Représentation de la ligne de contact mobile dans les équations de la mécanique des fluides

Although the contact angle at equilibrium has a well understood theory for the case of flat homogeneous solid surfaces, the displacement of the contact line is still not well understood. We propose to introduce in the dynamics of the contact line a mobility relation between the deviation of the contact angle out of its equilibrium value and the speed of the line on the solid. When the line slides on the solid thanks to an evaporation/condensation process, this introduces a dynamical Arrhenius factor that may be sufficiently small to make the mobility of the contact line the limiting factor of the dynamics in many physical situations. Then, the shape of the liquid/vapor interface will be in quasi equilibrium giving a contact angle that will define ultimately the speed of the contact line.     

Sur l'intégrale de ligne et les fréquences irrégulières dans les calculs de tenue à la mer

The first results obtained using two seakeeping computation codes developed at Ecole Centrale de Nantes (Aquaplus) and at the LEA-Poitiers (Poseidon) are presented. Both use the diffraction–radiation with forward speed Green function, but with two different formulations, in a panel code in the frequency domain. Results obtained with both codes are in good agreement and also retrieve test measurements or other calculations available. However, irregular frequencies and their links with the waterline integral are made evident.     

Interprétation de la double structure observée dans l'onde de détonation du nitrométhane gazeux

Calculations of the reaction zone of the detonation of gaseous nitromethane, either pure or diluted with oxygen, in the range of equivalence ratio Φ between 0.1 and 1.75, show that for 1.75⩾Φ⩾1.3 the chemical energy is released in two main successive reaction steps characterized by very different induction times. These results corroborate the experimental observations of two levels of cellular structures in the same range of equivalence ratios. To our knowledge this work is the first which deals with the problem of nonmonotonous chemical energy release behind the leading shock of a detonation wave.     

Analyse mathématique de l'équation de Galbrun en écoulement uniforme

We consider Galbrun's equation, used in linear aeroacoustics. For a simple case (rigid duct with uniform flow) in the time harmonic regime, we show that an approach based on a regularized variational formulation of the problem ensures the convergence of a nodal finite-element method.     

Fonction de distribution pour les gaz polyatomiques dans la couche de Knudsen. Solution approchée de l'équation de Boltzmann

Polyatomic gases in strong non equilibrium vibrational state are studied in the Knudsen layer. A kinetic equation is derived from the Boltzmann equation for a stationary gas without macroscopic velocity. The simplification are basically deduced from the order of magnitude of adimmensional gradient terms. The approximate solution of this equation is deduced from a recurrent algorithm on the adimensional space variable power. Furthermore, the boundary condition allows us to obtain density and temperature jumps at the wall.     

Evaluation de la fraction volumique locale de la phase solide dans un écoulement diphasique

Local particle volume fraction measurements in two-phase flows are rare. Generally, the concentration is supposed to be spatially homogeneous in the sedimentation flows fundamental experiments. This is far to be realistic in regimes different from Stokes' regime, particularly near the walls. This paper compares two methods of evaluation of the volume fraction in a three-dimensional two-phase flow.     

Analyse contrastive de modèles incrémentaux et hypoplastiques

In this paper we first establish two necessary and sufficient conditions in order that incremental constitutive equations expressing the strain rate tensor as a function of the Jaumann's derivative of the Cauchy's stress tensor can be inverted under the general form of hypoplastic models when the stress state is located inside the domain bounded by the limit state surface. We are then interested in the physical meaning of these conditions with regard to the incremental response of the material.     

Sur une méthode de pénalisation tensorielle pour la résolution des équations de Navier–Stokes

An original reformulation of the viscous stress tensor is proposed for the motion equations dedicated to an incompressible fluid. Four different tensors appear in this decomposition, associated with viscosities of compression, elongation, shearing and rotation. This new model allows us to build a numerical solver of the Navier–Stokes equations based on a technique of tensorial penalization which is generalized with all the stresses acting on a flow. The processing of incompressibility and the rotation of a rigid body in a flow are described thanks to the model. Several numerical applications are proposed to illustrate the abilities of the new penalization method.     

Modèles discrets de structures tissées : Analyse de stabilité et de drapé

A discrete model of a woven fabric structure is established, whereby nodes endowed with a mass and a rotational rigidity are connected by rigid bars to form a two-dimensional truss. The set of four bars that delineate a quadrilateral area is further endowed with a torsion deformation mode. The kinematics of the truss reproduces the large rotations and displacements encountered for real tissues. The equilibrium shape of such a structure is obtained as the minimum of its total potential energy versus the whole set of kinematic translational and rotational variables, accounting for eventual kinematic constraints due to contact with a rigid surface by the Lagrange multipliers method. A stability analysis is conducted, and the potentiality of the model is illustrated by fabric draping simulations. To cite this article: B. Ben Boubaker et al., C. R. Mecanique 330 (2002) 871–877.     

Des modèles d'arcs élastiques suivant l'ordre de la courbure et les types de chargement

After reconsidering a classification of the homogeneous isotropic elastic arches, based on the curvature of the middle line, we determine a set of asymptotic models for each category of arch in terms of the assumptions made regarding the work of applied efforts.     

Modélisation du frottement pariétal dans un écoulement à bulles

In the present study, we propose a wall friction modeling in a vertical upward bubbly flow under the assumptions of bidimensional stationary and fully developed flow. This approach is based on the two-fluid model and on the hypothesis that the averaged flow is parallel to the wall. The turbulence modeling is an essential part in this model. Comparison with experimental data (presently available) exhibits satisfactory agreement. Other experimental studies, especially at a high void fraction, are desirable to examine further the model validity.     

Étude expérimentale et numérique de la convection thermomagnétique dans un fluide non électroconducteur

We present an experimental and numerical study of convection driven by a central heat source in a vertical and cylindrical cavity with a higth aspect ration, filled by air and submitted to the action of non homogeneous intence magnetic field. We show how the magnetization force applying on oxygene is able to intensify, reduce, stop or even reverse the natural convection fluid flow.     

Modélisation de l'effet de portance dans un écoulement à bulles

We propose here a lift coefficient modeling in a turbulent bubbly boundary layer under the assumption of bidimensional stationary and vertical upward fully developed flow. The basic frame of this approach is to consider that the volumetric flux of bubbles is composed of the convective flux by the liquid, the contribution by the gravitational field and those of the lift force and the bubble dispersion terms. A discussion of results completes this study.     

Mise en évidence par granularité en lumière blanche de phénomènes de multilocalisation de la déformation pour les bétons de poudres réactives sollicités en traction

From kinematic observations by granularity in whiting light mode based on a technique of digital speckle images correlation, the behaviour in tension of a reactive powders concrete is studied. The measures show several localisation areas of the deformation fields and the role of the fibres in the transmission of the stresses in the neighbourhood of a damaged area.     

Extension de la DRBEM à la propagation guidée en écoulement cisaillé

The present study aims to extend the Dual Reciprocity Boundary Element Method in order to solve acoustic wave propagation equations in the frequency domain for a parallel shear flow. The Linearized Euler Equations are written as a coupled pair of equations, which are second-order in terms of acoustic pressure and first-order in terms of normal acoustic velocity. Good agreement between numerical results and analytical solutions for a low Mach number shear flow (M<0.1) shows the interest of the method.     

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.