[general] about the future of the FEM workbench

About the development of the FEM module/workbench.

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NewJoker
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Re: [general] about the future of the FEM workbench

Post by NewJoker »

jnxd wrote: Thu Aug 18, 2022 4:40 pm Apparently it uses some magic behind the scenes even with linear elements (something related to making them higher order p-type and giving solutions at mesh vertices).
Abaqus uses a standard approach of outputting displacements at nodes and stresses at integration (Gauss) points but it offers many special element types like continuum shell, axisymmetric with asymmetric deformation, cylindrical and even special elements for gaskets and chains used to attach pipelines to the seabed. What you are talking about seems somewhat related to so-called modified elements which may offer an additional performance boost.

The power of Abaqus lies mainly in its capabilities for nonlinear analyses, especially when it comes to contact (including general contact algorithm) but also material nonlinearity.

jnxd wrote: Thu Aug 18, 2022 4:40 pm There are also the UMAT (user defined material) routines that researchers have developed over, sometimes, decades. Translating them to any other software will take up significant effort. I suppose if someone wants to use them in an open source alternative calculix is the way to go. Disclaimer: not sure if it is actually supported, but at the very least it is a reason why Abaqus continues to be important.
Yes, subroutines and scripting are powerful features in Abaqus. CalculiX also offers some subroutines including UMAT, DLOAD and a few more.

jnxd wrote: Thu Aug 18, 2022 4:40 pm Lastly, at least in research fields I have seen people directly working with INP files rather than through GUI. Sometimes even the official release of Abaqus does not have the options desired in their GUI (I suppose its implemented later). I believe there was an option to add a few lines to input file first before sending it off to the solver.
Right, Abaqus has very intuitive keyword syntax and one of the main advantages of CalculiX is that it uses almost the same syntax. It's really straightforward and allows for an easy definition of various analysis features. As you said, some functionalities of Abaqus are not supported in GUI (and it usually stays like that) and have to be defined with keywords. Abaqus offers Keyword Editor that can be used to add keywords without the need to export the .inp file and edit it in a text editor.

GUI of Abaqus can be considered outdated (it doesn't have a modern look) but it's extremely convenient once you gain some experience.
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Re: [general] about the future of the FEM workbench

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Just a reminder to this thread participants, per uwe
uwestoehr wrote: Wed Aug 17, 2022 6:10 pm This thread is not meant to discuss what solver is the best.
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NewJoker
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Re: [general] about the future of the FEM workbench

Post by NewJoker »

Kunda1 wrote: Thu Aug 18, 2022 6:00 pm Just a reminder to this thread participants, per uwe
uwestoehr wrote: Wed Aug 17, 2022 6:10 pm This thread is not meant to discuss what solver is the best.
Discussions about each solver's usability, strengths and weaknesses might be relevant to the topic of the development of the FEM module. Uwe wanted to focus on his idea of a loop between design and analyses but there are also other important aspects to consider when talking about the future of this workbench.
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Re: [general] about the future of the FEM workbench

Post by HarryvL »

thschrader wrote: Thu Aug 18, 2022 4:26 pm You can run 2 simulations:
1. Nonlinear stress/strain with given load
2. Design restistance analysis
With option 2 the solver triggers up the load until the max accepted plastic strain is reached, here 5%.
The check for your second approach is very easy to add to FreeCAD as a post-processing step for CCX. See my post here: https://forum.freecadweb.org/viewtopic.php?f=18&t=35893

All the information for plotting the position on the user-defined stress-strain curve is also readily available in FC.

The effort to get this working is minimal.
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Re: [general] about the future of the FEM workbench

Post by Jee-Bee »

I was looking into the current solvers (mainly the two calculix and Elmer).
The standard calculix is easy. If i open the solver i got a few settings where i choose the analysis i want to do.
Screenshot 2022-08-19 at 20.28.41.png
Screenshot 2022-08-19 at 20.28.41.png (73.54 KiB) Viewed 1578 times
Then the non standard Calculix solver and the Elmer solver i can't set the analysis i want. But i can create equations / analysis types.
Since i never used the FEM module this way i'm a bit curious. I have created a solver with two equations
Screenshot 2022-08-19 at 20.23.40.png
Screenshot 2022-08-19 at 20.23.40.png (26.2 KiB) Viewed 1578 times
Does it work this way? and if yes is the forces as result of heat / heat changes the input for elasticity? or are this two separate calculations...

