Parallel misalignment modeling and coupling bending stiffness measurement of a rotor-bearing system

This paper sheds the light on vibration modeling and diagnosis of misalignment beyond traditional approaches. Firstly, the paper presents a detailed finite element and dynamic simulation model of a vibration test rig. The model includes the construction of mass, stiffness and damping matrices of a test rig and the inclusion of a time invariant, nonlinear rolling element bearing model, a misalignment model and residual unbalance force excitation. Secondly, a detailed measurement setup and signal processing methodology to characterize the coupling bending stiffness and misalignment forces as a function of the rotation angle and amount of parallel misalignment is developed and presented. Thirdly, equations of motions of the model were formulated and solved using a variable step solver. The displacements at the motor and rotor sides of the coupling were used along with the interpolated coupling stiffness values to calculate the misalignment forces, which were then fed to the system as excitation forces. The stiffness of the coupling was interpolated as a function of the shaft rotational speed and the level of misalignment. Finally experimental and simulated results are presented and discussed. Results from simulated data were compared to those measured experimentally. Both simulated and experimental results exhibited similar behavior. An increase of lower and higher harmonics of the shaft speed of the acceleration vibration signal was observed with smearing noticed at higher orders. A low-frequency modulation was reported in the measured signal with similar behavior captured in the simulated signal. Further investigation still needs to be carried out to provide a solid understanding of this interaction.