基于PCM+的埋地钢制管道不开挖检测技术

文中分析了PCM+检测的基本原理,结合某燃气管网100 km管道检验实例,对PCM+检测结果进行验证分析。结果显示:PCM+可有效检测埋地钢管走向埋深、定位防腐层破损点、评价防腐层质量;管道沿线山林、荒地及公路附近区域是防腐层破损点高发区;检测大破损信号覆盖临近小破损信号,造成小破损点漏检;受检管道附近存在导电性较好的结构体并行时,信号在结构体上流失,造成误检。     

基于声发射技术的管道泄漏检测与定位方法研究

为提高管道无损检测中对小孔径泄漏检测灵敏度、泄漏信号判别准确率以及泄漏点定位精确度,提出一种基于声发射技术并结合信号频域特征提取算法的管道泄漏识别和定位方法。设计管道泄漏检测实验平台进行管道泄漏检测实验,采用经验模态分解方法和小波分解重构相结合的信号处理算法进行降噪并提取信号频域特征,研究不同孔径和不同管道压力下管道泄漏检测和泄漏点定位问题。验证了基于声发射技术并结合信号频域特征提取算法的管道泄漏检测方法的有效性。     

长输管道智能球检漏技术应用

为研究长输管道微泄漏检测的方法,对声波检漏智能球检测性能进行了现场检测验证。智能球通过在管道内部运行,连续记录管道内的声学信号、压力信号等,通过分析检测数据中信号异常点,找出管道的泄漏点,实现对管道的微泄漏检测。通过对模拟长输管道以及成品油、原油管道进行试检测,成功检测出成品油管道上的泄漏量为0.19 L/min的漏点。通过试检测,确认了微泄漏智能球对长输管道的微泄漏有很好的识别效果。     

管道检测中伪随机码技术应用研究

将伪随机码技术引入管道检测,通过对伪随机码信号的分析,提出根据接收信号幅频特性中的幅度相差23 dB的频率点及环境的其他参数,计算出管道绝缘电阻的参数,从而确定管道腐蚀状况的一种新方法,经过仿真和实验验证了伪随机码在管道检测中应用的可行性。     

基于LabVIEW管道泄漏检测系统的研究

介绍了管道泄漏检测系统的设计原理.利用LabVIEW中的小波分析函数对采集到的信号进行处理,并利用小波变换模极大值捕捉压力信号的突变点,从而得出负压波传播到上下游监测点的时间差,进而利用负压波定位原理进行泄漏点的定位.另外,对于优化程序内存和提高CPU的利用率提出了一些有效的解决方法.     

基于超声导波的管道结构特性识别

文中分析了基于导波频散检测频率优化选择及限制频率等问题,研究了检测参数选择问题。根据不同换能器荷载施加方式、管道实际情况等对导波激励影响,就管道中存在的轴向连续单损及非连续性损伤,提出一种基于优化波形字典的追踪方法,分解损伤信号,评估损伤类型、大小等。文中研究了管道存在的变形损伤类型,分析了新导波检测可行性,为后续管道检测提供参考。     

负压波在管道泄漏检测与定位中的应用

文中基于负压波检测原理,对压力管道泄漏进行实时检测及定位.分别在管线上下游设置压力传感器,泄漏产生的负压波通过管道和介质自泄漏点向管线上下游传播,其压力波信号被压力传感器检测.通过分析压力传感器采集的数据,得到上下游的泄漏负压波传播速度,并结合压力传感器捕捉到的压力波波形和上下游压力传感器接收到压力波信号的时间差对泄漏点进行定位.结果表明:该方法对泄漏的判断与定位精度取决于负压波传播速度的测定精确度.     

