Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session P12: Granular Materials II |
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Sponsoring Units: DFD Chair: Colin Denniston, University of Western Ontario Room: B110-B111 |
Wednesday, March 17, 2010 8:00AM - 8:12AM |
P12.00001: From granular to Newtonian flow: three-dimensional imaging and rheology of suspensions Joshua A. Dijksman, Steven Slotterback, Elie Wandersman, Chris Berardi, William Derek Updegraff, Martin van Hecke, Wolfgang Losert We show that in sedimenting suspension flows, the microscopic dynamics mimics that of dry granular flows. To probe the dynamics of the suspension, we employ three-dimensional flow imaging and rheological measurements in a split-bottom geometry. We explore the range of flow rates from the rate-independent regime to the onset of rate dependence. In slow flows, we recover ``dry granular flow'' behavior, well studied in the split-bottom geometry. When the shear rate becomes comparable to the rearrangement timescale of the particles, we observe essentially Newtonian behavior. We show that these observations are consistent with the inertial number theory adapted to suspension flows. [Preview Abstract] |
Wednesday, March 17, 2010 8:12AM - 8:24AM |
P12.00002: Deformation of Quasi-2D Oil-in-Water Emulsions Laura Golick, Kenneth Desmond, Eric R. Weeks We create a quasi-2D nearly frictionless granular system, analogous to 2D granular systems of photoelastic disks but without static friction. To do this, we confine an oil-in-water emulsion between two glass plates such that the gap between the plates is smaller than the undeformed oil droplet diameter. For a range of droplet area fractions and plate separations, we observe the deformations the oil droplets experience due to contact with each other. The deformation of the droplet is correlated to the force its neighbors exert on it. As area fraction increases, the deformation of the droplets increases. By looking at the pattern of deformations throughout the system we visualize the location of force networks due to droplet-droplet interactions. [Preview Abstract] |
Wednesday, March 17, 2010 8:24AM - 8:36AM |
P12.00003: Geometry Dominance in the Formation of Clusters in Systems of Rigid Gapped Rings Christopher LaSota, Rachel Cary, Ariel Helfer We have examined the formation of clusters in kinetically agitated collections of rigid rings with angular gaps in them. Even for small gap angles, large clusters form readily and are sufficiently tangled so as to remain tangled under semi-static gravitational stresses without decomposing. We have measured the average largest cluster size as a function of gap angle, and witness behavior similar to that of a percolation phase transition. This was done for a variety of materials having different friction coefficients. The critical gap angle at which clusters disappear appears to be nearly independent of the friction coefficient, suggesting that cluster formation is dominated by geometry effects. [Preview Abstract] |
Wednesday, March 17, 2010 8:36AM - 8:48AM |
P12.00004: Constitutive relations in dense granular flows John Drozd, Colin Denniston We use simulations in a vertical chute configuration to investigate constitutive relations in dry granular flow. We study relations describing the local stresses, heat flow, and dissipation in different granular regions or phases and compare our results to both theory and experiments. Particularly we investigate a free-fall dilute granular gas region at the top of the chute, a granular fluid in the middle and a glassy region at the bottom. We show that while the pressure can be reasonably described by hard sphere gas models, transport coefficients such as viscosity and heat conductivity cannot. In contrast to a hard sphere gas, the viscosity and heat conductivity increase with decreasing temperature in the fluid and glassy phases. In the fluid region, we compare our simulation values for viscosity and heat conductivity with published theoretical expressions based on Enskog expansions. In the glassy region, we observe signs of a finite yield stress and examine relations involving an internal friction coefficient. We show that the static sand pile is a limit of our glassy state, and we also solve for the eigenvectors of the stress tensor independent of any particular model. [Preview Abstract] |
Wednesday, March 17, 2010 8:48AM - 9:00AM |
P12.00005: Properties of grains driven by an oscillating disk Kiri Nichol, Martin van Hecke A container of glass beads driven by a rotating disk exhibits properties of a liquid - low density objects float at the depth predicted by Archimedes' law and sinking objects experience a viscous drag force. However, when the beads are driven by oscillating the disk, a surprising state emerges which exhibits unliquid-like behaviour: a light object submerged in the grains remains stuck, as if in a solid. As the oscillation amplitude is increased, the liquid-like character of the system is restored, although some surprising effects are observed due to contraction and dilation that occurs when the disk reverses direction. [Preview Abstract] |
Wednesday, March 17, 2010 9:00AM - 9:12AM |
