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.     

A heterogeneous lattice gas model for simulating pedestrian evacuation

Based on the cellular automata method (CA model) and the mobile lattice gas model (MLG model), we have developed a heterogeneous lattice gas model for simulating pedestrian evacuation processes in an emergency. A local population density concept is introduced first. The update rule in the new model depends on the local population density and the exit crowded degree factor. The drift D, which is one of the key parameters influencing the evacuation process, is allowed to change according to the local population density of the pedestrians. Interactions including attraction, repulsion, and friction between every two pedestrians and those between a pedestrian and the building wall are described by a nonlinear function of the corresponding distance, and the repulsion forces increase sharply as the distances get small. A critical force of injury is introduced into the model, and its effects on the evacuation process are investigated. The model proposed has heterogeneous features as compared to the MLG model or the basic CA model. Numerical examples show that the model proposed can capture the basic features of pedestrian evacuation, such as clogging and arching phenomena.     

A modified heuristics-based model for simulating realistic pedestrian movement behavior

Pedestrian movement simulation models are used in various areas, such as building evacuation, transportation engineering, and safety management of large events. It also provides effective means to uncover underlying mechanisms of collective behaviors. In this work, a modified heuristics-based model is presented. In this model, the potential collisions in the moving process are explicitly considered. Meanwhile, a series of simulations is conducted in two typical scenarios to demonstrate the influence of critical parameters on model performance. It is found that when facing a wide obstacle in a corridor, the larger the visual radius, the earlier the pedestrian starts to make a detour. In addition, when a pedestrian observes a large crowd walking toward him, he chooses to make a detour and moves in the flow in a uniform direction. Furthermore, the model can reproduce the lane formation pedestrian flow phenomena in relatively high-density situations. With the increase of pedestrian visual radius and the weight of potential collision resistance, more stable pedestrian lanes and fewer moving-through-the-counterflow pedestrians can be observed. In terms of model validation, the density-speed relationship of simulation results accords well with that of the published empirical data. Our results demonstrate that the modified heuristics-based model can overcome the deficiency of the original model, and reproduce more realistic pedestrian movement behavior.     

基于质心Voronoi图重构的UDSM边折叠简化

城市数字表面模型网格(UDSM)的相邻网格常常出现曲率剧变,而这些位置是UDSM的细节部分,简化过程中应当尽量保持。针对该情况,引入了质心Voronoi图重划分网格,将曲率较小的表面的点云密度大大降低。重划分的网格表面细节与周围的平滑表面的三角网格尺寸悬殊,在该基础上使用二次误差矩阵边折叠进行LOD构建时网格发生明显变化,范围大大减少。算法在时间性能与网格误差与直接边折叠相近的前提下,更多地保存简化后的网格细节。     

The fundamental diagram of pedestrian model with slow reaction

The slow-to-start models are a classical cellular automata model in simulating vehicle traffic. However, to our knowledge, the slow-to-start effect has not been considered in modeling pedestrian dynamics. We verify the similar behavior between pedestrian and vehicle, and propose an new lattice gas (LG) model called the slow reaction (SR) model to describe the pedestrian’s delayed reaction in single-file movement. We simulate and reproduce Seyfried’s field experiments at the Research Centre Jülich, and use its empirical data to validate our SR model. We compare the SR model with the standard LG model. We tested different probabilities of slow reaction _ps$p_s$ in the SR model and found the simulation data of _ps=0.3$p_s=0.3$ fit the empirical data best. The RMS error of the mean velocity of the SR model is smaller than that of the standard LG model. In the range of _ps=0.1–0.3$p_s=0.1–0.3$, our fundamental diagram between velocity and density by simulation coincides with field experiments. The distribution of individual velocity in the fundamental diagram in the SR model agrees with the empirical data better than that of the standard LG model. In addition, we observe stop-and-go waves and phase separation in pedestrian flow by simulation. We reproduced the phenomena of uneven distribution of interspaces by the SR model while the standard LG model did not. The SR model can reproduce the evolution of spatio-temporal structures of pedestrian flow with higher fidelity to Seyfried’s experiments than the standard LG model.     

