Pro/MECHANICA Thermal Unconstrained DOF 1

gkatsanis · Sep 21, 2009

I’m trying to use the thermal portion of Pro/Mechanica for the first time. As a first model to get me going I have mocked up a simple cube with a surface heat load on one side, a fixed temperature on the opposite side, and convection on the other four walls. I keep getting the following error:

“The design study terminated abnormally.

The model is insufficiently constrained for the analysis.
Please review the element connections, properties, and
constraints.

You may be able to locate your model's problem area by
using Mechanica database ID numbers. ID numbers can be
queried using the "Entity ID" macro in Pro/MECHANICA
Standalone. The following ID numbers are associated
with this error:

3292

The unconstrained degree of freedom can be seen by running
a constrained Modal Analysis with rigid mode search.
Animating the rigid modes will display the unconstrained
degrees of freedom. If the error still occurs, then the
issue could be caused by material properties or unattached
spring/mass idealizations.”

I do not have any structural boundary conditions in my model – is that my problem? If so, why would you need such constraints for a thermal only analysis (I am not doing coupled thermal/structural)? I am baffled with this – any help is much appreciated.

gkatsanis · Sep 21, 2009

Update: I have tried adding a structural constraint (I fixed one of the surfaces in all rotations and translations. When I run the Modal Analysis in the Structural portion of Mechanica the model returns no rigid body modes.

I also tried using the Entity ID macro in the Pro/MECHANICA standalone as stated above and the query for the noted ID above simple returns: “The entity with ID 3292 is a Pro Address”.

This is very strange … please help.

brep · Sep 22, 2009

What sort of analysis are you running? Stead-state thermal? Transient thermal? Adding structural constraints and performing a modal analysis would be of no help troubleshooting if this is the case...

I just tried an example with your stated thermal loads and BC's, and as expected it worked just fine.

gkatsanis · Sep 22, 2009

I am running steady state thermal analysis. I agree that structural BC’s should not have any impact for pure thermal analysis.

I do not understand what I am doing wrong. I even tried a cube with one surface featuring a fixed temp, the opposite side at a different fixed temp, and all other sides unconstrained (adiabatic). I still got similar “insufficiently constrained” errors.

I am thinking that I am missing something basic here, as I get the error regardless of what I try to do. Each run I set boundary conditions, select a material, and assign the material to the part. I am not manually meshing the model; instead I am allowing AutoGEM to automatically create my elements during the analysis run. This is driving me crazy.

brep · Sep 22, 2009

Hmmmm, perhaps you could post the example prt file here?

seymours2571 · Sep 23, 2009

Is it possible that your thermal conductivity value has not been set?

Just a thought.

Stephen Seymour, PE
Seymour Engineering & Consulting Group

http://www.seymourecg.com

gkatsanis · Sep 23, 2009

Well – I knew that it would be something simple! Turns out that I never set a thermal conductivity. The library of materials that we use have assigned structural parameters, but the thermal parameters are not filled in – I never thought to check this!

Thanks a bunch for your help brep and seymours2571!!!

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Pro/MECHANICA Thermal Unconstrained DOF 1

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