Units inside CalculiX

About the development of the FEM module/workbench.

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bernd
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Units inside CalculiX

Post by bernd »

It is about units in FemWB.

1. Units in FreeCAD.
Since the FemWB will be upraded to the FreeCAD unit system one day we'll be independet from a special unit inside FemWB.

1. Units in CalculiX.
Currently the origin units of FreeCAD are used in CalculiX. see

- 8th line on http://freecadweb.org/wiki/index.php?ti ... ysis#Units
- viewtopic.php?f=18&t=7172&start=10#p65484
- https://github.com/FreeCAD/FreeCAD_sf_m ... nalysis.py )

Length, Time, Mass, Force, Pressure, Velocity, Density, Energy, Gravity
mm, s, kg, mN, kPa, mm/s, M kg/l, micro J, 9.81e+3

and thus
Young's Modulus and stress --> mN/mm2 = kPa


This was decided at a time when there was no unit system in FreeCAD. Just would like to ask for the opinion of others in this regard. From a advanced user point of the FemWB (the one who may be changes the CalculiX Inputfile for own needs) it would be much easier if the units in the CalculiX file would be a widely used unit system like N and mm instead of mN and mm. In my opinion it makes also sense to use in CalculiX a unit system which is widely used in CalculiX to eliminate any numerical instability or numerical inaccuracy.
Does it make sense using the 10th line of http://freecadweb.org/wiki/index.php?ti ... ysis#Units in CalculiX input file?

Length, Time, Mass, Force, Pressure, Velocity, Density, Energy, Gravity
mm, s, Mg (ton), N, MPa, mm/s, Mg/mm3, mJ, 9.81e+3,

and thus
Young's Modulus and stress --> N/mm2 = MPa

which is widely used in CalculiX. See table 1 in CalculiX manual http://web.mit.edu/calculix_v2.7/Calcul ... node4.html

bernd
Last edited by bernd on Fri Mar 13, 2015 12:30 pm, edited 1 time in total.
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shoogen
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Re: Units inside CalculiX

Post by shoogen »

+1 :D
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bernd
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Re: Units inside CalculiX

Post by bernd »

pull request is out there: viewtopic.php?f=17&t=10129
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Re: Units inside CalculiX

Post by saso »

This is good, thanks for pushing the FEM WB forward!
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