The SPACE GRAINS project is devoted to the study of dynamical and statistical behaviors of granular matter in low-gravity environment. Indeed, it is of primary interest to better understand global and fluctuating motions occurring in granular media submitted to vibrations. The team of scientists is composed of experts from France, Belgium, Germany, Spain, China,…

In order to reach scientific objectives, an instrument, called VIPGRAN (Vibration Induced Phenomena in Granular Materials), is developed by the European Space Agency (ESA) and DTM s.r.l., and is scheduled to be included in the European Drawner Rack (EDR) within the International Space Station (ISS) in few years.

VIP-Gran AutoCADThe instrument consists of a container filled with particles where two opposite container walls act as vibrating pistons. Control parameters are the number of particles, the geometry of the container, and the amplitude and the frequency of vibrations. Cameras and impact sensors will be implemented. Different cells are planned for the study of 2d and 3d systems. Compartments are also considered in cells for testing  the Maxwell’s demon experiment.

Simulation of a gas-cluster transition, from E.Opsomer.

Motivation for low gravity is to achieve an experimental situation in which inelastic collisions between particles are the only interaction mechanism. The only time scale for such a granular system in low-gravity is the period of vibrations that thus strongly simplifies the modelisation of the system by using simple dimensional analysis. Long run experiments are also necessary since transient phenomena are of quite long duration for dense enough granular systems.

Comparison between MiniTexus experiments [E. Falcon et al., Phys. Rev. Lett. 83, 440 (1999)] and numerical simulations [E. Opsomer et al., Phys. Rev. E 84, 051306 (2011)].

Typical experiments with the instrument concern the study of phase transitions occurring in a granular matter between a liquid-like phase and a gas-like one when submitted to mechanical vibrations. One aim is to test the limit of validity of kinetic theory of granular gases when the solid fraction is changed from a dilute regime to a dense one. Indeed, theoretical works try to extend  the validity range the hydrodynamic limit of kinetic theory to dense system (see WP1). Another set of experiments (WP3) will concern the study of global granular motions induced by convection when both pistons vibrate differently («thermal gradient»-like forcing). Although studied on ground with one or two different species (segregation by convection, rotating drums), no convection-like behaviors with one species has been observed in wheightlessness to our knowledge. Third, experiments devoted to dense granular system will be also performed to better understand mechanical stresses and sound propagation (WP2). Finally, the effect of aspherical particles or different species will be also investigated (WP4). The proposed experiments are selected within Work Packages.

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