Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L13: Granular Flows III: Jamming, Cooling and Force Transmission 
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Chair: Shankar Subramaniam, Iowa State University Room: 301 
Monday, November 25, 2013 3:35PM  3:48PM 
L13.00001: Relaxation Time Scales for Dense Granular Systems Shaolin Mao In study of shock waves, it is a common practice to assume that the thickness of a shock wave in thin, and that the equation of state of the material is applicable before and after the shock. While these assumptions are correct on gases with simple molecules. These assumptions need to be reexamined for granular systems, especially for dense granular systems, because the time scale to reestablish a steady or equilibrium state after an external perturbation could be comparable to the time scale of the physical problem itself. We study the physical time scales of particulate systems by using discrete element method (DEM). First, a simple shear force is imposed to a system with periodic perturbation of energy to mimic the temperature field. The calculation of contact stress and the velocity fluctuation shows the stress relaxation mechanism and the process of the system recovery to its original state after an external perturbation. In this talk, we also discuss the relationship between the segregation of a system and the stress relaxation of the symmetric and asymmetric components. [Preview Abstract] 
Monday, November 25, 2013 3:48PM  4:01PM 
L13.00002: Earthquakes in the Laboratory: Continuumgranular coupling Drew Geller, Sergiy Gerashchenko, Scott Backhaus, Robert Ecke Earthquakes in nature feature large tectonic plate motion at large scales of 10100 km and local properties of the earth on the scale of the rupture width, of the order of meters. Fault gouge generally fills the gap between the large slipping plates and may play an important role in the nature and dynamics of earthquake events. We have constructed a laboratory scale experiment that represents a similitude scale model of this general earthquake description. Two photoelastic plates (50 cm $\times$ 25 cm $\times$ 1 cm) confine approximately 3000 bidisperse nylon rods (diameters 0.12 and 0.16 cm, height 1 cm) in a gap of approximately 1 cm. The plates are held rigidly along their outer edges parallel to the gouge with one held fixed while the other edge is driven at constant speed over a range of about 5 cm. The local stresses exerted on the plates are measured using their photoelastic response, the local relative motions of the plates, i.e., the local strains, are determined by the relative motion of small ball bearings attached to the top surface, and the configurations of the nylon rods are investigated using particle tracking. We report statistical analyses of data obtained from these experimental probes and compare with different avalanche models. [Preview Abstract] 
Monday, November 25, 2013 4:01PM  4:14PM 
L13.00003: Statics and Dynamics of Force Networks in Dense Particulate Systems Lou Kondic, Miroslav Kramar, Arnaud Goullet, Konstantin Mischaikow The talk will focus on the properties of force networks found in discrete element simulations of isotropically compressed particulate systems. We will discuss how these properties evolve as the system goes through the jamming transition, with particular focus on the influence of interparticle friction and polydispersity. Then, we will discuss new measures that can be used to quantify the temporal evolution of force networks, and discuss this evolution as the systems go through jamming. The implemented computational technique is based on persistence analysis that allows to consider global properties of force networks. This technique, that has been only very recently applied to particulate matter,\footnote{Phys. Rev. E {\bf 87}, 0422207 (2013)} allows to extract significant new information, going much beyond separation into ``strong'' and ``weak'' force networks. The proposed approach describes the considered networks in a precise and tractable manner, allowing to identify novel features which could be difficult or impossible to describe using other approaches. [Preview Abstract] 
Monday, November 25, 2013 4:14PM  4:27PM 
L13.00004: Shear Jamming for Slippery Granular Particles Dong Wang, Joshua Dijksman, Jie Ren, Robert Behringer Shear Jamming of granular materials was first found for systems of frictional disks, with a static friction coefficients $\mu_s \simeq 0.6$. Jamming by shear is obtained by starting from a zerostress state with a packing fraction $\phi_S \leq \phi \leq \phi_J$ between $\phi_J$ (isotropic jamming) and a lowest $\phi_S$ for shear jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of ``force chains,'' which are stabilized and/or enhanced by the presence of friction. The issue that we address experimentally is how reducing friction affects shear jamming. We use either Teflon disks, or disks that have been wrapped with Teflon, lowering the friction coefficient substantially from previous experiments. The Teflon disks were placed in a 2D shear apparatus (Ren et al., PRL 110, 018302 (2013)), with two rows of uncoated photoelastic particles at the periphery. The interior Teflon particles formed the ``system,'' and the outer ring of photoelastic particles provided force data. For Teflon disks, shear jamming was also observed, but the difference $\phi_J  \phi_S$ was smaller than for higher friction particles. Ongoing work is focused on studies using the Teflonwrapped particles, which completely fill the apparatus. [Preview Abstract] 
Monday, November 25, 2013 4:27PM  4:40PM 
