Topology Properties,Mechanism Of Cascading Failure And Invulnerability For Hazardous Materials Transportation Network Based On Complex Network

With the rapid development of energy and chemical industry in China, the hazardous materials transportation (HMT) has become an important economic activity, and which leading to the road mileage and network density of hazardous materials transportation network (HMTN) serving to HMT have been significantly improved, so have the integration and complexity of road network. Compared to the general cargo transportation, the objects of HMT generally have flammable, explosive, corrosive and highly radioactive, such as gasoline, explosives, acids, peroxides, etc. So if there was an accident or a terrorist attack during the transportation. In addition to damage the normal operation of surrounding environment, residents and economic activity, the HMTN is also vulnerable. In particular, when the accident site is the frailest section or intersection of network, it may lead the network to collapse. Therefore, it is good for improving awareness and reducing unknown risk of the damage by researching the topological properties, mechanism of cascading failure and invulnerability of HMTN.This dissertation regards the HMTN as researching objects, and establishes the complex network model for HMTN by using complex network theory. Based on this, it studies the mechanism of cascading failure under different conditions and network invulnerability. The main contents of this dissertation include six parts as follows:(1) Analysis on topological properties and optimization strategies for HMTN based on complex network theory. On the basis of double properties of HMTN, we propose two different ways to construct the cyberspace of HMTN and construct their complex network models respectively. Among them, one is the physical network model of HMTN based on the primal approach. Another is the service network model of HMTN based on the neighboring nodes. The Dalian HMTN is regarded as a researching case, and the statistical analysis results show that:1) the cumulative node degree of physical network is subjected to exponential distribution, showing the network characteristics of random network; 2) the HMTN has small characteristic path length and large network clustering coefficient, which is a typically small-world network; 3) the cumulative node degree of service network is subjected to power-law distribution, showing the network characteristics of scale-free network; 4) the relationship between nodes strength and its descending order ordinal and the relationship between nodes strength and cumulative nodes strength are both subjected to power-law distribution, also showing the network characteristics of scale-free network; 5) by reducing the physical network average road length in the similar conditions (the size of network, the characteristic path length, etc.), expanding the size of network and taking a planning mode with sparse and dense network etc. are all good for improving the network characteristics of small-world network(2) Simulation and model of cascading failure for HMTN based on single attack under deliberate attack. On the basis of multiples node status of HMTN and single node’s failure may cause cascading failure after network is attacked under deliberate attack, we establish the cascading failure invulnerability model of HMTN. Under the condition of the deliberate attack, we define the node status:"normal", "’failure" and "pause", a cascading failure invulnerability model for HMTN is established based on discussing the cascading failure process of HMTN. From the perspective of "result" and "process", the invulnerability indicators and their calculation which are "node survival rate" and "number of the second relative cascading failure" are proposed, taking qunatificationally research through different node’s degree, different capacity coefficient and different planning mode by establishing simulation scene. The results show that:1) in the early planning period of HMTN, we should pay attention to the cascading failure properties of network which will influence the network invulnerability, especially the deliberate attack which may lead to the collapse; 2) in the middle planning period of HMTN, we can take some measures to improve the network invulnerability:①the node capacity of HMTN should be bigger than the road transportation network’s;②we’d better use the planning mode that the nodes with small node degree adjoin to the nodes with big node degree; ③the nodes with small node degree must have a big node capacity when the planning mode is the small one adjoin to the small one; ④the node degree of HMTN should not be too big when its capacity coefficient is small, namely, a simple structure is good for HMTN.3) in the late planning period, we can simulate the cascading failure invulnerability of network by establishing the emergency scene in deliberate attack.