Graphical Output–Oriented Computer Model of a Railroad Freight Car With Conventional Trucks

The paper describes a 13-degree-of-freedom, frequency domain, computer model of a railroad freight car riding on conventional North American three-piece trucks. These 13 degrees of freedom incorporate roll, pitch, bounce, bending, and twisting of the body, as well as lateral, swivel, and parallelogramming of each truck. This idealized freight car is driven at 200 discrete frequencies from 0.1 to 20.0 cycles per second. The driving functions are derived from the Fourier components of track geometry measurements taken from actual test tracks. Although the model is linear, coulomb damping is approximated by equivalent viscous coefficients at each frequency. Printed output is provided; however, the basic product of the program is a series of two-color graphs produced on a mechanical plotter. These include a Nyquist diagram, giving indications of the freight car’s lateral stability on tangent track, and PSD plots illustrating the frequency breakdown of the various vehicle responses. Comparisons are made between the computed PSD plots and actual test data for specific conditions.