Extending EPANET hydraulic solver capacity with rigid water column global gradient algorithm

EPANET is one of the most commonly used open-source programs in hydraulic modelling water distribution networks (WDNs), based on steady-state and extended period simulation approaches. These approaches effectively estimate flow capacity and average pressures in networks; however, EPANET is not yet fully effective in modelling incompressible unsteady flows in WDNs. In this study, the hydraulic solver capacity of EPANET 3 is extended with the Rigid Water Column Global Gradient Algorithm (RWC-GGA) to model incompressible unsteady flow hydraulics in WDNs. Moreover, we incorporated dynamically more accurate valve expressions than the existing ones in the default EPANET code and introduced a new global convergence algorithm, Convergence Tracking Control Method (CTCM), in the solver code. The RWC-GGA, CTCM, and valve expressions are tested and validated in three different WDNs varying from simple to sophisticated set-ups. The results show that incompressible unsteady flows can be modelled with RWC-CGA and dynamic valve representations. Finally, the convergence problem due to the valve motion and the pressure-dependent algorithm (PDA) is solved by the implemented global convergence algorithm, i.e. CTCM.     

Hydraulic Analysis of Water Distribution Systems Based on Fixed Point Iteration Method

Water distribution systems with complex configurations are important urban facilities and the hydraulic analysis is essential for system design, optimization and management. Hydraulic analysis involves the procedure of calculating the hydraulic parameters of nodal pressure heads and pipe flow rates under steady-state condition. The equations governing the heads and flows are nonlinear and the most popular method for solving the equations is the Newton-Raphson method, which is the basis of existing hydraulic simulator (EPANET 2). In this paper, fixed point iteration method is proposed for hydraulic analysis after transformation of the original nonlinear equations. Compared to EPANET 2, the proposed method can analyze a water distribution system without differentiation for the convergence for some problems which cannot be solved by EPANET 2. Three test networks were analyzed by the proposed method and EPANET 2. It is proved that the proposed method could get the convergence after a series of iterations, even in cases that EPANET 2 fail. And the initial values of nodal pressure heads and the specified calculation accuracy are considered to have influences on the calculation procedure.     

Method for Extended Period Simulation of Water Distribution Networks with Pressure Driven Demands

This paper proposes a non-iterative method to perform the simulation of water distribution systems with pressure driven demands using EPANET2 without the need to use its programmer’s toolkit. The method works for single period simulation (snapshot) and for extended period simulation (EPS) as well. It is based on the addition of a flow control valve (FCV), a throttle control valve (TCV), a check valve (CV) and a reservoir to each demand node in the network, in addition to a list of simple controls to modify the setting of the FCV and TCV in each time step. The main advantages of this approach are: 1. the source code of EPANET2 is not modified, 2. the toolkit functions are not needed for the simulation and they remain available for further uses, 3. the extended period simulation (EPS) is performed by EPANET2 and it carries tank levels, demand variation and other time-changing variables internally. The performance of the method is tested in two benchmark networks and a real size network with pumps, tanks and a 24 h demand pattern. The results show that the method computed the pressures and outflows accurately and that the computational time required is not significantly higher than a demand driven execution in most cases.     

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.     

Evolutionary Testing of Hydraulic Simulator Functionality

A method for automatic functional testing of hydraulic simulators is proposed. The method is based on using genetic algorithms to search for network parameter values at which the simulator under test computes solutions that do not satisfy the governing network equations. The search is made by maximizing the residual of the governing equations. The application of the method to the latest version of the EPANET hydraulic simulator demonstrates its efficiency in detecting incorrect results. The results of quantitative assessment of the functional adequacy of the EPANET solver by random testing are presented. The paper provides examples of hydraulic networks and of parameter value combinations for which incorrect results occur. An example of the use of automatic functional testing together with automatic convergence testing in a comprehensive study of the flow control valve model of the EPANET solver is given.     

