Multiscale Modeling Of Pedestrian Dynamics And Consensus Control For Emergency Evacuation

Rail transit has the advantages of large capacity,high efficiency,safety and conve-nience,and environmental protection.It plays an important role in meeting the travel needs of the people and alleviating urban congestion.The passenger flow of the rail tran-sit is large,and the operating environment is relatively closed.In the event of a sudden accident,the evacuation of the crowd with the station as a typical scene is difficult;that is likely to cause serious casualties and economic losses.The study on dynamic charac-teristics and evacuation of pedestrian crowds in public places such as rail transit stations have attracted extensive attention of scholars around the world,and have become one of the research frontiers and hotspots emerging in the transportation field.Through the analysis of the microscopic movement mechanism of pedestrians and the macroscopic self-organization phenomenon of the crowd,it is of great scientific significance and prac-tical application value to study reasonable evacuation strategy and effective crowd control method.This thesis will foc.us on the multi-scale modeling of pedestrian dynamics and consensus control for emergency evacuation.The main research contents are summarized as follows:1.A new two-time-scale traffic model is introduced to describe pedestrian crowd dy-namics in a typical unidirectional environment.Pedestrian movements are represented in a two-dimensional space that is further divided into narrow virtual lanes.Consequently,pedestrians either move in a lane following each other or change lanes when it is desir-able.Within this framework,the motions of pedestrians are modeled as a two-directional and two-time-scale hybrid system.A pedestrian’s movement along the crowd direction is labeled as the x-direction and modeled by a real-valued process,a solution of a differen-tial equation in continuous-time;the lane change is labeled as the y direction.In contrast to the x-direction dynamics,the movements in the y direction only happen at some time epoch.Stability and convergence analysis is carried out rigorously by using properties of circular matrices,stability of networked systems,and stochastic approximations.Simu-lation studies are used to demonstrate the main properties of our modeling approach and establish its usefulness in representing pedestrian dynamics.2.The proposed two-time-scale model is modified and extended.The dynamic characteristics of the crowd are further studied based on the modified models.Firstly,considering the influence of pedestrian speed and inter-person distance,the "following"behavior of the pedestrians in x-direction is extended from the original first-order differ-ential equation model to the second-order one,and the stability of the crowd system is analyzed.The stable condition of the system is provided.Secondly,the "lane changing"behavior of the pedestrians in y-direction is modeled as the Markov decision process,and the quantized consensus of the crowd system is analyzed.It reveals the speed-density characteristics of crowd movement under normal conditions and the evolution mecha-nism of the transition from free movement state to stop-and-go state under congestion conditions.3.An active collision avoidance model for pedestrian dynamics is established and the influence of leaders for evacuation dynamics is analyzed.Firstly,considering the perception ability of pedestrians and the rejection effect of the neighbors(obstacles),this chapter proposes the active collision avoidance model,in which the pedestrian will search for the quickest path to the destination in his vision field.By combining the critical factors of pedestrian movement,such as positions of the exit and obstacles and velocities of the neighbors,the choice of path has been rendered to a discrete optimization problem.This model is verified by comparing with the fundamental diagram and actual data.The simu-lation results of individual avoidance trajectories and crowd avoidance behaviors demon-strate the reasonability of the model.It solves the problem that pedestrian movement will rebound and oscillate in the traditional social force model.Secondly,considering the herd behavior and attraction effect of leaders,the rules of pedestrian movement under e-mergency conditions such as limited vision are improved,and the crowd behaviors under guidance and the different number and location distribution of leaders are discussed.The results can provide effective supports for the design of reasonable evacuation strategies.4.Imbalanced exit usage can greatly affect the escaping efficiency of pedestrians during an evacuation.This part aims to provide practical guidance for pedestrian flow control so that the evacuees are distributed roughly equally to available exits.A new crowd management framework is introduced based on recently developed weighted con-sensus control methods for networked systems.In this framework,a building with multi-ple exits is modeled as a network with the exits being its nodes.The number of pedestri-ans using each exit is chosen as the state variable.The updating of the state is governed by a recursive equation which can only take values of integers.By redirecting pedestrians from one exit to its neighboring exits,the consensus control achieves global balanced exit usage.Simulation studies are used to demonstrate the convergence,robustness,and scala-bility of the control method.The control law is further tested on a microscopic pedestrian simulation for a lecture hall with three exits.The results show that this approach can provide efficient and feasible crowd control strategies to realize balanced exit usage.