Wave propagation phenomena in anisotropic-viscoelastic tubes

Within the scope of the atherosclerosis project research is done on the genesis of this condition. Theimportance cf h-mc!yâmieal fâctûïs io the deveiopment of aineroscierotic lesions is generallyrecognised. Also with respect to the diagnostics of atherosclerotic disease, it is of great clinical interest togain insight in the complicated flow field in arteries and to investigate the influence of arterial mechanicalproperties on local flow phenomena.In this study a cylindrical-orthotropic tube showing nonlinear viscoelastic behaviour was developed. Themodel was made of EPDM rubber reinforced with lycra fibres. The rubber was viscoelastic and the fibresintroduced nonlinearity and anisotropy.The properties of the model were tested by means of wave propagation experiments. To determine theinfluence of the presence of the fibres on the propagation of the pressure pulse, identical experimentswere performed on an isotropic EPDM rubber tube and the results were confronted. Large differenceswere observed between the development of the pressure pulse in the two models. A change in the shapeof the pulse travelling in the anisotropic tube was clearly visible. During the propagation the steepness ofthe ascending slope of the pulse increased and the steepness of the descending slope decreased. Thevelocity of the pulse was not constant as in the isotropic model but decreased with travelling distance, dueto pressure attenuation. High frequent oscillations with large amplitudes probably caused by the Korotkoffeffect were observed.From the equation of motion of the wall of the tube and the fluid, an expression for the wave velocity in theanisotropic model was derived. The wave propagation experiments performed on the two tubes weresimulated by means of a linear quasi-one-dimensional model. The mathematical model gave an excellentdescription of the wave propagation in the isotropic tube but more or less failed to predict the propagationof the pulse in the anisotropic one.