Transient-based Methods Research Articles

Gradient-based optimization for spectral-based multiple-leak identification

This study tailors an efficient optimization procedure for multiple-leak identification in the frequency domain. Firstly, the maximum likelihood estimation is adopted to build a multi-dimensional optimization problem whose objective function is only in terms of the leak locations. Then, closed-form formulations to compute the gradient of the proposed objective function are presented. Finally, to demonstrate the effectiveness of the developed analytical formulations, the steepest-descent method with multiple initializations is implemented to solve the optimization problem. An initialization algorithm based on a set of points with maximum leak reflections is proposed. The use of the most classical gradient-based technique to find the optimum allowed for a deeper understanding of the multi-dimensional optimization required to pinpoint multiple leaks in transient-based methods in terms of complexity and solvability of the problem. The cases of three leaks and various numbers of resonant frequencies with a clear manifestation of the performance of gradients and their applications in the steepest descent method are investigated and discussed. The procedure is also validated against a laboratory case study having two leaks. The main advantages of the proposed technique, which distinguishes it from previous studies, are (i) the versatility of the process to find leaks with even a single spatial measurement vector and (ii) the efficiency and accuracy of the underlying optimization, as closed-form formulations are employed in the scheme. This work may provide a benchmark for investigating and assessing other methods dealing with multiple leaks due to its comprehensive presentation of the local extrema and the entire identification process.

Efficient leak detection in single and branched polymeric pipeline systems by transient wave analysis

The widespread use of plastic pipes in different fluid conveyance systems has greatly driven the recent development and application of transient-based methods (TBMs) for leak detection in viscoelastic/polymeric pipelines. Current TBMs for viscoelastic pipe leak detection are usually achieved by a two-step procedure, namely viscoelastic parameters identification and leak detection, which requires the pre-knowledge of intact system states (i.e., non-leak) for comparative analysis. This paper presents an efficient single-step frequency domain inverse transient analysis (FDITA) method for simultaneous identifications of viscoelastic parameters and leaks in plastic pipes, so as to enhance the applicability and accuracy of TBMs. Both the single and branched polymeric pipe systems are applied for the method development and application. To this end, analytical solutions of single and branched systems from the transfer matrix method are firstly derived to represent the transient frequency responses of viscoelastic pipelines with leaks. A global optimized nonlinear curve fitting method is then employed to identify both viscoelastic parameters and potential leaks by knowing/measuring other system and flow conditions. Extensive experimental validations and numerical applications of both single and branched pipe systems demonstrate the very good efficiency and accuracy of the developed method for leak detection in different viscoelastic pipe systems. Furthermore, the mechanism of transient wave-leak-viscoelasticity is analysed based on these application results and theoretical evidence. Finally, a sensitivity analysis is performed to quantify and discuss the advantages and potential limitations of the developed method in the paper.

Case study of leak detection based on Gaussian function in experimental viscoelastic water pipeline

Abstract Leakage in transmission pipelines and water distribution networks causes water and energy loss and reduces water quality. The accuracy of leakage detection using transient-based methods depends on several factors. This study investigated the sensitivity of location and size of leaks in simple polyethylene transmission pipelines to dynamic parameters, flow regime, sample size, spatial-step increment, and leak size and location. For this purpose, a hydraulic transient solver was first developed to take into account the dynamic effects of unsteady friction, viscoelasticity of the pipe wall, and the leak. The leakage was assumed to function with a quasi-normal distribution around its real location to reduce problem dimensionality and unnecessary computations. This approach was evaluated based on experimental transient data in which leaks were simulated in different sizes and locations. Results revealed that the hydraulic transient model that includes only viscoelasticity effects could pinpoint leakage characteristics. The sample size evaluation indicated that half and a single period of the pressure signal are sufficient to determine the leakage location and size in simple viscoelastic transmission pipelines, respectively. The optimal ratio of the spatial step to pipe length (Δx/L) was 0.025.

State-of-the-art review on the transient flow modeling and utilization for urban water supply system (UWSS) management

AbstractIn the context of smart city development and rapid urbanization worldwide, urban water supply system (UWSS) has been of vital importance to this process. This paper presents a comprehensive review on the transient flow research for UWSS management. This review consists of two aspects as follows. The first aspect is about the development and progress of current transient theory, including transient flow models, unsteady friction and turbulence models, and numerical simulation methods. The other aspect is about the utilization and application of transient-based methods for effective UWSS diagnosis and management, including leakage, discrete and extended partial blockages, unknown branch, and other defects in water pipelines. A total of 228 publications have been reviewed and analyzed in this paper. In addition to the state-of-the-art progress and achievement of the research on transients, the advances and recommendations of future work in this field are also discussed for the development and management of next-generation smart UWSS in the paper.

Surge Compression for Improved Fault Location Accuracy in Full Transient-Based Methods

This paper proves that the accuracy of single-ended fault location techniques based on the correlation of fault transients in power lines can be significantly improved by inverse-filtering transients first. The reason for this improved accuracy is found in the reduction of the duration of the fault surge signal, thus increasing the sensitivity of fault-location metrics to the fault position. Reported results show that by using the proposed filtering strategy, faster sampling rates systematically and significantly improve the location accuracy, as opposed to the case when no filter is applied, for which virtually no improvement is observed. Because of its higher spatial selectivity, the proposed fault-location technique required the development of a new synchronization method, which ensures a precise transient synchronization without the need for high-speed sampling. It is concluded that by jointly using the proposed transient filtering and synchronization solutions, correlation-based fault location can be significantly improved even when using sampling rates as low as 100 kHz. Extensive numerical simulations for a three-phase transmission line confirm an improvement exceeding one order of magnitude in the fault location accuracy, for both low- and high-impedance faults.

