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This paper aimed to justify the performance of a non-oscillatory TPA-based model proposed by the authors for capturing transient mix flow in sewer systems consisting of a variety of pipe shapes. The model utilizes a first-order Godunov Finite volume numerical scheme in which a Harten–Lax–van Leer (HLL) Riemann solver was used for calculating the fluxes at the cells’ boundaries. The spurious numerical solution associated with the transient mix flow analysis is suppressed by enhancing the numerical viscosity of the scheme when the pipe pressurization is imminent. Due to the lack of experimental data for systems with pipe shapes other than circular and rectangular, a hypothetical pipe system for which analytical solutions exist was employed to verify the model performance. The results reveal that for all pipe shapes considered, the model provides oscillation-free solutions even at a high acoustic speed of 1400 m/s. It is also observed that the numerical results are in perfect agreement with the analytical solution. The obtained results conclude that the proposed model can be utilized to capture transient responses of sewer systems with any pipe shape.

Construction of a conveyance tunnel through rock often induces the ingress of groundwater into the tunnel, a flow that changes both the hydrogeological regime of the tunnel and its environment. To explore this key interaction, a novel modeling approach using the conduit flow process (CFP) is developed that considers both the hydraulic head and the ingress of water from the rock matrix during excavation. The resulting flow values are predicted through an adapted MODFLOW numerical model into which the tunnel is introduced with the aid of the new CFP approach. The CFP approach can simulate both laminar and turbulent flow in the tunnel whether the flow is free surface or pressurized. Several simulations, including one for which the permeability of the tunnel perimeter is assumed to be identical to the hydraulic conductivity of the surrounding rock matrix, are then used to explore the sensitivity of the predicted head and flow conditions to the permeability of the tunnel perimeter. Comparisons of the numerical results with field data from the Kerman Water Conveyance Tunnel in Iran show that the proposed approach accurately predicts the spatial variation of both groundwater ingress and hydraulic head.

Purpose The velocity head is usually neglected in the energy equation for a pipeline junction when one-dimensional (1D) hydraulic transient flow is solved by method of characteristics. The purpose of this paper is to investigate the effect of velocity head on filling transients in a branched pipeline by an energy equation considering velocity head. Design/methodology/approach An interface tracking method is used to locate the air–water interface during pipeline filling. The pressured pipe flow is solved by a method of characteristics. A discrete gas cavity model is included to permit the occurrence of column separation. A universal energy equation is built by considering the velocity head. The numerical method is provisionally verified in a series pipeline and the numerical results and experimental data accord well with each other. Findings The numerical results show that some differences in filling velocity and piezometric head occur in the branched pipeline. These differences arise because the velocity head in the energy equation can become an important contributor to the hydraulic response of the system. It is also confirmed that a local high point in the profile is apt to experience column separation during rapid filling. Significantly, the magnitude of overpressure and cavity volume induced by filling transients at the local high point is predicted to increase with the velocity in the pipes. Originality/value The velocity head in the energy equation for a pipeline junction could play an important role in the prediction of filling velocity, piezometric head and column separation phenomenon, which should be given more attention in 1D hydraulic transient analysis.

The rapid filling behaviour of a bypass pipeline is analysed numerically using an elastic model combined with the polytropic law for the air phase. These explorations show that the system can be readily filled when the entrapped air in the bypass line could be released into the atmospheric air, but that large pressure surges are predicted due to the collision of the filling fronts coming from the opposite ends of the bypass line. As expected, both the distance to the upstream reservoir and the size of the bypass line influence the magnitude of resulting overpressures. The magnitude of these predicted surges is naturally reduced by modelling the presence of the compressible air, the presence of which tends to cushion the impact of the filling fronts. A decrease in the volume of initially entrapped air increases the magnitude of the pressure surge and decreases the period of oscillation. In general, entrapped air is beneficial during rapid filling; however, such air is certainly problematic for cond...

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Based on Inverse Transient Analysis (ITA) method, a real-time leak detection method is proposed to capture leak location and the associated leak rate in oil pipe conveyance systems. In the proposed approach, location and flow rate of leak (if any), the fluid properties, as well as physical parameters of the system, are calculated in consecutive periods through minimizing the discrepancy between the calculated and measured flow parameters of the system. The method of characteristics is employed to numerically calculate the transient responses of the system and the genetic algorithm is utilized as the optimization engine. The proposed approach was applied to several real pipeline systems in which the required transient flow data are either directly collected from the field or fabricated with a third-party numerical software. Extensive numerical explorations were conducted to investigate the performance of the proposed method in real-time leak detection and to determine the extent to which field data errors, stemming from Supervisory Control and Data Acquisition (SCADA) systems and measurement equipment, affect the leak flow rate and location detectability of the proposed approach. The results show that the proposed approach provides promising results under a variety of transient and steady-state flow conditions even in the case with small leak flow rate of around 2% of the line rate. The results also reveal that the noises in the measurement data and the errors originated from SCADA systems do not significantly compromise the leak detectability of the proposed approach, confirming that the proposed approach can be utilized in practice.

