A fast damping ratio identification method for rotating machinery based on the singular value of a directional power spectra density function matrix

Abstract It is of great importance to accurately evaluate the stability margin of a turbomachine both in shop tests and in operation. The damping ratio of the first forward whirl mode is the key indicator of rotordynamic stability. In this paper, a fast operational modal analysis (OMA) technique based on the singular value of the directional power spectra density function (dPSDF) matrix was developed to estimate the damping ratios of the first forward and backward whirl modes. Numerical simulations and experiments were carried out to verify the accuracy of this method on a high-speed test rig. Moreover, the dPSDF-based method was compared to two conventional OMA methods - data-driven and covariance-driven stochastic subspace identification (SSI) methods - resulting in more stable and accurate estimates for the damping ratio along with a much faster identification time (less than 0.5 s). This study provides an accurate and fast method for performing stability shop tests for turbo machines and stability online monitoring.