Application of modal analysis to establish the wavelength fixing mechanism for rail corrugation

Modal Analysis is conducted to establish the correlation between the resonance frequencies of a locomotive wheelset and the rail corrugation frequencies. Rail corrugation exists on the railway track owned by Transnet. The corrugated track runs from Belfast to Steelpoort in the Limpopo Province of South Africa. Modal analysis was conducted at the Transnet Engineering Koedoespoort Facility in the wheels department. One locomotive wheelset consisting of two wheels and a traction gear pressed onto an axle was used for modal analysis. The aim of this experiment was to investigate how the D39 200 locomotive class wheels behave under vibrational excitation, and to obtain the contact point Frequency Response Functions (FRF). Corrugation frequency was calculated using train speeds and corrugation wavelengths. The modal analysis performed shows a discernible correlation between the lateral (transverse) natural frequencies of the locomotive wheelset and corrugation frequencies calculated for rails at the Belfast to Steelpoort line. The D39 200 locomotive class is the only class of locomotives that hauls trains on the Belfast to Steelpoort line. Corrugation wavelengths are also correlated to train and track geometry parameters such as train speeds, track curve radius and tractive effort. There is a strong discernible relationship between corrugation wavelengths and train speeds; this is true especially for loaded trains. The train speeds are directly proportional to the wavelengths, whereas the tractive efforts are inversely proportional. This makes sense given the fact that in general, tractive efforts are inversely proportional to train speeds. The greater the curve radius, the longer the wavelengths. In order to avoid long-pitch corrugation, the track curve radius should be reduced to less than 400 m. This means smaller radius curves have mostly short-pitch corrugation (wavelength < 80 mm) and large radius curves have mostly long-pitch (wavelength > 80 mm).