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Over the years, anomaly detection of fluid pipes has been a focus of water authorities as well as oil and gas operators to advance the operation and management of these mechanical systems. This paper presents a comprehensive review on the development and application of transient wave-based methods for the detection of different anomalies in fluid pipes. A brief introduction of the fundamental physics and mechanism of transient waves in both intact and defective pipes is first presented. Different techniques and principles for transient wave generation and measurement are then discussed. In addition, the signal processing techniques commonly used for feature extraction from the measured signals are summarized. The main focus of this paper is on the comprehensive review of the technological advances and characteristics of five common types of transient wave-based anomaly detection methods for fluid pipe systems, namely (1) reflection-based method; (2) damping-based method; (3) FRF peak pattern-based method; (4) time domain full-waveform inversion method; and (5) frequency domain full-waveform inversion method. Afterwards, two practical applications of transient wave-based methods for anomaly detection in real-life fluid pipe systems are introduced and discussed. Finally, recommendations for future work in this research field are given. © 2021 Elsevier Ltd

Entrapped air blocking the flow in pipeline systems is a common cause of increased pumping costs. At present, air is generally removed via valves or pipeline excavation and drilling. This becomes inefficient in large networks where the precise location of the air is unknown. Fluid transients are a potential tool for detecting and locating air in pipelines. The effect of a stationary air pocket part of the way along the pipe, which occupies the main flow path and acts as a blockage without causing a hydraulic jump or column separation, has not previously been studied experimentally. This paper presents experimental results for a transient pulse interacting with an in-line air pocket for a range of pocket sizes and system pressures. In accordance with the impedance theory, the reflective power of the air increases with pocket size. Other notable characteristics of the interaction include frequency-dependent transmissivity, an out-of-phase reflection, and a substantial reflection under zero base flow. These effects set air pockets apart from solid blockages, allowing a transient detection methodology to differentiate between the two cases, although they have similar effects at steady-state. © 2019 American Society of Civil Engineers.

Entrapped air in pipeline systems can compromise the operation of the system by blocking flow and raising pumping costs. Fluid transients are a potential tool for characterizing entrapped air pockets, and a numerical model which is able to accurately predict transient pressures for a given air volume represents an asset to the diagnostic process. This paper presents a detailed study on our current capability for modeling and predicting the dynamics of an inline air pocket, and is one of a series of articles within a broader context on air pocket dynamics. This paper presents an assessment of the accuracy of the variable wave speed and accumulator models for modeling air pockets. The variable wave speed model was found to be unstable for the given conditions, while the accumulator model is affected by amplitude and time-delay errors. The time-delay error could be partially overcome by combining the two models. © 2019 by ASME.

Blockages in urban water supply systems are commonly formed from various complicated physical, chemical, and biological processes; thus, they usually constrict randomly and nonuniformly along their lengths. Although the transient-based method has been developed for blockage detection, the applications of this method are mainly limited to blockages of uniform constriction along their lengths (termed as uniform blockages). The influence of blockages with linearly varying diameters (termed as linear nonuniform blockages) on transient frequency responses was studied by the authors in a previous study. It was found that the resonant frequency shifts induced by linear nonuniform blockages have totally different patterns from that of uniform blockages. Specifically, the resonant frequency shifts induced by linear nonuniform blockages become less evident for higher harmonics. But the physical mechanism of this pattern is still unclear. This study intends to clarify this phenomenon from an energy perspective. For this purpose, the energy transmission coefficient of an unbounded pipeline containing various blockages is analytically derived, which is numerically validated by the method of characteristics. Afterward, the influence of nonuniform blockage properties on the energy transmission is investigated systematically based on the validated result. The results indicate that the impedance of nonuniform blockages is frequency dependent, which becomes smaller for higher frequency waves. This means that nonuniform blockages have a less blocking effect on the propagation of higher frequency waves; thus, the resonant frequency shifts induced by nonuniform blockages become less evident. © 2019 American Society of Civil Engineers.

