For any modal parameter estimation (MPE) method, there are a few control inputs that can have an impact on the modal parameter estimates. These control inputs are typically involving parameters like the maximum model order and how many time values or frequency lines that should be included in the MPE. In this paper, a comprehensive study on the influence of these parameters is conducted using the multi-reference Ibrahim Time Domain algorithm (similar to the cov-SSI method). Data from a laboratory Plexiglas plate are investigated, and an automated Operational Modal Analysis (OMA) algorithm is used to systematically select physical poles. The effect of each of the various control parameters are discussed in the paper.

There are many advanced algorithms used to estimate modal parameters. In this paper, the modal parameters extracted from the Poly-reference Least Squares Complex Frequency (PLSCF) algorithm and the Multi-reference Ibrahim Time Domain (MITD) algorithm, are compared. The former, is widely used in the industry and is known to produce almost crystal clear stabilization diagrams with barely any spurious pole estimates. The latter, is less common and the stabilization diagrams typically contain some spurious pole estimates. An Automated Modal Analysis (AMA) algorithm, that utilizes the statistical representation of the pole estimates combined with a number of decision rules based on the Modal Assurance Criteria (MAC), is employed, to detect probable physical poles. Simulated data from a Plexiglas plate is used in the study. Results indicate that the absolute bias error associated with the modal parameter estimates output by the PLSCF algorithm is higher than the bias error related to the modal parameter estimates output by the MITD algorithm. It was not conclusive which of the two methods that had the lowest random error. It should also be mentioned that, while the MITD algorithm could process all references and responses, the PLSCF algorithm relied strongly on a delicate selection of representative references and that not too many references were used.

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