Theoretical And Experimental Study Of A Multi-grid Model For Pedestrian Evacuation

In case of emergency such as fire,safety evacuation is the important means to ensure the safety of life.How to prevent and reduce the casualties during fire emergency,especially prevent the outcome of tragedy has become the most important thing of public safety in the world.The study of typical characters and fundamental rules of pedestrian evacuation are the main methods in fire disaster prevention,which can provide the scientific guiding principle for the design of buildings and the emergency evacuation plan.Social force model and Cellular Automata model,which can successfully simulate the most typical phenomena observed in pedestrian dynamics,are the two well-known models in evacuation modeling.However,the simulation efficiency of the social force model is low because of its complex rule,and the CA model is not so accuracy due to the lack of detailed interactions among pedestrians and those among pedestrians and constructions.Thus,we propose a new CA model entitled "Multi-grid model" in this dissertation.It has the following characteristics:1) In contrast to the traditional CA model,the new model adopts a finer discretization of the space.Then, one pedestrian occupies more cells instead of one.When the grid density is large enough,the walking velocity and position of pedestrians become continuous,which is similar to the social force model.2) The partial grids of the pedestrian are allowed to be overlapped by other pedestrians or constructions in the model,thus,the interaction forces among pedestrians or those among pedestrians and constructions can be calculated quantitatively by the number and position of the overlapping grids.The movement of pedestrians is decided by the resultant of self-driven force and the exerted forces,referring to the rules of resultant force in social force model.3) For a finer discretization of the space,the size of constructions and boundaries are figured more accurately.The simulation results indicate that the new model can reproduce some typical self-organization phenomena in evacuation dynamics such as arching and clogging at a bottleneck and discontinuous outflow.The model consists well with the social force model on human behaviors and the computational efficiency of which is equivalent to the classic CA model.The dislocable distribution of pedestrians,variable walking speed and the interactions among pedestrians due to the finer lattice in Multi-grid model have important impact on evacuation dynamics.The dislocable distribution of pedestrians in initial status as well as movement process enhances the interactions among pedestrians.The walking speed is adjustable because the pedestrian can move one or more small grids in each time step.The exit is figured more accurately because of the finer lattice,which reduces the probability of pedestrians passing the exit abreast. When one pedestrian walks in the middle of an exit and no pedestrian could share the exit with him,then the evacuation efficiency is decreased.This is called exclusive phenomenon at the exit.The discretization effect in Multi-grid model is discussed in two movement modes(fixed or variable walking speed) and there update rules (parallel,sequential order or shuffled update order).According to the particularity of human behavior in staircase evacuation,we propose a special Multi-grid model for staircase evacuation.The rectangular body size, the inner-side bias walking and the turning behavior at the turning point between two flights are taken into account in the model.In addition,for a finer discretization of space,the size of structures and boundaries are figured more accurately and the walking speed is variable according to the crowd density.The simulation results are compared with an evacuation drill of a four-story student apartment.We analyze the average inflow and outflow rate of each floor,the change of the number of pedestrians in the staircase and the empty time of each floor,etc.It indicates that the results of the composed model agree well with the egress drill data.On basis of the Multi-grid model,we developed a pedestrian evacuation evaluation software named MultiGo(Software Copyright No.133852) for the performance-based assessment of buildings.