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Hello,
I'm facing the following problem:
A beam is sliding on a fixed part without friction. The reaction forces should be the same on the moving nodes as on the fixed ones. But I get a difference:
- Y reaction force on the fixed nodes: 46.3 N
- Y reaction force on the moving nodes: 44.3 N
- normal contact force RN: 44.3 N
Where do these 2N on the fixed nodes come from? I guess I'm missing something very simple but I cannot find what.
Thank you for your help,
Konyaro
Last edited by konyaro (2018-11-25 06:54:14)
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The comm and med files.
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Compared with another software, the reaction force of the fixed nodes is similar (cf. attached picture).
Nevertheless I still can't figure out why the reaction force of the moving nodes is not the same in the CA simulation...
Last edited by konyaro (2017-02-21 16:18:11)
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Exactly, I expect to get the same reaction forces on both sides.
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there are warnings about the time step (=increment ?) which is not adapted
during the calculation.
The results do not seem correct as the X component oscillates from one step to another, like numerical stick-slip
Last edited by bbd (2017-02-21 16:22:47)
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Thank you for your advice. I tried with a very small time step but the results are still the same. The X force is strange indeed, it should be around 0 as there is no friction and almost no deformation of the contact surface.
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maybe, but as I already use the ORIE_PEAU_2D I can't see what else I could change...
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I don't think it's due to the mesh. Even with a crazy refined quadratic mesh the reaction forces do not change.
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Not exactly, but close, as depicted on the attached plot.
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I removed line 103 :
# DEFORMATION='GROT_GDEP',
and it works. I mean the balance of forces is correct.
then I read http://www.code-aster.org/forum2/viewtopic.php?id=18029 and it was written that for non linear calculations (either material and geometry) you must use 3D shells.
Hope it helps.
Last edited by bbd (2017-02-23 19:54:46)
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Thank you for your help bbd,
You are right, the reaction forces are not correct with C_PLAN elements and GROT_GDEP deformations ! I made a simple comparison on a beam in flexure:
1) C_PLAN and PETIT deformations: forces OK
2) C_PLAN and GROT_GDEP deformations: forces KO
3) 3D and PETIT deformations: forces OK
4) 3D and GROT_GDEP deformations: forces OK
That is not a good news as most of my calculations are C_PLAN/GROT_GDEP... I found nothing in the documentation that mentions this limitation.
Last edited by konyaro (2017-02-24 23:12:33)
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I believe it is written in U2.02.01 section 2.3.2
but I agree the way it is presented is not clear.
The 'available' behaviors and laws are listed in a table but it's worth telling a few words about the risks of using this combination of asumptions (elements and calculation type) as nothing prevents us using such combinations.
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According to U4.51.11 section 4.5.2 it should work...
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Oui, je vais le faire.
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I never closed this topic but is is solved.
There is a mandatory workaround since 2017: the following error occurs when using GROT_GDEP with C_PLAN and elastic material :
! On ne peut pas utiliser les contraintes planes en élasticité avec une !
! déformation de type GROT_GDEP. !
! Conseil: utilisez une loi élastoplastique sur laquelle vous aurez mis une !
! limite d'élasticité très grande. !
The trick is to define a non linear material with a very high yield strength, for instance :
mat01 = DEFI_MATERIAU(ECRO_LINE=_F(D_SIGM_EPSI=1.0,
SY=1e+15),
ELAS=_F(E=200000.0,
NU=0.3))
and to use the following relation in COMPORTEMENT :
RELATION='VMIS_ISOT_LINE'
Last edited by konyaro (2018-11-25 12:49:53)
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