P12.00006: Ring Kinetic Theory for Granular Response Functions James Dufty The response functions for an isolated (cooling or thermostated) granular gas are described by kinetic theory [1]. The linear kinetic equation is obtained by a systematic expansion of the dimensionless BBGKY hierarchy scaled relative to the mean free time and mean free path [2]. At first order beyond Boltzmann the effects of ring (repeated) collisions and associated mode coupling are included. Qualitative differences from the Boltzmann approximation are described. \\[4pt] [1] ``Kinetic Theory of Response Functions for the Hard Sphere Granular Fluid,'' A. Baskaran, J. Dufty, and J. Brey, J. Stat. Mech. 12, p12002 (2007); ``Linear Response for Granular Fluids,'' J. Dufty, in Frontiers in Nonequilibrium Physics, Prog. of Theor. Phys. Supp., (to appear). \\[0pt] [2] ``Kinetic Theory and Hydrodynamics for a Low Density Granular Gas,'' J. Dufty in Challenges in Granular Physics, T. Halsey and A. Mehta, eds. (World Scientific, N. J. 2002). [Preview Abstract] |
Wednesday, March 17, 2010 9:12AM - 9:24AM |
P12.00007: Non-affinity of displacement fields in sheared granular systems Kinga Lorincz, Peter Schall The jamming transition, i.e. the transition in a granular system from rest to flow is a fundamental problem of great importance to the understanding of a wide class of disordered materials. Using the experimental method of laser sheet imaging we can accurately visualize individual particles in a sheared three-dimensional granular packing immersed in an index matching liquid. We study fluctuations in the displacements of the particles as a function of varying confining pressures and shear stresses. We characterize these fluctuations by investigating the non-affine regions in the displacement fields. [Preview Abstract] |
Wednesday, March 17, 2010 9:24AM - 9:36AM |
P12.00008: Sound Waves in a Homogeneously Driven Granular Fluid in Steady State Katharina Vollmayr-Lee, Annette Zippelius, Timo Aspelmeier We study the collective dynamics of a granular fluid of hard spheres, driven into a stationary non-equilibrium state by balancing the energy loss due to inelastic collisions with the energy input due to driving. The driving is chosen to conserve momentum, so that fluctuating hydrodynamics predicts the existence of sound modes. We present results of computer simulations which are based on an event driven algorithm. The dynamical structure factor $F(q,\omega)$ is determined for volume fractions 0.05, 0.1 and 0.2 and coefficients of normal restitution 0.8 and 0.9. We observe sound waves, determine their dispersion and compare our results with the predictions of generalized fluctuating hydrodynamics. [Preview Abstract] |
Wednesday, March 17, 2010 9:36AM - 9:48AM |
P12.00009: Flow fluctuations and the local flowrule of granular suspensions Elie Wandersman, Joshua Dijksman, Werner de Groot, Martin van Hecke We study particle fluctuations and the local flowrule in slowly driven sedimenting suspension flows. We employ a fully three-dimensional particle tracking method that allows us to track the spatial trajectories of all the particles across the system. This flow information is coupled to rheometric experiments, and applied to both Couette and a split-bottom geometry. We show that the non-affine part of the particle displacements evolves nonlinearly with the local strain-rate and further discuss our results in the context of recently proposed non-local rheology models for flowing disordered materials. [Preview Abstract] |
Wednesday, March 17, 2010 9:48AM - 10:00AM |
P12.00010: Packing structure of cyclically sheared dense granular spheres Andreea Panaitescu, Arshad Kudrolli We characterize the structure of densely packed frictional granular spheres cyclically sheared between parallel walls under constant pressure boundary conditions with a fluorescent refractive index matched liquid imaging technique. This technique allows us to measure the three dimensional particles position and obtain the Voronoi tessellation corresponding to the particles in the bulk. We calculate the radial distribution function, g(r) from the measured position and show that its significant features can be captured by the Percus-Yevick formula derived for frictionless random packed spheres for initial volume fraction $\Phi $ = 0.59{\$}. However, small but systematic deviations are observed because of the splitting of the second peak as $\Phi $ is increased by 3{\%}. The angular correlation of the particles as measured by the bond order metric, Q$_{6}$ shows disorder compared to a close packed structure, but similar to those shown by frictionless spheres. The distribution of the Voronoi free volume is described by a three-parameter gamma distribution postulated for random packing of spheres. Overall, these measure show significant similarity of the observed granular packing compared with random packing of frictionless spheres, but some systematic differences as well. [Preview Abstract] |
Wednesday, March 17, 2010 10:00AM - 10:12AM |
P12.00011: Networks of Broken Links in Granular Flows Mark Herrera, Shane McCarthy, Michelle Girvan, Wolfgang Losert Shear zones and reproducible flow fields are key features of granular flows. We experimentally study flows in a split bottom geometry by tracking the motion of all particles in three dimensions. In particular, we investigate how shear zones emerge from individual particle rearrangements, and how the rearrangements transition from reversible to irreversible with increasing strain. In order to analyze rearrangements at the level of particle motion, we define a broken links network, the set of particle pairs that have separated from each other and are no longer in contact. The emergence of a giant component occurs at the same characteristic strain at which a steady shear zone forms. We propose network theory as a new framework to characterize granular flows at the intermediate scale. [Preview Abstract] |
