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Any transient event in a pipeline system is an energy process, implying that the dynamic response can be interpreted and analyzed through energy transfer between different forms, including potential (internal), kinetic, and losses. This water hammer energy approach to investigating the impacts of leaks uncovers notable insights about transient-leak interaction in fluid-filled pipelines. In this paper, the energy exchanges in leaky conveyance pipeline systems, including elastic and viscoelastic pipes with various leak sizes and locations, are analyzed and compared with intact pipe cases, thus revealing the extent to which a leak can vary the transient internal and kinetic energy intensity. The results are supported by an extensive numerical analysis that describes transient energy in different cases and illustrates transient stability conditions from a new perspective. Finally, practical implications for developing transient-based leak detection methods are drawn specifically when data from multiple stations are available, and the limitations of this study are summarized in the end of the paper. [ABSTRACT FROM AUTHOR]

Two- and three-dimensional analyses of transient flows considering the air–water interaction have been a challenge for researchers due to the complexity in the numerical resolution of the multiphase during emptying in pressurized water pipelines. The air–water dynamic interaction of emptying processes can be analyzed using thermodynamic and hydraulic laws. There is a lack in the current literature regarding the analysis of those phenomena using 3D models. In this research, several simulations were performed to study the complex details of two-phase flows. A 3D model was proposed to represent the emptying process in a single pipeline, considering a PVoF model and two-equation turbulence model. The model was numerically validated through 12 experimental tests and mesh sensitivity analysis. The pressure pulses of the air pockets were evaluated and compared with the experimental results and existing mathematical models, showing how the 3D models are useful for capturing more detailed information, such as pressure and velocity patterns of discrete air pockets, distribution of air and water velocity contours, and the exploration of temperature changes for an air pocket expansion. [ABSTRACT FROM AUTHOR]

The transient flow phenomenon in a pipeline accounts for the flow variations with time and space. The transient energy analysis (TEA) overlooks the process as it sums the energy of the entire pipe domain and reports it at each moment. The current research takes advantage of this approach to investigate different influential factors in water pipelines, including steady friction, unsteady friction, and pipe wall viscoelasticity, to figure out the energy conversion and dissipation during a transient flow process. To this end, energy expressions are derived and compared for both elastic and viscoelastic pipeline systems. Two different viscoelastic materials—oriented polyvinyl chloride (PVC-O) and high-density polyethylene (HDPE)—are applied in the analysis to compare the proportions of the energy dissipation by different influential factors. The results reveal that at small transient perturbations, the influence of the steady friction is dominant in the energy dissipation, and the impact of viscoelasticity grows with the excitation intensity and valve's oscillation frequency. Besides, spatial variations of energy dissipation (per unit of length) along the pipeline have been investigated in single and branched systems, demonstrating significant deviations by distance from the excitation source. [ABSTRACT FROM AUTHOR]

Air pockets trapped in water pipelines are a common phenomenon and can lead to different air-water two-phase flow patterns: stratified, blowback, plug, and bubbly flows. The two former flows contain a large amount of air and should be carefully monitored for pipeline safety, while the two latter flows have relatively low air fractions and can be regarded as normal operating states of pipelines. Hence, flow pattern identification is key to diagnosing the operating state of pipelines. In this paper, a new data analysis method based on complex network theory is proposed to identify the features of flow patterns using pressure signals. The pressure signals of different flow patterns, collected from an experimental facility, were used to characterize the nodes and edges (i.e., connections) in the complex network. The closely linked nodes with dense edges could be aggregated to form a cluster (i.e., community). An unsupervised machine learning technique is then used for community clustering in the network. The results show that the complex network constructed from pressure signals can be divided into several communities, representing different phases (i.e., air, water, or mixed phases) of the air-water flows. Therefore, the flow patterns can be identified in terms of the cluster features and topological features, which are represented by indicators including modularity, graph density, average path length, and transitivity. The impacts of two structural parameters of the complex network, i.e., window size and sliding step, are analyzed. Sliding step is shown to have a more significant impact on the flow pattern identification than window size. This study shows that the complex network approach is effective for flow pattern identification in air-water two-phase flows and could be potentially used for identification of pipeline operational states. [ABSTRACT FROM AUTHOR]

