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.     

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.     

步行通道内行人流拉链现象的生成机理与仿真研究

以步行通道内的单向行人流为研究对象,分析研究行人拉链现象的生成机理,并建立基于Voronoi图的速度修正模型对其仿真研究.首先,从行人追求视野最佳和步行舒适的角度分析拉链现象的生成机理,以行人的视野关注和视野遮挡描述影响行人移动过程中产生拉链偏移的因素;以行人局部密度描述行人的步行舒适度;引入拉链敏感系数描述行人客观偏移的意愿程度;提出单个行人侧向偏移的机制,获得行人最佳的偏移位置.然后,构建基于Voronoi图的行人速度修正仿真模型,考虑行人是否有偏移倾向的主观意愿,并嵌入偏移规则,模拟再现行人的拉链现象.仿真发现:行人的拉链层数与通道宽度成正比,该模型速度密度关系图与实证数据吻合较好;与不考虑拉链效应相比,倾向主动进行侧向偏移的行人占比越大,越有助于提高通道内行人的移动速度、舒适度和空间利用率.     

Simulating pedestrian flow through narrow exits

Introduction: The flow of pedestrians through narrow doorways is one of the most common features of crowd motions and evacuations. It is particularly an important aspect of pedestrian simulations models since their accuracy depends highly on their ability to produce realistic exit flow rates. The problem has been extensively studied in the literature, but many aspects of it have remained controversial with mixed (and often contradictory) evidence emerging from different studies and different methods. Methods: We discuss the significance of parameter calibration for accurate simulation of pedestrian flow through narrow exits using social force model. Based on sensitivity analyses, we show how simulated exit throughput rate can vastly differ by changing the value of certain parameters. We identify the two parameters that are most critical, and then calibrate them based on a set of experimental observations (at macro level). Using these calibrated parameters, we then re-examine three fundamental questions related to pedestrian flow at bottlenecks, (1) the relation between desired velocity and simulated egress time; (2) the effect of barricade at exits; and (3) the effect of exit in the corner versus the middle. Results: Our numerical analyses showed that, with the calibrated parameters, increasing the desired velocity in the social-force model results in monotonically shorter egress times (at a marginal rate that rapidly diminishes as the desired velocity increases). We showed that placing a panel-like barricade at exit can facilitate the outflow and reduces the egress time, but its effect depends on the widths of exit, as well as the size of the barricade and its distance to exit. We show that the positioning the exit in the corner is also effective in terms of reducing egress time, but only for very narrow exits. The benefit diminishes quickly as the exit becomes wider. Applications: These outcomes demonstrated the significance of parameter calibration for accurate simulation of crowd flows. The findings may also help to identify simple modifications that can facilitate crowd flows at narrow bottlenecks.     

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.     

火灾逃生过程的模拟与讨论—–以吉林禽业火灾为例

2013年6月3日,吉林禽业公司发生大火,300多名员工中120人遇难,是我国2000年以来死亡人数最多的一次火灾.此次火灾造成巨大伤亡的一个重要原因是厂房的6个出口只有3个可用,并且员工不知道每个出口的可用性信息.本文运用经典的地面场模型对吉林禽业火灾逃生过程进行模拟,研究了厂房各出口的重要性差异以及出口的可用性对逃生效果的影响.结果表明,如果多开一个出口,最多可挽救54.3%的遇难者,如果6个出口全部可用,76.6%的遇难者能够逃离.另外,在出口可用性信息完全掌握的情况下,遇难人数也会减少21.6%.由此可见,保证人群集聚现场出口的可用性以及信息的及时流通对于保护人民的生命财产安全至关重要.     

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     

Discrete element crowd model for pedestrian evacuation through an exit

A series of accidents caused by crowds within the last decades evoked a lot of scientific interest in modeling the movement of pedestrian crowds. Based on the discrete element method, a granular dynamic model, in which the human body is simplified as a self-driven sphere, is proposed to simulate the characteristics of crowd flow through an exit. In this model, the repulsive force among people is considered to have an anisotropic feature, and the physical contact force due to body deformation is quantified by the Hertz contact model. The movement of the human body is simulated by applying the second Newton's law. The crowd flow through an exit at different desired velocities is studied and simulation results indicated that crowd flow exhibits three distinct states, i.e., smooth state, transition state and phase separation state. In the simulation, the clogging phenomenon occurs more easily when the desired velocity is high and the exit may as a result be totally blocked at a desired velocity of 1.6 m/s or above, leading to faster-to-frozen effect.     

