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The paper provides a detailed analysis of the current state of the problem. A mathematical model is presented to determine the dynamic behavior of earth dams, considering the viscoelastic properties of soil, using the hereditary Boltzmann-Volterra theory with the A.R. Rzhanitsyn kernel under periodic kinematic impacts. To solve the problems considered, the finite element method and complex arithmetics were used to reduce integrodifferential equations to a high-order complex algebraic equation. The accuracy of the methods was verified by solving test problems. Steadystate forced vibrations of the Pskem earth dam 195 m high are studied considering the real geometry and soil properties under resonant vibration modes. It was stated that the largest stress amplitudes in the body of the dam occur not only under the first resonance, but they can occur under other dense spectra of the eigenfrequencies of the dam, due to the interaction between close natural modes of vibration. The strength of various sections of the dam body was tested under kinematic impact using the Coulomb- Mohr theory of strength; the most dangerous sections of the dam were identified in terms of the highest stress.

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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]

A visco-elastic model for polymeric foams under cyclic compression. A block of polyurethane foam subject to cyclic compression exhibits a softening phenomenon as the number of cycles increases. In particular, one observes a stepping down of the loading curves while the unloading curves remain the same. In tests performed by the authors, it has been observed a partial recovery of the initial stiffness after a resting period was observed. This behaviour can be described as a long memory effect. We propose a viscoelastic model, coupling a non convex energy with a dissipation of viscous type. The model is in a good qualitative agreement with the experiments. [ABSTRACT FROM AUTHOR]

In this paper, the possibility of reducing pressure surges in a quasi-rigid pipe network by replacing one of the pipes of the network by a viscoelastic one is examined. The mathematical model consists of a system of two hyperbolic, partial differential equations which are resolved by the method of characteristics using linear interpolation. The calculation at the network junctions is realised by resolving a linear system of equations including the manner various boundary conditions are introduced into the solution. The behaviour law of the viscoelastic pipe is described by the Kelvin-Voigt model. In order to simplify calculations, only the elastic element of this model is considered. For the applications, a constructed computer progrmn written in FORTRAN language is elaborated. The numerical results show the effect of the pipe wall elasticity on the damping of the pressure waves in the networks. [ABSTRACT FROM AUTHOR]

The interaction between a flowing fluid and the transmission mains is in relation with the applied pressure level as well as the sought structure lifetime. The numerical approach developed in this study is based on a global modeling of the fluid and the deformation of the duct under transient conditions. The viscous tangential stress is expressed using a mixed polynomial development representing the variation of the radial profile of the fluid speed. The resolution of the obtained system of equations is carried out using the method of the characteristics coupled with the finite differences method. In the case of a Newtonian fluid, the results were compared to the experimental data of Holmboe and the theoretical ones of Zielke. This comparison allowed confirming the validity of the adopted calculation scheme. An extension of calculations in a similar way was carried out for the same installation in the case of a linear viscoelastic fluid. [ABSTRACT FROM AUTHOR]