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2017 Vol.25 Issue.4,Published 2017-12-30

205 A select link analysis method based on logit-weibit hybrid model
Pengjie Liu, Xiangdong Xu, Anthony Chen, Chao Yang, Longwen Xiao
Select link analysis provides information of where traffic comes from and goes to at selected links. This disaggregate information has wide applications in practice. The state-of-the-art planning software packages often adopt the user equilibrium (UE) model for select link analysis. However, empirical studies have repeatedly revealed that the stochastic user equilibrium model more accurately predicts observed mean and variance of choices than the UE model. This paper proposes an alternative select link analysis method by making use of the recently developed logit-weibit hybrid model, to alleviate the drawbacks of both logit and weibit models while keeping a closed-form route choice probability expression. To enhance the applicability in large-scale networks, Bell's stochastic loading method originally developed for logit model is adapted to the hybrid model. The features of the proposed method are twofold:(1) unique O-D-specific link flow pattern and more plausible behavioral realism attributed to the hybrid route choice model and (2) applicability in large-scale networks due to the link-based stochastic loading method. An illustrative network example and a case study in a large-scale network are conducted to demonstrate the efficiency and effectiveness of the proposed select link analysis method as well as applications of O-D-specific link flow information. A visualization method is also proposed to enhance the understanding of O-D-specific link flow originally in the form of a matrix.
2017 Vol. 25 (4): 205-217 [Abstract] ( 633 ) [HTML 1KB] [ PDF 1511KB] ( 579 )
218 A multifunctional battery module design for electric vehicle
Meng Wang, Liangliang Zhu, Anh V. Le, Daniel J. Noelle, Yang Shi, Ying Zhong, Feng Hao, Xi Chen, Yu Qiao
Reducing the overall vehicle weight is an efficient, system-level approach to increase the drive range of electric vehicle, for which structural parts in auto-frame may be replaced by battery modules. Such battery modules must be structurally functional, e.g., energy absorbing, while the battery cells are not necessarily loading-carrying. We designed and tested a butterfly-shaped battery module of prismatic cells, which could self-unfold when subjected to a compressive loading. Angle guides and frictionless joints were employed to facilitate the large deformation. Desired resistance to external loading was offered by additional energy absorption elements. The battery-module behavior and the battery-cell performance were controlled separately. Numerical simulation verified the experimental results.
2017 Vol. 25 (4): 218-222 [Abstract] ( 752 ) [HTML 1KB] [ PDF 1499KB] ( 533 )
223 Optimal energy saving in DC railway system with on-board energy storage system by using peak demand cutting strategy
Chaiyut Sumpavakup, Tosaphol Ratniyomchai, Thanatchai Kulworawanichpong
A problem of peak power in DC-electrified railway systems is mainly caused by train power demand during acceleration. If this power is reduced, substation peak power will be significantly decreased. This paper presents a study on optimal energy saving in DC-electrified railway with on-board energy storage system (OBESS) by using peak demand cutting strategy under different trip time controls. The proposed strategy uses OBESS to store recovered braking energy and find an appropriated time to deliver the stored energy back to the power network in such a way that peak power of every substations is reduced. Bangkok Mass Transit System (BTS)-Silom Line in Thailand is used to test and verify the proposed strategy. The results show that substation peak power is reduced by 63.49% and net energy consumption is reduced by 15.56% using coasting and deceleration trip time control.
2017 Vol. 25 (4): 223-235 [Abstract] ( 679 ) [HTML 1KB] [ PDF 2310KB] ( 410 )
236 Risk assessment:method and case study for traffic projects
Xin Yu, Panos D. Prevedouros
A comprehensive project evaluation and decision-making method considering multiple objectives, stakeholders, and attributes of proposed traffic treatments is inherently complicated. Although individual techniques in evaluating operations, safety, economic, and stakeholder objectives are available, a practical method that integrates all these risk factors and their uncertainties into a multiattribute decision-making tool is absent. A three-level project decision-making process was developed to model and assess multiple-attribute risk in a proposed traffic treatment from the perspective of multiple stakeholders. The direct benefits from reducing delay and safety risk (basic objectives of traffic treatments) are computed in Level 1 with established methods. Feasibility and performance analysis in Level 2 examine site-specific constraints and conduct detailed performance analysis using advanced analysis tools. In Level 3, this paper introduces an innovative and integrated multiple attributes evaluation process under fuzziness and uncertainty (MAFU) process for evaluation and decision-making. The MAFU is a comprehensive and systematic assessment and decision-making procedure that can assess the magnitudes of project performance and to integrate conflicting interests and tradeoffs among stakeholders. A case study illustrates the application of MAFU for the selection of a traffic alternative involving several evaluation attributes and stakeholders. Results show that the MAFU produced the smallest variance for each alternative. With traditional cost-benefit evaluation methods, the uncertainty associated with performance of a traffic project in terms of operation, safety, environmental impacts, etc., is unrestricted and cumulative. Therefore, a reliable multi-attribute evaluation of complex traffic projects should not be made with conventional cost-benefit analysis alone but with a process like MAFU.
