Showing papers on "Aquatic locomotion published in 2007"
TL;DR: A key result of this study is its suggestion that the dynamical effect of the vortex wake on locomotion is to replace the real animal fin with an `effective appendage', whose geometry is dictated by the FTLE field and whose interaction with the surrounding fluid is wholly dictated by inviscid concepts from potential flow theory.
Abstract: Swimming and flying animals generate unsteady locomotive forces by delivering net momentum into the fluid wake. Hence, swimming and flying forces can be quantified by measuring the momentum of animal wakes. A recently developed model provides an approach to empirically deduce swimming and flying forces based on the measurement of velocity and vortex added-mass in the animal wake. The model is contingent on the identification of the vortex boundary in the wake. This paper demonstrates the application of that method to a case study quantifying the instantaneous locomotive forces generated by the pectoral fins of the bluegill sunfish (Lepomis macrochirus Rafinesque), measured using digital particle image velocimetry (DPIV). The finite-time Lyapunov exponent (FTLE) field calculated from the DPIV data was used to determine the wake vortex boundary, according to recently developed fluid dynamics theory. Momentum of the vortex wake and its added-mass were determined and the corresponding instantaneous locomotive forces were quantified at discrete time points during the fin stroke. The instantaneous forces estimated in this study agree in magnitude with the time-averaged forces quantified for the pectoral fin of the same species swimming in similar conditions and are consistent with the observed global motion of the animals. A key result of this study is its suggestion that the dynamical effect of the vortex wake on locomotion is to replace the real animal fin with an `effective appendage', whose geometry is dictated by the FTLE field and whose interaction with the surrounding fluid is wholly dictated by inviscid concepts from potential flow theory. Benefits and limitations of this new framework for non-invasive instantaneous force measurement are discussed, and its application to comparative biomechanics and engineering studies is suggested.
61 citations
01 Jan 2007
TL;DR: In this paper, a computational study on the unsteady hydrodynamics of pectoral fin locomotion of Rhinoptera Bonasus and Dasyatis Sabina is carried out and presented, which represent the undulatory and oscillatory locomotion, respectively.
Abstract: The mechanics of aquatic locomotion are of interest to biologists, dynamicists and engineers. Batoid fishes (skates and rays) propel themselves through the water primarily with their greatly expanded pectoral fins (pectoral-fin-based locomotion). Batoids exhibit two modes of pectoral swiminng behavior: (1) undulatory locomotion, termed ‘rajiform’, and (2) oscillatory locomotion, termed ‘mobuliform’. A computational study on the unsteady hydrodynamics of pectoral fin locomotion of Rhinoptera Bonasus and Dasyatis Sabina is carried out and presented, which represent the undulatory and oscillatory locomotion, respectively. Unsteady hydrodynamics around a pectoral fin is solved by a time-accurate solution of incompressible, laminar Navier-Stokes equations. Kinematic data of the pectoral fin locomotion used in the computational modeling are based on the experimental results. The pressure distribution of the pectoral fin was computed and integrated to give forces which were decomposed into lift and thrust. The velocity and vorticity field variation on the surface of pectoral fins and in the near-wake was computed throughout the swimming cycle. In the present study, we analyzed and compared the hydrodynamics and mechanmism of the Batoid pectoral fin locomotion between the two modes, and discovered how these patterns change with controllable factors, such as Renolds number, frequency, amplitude etc. The results show that forces on the fins of Rhinoptera Bonasus are much larger than that of Dasyatis Sabina. The load-bearing areas of Rhinoptera Bonasus are at the areas from the leading edge to the medial of the wing; while the load-bearing area of Dasyatis Sabina is the whole wavy fin. These characters are associated with the morphology of the wing skeleton. The propulsive mechanism of pectoral-fin-based locomotion is similar to that of the caudal-fin-based locomotion. A strong backward jet-stream in the wake contributes the net thrust, which is induced by the reversed von Karman vortex street. The effect of controllable factors on the hydrodynamics in Rhinoptera Bonasus swimming are similar to that in Dasyatis Sabina swimming.