Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session R24: Granular Flows: Jamming and Cooling |
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Chair: Paulo Arratia, University of Pennsylvania Room: 2003 |
Tuesday, November 25, 2014 1:05PM - 1:18PM |
R24.00001: Unjamming of a granular sediment with high-intensity ultrasound Pierre Lidon, S\'ebastien Manneville, Nicolas Taberlet Despite an increasing number of experimental, numerical and theoretical studies during the last decades, a comprehensive understanding of the jamming transition in disordered materials is still lacking. Among the wide variety of jammed materials, granular media are model athermal systems and have emerged as ideal candidates to study jamming, although solid friction between grains complexifies the jamming phase diagram. In this work, we study the unjamming of a granular sediment immersed in water. While fluidization is generally induced by shaking the walls of the container or by shearing the granular material, here we use high-intensity focused ultrasound to apply a remote force on the grains through nonlinear acoustic effects. We first study the fluidization dynamics by performing particle image velocimetry from high speed movies. Then we show that the unjamming transition displays hysteresis when the granular sediment is submitted to cycles of pulses with varying amplitude. We moreover report intermittent fluidization when series of pulses at constant amplitude are sent on the pile. Finally we performed molecular dynamics simulations to account for the observed phenomena. [Preview Abstract] |
Tuesday, November 25, 2014 1:18PM - 1:31PM |
R24.00002: Dynamic shear jamming in granular suspensions Ivo Peters, Sayantan Majumdar, Heinrich Jaeger Jamming by shear allows a frictional granular packing to transition from an unjammed state into a jammed state while keeping the system volume and average packing fraction constant. Shear jamming of dry granular media can occur quasi-statically, but boundaries are crucial to confine the material. We perform experiments in aqueous starch suspension where we apply shear using a rheometer with a large volume (400 ml) cylindrical Couette cell. In our suspensions the packing fraction is sufficiently low that quasi-static deformation does not induce a shear jammed state. Applying a shock-like deformation however, will turn the suspension into a jammed solid. A fully jammed state is reached within tens of microseconds, and can be sustained for at least several seconds. High speed imaging of the initial process reveals a jamming front propagating radially outward through the suspension, while the suspension near the outer boundary remains quiescent. This indicates that granular suspensions can be shear jammed without the need of confining solid boundaries. Instead, confinement is most likely provided by the dynamics in the front region. [Preview Abstract] |
Tuesday, November 25, 2014 1:31PM - 1:44PM |
R24.00003: Shear Jamming in Particulate Media Thibault Bertrand, Corey S. O'Hern, Mark D. Shattuck More than two decades ago, Liu and Nagel introduced the concept of jamming and proposed a phase diagram for the jamming transition as a function of applied shear stress, density, and temperature. Since then, numerous computational as well as experimental studies have underscored the usefulness of this concept in systems ranging from colloidal glasses to packings of granular materials. Recently, Bi et al. presented experimental results that suggested that jamming via isotropic compression can lead to different packings than those generated via shear. To investigate fundamental aspects of shear-induced jamming, we performed numerical simulations and theoretical analyses of frictionless and frictional particulate media undergoing simple shear. We are able to predict the form of the boundaries in the shear-jamming phase diagram and determine how they change with system size. We also study the relationship between the shear-jamming phase diagram and the fluctuations in the stress versus strain for packings undergoing continuous shear in the context of geometrical families of packings. [Preview Abstract] |
Tuesday, November 25, 2014 1:44PM - 1:57PM |
R24.00004: Effect of friction on shear jamming Dong Wang, Jie Ren, Joshua Dijksman, 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 zero-stress 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 photoelastic disks that have been wrapped with Teflon, lowering the friction coefficient substantially from previous experiments. The Teflon-wrapped disks were placed in a well-studied 2D shear apparatus (Ren et al., PRL, {\bf 110}, 018302 (2013)), which provides uniform simple shear without generating shear bands. Shear jamming is still observed, but the difference $\phi_J - \phi_S$ is smaller than for higher friction particles. With Teflon-wrapped disks, we observe larger anisotropies compared to the previous experiment with higher friction particles at the same packing fraction, which indicates force chains tending to be straight in the low friction system. [Preview Abstract] |
Tuesday, November 25, 2014 1:57PM - 2:10PM |
R24.00005: Large Amplitude Oscillatory Shear near Jamming Brian Tighe, Simon Dagois-Bohy, Ellak Somfai, Martin van Hecke Jammed solids such as foams and emulsions can be driven with oscillatory shear at finite strain amplitude and frequency. On a macro scale, this induces nonlinearities such as strain softening and shear thinning. On the micro scale one observes the onset of irreversibility, caging, and long-time diffusion. Using simulations of soft viscous spheres, we systematically vary the distance to the jamming transition. We correlate crossovers in the microscopic and macroscopic response, and construct scaling arguments to explain their relationships. [Preview Abstract] |
Tuesday, November 25, 2014 2:10PM - 2:23PM |
R24.00006: Dynamically Jammed Fronts under impact in shear thickening suspensions Shomeek Mukhopdhyay, Benjamin Allen, Lucia Korpas, Eric Brown Shear thickening fluids such as cornstarch and water show remarkable impact response allowing, for example, a person to run on the surface but sinking at lower velocities. We perform constant velocity impact experiments and imaging in shear thickening fluids at velocities lower than 500 mm/s and suspension heights of a few cm. In this regime where inertial effects are insignificant, we discover the existence of two dynamically jammed fronts which reach the opposite boundary to support large stresses like a solid. These stresses are large enough to support the weight of a running person. We also find a shear thickening transition under impact which is due to collision of the fronts with the boundary. The jammed front show similarities to granular materials like localization of stress. There is a critical velocity required to generate these impact activated fronts. [Preview Abstract] |
