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Nastran Normal Modes Analysis - getting the same modes?

Nastran Normal Modes Analysis - getting the same modes?

Nastran Normal Modes Analysis - getting the same modes?

(OP)
I am doing a simple normal modes analysis on a high AR wing which has been meshed and verified. All I want to do is compared the normal modes of the clean wing to a wing with added point masses (added through CONM2 elements).

For some inexplicable reason I am getting exactly the sames modes for the wing with point masses as the one without point masses?

I must have missed something utterly basic, does anyone know what it could be?

RE: Nastran Normal Modes Analysis - getting the same modes?

At a guess I would imagine it would depend on which part showed which modes. Overall the increase in mass should lower the frequency, but if it's a panel, for example, that has no additional mass then that mode won't change.

RE: Nastran Normal Modes Analysis - getting the same modes?

You should come up with a term to describe that process, Greg.  Maybe "de-bugging"?   

RE: Nastran Normal Modes Analysis - getting the same modes?

(OP)
Thanks for all the help chaps, it works now, turns out there was a pretty major problem with the QUAD element definitions in the entire model.

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