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I am tying to solve a non-linear problem using Ls-Dyna IMPLICIT solver. However, I am unable to achieve convergence.  

 

mohammad_basri
(@mohammad_basri)
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Joined: 9 months ago
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January 6, 2020 12:37 pm  

Error - "Non-linear solver failed to find equilibrium"

convergence issue while attempting to compress a specimen with large deformations using IMPLICIT Solver of Ls-Dyna


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Negative Volume
(@negativevolume)
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Posts: 285
January 7, 2020 1:09 am  

Hi @mohammad_basri,

To start, Implicit is much more sensitive than explicit so the debugging process can be a long, drawn out process. If you are doing a simple simulation that is in the range of seconds, consider an explicit simulation. If it's longer than that, then yeah, you will have to use Implicit.

Is the issue happening immediately or a little while into the simulation?

 

The link below has a lot of great tips for both debugging errors and improving implicit simulation performance. I would start with the control settings on slide 14 and go from there. 

https://www.dynamore.de/de/download/presentation/dokumente/download-informationstag-Implizit-2016/05-2016-02-dynamore-infotag-implizit-tipstricks.pdf

Let me know if you have any specific questions regarding this. 


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mohammad_basri
(@mohammad_basri)
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Joined: 9 months ago
Posts: 6
January 7, 2020 5:45 am  

@negativevolume

The reason for using Implicit code is to simulate a quasi-static compression problem. 

This error comes after a while and not in the beginning. For a few iterations, it achieves equilibrium and it is after some iterations, it is unable to achieve equilibrium. After which it shows Error termination. 

And, Yes, I have already studied these guidelines for Implicit and used the suggested control settings. 
However, the result is more or less the same. I still get Error termination. 

I am trying to compress a specimen and the process is similar to Crashbox crushing. During the analysis, it shows the following error:

"divergence (increasing translational residual norm) detected"


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Negative Volume
(@negativevolume)
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January 9, 2020 3:44 pm  

@mohammad_basri

If you are getting an error in the middle of your simulation, it could be an issue with the material model or the contacts. Are there any contacts in this simulation? If so, that could definitely be the cause. This link may be helpful

https://www.dynasupport.com/howtos/implicit/implicit-contact-treatment

From my experience, implicit simulations require more than just baseline contact settings so you are probably going to need to activate the options ABC in the contact in LS-Prepost (below) and set IGAP to 1. IGAP has a huge effect on implicit contact stability. 

 

1578584644-igap_contact.jpg

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mohammad_basri
(@mohammad_basri)
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Joined: 9 months ago
Posts: 6
January 13, 2020 11:45 am  

@negativevolume

I have already given and tried the IGAP =1 in Contact Card. 
I am currently using Mortar Contacts. 

I will try changing the contacts once. 

also, do you have some idea about the control card CONTROL_IMPLICIT_SOLUTION? Since the solving process os governed by this itself, I believe there is something missing in that itself.


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mohammad_basri
(@mohammad_basri)
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January 17, 2020 11:26 am  

Can you have a look at my Message file and suggest changes in the CONTROL_IMPLICIT_SOLUTION?


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Negative Volume
(@negativevolume)
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February 4, 2020 2:59 pm  

@mohammad_basri

Did you send the message file to my email? I’m sorry, this slipped by me.


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mohammad_basri
(@mohammad_basri)
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Joined: 9 months ago
Posts: 6
February 4, 2020 3:17 pm  

@negativevolume

I had actually uploaded the file. But somehow it didn't. Can you share your email id?


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Negative Volume
(@negativevolume)
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Joined: 2 years ago
Posts: 285
February 5, 2020 6:30 pm  

@mohammad_basri

Just change the extension of the file from .msg to .txt and upload it. 


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mohammad_basri
(@mohammad_basri)
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Joined: 9 months ago
Posts: 6
February 7, 2020 7:13 am  

@negativevolume

I am attaching the message file. 


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