排流网情况下地铁迷流分布规律的研究

地铁列车运行时产生的迷流,会对地铁系统及埋地金属结构产生电化学腐蚀,影响其使用寿命及安全运行。地铁迷流很难直接测量,一般通过钢轨纵向电阻、钢轨对地电阻和对地电压等参数来间接计算。作者提出了无排流网情况下的地铁迷流计算公式,建立了考虑排流网情况下的地铁迷流解析公式,修正了原来的迷流估算公式。指出虽然总的迷流并不会因为安装排流网而减少,但流入结构钢筋的迷流明显减小;在排流网与钢轨纵向电阻相同的条件下,流入结构钢的迷流与负荷电流的比值,将减小为无排流网时的平方倍,这证实了排流网的有效性,为迷流的监测与防治提供了理论依据。

排流网情况下地铁杂散电流分布数值模拟研究

针对地铁杂散电流的腐蚀及预防问题,对排流网情况下地铁杂散电流及相关因素的影响分布进行了研究,在原有的走行轨—金属网模型基础上,提出并建立了走行轨—排流网—金属网系统的物理模型,基于基尔霍夫定律建立相应的数学模型,利用MATLAB对数学模型进行了程序编写,分别研究了排流网影响效果,以及排流网条件下变电所间距、过渡电阻和走行轨纵向电阻对走行轨电流、走行轨电压、杂散电流和排流网中电流的影响。结果表明:排流网可以排流大部分杂散电流,从而降低腐蚀危害;变电所的间距不宜大于2 km,过渡电阻宜设定在15Ω·km以上,尽可能降低走行轨纵向电阻。

排流网与地网排流时对杂散电流分布影响的探讨

地铁系统在道床内铺设排流网来收集杂散电流以减少其腐蚀危害。当杂散电流数量较大时需要对排流网排流将杂散电流引回变电所负极。为了防止杂散电流沿着埋地金属物向远离变电所的方向流出腐蚀埋地金属物,有的地铁公司采取对地网排流的方法。用仿真的方法讨论了分别与同时给排流网和地排流对杂散电流分布的影响,同时讨论了对排流网和地网排流的可行性。

辅助排流网与接地的关系和处理方案

"杂散电流腐蚀防护措施与接地之间存在矛盾"是当前的普遍看法,认为问题出在两个系统被孤立对待,没有整体分析它们的工作机理和内在关系。通过分析,提出常态与非常态下辅助排流网与接地的关系,明确接地系统应注意的事项。

城市轨道交通排流网对杂散电流分布的影响

为减少杂散电流对城市轨道交通自身及周边设施的腐蚀影响,一般将区间内道床结构钢筋贯通作为排流网,牵引变电所设排流柜,可以将结构钢筋中的杂散电流单方向回流到变电所内的负母线,减小杂散电流的泄漏。本文通过建立直流牵引回流系统离散模型,利用MATLAB仿真分析了排流网纵向电阻变化时、排流网对地过渡电阻变化时对杂散电流分布的影响,对比了排流前后杂散电流的变化规律,总结出排流对杂散电流的分布的影响。

排流网钢筋的优化设计

介绍地铁杂散电流的腐蚀原理和危害的同时,阐述地铁排流网系统的构造和作用等。以此构建新的杂散电流电阻分布模型,并在此新模型上,从排流网结构钢筋的纵向电阻分析,讨论如何优化杂散电流钢筋网,以达到杂散电流防护的目的。

设置排流网供电方式下杂散电流的分布研究

目前地铁大都采用走形轨回流的直流牵引供电方式,因而在运营中将不可避免地产生流经大地的杂散电流。地铁杂散电流严重腐蚀地下金属结构,影响地铁安全运营,因此全面考虑地铁杂散电流腐蚀问题,探讨更为有效的杂散电流腐蚀防护措施,保证地铁安全运营具有十分重要的意义。鉴于实际地铁供电模式均为双边供电,本文以双边供电的分布模型推导了排流与未排流时杂散电流分布情况并得到其分布规律。

加设排流网情况下杂散电流场仿真分析

选取盾构形地铁隧道在均匀土壤介质中建立加设排流网情况下的地铁杂散电流场三维有限元模型,通过设置边界条件、加载电流进行仿真计算,得出计算域各个位置的电位,包括排流网本身的电位及与周围混凝土的电位差,分析了加设排流网情况下杂散电流的分布情况,该仿真分析可对排流网钢筋是否遭受腐蚀进行评估。