An extra question regarding Calulix with this method... is Frequency / and buckling not supported?
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Re: [general] about the future of the FEM workbench

Post by fandaL »

Jee-Bee wrote: Fri Aug 19, 2022 6:39 pm An extra question regarding Calulix with this method... is Frequency / and buckling not supported?
When you click on the solver object, property view gives you plenty of options for Calculix (both ccx solver objects should support same options), including analysis type.
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Re: [general] about the future of the FEM workbench

Post by johnwang »

Jee-Bee wrote: Fri Aug 19, 2022 6:39 pm Does it work this way? and if yes is the forces as result of heat / heat changes the input for elasticity? or are this two separate calculations...
I think so. The two are coupled. A feed b, then b feed a and repeat.

I guess fc first has caculix, then Elmer. Then need to rethink the code, so there is the testing caculix. So the two solvers could behave similar under one code frame.
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Re: [general] about the future of the FEM workbench

Post by uwestoehr »

Jee-Bee wrote: Fri Aug 19, 2022 6:39 pm Then the non standard Calculix solver and the Elmer solver i can't set the analysis i want.
Please check the docs:
https://wiki.freecadweb.org/FEM_SolverElmer

How to perform a buckling analysis, see the Elasticity equation Wiki page:
https://wiki.freecadweb.org/FEM_EquationElasticity
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Re: [general] about the future of the FEM workbench

Post by S-Y.Chen »

NewJoker wrote: Wed Aug 17, 2022 9:36 am
uwestoehr wrote: Tue Aug 16, 2022 11:26 pm Since in different threads we speak about the general things, I open this thread.
Maybe a development roadmap wiki page for the FEM workbench would be a good idea, TechDraw and Path workbenches have something like that.

uwestoehr wrote: Tue Aug 16, 2022 11:26 pm For case 1., there is already ElmerGui available. it offers nice visualization, is feature complete (all kinds of physics covered), has a good documentation and an active community. So for this application case FreeCAD is not necessary, would just reinvent the wheel and never be as good feature-complete as ElmerGUI.
Yes, Elmer has a GUI but I wouldn't say that FreeCAD shouldn't try to offer similar capabilities. Its workflow is totally different and FreeCAD offers more than ElmerGUI in some ways. For example, postprocessing features derived from ParaView and integration with CAD modeling.

Your focus is on Elmer but maybe the development of FEM module should focus more on CalculiX which is still the main and default solver, likely the most general and versatile for most applications (Elmer doesn't even have well-established contact if I'm correct). CalculiX doesn't have its own fully complete and user-friendly GUI so I think that the way to go is to support more features of CalculiX. I would vote for those first:
1. Rigid body constraint
2. Support for multiple meshes
3. Beams with arbitrary cross-section
4. Simple creation of node and element sets
5. Advanced material models (orthotropy, hyperelasticity, creep and so on)

Let's keep in mind that FEM modules in CAD software are not meant for analysts but for designers and should be kept relatively simple. FreeCAD's users are usually even less advanced since there are many hobbyists without experience in other CAD/CAM/CAE software. But nowadays even professional FEM software meant for specialists tries to be as user-friendly as possible. After all, there's no reason to make our job harder with an unintuitive interface just because we are FEM experts. And that's the problem with almost all open-source FEA codes - some don't have a GUI at all while others (like Code_Aster) have extremely unintuitive GUI. FreeCAD's FEM module is one of a very few exceptions and I would stick to that.

I agree that the possibility to easily run multiple analyses with different settings in FreeCAD would be great. Currently, it's even necessary to manually delete all the results before rerunning the analysis because postprocessing objects are not updated. Maybe we should start by changing that. A way to run parametric studies (like parametric sweep in Comsol) would be great. The rest could require scripting.

uwestoehr wrote: Tue Aug 16, 2022 11:26 pm For example my project was to calculate the deformation and stress of a squeezed rubber tube. I got nice-looking results but reality is different than what I got. And stupid me, for elastic materials one needs another equation from Elmer that is not yet supported by FreeCAD.
Do you mean hyperelasticity ? It's usually necessary for analyses involving rubber. CalculiX offers multiple models for hyperelastic materials, Elmer has only the Neo-Hookean model, from what I know.
I will vote for this (again) :
2. Support for multiple meshes

Once this is done, a lot of things can be done and can be added on the script level. I really recommand getting this done first.
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Re: [general] about the future of the FEM workbench

Post by bernd »

NewJoker wrote: Wed Aug 17, 2022 10:08 am
Jee-Bee wrote: Wed Aug 17, 2022 10:01 am Part of the workflow can be / should be sequental calculations (what we don't have now (at least not in Calculix)) for example: static and frequency.
CalculiX allows multistep analyses like frequency or buckling with preload and you are right that having them supported in FreeCAD would be great. But implementation of such a feature could require some significant changes in the current handling of ccx analyses.
exactly. It was in my mind a few times over the last few years to support multiple steps, but every time realised it needs these significant changes and gave up. To support just one step has made things very easy in implementing.
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