Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session HV: Swimming III |
Hide Abstracts |
Chair: Matthew Ringuette, University of Buffalo, SUNY Room: 205A-D |
Monday, November 23, 2009 10:30AM - 10:43AM |
HV.00001: A Fast-Starting Robotic Fish Yahya Modarres-Sadeghi, Matthew Watts, Joe Conte, Franz Hover, Michael Triantafyllou We have built a simple mechanical system to emulate the fast-start performance of fish. The system consisted of a thin metal beam covered by a urethane rubber fish body. The body form of the mechanical fish in this work was modeled from a pike species, which is the most successfully studied fast-start specialist species. The mechanical fish was held in curvature and hung in water by two restraining lines, which were simultaneously released by pneumatic cutting mechanisms. The potential energy in the beam was transferred into the fluid, thereby accelerating the fish, similar to a pike. We measured the resulting velocity and acceleration, as well as the efficiency of propulsion for the mechanical fish model and also ran a series of flow visualization tests to observe the resulting flow pattern. We also studied the influence of stiffness and geometry of the tail on the efficiency of propulsion and flow pattern. The hydrodynamic efficiency of the fish, calculated by the transfer of energy, was around 10{\%}. Flow visualization of the mechanical fast-start wake was also analyzed, showing that the acceleration is associated with the fast movement of an intense vortex in a near-lateral direction. [Preview Abstract] |
Monday, November 23, 2009 10:43AM - 10:56AM |
HV.00002: Biologically inspired impulsive starting and maneuvering for solitary and aggregate systems Alexandra Techet Fast starting and maneuvering in the aquatic realm typically involve the formation of distinct vortex rings that deliver an impulsive change in the animal's momentum. This enables these aquatic animals to maneuver in smaller spaces than that required by conventional underwater vehicles. PIV and dye visualization results from fast-starting and jumping fish, as well as impulsively starting flapping foils and propellers will be compared with unsteady propulsion by salps. Salps, or pelagic tunicates, are common gelatinous organisms in oceanic waters, which swim and maneuver by jet propulsion. Inspecting the wake generated by a rapidly maneuvering fish, foil or propeller offers insight into the impulse imparted on the system during the maneuver. Modeling the wake of maneuvering systems as a series of vortex ring impulses, with considerations taken for added mass effects, allows for relatively straightforward analysis. The swimming and maneuvering of aggregate swimmers, e.g. those chained together in series or parallel, can be modeled using a series of distinct vortex rings generated by each individual in the chain, with some phase shift between each individual. [Preview Abstract] |
Monday, November 23, 2009 10:56AM - 11:09AM |
HV.00003: Vortex Formation and Acceleration of a Fish-Inspired Robot Performing Starts from Rest Adam DeVoria, Jonathan Bapst, Matthew Ringuette We investigate the unsteady flow of a fish-inspired robot executing starts from rest, with the objective of understanding the connection among the kinematics, vortex formation, and acceleration performance. Several fish perform ``fast starts,'' where the body bends into a ``C'' or ``S'' shape while turning (phase I), followed by a straightening of the body and caudal fin and a linear acceleration (phase II). The resulting highly 3-D, unsteady vortex formation and its relationship to the acceleration are not well understood. The self-propelled robotic model contains motor-driven joints with programmable motion to emulate phase II of a simplified C-start. The experiments are conducted in a water tank, and the model is constrained to 1 direction along rails. The velocity is measured using digital particle image velocimetry (DPIV) in multiple planes. Vortex boundaries are identified using the finite-time Lyapunov exponent, then the unsteady vortex circulation is computed. The thrust is estimated from the identified vortices, and correlated with the circulation and model acceleration for different kinematics. [Preview Abstract] |
Monday, November 23, 2009 11:09AM - 11:22AM |
HV.00004: 3D Numerical simulations of the C-start of a Bluegill Sunfish Venkat R.T. Narayanan, Iman Borazjani, Fotis Sotiropoulos, Eric D. Tytell, George V. Lauder Obtaining the 3D flow field, forces, and power produced during the fast start maneuvers of fish is essential for studying this behavior from the hydrodynamics perspective. During a typical fast start, which is typically referred to as the C-start, the fish initially bends its body in a C shape manner and then with a fast stroke bends out of the C shape. We carry out high-resolution, 3D simulations of a bluegill sunfish performing a C-start maneuver. The body geometry and motion during the C-start are obtained from the experimental. We used high-speed video and particle image velocimetry to quantify body motion and flows produced during the C-start. We carry out simulations both with the entire motion prescribed and by prescribing only the deformation of the body but predicting the motion of the fish center of mass via a fluid-structure interaction approach. The computed results are compared with experimental observations and analyzed to further elucidate dynamics and three-dimensional structure of the C-start flowfields. [Preview Abstract] |
Monday, November 23, 2009 11:22AM - 11:35AM |
HV.00005: A wake-based correlate of swimming performance in seven jellyfish species John Dabiri, Sean Colin, Kakani Katija, John Costello Animal-fluid interactions have been hypothesized as a principal selective pressure on the evolution of aquatic and aerial animals. However, attempts to discover the fluid dynamic mechanisms that dictate the fitness of an animal---or even to quantify `fitness'---have been limited by an inability to measure the fluid interactions of freely moving animals (i.e., in the absence of tethers or artificial water/wind currents) in comparative studies of multiple species with similar evolutionary histories. We used digital particle image velocimetry (DPIV) measurements to calculate wake kinetic energy, drag, and swimming speed of the seven co-occurring species of free-swimming jellyfish. Using this new data, we demonstrate that the swimming and foraging behavior are related to a robust fluid dynamic threshold between two distinct configurations of the wake vortices. The transition between the two wake vortex configurations is known as optimal vortex formation, because it maximizes the fluid dynamic thrust generated for a given energy input (Krueger and Gharib, Phys. Fluids 2003). By comparing the observed wake structures created by each jellyfish species with the optimal vortex configuration, we are able to predict their relative swimming efficiencies and proficiencies and to deduce their corresponding ecological niches. [Preview Abstract] |
