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 EH: Biofluids IV: Swimming |
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Chair: John Dabiri, California Institute of Technology Room: Salt Palace Convention Center 250 B |
Sunday, November 18, 2007 4:10PM - 4:23PM |
EH.00001: A Comparative Analysis of Swimming Styles in Competitive Swimming Alfred von Loebbecke, Rajat Mittal, Varun Gupta, Russell Mark High-fidelity numerical simulations are being used to conduct a critical evaluation of swimming strokes in competitive swimming. We combine computational fluid dynamics (CFD), laser body scans, animation software, and video footage to develop accurate models of Olympic level swimmers and use these to examine contrasting styles of the dolphin kick as well as the arm strokes in back and front crawl stroke. In the dolphin kick, the focus is on examining the effects of Strouhal number, kick amplitude, frequency, and technique on thrust production. In the back stroke, we examine the performance of the so called ``flat stroke'' versus the ``deep catch,'' The most important aspect that separates the two major types of back stroke is the alignment or angle of attack of the palm during the stroke. In one style of front crawl arm stroke, there is greater elbow joint flexion, shoulder abduction and sculling whereas the other style consists of a straight arm pull dominated by simple shoulder flexion. Underlying the use of these two styles is the larger and more fundamental issue of the role of lift versus drag in thrust production and we use the current simulations to examine this issue in detail. [Preview Abstract] |
Sunday, November 18, 2007 4:23PM - 4:36PM |
EH.00002: Progress toward 3D wake structure measurements of aquatic animals using SCUVA John Dabiri, Kakani Katija Recent developments in multi-camera DPIV techniques now enable measurement of three-dimensional wake structure in aquatic animals. The present goal is to integrate those techniques with a self-contained underwater velocimetry apparatus (SCUVA), in order to facilitate in situ measurements of 3D wake structure by SCUBA divers in the field. SCUVA presents an additional constraint in that the flow imaging must be accomplished by a single camera viewing the flow from a single direction. We present progress toward the incorporation of 3D wake measurement techniques into a single-camera platform. The approach relies on the image defocusing concept and calculation of Lagrangian coherent structures directly from fluid particle trajectories. The results may benefit laboratory methods as well as the field techniques that are the present focus. [Preview Abstract] |
Sunday, November 18, 2007 4:36PM - 4:49PM |
EH.00003: Energetics of jellyfish locomotion determined from field measurements using a Self-Contained Underwater Velocimetry Apparatus (SCUVA) Kakani Katija, John O. Dabiri We describe the development and application of a Self-Contained Underwater Velocimetry Apparatus (SCUVA), which enables a single SCUBA diver to make DPIV measurements of animal-fluid interactions in the field. The device is used to study \textit{Aurelia labiata} swimming in the coastal waters of Long Beach, California. SCUVA measurements of animals over a range of sizes are used to directly quantify the kinetic energy in the flow field induced by the swimming motions of individual medusae and are compared with existing theoretical models. The method provides details regarding the temporal evolution of the energetics during the swimming cycle and their scaling with bell diameter. These types of measurements will allow for the determination of propulsive efficiency, which can be used to compare various methods of biological propulsion. [Preview Abstract] |
Sunday, November 18, 2007 4:49PM - 5:02PM |
EH.00004: Optimal stroke patterns for a model jellyfish swimmer with thin, flexible body Jifeng Peng, John Dabiri In this study, a numerical model is built to simulate swimming of oblate jellyfish (e.g. \textit{Aurelia aurita}). The model swimmer is a thin, axisymmetric circular plate which is flexible and is able to deform, mimicking contraction and relaxation of a jellyfish. Using body deformation, the swimmer is able to swim by shedding vortices into fluid wake. A prescribed body motion extracted from a free-swimming \textit{Aurelia aurita} is applied to the swimmer. The induced vortex wake is solved by a vortex sheet method and is compared with the wake of the free-swimming \textit{Aurelia aurita} measured by PIV. The stoke pattern of the swimmer is optimized for minimal cost of locomotion. The body kinematics are parameterized and cost of locomotion is calculated from simulation using the vortex sheet method. A surrogate management framework is used as the optimization scheme. The vortex wake induced by the optimal stroke pattern is investigated to identify the characteristics of the wake which enhance swimming performance. [Preview Abstract] |
Sunday, November 18, 2007 5:02PM - 5:15PM |
EH.00005: Experimental comparison of steady and unsteady propulsion of a self-propelled swimmer Lydia Trevino, John Dabiri Aquatic animals differ from typical engineering systems in their use of unsteady flows for transportation. Traditional definitions of propulsive efficiency have not taken these effects into account and are typically based on steady flow through propellers or rocket motors. The purpose of this study is to develop a metric for fluid dynamic efficiency which will allow for a quantitative comparison between biological and engineering propulsion systems. For this study, we designed a submarine that has the capability to produce either a steady or an unsteady jet for propulsion. Several methods for the evaluation of propulsive performance were implemented including propulsive efficiency and power output. The unsteady Froude efficiency, which uses an equivalent jet speed based on energy considerations, was also measured. [Preview Abstract] |
