This research aims to model the dynamic viscoelastic effects of polyethylene pipes under waterhammer pressures. As known, following the water hammer event, a cyclic loading and unloading due to the pressure fluctuations occurs. Loading on polymeric materials results in deformations that unlike the elastic materials do not immediately return after unloading. This retarded behaviour gradually reduces the wave speed causing to a different transient response. Herein, the viscoelastic effects of polyethylene pipes on the transient flow is numerically simulated and studied using the Kelvin-Voigt model. The developed model is then verified using some experimental data from the literature. Afterwards, a simple hypothetical reservoir-pipe-valve system is defined to investigate several aspects of viscoelasticity. It is concluded that in a standard water hammer caused by valve closure, the minimum pressure head is more affected by viscoelasticity than the maximum one. Furthermore, with the increase of initial flow, viscoelasticity takes part more to damp out the destructive dynamic effects of water hammer. This makes the viscoelastic properties of polyethylene pipes to be figured out as an adaptive procedure to automatically alleviate the water hammer issues in water supply systems.
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