# Question about using overset mesh in FSI two-way coupling

**URL:** <https://precice.discourse.group/t/question-about-using-overset-mesh-in-fsi-two-way-coupling/1446>\
**Category:** Using preCICE\
**Created:** [June 10, 2023, 12:42pm UTC](https://precice.discourse.group/t/question-about-using-overset-mesh-in-fsi-two-way-coupling/1446 "2023-06-10T12:42:30Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Stan](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/stan/32/599_2.png) [@Stan](https://precice.discourse.group/u/Stan)\
**Post date:** [June 10, 2023, 12:42pm UTC](https://precice.discourse.group/t/question-about-using-overset-mesh-in-fsi-two-way-coupling/1446/1 "2023-06-10T12:42:30Z")

</div>

Hi all,  
Recently I’ve been trying to use overset mesh in OpenFOAM to do two-way coupling with our in-house solid solver. The reason I tried to adopt overset mesh is to achieve large deformation of the structure without making the fluid domain not converge due to excessive mesh deformation.

The case is about waves impacting a flexible structure (It ran successfully when using general dynamic mesh). However, while using overset mesh, the water phase around the structure got wrong as soon as the simulation began, and the simulation crashed pretty fast. Has anyone experienced this problem?

 ![image](https://global.discourse-cdn.com/free1/uploads/precice/original/2X/6/6e029a8312ad6126f7953afea06375c896a0f8a7.png)  
Initial water level  
 ![image](https://global.discourse-cdn.com/free1/uploads/precice/original/2X/a/ad92f242d218ea426c1e39f2f059b54c68cf2a5c.png)  
Wrong water phase when the simulation crashed

---

<div class="post-metadata">

**Author:** ![fsimonis](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/fsimonis/32/6_2.png) [@fsimonis](https://precice.discourse.group/u/fsimonis)\
**Post date:** [June 16, 2023, 11:23am UTC](https://precice.discourse.group/t/question-about-using-overset-mesh-in-fsi-two-way-coupling/1446/2 "2023-06-16T11:23:53Z")

</div>

Hi,

I assume you are using 2 volume-coupled meshes in the overlapping region.  
In this case, the mapping and constraint plays a crucial role in the setup and could explain the behaviour.  
Which one are you using? Are both meshes matching? Can you provide the preCICE config?

Best  
Frédéric

---

<div class="post-metadata">

**Author:** ![Stan](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/stan/32/599_2.png) [@Stan](https://precice.discourse.group/u/Stan)\
**Post date:** [June 19, 2023, 7:48am UTC](https://precice.discourse.group/t/question-about-using-overset-mesh-in-fsi-two-way-coupling/1446/3 "2023-06-19T07:48:22Z")

</div>

Hi @fsimonis ,  
Sorry for the late reply.

> [@fsimonis](#):
>
> Are both meshes matching? Can you provide the preCICE config?

Yes, both meshes are matched. The preCICE config file is attached here.  
[precice-config.xml](https://precice.discourse.group/uploads/short-url/GZf5qRIRwVjw0jGQn0QtiKwjkc.xml) (2.6 KB)  
Thanks in advance!

---

<div class="post-metadata">

**Author:** ![Makis](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/makis/32/25_2.png) [@Makis](https://precice.discourse.group/u/Makis)\
**Post date:** [June 19, 2023, 8:53am UTC](https://precice.discourse.group/t/question-about-using-overset-mesh-in-fsi-two-way-coupling/1446/4 "2023-06-19T08:53:19Z")

</div>

I think your case needs many features that are currently experimental or under development and undocumented.

- Overset meshes: We don’t have any example, but I have seen from other users that defining a surface-coupled interface inside an overset region should work. I don’t know how to configure it, though.
- Two-phase flows for FSI: This should work, as for example in [Adds breaking dam test cases by KyleDavisSA · Pull Request #279 · precice/tutorials · GitHub](https://github.com/precice/tutorials/pull/279) (currently in review, relatively low on my priority list).

Note that you are using a serial-explicit coupling scheme and nearest-neighbor mapping. These are the simplest and least accurate methods that preCICE offers. Better try serial-implicit with IQN, and an RBF mapping.

Important question: does the flap move outside the overset region? You wrote that it crashes in the beginning of the simulation, so maybe this question is not yet relevant.