As much as there has been a significant increase in the development of railway systems in recent years, one of the significant drawbacks on this mode of transport is ground-borne vibrations and noise emanating from vehicle-track interaction in service. This greatly affects the ecology and physical surroundings of the railway track. Experimental tests and Finite Element modal and complex eigenvalue analysis are conducted to investigate the dynamics of a traction wheelset and rail track. This is done to establish the correlation between the short pitch rail corrugation in the Belfast to Steelpoort railway line, in the Limpopo Province of South Africa, with railway wheel-tract resonance at low frequencies of excitation. A 3D Finite Element Method (FEM) and complex eigenvalue analysis are used to validate the resonance modes of the wheelset and rail track obtained through experimental modal analysis. Mode shapes are determined for natural frequencies that match the excitation frequency induced by short pitch rail corrugation. The results show that based on average train speeds around track curves, the excitation frequency induced by corrugation matches (quite reasonably) natural frequencies of the wheelset. Whilst the wheelset FEM results are in better agreement, they rather prove the correlation to occur at 100 Hz. In a previous study by the authors, at the average speeds per track curve, the corrugation excitation frequency was found to be 108 Hz. The current study goes further by investigating natural frequencies of rail tracks. Moreover, mode shapes of a traction wheelset and rail tracks are also investigated, and the results are presented herein.
Rail–wheel interaction is one of the most significant and studied aspects of rail vehicle dynamics. The vibrations caused by rail–wheel interaction can become critical when the radial, lateral and longitudinal loads of the vehicle, cargo and passengers are experienced while the vehicle is in motion along winding railroad paths. This mainly causes an excessive production of vibrations that may lead to discomfort for the passengers and shortening of the life span of the vehicle’s body parts. The use of harmonic response analysis (HRA) shows that the wheel experiences high vibrational amplitudes from both radial and lateral excitation. The present study describes a numerical and experimental design procedure that allows mitigation of the locomotive wheel resonance during radial and lateral excitations through viscoelastic layers. It is proven that these high frequencies can be reduced through the proper design of damping layer mechanisms. In particular, three parametric viscoelastic damping layer arrangements were analyzed (on the web of both wheel sides, under the rim of both wheel sides and on the web and under the rim of both wheel sides). The results demonstrate that the correct design and dimensions of these viscoelastic damping layers reduce the high-amplitude resonance peaks of the wheel successfully during both radial and lateral excitation.
In South Africa, one of the main lines situated in its Limpopo Province presents symptoms of excessive vehicle-track vibrations. A modal method is adopted to study the difference in dynamic response of corrugated rails resting on the Hytrel/6385 and High Density Polyethylene (HDPE) rail pads. The results for dynamic response of rails on these two types of rail pads are analysed in form of Frequency Response Functions (FRFs). Two positions are considered in obtaining these point FRFs; those are mid-span and on top of sleeper. Resonance modes of significance are excited in a frequency range of 0 – 500Hz on rails resting on both types of rail pads. In view of the entire vibration response window, the FRFs show a more damped vibration response by rail resting on the HDPE than that resting on the Hytrel/6358 rail pad. A Finite Element (FE) modal analysis method is used to investigate vibration mode shapes and corresponding frequencies of the wheelset used by the locomotive operating in the line. In the high frequency range of 350 – 500Hz, the gear-side wheel of a locomotive wheelset proves to be vibrating more erratically than the non-gear side wheel. Clearly pronounced mode shape excited at a frequency of 350Hz and higher are presented.
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