Node mass in ABAQUS

[tuss]

Hi,
When I am trying to run a model in ABAQUS Explicit, I get the following error message:

"Node 50000 has zero mass but not all spatial degrees of freedom are fully constrained at this node. Please assign a physically reasonable mass to this node."

But how do I do that? I haven't been able to find how to assign a mass to a node!?

 

[brad]

*ELEMENT, TYPE=MASS, ELSET= . ..
*MASS, ELSET= . . .

(for rotational, see *ROTARY INERTIA)

 

[GregLocock]

But it looks like a modelling problem. Why do you have an unconstrained node that is not in an element?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[tuss]

I have a "dummy" node just to apply the prescribed displacement at. This node is connected to one of the boundaries by a set of equations. If I just apply the prescribed displacement directly on the whole boundary, I will not obtain correct boundary conditions.

 

[GregLocock]

So it sounds like it is under-constrained. At the same time I know how hard it can be to correctly restrain dummy nodes without artificially stiffneing the structure. In my most recent project I have ended up by modelling the test fixtures and the measurement points properly to prevent that happening! Sure it was a bit of extra agony I didn't need, but the correlation improved beyond my expectations.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.