Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session L19: Bio: Flapping and Swimming III |
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Chair: Oscar Curet, Florida Atlantic University Room: D136 |
Monday, November 21, 2016 4:30PM - 4:43PM |
L19.00001: Scaling of hydrodynamics and swimming kinematics of shelled Antarctic sea butterfly Deepak Adhikari, Donald Webster, Jeannette Yen A portable tomographic PIV system was used to study fluid dynamics and kinematics of pteropods (aquatic snails nicknamed `sea butterflies') in Antarctica. These pteropods (\textit{Limacina helicina antarctica}) swim with a pair of parapodia (or ``wings'') via a unique flapping propulsion mechanism that incorporates similar techniques as observed in small flying insects. The swimming velocity is typically 14 -- 30 mm/s for pteropod size ranging 1.5 -- 5 mm, and the pteropod shell pitches forward-and-backward at 1.9 -- 3 Hz. It has been shown that pitching motion of the shell effectively positions the parapodia such that they flap downwards during both power and recovery strokes. The non-dimensional variables characterizing the motion of swimming pteropods are flapping, translating, and pitching Reynolds numbers (i.e. \textit{Re}$_{f}$, \textit{Re}$_{U}$, and \textit{Re}$_{\mathrm{\Omega }})$. We found that the relationship between these Reynolds numbers show an existence of a critical \textit{Re}$_{\mathrm{\Omega }}$, below which pteropods fail to swim successfully. We explore the importance of this critical \textit{Re}$_{\Omega }$ by changing the viscosity of the seawater using methylcellulose. At higher viscosity, our results indicate that pteropods do not swim with optimal propulsion efficiency. Finally, we examine the wake signature of swimming pteropod, consisting of a pair of vortex rings, in the modified viscosity environment. [Preview Abstract] |
Monday, November 21, 2016 4:43PM - 4:56PM |
L19.00002: The Complex Hydrodynamics of Swimming in the Spanish Dancer Zhuoyu Zhou, Rajat Mittal The lack of a vertebra seems to have freed marine gastropods to explore and exploit a stupendous~variety of swimming kinematics. In fact, examination of just a few animals in this group reveal~locomotory~modes ranging from insect-like flapping, to fish-like~undulatory~swimming, jet propulsion, and~rajiform~(manta-like) swimming. There are also a number of marine gastropods that have bizarre swimming gaits~with~no equivalent among fish or marine mammals. In this latter category is the Spanish Dancer (\textit{Hexabranchus~sanguineus})~a sea slug~that swims with~a complex combination of body undulations and flapping~parapodia.~~ While the neurobiology of these animals has been~relatively~well-studied, less is known about their propulsive mechanism~and swimming energetics. In this study,~we focus on the hydrodynamics of two distinct swimmers: the Spanish Dancer, and the sea hare~Aplysia;~the latter~adopts a~rajiform-like mode of swimming~by passing travelling waves along~its~parapodia.~In the present study an immersed boundary method is employed to examine~the~vortex~structures,~hydrodynamic~forces and energy costs of~the swimming in~these animals.~~ [Preview Abstract] |
Monday, November 21, 2016 4:56PM - 5:09PM |
L19.00003: Swimming of the Honey Bees Chris Roh, Morteza Gharib When the weather gets hot, nursing honey bees nudge foragers to collect water for thermoregulation of their hive. While on their mission to collect water, foragers sometimes get trapped on the water surface, forced to interact with a different fluid environment. In this study, we present the survival strategy of the honey bees at the air-water interface. A high-speed videography and shadowgraph were used to record the honey bees swimming. A unique thrust mechanism through rapid vibration of their wings at 60 to 150 Hz was observed. [Preview Abstract] |
Monday, November 21, 2016 5:09PM - 5:22PM |
L19.00004: Development of a Diver-Operated Single Camera Volumetric Velocimetry System Valerie Troutman, John Dabiri The capabilities of a single camera, volumetric velocimetry system for in situ measurement in marine environments are demonstrated by imaging a well-characterized flow in a laboratory environment. This work represents the first stages in the design of a SCUBA-diver operated system to study organisms and biological processes under the natural light in the water column. This system is primarily composed of a volumetric particle tracking diagnostic to investigate fluid-animal interactions. A target domain size of a 20 cm sided cube is sought as a key design feature for the capability of capturing the flow around a variety of benthic and freely swimming organisms. The integration of the particle tracking system with additional diagnostics will be discussed. [Preview Abstract] |
Monday, November 21, 2016 5:22PM - 5:35PM |
L19.00005: A study of sea lion hydrodynamics using a robotic foreflipper platform Aditya A. Kulkarni, Rahi K. Patel, Megan C. Leftwich Unlike most fish and mammals---that utilize BCF swimming---sea lions rely on their foreflippers to generate thrust without a characteristic flapping frequency. This unique swimming style allows the sea lion to be highly maneuverable, while also producing high amounts of thrust. To explore this motion, and the physics that underlies it, we use novel markerless tracking techniques on untrained sea lions at the Smithsonian National Zoo in Washington, D.C to get the complete motion during different maneuvers. High speed video and three-dimensional surface reconstruction techniques are used to extract the foreflippers kinematics during the thrust phase. Using this data, pitch angle is calculated with respect to the base of the flipper to build a scaled robotic flipper. Dye visualization is carried out in a water channel by injecting dye upstream of the leading edge of the flipper with flow speed set to explore different parameters, like Reynolds number or angular velocity. Results show low pressure on the upper surface of the flipper causes the fluid to be pulled around the flipper forming a vortex that moves fully out of the plane. [Preview Abstract] |
