Passenger Vehicle Characterization, Modeling, Validation, and Sensitivity Analysis

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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.