2017 Vol. 25 (4): 236-249 [Abstract] ( 628 ) [HTML 1KB] [ PDF 1481KB] ( 317 )
250 Longitudinal train dynamics of electric multiple units under rescue
Wei Shan, Lai Wei, Kai Chen
Once operating trains are disabled on the railway lines, an efficient manner is to utilize the train for train rescue. Owning to the different train and coupler types, it is difficult to formulate uniform regulations for train to train rescue. In this paper, the longitudinal train dynamics of electric multiple units under rescue were analyzed by field and laboratory tests. The angling behavior of the brakinginduced coupler under compressed in-train forces was analyzed. A dynamic model for the train and draft gear system was developed considering accurate boundary limitations and braking characteristics. The safety indices dynamic evaluations of different train to train rescue scenarios were analyzed. It is indicated that the coupler vertical rotation occurs during the emergency braking applied by the assisting train. The vertical force components of intrain forces lead to the carbody pitch behavior and even cause local destructions to the coupler system. The carbody pitch motion can arise the inference of in-train devices. Based on the safety evaluation of train and coupler system, the regulations for typical train to train rescue scenarios were formulated.
2017 Vol. 25 (4): 250-260 [Abstract] ( 497 ) [HTML 1KB] [ PDF 1911KB] ( 446 )
261 The role of microstructure and its stability in performance of wheels in heavy haul service
Cong Qiu, John Cookson, Peter Mutton
Thermal or thermo-mechanical loading is one of the major causes of wheel surface damage in Australian heavy haul operations. In addition, multi-wear wheels appear to be particularly sensitive to thermo-mechanical damage during their first service life. Such damage can incur heavy machining penalties or even premature scrapping of wheels. The combination of high contact stresses as well as substantial thermal loading (such as during prolonged periods of tread braking) can lead to severe plastic deformation, thermal fatigue and microstructural deterioration. For some high-strength wheel grades, the increased sensitivity to thermo-mechanical damage observed during the first service period may be attributed to the presence of a near-surface region in which the microstructure is more sensitive to these loading conditions than the underlying material. The standards applicable to wheels used in Australian heavy haul operations are based on the Association of American Railroads (AAR) specification M-107/M-208, which does not include any requirements for microstructure. The implementation of acceptance criteria for the microstructure, in particular that in the near-surface region of the wheel, may be necessary when new wheels are purchased. The stability of wheel microstructures during thermo-mechanical loading and the effects of alloying elements commonly used in wheel manufacturing are reviewed. A brief guide to improving thermal/mechanical stability of the microstructure is also provided.
2017 Vol. 25 (4): 261-267 [Abstract] ( 655 ) [HTML 1KB] [ PDF 1113KB] ( 445 )
268 Travelers' attitudes toward carpooling in Lahore:motives and constraints
Muhammad Ashraf Javid, Tahir Mehmood, Hafiz Muhammad Asif, Ahsan Ullah Vaince, Mohsin Raza
Traffic congestion has become a critical issue in developing countries, as it tends to increase social costs in terms of travel cost and time, energy consumption and environmental degradation. With limited resources, reducing travel demand by influencing individuals' travel behavior can be a better long-term solution. To achieve this objective, alternate travel options need to be provided so that people can commute comfortably and economically. This study aims to identify key motives and constraints in the consideration of carpooling policy with the help of stated preference questionnaire survey that was conducted in Lahore City. The designed questionnaire includes respondents' socioeconomic demographics, and intentions and stated preferences on carpooling policy. Factor analysis was conducted on travelers' responses, and a structural model was developed for carpooling. Survey and modeling results reveal that social, environmental and economic benefits, disincentives on car use, preferential parking treatment for carpooling, and comfort and convenience attributes are significant determinants in promoting carpooling. However, people with strong belief in personal privacy, security, freedom in traveling and carpooling service constraints would have less potential to use the carpooling service. In addition, pro-auto and pro-carpooling attitudes, marital status, profession and travel purpose for carpooling are also underlying factors. The findings implicate that to promote carpooling policy it is required to consider appropriate incentives on this service and disincentives on use of private vehicle along with modification of people's attitudes and intentions.
2017 Vol. 25 (4): 268-278 [Abstract] ( 535 ) [HTML 1KB] [ PDF 636KB] ( 314 )
279 Stress concentration coefficients of optimized cope-hole welded detail
Ping Liao, Renda Zhao, Xing Wei, Yi Jia, Lingzhi Cui, Yongbao Wang
The fatigue performance of optimized welded detail has been investigated by fatigue experiments of three welded specimens under different loadings. In addition, local finite element models of this welded detail were established using finite element software ANSYS. The influences of different factors such as plate thickness, plate gap and initial geometric imperfections on the stress concentration coefficient (SCC) were discussed. The experimental results indicate that the fatigue life of three specimens for this welded detail is 736,000, 1,044,200 and 1,920,300 times, respectively. The web thickness, the filler plate thickness and the initial geometric imperfection have relatively less effect on the SCCs of this welded detail. However, cope-hole radius is influential on the SCCs of the web and the weld. The SCC of weld is significantly affected by the weld size and plate gap, but the SCCs of other parts of the welded detail are hardly affected by the plate gap.
2017 Vol. 25 (4): 279-286 [Abstract] ( 552 ) [HTML 1KB] [ PDF 2171KB] ( 583 )
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