What are simulation components?

Simulation components, or simcomps fo short, incapsulate additional functionality that may be useful for certain cases but not necessary to run the solver. This can include computation and output of additional fields, in-situ post-processing operations, data sampling, etc.

By design, simulation components can tap into every aspect of the simulation, so they can be quite powerful. As the code grows, we expect to add more and more simcomps to the code.

Adding simulation components to the case

Each simcomp is defined as a single JSON object at are added to an array of objects called simulation_components, which resides directly under the case object.

Controling execution and file output

Each simulation component is, by default, executed once per time step to perform associated computations and output. However, this can be modified by using the compute_control and compute_value parameters for the computation and the output_control and and output_value for the output to disk. The parameters for the _control values are the same as for the fluid and checkpointing. Additionally, one can set output_control to global and never. The former will sync the output_ parameter to that of the fluid. Choosing never will suppress output all together. If no parameters for the output_ parameters are provided, they are set to be the same as for compute_.

For simcomps that compute 3D fields, the output can be either added to the main .fld file, containing velocity and pressure, or saved to a separate file. For the latter, the output_filename keyword should be provided. One can additionally provide the precision keyword, which can be set to either single or double to control the precision of the written data.

For example, in the tgv example case the vorticity component is executed once per 50 time steps. The output_ parameters are synced to that, and the vorticity fields will be added to the main .fld file.

{
    "type": "vorticity",
    "compute_control": "tsteps",
    "compute_value": 50
}

List of simulation components

vorticity

Computes the vorticity field an stores in the field registry as omega_x, omega_y and omega_z. Currently produces no output.

lambda2

Computes \( \lambda_2 \) for the velocity field and stores it in the normal output files as the first unused field. This means that \( \lambda_2 \) can be found in the temperature field in then fld files if running without a scalar and s1 if neko is run with one scalar.

probes

Probes selected solution fields at the points given inside an input file. Example usage:

{
  "type": "probes",
  "compute_control": "simulationtime",
  "compute_value"    : 1,
  "points_file":  "probes.csv",
  "output_file":  "output.csv",
  "fields": ["w","s"]
}

This probes the fields 'w', and 's' in the points described by points.csv and outputs into output.csv every 1 time units.

The probed information will be saved in the output file in the following format:

N_p, N_f, fields[0], fields[1], ..., fields[N_f-1]
p_0_x, p_0_y, p_0_z
p_1_x, p_1_y, p_1_z
...
p_N_p_x, p_N_p_y, p_N_p_z
time_0, p_0_field_0, p_0_field_1, ..., p_0_field_N_f-1
time_0, p_1_field_0, p_1_field_1, ..., p_1_field_N_f-1
...
time_0, p_N_p_field_0, p_N_p_field_1, ..., p_N_p_field_N_f-1
time_1, p_0_field_0, p_0_field_1, ..., p_0_field_N_f-1
time_1, p_1_field_0, p_1_field_1, ..., p_1_field_N_f-1
...
time_N_p, p_N_p_field_0, p_N_p_field_1, ..., p_N_p_field_N_f-1

field_writer

Outputs registered 3D fields to an .fld file. Requires a list of field names in the fields keyword. Primarily to be used for outputting new fields defined in the user file. The fields are added to then neko_field_registry object and are expected to be updated in the user file, or, perhaps, by other simcomps. Since this simcomp does not compute anything compute_ configuration is irrelevant.

{
  "type": "field_writer",
  "fields": ["my_field1", "my_field2"],
  "output_filename": "myfields",
  "precision": "double",
  "output_control" : "simulation_time",
  "output_value" : 1.0
}

Table of Contents