Nonlinear dynamics of unsymmetrical rotor-bearing system with fault of parallel misalignment

Coupling misalignment in rotating machinery is an important problem; however, its dynamic characteristics have not been fully understood. In this work, the nonlinear dynamic behaviors of an unsymmetrical generator rotor system supported on the journal bearings are investigated. The motion equations of the rotor system are derived based on Lagrange method after taking into account a holonomic constraint characterized by the parallel misalignment between two rotors. Then, the dynamic responses and the vibration features of the rotor system are discussed based on the numerical technique, such as the rotor orbits and its frequency spectra, Poincare maps, and largest Lyapunov exponent. The results show that the super-synchronous component in the frequency spectra 2X is significant for the identification and diagnosis of the rotor misalignment. Furthermore, the misalignment may induce the break of quasi-periodic torus and period-doubling bifurcation cascaded to chaos with the jump phenomena in response amplitudes.