Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session GF: Biofluids VIII: Swimming |
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Chair: Aline Cotel, University of Michigan Room: Salt Palace Convention Center 151 G |
Monday, November 19, 2007 10:30AM - 10:43AM |
GF.00001: DPIV Measurements on Dolphins: Examining Gray's Paradox Paul Legac, Frank Fish, Terrie Williams, Timothy Wei In 1936 James Gray attempted to evaluate the strength of a dolphin by calculating the drag a dolphin must overcome while swimming and comparing that to the theoretical amount of thrust the dolphin can produce using its musculature. According to Gray, the muscles of a dolphin are not powerful enough to overcome the drag produced; this is now known as `Gray's Paradox'. To solve the problem, Gray surmised that the flow over the dolphin would need to stay laminar in order to reduce the drag. To examine `Gray's Paradox', DPIV has been modified to be used on a dolphin swimming in a tank of stationary water. 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. Data from two dolphins and multiple runs will be presented. [Preview Abstract] |
Monday, November 19, 2007 10:43AM - 10:56AM |
GF.00002: A Study of a Mechanical Swimming Dolphin Lilly Fang, Daniel Maass, Megan Leftwich, Alexander Smits A one-third scale dolphin model was constructed to investigate dolphin swimming hydrodynamics. Design and construction of the model were achieved using body coordinate data from the common dolphin (Delphinus delphis) to ensure geometric similarity. The front two-thirds of the model are rigid and stationary, while an external mechanism drives the rear third. This motion mimics the kinematics of dolphin swimming. Planar laser induced florescence (PLIF) and particle image velocimetry (PIV) are used to study the hydrodynamics of the wake and to develop a vortex skeleton model. [Preview Abstract] |
Monday, November 19, 2007 10:56AM - 11:09AM |
GF.00003: Velocity Measurements of a Pistol Shrimp's Micro Water Jet Using High Speed PIV J. Torres, K. Washington, S. Wong, M. Zarzecki, Y. Cheng, F.J. Diez The pistol shrimp generates a high speed micro water jet that was studied experimentally using time resolved particle image velocimetry. The pistol shrimp, with an average size of about 5.5 cm, is considered to be one of the loudest animals in the world. The sound generated can reach intensity levels as high as 200 db. In the past, it was believed that the loud noise was produced by the shrimp closing its claws. Recent research has revealed that the sound is actually generated by a bubble that is created when the claw is shut. The generated bubble is followed by a micro jet. This process is used by the shrimp to stunt and attack preys and to defend itself. In this cavitation process, the bubble is created by a sudden drop in pressure as the claw closes at speeds of 100 km/hr. The temperature inside the bubble can range from 5,000 to 10000 degrees Kelvin and generates infrared light. This whole process is estimated to last around 300 microseconds. The phenomenon of the bubble itself is believed to take at most 10 nanoseconds. This research focuses in visualizing the bubble and the micro jet produced during the closing of the claw and characterizing the velocity field generated by the micro jet by taking PIV images at a rate of up to 40,000 frames per second. [Preview Abstract] |
Monday, November 19, 2007 11:09AM - 11:22AM |
GF.00004: A theoretical framework for fish-eddy interactions Aline Cotel, Paul Webb The natural habitats of fishes are characterized by water movements driven by a multitude of physical processes of either natural or human origin. The resultant unsteadiness is exacerbated when flow interacts with surfaces, such as the bottom and banks, and protruding objects, such as corals, boulders, and woody debris. There is growing interest in the impacts on performance and behavior of fishes swimming in ``turbulent flows''. The ability of fishes to stabilize body postures and their swimming trajectories is thought to be important in determining species distributions and densities, and hence resultant assemblages in various habitats. Understanding impacts of turbulence on fishes is also important as human practices modify water movements, and as turbulence-generating structures ranging from hardening shorelines to control erosion, through designing fish deterrents, to the design of fish passageways become common. A new theoretical framework is proposed to quantify fish-eddy interactions. Dimensionless parameters are derived based on a common element: eddy circulation. A set of variables defines the flow field whereas a second set quantifies fish characteristics as an embedded body in the flow. By comparing both sets of variables, different regimes are predicted describing fish responses to a wide range of physical perturbations. [Preview Abstract] |
