No abstract

As part of the vehicle qualification process, the Federal Railroad Administration (FRA) currently requires in its track and passenger equipment safety standards that a validated vehicle model be used to demonstrate safe dynamic vehicle response to allowable track geometry variations. Transportation Technology Center, Inc. (TTCI) was contracted by FRA to characterize, model, and analyze a high speed passenger vehicle in order to provide guidance related to the vehicle qualification process. The overall objective of the project was to evaluate methods required to demonstrate the validity of a vehicle dynamics model project and investigate how different input parameters affect the accuracy of the model. The project consisted of four main tasks: (1) characterize a high speed passenger vehicle; (2) develop a mathematical model of the vehicle using measured parameters; (3) validate the mathematical model using on-track tests; and (4) conduct a sensitivity analysis of the vehicle model to determine the critical parameters. FRA tasked TTCI with applying the testing and modeling methodology to FRA’s DOTX 216 geometry car. Specific parameters were identified that needed to be measured in order to develop a dynamic vehicle model of the car. A characterization test regime was outlined and performed to determine the necessary mass, stiffness, and damping characteristics, and the measured parameter values were used to create a mathematical model of the vehicle using TTCI’s NUCARS®* dynamic modeling software. A series of on-track validation tests were performed on different tracks at the Transportation Technology Center (TTC) using the DOTX 216 car to facilitate model validation efforts. The model was then used to simulate the on-track testing regime conducted at TTC. Model validation was evaluated using displacement, acceleration, and wheel/rail force measurements. Results from the simulations and test data were compared using multiple methods to demonstrate the validation of the DOTX 216 model. TTCI also conducted a parameter sensitivity analysis using the validated model to assess its sensitivity to changes in different parameter values and to identify the most critical parameters for simulating passenger vehicles. The testing, modeling, and model validation methodology described in this work provide a practical example of developing a validated vehicle model for use in the vehicle qualification process.

Rail seat deterioration (RSD) of concrete ties is manifested by the loss of concrete material in the rail seat area supporting the rail. This failure mode can lead to track that performs poorly and, in extreme cases, can result in the loss of rail clip hold down, reverse rail cant, and rail rollover derailments. This paper describes the use of a multibody vehicle–track dynamics model developed to study the load environment of concrete tie rail seats, specifically addressing the failure mode of RSD. Vehicle–track interaction simulations were conducted to determine the effect of track geometry perturbations on the overall load environment. Various types and magnitudes of track geometry perturbations, including combinations of surface (vertical) and alignment (lateral) perturbations were considered. Fastening system parameters such as clip hold-down force, tie pad stiffness, and broken insulator conditions were also considered. Results of these simulations suggest that concrete crushing, a hypothesized mechanism of RSD, is unlikely in realistic revenue service conditions. Under the load environments considered, the results augment support for an abrasion-related mechanism of RSD that may be more dependent on tonnage and infiltration of fine particles in the rail seat, two factors not addressed in this model. Results from in-track testing are also presented to compare model outputs with measured in-track forces under artificial track geometry perturbations installed at the Transportation Technology Center’s Facility for Accelerated Service Testing. More broadly, the use of this model to explore the effects of vehicle track interaction on tie and fastener load environment is also discussed.