Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D6: Granular Flows: Jamming and Cooling |
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Chair: Matthieu Wyart, NYU Room: 105 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D6.00001: Unified Theory of Inertial Granular Flows and Non-Brownian Suspensions matthieu wyart, eric degiuli, edan lerner, gustavo during Rheological properties of dense flows of hard particles are singular as one approaches the jamming threshold where flow ceases, both for aerial granular flows dominated by inertia, and for over-damped suspensions. Concomitantly, the lengthscale characterizing velocity correlations appears to diverge at jamming. Here we introduce a theoretical framework that proposes a tentative, but potentially complete scaling description of stationary flows. Our analysis, which focuses on frictionless particles, applies \textbraceleft $\backslash $it both\textbraceright to suspensions and inertial flows of hard particles. We compare our predictions with the empirical literature, as well as with novel numerical data. Overall we find a very good agreement between theory and observations, except for frictional inertial flows whose scaling properties clearly differ from frictionless systems. For over-damped flows, more observations are needed to decide if friction is a relevant perturbation or not. Our analysis makes several new predictions on microscopic dynamical quantities that should be accessible experimentally. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D6.00002: Effect of friction on shear jamming Dong Wang, Jonathan Bares, Joshua Dijksman, Jie Ren, Hu Zheng, Robert Behringer Shear jamming of granular materials was first found for systems of frictional disks, with a static friction coefficient $\mu \approx 0.6$ (Bi et al. Nature (2011)). Jamming by shear is obtained by starting from a zero-stress state with a packing fraction $\phi$ 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. Whether shear jamming occurs for frictionless particles is under debate. The issue we address experimentally is how changing friction affects shear jamming. By applying a homogeneous simple shear, we study the effect of friction by using photoelastic disks either wrapped with Teflon to reduce friction or with fine teeth on the edge to increase friction. Shear jamming is still observed; however, the difference $\phi_J-\phi_S$ is smaller with lower friction. We also observe larger fluctuations due to initial configurations both at the lowest and the highest friction systems studied. Ongoing work is to characterize response from different friction systems under shear with information at local scale. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D6.00003: ABSTRACT WITHDRAWN |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D6.00004: Relaxation of densely packed gel particles under cyclic shearing J.C. Tsai, M.R. Chou, P.C. Huang, H.T. Fei, J.R. Huang We study experimentally the rheological response of fluid-immersed hydrogel particles. The particles are centimeter-sized and are driven by a roughened cone-shaped upper boundary, which imposes a cyclic shearing with a substantial stall period inserted between each reversal of its motion. The stall period reveals a characteristic timescale of relaxation belonging to these soft materials, in contrast to the build-up of stress that reflects a characteristic strain accumulated since each re-start of the shearing. We provide a coherent explanation on how the relaxation and the residual stress are related to observed steady-state rheology at different strain rates, and the use of a previously developed tomographical imaging technique allows us to look into the particle displacements during the relaxation. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D6.00005: Yielding in a strongly aggregated colloidal gel: 2D simulations and theory Saikat Roy, Mahesh Tirumkudulu We investigated the micro-structural details and the mechanical response under uniaxial compression of the strongly aggregating gel starting from low to high packing fraction.The numerical simulations account for short-range inter-particle attractions, normal and tangential deformation at particle contacts,sliding and rolling friction, and preparation history. It is observed that in the absence of rolling resistance(RR),the average coordination number varies only slightly with compaction whereas it is significant in the presence of RR. The particle contact distribution is isotropic throughout the consolidation process. In both cases, the yield strain is constant with the volume fraction. The modulus values are very similar at different attraction, and with and without RR implying that the elastic modulus does not scale with attraction.The modulus was found to be a weak function of the preparation history. The increase in yield stress with volume fraction is a consequence of the increased elastic modulus of the network. However, the yield stress scales similarly both with and without RR. The power law exponent of 5.4 is in good agreement with previous simulation results. A micromechanical theory is also proposed to describe the stress versus strain relation for the gelled network. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D6.00006: Experiments on Memory in a Sheared Soft Solid Nathan Keim, Devin Wieker, Luke Horowitz We consider how a soft 2D jammed material may form memories of past deformation. Our experiments cyclically shear a material made of repulsive particles at an oil-water interface, observing the motion of many particles. Under repeated shearing, the system can evolve toward a ``limit cycle'' in which the same particle rearrangements recur on each cycle of shear; the set of rearrangements is specific to the strain amplitude. We discuss how the material’s history-dependence may be viewed as a memory of the strain amplitude, and we report on progress in describing this behavior, including whether memories of multiple strains may coexist. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D6.00007: Controlling the shear profile of highly strained granular materials Jonathan Bares, Bob Behringer Bi et al. (Nature 2011) have shown that, if sheared, a granular material can jam even if its packing fraction ($\phi$) is lower than the critical isotropic jamming point $\phi_J$. They have introduced a new critical packing fraction value $\phi_S$ such that for $\phi_S$<$\phi$<$\phi_J$ the system jams if sheared. Nevertheless, the value of $\phi_S$ as a function of the shear profile or the strain necessary to observe jamming remain poorly understood because of the experimental complexity to access high strain without the formation of shear bands. We present a novel 2D periodic shear apparatus made of 21 independent, aligned and mirrored glass rings. Each of ring can be moved independently which permits us to impose any desired shear profile. The circular geometry allows access to any strain value. The forces between grains are measured using reflective photoelasticity. This talk will present this novel apparatus and discuss the effect of the shear profile and shear amplitude on the jamming transition. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D6.00008: Self organization and jamming in magnetic photoelastic particles Meredith Cox, Jonathan Bares, Dong Wang, Robert Behringer Many experimental studies of simple particles in granular systems have been conducted, but the behavior of complex particles in such systems has not been addressed. There has been a growing interest in functionalized microparticles, and the study of these complex particles may reveal interesting analogues between micro- and macroparticles. We perform experiments to investigate magnetic particles in a 2D granular material close to the jamming transition. We incrementally compress photoelastic particles containing magnets and image the interparticle forces in each compression using a photoelastic technique. To track the orientation of individual particles, we draw UV-visible bars on each particle and image each compression of the system under ultraviolet light. We repeat the experimental procedure using varying ratios of magnetic to nonmagnetic particles from 0\% magnetic to 100\% magnetic. By using custom software to resolve particle deformations, we extract particle contact forces and demonstrate that as the concentration of nonmagnetic particles grows, the rate of increase of pressure with strain also grows. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D6.00009: Granular flow and clog in silo with moving outlet Kiwing To, Hsiang-Ting Tai When grains flow out of a silo, the flow rate increases with the outlet size $d$. If $d$ is too small, an arch may form and blocks the flow at the outlet. To recover from clogging, the arch have to be destroyed. Oscillating the outlet mechanically is one simple way of destroying the arch. In this paper, we report the effect of oscillating the outlet on the processes of clogging as well as recovery from clogging in two-dimensional silo equipped with movable outlet. We measure the flow rate $Q(d)$ and find that, in the presence of outlet oscillation, $Q(d)$ may remain finite even when $d$ is only slightly larger than the grain diameter. Transition from continuous flow to intermittent flow occurs by decreasing $d$ or by reducing the oscillation speed. In addition, at small $d$ when the flow is intermittent, the flow time (duration of flow before clogged) follows Poisson distribution whereas the recovery time (duration of clog before flow recovery) follows power law distribution. [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D6.00010: Shear-induced dynamical phase-transitions in a granular system Jie Zhang, Yingqiao Wang, Hongyang Tang In this study, we investigate the granular materials in a 2D Couette cell under shear using photo-elastic disks. For initial packing fractions $\phi$ smaller than $\phi_c = 82${\%}, an initially stress-free state can be first shear jammed and then gradually relaxes to a steady state with strong stress fluctuations. Such a steady state will then make a stochastic transition to an unjammed state under the continuous shear. For packing fractions $\phi$ larger than $\phi_c$, we observe no such transitions. The characteristic strain of the transition diverges as a function of \textbar $\phi-\phi_c$\textbar $^{-2}$ which resembles a second-order dynamical phase transition. We interpret some portion of the results of such phase transitions using a mean-field model that was originally proposed to explain the discontinuous shear thickening and the shear jamming of the frictional granular materials. We are currently still investigating such an intriguing phenomenon in order to understand the detailed dynamics of the transition. [Preview Abstract] |
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