Dynamical clustering in driven granular gas

in Europhysics Letters [=EPL] (2012), 99

Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another ... [more ▼]

Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another dynamical clustering is observed when the system is continuously excited. In this paper, the physical processes that trigger the transition from a granular gas to a dynamical cluster are evidenced through numerical simulations. At the granular scale, the transition is evidenced by the observation of caging effects. At the scale of the system, the transition is emphasized by density fluctuations. Physical arguments, based on relaxation times, provide an analytical prediction for the edge between dynamical regimes. [less ▲]

How relative humidity affects random packing experiments

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2012), 85

The influence of relative humidity (RH) on the extremely slow compaction dynamics of a granular assembly has been experimentally investigated. Millimeter-sized glass beads are considered. Compaction ... [more ▼]

The influence of relative humidity (RH) on the extremely slow compaction dynamics of a granular assembly has been experimentally investigated. Millimeter-sized glass beads are considered. Compaction curves are fitted by stretched exponentials with characteristic time τ and exponent δ, which are seen to be deeply affected by the moisture content. A kinetic model, taking into account both triboelectric and capillary effects, is in excellent agreement with our results. It confirms the existence of an optimal condition at a relative humidity ≈45% for minimizing cohesive interactions between glass beads. The exponent δ is seen to depend strongly on the diffusive character of grains and voids inside the packing: diffusion for cohesiveless particles and subdiffusion when cohesion plays a role. As a consequence, the RH represents a relevant parameter that should be reported for every experimental work on a slowly driven dense random packing. [less ▲]

Influence of a reduced gravity on the volume fraction of a monolayer of spherical grains

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2011), 84

Phase transitions in vibrated granular systems in microgravity

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2011)

van der Waals cohesion in Non Smooth Contact Dynamics : application to powder mixtures

in Canadian Journal of Physics (2011)

Characterization of tap intensity for granular compaction

in Powders and Grains 2009 (2009)

Energetic approach for the characterization of taps in granular compaction

in Europhysics Letters [=EPL] (2008), 84(4),

We report numerical investigations for the compaction dynamics of dense granular assemblies. The studies are based on the non-smooth contact dynamics model. Our work suggests that the dimensionless ... [more ▼]

We report numerical investigations for the compaction dynamics of dense granular assemblies. The studies are based on the non-smooth contact dynamics model. Our work suggests that the dimensionless acceleration parameter Gamma, used by a large majortiy of authors, is not appropriate for rescaling the data. We prove that the dimensionless energy Xi, injected in the granular system at lift-off, is more appropriate and leads to robust interpretations of the compaction dynamics. Indeed, the injected energy allows to pass energy barriers that separate local equilibrium states. Using the Eyring picture of relaxation dynamic, we show that the consideration of Xi leads to a new law for compaction. [less ▲]

The influence of grain shape, friction and cohesion on granular compaction dynamics

in European Physical Journal E -- Soft Matter (2007), 22(3), 241-248

This article is a review of our recent and new experimental works on granular compaction. The effects of various microscopic parameters on the compaction dynamics are addressed, in particular the ... [more ▼]

This article is a review of our recent and new experimental works on granular compaction. The effects of various microscopic parameters on the compaction dynamics are addressed, in particular the influence of the grain shape, the friction and the cohesion between the grains. Two dimensional and three dimensional systems are analysed. And the role of dimensionality will be emphasized. Theoretical and numerical investigations provide additional informations about that phenomenon. Indeed numerical models permit us to study the influence of some parameters not easily accessible experimentally. Our results show that the above mentioned parameters have a deep impact on the compaction dynamics. Anisotropic grains lead to two different compaction regimes separated by a "burst" of the packing fraction. Friction is observed to modify how the grains are arranged in the pile. This is confirmed by numerical simulations. Cohesive forces between particles inhibit compaction and lead to extremely low values of the packing fraction. [less ▲]

Compaction of granular materials: experiments and contact dynamics simulations

in Journal of Physics: Conference Series [=JPCS] (2006), 40

We present an original experimental study of the slow compaction dynamics for two- dimensional isotropic granular systems. Compaction dynamics is measured at three different scales : the macroscopic scale ... [more ▼]

We present an original experimental study of the slow compaction dynamics for two- dimensional isotropic granular systems. Compaction dynamics is measured at three different scales : the macroscopic scale through the normalized packing fraction ˜ ρ, the mesoscopic scale through the normalized fraction ˜ φ of domains ideally ordered in the system, and the microscopic scale through the grain mobility μ. The domains ideally ordered are found to obey a growth process dominated by the displacement of domain boundaries. We present also preliminary results of three-dimensional simulations with a model of contact dynamics. These results allow to discuss the difference between the two-dimensional and the three-dimensional cases. [less ▲]

Reversing the Brazil nut effect

in European Physical Journal E -- Soft Matter (2005), 18(4), 367-372

We propose a lattice model for studying the Brazil Nut Effect (BNE), i.e. the phase segregation occuring when a granular material is vertically shaked. The model considers the tap intensity and the ... [more ▼]

We propose a lattice model for studying the Brazil Nut Effect (BNE), i.e. the phase segregation occuring when a granular material is vertically shaked. The model considers the tap intensity and the mobility mu of the grains as the main physical parameters. Different mobilities for different grain species lead to segregation (BNE) patterns, reverse segregation (RBNE) patterns, "sandwhich" layered structures or vertical domains. A phase diagram (decompaction chi, mobility difference between both species Delta mu) is obtained in which the different phases are emphasized. In a narrow region of the diagram, different phases coexist. It is shown that the BNE segregation could be reversed by increasing the tap intensity or the characteristics of the grains. Numerical results are compared with earlier experimental works. [less ▲]