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Abstract
The effect of local drop of wall stiffness in pressurized waterways on the pressure wave speed and the wave attenuation during transients is investigated experimentally. A new signal-processing procedure to identify the presence of a weak reach is introduced and validated by physical experimentation based on assessing the pressure and vibration records acquired at both ends of a multi-reach steel test pipe. Water-hammer was generated by closing a downstream valve, whereas the weak reaches were simulated by replacing the steel portions with aluminium and PVC material. The wave speed and wave attenuation factor during transients are considered as global indicators of local and large changes in stiffness of the pipe wall. The method is capable of locating the stiffness weakness along the test pipe if one PVC reach is used. The error in estimating the position of such a reach relative to the real position of its mean value varies up to 23%.
Acknowledgements
The study is part of the research project HydroNet for the design, manufacture and operation of pumped storage plants funded by the Swiss Competence Center Energy and Mobility (CCEM-CH), the Swiss Electrical Research and the Swiss Office for Energy. The authors wish to acknowledge the financial support of the Lombardi Foundation and thank Prof. Didia Covas for her valuable comments during her stay at LCH-EPFL.