Viscoelastic models for the simulation of transients in polymeric pipes

In this paper simple viscoelastic models are implemented to assess their reliability in the simulation of transients in polymeric pipes. Two approaches are followed, i.e. the combination of elastic and viscous elements based on ordinary derivatives, and the use of fractional elements, based on fractional derivatives. The implementation of the viscoelastic component in an efficient numerical model, based on the frequency domain integration, allows the direct scrutiny of the optimization function used in the calibration and provides some general remarks about the viscoelastic parameter estimation. The numerical simulations are compared with the experimental data acquired during transient tests with pipes made of high density polyethylene (HDPE) and oriented polyvinyl chloride (PVC-O). The results show that the convergence toward the optimal solution depends in a different manner on the model parameters. The fractional model performs better than the others, although further studies are needed to verify its reliability and efficiency.