On the basis of the two-component pressure approach, we developed a numerical model to capture mixed transient flows in close conduit systems. To achieve this goal, an innovative Godunov finite-volume numerical scheme is proposed to suppress the spurious numerical oscillations occurring during rapid pipe pressurization. To dissipate the spurious numerical oscillations, we admit artificial numerical viscosity to the numerical scheme through applying a proposed Harten, Lax, and van Leer (HLL) Riemann solver for calculating the numerical fluxes at the computational cell interfaces. The proposed solver controls the magnitude of the numerical viscosity through adjusting the left and right wave velocities. A wave velocity calculator is proposed to optimally distribute the numerical viscosity over several computational cells around the computational cell in which the pressurization front is located. The proposed solver admits significant artificial numerical viscosity when the pipe pressurization is imminent and automatically reduces it in other places, in this way the numerical diffusion and data smearing is minimized. The validity of the proposed model is justified by the aid of several test cases in which the numerical results are compared with both experimental data and the results obtained from analytical methods. The results reveal that the proposed model succeeds in completely removing the spurious numerical oscillations, even when the pipe acoustic speed is over 1000 m/s. The numerical results also show that the model can successfully capture occurrence of negative pressures during the course of transient flow.

Experimental studies show that the parameters that contribute to fatigue in PVC pipes include the number of pressure cycles, the amplitude of the transient pressures, and the average pressure to which PVC material is exposed during the transient. Based on such experimental studies, design standards have been set to provide the required data for calculating the permissible number of pressure cycles below which the PVC pipes are considered safe against fatigue. However, the key challenge is to determine the amplitude and the number of transient pressure cycles, values which should be the outcome of a thorough transient analysis. Using a quite simple concept, the Plastic Pipe Institute developed the computer program PACE for the analysis of the fatigue failure mode in PE and PVC pipes. However, the concept behind this program disregards the intensity of the transient in the system, and thus its results are questionable in more realistic systems. The current research aims to explain and improve on the underlying concept of the program PACE. To this end the fatigue analysis of a hypothetical pumping system is made by the aid of both the program PACE and the results of a thorough transient analysis considering different mode of operation of the pumping system. The results show, somewhat predictably, that the analysis of fatigue in PVC pipes is a crucially system dependent; thus, the concept utilized by the PACE program is overly simplistic. In addition, the numerical results obtained imply that PVC pipes are safe against fatigue failure in a wide verity of operational conditions and that a reliable fatigue analysis can be only achieved through utilizing the data obtained from a though transient analysis.

A new mechanism for inducing column separation and rejoinder during rapid filling of gravity pipe systems is numerically and conceptually identified. A shock-fitting model is combined with the discrete gas cavity model to compute the resulting water hammer due to column rejoinder. Numerical explorations show that column separation may be induced during rapid filling when the water column encounters a flow restriction such as a partially open valve followed by a “V-shaped” pipe profile. Interestingly, the resulting pressure spikes are sometimes capable of inducing a new or secondary column separation event near the front of the advancing water column front, an event associated with the sudden jump in velocity carried by the propagating rejoinder shock wave. A physical interpretation of the captured events is provided and model results are shown to compare favourably to a previously published set of experimental data involving column separation and rejoinder.

The Preissmann Slot Method concept is implemented by a first-order Godunov type numerical model. In order to remove the spurious numerical oscillations, an approximate HLL Riemann solution is proposed to automatically augment the numerical viscosity whenever the water level is in the vicinity of the conduit roof and the pressurization of the conduit is proximate. The comparison of the model's results with analytical solutions show that the proposed model can provide non-oscillatory solutions over a wide range of the wave velocities between 10 to 1000 ms -1 . The results confirm that the proposed model also limits data smearing to a reasonable level.