Partial blockages commonly exist in water pipelines due to various physical, chemical, and biological processes, including sediment, corrosion, and biofilm. The formed blockages can result in low flowing capacity, additional energy loss, and water quality deterioration during the water conveyance process, such as urban water supply and drainage systems. This paper presents an investigation on the interaction of transient pressure waves with pipe-wall roughness and blockages in water pipelines. The analytical expression of wave propagation in a pipeline with rough blockages is firstly derived by multiscale wave perturbation analysis for transient pipe flows. The analytical results and analysis demonstrate that the wave scattering (amplitude damping and phase shifting) is dependent on the relationship between the incident wavelength and the correlation length of roughness-blockage disorders in the pipeline. The relative importance of pipe-wall roughness friction and pipe blockage constriction to wave scattering in terms of wave envelope attenuation and wave phase change is then investigated based on the analytically derived results. Two dimensionless parameters, which are functions of the properties of incident waves, pipe-wall roughness, blockage severity and range, and internal fluid conditions, are formulated to characterize such relevance and importance. For validation, the analytical results are compared with experimental data collected in this study based on a laboratory experimental test system. Finally, the key results and findings of this study are discussed for their applicability and implication to transient pipe flow modeling and pipeline condition assessment in practical applications. [ABSTRACT FROM AUTHOR]

Actively generated pressure waves are studied widely and applied in transient-based leak detection for pipe systems. High-frequency (HF) waves, the wavelength of which is on the order of the pipe diameter or smaller, provide higher resolution to pinpoint defects. However, the mechanism of how HF waves interact with a leak is not yet well understood. This paper investigated the effect of a leak on the HF waves in a water-filled pipe using computational fluid dynamics (CFD) simulations. To facilitate the analysis, only the plane wave and the first high-order radial modes were considered. The interaction between the leak and the two modes was analyzed. The group velocity of the first high mode was analyzed to investigate the effect of the leak on the cut-off frequency. However, the shift in cut-off frequency was not observed for the moderate leak size investigated in this paper. Therefore, it was concluded that the shift of the cut-off frequency is very small and should not be used as a signature for leak detection. On the other hand, the results showed that the leak induces very significant scattering of the excited modes. Such scattering provides clear information that may be utilized for leak detection. [ABSTRACT FROM AUTHOR]

Surges caused by the sudden compression of entrapped air pockets are a source of serious issues in various hydraulic conveyance systems. Such surges may appear during rapid filling of storm-water sewers and storage tunnels, priming of water pipelines, and other applications when air is quickly displaced by inflows. When ventilation is inadequate during rapid filling conditions, sudden air compression can occur leading to pressures that may exceed design limits and cause structural damage. Past studies have provided various insights in air-water interactions in closed pipes during rapid filling conditions, but the focus of the majority of these studies was to support the development and improvement of numerical models. Fewer experimental studies focused on the effect of geometric characteristics such as pipe diameter and length/diameter ratios, as well as systematic investigation of various air pocket volumes and filling flow rates. The present work addresses this knowledge gap, measuring pressure surge peaks and the damping of pressure surges following the first peak. In this investigation, kinetic energy and linear momentum dimensionless groups were analyzed as potential alternatives to represent peak surges as as well surge damping. Findings in this study provide further insight into parameters governing air-water surge magnitudes, and on the peak surge attenuation following sudden compression. [ABSTRACT FROM AUTHOR]

Elevated high points along a pipeline profile are the most common places where air vacuum valves (AVVs) are installed. This paper uses basic water hammer theory to semianalytically explore the effects of such AVVs. A simple frictionless reservoir-pipe-reservoir system with an exaggerated intermediate high point is considered with a sudden flow curtailment assumed upstream. Key design parameters such as the maximum air pocket volume, the duration of air pocket growth and collapse, and the maximum magnitude of the pressure spike resulting from water column rejoinder are semianalytically developed for various high point locations. The magnitude of the reduced pressure wave created by the refraction at the high point, and both its vertical and horizontal position, are demonstrated to crucially determine system performance. Numerical examples are compared with the semianalytical expressions to highlight the accuracy of the derived expressions. The effect of friction is later introduced to help reveal friction's influence on air valve performance. [ABSTRACT FROM AUTHOR]

