Determination of liquid water content and dielectric constant in porous media by the capacitive methodDétermination,par la méthode capacitive,de la teneur en eau liquide et de la constante diélectrique dans un milieu poreux

A capacitive sensor-based apparatus has been settled to determine the liquid water amount and dielectric constant in consolidated porous media. This technique relies on the dielectric properties of water, air, and mineral substrate. The experimental procedure is described for successively oven-dried samples at 323 K. It allows us to determine the sample dielectric constant as a function of the sample water amount. For limestones from Caen region, an affine relationship is found at 293 K. This is then compared with other empirical soils data and with existing homogeneisation techniques applied to undeformable heterogeneous dielectrics. To cite this article: T. Fen-Chong et al., C. R. Mecanique 332 (2004).     

Stabilité de la forme de la goutte d'eau formée entre deux grains solides : méthode de résolutionStability of the shape of a liquid drop placed between two solid grains: method of resolution

We discuss the positiveness of the second variation of a Lagrangian Action subjected to an integral constraint when the end-points of the range of integration of the integrals can be displaced along prescribed curves. The Lagrangian does not depend explicitly on the variable of integration. The results are illustrated by the problem of a liquid drop placed between two solid grains. To cite this article: P. Bérest et al., C. R. Mecanique 332 (2004).     

Comportement macroscopique des matériaux poreux à microstructure en feuilletsMacroscopic behavior of porous materials with lamellar microstructure

The solid phase of the porous material considered in this Note is made up of lamellar particles. The influence of interaction forces between platelets on the macroscopic behavior is addressed. The results provide a micromechanical basis to the modelling of the behavior of clays of the smectite group, for which repulsive forces arise from the electrical interaction between the solid platelets and the interstitial fluid. To cite this article: L. Dormieux et al., C. R. Mecanique 334 (2006).     

On the existence of the low-frequency surface waves in a porous mediumSur l'existence des ondes de surface basse fréquence en milieux poreux

The existence and propagation of the surface waves at a vacuum/porous medium interface are investigated in the low frequency range. Two types of surface waves are shown to be possible: the generalized Rayleigh wave, which always exists, and the Stoneley wave, which exists for a limited range of wave numbers. Moreover, within the k-domain of existence the Stoneley wave cannot appear for certain values of elastic parameters of the solid phase. The bifurcation behavior of both the Stoneley wave and the Biot (P2) bulk wave, depending on the wave number, is revealed. The asymptotic formulas for the phase velocities of the surface waves are derived. To cite this article: I. Edelman, C. R. Mecanique 332 (2004).     

Colmatage des réacteurs gaz–liquide à lit fixePlugging in two-phase flow packed beds

A 1-D transient two-fluid deep-bed filtration model was formulated for the capture of colloidal fines in porous media experiencing gas–liquid trickling and dispersed bubble flow regimes. The deposit prediction resulted from solving the coupled volume-average fines' advection–dispersion, Navier–Stokes, volume and mass conservation equations for the three phases. To make the system solvable, it was augmented by auxiliary closures expressing the coupling between fluids and porous medium via the drag interfacial forces, the filter coefficient in the so-called mono- and multi-layer modes, and the growth of the specific surface area of the filter bed for liquid-solid drag. To cite this article: I. Iliuta, F. Larachi, C. R. Mecanique 330 (2002) 563–568.     

Analytic calculation of the stresses in an ensiled granular mediumCalcul analytique des contraintes dans un matériau granulaire ensilé

We present in this Note a new analytic approach, of continuous medium type, which improves the Janssen theory and enables us to calculate the stresses in an ensiled granular medium. This approach is based on the two dimensional equilibrium equations, coupled with the Mohr–Coulomb criterion and a slip condition at the walls of the silo. An analytic resolution is developed to compute the stresses for cohesive and non cohesive materials in the whole silo. To cite this article: O. Millet et al., C. R. Mecanique 334 (2006).     

