"Model is inssufficiently constrained" error. Any ideas?

[pshepherdson]

Hi All,

Well, am new to Creo Simulate, and am trying to get results of a real world part (not a sample from a book)

This is a 3-part assembly, all sheet metal. I've run about 20+ Analisys, and get fairly different results each time. The issues I'm now running into is this:

I've got the the parts constrained & modeled. When I run my analysys, I get the error "Model is insufficiently constranted for the analisys", and I have 4 tets that don't seem to play nice. Now, this is about the 5th times I get the message, and the last two are as pictured (the previous two were in the upper part of the 2nd part, so there seems to be some inconsistency..) I have the model set to '3D' and 'contact' interface. (If I have it set to 'bonded, it works, but two of my 'edge to surface' constrains are lost, and I get results, although predictable of a non contrained connection, is still not what I expect / hope for)

Any ideas on how to fix this?

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[346gnu]

Paul,

for each part, pick a surface and add a constraint to fully constrain then re-run.

There should be nothing unconstrained,

Sequentially remove each constraint until you locate a culprit.

Then post more info

My suspicion is that you ought to be setting the default interface to bonded and then putting contact in those connections which are an exception to this general rule.

bfn

[pshepherdson]

I'm assuming in assembly mode. All parts are "fully constrined". But I will remove them all & reconstrain the parts.

(I'm sooo frustrated right now, I feel like i'm just taking pot-shots to get .. anything!!)

edit:

just reconstrained teh three parts. All have 3 constrained and Creo reports "fully constrined" on each part. 2 of the three are face-face constraints, 'coincidence' teh bottom one is face-face, face-face, face-edge, becasue it's an angular face, and only contacts the 3rd part on the edge. (sheet emtal bend / wall) Wondering it that's a pit-fall..

[pshepherdson]

OK, reconstrained a few times, removeing & adding as I need / as you've suggested.. I've changed the model to "bonded, and re-run. All good, except the 'contact areas removed' message.

I've added an interface between the faces, where the face-edge constrains are. again,. they get ignored, and the model perfoms as original; deforms thru itself.

(And, i might add, I got 300inches deformation orignally, now I'm gettin close to 1001 inches on a 2 inch part! a singularity is there, but that's my next headache..)

So, in my mind, regardless of if I add additional contact interfaces, tehy all get ignored. just reported as a yellow dot..

[sdensberger]

It sounds like your contact interface is allowing rigid body motion. Can you post the model? If not, then what you can do is run a modal analysis with rigid body mode search on to locate the exact part(s) that are moving. After that, you can apply several weak ground springs to prevent the rigid body motion.

[pshepherdson]

KK, runnign the ridgid modal analisys.. 4th time!

Uhm, not too sure what I'm trying to find. thsi is a foot on a leg, with a (not modeled) caster on the end. I'm expectign it to swing & twirl about..

[sdensberger]

I'm expectign it to swing & twirl about..

Keep in mind that you can't have object undergoing rigid body motion...

[pshepherdson]

OK, I've changed those contact areas to 'rigid links' And I seem to be back to where i was a few days ago when I first started (when I was playing with this model as 'shell elements' / shell pairs.')

Now, I still have that singularity(s) to remove..

"Paul's frustration, the sequel!"

thanks guys!!

[pshepherdson]

Hi All,

Well, I am new ot Creo & the whole PTC world. Lets chalk this one up to a major dose of frustration (clouded judgement) and the PTC interface. While I thought I had changed a few setting, and removed a few, the settings didn't change, and I just added on top of growing list of constrains, loads, materials, shells, links, etc..

With a clear head, I tried it all yesterday and got 'realistic / better' results..

As for the regions part, I've copied (backup) the assembly to a personal directiory, and went form there, as to not damage any of our real parts. I would have thought that these three parts, in a separate directory, in a different 'working directory' wouldn't be affected. A collegue also thinks there are someconfig settigns tha need to be tweaked as per the other post of a similiar nature.

[TomD.inPDX]

Funny, I just now went through this. I appeared it just didn't like the complexity of the geometry but that wasn't it. For some reason, I had to change the fixed constraints to a moving constraint assigning a small X displacement and I gained a lot more freedom.

[pshepherdson]

Hi Steven,

Sorry, not really allowed to upload our models. As mentioned, i'm, new to Creo & new to the whole FEA world. The others I work witrh heve their own habits & work around. I have 20+ years of Acad, Mech Desktop & Inventor.. i feel like I have to learn Chinese or something!! (Generally jsut feeling pretty stupid!) Always a new challenge, Always a new error mesage, Always a new setting that should hve been chnaged / set / thought of..

Singularities & Re-entrant corners are the next big hurdle.. And how models should be set up for an FEM study..