Nastran Normal Modes Analysis - getting the same modes?

[nd308]

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?

 

[corus]

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.

 

[GregLocock]

At a guess you did smething wrong with the added point masses. Look at the deck to find out what.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[btrueblood]

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

 

[nd308]

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.