Noniterative Implementation of Pressure-Dependent Demands Using the Hydraulic Analysis Engine of EPANET 2

To analyze water distribution networks under pressure-deficient conditions, most of the available hydraulic simulators, including EPANET 2, must be either modified by embedding pressure-dependent demands in the governing network equations or run repeatedly with successive adjustments made to specific parameters until a sufficient hydraulic consistency is obtained. This paper presents and discusses a simple technique that implements the square root relationship between the nodal demand and the nodal pressure using EPANET 2 tools and allows a water distribution network with pressure-dependent demands to be solved in a single run of the unmodified snapshot hydraulic analysis engine of EPANET 2. In this technique, artificial strings made up of a flow control valve, a pipe with a check valve, and a reservoir are connected to the demand nodes before running the engine, and the pressure-dependent demands are determined as the flows in the strings. The resistance of the artificial pipes is chosen such that the demands are satisfied in full at a desired nodal pressure. The proposed technique shows reasonable convergence as evidenced by its testing on example networks.     

基于EPANET的供水系统中变频变压供水方式的模拟

供水系统中取水泵站的变频运行属于变频变压供水方式.EPANET为模拟供水系统提供了通用的框架,其中的水泵模型可以用来模拟各种工况下的水泵运行.水泵的外特性曲线、水泵转速及转速模式决定了水泵变频运行的模拟精度.通过联合应用EPANET内的水泵模型和压力破除阀模型,建立了供水系统中变频变压供水方式的模拟方法.将此方法应用于模拟我国南方某城市原水系统取水泵站的变频运行.经过模型校核及验证,结果表明该方法可以较为准确地反映此取水泵站系统的运行状况.     

基于非线性映射理论的城市供水管网压力监测点布置方法研究

通过对非线性映射理论及技术的研究和应用,提出了一种新的城市供水管网压力监测点布置方法。以某开发区供水管网为例,首先利用EPANET水力模拟软件对供水管网不同运行工况进行水力模拟,得到各节点压力模拟数值矩阵。然后,采用非线性映射分析方法对该压力模拟数值矩阵进行非线性映射变换,得到一系列独立的二维点群,实现压力变化特征相似节点的聚类和分组。最后,根据各节点压力变化的近似程度和特征,提出供水管网压力监测点的布置方案。应用表明,该方法实用性强,提高了节点压力分析的直观程度和可视化水平。     

Simulation of Water Distribution Network under Pressure-Deficient Condition

Pressure deficient condition occurs in the water distribution network (WDN) when the nodal demands are in excess of the design discharge as in the case of fire demand, pump failure, pipe breaks, valve failure etc. It causes either no-flow or partial-flow depending upon the available pressure head at the nodes. To evaluate the nodal flows in such condition, node flow analysis (NFA) gives reasonable results in comparison to demand-driven analysis (DDA) and head-dependent analysis (HDA). The NFA works on the predefined pressure-discharge relationship to evaluate the nodal flows. However, this approach requires human intervention and hence cannot be applied to large WDN. Recently, modified pressure-deficient network algorithm (M-PDNA) has been developed by Babu and Mohan (2012) for pressure-deficient analysis with EPANET toolkit. However, it requires modification of the source code of EPANET. In this study a relationship with the M-PDNA and node flow analysis (Gupta and Bhave 1996) has been investigated and it is found that M-PDNA is the simplified version of NFA. Further, the working principle of M-PDNA has been investigated with suitable examples of Babu and Mohan (2012). The theoretical basis of M-PDNA has not been investigated in terms of head-discharge relationship. Herein, a head-discharge relationship based on the working principal of M-PDNA is proposed. Some of the toolkits are also readily available to modify demand driven solver of EPANET 2 to suit for the pressure-driven analysis and then it can be used for analysing pressure deficient network. Also in this study, a modification in M-PDNA approach is proposed which does not require the use of EPANET toolkit which is found to be capable of simulating both pressure-sufficient and pressure-deficient conditions in a single hydraulic simulation. Using the proposed approach, pressure-deficient condition is analysed with constant and variable demand pattern.     

