Post-processing#

Lethe has built-in post-processing capabilities. All post-processing results are written as VTU, PTVU, PVD, CSV and/or DAT files.

The post-processing subsection of the .prm file is according to the following example:

subsection post-processing
   # Enable output of grid, granular temperature, and particles' average velocity
   set lagrangian post-processing = false

   # Enable output of force chains
   set force chains = false

   # Enable particle-wall collision statistics
   subsection particle wall collision statistics
     set enable particle wall contact statistics = false
     set collision statistics file               = collision_statistics.csv
     set verbosity                               = quiet # Choices are quiet|verbose
     set log collisions with all walls           = true
     set wall boundary ids                       = 0
   end
end

Note

By default, post-processing options are set to false to reduce the number of files generated.

Lagrangian post-processing#

The lagrangian post-processing enables VTU files output generated with the same output frequency as the particles’ results (see the Simulation Control section of this guide). The name of the generated files is set by the output name parameter in the simulation_control section plus the suffix -postprocess_data. The files include:

  • The grid of the domain, with the distribution of the subdomains generated by the load balance (more information about load balancing is provided in the Model Parameters section of this guide).

  • The spatial average of the particle’s velocity (in x, y, z and its norm) for each cell.

  • The granular temperature for each cell.

Important

The particles’ average velocity and the granular temperature are cell based results calculated instantaneously at each outputting time-step. This means that they are only instantaneous spatial averages, i.e, DO NOT correspond to temporal averages measured between the outputs. For a higher resolution of the results in time, we recommend the use of a lower output frequency (Simulation Control).

Force chains post-processing#

The force chains feature enables VTU, PTVU, and PVD files to visualize force chains between particles. The name of the generated files is set by the output name parameter in the simulation_control section plus the suffix -force_chains. The files include:

  • Lines to represent normal forces between particles in contact (use wireframe display with paraview).

  • The force value for each line.

Warning

The force chains feature is not implemented for contact occurring through periodic boundaries.

The following video shows force chains for the Rectangular Hopper example.

Particle-wall collision statistics#

The particle-wall contact statistics logging feature allows to log the statistics of collisions between particles and walls in a .dat file or a .csv file. This feature is useful for post-processing and analysis of particle-wall interactions.

  • enable particle wall collision statistics enables the feature.

  • collision statistics file is the name of the file where the particle-wall contact statistics will be logged. The file will be created from the working directory of the simulation. If the name does not specify the format, the file will be created in .csv format. If the name ends with .dat or .csv, the file will be created in the corresponding format.

  • verbosity controls the verbosity of the particle-wall collisions. The available options are quiet (the default option) and verbose. If set to verbose, the start and the end of a collision are printed in the terminal.

  • log collisions with all walls is a boolean parameter that controls whether the particle-wall contact statistics will be logged for all walls or only for the walls defined by the wall boundary ids parameter. If set to true, the statistics will be logged for all walls. If set to false, the statistics will be logged only for the walls defined by the wall boundary ids parameter.

  • wall boundary ids is the list of the wall boundary IDs where the particle-wall contact statistics will be logged when log collisions with all walls is set to false. When log collisions with all walls is set to true, this parameter is ignored. Each wall boundary ID must be separated by a comma.