A resonance peak should appear at the same frequency in every FRF, except where node points (zero residues) of the mode shape occur.
Execute Format | Overlay to overlay the FRFs and look for resonance peaks at the same frequency in all FRFs
Execute Transform | Inverse FFT to transform each FRF into its corresponding IRF
All of the IRFs should exhibit a damped sinusoidal decay to almost zero at the end of each time waveform, as shown below
Wrap around error (shown below) is not harmful to frequency domain curve fitting.
Impulse Response Functions.
Press the Count Peaks button on the Mode Indicator tab to count the number of resonance peaks (modes) in a cursor band
Execute Curve Fit | Quick Fit and inspect the results
Curve fit only those portions of the data that contain valid resonance peaks
If the Band cursor is displayed, only data in the cursor band is used for curve fitting.
Otherwise, all of the data in each M# is used for curve fitting.
Low frequency modes have simple bending and torsional mode shapes.
Points that animate substantially different from neighboring Points on the structure model are indications of poor measurements, poor curve fits, or both.
Estimate modal parameters for a few of the lower frequency (fundamental) modes
Save the results into a Shape Table and display the mode shapes in animation to verify their validity.
Curve fit the FRFs using more than one curve fitting method, and compare mode shapes from different methods.
Execute Display | MAC (Modal Assurance Criterion) to numerically compare mode shapes between different curve fitting methods.
Execute Animate | Compare Shapes to display shapes in animation from two Shape Tables.