基于机器学习的跨海管道泄漏位置预测模型

为解决跨海管道泄漏位置定位问题,利用EPANET 软件对海底管道泄漏探测进行建模,采用BP 神经网络模型和经K-CV 改进的SVR 模型进行泄漏位置预测。对BP 神经网络的隐含层数和学习函数进行优化和选择,使用K-CV 方法对SVR 算法的惩罚系数c 和核函数参数g 进行最优组合探寻。利用EPANET 软件建模数据形成训练集,随机选取测试集进行预测,同时使用均方根误差和相关系数对预测结果进行评价。实例验证结果表明:K-CV 方法能够有效提高SVR 模型预测精度;与水力学稳态方程相比,BP 神经网络模型在泄露位置预测问题中应用范围更广、预测精度更高。     

Automatic Generation of Water Distribution Networks from Streets Layout

This article focuses on creating a model for the automatic generation of the EPANET input file from the layout of the arrangement of the streets designed in a CAD environment. From this layout a binary image is built, in which each pixel will be black if is inside the street and, otherwise, white. In order to determine the location of the pipes and nodes that are in the middle of the streets, the Zhang and Suen method of thinning binary images was used. After the image was thinned, the main challenge was to identify the pixels that will be considered as nodes of the network due to the irregular geometry of the streets. To solve this problem, a set of algorithms was developed on the theme of binary image processing. Two street layouts were used, one hypothetical and the other real. For both layouts, the model proved to be efficient, automatically generating the EPANET input format file with the pipes located within the streets.

     

Pressure-Dependent EPANET Extension

In water distribution systems (WDSs), the available flow at a demand node is dependent on the pressure at that node. When a network is lacking in pressure, not all consumer demands will be met in full. In this context, the assumption that all demands are fully satisfied regardless of the pressure in the system becomes unreasonable and represents the main limitation of the conventional demand driven analysis (DDA) approach to WDS modelling. A realistic depiction of the network performance can only be attained by considering demands to be pressure dependent. This paper presents an extension of the renowned DDA based hydraulic simulator EPANET 2 to incorporate pressure-dependent demands. This extension is termed “EPANET-PDX” (pressure-dependent extension) herein. The utilization of a continuous nodal pressure-flow function coupled with a line search and backtracking procedure greatly enhance the algorithm’s convergence rate and robustness. Simulations of real life networks consisting of multiple sources, pipes, valves and pumps were successfully executed and results are presented herein. Excellent modelling performance was achieved for analysing both normal and pressure deficient conditions of the WDSs. Detailed computational efficiency results of EPANET-PDX with reference to EPANET 2 are included as well.     

Integration of Hydraulic and Water Quality Modelling in Distribution Networks: EPANET-PMX

Simulation models for water distribution networks are used routinely for many purposes. Some examples are planning, design, monitoring and control. However, under conditions of low pressure, the conventional models that employ demand-driven analysis often provide misleading results. On the other hand, almost all the models that employ pressure-driven analysis do not perform dynamic and/or water quality simulations seamlessly. Typically, they exclude key elements such as pumps, control devices and tanks. EPANET-PDX is a pressure-driven extension of the EPANET 2 simulation model that preserved the capabilities of EPANET 2 including water quality modelling. However, it cannot simulate multiple chemical substances at once. The single-species approach to water quality modelling is inefficient and somewhat unrealistic. The reason is that different chemical substances may co-exist in water distribution networks. This article proposes a fully integrated network analysis model (EPANET-PMX) (pressure-dependent multi-species extension) that addresses these weaknesses. The model performs both steady state and dynamic simulations. It is applicable to any network with various combinations of chemical reactions and reaction kinetics. Examples that demonstrate its effectiveness are included.     

南方丘陵地区城乡一体化供水管网规划研究

针对丘陵地区城镇供水管网的特点,提出了管网规划中控制点和最小服务水头的选取方法,应用EPANET建立管网规划模型,分析了管网的分区供水及增压方式选择等问题,通过模拟计算对管网进行优化调整,确定城乡间联络管直径,并分析了城乡间调水的可行性。     

EPANET软件在区域供水管网改造设计中的应用

以天津市某区域的供水管网为例,利用EPANET软件对其进行水力计算,指明现有管网的缺陷.为了保障其安全性,根据实际调研设计管网改造方案,选取关键节点作为改造前后对比分析的依据.根据最终水力计算结果,验证改造方案的合理性,为实际的改造工程提供理论依据.     

