Fretting fatigue behavior of high-strength steel monostrands under bending load

In this paper, the fretting fatigue behavior of pretensioned high-strength steel monostrands is investigated. To measure the local deformations on the strands, a novel method based on the digital image correlation (DIC) technique was used to quantify the relative movement between individual wires along the length of the monostrand. Information about the monostrand bending stiffness and the extent of relative displacement between core and outer wires of a monostrand undergoing flexural deformations is provided. From the series of dynamic fatigue tests, a fretting fatigue spectrum is derived and compared with the localized bending fatigue spectrum. The presented spectra can be used for the estimation of monostrand bending fatigue life. The results presented herein form the basis for the development of a fretting failure criterion for monostrand cables experiencing transverse displacements and are of special interest for the fatigue analysis of modern stay cable assemblies where fretting constitutes a major mechanism of the fatigue life reduction.     

In-depth analysis of drivers’ merging behavior and rear-end crash risks in work zone merging areas

This study investigates the drivers’ merging behavior and the rear-end crash risk in work zone merging areas during the entire merging implementation period from the time of starting a merging maneuver to that of completing the maneuver. With the merging traffic data from a work zone site in Singapore, a mixed probit model is developed to describe the merging behavior, and two surrogate safety measures including the time to collision (TTC) and deceleration rate to avoid the crash (DRAC) are adopted to compute the rear-end crash risk between the merging vehicle and its neighboring vehicles. Results show that the merging vehicle has a bigger probability of completing a merging maneuver quickly under one of the following situations: (i) the merging vehicle moves relatively fast; (ii) the merging lead vehicle is a heavy vehicle; and (iii) there is a sizable gap in the adjacent through lane. Results indicate that the rear-end crash risk does not monotonically increase as the merging vehicle speed increases. The merging vehicle's rear-end crash risk is also affected by the vehicle type. There is a biggest increment of rear-end crash risk if the merging lead vehicle belongs to a heavy vehicle. Although the reduced remaining distance to work zone could urge the merging vehicle to complete a merging maneuver quickly, it might lead to an increased rear-end crash risk. Interestingly, it is found that the rear-end crash risk could be generally increased over the elapsed time after the merging maneuver being triggered.     

Effect of variable stroke on fuel combustion and heat release of a free piston linear hydrogen engine

Variable stroke (or compression ratio) has been expected as a potential technology for optimizing engine combustion all the time. The free piston motion of linear engines introduced by its unconstrained dynamics is well suited for this expectation. This paper introduces a numerical analysis to explore the effects of variable stroke operation on the combustion and heat release of a linear hydrogen engine (LHE). A system model which couples zero-dimensional dynamics, multi-dimensional combustion, and one-dimensional gas exchange is established and verified experimentally to predict the combustion of the LHE, and then a series of simulations are performed over a range of motion stroke from 62 mm to 72 mm in 2 mm interval to evaluate its effect on LHE combustion. Results indicates that short stroke operation of the LHE shows obvious advantages in thermal efficiency and high peak combustion pressure, although the completion level of hydrogen combustion is slightly poor. Fast combustion, large heat release, and low level of post-combustion effect can be obtained by neither lengthening nor shortening from the certain stroke length of 68 mm, while serious NO emission is indicated. Long-stroke operation makes the LHE clean, although it induces slow engine speed, low thermal efficiency and output power.     

The effect of motion on fuel diffusion and mixture preparation of a free-piston linear hydrogen engine

The most notable difference between linear hydrogen engine (LHE) and conventional crank hydrogen engine (CHE) is that the former supports variable motion operation for combustion optimizing. This article presents a study to reveal the effect of variable motion on hydrogen fuel diffusion and mixing of a direct injection LHE. A multi-dimensional model of coupled dynamics is proposed to describe the motion effect on mixture formation. The fuel mixing characteristic of the LHE is evaluated by comparing a corresponding CHE. Result indicates that compared with the CHE, the LHE behaves a slight lower uniformity of the hydrogen-air mixture during injection stage due to its slower motion, but the slower motion also provides longer time for hydrogen diffusion to form more homogeneous mixture before sparking ignition. Moreover, the effect of variable motion stroke on the hydrogen-air mixing of the LHE is also analyzed. Study reveals that the variable stroke has little effect on the hydrogen-air mixing during the injection stage, and the mixture uniformity varies in positive correlation with the stroke length at the occurrence of spark ignition. Suggesting that in order to achieve homogeneous combustion mode, the long motion stroke operation is a good choice for the LHE.     