排流装置对直流牵引供电系统杂散电流分布的影响

直流牵引供电系统中,排流装置投入后究竟是改善还是恶化杂散电流一直饱受争议。为此,该文建立了考虑排流装置的钢轨回流系统模型,并结合叠加原理推广应用于多牵引变电所时的杂散电流与钢轨电位计算。通过CDEGS仿真和排流装置的投退实验验证了模型在计算杂散电流和钢轨电位方面的准确性。并在此基础上,分析了一次杂散电流和排流网收集杂散电流效率的影响因素。研究结果表明,国内轨道交通工程排流网收集杂散电流的效率偏低,排流装置投入后,一次杂散电流增大为未排流的4.87倍、5.34倍,二次杂散电流增大为未排流时的5.41倍和4.63倍。

地铁走行轨对地过渡电阻杂散电流分布的影响

城市轨道交通直流牵引系统杂散电流可能导致钢轨、道床钢筋、结构钢筋和地下金属管线等发生不同程度的腐蚀,杂散电流分布及对腐蚀定量影响目前国内外还缺乏研究。针对目前规范中典型的3种走行轨对地过渡电阻状态:15?·km(新建线路验收限值)、3?·km(运行线路限值)和0.5?·km(不良状态),数值计算对比了机车距离变电所负极距离0.5、1.0、1.5、2.0、2.5和3.0 km 6种位置时沿线钢轨对地电位分布以及钢轨和杂散电流分布。研究结果显示:走行轨对地电阻越小,钢轨泄漏的杂散电流越大。机车在距离牵引变电所负极越远的位置运行时,沿线钢轨的和排流网上的最大杂散电流密度以及沿线钢轨对地电位越大。土壤电阻率为100?·m,走行轨对地过渡电阻为0.5?·km情况下钢轨最严重部分损失占33%,年腐蚀量可达203.62 g/m。该研究为城市轨道交通杂散电流危害定量评估影响提供了依据,清晰地反映了走行轨对地过渡电阻工程控制的必要性。

兰州地铁1号线杂散电流分布规律试验研究

为了获得兰州地区不同土壤环境条件下杂散电流的分布规律,以兰州轨道交通1号线上西客站、马滩站的土壤为研究对象,对不同土壤环境、加设金属管道、铺设排流网以及单/双边供电等条件下的杂散电流进行了测试。测试结果表明:杂散电流在正常土壤中数值最大,在含石头层的土壤中数值最小,且杂散电流值随土壤湿度的增加而增加;加设金属管道后,杂散电流有较小幅度上升;铺设排流网之后,杂散电流有明显的下降趋势,且在埋深为7 cm时效果最差,在埋深3 cm和5 cm时效果较好;双边供电时,2个测试站点的杂散电流值较单边供电时均有较大幅度下降。该研究为兰州轨道交通的杂散电流腐蚀防护提供了理论参考,对兰州轨道交通的安全运营具有重要的指导意义。

基于CDEGS的城市轨道交通杂散电流腐蚀研究

目前对城市轨道交通杂散电流的研究多是基于电路模型,不能很好地模拟实际电流场工况。开展轨道交通牵引回流和杂散电流分布及防护的相关研究,对我国城市轨道交通体系的建设和发展具有十分重要的意义。针对目前国家规范中典型的走行轨对地过渡电阻状态15·km（新建线路验收限值）,计算了列车在牵引区间内不同距离时沿线杂散电流大小,得到区间沿线的分布情况,比较机车不同位置下杂散电流腐蚀情况。

某地铁五号线杂散电流防护方案研究与设计

本文结合某地铁五号线工程的特点,综合提出了某地铁五号线的杂散电流防护设计的原则和相应的防护方案。

福州地铁1号线直流牵引供电系统参数动态变化仿真分析

当前,城市轨道交通普遍采用直流牵引供电、走行轨回流方式,系统直流侧多列车并列运行,功率波动频繁,且列车之间功率耦合强。为分析福州地铁1号线直流牵引供电系统参数动态变化情况,本文基于直流牵引供电系统多列车动态运行仿真模型及福州地铁1号线实际线路参数进行仿真分析,包括列车功率位置曲线、牵引网压、牵引电流、钢轨电位、排流网电位等参数的动态变化以及固定时刻下上述参数的全线分布情况,通过上述参数仿真分析为福州地铁1号线实际运营问题分析提供基础。

