A shockwave profile model for traffic flow on congested urban arterials

In this paper a new traffic flow model for congested arterial networks, named shockwave profile model (SPM), is presented. Taking advantage of the fact that traffic states within a congested link can be simplified as free-flow, saturated, and jammed conditions, SPM simulates traffic dynamics by analytically deriving the trajectories of four major shockwaves: queuing, discharge, departure, and compression waves. Unlike conventional macroscopic models, in which space is often discretized into small cells for numerical solutions, SPM treats each homogeneous road segment with constant capacity as a section; and the queuing dynamics within each section are described by tracing the shockwave fronts. SPM is particularly suitable for simulating traffic flow on congested signalized arterials especially with queue spillover problems, where the steady-state periodic pattern of queue build-up and dissipation process may break down. Depending on when and where spillover occurs along a signalized arterial, a large number of queuing patterns may be possible. Therefore it becomes difficult to apply the conventional approach directly to track shockwave fronts. To overcome this difficulty, a novel approach is proposed as part of the SPM, in which queue spillover is treated as either extending a red phase or creating new smaller cycles, so that the analytical solutions for tracing the shockwave fronts can be easily applied. Since only the essential features of arterial traffic flow, i.e., queue build-up and dissipation, are considered, SPM significantly reduces the computational load and improves the numerical efficiency. We further validated SPM using real-world traffic signal data collected from a major arterial in the Twin Cities. The results clearly demonstrate the effectiveness and accuracy of the model. We expect that in the future this model can be applied in a number of real-time applications such as arterial performance prediction and signal optimization.     

A network option portfolio management framework for adaptive transportation planning

A real option portfolio management framework is proposed to make use of an adaptive network design problem developed using stochastic dynamic programming methodologies. The framework is extended from Smit’s and Trigeorgis’ option portfolio framework to incorporate network synergies. The adaptive planning framework is defined and tested on a case study with time series origin-destination demand data. Historically, OD time series data is costly to obtain, and there has not been much need for it because most transportation models use a single time-invariant estimate based on deterministic forecasting of demand. Despite the high cost and institutional barriers of obtaining abundant OD time series data, we illustrate how having higher fidelity data along with an adaptive planning framework can result in a number of improved management strategies. An insertion heuristic is adopted to run the lower bound adaptive network design problem for a coarse Iran network with 834 nodes, 1121 links, and 10 years of time series data for 71,795 OD pairs.     

输气管道置换优化研究

置换是输气管道投产试运过程中的重要工艺环节,是复杂的扩散、对流过程.文中介绍了输气管道投产前用氮气置换空气的几种方法,阐述了它们的工作原理与实施步骤,对比分析了它们的优缺点,优选了置换方式,并采用Fluent流体模拟软件建立了输气管道氮气置换数学模型,进行了三维稳态和非稳态数值计算,研究了置换过程中混气段长度随管径、管长、流速变化规律,将理论推导、数值计算和现场数据进行了对比,验证了理论结果的正确性,为现场施工提供了科学依据.     

Recursive estimation of average vehicle time headway using single inductive loop detector data

Vehicle time headway is an important traffic parameter. It affects roadway safety, capacity, and level of service. Single inductive loop detectors are widely deployed in road networks, supplying a wealth of information on the current status of traffic flow. In this paper, we perform Bayesian analysis to online estimate average vehicle time headway using the data collected from a single inductive loop detector. We consider three different scenarios, i.e. light, congested, and disturbed traffic conditions, and have developed a set of unified recursive estimation equations that can be applied to all three scenarios. The computational overhead of updating the estimate is kept to a minimum. The developed recursive method provides an efficient way for the online monitoring of roadway safety and level of service. The method is illustrated using a simulation study and real traffic data.     

A stochastic model of traffic flow: Theoretical foundations

In a variety of applications of traffic flow, including traffic simulation, real-time estimation and prediction, one requires a probabilistic model of traffic flow. The usual approach to constructing such models involves the addition of random noise terms to deterministic equations, which could lead to negative traffic densities and mean dynamics that are inconsistent with the original deterministic dynamics. This paper offers a new stochastic model of traffic flow that addresses these issues. The source of randomness in the proposed model is the uncertainty inherent in driver gap choice, which is represented by random state dependent vehicle time headways. A wide range of time headway distributions is allowed. From the random time headways, counting processes are defined, which represent cumulative flows across cell boundaries in a discrete space and continuous time conservation framework. We show that our construction implicitly ensures non-negativity of traffic densities and that the fluid limit of the stochastic model is consistent with cell transmission model (CTM) based deterministic dynamics.     

原油管线在线等质量取样系统设计及实现

为了有效解决原油长输管线反复出现的原油途耗异常问题,通过对原油油种、工艺条件和原油输送方式等的分析,设计了等质量流量比例采样系统,由该系统实现原油管线在线自动取样.系统投用后,实现了实时对量,及时发现损耗异常情况,有效控制了原油途耗不稳定的问题.采用等质量流量比例采样模式,较好地解决了多油种、边收边付、多种输送方式以及流量范围宽等不利因素影响计量的问题,具有较好的参考和推广价值.     

超声波流量计在输油管道泄漏监测系统中的应用

为提高负压波法管道泄漏监测系统的报警可靠性,有必要将超声波流量信息引入管道泄漏监测系统。为保证管道泄漏监测系统中超声波流量计的应用效果,分析了超声波流量计的测量原理和测量精度影响因素,总结了输油管道超声波流量计在选型设计、现场安装及运行维护等方面的应用经验。开展了基于超声波流量计的管道泄漏监测技术的现场应用测试和结果分析,测试结果表明超声波流量计对提升管道泄漏监测系统报警可靠性具有显著作用。     

基于壅塞理论的CNG加气管流量计算分析

为了计算CNG加气系统的高压胶管的流量,以气体动力学为基础,建立等截面一维定常绝热摩擦流动的数学模型.利用VC+ +语言编制界面计算程序对模型进行编程求解,对壅塞状态和非壅塞状态下流量以及出口压力进行计算和拟合.当天然气汽车储瓶内的压力小于临界压力时,加气流量最大,且与胶管两端的压差无关,并计算出最大流量与胶管管长的关...     

高压燃气管道储气能力分析

高压燃气管道储气能力与两端压力和管长有着密切的联系.为了得到高压管道的储气量与压力和管长的关系,利用稳态仿真模型,采用四阶龙格-库塔法对模型进行求解,对求出的沿线压力进行线性拟合,得到沿线压力变化公式.结合储气定义推导出储气量与管长的关系式,并得到实例验证.从关系式来看,当管长等于最优管长时储气量最大.     

Real-time freeway traffic state estimation based on extended Kalman filter: Adaptive capabilities and real data testing

This paper reports on real data testing of a real-time freeway traffic state estimator, with a particular focus on its adaptive capabilities. The pursued general approach to the real-time adaptive estimation of complete traffic state in freeway stretches or networks is based on stochastic macroscopic traffic flow modeling and extended Kalman filtering. One major innovative feature of the traffic state estimator is the online joint estimation of important model parameters (free speed, critical density, and capacity) and traffic flow variables (flows, mean speeds, and densities), which leads to three significant advantages of the estimator: (1) avoidance of prior model calibration; (2) automatic adaptation to changing external conditions (e.g. weather and lighting conditions, traffic composition, control measures); (3) enabling of incident alarms. These three advantages are demonstrated via suitable real data testing. The achieved testing results are satisfactory and promising for subsequent applications.