Effect of speed humps on instantaneous traffic emissions in a microscopic model with limited deceleration capacity

As a common transportation facility, speed humps can control the speed of vehicles on special road sections to reduce traffic risks. At the same time, they also cause instantaneous traffic emissions. Based on the classic instantaneous traffic emission model and the limited deceleration capacity microscopic traffic flow model with slow-to-start rules, this paper has investigated the impact of speed humps on traffic flow and the instantaneous emissions of vehicle pollutants in a single lane situation. The numerical simulation results have shown that speed humps have significant effects on traffic flow and traffic emissions. In a free-flow region, the increase of speed humps leads to the continuous rise of CO_(2), NO_(X) and PM emissions. Within some density ranges, one finds that these pollutant emissions can evolve into some higher values under some random seeds. Under other random seeds, they can evolve into some lower values. In a wide moving jam region, the emission values of these pollutants sometimes appear as continuous or intermittent phenomenon. Compared to the refined Na Sch model, the present model has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher volatile organic components(VOC) emissions. Compared to the limited deceleration capacity model without slow-to-start rules, the present model also has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher VOC emissions in a wide moving jam region. These results can also be confirmed or explained by the statistical values of vehicle velocity and acceleration.

Effect of welding current and speed on occurrence of humping bead in high-speed GMAW

The developed mathematical model of humping formation mechanism in high-speed gas metal arc welding （GMAW） is used to analyze the effects of welding current and welding speed on the occurrence of humping bead. It considers both the momentum and heat content of backward flowing molten jet inside weld pool. Three-dimensional geometry of weld pool, the spacing between two adjacent humps and hump height along humping weld bead are calculated under different levels of welding current and welding speed. It shows that wire feeding rate, power intensity and the moment of backward flowing molten jet are the major factors on humping bead formation.

Traffic Calming in Quebec： Speed Humps and Speed Cushions

Speed management is an essential tool in ensuring the improved safety of users of urban roads, particularly vulnerable users. It relies on several measures： awareness campaigns, speed control, as well as the development and operation of the road infrastructure. Municipalities in Quebec are increasingly resorting to the development of traffic calming measures, and are facing numerous questions concerning their installation and their effectiveness. To respond to this need, the ministere des Transports du Quebec （Quebec Department of Transport） has begun publishing a series of fact sheets on a variety of traffic calming measures, including speed humps and speed cushions, raised crosswalks and intersections, neckdowns, centre islands and chicanes. A general fact sheet introduces all of the measures and notably outlines the procedure for pre-implementation analysis. Each fact sheet dedicated to an individual measure outlines the implementation context, advantages and disadvantages, geometric characteristics, effectiveness at reducing speed, and maintenance requirements, including winter maintenance. Two fact sheets are already published： the general fact sheet and the fact sheet on speed humps and speed cushions. The fact sheets as well as examples of measures implemented in municipalities are available on the minist6re＇s web site under Partenaires-Municipalites-Securite routiere.

Influence of backward flowing molten jet on humping bead formation during high-speed GMA welding

Considering the influence of backward flowing molten jet observed by experiments, a new pool surface deformation formula and droplets heat content model are used to investigate the humping formation mechanism during high-speed gas metal arc （GMA） welding. Three-dimensional geometry of the humping bead is numerically simulated only if some extra force and heat acted at the rear part of weld pool are taken into account in the model. It has proved that both the momentum and heat content of backward flowing molten jet must be appropriately treated to quantitatively analyze the physical mechanism of the humping phenomenon.

Suppressing of humping bead using an external magnetic field in high-speed gas metal arc welding

During high-speed gas metal arc welding （GMAW）, the backward flowing molten jet with high momentum in the weld pool is considered to be responsible for the occurrence of humping bead. To suppress humping bead, an electromagnetic device is developed and coupled with the welding system. By adjusting the conditions of external magnetic field, forward electromagnetic force is obtained to reduce the momentum of the backward flow of molten metal in weld pool. Consequently, the humping bead can be suppressed by adjusting the external magnetic field. Bead-on-plate welding experiment was conducted on mild steel plates, and the influence of magnetic flux density on the arc deflection angle and weld bead quality is investigated. It is found that external magnetic field can remarkably adjust the momentum of backward flow jet and significantly improve the quality of weld bead.