Air valves are normally installed at high points along undulating pipelines to allow for air discharge or intake during filling or dewatering. Initial filling of a newly constructed pipeline, or refilling a portion of an existing pipeline after a shut-down for maintenance purposes, can produce destructive pressure surges caused by air-valve closure. Methodologies for determining safe filling rates for the pipeline, taking into account factors such as air-valve characteristics, riser dimensions, driving head, and allowable working pressure, are proposed in this paper. An optimal filling method can be achieved either by a two-stage filling procedure, which comprises a fast filling rate during the first stage and a slower filling rate during the second stage when the water level approaches the highest air valve, or by using an antislam air valve. The comparison of computed transient pressures with test data indicates that the analytical models produce reasonable predictions of pressure surges caused by air-valve closure. [ABSTRACT FROM AUTHOR]

Liquid column separation (LCS) in pressurized pipelines may occur if a water hammer event drops the local pressure to the liquid’s vapor point. Numerical simulations of LCS have traditionally been based on one-dimensional (1D) transient flow theory; here, a two-dimensional (2D) computational fluid dynamics (CFD) model is used to investigate the complicated nature of LCS and to help characterize the limitations of the traditional 1D models. To this end, the Schnerr–Sauer cavitation model with a shear-stress transport (SST) k − ω turbulence model is employed, whereas the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations are solved for the mixture of liquid and vapor. 2D model results are compared to both experimental data and to those of the 1D discrete vapor-cavity model (DVCM), thus demonstrating that the 2D method effectively simulates the pressure variations while helping to visualize the associated physical processes. More specifically, the 2D simulations vividly reveal the growth and the collapse of the cavity, including the formation of an intermediate cavity and both the location and shape of the region undergoing distributed vaporous cavitation. [ABSTRACT FROM AUTHOR]

To alleviate problems caused by reservoir sedimentation, the hydrosuction removal of sediment deposits is an attractive option. In this technique, pumping or siphoning is used to draw water and sediment into the inlet of a pipe and convey the slurry to settling ponds. A key performance target is then to maximize the delivered sediment concentration. For fine sediment (silt and clay), deposit behavior largely depends on its degree of consolidation. To investigate how this parameter affects hydrosuction performance, a series of laboratory experiments were conducted using a small-scale suction pipe equipped with an online densimeter to measure the time evolution of the outflow sediment concentration. To help interpret the resulting signals, the evolving shape of the deposit surface near the pipe inlet was recorded. Measurements were then compared with predictions from inviscid selective withdrawal theory. Depending on the duration of self-weight consolidation prior to hydrosuction, a transition was observed between two highly contrasted sediment responses. Up to a degree of consolidation of approximately 90%, loose deposits respond much like a dense inviscid layer. Beyond this degree, consolidated deposits resist withdrawal, causing rapid freshwater breakthrough and an abrupt drop in hydrosuction performance. [ABSTRACT FROM AUTHOR]

Unexpected, unknown or unused side pipe branches, termed dead-end side branches in this study, commonly exist in water pipe systems because of incorrect device installations or illegal connections. These connections are detrimental to the water quality and the operation and management of pipe networks. This paper investigates a transient-based frequency domain method for detecting side branches in pipe systems. The frequency response function for a pipe system with a single dead-end side branch is first derived by the transfer matrix method and the side branch was found to cause shifts in the system resonant frequencies. The nature of the resonant frequency shifts can be used to inversely determine the location and size of the side branch. A two-step genetic algorithm based optimization is proposed in this study to efficiently solve the derived analytical expression for the resonant frequency shifts. The developed method is validated through numerical simulations, and the results demonstrate the feasibility of this method for detecting side branches. The accuracy for locating the side branch is higher than the accuracy in sizing the branches. The sensitivity of the method to the magnitude and bandwidth of the transient wave signal is also discussed in the paper. [ABSTRACT FROM AUTHOR]

In this study, the relationship between the conventional power equation and the fixed and variable area discharges (FAVAD) equation for modeling leakage as a function of pressure was investigated. It is shown that different leakage exponent (or ) values are obtained for the same leak when measured at different pressures. An analytical exploration of the two equations shows that the leakage exponent tends to 0.5 when the system pressure tends to zero, and to 1.5 when the system pressure tends to infinity. A dimensionless leakage number is defined as the ratio between the variable and fixed portions of a leak, and it is shown that a single function can be used to describe the relationship between the leakage number and leakage exponent. This model was combined with previous research to accurately predict the leakage exponents of several published studies in cases where elastic deformation occurred. [ABSTRACT FROM AUTHOR]

