# Code_Aster forums

Welcome on the forums. Please post in English or French.

You are not logged in. You won't be able to post until you register and log in using the top-right bar.

## #1 2012-05-08 15:59:17

alberich
Member
Registered: 2011-01-31
Posts: 57

### [SOLVED] non convergence with simple geometry and large displacements

Hello,

I would like to resume the problem reported here http://www.code-aster.org/forum2/viewtopic.php?id=16566
Now I am using the code-aster version 11.1.20.

Again, I attached the described example. Some hints for the files: the file disc-spring.py generates the mesh when executed in SALOME (you'll have to modify the script, line 31 to define your working directory). It will produce two meshes: a discspring.med and a support.med; The discspring_contact.comm expects the support as unit 21 and the discspring as unit 20. The creation of the *.export file is then straight forward.

As apparent from the *.comm file, there are two models: with and w/o contact. One can select the desired model with the boolean in line 170: sans_contact=False or  sans_contact=True

Some explanations to the limit conditions of the model (axis-symmetric):

inner top circumference            |      ____
inner bottom circumference      .     |___   -------  _____   outer top circumference
|              -------- _____|   outer bottom circumference
.
| (support not shown)

For the case w/o contact, there are the following limit conditions (model A):
support:
bottom line fixed (DX=DY=0; line 121)
disc-spring:
inner top circumference: imposed deflection DY=smax (to be set in lines 120 and 122)
outer top circumference: DX=0 (line 125)
outer bottom circumference: DY=0 (line 124)

These limit conditions correspond very much to the effect of the support when calculating with contact (model B):
support:
bottom line fixed (DX=DY=0; line 121)
disc-spring:
inner top circumference: imposed deflection DY=smax (to be set in lines 120 and 122)
The outer top circumference and the outer bottom circumference are subject to the contact and do thus not require a limit condition.

The simulation increases in a first step the imposed deflection at the inner top circumference from 0 to smax. The number of steps can be adjusted in line 132. The pressure at the top face of the disc-spring is 0 in that first step.
In a second step, I applied a follower pressure from 0 to the value set in line 126. The imposed deflection at the inner top circumference is smax.

Solving the system does unexpectedly not work for large deflections and/or pressures. It performs even worse for model A, hence, the case w/o contact (i.e. Model B, the contact-model works better sic.) If smax=-0.8 both, model A and model B work for the first step (increasing imposed deflection). When smax=-0.9, the model A (i.e. w/o contact) fails. It enters a flip-flop at node 269 (which is a node close to the inner bottom circumference; no limit condition there) thus diverges. It is surprising to encounter troubles already at such small deflections since the radius of the disc-spring is 125.
The contact version (model B) does not have any problems with really large imposed deflections (until smax=-15, which is quite well beyond the height of the disc-spring).

Both models fail, however, when adding a follower pressure (to compare the two models, only an imposed deflection smax=-0.8 is used since model A does not work beyond that). The contact model (model B) works until a pressure of 0.9. It fails at a pressure of 1.0 (line 126). There again, it enters a flip-flop at node 2 (which is the outer top circumference). Model A fails already at a pressure of 0.7 at node 22 which is close to the outer top circumference. A pressure of 0.7 and 0.9 is still quite low considering the geometry of the disc-spring.

Does anyone have an idea why this happens? I'd be grateful for any hints.

al

Last edited by alberich (2012-05-22 21:58:16)

Attachments:

Offline

## #2 2012-05-18 23:11:49

alberich
Member
Registered: 2011-01-31
Posts: 57

### Re: [SOLVED] non convergence with simple geometry and large displacements

Hello,

In order to exclude that it appears only on my system, could anybody confirm the above described behaviour?
Did anybody spot an error in my scripts or model?
If not, any ideas for a work around?

Or do I have to assume that code-aster can simply not solve this model?

al

Offline

## #3 2012-05-21 16:56:00

Thomas DE SOZA
Guru
From: EDF
Registered: 2007-11-23
Posts: 2152

### Re: [SOLVED] non convergence with simple geometry and large displacements

Hi,

Just tried with 11.1.22 on my computer : both simulations end OK (with and without contact at smax=-0.9).

Note that following pressure was fixed on 11.1.21 version which might explain the difficulties.

TdS

Attachments:

Offline

## #4 2012-05-21 17:23:39

jeanpierreaubry
Ex-Guru
From: nantes (france)
Registered: 2009-03-12
Posts: 1748
Website

### Re: [SOLVED] non convergence with simple geometry and large displacements

hello

i tried it and it works on "Version 11.1.15 du 28/03/2012", not on 10.6
i just commented the last POST_ELEM line as the GEOMETRIE seems to be unknown
i did not check the results though

TdS took the lead by a few teens of minutes

jean

Last edited by jeanpierreaubry (2012-05-21 17:24:19)

Offline

## #5 2012-05-22 21:57:54

alberich
Member
Registered: 2011-01-31
Posts: 57

### Re: [SOLVED] non convergence with simple geometry and large displacements

Hello,

> Note that following pressure was fixed on 11.1.21 version which might explain the difficulties.
You're right, that explains the difficulties.

Thank you for the replies.

al

Offline