基于随机子空间辨识的服役阶段海上风力机塔筒结构频率识别

As the unit capacity of offshore wind turbines continues to increase，leading to taller towers and longer blades，the coupling effects among the structure，control strategies，and environmental actions become increasingly significant. Accurately identifying the natural frequency during the service life is of great importance for avoiding resonance and reducing fatigue damage. To address the challenge of modal identification under the coexistence of strong ambient noise and operational excitation，this paper proposed a parameter optimization and spurious mode suppression method based on stochastic subspace identification. Firstly，an intelligent health monitoring system integrating vibration responses and SCADA operational data was established to achieve remote，continuous，and synchronous data acquisition for offshore wind turbines. Secondly，the covariance-driven stochastic subspace identification method was employed. The optimal range for the system order and the number of block rows in the Hankel matrix was determined through a sensitivity analysis that considered both identification process stability （condition number）and result reliability（coefficient of variation）. Finally，a density peak clustering algorithm was introduced to eliminate spurious modes in the stabilization diagram，enabling accurate identification of the structural frequency. Taking a three-blade offshore wind turbine in eastern China as a case study，a five-month continuous monitoring campaign was conducted to analyze the influence of wind speed，rotational speed，and pitch angle on the frequency. The results indicate that the fundamental frequency of the structure is stable at 0. 33 Hz and does not vary with wind speed or rotational speed. The 3P blade passing frequency has the most significant impact on vibration. When the rotational speed approaches 6. 7 r/min，the 3P frequency coincides with the fundamental frequency，leading to a noticeable increase in the acceleration response of the tower and structural resonance. The study confirms that the fundamental frequency of this turbine falls within the 3P frequency band（0. 2-0. 6 Hz）. It is recommended to avoid the rotational speed range of 6. 0-7. 4 r/min during actual operation or to add artificial damping.