Monday, November 19, 2007 11:22AM - 11:35AM |
GF.00005: An efficient algorithm for fully resolved simulation of freely swimming bodies Anup Shirgaonkar, Neelesh Patankar, Malcolm MacIver There is a need to better understand the physical principles underlying the extraordinary mobility of swimming and flying animals. To that end, we present a fully resolved simulation scheme for aquatic locomotion that is sufficiently general to potentially function for small flying animals as well. The method combines the rigid particulate scheme of Patankar et al. (IJMF, 2001) with a momentum redistribution scheme to consistently solve for fluid-body forces as well as the swimming velocity. The input to the algorithm is the deforming motion of the fish body or its fins in the frame of reference of the fish. The method is designed to be efficient, parallelizable, and can be easily implemented into existing fluid dynamics codes. We demonstrate that the new method is capable of simulating variety of fish forms including flexible bodies such as an eel, or bodies with flexible fins attached to them such as the blackghost knifefish (Apteronotus albifrons). Insights into the hydrodynamics of aquatic locomotion based on our simulations will be summarized. The proposed technique is also applicable to variety of problems such as designing underwater vehicles, neuromechanical modeling, understanding the role of hydrodynamics on the evolution of fish forms, and animation. [Preview Abstract] |
Monday, November 19, 2007 11:35AM - 11:48AM |
GF.00006: High-fidelity simulations of simple models of biomorphic aquatic locomotion Jeff Eldredge, Daniel Hector, Megan Wilson Aquatic creatures self-propel and maneuver with an incredible diversity of mechanics, even at the moderate Reynolds numbers appropriate for bio-inspired autonomous vehicles. In this work, we explore simple two-dimensional abstractions of two such mechanisms---undulatory and jellyfish-like locomotion---effected by prescribed hinge motion in articulated rigid body systems. These mechanisms are explored using a high-fidelity Navier-Stokes solver based on the viscous vortex particle method, strongly coupled with the rigid-body dynamics of the system. Such coupling enables an investigation of untethered swimming and maneuvering, which is essential for developing reduced-order models for motion planning and control. In the case of undulatory locomotion, it is shown that swimming effectiveness depends on both the relative phase and amplitude of the oscillatory hinge motions. The optimal shape control at these finite Reynolds numbers is contrasted with optima found for zero Reynolds number and inviscid swimmers. The jellyfish motion is enabled by periodic contractions of the bell shape, adapted from experimentally-measured kinematics of medusan swimmers (Dabiri et al., J. Exp. Biol., 2005). The vortex formation processes, energy budgets and fluid forces are explored for their relationship with forward propulsion. [Preview Abstract] |
Monday, November 19, 2007 11:48AM - 12:01PM |
GF.00007: Wake structure of rigid pitching panels with biologically inspired geometry Melissa Green, Alexander Smits Digital Particle Image Velocimetry (DPIV), planar laser induced florescence (PLIF), and white light flow visualization were used to investigate the wakes of three rigid pitching panels, with trapezoidal panel geometry chosen to idealize fish caudal fins. The panel geometries are determined by sweep angle and have a fixed surface area. Experiments were performed for a range Strouhal numbers from 0.23 to 0.65. A classic reverse von Karman vortex street pattern was observed along the mid-span of the near wake, but the complexity and three-dimensionality of the wake increases away from the mid-span as streamwise vortices interact with the swept edges of the panel. There exists a critical Strouhal number to sweep angle ratio above which streamwise vortices flow freely around the spanwise edge. Below this critical ratio, the streamwise structures become trapped one one side of the panel and interact strongly with the vortices shed by the trailing edge. [Preview Abstract] |