Multi-criteria mathematical model for designing the distribution network of a consumer goods company

This paper describes a multiple criteria mixed-integer linear program used for designing the best possible supply chain distribution network for a consumer goods company. The model determines the optimal configuration of the manufacturing plants, distributors and customers in the distribution network. The model is intended for making tactical decisions for designing distribution networks, or more specifically, for designing the flow of products from the manufacturing plants to the customers. The customers have four options for receiving products in this model. Products can be supplied from (1) the regional distribution center (DC), (2) the manufacturing plant, (3) an independent distributor who is supplied from the regional DC, or (4) an independent distributor who is supplied directly from a manufacturing plant. The model selects the best option for each customer/distributor based on several criteria: profit, lead time, power, credit performance, and distributors’ reputation. The model is validated with real data from a consumer goods company to show its functionality. To account for variability in demand, the model is run under multiple scenarios and the results are analyzed to obtain the best solution. The company uses two DC’s located in the same region, but the model assumes only one regional DC with infinite capacity. With the proposed network, we show that one of the regional DC’s could be eliminated and distribution costs would be reduced from 12% to 3% of the Net Sales (approximately a monthly reduction of $574,000 in distribution expenses).     

UAV image stitching by estimating orthograph with RGB cameras

In the field of image stitching, cases with large camera optical center movement and large parallax have been the virgin territory of research. The goal of image stitching is to overcome the parallax and stitch a natural image. We look into this problem in the context of ultra-low altitude flight of a UAV. We model the 3D world in this scenario and quickly estimate orthographic projection by pairs of homography matrices. Our stitching method can achieve precise alignment since it takes parallax well into consideration. The stitching results are natural and the extra time consumed is short.     

Analysis of injury severity of large truck crashes in work zones

Work zones are critical parts of the transportation infrastructure renewal process consisting of rehabilitation of roadways, maintenance, and utility work. Given the specific nature of a work zone (complex arrangements of traffic control devices and signs, narrow lanes, duration) a number of crashes occur with varying severities involving different vehicle sizes. In this paper we attempt to investigate the causal factors contributing to injury severity of large truck crashes in work zones. Considering the discrete nature of injury severity categories, a number of comparable econometric models were developed including multinomial logit (MNL), nested logit (NL), ordered logit (ORL), and generalized ordered logit (GORL) models. The MNL and NL models belong to the class of unordered discrete choice models and do not recognize the intrinsic ordinal nature of the injury severity data. The ORL and GORL models, on the other hand, belong to the ordered response framework that was specifically developed for handling ordinal dependent variables. Past literature did not find conclusive evidence in support of either framework. This study compared these alternate modeling frameworks for analyzing injury severity of crashes involving large trucks in work zones. The model estimation was undertaken by compiling a database of crashes that (1) involved large trucks and (2) occurred in work zones in the past 10 years in Minnesota. Empirical findings indicate that the GORL model provided superior data fit as compared to all the other models. Also, elasticity analysis was undertaken to quantify the magnitude of impact of different factors on work zone safety and the results of this analysis suggest the factors that increase the risk propensity of sustaining severe crashes in a work zone include crashes in the daytime, no control of access, higher speed limits, and crashes occurring on rural principal arterials.     

A case history of shield tunnel crossing through group pile foundation of a road bridge with pile underpinning technologies in Shanghai

According to the planning of Shanghai metro line 10, the interval tunnel from Liyang Road station to Quyang Road station has to cross through the group pile foundation of Shajinggang Bridge on Siping Road. Therefore, how to guarantee the normal traffic function and the safety of bridge structure during the tunneling process becomes a challenge to engineers and technicians. To solve this problem, the pile underpinning technology was recommended for this project. This specific scheme mainly comprises following steps, i.e. ground improvement behind abutment, foundation pit excavation under bridge deck, underpinning pile with raft and cutting pile with shield machine directly, etc. In order to verify the feasibility of this scheme, a series of theoretical analysis and numerical simulation were carried out on the entire construction process to explore the load transfer mechanism of bridge structure. The calculation results show that both the bridge static loads and traffic live loads can be successfully transferred from pile foundation to raft after pile underpinning, and the removal of obstructed piles during tunneling has very limited influence on bridge structure. Furthermore, real-time field monitoring activities, including settlement of bridge deck surface, deformation of surrounding buildings and pipelines, etc. were also conducted to ensure smooth construction. The monitored results agree well with the numerical calculation ones, which prove again that the proposed scheme is reasonable and the calculation results are reliable.     

基于安全性分析的山区公路弯坡组合路段设计指标研究

我国当前设计方法对于山区公路,尤其是弯坡组合路段安全性考虑不足。基于车辆在弯坡组合路段行驶的安全性分析,以事故临界状态为限制条件建立弯坡组合路段安全模型。基于安全模型计算讨论了大小代表车型下,弯坡组合路段最小半径、最大坡长等关键设计指标受车路参数的影响及变化规律,利用Carsim仿真软件对变化规律进行了一致性验证,验证了该安全模型的有效性。根据安全模型及仿真计算结果,弯坡组合路段最小半径值与设计车速、路段坡度成正比,与路段超高、横向附着系数值成反比;弯坡组合路段最大坡长值与道路滚动阻力系数、滑移率成正比,与设计车速、路段坡度,以及车型大小成反比,但总体受超高值影响较小。进一步计算分析了考虑车辆实际运行车速下的弯坡组合路段设计指标阈值,并指出对于弯坡组合路段应尽可能采取小纵坡并增大最小半径值,以提高山区公路弯坡组合路段安全水平。