基于Voronoi图盲区的无线传感器网络覆盖控制部署策略

针对无线传感器网络在二维平面应用场景中的覆盖控制问题, 提出了一种基于泰森盲区多边形形心的覆盖控制部署策略(blind-zone centroid-based scheme, BCBS). BCBS先对监测区域做Voronoi图划分以得到被每个传感器节点覆盖的泰森多边形, 而后根据泰森多边形顶点的覆盖情况分析得出泰森多边形内的盲区, 并构造与盲区形状相近的多边形, 最后以该多边形的几何中心作为传感器节点移动的候选目标位置, 从而达到提高网络覆盖率的目的. 仿真实验结果表明, BCBS在覆盖率、节点分布均匀性与节点覆盖效率等方面相比CBS有明显优势. 关键词： 无线传感器网络 节点覆盖 Voronoi图 多边形形心     

A new method for simulating spin-lattice dynamics at finite temperatures

A method is developed for simulating spin-lattice dynamics at finite temperatures for a system of particles with spin-lattice coupling. Thermodynamic equilibrium is ensured by including several additional variables that simulate the thermostat, affect particles, and satisfy supplementary equations of evolution. The results from calculating the heat capacity and magnetization of a Heisenberg ferromagnetic with vibrational degrees of freedom are given to demonstrate the possibilities of the method.     

基于分子动力学模拟的主链型液晶聚合物的新模型

在传统的Gay-Berne (GB)/Lennard-Jones (LJ)模型的基础上，发展了一种用于模拟半刚性主链型液晶聚合物(LCP)的分子级模型，命名为Solo-LJ-SP-GB 模型.单一的LJ联合体和非线性弹簧被用于描述LCP分子中的间隔体.用分子动力学模拟半刚性主链型LCP系统(该系统由169条分子链组成，每两个刚性体之间的间隔体个数为6)时，该模型所需的计算时间不到传统的GB/LJ 模型所需时间的十分之一，大大地提高了计算效率.通过采用该模型模拟半刚性主链型LCP的相变问题，观察到了与半刚性主链型LCP分子中间隔体个数相关的热力学的奇偶效应以及从等方相到向列相的相转变过程.这些模拟结果与当前的试验结果相当符合，从而表明了该模型可以较为准确地描述出半刚性主链型LCP的结构特性. 关键词： Solo-LJ-SP-GB模型 液晶聚合物 分子动力学模拟     

基于元胞自动机的对向行人交通流仿真研究

基于元胞自动机对对向行人交通流进行仿真研究. 模型利用四个动态参数反映行人移动区域和其视野范围内的实际情况,从而决定行人的行为选择,行人可以根据自身周围的情况选择前进、后退、等待、左右移动、交换位置等行为. 仿真研究不同方向比例与不同系统规模的对向行人流的速度-密度、流量-密度关系. 研究结果表明,系统存在相位转换和临界密度,方向比例和系统规模对行人流的速度-密度、流量-密度关系曲线的形状和系统临界密度值有一定的影响. 关键词： 元胞自动机 对向行人流 动态参数 临界密度     

Phase diagram of water based on a lattice model

This model is a variant on Baker's lattice model for liquids; it takes certain features of water into account by means of a hydrogen-bond parameter in the Hamiltonian. Solutions for the complete phase diagram are obtained by means of the cluster variation method. The model displays three phases chosen to correspond with the vapor, open ice and liquid state. The isotherms show a density maximum. We discuss the shortcomings of the model and what to do about them.     

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.     

Constructal theory of pedestrian dynamics

The standard benefit of modeling pedestrian streams is the ability to quantify and understand flow patterns, which can be helpful to avoid some potentially dangerous situations. Here we show that the most basic features of pedestrian dynamics can be put on a unifying theoretical basis, which is provided by the constructal law. This law states that every flow system evolves in time so that it develops the flow architecture that maximizes flow access under the constraints posed to the flow. In this Letter, we develop a model of pedestrian streams that accounts for the influence of pedestrian density. The constructal law is invoked in order to quantify both the so-called optimal level of service and system capacity for pedestrian streams.     

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.     

Simulating hydrodynamics: A pedestrian model

A Hele Shaw cell contains two fluids seperated by an interface. Because the fluids are held in a narrow regions between two plates the cell can be described by a set of two-dimensional hydrodynamic equations, which determine the velocity fields in the fluids as well as the motion of the interface between them. A discretized version of these equations can be implemented in terms of the motion of random walkers. The walkers have the effect of carrying pieces of the fluid from one place to another. They simulate a discrete version of the Laplace equation and obey the appropriate boundary conditions for the fluid. The walker-hydrodynamic connection is explored in the limiting situation in which the viscosity of one of the fluids vanishes. An algorithm is constructed and a few exemplary simulations are shown.     