Monday, November 19, 2007 12:01PM - 12:14PM |
GF.00008: Does the sailfish skin reduce the skin friction like the shark skin? Woong Sagong, Sangho Choi, Chulkyu Kim, Woo-Pyung Jeon, Haecheon Choi The shape of shark skin - riblet - reduces the skin friction up to 8\% in a turbulent boundary layer, as compared to a smooth surface. The sailfish is the fastest sea animal, reaching its maximum speed of 110km/h. On the sailfish skin, we observe a number of V-shaped protrusions pointing downstream. So, we investigate the possibility of skin-friction reduction using this shape. We perform an extensive parametric study by varying the width and height of V-shaped protrusion, the spanwise and streamwise spacings between adjacent ones, and the overall distribution pattern (parallel, staggered and random), respectively. For all the cases considered, drag is either increased or unchanged. Each surface protrusion generates a pair of streamwise vortices, producing low and high shear stresses at the center and side of the protrusion, respectively, but total skin friction is nearly same as or higher than that of a smooth surface. Since this shape is very similar to but opposite in direction to that used in Sirovich \& Karlsson (Nature 1997), we perform another experiment on the V-shaped protrusions pointing upstream following their study. Unlike their result, we do not obtain any drag reduction even with random distribution of these V-shaped protrusions. [Preview Abstract] |
Monday, November 19, 2007 12:14PM - 12:27PM |
GF.00009: Flow Measurements over a Biomimetic Surface Roughness Microgeometry Amy Lang, Pablo Hidalgo, Matthew Westcott Certain species of sharks (e.g. shortfin mako) have a skin structure that results in a bristling of their denticles (scales) during increased swimming speeds. This unique surface geometry results in the formation of a 3D array of cavities* (d-type roughness geometry) within the shark skin, thus causing it to potentially act as a means of boundary layer control. Initial work is confined to scaling up the geometry from 0.2 mm on the shark skin to 2 cm, with a scaling down in characteristic velocity from 10 - 20 m/s to 10 - 20 cm/s for laminar flow boundary layer water tunnel studies over a shark skin model. The hypothesized formation of cavity vortices within the shark skin replica has been measured using DPIV. We have also shown that with the sufficient growth of a boundary layer upstream of the model (local Re = 200,000), transition is not tripped by the surface and the flow skips over the cavities. Support for this research by a NSF SGER grant (CTS-0630489), Lindbergh Foundation Grant and a University of Alabama RAC grant is gratefully acknowledged. * Patent pending. [Preview Abstract] |
Monday, November 19, 2007 12:27PM - 12:40PM |
GF.00010: Biomemetic pumping by gill plate arrays: Reynolds number effects in mayfly nymphs Andrew Sensenig, Jeffrey Shultz, Ken Kiger Mayfly nymphs are entirely aquatic and must alter behavior and metabolism to accommodate changes in ambient dissolved oxygen levels. Many species can generate a ventilation current to compensate for low oxygen levels by beating two linear arrays of plate-like gills that line the lateral edge of the abdomen. The characteristic Reynolds number associated with the gill motion changes with animal size, varying over a span of Re = 5 to 100 depending on age and species. Thus mayflies provide a novel system model for studying ontological changes in pumping mechanisms associated with transitions from a viscous- to inertia-dominated flow. Indeed, observation of other animals and theoretical analysis[1] indicate that a bifurcation should exist for inertial thrust generation by a reciprocal flapper for Reynolds numbers on the order of 10-20. In the ongoing work, the gill kinematics and resulting fluid motion is recorded experimentally through the use of high-speed stereo imaging and cinematographic planar PIV. Results show that the gills transition from a strongly asymmetric motion at Re=5 to a more reciprocal motion by Re=21. Details of the hydrodynamic mechanisms and pumping effectiveness will be discussed. \newline [1] Childress, S. \& Dudley, R. (2004), \textit{J. Fluid Mech.} \textbf{498}, 257--288. [Preview Abstract] |
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