FRA derailment statistics between 1996 and 2009 show an average of 13 derailments each year industry-wide are attributed to extreme winds, roughly 7 of which result in vehicles blowing over and derailing. BNSF Railway has developed a hybrid process to identify critical crosswind speeds for various types of railcars to mitigate future blow-over derailment risk. The method uses computational fluid dynamics to compute the wind effects based on the car envelope. These wind effects are simplified in an empirical spreadsheet tool for various wind and train speeds, and wind heading angles. CFD analysis and reduction into the empirical spreadsheet tool have been completed for alimited set of car types. With the resulting external wind loads, vehicle dynamic simulations are used to evaluate the propensity for wheel unloading. Both VAMPIRE® and NUCARS® dynamics routines were used for various parts of this study. In all cases, the wind onset has been assumed to ramp from a zero to full wind condition which remains steady from there forward. The main paper will cover several steps within this project: aerodynamic investigations and generation of appropriate load sets, preliminary and secondary vehicle dynamic simulations, and simplified train operating guidelines proposed thus far. The paper is summarized with a discussion of how these results may be applied to further mitigate wind blow-over derailments in terms of operating rules and the operating environment. An appendix is provided which outlines the relationships between the CFD wind loads and assumed train simulation speeds.
The operating dynamic clearance envelope has historically been a sum of estimated dimensional tolerances, sometimes even called “black magic” [1]. These tolerances exist by design within the car and the track, as well as between the wheel flanges and the rail gage face. Field observations of operating clearance have augmented these estimates. Recently a review of such expectations was desired as related to wide and/or tall payloads, with particular respect to train speed and track roughness. This project reexamines the factors affecting car body envelopes, including track curvature and elevation, and car parameters such as length, center of gravity (CG), and side bearing type. A particular goal of this study was to gain a rough understanding of the behavior expected relative to wide loads in the speed range of 30–50 mph. Both static analyses and dynamic negotiation of typical revenue track have been predicted. The NUCARS® multibody simulation software has been used to examine the influence of operating speed and FRA track class on the dynamic envelope. A summary of results is presented along with a discussion of general guidelines and additional considerations.
A paper written for and presented at the ASME 2010 Joint Rail Conference explored the science and methodology that BNSF Railway has taken to avoid wind-caused derailments.1 This paper further develops this topic with the approach Norfolk Southern Corp (NS) has taken. The foundational fluid flow dynamics and vehicle dynamics modeling and analysis are reviewed. The modeling included doublestack platforms loaded with empty boxes, trailer-on-flatcar (“piggyback”) equipment, high-cube boxcars, hoppers/coal gondolas, and multilevel (“autorack”) flatcars. The implementation of the modeling is outlined as a description of NS’ Speed Restriction System (SRS). The SRS uses real-time weather data and a lookup table of vehicle responses to provide the traffic controller (dispatcher) with recommended train speeds. Thoughts and suggestions on further development of a blowover risk reduction system are presented.
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