Stability analysis of reduced rotor pedestal looseness fault model

In this paper, the nonlinear dynamic characteristics of a rotor system supported by ball bearings with pedestal looseness are analyzed. The model of seven-degrees of freedom (DOFs) rotor system is established by the Newton’s second law, which comprises a pair of ball bearings with pedestal looseness at one end. Energy analysis of the original model states that the first two-order proper orthogonal modes occupy almost all the energy of the system, and it demonstrates that the reduced model reserves main dynamical topological characteristics of the original one. A modified proper orthogonal decomposition method is applied in order to reduce the DOFs from seven to two, and the reduced system preserves the bifurcation and amplitude–frequency characteristics of the original one. The harmonic balance method with the alternating frequency–time domain technique is used to calculate the periodic response of the reduced system. Moreover, stability of the two-DOFs model is analyzed based on the known harmonic solution by the Floquet theory.