# Problem definition
A rotating drum is randomly filled with two particle sizes and rotated to observe particle segregation. The focus of this tutorial is to show how to use the preprocessing tool `particlesPhasicFlow` to create the initial mixture of small and large particles.
**Note:** It is supposed that you have reviewed [simulating a rotating drum](https://github.com/PhasicFlow/phasicFlow/wiki/Simulating-a-rotating-drum) tutorial before starting this tutorial.
a view of the rotating drum with small and large particles after 7 seconds of rotation
***
# Case setup
In the file `caseSetup/sphereShape` two particle types with the names `smallSphere` and `largeSphere` and the diameters 3 and 5 mm are defined.
[Simulation case setup files can be found in tutorials/sphereGranFlow folder.](https://github.com/PhasicFlow/phasicFlow/tree/main/tutorials/sphereGranFlow/binarySystemOfParticles)
### Shape definition
In the file `caseSetup/sphereShape` two particle types with the names `smallSphere` and `largeSphere` and the diameters 3 and 5 mm are defined.
in caseSetup/sphereShape file
```C++
names (smallSphere largeSphere); // names of shapes
diameters (0.003 0.005); // diameter of shapes (m)
materials (prop1 prop1); // material names for shapes
```
### Positioning and initial mixture
In the dictionary `positionParticles` located in file `settings/particlesDict`, 30000 particles are located in a cylindrical region. These particles are positioned in order along `z`, `x` and then `y` axis with 0.005 m distance between their centers.
in settings/particlesDict file
```C++
// positions particles
positionParticles
{
method ordered; // other options: random or empty
orderedInfo
{
diameter 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
}
regionType cylinder; // other options: box and sphere
cylinder // cylinder region for positioning particles
{
p1 (0.0 0.0 0.003); // begin point of cylinder axis (m m m)
p2 (0.0 0.0 0.097); // end point of cylinder axis (m m m)
radius 0.117; // radius of cylinder (m)
}
}
```
In the `setFields` dictionary, located in the `settings/particlesDict` file, you define the initial `velocity`, `acceleration`, `rotVelocity` and `shapeName` fields for all 30000 particles in the simulation. In the `selectors' dictionary, you can select subsets of particles and set the field value for those subsets. The `selectRange` selector is defined in the `shapeAssigne` subdictionary. It defines a range with `begin`, `end` and `stride` to select particles. And in the `fieldValue` subdictionary the field values for selected particles are set (any number of field values can be set here).
**Note:** Other selectors are: `selectBox` that selects particles inside a box and `randomSelect` that selects particles randomly from a given index range.
in settings/particlesDict file
```C++
setFields
{
/*
Default value for fields defined for particles
These fields should always be defined for simulations with
spherical particles.
*/
defaultValue
{
velocity realx3 (0 0 0); // linear velocity (m/s)
acceleration realx3 (0 0 0); // linear acceleration (m/s2)
rotVelocity realx3 (0 0 0); // rotational velocity (rad/s)
shapeName word smallSphere; // name of the particle shape
}
selectors
{
shapeAssigne
{
selector stridedRange; // other options: box, cylinder, sphere, randomPoints
stridedRangeInfo
{
begin 0; // begin index of points
end 30000; // end index of points
stride 3; // stride for selector
}
fieldValue // fields that the selector is applied to
{
/*
sets shapeName of the selected points to largeSphere
*/
shapeName word largeSphere;
}
}
}
```
# Running the simulation
Enter the following command in terminal:
`> geometryPhasicFlow`
`> particlesPhasicFlow`
`> sphereGranFlow`
### Note on using particlesPhasicFlow
Each executable in PhasicFlow comes with some command line options that you can see them by using flag `-h` in front of that command.
`> particlesPhasicFlow -h` prints out the following output:
```
Usage: particlesPhasicFlow [OPTIONS]
Options:
-h,--help Help for using createParticles of phasicFlow v-0.1
-v,--version Program version information
--discription What does this app do?
--positionParticles-only Exectue the positionParticles part only and store the created pointStructure in the time folder.
--setFields-only Exectue the setFields part only. Read the pointStructure from time folder and setFields and save the result in the same time folder.
```
so, with flag `--setFields-only`, you can execute the `setFields` part of `particlesDict`. Now suppose that you have a simulation case which proceeded up to 2 seconds and for any reason you want to change some field value at time 3 s and continue the simulation from 3 s. To this end, you need to change `startTime` in settings dictionary to 3, execute `particlesPhasicFlow --setFields-only`, and start the simulation.
