Using three-parameter sine fitting for scaling mode shapes with omah

Scaling mode shapes obtained by operational modal analysis (OMA) is sometimes desirable, for example if the modal model is going to be used for model calibration, or for some structural health monitoring applications. A new method for scaling mode shapes from OMA, utilizing harmonic excitation and called OMAH, was recently proposed by the authors. In the present paper, we briefly describe this new technique, and then investigate a particular method, the three-parameter sine fit technique, for estimating the harmonic force and responses under different signal-to-noise (SNR) cases. This technique is shown to provide good performance even in severe SNR cases, and the method also has the advantage that the accuracy of the estimate of the harmonics can be estimated alongside the harmonic estimates, and can be improved by adding more data to the measurement. This allows to develop an iterative technique, allowing to estimate the harmonics iteratively, until a sufficient accuracy is obtained. The method is demonstrated on simulated OMA measurement data.