Nonlinear dynamic characteristics of journal bearing-rotor system considering the pitching and rolling motion for marine turbo machinery

Rotating machinery in marine engine systems experiences the base excitation and the additional gyroscopic moment from the pitching and rolling motion of the ship. For some cases, the motion can cause the rotor system damage. The nonlinear model of the journal bearing-rotor system for marine turbo machinery considering the pitching and rolling motion is established by coupling the basement motion and nonlinear oil film force together. Then the nonlinear dynamic characteristics for the system with the unbalanced mass are studied. By employing the Newmark method, the dynamic response of the rotor-bearing system is simulated. The orbit diagram, spectrum diagram, waterfall diagram, amplitude versus rotating speed diagram and the bifurcation diagram are obtained. The effect of the pitching and rolling motion on the journal bearing-rotor system is investigated. The results indicate that the additional stiffness matrix, additional gyroscopic and additional exciting force vector will act on the journal bearing-rotor system, which are generated from the pitching and rolling motion for marine turbo machinery. The dynamic characteristics of the system such as destabilizing angular velocity will be changed by affecting the nonlinear oil film force.