Numerical Modelling of TransientFlow in Viscoelastic Pipe Network

The present research deals with the introduction and simulation of viscoelastic effects in transient flows in polymeric pipes widely used in pipe network. The viscoelastic properties result in appearing newterms in transient flow governing equations which are generally absent in available models. In this study, the governing equations are rewritten and manipulated for considering the viscoelastic properties. The equations are then solved using the method ofcharacteristics coupled with the finite difference method. In order to calibrate the unknown parameters including the unsteady friction and creep coefficients as well as to verify the model, a model of viscoelastic pipe network was made at the hydraulics laboratory of Water Sciences Engineering department of Shahid Chamran University. The configuration of the experimental set-up consists of a pipe network with six square loops, having each loop 3m×3m. The pipes are made of PE with 50 mm nominal diameter and 5.5 mm of wall thickness. The data of dynamic pressure oscillation during these transient events were collected by Pressure transducers. Appling the inverse transient analysis method and with the aid of a genetic algorithm, the friction and creep coefficients of the experimental pipe are determined. The results show that the classical water hammer solver cannot accurately analyze the transient flows in polyethylene pipes. In fact, modeling both dynamic effects of unsteady friction losses and viscoelasticity for such pipes is quite necessary. However, it is also found that the viscoelasticity is obviously more effective than the unsteady friction effects in formation and attenuation of transient signals so that, considering onlyviscoelastic effects would result in acceptable responses.