Problem with defining the contact situation

a.obaei · 2023-04-17 12:38:43

Hi,

I'm trying to simulate an experiment in which there is a masonry wall in the concrete frame and during a test, the bottom of the wall will detach from the frame and go up.
I tried to manage it by fixing a frame and defining DEFI_CONTACT between the wall and the frame (the goal here is to have no boundary condition for the wall and the frame acts as it),
Meanwhile, I had an error and fixed it by illuminating groups of common nodes (by SANS_GROUP_MAILLE) between the wall and the frame but it somehow seems like that in the four angles the wall and the frame are fixed together.
In order to fix this problem, I changed the way I compounded these two together and there was no longer this error but, it is nessecery to define a boundary condition for the wall itself too (which is not our goal).

Can you please help me with the way that I can simulate my project in a way that defines a contact situation between the wall and the frame (so it will be fixed to the top frame and can be separated from the bottom) and the frame is the only boundary condition of the wall?

Merci par avance

Last edited by a.obaei (2023-04-17 12:39:19)

Attachments:
CONTACT.rar, Size: 40.09 KiB, Downloads: 17

a.obaei · 2023-04-23 19:38:59

Hi again,

Regarding my problem with the boundary condition, I want to try to glue two lines together (the upper edge of the wall with the corresponding edge of the upper frame on one side, and the exact situation for the bottom part of the wall and its frame).
This can be ideal if it works in a way that only and only two edges are glued together.

I tried to use the LIASION_MAIL command but unfortunately, I found that it works only for volumetric shapes (if I'm not wrong).
I tried to test other Liasion objects but I couldn't make it work.

So I wonder what is a way to glue two adjected lines -edges- (with different properties of course) together?

I would appreciate if you can help me with it.

Thanks

jeanpierreaubry · 2023-04-24 07:46:49

hello

your contact setup seems correct

the volume MUR is completely free floating in space in Z direction
as written in the message file

 - Si vous faites du contact, il ne faut pas que la structure ne "tienne" que par le contact.

you have to restrain its displacement with some soft springs

most of the commercial software will do this silently (without you knowing what is done)

code_aster does not do that

jean pierre aubry

a.obaei · 2023-04-24 09:13:53

Hi,

Thanks for your response, I really appreciate it,

But I don't know how to apply soft spring to the MUR, would you please help me with its command?

And in order to glue two edges of the wall and the frame (just two lines), which command do you propose to use?
I tried LIASON_MAIL but it needs 2D or 3D mailles.

Thanks again for your time.

jeanpierreaubry · 2023-04-24 13:09:20

this cannot be done only in the command file

you have to set up on the mesh some lines maybe 3 of some length that connect MUR to the space
mesh them as SEG2 with only one element in the length
fix the ends of these lines
uses discrete elements K_TR_D_L properties with very low stiffness on them

check at post processing time that they carry as little load as practical

a.obaei · 2023-04-25 14:16:10

Thanks a lot for your help and response.

So just to ensure that I got you correct, it means that I have to define some lines (entre le mur et le cadre) and just mesh them in the thickness direction, fix them and model them right?
I'll try it and hope to understand it well, Thank you.

Furthermore, defining these soft springs can be a solution but meanwhile, I'm trying to glue the frontal edge of the wall and the cadre together to simulate the deformed form that we obtained during the test ( the wall is subjected to heat and due to it, we got an expansion vers the exposed face, these frontal edges were always in contact with the cadre but other side get apart).
I tried to use LIASION_GROUP to achieve this but still, I got the same error (I believe that the problem is in the way I defined it, because, without LIASON_GROUP, I could run the model). I attached the message file to this post.
Would you please help me with this error?
And the other important question is, does glue these two edges together (upper and bottom sides) will fix the problem free floating du mur?

I really appreciate all your help.
Armita

Attachments:
message, Size: 240.02 KiB, Downloads: 12

jeanpierreaubry · 2023-04-26 10:25:43

i am afraid you undetake too many things at a time

regarding the contact study the attached files

it is 2 cubes with a contact

Attachments:
example-cubes.zip, Size: 38 KiB, Downloads: 16

a.obaei · 2023-04-27 16:16:10

Hi,

Thanks for the example you provided it was very kind of you and so helpful to me.

However, I have to say I still have problems with it, I defined springs attached to the wall (exactly like the example you sent and with the same values), but still I have the boundary condition error.
With still having those springs, I tried to fix one surface of the wall and saw that it goes well (which fixing the wall surface is not the thing I'm looking for).
So would you please help me another time with this? Am I defining the springs wrongly or their length or values are not enough to act as a boundary condition of the wall? (You can find the files in the attachment).

I really appreciate your help and support.

Thanks a lot,
Armita

Attachments:
Soft_Spring.rar, Size: 117.54 KiB, Downloads: 12

jeanpierreaubry · 2023-04-28 07:23:07

when doing a non linear analysis it is always a good idea to separate the CHARGE

1- with the boundary conditions strictly speaking i.e. ground fixation
2- the loads, here the gravity

and the varying load here the gravity should be applied with a FONC_MULT, a ramp,

also there should be an INCREMENT in the STAT_NON_LINE and the one you supply here is the same as in THER_NON_LINE
i do not understand what you intend to do with that

a.obaei · 2023-05-04 11:13:08

Hi again,

Thank you for your response and I'm sorry for my late reply, I was trying to work on it in order to less disturb you but unfortunately, I'm still blocked in this part.

