Wheel/Rail Interaction ’08:
Data to Information
(Part 1 of 2)
As research into wheel/rail interaction has evolved, the emphasis has moved toward implementation of available technology and conversion of data into information. Such was the case at Wheel/Rail Interaction ’08, the 14th annual seminar produced by Advanced Rail Management and sponsored by Progressive Railroading magazine. Railroaders, researchers and suppliers presented information on current efforts to improve the performance of vehicle and track components and the overall operating parameters associated with vehicle/track interaction.
Norfolk Southern (NS) presented some initial findings of a pilot program to implement electronically controlled pneumatic (ECP) braking on a portion of its coal fleet. As of May 2008, NS is operating six ECP train sets in two operating regions. The project, which is supported by the NS Coal Business Group, Mechanical Department and Research & Tests, along with the Association of American Railroads (AAR), Transportation Technology Center, Inc. (TTCI), and Federal Railroad Administration (FRA), is designed to quantify the performance, safety and cost benefits of ECP braking.
Factors that led NS to implement ECP braking include:
• Shorter stopping distances, which will improve collision avoidance and allow for better signal spacing.
• Elimination of derailment-causing slack action, and better distribution of braking forces through the track.
• Extended mileage intervals for required Class I inspections.
• Reduced wheel change-outs due to slid flats.
• Reduced fuel consumption.
NS has been operating (under an FRA waiver) two 115-car train sets of gondolas in Pennsylvania; two 100-car train sets of automatic dump cars in Virginia; and two 85-car train sets of automatic dump cars in North Carolina.
“The crews and supervisors love them,” said Walter Rosenberger, NS Operations Engineer - Research and Tests.
Results from Pennsylvania indicate that stopping distances under a full service brake application for a loaded train traveling at 31 mph were 1,227 feet, compared to 2,242 feet for a conventional braking system — a 45% reduction in stopping distances.
NS plans to continue testing to further asses the benefits of ECP braking on its fleet in various corridors.
With the recent surge in fuel prices, railroads are taking a broader perspective on fuel consumption and operating efficiency.
“Fuel consumption is a function of several factors, including the resistance generated by freight cars while traveling through curves,” said Matthew Dick, Assistant Vice President of Engineering and Dynamic Studies, at Rail Sciences, Inc.
Since freight car axles are rigid and restrained in a three-piece truck, micro-slip occurs at the wheel/rail contact patch during curving. This micro-slip, known as “creepage,” and its energy loss is equivalent to the resistance of freight car steady-state curving. While many factors can affect creepage, Dick said, the two primary factors that can be controlled through train operation are coupler force and train speed.
Rail Sciences evaluated these variables using VAMPIRE™ vehicle dynamics software to simulate a nominal coal car in a unit train in both loaded and empty conditions in order to determine the influences of coupler force and train speed on freight car curving. Incremental coupler loads from 350 - 350 kips and train speeds from 10 - 60 mph were simulated on curves up to 16 degrees.
Results indicated that buff coupler loads and overbalance speeds produced favorable or neutral effects on curving resistance, while draft coupler loads and underbalance speeds created unfavorable effects on curving resistance.
While important, curving resistance is just one of many types of resistance on a moving train, Dick said. Inertial and grade-related forces, suspension damping, track deflection, bearing and wheel/rail friction are also at work. Energy loss through wheel/rail contact and vertical and lateral track deflection were also investigated.
Rail Sciences used a Train Operations Simulator (TOS) to model a specific 200-mile mainline route with maximum grades of +/- 1.2% and 8 degrees maximum curvature. Train handling was selected by the TOS automatic train handling algorithm (to maintain target 30-, 40- and 50-mph speeds). Simulations were run in both directions with the actual curvature and on tangent track with all curves removed.
VAMPIRE™ simulation indicated that curving resistance could realistically be reduced by 30% - 40%, best case, and 15% to 20% on average. The lowest curving resistance generally occurred at higher speeds and higher buff drawbar forces.
The simulations further projected that the total train resistance could be reduced by modifying train speed and drawbar forces by no more than 3.3% in the best-case scenario, but more typically by less than 1%. Simulations further determined that these reductions may be negated by increased speed — more locomotives and increased aerodynamic and suspension damping resistance. As a result, Rail Sciences concluded that modifying train speed and drawbar forces does not appear to be an effective way to reduce train resistance and fuel consumption.
"Managing Wheel/Rail Interaction on Rail Transit Systems"
"Tuning in to the Systems Approach"
"Examining Wheel/Rail Interaction"
"Examining Wheel/Rail Interaction on Rail Transit Systems"
"Improving Truck Designs to Reduce Forces Transmitted to Track"
"Design Considerations to Meet the M976 Specification"
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