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#1 2020-03-09 17:04:17

Johannes_ACKVA
Member
From: Ingenieurbüro für Mechanik, DE
Registered: 2009-11-04
Posts: 698
Website

contact "rasant"

hello
sometimes in a transient analysis with contact there is this alarm:

   !--------------------------------------------------------------------------------------------------------------------------!
   ! <A> <CONTACT3_98>                                                                                                        !
   !                                                                                                                          !
   ! Contact et détection de collision.                                                                                       !
   !     Le contact semble "rasant", c'est-à-dire que le jeu est nul mais que la pression de contact est quasiment            !
   !     nulle également.                                                                                                     !
   !     -> Risque & Conseil :                                                                                                !
   !       La découpe automatique du pas de temps ne sera probablement pas efficace. Si vous constatez de fortes oscillations !
   !       de la vitesse ou du déplacement au point de contact pour cet instant de calcul malgré l'activation du mode de      !
   !       traitement automatique de la collision, vous pouvez essayer d'éviter l'instant pour lequel le contact "rasant"     !
   !       apparaît de deux manières différentes:                                                                             !
   !        - changer la discrétisation en temps initiale                                                                     !
   !        - changer la valeur de SUBD_INST                                                                                  !
   !                                                                                                                          !
   !                                                                                                                          !
   ! Ceci est une alarme. Si vous ne comprenez pas le sens de cette                                                           !
   ! alarme, vous pouvez obtenir des résultats inattendus !                                                                   !
   !--------------------------------------------------------------------------------------------------------------------------!

I understand the french, but not the intention of this message, can someone please help? I think the doc does not really explain the sense or what is the problem with the contact "rasant". For english speaking persons: "rasant" means that the contact is very slight: contact force is nearly zero and the contact status is hardly "yes".

My first question: do I risk to have wrong, i.e. unphysical results?

This question is not answered in the message, there is only written that subdividing the time steps will not help to avoid the contact rasant. Which is obvious, I think, because the contact rasant will always appear at the same time point betw "no contact" and "yes contact". Next, the message explains, that a different discretisation of time can avoid this contact rasant. Also obvious.

I attach a Code-Aster run with such a message. As can be seen there is a considerable penetration (which should not happen!). Might this tell that we must never accept a contact "rasant"? If so, why is the contact "rasant" only an alarme message, Code-Aster should then really stop

Regards

Johannes


*** CODE-ASTER  DYNAMIC ANALYSIS
     19-20 March  2020

*** CODE-ASTER INTRO + CONTACT + MATERIAL
     04-08 May 2020


Ingenieurbüro für Mechanik
D 91717 Wassertrüdingen / Germany

www.code-aster.de                                                Training & Support for NASTRAN and CODE-ASTER

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#2 2020-03-09 17:07:06

Johannes_ACKVA
Member
From: Ingenieurbüro für Mechanik, DE
Registered: 2009-11-04
Posts: 698
Website

Re: contact "rasant"

here the attachment w example


Attachments:
spiral2d_ToForum.zip, Size: 285.84 KiB, Downloads: 70

Ingenieurbüro für Mechanik
D 91717 Wassertrüdingen / Germany

www.code-aster.de                                                Training & Support for NASTRAN and CODE-ASTER

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#3 2020-08-23 06:09:14

Duc Vu
Member
Registered: 2020-04-03
Posts: 19

Re: contact "rasant"

Hi,
I take a look to your result file and it seems like I had the same question with yours.
I got the result with the same alert but the stress value was very strange (too small = "rasant" as you said) and my object which must slide on the other one passed through instead.
Do you have the answer for this and did we misunderstood something?
Thanks.

Last edited by Duc Vu (2020-08-23 06:10:32)

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#4 2020-08-23 12:12:05

sameer21101970
Member
Registered: 2019-09-06
Posts: 245

Re: contact "rasant"

i had faced similar problem, when i was defining 2 operations by single time step.
first step object 1 travelling to contact face.
second step object 1 bending object 2 in contact.

but after defining different timestep & function for both operation it worked fine.

or else build proper contact face of object 1 and object 2. run with single time step. it runs.

i have not seen your zip file, just sharing my experience.

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