Partial blockages commonly exist in pressurized pipeline systems, and the rapid remediation of such faults is required to reduce the wastage of energy as well as to maintain the serviceability of the pipe network. Numerous transient test-based techniques (TTBT) have been developed for detecting pipe defects, with each technique providing different advantages. Two previously developed techniques-pressure signal analysis (PSA) and frequency response analysis (FRA)-are experimentally tested in this study on systems of different pipe material and characteristics. Each method is validated using the experimental data, and the results show that PSA is most accurate for locating the blockage while FRA is most accurate for determining the radial constriction and length of the blockage section. To take advantage of the different strengths of the techniques, a coupling of the two methods is proposed. Experimental application results reveal that both detection accuracy and calculation efficiency are improved when the coupled method is used instead of the original techniques applied individually. Moreover, the results indicate that current TTBTs for partial blockage detection are more reliable in elastic (metallic) pipelines compared to viscoelastic (plastic) pipes. [ABSTRACT FROM AUTHOR]

The phenomenon of white mist in a rapidly filling pipeline containing an entrapped air pocket is numerically and experimentally investigated. The air-water flow patterns, pressure, and temperature histories are synchronously recorded to illustrate their interrelations. The white mist phenomenon is particularly observed during fast transients, especially during the first compression of the air pocket. Comparisons between calculations and experiments indicate that the white mist primarily reflects a condensation process. More specifically, the air temperature increases because of rapid compression of an entrapped air pocket, and the high temperature could cause water to adhere to vapor at the pipe surface. For fast transients, the first compression causes a near-adiabatic air compression, but heat exchange effects become more significant in the subsequent compression and expansion cycles. As the initial air length decreases, the maximum pressure first increases and then declines, with the most dangerous air length occurring when about 3.4% is initially occupied by air. The ratio of the maximum pressure to the driving pressure increases approximately linearly with respect to the upstream pressure. A local-interpolation elastic-water model is developed by considering air-temperature change and its validity is confirmed by comparing the model and experimental results. [ABSTRACT FROM AUTHOR]

In order to avoid operational issues related to entrapped air in water transmission mains, water refilling procedures are often performed carefully to ensure no pockets remain in the conduits. Numerical models may be a useful tool to simulate filling events and assess whether air pockets are adequately ventilated. However, this flow simulation is not straightforward mainly because of the transition between free surface and pressurized flow regimes and the air pressurization that develops during the filling event. This paper presents a numerical and experimental investigation on the filling of water mains considering air pressurization aiming toward the development of a modeling framework. Two modeling alternatives to simulate the air phase were implemented, either assuming uniform air pressure in the air pocket or applying the Euler equations for discretized air phase calculations. Results compare fairly well to experimental data collected during this investigation and to an actual pipeline filling event. [ABSTRACT FROM AUTHOR]

Transient pressure associated with a rapidly filling pipeline containing two entrapped air pockets is investigated experimentally and numerically. A multiple-air-pocket elastic-water model considering multiple moving boundaries of water columns is developed by neglecting inertia and head loss of a short water column near air-water interfaces. The proposed model is validated by experimental data. Results show that when two air pockets in length are much different, the maximum pressure always arises in the smaller air pocket regardless of the blocking column's length. The case of the upstream air pocket with a similar length to the downstream is the most complicated and dangerous because (1) the maximum pressure may alternately arise in two air pockets as the blocking column increases, and (2) interaction of two air pockets could cause a huge pressure surge, which is likely much higher than with only one air pocket. The existing single-air-pocket model cannot effectively simulate pressure surge of the two air pockets. [ABSTRACT FROM AUTHOR]

The application of inverse transient analysis (ITA) to estimate the location and magnitude of lost lining and internal corrosion of metal pipelines is demonstrated for a field pipeline. The method uses a transient model and inverse search algorithm to analyze patterns of measured pressure reflections obtained after a transient pressure wave is induced in a pipeline. The method is applied in the field on a 6 km long section of a 750 mm nominal diameter steel pipeline with internal cement mortar lining. The equipment used for generating hydraulic transients and measuring pressure responses in the pipeline is described. Results of the field tests are analyzed to estimate the location and extent of internal wall damage along the pipeline. Extensive ultrasonic thickness survey results are used to corroborate the approximate location and magnitude of predicted pipeline wall damage. [ABSTRACT FROM AUTHOR]

