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 parameters,to reproduce experimental unsteady flow tests in a polymeric pipe. During the tests, different pipe lengths—which give rise to differentperiods of the pressure oscillations—and initial discharges have been considered. The mechanical parameters of the viscoelastic models areestimated using both one-dimensional (1D) and quasi two-dimensional (2D) models. The calibration of Kelvin-Voigt models with 2, 3, 5, and7 parameters, respectively, proves the substantial independence of the elastic modulus and the dependence of the retardation time on the pipeperiod (i.e., the pipe length). Moreover, in most cases, the increase in the number of mechanical parameters allows a better simulation of asingle transient. However, the larger the number of parameters, the greater the risk of overfitting, and the more difficult the search for generallaws of dependence of the parameters on the characteristics of the pipe—primarily of the retardation time on the period of the pressureoscillations.