THE INFLUENCE OF RAILS ON TRAIN NOISE

This paper presents an evaluation of the dynamic interaction of steel wheels on steel railsand an estimation of the contribution of sound radiated by rails to total train noise levels. The interaction is modeled as a random process, for which dynamic forces at the wheel/rail interface are related to wheel and rail impedances and roughness wavenumber spectra. Roughness spectra, estimated from rail vibration data, are found to be proportional to (wavenumber) −4 . Comparing analytical predictions with measured data shows that the rail can be adequately modeled as a beam on an elastic foundation. Modeling the wheel as a simple mass reveals that at intermediate frequencies the wheel impedance is much higher than the rail impedance. Therefore, rail vibration levels are expected to be substantially higher than levels of wheel vibration. Analytical models of rail radiation, confirmed by experimental data acquired by shaking a rail in a reverberant chamber, show that rail radiation is efficient above about 500 to 1000 Hz. When these models and data are combined, it is found that rail radiation may dominate at mid- and high frequencies (∼500 and 5000 Hz), but it is less important than other sources outside of these frequency regimes.