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Density Waves in the Flows of Granular Media  [PDF]
Jysoo Lee
Physics , 1993, DOI: 10.1103/PhysRevE.49.281
Abstract: We study density waves in the flows of granular particles through vertical tubes and hoppers using both analytic methods and molecular dynamics (MD) simulations. We construct equations of motion for quasi one-dimensional systems. The equations, combined with the Bagnold's law for friction, are used to describe the time evolutions of the density and the velocity fields for narrow tubes and hoppers. The solutions of the equations can have two types of density waves, kinetic and dynamic. For tubes, we can show the existence of kinetic waves, and obtain the condition for dynamic waves for tubes from the equations. For hoppers, we obtain the solutions of the equations up to the first order of the opening angle, which also show the existence of kinetic waves. We reproduce density waves in the MD simulations for tubes. The waves are believed to be kinetic based on a few evidences, including a well defined flux-density curve. In MD simulations of flows in hoppers, we find density waves, which are also believed to be kinetic.
Patterns and Collective Behavior in Granular Media: Theoretical Concepts  [PDF]
Igor S. Aranson,Lev S. Tsimring
Physics , 2005, DOI: 10.1103/RevModPhys.78.641
Abstract: Granular materials are ubiquitous in our daily lives. While they have been a subject of intensive engineering research for centuries, in the last decade granular matter attracted significant attention of physicists. Yet despite a major efforts by many groups, the theoretical description of granular systems remains largely a plethora of different, often contradicting concepts and approaches. Authors give an overview of various theoretical models emerged in the physics of granular matter, with the focus on the onset of collective behavior and pattern formation. Their aim is two-fold: to identify general principles common for granular systems and other complex non-equilibrium systems, and to elucidate important distinctions between collective behavior in granular and continuum pattern-forming systems.
Dynamic self-assembly and patterns in electrostatically driven granular media  [PDF]
M. V. Sapozhnikov,Y. V. Tolmachev,I. S. Aranson,W. -K. Kwok
Physics , 2002, DOI: 10.1103/PhysRevLett.90.114301
Abstract: We show that granular media consisting of metallic microparticles immersed in a poorly conducting liquid in strong DC electric field self-assemble a rich variety of novel phases. These phases include static precipitate: honeycombs and Wigner crystals; and novel dynamic condensate: toroidal vortices and pulsating rings. The observed structures are explained by the interplay between charged granular gas and electrohydrodynamic convective flows in the liquid.
Density waves in dry granular media falling through a vertical pipe  [PDF]
T. Raafat,J. P. Hulin,H. J. Herrmann
Physics , 1996, DOI: 10.1103/PhysRevE.53.4345
Abstract: We report experimental measurements of density waves in granular materials flowing down in a capillary tube. The density wave regime occurs at intermediate flow rates between a low density free fall regime and a high compactness slower flow.
The role of tap duration for the steady state density of vibrated granular media  [PDF]
J. A. Dijksman,M. van Hecke
Physics , 2009, DOI: 10.1209/0295-5075/88/44001
Abstract: We revisit the problem of compaction of a column of granular matter exposed to discrete taps. We accurately control the vertical motion of the column, which allows us to vary the duration T and the amplitude A of single-cycle sinusoidal taps independently. We find that the density of the material at the reversible branch depends both on A and T. By comparing the densities on the reversible branches obtained for a range of values of T, we find that we can collapse all data when plotted as function of A/T, which scales similar to both the liftoff velocity and the time of flight of the packing. We further show that switching between states obtained for different A and T, but chosen such that their densities on the reversible branches match, does not lead to appreciable hysteresis. We conclude that the appropriate control parameter for sinusoidal tapping is not the peak acceleration \Gamma \sim A/T^2, as is usually assumed, but rather \Gamma T \sim A/T.
Interstitial gas and density-segregation in vertically-vibrated granular media  [PDF]
M. Klein,L. L. Tsai,M. S. Rosen,T. Pavlin,D. Candela,R. L. Walsworth
Physics , 2005, DOI: 10.1103/PhysRevE.74.010301
Abstract: We report experimental studies of the effect of interstitial gas on mass-density-segregation in a vertically-vibrated mixture of equal-sized bronze and glass spheres. Sufficiently strong vibration in the presence of interstitial gas induces vertical segregation into sharply separated bronze and glass layers. We find that the segregated steady state (i.e., bronze or glass layer on top) is a sensitive function of gas pressure and viscosity, as well as vibration frequency and amplitude. In particular, we identify distinct regimes of behavior that characterize the change from bronze-on-top to glass-on-top steady-state.
Importance of convection in the compaction mechanisms of anisotropic granular media  [PDF]
Philippe Ribiere,Patrick Richard,Renaud Delannay,Daniel Bideau
Physics , 2005, DOI: 10.1103/PhysRevE.71.011304
Abstract: We report the experimental observation of novel vortex patterns in a vertically tapped granular media. Depending on the tapping acceleration two behaviors are observed. For high acceleration a convection vortex appears in the whole media whereas for low acceleration two unstable vortices appear in the upper part of the media and slowly compact the lower part. We explain the formation of the vortices and relate them to granular convection. Our results demonstrate the importance of compression waves propagation on granular compaction.
Memory in aged granular media  [PDF]
A. Barrat,V. Loreto
Physics , 2000, DOI: 10.1209/epl/i2001-00100-3
Abstract: Stimulated by recent experimental results, we simulate ``temperature''-cycling experiments in a model for the compaction of granular media. We report on the existence of two types of memory effects: short-term dependence on the history of the sample, and long-term memory for highly compact (aged) systems. A natural interpretation of these results is provided by the analysis of the density heterogeneities.
Stationary Probability Distribution in Granular Media  [PDF]
Antonio Coniglio,Annalisa Fierro,Mario Nicodemi
Physics , 2003, DOI: 10.1016/j.physd.2004.01.042
Abstract: We discuss recent developments in the formulation of a Statistical Mechanics approach to non thermal systems, such as granular media. We review a few important numerical results on the assessment of Edwards' theory and, in particular, we apply these ideas to study a mean field model of a hard sphere binary mixture under gravity, which can be fully analytically investigated. As a consequence, we derive the rich phase diagram and predict the features of segregation patterns of the mixture.
Liquid migration in sheared unsaturated granular media  [PDF]
Roman Mani,Dirk Kadau,Hans J. Herrmann
Physics , 2012,
Abstract: We show how liquid migrates in sheared unsaturated granular media using a grain scale model for capillary bridges. Liquid is redistributed to neighboring contacts after rupture of individual capillary bridges leading to redistribution of liquid on large scales. The liquid profile evolution coincides with a recently developed continuum description for liquid migration in shear bands. The velocity profiles which are linked to the migration of liquid as well as the density profiles of wet and dry granular media are studied.
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