Operational Modal Analysis (OMA) has lately been a more and more common tool in structural dynamics. The benefits compared to Experimental Modal Analysis (EMA) are that one does not need any artificial excitation and that the structure does not have to be at rest, which is a requirement of EMA.

 

So far, OMA has won terrain for modal analysis of large structures such as buildings and bridges, and for vehicles such as helicopters and ships.

Basement of turbo-generator: animation of extracted mode at 6.4 Hz

This video shows the deflection shape of the turbo-generator skid at the resonance frequency detected with the operational modal analysis (OMA). 

 

With this procedure it’s possible to identify the modal parameters of the structures using the intrinsic excitation of the system. 

 

It’s a very useful technique that permit to extract the modal parameters without stopping machine or use an external excitation (example instrumented hammers, shakers, etc...).