Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics最新文献

The present note describes work related to anisotropy of acoustical properties of felt materials being compressed with a rate $\text{n}$ varying from 1 to 4. Following a recent note [1], it is shown that such compression induces some anisotropy, which is small but still significant, clearly visible on the elliptical shape of the tortuosity spatial distribution, and also on the Brewster angle shifts, which are predictible. Some fine experimental studies of the reflection coefficient versus the angle of incidence have been performed and discussed.

The onset of Soret-driven convection in an infinite cell filled with a porous medium saturated by a binary fluid is studied. The impermeable horizontal walls are maintained at different and uniform temperatures. For a cell heated from below, the motionless solution loses its stability via a stationary bifurcation when the separation ratio $\text{ψ}$ is higher than a Lewis and normalized porosity dependent value $\text{ψ}{}_0$; for $\text{ψ<ψ}{}_0$, it loses its stability via a Hopf bifurcation. For a cell heated from above, the motionless solution is infinitely linearly stable if $\text{ψ>0}$, while a stationary bifurcation occurs if $\text{ψ<0}$. These results are widely corroborated by direct numerical simulations.

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.

A micromechanical analysis of brittle damage is proposed. This analysis consists of a 3-D generalization of the study performed by Andrieux et al. In this approach, the macroscopic free energy for open microcracks and frictionless closed microcracks is built. The conditions for unilateral contact (opening/closure criterion, elastic moduli recovery) are also presented. The proposed construction ensures at the macroscopic level the symmetry of the elastic stiffness tensor and the continuity of stress at the damage deactivation.

We propose an improvement of the bolus passive viscoelastic wall model [1], by adding an active muscular layer situated on the internal side of the wall. This new model permits, for a suitable choice of the active force, to obtain analytically a closed bolus on its two ends and to get a close approach of the medical observations.

In this note we discuss the application of a methodology combining distributed Lagrange multiplier based fictitious domain techniques, finite element approximations and operator splitting, to the numerical simulation of the motion of an elliptic body falling in a Newtonian incompressible viscous fluid. The motion of the body is driven by the hydrodynamical forces and gravity. As qualitatively expected, the elliptic body rotates so that its broad side tends to be perpendicular to the flow direction.

A new nonparametric probabilistic approach is presented for modeling random uncertainties in transient linear elastodynamics. The information used does not require a description of the local parameters of the mechanical model. The probability model is constructed in the generalized coordinates associated with the elastic eigenmodes. The available information is constituted of the algebraic properties of the generalized mass, damping and stiffness matrices which have to be positive-definite symmetric matrices, and the knowledge of these matrices for the mean reduced matrix model. The convergence of the stochastic solution with respect to the dimension of the random reduced matrix model is analysed.

The three-dimensional perturbation of a Blasius boundary layer induced by a small hump (or a trough) placed at the wall is studied for a Reynolds number going to infinity. For certain dimensions of the hump, a four deck structure is obtained. The main features of this structure are described.

We suggest a new expression of the scattering kernel for a polyatomic gas lying in the Knudsen layer when impinging on the wall. We consider a vibrational strong non-equilibrium case for the gas. The global scatterring kernel is a linear combination of partial operators describing the reflection of the various mode of energy. The scattering kernel allows to write a consistent boundary condition for the kinetic equation of polyatomic molecules.

We study the initial-boundary value problem for a system of quasilinear equations of one-dimensional nonlinear thermoviscoelasticity with rapidly oscillating nonsmooth coefficients and initial data. We rigorously justify the passage to the corresponding limit initial-boundary value problem for a system of two-scale homogenized integro-differential equations, including the existence theorem for the limit problem. The results are global with respect to the time interval and the data.