Distributed support modelling for vertical track dynamic analysis

The finite length nature of rail-pad supports is characterised by a Timoshenko beam element formulation over an elastic foundation, giving rise to the distributed support element. The new element is integrated into a vertical track model, which is solved in frequency and time domain. The developed formulation is obtained by solving the governing equations of a Timoshenko beam for this particular case. The interaction between sleeper and rail via the elastic connection is considered in an analytical, compact and efficient way. The modelling technique results in realistic amplitudes of the ‘pinned–pinned’ vibration mode and, additionally, it leads to a smooth evolution of the contact force temporal response and to reduced amplitudes of the rail vertical oscillation, as compared to the results from concentrated support models. Simulations are performed for both parametric and sinusoidal roughness excitation. The model of support proposed here is compared with a previous finite length model developed by other authors, coming to the conclusion that the proposed model gives accurate results at a reduced computational cost.     

Influence of repeated and delayed excitations in combined subspace identification

The application of combined subspace identification methods to land vehicles would allow the modal parameters of the vehicle to be obtained, while it is in operation, thus improving the vehicle modal characterisation. However, when a land vehicle is circulating through a straight line, the excitations applied to the different axles are identical among them but with a certain time delay. The presence of repeated excitations with different time delays implies that the past and future subspaces include common vectors that may lead to problems in the application of the method. To analyse its influence, an index called the reduction coefficient resulting from excitations (RCE) has been defined. RCE evaluates the amount of information eliminated in the oblique projection due to the effect of repeated excitations. The use of RCE enables the selection of analysis parameters, particularly the sampling frequency, the signals grouping and some specific parameters of the subspace identification methods.     

A new method for the solution of the normal contact problem in the dynamic simulation of railway vehicles

Due to requirements related to computational efficiency, in the majority of railway dynamic simulators the Hertz theory is used for solving the normal problem in wheel/rail contact. This theory is based on a large number of assumptions. Particularly noteworthy is the assumed simplification that the undeformed distance between the bodies in contact can be assimilated by a quadratic function. There are many situations in which the undeformed distance cannot be represented by this kind of function. As such, the results obtained with Hertz theory in these cases are not accurate.

In this paper, a new method for solving the normal problem that overcomes the above-mentioned limitation is presented. First, the exactness of the new method is tested with Hertzian cases. The results obtained are almost exact. Second, the results calculated with the new method in more general cases are compared with the ones obtained with the variational method of Kalker (more exact but computationally less efficient).     

Locating refuelling stations for alternative fuel vehicles: a review on models and applications

The recent concerns on environmental issues have expedited the technological development of alternative fuel vehicles (AFVs), but the deployment of AFVs still remains at the initial stage mainly because of the lack of refuelling facilities. Recognising this, researchers have conducted various studies, proposing a variety of approaches to strategically locating refuelling stations. This paper presents a comprehensive review of the approaches, focusing more on applications than computational issues. The review identifies two main elements of the approaches: location modelling and refuelling demand estimation. Examining how the elements were handled in refuelling location studies, this paper suggests that future refuelling location models should properly reflect the intricate and various perspectives of three major AFV stakeholders: drivers, government agencies and refuelling service providers. This study is expected to help researchers efficiently set up their refuelling location problems and identify critical factors for seeking the solutions.     

Investigating travel utility elements in association with travel time and mode choice: the case of Seoul,South Korea

In this paper, travel utility is conceptualized into the elements of disutility, or derived utility, and positive utility, which includes synergistic and intrinsic utility, and then analyzed in terms of the effects of these elements on weekly travel time according to three travel modes – the automobile, public transit, and nonmotorized modes – and on the choice of the annually most used mode. Linear regressions on mode-specific travel time and a multinomial logistic regression on mode choice show that, compared to life situation and land-use characteristics, utility elements are among the strongest travel determinants. Specifically, while some utility elements contribute exclusively to shifting the mode of travel and others to increasing nonmotorized travel, modal shift is most strongly affected by a disutility element, trip timeliness, and the increase in nonmotorized travel by a positive utility element, amenities.     

A study of economic efficiency in port security inspection

The purpose of this paper is to study an economic efficiency for the prediction of additional truck turnaround time and for determining the number of the port security inspection equipment required at a terminal inspection station. The economic efficiency with six base models was developed to assist terminal operators' decision‐making. In addition, this study developed an optimal procedure that terminal operators could use to optimally run in terms of various statistics processes including exponential, deterministic, and others, seeking a solution that was beneficial for both terminal operators and truckers. As a result of this research of the additional cargo turnaround time for port security delay, the following conclusion can be drawn and made. The average additional delay time in the inspection station is very dependent on the inspection rate of the lower stage. The higher weighted inspection time based on raising security level allows less number of trucks to be inspected, which will derive high delay in the inspection station. Increase of rate of Green Lane usage will allow a decrease in the arrival rate, which may derive improvement of inspection equipment efficiency and average delay time at the inspection station. In multiple stage model, total number of trucks and delay time very closely follow those of low inspection stage rate and number of inspection units. Free Lane is to be followed by Customs‐Trade Partnership Against Terrorism and standardization of customs, packing, loading and unloading, documents, procedure, and exchange working in each country. Copyright © 2012 John Wiley & Sons, Ltd.     

Introduction of a friction coefficient dependent on the slip in the FastSim algorithm

One of the main limitations of algorithms relating forces and creepages at the wheel/rail contact is the use of a friction coefficient independent of the slip. This paper overcomes this limitation through a modification of the FastSim algorithm (based on the Simplified Theory of Kalker). A friction law based on the local value of the slip is established and the required formulation of the local slip elsewhere in the contact area is presented. Some difficulties of the method and the solutions adopted by the authors are also presented. Finally, the achieved improvements are shown through comparison of the results obtained both with the original and the modified FastSim algorithms.