# Divergence in simple model **URL:** \ **Category:** Uncategorized\ **Created:** [February 16, 2025, 6:16pm UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599 "2025-02-16T18:16:52Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![teofil75](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/teofil75/32/3276_2.png) [@teofil75](https://calculix.discourse.group/u/teofil75)\ **Post date:** [February 16, 2025, 6:16pm UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599/1 "2025-02-16T18:16:52Z")
**Dear Discourse Group,** I have created this simple shell model, but when I turn on NLGEOM, the simulation diverges. It is quite a simple model, without contacts and using only plasticity. I would like to post the gz model (only 14kB), but I can’t figure out how to do it. ![image](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/4/4b51b1937cd994376c275536e7a4fdd48c2526cf.png) In the image the solution whitout the NLGEOM=ON Any ideas? ---
**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:** [February 16, 2025, 6:32pm UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599/2 "2025-02-16T18:32:24Z")
> [@teofil75](#): > > I can’t figure out how to do it. You can use some hosting service and share the link here. Are you using rigid body constraints ? They are known to cause convergence issues when used with shells and Nlgeom. ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [February 16, 2025, 7:12pm UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599/3 "2025-02-16T19:12:25Z")
If that deformation is real scale I would also perform a Linear buckling analysis to see if it could be buckling. ---
**Author:** ![teofil75](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/teofil75/32/3276_2.png) [@teofil75](https://calculix.discourse.group/u/teofil75)\ **Post date:** [February 16, 2025, 7:32pm UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599/4 "2025-02-16T19:32:23Z")
You caught the target! I’ll avoid to use \*rigid to apply load and constraints and let you know ---
**Author:** ![teofil75](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/teofil75/32/3276_2.png) [@teofil75](https://calculix.discourse.group/u/teofil75)\ **Post date:** [February 16, 2025, 8:20pm UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599/5 "2025-02-16T20:20:12Z")
Thank you, it solved my simulation. But you also know the theoretical reason? Does it matter on how the shell are expanded in CalculiX? ---
**Author:** ![xyont](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/xyont/32/3553_2.png) [@xyont](https://calculix.discourse.group/u/xyont)\ **Post date:** [February 17, 2025, 2:07am UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599/6 "2025-02-17T02:07:08Z")
rigid body and shell element in CalculiX is a bit different, edge clamping not restrained and may cause a problem in case of geometric nonlinearity and material plasticity. ---
**Author:** ![teofil75](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/teofil75/32/3276_2.png) [@teofil75](https://calculix.discourse.group/u/teofil75)\ **Post date:** [February 17, 2025, 5:42am UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599/7 "2025-02-17T05:42:33Z")
It is magnified of about x50 ---
**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:** [February 17, 2025, 8:00am UTC](https://calculix.discourse.group/t/divergence-in-simple-model/2599/8 "2025-02-17T08:00:12Z")
> [@teofil75](#): > > But you also know the theoretical reason? Does it matter on how the shell are expanded in CalculiX? Guido (ccx dev) explained it here: [Rigid-body constraint convergance problems - #25 by dhondt](https://calculix.discourse.group/t/rigid-body-constraint-convergance-problems/369/25)