I started learning FEM by this video. However, my model doesn't seem to be analyzed correctly:
I would expect the upper "bar" has some stress (some red areas), just like in "Abs displacement" mode:
However, in "Abs displacement" mode I can see no stress on the "lower bar".
I don't know what "Abs displacement" or "Tresca" means (I'm following the French Cafe technique) but I can't obtain a result that is similar to my expectation (which is something like combination of the "Abs displacement" and "Tresca" modes).
Is it my lack of knowledge or are there some missing/wrong steps here?
[SOLVED] FEM output does not seem to be correct (beginner question)
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[SOLVED] FEM output does not seem to be correct (beginner question)
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Last edited by ceremcem on Fri Aug 02, 2019 11:42 am, edited 2 times in total.
Assembly 3 notes: https://github.com/ceremcem/freecad-notes
Re: FEM output does not seem to be correct (beginner question)
Looks good to me. Tested on my setup - visually the same results.
My tutorial - FEM in 60 seconds - https://peertube.social/videos/watch/d7 ... 91a69a1446
My tutorial - FEM in 60 seconds - https://peertube.social/videos/watch/d7 ... 91a69a1446
Re: FEM output does not seem to be correct (beginner question)
looks got to me too ...
Re: FEM output does not seem to be correct (beginner question)
what you see is correct. The options show what data of the result is used to color the part. "Abs displacement" means it uses the displacement vector, the absolute value of it. Hence sqrt(dx^2+dy^2+dz^2) where dx and dy is the displacement in x and y direction. So you see no color at the bottom truss as it is closer to the contraint and hence moves way less than the top truss.
So your pictire has nothing to do with the stress in the part. To see the stress you should use "Von Mises stress".
So your pictire has nothing to do with the stress in the part. To see the stress you should use "Von Mises stress".
Re: FEM output does not seem to be correct (beginner question)
There is a strip of yellow at the top and bottom of the beam if you take a close look. Red is the top of the scale - try to play with a simple beam and different support and different forces - you'll get a feeling quickly what to expect and where in terms of stress and displacement.
Re: FEM output does not seem to be correct (beginner question)
If you all say so, then it's probably my misinterpretation.
Well, now I started to get the idea. Moreover I couldn't notice any difference between "Von Mises Stress" and "Max Shear Stress" by the naked eyes. However, taking two screenshots and subtracting one from the other pixel by pixel outputs the slight difference:
I'm going to stick with "Von Mises Stress" till I understand what "Tresca" means.
Well, now I started to get the idea. Moreover I couldn't notice any difference between "Von Mises Stress" and "Max Shear Stress" by the naked eyes. However, taking two screenshots and subtracting one from the other pixel by pixel outputs the slight difference:
I'm going to stick with "Von Mises Stress" till I understand what "Tresca" means.
Is there a way to customize the scale where I would like to highlight any area whose stress (or displacement) exceeds a specific limit? (Or better, I'd like to make whole model highly transparent and make the high stress areas more opaque which would provide an X-ray like vision at any angle)
I got what you suggested. Here is a screenshot that looks like just I would expected:try to play with a simple beam and different support and different forces - you'll get a feeling quickly what to expect and where in terms of stress and displacement.
Assembly 3 notes: https://github.com/ceremcem/freecad-notes
Re: [SOLVED] FEM output does not seem to be correct (beginner question)
"Von Mises Stress" and "Max Shear Stress" are two approaches to answer same question: how to get equivalent stress (one simple number instead of normal and shear stresses in all directions). So they give similar value.
Try to play with Pipeline postprocessing, e.g. with “Scalar Clip Filter”. Some hints according to this are on the end of this tutorial https://www.freecadweb.org/wiki/FEM_She ... site_Blockceremcem wrote: ↑Fri Aug 02, 2019 11:41 am Is there a way to customize the scale where I would like to highlight any area whose stress (or displacement) exceeds a specific limit? (Or better, I'd like to make whole model highly transparent and make the high stress areas more opaque which would provide an X-ray like vision at any angle)
Re: FEM output does not seem to be correct (beginner question)
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Re: [SOLVED] FEM output does not seem to be correct (beginner question)
I appreciate all of you for your helps and tips. I could barely understand the difference between Von Mises Stress and Tresca. I suppose choosing either one won't make much difference for me at this stage.
I finally managed to follow the tutorial. Here is my result. Thanks!fandaL wrote: ↑Sat Aug 03, 2019 11:55 am Try to play with Pipeline postprocessing, e.g. with “Scalar Clip Filter”. Some hints according to this are on the end of this tutorial https://www.freecadweb.org/wiki/FEM_She ... site_Block
Assembly 3 notes: https://github.com/ceremcem/freecad-notes