This paper focuses on the analysis of unsteady pipe flows caused by a pump trip in a water pipeline system. Field experiments have been carried out to collect transient pressure and steady-state flow rate data in the Prado-Instituto Politécnico da Guarda (IPG) pumping system located in Guarda, Portugal. Observed transient pressures were compared with numerical results. Results obtained were excellent both in terms of damping and phase shift of the transient pressure signal, provided that unsteady friction effects were taken into account and an appropriate downstream end boundary condition was considered. The downstream end boundary condition was described by small tanks with variable level and with free discharge into the storage tank; the variation of water level in these small tanks results in the relief of extreme transient pressures (conversely to what is observed in the line-packing effect) and changes the shape of transient pressure waves. This analysis has shown that classical water hammer theory (neglecting unsteady friction) and the consideration of a constant-level reservoir at the downstream end do not accurately describe the observed transient behavior of pressurized pipe systems. [ABSTRACT FROM AUTHOR]

The authors previously described a new method [based on the new discrete vapor cavity model (new DVCM)] for numerical prediction of pressure changes during the water hammer with liquid column separation together with results of preliminary experimental verification of this method. This paper is a continuation of the research and includes results of additional laboratory tests and visualization of the cavitation zones generated during transient flow with liquid column separation. The results of these studies provide a better understanding of the phenomenon. It is shown that the phenomenon can have a distributed nature, which means that gas-vapor zones may be observed not only locally, in the vicinity of the shutoff valve, but may be spread along the pipeline length, and the intensity of this phenomenon decreases with distance from the valve. Laboratory test results were also used for further verification of the new DVCM. This verification shows that agreement between calculated and experimental results strongly depends on the friction model incorporated into the calculation. This agreement also depends on the intensity of liquid column separation: for cases of severe separation, the differences between numerical and measured pressure changes are small and accepted from the practical point of view. [ABSTRACT FROM AUTHOR]

This work presents a modification to steady-state water distribution network (WDN) simulation models to account for directional devices such as check valves (CHVs) and flow-control valves (FCVs). These devices, allowing water flow control in a definite direction, are important to manage the hydraulic system functioning over time by considering the variation of some boundary conditions (e.g., required demands and tank levels). However, the simulation models are built on the assumption that water can flow in both directions of each pipe in the hydraulic system, and the information on directionality of some devices is not automatically allowed. Thus, in WDN models, those devices are currently modeled using a heuristic approach intermixed with solving the problem of steady-state WDN analysis. For this reason, a different approach using content and cocontent theory was recently proposed to define the conditions that guarantee the existence and uniqueness of the solution. The alternative proposed in this paper presents an adjustment of the energy balance equations to account for flow-control valves. Check valves are treated as a special case of flow-control valves, whereas the directionality of pumps, which are equipped with a check valve to avoid reverse flow, is modeled by means of their implicit check valve. Once the status of such directional devices is identified, a topological analysis of the network is performed. The methodology is applied to the demand-driven and pressure-driven analysis of a WDN solved by means of the global gradient algorithm, although it could be easily extended to other algorithms. [ABSTRACT FROM AUTHOR]

The classical assumption of representing total demand along a pipe as two lumped withdrawals at its terminal nodes is hitherto common. It is a simplification of the network topology which is useful in order to drastically reduce the number of nodes during network simulation. Conversely, this simplification does not preserve energy balance equation of pipes and, for this reason, it is an approximation that could generate significant head loss errors. This paper presents a modification of the global gradient algorithm (GGA) which entails an enhancing of GGA (EGGA) permitting the effective introduction of the lumped nodal demands, without forfeiting correctness of energy balance, by means of a pipe hydraulic resistance correction. The robustness and convergence properties of the algorithm are compared with those of the classical GGA. Furthermore, the effectiveness of EGGA is demonstrated by computing the network pressure status under different configurations of the connections along the pipes of a test network. [ABSTRACT FROM AUTHOR]

