Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W24: Granular Flow I |
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Sponsoring Units: DFD GSNP DCMP Chair: Wolfgang Losert, University of Maryland Room: LACC 411 |
Thursday, March 24, 2005 2:30PM - 2:42PM |
W24.00001: Hysteresis and competition between disorder and crystallization in sheared and vibrated granular flow Karen E. Daniels, Robert P. Behringer Experiments in a 3D annular shear cell vibrated from below and sheared from above show a hysteretic freezing/melting transition. Under sufficient vibration a crystallized state is observed, which can be melted by sufficient shear. The critical line for this transition coincides with equal kinetic energies for vibration and shear. The force distribution is double-peaked in the crystalline state and single-peaked with an approximately exponential tail in the disordered state. A linear relation between pressure and volume ($dP/dV > 0$) exists for a continuum of partially and/or intermittently melted states over a range of parameters. This work has been supported by the NASA microgravity program, grant NNC04GB08G. [Preview Abstract] |
Thursday, March 24, 2005 2:42PM - 2:54PM |
W24.00002: Ordered Packing Induced by Simultaneous Shear and Compaction Bruno Hancock, Meenakshi Dutt, Craig Bentham, James Elliott We study a system of monodisperse frictional particles confined between two surfaces and being simultaneously sheared and unaxially compacted by the upper surface. The upper surface is made of particles identical to those in the bulk, arranged randomly, or in a square or triangular lattice. The particles between the surfaces are allowed to compact under gravity after being poured onto the bottom surface, followed by simultaneous constant strain compaction and shear by the upper surface. We focus on the evolution of the packing structure with interparticle friction, arrangements of the particles on the surfaces, initial height of the confined gravitationally compacted particles and the shear and compaction strain rates. We compute the coordination number, packing fraction, contact orientation, distribution of contacts and other relevant quantities to provide quantitative insight on the packing structure. We have found, for a 5 diameter layer of confined particles, the compaction speed has a greater effect on the packing structure of the particles in comparison to the shear speed. For a shearing surface formed of particles arranged in a square lattice, the packing structure of the confined particles evolves to interdigitating layers of 3D close-packed spheres. The numerical experiments have been performed via Discrete Element Method simulations (Dutt et al., 2004 to be published) using Microcrystalline Cellulose spheres. [Preview Abstract] |
Thursday, March 24, 2005 2:54PM - 3:06PM |
W24.00003: Shear-induced size segregation and crystallization in an annular geometry J.P. Gollub, N. Travers, J.C. Tsai In previous experiments [1] on slow shearing of a mono-disperse annular layer of granular material by a rotating lid at constant pressure, we showed that the material crystallizes after a sufficient accumulated displacement, and that the rheological properties of the material (e.g. the flow profile and shear force) are then substantially different. Here, we extend this work to the case of a bi-disperse mixture of 0.6 mm and 1.0 mm particles. We find that when the layer is sufficiently thick, the material first separates into two mono-disperse layers, and the separate layers then crystallize. The boundary between the two layers remains somewhat disordered. For layers thinner than about 15d, where d is the small particle diameter, complete segregation is not observed. We also discuss the trajectories of individual particles, and the velocity profile of the segregated system. [1] J.C. Tsai and J.P. Gollub, Phys. Rev. E. 70, 031303 (2004) [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:18PM |
W24.00004: A Particle-Substrate Model and Its Applications Robert Behringer, Meenakshi Dutt Systems of monodisperse particles moving on a substrate which is driven externally have been studied from the perspective of understanding the nonlinear behavior responsible for phenomena such as subharmonic waves, pattern formation or supersonic behavior. A complete understanding of the microscopic dynamics in such systems must encompass the effects of collisions and the substrate on the particles. We begin from first principles by considering collections of spherical frictional particles that roll and slip on a flat static substrate. Experiments performed by Painter et al. (Phys. Rev E (2000)) on two particle collisions emphasized the importance of the role played by substrate friction, in particular kinetic friction, on the particle dynamics after collision on a substrate. We present a numerical model which accounts for collisional and surface frictional dissipation and their influence on particle dynamics for a quasi 2-dimensional cooling granular material. We apply this model to a simulation of the granular collider experiment (Painter et al., Physica D (2003)), in which collections of particles collided as they moved radially inward on a substrate. We find an agreement between the experimental and numerical results. We will also be presenting further applications of the model. [Preview Abstract] |
