Dealing with Data Missing and Outlier to Calibrate Nodal Water Demands in Water Distribution Systems

Water Resources Management - Model parameters of the water distribution system (WDS) such as nodal water demands, should be carefully calibrated by measurements. However, the inconvenience of data...     

Calibration via Multi-period State Estimation in Water Distribution Systems

Calibration of model parameters is of utmost importance to ensure the good performance of hydraulic simulation models. In this work, calibration is conceived within a joint multi-period parameter and state estimation approach, where model parameters (i.e. roughness coefficients) and hydraulic variables should be computed from available measurements at different times. The aim of this paper is twofold: (1) to present a novel methodology for the calibration of water networks via multi-period state estimation, and (2) to adapt observability analysis to this approach. The novelty of this work is that such a large-scale non-linear optimisation problem is here solved using mathematical programming decomposition techniques. On the other hand, observability analysis requires the construction of the multi-period measurement and parameter Jacobian matrix of the problem. The proposed approach enables computation of the observable roughness coefficients from available readings over time, making possible the periodic reassessment of roughness values based on recent online measurements. The potential of the method is illustrated by means of a case study, which shows how such a methodology would contribute to make the most of telemetry data for calibration purposes.     

Nodal Analysis of Urban Water Distribution Networks

There are three methods for analysing the flow and pressure distribution in looped water supply networks (the loop method, the node method, the pipe method), accounting for the chosen unknown hydraulic parameters. For all of these methods, the nonlinear system of equations can be solved using iterative procedures (Hardy–Cross, Newton–Raphson, linear theory). In the cases of the extension or the rehabilitation of distribution networks, the unknown parameters are the hydraulic heads at nodes, and the nodal method for network analysis is preferred. In this paper, a generalised classic model is developed for the nodal analysis of complex looped systems with non-standard network components and the solvability of new problems, along with the determination of the pressure state in the system. In addition, this paper exhibits a different approach to this problem by using the variational formulation method for the development of a new analysis model based on unconditioned optimisation techniques. This model has the advantage of using a specialised optimisation algorithm, which directly minimises an objective multivariable function without constraints, implemented in a computer program. The two proposed models are compared with the classic Hardy–Cross method, and the results indicated a good performance of these models. Finally, a study is performed regarding the implications of the long-term operation of the pipe network on energy consumption using these models. The new models can serve as guidelines to supplement existing procedures of network analysis.     

A New Method for Simultaneous Calibration of Demand Pattern and Hazen-Williams Coefficients in Water Distribution Systems

Water distribution systems, where flow in some pipes is not measured or storage tanks are connected together, calculation of demand pattern coefficients of the network is difficult. Since, Hazen-Williams coefficients of the network are also unknown; the problem is becoming unintelligible further. The present study proposes a new method for simultaneous calibration of demand pattern and Hazen-Williams coefficients that uses the Ant Colony Optimization (ACO) algorithms coupled with the hydraulic simulator (EPANET2) in a MATLAB code. In this paper demand pattern and Hazen-Williams coefficients are the calibration parameters and measured data consist of nodal pressure heads and pipe flows. The defined objective function minimizes the difference between the measured and simulated values. The new proposed method was tested on a two-loop test example and a real water distribution network. The results show that the new calibration model is able to calibrate demand pattern and Hazen-Williams coefficients simultaneously with high precision and accuracy.     

An Integrated Model to Evaluate Losses in Water Distribution Systems

To evaluate non revenue water (NRW) and losses in water distribution networks a methodology is developed by applying “annual water balance” and “minimum night flow” analyses. In this approach the main NRW components such as leakage from reported and un-reported bursts and background leakage, with real or estimated data, enabling assessment of indices of leakage performance are evaluated. Also, a novel procedure is introduced in this paper that can determine the nodal and pipe leakage by using a hydraulic simulation model. Recognising the pressure dependency of leakage the total consumption is divided into two parts, one pressure dependent and the other independent of local pressure, and the hydraulic behaviour of the network is analyzed. A computer code is developed to evaluate all components of water losses based on the proposed methodology. For better representation of the results and management of the system, the outputs are exported to a GIS model. Using the capabilities of this GIS model, the network map and attribute data are linked and factors affecting network leakage are identified. In addition, the effects of pressure reduction are investigated. The model is illustrated by a real case study. The results show that the suggested model has overcome the shortcomings of the existing methodologies by accounting for the leakage and other NRW components in water distribution networks more realistically.     

