A mesoscopic model for large-scale simulation of pedestrian dynamics

A mesoscopic pedestrian model is proposed, considering pedestrians as individuals and describing their movement by means of aggregate density-flow relationships. The model builds on a stochastic process, describing transition rates among adjacent sites on a lattice. Each lattice can contain several pedestrians. The approach is minimal and fast to simulate, and, by construction, capable of capturing population heterogeneity as well as variability in walking behaviour and en-route path choice. The model is more efficient than microscopic models, and potentially more accurate than macroscopic ones. We calibrate and validate the model using real data and carry out several numerical experiments to present its key properties and possible applications for simulation of large-scale scenarios.     

Scalable stability analysis on large connected vehicle systems subject to stochastic communication delays

In this paper large connected vehicle systems are analyzed where vehicles utilize vehicle-to-vehicle (V2V) communication to control their longitudinal motion. It is shown that packet drops in communication channels introduce stochastic delay variations in the feedback loops. Scalable methods are developed to evaluate stability and disturbance attenuation while utilizing the mean, second moment, and covariance dynamics in open chain and closed ring configurations. The stability results are summarized using stability diagrams in the plane of the control parameters while varying the packet delivery ratio and the number of vehicles. Also, the relationship between the stability of different configurations is characterized. The results emphasize the feasibility of V2V communication-based control in improving traffic flow.     

Link-based day-to-day network traffic dynamics and equilibria

A general dynamical system model with link-based variables is formulated to characterize the processes of achieving equilibria from a non-equilibrium state in traffic networks. Several desirable properties of the dynamical system model are established, including the equivalence between its stationary state and user equilibrium, the invariance of its evolutionary trajectories, and the uniqueness and stability of its stationary points. Moreover, it is shown that not only a link-based version of two existing day-to-day traffic dynamics models but also two existing link-based dynamical system models of traffic flow are the special cases of the proposed model. The stabilities of stationary states of these special cases are also analyzed and discussed. In addition, an extension is made to the case with elastic demand. The study is helpful for better understanding the day-to-day adjustment mechanism of traffic flows in networks.     

A pedestrian flow model considering the impact of local density: Voronoi diagram based heuristics approach

Local density, which is an indicator for comfortable moving of a pedestrian, is rarely considered in traditional force based and heuristics based pedestrian flow models. However, comfortable moving is surely a demand of pedestrian in normal situations. Recently, Voronoi diagram had been successfully adopted to obtain the local density of a pedestrian in empirical studies. In this paper, Voronoi diagram is introduced into the heuristics based pedestrian flow model. It provides not only local density but also other information for determining moving velocity and direction. Those information include personal space, safe distance, neighbors, and three elementary characteristics directions. Several typical scenarios are set up to verify the proposed model. The simulation results show that the velocity-density relations and capacities of bottleneck are consistent with the empirical data, and many self-organization phenomena, i.e., arching phenomenon and lane formation, are also reproduced. The pedestrians are likely to be homogeneously distributed when they are sensitive to local density, otherwise pedestrians are non-uniformly distributed and the stop-and-go waves are likely to be reproduced. Such results indicate that the Voronoi diagram is a promising tool in modeling pedestrian dynamics.     

Changes to commute mode: The role of life events,spatial context and environmental attitude

It has been suggested that commuting behaviours become habitual and that changes to commute mode are more likely at the time of major life events. However, evidence to support this has so far been limited to analyses of small-scale samples. To address this evidence gap, we use two waves of panel data from the UK Household Longitudinal Study (2009/10 and 2010/11) to identify and explain the prevalence of individual change in commute mode from year to year amongst a representative sample of the English working population (n = 15,200). One third of those that cycle or get the bus to work, and one quarter of those that walk to work, are shown to change commuting mode by the following year. Car commuting is more stable, with only one in ten car commuters changing mode by the following year. Commute mode changes are found to be primarily driven by alterations to the distance to work which occur in association with changing job or moving home. Switching to non-car commuting becomes much more likely (9.2 times) as the distance to work drops below three miles. High quality public transport links to employment centres are shown to encourage switches away from car commuting and mixed land uses are shown to encourage switches to active commuting (walking and cycling). Switches away from car commuting are found to be more likely (1.3 times) for those with a pro-environmental attitude. The attitude orientation is shown to precede the behaviour change, demonstrating evidence of ‘cause and effect’. Overall, the study shows that changes in commuting behaviour are strongly influenced by life events, spatial context and environmental attitude.     