The research described in this article concerns contaminant intrusion into a water distribution system associated with transient events. A Lagrangian-based contaminant transport model was coupled with an Eulerian-based transient hydraulic model to study contaminant intrusion and its propagation in a water distribution system. The hydraulic model was used to detect negative pressures during normal system operations. The Lagrangian-based contaminant transport model reduced simulation time and avoided numerical dissipation and dispersion errors that often occur with Eulerian-based modeling. The proposed water quality model was used to evaluate two systems described in the literature for their potential vulnerability to contaminant intrusion. The new transient water quality model realistically simulated intrusion events and contaminant propagation in both systems.

Air can be entrapped in water and wastewater systems under a variety of conditions, and if such air is not managed properly, it can impose considerable operational penalties. To avoid these problems and the dangers associated with air pockets, several air management strategies have been routinely suggested. However, the devastating consequences of air pockets frequently documented in the literature imply the need for further development in this area. Improving air management obviously requires a thorough understanding of the current strategies and their shortcomings. This paper overviews the sources of air in pipes and key consequences associated with its presence. Current measures for managing air in water pipes are reviewed and critiqued. Finally, knowledge gaps that limit the efficient application of current air management strategies to real world problems are identified, and suggestions for future development are presented.

This paper investigates the source of the spurious numerical oscillations often observed in simulations using the well-known Preissmann slot method and proposes a nonoscillatory numerical fix that can efficiently suppress the numerical oscillations. The root of these oscillations is identified by comparing the orbits calculated by a first-order Godunov type model with an ideal numerical orbit in the phase plane. It is found that in the very thin layer in the vicinity of the conduit roof the numerical model has insufficient numerical viscosity to avoid the often-observed oscillations. In order to remove these spurious oscillations, an approximate Riemann solution is proposed that automatically enhances the numerical viscosity whenever the water level is in the vicinity of the conduit roof and the pressurization of the conduit is proximate. A comparison of results from the proposed model with both experimental data and analytical solutions show that it can provide nonoscillatory solutions over a wid...

A global energy-auditing approach is used to describe the complex transient flow associated with sudden pressurization of a confined pipe system containing entrapped air pockets. The key concept is that the greatest pressures following pressurization are directly related to the amount of energy absorbed by the air pockets. The energy approach leads to an insightful understanding of the transient pressurization event, one that clarifies the underlying physics and that better explains several previously published observations. Moreover, the energy formulation leads to analytical algebraic expressions that can be numerically confirmed.

On the premise of water hammer theory, a numerical model is proposed for simulating the filling process in an initially empty water conveyance pipeline with an undulating profile. Assuming that the pipeline remains full and ignoring air and water interactions in the already filled pipeline, the ongoing filling is simulated using the method of characteristics on an adaptive computational grid. The performance of the model is verified using previously published experimental and rigid column data. The model nicely replicates published experimental data. The model shows that the movement of the filling front into the system can be assumed as a rigid column as long as the flow away from the filling front is undisturbed elsewhere. Furthermore, applying the model to a hypothetical pipe system with an inline-partially open valve shows that the proposed model is robust enough to capture the transient events initiated within the moving column, a vital capability that the existing rigid water column models lack.

One key alternative for removing, preventing, and effectively coping with the often vexing presence of air in water pipelines is the combination air-vacuum valve. Despite their often effective role, such valves can be highly problematic if not well designed and maintained. This paper critically reviews the current design, application, functionality, and simulation of air valves and the associated shortcomings, with a primary focus on air/vacuum valves (AVVs). It is argued that the efficient number of air valves along undulating pipelines is yet to be fully articulated. Air-valve simulations should expressively consider their dynamic behavior, the physical behavior of any air pockets that might form below an air valve, and the varying character of the water surface at the air valve location. There is a pressing need for a comprehensive and systematic study on the proper sizing and location of AVVs for the transient protection of systems. Overall, the efficient application of AVVs requires broad res...

Concepts relating to energy transformations within built and natural systems have been some of the most fruitful in the history of science and engineering. The property of energy summarizes essential changes both in a system’s state and key interactions with its environment. Traditional unsteady flow analyses, based on momentum and continuity relations, have been dominated by considerations of wave mechanics, such as unsteady fluid friction which is typically accommodated via adjustments to the momentum equation. The current paper demonstrates how conventional analyses can be supplemented with metrics that can provide a complementary understanding of transient flows. Specifically, this study considers the classical Joukowsky equation, mass oscillations, and the role of energy in analyzing the performance of transient protection devices. The goal is to gain insight by considering energy transformations and interactions.

