Spectral Analysis of Freight Car Truck Lateral Response

This paper summarizes methods used to quantify the lateral response of freight car trucks to random track irregularity inputs. Spectral analysis is applied to the results of an extensive series of experiments using a one-fifth scale model of a truck and half carbody, in which all inertial, friction, creep, and stiffness forces are dynamically scaled. The repeatability and confidence limits for estimates of the spectral densities of track inputs and truck response variables are determined. The influence of forward velocity, truck internal friction, and axle load on the dominant truck response modes is presented. Cross spectral methods are used to reference signals to the true track centerline, and to compute lateral response transfer functions and coherence levels. The low levels of coherence between track inputs and freight car truck/carbody response indicate that linear transfer functions do not represent the response adequately, and that measured output spectra are superior to transfer functions for comparison of truck configurations.