Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session G18: Biofluids: Locomotion V - Swimming Experiments |
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Chair: John Bush, Massachusetts Institute of Technology Room: 306/307 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G18.00001: Flying fish accelerate at 5 G to leap from the water surface Patricia Yang, Sulisay Phonekeo, Ke Xu, Shui-Kai Chang, David Hu Flying fish can both swim underwater and glide in air. Transitioning from swimming to gliding requires penetration of the air-water interface, or breaking the ``surface tension barrier,'' a formidable task for juvenile flying fish measuring 1 to 5 cm in length. In this experimental investigation, we use high-speed videography to characterize the kinematics of juvenile flying fish as they leap from the water surface. During this process, which lasts 0.05 seconds, flying fish achieve body accelerations of 5 times earth's gravity and gliding speeds of 1.3 m/s, an order of magnitude higher than their steady swimming speed. We rationalize this anomalously high speed on the basis of the hydrodynamic and surface tension forces and torques experienced by the fish. Specifically, leaping fish experience skin friction forces only on the submerged part of their body, permitting them to achieve much higher speeds than in steady underwater swimming. We also perform experiments using a towed flying fish mimc to determine optimality of various parameters in this process, including body angle and start position with respect to the water surface. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G18.00002: Flexibility increases lift on passive fluttering wings Daniel Tam, John Bush We examine the influence of flexibility on the side-to-side fluttering motion of passive wings settling under the influence of gravity. This effect is examined through an experimental investigation of deformable rectangular wings falling in a water tank. Our results demonstrate the existence of an optimal flexibility, for which flexible wings remain flying twice longer and hence settle twice slower compared to rigid wings of identical mass and geometry. Flow visualizations and measurements provide key insight to elucidate the role of flexibility in generating increased lift and wing circulation by shedding additional vorticity at the turning point. Theoretical scalings are derived from a reduced model of the flight dynamics in qualitative and quantitative agreement with experiments. These scalings rationalize the strong positive correlation between flexibility and time of flight. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G18.00003: Synthetic C-start maneuver in fish-like swimming R. Zenit, R. Godoy-Diana We investigate the mechanics of the unsteady fish-like swimming maneuver using a simplified experimental model in a water tank. A flexible foil (which emulates the fish body) is impulsively actuated by rotating a cylindrical rod that holds the foil. This rod constitutes the head of the swimmer and is mounted through the shaft of the driving motor on an rail with an air bearing. The foil is initially positioned at a start angle and then rapidly rotated to a final angle, which coincides with the free-moving direction of the rail. As the foil rotates, it pushes the surrounding fluid, it deforms and stores elastic energy which drive the recovery of the straight body shape after the motor actuation has stopped; during the rotation, a trust force is induced which accelerates the array. We measure the resulting escape velocity and acceleration as a function of the beam stiffness, size, initial angle, etc. Some measurements of the velocity field during the escape were obtained using a PIV technique. The measurements agree well with a simple mechanical model that quantifies the impulse of the maneuver. The objective of this work is to understand the fundamental mechanisms of thrust generation in unsteady fast-start swimming. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G18.00004: The swimming mechanics of Artemia Salina A. Ruiz-Angulo, A.K. Ramos-Musalem, R. Zenit An experimental study to analyze the swimming strategy of a small crustacean (Artemia Salina) was conducted. This animal has a series of eleven pairs of paddle-like appendices in its thorax. These legs move in metachronal-wave fashion to achieve locomotion. To quantify the swimming performance, both high speed video recordings of the legs motion and time-resolved PIV measurements of the induced propulsive jet were conducted. Experiments were conducted for both tethered and freely swimming specimens. We found that despite their small size, the propulsion is achieved by an inertial mechanism. An analysis of the efficiency of the leg wave-like motion is presented and discussed. A brief discussion on the mixing capability of the induced flow is also presented. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G18.00005: Fluid elasticity enhances the locomotion of multi-tail swimmers F.A. Godinez, S. Gomez, R. Zenit, E. Lauga We conducted experiments on the locomotion of magnetic robots with multiple rigid flagella to evaluate the impact of fluid viscoelasticity on their swimming performance. Each swimmer was composed of a air-filled cylindrical head with a permanent magnet attached at one of its ends. At the other end, two or more rigid helices were glued on the outer surface of the cylinder maintaining the same distance from each other along the periphery and remaining parallel to the rotation axis. The robots were driven by an external magnetic field allowing to vary the swimming speed. Each swimmer was tested in two different fluids with the same shear viscosity: a Newtonian and a Boger fluid. The single-flagellum device showed essentially the same velocity in both fluids. In contrast, multi-flagella robots swam in the Boger fluid at much higher speeds than in the equivalent Newtonian case. These results are discussed in the last of past similar studies. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G18.00006: High Speed Tomographic PIV Measurements of Copepod Sensitivity to a Suction-Feeding Predator Mimic J. Yen, D.W. Murphy, L. Fan, A. Skipper, D.R. Webster Copepods, which sense their fluid environment with long, setae-bearing antennules, often serve as prey to fish. The fluid disturbance created by fish feeding is a combination of a bow wave created by swimming towards the prey with an open mouth and a sudden, high speed flow into the fish's mouth created by suction. The sensitivity and reaction of copepods to the dynamic, high acceleration flow created by a suction feeding fish have not been well explored. In the present study, a suction feeding piscine predator mimic is developed and tested with copepods from a fish-containing (marine) environment (\textit{Calanus finmarchicus}) and with copepods from a fish-less (alpine lake) environment (\textit{Hesperodiaptomus shoshone}). Flow fields created by the impulsive siphon are measured with a high-speed tomographic particle image velocimetry (PIV) system. Escape success and kinematics of the two species are compared. Finally, using volumetric flow measurements, the hydrodynamic signal measured along each copepod's antennules at the time point of escape is compared between species. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G18.00007: Thin Layer Sensory Cues Affect Antarctic Krill Swimming Kinematics A.C. True, D.R. Webster, M.J. Weissburg, J. Yen A Bickley jet (laminar, planar free jet) is employed in a recirculating flume system to replicate thin shear and phytoplankton layers for krill behavioral assays. Planar laser-induced fluorescence (LIF) and particle image velocimetry (PIV) measurements quantify the spatiotemporal structure of the chemical and free shear layers, respectively, ensuring a close match to \textit{in situ} hydrodynamic and biochemical conditions. Path kinematics from digitized trajectories of free-swimming \textit{Euphausia superba} examine the effects of hydrodynamic sensory cues (deformation rate) and bloom level phytoplankton patches ($\sim$1000 cells/mL, \textit{Tetraselamis spp.}) on krill behavior (body orientation, swimming modes and kinematics, path fracticality). Krill morphology is finely tuned for receiving and deciphering both hydrodynamic and chemical information that is vital for basic life processes such as schooling behaviors, predator/prey, and mate interactions. Changes in individual krill behavior in response to ecologically-relevant sensory cues have the potential to produce population-scale phenomena with significant ecological implications. Krill are a vital trophic link between primary producers (phytoplankton) and larger animals (seabirds, whales, fish, penguins, seals) as well as the subjects of a valuable commercial fishery in the Southern Ocean; thus quantifying krill behavioral responses to relevant sensory cues is an important step towards accurately modeling Antarctic ecosystems. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G18.00008: Quantifying copepod sensing and swimming in unsteady flow fields using time-resolved tomographic PIV $+$ 3D PTV Deepak Adhikari, Ellen Longmire Copepods respond to hydrodynamic disturbances by executing an escape response jump (Buskey et al 2002; Fields and Yen 1996; Ki{\o}rboe et al 1999; Strickler and Bal 1973). 3D PTV and tomographic PIV are combined to track the motion of the copepods and the surrounding fluid velocity field respectively, to provide quantitative measure on their sensing and swimming behavior. The measurements are time-resolved to obtain the entire trajectories of copepods. Fluid velocity and velocity gradients are estimated at the location of the copepod by applying a Taylor-series least-square method to the surrounding PIV grid points. Copepod sensing and swimming are analyzed upstream and downstream of a wall-mounted cylinder in cross-flow at Re $\sim $ 930. At the upstream location, when copepods approach the cylinder, they respond by rapidly accelerating (or jumping) away from it. Their jump location suggests that they sense and respond to a range of flow velocity gradients. Preliminary results indicate that copepods in the cylinder wake do not jump frequently as compared to upstream. The velocity gradient thresholds for sensing and range of maximum velocities during jumping will be presented and discussed. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G18.00009: Investigating the relationship between planform and performance in bio-inspired aquatic propulsion Oliver J. Badaoui, Daniel B. Quinn, Peter A. Dewey, Alexander J. Smits Experiments are conducted to investigate the effects of caudal fin planform shape on the hydrodynamic performance of bio-inspired aquatic propulsors. To isolate the effect of planform shape the surface area of the fins is held constant while the planform shape is systematically varied to incorporate bio-inspired designs that are consistent with those observed in nature. The self-propelled swimming speed and power consumption of heaving flexible panels of varying planform are measured in a stationary water tank. Particle image velocimetry is also employed to better understand the connection between the wake structures produced by the oscillating fins and their performance characteristics. Results are compared and analyzed in an effort to identify specific shape features that lead to a performance benefit or detriment. [Preview Abstract] |
Monday, November 25, 2013 9:57AM - 10:10AM |
G18.00010: Free swimming of an internally actuated elastic swimmer Peter Yeh, Alper Erturk, Alexander Alexeev We use fully coupled three-dimensional simulations to examine the underwater locomotion of an internally powered elastic swimmer. The swimmer is modeled as a thin, rectangular, elastic plate with two sections. The first section is internally powered by an oscillating internal moment that produces bending. The second section, a passive fin, undergoes bending oscillations in response to the actuated section. We measure the forward swimming velocity and performance for our hybrid swimmer. We find that the hybrid swimmer with the passive component swims at a higher velocity than that of a fully actuated one. This is in agreement with experiments involving piezoelectric internally powered swimmers. The experiments have shown that thrust is increased when a passive fin is attached to a fully internally actuated swimmer. We investigate the details of the flow structures and bending pattern of the swimmer and show how they affect the forward motion. The results are useful for designing self-propelling bio-inspired robots with internally powered fins. [Preview Abstract] |
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