# Convergence issue with c3d10

**URL:** <https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453>\
**Category:** Uncategorized\
**Created:** [October 25, 2024, 12:52pm UTC](https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453 "2024-10-25T12:52:20Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![Iacobellis88](https://avatars.discourse-cdn.com/v4/letter/i/9de0a6/32.png) [@Iacobellis88](https://calculix.discourse.group/u/Iacobellis88)\
**Post date:** [October 25, 2024, 12:52pm UTC](https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453/1 "2024-10-25T12:52:20Z")

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Hello all,  
I am running a big model with c3d10, with a lot of sliding contacts.  
When I run the analysis I get the same identical value of residual displacement force on a intermediate node for each iteration.  
What can I do? I know that it is not possible to use STABILIZE on contact.  
The simulation got converge with c3d4 elements

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**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [October 25, 2024, 12:59pm UTC](https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453/2 "2024-10-25T12:59:20Z")

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How does the incrementation progress ? Perhaps the model is underconstrained.

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<div class="post-metadata">

**Author:** ![Iacobellis88](https://avatars.discourse-cdn.com/v4/letter/i/9de0a6/32.png) [@Iacobellis88](https://calculix.discourse.group/u/Iacobellis88)\
**Post date:** [October 25, 2024, 1:56pm UTC](https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453/3 "2024-10-25T13:56:08Z")

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At the beginning I tried 0.1 time step. Now 0.025 but I have the same problems.  
Now I used some springs with a very small stiffness to avoid underconstrained.  
Hpwever it is very strange because c3d4 model get converged.

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<div class="post-metadata">

**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [October 25, 2024, 2:19pm UTC](https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453/4 "2024-10-25T14:19:12Z")

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I meant how it changes the increment size - output from the .sta file. A screenshot will suffice.

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<div class="post-metadata">

**Author:** ![Iacobellis88](https://avatars.discourse-cdn.com/v4/letter/i/9de0a6/32.png) [@Iacobellis88](https://calculix.discourse.group/u/Iacobellis88)\
**Post date:** [October 25, 2024, 2:39pm UTC](https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453/5 "2024-10-25T14:39:16Z")

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I stopped the run, becuase I did 50 iterations with the same values of residual force on the same nodes, So on sta. nothing has been written

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<div class="post-metadata">

**Author:** ![jbr](https://avatars.discourse-cdn.com/v4/letter/j/ecccb3/32.png) [@jbr](https://calculix.discourse.group/u/jbr)\
**Post date:** [October 26, 2024, 11:25am UTC](https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453/6 "2024-10-26T11:25:24Z")

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Do a modal extraction to see if there is anything unconnected. Check for adjustments in the mesh, and try to simplify as much as you can.

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<div class="post-metadata">

**Author:** ![Iacobellis88](https://avatars.discourse-cdn.com/v4/letter/i/9de0a6/32.png) [@Iacobellis88](https://calculix.discourse.group/u/Iacobellis88)\
**Post date:** [November 4, 2024, 10:30am UTC](https://calculix.discourse.group/t/convergence-issue-with-c3d10/2453/7 "2024-11-04T10:30:59Z")

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Hello ,  
I did a lot of attempts but I have always huge residual and this residual does not change at all (same value in each iteration that is very strange).  
I tried to reduce model and it works.  
So I think that the problem it is not model but the ccx\_i8 executable.