Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session A2: Granular Flows I |
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Chair: Lou Kondic, New Jersey Institute of Technology Room: 302 |
Sunday, November 20, 2011 8:00AM - 8:13AM |
A2.00001: Predictive Capabilities of a Relaxation Model for Parcel-Based Granular Flow Simulations Stefan Radl, Sankaran Sundaresan Parcel-based methods have a great potential to reduce the computational cost of particle simulations for dense flows. Here we investigate a relaxation model, similar to that of Bhatnagar-Gross-Krook (BGK), when applied to such a parcel-based simulation method. Specifically, we have chosen the simulation methodology initially proposed by Patankar and Joseph [1], and combined it with the relaxation model published by O'Rourke and Snider [2]. We show that a relaxation model is key to correctly predicting macroscopic flow features, e.g., the scattering pattern of a granular jet impinging on a flat surface, studied experimentally by Cheng et al. [3]. Simple shear flow simulations reveal that calculation of the locally-averaged velocity is a critical ingredient to correctly predict streaming and collisional stresses. \\[4pt] [1] N.A. Patankar, and D.D. Joseph, Int. J. Multiphase Flow 27, 1659 (2001). \\[0pt] [2] P.J. O'Rourke, and D.M. Snider, Chem. Eng. Sci. 65, 6014 (2010). \\[0pt] [3] X. Cheng et al., Phys. Rev. Lett. 99, 188001 (2007). [Preview Abstract] |
Sunday, November 20, 2011 8:13AM - 8:26AM |
A2.00002: Three dimensional imaging of soft sphere packings under shear Robert Behringer, Joshua Dijksman, Eric Sia The (microscopic) flow of three dimensional disordered athermal granular packings remains poorly understood. However, experimentally studying flow and deformations in a three dimensional packing of grains is challenging due to the opacity of such packings. Our goal is to study triaxial shear of granular materials, using refractive index matched scanning. We will present results on a study of the deformation of a three dimensional soft sphere packing under quasi static compression. The spheres are made from hydrogel and virtually frictionless, similar to the study by by Mukhopadhyay et. al. (2011). We track particles and image contact deformations, and look at the effect of cyclic shear flow. [Preview Abstract] |
Sunday, November 20, 2011 8:26AM - 8:39AM |
A2.00003: Emergence of Order in Sheared Systems of Elliptical Particles Somayeh Farhadi, Robert P. Behringer We have studied the emergence of order in shear-jammed systems composed of quasi-2D elliptical particles, using both biaxial and Couette shear. The particles are photoelastic ellipses with aspect ratio 2. Using photoelastic particles enables us to determine grain-scale forces, and hence the microscopic force structure of the system. We obtain forces by solving the inverse photoelastic problem for ellipses subject to boundary point forces, similarly to the approach that we have developed for circular particles. We will present data for local packing fraction, orientation and force. Using configurational and force data shows that local smectic order plays a crucial role in jamming of elliptical particles. [Preview Abstract] |
Sunday, November 20, 2011 8:39AM - 8:52AM |
A2.00004: Cyclic Simple Shear in a Two-Dimensional Granular System Jie Ren, Joshua Dijksman, Robert Behringer We study the irreversibility transition observed by Pine et al (2005) in a 2D dry granular system, for which our novel experimental apparatus can create quasi-static, quasi-uniform simple shear. We use bi-disperse, photo-elastic disks and expose them to a large number of small amplitude shear cycles. We track the particles dynamics over time and evaluate their translational and rotational motion, as well as the inter-particle forces. We have found that both translational and rotational diffusivity increase rapidly when the system's particle density exceeds a certain threshold. This is an indication of the existence of an irreversibility transition. Interestingly, we have found this density threshold to be dependent on the amplitude of cyclic shear, but always smaller than the density for the isotropic jamming transition. To further understand this irreversibility transition, we analyze the system's structural and force evolution. [Preview Abstract] |
Sunday, November 20, 2011 8:52AM - 9:05AM |
A2.00005: High-velocity drag friction in dense granular media Yuka Takehara, Ko Okumura We study drag force acting on an obstacle in granular media, focusing on a high-velocity region where only a few direct studies are available. The granular media are two-dimensional and consist of small-sphere particles. A larger-disk obstacle moves in the medium at different constant speeds. The drag force is found to be proportional to the square of the velocity. This clear experimental relation is convincingly explained by a simple and original theory. A crucial assumption of this theory is supported by image analysis for the size of the cluster of grains around the disk. As a result, we conclude that the friction we observed here is physically different from a hydrodynamic inertial friction, which has been discussed in dilute granular flows and in impact experiments. Furthermore we demonstrate how the drag force depends on packing fraction to discuss the possibility of a dynamical jamming transition in our drag experiment.\\[4pt] [1] Y.Takehara, S. Fujimoto and K. Okumura, High-velocity drag friction in dense granular media, \textit{EPL}, \textbf {92} (2010) 44003 [Preview Abstract] |
Sunday, November 20, 2011 9:05AM - 9:18AM |
