## pyBar

A forum dedicated to the Draft, Arch and BIM workbenches development.
yorik
Posts: 12146
Joined: Tue Feb 17, 2009 9:16 pm
Location: Brussels, Belgium
Contact:

### Re: pyBar

Excellent! Thanks! I'll have a look at hwat OCC gives us, but this gives us already a good start.
bernd
Posts: 11096
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: pyBar

Wow looks great. Since I'm on the out of home for a few days more comments in this regard later on ... just regarding the quadratic moments (moment of inertia, https://en.wikipedia.org/wiki/Moment_of_inertia)
yorik wrote:...
A little question that annoys me, the pybar files needs the quadratic moments from the sections of the structural members. Calculating that is not hard for rectangular sections, but we should have something that works for any kind of section. Anyone of you engineering gurus has an idea on the subject?
try one of these:

Code: Select all

``````import Part
box = Part.makeBox(1,10,5)
Part.show(box)

box.StaticMoments
box.MatrixOfInertia``````
Walgri
Posts: 32
Joined: Sat May 09, 2015 10:16 pm

### Re: pyBar

Hi, I'm a bit rusty at this, but the real difficulty is to determine the torsional moment of inertia for non simple sections.
Maybe the FEM module could be used to numerically evaluate it.

Anyway I'm interested on the work beeing done here, at some point I would like to integrate Frame3dd.sf.net in freecad, unfortunately it may be in a not so close future.

Ciao
looo
Posts: 3498
Joined: Mon Nov 11, 2013 5:29 pm

### Re: pyBar

box.MatrixOfInertia
haha it would have been so easy.
Hi, I'm a bit rusty at this, but the real difficulty is to determine the torsional moment of inertia for non simple sections.
this should be the z value in the 3. row in MatrixOfInertia. Also the polar Moment could be calculated with the same method I have posted before, using gauss to reduce the area integral to the boundary. But as r^2 = x^2 +y^2 the polar Moment becomes simple the sum of Ix + Iy. https://en.wikipedia.org/wiki/Second_mo ... is_theorem
Walgri
Posts: 32
Joined: Sat May 09, 2015 10:16 pm

### Re: pyBar

looo
Posts: 3498
Joined: Mon Nov 11, 2013 5:29 pm

### Re: pyBar

I see, this task is a bit more difficult
Maybe the FEM module could be used to numerically evaluate it.
You are right, maybe the calculix heat-equation could be (ab)used for this task.
bernd
Posts: 11096
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: pyBar

yorik wrote:After a long time, some updates on this subject!

yorik wrote:... I'm trying to convince him to make pybar translatable...
That would sure be needed!
yorik wrote:... I'm planning to:
- Add a couple of tools to edit the structural nodes of the Arch structures, so one can make them meet
Would be very useful for Beam FEM in FemModul as well.
yorik wrote: After that we could look at how we could define loads on the Arch structures (that could be used in FEM too), but that's another story...
...
Definition of constraints of the structural elements to each other (joints) and the constraints of the structure (supports) is needed too. All this could be used later in Fem too (Fem Constraints could be generated out of the Definitions in Arch). But as you wrote all this is another story only worth to go if first steps are sucessful.
yorik wrote:Yes, we could upgrade the system... It could even be pretty simple, use the same Nodes property, since we only need 2 vectors to define a plane. Then, depending on the role of the element, we show a line/polyline or a plane.
How about the face axis? They would be very useful for Shell FEM in FemModule as well.

For Beam and Shell FEM see viewtopic.php?f=18&t=11196#p92590
yorik
Posts: 12146
Joined: Tue Feb 17, 2009 9:16 pm
Location: Brussels, Belgium
Contact:

### Re: pyBar

Yes I noticed the 1D object in FEM, but didn't look any further... I really need to start playing with it.
Very cool how all these areas converge, sooner or later they will blend
bernd
Posts: 11096
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

### Re: pyBar

I would like trying to calculate the same structure you calculated in pypar in FemWB. In FEMWB we will not get the wonderful bending moment and force diagramms of pybar but the deformation will be comparable.

To mesh the structure gmsh needs a shape which will be exported to step. See viewtopic.php?f=22&t=11182#p92187 Is there any possibility to get a shape (edges) out of the structural ArchAxis?
yorik
``Part.makePolygon(myObj.Nodes)``