For the bearing pedestal looseness fault of dual rotors system

after taking into account three DOF(degree of freedom) planar rigid motion of loose bearing pedestal and introducing collision recovery coefficient

a dual rotor system dynamics model including loose bearing pedestal was set up based on the dual rotor structure of experiment rig. Using the finite element method and rigid body kinematics

and adopting the Newmark-β algorithm for numerical simulation based on Timoshenko beam elements

the dynamic characteristics of the inner and outer rotors and the bearing pedestal plane rigid body motion in occurrence of bearing pedestal looseness fault were studied. Meanwhile

the loose experiments of dual rotor system under two different speeds' combination were carried out

and the experimental results were basically the same. The simulation results with the bearing pedestal looseness fault of dual rotors bench were compared

indicating loose rotor vibration displacement waveforms had "clipping" phenomenon. When the bearing pedestal looseness fault occurred

the inner and outer rotors' vibration spectrum not only contained the difference and the sum frequency between the two rotors' fundamental frequency

but also contained loose support rotor second and third harmonics components

etc; there were more low frequency spectrums containing dividing component

etc; the rotor displacement spectrum also contained fewer combination frequency components

etc; when unilateral bearing pedestal was loosened

the inner rotor axis trajectory was drawn into similar-ellipse shape.