Simulation of Water Hammer in Viscoelastic Pipes. (Dept. M.)

Abstract

The mechanical behavior of the pipe material affects the pressure response of a fluid system during water hammer. In viscoelastic pipes, the pressure fluctuations are rapidly attenuated, and the pressure wave is delayed in time. This is due the retarded deformation of the pipe -wall. In this work, a mathematical model to simulate water hammer in viscoelastic pipes taking into account the viscoelastic behavior of pipe walls, applying the Kelvin- Voigt model, has been developed. The developed model was solved using the method of characteristics (MOC), neglecting fluid-structure interactions (FSI) and unsteady friction effects. The model results were tested against the experimental results obtained by Covas et al. [1[, which carried out on a high-density polyethylene (HDPE) pipe-rig at Imperial college, London. The effects of time step and wave speed were studied. The pressure fluctuation obtained with the proposed viscoelastic model showed a good agreement with the experimental results. Conversely, the pressure obtained by the elastic model solution showed a large discrepancy with the experimental and numerical data. The time step affected the pressure-head wave amplitude and frequency, while wave speed affected only the wave frequency. The best results were obtained at higher time step values, corresponding to a Courant number ranging from 0.983 to unity, as the average amplitude and frequency of the numerical solution are 96%and 95.1% of their corresponding values for the experimental results, respectively. The best wave speed was at about 388.7 m/s.