General post-processings

In this section, we describe the post-processing options available in MFEM-MGIS.

Warning

This section is under construction

The ParaviewExport post-processing

This post-processing allows exporting the unknowns of a nonlinear evolution problem for visualization in paraview:

• Key: ParaviewExportResults

Example:

problem.addPostProcessing(ctx, "ParaviewExportResults",
                          {{"OutputFileName", "SatohTestOutput"}}) |
    or_die;

Results

It is also possible to extract only portions of the mesh by defining either the boundary zones or the materials (domain attributes). This is particularly useful for reducing the size of output files when only a small part is to be studied.

Example

std::vector<mfem_mgis::Parameter> materials{"Attr1", "Attr2"};
std::vector<mfem_mgis::Parameter> bdrs{"left", "right"};
/** You can not define Materials and Boundaries in a single post processing
 */
problem.addPostProcessing(
    ctx, "ParaviewExportResults",
    {{"OutputFileName", "TestPPSubMeshOutputDir/AllMesh"},
     {"Materials", materials},
     {"OutputFieldName", "Displacement"},
     {"Verbosity", 1}}) |
    or_die;
problem.addPostProcessing(
    ctx, "ParaviewExportResults",
    {{"OutputFileName", "TestPPSubMeshOutputDir/Attribute1"},
     {"OutputFieldName", "Displacement"},
     {"Material", "Attr1"},
     {"Verbosity", 1}}) |
    or_die;
problem.addPostProcessing(
    ctx, "ParaviewExportResults",
    {{"OutputFileName", "TestPPSubMeshOutputDir/Attribute2"},
     {"OutputFieldName", "Displacement"},
     {"Material", "Attr2"},
     {"Verbosity", 1}}) |
    or_die;
problem.addPostProcessing(
    ctx, "ParaviewExportResults",
    {{"OutputFileName", "TestPPSubMeshOutputDir/Boundaries"},
     {"OutputFieldName", "Displacement"},
     {"Boundaries", bdrs},
     {"Verbosity", 1}}) |
    or_die;

Note

Boundary and Material names are defined by the problem using the key words: “Boundaries” or “Materials” such as:

• {“Materials”, mfem_mgis::Parameters{{“Attr1”, 1}, {“Attr2”, 2}}}

• {“Boundaries”, mfem_mgis::Parameters{{“left”, 1}, {“right”, 2}}}

Results

Key	Description
OutputFileName	Name of the output directory
OutputFieldName	Name of the field that will appear in ParaView (default: "u")
Material/Materials	List of materials; a submesh will be used instead of exporting the entire mesh
Boundary/Boundaries	List of boundaries; a submesh will be used instead of exporting the entire mesh
Verbosity	If this value is >= 1, submesh information will be displayed when using attributes
ExecuteInitialPostProcessing	Export the results at the initial time of the simulation (default: true)

Export Integration Point Results At Nodes

• Key: ParaviewExportIntegrationPointResultsAtNodes

Example:

auto results = std::vector<mfem_mgis::Parameter>{
    "Stress", "ImposedTemperature", "HydrostaticPressure"};
problem.addPostProcessing(
    ctx, "ParaviewExportIntegrationPointResultsAtNodes",
    {{"OutputFileName", "SatohTestIntegrationPointOutput"},
     {"Materials", {"plate"}},
     {"Results", results}}) |
    or_die;

The optional ExecuteInitialPostProcessing boolean parameter (true by default) states if the results are exported at the initial time of the simulation.

Results

Compute Mean Thermodynamic Forces

This post-processing computes the mean value of each component of the thermodynamic forces in each material. For a mechanical behaviour, the thermodynamic forces are the stresses.

• Key: MeanThermodynamicForces

Example:

problem.addPostProcessing(ctx, "MeanThermodynamicForces",
                          {{"OutputFileName", "avgStress"}}) |
    or_die;

Results

These results come from the example Representative Volume Element of Combustible Mixed Oxides for Nuclear Applications. Its RVE contains 83 % of matrix and 17 % of inclusion. These commands compute the average stress SZZ over the RVE and plot it:

awk '{if(NR>13) print $1 " " 0.83*$4+0.17*$10}' avgStress > res-mfem-mgis.txt
plot "res-mfem-mgis.txt" u 1:2 w l title "mfem-mgis"

Compute Stored Energy

• Key: StoredEnergy

Example:

problem.addPostProcessing(ctx, "StoredEnergy",
                          {{"OutputFileName", "energy.txt"}}) |
    or_die;

Compute dissipated Energy

• Key: DissipatedEnergy

Example:

problem.addPostProcessing(ctx, "DissipatedEnergy",
                          {{"OutputFileName", "dissipated_energy.txt"}}) |
    or_die;

Materials with several behaviour integrators

The ComputeResultantForceOnBoundary, MeanThermodynamicForces, StoredEnergy and DissipatedEnergy post-processings accept an optional BehaviourIntegrator parameter. It selects the behaviour integrators of each material:

• an integer: the behaviour integrator of this index in each material,

• "All": all the behaviour integrators, whose contributions are summed.

Without this parameter, each material must have a single behaviour integrator.

Example:

problem.addPostProcessing(ctx, "StoredEnergy",
                          {{"OutputFileName", "energy.txt"},
                           {"BehaviourIntegrator", "All"}}) |
    or_die;