I did the thing you proposed and separated the loading (first fixing the cadre en bas, then springs, then symmetrical condition of the wall, and at the end gravity), but I got Erreur de programmation ! (You can find the mesh file, com, and mess in the attachment).
I'm so sorry for this but I have no idea which part I did wrong that I can't get the answer.
Moreover, regarding the increments, I'm trying to simulate the Theromo Mechanical calculation, so first I imposed the thermal loading to one side of the wall for 2 hours (THER_NON_LINE), and then calculate the mechanical respond of it with considering the thermal load during this 2 hours (not sure if it's a best way to do it or not!).

And indeed, in order to understand better, I tried to run your simulation but I couldn't. Do you used another version? Because I get weird error for running your code (I attached the message file of it too).

I really appreciate all your help and guideness,

Thanks a lot,
Armita

Attachments:
Soft_Spring.zip, Size: 387.01 KiB, Downloads: 11

jeanpierreaubry · 2023-05-04 13:14:23

regarding My_file folder

1/ please read the message file

le noeud:  N898 composante:  DX  est bloqué plusieurs fois.

this is a node on the top of the wall, it belongs to two CHARGE
this is not allowed

2/ once this is solved i cannot see any FONCT_MULT applied to GRAVITY to perform the non linear analysis

a.obaei · 2023-05-25 08:21:59

Hi again,

Thanks for your help and guidance,
I somehow solved the problem but not totally, I will explain the progress.

As I've told you, I want to simulate a wall (with no boundary condition) and the frame on top and at the bottom of it as its boundary condition.
I started to simulate the wall with just the bottom frame (which is fixed in 3 directions) and restrict the wall with the soft springs as you proposed. There is a contact condition between the wall and the frame.

With 4 springs connected to the wall and the dimensions of the frame I couldn't solve it so I tried to increase the number of the springs and also the dimension of the bottom frame.
I thought maybe due to the slender ratio of the wall and the definition of the contact, the bottom frame should be larger. I tested many cases and changed the dimension of both wall and frame and in the end, I could model the wall with 14 springs (which couldn't be possible with 4), and the larger bottom frame together.

After this step, I wanted to add the top frame too. There is again a contact condition between the top frame and the wall and as the boundary condition for the top frame, it is fixed in x and y and just can move in the z-direction. So just like the wall, I tried to use springs for the top frame but I got again the boundary condition error. I tried to play with the number of springs for the top frame and its dimension but I still can not solve the problem. [it is worth to be mentioned that just for test I fixed the top frame in z-direction and it runs.]

Would you please help me with this? I'm not really sure that I understand completely the logic of it.
I thought maybe the problem with the top frame is due to the contact condition, so I used the same dimension as the bottom frame but it still doesn't work. I'm really blocked at this stage.

I attached the files here and so I'm so thankful for all your help.
Thanks again
Armita

Attachments:
MUR_CADRE.rar, Size: 376.43 KiB, Downloads: 8

jeanpierreaubry · 2023-05-25 09:28:37

before looking any further
i have to point out

from your command file it looks like your model is an kg m s
thus the soft spring with a value of 0.1 that is to say a force of 0.1 N produces an elongation of 1 meter
is very very soft
while the example i gave you is is in N mm
the stiffness is not dimension less

regarding the number of spring you use is way to much in my opinion
in theory 3 if well placed should do the job

and this message

Degré de liberté physique associé au noeud N14459 et à la composante DZ.

should help you to identify where the instability come from

jacob · 2023-05-25 17:14:33

I am facing also this kind of problems.
Increasing number of NPREC to 10 or 12 or set it to -1 will help with this kind of error, however I still don't know why this is happening.
Or, of course, increasing the stiffness of soft springs.

Last edited by jacob (2023-05-25 17:17:55)

#1 2023-04-17 12:38:43

Problem with defining the contact situation

#2 2023-04-23 19:38:59

Re: Problem with defining the contact situation

#3 2023-04-24 07:46:49

Re: Problem with defining the contact situation

#4 2023-04-24 09:13:53

Re: Problem with defining the contact situation

#5 2023-04-24 13:09:20

Re: Problem with defining the contact situation

#6 2023-04-25 14:16:10

Re: Problem with defining the contact situation

#7 2023-04-26 10:25:43

Re: Problem with defining the contact situation

#8 2023-04-27 16:16:10

Re: Problem with defining the contact situation

#9 2023-04-28 07:23:07

Re: Problem with defining the contact situation

#10 2023-05-04 11:13:08

Re: Problem with defining the contact situation

#11 2023-05-04 13:14:23

Re: Problem with defining the contact situation

#12 2023-05-25 08:21:59

Re: Problem with defining the contact situation

#13 2023-05-25 09:28:37

Re: Problem with defining the contact situation

#14 2023-05-25 17:14:33

Re: Problem with defining the contact situation

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