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2017 Vol.25 Issue.1,Published 2017-03-30

Articles
 
Articles
1 Identifying Achilles-heel roads in real-sized networks
Saeed Asadi Bagloee, Majid Sarvi, Russell George Thompson, Abbas Rajabifard
Ensuring a minimum operational level of road networks in the presence of unexpected incidents is becoming a hot subject in academic circles as well as industry. To this end, it is important to understand the degree to which each single element of the network contributes to the operation and performance of a network. In other words, a road can become an "Achilles-heel" for the entire network if it is closed due to a simple incident. Such insight of the detrimental loss of the closure of the roads would help us to be more vigilant and prepared. In this study, we develop an index dubbed as Achilles-heel index to quantify detrimental loss of the closure of the respective roads. More precisely, the Achilles-heel index indicates how many drivers are affected by the closure of the respective roads (the number of affected drivers is also called travel demand coverage). To this end,roads with maximum travel demand coverage are sorted as the most critical ones, for which a method—known as "link analysis"—is adopted. In an iterative process, first, a road with highest traffic volume is first labeled as "target link", and second, a portion of travel demand which is captured by the target link is excluded from travel demand. For the next iteration, the trimmed travel demand is then assigned to the network where all links including the target links run on the initial travel times. The process carries on until all links are labeled. The proposed methodology is applied to a largesized network of Winnipeg, Canada. The results shed light on also bottleneck points of the network which may warrant provision of additional capacity or parallel roads.
2017 Vol. 25 (1): 1-11 [Abstract] ( 3327 ) [HTML 1KB] [ PDF 1226KB] ( 621 )
12 Development of a tracking-based system for automated traffic data collection for roundabouts
Hai Dinh, Hua Tang
Traffic data collection is essential for performance assessment, safety improvement and road planning. While automated traffic data collection for highways is relatively mature, that for roundabouts is more challenging due to more complex traffic scenes, data specifications and vehicle behavior. In this paper, the authors propose an automated traffic data collection system dedicated to roundabout scenes. The proposed system has mainly four steps of processing. First, camera calibration is performed for roundabout traffic scenes with a novel circle-based calibration algorithm. Second, the system uses enhanced Mixture of Gaussian algorithm with shaking removal for video segmentation, which can tolerate repeated camera displacements and background movements. Then, Kalman filtering, Kernel-based tracking and overlap-based optimization are employed to track vehicles while they are occluded and to derive the complete vehicle trajectories. The resulting vehicle trajectory of each individual vehicle gives the position, size, shape and speed of the vehicle at each time moment. Finally, a data mining algorithm is used to automatically extract the interested traffic data from the vehicle trajectories. The overall traffic data collection system has been implemented in software and runs on regular PC. The total processing time for a 3-hour video is currently 6 h. The automated traffic data collection system can significantly reduce cost and improve efficiency compared to manual data collection. The extracted traffic data have been compared to accurate manual measurements for 29 videos recorded on 29 different days, and an accuracy of more than 90% has been achieved.
2017 Vol. 25 (1): 12-23 [Abstract] ( 3442 ) [HTML 1KB] [ PDF 2164KB] ( 530 )
24 Use of generated artificial road profiles in road roughness evaluation
Giuseppe Loprencipe, Pablo Zoccali
In the evaluation of road roughness and its effects on vehicles response in terms of ride quality, loads induced on pavement, drivers' comfort, etc., it is very common to generate road profiles based on the equation provided by ISO 8608 standard, according to which it is possible to group road surface profiles into eight different classes. However, real profiles are significantly different from the artificial ones because of the non-stationary feature of the first ones and the not full capability of the ISO 8608 equation to correctly describe the frequency content of real road profiles. In this paper, the international roughness index, the frequency-weighted vertical acceleration awz according to ISO 2631, and the dynamic load index are applied both on artificial and real profiles, highlighting the different results obtained. The analysis carried out in this work has highlighted some limitation of the ISO 8608 approach in the description of performance and conditions of real pavement profiles. Furthermore, the different sensitivity of the various indices to the fitted power spectral density parameters is shown, which should be taken into account when performing analysis using artificial profiles.