A2.00006: Strange eigenmodes of chaotic granular flow in a tumbler Ivan C. Christov, Julio M. Ottino, Richard M. Lueptow Through a combined computational--experimental study of monodisperse granular flow in a slowly-rotating quasi-two-dimensional container we show the presence of naturally-persistent mixing patterns, i.e., ``strange'' eigenmodes of the advection- diffusion operator governing the mixing process in the Eulerian frame. A comparative analysis of the structure of eigenmodes and the corresponding Poincar\'e section and finite-time Lyapunov exponent field of the flow highlights the relationship between the Eulerian and Lagrangian descriptions of mixing. In addition, we show how the mapping method for scalar transport can be modified to include diffusive effects, which are more significant in a granular flow (in laboratory size equipment) than in a similar fluid flow. This allow us to examine (for the first time in a granular flow) the change in shape, lifespan, and eventual decay of eigenmodes due to diffusive effects at larger numbers of revolutions. Finally, it is shown that segregation patterns in bidisperse mixtures correspond to permanently-excited eigenmodes. [Preview Abstract] |
Sunday, November 20, 2011 9:18AM - 9:31AM |
A2.00007: Pattern formation and pinning-depinning transition in a subharmonic granular wave pattern Claudio Falc\'on, Jerem\'ias Garay, Marcel Clerc, Ignacio Ortega We present an experimental and theoretical study of the pattern formation process of standing subharmonic waves in a fluidized quasi-one-dimensional shallow granular bed. The fluidization process is driven by means of a time-periodic air flow, analogous to a tapping type of forcing. Measurements of the amplitude of the critical mode close to the transition are in quite good agreement with those inferred from a universal stochastic amplitude equation. This allows us to determine both the bifurcation point of the deterministic system and the corresponding noise intensity. Then, we charaterize the stationary to drifting transition of this subharmonic wave pattern in the presence of inhomogeneities and drift forces. The transition is mediated by the competition of the inherent periodicity of the subharmonic pattern, the asymmetry of the system and the finite size of the cell. We measure the mean phase velocity of the subharmonic pattern, which is in good agreement with those inferred from an amplitude equation taking into account asymmetry and finite size effects of the system. [Preview Abstract] |
Sunday, November 20, 2011 9:31AM - 9:44AM |
A2.00008: The Dynamics of Granular Materials Miroslav Kramar, Konstantin Mischaikow, Lou Kondic, Arnaud Goullet We will present a novel approach to study force chain structures of particulate systems. We concentrate on systems undergoing compression. Our method distinguishes different types of friction as well as different rate of poly dispersity. The topological measures can be also used to understand the dynamic features of the system and correlate these measures to phenomena such as jamming. [Preview Abstract] |
Sunday, November 20, 2011 9:44AM - 9:57AM |
A2.00009: Theory for shear-induced segregation of dense granular mixtures Yi Fan, Kimberly Hill It is well-known that a mixture of different sized particles will segregate in a gravitational field. However, it has only recently been shown that a gradient of shear rate alone can drive segregation in dense sheared systems. In contrast with sparse energetic granular materials, in dense sheared systems, large particles segregate to the regions with higher shear rates. We develop a model for shear-induced segregation in dense mixtures of different sized particles. The model is comprised of two primary parts. The first involves the tendency of a gradient in kinetic stress -- stress associated with velocity fluctuation correlations -- to drive all particles toward regions of low shear rate. The second is essentially a kinetic sieving effect in which small particles are more likely to find voids into which they can travel than large particles. The two features together segregate small particles to regions of low shear rate and squeeze large particles in the opposite direction. We validate this model via 3D Discrete Element Method (DEM) simulations in a vertical chute. [Preview Abstract] |
Sunday, November 20, 2011 9:57AM - 10:10AM |
A2.00010: Complex Dynamics of a Floating Sheared Granular Layer Quentin Sherman, Zachary Needell, Douglas Durian, Jerry Gollub We investigate the complex shear flow dynamics of a two-dimensional layer of cohesive particles floating on a magnetically driven fluid. Capillary forces provide cohesion, which can be adjusted using a surfactant. The layer shows a yield force that rises with packing fraction and cohesion. Using a Voronoi tessellation of the particle positions, we find that the distribution of the local free areas follows a Gamma distribution with an additional tail resulting from voids. The deformation gradient of the related Delaunay triangulation of the particle positions provides a useful way to characterize the dynamics. We focus especially on the rotation and stretching rates of these triangles, which are found to be only weakly correlated with the local free area. It appears that local structural quantities cannot reliably predict the evolving regions of large deformation. We note asymmetries of these fluctuations that correspond to elongated regions of high deformation (e.g.slip lines). Finally, we consider the mean square non-affine particle displacements, which appear to grow diffusively in time. [Preview Abstract] |
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