PCM+在长输管道外防腐层检测中的应用

通过比较各种长输管道外防腐层检测技术,得出PCM+(多频管中电流法)的优越性,同时介绍了PCM+检测技术原理,详细分析了PCM+在长输管道外防腐层检测中破损点严重程度评定和定位技术,及在管道整体外防腐层等级综合评价中的应用,在实际检验中得出破损点性质判定规律及如何根据信号图来判断缺陷方法。文中得出一些规律有利于提高PCM+在长输管道外防腐层检测中的缺陷检测率和准确率。     

基于虚拟仪器的输水管路泄漏检测系统

讨论了一种基于虚拟仪器的输水管路泄漏检测系统的设计和实现。重点介绍了泄漏检测系统的泄漏定位方法、硬件设计和在LabVIEW环境下的软件模块化设计。对于突发的输水管路泄漏 ,综合运用了包括小波分析在内的多种信号处理方法 ,能够及时准确地定位泄漏点。实践证明 ,这种基于虚拟仪器的输水管路泄漏检测系统具有很强的灵活性和可扩展性     

基于机器视觉的燃气管道泄漏点故障定位方法

针对燃气管道泄漏点传统定位方法中燃气管道泄漏点角度问题,提出了基于机器视觉的燃气管道泄漏点故障定位方法.首先,采集燃气管道两侧压力信号,检测燃气管道泄漏故障;另外,采用机器视觉系统,采集燃气管道图像,根据机器视觉显著性,缩小燃气管道泄漏点标记范围;最后,建立故障定位模型,定位燃气管道泄漏点位置.试验结果表明,在象限坐标...     

Selection of expert system shells for traffic signal design

Although the use of expert systems (ESs) as a problem-solving tool is relatively new in the transportation profession, it has been recognized that a well-designed ES can contribute in areas where the knowledge domain requires an integration of expertise from various disciplines or is very complex and difficult to quantify. To minimize the effort involved in developing essential ES mechanisms, researchers often prefer to use ES shells which provide a standard inference procedure, knowledge representation, and a user-friendly design environment. However, commercial ES shells tend to be designed for only certain classes of problems, and are not as general and flexible as programming languages. More than 150 commercial ES shells are available in the microcomputer market. Most ES shells are usually claimed by their vendors to be usable for almost any conceivable applications, but such claims have often proved to be extravagant. Hence, the selection of an efficient yet costeffective commercial shell is one of the most critical tasks in ES development. In reviewing the vital task of ES shell selection, this paper presents our experience in evaluating more than 30 ES shells for developing an ES for signal design. The proposed ES includes signal settings, phasing plans, controllers, and detector locations.     

Multicomponent decomposition of a time-varying acoustic Doppler signal generated by a passing railway vehicle using Complex Shifted Morlet Wavelets

Complex Shifted Morlet Wavelets (CSMW) present a number of advantages, since the concept of shifting the Morlet wavelet in the frequency domain allow the simultaneous optimal selection of both the wavelet center frequency and the wavelet bandwidth. According to the proposed method, a cluster of CSMW wavelets is used, covering appropriate ranges in the frequency domain. Then, instead of directly processing the instantaneous frequency of each CSMW, an invariance approach is used to indirectly recover the individual harmonic components of the signal. This invariance approach is based actually on the same rotational approach, using the same matrix properties, which consists the core of the well known ESPRIT algorithm. Moreover, the DESFRI (DEtection of Source Frequencies via Rotational Invariance) approach is introduced to support the proposed CSMW method to semi-automated selection of the center frequency of the applied Morlet window. This approach is based on the singular values that are extracted as an intermediate product of the proposed decomposition process. By the application of the method in a multi-component synthetic signal a way to select the critical parameters of the Morlet wavelet, is investigated. The method is further tested on a time-varying acoustic Doppler signal generated by a passing railway vehicle, indicating promising results for the estimation of the variable instantaneous frequency and the multi-component decomposition of it.     

Optimal operation of displaced left-turn intersections: A lane-based approach

Displaced left-turn (DLT) intersections that resolve the conflict between left-turn and opposing-through movements at the pre-signal are probably the most extensively used innovative intersection designs. The DLT intersection concept can be extended to ten different types according to the location of the left-turn transition area, the number of DLT approaches, and the possible setting of the bypass right-turn lane. This paper presents a generalized lane-based optimization model for the integrated design of DLT intersection types, lane markings, the length of the displaced left-turn lane, and the signal timings. The optimization is formulated as a mixed-integer non-linear program. This program is further transformed to a series of mixed-integer linear programming problems that can be solved by the standard branch-and-bound technique. Results from extensive numerical analyses reveal the effectiveness of the proposed method, as well as the promising property of assisting transportation professionals in the proper selection of DLT intersection types, and the design of geometric layout and signal timings.     

