postprocess for segregation

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Hamidreza
2025-07-08 01:06:25 +03:30
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# Post-processing for Evaluating Segregation of Particles
- Compatibility: phasicFlow-v-1.0
- Solvers and tools: sphereGranFlow, postprocessPhasicFlow
## Background
In particle-based simulations, it's often necessary to perform operations on particle fields to obtain bulk properties of the powder system (such as sums or averages). For example, we may need to calculate the mass-averaged velocity of particles in a granular flow. For bulk-processing of particle fields, we can use a mesh structure to obtain bulk properties of the powder in each cell. In this tutorial, we use a rectangular mesh in which a cuboid is divided into equal sub-spaces (cells).
This tutorial demonstrates how to obtain three important bulk properties:
- Mass-averaged solid velocity (and its fluctuations)
- Solid volume fraction
- Volume fraction of small particles (segregation measurement)
## Problem Definition
We will post-process the simulation results from the case [rotating drum with binary particles](../sphereGranFlow/binarySystemOfParticles/). The goal is to create a rectangular mesh with cuboid cells and calculate bulk properties on this mesh to analyze particle segregation patterns.
***
## Case Setup
This tutorial focuses solely on the post-processing aspect of the simulation. It assumes you have already executed the simulation and the results are available for post-processing.
**Important Note:** Postprocessing in phasicFlow can be performed in two modes:
1. **In-simulation postprocessing**: Activated during simulation runtime, allowing calculations on live simulation data
2. **Post-simulation postprocessing**: Performed after the simulation has completed
For more detailed information about different modes of postprocessing, please refer to the [official documentation page](../../../src/PostprocessData/readme.md).
### Configuration File
In `settings/postprocessDataDict`, you configure the post-processing parameters:
```C++
// file: settings/postprocessDataDict
// Enable in-simulation postprocessing (set to "no" for post-simulation only)
runTimeActive yes;
// Shape type used in the simulation
shapeType sphere;
components
(
on_rectMesh
{
// Use Gaussian distribution for sampling and distributing
// particle properties over cells
processMethod GaussianDistribution;
processRegion rectMesh;
// Use time control in settingsDict file
timeControl settingsDict;
// A rectangular mesh is constructed using corner points of the
// mesh region and number of divisions in each direction
rectMeshInfo
{
min (-0.12 -0.12 0.00);
max (0.12 0.12 0.1);
nx 36;
ny 36;
nz 15;
}
operations
(
// Calculate mass-averaged particle velocity
avVelocity
{
function average;
field velocity;
fluctuation2 yes;
threshold 4;
phi mass;
}
// Calculate solid volume fraction
solidVolFraction
{
function sum;
field volume;
divideByVolume yes;
threshold 4;
}
// Calculate volume fraction of small particles
smallSphereVolFraction
{
function average;
field one;
phi volume;
divideByVolume no;
threshold 4;
includeMask lessThan;
lessThanInfo
{
field diameter;
value 0.0031;
}
}
);
}
);
```
### Understanding the Configuration
#### Mesh Configuration
In the `rectMeshInfo` dictionary:
- `min` and `max` define the corner points of the entire domain
- `nx`, `ny`, and `nz` define the number of divisions in each direction
#### Operations
We define three operations to extract bulk properties:
1. **avVelocity**: Calculates mass-averaged particle velocity
The `average` function is defined mathematically as:
$$\text{average} = \frac{\sum_j w_j \cdot \phi_j \cdot \text{field}_j}{\sum_i w_i \cdot \phi_i}$$
When `field` is set to velocity and `phi` is set to mass, we calculate the mass-averaged velocity of particles in each cell. With `fluctuation2` set to yes, we also calculate velocity fluctuations around the mean value.
Note that:
- Cells with fewer than 4 particles are excluded (via the `threshold` parameter)
- $w_j$ is the weight factor determined by the Gaussian distribution function
2. **solidVolFraction**: Calculates solid volume fraction in each cell
The `sum` function is defined as:
$$\text{sum} = \sum_j w_j \cdot \phi_j \cdot \text{field}_j$$
By setting `field` to volume and `divideByVolume` to yes, we sum the volumes of all particles in each cell and divide by the cell volume, giving us the solid volume fraction.
3. **smallSphereVolFraction**: Calculates volume fraction of small particles in each cell
This operation measures the volume fraction of small particles relative to total particle volume. The `includeMask` parameter filters particles by diameter, selecting only those smaller than 0.0031 units.
The numerator of the `average` function calculates the sum of small particle volumes, while the denominator calculates the total volume of all particles.
### Particle Filtering with includeMask
The `includeMask` parameter allows filtering particles based on field values. Available options include:
* `all`: Include all particles (default)
* `lessThan`: Include particles where field < value
* `lessThanEq`: Include particles where field ≤ value
* `greaterThan`: Include particles where field > value
* `greaterThanEq`: Include particles where field ≥ value
* `equal`: Include particles where field = value
* `between`: Include particles where value1 < field < value2
* `betweenEq`: Include particles where value1 ≤ field ≤ value2
## Running the Post-processing Tool
After completing the simulation, execute the post-processing tool with:
```bash
postprocessPhasicFlow
```
The results will be stored in the `./postprocessData` folder.
**Tip:** Run `postprocessPhasicFlow -h` to see all available command-line options, including time range selection for post-processing.

