Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H24: Granular Flows: Locomotion and Drag |
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Chair: Ho-Young Kim, Seoul National University Room: 2003 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H24.00001: Switch of states of a short chain in response to vibrations Yu-Cen Sun, Jung-Ren Huang, Chiao-Yu Tao, Jih-Chiang Tsai We study experimentally the dynamics of a short ball chain confined in a quasi-2D vertical channel under different vibrational strengths(VS). For a substantial range of VS, the chain maintains period-1 bouncing with the channel, but also undergoes transitions from a uniform response to various states of excitations as VS increases. In the transitional zone, we find that the unexcited and excited states exhibit bistability and switch spontaneously at fixed values of VS. This coexistence of different states explains the stocastic switch of ratcheting behaviors we reported previously in Phys. Rev. Lett. 112, 058001 (2014) where a spatial gradient of vibration is imposed. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H24.00002: Photoelastic gelatin spheres for investigation of locomotion in granular media Seyed Amir Mirbagheri, Ericson Ceniceros, Mehdi Jabbarzadeh, Zephyr McCormick, Henry Fu We describe a force measurement method in granular media which uses highly-sensitive photoelastic gelatin spheres and its application to measuring forces exerted as animals burrow through granular media. The method is applicable to both freshwater and marine organisms. We fabricate sensitively photoelastic gelatin spheres and describe a calibration method which relates forces applied to gelatin spheres with photoelastic signal. We show that photoelastic gelatin spheres can detect forces as small as 1 microNewton, and quantitatively measure forces with up to 60 microNewton precision, a two order of magnitude improvement compared to methods using plastic disks. Gelatin spheres can be fabricated with a range of sizes to investigate a variety of granular media. Finally, we used the calibrated gelatin spheres in a proof-of-principle experiment to measure forces during earthworm locomotion. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H24.00003: A Nondimensional Model for Axial Digging in Granular Materials Hao Li, Dawn Wendell, Anette Hosoi, Pawel Zimoch We investigate the mechanics of thin diggers in a packing of granular materials. Experiments are conducted with diggers of varying thickness and force-depth data is recorded. Accounting for buckling and drag force, we propose a continuum model thats predicts an optimal digger thickness that maximizes digging depth. Model predictions are compared to experimental data. This model is refined when digger thickness approaches the grain scale to account for stochasticity. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H24.00004: Helical swimming in granular media Roberto Zenit, Elsa de la Calleja, Francisco Godinez In nature, many organisms are capable of swimming in sand by performing an undulatory motion. Recently, Goldman and collaborators showed that a modification of the low-Re number resistive force theory can be used to explain the phenomena. In this investigation we use a self-propelled magnetically-driven swimmer with a helical tail to further investigate the swimming performance in sand. We successfully produced devices that effectively swam in sand the the rotating action of a helical tail. We measured the swimming speed for a range of rotational speeds and tail geometries. Preliminary results will shown and discussed. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H24.00005: Legless locomotion in lattices Perrin Schiebel, Daniel I. Goldman Little is known about interactions between an animal body and complex terrestrial terrain like sand and boulders during legless, undulatory travel (e.g. snake locomotion). We study the locomotor performance of Mojave shovel-nosed snakes ($\textit{Chionactis occipitalis}$, $\approx 35$ cm long) using a simplified model of heterogeneous terrain: symmetric lattices of obstacles. To quantify performance we measure mean forward speed and slip angle, $\beta_s$, defined as the angle between the instantaneous velocity and tangent vectors at each point on the body. We find that below a critical peg density the presence of granular media results in high speed ($\approx 60$ cm/s), low average slip ($\overline{\beta_s} \approx 6^\circ$) snake performance as compared to movement in the same peg densities on hard ground ($\approx 25$ cm/s and $\overline{\beta_s} \approx 15^\circ$). Above this peg density, performance on granular and hard substrates converges. Speed on granular media decreases with increasing peg density to that of the speed on hard ground, while speed on hard ground remains constant. Conversely, $\overline{\beta_s}$ on hard ground trends toward that on granular media as obstacle density increases. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H24.00006: Self-burrowing seeds: drag reduction in granular media Wonjong Jung, Sung Mok Choi, Wonjung Kim, Ho-Young Kim We present the results of a combined experimental and theoretical investigation of drag reduction of self-burrowing seeds in granular media. In response to environmental changes in humidity, the awn (a tail-like appendage of seed) of Pelargonium carnosum exhibits coiling-uncoiling deformation which induces the thrust and rotary motions of the head of the seed against the surface of the soil. Using various sizes of glass beads that mimic the granular soil, we measure the thrust forces required for the seed of Pelargonium carnosum to penetrate into granular media with and without rotation. Our quantitative measurements show that the rotation of the seed remarkably reduces the granular drag as compared to the drag against the non-spinning seed. This leads us to conclude that the hygroscopically active awns of Pelargonium carnosum enables its seed to dig into the relatively coarse granular soils. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H24.00007: A Model for Solid-Solid drag in Bidisperse Gas-solid Flows Eric Murphy, Shankar Subramaniam Computational models for gas-solid mixtures often require closures for interphase momentum and energy transfer. One of the most important interactions for polydisperse systems is a so-called solid-solid drag, i.e. the momentum transfer between different particulate phases traveling at different mean velocities. Modeling of these, and additional terms has been a focus of the granular physics community for nearly three decades and is no easy task. Flows of bidisperse particles are often high Mach number, Ma\textgreater \textgreater 1. As a result, many theories developed for low Mach number applications using the Chapman-Enskog(CE) theory are not strictly applicable. Still, many other analytic moment methods did not properly couple granular temperature and slip between particulate phases. We have developed a moment theory for the slip and temperature evolution employing the pseudo-Liouville operator technique, which correctly accounts for the coupling between phasic slip and temperatures. The theory is compared with other existing moment models for solid-solid drag. It is found that the drag model is a weighted sum of terms arising in both (CE) and existing moment theories. Additionally, new phase specific temperature evolution terms are obtained that shed light on phenomena such as non-equipartition of energy in bidisperse granular gases. Lastly, we explore some of the segregation behavior implied by the model for homogeneous gas-solid flows with bidisperse particles. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H24.00008: Giant drag reduction due to interstitial air in sand Devaraj van der Meer, Tess Homan When an object impacts onto a bed of very loose, fine sand, the drag it experiences depends on the ambient pressure in a surprising way: Drag is found to increase significantly with decreasing pressure. We use a modified penetrometer experiment to investigate this effect and directly measure the drag on a sphere as a function of both velocity and pressure. We observe a drag reduction of over 90\% and trace this effect back to the presence of air in the pores between the sand grains. Finally, we construct a model based on the modification of grain-grain interactions that is in full quantitative agreement with the experiments. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H24.00009: Modulation of orthogonal body waves enables versatile maneuverability in limbless locomotion Daniel Goldman Limbless organisms can create different motions by modulating axial undulations that pass through their bodies. Sidewinding snakes generate horizontal and vertical waves, with a phase offset of $\pi/2$, resulting in posteriorly-propagating alternating regions of static contact with the substrate and elevated motion, resulting in a ``stepping'' motion of body segments. We have discovered that sidewinder rattlesnakes ({it Crotalus cerastes}) are quite maneuverable and possess at least two turning methods: ``differential turning'' and ``reversal turning.'' In differential turning, the amplitude of the horizontal wave changes along the body length, resulting in turns of average $25.6 \pm 12.9$, maximum $86.1^\circ$per cycle. In reversal turning, the vertical wave's phase rapidly changes by $\pi$, resulting in a sudden, large change in movement direction (average $77.8 \pm 27.4$, maximum $160.5^\circ$ per cycle) without body rotation. We applied these control mechanisms to a 16-link snake robot capable of sidewinding on sand. By modulation of horizontal wave amplitude gradient along the body, we replicated differential turning, and by producing a $\pi$ phase shift in the vertical wave, we replicated a reversal turn. More complex wave modulations lead to enhanced robot maneuverability. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H24.00010: Design of a Localized Fluidization Burrowing Robot Daniel Dorsch, Amos Winter This presentation will focus on the critical fluid and granular mechanics principles that drove the design of RoboClam 2.0, a self-actuated, radially expanding underwater burrowing device. RoboClam 2.0 was inspired by the Atlantic razor clam, Ensis directus, which burrows by contracting its valves and fluidizing the surrounding soil to reduce burrowing drag. This contraction results in a localized fluidized region occurring 1---5 body radii away from the animal. Moving through a fluidized, rather than static, soil requires energy that scales linearly with depth, rather than depth squared. In addition to providing an advantage for the animal, localized fluidization may yield significant value to engineering applications such as subsea robot anchoring and pipe installation. RoboClam 2.0 is sized to be an anchoring platform for autonomous underwater vehicles. We will present the scaling relationships that can be used to design RoboClam derivatives for different size scales and applications. The critical speed, displacement and force with which the device must contract to create fluidization are calculated based on soil parameters. These parametric relationships allow for choosing actuators of appropriate size and power output for desired burrowing performance. [Preview Abstract] |
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