Non Linear Physics Group - Eric Falcon



Granular media in low-gravity environment

ESA Vip-Gran Instrument for studying granular media in International Space Station (2011-2019) operational from 2019

In parabolic flights and in sounding rockets (1999-2006) - see below

Electrical Transport in Granular Media

Discovered in 1890, coheration or ``Branly effect'' is an electrical conduction transition (from an isolating to a conductive state) in metallic granular media. Our experiment allows to understand the phenomena linked to this transition by focusing on the nature of the contacts instead of the structure of the granular network as usual:
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Current through a metallic granular powder is noisy, and the noise has interesting self-similar properties, including intermittency and scale invariance, with similarities and differences with fluid turbulence:
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Granular Gases

cluster Zero-G The macroscopic properties of granular media are strongly related to the physics of the collisions between grains, and to the absence of thermal agitation.

In a general way, the collisions are characterized by a dissipation of energy (inelastic collision). It is thus  necessary to supply continuously some energy to this system (e.g. by vibration) in order to keep it in a stationnary state.

gaz amasThis inelasticity of collisions leads to particularly interesting dynamic regimes: when the number of particles increases, a transition appears between a spatially homogeneous fluidized state (gas) and a phenomenon of aggregation of particles (cluster)

In the kinetic regime, due to the inelasticity of the collisions, the pressure and the temperature of such a granular gas are governed  by a
state equation which differs qualitatively from that of a usual gas.

A model of coefficient of restitution dependent on the speed of impact between grains allows to find numerically these experimental results both qualitatively and quantitatively.

The study of the collision statistics of a dissipative granular gas, performed in microgravity (parabolic flights - sounding rocket), show even there surprising results.

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Granular Dynamics

Dynamical behaviors linked to the contact between beads (Hertz contact): 

Collective processes of collision and
solitary waves propagation in granular media.
Behavior of an inelastic bouncing ball: When the collisional singularity or the so-called ''inelastic collapse`` vanishes...
Instabilities in Granular Materials

corrug.gif hexfluid hexcompWe report free-surface instabilities in a deep bed of fine granular material (powder) under vertical vibrations: heap corrugation and hexagon formation. These secondary instabilities are due to the presence of the surrounding gas (air).

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