normal mode analysis in patran

[Anshu8]

I am doing normal mode analysis in MSC-PATRAN using MSC- NASTRAN.my 1st elastic frequency(7th mode in free body analysis) and 1st elastic frequency(1st mode with constrained model) is not equal.
7th mode freq with free body analysis =1847hz.
1st mode freq with constrained model analysis =647 hz.
what is the error/problem.
hw to correct it.
Thanks in advance.

 

[rb1957]

is your constrained model over constrained ? do the constraints react only the 6 rigid body motions ? have you fixed a bunch of points, or though carefully about the constraints >

Quando Omni Flunkus Moritati

 

[Anshu8]

ok i'll check it out by removing constraints and reapplying them.thanks