It was found in a previous study that the transient frequency shifts induced by nonuniform blockages in water pipelines become less evident as the frequency increases, but its physical mechanism is unclear. This paper explains this non-uniform blockage induced frequency shift pattern from an energy perspective. The results indicate that the non-uniform blockages have a less blocking effect on the propagation of high frequency waves; thus, the induced frequency shifts become less evident. In practical applications of non-uniform blockage detection, the frequency of the incident wave should be selected carefully to ensure that the reflected wave contains enough energy. © BHR Group 2018 Pressure Surges 13

Extended partial blockages in urban water supply systems (UWSS) are formed from complicated physical, chemical, and biological processes; thus, these blockages are commonly in random and nonuniform geometries. The transient-based blockage detection method (TBBDM) has been evidenced in many applications to be a promising way to diagnose these blockages. Despite the successful validation and application of the TBBDM in the literature, pipe blockages used in these studies were idealized and simplified to regular and uniform shape, which are however not common in practical UWSS, and thus invalidity and inaccuracy of this TBBDM has been widely observed in practical applications. This paper presents fundamental research on understanding the influence of more realistic and nonuniform blockages on transient wave behavior and the accuracy of current TBBDM. The blockage with a linearly varying diameter (termed as nonuniform blockage) is firstly investigated by the frequency domain analytical analysis for its impact on transient wave behavior, which is thereafter incorporated in the overall transfer matrix of transient frequency response for reservoir-pipeline-valve systems. The results indicate the nonuniform blockage may induce very different modification patterns on the frequency shift and amplitude change of transient waves from the uniform blockage situation. © 2018 American Society of Civil Engineers.

The system frequency response (SFR) based method has been widely developed and applied for the modelling of transient pipe flow and the assessment of pipeline system conditions. The linearization assumption is commonly imposed for the nonlinear turbulent friction term in the SFR model. Previous studies have demonstrated the impact of the linearization approximation on the accuracy of SFR-based modelling and analysis. This paper aims to improve the traditional SFR-based method by incorporating the nonlinear component of the friction term in a two-step analytical extension of the SFR expression. Numerical comparisons with the method of characteristic (MOC) highlight the improved accuracy that the extended SFR result provides over the traditional approach under various flow conditions.

Unsteady friction and its modeling have been widely studied in transient pipe flows for its influences and modification effect on pressure waves. Such a feature is of great importance particularly in pipe systems where the extreme pressure values are due to the overlapping of pressure waves generated in different sections. This paper investigates the relevance of unsteady friction term by considering different models available in the literature. In particular, attention is focused on the following two commonly used one-dimensional (1D) models: the weighting function-based (WFB) model and the instantaneous acceleration-based (IAB) model. The investigation is executed using laboratory experiments and field tests as well as 1D/2D numerical simulations in simple pipeline systems. Realistic ranges of both initial (pretransient) conditions and geometrical characteristics are considered. The data collected in experimental tests are first used to calibrate the unsteady friction models under investigation. The validated models are then applied to identify their respective domains of applicability and the limitations. The differences between models and data are measured using the local transient analysis (LTA) norm and the integral total energy (ITE) norm along the pipeline, and the reasons for such discrepancies are explored in the paper. The practical implications of the use and improvements of different unsteady friction models for transient pipe flow simulations are discussed in the paper.

In the last two decades, energy dissipation in unsteady-state pressurized pipe flow has been examined by various authors, where the instantaneous wall shear stress is split into a quasi-steady and an unsteady shear stress component. The focus of most past studies is on formulating expressions for the unsteady wall shear stress, but there has been less work on the key parameters governing the dominance of unsteady friction in transient flows. This paper derives an expression for the head envelope damping for turbulent flows in smooth and rough pipes and provides new and carefully measured field data for the initial (i.e., pretransient) Reynolds number, R0, that ranges from 97,000 to 380,000. The analytical solutions is derived on the basis of one-dimensional (1D) water hammer equations in which the unsteady component is represented by existing convolutional unsteady friction formulas for both smooth and rough turbulent subregimes. The analytical solution is used to formulate general, encompassing and theoretically-based dimensionless parameters to assess the importance of unsteady friction in comparison to the quasi-steady component. In addition, the analytical solution furnishes the similitude relations that allowed the damping behavior from existing laboratory tests, the field tests conducted as part of this research, and the weighting function-based (WFB) models to be investigated and compared in a coherent manner in a single graph. The analysis confirms that the magnitude of R0 has a significant impact on the damping for transients generated by flow stoppage. In addition, the results show that convolutional unsteady friction model that uses the frozen eddy viscosity hypothesis and R0 has accuracy that decreases with time. An improvement for this shortcoming is proposed and verified and involves the use of the instantaneous Reynolds number in lieu of the pretransient Reynolds number in the evaluation of the WFB models. The result is a modified unsteady friction mo

