Pressure-driven Analysis Research Articles

Development of a Fuzzy-Function-Based Performance Indicator for Water Distribution System’s Emergency Condition

Emergency interconnected operation (EIO) between adjacent blocks in a water distribution system (WDS) is one of the most effective countermeasures of a water utility when abnormal conditions (e.g., suspended water supply, pipe burst) occur at a certain location. For improved WDS operation and management, calculating a reliable performance indicator that accurately represents the states of consumers under both normal and abnormal conditions is essential. In this study, a water supply performance indicator (WSPI) was developed for assessing the hydraulic performance of a WDS in terms of consumer usability and satisfaction. A fuzzy function is used to represent the consumer satisfaction with the water supply level, and the satisfaction of different consumers can be adjusted by setting the variables of the fuzzy function. The WSPI can be applied to a hydraulic analysis model based on data from an actual WDS to assess the water supply capacity for each node and the entire network. It can also be used in an advanced pressure-driven analysis model to assess the WDS performance under various abnormal conditions. The proposed WSPI was applied to six suspended water supply scenarios of an actual WDS with and without EIO to assess the effectiveness of this countermeasure.

A New Set of Local Indices Applied to a Water Network through Demand and Pressure Driven Analysis (DDA and PDA)

In the analysis of drinking Water Distribution Networks (WDNs), performance indices are widely used tools for obtaining synthetic information about the WDN operating regime (pressures and flows). This paper presents applications of a series of local surplus indices that act in a new mathematical framework. This framework allows reworking many well-known performance and energetic indices and simultaneously allowing analysis of specific aspects of the WDN. The analyses are carried out using different resolutive hydraulic approaches: the Demand-Driven Analysis (DDA) and the Pressure-Driven Analysis (PDA), typical of software such as EPANET and WaterNetGen. The authors analyse the hypotheses necessary for the application of these models, and how these influence the results of both the hydraulic modeling and the resilience indices assessment. In particular, two resilience indices are reformulated through the new local surplus indices and all of them are then simulated in different conditions for a water network known in literature as the Kang and Lansey WDN. The solving model assumption effects are deepen, reporting graphical and numerical results for different consumption scenarios and the different hydraulic approaches used.

Accelerated Monte Carlo analysis of flow-based system reliability through artificial neural network-based surrogate models

Conventional Monte Carlo simulation-based methods for seismic risk assessment of water networks often require excessive computational time costs due to the hydraulic analysis. In this study, an Artificial Neural Network-based surrogate model was proposed to efficiently evaluate the flow-based system reliability of water distribution networks. The surrogate model was constructed with appropriate training parameters through trial-and-error procedures. Furthermore, a deep neural network with hidden layers and neurons was composed for the high-dimensional network. For network training, the input of the neural network was defined as the damage states of the k-dimensional network facilities, and the output was defined as the network system performance. To generate training data, random sampling was performed between earthquake magnitudes of 5.0 and 7.5, and hydraulic analyses were conducted to evaluate network performance. For a hydraulic simulation, EPANET-based MATLAB code was developed, and a pressure-driven analysis approach was adopted to represent an unsteady-state network. To demonstrate the constructed surrogate model, the actual water distribution network of A-city, South Korea, was adopted, and the network map was reconstructed from the geographic information system data. The surrogate model was able to predict network performance within a 3% relative error at trained epicenters in drastically reduced time. In addition, the accuracy of the surrogate model was estimated to within 3% relative error (5% for network performance lower than 0.2) at different epicenters to verify the robustness of the epicenter location. Therefore, it is concluded that ANN-based surrogate model can be utilized as an alternative model for efficient seismic risk assessment to within 5% of relative error.

Hindcasting the Functional Loss and Restoration of the Napa Water System Following the 2014 Earthquake Using Discrete-Event Simulation

Models that simulate postearthquake functional loss and restoration of water distribution systems support the development and implementation of more informed resilience-enhancing strategies. This study uses pipe damage, repair data, and a discrete-event simulation (DES) model to hindcast the water system damage and functional loss and restoration, following the 2014 South Napa earthquake. The DES model represents the water system as a set of entities (e.g., pipes, tanks, pumps) that interact through a sequence of events (e.g., earthquake damage, inspection) of variable duration that may be triggered at different points in time depending on the entity attributes (e.g., pipe vulnerability), access to resources (e.g., inspection crews), and the completion of other events. In addition to pipe damage and time-dependent inspection and repair processes, the DES model incorporates a pressure-driven analysis (PDA) that captures the restoration of water availability following the event. The tuned DES model is then used to simulate the postearthquake disruption and restoration of the City of Napa’s water supply for a Mw 6.7 event on the West Napa fault. By propagating the uncertainties in the damage to the network components (e.g., pipe) conditioned on the shaking intensity and the temporal (e.g., repair time) and resource-related (e.g., the number of inspection crews) variables, probabilistic descriptions of network component repair and water service restoration are generated.

