Operational Modal Identification for Rotating Machinery under Environment Excitation

With the development of high-speed turbo machinery with the large span and flexible structure, the rotordynamic stability of the rotor-bearing system faces server challenges. The shop test to ensure the unit with an enough rotordynamic stability margin is an important process to reduce the risk of the instability fault of field units. Using the stochastic subspace identification (SSI) method, which is suitable for the random stationary environment excitations, to identify the modal parameters of units can avoid the traditional method that needs an additional electromagnetic exciter installed at the none-drive end of the rotor. The first forward and backward modal parameters are distinguished by analyzing the whirl directions of modal shapes. The unstable noise and physical poles are eliminated by combining the 3-σ clustering algorithm, and the stabilization diagram that can distinguish the forward and backward whirl modes of rotor system is also obtained. The numerical simulation results indicate that the SSI method can effectively identify the system modal parameters, and forward and backward whirl modes can be distinguished with the whirl direction analysis method of modal shapes in rotating machinery. Moreover, the traditional modal parameters identification method with sine-swept excitations is used to experimentally validate the identification accuracy of SSI method and its feasibility for industrial tests. The study result can provide technical and theoretical support for the stability test for turbo machinery units. © 2019 Journal of Mechanical Engineering.