Cascading Failure Paths And Node Importance Analysis On Lifeline System

Lifeline system is the central nervous system for protecting the normal functioning of city "life" and it is also the basic engineering facilities to maintain the functions of modern urban and regional economic. It is collectively referred to as the urban water supply system, power supply system, communication system, transportation system, gas supply system, oil supply system and other key engineering systems.Natural disasters are endangering human life, property and living conditions. After disasters, urban water supply system, power supply system, communication system, transportation system, gas supply system and other key lifeline systems are usually destroyed and lose their service capabilities. It gives rise to a huge pain and suffering for people’s life. At the same time, it may also cause other secondary disasters. This makes the whole city paralyzed. Frequent occurrences of natural disasters in recent years make researching the failure mode of lifeline systems under disasters more and more important. In disasters, the failure mode of lifeline systems is the destruction (disasters or human factors) of some node or edge in the network often leads to the cascading failure of the entire network. In the most serious situation, the cascading failure can lead the disastrous consequence of the entire lifeline system. However, till now, there are very few research results about the failure mode of lifeline systems under disasters and the methods for improving their disaster reliability home and abroad and many problems still exist in the results.So the paper discussed the failure mode of lifeline systems deeply from two aspects of cascading failure path and node importance.Firstly, a concept of failure relational grade of node in lifeline system was proposed and its calculating method was also given. The paper took water supply network as an example and simulated its disaster environment by a program which was developed based on EPANET2.0. The failure relational grade between the damaged nodes and other nodes was calculated and compared by gray relation analysis, and then the cascading failure process of water supply network was analyzed from two aspects:distribution and transmission of resources and network topology. Based on this, the paper researched the cascading failure paths of lifeline system under disasters. The paper defined the concepts of cascading failure path and critical failure path and proposed a method to identify the cascading failure path and the critical failure path in the network. The research and demonstration results showed that the method is accurate and practical and the critical failure path which is the most important one in the entire lifeline system can be found quickly and exactly by using this method. So, with the limitation of cost and so on, the relevant decision makers can only improve the function redundancy of the critical cascading failure path to enhance the overall disaster reliability of lifeline system.Secondly, the paper proposed a method to evaluate the node importance of lifeline system under disasters. The paper took water supply system as an example and established the node importance evaluation index system which including both network topology factors and resource supply factors and taking into account the cascading failure characteristic of lifeline system. The variable fuzzy clustering method was adopted for cluster analysis of nodes in the water supply network in the case. Case study showed that the clustering and node importance sorting results can be obtained by the variable fuzzy clustering method objectively and reasonably so that the key nodes in the network can also be identified. On the basis of this, the paper drew a conclusion that improving the function redundancy of the key nodes can make the lifeline system avoid from the cascading failure and optimize the disaster reliability of the entire lifeline system.