Extended partial blockages are common in pressurized water pipelines and can result in the wastage of energy, the reduction in system carrying capacity and the increased potential for contamination. This paper investigates the transient wave-blockage interaction and its application to extended blockage detection in pipelines, where blockage induced changes to the system resonant frequencies are observed. The frequency shifting is first inspected and explained in this study through wave perturbation analysis, providing a theoretical confirmation for the result that unlike discrete blockages, extended blockages cause resonant frequency shifts in the system. Furthermore, an analytical expression is derived for the relationship between the blockage properties and the resonant frequency shifts and is used to detect the blockages in this study. The obtained results are validated through both numerical applications and laboratory experiments, where the accuracy and efficiency of the developed method for extended blockage detection are tested. (C) 2013 Elsevier Ltd. All rights reserved.

Transient flows are commonly encountered in pressurized water pipelines and have been studied for the purpose of systems design as well as defects detection and management. The representation and analysis of the transient response in the frequency domain is an attractive approach for fault detection due to its high noise tolerance and the linearized equations allows for the clear analytical characterization of system behaviour. Recent studies have demonstrated that an extended partial constriction of the pipe flow area causes changes in the system resonant frequencies and these changes can be used for locating and sizing partial blockages in pipes. Despite the successful application of this technique under field conditions, so far there is little work on the link between the changes in the system resonant conditions and the wave-blockage interaction. This paper provides a fundamental basis for the observation that unlike localised, discrete blockages, an extended blockage creates changes in the system resonant frequencies. Analytical methods using wave perturbation analysis and transfer matrix are shown in this study, and the obtained results are compared with numerical simulations and experimental data. The analytical analyses are used to explain the blockage-induced frequency shifts and to provide insights for its practical applications in pressurized water pipelines. © 2013 The Authors.

Transient flows are commonly encountered in pressurized water pipelines and have been studied for the purpose of systems design as well as defects detection and management. The representation and analysis of the transient response in the frequency domain is an attractive approach for fault detection due to its high noise tolerance and the linearized equations allows for the clear analytical characterization of system behaviour. Recent studies have demonstrated that an extended partial constriction of the pipe flow area causes changes in the system resonant frequencies and these changes can be used for locating and sizing partial blockages in pipes. Despite the successful application of this technique under field conditions, so far there is little work on the link between the changes in the system resonant conditions and the wave-blockage interaction. This paper provides a fundamental basis for the observation that unlike localised, discrete blockages, an extended blockage creates changes in the system resonant frequencies. Analytical methods using wave perturbation analysis and transfer matrix are shown in this study, and the obtained results are compared with numerical simulations and experimental data. The analytical analyses are used to explain the blockage-induced frequency shifts and to provide insights for its practical applications in pressurized water pipelines. © 2013 The Authors.

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The operation of the transmission line models requires an input signal in the frequency domain describing the nature of the transient disturbance (for example, a valve closure) and an exact solution of the linearized mass and momentum equations for unsteady pipe flow. The use of the transmission line models does not require a strict adherence to a time-space discretization grid governed by the Courant condition, but it does require that the input signal be discretized in the frequency domain. This paper investigates the errors induced by the discretization of the input signal and provides guidelines for the appropriate selection of discretization size for the linear transmission line models. The accuracy of the model is quantified through comparison with a finely discretisated method of characteristics (MOC) model. The results show that the transmission line models are sensitive to the time-frequency discretization size and unlike the MOC, the appropriate size of the discretization changes depending on the transient event being modelled as well as the energy losses in the system.