Thursday, March 24, 2005 3:18PM - 3:30PM |
W24.00005: Maximum angle of stability of a wet granular pile Sarah Nowak, Azadeh Samadani, Arshad Kudrolli We investigate the impact of liquids on the maximum angle of stability ($\theta_m$) using a rotating drum apparatus. The angles are measured by imaging the surface. The maximum angle of stability is observed to increase and saturate as a function of the volume fraction of the fluid. We first show that the angles are affected by the side walls and higher angles are observed unless a wide drum that is a few hundred times the grain diameter is used. We present a new model that predicts $\theta_m$ of the wet pile in the saturation regime. Our model considers the stability of the beads along planes with slopes between $\theta_m$ for dry beads and the pile's surface. We claim that while these planes are not geometrically stable, they are stabilized with the additional cohesive forces between the grains due to liquid bridges. The model is able to reproduce the grain size, surface tension and system size dependence observed in our experiments. [Preview Abstract] |
Thursday, March 24, 2005 3:30PM - 3:42PM |
W24.00006: Packing Fraction and Maximum Stability Angle of Granular Heaps Jeremy Olson, Marquita Priester, Jin-ying Luo, Sameer Chopra, Rena Zieve From rotating drum measurements in two dimensions, we show that the packing fraction of a granular heap plays a dual role in predicting its stability. For a fixed grain shape, the stability increases with packing fraction. We have measured this effect for several grain shapes. However, in determining the relative stability of different grain shapes, those with the {\em lowest} average packing fractions tend to have the highest maximum angle of stability. A possible explanation is that a low packing fraction indicates that a heap can support a wide range of stable configurations. With more stable arrangements available, the heap has to be tilted farther, on average, to reach an unstable configuration that triggers an avalanche. We also find a lack of correlation between angles of successive avalanches. This shows that only the grain arrangement close to the surface of the pile, which changes from one avalanche to the next, figures prominently in triggering the avalanches. [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 3:54PM |
W24.00007: Boundary effects on the stability of thin submerged granular piles S.B. Ogale, R.N. Bathe, R.J. Choudhary, S.N. Kale, Abhijit S. Ogale, A.G. Banpurkar, A.V. Limaye The stability of a pile of steel balls formed in a thin cell is studied for different liquids and air. The dependence of the angle of repose (AOR) on the medium and the cell thickness is examined. The AOR is observed to increase considerably with a decrease in cell width. In a thin cell (width comparable to a few times the ball diameter) the AOR is seen to depend on liquid viscosity, in contrast to the case of thick cells. A Voronoi polygon analysis of ball position correlations is made to enumerate the near-neighbor distributions as a function of AOR. The viscosity dependence in thin cells is attributed to the boundary wall effects, presumably caused by the influence of viscosity on granular arching. Interestingly, the AOR is found to be smaller in a thinnest cell with the cell width comparable to the bead diameter possibly due to absence of arching. The case of a pile formed in a thin cell in air stands out to be distinctly different as compared to the piles formed in liquids. Various issues such as the surface roughness of the balls, possible air trapping in micro-cavities and related formation of liquid bridges, effects of energy of impact on pile equilibrium etc. are addressed in the analysis. [Preview Abstract] |
Thursday, March 24, 2005 3:54PM - 4:06PM |
