Study Of Traffic Flow And Transport Dynamics On Networks

Traffic flow and transportation are dynamic processes prevalent in the human society and the nature,and have been widely studied by physicists for a long time.Two representative researches are the traffic flow on the urban roads and the data packet transport on complex networks.With the intensification of social urbanization,the traffic congestion has become more and more serious,which not only causes inconvenience to people's travel,but also has immeasurable impact on healthy development of the environment and city.To this end,the physicists have focused on the factors of traffic congestion,especially on the phenom-ena of spontaneous traffic congestion in absence of traffic accidents,to discover the basics mechanism underlying traffic congestion.Meanwhile,with an increase of network sizes and data volumes,the focus now shifts to the influence of network structure and routing strat-egy on the network capacity.To address these two fundamental issues,a typical way is to generalize studying objects into single particles from a microscopic perspective,then create a dynamic model based on the interaction between them,subsequently analyze the demon-strated macroscopic properties/behaviors of the model,and therefore propose solutions to the real problems in practice.The doctoral dissertation contains two parts:the first part is mainly focused on the traf-fic flow research based on cellular automata models.The NSOS model is proposed by con-sidering the overtaking behavior of drivers.Through numerical simulations and the mean-field theory,the NSOS model is analyzed,and the characteristics of the synchronized flow are discussed under the framework of three-phase traffic flow theory.In the second part,the transport dynamics of mobile nodes is investigated.By considering heterogeneity of the communication radii of mobile nodes,the accordingly network structure is studied and the packet transport is characterized along with statistical analysis.The three innovate research works are listed as follows:1.Based on the Nagel-Schreckenberg(NS)model with periodic boundary conditions,the NSOS model is proposed by considering the overtaking strategy(OS).In this model,overtaking vehicles are randomly selected with probability q at each time step,and the suc-cessful overtaking is determined by their velocities.The simulation results show that(?)Traffic congestions could be spontaneously happened in the NSOS model.(?)Compared to the NS model,the NSOS model can improve traffic flow in the area where the flow exceed the maximum flow density.In addition,the phase transition of the NSOS model(from a free flow phase to a jammed phase)is studied,by analyzing the overtaking success rate,order parameter,relaxation time and correlation function,respectively.A different behavior in the jammed regime is observed in the NSOS model compared to the NS model,and braking probability as a major factor that influence transition density.Moreover,theoretical analysis of the NSOS model is performed by using a mean-field approach and then compared with the simulation results.2.Within the framework of three-phase traffic flow theory,the property of synchro-nized flow in the NSOS model is studied,and numerical simulations are performed for both closed and open boundary conditions.The fundamental diagram,space-time diagram,and spatial-temporal distribution of speed are investigated.In order to identify the synchronized flow state,both the correlation functions(autocorrelation and cross-correlation)and the one-minute average flow rate vs.density diagram are studied.All the results verify that synchro-nized flow does occur in the NSOS model.3.Based on the network transport model of mobile nodes,this doctoral dissertation dis-cusses the condition under which the communication radii of mobile nodes obey a power-law distribution.The analysis of network structure indicates that the out-degrees obey a power-law distribution,while the in-degrees follow a Poisson distribution.Simulation results reveal that:(?)there exists a critical value of package generate rate Pc,which defines the free-flow state and congested state.(?)In the free-flow regime,the average traveling time is small and independent of the packet generation rate,but the average path length increases with the growth of packet generation rate and is related to a traffic awareness parameter h.(?)The larger the heterogeneous exponent of the communication radii is,the lower the transport efficiency of the network would be.(iv)There exists an optimal traffic awareness parameter h that maximizes the critical value Pc.(?)The critical value Pc decreases with the heteroge-neous exponent a,increases with the network size N,and decreases with the speed v until v reaches an appropriate value.