Integrated fuzzy signal and ramp‐metering at a diamond interchange

We propose a fuzzy logic control for the integrated signal operation of a diamond interchange and its ramp meter, to improve traffic flows on surface streets and motorway. This fuzzy logic diamond interchange (FLDI) comprises of three modules: fuzzy phase timing (FPT) module that controls the green time extension of the current phase, phase logic selection (PLS) module that decides the next phase based on the pre‐defined phase sequence or phase logic and, fuzzy ramp‐metering (FRM) module that determines the cycle time of the ramp meter based on current traffic volumes and conditions of the surface streets and the motorways. The FLDI is implemented in Advanced Interactive Microscopic Simulator for Urban and Non‐Urban Network Version 6 (AIMSUN 6), and compared with the traffic actuated signal control. Simulation results show that the FLDI outperforms the traffic‐actuated models with lower system total travel time, average delay, and improvements in downstream average speed and average delay. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimality versus run time for isolated signalized intersections

Simulation-based optimization of traffic signal timing has become pervasive and popular, in the field of traffic engineering. When the underlying simulation model is well-trusted and/or well-calibrated, it is only natural that typical engineers would want their signal timing optimized using the judgment of that same model. As such, it becomes important that the heuristic search methods typically used by these optimizations are capable of locating global optimum solutions, for a wide range of signal systems. However off-line and real-time solutions alike offer just a subset of the available search methods. The result is that many optimizations are likely converging prematurely on mediocre solutions. In response, this paper compares several search methods from the literature, in terms of both optimality (i.e., solution quality) and computer run times. Simulated annealing and genetic algorithm methods were equally effective in achieving near-global optimum solutions. Two selection methods (roulette wheel and tournament), commonly used within genetic algorithms, exhibited similar effectiveness. Tabu searching did not provide significant benefits. Trajectories of optimality versus run time (OVERT) were similar for each method, except some methods aborted early along the same trajectory. Hill-climbing searches always aborted early, even with a large number of step-sizes. Other methods only aborted early when applied with ineffective parameter settings (e.g. mutation rate, annealing schedule). These findings imply (1) today’s products encourage a sub-optimal “one size fits all” approach, (2) heuristic search methods and parameters should be carefully selected based on the system being optimized, (3) weaker searches abort early along the OVERT curve, and (4) improper choice of methods and/or parameters can reduce optimization benefits by 22–33%.     

Modeling and simulation of vehicle projection arrival–discharge process in adaptive traffic signal controls

Real‐time signal control operates as a function of the vehicular arrival and discharge process to satisfy a pre‐specified operational performance. This process is often predicted based on loop detectors placed upstream of the signal. In our newly developed signal control for diamond interchanges, a microscopic model is proposed to estimate traffic flows at the stop‐line. The model considers the traffic dynamics of vehicular detection, arrivals, and departures, by taking into account varying speeds, length of queues, and signal control. As the signal control is optimized over a rolling horizon that is divided into intervals, the vehicular detection for and projection into the corresponding horizon intervals are also modeled. The signal control algorithm is based on dynamic programming and the optimization of signal policy is performed using a certain performance measure involving delays, queue lengths, and queue storage ratios. The arrival–discharge model is embedded in the optimization algorithm and both are programmed into AIMSUN, a microscopic stochastic simulation program. AIMSUN is then used to simulate the traffic flow and implement the optimal signal control by accessing internal data including detected traffic demand and vehicle speeds. Sensitivity analysis is conducted to study the effect of selecting different optimization criteria on the signal control performance. It is concluded that the queue length and queue storage ratio are the most appropriate performance measures in real‐time signal control of interchanges. Copyright © 2010 John Wiley & Sons, Ltd.     

