i have 3D model for entire structure. Not an FEM model expert yet. I need to find out frequency of local area. Is there an easy way to find out which mode shape governs?
Look at mass participations for each mode. If mass participation is low (5% or less), you probably have a local mode. Then, look at the mode shapes. Amplify deflections until you see the local area that you are interested in deflecting by itself.
You should be able to change the frequency of the local mode by increasing the stiffness. It may no longer be the 1st mode...or a specific mode number as you may be able to drive the frequency out of the range of concern.