Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session U30: Focus Session: Fluid Dynamics of Animal Motion |
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Sponsoring Units: DFD Chair: Meredith Betterton, University of Colorado Room: Colorado Convention Center 304 |
Thursday, March 8, 2007 8:00AM - 8:36AM |
U30.00001: Modeling Bodies Locomoting through Fluids Invited Speaker: Locomotion of an organism through a fluid is one of the most fascinating fluid-structure interactions. How an organism accomplishes this feat depends on many things, such as whether the fluid is inertial (i.e., big bodies, high Reynolds number), overdamped(small bodies, low Reynolds number), or somewhere in between. The presence of boundaries, or of other moving bodies in the fluid, or non-Newtonian behavior of the fluid, makes the problem richer. I will not discuss the biology of locomotion per se, but rather focus on what mathematical models and simulations of prototype physical systems reveal of the core physical interactions that underlie locomotion. This includes how bodies can locomote by taking advantage of symmetry breaking instabilities in fluidic response, the instability and persistence of orientational order in active suspensions, and the effect of visco-elasticity at low Reynolds number. [Preview Abstract] |
Thursday, March 8, 2007 8:36AM - 8:48AM |
U30.00002: ABSTRACT WITHDRAWN |
Thursday, March 8, 2007 8:48AM - 9:00AM |
U30.00003: Swimming in a viscoelastic fluid Eric Lauga The fluid mechanics of swimming microorganisms was pioneered by G.I. Taylor more than fifty years ago, and is one of the most mature branch of biophysics. Most previous studies have assumed the fluid to be Newtonian. However, a variety of biologically relevant situations involve non-Newtonian fluids, including sperm motion in cervical mucus as well as ciliary transport of mucus in the lungs. In this talk, we present simple models of swimming in viscoelastic fluids and discuss the impact of elastic stresses on swimming kinematics and energetics. [Preview Abstract] |
Thursday, March 8, 2007 9:00AM - 9:12AM |
U30.00004: A Model for the Viscous Synchronization of Bacterial Flagella Qian Bian, Leila Setayeshgar, Thomas R. Powers, Kenneth Breuer Many flagellated bacteria propel themselves by rotating several helical flagella. The motors that rotate these filaments operate in a constant torque mode, and can alternate between counter-clockwise and clockwise motion. Although they reverse direction independently and randomly, the filaments are observed to coordinate and form a bundle during the run phase of the cell motion. We bring both experimental and theoretical tools to study a model problem which considers rotating paddles rather than helical filaments. The paddles are simpler both to construct and to model, and exhibit stronger viscous interactions than thin helices. Experimentally, we find that the paddles coordinate in about 15 rotations, and stay in synchronized motion with a phase difference of $\pi/2$, although this phase difference increases if there is a torque mismatch between the two motors. The synchronization is observed to persist indefinitely. However, as the paddle separation increases, the synchronization is weaker, and can exhibit instabilities. Theoretical models based on the long-range hydrodynamic interaction of Stokes flow are compared with the experimental results. [Preview Abstract] |
Thursday, March 8, 2007 9:12AM - 9:24AM |
U30.00005: The mechanics of slithering David Hu, John Bush, Michael Shelley Snakes propel themselves over land using a variety of techniques, including a unidirectional accordion-like mode, lateral sinuous slithering and sidewinding. We explore these friction-based propulsion mechanisms through a combined experimental and theoretical investigation. Particular attention is given to classifying the gaits of snakes according to Froude number and the relative magnitudes of the frictional forces in the tangential and normal directions. While the term ``gait'' is usually used to describe a sequence of foot movements, here it refers to a sequence of undulations made by the limbless snake. In a simple mass-spring model, we prescribe the muscle activity of the snake and then calculate its motion as required by the torque and force balances on its body. A key feature of our model is that it allows us to rationalize the mode of locomotion of the snake on the basis of propulsive efficiency. [Preview Abstract] |
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