Monday, November 21, 2016 5:35PM - 5:48PM |
L19.00006: Exploring the neural bases of goal-directed motor behavior using fully resolved simulations Namu Patel, Neelesh A. Patankar Undulatory swimming is an ideal problem for understanding the neural architecture for motor control and movement; a vertebrate’s robust morphology and adaptive locomotive gait allows the swimmer to navigate complex environments. Simple mathematical models for neurally activated muscle contractions have been incorporated into a swimmer immersed in fluid. Muscle contractions produce bending moments which determine the swimming kinematics. The neurobiology of goal-directed locomotion is explored using fast, efficient, and fully resolved constraint-based immersed boundary simulations. Hierarchical control systems tune the strength, frequency, and duty cycle for neural activation waves to produce multifarious swimming gaits or synergies. Simulation results are used to investigate why the basal ganglia and other control systems may command a particular neural pattern to accomplish a task. Using simple neural models, the effect of proprioceptive feedback on refining the body motion is demonstrated. Lastly, the ability for a learned swimmer to successfully navigate a complex environment is tested. [Preview Abstract] |
Monday, November 21, 2016 5:48PM - 6:01PM |
L19.00007: Coarse-grained models for interacting, flapping swimmers Anand Oza, Leif Ristroph, Michael Shelley We present the results of a theoretical investigation into the dynamics of interacting flapping swimmers. Our study is motivated by ongoing experiments in the NYU Applied Math Lab, in which freely-translating, heaving airfoils interact hydrodynamically to choose their relative positions and velocities. We develop a discrete dynamical system in which flapping swimmers shed point vortices during each flapping cycle, which in turn exert forces on the swimmers. We present a framework for finding exact solutions to the evolution equations and for assessing their stability, giving physical insight into the preference for certain observed "schooling states". The model may be extended to arrays of flapping swimmers, and configurations in which the swimmers' flapping frequencies are incommensurate. Generally, our results indicate how hydrodynamics may mediate schooling and flocking behavior in biological contexts. [Preview Abstract] |
Monday, November 21, 2016 6:01PM - 6:14PM |
L19.00008: More efficient swimming by spreading your fingers Willem van de Water, Josje van Houwelingen, Dennis Willemsen, Wim Paul Breugem, Jerry Westerweel, Rene Delfos, Ernst Jan Grift A tantalizing question in free-style swimming is whether the stroke efficiency during the pull phase depends on spreading the fingers. It is a subtle effect--not more than a few percent--but it could make a big difference in a race. We measure the drag of arm models with increasing finger spreading in a wind tunnel and compare forces and moments to the results of immersed boundary simulations. Virtual arms were used in the simulations and their 3D-printed real versions in the experiment. We find an optimal finger spreading, accompanied by a marked increase of coherent vortex shedding. A simple actuator disk model explains this optimum. [Preview Abstract] |
Monday, November 21, 2016 6:14PM - 6:27PM |
L19.00009: Vortices revealed: Swimming faster Josje van Houwelingen, Willem van de Water, Rudie Kunnen, GertJan van Heijst, Herman Clercx Understanding and optimizing the propulsion in human swimming requires insight into the hydrodynamics of the flow around the swimmer. Experiments and simulations addressing the hydrodynamics of swimming have been conducted in studies before, including the visualization of the flow using particle image velocimetry (PIV). The main objective in this study is to develop a system to visualize the flow around a swimmer in practice inspired by this technique. The setup is placed in a regular swimming pool. The use of tracer particles and lasers to illuminate the particles is not allowed. Therefore, we choose to work with air bubbles with a diameter of \textasciitilde 4 mm, illuminated by ambient light. Homogeneous bubble curtains are produced by tubes implemented in the bottom of the pool. The bubble motion is captured by six cameras placed in underwater casings. A first test with the setup has been conducted by pulling a cylinder through the bubbles and performing a PIV analysis. The vorticity plots of the resulting data show the expected vortex street behind the cylinder. The shedding frequency of the vortices resembles the expected frequency. Thus, it is possible to identify and follow the coherent structures. We will discuss these results and the first flow measurements around swimmers. [Preview Abstract] |
Monday, November 21, 2016 6:27PM - 6:40PM |
L19.00010: Bird beaks bear the brunt of bashing impact Saberul Islam Sharker, Sean Holekamp, Frank Fish, Jesse Belden, Tadd Truscott Seabirds can dive from 30 meters reaching speeds of 24 meters per second as they impact the water reaching depths of 9 meters due to their momentum, and a further 25 meters by active flapping. It is thought that their geometry, particularly the beak, allows them to endure relatively high impact forces that could kill non-diving birds. Acceleration data of simplified models of diving birds agree with simulated data for one species, however, no reliable experimental data with real bird geometries exist for comparison. We experimentally measured the impact accelerations of twelve 3D printed models of diving birds (seven surface diving and five plunge diving) during water-entry at different impact velocities using accelerometers. [Preview Abstract] |
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