Quench dynamics and nonequilibrium phase diagram of the bose-hubbard model

We investigate the time evolution of correlations in the Bose-Hubbard model following a quench from the superfluid to the Mott insulator. For large values of the final interaction strength the system approaches a distinctly nonequilibrium steady state that bears strong memory of the initial conditions. In contrast, when the final interaction strength is comparable to the hopping, the correlations are rather well approximated by those at thermal equilibrium. The existence of two distinct nonequilibrium regimes is surprising given the nonintegrability of the Bose-Hubbard model. We relate this phenomenon to the role of quasiparticle interactions in the Mott insulator.     

Simulation of pedestrian flow on square lattice based on cellular automata model

Simulations of two-way and four-way pedestrian flow on the square lattice for small systems will be presented based on cellular automata (CA) in this paper. For the reason that the decision-making process of pedestrians in their movements is complex and intelligent, pedestrian movement is more flexible and adaptive to dynamic conditions than vehicular flow. First, a special technique will be introduced to simplify tactically the process into the interaction of four dynamic parameters, which can reflect the pedestrian judgment on the surrounding conditions and decide the pedestrian's choice of action such as moving ahead, stopping to wait, position exchange, lane switching, back stepping, etc. Second, the simulation method and the relationships of velocity-density and flow-density will be studied and analyzed. It is found that there are phase transitions at the critical density point and at different phases the relationships of velocity-density and flow-density are different from each other. Moreover, the different weight coefficients of four dynamic parameters affect the simulation results of these two models.     

A least-effort principle based model for heterogeneous pedestrian flow considering overtaking behavior

In the context of global aging, how to design traffic facilities for a population with a different age composition is of high importance. For this purpose, we propose a model based on the least effort principle to simulate heterogeneous pedestrian flow. In the model, the pedestrian is represented by a three-disc shaped agent. We add a new parameter to realize pedestrians' preference to avoid changing their direction of movement too quickly. The model is validated with numerous experimental data on unidirectional pedestrian flow. In addition, we investigate the influence of corridor width and velocity distribution of crowds on unidirectional heterogeneous pedestrian flow. The simulation results reflect that widening corridors could increase the specific flow for the crowd composed of two kinds of pedestrians with significantly different free velocities. Moreover, compared with a unified crowd, the crowd composed of pedestrians with great mobility differences requires a wider corridor to attain the same traffic efficiency. This study could be beneficial in providing a better understanding of heterogeneous pedestrian flow, and quantified outcomes could be applied in traffic facility design.     

成对行为对行人疏散动力学的影响研究

熟悉的行人之间经常存在着聚集运动的整体跟随行为现象.为了研究这种行为对疏散过程的影响,考虑了行人的并排成对、前后成对、混合成对三种方式,建立了一个新的元胞自动机模型,研究了三种成对方式对双出口房间内行人疏散过程的影响,并分析、讨论了不同参数下成对方式之间的差异. 关键词： 行人流 元胞自动机 成对疏散 计算机模拟     

A higher-order macroscopic model for pedestrian flows

This paper develops a higher-order macroscopic model of pedestrian crowd dynamics derived from fluid dynamics that consists of two-dimensional Euler equations with relaxation. The desired directional motion of pedestrians is determined by an Eikonal-type equation, which describes a problem that minimizes the instantaneous total walking cost from origin to destination. A linear stability analysis of the model demonstrates its ability to describe traffic instability in crowd flows. The algorithm to solve the macroscopic model is composed of a splitting technique introduced to treat the relaxation terms, a second-order positivity-preserving central-upwind scheme for hyperbolic conservation laws, and a fast-sweeping method for the Eikonal-type equation on unstructured meshes. To test the applicability of the model, we study a challenging pedestrian crowd flow problem of the presence of an obstruction in a two-dimensional continuous walking facility. The numerical results indicate the rationality of the model and the effectiveness of the computational algorithm in predicting the flux or density distribution and the macroscopic behavior of the pedestrian crowd flow. The simulation results are compared with those obtained by the two-dimensional Lighthill-Whitham-Richards pedestrian flow model with various model parameters, which further shows that the macroscopic model is able to correctly describe complex phenomena such as “stop-and-go waves” observed in empirical pedestrian flows.