焊接位置对激光-电弧复合焊接底部驼峰的影响

目的通过改变焊接位置来抑制底部驼峰的形成进而降低生产成本。方法使用高速摄像机观察平向焊接和横向焊接2种不同焊接位置下熔池的匙孔和底部驼峰的形成过程,并对底部凸起受到的金属蒸气反冲压力、熔融金属重力以及表面张力进行受力分析。结果在S355J2W耐候钢的激光-电弧复合焊接平焊过程中,受金属蒸气反冲作用力的影响,熔融金属迅速从匙孔底部排出,流入匙孔底部凸起区域,底部凸起的增长速度极快,仅需7.5 ms即可形成大尺寸的驼峰。而在横向焊接中,匙孔前壁凸起数量减少,导致金属蒸气反冲压力减小,匙孔排出的熔融金属量减少,底部凸起的增速减缓,在13.6 ms时才达到最大高度,使驼峰在底部熔池凝固之前难以形成。结论采用横向焊接的方式可以有效避免驼峰的产生,降低生产成本。同时,该方式在焊缝背部成形效果方面也表现良好,为优化焊接工艺提供了重要参考。

基于巡航控制极限模型的瞬时交通排放仿真分析

本文基于巡航控制极限模型,研究了减速带对交通流系统排放的影响。仿真结果表明,在周期性边界条件下,如果车辆密度较小,减速带的增多会导致二氧化碳(CO_(2))和颗粒物(PM)排放量显著上升;如果车辆密度足够大,减速带对系统排放几乎没有影响。将本文模型与NaSch模型的计算结果进行比较,发现当道路车流密度低且减速带数量设置合理时,系统拥有更大的交通流量和行驶速度,同时CO_(2)和PM排放会更少。

TDJ-302MW型免维护减速顶的研制

TDJ-302MW型免维护减速顶由滑动油缸组合件和壳体组合件两大部分组成,用双头螺栓紧固在钢轨内侧,具有结构简单、性能稳定、安全可靠、安装后无需维修等特点。免维护减速顶能够实现一个报废周期内(6年)无需任何室内外的维修,无需设置专门的维修车间及人员,免除用户后顾之忧,减少故障环节,从而保障现场调车作业安全。

利用管理系统提升减速顶维修的质量

临沂站驼峰调速采用分布式微机可控顶控制系统,该系统适合于中小型驼峰的调车调速控制,具有自动调整道岔间隔,保证车辆分勾,控制精度高,对车辆进行连续式控制,无控制死角,以及节约能源、降低噪音污染、提高运输效率等特点。为了提升减速顶维护的管理水平,临沂站开发了一套减速顶管理系统,该系统现已开始运行。现在临沂站的减速顶管理实现了彻底的档案化和现代化。

驼峰车辆减速器制动性能影响因素分析

驼峰作业过程中,溜放车辆经减速器制动后容易出现超速、夹停、轻车挤出等制动问题。通过理论分析和实验方法,分析制动高度、制动宽度、轮辋外径变化、摩擦系数等因素对减速器制动性能的影响情况。结果表明:提高摩擦系数和制动高度、增大杠杆比、减少制动宽度等,能有效降低减速器超速的发生概率;提高制动高度、减少附加制动力系数、提高制动轨强度、降低摩擦系数等,能有效降低轻车挤出的发生概率;提高传动系统动力、减少零部件摩擦阻力、增大曲拐偏心等,能有效避免夹停问题的发生。由此提出解决减速器制动问题的措施和建议,为减速器设计、安装施工、维修维护等,提供理论支持和设计依据。

Experimental determination of the critical welding speed in high speed MAG welding

In high speed MAG welding process, some weld formation defects may be encountered. To get good weld quality, the critical welding speed beyond which humping or undercutting weld bead can occur must be known for different conditions. In this research, high speed MAG welding tests were carried out to check out the effects of different factors on the critical welding speed. Through observing the weld bead profiles and the macrographs of the transverse sections of MAG welds, the occurrence tendency of humping weld was analyzed, and the values of critical welding speed were determined under different levels of welding current or voltage, and the effect of shielding gas compositions on the critical welding speed was also investigated.