Multi-Directional Maximum-Entropy Approach to the Evolutionary Design Optimization of Water Distribution Systems

A new multi-directional search approach that aims at maximizing the flow entropy of water distribution systems is investigated. The aim is to develop an efficient and practical maximum entropy based approach. The resulting optimization problem has four objectives, and the merits of objective reduction in the computational solution of the problem are investigated also. The relationship between statistical flow entropy and hydraulic reliability/failure tolerance is not monotonic. Consequently, a large number of maximum flow entropy solutions must be investigated to strike a balance between cost and hydraulic reliability. A multi-objective evolutionary optimization model is developed that generates simultaneously a wide range of maximum entropy values along with clusters of maximum and near-maximum entropy solutions. Results for a benchmark network and a real network in the literature are included that demonstrate the effectiveness of the procedure.     

Parameter Estimation in Water Distribution Networks

Estimation of pipe roughness coefficients is an important task to be carried out before any water distribution network model is used for online applications such as monitoring and control. In this study, a combined state and parameter estimation model for water distribution networks is presented. Typically, estimation of roughness coefficient for each individual pipe is not possible due to non-availability of sufficient number of measurements. In order to address this problem, a formal procedure based on K-means clustering algorithm is proposed for grouping the pipes which are likely to have the same roughness characteristics. Also, graph-theoretic concepts are used to reduce the dimensionality of the problem and thereby achieve significant computational efficiency. The performance of the proposed model is demonstrated on a realistic urban water distribution network.     

给水管网微观模型中节点流量在线预测计算方法研究

阐述了研究区域时总用水量数据整理、时总用水量预测、制作用水模式曲线、节点流量预测值计算 ,建立了给水管网微观模型中节点流量在线预测计算方法 ,并在实践中加以验证。     

Identifying Pipes and Valves of High Importance for Efficient Operation and Maintenance of Water Distribution Systems

Failure of a pipe or valve in a water distribution system causes service disruption and other inconveniences to the customers at or downstream of the failure location. To minimize the impact of such a pipe or valve failure, it is crucial to identify those pipes or valves whose failure will have the most severe consequences in degrading the performance of the system relative to that of other pipes or valves. In this paper, we develop two failure analysis methodologies, Pipe-by-Pipe and Valve-by-Valve, to prioritize the importance of pipes and valves in a water distribution system. The relative importance of individual pipes and valves is evaluated according to the number of customers who are forced out of service as a consequence of a pipe or valve failure. The methodologies are based on a segment-finding algorithm which defines a series of isolated pipes in the case of pipe or valve failure. A procedure based on the Breadth First Search is also developed to find sections of pipes that are unintentionally isolated in the isolation procedure for failed pipes. The number of unintentionally isolated customers is included in the Pipe-by-Pipe and Valve-by-Valve analyses in order to incorporate this negative effect of unintended isolation of pipes. The methodologies are applied to a case study of a water distribution system for which the most important pipe and valve are identified. The results are analyzed to form a guideline for improving the system reliability. The proposed methodologies were found to be a valuable tool for ensuring efficient operation and developing appropriate maintenance strategies, and thereby for improving the reliability of many water distribution systems.     

Optimal Localization of Pressure Reducing Valves in Water Distribution Systems by a Reformulation Approach

Leakage reduction represents one of the most challenging tasks in managing water distribution systems (WDSs). An effective way to leakage reduction is to carry out network operational pressure management through optimizing locations and regulations for pressure reducing valves (PRVs) and system pressures. This leads to a mixed-integer nonlinear program (MINLP) with a large number of binary variables which make it difficult to solve by an available software package. In this study, instead of directly solving the MINLP problem, we reformulate it to a mathematical program with complementarity constraints which can be efficiently solved by available NLP algorithms. The binary variables are replaced by continuous ones with complementarity constraints to be satisfied by a penalization scheme. To improve the quality of the solution and also to accelerate the convergence, in each relaxed NLP the results of the binary variables are rounded to binary values with which the NLP problem is solved again to achieve a MINLP solution. The final solution will be determined by the best one among the MINLP solutions. The results from two case studies reveal new and better combinations of PRVs as compared with those given in the literature.     

Assessment of Penalty-Free Multi-Objective Evolutionary Optimization Approach for the Design and Rehabilitation of Water Distribution Systems

This paper describes a penalty-free multi-objective evolutionary optimization approach for the phased whole-life design and rehabilitation of water distribution systems. The optimization model considers the initial construction, rehabilitation and upgrading costs. Repairs and pipe failure costs are included. The model also takes into consideration the deterioration over time of both the structural integrity and hydraulic capacity of every pipe. The fitness of each solution is determined from the trade-off between its lifetime costs and its actual hydraulic properties. The hydraulic analysis approach used, known as pressure-dependent modelling, considers explicitly the pressure dependency of the water supply consumers receive. Results for two sample networks in the literature are included that show the algorithm is stable and finds optimal and near-optimal solutions reliably and efficiently. The results also suggest that the evolutionary sampling efficiency is very high. In other words, the number of solutions evolved and analysed on average before finding a near-optimal solution is small in comparison to the total number of feasible and infeasible solutions. We found better solutions than those reported previously in the literature for the two networks considered. For the Kadu network, for example, the new best solution costs Rs125,460,980—a significant improvement. Additional statistics that are based on extensive testing are included.     

