城市供水管网抗震可靠性评估的随机模拟方法

在进行管网抗震可靠性评估时,现有方法大多采用相同方式进行管道的渗漏与爆管水力模拟,这会导致管网水力模拟及可靠性评估结果的不准确。考虑到地震时管道破损具有很大的随机性,对城市供水管网抗震可靠性评估的随机模拟方法进行研究。应用蒙特卡洛模拟产生管网震损场景,用泊松随机数与均匀随机数判定管道工作状态,用正态随机数确定管道渗漏系数;利用EPANET软件中喷嘴及管道关闭功能实现管道渗漏及爆管等效模拟,提出将长管道分段并应用"分步迭代"法求解低压管网水力方程,提高震损管网水力模拟精度。以震损场景下节点流量统计平均值与正常时节点流量的比值作为可靠度指标,分别采用所提出算法及GIRAFFE软件对云南某古镇供水管网在VIII、IV烈度时抗震可靠性进行评估,评估结果证明了所提出算法的可行性。评估结果还表明,除地震烈度外,管网本身水力条件对供水可靠性影响较大,管网末端、支管服务区域及地势较高区域供水可靠性远低于干管服务区。     

Application of modified complementary reservoir approach in analysis of water distribution networks under pressure-deficient conditions

Hydraulic simulation models which simulate water distribution systems in different operating conditions are essential tools to evaluate network reliability. Simulation models found in most commercial software are not effectively capable of analyzing demand nodes under critical conditions such as fire-fighting demand or network pipe breakage. In the current study, a combination of hydraulic model and complementary reservoir solution (CRS) method is used for solving network's problems in critical conditions for both series-looped networks and a part of water network in Ilam city (Iran). Obtained results show that CRS provide more than actual need on the demand node for some reservoir total pressure heads. Thus, two modified versions of CRS method are proposed to deal with failures of CRS in such cases. Obtained results demonstrate improved efficiency in the combined model for analyzing networks in abnormal conditions.     

Reliability based optimal design of water distribution networks considering life cycle components

Water distribution systems play an important role in supplying water to consumers in a timely and efficient manner. The importance and complexity of such systems lead to extensive research in the area of optimal design of water distribution networks. Traditionally, only system costs are considered in design with few models incorporating environmental impacts. This paper presents a model for designing sustainable water distribution networks by minimising life cycle costs and life cycle CO₂ emissions, while ensuring hydraulic reliability for the life time of the system. The model integrates a multi-objective genetic algorithm with water network simulation software, EPANET. A traditional benchmark water distribution network is used to demonstrate the model. Eight scenarios have been developed to test and validate the model for a variety of objectives with different constraints. Trade-offs between life cycle costs and life cycle emissions, along with hydraulic reliability of the system are illustrated.     

Approximate methods for uncertainty analysis of water distribution systems

Monte Carlo simulation (MCS) has been commonly applied for uncertainty analysis of model predictions. However, when modelling a water distribution system under unsteady conditions, the computational demand of MCS is quite high even for a reasonably sized system. The aim of this study is to evaluate alternative approximation schemes and examine their ability to predict model prediction uncertainty with less computational effort. Here, MCS is compared with a point estimation method, the first-order second-moment (FOSM) method, and a quasi-MCS method, Latin hypercube sampling (LHS). Hydraulic and water quality simulations are performed using EPANET and the evaluated model outputs are nodal pressure, water age and chlorine concentration. Six input parameters, pipe diameter and roughness coefficient, nodal spatial and temporal demands and bulk and wall decay coefficients, are considered. To examine the effect of the magnitude of input uncertainty on model output, three uncertainty levels are evaluated. The study is performed for a real system with 116 pipes and 90 nodes. Results demonstrate that LHS provides very good estimates of the predicted output range for steady and unsteady conditions compared with MCS, while FOSM did well for steady conditions but poorly for some periods in the extended-period simulation for chlorine concentration.     

Accounting for uniformly distributed pipe demand in WDN analysis: enhanced GGA

The global gradient algorithm (GGA) is the most widely adopted method for steady-state analysis of water distribution networks. It is used to solve the non-linear system of equations describing mass and energy conservation laws. Nonetheless, it has been recently proved that the usually adopted representation of distributed pipe demands as lumped withdrawals at ending nodes causes inconsistent calibration results and pipe head loss errors which could be non negligible in some network conditions. The original GGA has been contextually modified by introducing a correction of pipe hydraulic resistance under the assumptions of a friction factor independent from the flow regime. This paper aims at providing researchers and software developers with a general formulation of the GGA which entails both the adoption of any generic monomial head loss formula and pipe hydraulic resistance dependence on flow regime. The results could be easily extended to other methods of network analysis.     