土路基-刚性基础板式轨道过渡段动力特性分析

研究目的：目前，我国拟在高速铁路的土路基上铺设无砟轨道，由于高速铁路的轨道要求有更高的平顺性和舒适性，因此本文从车辆-轨道耦合大系统的角度出发，探讨土路基与刚性基础的过渡区段的动力特性，以期为过渡段的设计和施工提供理论支持和参考依据。 研究方法：基于车辆-轨道耦合动力学理论，建立了土路基-刚性基础过渡段模型，编制了动力学仿真计算程序，对过渡段的动力特性进行了仿真计算分析。 研究结论：在土路基-刚性基础过渡区段，轨道基础刚度差产生动力作用不是很大，但钢轨挠度变化显著；差异沉降对轮轨系统的动力作用十分剧烈，考虑30mm／10m的差异沉降，车体加速度达到1．0m／s。时，接近舒适度管理目标值0．13g；随着速度的提高，动力作用加剧，当运行速度从250km／h提高到350km／h时，最大轮轨垂向作用力从92kN提高到104kN，而最大车体加速度从1．0m／s^2提高到1．4m／s^2，此时已经超过了安全限值；过渡段的设置长度宜以车体加速度为主，最大差异沉降为30mm的过渡区段，过渡段的长度可以设置在25—30m之间。     

翼身融合水下滑翔机运动仿真分析

针对回转体形状的水下滑翔机浅海水域滑翔能力弱的问题,以翼身融合水下滑翔机为研究对象,对其进行垂直面动力学模型的建立,并采用MATLAB/Simulink搭建运动模型仿真系统进行开环运动响应研究,分析执行机构的调节速度、浮力调节机构布局方式对水下滑翔机运动性能的影响,得到有利于浅海水域滑翔作业的解决方案;研究水下滑翔机系统输入对运动响应参数的影响程度和定量关系,分析水下滑翔机翼身融合水下滑翔机滑翔比与运动角度关系,得到小角度滑翔可充分利用大滑翔比优势适应浅海水域滑翔作业的结论。     

汽车钢板弹簧多体动力学建模综述

本文中首先综述了板簧设计与建模的研究现状。接着,系统分析了螺旋弹簧模型、beam element模型、ANSYS模型、SAE三连杆模型这4种板簧模型的优缺点及适用情况,在模型复杂程度、仿真速度、参数化等方面进行了对比。最后,以某8×4重型货车为例,分别建立了包含4种板簧模型的整车模型,进行平顺性和操纵稳定性的仿真,并与实车试验进行了对比。结果表明,在4种板簧模型中,SAE三连杆板簧模型的综合性能最好。     

基于弹性绳理论的自主车辆防碰撞的路径规划

基于人工势场的引导策略,通过建立包括车道边界和障碍车的道路危险势场,采用弹性绳模型实现了车辆在高速公路上的车道保持和紧急避障功能。为了保证车辆在高速情形下避障的安全性,在障碍车辆原有势场基础上,在障碍车辆的前后各增加一个引导势场,使车辆能够提前避障,从而避障过程更安全。再结合Carsim仿真,在车辆的路径跟随过程中观察主车的横摆角速度的变化来判断车辆的稳定性。对直道和弯道两种情形进行避障仿真对比分析,结果表明:在障碍车辆前后添加引导势场能提前避障,从而使避障过程更安全。     

船舶建造工程变更对成本的影响因素分析

船舶建造工程属于复杂系统工程,多发的工程变更为系统增加了更多的不确定性。文章以系统动力学理论为基础,从成本管理视角,通过对船舶建造工程变更对成本影响的因果分析,建立了工程变更系统动力学成本模型,并利用Vensim软件对模型进行了仿真,实现了复杂问题的定量化研究。文章的研究结果为企业进行工程变更决策提供有用的参考。