An Ensemble-Learning-Based Method for Short-Term Water Demand Forecasting

Water Resources Management - Short-term water demand forecasting has always been a hot research topic in the field of water distribution systems, and many researchers have developed a wide variety...     

Pressure Zoning Approach for Leak Detection in Water Distribution Systems Based on a Multi Objective Ant Colony Optimization

Leakages result in considerable loss of water in water pipe networks. Therefore it is an important issue to detect leakage amount and its approximate location. Leakages in water distribution system are directly related to the operating pressure. In the current study, a new model is proposed for leakage amount and location detection and it is applied into two benchmark water distribution networks. In the proposed method, the water distribution networks are divided into three pressure zones in order to consider the leakage differences in different operating pressures. Then, nodal pressures and demands are calibrated using a new multi objective ant colony based optimization model. In this method, leaks are simulated as extra nodal demands. For determining the nodes where leakage happens, a probability based scheme is used. The leakage occurrence probability varies depending on the pressure zone that each node is located. The results illustrate the applicability of the proposed model for detecting the leakages in water distribution systems.     

A Two-stage Approach to Basin-scale Water Demand Prediction

Water demand prediction (WDP) is the basis for water allocation. However, traditional methods in WDP, such as statistical modeling, system dynamics modeling, and the water quota method have a critical disadvantage in that they do not consider any constraints, such as available water resources and ecological water demand. This study proposes a two-stage approach to basin-scale WDP under the constraints of total water use and ecological WD, aiming to flexibly respond to a dynamic environment. The prediction method was divided into two stages: (i) stage 1, which is the prediction of the constrained total WD of the whole basin (T _w ) under the constraints of available water resources and total water use quota released by the local government and (ii) stage 2, which is the allocation of T _w to its subregions by applying game theory. The WD of each subregion (T _s ) was predicted by calculating its weight based on selected indicators that cover regional socio-economic development and water use for different industries. The proposed approach was applied in the Dongjiang River (DjR) basin in South China. According to its constrained total water use quota and ecological WD, T _w data were 7.92, 7.3, and 5.96 billion m³ at the precipitation frequencies of 50%, 90%, and 95%, respectively (in stage 1). Industrial WDs in the domestic, primary, secondary, tertiary, and environment sectors are 1.08, 2.26, 2.02, 0.44, and 0.16 billion m³, respectively, in extreme dry years (in stage 2). T _w and T _s exhibit structures similar to that of observed water use, mainly in the upstream and midstream regions. A larger difference is observed between T _s and its total observed water use, owing to some uncertainties in calculating T _w . This study provides useful insights into adaptive basin-scale water allocation under climate change and the strict policy of water resource management.     

Topographic Energy Management in Water Distribution Systems

A significant amount of energy is required to operate pressurised water distribution systems, and therefore, improving their efficiency is crucial. Traditionally, more emphasis has been placed on operational losses (pumping inefficiencies, excess leakage or friction in pipes) than on structural (or topographic) losses, which arise because of the irregular (unchangeable) terrain on which the system is located and the network’s layout. Hence, modifying the network to adopt an ecologically friendly layout is the only way to reduce structural losses. With the aim of improving the management of water distribution systems and optimising their energy use, this work audits and classifies water networks’ structural losses (derived from topographic energy), which constitutes the main novelty of this paper. Energy can be recovered with PATs (pumps as turbines) or removed through PRVs (pressure reducing valves). The proposed hydraulic analysis clarifies how that energy is used and identifies the most suitable strategy for improving efficiency as locating the most suitable place to install PRVs or PATs. Two examples are discussed to illustrate the relevance of this analysis.

     

Pressure Control for Leakage Minimisation in Water Distribution Systems Management

A model to support decision systems regarding the quantification, location and opening adjustment of control valves in a network system, with the main objective to minimise pressures and consequently leakage levels is developed. This research work aims at a solution that allows simultaneously optimising the number of valves and its location, as well as valves opening adjustments for simulation in an extended period, dependently of the system characteristics. EPANET model is used for hydraulic network analysis and two operational models are developed based on the Genetic Algorithm optimisation method for pressure control, and consequently leakage reduction, since a leak is a pressure dependent function. In these two modules, this method has guaranteed an adequate technique performance, which demands a global evaluation of the system for different scenarios. A case study is presented to show the efficiency of the system by pressure control through valves management.     

