Vibrations in roller coaster systems. Part II: Irregularity-induced oscillations and effects of track elasticity

Roller coaster systems are well known for experiencing vibrations, which can lead to passenger discomfort and accelerated material wear. Despite significant technological advancements, such as a more precise track manufacturing and the use of wheel pretension devices, no satisfactory solution has yet been found to effectively mitigate these vibrations. Moreover, the underlying causes of these vibrations remain only partially understood, adding an element of unpredictability to the design process. In a companion paper (Part I), the emergence of friction-induced self-excited vibrations is analyzed. In contrast, the present study investigates the impact of rail irregularities and the interaction between the train and elastic track subsystems on the vibration behavior of roller coasters. It is observed that contact nonlinearities play a critical role in determining the vibration frequencies, which differ from those directly associated with the wavelengths of the track irregularities. Variations in the g-load profiles alter the instantaneous wheel-rail interpenetration depth, leading to changes in the effective contact stiffness, which is closely linked to the eigenfrequencies of the system. Additionally, the vibrations of the elastic track subsystem, along with the presence of friction, can further modify the frequency distribution, whether these factors act independently or in conjunction with track irregularities. Analysis of empirical data supports these findings, showing a similar pattern in the evolution of the natural frequencies of the train.