A. Aradian

Dewetting on porous media with aspiration

Abstract.We consider a porous solid covered with a water film (or with a drop) in situations where the liquid is pumped in, either spontaneously (if the porous medium is hydrophilic) or mechanically (by an external pump). The dynamics of dewetting is then strongly modified. We analyse a few major examples, a) horizontal films, which break at a certain critical thickness, b) the “modified Landau-Levich problem” where a porous plate moves up from a bath and carries a film: aspiration towards the plate limits the height H reached by the film, c) certain situation where the hysteresis of contact angles is important.

Thick surface flows of granular materials: effect of the velocity profile on the avalanche amplitude.

A few years ago, Bouchaud et al. introduced a phenomenological model to describe surface flows of granular materials [J. Phys. I 4, 1383 (1994)]. According to this model, one can distinguish between a static phase and a rolling phase that are able to exchange grains through an erosion or accretion mechanism. Boutreux et al. [Phys. Rev. E 58, 4692 (1998)] proposed a modification of the exchange term in order to describe thicker flows where saturation effects are present. However, these approaches assumed that the downhill convection velocity of the grains is constant inside the rolling phase, a hypothesis that is not verified experimentally. In this article, we therefore modify the above models by introducing a velocity profile in the flow, and study the physical consequences of this modification in the simple situation of an avalanche in an open cell. We present a complete analytical description of the avalanche in the case of a linear velocity profile, and generalize the results for a power-law dependency. We show, in particular, that the amplitude of the avalanche is strongly affected by the velocity profile.

A Simple Description of Thick Avalanches at the Surface of a Granular Material

Some years ago, Bouchaud et al. introduced a phenomenological model to describe surface flows of granular materials [J. Phys. Fr. I 4, 1383 (1994)]. According to this model, one can distinguish between a static phase and a rolling phase that are able to exchange grains through an erosion/accretion mechanism. Later, Boutreux et al. [Phys. Rev. E 58, 4692 (1998)] proposed a modification of the exchange term in order to describe thicker flows where saturation effects are present. However, these two approaches assumed that the downhill convection velocity of the grains is constant inside the rolling phase, a hypothesis that is not verified experimentally. We have recently modified the above models by introducing a velocity profile in the flow, and analyzed the physical consequences of this modification in the simple situation of an avalanche in an open cell. We here emphasize the physical predictions of our model, and show, in particular, that the thickness of the avalanche depends strongly on the velocity profile.