The entrapment and compression of air in closed conduits is a relevant problem in pipeline systems that experience unsteady flow regimes. Severe surging result…

Water column separation during rapid pipeline filling is numerically explored using a one-dimensional (1D) model that employs the method of characteristics to solve the governing equations and the well-known discrete gas cavity model (DGCM) to represent column separation. Extensive numerical experiments helped to identify the conditions under which column separation may occur during the rapid filling and to gain a physical sense of when the local rejoining pressures can be most severe. The major findings are that local V-shaped pipeline profiles following knee points are prone to the occurrence of water column separation and that the magnitude of the resultant overpressures markedly depends on the geometrical and hydraulic characteristics of the profile. Significantly, the propagation and reflection of the first pressure spike following column rejoining at a knee point can cause the onset of column separation in other parts of the pipe system. It is also found that short pipes must usually be stee...

Rapid pressurization of liquid pipelines containing entrapped air may result in extreme overpressures. Both experimental and numerical studies have shown that the magnitude of the induced pressure has important sensitivities to many physical parameters even though the complex nature of the system’s transient responses has tended to obscure the physical mechanisms themselves. To provide insight and guidance to key design issues, this paper proposes an energy auditing approach to elucidate the physics of the transient events leading to the extreme pressure rise during pipe rapid pressurization events. The proposed approach is then utilized to provide physical understanding of the features of the flow and the system parameters affecting the maximum pressure rise during rapid pressurization of pipe system. Both rigid column and elastic numerical models are then employed to verify the results obtained from the proposed approach.Copyright © 2014 by ASME

This paper presents a quasi-two-phase flow model for simulating filling in water pipe systems. The model employs a shock-fitting algorithm for tracing the water column advancement during filling. The method of characteristics (MOC) along with Discreet Gas Cavity Model (DCGM) is utilized to capture the possible water column separation and induced water hammer pressures during filling. The state-of-the-art air valve boundary condition is improved to account for the two-phase flow usually established in the pipe on the downstream side of the air valve. The results show that the proposed model can (1) replicate the negative pressure and consequent water column separation; (2) reproduce the secondary transient pressure following the releasing of the air at air valve locations; (3) simulate controlled air release, a strategy usually employed for alleviating the severity of secondary transient events; (4) capture the final steady state flow condition even when the pipe system maintains both open channel and pressurized flow simultaneously; and (5) reproduce air binding and consequent flow reduction in the case that an air valve fails to release the air from the system.

This paper presents a novel hierarchical multilevel decentralized optimal power flow (OPF) for power loss minimization in three-phase unbalanced large-scale distribution systems via optimal reactive power scheduling of rooftop photovoltaics generators. The system is decomposed into three levels corresponding to: 1) the primary; 2) the lateral; and 3) the secondary feeder subnetworks of distribution systems. A distributed sequential coordination scheme based on analytical target cascading method is developed to minimize power losses while considering the operational constraints. Results based on the proposed method are compared with centralized OPF for validation. Control based on the proposed method is compared with no reactive power control and local reactive power control to identify its effectiveness. Further, a virtual feeder is introduced to separate the coupled subnetworks into decomposed layers, which enables parallel processing of the optimization problems to reduce computational complexity and provide faster solution. A 559-node large-scale distribution network built based on the IEEE 37 node test system is used to demonstrate performance of the proposed algorithm.

The current study discusses the benefits of combining an integrated, system-wide energy approach with conventional transient analyses from the perspective of anticipating, modelling, understanding, and mitigating the negative impacts of transient flows. A case study comprising a pumping pipeline demonstrates how an energy approach provides additional perspective and leads to a better understanding of the underlying transient behavior, and understanding that can lead to a more efficient selection of protection strategy. This study is nicely complementary to conventional approaches, and highlights the insights and checks that are sometimes available by using an energy approach to track system transformations and system states.

This study evaluated substance use among a sample of 205 psychiatric inpatients (70 women and 135 men) chosen randomly. The subjects (who had schizophrenia or mood disorders) were evaluated on a confidential questionnaire by interview. Their mean age was 35 yr. ( SD = 10.4, range 16 to 69). Of these participants, 76% of the 135 men and 34% of the 70 women admitted use of substances: cigarettes (74% of men, 31.4% of women), opiates (31.9% of men, 4.3% of women), alcohol (23.7% of men, 4.3% of women), hashish (8.9% of men, no women), marijuana (3.7% of men, no women), and cocaine or LSD by none. Only 27% of the women and 63% of the men reported still using substances regularly; some reported using more than one substance. Of the current users, 61.8% of the schizophrenics, 20% of unipolar depressed, and 37.5% of bipolar patients reported current use. The reasons for substance use in order of frequencies of mention were release of tension, seeking pleasure, and need (to avoid withdrawal symptoms) by men and habit, seeking pleasure, and need by women.