Estimating modal parameters from measurements in operational conditions

Today, modal analysis has become a widespread means of finding the modes of vibration of complex machines and constructions. In many applications, however, the vibration measurements have to be performed in “operational” conditions where the structure is excited by the natural (ambient) excitation sources. The need to perform modal analysis in operational conditions probably emerged first in civil engineering for Structural Health Monitoring applications. But also in other engineering fields Operational Modal Analysis (OMA) proved to be very useful. Example are Flight Flutter Monitoring of an airplane during real flight conditions or Conditioning Monitoring of complex mechatronic systems such as offshore wind turbines.

Traditionally, one has to assume that the unknown ambient excitations are white noise sources. This assumption is often not valid due to, for instance, the presence of harmonic components. The Brussels Acoustics & Vibration Research Group (AVRG) developed a novel method to determine the modal parameters without having to make any assumption of the excitations.

Transmissibility-based Operational Modal Analysis (TOMA)
The Brussels Acoustics & Vibration Research Group (AVRG) developed a novel method to determine the modal parameters without having to make any assumption of the excitations.
AVRG proved that transmissibility functions can be used to identify modal parameters from operational data. This new approach is able to derive the modal parameters directly from parametrically identified models by introducing a dedicated parametric estimator.
AVRG has a strong track record in the field of modal analysis. The research group developed the PolyMAX modal parameter estimator in collaboration with LMS (now Siemens PLM Software). The introduction of the PolyMAX estimator around 2005 resulted in a significant break-through in the field of noise and vibration engineering.