汽车下河码头架空斜坡道的结构瞬态动力分析

针对某港区汽车下河码头的架空斜坡道,采用有限元软件MIDAS分别建立其简支梁和连续梁结构的瞬态动力模型,数模计算结果表明:在最不利工况下,连续梁跨中的最大位移和最大弯矩均小于简支梁结构,连续梁可比简支梁节省纵向配筋约10％,本研究的结论可供类似工程参考.     

鹦鹉洲接线工程立交匝道桥计算方法和设计要点

立交匝道桥由于其结构受力与直线桥存在差异,特别是由于弯扭耦合作用,其转矩通常比直线箱梁桥大。介绍了鹦鹉洲接线工程立交匝道桥的计算方法和特殊构造细节,如箱梁横隔板、抗扭钢筋、伸缩缝及支座选用布置等设计要点。     

B型喇叭立交环形匝道线形安全性设计探讨

通过分析车辆在B型喇叭立交环形匝道上的交通特性,提出了B型喇叭立交环形匝道线形指标的取值范围(如设计速度、平曲线半径等);通过分析B型喇叭立交安全运行的影响因素,总结了六种提高B型喇叭立交运行安全性的措施;最后建议B型喇叭立交环形匝道宜采用水滴形卵形曲线来布设,并结合实例阐述了该方法在B型喇叭立交设计中的具体应用。     

自动变速车辆坡道行驶工况下换挡规律的研究

从采用一般换挡规律的AMT车辆在坡道行驶时容易出现的问题出发,分析了换挡循环问题、意外换挡问题和紧急制动问题的原因;提出通过计算理论加速度判断坡道工况的方法;制定修正后的坡道综合控制换挡规律。通过仿真分析,验证此方法可以有效解决各种坡道换挡问题。     

百罗高速公路3^#避险车道适应性分析

为使百罗高速公路3^#避险车道的设置能有效地为刹车失灵车辆提供减速停车的避险作用,文章采用理论分析的方法,结合国内外避险车道的研究、设计和应用经验,对百罗高速公路3^#避险车道的适应性进行分析评价,并针对不足之处提出合理的整治建议,为百罗高速公路长大下坡路段3^#避险车道的改造提供参考依据。     

基于轮胎-颗粒流动力学模型的避险车道参数匹配方案研究

为了优化山区公路避险车道参数设计方案，基于离散元基本理论与方法，建立轮胎与避险车道集料颗粒流模型。利用自主研发的轮胎性能测试系统对货车轮胎垂直特性进行了室内台架试验研究，通过检测不同输入条件下的响应，标定了轮胎颗粒流模型细观参数。采用漏斗法测量了避险车道集料休止角，结合离散元颗粒流仿真方法，对集料颗粒流模型表面摩擦因数进行了标定。基于所建立的轮胎与避险车道的集料颗粒流模型，仿真分析了轮胎在避险车道中的行驶过程，模拟了车辆在运行过程中的行驶距离、行驶速度与轮胎转速的变化趋势。在甘肃S308省道K209+400处避险车道进行了实车道路试验，试验结果验证了该仿真方法的正确性。通过所建立的轮胎-颗粒流模型对比分析了不同铺设厚度，不同集料大小下的仿真结果。综合考虑减速效果和施工成本，确立了避险车道铺设厚度、铺设长度、颗粒材料等设计技术参数。研究结果表明：离散元法能够很好地模拟车辆在避险车道中的行驶过程；考虑到颗粒固结等因素，建议避险车道铺设厚度不小于0.8 m；针对行驶速度大于90 km·h^-1的载货汽车，避险车道设计长度建议大于130 m；避险车道集料方面，建议选用粒径为1~3 cm且圆度较高的砾石作为路床材料。     

