Study On Propagation Mechanism Of Urban Road Network's Brittleness

With the continuous development of China's urbanization,the urban road network is also becoming more complicate.In recent years,the cascade failures in the urban road network and even the serious traffic accidents have occurred because of the unexpected events inside and outside the system.Brittleness as a basic characteristic of complex system,its theory can explain the behavior of urban road network well,so it is imminent to study the brittleness of urban road network.On the basis of the complex system brittleness theory,this paper studies the brittle structure and excitation mechanism of urban road network,and explores the propagation law of brittleness in urban road network nodes.Firstly,the definition of urban road network brittleness is given,and on this basis,the basic characteristics of road network brittleness are obtained.The layered structure of road network brittleness is also studied.It is divided into brittle factor layer,brittle event layer,system structure layer and brittle risk layer from bottom to top,and further analyzes the road network's brittleness excitation factors from the internal and external two aspects,the brittleness excitation process and the brittle contact function of each node in the network are given.Secondly,the propagation path of urban road network brittleness is studied.The propagation of network brittleness is affected by its brittleness structure,mainly including two aspects: brittle adjacency matrix and network topology.In this paper,the graph theory is applied to establish the brittleness graph model of the urban road network,and the concept of the maximum collapse path of the brittleness map is given.Then the finding of the maximum crash path is considered as a special traveling salesman problem(TSP),and the model of the maximum collapse path of the brittle map based on ant system model is established,and the algorithm flow is given.Because the state of the road network will change constantly during the brittle propagation process,an adaptive Agent graph model which can simulate the dynamic changes of the network is built on the basis of the brittle map,and the IF/THEN criterion for the realization of the adaptive behavior of the model is given.The dynamic model is studied and the full bar of the network collapse synchronization is obtained.A.The change rule of global entropy of urban road network under different conditions is calculated.It is found that the influence of different initial weight matrices on the global entropy of road network is not significant.The change of the global entropy of the road network is mainly determined by the topology of the road network,and the change law of the brittle propagation behavior of the road network under different topological structures is analyzed.Finally,this paper takes the local road traffic network of Xi'an as the research object,carries out a specific model construction,obtains the optimal parameter combination of the model through the experiment method,and uses the MATLAB software to calculate the maximum collapse path and its corresponding weights,then consider the joint behavior of the nodes and do not consider the adaptability of the nodes.The two cases of behavior are calculated respectively,and the global entropy change curve of the road network is obtained,and the brittleness propagation behavior is analyzed.