Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D26: Biofluids: Flexible Swimmers II |
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Chair: Mattia Gazzola, Harvard University Room: 306 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D26.00001: Simulations of elastic, stretchable, shearable curves interacting with a liquid Mattia Gazzola, Andrew McCormick, L Mahadevan We present a general numerical approach for the simulations of soft filaments deforming in three-dimensional space. Unlike the vast literature on inextensible and unshearable rods, we enable all possible deformation modes at every cross-section consistent with the full Euclidean group SE(3), namely, bending, twisting, shear and stretch. Additionally, we also allow elastic curves to interact with the environment via muscular activity, self-contact, surface friction and hydrodynamics. We demonstrate the capabilities of our approach on a range of biophysical problems, with an emphasis on limbless locomotion on dry surfaces, thin liquid films and in bulk liquids. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D26.00002: From Tadpoles to Trout: Scale-invariant features of optimally efficient swimming Alexander Wiens, Anette Hosoi The Strouhal number ($St$) was thought to be an invariant feature of efficient inertial swimming, however, recent studies by Eloy and Gazzola have shown that $St$ actually varies throughout nature based on animal size, shape, and speed. This finding leads us to ask whether there is any truly invariant property of efficient inertial swimming. Using Lighthill's large-amplitude elongated-body theory, we show that there is. Lighthill's model predicts that efficient swimmers must tune their gait such that the unsteady motions of their body generate uniform steady thrust. Mathematically, we show that this behavior can be fully quantified through a single variable which should be constant for all inertial swimmers. Comparison with data from existing literature shows that animals ranging in size from tadpoles to trout adhere to the optimum value predicted by Lighthill's model. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D26.00003: Biofluiddynamics of balistiform and gymnotiform locomotion: Revisited Brennan Sprinkle, Rahul Bale, Amneet Singh, Nelson Chen, Malcom MacIver, Neelesh Patankar Gymnotiform and balistiform swimmers are those which have an undulatory fin affixed to a rigid body unlike anguilliforms who undulate their entire body. Is there a mechanical advantage to gymnotiform and balistiform swimming? This question was investigated by Lighthill \& Blake in a four paper series \textit{Biofluiddynamics of balistiform and gymnotiform locomotion}. We revisit this work using fully resolved numerical simulations of the types of swimmers considered by Lighthill \& Blake to interrogate the issue of mechanical advantage for rigid body swimmers. In doing so, we find that while there is advantage to rigid body swimming, the mechanism of `momentum enhancement,' proposed by Lighthill and Blake, is not the cause. Further, we use our results and simulations to explain why some gymnotiform and balistiform swimmers have their propulsor attached to their bodies at an angle. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D26.00004: A model of a flexible anguilliform swimmer driven by a central pattern generator with proprioceptive feedback Christina Hamlet, Eric Tytell, Kathleen Hoffman, Lisa Fauci The swimming of a simple vertebrate, the lamprey, can shed light on how a flexible body can couple with a fluid environment to swim rapidly and efficiently. Animals use proprioceptive sensory information to sense how their bodies are bending, and then adjust the neural signals to their muscles to improve performance. We will present recent progress in the development of a computational model of a lamprey swimming in a Navier-Stokes fluid where a simple central pattern generator model, based on phase oscillators, is coupled to the evolving body dynamics of the swimmer through curvature and curvature derivative feedback. Such feedback can be positive (frequency decreasing), negative (frequency increasing), or mixed (positive to one side of the body and negative to the other, or vice versa). We will examine how the emergent swimming behavior and cost of transport depends upon these functional forms of proprioceptive feedback chosen in the model. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D26.00005: Efficient swimmers use bending kinematics to generate low pressure regions for suction-based swimming thrust Sean Colin, Brad Gemmell, John Costello, Jennifer Morgan, John Dabiri A longstanding tenet in the conceptualization of animal swimming is that locomotion occurs by pushing against the surrounding water. Implicit in this perspective is the assumption that swimming involves lateral body accelerations that generate locally elevated pressures in the fluid, in order to achieve the expected downstream push of the surrounding water against the ambient pressure. Here we show that to the contrary, efficient swimming animals primarily pull themselves through the water by creating localized regions of low pressure via waves of body surface rotation that generate vortices. These effects are observed using laser diagnostics applied to normal and spinally-transected lampreys. The results suggest rethinking evolutionary adaptations observed in swimming animals as well as the mechanistic basis for bio-inspired underwater vehicles. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D26.00006: Swimming Performance of Toy Robotic Fish Nina Petelina, Leah Mendelson, Alexandra Techet HEXBUG AquaBots$^{\mathrm{TM}}$ are a commercially available small robot fish that come in a variety of ``species''. These models have varying caudal fin shapes and randomly-varied modes of swimming including forward locomotion, diving, and turning. In this study, we assess the repeatability and performance of the HEXBUG swimming behaviors and discuss the use of these toys to develop experimental techniques and analysis methods to study live fish swimming. In order to determine whether these simple, affordable model fish can be a valid representation for live fish movement, two models, an angelfish and a shark, were studied using 2D Particle Image Velocimetry (PIV) and 3D Synthetic Aperture PIV. In a series of experiments, the robotic fish were either allowed to swim freely or towed in one direction at a constant speed. The resultant measurements of the caudal fin wake are compared to data from previous studies of a real fish and simplified flapping propulsors. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D26.00007: A bioinspired aquatic robot propelled by an internal rotor Phanindra Tallapragada, Beau Pollard Low dimensional models of fish-like swimming of a deformable Joukowski foil shedding singular distributions of vorticity have been well known for two decades. The deformation of the foil can be interpreted to be periodic changes in an abstract shape space and the creation of vorticity can be shown to act as a nonholonomic constraint. With this geometric insight, it can be demonstrated that a Joukowski foil (or in general any body) can possibly swim to the motion of an internal rotor, that acts as a shape variable. The motion of the rotor pumps in angular momentum and the simultaneous creation of vorticity allows this to be `converted' into linear momentum of the foil. We demonstrate the feasibility of this theoretical prediction with a robot shaped as a Joukowski foil propelled by the motion of an internal momentum wheel. We also demonstrate that the internal rotor acts both as a means of propulsion as well as a means of controlling the heading of the robot. Some maneuvers of the robot and features of its physical and `mathematical' resemblance to fish-like motion are demonstrated. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D26.00008: CFD Study of Pectoral Fins of Larval Zebrafish: Effect of Reynolds Number and Fin Bending in Fluid Structures and Transport Toukir Islam, Oscar M. Curet Zebrafish exhibits significant changes in fin morphology as well as fin actuation during its physical development. In larval stage (Re $\sim$ 10), they beat pectoral fins asymmetrically during slow swimming and prey tracking and a hypothesis suggests pectoral fin motion enhances fluid mixing to assist respiration. We performed a series of computational simulations to study effect of Reynolds number (\textit{Re}) and pectoral fin kinematics in the fluid dynamics and mixing around a larval zebrafish. The CFD algorithm is based on a constraint formulation where the kinematics of the zebrafish are specified. We simulated experimental zebrafish kinematics at different \textit{Re} (17 to 300) and considered variations on the fin kinematics to evaluate role of fin deformation in the fluid structures generated by the pectoral fins. Using Lagrangian Coherent Structures and Lagrangian fluid tracers, we identified distinctly dynamic fluid regions and found that mixing around the pectoral fin significantly increases with \textit{Re} and fin bending enhance fluid mixing at low \textit{Re}. However, as zebrafish matures and its \textit{Re} increases, the need to beat the pectoral fins to enhance mixing is reduced. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D26.00009: Scaling the Thrust Production and Energetics of Inviscid Intermittent Swimming Emre Akoz, Keith Moored Many fish have adopted an intermittent swimming gait sometimes referred as a burst-and-coast behavior. By using this gait, fish have been estimated at reducing their energetic cost of swimming by about 50\%. Lighthill proposed that the skin friction drag of an undulating body can be around 400\% greater than a rigidly-held coasting body, which may explain the energetic savings of intermittent swimming. Recent studies have confirmed the increase in skin friction drag over an undulating body, however, the increase is on the order of 20-70\%. This more modest gain in skin friction drag is not sufficient to lead to the observed energy savings. Motivated by these observations, we investigate the inviscid mechanisms behind intermittent swimming for parameters typical of biology. We see that there is an energy savings at a fixed swimming speed for intermittent swimming as compared to continuous swimming. Then we consider three questions: What is the nature of the inviscid mechanism that leads to the observed energy savings, how do the forces and energetics of intermittent swimming scale with the swimming parameters, and what are the limitations to the benefit?\footnote{Supported by the Office of Naval Research under Program Director Dr. Bob Brizzola, MURI grant number N00014-14-1-0533} [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D26.00010: Jumping hoops on water Eunjin Yang, Ho-Young Kim Small aquatic arthropods, such as water striders and fishing spiders, are able to jump off water to a height several times their body length. Inspired by the unique biological motility on water, we study a simple model using a flexible hoop to provide fundamental understanding and a mimicking principle of small jumpers on water. Behavior of a hoop on water, which is coated with superhydrophobic particles and initially bent into an ellipse from an equilibrium circular shape, is visualized with a high speed camera upon launching it into air by releasing its initial elastic strain energy. We observe that jumping of our hoops is dominated by the dynamic pressure of water rather than surface tension, and thus it corresponds to the dynamic condition experienced by fishing spiders. We calculate the reaction forces provided by water adopting the unsteady Bernoulli equation as well as the momentum loss into liquid inertia and viscous friction. Our analysis allows us to predict the jumping efficiency of the hoop on water in comparison to that on ground, and to discuss the evolutionary pressure rendering fishing spiders select such dynamic behavior. [Preview Abstract] |
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