水力平差模型在供水规划中的应用

在供水规划中,管网设计是重要的组成部分,为了降低管网建成后的漏损及运行费用,需要在规划设计阶段对管网进行水力平差计算.针对规划管网水力平差的特点,提出应用GIS的分析功能及EPANET水力计算软件构建管网的水力平差模型,进行规划管网的水力计算,并根据计算结果对管网进行调整,得到满足规划供水量及水压要求的供水管网布置方案,为供水规划管网设计提供科学的依据.     

基于精细积分法的城市配水系统动态建模

基于功率键合图理论,将所研究的城市配水系统的动态结构绘制成功率键合图,从功率键合图推导出系统的非线性状态空间方程.首先通过增维法将非齐次系统方程转化成齐次方程的形式,避免了系统矩阵求逆,节省计算时间,增强了计算稳定性.模型应用精细积分法迭代求解.实例计算表明,模型计算得到的稳态值同EPANET软件的稳态计算结果一致,验证了算法的正确性.     

Validation and Examination of Existing Water Distribution Network for Continuous Supply of Water Using EPANET

Dire Dawa, the second largest city of Ethiopia, was facing about the distribution system adopted for supplying clean water. It was being observed that an intermittent type of supply with main and secondary distribution pipes. It was observed that, the current water demand has surpassed the present existing supply about 65%. Hence, in order to provide sufficient quantity and good potable water with continuous (24 X 7) water supply for various sectors of study area: Sabiyan region, Dire Dawa, Ethiopia, was selected. Also, Dire Dawa Water Supply & Sewerage Authority has taken a strong decision in order to validate and examine the existing water distribution network for improved water supply. On the other hand, the main important factor which effects the validation is that the age of pipes and other accessories in present existing network were longstanding. Therefore, to avoid the leakage losses and various problems encountered with the present system, a detailed is study is conducted and the analysis is carried out using EPANET tool to design for continuous water supply. After thorough analysis by considering future concerns, it was suggested that, two GLSRs of each with 2.7 Mm³ capacity may be provided in order to meet the future demands. The tanks are provided at required elevation to ensure that the water flows in all pipes of the network efficiently. Based on the output it was observed that the diameter of pipes from the existing system ought to be revised. Additionally, other parameters which effect the network like frictional losses, velocity of flow in the pipes, residual head and pressure at nodes were also examined thoroughly by the use of different tools like WaterGEMS and Auto CAD in addition to EPANET.     

A New Optimization Approach for the Least-Cost Design of Water Distribution Networks: Improved Crow Search Algorithm

Due to large number of decision variables and several hydraulic constraints, optimal design of water distribution networks (WDNs) is considered as one of the most complex optimization problems. This paper introduces and applies a new optimization approach, improved crow search algorithm (ICSA), based on the improvement of original crow search algorithm (CSA) by adding an operator parameter. Both approaches (i.e., CSA and ICSA) were applied to two case studies (i.e., Two-Reservoir and Khorramshahr City networks) by linking the hydraulic simulator (e.g., EPANET 2.0). The proposed ICSA saved the total construction cost by 2.16% and 1.79% for the Two-Reservoir and Khorramshahr City networks compared to the original CSA based on optimal network design, respectively. Results revealed that the proposed ICSA provided outstanding design for the both WDNs compared to previous studies and original CSA.

     

基于GIS的给水管网动态水力计算模型的建立与应用

基于GIS和给水管网水力计算方法,采用一种新的更符合实际的节点流量分配方法,建立了给水管网动态水力计算模型,实现了模拟结果和GIS图形信息的良好结合,解决了工况结果难以在GIS中显示和输出的问题。将模型应用于天津市津南区咸水沽镇供水管网,并将计算结果与MIKENET模拟值、EPANET2.0计算值进行比较,验证了模型的实用性。