Detection and correction of synchronization-induced errors in operational modal analysis

Operational modal analysis (OMA) methods are frequently applied for obtaining information on structural dynamic parameters, such as natural frequencies and mode shapes. While synchronization between acceleration response data sets used in OMA is not a prerequisite for estimating natural frequencies, synchronization discrepancies may lead to non-negligible errors in the estimation of mode shapes. Synchronization discrepancies are predominantly associated with wireless structural health monitoring systems, where each wireless sensor node functions as a separate data acquisition unit (DAQ), and clock synchronization is therefore not intrinsic. However, synchronization discrepancies may also occur in cable-based systems, particularly when more than one DAQ is used. In this paper, a synchronization method for detecting and correcting synchronization-induced errors in OMA is proposed. Unlike existing approaches on removing synchronization-induced errors at the output stage, the method proposed herein yields synchronized structural response data at an intermediate stage of OMA. Specifically, time lags between acceleration response data sets are detected based on estimates of the mode shapes obtained either from preliminary structural analysis or from engineering judgment assuming classical damping. The applicability of the proposed method is verified through simulations of a multi-degree-of-freedom oscillator and validated through ambient vibration field tests on a pedestrian overpass bridge.

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