ccxInputWriter vs. Faces
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ccxInputWriter vs. Faces
Hello,
ccxInputWriter seems a little bit confused about faces and their normals.
This is a solid cube under pressure from outside. Deflection as expected. Same box meshed from shells with unexpected result. Of course with files: Perhaps its gone after ulrich1a has blown up the whole thing https://forum.freecadweb.org/viewtopic. ... 20#p169893
done with:
OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.10802 (Git)
Build type: Release
Branch: master
Hash: 10ce910c03347a90712327a7cc7be2bcdee13afc
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.0.0
ccxInputWriter seems a little bit confused about faces and their normals.
This is a solid cube under pressure from outside. Deflection as expected. Same box meshed from shells with unexpected result. Of course with files: Perhaps its gone after ulrich1a has blown up the whole thing https://forum.freecadweb.org/viewtopic. ... 20#p169893
done with:
OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.10802 (Git)
Build type: Release
Branch: master
Hash: 10ce910c03347a90712327a7cc7be2bcdee13afc
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.0.0
Re: ccxInputWriter vs. Faces
Yes this is clearly a bug in ccxInputWriter. The input file has the following lines for the pressure load:UR_ wrote:Same box meshed from shells with unexpected result.
Code: Select all
***********************************************************
** Element + CalculiX face + load in [MPa]
** written by write_constraints_pressure function
** FemConstraintPressure
*DLOAD
** FemConstraintPressure: face load
489,P1,100.0
489,P5,100.0
489,P4,100.0
489,P3,100.0
489,P2,100.0
490,P1,100.0
...
But as we can read here about facial distributed loading on shells: https://www.feacluster.com/CalculiX/ccx ... de174.html
This means: the numbers P1 to P5 are wrong but not used. So there is no error from calculix. Calculix uses instead the normal of that face, which seems to have in this case the other direction.For shell elements no face number is needed since there is only one kind of loading: pressure in the direction of the normal on the shell.
A bug report is needed.
Ulrich
Re: ccxInputWriter vs. Faces
thanks for reporting! I'm not surprised this does not work. I have never explicit tested this kind of load during shell implementations. But for sure this should work. If you make a bug report you could assign it to me!
Re: ccxInputWriter vs. Faces
thanks for reporting! I'm not surprised this does not work. I have never explicit tested this kind of load during shell implementations. But for sure this should work. If you make a bug report you could assign it to me!
Re: ccxInputWriter vs. Faces
ulrich this is similar to the problem you described with shell and fixed constraints. The constraints are defined on a face but the input file depends on the kind of elements used. The lines are different for shell and solid meshes. Solve this on either shell or solid mesh is possible, but on mixed meshes we really are in trouble ...
I'm starting to understand your concerns ...
I'm starting to understand your concerns ...
Re: ccxInputWriter vs. Faces
I answered here: https://forum.freecadweb.org/viewtopic. ... 24#p170124bernd wrote:I'm starting to understand your concerns ...
Ulrich
Re: ccxInputWriter vs. Faces
Just had a look at this. The pressure constraint has never been working on shell meshes. I'm surprised ccx gives some results ?!?bernd wrote:thanks for reporting! I'm not surprised this does not work. I have never explicit tested this kind of load during shell implementations. But for sure this should work. If you make a bug report you could assign it to me!
For reference ...
- https://github.com/FreeCAD/FreeCAD/blob ... #L885-L900
- https://github.com/FreeCAD/FreeCAD/blob ... #L156-L178
- https://github.com/FreeCAD/FreeCAD/blob ... #L539-L546
Re: ccxInputWriter vs. Faces
The link does not work for me ...ulrich1a wrote:But as we can read here about facial distributed loading on shells: https://www.feacluster.com/CalculiX/ccx ... de174.html
Re: ccxInputWriter vs. Faces
See http://www.dhondt.de/ccx_2.12.pdf
Page 282
cit:
cit:
Page 282
cit:
Page 348For shell elements no face number is needed since there is only one kind of
loading: pressure in the direction of the normal on the shell.
Applying a pressure to a face for which a pressure was specified in a previous
step replaces this pressure.
cit:
For shell elements no face number is needed since there is only one kind of
loading: pressure in the direction of the normal on the shell.
The surface loading is entered as a uniform pressure with distributed load
type label Px where x is the number of the face. Thus, for pressure loading the
magnitude of the load is positive, for tension loading it is negative. For nonuniform pressure the label takes the form PxNUy, and the user subroutine dload.f
must be provided.
Re: ccxInputWriter vs. Faces
UR_ has answered already. The link worked last week for me. Here is an alternative: http://web.mit.edu/calculix_v2.7/Calcul ... de147.html
Ulrich
At least FreeCAD writes something into the Pressure constraint. And Calculix does not use the wrong references to the face numbers of the shell elements in case of shells, so it has no reason to complain.bernd wrote:Just had a look at this. The pressure constraint has never been working on shell meshes. I'm surprised ccx gives some results ?!?
Ulrich