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A method for the harmonic removal in operational modal analysis of rotating blades

机译：旋转叶片运行模态分析中的谐波去除方法

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摘要

The operational modal analysis, OMA, allows estimating the dynamic properties of a structure, natural frequencies, damping ratios, and mode shapes, without measuring the input forces. According to the main hypothesis concerning the input excitation, i.e., stochastic with frequency independent spectra (at least in the frequency band of interest), it is not theoretically possible to apply the OMA procedures in structures characterized by the presence of harmonic components in the excitation loading. In this paper, an approach capable to identify the presence of harmonic excitations, acting together with a broad band stochastic loading, and then to remove their effects in the modal parameter estimate is presented. The approach is based on the joint use of the statistical parameter called "entropy" and the already developed output-only procedure based on the application of the Hilbert transform properties to the output response signals. The capability to improve the OMA procedures is investigated numerically and through whirl tower experimental tests of a rotating blade in which both stochastic and harmonic contributions to the dynamic excitations have been provided by the perturbations arising from the operative conditions. A sensitivity analysis has been also performed to evaluate the effects of the filtered responses, in the time domain, on the statistical characterization, required to distinguish the operational frequencies from the natural ones.
机译：操作模态分析OMA可以估算结构的动态特性，固有频率，阻尼比和振型，而无需测量输入力。根据与输入激励有关的主要假设，即与频率无关的频谱（至少在感兴趣的频带内）是随机的，从理论上讲不可能将OMA程序应用于以激励中存在谐波分量为特征的结构加载中。在本文中，提出了一种方法，该方法能够识别谐波激励的存在，并与宽带随机负载一起起作用，然后消除其在模态参数估计中的影响。该方法基于称为“熵”的统计参数和基于希尔伯特变换属性应用于输出响应信号的已开发的仅输出过程的联合使用。通过旋转叶片的涡流塔实验测试，通过数值方法研究了改进OMA程序的能力，在旋转叶片中，由于工作条件引起的扰动，为动态激励提供了随机和谐波贡献。还进行了灵敏度分析，以评估时域中滤波后的响应对统计特征的影响，以区分工作频率与自然频率。

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