Research On Invulnerability Of Urban Bus-Metro Double Layer Network

The efficient and orderly operation of the city is inseparable from the support of the urban public transportation system.However,the urban public transportation system is often affected by internal and external emergencies such as vehicle failures,traffic accidents,sudden disasters,bad weather and large passenger flow surges in daily operations,which has a serious impact on the normal and safe operation of the urban public transportation system.Therefore,the theory and method of complex network and transportation engineering are comprehensively used to study the network characteristics,static invulnerability and cascading failure invulnerability of the bus-metro double layer network,aiming to provide some reference for the planning,design and safe operation of the urban public transportation system.The main work of this thesis is as follows:Firstly,the research on static invulnerability and cascading failure invulnerability of the urban public transportation network at home and abroad is sorted out and summarized,and the basic theories of complex network such as the definition and representation of complex network,typical topological network,network statistical characteristics,network invulnerability definition and cascading failure model are introduced.Secondly,the Space-L method is used to construct the bus-metro double layer network model,and the aggregate passenger flow based on line density and departure frequency is used as the edge weight of the network.Taking the bus network,metro network and bus-metro double layer network in Xiamen as examples,the network characteristics of the three types of networks are analyzed and compared.The results show that the degree distribution of the metro network is similar to the Poisson distribution.The cumulative degree distribution of the bus network and the bus-metro double layer network conforms to the power-law distribution and both networks have the scale-free network characteristics.The bus network and the bus-metro double layer network have the characteristics of small-world network.The cooperation and connection between bus and metro can improve the transportation efficiency of the urban public transportation network.Thirdly,the static invulnerability model of the bus-metro double layer network is constructed,which mainly includes three attack strategies: random attack,degree attack and betweenness attack,and two static invulnerability metrics: network efficiency and maximum network connectivity.Taking the bus network,metro network and bus-metro double layer network in Xiamen as examples,the static invulnerability of the three types of networks is analyzed and compared.The results show that the three types of networks are robust to random attack strategy and vulnerable to deliberate attack strategy.Among them,the degree attack strategy has the greatest impact on the invulnerability of the bus network and the bus-metro double layer network,and the betweenness attack strategy has the greatest impact on the invulnerability of the metro network.The invulnerability of the bus-metro double layer network is better than that of the single layer network.Finally,the improved cascading failure model of the bus-metro double layer network is proposed,which considers the nonlinear relationship between the initial load and capacity of the station and the load redistribution method based on the real-time residual capacity of adjacent stations.The time period index to measure the dynamic evolution process of cascading failure is proposed.Taking the bus-metro double layer network in Xiamen as an example,the effects of different types of station failures,adjustable capacity parameters and different attack strategies on network cascading failure are analyzed,and the control variable method is used to measure the invulnerability of network cascading failure.The results show that the increase of capacity parameter α or the decrease of capacity adjustable parameter βcan significantly improve the network invulnerability.In the single station failure mode,the highest intensity station failure has the greatest impact on the network invulnerability;α is slightly increased when α is at the critical threshold,and the network invulnerability shows a sudden increase.In the cyclic attack mode,the network is robust to random attack strategy and vulnerable to deliberate attack strategy,among which the strength attack strategy has the greatest impact on the network invulnerability.The network has high invulnerability and can resist 383 deliberate attacks with low cost resource consumption when α=0.9 and β=0.5.