W24.00008: Effects of Size Polydispersity on Pharmaceutical Particle Packings Meenakshi Dutt, Bruno Hancock, Craig Bentham, James Elliott Pharmaceutical powder blends are multicomponent mixtures of excipients and the drug powder particles which have irregular shapes with equivalent diameters typically ranging from 40 microns to 300 microns. We consider idealizations of such systems with emphasis on the size dispersity in a pure excipient powder comprised of spherical particles. We study the characteristics of the particle packings generated through gravitational compaction followed by uniaxial compaction via Discrete Element Method simulations (Dutt et al., 2004 to be published). We present results for two common excipients: microcrystalline cellulose (MCC) and sucrose. For each excipient, we vary the degree of dispersity in the diameters of the particles. For insight into the geometrical characteristics of the particle packings, we calculate the coordination number, packing fraction, radial distribution functions and contact angle distributions for the various mixtures. The evolution of the force and stress distributions along with the stress-strain relations are calculated for each system. We discuss comparisons of these quantities for systems with different size dispersity and material properties. For MCC and sucrose mixtures with narrow size distributions (195-225 microns, 170-260 microns), the average packing fraction and coordination number prior to and after uniaxial compaction decreases with interparticle friction, in agreement with results for monodisperse spheres (Silbert et al., Phys. Rev. E (2002)). [Preview Abstract] |
Thursday, March 24, 2005 4:06PM - 4:18PM |
W24.00009: Studies of Particle Packings in Mixtures of Pharmaceutical Excipients Craig Bentham, Meenakshi Dutt, Bruno Hancock, James Elliott Pharmaceutical powder blends used to generate tablets are complex multicomponent mixtures of the drug powder and excipients which facilitate the delivery of the required drug. The individual constituents of these blends can be noncohesive and cohesive powders. We study the geometric and mechanical characteristics of idealized mixtures of excipient particle packings, for a small but representative number of dry noncohesive particles, generated via gravitational compaction followed by uniaxial compaction. We discuss particle packings in 2- and 3- component mixtures of microcrystalline cellulose (MCC) \& lactose and MCC, starch \& lactose, respectively. We have computed the evolution of the force and stress distributions in monodisperse and polydisperse mixtures comprised of equal parts of each excipient; comparisons are made with results for particles packings of pure blends of MCC and lactose. We also compute the stress-strain relations for these mixtures. In order to obtain insight into details of the particle packings, we calculate the coordination number, packing fraction, radial distribution functions and contact angle distributions for the various mixtures. The numerical experiments have been performed on spheroidal idealizations of the excipient grains using Discrete Element Method simulations (Dutt et al., 2004 to be published). [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:30PM |
W24.00010: Rising through the sand: penetration of a granular medium from below Thomas Scheidemantel, Ke Chen, Matthew Lohr, Casey Conger, Kit Klein, Matthew Stone, Peter Schiffer We report measurements of the drag force experienced by a flat plate traveling upward through a dense granular medium. Our apparatus consists of a container in which a plunger can be pushed upward from the bottom of the grains. We present results as a function of plunger size, penetration speed, and overload weight. As expected, the largest forces are experienced during the initial jamming and reorganization as the plunger pushes from the bottom of the container. [Preview Abstract] |
Thursday, March 24, 2005 4:30PM - 4:42PM |
W24.00011: Point-force Response Functions for Model Solid Foams Erin Miller, David Wells, Lucas Wharton, Gerald Seidler It has been suggested that the elastic response to point-perturbations can be used as a fingerprint of the appropriate theory of elasticity for granular and other mesoscale disordered materials. Additionally, this sort of test may be able to provide information as to the appropriate length scale over which a continuum model is valid. Here, we investigate the point-force response function for one example of a mesoscale disordered material -- solid foam. We will present results for a variety of model 2-D solid foams, covering the range from very low-density foams, where it has been proposed by Blumenfeld (J. Phys. A, 2003) that foams may exhibit the same type of non-traditional elasticity as has been discussed for granular media, to the high-density limit where traditional theories of elasticity are certainly appropriate on some length scale. [Preview Abstract] |
Thursday, March 24, 2005 4:42PM - 4:54PM |
