History independence of steady state in simultaneous two-phase flow through two-dimensional porous media.

It is well known that the transient behavior during drainage or imbibition in multiphase flow in porous media strongly depends on the history and initial condition of the system. However, when the steady-state regime is reached and both drainage and imbibition take place at the pore level, the influence of the evolution history and initial preparation is an open question. Here, we present an extensive experimental and numerical work investigating the history dependence of simultaneous steady-state two-phase flow through porous media. Our experimental system consists of a Hele-Shaw cell filled with glass beads which we model numerically by a network of disordered pores transporting two immiscible fluids. From measurements of global pressure evolution, histograms of saturation, and cluster-size distributions, we find that when both phases are flowing through the porous medium, the steady state does not depend on the initial preparation of the system or on the way it has been reached.

Diffusive waves in a dilating scattering medium.

We consider the propagation of a diffusive wave in a scattering medium submitted to a homogeneous expansion. The light multiply scattered by a glass spheres sample is measured. We analyze the variations of the scattered light when the material and the optical wavelength are dilated. We experimentally show that an isotropic expansion of the material is equivalent to a contraction of the wavelength. Moreover, the effect of an expansion of the material on the scattered wave may be canceled by a proportional increase of the wavelength, keeping the phase of the scattered wave unchanged. Applications to the characterization of deformation of disordered materials are outlined.

Diffusive wave spectroscopy applied to the spatially resolved deformation of a solid.

We propose an experimental setup based on diffusive wave spectroscopy for studying deformations of a solid material. The scattered waves are measured during the deformation of the solid material at different locations of its surface. The correlations of the scattered intensities are measured. The loss of correlation can be related to the invariants of the strain tensor of the solid, giving us a spatially resolved determination of the deformation near the surface. Experiments dealing with a point stress on plate for two kinds of elastic materials are presented and compared with the theoretical predictions.