Locating leaks in underground water pipes using the complex cepstrum

Abstract

It is possible to detect the presence of leaks in underground water pipes by measuring, at remote locations such as hydrants, the noise or vibration caused by the leak. The time delay of the leak noise reaching the different sensors can be computed using the cross correlation, and with knowledge of the wave-speed in the pipe, the location of the leak may be pinpointed. This paper presents a new technique for leak detection that employs the cepstrum, rather than the cross correlation, for estimation of the delay time. The delay time manifests as a series of peaks in the cepstrum, rather than a single peak in the correlation, allowing a more robust estimate. A number of cepstrum formulations are presented that are derived from correlation estimators, and it is found that the time delay information is actually contained in the phase component of the cross spectrum. Based on this, a phase cepstrum estimator is developed.

Keywords:

• Leaks
• underground water pipes
• cepstrum
• cross correlation

Additional information

Notes on contributors

D Hanson

Dr David Hanson is a test and analysis engineer with the Dynamics Group at Sinclair Knight Merz. He joined the group in 2006 after completing a PhD in Operational Modal Analysis at the University of New South Wales. David had previously completed an undergraduate degree in Mechanical Engineering at the University of Newcastle while working as a cadet engineer for United Goninan (now United Group Limited – Rail). He is the author or co-author of 15 papers in the fields of operational modal analysis, rail vehicle dynamics, underwater acoustics and mechanical applications of signal processing.

R B Randall

Bob Randall is a visiting Emeritus Professor in the School of Mechanical and Manufacturing Engineering at the University of New South Wales, Sydney, which he joined as a Senior Lecturer in 1988. Prior to that, he worked for the Danish company Bruel & Kjaer for 17 years, after 10 years experience in the chemical and rubber industries in Australia, Canada and Sweden. He was promoted to Associate Professor in 1996 and to Professor in 2001. He has degrees in Mechanical Engineering and Arts (Mathematics, Swedish) from the universities of Adelaide and Melbourne, respectively. He is the invited author of chapters on vibration measurement and analysis in a number of handbooks and encyclopaedias, and a member of the editorial boards of two journals including Mechanical Systems and Signal Processing. He is the author of more than 150 papers in the fields of vibration analysis and machine diagnostics, and has successfully supervised 12 PhD and three Masters projects in those areas.

G Brown

Dr Graham Brown is the leader of the Dynamics Group at Sinclair Knight Merz. The group consults globally on noise, vibration, fatigue, finite element analysis and computational fluid dynamics. Graham has over 12 years experience in the fields of noise and vibration modelling and control, including stints with Ford Australia in the Vehicle Refinement and Dynamics Group and with Bishop Austrans as a noise and vibration specialist.

Graham has a degree in Mechanical Engineering from the University of Technology of Sydney, and a Masters and PhD from the University of New South Wales. He has authored or co-authored more than 10 papers and his current research interests include rolling noise, noise and vibration control, rail regenerated noise and vibration, and stadium dynamics.

R Emslie

Ross Emslie is a Mechanical Engineer with 27 years of consulting experience in structural dynamics, noise, vibration and fatigue. He is Fellow of Engineers Australia, and a member of the Australian Acoustical Society and American Society of Mechanical Engineers.

Ross joined Sinclair Knight Merz in 1990 as Engineering Manager of the Structural Dynamics Group. He was appointed Manager of the Structural Dynamics Group in 1993 and a company Principal in 1995. In 2007 Ross was appointed Practice Leader – Vibration Dynamics and Fatigue, which is a corporate role with responsibilities for the technical quality of SKM’s services in these disciplines.

Ross has managed the resources and technical quality of over 300 studies relating to finite element analysis, fatigue, noise, vibration and forensic engineering for a wide range of industrial structures and machines. He is the author or coauthor of more than 30 papers encompassing not only these areas of technical proficiency, but also graduate development and leadership.