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#1 2017-02-10 17:21:31

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

[SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

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)


Attachments:
ReactionForces.png, Size: 90.36 KiB, Downloads: 410

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#2 2017-02-10 17:22:37

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

The comm and med files.


Attachments:
BeamWithContact.zip, Size: 74.2 KiB, Downloads: 356

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#3 2017-02-20 17:24:14

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

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)


Attachments:
Force_comparaison.png, Size: 131.36 KiB, Downloads: 412

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#4 2017-02-21 15:46:40

bbd
Member
From: Vandoeuvre, F
Registered: 2016-09-30
Posts: 189
Website

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

there is something I don't understand.
Your second calculation seems relevant.
Then the conclusion is the code_aster simulation is not correct, isn't it ?

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#5 2017-02-21 16:17:48

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

Exactly, I expect to get the same reaction forces on both sides.


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#6 2017-02-21 16:21:38

bbd
Member
From: Vandoeuvre, F
Registered: 2016-09-30
Posts: 189
Website

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

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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#7 2017-02-21 16:54:20

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

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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#8 2017-02-21 17:33:17

bbd
Member
From: Vandoeuvre, F
Registered: 2016-09-30
Posts: 189
Website

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

newbie question. Isn't there a pb of orientation of edges ?

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#9 2017-02-22 08:20:32

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

maybe, but as I already use the ORIE_PEAU_2D I can't see what else I could change...


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#10 2017-02-22 08:32:11

bbd
Member
From: Vandoeuvre, F
Registered: 2016-09-30
Posts: 189
Website

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

the mesh.Refine locally

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#11 2017-02-22 15:52:04

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

I don't think it's due to the mesh. Even with a crazy refined quadratic mesh the reaction forces do not change.


Attachments:
MeshAffineQuad.PNG, Size: 83.84 KiB, Downloads: 301

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#12 2017-02-22 17:50:17

bbd
Member
From: Vandoeuvre, F
Registered: 2016-09-30
Posts: 189
Website

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

exactly same values ?

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#13 2017-02-23 07:40:46

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

Not exactly, but close, as depicted on the attached plot.


Attachments:
Forces.png, Size: 145.89 KiB, Downloads: 267

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#14 2017-02-23 13:55:20

bbd
Member
From: Vandoeuvre, F
Registered: 2016-09-30
Posts: 189
Website

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

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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#15 2017-02-24 23:08:45

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

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)


Attachments:
Image_2D_3D_Forces.png, Size: 240.05 KiB, Downloads: 298

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#16 2017-02-25 08:03:57

bbd
Member
From: Vandoeuvre, F
Registered: 2016-09-30
Posts: 189
Website

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

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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#17 2017-02-25 15:02:59

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

According to U4.51.11 section 4.5.2 it should work...


Attachments:
U4_51_11_P59.png, Size: 39.99 KiB, Downloads: 280

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#18 2017-03-07 15:57:17

bbd
Member
From: Vandoeuvre, F
Registered: 2016-09-30
Posts: 189
Website

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

il faudrait peut-être signaler le bug ?

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#19 2017-03-08 06:32:27

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

Oui, je vais le faire.


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#20 2018-11-25 06:53:55

konyaro
Member
From: Genève
Registered: 2016-04-02
Posts: 262

Re: [SOLVED] Reaction forces not equal with C_PLAN/GROT_GDEP

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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