Coupled journal and thrust bearing dynamics considering five degree of freedom model and using second-order bearing coefficients

This article presents a comprehensive investigation into the coupled behavior of hydrodynamic journal and thrust bearings, employing a 5-degree-of-freedom model and focusing on the impact of considering the second-order analysis on the evaluation system's stability. By employing the finite difference method (FDM) and the infinitesimal perturbation technique, the bearing coefficients derived from the governing Reynolds equation are obtained. The influence of Sommerfeld and misalignment angle on the first- and second-order dynamic coefficients of journal bearings is investigated. Furthermore, a dynamic analysis of a rotor-bearing system is conducted, considering the coupling between journal and thrust bearings, to investigate the influence of the second-order dynamic coefficients on system dynamics and stability. Additionally, the investigation focuses on the stability of Hopf bifurcation and the continuation of the system's steady state solution. The analysis findings emphasize the significant influence of the interaction between journal and thrust bearings on the stability of the rotor-bearing system. Key results reveal that Sommerfeld number and misalignment angle exhibit nonlinear influences on dynamic coefficients. The study also demonstrates that the second-order dynamic analysis is critical for accurately predicting Hopf bifurcation stability, where high stiffness combined with large Sommerfeld numbers yields supercritical bifurcation, while very low Sommerfeld numbers give rise to subcritical bifurcation. These insights advance the understanding of coupling-induced nonlinear dynamics in rotor-bearing systems.