I. Ippolito

Study of tracer dispersion in self‐affine fractures using lattice–gas automata

This paper studies the problem of hydrodynamic dispersion of a tracer in a fluid flowing through a two‐dimensional rough channel bounded by self‐affine surfaces. Changing the surface roughness exponent H, rough walls having different microstructure are obtained. In order to simulate hydrodynamics, a lattice–gas automata modified to introduce two different species of particles is used. In the studied range of Peclet numbers (20–50), the concentration profiles along the channel are well described by Gaussian‐type dispersion. A clear enhancement of the dispersion due to roughness is observed. For the studied regime of Peclet numbers, a simple approach is proposed which allows us to interpret the dispersion enhancement in terms of surface roughness. It is shown that the dispersion enhancement in the rough channel is due to the presence of two characteristic lengths, the hydraulic diameter δH which determines the velocity in the channel and the average aperture δav which determines the transverse diffusion len...

Motion of grains down a bumpy surface

We summarize in this article an extensive experimental and theoretical effort carried out to understand the behavior of a single ball when rolling down a bumpy surface. This may appear to be a simple problem but in fact is one that displays a rich variety of different behaviors which allow us to understand better dissipative systems such as granular media. Studies performed previously have shown that the motion of the single ball on the rough surface can be characterized by three different dynamic regimes according to the different values of the two control parameters, the inclination angle theta and the ratio Phi=R/r, where R is the radius of the rolling ball and r the radius of the glass beads which make up the rough surface. The three regimes are a decelerated regime A, a stationary regime B, characterized by a constant average velocity and a jumping regime C. This result was found to be independent of the composition of the rolling ball and the rough surface. It has been demonstrated that regime B is characterized by a viscous-like friction force that appears for specific parameter values. This friction force can be explained by a model whose central ingredient is the geometry of the surface. The trajectory of the ball in regime B can be pictured as a driven random walk motion where the fluctuations of the local velocities are due to collisions of the moving sphere and the surface grains. A detailed analysis of diffusive properties of the motion is discussed. (c) 1999 American Institute of Physics.

ENERGY DISSIPATION AND TRAPPING OF PARTICLES MOVING ON A ROUGH SURFACE

We report on an experimental, numerical, and theoretical study of the motion of a ball on a rough inclined surface. The control parameters are

Effects of geometry on the characteristics of the motion of a particle rolling down a rough surface

D

Granular packing: influence of different parameters on its stability

, the diameter of the ball,

Surface fluctuations in a slowly driven granular system

ensuremath{theta}

Granular mixing in a Galton board

, the inclination angle of the rough surface, and

Force–displacement distributions and percolation properties in simulated 2-D packings

{E}_{mathrm{ki}},

Avalanche Parameters: Dependence on the Size of the Granular Packing

the initial kinetic energy. When the angle of inclination is larger than some critical value,

Dynamics of a Ball Rolling Down a Rough Inclined Surface

ensuremath{theta}g{ensuremath{theta}}_{T},