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

We consider the control of mechanical systems based on sliding mode control techniques. Recently developed simplex control methods are shown to converge in a finite time when applied to nonlinear systems under bounded deterministic uncertainty. Applications are considered to the control of mechanical systems in which the control action is provided by monodirectional devices.

Infrared thermography observations permit to show thermal phenomena occurring on a plain concrete during a compressive test. A modelling of the thermomechanical behaviour of this materials is proposed as an extension of M. Frémond and B. Nedjar's model. It permits an interesting dialog between the experimental results and those obtained by a numerical simulation of a simple compressive test.

A new method based on the flux conservation for acoustic computations in unbounded domain is presented. The domain is divided in outer and inner regions by a fictitious boundary. The inner problem is solved by a control volume finite element method while the outer flow is treated with a boundary element method. The coupling of the two sub-domains is performed using an appropriate expression for the outgoing fluxes satisfying the Sommerfeld condition. A two-dimensional configuration with a circular interface is considered to show that the method is effective. Results of this method are compared to an analytical solution and to results from the literature.

A multi-particle model called M4-5n is proposed for the study of multi-layers having elastic and inelastic strains in the layers and non-continuous displacements at the interfaces between layers. We use Hellinger–Reissner's variational formulation to set up the model. Inelastic fields are supposed to be known in the modelling.

The stability of a free shear layer, with one-directional velocity field, is addressed. The studied configuration is a special case among the quasi-two-dimensional motions, induced in an electro-conducting and incompressible fluid by a strong magnetic field, superimposed to electric current. The limit of unconditional stability of the shear flow is computed. When the electric current is under the threshold, every deviation from the basic state is monotonically damped. The result holds without any restriction, connected with the size of the perturbations. Patterns set on just above the unconditional stability limit, in the form of small vortices, on the slow side of the shear layer.

It is shown in a very simple manner how any bulk modulus and any conductivity of isotropic two-phase composites located between the Hashin and Shtrikman bounds can be realized exactly by suitable microstructures. The latter are assemblages of two types of composite spheres.

This work deals with the determination of a general formulation of the Hamiltonian approach applicable to an arbitrary distribution of vorticity. The numerical results display the importance of the respect of the laws of conservation. A model which guarantees the respect of them is presented.

To ensure the exit of vortices from an open computational domain, new boundary conditions for compressible Navier–Stokes equations, called ‘absorbing conditions’, are introduced. They use a layer around computational domain which eliminates nonphysical perturbations. They are compared to three kinds of boundary conditions based on characteristic relations. Computations of two test cases show the best behaviours of the new boundary conditions. These last ones involve a very small perturbation and can be used to solve aeroacoustic problems.

Like most of the alloys containing shearable precipitates, the under-aged Waspaloy hardens in low-cycle fatigue to a maximum stress and presents a subsequent softening period. Although this phenomenon is known to be due to repeated precipitate shearing by dislocations, the softening corresponds to a decrease of the kinematic hardening. Microscopic observations lead to understand the physical origin of the softening and the importance of the reversibility.