nice picture in FEM module wiki, but it is wrong IMHO

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bernd
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nice picture in FEM module wiki, but it is wrong IMHO

Postby bernd » Wed Apr 17, 2019 2:31 pm

Someone has added a nice picture to our FEM wiki ... https://www.freecadweb.org/wiki/FEM_Module#Workflow but IMHO it is wrong! It really makes sense to create the constraints BEFORE the mesh not after the mesh.

bernd

vocx wrote: ping
Jee-Bee
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby Jee-Bee » Wed Apr 17, 2019 4:59 pm

I think the one who have made the picture didn't use FEM much :lol:

Of course constraints can be made after creating a mesh... But it is more work.
But also the Input don't have to be a solid. 2D shape is also possible! Only combination of 2D and 3D isn't possible
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby vocx » Wed Apr 17, 2019 5:09 pm

bernd wrote:
Wed Apr 17, 2019 2:31 pm
Someone has added a nice picture to our FEM wiki ... https://www.freecadweb.org/wiki/FEM_Module#Workflow but IMHO it is wrong! It really makes sense to create the constraints BEFORE the mesh not after the mesh.
The order doesn't really matter. You can do it before or after setting up the mesh. In the end, to run an analysis you need both, the mesh and the setup.

I made the picture to follow the procedure described in the text, which shows that order.
The steps to carry out a finite element analysis are:
  1. Preprocessing: setting up the analysis problem.
    1. Modeling the geometry: creating the geometry with FreeCAD, or importing it from a different application.
    2. Creating an analysis.
      1. Creating a finite element mesh for the geometrical model, or importing it from a different application.
      2. Adding simulation constraints such as loads and fixed supports to the model.
      3. Adding a material to the analysis model.
That was written by you, I think. I just formatted it. But it's free documentation! We can change the order if you want, no problem!

I also wonder why you add the material at the end. I would add it at the begining, but as I said, the order doesn't really matter, it's just personal preference.
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby vocx » Wed Apr 17, 2019 5:14 pm

Jee-Bee wrote:
Wed Apr 17, 2019 4:59 pm
I think the one who have made the picture didn't use FEM much :lol:

Of course constraints can be made after creating a mesh... But it is more work.
But also the Input don't have to be a solid. 2D shape is also possible! Only combination of 2D and 3D isn't possible
The image is meant as a visual aid for those starting to use the workbench, to understand the general process. Of course, if you go into the details, you have many exceptions and steps that you have to follow to perform a good analysis. But that's including too much complexity in what is supposed to be a simple overview. You can edit the image as well.
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby bernd » Wed Apr 17, 2019 5:31 pm

I really like the picture!

It is the choice of every one when does he do the mesh, but in a work flow where the contraints are applied to the geomezry and not to the mesh the contraints may influence the mesh and thus it makes sense to make the mesh at last. IMHO we should change this and put the medh at last. When the material is applied does not matter AFAIR it could be done before constraints or after contraints but again it makes sense before the mesh because they may influence the mesh too.

Ahh sure as input any shape cold be used 1D 2D or 3D depending of the kind of analysis, but standard might be 3D in most cases.
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby Jee-Bee » Wed Apr 17, 2019 7:02 pm

vocx wrote:
Wed Apr 17, 2019 5:14 pm
The image is meant as a visual aid for those starting to use the workbench, to understand the general process. Of course, if you go into the details, you have many exceptions and steps that you have to follow to perform a good analysis.
True.
I think you add to much complexity allready. I think a general workflow would more look like these:
Screen Shot 2019-04-17 at 21.02.01.png
Screen Shot 2019-04-17 at 21.02.01.png (24.74 KiB) Viewed 163 times
I just created fast but i think you get my idea
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby bernd » Wed Apr 17, 2019 7:13 pm

still I would move the mesh between constraints/material and solver.
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby Jee-Bee » Wed Apr 17, 2019 7:23 pm

My personal workflow is materials first than constraint and final the mesh.
The reason i put mesh on the bottom is that it interacts with external software. When the arraows are added it gives more unneeded clutter.
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby -alex- » Wed Apr 17, 2019 8:19 pm

Personnaly I do the mesh first, because to mesh a model can be somtimes tricky if the geometry is complexe or if there is a problem on the 3D model (small holes not removed, small offsets not cleaned, etc..).
So, IMHO the early you mesh the model the less you waste your time after.
If you can't success to mesh your model you have to modify the 3d model, in order to clean it or to simplify it. If you already have constrained it, your constraints or loads will be broken because of toponaming problem.
So, IMHO, mesh first if possible. I am wrong?
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Re: nice picture in FEM module wiki, but it is wrong IMHO

Postby bernd » Wed Apr 17, 2019 8:27 pm

I must admit, Surely this has some points too. For the geometry I have I never did this, but my geometry usually does not have geometrical errors and is rather simple for our meshers.

We might should the user let decide ... and put them all 3 as Jee-Bee had it on the same step.