FreeCAD as pre-post processor for MBDyn

About the development of the FEM module/workbench.

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josegegas
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Re: FreeCAD as pre-post processor for MBDyn

Post by josegegas »

T-Garnier wrote: Thu Dec 02, 2021 11:47 pm About the App::PropertyLinkSubList, did you check those links:
https://forum.freecadweb.org/viewtopic.php?t=37288
https://wiki.freecadweb.org/LinkSubList
Yes, this helped!

Also, this helped me a lot:

https://forum.freecadweb.org/viewtopic.php?f=22&t=64180

I have changed the code for the revolute pin and hinge joints, to include App::PropertyLinkSubList, and these are now fully parametric. The user can now do basically whatever he wants with the assembly, without breaking the MBD model:

phpBB [video]
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Pauvres_honteux
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Re: FreeCAD as pre-post processor for MBDyn

Post by Pauvres_honteux »

josegegas wrote: Sat Dec 04, 2021 5:10 pm The new version works with links to parts, so that the independent parts are in separate files.
Judging from your linked Youtube video, I'd say you've extracted/copied the solids out of the files and placed/pasted them solids in a new file together with other pasted solids.

So my question remains: Any chance some future version will work with files? That is, moving the whole file with all its content with respect to other files (with all their content).
josegegas
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Re: FreeCAD as pre-post processor for MBDyn

Post by josegegas »

[/quote]

Judging from your linked Youtube video, I'd say you've extracted/copied the solids out of the files and placed/pasted them solids in a new file together with other pasted solids.

[/quote]

I did not copy the solids, I just use links to the solids.

[/quote]

So my question remains: Any chance some future version will work with files? That is, moving the whole file with all its content with respect to other files (with all their content).

[/quote]

Sorry, I don´t understand your question. What do you mean by "moving the whole file with all its content with respect to other files". Do you mean moving the independent parts within the original files? Or, moving the whole files from where to where? Not sure what you mean...
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Pauvres_honteux
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Re: FreeCAD as pre-post processor for MBDyn

Post by Pauvres_honteux »

josegegas wrote: Sat Dec 04, 2021 5:10 pm ... links to parts ...
josegegas wrote: Tue Dec 14, 2021 11:34 pm I did not copy the Solids, I just use links to the Solids
Okey, I think we have a descrepancy in terminology definition here.
Seen from my point of view a:
- Part is a file describing a physical object you can put your hands on.
- Body is a container of solid objects.
- Solid is a three demensional representation of real world object.
- Surface, and its subobject face, is a 2- or 3-D mathematical representation of e.g. a piece of a Solid.
- Link, in this context, is a "copy of a Solid with link". This linked Solid's definition can not be altered. However, it can be further worked upon with e.g. booleans.

I would say my interpretation still holds, i.e. you've copied the solids from one file into another file.

Regarding files; a real and proper assembly consist of an assembly-file containing links to other files. Those other files are loaded into the scene graph (what you see on the screen) in such a way that you can see and move them around with respect to each other at the same time in the same view port. N.b. the files and everything in them files.

That's how I imagine things. Do you think we are on the same page now, so to speak?
chrisb
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Re: FreeCAD as pre-post processor for MBDyn

Post by chrisb »

Pauvres_honteux wrote: Thu Dec 16, 2021 5:50 am Seen from my point of view a:
- Part is a file describing a physical object you can put your hands on.
- Body is a container of solid objects.
- Solid is a three demensional representation of real world object.
- Surface, and its subobject face, is a 2- or 3-D mathematical representation of e.g. a piece of a Solid.
- Link, in this context, is a "copy of a Solid with link". This linked Solid's definition can not be altered. However, it can be further worked upon with e.g. booleans.
These are not the notions used in FreeCAD:

- a Std_Part is a collection of arbitrary objects, especially solids, which can be moved together. It can be used for assemblies.
- a Body is a sequence of features forming one single solid.
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Pauvres_honteux
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Re: FreeCAD as pre-post processor for MBDyn

Post by Pauvres_honteux »

chrisb wrote: Thu Dec 16, 2021 6:01 am - a Std_Part is a collection of arbitrary objects, especially solids, which can be moved together. It can be used for assemblies.
- a Body is a sequence of features forming one single solid.
Which are all about to change...
Dassault, we're coming for you! :twisted:
JamesLiu
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Re: FreeCAD as pre-post processor for MBDyn

Post by JamesLiu »

[/quote]

Hi. Sure. I´ve been working the past few months on a new version of the workbench, fixing many problems the one in Gitlab has. Mainly the new version makes use of FreeCAD units and quantities, while the previous one treats numbers simply as floats... I will create a new repository and upload the new version, along with this and other examples, soon...
[/quote]

Any timing plan on the new release? Can't wait to try it.
josegegas
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Re: FreeCAD as pre-post processor for MBDyn

Post by josegegas »

JamesLiu wrote: Thu Dec 16, 2021 10:16 am

Hi. Sure. I´ve been working the past few months on a new version of the workbench, fixing many problems the one in Gitlab has. Mainly the new version makes use of FreeCAD units and quantities, while the previous one treats numbers simply as floats... I will create a new repository and upload the new version, along with this and other examples, soon...
[/quote]

Any timing plan on the new release? Can't wait to try it.
[/quote]

I´m setting-up a bunch of examples to upload with the release, so that people can have a look at how they are put together. Hopefully I´ll finish this year :D
josegegas
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Re: FreeCAD as pre-post processor for MBDyn

Post by josegegas »

Some time ago I was able to simulate the inverse kinematics for a SCARA robot assembly:

phpBB [video]


The idea is to allow the user convert a set of edges from a part into a scalar function, containing either Cartesian or polar coordinates of any number of points evenly distributed along the edges. The user can then use these scalar functions for any purpose in the MBD model.

I have struggled for months to perform the same inverse kinematics simulation, but for a 6 axis robotic arm. The initial assembly constantly failed in this case. Today I found the problem, and it is embarrassingly simple: my robot model did not have 6 axis! It had 5, and so of course it was impossible to solve the model. I clanged the CAD to include one joint more and it worked like a charm:

phpBB [video]


All this time I was thinking that there was an error in my code, and I never counted the joints....
ChainSalad
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Re: FreeCAD as pre-post processor for MBDyn

Post by ChainSalad »

I'm impressed at the progress achieved!
I saw the videos "elastic contact" and "Bouncing Brick". While it seems like in "elastic contact" the contact force is a structural z-force where the modifier probably depends on the distance between the plane and the ball center, I'm curious how this was done in the case of the bouncing brick.
It would be great if it would be possible to define groups of surfaces which can collide, with elastic contact force direction, perhaps even friction being calculated automatically.
I believe this would be more important to users like me (mechanical engineer) than integrated FEM (where once you have joint forces you can calculate things per body, one by one)
Is this possible yet?
I regularly use the 2D simulation tool "Algodoo", which has a similar feature with added friction and bounce energy dissipation values. Very useful!
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