Influence de la température sur la courbe de rétention d'eau de milieux poreuxInfluence of temperature on the water retention curve of porous media

This paper concerns the influence of temperature on the water retention curve of porous media. We present a model based on the differential of suction as a function of temperature, water content and void ratio. When adjusted for a given temperature, this model is able to predict the curve for any temperature. The model was validated by several tests on a ceramic (terra cotta) and a clayey silty sand at 20 and 60?°C. The application of the model to data found in the literature confirms its predictive power for a wide range of porous materials. To cite this article: S. Salager et al., C. R. Mecanique 334 (2006).     

Étude expérimentale de la dispersion active d'un polluant hydrocarboné en milieu poreux hétérogèneActive dispersion of a hydrocarbon pollutant in heterogeneous porous media: experimental study

This study deals with Non Aqueous Phase Liquid (NAPL) dissolution in subsurface water in order to predict the pollutant plume development and to optimize remediation processes. An experimental study of NAPL dissolution in porous media is presented. Local water saturation and effluent pollutant concentration measurements are presented for several kinds of porous media. Experimental results show clearly the influence of microscopic and/or macroscopic heterogeneities of the porous media and the distribution of the pollutant on the active dispersion of the NAPL. The NAPL dissolution occurs in several steps which highlights the existence of non-local equilibrium related to the heterogeneity of the porous media. To cite this article: A. Yra et al., C. R. Mecanique 334 (2006).     

Simulation numérique des détonations à double structure cellulaireNumerical simulation of detonations with double cellular structure

We present the results of numerical two-dimensional simulations of detonation cellular structures under non-monotonous heat release provided by a chemical reaction comprising two successive exothermic steps. The influence of the rate of the second step of chemical reaction on the detonation cellular structure has been investigated. Our simulations are the first that reproduce a cellular structure composed of two clearly distinct sets of cells with different characteristic sizes where fine cells completely fill up larger ones, as has been observed experimentally. To cite this article: V. Guilly et al., C. R. Mecanique 334 (2006).     

Sur le caractère thermo-extensif de la surface de charge d'un sol non saturéOn the thermo-extensive nature of the yield surface for an unsaturated soil

A study of temperature influence on the yield surface for one unsaturated soil at constant suction is presented. Mechanical consolidation tests are realized at different temperatures on clayey silty sand. A specific triaxial apparatus for unsaturated soils with temperatures included between 30 °C and 60 °C is used. Experimental results show without ambiguity a thermo-extensive nature of the yield surface. The physical interpretation proposed calls for microscopic considerations on the menisci capillary evolution according to temperature and suction. To cite this article: F. Jamin et al., C. R. Mecanique 332 (2004).     

Freezing and thawing porous media: experimental study with a dielectric capacitive method

A capacitive sensor-based apparatus has been used to study the ice/water phase change in consolidated porous media subjected to freezing and thawing. This technique relies on the dielectric properties of water, ice, air, and the mineral substrate in the radio-frequency range. It gives directly the freezing and thawing temperature depressions and indirectly provides an estimation of pore size distribution through the Gibbs–Thomson relation. It also holds good promise for evaluating the amount of liquid water in frozen porous media by combining drying and freezing tests. To cite this article: T. Fen-Chong, A. Fabbri, C. R. Mecanique 333 (2005).     

A model for gas–liquid slug flow in downwardly inclined ductsUn modèle pour les écoulements gaz–liquide à bouchons en conduite inclinée

A simple theoretical model is proposed in order to represent gas–liquid slug flows in inclined ducts of arbitrary shape. To cite this article: A. Dyment, A. Boudlal, C. R. Mecanique 332 (2004).     

Remarques sur les contraintes résiduellesSome comments on residual stresses

Residual stresses which are currently observed in solid bodies can result from non-compatible initial strains. Theses stresses can then be determined, in general, from the incompatibility tensor associated to the initial strains tensor. However, even if the incompatibility tensor is zero, residual stresses may exist, when the solid is not simply-connected or when discontinuity surfaces are present. Several examples are provided. To cite this article: P. Bérest, G. Vouille, C. R. Mecanique 331 (2003).     