This paper investigates the importance of pipe system scale-specifically pipe length and diameter-on unsteady friction in pipe transients. A dimensionless analysis is conducted for the one-dimensional (1D) water-hammer model in this study and the analytical expression for the relative importance of unsteady friction damping to the total friction damping is obtained in the frequency domain. In addition, a two-dimensional (2D) waterhammer model coupled with a 2D kappa-epsilon turbulence model is applied to a reservoir-pipe-valve system. A parametric study covering a number of pipe diameters, pipe lengths, and initial Reynolds numbers is conducted. The investigation spans a range of water-hammer travel time and turbulent radial diffusion timescales. In each case, the transient is generated by a sudden and complete valve closure. The analytical solution for the importance of unsteady friction is verified by the numerical simulations and the results show that unsteady friction damping has less effect on the damping rate of the transient envelope as (1) the ratio of the wave travel timescale to the radial diffusion timescale increases and (2) the product of the initial friction factor and Reynolds number increases. Furthermore, the findings of this study are validated by both laboratory and field experiments from literature. The implication of the findings is that the role of unsteady friction on the damping rate of the transient envelope diminishes with the scale ratio of pipe length and pipe diameter and that laboratory experiments, which are usually limited to relatively small scale ratios of pipe lengths and diameters, have lead researchers to overestimate the importance of unsteady friction on the damping of the transient envelope in real large pipe-scale systems. DOI: 10.1061/(ASCE)HY.1943-7900.0000497. (C) 2012 American Society of Civil Engineers.

Waterhammer models are used to design and analyze pressurized pipe flow systems and to locate leaks and other defects in water supply pipelines. This thesis analyses the importance of unsteady friction and visco-elastic damping as well as parameter uncertainty on the accuracy and reliability of waterhammer models. The analysis is performed by using analytical and numerical methods. It is found that unsteady friction damping has less effect on the damping rate of the transient envelope as the timescales of the wave travel period and radial diffusion becomes larger. The implication is that the role of unsteady friction on the damping rate of the transient envelope diminishes with system scales and that the results of laboratory experiments, which are limited to relatively small pipe lengths and diameters, have led researchers to overestimate the importance of unsteady friction on the damping of the transient envelope in real pipe systems. In addition, the pressure head attenuation attributable to unsteady friction is comparable to the visco-elastic effect during the initial transient stage while the visco-elastic effect becomes dominant both in terms of damping and phase shift at later stages. Moreover, the visco-elastic damping becomes more critical if the visco-elastic retardation time is less than the wave travel time along the entire pipeline length, indicating that the visco-elastic damping is important for long pipes. As far as leak and other pipe defect detection in pipelines, the role of transient wave reflections is found to be far more important than the transient damping. This finding has implications on the design of transient signals for pipe defects detection and suggests high bandwidth signals with clear reflections are preferable to this technology. The effects of uncertainties in geometric and dynamic parameters on wave envelope and wave scattering indicate that (i) traditional deterministic waterhammer models tend to overestimate the magnitude of the

This paper proposes a technique for the detection of extended blockages in pressurized water pipelines by using the system frequency responses under transient conditions. The impact of extended blockages on the system frequency responses is illustrated by using the analytical transfer matrix method, and the results indicate that extended blockages cause the resonant frequencies of the system to shift, and the blockage locations and sizes can be determined by analyzing the occurrences of the resonant peaks in the frequency axis. The analytical derivations of the blockage effect on the resonant frequencies are validated through different numerical experiments, and the applied results demonstrate that the extended blockages in pipeline can be detected by the proposed method as long as the system resonant frequencies are accurately determined. Practical implementations of the findings are discussed at the end of this paper. © 2012 American Society of Civil Engineers.

Systematic transient analysis in water supply systems is intended to determine the reliability of water supply and the integrity of hydraulic devices when hydraulic transients (i.e., water hammers) occur. In the analysis, parameters such as wavespeed, pipe diameter, friction, and others, usually considered as known inputs in traditional water hammer models, are actually subject to uncertainties due to natural or human behaviors. The paper considers these uncertainties and investigates their effects on the reliability of water transportation systems and water supply networks under transient conditions with or without protection devices. In addition, the optimization of transient protection devices is also evaluated based on the probabilistic analysis. The results show that the probabilistic analysis method could inspect the influence of the different input uncertainties on the system responses under transient conditions and provide detailed information on the design for water supply systems and protection devices. A one-dimensional water hammer model of pipe fluid systems and Monte Carlo simulation method are used in this investigation. © 2010 ASCE.