Lane‐based optimization of traffic equilibrium settings for area traffic control

Area traffic control is an important element in Intelligent Transportation System (ITS). This paper extends the lane‐based optimization method to a traffic equilibrium network, which improves the operational performance of signal‐controlled network. We formulate a decomposition approach to simultaneously optimize the lane markings and signal settings for a signal‐controlled network that comprises two levels of optimization. At the junction level, the lane markings, control sequence, and other aspects of the signal settings are optimized for individual junctions, whereas at the network level, the group‐based signal settings are optimized to take into account the re‐routing characteristics of travelers and signal coordination effects that are based on a TRANSYT traffic model, which is a well‐known procedure for evaluating the performance of signal‐controlled networks. We use a numerical example to demonstrate the effectiveness of the proposed methodology.     

Multi-modal traffic signal control with priority,signal actuation and coordination

Both coordinated-actuated signal control systems and signal priority control systems have been widely deployed for the last few decades. However, these two control systems are often conflicting with each due to different control objectives. This paper aims to address the conflicting issues between actuated-coordination and multi-modal priority control. Enabled by vehicle-to-infrastructure (v2i) communication in Connected Vehicle Systems, priority eligible vehicles, such as emergency vehicles, transit buses, commercial trucks, and pedestrians are able to send request for priority messages to a traffic signal controller when approaching a signalized intersection. It is likely that multiple vehicles and pedestrians will send requests such that there may be multiple active requests at the same time. A request-based mixed-integer linear program (MILP) is formulated that explicitly accommodate multiple priority requests from different modes of vehicles and pedestrians while simultaneously considering coordination and vehicle actuation. Signal coordination is achieved by integrating virtual coordination requests for priority in the formulation. A penalty is added to the objective function when the signal coordination is not fulfilled. This “soft” signal coordination allows the signal plan to adjust itself to serve multiple priority requests that may be from different modes. The priority-optimal signal timing is responsive to real-time actuations of non-priority demand by allowing phases to extend and gap out using traditional vehicle actuation logic. The proposed control method is compared with state-of-practice transit signal priority (TSP) both under the optimized signal timing plans using microscopic traffic simulation. The simulation experiments show that the proposed control model is able to reduce average bus delay, average pedestrian delay, and average passenger car delay, especially for highly congested condition with a high frequency of transit vehicle priority requests.     

Selection bias in build-operate-transfer transportation project appraisals

Recent empirical studies have found widespread inaccuracies in traffic forecasts despite the fact that travel demand forecasting models have been significantly improved over the past few decades. We suspect that an intrinsic selection bias may exist in the competitive project appraisal process, in addition to the many other factors that contribute to inaccurate traffic forecasts. In this paper, we examine the potential for selection bias in the governmental process of Build-Operate-Transfer (BOT) transportation project appraisals. Although the simultaneous consideration of multiple criteria is typically used in practice, traffic flow estimate is usually a key criterion in these appraisals. For the purposes of this paper, we focus on the selection bias associated with the highest flow estimate criterion. We develop two approaches to quantify the level and chance of inaccuracy caused by selection bias: the expected value approach and the probability approach. The expected value approach addresses the question “to what extent is inaccuracy caused by selection bias?”. The probability approach addresses the question “what is the chance of inaccuracy due to selection bias?”. The results of this analysis confirm the existence of selection bias when a government uses the highest traffic forecast estimate as the priority criterion for BOT project selection. In addition, we offer some insights into the relationship between the extent/chance of inaccuracy and other related factors. We do not argue that selection bias is the only reason for inaccurate traffic forecasts in BOT projects; however, it does appear that it could be an intrinsic factor worthy of further attention and investigation.     

Transportation education in the United States

Abstract

In the last decade the importance of attitude‐related residential self‐selection has frequently been recognized. In addition people can theoretically self‐select them with respect to other location choices, such as job locations, with respect to travel behaviour, or with respect to the exposure to transport externalities such as noise and congestion. In this paper, we argue that insights into self‐selection processes might significantly improve our knowledge on location choices, travel behaviour and transport externalities. We elaborate on options for self‐selection and briefly formulate methodologies for research into self‐selection.