Water quality models based on accurate mixing data at cross junctions are important for estimating concentrations of chemical species in municipal water distribution systems. Recent studies indicate that the instantaneous complete (thus “perfect”) mixing assumption potentially can result in an erroneous prediction of water quality. The present study examines the updated “incomplete” solute mixing model at cross junctions in a network having multiple cross junctions. The model performance in predicting solute transport was evaluated through a series of tracer experiments in a pressurized 5×5 network with 9 cross junctions. The perfect mixing model consistently overestimated solute dilution at cross junctions and predicted evenly distributed solute concentration throughout the network. In contrast, the incomplete mixing model demonstrated uneven distribution patterns with a distinct solute plume, and the corresponding results were significantly more accurate than those based on the perfect mixing assumption. Average prediction errors in tracer concentrations were 15 and 66% using the updated and perfect mixing models, respectively, and the difference was statistically significant (P-value <0.001). Therefore, this study concludes that the incomplete mixing model can drastically improve the prediction of solute transport in pressurized pipe systems that have multiple cross junctions. [ABSTRACT FROM AUTHOR]

A pressurized water system may be subjected to high pressure surges because of the expulsion of a trapped air pocket through an orifice at the downstream end of the pipe. Results are presented of laboratory experiments, in which pressure histories were recorded for different upstream heads, air pocket volumes, and orifice sizes. The resulting pressure oscillation pattern was divided into two distinct stages: a first phase of low-frequency pressure oscillation during the air release, followed by a sudden pressure increase with water hammer characteristics when the water column reaches the orifice. The experimental results show that the duration of the first phase decreases substantially with increasing upstream head and orifice size, and increases with air pocket volume. A simple relationship was deduced, which agrees well with experimental data. The maximum pressure peaks, always observed in the water hammer phase, increased with upstream head and orifice size, whereas the volume of the air pocket appeared to be a less significant factor in the range investigated. A simple predictive equation was deduced based on Allievi–Joukowski results. [ABSTRACT FROM AUTHOR]

Surge protection devices, such as surge tanks and air chambers, have been modeled with the impulse response method for transient analysis of water distribution systems. The lumped inertia model and continuity equation are used to represent nonpipe hydraulic elements. Results of pressure or discharge variations obtained by using the impulse response method and the method of characteristics are in good agreement. The impulse response method provides total pressure and discharge along any pipeline segment by direct integration of the ratio of complex head or complex discharge to a complex downstream discharge, respectively. A modification is proposed so that transition between turbulent and laminar flows can be considered. The representation of hydraulic devices has been incorporated into the impedance matrix method, which was developed for heterogeneous and multilooped pipe network systems. The potential advantages of the proposed method over other conventional approaches were investigated by applying the proposed method to hypothetical pipe network systems. [ABSTRACT FROM AUTHOR]

Maintenance or repair of water mains may require the interruption of flow. Reinitiation of flow may present opportunities for the interaction of air and the accelerating water, resulting in undesirable pressure transients. This study focuses on air intrusion during flow startup in an initially filled horizontal pipeline supplied by a constant-head reservoir. Flow was initiated by opening the downstream end, allowing a free discharge at that point. During the initial phases of flow startup, an air cavity intruded in the upper portion of the pipe cross section while water exited the pipeline through the lower portion. The initial reservoir head controlled the rate of water velocity increase and, thus, the air intrusion advance. Air intrusion occurred until the water velocity was sufficient to arrest the intrusion. Higher reservoir heads resulted in the subsequent expulsion of the intrusion from the pipeline. However, for lower reservoir heads, the intrusion was not expelled, but readvanced to a final position that was controlled by shear forces. Criteria are developed for the flow conditions necessary to arrest the air intrusion in a horizontal pipeline as well as the intrusion lengths to be expected. [ABSTRACT FROM AUTHOR]

The analysis of the dynamic response of a pressurized water pipeline system is important for the design and also the integrity monitoring of these systems. An efficient method for summarizing the behavior of a pipeline system is through the determination of their system response functions. These functions can be extracted by injecting a pressure signal with a wide bandwidth that persists over the length of a pipeline system. Unlike electrical and mechanical systems, generating such signals in pressurized water systems is difficult. Valves capable of generating a signal against the system back-pressure often lack the necessary maneuverability to ensure the signal is sharp (and hence with high-frequency content) and the generated transient is often large in amplitude, risking damage to the system. A method for generating a small amplitude transient signal with a wide band of frequencies is desirable. This paper presents the design for a side discharge valve for generating a pseudorandom binary sequence of pressure changes that are of a small magnitude in relation to the steady state head of the pipeline. The pseudorandom pressure sequence is used to provide an estimate of the system response function. The continuous form of the signal allows the amplitude of each individual pulse within the signal to be small while maintaining the same signal bandwidth. The valve has been tested experimentally and was found to provide a good match with the theoretical response of the pipeline. The method provides a practical alternative to frequency sweeping using sinusoidal signals or sharp valve closures for the extraction of the response functions. Once determined, the system response function can be utilized to detect system faults such as leaks and blockages. [ABSTRACT FROM AUTHOR]

