Nonlinear vibration of parabolic springs employed in suspension system of a freight car has been studied in this paper. First, dynamical behavior of the springs is investigated by using finite element method and the obtained results are then used in vibration analysis of a railway freight car. For this purpose, dynamics of a parabolic spring subjected to a cyclic excitation has been studied in the frequency range of 2 to 15 Hz. By utilizing an experimental setup, equivalent static and dynamic stiffness and damping of the spring have been obtained and compared with theoretical results. Different classes of rail irregularities are taken into account to excite the vehicle. Bond Graph method is employed to extract the equations of motion of the system and validity of the obtained equations is investigated. Finally, a parametric study is carried out and the influence of vehicle velocity and rail irregularity on vertical acceleration of the freight car has been examined.

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