Output-only Modal Analysis on Operating Wind Turbines: Application to Simulated Data

摘要

Output-only (Operational) Modal Analysis (OMA) is a modern branch of experimental modal analysis; the main advantage of OMA is its ability to extract modal model using only measured responses. This makes OMA extremely attractive for modal analysis of big structures such wind turbines. However, there are issues preventing straightforward application of OMA to operational turbines, e.g. structure invariance during the test. The effect of rotor rotation manifests itself in the equation of motion with time-dependent coefficients. Formulating and solving eigenvalue problem lead to time-dependent eigenvalues and eigenvectors which become meaningless as modal parameters. Fortunately, so-called Coleman coordinate transformation (also known as multi-blade coordinate transformation) allows one to eliminate time dependency of the system matrices, thus converting the original time-varying eigenvalue problem to a time-invariant one.