Exercise

While the GNOME graphical interface is suitable for general tasks, OpenFOAM relies entirely on the Terminal (the command-line interface). To facilitate the transition to this workflow, the following exercise bridges the gap between graphical file management and terminal commands.

Part 1: Graphical File Management

The workspace must first be prepared using the graphical interface. OpenFOAM simulations are organized into “cases,” which are essentially directories (folders) containing specific configuration text files.

1. Download the archive file 1_linux_introduction.zip containing a dummy OpenFOAM case repository.
2. Open the File Manager by pressing the Super key, type files, and press Enter.
3. Extract the archive:
   • Navigate to the Downloads directory.
   • Right-click 1_linux_introduction.zip and select Extract Here.
4. Organize the workspace:
   • Select Home from the left sidebar.
   • Right-click in the empty space, select New Folder, and assign the name OpenFOAM_Projects.
   • Return to the Downloads directory, copy the extracted 1_linux_introduction folder, and paste it into the newly created OpenFOAM_Projects folder.

The mock simulation directory has now been downloaded, extracted, and organized using the graphical user interface. The next section demonstrates how to interact with this exact same directory using the Terminal.

Part 2: Terminal Interaction

Execute the following commands sequentially in the Terminal, pressing Enter after each line. Read the accompanying explanations to understand the function of each command.

Verify the current location

pwd

This confirms the Terminal is operating within the Home directory. This is the exact same location as clicking Home in the graphical file manager.

View directory contents with details

ls -l

Adding the -l (long) flag to the ls command displays the directory contents in a detailed list, showing permissions, ownership, and modification dates. The newly created OpenFOAM_Projects directory will be visible here.

Navigate using Tab Completion

Typing long directory names is inefficient. Instead, type the first few letters and use auto-complete.

cd OpenFOAM_Projects

Enter and inspect the case directory

cd 1_linux_introduction
ls

Running ls here will display four items: The three folders 0, constant, and system, and a script called Allrun. This is the strict standard directory structure required for every OpenFOAM case.

Create a case backup

In CFD workflows, duplicating a working case before modifying the setup is standard practice. To copy an entire directory, the -r (recursive) flag must be included. Go to the parent directory and copy the OpenFOAM case.

cd ..
cp -r 1_linux_introduction 1_linux_introduction_backup
ls

Rename the backup directory

The mv (move) command is dual-purpose: it moves files to new locations, but it is also the standard way to rename files and directories.

mv 1_linux_introduction_backup 1_linux_introduction_v2
ls

The backup directory has now been renamed to 1_linux_introduction_v2.

Delete a directory

If a simulation setup fails, the directory often needs to be deleted. The rm (remove) command handles this. Similar to copying, deleting a directory requires the -r flag.

rm -r 1_linux_introduction_v2
ls

Terminal deletion is permanent. Files removed with rm do not go to a graphical trash bin.

Inspect a configuration file

OpenFOAM does not feature a graphical setup menu. Simulation parameters are defined in text files, often called “dictionaries” or “dicts”. Enter the OpenFOAM case folder and display the content of the file controlDict in the system folder.

cd 1_linux_introduction
cat system/controlDict

Manipulate a configuration file

While cat can be used to display the content of files, text editors like nano can be used to manipulate the content of text files. Use nano to open the controlDict and change the value of the endTime entry from 0.3 to 0.5.

nano system/controlDict

Save the file and exit nano as follows:

1. Press Control + X for starting the exis process
2. When asked “Save modified butter?” press y (yes)
3. Onced asked for the filename press Enter to confirm the current name

Clean up the workspace

To complete the exercise, clean the terminal screen of all previous command outputs.

clear

The terminal is now reset to a blank slate, ready for the next task.