Technical Reports

A Mathematical-Computer Simulation of the Dynamics of a Freight Element in a Railroad Freight Car

  • 01
  • May
  • 1977
AUTHOR: Kowk L. Shum, Terrence Willis
SUBJECT: Evaluation
KEYWORDS: Vibrations, Freight Dynamics, Computer Simulation, Railroad Car Vibrations
ABSTRACT: This research studies the dynamic response of a freight element, inside a typical freight box car under service conditions, by a computermodel simulation technique. A 27 degree of freedom mathematical model has been developed to represent the freight car, truck and freight element, with the car body as a single rigid mass. This model has been validated against published railroad research data. This model is a more detailed one than most previously published simulations, and has additional characteristics. One is the option of modeling dry friction dampers by either COUlOI,.b friction or equivalent viscous damping. A second improvement is the facility to express the response of the system in either time or frequency domain. The computer simulation shows that the critical roll mode speed of a representative 70-ton box car is around 17.5 mph. The maximum car body roll angle is 11. 4 0 peak to peak, the maximum wheel load is 69,000 lb/wheel, and wheel lift durations are 0.2-0.4 sec. For a specific freight element near the roof maximum lateral accelerations of 1.5 g peak to peak at 0.64 Hz were calculated. At 50 mph, this value becomes 0.2 at 2 Hz. -;. g Vertical acceleration of 0.1 g at 1.25 Hz is computed for freight near the car body center of gravity at 50 mph. The mathematical model can be used for parametric studies on designs of the car body and truck Cushioning requirements for freight/package systems subjected to vibrations inside a freight car can also be established.