Lattice gas simulation and experiment study of evacuation dynamics

In this paper, evacuation dynamics in an office building is studied by experiment and simulation. A lattice gas (LG) model is developed. A parameter called ‘exit bias’ is introduced into the model to describe the occupants’ familiarity with different exits in a building. The evacuation experiment, which consists of seven scenarios under various conditions, is conducted to verify the model and calibrate the model’s input parameters such as pedestrian speed and exit bias. The effect of exit width on flow rate, and the effect of occupants’ familiarity with the building on their route selections, are studied. It is found that the accuracy of simulation depends a lot on the model’s pedestrian speed. The optimal pedestrian speed is decided by not only occupant characteristics, but also flow features determined by people distribution, building structure, environment pressure, etc. LG models with proper pedestrian speed are capable of simulating the dynamic process of orderly emergency evacuations.     

三维空间行人疏散的元胞自动机模型

为了有效刻画行人在三维空间中的疏散状况,结合阶梯因素提出了一种新的三维元胞自动机模型,该模型首先基于位置吸引力和碰撞可能性给出了行人移动概率的计算公式,并通过定义元胞演化过程阐述其疏散策略,同时,利用建立的仿真平台进行实验,深入分析了疏散时间、出口流率、出口宽度、初始行人密度以及系统平均速度之间的关系,以此获得更加符合实际情况的行人流特征,结果表明,疏散时间、出口流率与初始行人密度呈现正相关,而与出口宽度呈现负相关,并且系统平均速度和出口宽度对于最优疏散时间存在一个理想阈值。     

双出口房间人群疏散的实验研究和数学建模

本文设计了一个双出口房间内人群疏散的实验方案,通过不同条件下疏散过程的实况录像及视频检测,得到不同人数疏散时间的许多定量结果.提出了双出口房间吸引区间的概念,证明了较小出口吸引区间的边界总是一段圆弧,可以解释行人流出口处的圆形成拱现象.通过类比地铁候车厅内人群疏散过程,建立了双出口房间内疏散时间的二次函数模型,成功拟合不同条件下的实测数据.疏散人数较少时,疏散时间随着人数增加而线性增长;人数较多,在出口附近出现待行区域时,疏散时间则呈二次函数增长.与一些已知疏散时间数学模型相比,本文模型对出口宽度变化的反应更敏感.     

Exit selection strategy in pedestrian evacuation simulation with multi-exits

A mixed strategy of the exit selection in a pedestrian evacuation simulation with multi-exits is constructed by fusing the distance-based and time-based strategies through a cognitive coefficient, in order to reduce the evacuation imbalance caused by the asymmetry of exits or pedestrian layout, to find a critical density to distinguish whether the strategy of exit selection takes effect or not, and to analyze the exit selection results with different cognitive coefficients. The strategy of exit selection is embedded in the computation of the shortest estimated distance in a dynamic parameter model, in which the concept of a jam area layer and the procedure of step-by-step expending are introduced. Simulation results indicate the characteristics of evacuation time gradually varying against cognitive coefficient and the effectiveness of reducing evacuation imbalance caused by the asymmetry of pedestrian or exit layout. It is found that there is a critical density to distinguish whether a pedestrian jam occurs in the evacuation and whether an exit selection strategy is in effect. It is also shown that the strategy of exit selection has no effect on the evacuation process in the no-effect phase with a low density, and that evacuation time and exit selection are dependent on the cognitive coefficient and pedestrian initial density in the in-effect phase with a high density.     

通过博弈的室内行人疏散动力学研究

在室内行人疏散过程中,行人博弈对疏散效率有着重要的影响.本文把抵制博弈策略更新的强度定义为抵制强度. 为了研究抵制强度对疏散效率的影响, 通过在行人博弈策略更新的概率中引入抵制强度,基于元胞自动机模型数值计算在不同的行人密度, 出口宽度下疏散总时间随抵制强度变化的关系.结果表明: 室内行人疏散过程中, 抵制强度小会使得争抢行为极其容易蔓延. 当行人密度小且出口宽大时, 输入以急速疏散为主的规范信息,鼓励行人模仿优胜者更新博弈策略, 当行人密度大且出口狭小时, 输入以避让为主的规范信息抑制行人争抢,都能提高疏散效率. 最后找出不同条件下与最短疏散总时间相对应的优化抵制强度, 为提高室内行人疏散效率提供一个新的视角.     

