on the first experiments of the airflow around a bat wing in free (but trained) flight in a low-turbulence wind tunnel. The aerodynamics of fixed wings at these Reynolds numbers are notoriously sensitive to small disturbances of the initially laminar, attached boundary layer, but these flight experiments show that the instantaneous flow fields around the flapping wing bear almost no resemblance to an equivalent fixed-wing experiment. The circulation increment due to the presence of a strong leading-edge vortex is estimated to provide a significant fraction of the total lift. Implications for the design and control of micro-air vehicles are considered. [Preview Abstract] |
Monday, March 10, 2008 10:24AM - 10:36AM |
A9.00011: Mechanics of Mammalian Swimming Timothy Wei, Paul Legac, Frank Fish, Terrie Williams, Russell Mark, Sean Hutchison Propulsion of large mammals ($i.e.$ dolphins and humans) has been of great interest for both technological and athletic reasons. The foundational question is how fast can a mammal swim? Digital Particle Image Velocimetry (DPIV) has been modified to be safely used on swimmers and dolphins. Experiments of dolphins performing various swimming behaviors were performed at the Long Marine Laboratory, University of California, Santa Cruz. Vortices generated by the dolphins' tail motions were used to estimate thrust production. Also, a two-dimensional dynamic force balance was constructed to study and improve the mechanics of elite swimmers. Paired with an underwater video camera, the forces seen could be directly related to the motion of the swimmer. These force measurements could be correlated to time resolved DPIV measurements of flow around the swimmers. Measurements made with swimmers, Megan Jendrick (2000 Olympic gold medalist) and Ariana Kukors (4x US National Champion), as well as data from trials with two dolphins will be presented. [Preview Abstract] |
Monday, March 10, 2008 10:36AM - 10:48AM |
A9.00012: Synchronization and hydrodynamic interactions Thomas Powers, Bian Qian, Kenneth Breuer Cilia and flagella commonly beat in a coordinated manner. Examples include the flagella that Volvox colonies use to move, the cilia that sweep foreign particles up out of the human airway, and the nodal cilia that set up the flow that determines the left-right axis in developing vertebrate embryos. In this talk we present an experimental study of how hydrodynamic interactions can lead to coordination in a simple idealized system: two nearby paddles driven with fixed torques in a highly viscous fluid. The paddles attain a synchronized state in which they rotate together with a phase difference of 90 degrees. We discuss how synchronization depends on system parameters and present numerical calculations using the method of regularized stokeslets. [Preview Abstract] |
Monday, March 10, 2008 10:48AM - 11:00AM |
A9.00013: An experimental and numerical study of fluid flow generated by a single nodal cilium Xingzhou Yang, Lisa Fauci, Arshad Kudrolli A rotating nodal cilia is said to generate fluid flow in the node of a developing embryo by posterior tilt leading to the left-right asymmetry of the mammalian body. In order to develop a physical understanding of the flow generated and the effect of the enclosing chamber, we perform scaled-up fluid-mechanics experiments and numerical simulations using the method of Regularized Stokeslets for zero Reynolds number. Important mechanical parameters, such as the geometry of the rods, dimensions of the tank, and the ratio of viscous to elastic stresses can be scaled to match typical cilia and cell. Digital imaging and tracer particle tracking techniques are used to measure the location and shape of the rods and the fluid flow. We will discuss the nature of the hydrodynamic velocity fields which are found to be more complex than anticipated by previous studies. [Preview Abstract] |
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