Local ramp metering with distant downstream bottlenecks: A comparative study

The well-known feedback ramp metering algorithm ALINEA can be applied for local ramp metering or included as a key component in a coordinated ramp metering system. ALINEA uses real-time occupancy measurements from the ramp flow merging area that may be at most a few hundred meters downstream of the metered on-ramp nose. In many practical cases, however, bottlenecks with smaller capacities than the merging area may exist further downstream, which suggests using measurements from those downstream bottlenecks. Recent theoretical and simulation studies indicate that ALINEA may lead to poorly damped closed-loop behavior in this case, but PI-ALINEA, a suitable Proportional-Integral (PI) extension of ALINEA, can lead to satisfactory control performance. This paper addresses the same local ramp-metering problem in the presence of far-downstream bottlenecks, with a particular focus on the employment of PI-ALINEA to tackle three distinct cases of bottleneck that may often be encountered in practice: (1) an uphill case; (2) a lane-drop case; and (3) an un-controlled downstream on-ramp case. Extensive simulation studies are conducted on the basis of a macroscopic traffic flow model to show that ALINEA is not capable of carrying out ramp metering in these bottleneck cases, while PI-ALINEA operates satisfactorily in all cases. A field application example of PI-ALINEA is also reported with regard to a real case of far downstream bottlenecks. With its control parameters appropriately tuned beforehand, PI-ALINEA is found to be universally applicable, with little fine-tuning required for field applications.     

Collaborative merging strategy for freeway ramp operations in a connected and autonomous vehicles environment

In a connected vehicle environment, vehicles are able to communicate and exchange detailed information such as speed, acceleration, and position in real time. Such information exchange is important for improving traffic safety and mobility. This allows vehicles to collaborate with each other, which can significantly improve traffic operations particularly at intersections and freeway ramps. To assess the potential safety and mobility benefits of collaborative driving enabled by connected vehicle technologies, this study developed an optimization-based ramp control strategy and a simulation evaluation platform using VISSIM, MATLAB, and the Car2X module in VISSIM. The ramp control strategy is formulated as a constrained nonlinear optimization problem and solved by the MATLAB optimization toolbox. The optimization model provides individual vehicles with step-by-step control instructions in the ramp merging area. In addition to the optimization-based ramp control strategy, an empirical gradual speed limit control strategy is also formulated. These strategies are evaluated using the developed simulation platform in terms of average speed, average delay time, and throughput and are compared with a benchmark case with no control. The study results indicate that the proposed optimal control strategy can effectively coordinate merging vehicles at freeway on-ramps and substantially improve safety and mobility, especially when the freeway traffic is not oversaturated. The ramp control strategy can be further extended to improve traffic operations at bottlenecks caused by incidents, which cause approximately 25% of traffic congestion in the United States.     

基于燃油计量阀的高压油泵动态特性仿真分析

以某型基于燃油计量阀的高压油泵为研究对象,在介绍其工作原理的基础上,利用AMESim软件建立高压油泵及共轨管的仿真模型,并通过高压油泵性能试验验证仿真模型的准确性,最后利用模型分析燃油计量阀控制信号的频率和占空比以及驱动轴转速对高压油泵动态特性的影响.结果表明:燃油计量阀控制信号的频率对高压油泵动态特性的影响较小,而燃油计量阀控制信号的占空比和驱动轴转速对高压油泵动态特性的影响较大.随着燃油计量阀控制信号占空比的减小以及驱动轴转速的增大,高压油泵输出高压燃油的响应加快,泵油能力增强.     

A multi-class model-based control scheme for reducing congestion and emissions in freeway networks by combining ramp metering and route guidance

The paper proposes a multi-class control scheme for freeway traffic networks. This control scheme combines two control strategies, i.e. ramp metering and route guidance, in order to reduce the total time spent and the total emissions in a balanced way. In particular, the ramp metering and route guidance controllers are feedback predictive controllers, i.e. they compute the control actions not only on the basis of the measured system state, but also on the basis of the prediction of the system evolution, in terms of traffic conditions and traffic emissions. Another important feature of the controllers is that they have a multi-class nature: different classes of vehicles are considered and specific control actions are computed for each class. Since the controllers are based on a set of parameters that need to be tuned, the overall control framework also includes a module to properly determine the gains of the controllers. The simulation analysis reported in the paper shows the effectiveness of the proposed control framework and, in particular, the possibility of implementing control policies that are specific for each vehicle type.