The dynamic effect of pipe-wall viscoelasticity in hydraulic transients. Part II - model development, calibration and verification

A state-of-the-art mathematical model has been developed to calculate hydraulic transients in pressurized polyethylene WE) pipe systems. This hydraulic transient solver (HTS) incorporates additional terms to take into account unsteady friction and pipe-wall viscoelasticity. Numerical results obtained were compared with the classic waterharnmer solution and with experimental data collected from a PE pipe-rig at Imperial College (London, UK). Unlike the classical model, the developed HTS is capable of accurately predicting transient pressure fluctuations in PE pipes, as well as circumferential strains in the pipe-wall. The major challenge was the distinction between frictional and mechanical dynamic effects. First. the HTS was calibrated and tested considering these two effects separately: if only unsteady friction was considered. a major disagreement between collected data and numerical results was observed; when only the viscoelastic effect was considered, despite the good agreement between data and numerical results, the calibrated creep function depended on the initial flow rate. In a second stage. the combination of these dynamic effects was analysed: creep was calibrated for laminar flow and used to test the solver for turbulent conditions. and a good agreement was observed. Finally, the HTS was tested using creep measured in a mechanical test, neglecting unsteady friction, and a good agreement was obtained.