9.7 KiB
Simulating a small rotating drum
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.
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.
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).
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.
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. wall1andwall2define two plane walls at two ends of the cylindrical shell with coplanar verticesp1, p2, p3andp4, materialnameprop1andmotioncomponentrotAxis`.
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. materialsdefines a list of material names in the simulation anddensitiessets 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) androllingFrictionModel` selects the model for the calculation of rolling friction. Other required properties should be defined in this dictionary.
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. updateFrequencyspecifies the frequency for updating the neighbor list andsizeRatiospecifies the size of enlarged cells (with respect to particle diameter) for neighbor list search. LargersizeRatio` includes more particles in the neighbor list and you need to update it less frequently.
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.
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.
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