# IQN fails for quickly changing forces during wetting in a free-surface FSI problem

**URL:** <https://precice.discourse.group/t/iqn-fails-for-quickly-changing-forces-during-wetting-in-a-free-surface-fsi-problem/248>\
**Category:** Using preCICE\
**Tags:** inactive\
**Created:** [May 28, 2020, 4:36pm UTC](https://precice.discourse.group/t/iqn-fails-for-quickly-changing-forces-during-wetting-in-a-free-surface-fsi-problem/248 "2020-05-28T16:36:15Z")\
**Posts on this page:** 1\
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**Author:** ![Alphaoo1](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/alphaoo1/32/497_2.png) [@Alphaoo1](https://precice.discourse.group/u/Alphaoo1)\
**Post date:** [September 18, 2020, 6:44pm UTC](https://precice.discourse.group/t/iqn-fails-for-quickly-changing-forces-during-wetting-in-a-free-surface-fsi-problem/248/10 "2020-09-18T18:44:24Z")

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Summary: With help of @KyleDavisSA, I was able to run the interFoam+CCX dam breaking simulation.  
Initially, the Young’s Modulus of the material was 10 times less than what it actually should be.  
I was also using the filter limit for `QR2` too high. `Forces` were included in the acceleration.

In the [interFoam case](https://github.com/Alphaoo1/tutorials/tree/master/FSI/flap_perp/OpenFOAM-CalculiX_interFoam), you can see the implicit coupling applied, this time including the `Forces` in the acceleration helped the simulation a lot.  
With decreasing the heavy fluid density to 100kg/m3 and increasing the Young’s modulus along with `IQN-ILS` acceleration, you can see the [results](https://github.com/Alphaoo1/tutorials/blob/master/FSI/flap_perp/OpenFOAM-CalculiX_interFoam/ani/interFoam-CCX_rho%3D100_t%3D5s_E%3D2.1MPa.mp4) for the simulation.

Next, I increased the density to match the density to that of water, keeping the rest of the settings the same.  
The simulation runs only until `t=1.33s`, but the [results](https://github.com/Alphaoo1/tutorials/blob/master/FSI/flap_perp/OpenFOAM-CalculiX_interFoam/ani/interFoam_E%3D2.1MPa_waterRho%3D1000_t%3D1.33.mp4) are sensible in terms of mapping.

The results do not differ much when using `IQN-IMVJ`

I think the simulation is failing on the OpenFoam side, due to excessive Courant number. (initially, it ran until `t=1.2`, with some modifications in `fvSchemes` and `fvOptions`, I was able to push it a bit farther.)

 ![](https://global.discourse-cdn.com/free1/uploads/precice/original/1X/19b73733d8b5e910f60a3522b1698ace52a21143.jpeg)

P.S: I could not upload the video here due to the large size file. But the links in the results have the video.  
The following are the 2 settings I used for which the simulation works.

```
<acceleration:IQN-ILS>
                <data name="Displacements0" mesh="Solid"/>
                <data name="Forces0" mesh="Solid"/>
                <preconditioner type="residual-sum"/>
                <filter type="QR2" limit="1e-2"/>
                <initial-relaxation value="0.1"/> 
                <max-used-iterations value="100"/>
                <time-windows-reused value="10"/> 
            </acceleration:IQN-ILS>

```

```
<acceleration:IQN-IMVJ>
                <imvj-restart-mode truncation-threshold="0.0001" chunk-size="8" reused-time-windows-at-restart="8" type="RS-SVD"/>
                <data name="Displacements0" mesh="Solid"/>
                <data name="Forces0" mesh="Solid"/>
                <preconditioner type="residual-sum"/>
                <filter type="QR2" limit="1e-2"/>
                <initial-relaxation value="0.1"/> 
                <max-used-iterations value="100"/>
                <time-windows-reused value="10"/> 
            </acceleration:IQN-IMVJ>

```

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