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#1 2017-05-19 12:31:03

Johannes_ACKVA
Member
From: Ingenieurbüro für Mechanik, DE
Registered: 2009-11-04
Posts: 588
Website

How to stop a geometric nonlinear analysis when instability occurs?

hello,

can somebody please explain how a geometric nonlinear analysis (STAT_NON_LINE(....COMPORTEMENT=_F(RELATION='ELAS', DEFORMATION='GROT_GDEP'..)  can be stopped using a list

list=DEFI_LIST_INST(DEFI_LIST=_F(LIST_INST = list0,),
                    ECHEC=_F(EVENEMENT='INSTABILITE',
                             #~ ACTION='CONTINUE',
                             ACTION='ARRET',      # --->  means that STAT_NON_LINE will stop in case of instab.
                             ),);

I wonder if I do not understand the correct setup, but I suppose there is a bug in Code-Aster.

I have added a zip-file with a case (modified testcase ssll105d). The .mess-file in included twice:

- ssll105d.mess (from an analysis with ACTION='CONTINUE')
- ssll105d_with-ARRET-in-case-of-instabity.mess (from an analysis with ACTION='ARRET', so to stop)

From a geometric linear analysis DEFORMATION='PETIT') it is known that buckling must appear at about time 1.1
(This can very easily be seen from the original testcase ssll105d)

But when using DEFORMATION='GROT_GDEP' Code-Aster  shows wrongly after each time step (already from the fist at time=0.05) the message

<Évènement> Instabilité détectée

If I analyse using the "do-not-stop-list"

list=DEFI_LIST_INST(DEFI_LIST=_F(LIST_INST = list0,),
                    ECHEC=_F(EVENEMENT='INSTABILITE',
                             ACTION='CONTINUE',
                             #~ ACTION='ARRET',      # --->  means that STAT_NON_LINE will stop in case of instab.
                             ),);

then the analysis completes until the end time =1.2 showing at all time steps this message of " Instabilité détectée". But from the eigenvalues I can clearly see that the sign of the smallest eigenvalue changes at about time=1.1 which is the indication for the instability, see printout of table in .resu. So when using the "stop-list" Code Aster should stop at 1.1, but it stops at 0.05

Regards
Johannes_ACKVA

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Last edited by Johannes_ACKVA (2017-05-19 13:19:43)


Attachments:
stop-analysis-in-case-of-instability.zip, Size: 453.42 KiB, Downloads: 13

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