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 H32: Granular Flows II |
Hide Abstracts |
Chair: Yang Ding, Georgia Institute of Technology Room: 33C |
Monday, November 19, 2012 10:30AM - 10:43AM |
H32.00001: Drag and lift forces in granular flows Fran\c{c}ois Guillard, Olivier Pouliquen, Yo\"el Forterre Forces exerted on obstacles moving in a granular medium are studied both experimentally and numerically. The experiment consists in an horizontal cylinder rotating around a vertical axis in a granular media. Both drag forces and lift forces experienced by the cylinder are measured. The first striking result is obtained during the first half rotation, before the cylinder crosses its wake. Despite the symmetry of the object, a strong lift force is measured, about 20 times the buoyancy. The scaling of this force is studied experimentally and discussed in the framework of a continuum model based on a frictional rheology. The second striking observation is made after several rotations. The drag force dramatically drops and becomes independent of depth, showing that it no longer scales with the hydrostatic pressure. The rotation of the cylinder induces a structure in the packing, which screens the weight of the grains above. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H32.00002: From antinode clusters to node clusters: The concentration dependent transition of floaters on a standing Faraday wave Ceyda Sanli, Detlef Lohse, Devaraj van der Meer A hydrophilic floating sphere that is denser than water drifts to an amplitude maximum (antinode) of a surface standing wave. A few identical floaters therefore organize into antinode clusters. However, beyond a transitional value of the floater concentration $\phi $, we observe that the same spheres spontaneously accumulate at the nodal lines, completely inverting the self-organized particle pattern on the wave. From a potential energy estimate we show that at low $\phi $ antinode clusters are energetically favorable over nodal ones and how this situation reverses at high $\phi $, in agreement with experiment. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H32.00003: Force and flow response of granular matter to simultaneous intruders Paul Umbanhowar, Lionel London, Daniel Goldman For two horizontal, parallel rods vertically penetrating into dense granular matter at constant velocity, we examine the grain flow and the vertical and horizontal components of the force as functions of rod separation $s$ using experiment and DEM simulation. In previous experiments we found that while the vertical force $F$ required to maintain constant velocity increases nearly linearly with the penetration depth $d,$ the dependence of the slope $F/d$ on $s$ is more interesting. As $s$ is increased from zero, $F/d$ increases to a maximum value and then slowly decreases to twice the value of $F/d$ for a single rod at large $s$. Here we present new results examining the relation between the horizontal and vertical forces acting on each rod and the associated granular flow as functions of $s,$ particle friction coefficient $\mu,$ and horizontal rod support compliance. Increasing $\mu$ increases the value of $s$ at which $F(s)/d$ is maximum, while decreasing compliance reduces the peak in penetration resistance while increasing the range of $s$ where penetration resistance is enhanced. The flow fields around each rod become more asymmetric in the horizontal as $s$ is decreased and exhibit correlations with both the mean and fluctuating components of the forces on the rods. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H32.00004: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 11:22AM - 11:35AM |
H32.00005: Force measurements on an intruder in pre-fluidized sand Tess A.M. Homan, Detlef Lohse, Devaraj van der Meer A container filled with sand is fluidized from below, and by slowly turning of the air flow a very loose packing is created. An intruder controlled by a linear motor is connected to a load cell to measure the force it experiences while moving through the bed. By varying several parameters, such as the intruder shape, velocity, and penetration depth, we aim to obtain a better understanding of the behavior of loosely packed granular materials. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H32.00006: A resistive force model for complex intrusion in granular media Tingnan Zhang, Chen Li, Daniel Goldman Intrusion forces in granular media (GM) are best understood for simple shapes (like disks and rods) undergoing vertical penetration and horizontal drag. Inspired by a resistive force theory for sand-swimming [1], we develop a new two-dimensional resistive force model for intruders of arbitrary shape and intrusion path into GM in the vertical plane. We divide an intruder of complex geometry into small segments and approximate segmental forces by measuring forces on small flat plates in experiments. Both lift and drag forces on the plates are proportional to penetration depth, and depend sensitively on the angle of attack and the direction of motion. Summation of segmental forces over the intruder predicts the net forces on a c-leg, a flat leg, and a reversed c-leg rotated into GM about a fixed axle. The stress profiles are similar for GM of different particle sizes, densities, coefficients of friction, and volume fractions. We propose a universal scaling law applicable to all tested GM. By combining the new force model with a multi-body simulator, we can also predict the locomotion dynamics of a small legged robot on GM. Our force laws can provide a strict test of hydrodynamic-like approaches to model dense granular flows.\\[4pt] [1] Maladen et al, J. R. Soc. Interface, 8, 1332, (2011) [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H32.00007: Sidewinding snakes on sand Hamidreza Marvi, Dante Dimenichi, Robert Chrystal, Joseph Mendelson, Daniel Goldman, David Hu Desert snakes such as the rattlesnake {\em Crotalus cerastes} propel themselves over sand using sidewinding, a mode of locomotion relying upon helical traveling waves. While sidewinding on hard ground has been described, the mechanics of movement on more natural substrates such as granular media remain poorly understood. In this experimental study, we use 3-D high speed video to characterize the motion of a sidewinder rattlesnake as it moves on a granular bed. We study the movement both on natural desert sand and in an air-fluidized bed trackway which we use to challenge the animal on different compactions of granular media. Particular attention is paid to rationalizing the snake's thrust on this media using friction and normal forces on the piles of sand created by the snake's body. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H32.00008: Lift-off performance of a jumping robot on hard and soft ground Jeffrey Aguilar, Alex Lesov, Kurt Wiesenfeld, Daniel Goldman We study lift-off during jumping on hard ground and granular media in a simple robot composed of a linear actuator in series with a spring. On hard ground, the robot jumps from a metallic base. On granular media (GM) composed of $0.3$ mm glass particles, a circular foot is attached to the spring and an air-fluidized bed sets the initial volume fraction, $\phi$. The actuator frequency and phase are systematically varied to find optimal performance. On both substrates, optimal jump height does not occur at the robot's resonant frequency $f_0$. Two distinct jumping modes emerge: a simple jump which is optimal above $f_0$ is achievable with a squat maneuver, and a ``stutter" jump which is optimal below $f_0$ is generated with a counter-movement. For hard ground, both modes exhibit similar performance. On closely packed GM ($\phi=0.62$), the simple jump becomes the favored mode. On loosely packed GM ($\phi=0.58$), jump height performance is significantly reduced due to greater yielding in the material. A dynamical model reveals how optimal lift-off results from non-resonant transient dynamics. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700