Water quality parameter estimation for water distribution systems

Wall decay coefficients vary between pipes and must be determined indirectly from field measured concentration data. A general calibration model for identifying these parameters is formulated here. The problem is solved using the shuffled frog leaping algorithm optimisation algorithm that is coupled with hydraulic and water quality simulation models using the EPANET Toolkit. The methodology is applied to two application networks to examine the robustness of the parameter estimation algorithm and to study the effects of the network flow conditions, data availability, model simplification, and measurement errors. To that end, different field conditions are considered, including a network with or without tanks, altering disinfectant injection policies, changing measurement locations, and varying the number of wall decay coefficients. Results from conditions with exact data show that the solution approach is robust and consistently finds the true parameter values. However, when the number of decay coefficients is increased, results suggest that the distribution and number of meter locations affects model parameter identifiability. It is also noted that the parameter sensitivity is relatively small and related to the velocities in the network. Finally, isolated tracer data can supplement information from normal operating conditions to improve decay coefficient calibration but, if sufficient data is available, the incremental improvement may not be significant. To confirm this result, model calibration must be extended to parameter and model prediction uncertainty.     

Accurate water demand spatial allocation for water networks modelling using a new approach

The paper presents an alternative approach regarding the spatial allocation of the actual water demand (at node level) when developing a pipe network's hydraulic simulation model. The process takes into account the respective demand patterns of the various types of water users, considering the water being lost through leaks/breaks occurring, as a competitive use. This new method accurately approximates the demand allocation of a network when there is no GIS data, thus having a significant impact on its cost effectiveness. Kos Town (Greece) water pipe network is used as the case study to demonstrate the entire process and the problems encountered. Finally, to prove its effectiveness the results of the new method were compared to MW-Voronoi diagram method's results and to field measurements.     

Optimal design of urban water supply pipe networks

This paper approaches the optimisation of looped water distribution networks supplied from one or more sources, according to demand variation. The pipe networks have concentrated outflows or uniform outflow along the length of each pipe. An optimisation model coupled with a computational iterative procedure of optimal discharges through pipes is developed on the basis of linear programming for the design of new or partially extended water distribution networks. The optimum solution obtained by this model consists of one or two pipe segments of different discrete sizes between each pair of nodes. The improved linear optimisation model guarantees a high reliability. Also, it is possible to take into account the network pipes with variable discharge on route. Additionally, the paper compares the linear optimisation model to some others, such as the classic model of economical velocities, the Moshnin model and a nonlinear model. This shows a good performance of the proposed model.     

OPTIMAL DESIGN OF WATER DISTRIBUTION NETWORKS USING FUZZY OPTIMIZATION

A new heuristic approach for the design of water distribution networks involving a robust fuzzy linear program optimization in which the capital costs of the network are minimized while maintaining the nodal heads at demand nodes within a satisfactory region as defined by the customers at those nodes is presented. Iterative interaction between the fuzzy linear program and a network solver is used to ensure hydraulic consistency. Level of service is modelled by the residual nodal head available at demand nodes with the subjective nature of customers’ satisfaction with the nodal head being represented through fuzzy sets which reflect more realistically consumers’ attitudes toward pressure variations in the supply of water. Non-probabilistic uncertainty in the demand is modelled by a trapezoidal possibility distribution function. The model is demonstrated by application to an example network.     

爆管事故对多水源管网供水分区的影响

基于图论理论,建立了多水源供水管网的供水分区模型,结合EPA管网模拟软件,采用C++平台实现了供水分区算法.通过对爆管事故发生管网前后供水分区的研究,得到了爆管事故对于多水源管网供水分区的影响规律,事故管段的输水能力强弱直接影响到供水分区变化的程度,并在实例管网中得到了很好的验证,为管网在事故发生及关阀抢修时的水量调配提供了技术支持.     

