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Field measurement of water hammer and signal analysis at pump stop due to power failure in long watersupply pipeline |
LIU Mei-Qing, LIANG Xing, LIU Zhi-Yong, LIN Qi, WU Yuan-Wei |
(School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei 430072, China) |
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Abstract The method of maximum entropy estimation was applied to analyze the transient pressure, rotational speed and discharge signals which were measured and recorded in a pump station for a pump at pump stop caused from power failure and to identify their timefrequency features. Before that, the wavelet packet theory was used to denoise the measured signals. It was found that the main pollutant in the signals was the noises with a higher than 50 Hz frequency. Then, both the wavelet pocket method and the fast Fourier transform (FFT) were used to remove the pollution. At last, the simulated water hammer signals were compared with the measured ones denoised to confirm effect of the surge tank combined with air valves on water hammer prevention. The results show that even waveforms of the two denoised signals respectively by the wavelet pocket method and FFT are similar. The latter method considerably reduces the useful information in pressure peaks, while the wavelet packet theory can eliminate noises effectively and allow the denoised signal to have a similarity to the original one. A surge tank with airvalves takes a substantial effect on preventing from water hammer. The column separation model can correctly predict the maximum values of pressure, backflow discharge in a pipeline and the reverse rotational speed of pump. Those data provide evidence for pumping system safety assessment. Unfortunate, the existing models fails to accurately simulate the attenuation process of water hammer wave, thus more precise models are needed.
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Received: 19 October 2011
Published: 13 April 2012
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