Evacuation from a classroom considering the occupant density around exits

An existing cellular automaton evacuation model is modified to simulate an evacuation experiment conducted in a classroom with obstacles. In the modified model, the impact of the occupant density around exits on human behavior in evacuation is considered. The simulation and experimental results prove that this improvement makes sense, because besides the spatial distance to exits, people may also choose the exit according to the occupant density around exits. The distribution of individual evacuation times as a function of initial positions and the dynamics of the evacuation process are studied. Comparison between the experimental and simulation results shows that the model can reproduce the experiment well. The improvement of the CA model is useful for further study.     

基于元胞自动机的行人疏散流仿真研究

基于元胞自动机对行人疏散流进行仿真研究.模型利用两个动态参数反映行人移动区域内的疏散情况,从而决定行人的行为选择.模型中行人可以根据自身周围的情况选择移动、等待行为.本文仿真研究了行人在正常疏散环境下,系统规模、疏散人数、安全出口宽度、多个安全出口布局对行人疏散时间的影响.研究结果表明,行人疏散时间随行人数量呈线性增加;随安全出口宽度呈负指数性减少;同时,多个安全出口布局的不平衡也会对行人的疏散过程和疏散时间产生一定的影响. 关键词： 元胞自动机 行人疏散流 动态参数 疏散时间     

Study on evacuation behaviors at a T-shaped intersection by a force-driving cellular automata model

A force-driving cellular automata model considering the social force on cell movement, such as the desirous willing of a pedestrian to exit, the repulsive interaction among pedestrians or between pedestrians and obstacles, was set up to investigate the evacuation behaviors of pedestrians at a T-shaped intersection. And an analogical formulation, taking reference of the magnetic force, was introduced to describe the above repulsive actions. Based on the model, the evacuation behaviors of pedestrians were simulated in terms of different pedestrian density, distribution and corridor width, and then evacuation time was obtained and analyzed. Furthermore, an experiment was conducted to verify the results of the presented model. The results demonstrate that when the density of pedestrians is greater than a certain threshold, pedestrians of a certain direction would be jammed by the repulsion from pedestrians of the counter flow from another direction, and the evacuation time of the former would be longer, even though they are closer to the exit, which would possibly result in a serious casualty in an emergency circumstance. And the phenomenon has been validated by the experiments well. In addition, a corresponding critical corridor width related to different DOPs, beyond which the evacuation time could be decreased rapidly due to a strong degradation of jamming behaviors near the T-shaped intersection, was also discovered and predicted by the proposed model.     

Effect of a static pedestrian as an exit obstacle on evacuation

Building exit as a bottleneck structure is the last and the most congested stage in building evacuation. It is well known that obstacles at the exit affect the evacuation process, but few researchers pay attention to the effect of stationary pedestrians (the elderly with slow speed, the injured, and the static evacuation guide) as obstacles at the exit on the evacuation process. This paper explores the influence of the presence of a stationary pedestrian as an obstacle at the exit on the evacuation from experiments and simulations. We use a software, Pathfinder, based on the agent-based model to study the effect of ratios of exit width ($D$) to distance ($d$) between the static pedestrian and the exit, the asymmetric structure by shifting the static pedestrian upward, and types of obstacles on evacuation. Results show that the evacuation time of scenes with a static pedestrian is longer than that of scenes with an obstacle due to the unexpected hindering effect of the static pedestrian. Different ratios of $D/d$ have different effects on evacuation efficiency. Among the five $D/d$ ratios in this paper, the evacuation efficiency is the largest when $d$ is equal to $0.75D$, and the existence of the static pedestrian has a positive impact on evacuation in this condition. The influence of the asymmetric structure of the static pedestrian on evacuation efficiency is affected by $D/d$. This study can provide a theoretical basis for crowd management and evacuation plan near the exit of complex buildings and facilities.     