Monday, November 23, 2009 11:35AM - 11:48AM |
HV.00006: Controlling pulsatile jet formation number with variable diameter exit nozzle for maximum impulse generation Mike Krieg, Tyler Thomas, Kamran Mohseni Both jellyfish and Squid propel themselves by ejecting high momentum vortex rings. A set of vortex ring generating thrusters were developed and tested for application in underwater vehicle propulsion. Vortex rings generated from a steady piston cylinder mechanism have a universal formation time, known as the formation number (Gharib et al. 1998), associated with reaching maximum circulation, where the vortex ring separates from its trailing shear flow. The non-dimensional jet formation time (also called the stroke ratio) plays a key role in the thrust output of the device; since thrusters operating above the formation number re-ingest the trailing jet. A variable diameter exit nozzle was used to increase the formation number of the jet to maximize thrust (which is a technique observed in squid and jellyfish locomotion). Visualization studies confirmed the ability to delay the onset of ring ``pinch-off'', using a variable nozzle, and the thrust was empirically shown to achieve a higher maximum. Additionally, a fluid slug model which was developed to predict the thrust output was adapted to incorporate a changing nozzle diameter. This model was verified with the empirical thrust data and was again shown to be accurate for stroke ratios below the formation number. [Preview Abstract] |
Monday, November 23, 2009 11:48AM - 12:01PM |
HV.00007: An Experimental Investigation of the Feeding Currents Generated by Upside-Down Jellyfish Arvind Santhanakrishnan, Laura Miller The flow characteristics of oblate medusan swimmers such as the moon jellyfish (\textit{Aurelia}) have been examined to understand the bio-fluid mechanics of feeding via unsteady propulsion (see Dabiri \textit{et al.}, J. Exp. Biol., 2005). The upside-down jellyfish (\textit{Cassiopea}) differs from the commonly observed swimming forms of scyphomedusae in that it is naturally found adhered to the muddy bottoms of shallow ocean waters. While they swim when disturbed, these organisms prefer to otherwise attach their bell surface to the floor and direct their oral arms upwards. Prey capture is accomplished by pulsatile contractions of the bell. The flow generated by the unsteady pulsations is examined using a combination of DPIV and morphological measurements. The phase-averaged flow field closely resembles a blowing jet centered about the body, with fluid entrainment occurring near the bell surface. Reversed flow regions are identified during both the contraction and relaxation phases. The effect of changing bell diameter on the jet as well as the production of flow structures is investigated. A qualitative comparison of the flow field between these organisms and swimming medusae will be presented. [Preview Abstract] |
Monday, November 23, 2009 12:01PM - 12:14PM |
HV.00008: Lagrangian coherent structures in jetting and paddling jellyfish swimming Doug Lipinski, Kamran Mohseni Lagrangian coherent structures (LCS) are a relatively new technique for visualizing and analysing structures and transport in complex fluid flows. In this study, we use LCS to examine the flow created by swimming jellyfish. We focus on identifying structures which contribute to feeding and propulsion and find several interesting results. Jellyfish which use different methods of propulsion create very different flow structures during swimming which are complimentary to the type of propulsion used. Additionally, we investigate the relationship between flow structures, pressure and swimming performance for the jetting Jellyfish, Sarsia tubulosa. We have previously detected structures within the bell of Sarsia tubulosa and we now focus on examining how these structures may impact the jellyfish's swimming. [Preview Abstract] |
Monday, November 23, 2009 12:14PM - 12:27PM |
HV.00009: Pulsed Jet Propulsive Efficiency of a Small Underwater Vehicle at Low \textit{Re} Ali Moslemi, Paul Krueger Propulsive efficiency of steady jet propulsion decreases as Reynolds number (\textit{Re}) decreases. Pulsed-jet propulsion can be an alternative option for traditional jet propulsion since it generates higher thrust than steady jet with the same mass flux rate. Moreover, previous work with a self-propelled pulsed-jet vehicle (Robosquid) at \textit{Re} in the range 1300 -- 2700 has shown: (a) an increase in pulsed jet efficiency at higher duty cycle (\textit{St}$_{L})$ and lower jet pulse length-to-diameter ratios ($L$/$D)$, and (b) the propulsive efficiency can be comparable to or exceed that for an equivalent steady jet when $L$/$D <$ 4 and \textit{St}$_{L} >$ 0.5. A simple analysis suggests further propulsive efficiency gains for pulsed jets over steady jets will be realized as Re is reduced. To test this prediction, Robosquid will be tested in glycerin to achieve \textit{Re} less than 1000. The effect of \textit{St}$_{L}$ and $L$/$D$ on propulsive efficiency will be measured at these lower \textit{Re} and compared with the previous results at higher \textit{Re}. [Preview Abstract] |
Monday, November 23, 2009 12:27PM - 12:40PM |
HV.00010: Stokesian Jellyfish Arthur Evans, Saverio Spagnolie, Eric Lauga Most studies into the swimming of microscopic organisms are directed at flagellated cells, ciliated bodies, or other biologically relevant models. However, biological systems need not be emulated in order to produce locomotion. We present here a proof-of-principle model for a closed bilayer vesicle swimming at low Reynolds number due to a prescribed physically-actuated shape change of the surface. By modulating the volume and membrane composition of the vesicle via osmotic or colloidal effects, the vesicle shapes change continuously in thermal equilibrium, leading to non-reciprocal deformation, and therefore swimming, if the proper conditions are satisfied. [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