Modes of vibration are used to characterize resonant vibration in machinery and structures.
All structures have specific natural frequencies at which they readily absorb energy
When a resonance is excited, it can cause excessive noise and vibration, resulting in premature structural failures
Each resonance, or mode of vibration, is defined by its natural frequency, damping, and mode shape
At or near a modal frequency, the response of a structure is usually dominated by the resonance
A frequency-based ODS will often look like the mode shape of a nearby resonance, if the resonant response dominates the ODS
However, mode shapes, along with their frequency and damping values, are more accurately obtained by curve fitting a set of FRF measurements, or a set of Fourier spectra, Cross spectra or ODS FRFs calculated from operating data.
Sine Dwell Animation of a Mode Shape .