Nonlinear vibration analysis of rotor systems with hydrodynamic journal bearings using harmonic balance method

This work presents nonlinear steady-state and stability analyses of rotor systems supported by hydrodynamic journal bearings. The rotor and fluid film are discretized using finite elements to incorporate shaft flexibility and various bearing configurations. The harmonic balance method is employed to analyze steady-state responses in the frequency domain, eliminating the need for time integration and handling both static and dynamic loads. Coupling between the rotor and fluid problems is achieved through an alternating frequency-time scheme, enabling parallelization to further improve computational efficiency. The stability of the solutions is evaluated using Floquet exponents derived from Hill's method, utilizing the by-products of the harmonic balance framework. Numerical results highlight the nonlinear effects in rotor systems with journal bearings, such as superharmonic and resonance behaviors that cannot be captured by a linearized approach. The proposed framework provides accurate predictions of steady-state responses and stability across various conditions, while preserving computational efficiency.