减速带对工作区路段污染物排放的影响研究

车辆在通过工作区上游时会因车道缩减而发生堵塞,导致更多车辆排放尾气。基于精细化的元胞自动机模型和污染物瞬时排放模型对不同减速带数目下污染物排放进行研究,针对工作区上游不同车道采用不同换道策略探究不同道路条件下的交通流特性。研究结果表明,在车流量较少路段可以设置减速带保证行车安全,较少的减速带使车辆速度降低而导致污染物排放的减少。随着减速带增多不同污染物排放差异较大。随着道路车辆占有率增多,污染物排放量逐渐减少。在工作区前方频繁发生堵塞的路段,设置减速带对于污染物排放影响不显著,并且会加剧堵塞。在实际交通中,可以设置适当减速带数目使工作区前方左右车道流量分布更均匀,提升道路利用率。该研究可对工作区道路设计提供参考,为道路交通安全提供有利保障。

车辆通过减速带引起的振动分析

由于橡胶减速带的高度相对于路面粗糙度大的多,当车辆快速经过时极易产生跳车现象。跳动的车辆对地面产生冲击作用,从而引起周边建筑物的较大振动。对于一般的载重汽车后轮承受重量比前轮大的多,跳车时后轮对地面的冲击力也将比前轮大的多。本文建立一种简化的跳车模型,在固定位置作用一个冲击力来模拟车辆跳车时车轮对地面的作用力,求解动力方程并求出车辆冲击荷载,然后通过计算半无限体在该作用力表面的振动情况来近似预测车辆跳车时引起的地面振动。最后选取一场地通过实测结果与理论计算分析进行对比。

低比转数离心泵驼峰工况附近内部流动特性分析

为了揭示驼峰的产生机理,采用CFD数值预报对低比转数离心泵驼峰工况附近内部流动特性进行了深入分析,建立了扬程与内部流动特性之间的关系.在0.1~1.6倍设计流量下扬程的模拟值与试验值的相对误差在3.62%以内,且预报驼峰所在工况与实测结果基本一致.对驼峰附近工况0.2,0.3,0.4倍设计流量下的内部流动进行了分析,预报结果表明：泵进口管道存在大量回流,造成叶轮进口预旋,诱发驼峰;各叶轮流道内均存在不同程度大小的旋涡,在0.2和0.3倍工况甚至堵塞了整个流道;存在旋涡的叶轮流道出口相对速度值较大,而绝对速度值较小.结合泵基本方程进一步分析,发现出口相对流速的增大使得扬程降低,引发驼峰.对比叶轮出口R/R2=0.9处绝对速度,小流量下波动更加严重,且其圆周分量下降非常明显,直接降低了这些工况下的扬程值;叶轮进口的预旋及出口回流是诱发驼峰的原因,消除或者减小这些非稳态现象可作为抑制驼峰的出发点.

高速TIG-MIG复合焊焊缝驼峰及咬边消除机理

搭建了TIG-MIG复合焊试验平台及电参数—高速图像同步采集系统,进行了一系列低碳钢高速TIG-MIG复合焊工艺试验,研究了高速TIG-MIG复合焊的电弧形态、熔滴过渡及熔池行为对焊缝成形的影响,并确定了合适的匹配参数.结果表明,MIG焊电流在240~300 A,且TIG焊电流与MIG焊电流相当时,TIG-MIG复合焊焊接过程稳定,即使在焊接速度高达2.5 m/min时,焊缝仍无驼峰、咬边等缺陷,与传统MIG焊相比,熔深增加,熔宽减小.TIG-MIG复合焊由于电弧间的相互作用,两电弧指向发生偏转,电弧压力减小,焊接过程不产生弧坑,且熔宽变窄,这是避免驼峰和咬边缺陷的主要原因.