Practical Head-Outflow Relationship Definition Methodology That Accounts for Varied Water-Supply Methods

Achieving reliable pressure-driven analysis (PDA) results that account for anomalies within water-pipe networks requires a head-outflow relationship (HOR) model that can calculate supply flow rate according to the supply pressure at each node. Many studies have suggested HOR models, but a methodology to define HORs that considers the actual residential environment of users and differing water-supply methods for residential buildings has not yet been proposed. This study considered water-use data from buildings and actual differences in residential environments in a surveyed area (including building heights, topography, and water systems within buildings) and water-supply methods (indirect/direct water supply, existence of a pump within buildings) to develop a methodology and derive a representative HOR for the target area for PDA. Further, a representative HOR was determined for each block by applying the developed methodology for two blocks with similar residential environments but different water-use patterns. It confirmed that the HOR induced through this process could provide high water-supply performance despite a low supply head and needed to reflect the diversity of the water-supply method. The proposed HOR-definition methodology can be easily applied in water-pipe network design and operation processes and ensure objectivity and rationality of HOR selection to yield reliable PDA results.

Multiphase DMA Design Methodology Based on Graph Theory and Many-Objective Optimization

Partitioning a water distribution system (WDS) into district metered areas (DMAs) is a difficult task due to the complex WDS structure and simultaneous consideration of multiple constraints. Further, alternative metrics can define DMA goals, and expressing and quantifying those objectives in an efficient algorithm is also challenging. To address the multifaceted set of objectives, a multiphase DMA design method is developed. DMA feed pipes are identified as the primary flow paths in a branched network. In the methodology presented here, the feed pipe network is first laid out by determining node clusters and boundary pipes that maximize the dissimilarity of pressures and modularities between clusters and minimize the number of cuts between clusters while defining the number of DMAs closest to the desired number. In the methodology’s second phase, secondary DMA feed pipes are identified by minimizing the number of secondary feed pipes and maximizing the nodal excess energy while maintaining desired pressure. Finally, a postoptimization analysis compares the performance of the Pareto solutions based on their availability, water quality, and daily leakage. System availability is calculated based on the minimum cut-set method combined with a new pressure-driven analysis method. To accelerate the optimization algorithm, two strategies are applied: step-by-step optimization and reducing the decision variable searching space by considering desirable DMA characteristics. The effectiveness of the methods is examined by applying it to the C-Town and real B-Town water distribution networks. Results demonstrate that the search space reduction method effectively decomposes the full network into DMAs in the face of multiple hydraulic and water quality metrics.

Development of a Binary Model for Evaluating Water Distribution Systems by a Pressure Driven Analysis (PDA) Approach

Investigation of Water Distribution Networks (WDNs) is considered a challenging task due to the unpredicted and uncertain conditions in water engineering. When in a WDN, a pipe failure occurs, and shut-off valves to isolate the broken pipe to allow repairing works are activated. In these new conditions, the hydraulic parameters in the network are modified because the topology of the entire system changes. If the head becomes inadequate, the Pressure Driven Analysis (PDA) is the correct approach to evaluate the performance of water networks. Hence, in the present study, the water distribution system was evaluated in pressure-driven conditions for 100 different scenarios and then using a type of neural network called Group Method of Data Handling (GMDH) as a stochastic technique. For this purpose, several most notable parameters including the base demand, pressure, and alpha (the percentage of effective supplied flow) were calculated using simulations based on a PDA approach and applied to the water distribution network of Praia a Mare in Southern Italy. In the second stage, the output parameters were used in a developed binary classification model. Finally, the obtained results showed that the GMDH algorithm can be applied as a powerful tool for modeling water distribution networks.

Improved Hydraulic Simulation of Valve Layout Effects on Post-Earthquake Restoration of a Water Distribution Network

To restore water pipes damaged by earthquakes, it is common to block the water flow by closing the associated shut-off valves. In this process, water supply suspension in the area connected to the isolated pipes is inevitable, which decreases the serviceability of the water distribution network (WDN). In this study, we identified the impact of valve layout (i.e., number and location) on system serviceability during a seismic damage restoration process. By conducting a pressure-driven-analysis (PDA) using EPANET 3.0, a more realistic hydraulic analysis could be carried out under the seismically damaged condition. Furthermore, by considering the valve-controlled segment in the hydraulic simulation, a more realistic water suspension area was determined, and efficient seismic damage restoration strategies were identified. The developed model was implemented on a WDN to demonstrate the effect of valve layout on the post-earthquake restoration process. Finally, effective restoration strategies were suggested for the application network.

