Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session HJ: Granular Media: Static and Near-Static Systems |
Hide Abstracts |
Chair: Eric Corwin, University of Chicago Room: Hilton Chicago Williford C |
Monday, November 21, 2005 1:20PM - 1:33PM |
HJ.00001: Angle of Repose and Packing Fraction of Large Granular Particles, as a Function of Shape Paul J. Dolan, Jr., Barbara A. Gordon Measurements of the angle of repose and the packing fraction of granular particles can be greatly affected by such factors as particle surface, static charging, moisture, interstitial gas, and the shape of the particles. The great majority of experimental data presented in the literature concerns small, spherical particles. In order to minimize effects of static charging and interstitial gas, we have studied the static properties of large, approximately 1 cm, monodisperse collections regular polyhedra (4-, 6-, 8- and 12-sided). We will present measurements of the Angle of Repose of these monodisperse, large granular particles as a function of particle shape, as well as measurements of the Packing Fraction of the particles in six differently shaped containers. Initial data for bi-disperse mixtures of these particles will also be presented. [Preview Abstract] |
Monday, November 21, 2005 1:33PM - 1:46PM |
HJ.00002: Experimental tests of a statistical mechanics of static granular media Matthias Schr\"oter, Stacy Sidle, Harry Swinney In 1989 Edwards and Oakeshott proposed a statistical mechanics theory of static granular materials described by a temperature-like state variable named compactivity [1]. We have made the first measurement of the compactivity of a granular material [2]. We have examined a granular column driven by flow pulses and have found that the system explores its phase space of mechanically stable configurations in a history-independent way. The system quickly approaches a steady state; the volume fluctuations about this steady state are Gaussian. The mean volume fraction can be varied by changing the flow rate of the pulses. We calculate the compactivity from the standard deviation of the volume fluctuations [3]. This talk will address the following two questions: (a) Are compactivity values measured with our ``thermometer'' different from values one might measure with a ``thermometer'' based on the grain volume distribution [4]? (b) Can compactivity be a control parameter of granular systems, for example, in size segregation in binary granular mixtures? \newline [1] Edwards and Oakeshott, Physica A {\bf 157}, 1080 (1989). \newline [2] Schr\"oter, Goldman, and Swinney, Phys. Rev. E {\bf 71}, 030301 (2005). \newline [3] Nowak, Knight, Ben-Naim, Jaeger, and Nagel, Phys. Rev. E {\bf 57}, 1971 (1988). \newline [4] Edwards, Bruji\'c, and Makse, in {\it Unifying Concepts in Granular Media and Glasses}, edited by Coniglio {\it et al.} (Elsevier, Amsterdam, 2004) [Preview Abstract] |
Monday, November 21, 2005 1:46PM - 1:59PM |
HJ.00003: Force Network Evolution in a Tilted Granular Bed Ashley Smart, Paul Umbanhowar, Julio Ottino The hierarchy of contacts between grains plays a central role in determining the properties of quasi-static granular materials. Viewed abstractly, the contacts form the connecting edges in a network of interacting nodes where the `weight' of the connection is proportional to the force between contacting grains. Force networks have become a popular method for presenting data produced by experiment and simulation. In this talk we discuss the key changes in the force network for a granular material in an inclined bed. We use particle dynamics to model the granular material as a two-dimensional system of polydisperse disks, and study the evolution of forces, contact angles and network topology as the system approaches the onset of flow. By applying novel network analysis techniques, we gain insight into how granular materials organize, restructure, and ultimately fail under shear. [Preview Abstract] |
Monday, November 21, 2005 1:59PM - 2:12PM |
HJ.00004: Twisted Sandpiles: A Structural Signature of Jamming in Granular Materials Eric Corwin, Heinrich Jaeger, Sidney Nagel When the temperature is increased, a glass loses its rigidity and begins to flow. If sufficient shear stress is applied to a granular material, it too will lose its rigidity and flow. There is no ambiguity between the rigid and flowing phases in both cases. However glasses and liquids have nearly identical structure. Are jammed states and flowing states in a granular system structurally different? And if so is there a measurement which would yield a signature of this difference? We have created an experimental technique that measures the contact-force distribution during shearing flow to address these questions. The distribution of forces is sensitive to minute variations in particle to particle distances. As such, it provides a microscopic view of the nearest-neighbor position correlations. At the onset of jamming we find a qualitative change in the force distribution. This, in turn, hints that there may be a similar structural signature in glasses. Further, we also measure a new granular temperature in granular systems which may be analogous to the glass-transition temperature in liquids. [Preview Abstract] |
Monday, November 21, 2005 2:12PM - 2:25PM |
HJ.00005: Cage Dynamics in a Uniformly Heated Granular Fluid Pedro Reis, Rohit Ingale, Mark Shattuck We report a novel experimental investigation of the dynamics of a uniformly heated, horizontal and quasi-2D granular fluid. Our study is done as a function of filling fraction, $\phi$, in the region prior to crystallization which we observe at $\phi_s=0.719\pm0.007$. We perform a statistical analysis based on two quantities that are typically employed in colloidal/molecular systems: the Mean Square Displacement (MSD) and the Self Intermediate Scattering Function (SISF). These are calculated from the trajectories obtained by tracking all particles inside a representative imaging window of the full system. At low $\phi$ the classic diffusive behavior of a disordered fluid is observed. As the filling fraction is increased towards $\phi_s$, the MSD (or SISF) develops a two-step increase (or decrease) analogous to what is commonly observed in glassy systems. This plateau at intermediate timescales is a signature of the slowing down of the motion of particles due to temporary trapping inside the cages formed by their neighbors. This caging is increasingly more pronounced as $\phi_s$ is approached from below. For $\phi>\phi_s$, each particle becomes fully arrested by its six neighbors, for the whole time accessible experimentally. Moreover, the relaxation time extracted from the SISF, as a function of $\phi$, is well described by the Vogel-Fulcher’s law. Our results are an important step in strengthening the analogy between colloidal/molecular glassy systems and dense granular materials under uniform thermalization. [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