Operational modal identification of offshore wind turbine structure based on modified stochastic subspace identification method considering harmonic interference
Operational modal identification of offshore wind turbine structure based on modified stochastic subspace identification method considering harmonic interference
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DOI：
10.1063/1.4881876
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发表时间：
2014-06
影响因子：
2.5
通讯作者：
Dong Xiaofeng;J. Lian;Min Yang;Wang Haijun
中科院分区：
文献类型：
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作者：
Dong Xiaofeng;J. Lian;Min Yang;Wang Haijun
经典的模态识别方法一般可以从未知激励引起的不同振动响应中获得结构模态参数信息，这些方法是基于结构输入与平稳随机白噪声完全相同或接近的假设。然而，对于海上风电机组结构等实际工程，由于转子的周期性旋转激励在振动响应中出现明显的谐波分量，所施加的载荷不能视为纯白噪声激励。当产生的谐波分量能量较大且频率接近于结构的任意固有模态频率时，在这种强谐波扰动下，经典方法无法将谐波模态与实际结构工作模态分离，从而产生假模态，严重影响识别精度。为了准确识别强谐波激励下的实际结构工作模式，本文提出了一种考虑谐波干扰的改进随机子空间识别方法——谐波修正SSI （HM-SSI）方法，该方法假设输入谐波频率已知且时不变。然后，通过一个简单的悬臂梁受各种谐波输入叠加在随机荷载上的数值模型，验证了HM-SSI方法的有效性和准确性。此外，还体现了噪声水平和谐波能量比例对识别结果的鲁棒性和准确性的影响。最后，基于某海上风力机高转速试验样机的实测数据，获得了不同工况下的模态参数信息，并对某海上风力机进行了运行安全性评估。
The structural modal parameter information can be generally obtained from different vibration responses triggered by unknown excitations using the classic modal identification methods which are based on the assumption that the input to the structure is exactly the same or close to the stationary random white noise. For the actual projects such as the offshore wind turbine structure, however, the imposed loads cannot be considered as the pure white noise excitation because the harmonic components emerge obviously in vibration responses due to periodic rotation excitations of the rotor. When the created harmonic components have greater energy and their frequencies are close to any natural modal frequency of the structure, the classic methods can no longer separate harmonic modes from actual structural operational modes under this strong harmonic disturbance, thus false modes may be generated and the identification accuracy may be badly affected. To identify the actual structural operational modes accurately under strong harmonic excitation, a modified stochastic subspace identification (SSI) method considering harmonic interference called the harmonic modification SSI (HM-SSI) method was proposed in this paper assuming the input harmonic frequencies are known and time-invariant. Then the effectiveness and accuracy of the HM-SSI method were verified through a simple numerical model of cantilever beam excited by various harmonic inputs superimposed on random loads. Besides, the superior robustness and better accuracy of identification results affected by the level of noise and the proportion of harmonic energy were reflected. Finally, the modal parameter information under different operational conditions was obtained and the safety assessment of an operational wind turbine was made based on the measured data from one offshore wind turbine test prototype at high running speed.