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

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.

In a fluid flow, fields are measurable up to a cut-off scale at which they are regularized. We show that, for a smooth velocity field, this regularization adds to the advection equation a diffusive term proportional to the strain tensor. We study in two dimensions its effect on the dynamics of velocity and vorticity, and on the conservation of quadratic invariants. Vorticity and energy are still conserved, while enstrophy and tracer variance are dissipated depending on the flow topology. These properties (conservation, dissipation, spatial selectivity) suggest the use of this selective strain–diffusion operator for numerical simulations of inhomogeneous flows in the quasi-two-dimensional approximation.

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.

The void defects present in composite parts are due to air entrapped during the injection process. We propose to use electrical conductivity measurements of the liquid to detect these defects. The saturation rate of the resin is measured as a function of time. Thanks to several sensors, placed along the mould, we are able to plot the resin front profile evolution versus the position. This method is a step forward in our knowledge of the parameter range for which no void is observed at the end of the injection.

The first and second moments of the strain (or stress) fields predicted by the classical and modified secant extensions of the self-consistent model in isotropic mixtures of isotropic incompressible power-law phases are shown to be identical if the same macroscopic strain (or stress) is applied. This proves directly that the modified extension does predict a softer overall behavior for such composites.

In order to study the evolution of damage in a delaminated structure, the assemblage of plates is considered under dynamic loading. Using a general result of the thermodynamic coupling approach, with the Hamiltonian formulation in the general case, the energy release rate associated with the propagation of the delamination is presented as a heat source.

The reinforcement of a 3D structure with composite panels is considered. The behaviour of those panels are to be optimized considering the external loading of the 3D structure. The study is within the framework of anisotropic linear elasticity. The 3D model takes into account the rigidity induced by Kirchhoff–Love plate reinforcement. An optimization of the behavior characteristics of the composite reinforcement (density and orientation of fibers at each point) is presented.

We examine the elimination of the Mach waves radiated by a supersonic jet by the addition of a secondary coaxial jet. The noise prediction is based on a numerical solution of the RANS (Reynolds Averaged Navier–Stokes) equations closed by a turbulence model, and a statistical description of acoustic sources. This method allows us to numerically reproduce results obtained in recent experiments where the aim was to find the mean flow configuration that minimizes acoustic radiation.

Passive control of the flow behind a bluff-body is obtained by integrating porous area on the body. The penalisation method is used to modelize the flow in three different media. In fact each medium can be considered as a porous medium. The fluid is identified as a porous medium of infinite permeability and the solid is identified as a porous medium of zero permeability. This way, it is easy to compute the flow in each medium using the same parameter. Some benefical effects are due to the porous interface: the flow is smoothed, and the enstrophy and drag are significantly reduced.

A weakly nonlinear analysis of cellular detonations at onset of the instability against transverse disturbances is carried out in the Newtonian limit at strong overdrive. A nonlinear integral-differential equation describing the formation of cusps representative of Mach-stems on the detonation front is obtained as an asymptotic solution of the reactive Euler equations. A numerical study of this equation exhibits patterns that are similar to the cellular structures observed experimentally in gaseous detonation waves.