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

An experimental device enabling to study the rheological behaviour of setting heterogeneous materials is first presented. Measurements are achieved by means of vibration tests using acoustic waves at low frequency (100 Hz–1 kHz). The results are presented for different mixtures of water-granulates-binders and gas bubbles: mortar and cellular concrete (different formulations). From the measurements of celerity and damping coefficients, various analyses led to quantify the evolution of the complex œdometric modulus of the material and the viscoelastic modulus of the interbubble matrix.

The Selendia simulation software dedicated for diesel engines is presented. Based on the filling and emptying method, it calculates the evolution of the engine and turbocharger rotation speed and the temperature and the pressure in different control volumes (manifolds, cylinders) during the dynamic operations of the engine. Its application to a sequentially turbocharged engine leads to the optimisation of the turbocharging system characteristics such as the time lag between the opening of the air and gas valves. Its predictive capacities permit to test by simulation the performances of a new engine and then to guide the engine designers.

We investigate the problem of optimizing the composition profile of a functionally graded interlayer inserted between a metallic tube and a ceramic coating so as to alleviate the thermal stresses occurring at the metal–ceramic interface. The optimization problem is set in the framework of optimal control and discretized using the direct transcription method. An application of the proposed approach shows (1) that as expected, functionally graded materials can be effective stress relievers by allowing gradual transitions between dissimilar materials and (2) that a stress-minimizer transition is not necessarily continuous.

A two-scale model for the wave equation with periodic coefficients is formulated. It has been derived using an asymptotic method based on a two-scale convergence and on the Bloch waves decomposition. The homogenized wave equation and the Bloch waves expansion are particular cases of this new formulation.

The aim of the present paper is to study the influence of the n -index in the porosity function of Richardson–Zaki on the heterogeneous behaviour in a fluidized bed. This parameter takes into account the group effect of particles on the drag of an isolated particle. We have shown up different behaviours of the bed when changing its value.

A methodology for the analysis of the mechanical behaviour of beams is presented, which relies on the lemma of stroboscopy. This problem traces back to Euler's work. Starting from a discrete model of the shape of the beam, stroboscopy enables us to built a continuous model for the variation of the angular position along the corrugated beam. The angular position is characterised as the solution of a differential equation. The main originality of the work is the study of buckling conditions of corrugated beams.

The ternary mixture `dry air–water vapor–liquid water' is a statically stable medium in general. This property is a consequence of the great number of physical properties of the medium, such as double diffusivity, heterogeneous medium equation of state, and equilibrium of saturation. Convective instability in that medium can be modelled with the help of a Rayleigh number Ra and a moist Rayleigh number Rh . In this paper, we establish necessary conditions for appearance of the instability for a given static distribution of temperature and water vapor concentration, with respect to physical characteristics of the medium. In particular, regimes of stationary instability (`moisture fingers') can exist, even if the dry medium is statically stable.

This article deals with the explanation of pressure fluctuations coupling between riser and plenum in a gas fluidized bed. It has been noticed by former experiments that the pressure fluctuations taking place in the riser due to bubbles eruptions is also observed underneath the distributor, in the plenum (also called windbow) under certain conditions. In order to explain how effective is the coupling depending on the bed and air distributor design but also on the flow characteristics, we have developped a simple model associated to an experiment presented hereunder.

The double overlap joint subjected to tensile loading is a well-known experimental setup. Within the brittle fracture mechanics, rewritten for a simplified model of adhesively bonded joint, we calculate the energy release rate for delamination and we deduce a parametric study for three configurations given by the asymptotic analysis.