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Abstract: This paper investigates the instability of a viscoelastic fluid in a saturated porous medium heated from below and subjected to an horizontal through-flow. The Oldroyd-B constitutive equation is used to describe the viscoelastic behavior of diluted polymeric solutions. In the absence of the horizontal flow, the onset of convection can be characterized either by stationary or oscillatory instabilities. A temporal stability analysis is carried out in order to study the combined influence of the viscoelastic properties of the fluid and the main flow on the linear characteristics of these two types of instabilities. It is shown that the presence of the through-flow has a destabilizing effect and that it favors the emergence of mobile transverse rolls (R.T.), among an infinity of three-dimensional unstable modes. The thresholds for the appearance of these R.T., as well as their wavelengths and frequencies, are determined as functions of the dimensionless parameters of the problem. [Copyright &y& Elsevier]

The behaviour of dynamical systems is modified by the use of viscoelastic materials. In order to lead realistic complex eigenvalues analysis on dynamical systems, one need to model the behaviour of viscoelastic materials. The experiments show that the stiffness and the damping of such materials are frequency dependent. A large number of models often used are not able to describe this dependence; this is why the generalised Maxwell's model has been chosen. This paper describes a method based on modulus and angle curves to identify the parameters of this model. Between all the different formulations of generalized Maxwell, the pole-zero formulation is the most suited to lead the identification. However, some formulas allow to find the parameters of others formulations like the Prony one. The identification method presented here is based on the asymptotic curves of generalised Maxwell's model. This identification is led in two step, first parameters are initialised and second they are optimised. This method is confronted to others ones. If several viscoelastic materials have to be modelled in the same dynamical system, the size of the finite element model grows as quick as the number of poles. A way to reduce this size consists in constraining the poles to be equal for all materials. The method presented in this paper allows to perform the identification by taking this new constraint into account. [ABSTRACT FROM AUTHOR]

Abstract: In this Note, we prove a Carleman''s estimate for the integro-differential hyperbolic system of the viscoelasticity problem and we use this estimate to obtain a stability result for the inverse problem of recovering a viscoelastic coefficient from a unique internal measure. To cite this article: M. de Buhan, A. Osses, C. R. Acad. Sci. Paris, Ser. I 347 (2009). [Copyright &y& Elsevier]

Abstract: The main purpose of this Note is the development of a new integral Mv separating mixed mode fracture during a crack growth process in a viscoelastic media. The mathematical developments are based on conservative laws, the independent path integrals and the combination of real and virtual displacement fields inducing a bilinear form of the strain energy density. The uncoupling fracture mode is based on a generalization of the virtual work principle. The introduction of the viscoelastic behavior through an incremental formulation of the free energy allows the generalization of this path independent path integral. To cite this article: R. Moutou Pitti et al., C. R. Mecanique 335 (2007). [Copyright &y& Elsevier]

Abstract: The aim of the present Note is to differentiate the relative contributions of the aggregation and the percolation phenomena to the viscoelastic behaviour of composites. This separation is performed through the development of a micromechanical model, by taking into account the percolation concept. To cite this article: P. Mélé et al., C. R. Mecanique 333 (2005). [Copyright &y& Elsevier]