Tuesday, November 25, 2014 2:23PM - 2:36PM |
R24.00007: Role of disorder in cyclically-sheared 2D solids Nathan Keim, Paulo Arratia We consider how materials with different degrees of disorder respond to finite deformations, through both shear rheometry, and simultaneous tracking of many particles. Our experiments use mutually repulsive particles adsorbed at an oil-water interface, that with bidisperse particle sizes form a more amorphous packing, and with monodisperse sizes form a more polycrystalline packing. Under cyclic shear, we use the reversible plastic regime --- in which rearrangements at a stable set of locations control deformation --- to probe the origins of plasticity and yielding in each material. We find that the polycrystalline material, with fewer disordered regions, hosts rearrangements in fewer locations. However, the responses of the two materials are otherwise strikingly similar, including the sizes of the rearranging regions. This suggests that maximally-disordered materials provide the starting point for understanding finite-amplitude deformation of a broad range of soft solids. [Preview Abstract] |
Tuesday, November 25, 2014 2:36PM - 2:49PM |
R24.00008: A theory for the compression of two dimensional strongly aggregated colloidal packings Mahesh Tirumkudulu, Saikat Roy The consolidation of suspended particulate matter under external forces such as pressure or gravity is of widespread interest. We derive a constitutive relation to describe the deformation of a two-dimensional strongly aggregated colloidal system by incorporating the inter-particle colloidal forces and contact dynamics. The theory accounts for the plastic events that occur in the form of rolling/sliding during the deformation along with elastic deformation. The theory predicts a yield stress that is a function of area fraction of the colloidal packing, the coordination number, the inter-particle potential, coefficient of friction and the normal and tangential stiffness coefficients. The predicted yield stress scales linearly with area fraction for low area fractions, and diverges at random close packing. Increasing the normal stiffness coefficient or the friction coefficient increases the yield stress. For stresses greater than the yield stress, both elastic and plastic deformations contribute to the overall stress. [Preview Abstract] |
Tuesday, November 25, 2014 2:49PM - 3:02PM |
R24.00009: Rheology of densely packed soft particles Jung-Ren Huang, M.-R. Chou, P.-C. Huang, C.-Y. Tao, Jih-Chiang Tsai We measure the rheological response of densely packed hydrogel particles in a density-matched solution over different volume fractions. The particles are sandwiched between two roughened cone-shaped surfaces. The top surface, driven by a motor, provides an oscillatory shear of variable strain amplitude. The irreversibility and the thixotropic loop observed in the stress-strain and stress-strain rate curves illustrate the transition from a nearly elastic response to a plastic flow. At large strain amplitudes and low oscillation frequencies, the system approaches the steady state and the intercept of stress extrapolated to zero strain rate becomes zero below a well-defined volume fraction. Internal imaging of immersed tracers provides clues behind these transitions. [Preview Abstract] |
Tuesday, November 25, 2014 3:02PM - 3:15PM |
R24.00010: Spatiotemporal Chaotic unjamming and jamming in granular avalanches Ziwei Wang, Jie Zhang The unjamming transition, is of crucial importance in studying natural disasters such as snow avalanches, landslides and earthquakes. Here we provides a new perspective to understand such transitions from the dynamical systems theory and show that in a novel toy-model system -- a rotating drum partially filled with bidisperse disks to create avalanches, the dynamical variable -- the first Lyapunov vector can be well defined and measured. We observed a strong spatial correlation between the modulus of the first Lyapunov vector and velocity field, and linear correlations between the global Lyapunov vector, its growth rate and the total velocity temporally. The anatomy of the velocity of each particle and the number of moving particles leads to a mean-field model, where both the spatial and temporal correlations between such quantities can be understood. What's more, we have investigated the fluctuations of particle motions, i.e. the non-affine motions, during the avalanche process, revealing an intrinsic disorder characteristic of the avalanche at the particle levels and the temporal correlations among geometrical and mechanical quantities at the macroscopic levels. [Preview Abstract] |
Tuesday, November 25, 2014 3:15PM - 3:28PM |
R24.00011: Attraction and repulsion between two static intruders immersed in a granular flow Ricardo Arturo L\'opez-de-la-Cruz, Gabriel Arturo Caballero-Robledo The interaction between a group of intruders immersed in a granular medium has gained attention because of the presence of flow mediated repulsive and attractive forces in projectile impact experiments [F. Pacheco-V\'{a}zquez and J. C. Ruiz-Su\'{a}rez, Nat. Commun. \textbf{1}, 123 (2010)]. The origin of the repulsive interaction has been well explained by means of the jamming of the grains moving between them, but the attractive behavior is not well understood yet. One possible explanation is that these forces originate by a Bernoulli like effect, i.e. because of a pressure difference in the regions between and outside the intruders due to a difference in flow velocity. On the other side, a Casimir like effect has also been proposed, claiming that the pressure difference originates in the fluctuations of the granular medium confined by the intruders. In this work, we present a series of Discrete Element Particle simulations aiming to confirm which phenomenon is the responsible of the interactions by fixing two intruders at different separations within a granular flow. [Preview Abstract] |
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