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Non-symmetric results for symmetric model and load?

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Non-symmetric results for symmetric model and load?

Why is it that displacement for a cone is not rotational symmetric for an internal pressure?

A sample model is attached (Creo 3.0) I've brought it back to the bare minimum. 1/4 cone, symmetry, default mesh etc.

It doesn't help if you refine to enormous amounts of elements, Large deformationm analysis makes it slightly better, but it is never right?

 

Why is that? it should not happen.

How do we solve this?

 

Extra: I've added a full 360 degree version in Creo2.0 format

resudisp.PNG

 

 

creo2version.PNGsimplecone.PNG

65 REPLIES 65

Re: Non-symmetric results for symmetric model and load?

I'm not able to open your model as I'm on Creo2, but when creating a similar model i find:

* when constraining the symmetry planes with theta=0 the results look strange

* when constraining the symmetry planes with a carthesian csys the results look okay

Not sure if that is the case in your model, but worth a try?

Re: Non-symmetric results for symmetric model and load?

Hi Patrick

Thanks for your efforts. There is also a Creo 2.0 model in the attachments. That one is 360 degrees, no use of symmetry BC's, severe non-symmetry in the results though. (see the 360 deg picture). we're studying out-of-roundness for a valve, so this result is thoroughly unacceptable (and totally unexpected). Would appreciate your solution

Erik

Re: Non-symmetric results for symmetric model and load?

Okay disregard my previous message. I was looking at stress, and that looked okay, but displacements were unsymmetric.

The results in your model are unexpected indeed. You should send this to support, they should work with this to improve the software.

A workaround I found is to set the max element size on the pressurised surface to 10mm.

But a simple model like this should not have such bad results using standard settings!

Re: Non-symmetric results for symmetric model and load?

I get symmetric results. I tried both planar constraints on symmetry surfaces, aswell as constraining "theta"-direction in a cylindrical csys. Default mesh + SPA gives a small deviaiton from perfectly symmetric results, mapped mesh (as in the picture) gives perfectly symmetric results.

/Mats L/

See attached model (Creo2)

Capture.JPG

Re: Non-symmetric results for symmetric model and load?

Hi Mats

Very good of you to join!

your model looks like it shows much better results, however: If I plot radial displacements of the top-edge, I get the following

Mats_unround_200MPa.PNG

It's only .5% unroundnes. But should be zero.

if I alter the diameter of your cone from 200 to half that, the calculated unroundness increases to 2.8%

Mats_unround_200MPa_smaller.PNG

I've attached your model again, with added cylindrical coordinate system and in the smaller diameter.

Please dig further. We need to solve this.

A colleague found the same effect in Wildfire 2.0, so it's been in there for quite some time.

Re: Non-symmetric results for symmetric model and load?

Indeed strange results... File an SPR-report at PTC support... Are there any PTC developers following this forum?

Re: Non-symmetric results for symmetric model and load?

Correct!

A circular symmetric object under internal (constant) pressure must show circular symmetry in displacements. in short: radial displacement needs to be a flat curve.

I've shown examples where the deviation is close to 10%. Totally unacceptable.

Re: Non-symmetric results for symmetric model and load?

Hi Steven

All sounds nice, but don't forget, Mat's model is a very finely hex mapped-mesh example.

The default model I used in my original post has a default mesh (typically what you would normally do and what should suffice if you "only" want to know the displacements).

The error in my original post (no tricks, just try the model in "conecreo2p0") the error is a staggering 65%.

horrible.PNG

It is now PTC support call nr. 12421022.

Let's see what can be done

Erik

Re: Non-symmetric results for symmetric model and load?

Yes the difference is small, with a symmetrical mesh, but it is still mathematically incorrect. It should decrease when you increase convergence more, but it doesn't. For some businesses, small differences are very important, so we do at least need an explanation for this behavior...