# Simulating a Rotating Drum (v-1.0)
## Problem Definition
The problem is to simulate a rotating drum with a diameter of 0.24 m and a length of 0.1 m, rotating at 11.6 rpm. It is filled with 30,000 spherical particles, each with a diameter of 4 mm. The timestep for integration is 0.00001 s. This tutorial demonstrates the basic setup for creating a rotation-based simulation using built-in geometry in PhasicFlow.
A view of the rotating drum
***
## Setting up the Case
PhasicFlow simulation case setup is based on text-based scripts provided in two folders located in the simulation case folder: `settings` and `caseSetup`. All commands should be entered in the terminal while the current working directory is the simulation case folder (at the top level of `caseSetup` and `settings`).
### Creating Particles
In the file `settings/particlesDict`, two dictionaries, `positionParticles` and `setFields`, position particles and set the field values for the particles.
The `positionParticles` dictionary uses the `ordered` method to position particles in a space defined by `box`. The box space is defined by two corner points: `min` and `max`. In the `orderedInfo` sub-dictionary, `numPoints` defines the number of particles (30,000), `distance` defines the spacing between adjacent particles (4 mm), and `axisOrder` defines the axis order for filling the space with particles.
in settings/particlesDict file
```C++
positionParticles
{
method ordered; // other options: random and empty
mortonSorting Yes; // perform initial sorting based on morton code?
orderedInfo
{
distance 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 information 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` sub-dictionary defines the initial values for particle fields (velocity, acceleration, rotational velocity, and shape name). The shape name field should be consistent with the name defined in the shapes file (here, "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)
rVelocity realx3 (0 0 0); // rotational velocity (rad/s)
shapeName word sphere1; // name of the particle shape
}
selectors
{
// Selectors can be used to modify properties for specific particle groups
}
}
```
To create the particles and store them in the `0` folder, enter the following command:
```
particlesPhasicFlow
```
### Creating Geometry
In the file `settings/geometryDict`, you define the motion model and geometry for the simulation. The `rotatingAxis` motion model defines a fixed axis which rotates around itself. The `rotAxis` dictionary specifies the axis endpoints and rotation speed.
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 defines all the walls in the simulation. This tutorial uses built-in geometries provided by PhasicFlow. The geometry consists of:
1. A `cylinder` dictionary defining a cylindrical shell with end radii (`radius1` and `radius2`), axis endpoints (`p1` and `p2`), material name (`prop1`), and motion component (`rotAxis`).
2. Two plane walls (`wall1` and `wall2`) at the ends of the cylindrical shell, each defined with four coplanar corner points, the same material name, and the same motion component.
in settings/geometryDict file
```C++
surfaces
{
/*
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
}
/*
This is a plane wall at the rear end of cylinder
*/
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
}
/*
This is a plane wall at the front end of cylinder
*/
wall2
{
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
}
}
```
To create the geometry and store it in the `0/geometry` folder, enter:
```
geometryPhasicFlow
```
### Defining Properties and Interactions
In the file `caseSetup/interaction`, you define properties of materials and their interactions. The `materials` entry lists material names, and `densities` sets the corresponding densities. The `model` dictionary defines the contact force and rolling friction models, along with other required properties.
in caseSetup/interaction file
```C++
materials (prop1); // a list of materials names
densities (1000.0); // density of materials [kg/m3]
contactListType sortedContactList;
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
mu (0.3); // dynamic friction
mur (0.1); // rolling friction
}
```
The `contactSearch` dictionary specifies the algorithm and parameters for finding particle-particle contacts. The `method` determines the broad search algorithm, `updateInterval` sets how often to update the neighbor list, and `sizeRatio` controls the enlarged cell size for finding neighbors.
in caseSetup/interaction file
```C++
contactSearch
{
method NBS;
updateInterval 10;
sizeRatio 1.1;
cellExtent 0.55;
adjustableBox Yes;
}
```
In the file `caseSetup/shapes`, you define particle shapes, including their names, diameters, and material properties:
in caseSetup/shapes file
```C++
names (sphere1); // names of shapes
diameters (0.004); // diameter of shapes
materials (prop1); // material names for shapes
```
### Simulation Domain and Boundaries
The file `settings/domainDict` defines a rectangular bounding box with boundaries. Particles that exit this box are automatically deleted.
in settings/domainDict file
```C++
// 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
}
}
```
### Other Settings
Additional parameters for the simulation are set in `settings/settingsDict`, including timestep, start and end times, saving intervals, and gravity:
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)
includeObjects (diameter); // save necessary (i.e., required) data on disk
// exclude unnecessary data from saving on disk
excludeObjects ();
integrationMethod AdamsBashforth2; // integration method
integrationHistory off; // to save space on disk
writeFormat ascii; // data writing format (ascii or binary)
timersReport Yes; // report timers (Yes or No)
```
## Running the Case
To execute the simulation, follow these steps in order:
1. Create the geometry:
```
geometryPhasicFlow
```
2. Create the initial particle fields:
```
particlesPhasicFlow
```
3. Run the simulation:
```
sphereGranFlow
```
Depending on your computational resources, the simulation may take from a few minutes to several hours to complete.
## Post Processing
After the simulation completes, you can visualize the results in ParaView by converting them to VTK format:
```
pFlowToVTK --binary
```
This command converts all simulation results (particles and geometry) to VTK format and stores them in a `VTK/` folder. You can then open these files in ParaView for detailed analysis and visualization.
For more specific field output, you can specify fields:
```
pFlowToVTK --binary --fields diameter velocity id
```
