Crowd Dynamics Models-Based Alleviation Research For Evacuation Bottleneck

In recent years,the development and application of evacuation management play an important role in social emergency prevention,which is a result of the increment of population in pubic area.Although there are numerous questions about evacuation management,the research of bottleneck is a key problem that influences evacuation efficiency and crowd safety.This work focuses on the alleviation of the bottleneck phenomenon during crowd evacuations.Since the bottleneck phenomenon in an evacuation is caused by contradictions between the crowd movement and screen configuration,it has many complex and important properties.Among these properties,the congestion has the most influence of the crowd evacuation.In this dissertation,we pay our attention to the alleviation of crowd congestion,and relevant theoretical problems are given as follows:1.The first step of crowd congestion alleviation is to achieve an accurate analyze of congestion.Given that the congestion is caused by the pedestrian movement,it is necessary to describe the relationship between crowd movement and congestion.Although congestion is a macroscopic phenomenon,it is finally acting on individual pedestrian,which means that congestion is a multi-scale property.For this reason,appropriate approaches are necessary for the analysis of the interaction between macroscopic and microscopic properties.2.The key point of congestion alleviation is to find the movement property that can represent a variety of crowd congestion.Because of the space limitation and the influence of panic,it is difficult to achieve congestion alleviation by psychological approaches.Therefore,the approach to solving the congestion problem should be physical.To solve the above questions and achieve the congestion alleviation,the form of constraints is used to represent the influence of crowd movement on congestion,and then analyzing congestion by calculating constraint forces.The congestion alleviation is achieved by adjusting the self-organization phenomenon in crowds by setting obstacles.Specifically,the contributions and innovations lie in the following aspects:1.A crowd dynamics models based approach is proposed to build movement constraints for representing the relationship between crowd movement and congestion.Concretely,the building of movement constraints is based on the multi-scale characteristics,oscillation phenomenon and pressure transfer in a crowd.To ensure the accuracy and improve the efficiency of the building of movement,we use the existing crowd dynamics models to provide the theoretical basis for the proposed approach.2.To analyze interactions between movement constraints on different scales,analytical tools from the Lagrange mechanics are used to solve this problem.The congestion is finally represented by calculating constraint forces acting on pedestrians.It is worth noting that the application of the Lagrange mechanics is based on the assumption which considers dense crowd is approximately in equilibrium state.3.An arch formation based approach is proposed to alleviate the crowd congestion.The concrete approach is setting obstacles near the exit to adjust the position of arch formation.An arch formation at an outer position is beneficial for congestion alleviation because it is unstable and collapses easily.The symmetrically placed obstacles,which have a similar role as anti-slide piles,are used to change the position of the arch formation in a crowd.4.To improve the adjustment effect of the obstacles,we present a modified model that originates from the soil mechanics in civil engineering to calculate the proper spacing between the symmetrically placed obstacles.This is because the spacing between the obstacles is an important parameter for adjusting an arch formation.The calculating of the proper spacing is based on the assumption that the arch in a crowd can be described by the reasonable arch axis.We have conducted numerical simulation experiments to verify the performances of the proposed methods in terms of congestion analysis and crowd congestion alleviation.