W24.00012: Non-linear stress transmission in granular materials Yael Roichman, Dov Levine The force chain model uses the highly singular lines along which stress propagates in granular materials (termed {\em force chains}) to describe stress transmission in granular materials. In this work we solve the full force chain model both in the mesoscopic and the macroscopic limit and define the two corresponding characteristic lengths. We calculate the macroscopic constitutive relation for granular materials and show that the average response of an ensemble of granular materials changes in a non-linear way with the applied force. In addition, we explain the measured deviations of granular materials from elastic-like behavior buy calculating the stress transmission in textured piles and the response to tilted forces. Finally, we demonstrate the effect of the non-linear behavior of granular materials by calculating the difference between the response to two forces applied simultaneously in close proximity and the superposition of the response to each force applied separately. [Preview Abstract] |
Thursday, March 24, 2005 4:54PM - 5:06PM |
W24.00013: Force Correlations in 2D Granular Materials Trush Majmudar, Robert Behringer We present experimental measurements on force correlations in a 2D granular system consisting of bi-disperse photo-elastic disks. A biaxial test apparatus is used and three different types of loading conditions are implemented: isotropic compression, uniaxial compression and pure shear. For each case, incremental deformations are applied and the system is imaged at each increment. We then calculate forces at each particle contact using an inverse algorithm and photoelasticity. From these forces, we calculate autocorrleation functions of the force magnitude for these images. We observe for uniaxial compression and most strongly for pure shear, that there is an approximately power-law decay along the dominant direction of the force chains, and short-range correlations in the transverse direction. Distributions of the vector contact forces show relatively little difference among the various preparation methods for the tangential forces, although the distributions of normal forces show some differences. We conclude that the force-force correlation function is the best statistical tool to differentiate among these states. [Preview Abstract] |
Thursday, March 24, 2005 5:06PM - 5:18PM |
W24.00014: Dry quick sand Detlef Lohse, Raymond Bergmann, Devaraj van der Meer, Remco Rauhe Sand supports weight. Force chains are known to play a prominent role therein. We considerably weaken the force chain structure by letting air flow through very fine sand. Even when the air is turned off and the bed has settled, the prepared sand does not support weight: Balls sink into the sand up to five diameters deep. We call this state of sand dry quick sand. The final depth of the ball scales linearly with its mass and above a threshold mass, a sand jet is formed which shoots sand straight and violently into the air.\\ Reference: Nature, in press, December 2004. [Preview Abstract] |
Thursday, March 24, 2005 5:18PM - 5:30PM |
W24.00015: Crossover between linear and volcanic response in a self-organizing driven mixture - interacting lattice gas computer simulation Ras Pandey, Joe Gettrust Transport, flow, and self-organizing structures are studied in a mixture of two immiscible components (A,B) driven by hydrostatic bias from a reservoir source. We consider a cubic lattice with an open top end and a source of particles at the bottom. Initially, particles (A,B) are distributed randomly on about half of the lattice sites with equal proportion. Apart from excluded volume (hard-core), similar particles attract and dissimilar particles repel each other with a nearest neighbor interaction. Empty sites (S) represent an effective medium which attract both components. Hydrostatic pressure bias (H) is implemented probabilistically to drive particles, against gravitational sedimentation, from the source at the bottom to open sink. The Metropolis algorithm is used to move particles stochastically to randomly selected neighboring sites. Periodic boundary conditions are used along the transverse direction. Particles are released into the lattice only from the bottom, but they can escape from top and bottom. A steady-state self-organized structure appears as the sedimentation competes with the hydrostatic bias in continuous flow. At low bias, the flow response is linear and becomes non-linear at high values where the rate of response of the higher molecular weight component diverges while it goes down (in the opposite direction) for the lighter component. [Preview Abstract] |
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