Parameters Guide#

Launching an application requires an executable of the required solver, and a parameters file (with extension .prm). The parameter file controls all aspects of Lethe and drives the simulation. The parameter file is structured with different subsections, as explained in the following:

Lethe also has a few head level parameters that are compatible with all applications:

set dimension        = 0
set print parameters = none
set comment message  =

  • dimension: Dimension of the simulated problem. Lethe supports 2D (dimension = 2) and 3D (dimension = 3) simulations.

    Attention

    This parameter must be defined in the parameters file. Otherwise, an error message will be printed:

    While reading the dimension from the input file, Lethe found a value that is
neither 2 or 3. Since August 2023, Lethe requires that the user explicitly
specify the dimension of the problem within the parameter file. This can be
achieved by adding set dimension = 2 or set dimension = 3 within the parameter
file.

  • print parameters: Prints the parameters of the simulation on the console before starting the simulation when set to changed only or all. The latter (all) prints the values of all the parameters declared and parsed by the application, while the former (changed only) prints only the values of the parameters that have been modified (non-default values). By default, print parameters is set to none resulting in no parameters being printed.

  • comment message: Prints a message on the console before starting the simulation when specified. On the console, the message is preceded by a line with Comment message: .

    Example

    In the parameters file, when

    set comment message = This test checks that the adaptive capillary time-step constraint is well \napplied for cases with a maximum capillary time-step ratio set to 10 (Δt/Δt_σ). \nThe mesh, the densities and the surface tension considered here remain constant.

    On the console, the following is displayed:

    Comment message:
This test checks that the adaptive capillary time-step constraint is well
applied for cases with a maximum capillary time-step ratio set to 10 (Δt/Δt_σ).
The mesh, the densities and the surface tension considered here remain constant.

    Tip

    A few escape sequences are supported by the comment message:

    • \n: Newline

    • \t: Horizontal tab

    • \r: Carriage return

    • \b: Backspace

    • \v: Vertical tab

Tip

The complete options for the parameters file, with information regarding the parameters that can be used, can be obtained by doing the following:

  • Go to /lethe/build/applications/navier_stokes_parameter_template/

  • Run the navier_stokes_parameter_template using the command ./navier_stokes_parameter_template

Two parameter files, with default values for all the parameters, are obtained for 2D and 3D respectively.

Note

  • The parameters are established one by one using the following syntax: set parameter name = value

  • Comments are preceded by the sharp symbol (e.g. #comment)

  • The parameter file format has a sanity checking mechanism in place and will throw an error if an unknown parameter or an invalid value is entered.

Warning

The radioactive particle-tracking (RPT) applications of Lethe has been migrated to a separate repository which is available here.