A model for pressure driven analysis-design of water distribution networks

Pressure Driven Analysis (PDA) method provides the ability to simulate Water Distribution Networks (WDNs) more realistically. Most of the PDA-based models use either the Newton–Raphson method or the gradient method for simulation. The computational cost of these models is high, so that in the solution process of them a large system of equations is solved in each iteration. This paper presents a new model for PDA-based design and analysis of WDNs. The proposed model developed employing the graph portioning approach is named GPDA model. This model provides the PDA-based design and analysis of WDNs without any need of iterative computations for governing equations. Two example networks are designed and analyzed using the proposed model and the results are discussed. The obtained results confirm the ability and computational efficiency of the GPDA model for the design and analysis of WDNs.

Flow-Based Optimal System Design of Urban Water Transmission Network under Seismic Conditions

In this paper, an optimal system design for the seismic performance enhancement of a water transmission network was proposed. The main purpose of the optimal design is to maximize the system performance within a limited construction cost. The proposed model evaluates network performance through the spatially correlated seismic attenuation law, determination of the failure status of the network facility, and numerical modeling of water networks. For hydraulic simulation, a MATLAB computer code was developed to enable the EPANET program with pressure-driven analysis. To demonstrate the proposed model, an actual water transmission network of A-city, South Korea was adopted, and a water network map was constructed based on the geographic information system data. Numerical results showed that the optimized network model increased system serviceability and nodal serviceability by 9.9% and 11%, respectively, and the average nodal pressure of the network increased by 3.6 m compared to existing models. In addition, the result of the optimal pipeline design was utilized to compare the performance against interdependencies and the elapsed time of pipelines. The optimized network exhibited higher performance than the existing network, depending on the elapsed time and interdependence. Therefore, to maximize the performance of the water network, it is necessary to use optimized network design parameters according to the appropriate construction budget.

Application of Clustered-NA-ACO in three-objective optimization of Water Distribution Networks

ABSTRACTOptimal operation of pumping stations in Water Distribution Networks (WDNs) is presented based on three conflicting objectives, including 1) pumping energy costs, 2) hydraulic reliability, and 3) quality reliability. We proposed a three-objective optimization algorithm called Clustered Non-dominated Archiving Ant Colony Optimization (Clustered-NA-ACO) and evaluated the efficiency of this algorithm through DTLZ test functions. Incorporating k-means clustering strategy with NA-ACO can greatly improve the distribution of solutions and reduce the run time compared to NA-ACO. A pressure-driven analysis tool called EPANET-Iterative Modifications to Nodal Outflows (EPANET-IMNO) is developed for dynamic analysis of WDNs and linked directly to Clustered-NA-ACO. We applied this simulation-optimization tool to two WDNs. The results show that it is necessary to consider hydraulic reliability and quality reliability as two separate objective functions in WDNs with storage tanks. We also suggested the combined form of the two reliability indicators in the optimization of WDNs without any storage tanks.

Management of water distribution systems in PDA conditions using isolation valves: case studies of real networks

Abstract The current paper reports on a case study investigating water distribution system management in emergency conditions when it is necessary to seal off a zone with isolation valves to allow repair. In these conditions, the pressure-driven analysis (PDA) is considered to be the most efficient approach for the analysis of a water distribution network (WDN), as it takes into account whether the head in a node is adequate to ensure service. The topics of this paper are innovative because, until now, previous approaches were based on the analysis of the network behaviour in normal conditions. In emergency conditions, it is possible to measure the reliable functioning of the system by defining an objective function (OF) that helps to choose the optimal number of additional valves in order to obtain adequate system control. The OF takes into account the new network topology by excluding the zone where the broken pipe is located. The results show that the solution did not improve significantly when the number of valves reached a threshold. The procedure applied to other real case studies seems to confirm the efficiency of the methodology even if further examination of other cases in different conditions is necessary.