多水源给水管网的技术经济计算

联立管网节点经济水压方程组并引入节点水压边界条件，建立包含起点水压已给和未给两种情况的多水源给水管网技术经济计算的数学模型。采用牛顿迭代法来求解各未知节点的经济水压，进而得出各管段的经济水头损失、经济管径和水源二级泵站的经济扬程。最后再将理论管径圆整为标准管径，并重新核算管网实际水力工况；据此编写了通用电算程序，经多水源给水管网实例验证，可快捷准确地进行技术经济计算，得出较满意的结果。     

给水管网耦合优化调度模型的建立及应用

引入节点水龄作为优化调度的约束条件,以EPANET 2.0作为管网水力平差计算和水质模拟工具,建立了一种多水源管网的耦合优化调度模型,并采用双重遗传算法对其进行求解.该模型简化了变量空间,加快了收敛速度,提高了求解效率.将此模型应用于实际管网,取得了较为明显的优化效果.     

供水管网地震漏损蒙特卡洛模拟分析

为研究供水管网在不同地震烈度下的漏损情况和水力特性,基于管道地震破坏评估模型和概率分析方法,对不同地震烈度下管线的破坏概率和渗漏状态进行了计算分析,引入折减系数对管段抗震可靠度分析方法进行改进,并与传统计算方法比较,验证了其合理性。发展了Monte Carlo模拟技术在供水管网流分析方面的应用,并考虑带渗漏和爆管两种出流方式。编制程序对一大型管网进行了模拟分析,给出了震后带漏损情况下管网的漏失率和破坏情况,结果与实际地震灾害情况相符。     

The impact of variable hydraulic operation of water distribution networks on disinfection by-product concentrations

This study assessed the magnitude of variations in the concentrations of disinfection by-products, specifically trihalomethanes and haloacetic acids, which occur in two UK water distribution networks of different sizes due to changes in the hydraulic operation of the networks. These operational changes included varying the fill levels of water storage tanks and pumping conditions within the network. This was investigated through modelling which combined a conventional distribution network flow model (EPANET) with previously developed models for disinfection by-product formation, and using network information obtained from water company partners. The modelling demonstrated that there is the potential for significant variations in disinfection by-product concentrations, up to a 40% change in some simulations, due to what may be considered routine variability in the hydraulic operation of the network. Smaller networks may be especially susceptible to these variations. These findings may influence how water companies plan disinfection by-product monitoring programmes for regulatory reporting.     

MD镇供水管网余氯衰减模拟

采用EPANET2建立了MD镇的管网水质模型,通过EPANET2的水质模拟分析与实际数据的对比,分析可能存在的问题。对可能存在的问题进行现场调查,进而对节点需水量和管壁衰减系数Kw进行调整,从而使模型中的模拟余氯与实测余氯相符。     

并联输水管道设计计算

为提高输水管道的供水安全性,通常并联敷设多条输水管道并设置连通管。基于各管道的水头损失相等,推导了并联输水管道系统各管道的流量计算公式,以及最不利管道发生事故时,为满足事故输水量要求,连通管最大布置间距的计算公式,并对公式进行了合理性分析。     

用EPANET水力模型优化乡镇供水管网

利用EPANET水力模型对常州市罗溪镇供水管网进行了水力计算,结合实际测量结果分析了管网供水压力不足的原因,并对现状管网进行了优化,满足了该镇居民对水量与水压的要求。     

异程布置的冷冻水系统管网水力特性计算方法

大型中央空调冷冻水系统管网水力特性精确计算是研究其优化设计和运行的必要条件,简化模型因计算误差大而无法应用于大型管网拓扑结构的水力计算。以异程布置的冷冻水系统为研究对象,在充分考虑末端支路温度调节阀调节特性的基础上,建立了管网水力特性精确数学模型,提出了虚拟流量的计算机逻辑算法。以10个AHU支路的异程式管网为仿真计算对象,计算该管网最小供回水压差以及不同供回水压差条件下的各支路温度调节阀开度和实际流量,计算结果符合异程式管网存在较大压力不平衡的固有特性。该计算方法能够确保计算收敛,实现了利用一个逻辑程序计算管网各种水力特性,为异程式管网水力特性研究提供了参考价值。     

热水地面辐射采暖常用加热管材水力计算

介绍了热水地面辐射采暖常用管材的水力计算方法,得出了6种常用管材的水力计算表并绘制了水力线算图。对塑料管材和金属Cu管材进行水力比较,结果表明相同条件下Cu管材水力较优;在塑料类管材中,PE—X管材水力较优。     

EPANET在供水管网平差计算中的应用

结合平差计算是供水管网设计中的重要环节,通过一个示例阐述了如何应用EPANET软件进行供水管网水力平差计算,并指出其优越性和局限性,总结出在实际工程中简便可行的使用方法.