Considerations in the application of spatial domain algorithms to operational modal analysis

The Complex Mode Indicator Function (or CMIF) is a popular spatial domain modal parameter estimation technique that utilizes the singular value decomposition of the frequency response function matrix for estimating the modal parameters of the system. Due to several advantages like identification of closely spaced modes, this technique is extremely popular for modal parameter estimation purposes. In recent times, the Frequency Domain Decomposition (FDD) technique [8] was developed that extends the CMIF algorithm to the operational modal analysis framework. The FDD technique works on the power spectrums unlike working on frequency response functions as in conventional modal analysis. Normally the FDD is followed by the Enhanced Frequency Domain Decomposition (eFDD) [9] to complete the overall parameter estimation procedure. In this paper an alternative to the eFDD, the previously introduced Enhanced Mode Indicator Function (EMIF), is reviewed and extended to the operational modal analysis framework. This algorithm differs from the eFDD in that the parameter estimation is carried out in the frequency domain. Further the paper analyzes the application of spatial domain algorithms to operational modal analysis framework in more detail. It discusses the critical issues and limitations associated with the application of spatial domain algorithms to the OMA framework under different excitation scenarios and proposes a simple tool, Singular Value Percentage Contribution (SVPC) plot to deal effectively with them.