排水沥青混合料比表面积的分形研究

对集料的粒径分布、级配、集料总体积、空隙率、表面积等做出相关分析,给定了集料各特征值的具体求法,建立体积分维DV和表面积分维DS之间的关系,并根据级配曲线的走向,按不同分段方式进行比表面积计算对比。结果表明:不同的分段方式对于排水沥青混合料的比表面积确定有很大的影响,在进行比表面积计算时,应按各筛级进行逐级分段计算。     

大桩帽轨道梁不同支承条件的受力分析

通过ANSYS软件对轨道梁的弹性点支承、刚性点支承、分布弹性支承以及空间模型进行有限元模拟,得出不同模型下的连续梁内力以及支座反力,并对不同模型的计算结果进行比较分析。计算结果表明,弹性点支承与刚性点支承模型在计算宽支座梁支座负弯矩时与分布弹性支承模型及空间模型差异较大,在支座边缘处采用弹性点支承模型计算弯矩削峰的方法已不再适用,同时得到宽支座梁支座反力、剪力等分布规律,可供大桩帽连续梁设计参考。     

A State-of-the-Art Review: Developments in Utility Theory,Prospect Theory and Regret Theory to Investigate Travellers' Behaviour in Situations Involving Travel Time Uncertainty

Abstract

Despite the wide use of utility theory to model travellers' behaviour, the interest in non-expected utility theories has increased due to their potential to capture more realistic behaviour. A main question raised is whether travellers are better described as utility maximizers or should be qualified differently.

This paper presents a literature review on the use of expected utility theory (EUT), prospect theory (PT) and regret theory (RT) to model travellers' behaviour. Gaps in the literature are identified and a discussion about advantages and disadvantages of each theory is presented. A case study illustrates the differences between the theories.

Under certain conditions, PT and RT restrict themselves to EUT. Their added value, however, is the possibility of capturing loss aversion, risk aversion and risk-seeking (PT) and regret aversion (RT). On the practical level, the use of EUT is well established, while contributions of PT and RT are marginal. On the theoretical level, however, RT seems to be (marginally) more suitable to model travellers' behaviour, while EUT and PT are equally suitable. This suggests that the large use of EUT is highly influenced by its very tractable framework. We do not claim the superiority of any theory, but propose to compare them through a systematic review.     

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本文旨在研究期望速度对速度—密度曲线的影响.通过引入期望速度建立了新的博弈表和相应的交通流中观模型,利用VBA和Matlab混合编程技术开发了相应的计算程序.对于一个期望速度类情况,分析了期望速度相同时不同的道路条件对应的速度—密度曲线,以及相同道路条件下,不同期望速度对应的速度—密度曲线.对于多个期望速度类的情况,研究了多个期望速度的变异系数对车流平均速度的影响,以及慢车比例对车流平均速度的影响.得出结论,驾驶员的期望速度差异是影响车流平均速度的主要因素之一.当密度较小时,交通流处于个体流模式,此时交通流平均速度主要由期望速度差异决定;当密度较大时,交通流处于集体流模式,此时交通流平均速度主要由密度决定.     

基于博弈论的多利益主体绿色供应链两阶段博弈分析

本文主要研究绿色供应链多利益主体的博弈行为和决策选择问题。首先提出了包含制造企业、政府、分销商与消费者的绿色供应链多方博弈分析框架。其次,通过博弈理论合理构建了两阶段博弈,第一阶段针对制造企业、政府、消费者三者进行博弈分析,第二阶段基于委托代理机制针对制造企业与分销商进行博弈分析。最后从理论上分析绿色供应链中各方优化协调的效率,重点分析在政府参与下,不同博弈策略对绿色供应链管理的影响。     

动车组牵引计算仿真系统设计

分析动车组牵引计算仿真系统研究的背景,总结我国主流牵引计算软件运用于动车组计算时存在的不足,结合调研结果和用户需求分析,在此基础上设计一个新的适合动车组牵引计算仿真系统,主要设计内容包括系统功能、关键技术和存在难点。     

快速公交系统通行能力研究

通行能力分析是快速公交系统规划、设计和优化的基础。基于GI/G/1排队论模型和车站有效停靠泊位数构建了快速公交系统通行能力计算方法,其参数设置涉及影响快速公交系统通行能力的各种因素。通过对北京、广州、厦门、郑州等多个中国城市快速公交系统运营状况的调查分析,对相关参数进行了标定,以使其反映中国各地快速公交系统运营实际。最后以广州、厦门、郑州三市的快速公交系统为例,对上述方法的应用进行说明。     

Stability and bifurcation in network traffic flow: A Poincaré map approach

Previous studies have shown that, in a diverge-merge network with two intermediate links (the DM network), the kinematic wave model always admits stationary solutions under constant boundary conditions, but periodic oscillations can develop from empty initial conditions. Such contradictory observations suggest that the stationary states be unstable. In this study we develop a systematic approach to investigate the stability property of stationary states in this and other networks within the framework of network kinematic wave theories. Based on the observation that kinematic waves propagate in a circular path when only one of the two intermediate links is congested, we derive a one-dimensional, discrete Poincaré map in the out-flux at a Poincaré section. We then prove that the fixed points of the Poincaré map correspond to stationary flow-rates on the two links. With Lyapunov’s first method, we demonstrate that the Poincaré map can be finite-time stable, asymptotically stable, or unstable. When unstable, the map is found to have periodical points of period two, but no chaotic solutions. We further analyze the bifurcation in the stability of the Poincaré map caused by varying route choice proportions. We apply the Poincaré map approach to analyzing traffic patterns in more general (DM)ⁿ and beltway networks, which are sufficient and necessary structures for network-induced unstable traffic and gridlock, respectively. This study demonstrates that the Poincaré map approach can be efficiently applied to analyze traffic dynamics in any road networks with circular information propagation and provides new insights into unstable traffic dynamics caused by interactions among network bottlenecks.     

Accommodating risk in the valuation of expected travel time savings

Valuation of travel time savings is a critical measure in transport infrastructure appraisal, traffic modelling and network performance. It has been recognised for some time that the travel times associated with repeated trips are subject to variation, and hence there is risk embedded in the treatment of expected travel time. In the context of the expected utility framework, we use a nonlinear probability weighting function to accommodate choice made under risk. Although the empirical findings suggest small differences between the value of expected travel time savings (VETTS) in the presence and absence of risk, the mean estimate does make a noticeable difference to time benefits when applied to real projects. By incorporating nonlinear probability weighting, our model reveals that the probabilities associated with specific travel times that are shown to respondents in the choice experiment are transformed, resulting in overweighting of outcomes with low probabilities and underweighting of outcomes with high probabilities. Copyright © 2011 John Wiley & Sons, Ltd.     

大吨位徐变仪球铰非线性接触分析

因研究桥用高强度混凝土材料徐变性能的需要,自主研制了大吨位徐变仪。对于处于接触受力状态的徐变仪球铰区域,先用Hertz接触理论估算球铰区域尺寸范围,然后利用ANSYS通用有限元软件对该区域分别取2种垫板凹槽球径的模型进行接触分析,通过对比球铰区域的最大接触压力、mises应力、第3主应力来进一步确定垫板凹槽的合理球径。用该徐变仪对2座大桥成功进行了高强度混凝土徐变试验,并实际验证了试验荷载下徐变仪球铰区域的受力性能,以及有限元接触分析结果的正确性。