2017 Vol. 25 (1): 24-33 [Abstract] ( 3459 ) [HTML 1KB] [ PDF 1261KB] ( 558 )
34 Influence of pantograph fixing position on aerodynamic characteristics of high-speed trains
Liang Zhang, Jiye Zhang, Tian Li, Weihua Zhang
To study the influence of the pantograph fixing position on aerodynamic characteristics of high-speed trains, the aerodynamic models of high-speed trains with eight cars were established based on the theory of computational fluid dynamics, and eight cases with pantographs fixed on different positions and in different operational orientations were considered. The pantographs were fixed on the front or the rear end of the first middle car or fixed on the front or the rear end of the last middle car. The external flow fields of the high-speed trains were numerically simulated using the software STAR-CCM?. The results show that the pantograph fixing position has little effect on the aerodynamic drag force of the head car and has a large effect on the aerodynamic drag force of the tail car. The influences of the pantograph fixing position on the aerodynamic lift forces of the head car, tail car and pantographs are obvious. Among the eight cases, considering the total aerodynamic drag force of the train and the aerodynamic lift force of the lifted pantograph, when the pantographs are fixed on the rear end of the last middle car and the lifted pantograph is in the knuckle-upstream orientation, the aerodynamic performance of the high-speed train is the best.
2017 Vol. 25 (1): 34-39 [Abstract] ( 3529 ) [HTML 1KB] [ PDF 2649KB] ( 558 )
40 Numerical implementation of a modified Mohr-Coulomb model and its application in slope stability analysis
Xu Xiang, Dai Zi-Hang
The hyperbolic function proposed by Abbo- Sloan was employed not only to approach the Mohr- Coulomb criterion but also to express the plastic potential function. A better approximation to the Mohr-Coulomb yield and potential surfaces was achieved by increasing the transition angle and proven to be highly efficient in numerical convergence. When a Gaussian integral point goes into plastic state, two cases on yield stress adjustments were introduced. They may avoid solving the second derivative of the plastic potential function and the inverse matrix compared with the existing subroutine. Based on the above approaches, a fully implicit backward Euler integral regression algorithm was adopted. The two- and three-dimensional user subroutines which can consider the associated or non-associated flow rule were developed on the platform of the finite element program—ABAQUS. To verify the reliability of these two subroutines, firstly, the numerical simulations of the indoor conventional triaxial compression and uniaxial tensile tests were performed, and their results were compared with those of the embedded Mohr-Coulomb model and the analytical approach. Then the main influential factors including the associated or nonassociated flow rule, the judgment criteria of slope failure, and the tensile strength of soil were analyzed, and the application of the two-dimensional subroutine in the stability analysis of a typical soil slope was discussed in detail through comparisons with the embedded model and the limit analysis method, which shows that this subroutine is more applicable and reliable than the latter two.
2017 Vol. 25 (1): 40-51 [Abstract] ( 3542 ) [HTML 1KB] [ PDF 2676KB] ( 1099 )
52 Synthesis and photoelectrical performance of nanoscale PbS and Bi2S3 co-sensitized on TiO2 nanotube arrays
Fanggong Cai, Min Pan, Yong Feng, Guo Yan, Yong Zhang, Yong Zhao
TiO2 films have been widely applied in photovoltaic conversion techniques. TiO2 nanotube arrays (TiO2 NAs) can be grown directly on the surface of metal Ti by the anodic oxidation method. Bi2S3 and PbS nanoparticles (NPs) were firstly co-sensitized on TiO2 NAs (denoted as PbS/Bi2S3(n)/TiO2 NAs) by a two-step process containing hydrothermal and sonication-assisted SILAR method. When the concentration of Bi3+ is 5 mmol/L, the best photoelectrical performance was obtained under simulated solar irradiation. The short-circuit photocurrent (Jsc) and photoconversion efficiency (η) of PbS/Bi2S3(5)/TiO2 NAs electrode were 4.70 mA/cm and 1.13%, respectively.
2017 Vol. 25 (1): 52-57 [Abstract] ( 3611 ) [HTML 1KB] [ PDF 1191KB] ( 1046 )
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