考虑车车与车路通讯并存的路侧单元优化布设方法

路侧单元(Road Side Unit, RSU)作为车路协同系统(Cooperative Vehicle Infrastructure System, CVIS)中路侧感知控制网与网联化车辆自组网的重要节点,其布设方案对车路交互效能、系统建设成本与协同服务水平均产生较大影响。现有RSU优化布设研究主要基于车路(Vehicle to Infrastructure, V2I)通讯,忽视了车车(Vehicle to Vehicle, V2V)通讯的转发和中继作用,也缺乏对RSU设备及线网布设成本的相关考量。针对上述问题,面向V2V和V2I通讯并存环境,考虑信息覆盖正向收益与设备/线网布设负向收益,构建面向综合收益最优的RSU布设方案优化模型。首先结合信息流-交通流耦合模型获取传播时间矩阵,提出权重约束可达性算法,构建布设方案与信息覆盖正向收益之间的关系方程。然后针对动态最优布设方案条件下的最优线网布设问题,提出改进的最小生成树模型,并以此设计综合收益最优的RSU优化布设模型。最后,基于井字形算例路网,进行模型验证和关键系数敏感性分析;并基于Sioux Falls路网,将所提出的模型与现有未...     

一种新的循环谱统计量频谱感知算法

为了提高认知无线电中感知用户对授权用户（主用户）的检测概率,提出一种新的基于循环谱统计量的主用户信号检测算法．该算法利用循环谱离散频域平滑方法,对信号的循环谱在循环频率处建立合理的检测统计量,然后求解得到对应不同虚警概率的判决门限,以使感知用户能检测信噪比更低的授权用户信号．该算法具有检测结构简单,易实现的特点．仿真结果表明,在高斯白噪声信道中,虚警概率为0．1,频域平滑累积次数为255,在信噪比为-16dB的条件下,与Dandawate-Giannakis（DG）方法相比,本文算法的检测概率提高23％．     

复杂应力场中裂纹疲劳扩展寿命预报

船舶作为一种大型焊接结构,其疲劳热点部位的应力应变场分布很复杂,要预报这些部位的裂纹疲劳扩展寿命,必须解决复杂场中裂纹的应力强度因子计算及其裂纹扩展方向问题.该文对船舶肘板处两种不同原因产生的裂纹的扩展路径、扩展速率进行了研究.裂纹扩展方向用第一主应力准则确定,在裂纹扩展方向上给定不同的裂纹增量,得到不同长度裂纹的复合裂纹等效应力强度因子,并拟合这些计算结果得出船舶肘板的应力强度因子计算式.结合裂纹扩展率单一曲线模型对肘板裂纹扩展寿命进行了预报,预报结果与实验结果符合得较好,说明所采用的方法可行.对建立船舶典型节点的裂纹扩展寿命预报方法有参考价值.     

基于软件无线电铁路安全信息无线移动接入系统的研究

在分析国内外铁路移动接入技术基础上,充分利用中国铁路现有无线列调系统所占用的450MHz频率资源,提出采用软件无线电技术,研究开发低成本多通道铁路安全信息无线移动接入系统,给出系统的基本原理、总体框架、体系结构,以及编码 解码、调制 解调、交织 反交织、通讯协议、过网和网络管理等实现算法。开发出一套原型系统,并在环形试验道进行了试验,试验结果表明,该系统传输速率高、误码率低,可以较好实现数据、话音和图像等信息的移动接入。该系统无需新的频率资源,具有很强的通用性,只需更换射频模块和相关软件,即可支持其它频段下的应用。     

交通事件下快速路拥堵蔓延消散时空范围模型

研究了交通事件下拥堵蔓延消散的时空范围分析方法与模型,交通事件引发的拥堵会以某一初始蔓延速度向上游蔓延,直至达到最大蔓延边界后开始消散.通过对事件下拥堵蔓延速度的影响因素进行量化分析,建立了时变的拥堵蔓延速度模型;然后通过收集处理数据,进行参数估计;最后利用实际数据,进行了模型的实例应用,对不同情况下的交通拥堵蔓延消散规律进行了研究.该模型可预测交通事件下的交通拥堵边界和持续时间,便于交管部门制定缓堵策略.     

A delay root cause discovery and timetable adjustment model for enhancing the punctuality of railway services

Knock-on delay, which is the key factor in punctuality of railway service, is mainly related to two factors including the quality of timetable in the planning phase and disturbances which may result in unscheduled trains’ waiting or meeting in operation phase. If the delay root cause and the interactions among the factors responsible for these can be clearly clarified, then the punctuality of railway operations can be enhanced by taking reactions such as timetable adjustment, rescheduling or rerouting of railway traffic in case of disturbances. These delay reasons can be used to predict the lengths of railway disruptions and effective reactions can be applied in disruption management. In this work, a delay root cause discovery model is proposed, which integrates heterogeneous railway operation data sources to reconstruct the details of the railway operations. A supervised decision tree method following the machine learning and data mining techniques is designed to estimate the key factors in knock-on delays. It discovers the root cause delay factor by logically analyzing the scheduled or un-scheduled trains meetings and overtaking behaviors, and the subsequent delay propagations. Experiment results show that the proposed decision tree can predict the delay reason with the accuracy of 83%, and it can be further enhance to 90% if the delay cause is only considered “prolonged passengers boarding” and “meeting or overtaking” factors. The delay root cause can be discovered by the proposed model, verified by frequency filtering in operation records, and resolved by the adjustment of timetable which is an important reference for the next timetable rescheduling. The results of this study can be applied to railway operation decision support and disruption management, especially with regard to timetable rescheduling, trains resequencing or rerouting, system reliability analysis, and service quality improvements.     

GB 14023《车辆、船和由内燃机驱动的装置无线电骚扰特性限值和测量方法》2006版与2000版的差异

主要分析国家标准GB14023《车辆、船和由内燃机驱动的装置无线电骚扰特性限值和测量方法》2006版与2000版在技术内容上的差异。     

基于BPNN-TD算法的城市轨道交通线网规模预测方法

科学预测城市轨道交通线网规模,对于轨道线网的规划建设与城市布局发展具有重要意义.基于轨道交通线网规模及其影响指标数据,综合两种模型优势,对城市轨道交通线网规模进行有效预测.首先,从政策、经济、城市规模、出行需求4个方面,简要分析城市轨道交通线网规模的影响因素,并利用相关性分析法,提取GDP、第三产业值、人口规模、建设用...     

Fatigue crack growth rates of rotor steel at elevated temperatures

Low fatigue samples were obtained from the outer edges of rotor steel （30CrlMolV） which had operated under different temperatures conditions. Based on this data, the effects of temperature on fatigue crack growth rates were investigated. This paper presents a derivation of the superposition expression of two natural logarithms governing crack growth rates and also discusses the relationship between a material’s constants and temperature. These results can provide experimental and theoretical references for fatigue life design of rotor steel in steam turbines.