Averaged model of a cross hydrodynamic–mechanic process in a double porosity mediumModèle homogénéisé d'un processus hydrodynamique–mécanique couplé en milieu de double porosité

For the single-phase flow of a compressible liquid in a deformable double porosity medium, the closed homogenized model is obtained with a total splitting between various cross mechanic–hydrodynamic effects. The transfer between matrix and fractures is completed by the peristaltic effect and the effect of flow arising due to shearing strain. In the equation of deformations, a new stress appears being generated by the cross effects and matrix relaxation. To cite this article: M. Panfilov et al., C. R. Mecanique 334 (2006).     

Écoulement de Couette Taylor diphasiqueTwo phase Couette Taylor flow

This paper presents the study of mutual interactions between dispersed and continuous phase in Couette Taylor flow. The introduction of the dispersed phase is obtained by ventilation or by pressure drop in an airtight chamber. In the first instabilities, the dispersed phase generate a modification of the flow state, the cavitating flow being moreover characterised by an advance to the third instability. The dispersed phase first stands along each of the apparent azimuthal waves as a string of individual bubbles located near the core of the Taylor cells and then migrates to the outflow regions near the inner cylinder. To cite this article: H. Djéridi et al., C. R. Mecanique 330 (2002) 113–119.     

Solution analytique pour le transfert de masse entre puits en milieu poreux hétérogèneAnalytical solution for mass transfer between wells in heterogeneous porous media

The analytical solution developed by Dagan and Indelman (Water Resources Res. 35 (12) (1999) 3639–3647) for modelling the transport of a tracer in an infinite heterogeneous porous media in a dipole flow is extended by accounting for the presence of no flow finite boundaries. The results obtained are compared to those corresponding to the infinite domain, emphasizing the important influence of the boundaries on the elution at the pumping well and the effect of the medium's heterogeneity. The analytical results are then compared to experimental data and provide good matching. To cite this article: J.-P. Carlier, P. Ackerer, C. R. Mecanique 331 (2003).     

Solutions multiples pour les écoulements tridimensionnels en rotationMultiple solutions for three-dimensional swirling flows

The symmetry-breaking in a swirling flow generated inside a cylindrical tank of aspect ratio h=1 by the rotation of one lid is studied numerically. Beyond a critical Reynolds number, the flow undergoes a bifurcation to three-dimensional solutions. The spatial and temporal behaviour on these branches are examined. To cite this article: E. Barbosa, O. Daube, C. R. Mecanique 330 (2002) 791–796.     

Champ de vitesse dans un échangeur à vortex en régime turbulentHeat exchanger velocity field with turbulent inlet condition

We consider the isothermal flow through a cylindrical flat chamber, a model of some particular heat exchanger, for which LDV measurements and a numerical simulation have been performed. Experimental results show the establishment of an important vortex zone, the secondary flow extending all along the chamber radius. This observation leads to an expected significant increase of the fluid mixing. Results issued from the numerical simulation appear to be in close agreement with experimental data. Nevertheless, the k–ε model used here must be improved to obtain a better approach near the vortex centre. To cite this article: S. Petitot et al., C. R. Mecanique 330 (2002) 593–599.     

Towards the efficient computation of effective properties of microstructured materialsVers le calcul efficace des propriétés effectives de materiaux microstructurés

An algorithm for partially relaxing multiwell energy densities, such as for materials undergoing martensitic phase transitions, is presented here. The detection of the rank-one convex hull, which describes effective properties of such materials, is carried out for the most prominent nontrivial case, namely the so-called T_k-configurations. Despite the fact that the computation of relaxed energies (and with it effective properties) is inherently unstable, we show that the detection of these hulls (T₄-configurations) can be carried out exactly and with high efficiency. This allows in practice for their computation to arbitrary precision. In particular, our approach to detect these hulls is not based on any approximation or grid-like discretization. This makes the approach very different from previous (unstable and computationally expensive) algorithms for the computation of rank-one convex hulls or sequential-lamination algorithms for the simulation of martensitic microstructure. It can be used to improve these algorithms. In cases where there is a strict separation of length scales, these ideas can be integrated at a sub-grid level to macroscopic finite-element computations. The algorithm presented here enables, for the first time, large numbers of tests for T₄-configurations. Stochastic experiments in several space dimensions are reported here. To cite this article: C.-F. Kreiner et al., C. R. Mecanique 332 (2004).