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#1 2018-02-09 16:51:22

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,616

[SOLVED]trouble with the use of LIAISON_GROUP

hello

i have trouble with the use of LIAISON_GROUP on 3D or plate models
the following code abstract produces good results

liaigrv = AFFE_CHAR_MECA(
    LIAISON_GROUP=(
        _F(
            COEF_IMPO=0.0,
            COEF_MULT_1=(1.0,),COEF_MULT_2=(-1.0,),
            DDL_1=('DX',),DDL_2=('DX',),
            GROUP_MA_1=('liaisg', ),GROUP_MA_2=('liaisd', ),
        ),
    	_F(
            COEF_IMPO=0.0,
            COEF_MULT_1=(1.0,),COEF_MULT_2=(-1.0,),
            DDL_1=('DY',),DDL_2=('DY',),
            GROUP_MA_1=('liaisg', ),GROUP_MA_2=('liaisd', ),
        ),
		_F(
            COEF_IMPO=0.0,
            COEF_MULT_1=(1.0,),COEF_MULT_2=(-1.0,),
            DDL_1=('DZ',),DDL_2=('DZ',),
            GROUP_MA_1=('liaisg', ),GROUP_MA_2=('liaisd', ),
        ),
    ),
    MODELE=modelv,
    INFO=2,
);

while this later one produces wrong results

liaigrv2 = AFFE_CHAR_MECA(
    LIAISON_GROUP=(
        _F(
            COEF_IMPO=0.0,
            COEF_MULT_1=(1.0, 1.0, 1.0,),
            COEF_MULT_2=(-1.0, -1.0, -1.0,),
            DDL_1=('DX', 'DY', 'DZ',),
            DDL_2=('DX', 'DY', 'DZ',),
            GROUP_MA_1=('liaisg', ),
            GROUP_MA_2=('liaisd', ),
        ),
    ),
    MODELE=modelv,
    INFO=2,
);

this with a 3D model
for plates one has to add the lines for DRX DRY DRZ
is this normal a behavior?
if yes the doc U4.44.01 is not very clear about this
and i failed to find a test case using LIAISON_GROUP on a 3D or plate model

files for an example are available

jean pierre aubry

Last edited by jeanpierreaubry (2018-02-12 11:19:22)

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#2 2018-02-12 10:30:00

Thomas DE SOZA
Guru
From: EDF
Registered: 2007-11-23
Posts: 3,066

Re: [SOLVED]trouble with the use of LIAISON_GROUP

Hello Jean-Pierre,

Basically the first example will yield for every node of "liaisg" corresponding to one of "liaisd" :

  • DX from the node of liaisg = DX from the node of liaisd

  • DY from the node of liaisg = DY from the node of liaisd

  • DZ from the node of liaisg = DZ from the node of liaisd

The second example however will apply the following conditions:
(DX+DY+DZ) from the node of liaisg = (DX+DY+DZ) from the node of liaisd

This behaviour is what is expected from LIAISON_GROUP.

I agree that the manual may be improved. Still the following remark is quite enlightening to me:

Remarque :
Le nombre total de relations imposées par une occurrence ne dépend pas du nombre
d'arguments de DDL_1 ou de DDL_2, qui servent uniquement à enrichir la relation.

We'll gladly improve the documentation following comments in this thread.

TdS

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#3 2018-02-12 11:18:49

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,616

Re: [SOLVED]trouble with the use of LIAISON_GROUP

hello Thomas

thanks for the answer
it is clear know

i expected example 2 to behave just like example 1
example 1 is what i wanted as a behavior

jean pierre aubry

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#4 2018-02-12 11:43:06

jeanpierreaubry
Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 3,616

Re: [SOLVED]trouble with the use of LIAISON_GROUP

hello Thomas

i marked solved a bit too quickly
what happens with example 2 in case of plates if i add DRX DRY DRZ
rotation cannot be summed up as simply as the tranlation vector

jean pierre aubry

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#5 2018-02-12 12:58:11

Thomas DE SOZA
Guru
From: EDF
Registered: 2007-11-23
Posts: 3,066

Re: [SOLVED]trouble with the use of LIAISON_GROUP

Hello Jean-Pierre,

jeanpierreaubry wrote:

what happens with example 2 in case of plates if i add DRX DRY DRZ
rotation cannot be summed up as simply as the tranlation vector

If one add DRX DRY DRZ to the second example then the linear relation that will be added is essentially :

(DX+DY+DZ+DRX+DRY+DRZ) from the node of liaisg = (DX+DY+DZ+DRX+DRY+DRZ) from the node of liaisd

As you point out, this wouldn't have any physical meaning as summing translation and rotation is silly. But a linear relation doesn't bother about that, it's just an algebraical equation.

In my opinion, this has to be separated from the LIAISON_GROUP feature. In code_aster, there are several features that, when used poorly, may lead to non meaningful results. Still, this is not a reason to remove them or alert about their usage.

TdS

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