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.     

Simulation of crowd dynamics in pedestrian evacuation concerning panic contagion: A cellular automaton approach

The study of the panic evacuation process is of great significance to emergency management. Panic not only causes negative emotions such as irritability and anxiety, but also affects the pedestrians decision-making process, thereby inducing the abnormal crowd behavior. Prompted by the epidemiological SIR model, an extended floor field cellular automaton model was proposed to investigate the pedestrian dynamics under the threat of hazard resulting from the panic contagion. In the model, the conception of panic transmission status (PTS) was put forward to describe pedestrians' behavior who could transmit panic emotions to others. The model also indicated the pedestrian movement was governed by the static and hazard threat floor field. Then rules that panic could influence decision-making process were set up based on the floor field theory. The simulation results show that the stronger the pedestrian panic, the more sensitive pedestrians are to hazards, and the less able to rationally find safe exits. However, when the crowd density is high, the panic contagion has a less impact on the evacuation process of pedestrians. It is also found that when the hazard position is closer to the exit, the panic will propagate for a longer time and have a greater impact on the evacuation. The results also suggest that as the extent of pedestrian's familiarity with the environment increases, pedestrians spend less time to escape from the room and are less sensitive to the hazard. In addition, it is essential to point out that, compared with the impact of panic contagion, the pedestrian's familiarity with environment has a more significant influence on the evacuation.     

A new collision avoidance model for pedestrian dynamics

The pedestrians can only avoid collisions passively under the action of forces during simulations using the social force model, which may lead to unnatural behaviors. This paper proposes an optimization-based model for the avoidance of collisions, where the social repulsive force is removed in favor of a search for the quickest path to destination in the pedestrian's vision field. In this way, the behaviors of pedestrians are governed by changing their desired walking direction and desired speed. By combining the critical factors of pedestrian movement, such as positions of the exit and obstacles and velocities of the neighbors, the choice of desired velocity has been rendered to a discrete optimization problem. Therefore,it is the self-driven force that leads pedestrians to a free path rather than the repulsive force, which means the pedestrians can actively avoid collisions. The new model is verified by comparing with the fundamental diagram and actual data. The simulation results of individual avoidance trajectories and crowd avoidance behaviors demonstrate the reasonability of the proposed model.     

Experimental study on the effect of background music on pedestrian movement at high density

Although crowding is often observed in large cities, it is still not known how to control it. Rhythm is a potential method to improve pedestrian flow. This paper investigates the effect of background music on pedestrian movement. Six experiments with different background rhythms and an experiment under normal condition (without any rhythm) are conducted to study the issue. Fundamental diagrams show that velocity and flow with background music at medium and high densities will be smaller than those under normal conditions. With music, stop-and-go behavior is more frequently observed due to a higher stopping headway and a higher restarting headway. Stopping duration analysis shows that pedestrians stop longer with music. Therefore it has to be considered as another factor for jam formation in pedestrian traffic besides density and inhomogeneities. Because of the weaker dynamic coordinate behavior (slower response to the motion of the frontal pedestrians), pedestrians need more time to prevent conflicts and step consecutively at high densities in the presence of music. Decreasing step frequency with rhythm at high density also results in stopping more frequently. Our study will be helpful for understanding the effect of music, especially background music, on pedestrian movement.     

Simulation of evacuation processes using a multi-grid model for pedestrian dynamics

Introducing the force concept of a social force model into the lattice gas (LG) model, a new LG-based discrete model entitled “multi-grid model” is composed. In the new model, finer lattice is used; thus each pedestrian occupies multiple grids instead of one, and the rules of interactions among pedestrians or pedestrians and constructions are built. The interaction forces including extrusion, repulsion and friction are considered as passive factors for evacuation. The strength of the drift, or the intensity of the pedestrians to move toward the exit rapidly, is considered an active factor. A simple situation is studied in which pedestrians try to evacuate from a large room with only one door. The influences of interaction forces and drift on evacuation time are analyzed. The mutual restriction relation of the two factors in the course of evacuating is found.     

