mode shape

[SEmil]

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?

 

[GBor]

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.

 

[SEmil]

I should be able to get rid of the local mode by increasing the member stiffness. Am I right?

 

[GBor]

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.