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@ -8,13 +8,29 @@ fileFormat ASCII;
/*---------------------------------------------------------------------------*/
materials (prop1); // a list of materials names
densities (1000.0); // density of materials [kg/m3]
contactListType sortedContactList;
contactSearch
{
method NBS;
updateInterval 10;
sizeRatio 1.1;
cellExtent 0.55;
adjustableBox Yes;
}
model
{
contactForceModel nonLinearNonLimited;
rollingFrictionModel normal;
Yeff (1.0e6); // Young modulus [Pa]
@ -25,29 +41,8 @@ model
en (0.7); // coefficient of normal restitution
et (1.0); // coefficient of tangential restitution
mu (0.3); // dynamic friction
mur (0.1); // rolling friction
}
contactSearch
{
method multiGridNBS; // method for broad search particle-particle
wallMapping multiGridMapping; // method for broad search particle-wall
multiGridNBSInfo
{
updateFrequency 10; // each 10 timesteps, update neighbor list
sizeRatio 1.1; // bounding box size to particle diameter (max)
}
multiGridMappingInfo
{
updateFrequency 10; // each 10 timesteps, update neighbor list
cellExtent 0.6; // bounding box for particle-wall search (> 0.5)
}
}

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@ -1,14 +0,0 @@
/* -------------------------------*- C++ -*--------------------------------- *\
| phasicFlow File |
| copyright: www.cemf.ir |
\* ------------------------------------------------------------------------- */
objectName particleInsertion;
objectType dicrionary;
fileFormat ASCII;
/*---------------------------------------------------------------------------*/
active no; // is insertion active?
collisionCheck No; // not implemented for yes

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@ -8,5 +8,7 @@ fileFormat ASCII;
/*---------------------------------------------------------------------------*/
names (smallSphere largeSphere); // names of shapes
diameters (0.003 0.005); // diameter of shapes
materials (prop1 prop1); // material names for shapes

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@ -3,5 +3,5 @@ cd ${0%/*} || exit 1 # Run from this directory
ls | grep -P "^(([0-9]+\.?[0-9]*)|(\.[0-9]+))$" | xargs -d"\n" rm -rf
rm -rf VTK
rm -rf postprocessData
#------------------------------------------------------------------------------

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@ -0,0 +1,49 @@
/* -------------------------------*- C++ -*--------------------------------- *\
| phasicFlow File |
| copyright: www.cemf.ir |
\* ------------------------------------------------------------------------- */
objectName domainDict;
objectType dictionary;
fileFormat ASCII;
/*---------------------------------------------------------------------------*/
// Simulation domain: every particles that goes outside this domain will be deleted
globalBox
{
min (-0.12 -0.12 0.00); // lower corner point of the box
max (0.12 0.12 0.11); // upper corner point of the box
}
boundaries
{
left
{
type exit; // other options: periodic, reflective
}
right
{
type exit; // other options: periodic, reflective
}
bottom
{
type exit; // other options: periodic, reflective
}
top
{
type exit; // other options: periodic, reflective
}
rear
{
type exit; // other options: periodic, reflective
}
front
{
type exit; // other options: periodic, reflective
}
}

