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Stress analysis convergence

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Message 1 of 7
olekristen9
979 Views, 6 Replies

Stress analysis convergence

I am trying learn how to use the stress analysis environment properly, but this convergence has stumped me. I'm not sure what to set the Maximum Number of h Refinements and Stop Criteria to. It seems that if i increase h refinements and decrease stop criteria, the stress goes up indefinitely. And on top of that, the max stress or convergence doesnt change when reduce either settings back to default or even further...

 

So in short, is it correct practice to slowly increase h refinements until the convergence goes below 10% and satisfied with the results I then get?

Also, is 10% convergence high? Does lower convergence mean more accurate results?

 

Thanks in advance.

6 REPLIES 6
Message 2 of 7
admaiora
in reply to: olekristen9

Hi Olek,Inventor let you increase the quality of your results with the refinement of the finite elements.

 

These refinements are type P and type H.

 

The P increase the polynomial degree, the number of nodes, the H reduce the size of the finite elements

 

You can control the H parameter, the P will be automatically controlled by Inventor, which will refine and increase finite elements in the critical areas.

 

The convergence can be manual or automatic.

 

It depens on the setting in "Convergence Setting"

 

Here you can find some additional infos and advises.

 

http://help.autodesk.com/view/INVNTOR/2014/ENU/?guid=GUID-E039A3C5-8266-470C-98E6-78CD3090F36F

 

http://help.autodesk.com/view/INVNTOR/2014/ENU/?guid=GUID-645C5159-32CA-4331-9C70-ED0AD99204C3

 

http://help.autodesk.com/view/INVNTOR/2014/ENU/?guid=GUID-B42DFA44-2B7D-4DAB-936F-B3837C863031

 

Hope that it can helps you.

Admaiora
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Message 3 of 7
olekristen9
in reply to: admaiora

Mkay, in the video it seems to work perfectly, but for me it doesn't. To help explain I will use an example from this book: http://www.amazon.co.uk/Running-Autodesk-Inventor-Professional-2013/dp/1475129351

 

You can click the image of the book open a preview, the example is on chapter 1 page 5.

The stress is calculated manually to be at max 296 MPa. I have done exatly as the book says but am getting slightly different results, this is not the problem though. If i run the simulation with everything on default, I get 278 MPa, which is not too far from what I want. But when I increase Maximum h Refinements and decrease Stop Criteria, the stress increases to no end.

 

As you can see in the pictures, the stress goes past 296 MPa and the convergence even goes from 5,552% to 10,7% with one one more h refinement!!!

The results get even more absurd if i keep increasing max h refinements...

I could only attach 3 pictures but the results after are even more excessive...

 

What is happening?

Message 4 of 7
admaiora
in reply to: olekristen9

The teorical calculation are corrects.

My inventor results (Inventor 2013) are quite similar

 

311 Mpa simple Stress Analysis

288 Mpa Shell Analysis

296 Mpa Beam Analysis

 

 

Happening this:  when you have stress singularities (and there are in this), increasing the refinement will increase the value of this stress singularities.

So, not always increase the refinements and set to max relative setting would be the right choice, it's needed to pay attention when stress singularities occurs.

Admaiora
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Message 5 of 7
olekristen9
in reply to: admaiora

Ah, of course. But now I have a new questions, how do I preform Shell and Beam analysis in Inventor?

Message 6 of 7
admaiora
in reply to: olekristen9

http://help.autodesk.com/view/INVNTOR/2014/ENU/?guid=GUID-3512208A-D415-4FD2-B195-F010F1CA2DD0

 

http://help.autodesk.com/view/INVNTOR/2014/ENU/?guid=GUID-B7B52B89-5521-480F-BDC9-C85A900F186A

 

Hope that it can helps you

Admaiora
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Message 7 of 7
olekristen9
in reply to: admaiora

Awesome, thanks for the help 🙂

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