Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E15: Biofluids: Large Swimmers II |
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Chair: Hossein Haj-Hajiri, University of Virginia Room: 28A |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E15.00001: Passive synchronization of finite dipoles in a doubly periodic domain Alan Cheng Hou Tsang, Eva Kanso We consider the interaction dynamics of finite dipoles in a doubly periodic domain. A finite dipole is a pair of equal and opposite strength point vortices separated by a finite distance throughout its time evolution. The finite dipole dynamical system has been proposed as a model that captures the far-field hydrodynamics interactions in fish schools or collections of swimming bodies in an inviscid fluid. In this work, we formulate the equations of motion governing the dynamics of finite dipoles in a doubly periodic domain. We show that a single dipole in a doubly-periodic box exhibits either regular or chaotic behavior, depending on the initial angle of orientation of the dipole. In the case of the two dipoles, we identify a variety of interesting interaction modes including collision, switching, and passive synchronization of the dipoles. In the case of three dipoles, we observe the formation of relative equilibrium in finite time when the dipoles move together in a way reminiscent to that of flocking behavior. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E15.00002: Optimal schooling formations using a potential flow model Andrew Tchieu, Mattia Gazzola, Alexia De Brauer, Petros Koumoutsakos A self-propelled, two-dimensional, potential flow model for agent-based swimmers is used to examine how fluid coupling affects schooling formation. The potential flow model accounts for fluid-mediated interactions between swimmers. The model is extended to include individual agent actions by means of modifying the circulation of each swimmer. A reinforcement algorithm is applied to allow the swimmers to learn how to school in specified lattice formations. Lastly, schooling lattice configurations are optimized by combining reinforcement learning and evolutionary optimization to minimize total control effort and energy expenditure. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E15.00003: Modeling of flapping-fin propulsion with Stuart-Landau oscillator equation Aren M. Hellum, Promode R. Bandyopadhyay Recently, the lowest order thrust measurements in an abstracted twisting and flapping fin have been modeled using a van der Pol-like oscillator (\textit{JFM }\textbf{702,} 298-331). A Stuart-Landau oscillator is used here as a higher order model of the interaction of the low aspect ratio flapping fin with its downstream thrust-producing reverse Karman vortex street. ``Quasi-steady'' equations for the forces produced on flapping fins or wings by the surrounding fluid assume that the lift and drag coefficients are based on `a$_{g}$(t)', a time-variable angle of attack based on the fin's instantaneous position and velocity. In this work, a wake-modified angle of attack `a(t)' is used, such that `a = a$_{g}$ + a$_{w}$' where `a$_{w}$(t)' is based on the circulation in the wake. This modification of the geometric angle of attack `a$_{g}$' is justified generally by the conservation of circulation within the fin-wake system, and we argue that a Stuart-Landau oscillator represents a good approximation of the circulation within the wake. Results of this modeling are compared with experimental data taken on the abstracted penguin wing planform; a strong quantitative agreement exists between the experimental and modeled systems. We also model the effects of Reynolds number and the dependence of system oscillation lock-in on initial condition. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E15.00004: Role of Strouhal number (St) in free swimming Mehdi Saadat, Hossein Haj-Hariri St of 0.2-0.4 has become synonymous with efficient self propulsion. Is it the cause, or an effect? As has been argued by a number of authors, St alone is insufficient to decide optimal motion because many inefficient combinations of amplitude and frequency lead to the same St. In this talk we show a simple ramification of free swimming where the swim speed and St are outputs. The iso-lines for speed, St, and thrust coincide so long as there is no massive leading-edge separation. It appears that St is simply related to how the drag coefficient and geometry of the body relates to the thrust coefficient and geometry of the propulsor. For a given combination of propulsor and body, St of motion is essentially independent of amplitude, frequency, and speed, and is only a function of shape. Some motions are efficient, and some are not. But they all have the same St. [Preview Abstract] |
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