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Home > Forums > Structural Engineers > Activities > Finite Element Analysis engineering Forum

Nastran Normal Modes Analysis - getting the same modes?

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nd308 (Aeronautics)

14 Mar 12 13:48

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 (Mechanical)

14 Mar 12 15:12

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 (Automotive)

14 Mar 12 18:04

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

Cheers

Greg Locock

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btrueblood (Mechanical)

15 Mar 12 11:04

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

nd308 (Aeronautics)

15 Mar 12 11:11

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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