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## #1 2021-04-08 13:24:55

ManiacBen
Member
Registered: 2019-08-22
Posts: 8

### Inducing a moment into 3D object

Hi,

I´m trying to induce a moment into a 3D object by attaching a rigid, discrete object to it. Unfortunately I´m getting a strange error message which I don´t understand.

Is this a possible way to do this or is it doomed from the start?

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## #2 2021-04-08 17:09:24

mf
Member
Registered: 2019-06-18
Posts: 197

### Re: Inducing a moment into 3D object

Hello,

of course, this is possible. There are many ways to do this. Although I do not now the source of your error, let me try to understand what you did:

1) In your mesh, your shaft and your box are in the same file. But they are not connected by elements. So, if you apply a DRX (rotation around X by angle in radians) to your shaft, it will just turn by itself (or rather the 2 0D elements will rotate). You'll need a LIAISON of some kind between your shaft and your box.
2) Also, the 'object' you want to rotate/turn (your shaft or a single 0D element would also be sufficient) needs to have rotational degrees of freedom, your 'shaft' is correct in that regard. But you assigned DIS_TR to 'shaft', so there are 2 separate DIS_TR on each of the 2 nodes, they are connected by an edge element (cannot transmit torque, also it does not have a thicknes like a beam). You could introduce a beam element there on the line (POUTRE), or do a LIAISON_SOLIDE (then you wouldn't need a material for it, it would be an infinitely stiff connection) between the two nodes of the shaft. As I said, there are many ways. Although it would be pointless to connect them with infinite stiffness, because then a single 0D-element would also be enough.
3) The 0D-elements need a AFFE_CARA_ELEM to function.

I have an example attached, that does similar with a single 0D-element. It connects to a face of a cube with a LIAISON. The 0D-element (K_TR_D_N: 'stiffness_translation_rotation_.....' although all stiffnesses are set to 0) is rotated by DRX=30° and due to the stiff connection to the surface, this surface is also rotated around X by 30° (right hand rule applies). So it is not a torque per se, just a rotation by an angle.

Maybe it helps, also there are many examples in the documentation and in this forum,

Mario.

Last edited by mf (2021-04-08 17:20:07)

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## #3 2021-04-09 08:46:22

ManiacBen
Member
Registered: 2019-08-22
Posts: 8

### Re: Inducing a moment into 3D object

Hi Mario,

I was not aware, that the edge in a discrete element is treated as non existent. I replaced the rod with a point on the surface.

In my original comm file I already had a LIAISON and I kept it after the modification, but the run still seems to crash while processing it:

connect = AFFE_CHAR_MECA (
MODELE = model,
LIAISON_ELEM = _F (
GROUP_MA_1 = 'con_c',
GROUP_MA_2 = 'torque',
OPTION = '2D_POU',
),
);

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