Convection mixte en régime transitoire de couche limite laminaire sur une plaque verticale

This work deals with transient laminar boundary layer along a vertical surface and system of equations is solved using finite difference implicite scheme. We show that the nature of the plate influence thermal and dynamical boundary layer thicknesses as well as the flow velocity. Moreover, we observe that a small perturbation of the velocity implies to flow laminar instabilities.     

Naissance des corrélations triples de vorticité dans une turbulence statistiquement homogène soumise à une rotation

A homogeneous and isotropic turbulence is suddenly subjected to a rigid body rotation, whose influence on the turbulent vorticity field is studied. It is shown that only the odd statistical moments are influenced by the rotation at the first order in time. This effect is shown in particular for triple correlations and should be more important for a small Rossby number.     

Homogénéisation d'une poutre périodique : limite des développements asymptotiques

Starting from the equations of two-dimensional elasticity, a double-scale asymptotic expansion method is applied to a thin structure which is periodic in the direction perpendicular to the thickness. Under the given loading, all the terms of the displacement and stress expansions are determined. These expansions have finite limits under some conditions depending on the number of cells and the solutions of the cellular problems. Application examples show the contribution of higher-order terms in case the number of cells is small.     

Vérification expérimentale de la relation de réciprocité d'Onsager pour l'électro-osmose et l'électro-filtration dans une argile naturelle

This Note is devoted to the experimental verification of the Onsager's reciprocal relations in the particular case of electro-osmosis and electro-filtration. A special set up has been designed to carry out the measurements of both the electro-osmotic permeability and the streaming potential. This has been performed by using a natural material i.e., saturated kaolinite. To cite this article: K. Beddiar et al., C. R. Mecanique 330 (2002) 893–898.     

Théorie thermodynamique condensée de l'Elasticité linéaire

Sans résumé     

Eclatement tourbillonnaire dans une cavité rotor–stator cylindrique

The rotating flow inside an enclosed cylindrical rotor–stator cavity is studied. Within a certain range of governing parameters, vortex breakdown phenomenon can arise along the axis. Very recent papers exhibiting some particular three-dimensional effects, have concentrated new interest on this topic. The study is carried out by a numerical resolution of the 3D Navier–Stokes equations, based on spectral approximations. Three-dimensional behaviours of the flow and in the structure of the associated vortex breakdown are numerically exhibited for the first time in a cavity of large axial aspect ratio.     

Écoulement turbulent dans une cavité rotor–stator fermée de grand rapport d'aspect

A direct numerical simulation is combined with laboratory study to describe the turbulent flow in an annular high speed rotor–stator cavity. Comparisons are made for a turbulent flow characterized by a Reynolds number $\mathit{Re}=\Omega R_2^2/\nu =9.5\times {10}^4$ in a shrouded cavity of large aspect ratio $G=(R_2?R_1)/h=18.32$, where $R_1$ and $R_2$ are the inner and outer radii of the rotating disk, and h is the inter-disk space. A close agreement is found between the computed results and the experimental data for the mean and turbulent fields.? To cite this article: S. Poncet, A. Randriamampianina, C. R. Mecanique 333 (2005).     

Naissance de la convection dans une cavité poreuse 3D soumise à des vibrations de hautes fréquences

Analytical techniques are used to study the onset of convection in three-dimensional boxes of fluid saturated porous material heated from below and subjected to vertical high-frequency vibration. Increasing the vibration amplitude delays the onset of convection and may even create subcritical solutions so as generate different structures of flows.     

Une méthode mécanique pour déterminer la porosité totale d'un sol

This paper presents a mechanical method for the determination of the total porosity of soil. The presented method consists in inserting a sample of soil into a cell that can be regulated by varying the volume of the gas by increments using a piston. The porosity of the soil is deduced from the variation of the total pressure of the gaseous phase during the realization of volume increments. The method has been validated on a soil considering five samples with different porosities. The experimental results on the total porosity are in good agreement with the theoretical results over all tests.     

Inductions électromagnétiques en relativité générale et principe de Fermat

Sans résumé Mémoire transmis par A. Lichnerowicz     

Évolution des propriétés élastiques en poroplasticité finie

The formulation of poroplasticity at large strains requires to clarify the influence of plasticity on the poroelastic properties. This effect is modelled within the framework of a micro–macro approach which takes into account the geometry changes of the microstructure. It is shown that the coupling between elasticity and plasticity introduces an additional term in the rate-type form of the macroscopic state equation which yields a modified form of the Jaumann rate.     

Fissuration multiple par corrosion sous contrainte : Modélisation du comportement mécanique par une méthode d'homogénéisation

Stress Corrosion Cracking (SCC) phenomenon is characterised by initiation and propagation of surface cracks frequently multiple. In order to model the mechanical behaviour of such materials we propose, as for composites, the use of homogenization techniques. Two materials are considered, first one corresponding to the cracked external volume and the second to the internal safe material. The cracked volume is considered as a two phase material, i.e., elastic matrix containing elliptical voids. The overall behaviour of the equivalent material is obtained applying the usual homogenization rules. Comparison between simulations and experimental results is done.     

Interprétation géométrique de la décomposition des équations de compatibilité en grandes déformations

In this paper, we establish compatibility equations satisfied by the right Cauchy–Green stress tensor by annihiling the associated curvature and torsion. The cancelation of torsion, using variables introduced by the polar decomposition, is not trivial as is usually the case. This point is the key to the decomposition of compatibility conditions in two first-order EDPs.     

Impact non-pénétrant sur le thorax : une contribution à l'étude de la propagation des ondes

The stress wave generated by a nonpenetrating impact on the thorax is likely to cause severe injury to the lung. Theoretical studies are necessary to help the understanding of injury mechanisms. Within the framework of elastodynamics, we study the transmission of a wave at the interface between two weakly coupled semi-infinite media representing the thoracic wall and the lung. By using an appropriate method, we describe the distribution of energy carried by the shear and pressure waves in the medium representing the lung. These results should contribute to a better interpretation of the experimental results.     

Calcul direct du rayonnement acoustique d'un écoulement affleurant une cavité

A direct numerical simulation is presented for the unsteady flow over a two-dimensional cavity at a Mach number of 0.5. The incoming flow is a laminar, subsonic boundary layer. Two values of the principal parameter L/δ_θ , where L is the cavity length and δ_θ the momentum thickness of the boundary layer, have been studied. The feedback mechanisms which induce self-sustained oscillations in the cavity have been well captured and two flow regimes were pointed out. The corresponding acoustic responses are specified in terms of the wall pressure in the cavity and the radiated acoustic field.