Modal Indicators for Operational Modal Identification

摘要

Modal validation is of paramount importance for all two-stage time domain modal identification algorithms. However, due to a higher noise/signal ratio in operational/ambient modal analysis, being able to determine the right model order and to distinguish between structural modes and computational modes become more significant than in traditional modal analysis. The two major modal indicators, i.e. Modal Confidence Factor (MCF) and Modal Amplitude Coherence (MAmC) are extended to two-stage time domain modal identification algorithms, together with a newly developed indicator, named as Modal Participation Indicator (MPI). The application of the three indicators is illustrated on different cases of operational/ambient modal identification. Three major time domain modal identification algorithms are used, the Polyreference Complex Exponential (PRCE), Extended Ibrahim Time Domain (EITD), Eigensystem Realization Algorithm (ERA). The three identification algorithms are implemented from a unified point-of-view with the modal indicators. Numerical simulations are conducted on a two-story building structure and on an aircraft model and it is investigated how the modal indicators work to distinguish the physical modes from the computational modes.