随地铁共同敷设高压电缆外表杂散电流研究

随着城市的快速发展,城市地下空间日趋紧张,利用市政公用隧道敷设高压电缆在世界范围内已经被广泛采用。近年来,随着以地铁为代表的城市交通大规模规划建设,利用地铁富余空间敷设电缆高压具有广阔的发展前景。在以直流供电系统供电的轨道交通中,作为回流通路的轨道往往不能做到对地完全绝缘,这就导致了一部分电流泄漏形成杂散电流,敷设于轨道附近的电缆外表导电层中同样会产生杂散电流。杂散电流会对随地铁敷设的高压电缆产生腐蚀,从而给电缆的长期安全稳定运行带来严重的危害。以南京地铁为例,依据地铁隧道工程图建立了地铁隧道内电阻分布的网络拓扑结构,并通过Matlab建模仿真对比了机车在单边供电和双边供电、加排流网和不加排流网以及排流网两端与轨道相连和排流网两端与电缆相连等不同工况下的杂散电流的分布情况,同时指出了杂散电流带来的危害以及必要的防护措施。

Bottleneck Analysis for Data Acquisition in High-Speed Network Traffic Monitoring

The increasing network throughput challenges the current network traffic monitor systems to have compatible high-performance data processing.The design of packet processing systems is guided by the requirements of high packet processing throughput.In this paper,we depict an in-depth research on the related techniques and an implementation of a high-performance data acquisition mechanism.Through the bottleneck analysis with the aid of queuing network model,several performance optimising methods,such as service rate increasing,queue removing and model simplification,are integrated.The experiment results indicate that this approach is capable of reducing the CPU utilization ratio while improving the efficiency of data acquisition in high-speed networks.

A New Treatment of Depression for Drainage Network Extraction Based on DEM

Depressions in landscapes function as buffers for water and sediment. A landscape with depressions has less runoff, less erosion and more sedimentation than that without depressions. Sinks in digital elevation models （DEMs） can be considered the real features that represent depressions in actual landscapes or spurious features that result from errors in DEM creation. In many hydrological and erosion models, all sinks are considered as spurious features and, as a result, these models do not deal with the sinks that represent real depressions. Consequently, the surface runoff and erosion are overestimated due to removing the depressions. Aiming at this problem, this paper presents a new method, which deal with the sinks that represent real depressions. The drainage network is extracted without changing the original DEM. The method includes four steps： detecting pits, detecting depressions, merging depressions, and extracting drainage network. Because the elevations of grid cells are not changed, the method can also avoid producing new fiat areas, which are always produced by the conventional filling methods. The proposed method was applied to the Xihanshui River basin, the upper reach of the Jialingjiang River basin, China, to automatically extract the drainage network based on DEM. The extracted drainage network agrees well with the reality and can be used for further hydrologic analysis and erosion estimation.

SO2 Emission Characteristics and BP Neural Networks Prediction in MSW/Coal Co-Fired Fluidized Beds

The SO2 emission characteristics of typical Msw components and their mixtures have been investigated in a φ150mm fluidized bed. Some influencing factors of SO2 emission in MSW fluidized bed incinerator were found out in this study. The SO2 emission is increasing with the growth of the bed temperature, and it is rising with the increasing oxygen concentration at furnace exit. When the weight percentage of auxiliary coal is being raised, the conversion rate of S to SO2 is largely going up. The SO2 emission decreases if the desulfurizing agent （CaCO3） is added during the incineration process, but the desulfurizing efficiency is weakened with the enhancement of the bed temperature. The fuel moisture content has a slight effect on the SO2 emission. Based on these experimental results, a 12 × 6 × 1 three-layer BP neural networks prediction model of SO2 emission in MSW/coal co-fired fluidized bed incinerator was built. The prediction results of this model give good agreement with the experimental results, which indicates that the model has relatively high accuracy and good generalization ability. It was found that BP neural network is an effectual method used to predict the SO2 emission of MSW/coal co-fired fluidized bed incinerator.

Stability of Kumar-Seidman Networks Under Longest Queue First Policy

This paper is concerned with the stability of multiclass queueing networks of 2 stations and4 buffers under the longest queue first served discipline(LQFS).For this network,the service priority of a customer is determined by the length of the queue that customer resides in at that time.The main result includes two parts.Firstly,the corresponding fluid model is established,and then it is shown that the queueing networks under LQFS are stable whenever the traffic intensity is strictly less than one for each station.

The Efect of Queueing Strategy on Network Trafc

In recent years, the transportation system has been faced by increasing challenge in congestion and inefficiency, and research in traffic network has become a significant area of interest. In this paper, we introduce a dynamic-information-based （DIB） queueing strategy into network traffic model under the efficient routing strategy. DIB makes a packet with higher priority to be delivered if there are less packets travelling along its path from the current node to the destination. It is found that, compared with the traditional first-in-first-out （FIFO） queueing strategy, DIB can effectively bMance the traffic load of the system via delaying packets to be delivered to congested nodes. Although the network capacity has no obvious changes, some other indexes which reflect transportation efficiency are efficiently improved in the congestion state. Besides, extensive simulation results and discussions are provided to explain the phenomena. The results may provide novel insights for research on traffic systems.