Water conveyance are the lifeline of 3 billion people globally; however, these vital systems are aging and fraught with defects, such as leakages and blockages, due to physical and/or chemical processes. These defects result in wastage of energy and financial resources, reduction in carrying capacity, and increased potential for contamination. In order to conduct accurate leak detection, people should first understand the particular change induced by the leak inside out and then detect the leak using this particular information. In this dissertation, both of the above study are conducted. The understanding of the impact induced by the leak is called forward problem, while the detection of leak using the particular information induced by the leak is called inverse problem. The fo...[ Read more ]

Water conveyance are the lifeline of 3 billion people globally; however, these vital systems are aging and fraught with defects, such as leakages and blockages, due to physical and/or chemical processes. These defects result in wastage of energy and financial resources, reduction in carrying capacity, and increased potential for contamination. In order to conduct accurate leak detection, people should first understand the particular change induced by the leak inside out and then detect the leak using this particular information. In this dissertation, both of the above study are conducted. The understanding of the impact induced by the leak is called forward problem, while the detection of leak using the particular information induced by the leak is called inverse problem. The forward problem focuses on the impact of leak on the resonant frequencies of the pipeline. The inverse problem promotes an leak detection method, which is called arrival time imaging.

This analytical and numerical research investigates from a basic physics perspective of the leaks and the controversy regarding their effect on the system response function of the pipeline.

This research explores two distinct aspects: (i) it clarifies an complementary knowledge about the application of leak detection method based on system response function in the frequency domain; (ii) proposes a new defect detection approach based on the system response function in the time domain.

For the complementary knowledge on the application of the leakage detection based on system response function in frequency domain, the impact of a leak on the resonant frequencies is investigated. Trajectories of resonant frequencies in the wavenumber complex plane are studied with varying leak size. The variation in the system response function in the frequency domain and at system resonant frequencies is discussed. The key parameter representing the leak size and controlling trajectories of the resonant frequencies is the ratio of pipe impedance to leak impedance. It is found that, as the impedance ratio becomes greater than zero (i.e., no leak), each normal resonant mode shifts towards the upper half of the complex plane in response to a leak, where the imaginary part stands for the leak-induced damping of the wave. When the impedance ratio is less than the order of one, the leak-induced shift in the normal mode is negligible, which supports the theory put forward by proponents of the hypothesis that leak does not induce additional peaks to the frequency response function function (FRF). When the impedance ratio is of order one or larger, not only the shift in FRF’s peak is significant, but new peaks also appear, which supports the theory raised by proponents of the hypothesis that leak induce additional peaks to the FRF. Moreover, as the impedance ratio tends to infinity, the leak behaves as a reservoir where the pipe is fully open to the atmosphere. The analysis presented in this thesis provides insights into the signature of a leak on normal resonant modes of the pipeline ranging from small leak size to extremely large leak size, which clarify and resolve the previous controversy regarding the leak’s impact on the frequency response of the pipeline.

For the development of the new defect detection approach based on the system response function in time domain, an arrival time imaging (ATI) method is developed and presented that utilizes the reflection information of the transient wave, is proposed. This method translates the time-domain impulse response signal into a space domain objective function along the pipe, which is able to combine the information obtained from multiple sensors and helps visualize the defects more directly and accurately. A boundary reflection erasure technique is carried out, which helps obtain a clearer objective function from the influence of reflections at the pipe boundary. Numerical simulation shows that the proposed ATI method can estimate leakage/blockage in a noisy environment for signal-to-noise ratios (SNR) as low as -4 dB. It also shows that the ATI method is able to detect leakages and blockages (multiple defects) simultaneously without the need to model leakage or blockage. This method does not require the use of an accurate simulation model or a leak-free benchmark. Knowledge of the pipe topology, flow and roughness values, or the role of unsteady friction on the transient event is unnecessary.

The investigation of a leak’s impact on the normal resonant modes of the pipeline provides improved understanding of the leak mechanism in frequency domain and raises the potential for further improvements in frequency domain leak detection methods. The new method of multiple defect detection significantly improves the present time domain reflectometry method and is proved to increase the accuracy of defect detection predictions.