Usage

Running a simulation

To run an AdditiveFOAM simulation, it is recommended to perform the following steps:

  1. Prepare the case directory structure using a provided template: 
    mkdir -p $FOAM_RUN/additivefoam
cd $FOAM_RUN/additivefoam
cp -r $WM_PROJECT_USER_DIR/AdditiveFOAM/tutorials/AMB2018-02-B userCase
cd userCase

  2. Modify the necessary input files according to your simulation requirements. These files are described in Case Files.

  3. Run the simulation using shell scripting. Examples are provided in the Allrun scripts in each tutorial which creates a mesh, decomposes the mesh across multiple processors, and runs the AdditiveFOAM case in parallel using MPI.

    #!/bin/sh
cd ${0%/*} || exit 1    # Run from this directory
   
# Source tutorial run functions
. $WM_PROJECT_DIR/bin/tools/RunFunctions

application=`getApplication`
   
runApplication blockMesh
runApplication decomposePar
runParallel $application

runApplication reconstructPar
  4. Visualize and post-process the results using ParaView 
    touch case.foam
paraview case.foam

AdditiveFOAM file structure

case files

An AdditiveFOAM case directory has a typical organization like:

|-- case-directory/
|   |-- 0/
|   |   |-- alpha.powder
|   |   |-- alpha.solid
|   |   |-- p_rgh
|   |   |-- T
|   |   |-- U
|   |
|   |-- constant/
|   |   |-- heatSourceDict
|   |   |-- scanPath
|   |   |-- transportProperties
|   |   |-- thermoPath
|   |
|   |-- system/
|   |   |-- blockMeshDict
|   |   |-- controlDict
|   |   |-- fvScheme
|   |   |-- fvSolution
|   |
|   +-- ..
  • 0: Directory containing the initial conditions and boundary conditions for each field. The fields are specified by their file name:
    • T: temperature (required)
    • U: velocity (optional)
    • p_rgh: reduced pressure (optional)
    • alpha.solid: solid volume fraction (optional)
    • alpha.powder: powder volume fraction (optional)

  • constant: Directory containing the definitions for material conditions, including:

    • transportProperties: File that defines the transport properties of the material. An example of this file for IN625 is: 
      solid
{
    kappa   (8.275  0.01472   0.0);
    Cp      (579.28 0.0       0.0);
}

liquid
{
    kappa   (4.889    0.014743  0.0);
    Cp      (750.65   0.0       0.0);
}

powder
{
    kappa   (-0.07707   0.00075   0.0);
    Cp      (747.568    0.0       0.0);
}

rho     [1 -3 0 0 0 0 0]    7569.92;   // reference density
mu      [1 -1 -1  0 0 0 0]  0.003032;  // dynamic viscosity
beta    [0 0 0 -1 0 0 0]    1.2e-4;    // coefficient of thermal expansion
DAS     [0 1 0 0 0 0 0]     10e-6;     // dendrite arm spacing (for drag)
Lf      [0  2 -2  0 0 0 0]  2.1754e5;  // latent heat of fusion

      The thermal conductivity kappa and specific heat Cp are given as temperature dependent second-order polynomials for the solid, liquid, and powder phases. The remaining transport properties are all assumed to be constant during the simulation.

    • heatSourceDict: File that defines the number and mathematical form of moving heat sources in the simulation. An example of this file is: 
      sources (beam);

beam
{
    pathName            scanPath;    

    absorptionModel     constant;
        
    constantCoeffs
    {
        eta             0.3;
    }
        
    heatSourceModel     superGaussian;
        
    superGaussianCoeffs
    {
        k               2.0;
        dimensions      (85.0e-6 85.0e-6 30e-6);
        nPoints         (10 10 10);
    }
}

      The available entries for the absorption models are:

      • constant
      • Kelly: An effective absorption is calculated based of the geometry and apsect ratio of the heat source shape to simulate keyhole formation.

      The available entries for the heatSourceModel are:

      • superGaussian
      • modifiedSuperGaussian

      Each heat source model can dynamically update its depth to the a specified isotherm position by setting the transient flag to True. The recommended value for isoValue is the alloy liquidus temperature for simulating keyhole formation.

    • thermoPath: File that tabulates the temperature-solid fraction relationship. An example path for a linear transition between the eutetic and liquidus temperatures for IN625 is: 
      (
    1410.0000    1.0000
    1620.0000    0.0000
)
  • system: Directory containing simulation configuration files.
    • controlDict: File that sets simulation time settings and numerical parameters.
    • fvSchemes: File that sets the discretization schemes used to solve the governing equations.

    • fvSolution: File that sets solution algorithms and convergence criteria.

      Fluid flow can be turned off by setting nOuterCorrectors to 0 in the PIMPLE dictionary.

      The thermodynamic algorithm settings are defined in the PIMPLE dictionary. The optional explicitSolve enables a first-order explicit solution to the temperature equation whenever the solution is numerically stable, providing computational speedup over the implicit solution.

      PIMPLE
{
    momentumPredictor no;
    nOuterCorrectors 0;
    nCorrectors     1;
    nNonOrthogonalCorrectors 0;
    pRefCell        0;
    pRefValue       0;


    nThermoCorrectors   20;
    thermoTolerance     1e-8;
    explicitSolve       true;
}

Scan path file

AdditiveFOAM supports a scan path file format that decomposes the laser path into segments that are either a) line sources (mode = 0) or b) point sources (mode = 1).

An example scan path file for a bi-directional raster with a hatch-spacing of 100 \(\mu m\) is:

Mode    X       Y       Z     Power   Parameter
1       0.000   0.000   0.0   0.0     0.0
0       0.002   0.000   0.0   195.0   0.8
0       0.002   0.0001  0.0   0.0     0.8
0       0.000   0.0001  0.0   195.0   0.8

The beam starts at (0, 0, 0) \(m\) and moves horizontally to (0.002, 0, 0.0) \(m\) with a power of 195 \(W\) and speed of 0.8 \(m/s\). Then, the laser turns off and moves vertically to (0.002, 0.0001, 0.0) \(m\) at a speed of 0.8 \(m/s\). Finally, the laser moves horizontally to (0.002, 0.0001, 0.0) \(m\) with a power of 195 \(W\) and speed of 0.8 \(m/s\). At this point, the laser turns off for the remainder of the simulation.

A summary of the entries defining a path segment for the scan path is provided in the following table:

Column Description
Column 1 Mode = 0: line source,
Mode = 1: point source
Columns 2-4 Mode = 0: the final (x,y,z) position of the beam in meters.
Mode = 1: the current (x,y,z) position of the beam in meters
Column 5 Value for laser power in watts
Column 6 Mode = 0: the speed of the beam in meters/second.
Mode = 1: the time the beam remains at its current position in seconds

AdditiveFOAM output

ExaCA data

AdditiveFOAM is can export thermal data to ExaCA, a cellular automata (CA) code for grain growth under additive manufacturing conditions.

This feature is enabled using the execute flag in the constant/foamToExaCADict file. The solidification conditions at the specified isotherm is tracked in the represenative volume element defined by box and a resolution defined by dx. An example file for tracking the liquidus temperature the RVE for the above scan path is:

execute     on;

box         (0 -0.0001 -0.0002) (0.002 0.0002 0);
dx          2.5e-6;
isotherm    1620;

It is recommended to track the liquidus isotherm to remain consistent with the assumptions in ExaCA. Users should be warned that this interpolation may requires significant computation overhead when the resolution of the ExaCA data is much finer than that of the AdditiveFOAM mesh, and therefore, this feature should be used selectively.