MSC Nastran CELAS1 strain energy

[antti]

Hey Folks,

I have a simple linear static model with a small number of CELAS1 and forces. It's simple enough to solve by hand. The results for external work, displacements, SPCs, element forces and strains is all fine, but the grid force balance and element strain energies are not. I have grid force balances that are not in equilibrium and strain energy not equal to external work!! There are no DMIG entries and cannot think of any other way I am screwing it up. Surely there isn't anything this simple fundemantally wrong with the code?? Has anybody ever had similar problems.

 

[Spirit]

One first check you could make is verifying that:
a)All GRIDs involved in CELAS Elements are coincident;
b)All GRIDs involved in CELAS Elements have the same displacement coordinate system.

Try to do a free-free normal modes analysis of your model, or if you are using NASTRAN 2001 include the following line in your NASTRAN file:

GROUNDCHECK(SET=ALL,DATAREC=YES,RTHRESH=99.9)=YES

just before the Case Control Deck.

Cheers,

Spirit




'Ability is 10% inspiration and 90% perspiration.'

 

[NicolasJobert]

antti,

I had the same problem with a 2 dof system (CMASS + CELAS2), running a static analysis.

All data but the Element Strain Energies (ESE) are correct.

This 'ESE' bug disappears when running a modal or transient analysis, so I guess that my FE-model is correct.

Guess what ? Never trust a FE code.

Cheers

 

[antti]

Thanks Nicolas,

I never really found out why this was happening. In modal analysis the model is fine, and I have had no problems with ESE in subsequent larger models.

Cheers,
Antti.