Fluidchen is a CFD Solver developed for the CFD Lab taught at TUM Informatics, Chair of Scientific Computing in Computer Science.

After forking, use this README.md however you want: feel free to remove anything you don't need, or add any additional details we should know to run the code.

Working with fluidchen

You will extend this code step-by-step starting from a pure framework to a parallel CFD solver. Please follow these instructions for work with git and submitting the assignments.

Software Requirements

This code is known to work on all currently supported Ubuntu LTS versions (22.04, 20.04). In particular, you will need:

• A recent version of the GCC compiler (>9.1). Other compilers should also work, but you may need to tweak the CMakeLists.txt file (contributions welcome). GCC 9.3, 11.2 and 13.2 are known to work.
• CMake, to configure the build.
• The VTK library, to generate result files. libvtk7 and libvtk9 are known to work.
• OpenMPI (not for the skeleton, but when you implement parallelization).

Get the dependencies on Ubuntu:

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install build-essential cmake libvtk7-qt-dev openmpi-bin libopenmpi-dev

Building the code

git clone https://gitlab.lrz.de/oguzziya/GroupX_CFDLab.git
cd GroupX_CFDLab
mkdir build && cd build
cmake ..
make

After make completes successfully, you will get an executable fluidchen in your build directory. Run the code from this directory.

Build options

By default, fluidchen is installed in DEBUG mode. To obtain full performance, you can execute cmake as

cmake -DCMAKE_BUILD_TYPE=RELEASE ..

or

cmake -DCMAKE_CXX_FLAGS="-O3" ..

You can see and modify all CMake options with, e.g., ccmake . inside build/ (Ubuntu package cmake-curses-gui).

A good idea would be that you setup your computers as runners for GitLab CI (see the file .gitlab-ci.yml here) to check the code building automatically every time you push.

Running

In order to run Fluidchen, the case file should be given as input parameter. Some default case files are located in the example_cases directory. Navigate to the build/ directory and run:

./fluidchen ../example_cases/LidDrivenCavity/LidDrivenCavity.dat

This will run the case file and create the output folder ../example_cases/LidDrivenCavity/LidDrivenCavity_Output, which holds the .vtk files of the solution.

If the input file does not contain a geometry file (added later in the course), fluidchen will run the lid-driven cavity case with the given parameters.

Special systems

macOS

Students have previously successfully ran Fluidchen on macOS. However, this is not a system we regularly test. Your contribution here is, therefore, essential in improving this documentation.

In macOS, you can use the default clang compiler. Do not install gcc, since it might cause problems with the standard library and VTK. Other dependencies can be installed by using homebrew package manager as

brew install cmake
brew install open-mpi
brew install vtk

macOS Troubleshooting

• In macOS, the default g++ command is linked to clang++ command, which means, g++ command does not run the GCC compiler but the Clang compiler.

• Setup of GCC compiler is expected to be cumbersome and clashes with lots of other dependencies, therefore please do not use GCC compiler on this project.

• If CMake cannot find the correct C++ binary, you can set it by

  export CXX=`which clang++``
  export CMAKE_CXX_COMPILER=`which clang++``

which is going to set the corresponding environment variables to the path of Clang compiler. Please note that if you run these commands on a terminal session, they are only going to be valid on that terminal session. In order to make these changes permanent, you can add these lines to your ~/.zshrc file.

• Although installation of VTK looks simple, sometimes it is possible that CMake cannot find some necessary libraries for VTK, most famous one being Qt5. If you face an error something like:

CMake Error at /usr/local/lib/cmake/vtk-9.0/VTK-vtk-module-find-packages.cmake:115 (find_package):
 By not providing "FindQt5.cmake" in CMAKE_MODULE_PATH this project has
 asked CMake to find a package configuration file provided by "Qt5", but
 CMake did not find one.

 Could not find a package configuration file provided by "Qt5" (requested
 version 5.15) with any of the following names:

   Qt5Config.cmake
   qt5-config.cmake

 Add the installation prefix of "Qt5" to CMAKE_PREFIX_PATH or set "Qt5_DIR"
 to a directory containing one of the above files.  If "Qt5" provides a
 separate development package or SDK, be sure it has been installed.

which means that CMake could not find Qt5. Solution is simple fortunately. First, make sure that you have Qt5 installed:

brew install qt5

Then extend CMAKE_PREFIX_PATH, which are the locations where CMake tries to find packages, by adding following lines to your .zshrc file

export CMAKE_PREFIX_PATH="/usr/local/opt/qt5:$CMAKE_PREFIX_PATH"

Please not that your installation might be in another location. The most possible another location is /usr/local/Cellar/qt@5/5.**.*/, which depends on the Qt5 version.

Troubleshooting

VTK not found

You might run into a problem where the VTK library is not found. To fix this, you can try the following steps:

1. Find the installation path of your VTK library
2. Define this path as an environment variable, as e.g. export VTK_DIR=".../lib/cmake/vtk-8.2"
3. Start in a clean build folder
4. Run cmake .. again

No rule to make target '/usr/lib/x86_64-linux-gnu/libdl.so'

We are investigating an issue that appears on specific systems and combinations of dependencies.