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2014 Vol.22 Issue.2,Published 2014-06-30

65 Analysis of steering performance of differential coupling wheelset
Xingwen Wu, Maoru Chi, Jing Zeng, Weihua Zhang, Minhao Zhu
In order to improve the curving performance of the conventional wheelset in sharp curves and resolve the steering ability problem of the independently rotating wheel in large radius curves and tangent lines, a differential coupling wheelset (DCW) was developed in this work. The DCW was composed of two independently rotating wheels (IRWs) coupled by a clutch-type limited slip differential. The differential contains a static pre-stress clutch, which could lock both sides of IRWs of the DCW to ensure a good steering performance in curves with large radius and tangent track. In contrast, the clutch could unlock the two IRWs of the DCW in a sharp curve to endue it with the characteristic of an IRW, so that the vehicles can go through the tight curve smoothly. To study the dynamic performance of the DCW, a multi-body dynamic model of single bogie with DCWs was established. The self-centering capability, hunting stability, and self-steering performance on a curved track were analyzed and then compared with those of the conventional wheelset and IRW. Finally, the effect of coupling parameters of the DCW on the dynamic performance was investigated.
2014 Vol. 22 (2): 65-75 [Abstract] ( 5161 ) [HTML 1KB] [ PDF 1975KB] ( 827 )
76 Parametric analysis of wheel wear in high-speed vehicles
Na Wu, Jing Zeng
In order to reduce the wheel profile wear of highspeed trains and extend the service life of wheels, a dynamic model for a high-speed vehicle was set up, in which the wheelset was regarded as flexible body, and the actual measured track irregularities and line conditions were considered. The wear depth of the wheel profile was calculated by the well-known Archard wear law. Through this model, the influence of the wheel profile, primary suspension stiffness, track gage, and rail cant on the wear of wheel profile were studied through multiple iterative calculations. Numerical simulation results show that the type XP55 wheel profile has the smallest cumulative wear depth, and the type LM wheel profile has the largest wear depth. To reduce the wear of the wheel profile, the equivalent conicity of the wheel should not be too large or too small. On the other hand, a small primary vertical stiffness, a track gage around 1,435-1,438 mm, and a rail cant around 1:35-1:40 are beneficial for dynamic performance improvement and wheel wear alleviation.
2014 Vol. 22 (2): 76-83 [Abstract] ( 5962 ) [HTML 1KB] [ PDF 1021KB] ( 813 )
84 Examining the effect of speed, roadside features, and roadway geometry on crash experience along a rural corridor
Donald C. Watson Jr., Ahmed Al-Kaisy, Nathan D. Anderson
This paper presents a current investigation into crash experience along a 15.7-mile rural corridor in southwest Montana with the aim of better understanding crash causal factors along the corridor. The study utilized ten years of crash data, geometric data, and observed freeflow speed data along the corridor. A systematic approach was used where every tenth of a mile was described in term of the crash experience, speed, alignment, and roadside features. Using bivariate and multivariate statistical analyses, the study investigated the crash experience along the corridor as well as some of the underlying relationships which could explain some of the crash causal factors. Results show a strong association between crash rates and horizontal curvatures even for flat curves that can be negotiated at speeds above the posted speed limit, per the highway design equations. Higher crash rates were also found to be associated with the difference between the observed free-flow speeds and the speed dictated by the curve radius or sight distance as per the design equations. Further, results strongly support the safety benefits of guardrails as evidenced by the lower crash rates and severities. The presence of fixed objects and the steepness of side slopes were also found to have an effect on crash rates and severities.
2014 Vol. 22 (2): 84-95 [Abstract] ( 5080 ) [HTML 1KB] [ PDF 551KB] ( 579 )
96 Leave the expressway or not? Impact of dynamic information
Hongcheng Gan, Xin Ye
This study investigates drivers' diversion decision behavior under expressway variable message signs that provide travel time of both an expressway route and a local street route. Both a conventional cross-sectional logit model and a mixed logit model are developed to model drivers' response to travel time information. It is based on the data collected from a stated preference survey in Shanghai, China. The mixed logit model captures the heterogeneity in the value of "travel time" and "number of traffic lights" and accounts for correlations among repeated choices of the same respondent. Results show that travel time saving and driving experience serve as positive factors, while the number of traffic lights on the arterial road, expressway use frequency, being a middle-aged driver, and being a driver of an employer-provided car serve as negative factors in diversion. The mixed logit model obviously outperforms the cross-sectional model in dealing with repeated choices and capturing heterogeneity regarding the goodness-of-fit criterion. The significance of standard deviations of random coefficients for travel time and number of traffic lights evidences the existence of heterogeneity in the driver population. The findings of this study have implications for future efforts in driver behavior modeling and advanced traveler information system assessment.