The hydraulic performance of pipelines can be significantly affected by the presence of biological growth on internal surfaces. The change in wall roughness brought about by the biofilms has been studied by the use of headloss tests, precleaning and postcleaning of the pipelines in three Tasmanian hydroelectric schemes. Results of the headloss testing show that improvements to hydraulic efficiency can be achieved from the cleaning of biofouling material. The data, when plotted as a Moody diagram, shows that the friction law for conduits roughened by biological growths may not always follow a Colebrook-White type relationship, although the results are too narrow in Reynolds number to be conclusive. It was found that bacteria made up the majority of the biofilm biomass in the pipelines studied. Based on molecular analysis, members of the class Alphaproteobacteria were the most frequently detected followed by members of the phylum Chloroflexi. [ABSTRACT FROM AUTHOR]

Transient tests can be reliably used for the diagnosis of pressurized pipe systems. As a matter of fact, the pressure signals acquired during these tests can reveal the presence of anomalies, e.g., leaks, since any irregularity in the pipe gives rise to reflected waves which in turn create discontinuities in the observed signal at the measurement section. In order to make the most of the interpretation of the pressure signals, as well as to improve the effectiveness of the location of leaks, wavelet analysis—a powerful tool within the realm of harmonic analysis—can be used. It aids in the diagnosis of pressure pipe systems by better exposing pressure signal discontinuities and precisely determining the arrival time of the pressure waves reflected by leaks, thus locating the leak itself. Since many wavelet transforms are available and the choice is driven by the specific application, both continuous and discrete wavelet transforms are considered in the paper, comparing different mother wavelets. Then the reliability of the technique with respect to the noise effects is tested on numerically simulated and experimental pressure signals. Specifically, it is shown that the wavelet analysis of numerical signals, with and without superimposed white noise, facilitates testing the ability of this tool to recognize small step variation—corresponding to small leaks—using low cost transducers. [ABSTRACT FROM AUTHOR]

On the basis of theoretical considerations, the technical note presents two practical formulas for the dimensioning of air valves when filling a pipe with water. One is to be used for designing air valves on the basis of the maximum allowed water hammer overpressures; the other when the maximum in pipe water velocity is set. The reliability of these formulas was tested with a numerical model based on the same hypothesis, which was in turn verified with experimental tests. [ABSTRACT FROM AUTHOR]

In this study optimum design of municipal water distribution networks for a single loading condition is determined by the branch and bound integer linear programming technique. The hydraulic and optimization analyses are linked through an iterative procedure. This procedure enables us to design a water distribution system that satisfies all required constraints with a minimum total cost. The constraints include pipe sizes, which are limited to the commercially available sizes, reservoir levels, pipe flow velocities, and nodal pressures. Accuracy of the developed model has been assessed using a network with limited solution alternatives, the optimal solution of which can be determined without employing optimization techniques. The proposed model has also been applied to a network solved by others. Comparison of the results indicates that the accuracy and convergence of the proposed method is quite satisfactory. [ABSTRACT FROM AUTHOR]

A methodology is presented for the detection of partial blockages in single pipelines by the frequency response method. A steady-oscillatory flow produced by the periodic opening and closing of a valve located at the downstream end is analyzed in the frequency domain by using the transfer matrix method, and a peak pressure frequency response at the valve is developed. The comparison between the peak pressure frequency responses obtained by using the frequency response method and the method of characteristics is satisfactory. If there is a single partial blockage in a piping system, its location may be detected by the pattern and the number of peaks in the peak pressure frequency response. The size of the partial blockage may be determined from the mean peak pressure fluctuation. For two partial blockages, the effective size of the blockages can be determined from the peak pressure frequency response. Knowing the pre- and postdevelopmental frequency responses of a system with an additional partial blockage, the location and size of this additional partial blockage can be detected. [ABSTRACT FROM AUTHOR]