Sunday, November 18, 2007 5:15PM - 5:28PM |
EH.00006: On the hydrodynamics of body/caudal fin locomotion for Carangiform swimmers Fotis Sotiropoulos, Iman Borazjani A systematic numerical investigation of body/caudal fin (BCF) locomotion for a typical Carangiform swimmer - a Mackerel - has been carried out for three different Reynolds numbers-Re = 300, 4000, and 8 (inviscid) and over a range of Strouhal numbers. Our results clearly show that swimming efficiency increases with Reynolds number, which explains why in nature BCF is the preferred mode of locomotion for fast swimmers. We also show that the friction drag is increased by the BCF undulations relative to the rigid body drag while the form drag can increase or decrease depending on the Strouhal number, thus, reconciling previous conflicting views reported in the literature. 3D visualizations of the coherent structures in the wake confirm and further clarify previously hypothesized wake models consisting of single and double row vortex loops. [Preview Abstract] |
Sunday, November 18, 2007 5:28PM - 5:41PM |
EH.00007: A Study of a Mechanical Swimming Lamprey Megan Leftwich, Marcus Hultmark, Alexander Smits In order to develop a comprehensive model of lamprey locomotion, we use a swimming robotic lamprey as a means of investigating the surface pressure, thrust and wake structure. A programmable microcomputer actuates 13 servomotors that produce a traveling wave along the length of the lamprey's body. This waveform is based on the motion of the American eel (Anguilla rostrata), as described by Tytell and Lauder (2004). Dye flow visualization and particle image velocimetry (PIV) are used to study the wake structure generated by the robot and the flowfield along the body. These visualization methods show that two distinct, oppositely signed vortices are shed each half cycle; whereas along the body, no large scale vortical shedding can be observed, suggesting that most of the thrust is produced by the tail. Thrust data based on momentum balances support this suggestion. The project is supported by NIH Grant 1RO1NS054271. [Preview Abstract] |
Sunday, November 18, 2007 5:41PM - 5:54PM |
EH.00008: Propulsive Forces of a Biomimetic Undulating Fin Kenneth Kalumuck, Alan Brandt, Mehran Armand Understanding gained from much recent work on force production mechanisms of aquatic organisms holds great promise for improved undersea vehicle propulsion and maneuvering. One class of fish locomotion is that of the median fin utilized by animals such as squid, cuttlefish, knifefish, and seahorse. It is characterized by undulatory motion that creates traveling waves along the fin. Results of experiments conducted on a submerged mechanical underwater undulating fin test bed are presented. The 0.5 m long fin is mounted to a cylindrical body and consists of a flexible skin attached to ribs driven by an adjustable cam mechanism and variable speed motor that enables changing the characteristics of the undulating wave(s). Forces produced were measured in a captive mode under quiescent conditions as well in the presence of an ambient current. Propulsive forces are characterized as a function of the fin width, oscillation frequency, amplitude, and wavelength. Free swimming experiments were also conducted to determine the point of self propulsion. Flow field structure visualization using dye tracers is presented for selected cases. Estimates of performance and applications for use with larger scale vehicles are discussed. [Preview Abstract] |
Sunday, November 18, 2007 5:54PM - 6:07PM |
EH.00009: Locomotion Performance of Biomimetic Fish-like Swimming Devices Brenden P. Epps, Pablo Valdivia y Alvarado, Alexandra H. Techet The swimming performance of a biomimetic, fish-like swimming device, designed to exploit the natural dynamics of its compliant body to achieve locomotion, is studied experimentally. A theoretical model combines beam-bending stress analysis and unsteady hydrodynamic forcing with known material properties of the robot to reveal desired geometry distributions and actuation modes. Swimming kinematics and corresponding performance of the device are also predicted and tested for a carangiform prototype device in a quiescent tank of water. Experimental swimming tests show good agreement with the simplified theoretical models. The hydrodynamic characteristics of the wake behind the device are investigated using time-resolved particle imaging velocimetry (PIV) over a range of tail beat frequencies, from 1 to 4 Hz, to asses vortical wake patterns and hydrodynamic forces. PIV data are compared to theoretical model predictions. Reynolds numbers for the swimming device are between 2500 and 8500 based on body length. [Preview Abstract] |
Sunday, November 18, 2007 6:07PM - 6:20PM |
EH.00010: Hamiltonian mechanics and planar fishlike locomotion Scott Kelly, Hailong Xiong, Will Burgoyne A free deformable body interacting with a system of point vortices in the plane constitutes a Hamiltonian system. A free Joukowski foil with variable camber shedding point vortices in an ideal fluid according to a periodically applied Kutta condition provides a model for fishlike locomotion which bridges the gap between inviscid analytical models that sacrifice realism for tractability and viscous computational models inaccessible to tools from nonlinear control theory. We frame such a model in the context of Hamiltonian mechanics and describe its relevance both to the study of hydrodynamic interactions within schools of fish and to the realization of model-based control laws for biomimetic autonomous robotic vehicles. [Preview Abstract] |
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