Relevance of pipe period on Kelvin-Voigt viscoelastic parameters: 1D and 2D inverse transient analysis

This paper presents the results of the calibration by means of a microgenetic algorithm, using Kelvin-Voigt viscoelastic param- eters, to reproduce experimental unsteady flow tests in a polymeric pipe. During the tests, different pipe lengths—which give rise to different periods of the pressure oscillations—and initial discharges have been considered. The mechanical parameters of the viscoelastic models are estimated using both one-dimensional (1D) and quasi two-dimensional (2D) models. The calibration of Kelvin-Voigt models with 2, 3, 5, and 7 parameters, respectively, proves the substantial independence of the elastic modulus and the dependence of the retardation time on the pipe period (i.e., the pipe length). Moreover, in most cases, the increase in the number of mechanical parameters allows a better simulation of a single transient. However, the larger the number of parameters, the greater the risk of overfitting, and the more difficult the search for general laws of dependence of the parameters on the characteristics of the pipe—primarily of the retardation time on the period of the pressure oscillations.