基于元胞自动机的行人视线受影响的疏散流仿真研究

基于元胞自动机对视线受影响的行人疏散流进行仿真研究.模型根据行人视野半径将疏散空间划分为可见安全出口区域、可见墙壁区域和盲目区域;利用两个动态参数描述行人在不同移动区域内的疏散特征,从而决定行人的行为选择,包括行人定向移动、沿墙移动和正常疏散移动等行为.仿真研究了行人在墙壁上存在疏散指示标志的疏散空间内,视线受影响时采用随机定向寻墙沿墙移动疏散策略的情况下,行人视野半径对行人疏散时间的影响.研究表明,行人疏散时间不仅受行人视野半径的影响,而且还与安全出口的宽度和安全出口利用率有关.     

拥堵疏散的行人拥挤力仿真研究

基于元胞自动机仿真研究拥堵疏散条件下行人拥挤力的产生、传递、吸收、抵消、累积等过程, 以安全出口前拱形的拥挤疏散行人流为研究对象, 研究拥挤致伤的生成机理. 基于行人位置距安全出口的距离, 生成趋于安全出口方向的拥挤力; 引入拥挤力效果与合力参数, 分别描述外界拥挤力对个体行人的作用效果与作用合力; 引入吸收系数与抗死伤系数, 分别描述拥挤力传递过程中行人对外界拥挤力的吸收与抵抗能力. 研究表明, 随吸收系数或抗死伤系数的增加, 能有效预防疏散行人流的拥挤致伤; 存在临界吸收系数与抗死伤系数, 将系统区分为弱保护相位、强保护相位和完全保护相位; 拥挤的死伤数量随疏散行人数量的增加而增加; 而且, 拥挤致伤的危险区域在安全出口前以安全出口中心线为对称轴呈“倒钟”形分布.     

Effect of varying two key parameters in simulating evacuation for a dormitory in China

Student dormitories are both living and resting areas for students in their spare time. There are many small rooms in the dormitories. And the students are distributed densely in the dormitories. High occupant density is the main characteristic of student dormitories. Once there is an accident, such as fire or earthquake, the losses will be cruel. Computer evacuation models developed overseas are commonly applied in working out safety management schemes. The average minimum widths of corridor and exit are the two key parameters affecting the evacuation for the dormitory. The effect of varying these two parameters will be studied in this paper by taking a dormitory in our university as an example. Evacuation performance is predicted with the software FDS + Evac. The default values in the software are used and adjusted through a field survey. The effect of varying either of the two parameters is discussed. It is found that the simulated results agree well with the experimental results. From our study it seems that the evacuation time is not in proportion to the evacuation distance. And we also named a phenomenon of “the closer is not the faster”. For the building researched in this article, a corridor width of 3 m is the most appropriate. And the suitable exit width of the dormitory for evacuation is about 2.5 to 3 m. The number of people has great influence on the walking speed of people. The purpose of this study is to optimize the building, and to make the building in favor of personnel evacuation. Then the damage could be minimized.     

Simulation of pedestrian evacuation with asymmetrical exits layout

A simulation of pedestrian evacuation from a room with asymmetrical exit layout is presented based on the improved Dynamic Parameter Model in this paper. A special technique is introduced to compute two basic dynamic parameters: Direction-parameter and Empty-parameter considering the effects of pedestrian jam around exits and the width of exits on evacuation path selection in order to reduce evacuation imbalance caused by the asymmetry of exits layout. Two new coefficients: cognition coefficient and imbalance coefficient are introduced to respectively describe pedestrian cognitive ability and the layout imbalance of exits. The simulation results of the improved and original models are compared and analyzed. Simulation results show that evacuation time depends on the cognition coefficient and imbalance coefficient under normal evacuation condition with reasonable pedestrian. It is also found that there are phase transitions and critical points in the simulation curves of evacuation time against cognition coefficient and that the pedestrian flow shows distinctive characteristics at different phases. The values of critical cognition coefficient points depend on the initial pedestrian density and imbalance coefficient.     

Simulation of exit choosing in pedestrian evacuation with consideration of the direction visual field

A modified floor field model is proposed to simulate the pedestrian evacuation behavior in a room with multiple exits by considering the direction visual field. Direction visual field is used to describe the pedestrian’s prediction on the propagation of pedestrian flow along some directions. The proposed model outperforms most of the similar models developed so far in such scenario that pedestrians are initially distributed in a room’s specified zone. Simulation results show that the consideration of direction visual field can better reproduce the evacuation process and reduce evacuation time apparently. Sensitivity analyses of the model parameters are presented.     

