Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H15: Biofluids: Animals |
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Chair: John Bush, Massachusetts Institute of Technology Room: 28A |
Monday, November 19, 2012 10:30AM - 10:43AM |
H15.00001: Drinking strategies in nature Wonjung Kim, John Bush We examine the fluid mechanics of drinking in nature. We classify the drinking strategies of a broad range of creatures according to the principal forces involved, and present physical pictures for each style. Simple scaling arguments are developed and tested against existing data. While suction is the most common drinking strategy, various alternative styles have evolved among creatures whose morphological, physiological, and environmental constraints preclude it. Particular attention is given to creatures small relative to the capillary length, whose drinking styles rely on relatively subtle interfacial effects. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H15.00002: Numerical and experimental hydrodynamic analysis of suction cup bio-logging tag designs for marine mammals Mark Murray, Alex Shorter, Laurens Howle, Mark Johnson, Michael Moore The improvement and miniaturization of sensing technologies has made bio-logging tags, utilized for the study of marine mammal behavior, more practical. These sophisticated sensing packages require a housing which protects the electronics from the environment and provides a means of attachment to the animal. The hydrodynamic forces on these housings can inadvertently remove the tag or adversely affect the behavior or energetics of the animal. A modification to the original design of a suction cup bio-logging tag housing was desired to minimize the adverse forces. In this work, hydrodynamic loading of two suction cup tag designs, original and modified designs, were analyzed using computational fluid dynamics (CFD) models and validated experimentally. Overall, the simulation and experimental results demonstrated that a tag housing that minimized geometric disruptions to the flow reduced drag forces, and that a tag housing with a small frontal cross-sectional area close to the attachment surface reduced lift forces. Preliminary results from experimental work with a common dolphin cadaver indicates that the suction cups used to attach the tags to the animal provide sufficient attachment force to resist failure at predicted drag and lift forces in 10 m/s flow. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H15.00003: Modeling huddling penguins Francois Blanchette, Aaron Waters, Arnold Kim We present a model of the behavior of huddling penguins. We focus on the densest huddles, formed during storms, where penguins may be considered to leave no openings in the interior of the huddle. We compute a temperature distribution around the huddle, accounting for the effects of the wind. The dynamics of the huddle are based on an iterative process where the most exposed penguin relocates to the most sheltered location available. We study the effects of wind strength, number of penguins, and random perturbations. We find that our model produces huddles that agree qualitatively with actual huddles in terms of shape and downwind displacement. Moreover, the exposure to the wind appears to be shared nearly equally among penguins, despite the fact that our model assumes only that each penguin aims to minimize its own heat loss. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H15.00004: Robot locomotion on weak ground Feifei Qian, Chen Li, Paul Umbanhowar, Daniel Goldman Natural substrates like sand, soil, and leaf litter vary widely in penetration resistance. Little is known about how animals (and increasingly robots) respond to this variation. To address this deficit, we built an air fluidized bed trackway, in which we control penetration resistance of $1~$mm granular substrates down to zero by increasing the upward flow rate, $Q,$ to the fluidization transition. Using a $2.5$ kg bio-inspired hexapedal robot as our model locomotor, we systematically study how locomotion performance (average forward speed, $v$) varies with penetration resistance, limb kinematics, and foot morphology. Average robot speed decreases with increasing $Q$, and decreases faster for robots with higher leg frequency or narrower leg width. A previously developed model, which captured the robot's performance on granular media with $Q=0$, also captures the observed performance for weakened states with $Q>0$. A single dimensionless control parameter from the model, which combines gait and ground parameters, determines $v$ for all penetration resistances. Our ground control technique and modeling approach provide a way to probe and understand the limits of locomotor performance on yielding substrates. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H15.00005: How does a Tiger beetle catches its prey? Z. Jane Wang, Andreas Haselsteiner, Cole Gilbert When a beetle chases its prey, what laws does it follow, if any? Theoretically, there are multiples strategies that a beetle could use to intercept its prey. By analyzing the pursuit dynamics of Tiger beetles, we found that the beetle adjusts its orientation to minimize the angle between its heading and the prey. The adjustment is linearly proportional the error angle with a time delay. We offer a mechanical explanation of this correlation between the angle and the angular rotation of the beetle. We further suggest an physical interpretation for the time delay constant. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H15.00006: Impact and intrusion of the foot of a lizard running rapidly on sand Chen Li, Tonia Hsieh, Paul Umbanhowar, Daniel Goldman The desert-dwelling zebra-tailed lizard (\emph{Callisaurus draconoides}, 10 cm, 10 g) runs rapidly ($\sim$10 BL/s) on granular media (GM) like sand and gravel. On loosely packed GM, its large hind feet penetrate into the substrate during each step. Based on above-ground observation, a previous study (Li et al., JEB 2012) hypothesized that the hind foot rotated in the vertical plane subsurface to generate lift. To explain the observed center-of-mass dynamics, the model assumed that ground reaction force was dominated by speed-independent frictional drag. Here we use x-ray high speed video to obtain subsurface foot kinematics of the lizard running on GM, which confirms the hypothesized subsurface foot rotation following rapid foot impact at touchdown. However, using impact force measurements, a resistive force model, and the observed foot kinematics, we find that impact force during initial foot touchdown and speed-independent frictional drag during rotation only account for part of the required lift to support locomotion. This suggests that the rapid foot rotation further allows the lizard to utilize inertial forces from the local acceleration of the substrate (particles), similar to small robots running on GM (Qian et al., RSS 2012) and the basilisk (Jesus) lizard running on water. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H15.00007: Ground resistance influences lizard burial in dry and wet sand Sarah Sharpe, Robyn Kuckuk, Daniel Goldman Many terrestrial animals move within soil in which water content can vary, and little is known about how water content affects locomotor performance. To investigate the effect of water content on burial, we created controlled dry and wet substrates. We used 0.3 mm glass particles and varied water content W, the mass of water to mass of dry loosely packed sand. Drag force on a submerged 1.6 cm diameter rod increased by a factor of 4 as W increased from 0 to 0.03, after which force increases were small. Drag force in wet media periodically fluctuated with time and corresponded with surface fracturing. We characterized how W affected burial performance and strategy of a generalist burrower, the ocellated skink lizard (\emph{Chalcides ocellatus}). High speed x-ray imaging was used to measure head, body and limb kinematics in substrates with W= 0 and W= 0.03. In both states during burial the body was maintained in a curved posture and the animal moved using a start-stop motion. During movement, the head oscillated and the forelimb on the convex side of the body was used to push the animal forward. Both speed and angular excursion of the head oscillation decreased in the W= 0.03 state. The differences in locomotion were attributed to the changing resistance force within the media. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H15.00008: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 12:14PM - 12:27PM |
H15.00009: Jumping of water striders on water Eunjin Yang, Jaehak Son, Piotr Jablonski, Ho-Young Kim Small insects such as water striders, springtails, fishing spiders freely move on water by adopting various modes of locomotion, such as rowing, galloping, jumping and meniscus-climbing. As the physics of jumping have not yet been fully understood among those ways of semi-aquatic propulsion, here we present the results of a combined experimental and theoretical investigation of the dynamics of water striders leaping off water. We first image and analyze the trajectories of the legs and body of jumping water striders of three different species with a high-speed camera. We then theoretically compute the forces acting on the body by considering the capillary interaction between the flexible legs and deforming water meniscus. Our theory enables us to predict the maximum take-off speed for given leg lengths. The experimental measurements suggest that the water striders drive their legs near the optimal speed to gain the maximum take-off speed. [Preview Abstract] |
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