Changing Self weight magnitude

[filippoinno1994]

Hi, I'm new, I hope I'm in the correct section..

I'm new to Freecad and I was trying to understand the FEM workbench futures.
I'm studying some static equivalent load applied to quite-complex shapes.
So I tried to use the Self-weight load changing the magnitude of the gravity but it doesn't work, I get the same result with like 1g or 10g.
So I tried it with a "beam" 1x0.01x0.01m and I got the same result.
I checked .inp file and also I tried to change the numbers directly from it but nothing changed.





OS: macOS 10.15
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16146 (Git)
Build type: Release
Branch: (HEAD detached at 0.18.4)
Hash: 980bf9060e28555fecd9e3462f68ca74007b70f8
Python version: 3.6.7
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: Italian/Italy (it_IT)

[fandaL]

Hello,
it might be a bit confusing because FreeCAD gui enables only to set direction vector (default is 0,0,-1), but it does not influence acceleration magnitude. By now, magnitude must be changed manually in *.inp file, e.g. for the Earth acceleration, there is by default 9810 mm/s^2,

Code: Select all

*DLOAD
Eall,GRAV,9810,0.0,0.0,-1.0

but if you would like to calculate with a Moon gravity acceleration 1625 mm/s^2 it would be

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*DLOAD
Eall,GRAV,1625,0.0,0.0,-1.0

[filippoinno1994]

Thanks a lot, you made my day

[filippoinno1994]

What if I want to combine 2 different accelerations for example 1000 on y and 5000 on z?
Do I need to compute like to put sqrt(1000^2 * 5000^2), that is 5099, as magnitude and then use:

Code: Select all

 
 *DLOAD
Eall,GRAV,5099,0.0,0.02,0.98
 

where 0.02 and 0.98 comes from the projection?

Can I combine two different loads like this:

Code: Select all

*DLOAD
Eall,GRAV,1000,0.0,1.0,0.0
*DLOAD
Eall,GRAV,5000,0.0,0.0,1.0

[bernd]

use version 0.19 there it might be possible. If not change value in file https://github.com/FreeCAD/FreeCAD/blob ... nstants.py in your FreeCAD mod directory.

For FEM you should use 0.19 FreeCAD version.

[fandaL]

It seems that superposition works. You can prescribe more accelerations, they will be combined. Direction vector is normalized by CalculiX, so you should obtain same results for these inputs

Code: Select all

*DLOAD
Eall,GRAV,1000,0.0,1.0,0.0
*DLOAD
Eall,GRAV,5000,0.0,0.0,1.0

Code: Select all

*DLOAD
Eall,GRAV,5099.0195,0.0,1.0,5.0

Code: Select all

*DLOAD
Eall,GRAV,5099.0195,0.0,10.0,50.0

where total magnitude is (5000**2+1000**2)**0.5 = 5099.0195

[bernd]

Try to input 2.0 in self weight object. It may use 2x9.810 but I am not sure. I am not on a computer on the weekend.

[fandaL]

Try to input 2.0 in self weight object. It may use 2x9.810 but I am not sure. I am not on a computer on the weekend.

Input fields in FreeCAD have effect on direction vector

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*DLOAD
Eall,GRAV,9820,0.0,0.0,-1.0

using 2 times value

Code: Select all

*DLOAD
Eall,GRAV,9820,0.0,0.0,-2.0

but it is the same for CalculiX, since it normalizes direction vector. Magnitude is still taken as 9820mm/s^2, which is hardcoded in FreeCAD.