Simulation of pedestrian evacuation based on an improved dynamic parameter model

An improved dynamic parameter model is presented based on cellular automata. The dynamic parameters, including direction parameter, empty parameter, and cognition parameter, are formulated to simplify tactically the process of making decisions for pedestrians. The improved model reflects the judgement of pedestrians on surrounding conditions and the action of choosing or decision. According to the two-dimensional cellular automaton Moore neighborhood we establish the pedestrian moving rule, and carry out corresponding simulations of pedestrian evacuation. The improved model considers the impact of pedestrian density near exits on the evacuation process. Simulated and experimental results demonstrate that the improvement makes sense due to the fact that except for the spatial distance to exits, people also choose an exit according to the pedestrian density around exits. The impact factors α, β, and γ are introduced to describe transition payoff, and their optimal values are determined through simulation. Moreover, the effects of pedestrian distribution, pedestrian density, and the width of exits on the evacuation time are discussed. The optimal exit layout, i.e., the optimal position and width, is offered. The comparison between the simulated results obtained with the improved model and that from a previous model and experiments indicates that the improved model can reproduce experimental results well. Thus, it has great significance for further study, and important instructional meaning for pedestrian evacuation so as to reduce the number of casualties.     

初始位置布局不平衡的疏散行人流仿真研究

行人初始位置布局不平衡的多安全出口疏散过程, 是行人疏散流仿真研究的热点. 利用行人流动态参数仿真模型, 在实际距离和假想距离"极大极小"路径选择机理的基础上, 改进假想距离的计算方法及其拥堵计算区域, 实现疏散过程的动态平衡; 提出行人位置布局的不平衡系数, 以描述疏散空间内行人初始位置布局的不平衡性. 从行人初始位置随机和固定布局的角度, 仿真研究正常疏散环境下行人布局的不平衡性对疏散时间的影响, 并将仿真结果与原始模型做对比分析. 研究表明, 模型能有效地实现行人流疏散过程的动态平衡, 行人疏散时间受行人位置或安全出口布局的影响较小, 而与安全出口总宽度、 行人的初始数量以及拥堵感知系数有关.     

Pedestrian evacuation at the subway station under fire

With the development of urban rail transit, ensuring the safe evacuation of pedestrians at subway stations has become an important issue in the case of an emergency such as a fire. This paper chooses the platform of line 4 at the Beijing Xuanwumen subway station to study the emergency evacuation process under fire. Based on the established platform, effects of the fire dynamics, different initial pedestrian densities, and positions of fire on evacuation are investigated. According to simulation results, it is found that the fire increases the air temperature and the smoke density, and decreases pedestrians' visibility and walking velocity. Also, there is a critical initial density at the platform if achieving a safe evacuation within the required 6 minutes. Furthermore, different positions of fire set in this paper have little difference on crowd evacuation if the fire is not large enough. The suggestions provided in this paper are helpful for the subway operators to prevent major casualties.     

菱形网格的行人疏散元胞自动机模型

利用改进的层次域元胞自动机模型,研究了正菱形网格空间中的行人疏散问题.这类网格可以避免行人贴近房间墙壁或障碍物,转移概率考虑了各种逃生受阻因素.数值仿真显示,出口处的行人分布与实验快照展示的行人分布基本相同,疏散时间和出口宽度呈线性关系,行人流率接近实验结果.     

Modeling of pedestrian evacuation based on the particle swarm optimization algorithm

By applying the evolutionary algorithm of Particle Swarm Optimization (PSO), we have developed a new pedestrian evacuation model. In the new model, we first introduce the local pedestrian’s density concept which is defined as the number of pedestrians distributed in a certain area divided by the area. Both the maximum velocity and the size of a particle (pedestrian) are supposed to be functions of the local density. An attempt to account for the impact consequence between pedestrians is also made by introducing a threshold of injury into the model. The updating rule of the model possesses heterogeneous spatial and temporal characteristics. Numerical examples demonstrate that the model is capable of simulating the typical features of evacuation captured by CA (Cellular Automata) based models. As contrast to CA-based simulations, in which the velocity (via step size) of a pedestrian in each time step is a constant value and limited in several directions, the new model is more flexible in describing pedestrians’ velocities since they are not limited in discrete values and directions according to the new updating rule.