2014 Vol. 22 (2): 96-103 [Abstract] ( 4845 ) [HTML 1KB] [ PDF 1155KB] ( 629 )
104 Finite element analysis of overlay incorporating stress absorbing membrane interlayers against reflective cracking
O. M. Ogundipe, N. H. Thom, A. C. Collop
A wheel tracking test was modelled to gain better understanding of the deflection and stress-strain distribution in an overlaid cracked pavements with and without membrane interlayer (SAMI). For this purpose, commercial finite element software Abaqus 6.7-1 was used. Two different models were considered, one incorporating stress absorbing membrane interlayers (SAMIs) and the other without SAMI. In the study, full bond condition was assumed for the boundaries between the layers, and a linear elastic model was used for the analysis. The results show that introduction of SAMI caused greater deflection of the pavement. It is found that although with SAMIs, low stiffness is required, a very low stiffness may yield undesirable results. The results show that the introduction of SAMIs results in high strain concentration around the crack region, whilst the strain in the overlay is smaller than the values predicted in the models without SAMIs.
2014 Vol. 22 (2): 104-111 [Abstract] ( 4371 ) [HTML 1KB] [ PDF 1451KB] ( 695 )
112 DC and AC transport properties on La0.8Sr0.2MnO3
Zhantao Wei, Xinsheng Yang, Li Lv, Min Zhang, Yong Zhang
Magnetoresistive sensor can be widely used in modern transportation field, such as the vehicle positioning and navigation system, vehicle detection system, and intelligent transportation system. In order to improve the efficiency of magnetoresistive sensor, we synthesized La0.8Sr0.2MnO3 polycrystalline bulks at different sintering temperatures and investigated their DC and AC transport properties in this work. As a result, all samples showed insulator-metal (I-M) phase transition, and the transition temperature (TI-M) shifted to higher temperature with the increase of sintering temperature. The TI-M measured at different AC frequencies was smaller than that measured at DC condition, which implied that the I-M phase transition was suppressed at AC frequencies. The resistivity measured at high AC frequencies was larger than that measured at low AC frequencies, which could be attributed to the change of the magnetic penetration depth (δ). However, the room-temperature AC-magnetoresistance (MR) at low frequencies was much larger than that at high frequencies and room-temperature DC-MR. These findings demonstrate that reducing the AC frequency is an effective way for enhancing the room-temperature MR, which can be used to promote the efficiency of magnetoresistive sensor.
2014 Vol. 22 (2): 112-117 [Abstract] ( 4924 ) [HTML 1KB] [ PDF 875KB] ( 549 )
118 The influence of Laval nozzle throat size on supersonic molecular beam injection
Xinkui He, Xianfu Feng, Mingmin Zhong, Fujun Gou, Shuiquan Deng, Yong Zhao
In this study, finite element analysis (FEA) has been used to investigate the effects of different Laval nozzle throat sizes on supersonic molecular beam. The simulations indicate the Mach numbers of the molecular stream peak at different positions along the center axis of the beam, which correspond to local minimums of the molecular densities. With the increase of the throat diameter, the first peak of the Mach number increases first and then decreases, while that of the molecular number density increases gradually. Moreover, both first peaks shift progressively away from the throat. At the last part, we discuss the possible applications of our FEA approach to solve some crucial problems met in modern transportations.
2014 Vol. 22 (2): 118-121 [Abstract] ( 5613 ) [HTML 1KB] [ PDF 1131KB] ( 787 )
122 A multi-scale point of view on the structure-property relationships of A15 superconductors
Yanlong Ding, Min Pan, Shuiquan Deng, Yong Zhao
Nb3Sn and other A15 members have been widely applied in nuclear power, nuclear magnetic resonance, and high-energy particle accelerators for their high critical current density (Jc) and upper critical field (Bc2). There have been comprehensive and intensive studies on the applications, the fundamental lattice dynamic and electronic properties, etc., of A15 superconductors. Various reviews on the preparations, structures, and properties have already been written in the last few years. Nevertheless, on account of the large amount of existing facts and views, a coherent view on the relations between the structures and properties has not appeared to unify the facts. This article sketches a multi-scale point of view on the relations between the multiscale structures and the corresponding properties.
2014 Vol. 22 (2): 122-126 [Abstract] ( 6319 ) [HTML 1KB] [ PDF 704KB] ( 616 )
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