System Reliability Of Urban Water Distribution Networks Under Cascading Failures

Water distribution networks (WDN) are important in modern lifeline system. Its stability and reliability are critical for guaranteeing high living quality and continuous operation of urban functions. Nowadays, WDN is developing into wide-range supply which carries fluid under high or less pressure. WDN is geographically distributed in a way which is sensitive to the natural or man-made damages. Cascading failures is a conductive failure process in the field of network security. When the network encounters natural or man-made disasters, the minor anomalous event of a point may spread to the whole system through cascade reaction, leading to large-scale consequences and secondary failures. Therefore, the research of system reliability of water distribution networks under cascading failures is important.Based on the review of existed WDN reliability models, this paper has taken the cascading failure, hydraulic calculation and the theory of reliability into consideration. The aim of this paper is to evaluate the system reliability of WDN under cascading failures. The main points of this work are as followed:(1) The model of nodal vulnerability under cascading failures has been developed. A load variation function is established to record the nodal failure reason and describe the relative differences between the load and the capacity. The node heterogeneity has been ignored in the topology-based method. In this paper, monitored pressures in different nodes and flows in different pipes have been used to estimate the network topological structure and the consequences of nodal failure. The simulation can provide information about flow performance and obtain more efficitive results.(2) Based on the vulnerability study, the system reliability of WDN has been introduced. The system reliability of WDN is evaluated by hydraulic analysis and cascading failures from complex network. The uncertain factors, i.e., the nodal pressure bounds, daily demand multipliers and the water demand have been taken into consideration. The function of node pressure has been defined to represent actual flows. The pressure-driven simulation is used to calculate the network capacity. The changes in flow and pressure are carried out by EPANET2. The crucial pipes are identified eventually. The demand multiplier has a great influence on the peak of reliability and the persistent time of the cascading failures in its propagation in WDN. The results indicate that the system reliability should be evaluated with the properties of WDN and the characteristics of cascading failures, so as to improve its ability of resisting disasters.(3) The cascading failures in WDN can lead to the flow re-distribution. Towards this phenomenon, the cascading dynamic model is estabilished to describe the dynamic process in WDN under node-based attack and pipe-based attack. The system reliability and persistent time of WDN under cascading failures can be explored. The process of pipe-based attack is firstly simulated. The changes in system reliability and persistent time have been summarized. The system reliability and persistent time in the node-based attack of WDN are also provided. The results have great significance for protecting WDN and are important in analyzing the potential problem.