Combining transient and steady-state methods for acoustic leak detection

Abstract

This thesis is concerned with the improvement of acoustic leak detection methods. While acoustic methods have been successfully used for detecting and locating leaks in metallic water pipes, they are generally less effective in plastic pipes due to the higher attenuation of acoustic waves in plastic pipes. Another motivation for the research is the need to fully utilise data acquired by monitoring devices installed in water distribution networks, for which existing acoustic methods are inadequate. Three specific problems associated with the application of existing acoustic methods are addressed in this thesis: long time required for identification of leaks, inaccurate leak localisation due to uncertainties in wave speed values, and non-robust time delay estimation (TDE). To deal with the first two issues, new transient and steady-state methods are developed by considering the acoustic leak detection problem from alternative perspectives, including transient/signal detection, multipath identification, and system identification. Transient methods are based on detecting and processing acoustic transients, while steady-state methods analyse signals generated by an ongoing leak. To facilitate transient analysis, a procedure for detecting, locating, and assessing the nature of acoustic transients is developed based on a change metric known as non-stationarity measure (NSM). An approach that combines multiple acoustic transient and steady-state methods is also developed. Alternative methodologies based on wavelet transforms, data-adaptive decompositions, and cepstral analysis are proposed for estimating time delays in leak signals. Also, new approaches for assessing accuracy of the time delay estimate are developed by exploiting the statistical properties of the cross-correlation function (CCF).
The alternative methods developed in this work offer practical benefits over existing methods. Application of transient/signal detection principles reduces the time required to detect the presence of a leak. The methods based on the multipath identification and system identification viewpoints do not require a priori knowledge of pipe material properties or wave speed to locate the leak. The synergy of methods in the combined approach ensures more reliable acoustic leak detection in a ‘self-contained’ manner, as essential leak detection tasks can be executed directly from measured leak signals without need for ‘third-party’ data or additional measurements. Unlike the commonly used generalised cross-correlation (GCC) methods, the alternative TDE methods proposed in this work do not require signals to be first filtered prior to estimating the time delay. Moreover, the new quality assessment metrics developed in this work provide a simple means to infer the accuracy of the time delay estimate as well as to select best parameters required for accurate TDE results. These new methods allow for fuller utilisation of data than is possible with currently employed acoustic methods. This is especially relevant considering the current drive towards massive deployment of transient loggers by water companies. A laboratory leakage test rig was designed and built specifically for the experimental investigation of the proposed methods.

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Identifiers

ORCID for Ndubuisi Uchendu: orcid.org/0000-0002-4199-5839

ORCID for Paul White: orcid.org/0000-0002-4787-8713

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