Water Distribution Network Reliability Assessment and Isolation Valve System

Mechanical reliability analysis of water distribution networks (WDNs) refers to the assessment to provide correct service to customers under abnormal functioning conditions due to system component failures. Mechanical reliability depends on the isolation valve system (IVS) effectiveness in isolating a network segment and on the failure probability. The main aim of this work was the formal development of reliability indicators considering pressure-driven analysis (PDA) for customer demand and topological changes. Three factors influencing reliability were identified: (1) the hydraulic behavior of the still-connected network; (2) the topological performance of the IVS; and (3) the topological performance of the IVS with respect to unintended isolation. The reliability performance assessment of the network over time depends on the hydraulic capacity of the WDN under abnormal functioning conditions and on two IVS performance topological indicators of the risk of disconnection and unintended isolations. The hydraulic capacity was computed using PDA, whereas the topological risks were computed considering the unsupplied demand in the isolated segment and the normalized failure probability, i.e., the probability of a segment disconnection for an assumed failure occurrence in the network. The development of a modularity index for an IVS was achieved in a consistent framework and the integrated design of an IVS and district metering areas was introduced. The framework allows the analysis of the isolation valve failure. A real Apulian WDN was used to discuss and demonstrate the theoretical findings.

Quantification of the Head-Outflow Relationship for Pressure-Driven Analysis in Water Distribution Networks

Pressure-driven analysis (PDA) has been applied as a general analysis technique because it can simulate a real water supply network based on reasonable theoretical assumptions. However, to provide reliable PDA results, it is necessary to determine a head-outflow relationship (HOR) expression that enables the calculation of the available outflow at each node at certain pressure intervals. In this study, experiment-based HOR quantification methods for PDA were proposed and the characteristics of HOR were first confirmed under various experimental conditions. To identify the hydraulic behaviors of WDNs (water distribution networks) for situations that are practically infeasible and cannot be reproduced, a WDN model was fabricated. Normal and abnormal conditions that cannot be immediately measured were configured to identify the relationship between the head and outflow under individual conditions via the WDN model. The goodness-of-fit of the various HORs were identified using the data from each node. Appropriate parameter values were defined and PDA uncertainty was confirmed. Finally, the HORs obtained through the experiments were selected instead of assumed HORs. Therefore, this study not only improves the reliability of PDA results, but also provides workers with an improved understanding of the correlation between heads and outflows at WDNs.

Using Nodal Infection Risks to Guide Interventions Following Accidental Intrusion due to Sustained Low Pressure Events in a Drinking Water Distribution System

Improving the risk models to include the possible infection risk linked to pathogen intrusion into distribution systems during pressure-deficient conditions (PDCs) is essential. The objective of the present study was to assess the public health impact of accidental intrusion through leakage points in a full-scale water distribution system by coupling a quantitative microbial risk assessment (QMRA) model with water quality calculations based on pressure-driven hydraulic analysis. The impacts on the infection risk of different concentrations of Cryptosporidium in raw sewage (minimum, geometric mean, mean, and maximum) and various durations of intrusion/PDCs (24 h, 10 h, and 1 h) were investigated. For each scenario, 200 runs of Monte Carlo simulations were carried out to assess the uncertainty associated with the consumers’ behavioral variability. By increasing the concentrations of Cryptosporidium in raw sewage from 1 to 560 oocysts/L for a 24-h intrusion, or by increasing the duration of intrusion from 1 to 24 h, with a constant concentration (560 oocysts/L), the simulated number of infected people was increased by 235-fold and 17-fold, respectively. On the first day of the 1-h PDCs/intrusion scenario, a 65% decrease in the number of infected people was observed when supposing no drinking water withdrawals during low-pressure conditions at nodes with low demand available (<5%) compared to no demand. Besides assessing the event risk for an intrusion scenario, defined as four days of observation, the daily number of infected people and nodal risk were also modeled on different days, including during and after intrusion days. The results indicate that, for the case of a 1-h intrusion, delaying the start of the necessary preventive/corrective actions for 5 h after the beginning of the intrusion may result in the infection of up to 71 people.

A Comparative Study on a Hydraulic and Water-Quality Analysis Method for Determining Rechlorination Injection Points for a Water-Supply Network

Water supply facilities are vulnerable to extreme weather events, such as droughts and floods. To establish a sustainable solution that resists accidents and disasters, a distributed system is required. To supply high-quality tap water using the existing water-supply network, rechlorination facilities must be installed to secure residual chlorine at the pipe end. In this study, a process is developed to determine the injection points and dosages of rechlorination using the latest pressure-driven analysis. The method was compared to the results of demand driven analysis methods. The proposed model was applied to P City in Korea to draw results. A detailed evaluation was performed to study how water pressure head and demand-based hydraulic and water quality analysis results impact the injection points and dosages of rechlorination. Thus, the existing demand-based model shows significant spatial deviations in the pressure head in the presence of water pressure drops, which subsequently lead to over-estimation of chlorine injection dosages for maintaining the concentration of residual chlorine. However, the proposed model involves a numerically validated theory and draws more reasonable results for hydraulic, water quality, and rechlorination dosages. The proposed model can be used as a decision-making tool based on hydraulic analysis for the supply of water of a stable quality.

