Stochastic Subspace Identification Technique in Operational Modal Analysis

Operational Modal Analysis also known as Ambient Modal Analysis has an increasing interest in mechanical engineering. Especially on big structures where the excitation and not less important the determination of the forces is most often a problem. In a structure like a wind turbine wing where the modes occur both close in frequency and bidirectional the ambient excitation has big advantages. In this paper modal parameters are identified from the wing by operational modal analysis. For the parameter identification a parametric techniques the so-called Stochastic Subspace Identification Technique (SSI) is used. This technique is an unbiased estimator utilizing the raw time data. With the latest improvement this technique has big advantage where the modal density becomes high due to close modes with high damping.