(3) Model of cascading failure for HMTN under series of deliberate attacks. On the basis of definition of three node status, we establish the model of cascading failure on HMTN under series of terrorist attacks by studying the cascading failure process of HMTN under single deliberate attack and series terrorist attacks. From the perspective of "result" and "process", the invulnerability indicators and their calculation which are "node survival rate" and "number of the second relative cascading failure" are proposed. By establishing the scene and simulation flow chart, the different times of attack, different node’s degree, different capacity coefficient and different planning mode of HMTN under cascading failure are quantitatively researched. The results show that:1) The bigger the node survival rate is, the higher the network invulnerability will be. When there is no cascading collapse in network, the smaller the number of the second relative cascading failure is, the higher the network invulnerability will be. When the network is in a cascading collapse, the bigger the number of the second relative cascading failure is, the higher the network invulnerability will be; 2) The network invulnerability under serious attacks is less than the single case, therefore, the damage of serious attacks is much higher than the single attack’s. The invulnerability of multiple nodes failure which are adjacent is stronger than the non-adjacent one’s. Therefore, we can make the nodes connecting to the failure ones be failed to reduce the damage causing by cascading failure; 3) we’d better take the planning mode that the nodes with small node degree are adjacent to the nodes with big node degree, if the planning mode that nodes with small node degree are adjacent to the nodes with small node degree is used, the nodes with small node degree should have a very big capacity coefficient; 4) We try not to select the node with big node degree as a node of HMTN; 5) The node capacity coefficient should be higher than road network.(4) Modeling and simulation of cascading failure for HMTN based on targeted attack strategies. Firstly, combined with the empirical research results, we establish the network generation algorithm of HMTN based on WS small-world network. Secondly, we establish the node initial load model with time stage characteristics and tunable parameters, and establish the preferential allocation probability model to "failure" node and node capacity model, by using node load dynamic allocation probability value, we describe node in the "normal", "pause" and "failure" three states, then the mechanism model of cascading failure on HMTN is established. Finally, by establishing two kinds of targeted attack strategies and regarding the average size of network cascading failure and phase transition critical value as the measure of invulnerability, a comparative study of different targeted attack strategies to invulnerability of HMTN is researched. Simulation results and theoretical analysis show that: 1) the model of cascading failure on HMTN is reasonable and effective; 2) the node capacity factor and overload capacity adjustment parameter aren’t sensitive to the change of targeted attack strategies, but it’s useful to reduce the average size of network cascading failure and improve the invulnerability of HMTN by increasing their value; 3) For the targeted attack strategies of node degree in descending order, the smaller the tunable parameter is, the stronger the invulnerability of HMTN will be, but for the targeted attack strategies of node degree in ascending order, the bigger the tunable parameter is, the stronger the invulnerability of HMTN will be, and the intersection of their phase transition critical value curves at tunable parameters is equal to 0.5.(5) Cascading failure model and coupling properties for interdependent networks of HMT based on complex. Firstly, the model for interdependent networks of HMT including physical network, service network and correlative-chain is proposed based on the characteristic of HMTN. Then, on the basis of establishing the node initial load model with time stage characteristics and tunable parameters, the node capacity model is proposed, and using the preferential allocation probability model to describe the three states of nodes, then the cascading failure model for interdependent networks of HMT is established. Finally, a comparative study of cascading failure mechanism and coupling properties for interdependent networks of HMT is researched by regarding the average size of network cascading failure based on node degree as the measure of invulnerability. Simulation results show that:in the same number of failure nodes, the conductivity between physical network and service network is different, and the number of failure nodes of physical network is bigger than the service network’s; the interdependent networks invulnerability can be improved by changing the network model parameters, and enhancing the network model parameters of service network is much more effective than physical network’s, etc.(6) Invulnerability simulation analysis for HMTN based on complex network. We analyze the interaction and impact between the networks by establishing the supemetworks of HMTN, and then the generating method of HMTN is established. We define the concept of "the shortest path of HMTN", "the average risk-path distance" and "the maximal connected subgraph", propose the "efficiency of network risk" and "maximal connected degree" as the measurement index of invulnerability model of HMTN. We establish betweenness centrality model of HMTN according to its flow characteristic. Then the performance of invulnerability of HMTN is respectively researched through different attack modes, different attack types and different attack strategies. The simulation results show that: 1) the methodology proposed by this paper is reasonable, the invulnerability of HMTN is closer to the scale-free network which is robustness to random attack and vulnerability to deliberate attack; 2) the invulnerability of HMTN is maintained by a small number of nodes and edges and the invulnerability of edge is higher than the node’s; 3) the maximal connected degree of HMTN outperforms the efficiency of network risk and to increase the redundancy of system appropriately can improve the invulnerability of HMTN.