This paper describes the proportional demand method and the target demand method, two techniques for adjusting estimated demands in hydraulic models of water distribution networks to produce solutions that are consistent with available supervisory control and data acquisition (SCADA) data. The two techniques assume that pipe resistances and SCADA data are accurate and that the combination of SCADA data and demand estimates produce overdetermined problems. Nodal demands are regarded as stochastic variables which fluctuate about an estimated mean value. The method of weighted least squares is used to obtain solutions that satisfy all of the constraints imposed by SCADA data with adjusted nodal demands that most closely resemble the estimates. The methods are intended for use in real-time modeling but are limited to quasi-steady state flow. The paper demonstrates the methods on two example problems. [ABSTRACT FROM AUTHOR]

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Pipe network computer models of water systems that include hydropneumatic tanks can be used to evaluate performance of existing water systems or in the design of new distribution facilities. Pipe network models allow the modeling of storage tanks in which the free water surface is variable with the inflow and outflow. Most existing pipe network models do not allow direct input of hydropneumatic tanks. Some writers describe modeling of hydropneumatic tanks as a fixed diameter tank of an equivalent area based on the maximum and minimum operating pressures of the tank. In real hydropneumatic tanks, the pressure change due to input or output of water is greater as more water is stored in the tank. A relationship to define the geometry of a free water surface tank that would exactly simulate a hydropneumatic tank was derived which can be input into a pipe network model using the variable area tank feature. [ABSTRACT FROM AUTHOR]

The article offers the authors' insights to comments regarding their study "Influence of Entrapped Air Pockets on Hydraulic Transients in Water Pipelines." It explains that all water regions except for water column with a length ΔLwi consider inertia and that the proposed model only ignores the water column's energy loss. It adds that the instability was caused by changes in the slope, and reasons for pressure attenuation are the pipe friction and turbulence production.

A non-intrusive fault detection technology for real time condition assessment of pipelines is highly desirable for pipeline operators and the use of artificially induced fluid transients for this purpose has been the topic of many studies in the past. Fluid transients are stress waves in the fluid that can propagate through pipelines at high speeds and can collect information on the pipe condition during its travel. Whilst many transient-based fault detection methods have been proposed in the literature, little work was done on the characteristics of the transient signal that is best suited for fault detection. Such a study is critical for the development of this technology as the generation of controlled pressure waves is a challenging key step of the procedure. This paper presents analytical, numerical and experimental results to illustrate the effect of signal bandwidth (frequency content) of the induced transient signals has on the spatial resolution, accuracy and range of transient based fault detection. The results demonstrate that higher bandwidth signals provide more accurate fault detection at the expense of detection range. [ABSTRACT FROM AUTHOR]

Modelling floods in urban areas generally requires the modelling of both surface and subsurface flows, along with the exchange discharges between these flows. These latter exchanges are studied on an experimental facility at the Ujigawa Open Laboratory of Kyoto University representing a typical urban drainage system with a single street connected through inlets to a drainage pipe located underneath. An exchange model is developed for the cases in which exchange flows are pressurized, applying a head balance between the surface and subsurface layers and using common head loss formulae. Results of the exchange model agree with experimental measurements and show that, for this experimental setup, the exchanges cannot be modelled by fitting a simple and commonly used orifice-type equation. A hydrodynamic model coupling the one-dimensional (1D) and two-dimensional (2D) shallow water equations for, respectively, the pipe and the street flows and including the analytical exchange model is used to simulate the experimental flows. The numerical model can simulate the global characteristics of both street and pipe flows but shows some discrepancies concerning local perturbations of street flow because of the exchange processes. [ABSTRACT FROM AUTHOR]

The article discusses the article "Method to Cope with Zero Flows in Newton Solvers for Water Distribution Systems," by Inna F. Kodzhespirov and colleagues. Topics include the Darcy-Weisbach formula, the global gradient algorithm (GGA), and the pipe conductivity truncation technique. It mentions the occurrence of zero flows, power failures and pipe failures at pump stations, and the use of mathematics packages.

The article discusses the influence of entrapped air pockets on the water pipeline with hydraulic transients. It says that a simplified model has been proposed to create the pressure variations on pipeline that contains an entrapped air pocket. It states that short water column near the air-water interface results on liquid inertia and energy loss. It adds that the result shows that the proposed model accurately predicts peak pressures.