*** ERROR # 941 *** NON-CONVERGENT NONLINEAR ITERATIONS FOR SUBCASE 1

MelZ
MelZ Altair Community Member
in Community Q&A

Hi, I have this error when running my analysis.

*** ERROR # 941 ***
NON-CONVERGENT NONLINEAR ITERATIONS FOR SUBCASE 1

I tried to adjust the NLPARM parameters: NINC to 30, DT to 0.02, Maxiter to 20, to solve this problem, but it's not helping. The analysis failed at 51% load step.

I applied a 10mm displacement to my model, However, if I change the displacement to 5mm or 20mm, both models work and converge. The model just won't converge when 10mm displacement is applied.

Does anyone know how to solve this problem? Appreciate any help and thank you!

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Answers

  • Rajashri_Saha
    Rajashri_Saha
    Altair Employee

    Hi,

    You should go through the nl.out file too to find out more information on the cause of non-convergence. Please check if any element distortion and penetration error is happening. you can even view the nl.h3d file and see the animation in hyperview which will give fair idea about the run failure.

    If there is any contact issue you can use CNTSTB card in loadstep with S0=0.01 and S1=0.01 value.This will stabilize the contacts.

    Also go through the below article on convergence issue.

    https://community.altair.com/community?id=kb_article&sys_id=a6b1eafedbfd4d10cfd5f6a4e2961906

    Thanks

    Rajashri

  • MelZ
    MelZ Altair Community Member

    Hi Rajashri,

    I reviewed the article, but it doesn't provide much helpful information since my model converges fully with 5mm and 20mm displacements, but the model fails to converge if I apply the intermediate value of 10mm displacement.

    If there is an issue with the contact settings, shouldn't the model fail when a 20mm displacement is applied as well? How is it possible that the model converges with a 20mm displacement but fails when a 10mm displacement is applied?

    I attempted to add S0 and S1 to the CNTSTB, and now the model converges up to 56%, but fails beyond that point. Here is the nl.out message:

    image.png

    Would it help if I create an NLADAPT bulk card and set the STABILIZ field to 0.01? Any suggestions would be greatly appreciated!

  • Rajashri_Saha
    Rajashri_Saha
    Altair Employee

    Hi Melz,

    From the nl.out file image , I can see element distortion is happening. Please check the animation and see those area, you will get an idea what is happening there. Also penetration error and max pressure error is showing the grid id which you need to review.

    You can use the stabilize option too.

    Review the contact id 5 and if it is not working properly duplicate it and interchange master and slave.

    You can also add STIFF=HARD in PCONT card if penetration issue is happening.

    Thanks

    Rajashri

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