Turek Hron FSI3

The Turek-Hron FSI cases are well-established numerical benchmarks and, therefore, well suited for verification of preCICE itself and the used adapters. In this tutorial, we focus on the FSI3 case, which presents the most challenging case in terms of added mass. Please note that the meshes of this case are significantly finer than for other tutorials. Running the simulation might take a few hours. We do not recommend to run this tutorials as your first preCICE tutorial.

Setup

The setup is shown schematically here:

FSI3 setup

For more information please refer to the original publication of the benchmark [1].

Configuration

preCICE configuration (image generated using the precice-config-visualizer ):

preCICE configuration visualization

Available solvers

Fluid participant:

Solid participant:

  • deal.II. For more information, have a look at the deal.II adapter documentation . This tutorial requires the nonlinear solid solver. Please copy the nonlinear solver executable to the solid-dealii folder or make it discoverable at runtime and update the solid-dealii/run.sh script.
  • Nutils. For more information, have a look at the Nutils adapter documentation .

Running the Simulation

Open two separate terminals and start each participant by calling the respective run script. For example:

cd fluid-openfoam
./run.sh

and

cd solid-dealii
./run.sh

You can also run OpenFOAM in parallel by ./run.sh -parallel. The default setting here uses 25 MPI ranks. You can change this setting in fluid-openfoam/system/decomposeParDict.

You may adjust the end time in the precice-config.xml, or interrupt the execution earlier if you want.

In the first few timesteps, many coupling iterations are required for convergence. Don’t lose hope, things get better quickly.

Post-processing

You can visualize the results of the coupled simulation using e.g. ParaView. OpenFOAM uses an OpenFOAM-specific format, and you can directly load the (empty) file fluid-openfoam.foam in Paraview or convert the results to VTK with foamToVTK. deal.II writes VTK files. Both Nutils solvers currently do not write VTK files (but use their own in-situ visualization), but this can be easily added similarly to the perpendicular flap solvers .

If you want to visualize both domains with ParaView, keep in mind that the different solvers may write results with different output frequencies, which you might want to synchronize .

There is a known issue that leads to additional “empty” result directories when running with some OpenFOAM versions, leading to inconveniences during post-processing. At the end of run.sh, we call openfoam_remove_empty_dirs (provided by tools/openfoam-remove-empty-dirs) to delete the additional files before importing the results in ParaView.

Moreover, as we defined a watchpoint at the flap tip (see precice-config.xml), we can plot it with gnuplot using the script plot-displacement.sh, which expects the directory of the selected solid participant as a command line argument. For example:

plot-displacement.sh solid-dealii

![FSI3 watchpoint](images/tutorials-turek-hron-fsi3-tip-plot.png)

Before running the simulation again, you may want to cleanup any result files using the script `clean-tutorial.sh`.

## Mesh refinement

In `fluid-openfoam/system/`, we provide three different fluid meshes:

* `blockMeshDict`: the default mesh with approximately 21k cells,
* `blockMeshDict_refined`: a refined mesh with approximately 38k cells,
* `blockMeshDict_double_refined`: a refined mesh with approximately 46k cells.

If you want to use one of the two refined meshes, simply swap the `blockMeshDict`:

```bash
mv blockMeshDict blockMeshDict_original
mv blockMeshDict_refined blockMeshDict

Acknowledgements

Thanks to the Technical University of Eindhoven for funding the development of the Nutils participants for this tutorial.

References

[1] S. Turek, J. Hron, M. Madlik, M. Razzaq, H. Wobker, and J. Acker. Numerical simulation and benchmarking of a monolithic multigrid solver for fluid-structure interaction problems with application to hemodynamics. In H.-J. Bungartz, M. Mehl, and M. Schäfer, editors, Fluid Structure Interaction II: Modelling, Simulation, Optimization, page 432. Springer Berlin Heidelberg, 2010.