Impact of Propagation Losses on Fault Location Accuracy in Full Transient-Based Methods

This paper studies how propagation and termination losses affect full transient-based fault location techniques. Their accuracy is discussed in terms of both location uncertainty, caused by a limited spatial resolution, and systematic errors, caused by a bias in the fault-location metrics. This last case is proven to be by far likelier when propagation losses are higher than the dissipation in line termination loads. Two different location metrics are studied, namely correlation and normalized projection, as found in the literature, with correlation proven to be unbiased, since it benefits from two location mechanisms, namely frequency and time-decay matching of a line resonances, as opposed to projection, which only relies on the former mechanism. A numerical analysis of realistic lossy overhead lines confirms theoretical predictions about biased fault location and loss of spatial resolution and the role played by the frequency content of transient data. When applied to the modal analysis of a three-phase transmission line, these results help explaining why faults are located with widely variable accuracy depending on their distance and the bandwidth of the recorded transient, confirming that wide-band transient sampling does not necessarily results in the best location accuracy.

The influence of non-uniform blockages on transient wave behavior and blockage detection in pressurized water pipelines

Blockages in piping systems are formed from potentially complex combinations of bio-film build up, corrosion by-products, and sediment deposition. Transient-based methods seek to detect blockages by analyzing the evolution of small amplitude pressure waves. In theory, such methods can be efficient, nearly non-intrusive and economical but, thus far, studies have only considered symmetrical blockages, uniform in both the radial and longitudinal directions. Laboratory experiments are described here that involve pipe blockages with various levels of irregularity and severity; the way the transient response is affected by a non-uniform blockage is investigated. The differences between uniform and non-uniform blockages are quantified in terms of the rate that wave envelopes attenuate and the degree that phases are shifted. Two different methods for modeling these impacts are compared, namely through an increase in pipe roughness and through a wave scattering model. Wave scattering is shown to play a dominant role in explaining both wave envelope attenuation and phase shift. The accuracy of existing transient-based methods of blockage detection in the frequency domain is also examined, and is found that the predictions of rough blockage locations and sizes by current method are in good agreement with data, with relatively larger discrepancies for rough blockage lengths.

High-frequency acoustic wave properties in a water-filled pipe. Part 1: dispersion and multi-path behaviour

ABSTRACTDefect resolution using transient-based detection methods (TBDDM) improves as frequency bandwidth of injected signals increases. High-frequency waves (HFW) excite radial and azimuthal modes, however, making the 1D water-hammer ineffective for these phenomena. This paper focuses on idealized HFW in inviscid, slightly compressible fluid in rigid, unbounded, circular conduits. HFW waves are generated by an axisymmetric wave source. High-order 2D finite volume scheme is developed for HFW. Results show that injected probing waves containing a cut-off frequency exhibit significant wave dispersion, and group velocity varies over a wide range of speeds, resulting in wave-energy spatial spreading with large amplitude reduction. Injected signals without any cut-off frequency remain spatially separated. Size of wave source significantly affects energy distribution within wave modes. Practical implications are that probing wave and defect resolution effectiveness may be increased using (i) probing HFW without cut-off frequencies contained in the bandwidth of the injected probing signal, and (ii) larger power sources for the injection of probing wave signals.

Short-Frequency Fourier Transform for Fault Diagnosis of Induction Machines Working in Transient Regime

Transient-based methods for fault diagnosis of induction machines (IMs) are attracting a rising interest, due to their reliability and ability to adapt to a wide range of IM’s working conditions. These methods compute the time–frequency (TF) distribution of the stator current, where the patterns of the related fault components can be detected. A significant amount of recent proposals in this field have focused on improving the resolution of the TF distributions, allowing a better discrimination and identification of fault harmonic components. Nevertheless, as the resolution improves, computational requirements (power computing and memory) greatly increase, restricting its implementation in low-cost devices for performing on-line fault diagnosis. To address these drawbacks, in this paper, the use of the short-frequency Fourier transform (SFFT) for fault diagnosis of induction machines working under transient regimes is proposed. The SFFT not only keeps the resolution of traditional techniques, such as the short-time Fourier transform, but also achieves a drastic reduction of computing time and memory resources, making this proposal suitable for on-line fault diagnosis. This method is theoretically introduced and experimentally validated using a laboratory test bench.

Essential system response information for transient-based leak detection methods

Many transient-based techniques have been developed for leak detection in piping fluid systems, and they are thought to use leak-induced damping and reflection effects to detect and locate the problem. This work investigates the relative importance of the damping and reflective effects from the leak to the leak detection methods with the importance of both effects tested using four representative methods, which vary significantly in their modes of operation and provide the coverage of the major developments in the transient leak detection field. It was found that all transient-based methods are unable to detect and locate the leak in the absence of the leak-reflected signal, whereas the leak is detected and located even in the absence of leak-induced damping. The results indicate that the information previously thought to be contained in the damping of slow transients was found to be low frequency reflections from the leak.