# Simulating a small rotating drum {#rotatingDrumSmall}
## Problem definition
The problem is to simulate a rotating drum with the diameter 0.24 m and the length 0.1 m rotating at 11.6 rpm. It is filled with 30,000 4-mm spherical particles. The timestep for integration is 0.00001 s.
a view of rotating drum
***
## Setting up the case
The PhasicFlow simulation case setup is based on the text-based scripts that we provide in two folders located in the simulation case folder: `settings` and `caseSetup` (You can find the case setup files in the above folders.
All commands should be entered in the terminal with the current working directory being the simulation case folder (at the top of the `caseSetup` and `settings` folders).
### Creating particles
Open the file `settings/particlesDict`. Two dictionaries, `positionParticles` and `setFields`, position particles and set field values for the particles.
In the dictionary `positionParticles`, the positioning method is `positionOrdered`, which positions particles in order in the space defined by `box`. The `box` space is defined by two corner points `min` and `max`. In the dictionary `positionOrderedInfo`, `numPoints` defines the number of particles, `diameter` the distance between two adjacent particles, and `axisOrder` the axis order for filling the space with particles.
in settings/particlesDict file
```C++
positionParticles
{
method ordered; // other options: random and empty
orderedInfo
{
diameter 0.004; // minimum space between centers of particles
numPoints 30000; // number of particles in the simulation
axisOrder (z y x); // axis order for filling the space with particles
}
regionType box; // other options: cylinder and sphere
boxInfo // box for positioning particles
{
min (-0.08 -0.08 0.015); // lower corner point of the box
max ( 0.08 0.08 0.098); // upper corner point of the box
}
}
```
In the `setFields` dictionary, the `defaultValue` dictionary defines the initial value for particle fields (here `velocity`, `acceleration`, `rotVelocity` and `shapeName`). Note that the `shapeName` field should match the name of the shape that you will later set for shapes (here a shape named `sphere1`).
in settings/particlesDict file
```C++
setFields
{
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 sphere1; // name of the particle shape
}
selectors
{}
}
```
Enter the following command in the terminal to create the particles and store them in `0` folder.
`> particlesPhasicFlow`
### Creating geometry
In file `settings/geometryDict` , you can provide information for creating geometry. Each simulation should have a `motionModel` that defines a model for moving the surfaces in the simulation. `rotatingAxisMotion` model defines a fixed axis which rotates around itself. The dictionary `rotAxis` defines an motion component with `p1` and `p2` as the end points of the axis and `omega` as the rotation speed in rad/s. You can define more than one motion component in a simulation.
in settings/geometryDict file
```C++
motionModel rotatingAxis;
.
.
.
rotatingAxisInfo
{
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)
}
}
```
The `surfaces` dictionary allows you to define all surfaces (walls) in the simulation. There are two main options: built-in geometries in PhasicFlow and providing surfaces with stl file. Here we will use built-in geometries. In the `cylinder` dictionary a cylindrical shell with end radii `radius1` and `radius2`, axis end points `p1` and `p2`, material name `prop1`, motion component `rotAxis` is defined. `resolution` sets the resolution of the cylinder hull. wall1` and `wall2` define two plane walls at two ends of the cylindrical shell with coplanar vertices `p1`, `p2`, `p3` and `p4`, `material` name `prop1` and `motion` component `rotAxis`.
in settings/geometryDict file
```C++
surfaces
{
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
}
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
}
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;
}
}
```
Enter the following command in the terminal to create the geometry and store it in `0/geometry` folder.
`> geometryPhasicFlow`
### Defining properties and interactions
The `caseSetup/interaction' file contains material properties. `materials` defines a list of material names in the simulation and `densities` sets the corresponding density of each material name. model dictionary defines the interaction model for particle-particle and particle-wall interactions. ContactForceModel selects the model for mechanical contacts (here nonlinear model with limited tangential displacement) and `rollingFrictionModel` selects the model for the calculation of rolling friction. Other required properties should be defined in this dictionary.
in caseSetup/interaction file
```C++
materials (prop1); // a list of materials names
densities (1000.0); // density of materials [kg/m3]
.
.
.
model
{
contactForceModel nonLinearNonLimited;
rollingFrictionModel normal;
Yeff (1.0e6); // Young modulus [Pa]
Geff (0.8e6); // Shear modulus [Pa]
nu (0.25); // Poisson's ratio [-]
en (0.7); // coefficient of normal restitution
et (1.0); // coefficient of tangential restitution
mu (0.3); // dynamic friction
mur (0.1); // rolling friction
}
```
Dictionary `contactSearch` sets the methods for particle-particle and particle-wall contact search. method' specifies the algorithm for finding the neighbor list for particle-particle contacts and `wallMapping' specifies how particles are mapped to walls for finding the neighbor list for particle-wall contacts. `updateFrequency` specifies the frequency for updating the neighbor list and `sizeRatio` specifies the size of enlarged cells (with respect to particle diameter) for neighbor list search. Larger `sizeRatio` includes more particles in the neighbor list and you need to update it less frequently.
in caseSetup/interaction file
```C++
contactSearch
{
method NBS; // method for broad search particle-particle
updateInterval 10;
sizeRatio 1.1;
cellExtent 0.55;
adjustableBox Yes;
}
```
In the file `caseSetup/sphereShape`, you can define a list of `names` for shapes (`shapeName` in particle field), a list of diameters for shapes and their `properties` names.
in caseSetup/sphereShape file
```C++
names (sphere1); // names of shapes
diameters (0.004); // diameter of shapes
materials (prop1); // material names for shapes
```
Other settings for the simulation can be set in file `settings/settingsDict`. The dictionary `domain` defines the a rectangular bounding box with two corner points for the simulation. Each particle that gets out of this box, will be deleted automatically.
in settings/settingsDict file
```C++
dt 0.00001; // time step for integration (s)
startTime 0; // start time for simulation
endTime 10; // end time for simulation
saveInterval 0.1; // time interval for saving the simulation
timePrecision 6; // maximum number of digits for time folder
g (0 -9.8 0); // gravity vector (m/s2)
domain
{
min (-0.12 -0.12 0);
max (0.12 0.12 0.11);
}
integrationMethod AdamsBashforth2; // integration method
```
## Running the case
The solver for this simulation is `sphereGranFlow`. Enter the following command in the terminal. Depending on the computational power, it may take a few minutes to a few hours to complete.
`> sphereGranFlow`
## Post processing
After finishing the simulation, you can render the results in Paraview. To convert the results to VTK format, just enter the following command in the terminal. This will converts all the results (particles and geometry) to VTK format and store them in folder `VTK/`.
`> pFlowToVTK`