FSI installation instructions

Fluid-structure interaction (FSI) simulations model the interactions between a moving structure and a fluid flowing around it. Below are instructions of how to run FSI with free open-source software.

Step-by-step instructions

Important: Although I include the links to the official websites for installation instructions, I recommend you follow these instructions for installation (unless they no longer work), since the official instructions contain some mistakes and omissions.

These instructions only work for Ubuntu or Windows 10.

Install OpenFOAM

Ensure you have installed OpenFOAM (v1812 or later) - installation instructions here.

Install FEniCS on Ubuntu

Update 05/02/2022 - These instructions are for FEniCS, which is now considered legacy. Ideally FEniCSx should be used instead (todo), but the FEniCSx-preCICE adapter is in its infancy, so FEniCS is still the best option. Note that around 50% of the documentation online is for FEniCS, 50% for FEniCSx, which adds to confusion.

FEniCS is an open-source Finite Element Method (FEM) library. We will use it to simulate how a solid bends as a result of applied forces.

The Ubuntu installation instructions as of 31/12/2021 are summarised below (adapted from this website):

sudo apt-get install software-properties-common
sudo add-apt-repository ppa:fenics-packages/fenics
sudo apt-get update
sudo apt-get install fenics

Install preCICE on Ubuntu

preCICE is an open-source library for coupling simulations together. We will use it to allow OpenFOAM and FEniCS to communicate with each other.

The Ubuntu installation instructions as of 31/12/2021 are summarised below (adapted from this website):

sudo apt update
sudo apt install build-essential cmake libeigen3-dev libxml2-dev libboost-all-dev petsc-dev python3-dev python3-numpy
cd ~
mkdir FSI
cd FSI

Now either install the Ubuntu package directly with the instructions below (which did not work for me)...

wget https://github.com/precice/precice/releases/download/v2.3.0/libprecice2_2.3.0_focal.deb
sudo apt install ./libprecice2_2.3.0_focal.deb

... or install from source:

tar -xzf v2.3.0.tar.gz
cd precice-2.3.0
mkdir build
cd build
cmake -DBUILD_SHARED_LIBS=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=~/FSI/precice-2.3.0 -DPRECICE_MPICommunication=ON ..     ### IMPORTANT! INCLUDE THE TWO DOTS!
make -j 4

Test that the cmake command worked as expected:

cd ~/FSI/precice-2.3.0/build
ctest --output-on-failure

If no errors were shown, install the software and test it worked:

make install
make test_install

Note: I used preCICE v2.3.0, but later versions should also work.

Install the OpenFOAM-preCICE adapter

This adapter allows OpenFOAM to talk to preCICE.

The Ubuntu installation instructions as of 23/01/2021 are summarised below (adapted from this website):

cd ~/FSI
git clone https://github.com/precice/openfoam-adapter
cd openfoam-adapter
export LD_LIBRARY_PATH=/usr/lib/x86_64-linux-gnu:$LD_LIBRARY_PATH   ### You might need this line, it depends.
./Allwmake

Install the FEniCS-preCICE adapter

This adapter allows FEniCS to talk to preCICE.

The Ubuntu installation instructions as of 31/12/2021 are summarised below (adapted from this website). This requires Python3, which should already be installed if you followed my previous instructions:

(optional, should not need this line) python3 -m pip install scipy
python3 -m pip install --user fenicsprecice

Summary of how the software works

The following four steps are run in a loop:

OpenFOAM sends the aerodynamic forces at each point on the solid to preCICE.
FEniCS reads the aerodynamic forces from preCICE, and calculates the displacement of the solid at each point.
FEniCS sends the displacement of the solid to preCICE.
OpenFOAM reads the displacement from preCICE, and calculates the new aerodynamic forces.

This is a simplification of the process (called a serial explicit coupling). In reality, a better method is to have all four steps occur simultaneously until the residual is low enough (called parallel implicit coupling). This is faster and more accurate.

Further information about coupling is available here.

Test the installation ran correctly

... by running this tutorial case:

cd ~/FSI
git clone --branch=master --depth 1 https://github.com/precice/tutorials.git
cd ~/FSI/tutorials/perpendicular-flap/fluid-openfoam
./run.sh

The command line output should have paused after this output. If it did not pause, something went wrong.

---[precice]  I am participant "Fluid"
---[precice]  Setting up master communication to coupling partner/s

Now open another Ubuntu terminal, and run these commands:

cd ~/FSI/tutorials/perpendicular-flap/solid-fenics
./run.sh

Both terminals should now have log outputs flying. After around 1 minute of computation, both terminals should finish at (roughly) the same time.

If you have installed ParaView on Windows and added the folder containing its .exe file to the Windows PATH environment variable, then you can run these commands to visualise the results:

cd ~/FSI/tutorials/perpendicular-flap/fluid-openfoam
paraview.exe fluid-openfoam.foam

Congratulations! You should now have a functional FSI installation.

Note that as of 31/12/2021, the unmodified FEniCS-preCICE adapter only works in 2D, so you will have to edit the adapter in order to add 3D FSI functionality, instructions here

Upgrade to 3D

Please see this page.