Wednesday, March 17, 2010 10:12AM - 10:24AM |
P12.00012: Experiments with 2D quasistatic and shaken arrays of permanent magnet N-mers ($N \geq 1$) Peter Koch, Mark Shattuck We extend methods used to study macroscopic grains (contact forces) to 2D ($x,y$) arrays of N-mers of cylindrical (L=D=3.18 mm) Nd-Fe-B magnets in a rectangular cell with glass plates $\Delta z \sim $3.3 mm apart and parallel to magnet faces. Aligned monomers repel with a measured $d^{-4}$ (dipole-dipole) force dependence, with $d$ the separation between cylinder axes. With fixed, aligned monomers separated by 6.35 mm along the cell walls, hundreds of aligned monomers can move in the cell subject to magnet-glass friction and gravity (either $\parallel $ or $\perp $ to $z$) but without contacting each other or the walls. Quasistatically moving one wall to decrease volume $V$ increases pressure $P$ on the magnetic particles and leads to ordering observed with annealing. Driving the array, e.g., by shaking one wall, can produce disorder; we study how this varies with driving strength at fixed $V$ or $P$. Replacing all non-wall monomers with similarly aligned tetramers (3 magnets magnetically bound to an inverted magnet) allows for more ordered states in quasistatic experiments; macroscopic, internal degrees of freedom into which energy can flow in driven experiments; and rearrangements (``chemical reactions") for strong driving. [Preview Abstract] |
Wednesday, March 17, 2010 10:24AM - 10:36AM |
P12.00013: Particle velocity distribution in a 3-dimensional vibration fluidized granular medium Hong-Qiang Wang, Klebert Feitosa, Narayanan Menon We report an experimental study of particle kinematics in a 3-dimensional system of inelastic spheres fluidized by intense vibration. The motion of particles in the interior of the medium is tracked by high speed video imaging, yielding a spatially- resolved measurement of the velocity distribution. The distribution is wider than a Gaussian and broadens continuously with increasing volume fraction. The deviations from a Gaussian distribution for this boundary-driven system are different in sign and larger in magnitude than predictions for homogeneously driven systems. We also find correlations between velocity components which grow with increasing volume fraction. [Preview Abstract] |
Wednesday, March 17, 2010 10:36AM - 10:48AM |
P12.00014: The Role of Extensional Viscosity in Sedimentation Theodore A. Brzinski, Paulo E. Arratia, Douglas J. Durian When two particles in a viscous fluid approach contact the motion of the interstitial fluid is dominated by extensional flow. We demonstrate how the details of these flows influence the process of sedimentation. We are able to highlight the effects of extensional flows on particle motion by comparing granular dispersions in which the continuous phases have the same shear viscosities, but drastically different extensional viscosities. We enhance the extensional viscosity by adding a flexible, high molecular weight polymer. In the case of a system without polymer we observe settling rates in accordance with a typical Stokes' model until all grains have settled into a random close-packed arrangement. In the polymeric fluid we observe initial behavior not unlike that observed in the Newtonian case, however the dispersions exhibit a secondary prolonged sedimentation process before finally reaching the final close- packed state. The dependence of this secondary settling process on grainsize and initial packing fraction suggests that an ensemble of dispersed grains acts primarily to enhance the impact of interstitial flows on the system's dynamics. [Preview Abstract] |
Wednesday, March 17, 2010 10:48AM - 11:00AM |
P12.00015: Sedimentation and Pressure Driven Flow in Fractures Tak Shing Lo, Joel Koplik Suspended particles are commonly found in reservoir fluids, which alter the rheology of the flowing liquids and may obstruct transport by narrowing flow channels due to gravitational sedimentation. An understanding of the transport and deposition dynamics of particulate suspensions is, therefore, important to many chemical, petroleum, environmental and geological processes. Realistic geological fractures usually have irregular rough surfaces with self-affine structures. We study the combined effects of sedimentation and transport of particles suspended in a Newtonian fluid in a pressure-driven flow in self-affine channels by using the lattice Boltzmann method, which is especially relevant to clogging phenomena where sediments may block continuous fluid flows in channels. The lattice Boltzmann method is flexible and particularly suitable for handling irregular geometry. We perform a systematic study covering a broad range in Reynolds and buoyancy numbers, and in particle concentrations. In particular, the transitions between the ``jammed'' and the ``flow'' states in fracture channels are investigated. [Preview Abstract] |
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