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@ -7,24 +7,43 @@ objectType dictionary;
fileFormat ASCII;
/*---------------------------------------------------------------------------*/
// motion model: rotating object around an axis
motionModel rotatingAxisMotion;
motionModel rotatingAxis;
rotatingAxisInfo // information for rotatingAxisMotion motion model
{
rotAxis
{
p1 (0.0 0.0 0.0); // first point for the axis of rotation
p2 (0.0 0.0 1.0); // second point for the axis of rotation
omega 1.214; // rotation speed (rad/s)
startTime 0.5;
}
}
surfaces
{
/*
A cylinder with begin and end radii 0.12 m and axis points at (0 0 0)
and (0 0 0.1)
A cylinder with begin and end radii 0.12 m and axis points at (0 0 0) and (0 0 0.1)
*/
cylinder
{
type cylinderWall; // type of the wall
p1 (0.0 0.0 0.0); // begin point of cylinder axis
p2 (0.0 0.0 0.1); // end point of cylinder axis
radius1 0.12; // radius at p1
radius2 0.12; // radius at p2
resolution 24; // number of divisions
material prop1; // material name of this wall
motion rotAxis; // motion component name
}
@ -34,11 +53,17 @@ surfaces
wall1
{
type planeWall; // type of the wall
p1 (-0.12 -0.12 0.0); // first point of the wall
p2 ( 0.12 -0.12 0.0); // second point
p3 ( 0.12 0.12 0.0); // third point
p4 (-0.12 0.12 0.0); // fourth point
material prop1; // material name of the wall
motion rotAxis; // motion component name
}
@ -47,25 +72,19 @@ surfaces
*/
wall2
{
type planeWall;
p1 (-0.12 -0.12 0.1);
p2 ( 0.12 -0.12 0.1);
p3 ( 0.12 0.12 0.1);
p4 (-0.12 0.12 0.1);
material prop1;
motion rotAxis;
type planeWall; // type of the wall
p1 (-0.12 -0.12 0.1); // first point of the wall
p2 ( 0.12 -0.12 0.1); // second point
p3 ( 0.12 0.12 0.1); // third point
p4 (-0.12 0.12 0.1); // fourth point
material prop1; // material name of the wall
motion rotAxis; // motion component name
}
}
}
// information for rotatingAxisMotion motion model
rotatingAxisMotionInfo
{
rotAxis
{
p1 (0.0 0.0 0.0); // first point for the axis of rotation
p2 (0.0 0.0 1.0); // second point for the axis of rotation
omega 1.214; // rotation speed (rad/s)
}
}

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@ -10,21 +10,20 @@ fileFormat ASCII;
// positions particles
positionParticles
{
method positionOrdered; // ordered positioning
method ordered;
maxNumberOfParticles 30001; // maximum number of particles in the simulation
mortonSorting Yes; // perform initial sorting based on morton code?
regionType cylinder;
cylinder // cylinder region for positioning particles
cylinderInfo
{
p1 (0.0 0.0 0.003); // begin point of cylinder axis
p2 (0.0 0.0 0.097); // end point of cylinder axis
radius 0.117; // radius of cylinder
}
positionOrderedInfo
orderedInfo
{
distance 0.005; // minimum distance between particles centers
distance 0.005; // minimum space between centers of particles
numPoints 30000; // number of particles in the simulation
axisOrder (z x y); // axis order for filling the space with particles
}
@ -35,8 +34,8 @@ setFields
/*
Default value for fields defined for particles
These fields should always be defined for simulations with
spherical particles.*/
spherical particles.
*/
defaultValue
{
velocity realx3 (0 0 0); // linear velocity (m/s)
@ -49,17 +48,17 @@ setFields
{
shapeAssigne
{
selector selectRandom; // type of point selector
selectRandomInfo
selector randomPoints; // type of point selector
randomPointsInfo
{
begin 0; // begin index of points
end 29999; // end index of points
number 10000; // number of points to be selected
number 10000;
}
fieldValue // fields that the selector is applied to
{
/*
sets shapeName of the selected points to largeSphere*/
shapeName word largeSphere;
}
}