基于雷达测速曲线的车辆减速器单位制动能高自动计算方法

基于雷达测速曲线和车辆减速器单位制动能高实际测算公式,提出车辆减速器单位制动能高自动计算方法。采用中值滤波法对雷达测速曲线进行滤波处理,通过速度积分与数据分析相结合的方法准确定位减速器的作用区段;基于随机抽样一致性的带噪声数据建模,计算减速器作用区段的加速度;将加速度带入减速器单位制动能高实测计算公式实现减速器单位制动能高的自动计算;对一段时间内的减速器单位制动能高进行统计分析,按时间顺序以散点图的方式展示。以实际调车场的作业为例,采用该计算方法进行计算,并将计算结果与手工计算结果进行对比。结果表明:采用该计算方法既可以得到减速器单位制动能高的实时值,也可以得到其在一定时间段的变化规律。该结果可用于指导减速器的养护维修,从而提高车组溜放速度的控制精度。

高速GMAW驼峰形成过程的数值分析

文中通过数值模拟来研究常速、高速熔化极气体保护焊的温度场和流场,并利用高速摄影观察熔池流动,分析了驼峰形成过程.结果表明,常速焊接熔池纵截面同时存在逆时针向内和顺时针向外两种流动方式,但随着焊接速度的提高,熔池纵截面仅存在逆时针向内单一流动方式.高速焊接时,较大动量的后向液体流和足够大的表面张力促进液态金属在熔池尾部不断堆积、变大.沿焊接方向,熔池受到不均匀的表面张力法向力作用而收缩,这是驼峰形成的两个重要因素.任何能降低表面张力的措施,都能抑制驼峰的形成.

驼峰等间隔溜放控制算法的研究

溜放车组的间隔控制直接影响着驼峰的推峰速度和解体能力。目前所采用的间隔控制方法基本上沿用着人工控制所获得的经验 ,自动化后可以接近或达到稳定的人工控制水平 ,但不能保证繁忙驼峰高速推峰的要求。本文针对驼峰间隔制动位控制问题 ,提出了新的控制数学模型———等间隔控制模型 ,探讨提高推峰速度的途径。根据数学模型进行的仿真试验获得的数据说明 ,当减速器控制精度保持在均方差为 0 5km·h- 1 时 ,在难易不利组合隔钩溜放时 ,推峰速度可以从当前的 3km·h- 1 ～ 5km·h- 1 提高到 6km·h- 1 ,使平均推峰速度达到 7km·h- 1 以上 ,可以实现自动化驼峰日解体能力 5 5 0 0辆以上的运营要求。

基于模糊神经网络间隔调速模型的研究

间隔调速控制是驼峰控制的重点,目前普遍使用的间隔调速算法是出口定速法,不能适应车辆行驶的动态过程,容易出现错误导致事故发生。为此,本文提出了一种基于模糊神经网络理论求得动态出口速度的模型,使用改进的误差反向传播学习算法进行学习,具有很好的自学习和自适应能力,能根据列车的溜放实际情况自动调整减速器出口速度。

道路减速垄布置设计新方法

提出将垄单元横向间断布设以解决车辆与减速垄反复碰撞造成车辆损坏、驾乘舒适性差、周边环境振动、噪音污染和减速垄损坏等问题,列出不等式组保证车辆通过垄单元时不发生倾斜。根据控速路段的限速要求和通行车辆车轴两侧轮间距选定设计参数,求解不等式组得到适合于具体路段的垄单元横向宽和通道宽。新方法使强制减速措施人性化,赋予其可设计性,并且造价低、布设简便、美观大方,具有较大的推广应用价值。