Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session GU: Granular IV |
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Chair: Deveraj van der Meer, University of Twente Room: 200I |
Monday, November 23, 2009 8:00AM - 8:13AM |
GU.00001: Collective dynamics of floaters on a Faraday wave Ceyda Sanli, Devaraj van der Meer, Detlef Lohse The dynamics of particles floating on a standing Faraday wave is studied experimentally. For low particle concentration it was shown [G. Falkovich et al. Nature 435, 1045 (2005)] that non-wetting particles accumulate at the antinodes of the standing wave. This was found to be a single particle effect. Here, we study what happens when the particle concentration is increased: Surprisingly, we observe that the same particles that cluster at the antinodes for low particle concentration move to the nodes for high concentrations. The explanation of this effect lies in the collective, attractive capillary interaction among particles which counteracts the tendency of the particles to move toward the antinodes. The transition between the two regimes is studied as a function of the concentration and is found to exhibit extremely long transients. [Preview Abstract] |
Monday, November 23, 2009 8:13AM - 8:26AM |
GU.00002: Coarsening of Faraday Heaps: Experiment, Simulation, and Theory Devaraj van der Meer, Henk Jan van Gerner, Gabriel A. Caballero-Robledo, Ko van der Weele, Martin A. van der Hoef When a layer of granular material is vertically shaken, the surface spontaneously breaks up in a landscape of small Faraday heaps that merge into larger ones on an ever increasing timescale. This coarsening process is studied in a linear setup, for which the average lifetime of the transient state with $N$ Faraday heaps is shown to scale as $N^{-3}$. We describe this process by a set of differential equations for the peak positions; the calculated evolution of the landscape is in excellent agreement with both the experiments and simulations. The same model explains the observational fact that the number of heaps towards the end of the process decreases approximately as $N(t) \propto t^{-1/2}$. [Preview Abstract] |
Monday, November 23, 2009 8:26AM - 8:39AM |
GU.00003: Granular compaction under confinement Nathan Mueggenburg We report on experiments that explore the impact of confinement on a compacting granular system. When a granular pack is subjected to successive vertical vibrations it undergoes a slow compaction process as individual grains rearrange and pack more closely together. We control the position and applied force of a confining boundary at the top surface of the granular system during these vibrations. This confinement limits the amount of dilation that occurs during the vibrations and significantly reduces the rate of compaction in comparison to the same system with a free top surface. [Preview Abstract] |
Monday, November 23, 2009 8:39AM - 8:52AM |
GU.00004: Shocks and Patterns in Continuum Simulations of Oscillated Granular Layers J. Bougie, K. Duckert We study interactions between shocks and standing wave patterns in continuum simulations of vertically oscillated granular layers. Layers of grains atop a plate with sinusoidal oscillations in the vertical direction leave the plate at some time during the cycle if the accelerational amplitude of oscillation is greater than the acceleration of gravity. Above a critical acceleration, standing waves form stripe patterns. In these same shaken layers, shocks are produced when layers collide with the plate after leaving the plate earlier in the cycle. We simulate vertically shaken layers using numerical solutions of continuum equations to Navier-Stokes order to find number density, average velocity, and granular temperature as functions of time and location within the cell. We compare shocks and standing waves coexisting in this system; pressure gradients produced by shocks play a significant role in the formation of standing wave patterns. [Preview Abstract] |
Monday, November 23, 2009 8:52AM - 9:05AM |
GU.00005: Measurement of Density Fluctuations in a Vertically Oscillated Granular Bed at the Onset of Vibrofluidization James Gilchrist, Kenneth Ford, Colin Armstrong, Richard Evans, Hugo Caram The transition from solid- to liquid-like behavior in vertically oscillated granular media is probed through measurements of density fluctuations near the point of vibrofluidization. The intracycle dynamics are used to define the critical vibration acceleration required for vibrofluidization in deep beds. Clear successive shock waves are formed, and the resulting density fluctuations initiated near the free surface propagate downward with increasing energy. When ``heating'' the bed by vibration, ``melting'' begins at the free surface. [Preview Abstract] |
Monday, November 23, 2009 9:05AM - 9:18AM |
GU.00006: Comparison of two quadrature-based moment methods for simulating dilute granular gases Rodney Fox, Alberto Passalacqua, Prakash Vedula, Jason Yuan A dilute non-isothermal inelastic granular gas between two stationary Maxwellian walls is studied by means of numerical simulations of the Boltzmann kinetic equation with a hard-sphere collision kernel for mono-dispersed particles. Two types of quadrature-based moment methods with different orders of accuracy in terms of the moments of the distribution function are used with four different inelastic collision models. The models differ in the manner with which the moment equations are closed and in the number of moments that can be controlled for a given number of quadrature points. Results from the kinetic models are compared with the predictions of molecular dynamics simulations of a nearly equivalent system. [Preview Abstract] |
Monday, November 23, 2009 9:18AM - 9:31AM |
GU.00007: Experimental measurement of the stress tensor in a granular gas Greg Voth, Wan Jun Yang, Jonas Mishara-Blomberger, Mark Shattuck We study a quasi-2D granular gas that is vertically vibrated. Precision particle tracking from video at 60 kHz allows us to accurately measure the momentum transfer from individual collisions as well as from particle motion. This allows experimental measurement of the stress tensor. The time averaged stress shows good agreement with the requirement of hydrostatic balance, indicating that we are adequately resolving the stress. Time resolved measurements of the collisional stress show the serrated structure that appears in the shock waves in this system. These measurements allow direct evaluation of the constitutive equation for stress used in hydrodynamic models. [Preview Abstract] |
Monday, November 23, 2009 9:31AM - 9:44AM |
GU.00008: A quadrature-based kinetic model for a dilute non-isothermal granular gas Alberto Passalacqua, Janine Galvin, Prakash Vedula, Christine Hrenya, Rodney Fox A dilute non-isothermal inelastic granular gas between two stationary Maxwellian walls is studied by means of numerical simulations of the Boltzmann kinetic equation with hard-sphere collisions. The behavior of a granular gas in these conditions is influenced by the thickness of the wall Knudsen layer: if its thickness is not negligible, the traditional description based on the Navier-Stokes-Fourier equations is invalid, and it is necessary to account for the presence of rarefaction effects using high-order solutions of the Boltzmann equation. The system is described by solving the full Boltzmann equation using a quadrature-based moment method (QMOM), with different orders of accuracy in terms of the moments of the distribution function, considering moments up to the seventh order. Four different inelastic collision models (BGK, ES-BGK, Maxwell hard-sphere, Boltzmann hard-sphere) are employed. QMOM results are compared with the predictions of molecular dynamics (MD) simulations of a nearly equivalent system with finite-size particles, showing the agreement of constitutive quantities such as heat flux and stress tensor. [Preview Abstract] |
Monday, November 23, 2009 9:44AM - 9:57AM |
GU.00009: ABSTRACT WITHDRAWN |
Monday, November 23, 2009 9:57AM - 10:10AM |
GU.00010: The effect of finite container size on granular jet formation Sylvain Joubaud, Stefan von Kann, Gabriel Caballero-Robledo, Devaraj van der Meer, Detlef Lohse When an object is dropped into a bed of fine, loosely packed sand, a surprisingly energetic jet shoots out of the bed. In this work we study the effect that boundaries have on the granular jet formation. We did this by (i) decreasing the depth of the sand bed and (ii) reducing the container diameter to only a few ball diameters. These confinements change the behavior of the ball inside the bed, the void collapse, and the resulting jet height and shape. From these results we propose a new explanation for the thick-thin structure observed experimentally and reported previously. [Preview Abstract] |
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