Study On Reliability Of Water Distribution Network In The City Considering The Changes Of Hydraulic Conditions

Urban water distribution network is an important part of water-supply system. And its reliability has significant influence on social and economic benefits of the water-supply system as a whole. Mechanical failure and hydraulic performance failure are two key factors that impact on reliability of water distribution network. But to date the most research has focused on reliability aspects arising from sole mechanical failure or from sole hydraulic performance failure, so the established reliability models on water distribution network system can't truly reflect practical reliability of realistic water distribution network system.On the basis of the existing achievements, a new method is presented in the dissertation for evaluation of reliability of water distribution network system by combining the layout of network with uncertainties of the hydraulic condition, namely by combining mechanical failure with hydraulic performance failure. Detailed work and major conclusion are as follows:Based on the nonlinear hydraulic model of water distribution network, the linear hydraulic model is established for analysis of the performance of the water distribution network under the hydraulic conditions so as the nodal demands, pipe roughness coefficients and reservoir levels change at random. Compared with Monte Carlo model, it is founded that the accuracy of the linear hydraulic model is very good for situations involving small variability in the nodal demands, pipe roughness coefficients and reservoir levels.The models for evaluation of nodal and system configuration reliabilities (narrow reliabilities) and generalized reliabilities of water distribution network are established through two stages respectively, and compared with each other. The fist stage, the model for evaluation of nodal and system configuration reliabilities is established through pipe availability and layout of network by simulating failure of single pipe. The second stage, based on the fist stage, the model for evaluation of nodal and system generalized reliabilities is then established by considering the changes of the hydraulic conditions. The result of comparison between two models shows ignoring the uncertainties of the hydraulic conditions can cause the overestimation of the nodal and system reliabilities of water distribution network.Provided that the network configuration is fixed, a series of sensitivity analyses are performed to examine the effects of the change of nodal demands, pipe roughness coefficients and reservoir levels on the nodal and system reliabilities. The results indicate that changes of hydraulic conditions decrease nodal reliability and system reliability, so it is important to optimize design and rebuilding of water distribution network system that changes of hydraulic conditions are considered fully, especially when elevating the water distribution network with considerable changes of hydraulic conditions .Evaluation of the sensitivity of nodal and system reliabilities to variation in the specified minimum service pressure is also performed. The result of analysis shows that it is important to precisely evaluate the nodal and system reliabilities of water distribution network in the city that minimum service pressure is set exactly.In the end, the above conclusions have good result when used in the practical project.