Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E19: Biological fluid dynamics: General I |
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Chair: David Saintillan, University of California, San Diego Room: Georgia World Congress Center B306 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E19.00001: How do wombats make cubed poo? Patricia J Yang, Miles Chan, Scott Carver, David L Hu Wombats are fossorial herbivorous Australian marsupials with the distinctive feature of producing cubic feces, which is unique in the animal kingdom. In the built world, cubic structures are created by extrusion or injection molding, but there are few examples of this feat in nature. We investigate how wombats produce cubic feces, through investigation of the structure and mechanics of two dissected alimentary systems of wombats--derived from veterinary euthanized individuals following motor vehicle collisions in Tasmania, Australia. In the final 8 percent of the intestine, feces changed from a liquid-like state into a solid state composed of separated cubes of length 2 cm. This shape change was due to the azimuthally varying elastic properties of the intestinal wall. By emptying the intestine and inflating it with a long balloon, we found that the local strain varies from 20 percent at the cube's corners to 75 percent at its edges. Thus, the intestine stretches preferentially at the walls to facilitate cube formation. This study addresses the long-standing mystery of cubic scat formation and provides insight into new manufacturing techniques for non-axisymmetric structures using soft tissues. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E19.00002: Experimental Simulation of Dolphin Blow Richard J. Gaeta, Jason Bruck, Jamey Jacob Marine mammals face increasing threats from human activities and other anthropogenic impacts such as pollution. To assess stress and heath in wild dolphins, pods can be tracked by boat and unmanned aircraft to analyze surfacing rates as an indicator of stress as well as physiological measures taken from blowhole mucus. While hormone samples have been taken from the blowhole exultations in whales with both poles and unmanned aircraft, dolphins are much less likely to remain close enough to boats to acquire samples in the former method. Remote technology represents the best potential tool for the non-invasive collection of critical measures of health including stress and reproductive hormones and parasite loads. In order to evaluate requirements, experimental simulators have been developed to model the dolphin blow flow field to evaluate the collection performance of unmanned aircraft. Two operational systems are compared with expected jet exit characteristics, including flow rates, jet velocities, and mucus entrainment. The resulting flow fields are evaluated and compared with in vivo observations. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E19.00003: Why Ant-Man and the Wasp Need Helmets to Breathe Maxwell Mikel-Stites, Anne Staples In the 2018 film, Ant-Man and the Wasp, the characters Scott Lang and Hope Van Dyne don suits with advanced technologies that allow them to shrink to insect size and become the eponymous superheroes of the film’s title. While some questionable physics is presented in the film and the earlier associated comic books, here we sketch out a physically realistic picture (also explored in our recent article in the journal Superhero Science and Technology) of some of the significant respiratory problems that would be encountered by humans shrinking to insect size. First, they would experience a rarefied atmospheric density similar to that in Mt. Everest’s “death zone.” Second, Kleiber’s law implies that their metabolic rates per unit mass would increase by approximately two orders of magnitude, greatly increasing the rate of oxygen intake, relative to their sizes, needed to survive. Finally, we discuss how existing microfluidic technologies could bridge the gap between Lang and Van Dyne’s mammalian respiratory systems which function inefficiently at the microscale, and the increased relative oxygen demands they would experience at the microscale. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E19.00004: Nectar foaming by butterflies and moths with long proboscises Artur Salamatin, Bochuan Sun, Daria Monaenkova, Wah-Keat Lee, Peter H Adler, Kostya Kornev The ability of many insects to drink nectar from long floral tubes questions the conventional “drinking straw” model of proboscis: the model requires an enormous suction pressure to move nectar through the proboscis to the suction pump in the insect head. Imaging of the behaviour of liquid films and droplets on proboscises of hawk moths, allowed us to show that liquid gets inside the food canal by penetrating through the fence of the linking dorsal and ventral hooks. And a thin liquid film is formed on the internal surface of the canal. X-ray phase-contrast imaging reveals that as the drop penetrates into the canal, the internal liquid films undergo an instability and form liquid bridges. Thus, the insect gets nectar from the bubble trains not from a continuous nectar column. These observations show the deficiency of the drinking straw model. We also report on the mechanism of bubble train formation theoretically and numerically showing that the bubble length and the time of its formation depend on permeability of the proboscis linking structures. Estimates for the energy dissipation of moving bubble trains show that fluid feeding insects with long proboscises may benefit from this mechanism as it reduces the required suction pressure. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E19.00005: Effects of oily marine aerosol in cardiovascular flow of embryonic Gulf Killifish Sanjib Gurung, Benjamin Dubansky, David W Murphy Exposure to spilled crude oil in water and sediments has been shown to negatively affect cardiovascular development in various embryonic organisms, but the effect of airborne oil exposure is not well known. Here we examine the effects of oily marine aerosol exposure on the cardiovascular fluid dynamics of embryonic Gulf Killifish (Fundulus grandis), which develop outside the water. We acquired high speed footage of in vivo blood flow at 40× magnification in the 17.5 µm diameter sinoatrial nodal artery in control and oil-exposed embryos at 10 and 11 days post fertilization. Image processing was used to register and mask images, subtract the average background, and normalize intensity, and particle image velocimetry was performed using erythrocytes as tracer particles. The mean Reynolds and Womersley numbers in the control group were 0.0024 and 0.0123, respectively. Oil-exposed groups had reduced cardiac output, mean blood flow velocity, hatching success, and body length and increased heart beat rate and hematocrit level as compared to the control group. Similarly, shear stress on the vessel walls is estimated to be lower for the oil-exposed group. These results suggest defects during cardiogenesis and degradation of cardiovascular performance due to oily marine aerosol exposure. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E19.00006: Hydrodynamic effects of sea star morphology and orientation to flow Mark Hermes, Mitul Luhar Live-animal experiments show that certain sea star species exhibit morphological plasticity in response to changes in hydrodynamic conditions. We investigated the hydrodynamic effect of changing shape by measuring drag and lift forces for 3D printed sea star models resembling Pisaster Ochraceus with varying arm length-to-width ratio (aspect ratio). An ATI Industrial Automation six-axis load transducer was used to measure forces for the model assembly. An automated positioning system oriented the models relative to mean flow direction. We found that drag forces increase with increased aspect ratio and lift forces decrease with increased aspect ratio. We also found that orienting the model with its arm rotated 36° relative to the flow direction reduces both the drag and lift forces compared to other orientations. These preliminary results indicate that, in wave exposed areas, the hydrodynamic loads acting on sea stars are minimized by decreasing aspect ratio and optimally orienting the body. |
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