Plastic material pipes such as high- or low-density polyethylene (HDPE or LDPE) are increasingly used in new or renewed water supply systems. Therefore, analysis of water hammer surge-waves initiated into such piping systems deserves investigation. The 1-D pressurized-pipe flow model embedding the Ramos formulation was used to describe the flow behavior in the elastic and plastic pipe-based hydraulic system. Numerical computations were performed using the method of characteristics. First, the numerical solver was validated against experimental data, available from the literature. Then, the proposed solver was applied to explore the transient pressure-wave behavior resulting from the power failure to a pumping station. Results evidenced the severity of such a scenario with regards to induced positive and negative pressure-wave magnitudes. Furthermore, the findings of this study suggested that plastic pipe-wall materials allowed a significant attenuation of pressure-wave magnitude in conjunction with the expansion of the pressure-wave oscillation period. It was also found that the observed attenuation and expansion effects depended strongly upon the plastic material type. In this respect, the results revealed that LDPE provided a better trade-off between the two last effects than HDPE.
The present study analyzes the effect of the pipe material type on the transient flow behavior in a pumping system due to an accidental pump shutdown. The material types addressed in this study include steel and High- or Low-Density PolyEthylene (HDPE) or (LDPE); involving elastic and plastic rheological pipe-wall behavior. The numerical solution is developed basing on the Method Of Characteristics used for the discretization of the Extended One-Dimensional pressurized-pipe flow model, incorporating the Kelvin-Voigt and Vitkovsky rules. Experimental data from the literature were used to validate the numerical solver. The proposed numerical algorithm is then used to investigate the transient pressure-wave behavior induced by the power failure to a pumping station composed of an inline connection using different pipe material types. The findings show the severity of such a scenario, in terms of the magnitudes of induced up-surge and down-surge pressure-waves. Furthermore, this research demonstrates that plastic pipe-wall materials allow for substantial attenuation of surge magnitude in conjunction with the expansion of the period of pressure-wave oscillations. The observed attenuation and expansion effects are also found to be highly dependent on the plastic material type. In this respect, the findings indicate that the (LDPE-Steel) piping system's specific layout allows for the best tradeoff between the two last effects.
This study outlines a methodology to inspect the resonant characteristics of in-series-pipes hydraulic systems. The numerical model is based on the impedance approach, assuming the sinusoidal fluctuations of flow-rate and pressure parameters, in conjunction with the Transfert Matrix concept, being implemented for automatic calculations within a complex piping systems framework. To verify the validity of the used numerical technique, the computed results were compared with a conventional numerical solution quoted in the literature. Applications address the free and forced vibration cases occurring into an in-series-pipes system. The free vibration case, is caused by an oscillating valve downstream with a constant level tank upstream; while the forced vibration case is caused by the closure of a turbine downstream. The obtained results show the reliability of the proposed numerical procedure to determine the natural frequencies of a complex in-series hydraulic system. However, this study unveils that the “equivalent pipe” concept is not accurate for analyzing the resonating behavior of a complex in-series pipe system.
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