L13.00005: Microscopic Order Parameter for Shear Anisotropy for Systems near Shear Jamming Jie Ren, Joshua Dijksman, Robert Behringer Sheared granular systems at packing fractions between $\phi_s \leq \phi \leq \phi_J$ can exist in states with zero and nonzero stress. A system, prepared in a stressfree states in this density range, upon being sheared exhibits first fragile, then shear jammed states, both having high stress and fabric anisotropy. The onset of shear jammed states resembles an orderdisorder transition. In recent work, we showed that the order appears in a force space (Bi et al. to appear, PRL). Here, we identify an order parameter associated with individual particles, making it possible to construct correlations in physical space. We identify local (particlescale) order with $\Gamma$, the deviatoric part of the forcemoment tensor. This is a real symmetric, traceless matrix characterized by two coefficients, $a$ and $b$, such that $\Gamma = aU_1 $+$ b U_2$, and where $U_1$ is diagonal with elements $\pm 1$, and $U_2$ has 0's on the diagonal, and 1 for the offdiagonal elements. The $U_i$'s are orthogonal under an appropriate scalar product. Then, ($a, b$) provides a vector particlescale order parameter. $\Gamma$ is additive over all particles, and is analogous to the magnetization in a spin system. Also, particles with orthogonal shear stresses now correspond to antiparallel vectors. We use this representation to investigate both the collective order of the system and also correlations. This talk presents analysis of experimental data that explore the properties of this new order parameter. [Preview Abstract] 
Monday, November 25, 2013 4:40PM  4:53PM 
L13.00006: Imaging Forces on Stressed Spheres Nicolas Brodu, Joshua Dijksman, Hu Zheng, Robert Behringer We study the quasistatic deformation of three dimensional sphere packings over a range of compressive stresses. We perform experiments on slightly polydisperse, nearly frictionless soft hydrogel spheres in a modified triaxial shear apparatus. We measure boundary stresses and access microstructural information by 3D imaging the entire packing. By resolving particle deformations via custom written image analysis software, we extract particle contacts and forces. We address whether sheared frictionless spheres display dilatancy pressure, we measure the nonlinear force response of a disordered packing under compression and explore the plastic rearrangements inside cyclically sheared and compressed packings. [Preview Abstract] 
Monday, November 25, 2013 4:53PM  5:06PM 
L13.00007: Shearrate Dependent Regime Transition in Homogeneously sheared systems of Frictionless Cohesive Granules Eric Murphy, Sriram Sundararajan, Shankar Subramaniam We study regime transition behavior in systems of cohesive micronsized granular particles in the absence of friction via soft sphere discrete element (DEM) simulations. Previous studies\footnote{Aarons, L. Sundaresan, S. Powder Tech. 169 (2006) 1021.}$^,$\footnote{Rognon, P.G. et al. J. Fluid Mech. 596 (2008) 2147.} have identified a shearrate dependent regime transition, from Bagnold to quasistatic scaling, occurring below jamming volume fractions. The transition of interest is welldescribed by theories for nonequilibrium phase transitions. Most notably, this regime transition is accompanied by the emergence of a diverging mesoscopic lengthscale based on the formation of local contact networks indicative of clustering. We identify the relevant nondimensional quantities, e.g. ratio of cohesive potential to granular kinetic temperature, which mark the location of the critical transition and show that the fabric tensor may serve as a promising orderparameter. The study of such simple systems has broad implications for the constitutive modeling of other athermal systems, and illuminates the growing need for the modeling of nonlocal effects in flows of macroscopic particles. [Preview Abstract] 

L13.00008: ABSTRACT WITHDRAWN 
Monday, November 25, 2013 5:19PM  5:32PM 
L13.00009: Mechanics of sequential jamming and unjamming phenomena in a multiexit orifice silo Amit Kunte, Ashish Orpe, Pankaj Doshi We have investigated the flow of a two dimensional granular assembly draining through a flat bottomed silo having multiple exit orifices using DEM simulations. The width of the central orifice of the silo is fixed at $3.5 d$ which is small enough to cause jamming (or noflow) through the orifice. Here $d$ is the mean particle diameter. The width of the other nearby orifices is kept much more than $3.5 d$, thus, ensuring continuous flow of particles through them. Interestingly, this continuous flow of particles in the vicinity interacts with the assembly of jammed particles above the central orifice causing rearrangements and ultimately unjamming the assembly leading to a smooth flow. During the entire drainage of the silo, the central orifice undergoes this sequence of jammingunjamming event several times, the frequency of which depends on its proximity to the nearby orifices. We focus primarily on understanding this jammingunjamming transition by investigating the contact force network and the normal force distributions. Our preliminary results show that the tails of the force distributions in the jammed region decay slower than those for the flowing regions. This qualitative behaviour is found to be independent of any prior rearrangement history. [Preview Abstract] 
Monday, November 25, 2013 5:32PM  5:45PM 
L13.00010: Shear jamming in granular materials Jie Zhang For frictionless particles with purely repulsive interactions, there is a critical packing fraction $\phi_J$ below which no jammed states exist. Recent experiments have shown that applying shear to a stressfree initial state can generate states which are either fragile or shear jammed depending on the way the forcenetwork is percolated (Bi et al Nature 2011). The nature of the jamming transition however is obscured because the existence of friction between the system and the third dimension. A new apparatus at SJTU has been designed to completely eliminate this friction by letting the particles float on the surface of a shallow water layer, which allows a study of the more detailed nature of the shearjammed states and the transition from an unjammed state to a shearjammed state. In this study, we also use highprecision force sensors to monitor the dynamical changes near the jamming transition. We further combine numerical simulations with the experiments to diagnose the nature of this jamming transition and its possible dependence on certain particle properties. [Preview Abstract] 
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