Analysis of water distribution network under pressure-deficient conditions through emitter setting

Abstract. Pressure-driven analysis (PDA) of water distribution networks necessitates an assessment of the supplying capacity of a network within the minimum and required pressure ranges. Pressure-deficient conditions happen due to the uncertainty of nodal demands, failure of electromechanical components, diversion of water, aging of pipes, permanent increase in the demand at certain supply nodes, fire demand, etc. As the demand-driven analysis (DDA) solves the governing equations without any bound on pressure head, it fails to replicate the real scenario, particularly when the network experiences pressure-deficient situations. Numerous researchers formulated different head–discharge relations and used them iteratively with demand-driven software, while some other approaches solve them by incorporating this relation within the analysis algorithms. Several attempts have been made by adding fictitious network elements like reservoirs, check valves (CVs), flow control valves (FCVs), emitters, dummy nodes and pipes of negligible length (i.e., negligible pressure loss) to assess the supplying capability of a network under pressure-deficient conditions using demand-driven simulation software. This paper illustrates a simple way of assessing the supplying capacity of demand nodes (DNs) under pressure-deficient conditions by assigning the respective emitter coefficient only for those nodes facing a pressure-deficit condition. The proposed method is tested with three benchmark networks, and it is able to simulate the network without addition of any fictitious network elements or changing the source code of the software like EPANET. Though the proposed approach is an iterative one, the computational burden of adding artificial elements in the other methods is avoided and is hence useful for analyzing large networks.

Speed factors computed for pumping schedules in Water Distribution Networks: DDA versus PDA formulations

This paper focuses on a methodology allowing to derive the pumping schedule in Water Distribution Networks (WDN), upon a time dependent water demand. The selected test case is a previously studied WDN. Two pumping algorithms give different pumping rules. By solving the nonlinear system of equations, consisting of energy balance equations, mass balance equations and pumping rules, one gets the pumps speed factors. Solutions attached to the Pressure Driven Analysis (PDA) correspond to energy and cost savings, with respect to the solutions given by the Demand Driven Analysis (DDA). The methodology described in this paper is simple and rapid, but the iterative numerical method used to solve the system of equations is highly dependent on the starting guess.

Optimal Placement of Pressure Gauges for Water Distribution Networks Using Entropy Theory Based on Pressure Dependent Hydraulic Simulation.

This study proposed a pressure driven entropy method (PDEM) that determines a priority order of pressure gauge locations, which enables the impact of abnormal condition (e.g., pipe failures) to be quantitatively identified in water distribution networks (WDNs). The method developed utilizes the entropy method from information theory and pressure driven analysis (PDA), which is the latest hydraulic analysis method. The conventional hydraulic approach has problems in determining the locations of pressure gauges, attributable to unrealistic results under abnormal conditions (e.g., negative pressure). The proposed method was applied to two benchmark pipe networks and one real pipe network. The priority order for optimal locations was produced, and the result was compared to existing approach. The results of the conventional method show that the pressure reduction difference of each node became so excessive, which resulted in a distorted distribution. However, with the method developed, which considers the connectivity of a system and the influence among nodes based on PDA and entropy method results, pressure gauges can be more realistically and reasonably located.

Development and Applications of K-NRisk for Pressure Dependent Demand Analysis in Water Distribution Networks

Hydraulic analysis of water distribution networks is important not only for the assessment current status, but also for the near and far future prediction with uncertainties. Hydraulic analysis models can be classified into demand driven analysis (DDA) and pressure driven analysis (PDA) depending on nodal outflow assumption. However, the EPANET2, which is globally used model, does not include PDA module, and therefore hydraulic analysis under abnormal conditions is impossible. In this study, a new multi-scenario based hydraulic analysis model for abnormal conditions, K-NRisk is developed by combining PDA technique. The K-NRisk is compared with the existing commercial softwares, and verified by multi-scenario based modeling for typical abnormal conditions. The results show that, the K-NRisk developed in this study can visualize pressure deficient area under abnormal conditions, and also can quantify the water shortage reasonably. Therefore, the K-NRisk can be used as a decision support tool to improve the efficiency of water distribution network operation, to enhance the revenue water ratio at pressure deficient area. Keywords: Water Distribution Networks, Pressure Driven Analysis, K-NRisk, Abnormal Condition Analysis