Simulation of pedestrian counter flow through bottlenecks by using an agent-based model

Considerable research has been conducted on the topic of unidirectional evacuations from exits. However, few studies aim at simulating counter flow through a bottleneck with complex conflict. This paper proposes an agent-based model to investigate bidirectional flow evacuation. Pedestrian speed is determined by the speed of the leading agent and the surrounding agents. The moving direction of pedestrian originates from four forces, namely, gradient force, repulsive force, resistance force, and random force. These four forces dominate the main stream of the pedestrian moving trajectory, the interaction between pedestrians and their local environment, the resistance or disinclination to movement, and the random variations and chaotic nature of pedestrian dynamics. The novelty of this research is in the agent-based model that combines the agent and forces while providing insights for the simulation of the pedestrian dynamic on the cognitive level. The experiment results show that the behavior that arises from this model is consistent with the observations from Guangzhou Metro and that this model could help capture the essence of pedestrian behavior near egresses.     

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.     

颗粒速度在颗粒流稀疏流-密集流转变中的作用

用实验和计算模拟的方法研究了颗粒流中的颗粒速度与颗粒流特性的关系.实验研究发现当入口流量固定时，在出口上方高速运动的颗粒会使颗粒流由稀疏流向密集流转变的临界出口尺寸变小.当颗粒流转变为密集流后，颗粒速度的作用被出口上方的颗粒堆积区所消耗，最终变得与颗粒速度无关.二维分子动力学模拟计算得到了与实验相同的结论.通过二维分子动力学模拟计算，还给出了不同颗粒速度下体系的密度和速率在空间的分布图.这些分布图显示随着颗粒到达出口上方的瞬间速度的不同，颗粒堆积区的密度和高度均会改变，并最终导致颗粒流流动状态的改变. 关键词： 颗粒流 颗粒气体 分子动力学模拟     

Drift mechanism caused by a nonlinear wave and the Cassini Division and Uranian rings formation

The mechanism leading to the observed coexistence of gaps and narrow ringlets in the planetary rings is found. It is based upon the quasi-stationary radial drift of the matter under action of two forces in the disk plane: the Coriolis force and the Reynolds stresses. To an accuracy of the factor of 2 the first force coincides with the Lorentz force, therefore the radial drift in rings is similar to the gradient drift of plasma in the magnetic field. The second force is produced by the wave generated by the nearby satellite in the resonance position. In inertial systems, the second force alone causes a matter flow in its direction, called acoustic streaming. Since the radial drift is caused by nonlinear time-averaged force of high-frequency harmonic interactions in the wave, it exists in the wave propagation zone: from the birth place of the wave-the resonance position, up to the reflection point of the wave, where its group velocity vanishes. Our estimations show that the size of the density wave propagation zone corresponding to the density wave which had been formerly generated the 2:1 orbital resonance with Mimas is consistent with the width of the Cassini Division. In our case the nature of the radial drift is such that first of all it clears out the farthest from the resonance position; later, the closer areas also get affected by the drift. The zone closest to the resonance position itself is the last to be involved in the process. The matter carried away by the drift is partially accumulated near the resonance position forming a narrow dense ringlet. (c) 1996 American Institute of Physics.     

Experiment and multi-grid modeling of evacuation from a classroom

The evacuation process of students from a classroom is investigated by both experiment and modeling. We investigate the video record of the pedestrian movement in the classroom, and find some typical characteristics of the evacuation, including variable velocity, dislocable queuing, monopolizing exit and so on. Based on the experimental observation, we improve the multi-grid model by considering the pre-movement time of each pedestrian, adopting variable velocity and using a new update procedure. With the improved multi-grid model, we simulate the evacuation process and compare the simulation results with the experimental results, and find that they agree with each other closely. In order to analyze the uncertainty of evacuation, we investigate the influences of the pre-movement time and its distribution on the evacuation. It is found that the evacuation times exhibit a (truncated) normal distribution and vary within a region of about 30% of the mean value. An interesting phenomenon is that the evacuation time of the egress experiment is close to the minimum value calculated with the model, due to the coordination among pedestrians during the experiment. The study may be useful in developing applicable egress models and understanding the basic egress behaviors.     

Simulation for pedestrian dynamics by real-coded cellular automata (RCA)

In this paper, we propose a new approach for pedestrian dynamics. We call it a real-coded cellular automata (RCA). The scheme is based on the real-coded lattice gas (RLG), which has been developed for fluid simulation. Similar to RLG, the position and velocity can be freely given, independent of grid points. Our strategy including the procedure for updating the position of each pedestrian is explained. It is shown that the movement of pedestrians in an oblique direction to the grid is successfully simulated by RCA, which was not taken into account in the previous CA models. Moreover, from simulations of evacuation from a room with an exit of various widths, we obtain the critical number of people beyond which the clogging appears at the exit.