3 Node Beam Elements not yet supported

[bernd]

finished the new beam section task panel ui. See https://github.com/berndhahnebach/FreeC ... meshregion Would be cool if you could give it a try. One thing still to discuss. I used diameter in task panel. From user point like it much more to input a diameter of a pipe instead of a radius. How about others? If we use diameter the property names needs to be adapted too.

[KgoaOT]

I guess it makes sense from a users point of view. So i'm happy with the changes.

Just need to swap the Diameter and Thickness inputfield boxes on the Pipe Beam section widget?

[bernd]

I guess it makes sense from a users point of view. So i'm happy with the changes.

Just need to swap the Diameter and Thickness inputfield boxes on the Pipe Beam section widget?

give it a try:
https://github.com/berndhahnebach/FreeC ... meshregion

[makkemal]

I did some test and is working nicely but i found a interesting thing. when using linear element and pipe section you get the following CALCULIX error.

Code: Select all

*ERROR reading *BEAM GENERAL SECTION:
*BEAM GENERAL SECTION can
only be used for B32R elements.
Element 1 is not a B32R element.

Using Linear elements with beams is a bit pointless since you are usually interested in bending stress which is only accurate in Higher order element.
Should we not make 3 node element the default mesh for 1D meshes ?

[bernd]

Should we not make 3 node element the default mesh for 1D meshes ?

The 3 node element is default for 1D meshes. See file attached.

OS: Windows 7
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.9232 (Git)
Build type: Release
Branch: master
Hash: 411e30bffd82f4a8944e35a68a7f11ae71165d01
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.0.0

standard-FEMmesh-edges.FCStd

(4.25 KiB) Downloaded 42 times

[KgoaOT]

@Bernd,

I am trying to implement a Fluid section for hydraulic network analysis. It works similarly as the Beam section but it uses D type elements.
The description for these elements can be found here: http://feacluster.com/CalculiX/ccx_2.10 ... ode57.html
So basically these elements are 3 noded 1D elements that have the same numbering as the B32 elements.

From here https://github.com/FreeCAD/FreeCAD/blob ... .cpp#L1091
i see that the only kind of 3 noded 1D element that is currently supported is the B32.

Is there a way to perhaps extend this to allow for B32R (for pipe beam sections) and D (for fluid sections) elements?

[bernd]

From here https://github.com/FreeCAD/FreeCAD/blob ... .cpp#L1091
i see that the only kind of 3 noded 1D element that is currently supported is the B32.

Is there a way to perhaps extend this to allow for B32R (for pipe beam sections) and D (for fluid sections) elements?

You found the culprit yourself. This method needs to be changed. I have a few ideas in mind how to make the Abaqus writer more flexible. It should support either writing nodes or elements or both, writing other element types (for example B32R or ohters like S8R), or other than the hard coded node set and element set names. At least it would be great to write different mesh dimensions for example volume meshes combined with shell meshes or shell meshes combined with edge meshes (latest is heavily used in structural engineering). But all this involves nearly a complete rewrite of this method which is a bit out of my scope because of my limited knowledge of C++

We may could start just by using the element type as an parameter value.

bernd

[KgoaOT]

We may could start just by using the element type as an parameter value.

bernd

Yes another situation where this is necessary is when we want to have more than 1 element type in analysis, say beam elements and fluid network elements in which we solve for flow in the hydraulic analysis and map the solution to the beam section for a static analysis. So currently the way it is done it seems that it doesn't even allow more than 1 element type.

[makkemal]

The specific type of element is very dependant on solver for Instance B32R and D will only be in Calculix. ELMER will have a different element formulation but they will all use 3 node beams element. So the based element Object should be a 3 noded beam. The specific element type is tne later defined depending on the solver used.

[bernd]

The specific type of element is very dependant on solver for Instance B32R and D will only be in Calculix. ELMER will have a different element formulation but they will all use 3 node beams element. So the based element Object should be a 3 noded beam. The specific element type is tne later defined depending on the solver used.

Thats exact the problem of the Abaquswriter. There are some element types in Abaqus format wich are represented by a 3 node edge but the abaqus writer does write a B32 for a 3 node edge. This should be adjustable. Same for the S4 4-node shell element. The B32 is just a C++ string hardcoded in the Abaqus writer method.