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@ -0,0 +1,82 @@
/* -------------------------------*- C++ -*--------------------------------- *\
| phasicFlow File |
| copyright: www.cemf.ir |
\* ------------------------------------------------------------------------- */
objectName processDataDict;
objectType dictionary;;
fileFormat ASCII;
/*---------------------------------------------------------------------------*/
runTimeActive yes;
shapeType sphere;
components
(
on_rectMesh
{
processMethod GaussianDistribution;
processRegion rectMesh;
timeControl settingsDict;
rectMeshInfo
{
min (-0.12 -0.12 0.00);
max (0.12 0.12 0.1);
nx 36;
ny 36;
nz 15;
}
operations
(
avVelocity
{
function average;
field velocity;
fluctuation2 yes;
threshold 4;
phi mass;
}
solidVolFraction
{
function sum;
field volume;
divideByVolume yes;
threshold 4;
}
smallSphereVolFraction
{
function average;
field one;
phi volume;
divideByVolume no;
threshold 4;
includeMask lessThan;
lessThanInfo
{
field diameter;
value 0.0031;
}
}
);
}
);

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@ -1,54 +0,0 @@
/* -------------------------------*- C++ -*--------------------------------- *\
| phasicFlow File |
| copyright: www.cemf.ir |
\* ------------------------------------------------------------------------- */
objectName postprocessDict;
objectType dictionary;;
fileFormat ASCII;
/*---------------------------------------------------------------------------*/
rectMesh
{
min (-0.12 -0.12 0.0); //minimum corner point
max (0.12 0.12 0.1); //maximum corner point
nx 24; // number of divisions in x direction
ny 24; // number of divisions in y direction
nz 10; // number of divisions in z direction
}
numberBased
{
// num particles in a cell
numParticles
{
field real 1.0; // uniform field with value 1
operation sum; // sum over all particles in a cell
includeMask all; // select all
}
// concentration of small particles (number based)
smallConc
{
field real 1.0; // uniform field with value 1
operation average; // average over all particles in a cell
threshold 1; // exclude cells with number of particles less than 1
includeMask lessThan; // include mask
lessThanInfo
{
field diameter; // include particles with diameter less than 0.004
value 0.004;
}
}
// average velocity of particles
avVelocity
{
field velocity; // read velocity field from time folder
operation average; // average over all particles in the cell
threshold 3; // exclude cells with number of particles less than 3
includeMask all; // select all
}
}

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@ -3,12 +3,16 @@
| copyright: www.cemf.ir |
\* ------------------------------------------------------------------------- */
objectName settingsDict;
objectType dictionary;;
objectType dictionary;
fileFormat ASCII;
/*---------------------------------------------------------------------------*/
run rotatingDrumSmall;
libs ("libPostprocessData.so");
auxFunctions postprocessData;
dt 0.00001; // time step for integration (s)
startTime 0; // start time for simulation
@ -21,20 +25,14 @@ timePrecision 6; // maximum number of digits for time folder
g (0 -9.8 0); // gravity vector (m/s2)
/*
Simulation domain
every particles that goes outside this domain is deleted.
*/
domain
{
min (-0.12 -0.12 0);
max (0.12 0.12 0.1);
}
includeObjects (diameter); // save necessary (i.e., required) data on disk
integrationMethod AdamsBashforth2; // integration method
writeFormat ascii;
integrationHistory off;
timersReport Yes; // report timers?
writeFormat ascii; // data writting format (ascii or binary)
timersReport Yes; // report timers (Yes or No)
timersReportInterval 0.01; // time interval for reporting timers