Optimal Placement of Isolation Valves in Water Distribution Systems Based on Valve Cost and Weighted Average Demand Shortfall

In this paper a method for optimal placement of isolation valves in water distribution systems is presented. These valves serve to isolate parts of the network (segments) containing one or more pipes on which maintenance work can be performed without disrupting service in the entire network or in large portions of it. The segments formed after the installation and closure of isolation valves are identified and characterised using an algorithm which is based on the use of topological matrixes associated with the structure of the original network and the one modified to take account of the presence of (closed) valves. A multi-objective genetic algorithm is used instead to search for the optimal position of the valves. In the application of the method different objective functions were used and compared to solve the problem as to the optimal placement of the valves. The results showed that the most appropriate ones are the total cost of the valves (to be minimised) and the weighted average “water demand shortfall” (likewise to be minimised); in particular, the weighted average shortfall is calculated considering the shortfalls associated with the various segments of the network (shortfall is the unsupplied demand after isolating a segment) and the likelihood of failures tied to mechanical factors occurring in the segments. The methodology was applied to a case study focusing on a simplified layout of the water distribution system of the city of Ferrara (Italy).     

Modelling Water Distribution Systems with Deficient Pressure: An Improved Iterative Methodology

In the last three decades, many researchers have proposed different models for water distribution network (WDN) hydraulic analysis by head-driven analysis (HDA). By considering a pressure-discharge relationship (PDR), head-driven analysis (HDA) can avoid deviation caused by traditional demand-driven analysis (DDA) under abnormal conditions. Generally, there are three types of HDA models: 1) models achieved by embedding a PDR into DDA, 2) models using EPANET structures such as emitter or tank to take place of PDR, 3) models aiming at modifying nodal outflows to satisfy PDR based on EPANET. Among these models, modifying nodal outflows is flexible to simulate network with different PDRs and specify parameters related to PDR. Most of the models use iterative algorithms to solve HDA problems; however, present ways to ensure convergence of models are still inadequate. The purpose of this paper is to present a new way to meet the iterative convergence when modifying nodal outflows based on PDR and leakage. This new methodology has been incorporated into the hydraulic network solver EPANET and is formalized algorithmically as EPANET-IMNO. Then two typical networks are used to test EPANET-IMNO, and the results demonstrate that EPANET-IMNO can converge well and applied successfully both in static simulation and extended period simulation. Different pressure deficiency conditions are tested to further confirm the flexibility and the convergence of EPANET-IMNO. Furthermore, quality analysis results back that pressure reduction can be a practical way in contamination accident response.     

An Optimization Strategy for Water Distribution Networks

An optimization strategy based on head losses minimization is developed for the least cost design of water distribution networks. A new weighting approach is suggested for calculating the initial flow distribution and optimum pipe diameters of the weighted flow distribution is presented by using least square method. In the mean time homogenous and isotropous head losses are maintained with implications of head loss path choice. The model is employed for designing and/or modifying pipe sizes while the classical Hardy-Cross network solver is used to balance the flows. The whole algorithm is programmed and applied to a two-looped network selected from the literature and the results are presented on a comparative basis. A FORTRAN software with the necessary steps in the flow chart is written for the optimization calculations in this paper.     

Model for Optimal Operation of Water Distribution Pumps with Uncertain Demand Patterns

An optimization model is presented for pump operation based upon minimizing operation costs and indirectly the maintenance costs of pumps considering uncertainty of specified demand (load) curves. The purpose of this model is to determine pump operation to meet the uncertain demands as well as to satisfy the pressure requirements in the water distribution system. In addition, constraints on the number of pump (‘on-off’) switches are included as a surrogate to indirectly minimizing the maintenance costs. This model is a mixed integer nonlinear programming (MINLP) problem using a chance constraint formulation of the uncertain demand constraint. The optimization model was solved using the LocalSolver option in A Mathematical Programming Language (AMPL). The model was first applied to the operation of an example pumping system for an urban water distribution system (WDS) illustrating a reduction in operation costs using the optimization model. The optimization model with the chance-constraint for demand was applied for a range of demand satisfaction uncertainties. A decrease in the operation costs was observed with an increased uncertainty in demand satisfaction, which shows that the model further optimizes the operations considering the relaxed constraints. Model application could be extended to operations of pumping systems during emergencies and contingencies such as droughts, component failures etc.