There are many applications where Operational Modal Analysis is the natural choice of technology for supplying structural information.
Nondestructive testing
In non-destructive testing, NDT, the objective typically is to monitor the health of a structure over time. For this reason it is also known as Structural Health Monitoring, SHM. Since the structure is observed during service no other modal tool can provide modal information in such a case.
Damage Detection
For many years Operational Moda Analysis has been the preferred tool in damage detection of large structures. Mode shapes has been used to identify local damages that caused curvature changes and e.g. the modal frequencies has been used to identify global damages. Research is still extensive in this area combining technologies such as modal analysis, neural networks or response surfaces, and stochastic decision theory.
Vibration Level Documentation
If the vibration level needs to be documented in locations where no measurements can be made, Operational Modal Analysis can do it if you have a Finte Element Model, FEM, available. From the modal test you will obtain the modal coordinates or modal response at some measurable locations. These modal responses will then be extrapolated to other unmeasured locations through the mode shapes of the FE model, and by superposition the actual responses at the location is estimated. Even though the FE models only return normal modes this extrapolation will be good most structures.
Fatigue Analysis
The above mentioned vibration level documentation can also be extended to estimate the accumulated damage at unmeasured location such as underwater joints etc. In this way, ordinary inspections at e.g. offshore facilities can be optimized, since a few measurement points can give the engineers valuable fatigue estimates to help in the inspection planning.
Scaled Mode Shapes
The drawback of Operational Modal Analysis has been that the mode shape scaling has been arbitrary causing incorrect modal participation factors. This has caused problems in applications such as response simulation and structural modification. Recently, however, techniques to obtain the right scaling has been developed and they are now being tested on full scale structures. The results of these tests indicates that for even larger structures it is possible to obtain an accurate Frequency Response Function, FRF, from response measurements only.
Refrence: Structural Vibration Solutions A/S Co.