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

This work deals with transient laminar boundary layer along a vertical surface and system of equations is solved using finite difference implicite scheme. We show that the nature of the plate influence thermal and dynamical boundary layer thicknesses as well as the flow velocity. Moreover, we observe that a small perturbation of the velocity implies to flow laminar instabilities.

In this paper, different vortex diagnostic methods are compared to obtain a better understanding of boundary layer influence on the transport of vortical structures involving a complete analysis of vorticity, the Vorticity Threshold Criterion (VTC), and the Weiss Criterion (WC). These three techniques are basically confronted to find a suitable understanding of all flow characteristics for a range of laminar to transitional Reynolds numbers. The computations on this dihedral plane are done using a 2D DNS method. The Weiss criterion, coming from the analysis of the incompressible Euler equations is validated and applied to low speed compressible flows (Mach number=0.2).

This work describes the mechanisms involved in the critical detonation transmission from a cylindrical tube into a half space through an annular orifice around a central obstacle. The numerical simulation reproduces faithfully the experimental observations and can be used as a predictive tool.

Insights and additionnal clarifications concerning the energy diffusion model [4] are in concern herein. We showed in former times under steady state conditions, that the diffusion model is well suited for an uncorrelated plane wave dynamics [7], energy behaviour modelling. We will prove, in this short note, that the later is not enough when transient dynamics is in concern. We thus propose a new equation alternative to the diffusion equation.

The expressions of the intraphase second moments of stress and strain in heterogeneous linear thermoelastic materials are derived; they are used to quantify the intraphase heterogeneity predicted by the ‘classical affine’ formulation for the homogenization of nonlinear composites. By analogy with the ‘modified secant’ approach, a ‘modified affine’ formulation that accounts for intraphase heterogeneity is proposed.

The optimal control theory is used to study the asymptotic behavior of elastoviscoplastic structures under cyclic loading. With this approach the asymptotic state is solution of a minimization problem. For practical applications an approximate problem is introduced consistently with a spatial discretization. In this framework, the only stationary points of the functional to minimize are the global minima.

An original mixed finite element well suited to stress intensity factor extraction in 3D composite structures is proposed in this study. A numerical example of insert/sandwich junction illustrates the approach.

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.

The stress wave generated by a nonpenetrating impact on the thorax is likely to cause severe injury to the lung. Theoretical studies are necessary to help the understanding of injury mechanisms. Within the framework of elastodynamics, we study the transmission of a wave at the interface between two weakly coupled semi-infinite media representing the thoracic wall and the lung. By using an appropriate method, we describe the distribution of energy carried by the shear and pressure waves in the medium representing the lung. These results should contribute to a better interpretation of the experimental results.

The main aspects of wood mechanics are approached through the role played by wood as the building material of the tree. The main concepts used by nature: progressive setting up of tree weight and architecture, multifunctional role of wood and adaptability to hazard and long-term evolution, are clarified together with their consequence on the multilayered, anisotropic nature of wood. The technological choices of the plant world as the cellular structure, the use of composite with oriented fibres and hydro-carbonated polymers, as well as the systematic prestressing of every new layer, bear obvious consequences on the type of mechanical behaviour of wood. The local control of the level of prestressing through minor modifications of the cell-wall biosynthesis allows the tree to adapt to conditions of light exploration that will evolve according to time and risk occurrence. This analysis of wood genesis process permits in return to improve our understanding of the mechanical behaviour of the material in relation with the parameters of the microstructure.