11 KiB
Simulating a small rotating drum
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 with a diameter of 4 mm. The time step 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 mentioned 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 the field values for the particles.
In dictionary setFields, dictionary defaultValue defines the initial value for particle fields (here, velocity, acceleration, rotVelocity, and shapeName). Note that shapeName field should be consistent with the name of shape that you later set for shapes (here one shape with name 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
{
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
{
shapeName word sphere1; // sets shapeName of the selected points to largeSphere
}
}
}
}
In dictionary `positionParticles`, the positioning `method` is `ordered`, which position particles in order in the space defined by `box`. `box` space is defined by two corner points `min` and `max`. In dictionary `orderedInfo`, `numPoints` defines number of particles; `diameter`, the distance between two adjacent particles, and `axisOrder` defines the axis order for filling the space by particles.
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in <b>settings/particlesDict</b> file
</div>
```C++
positionParticles
{
method ordered; // other options: random and empty
mortonSorting Yes; // perform initial sorting based on morton code
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 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 dictionary setFields, dictionary defaultValue defines the initial value for particle fields (here, velocity, acceleration, rotVelocity, and shapeName). Note that shapeName field should be consistent with the name of shape that you later set for shapes (here one shape with name 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. rotatingAxis 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)
}
}
In the dictionary surfaces you can define all the surfaces (walls) in the simulation. Two main options are available: built-in geometries in PhasicFlow, and providing surfaces with stl file. Here we use built-in geometries. In 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 number of division for the cylinder shell. wall1 and wall2 define two plane walls at two ends of cylindrical shell with coplanar corner points p1, p2, p3, and p4, material name prop1 and motion component rotAxis.
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
In the file caseSetup/interaction , you find properties of materials. 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 calculating 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. Larger sizeRatio include more particles in the neighbor list and you require to update it less frequent.
contactSearch
{
method NBS; // method for broad search
updateInterval 10;
sizeRatio 1.1;
cellExtent 0.55;
adjustableBox Yes;
}
In the file caseSetup/shapes, 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.
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 (rVelocity.dy1 pStructPosition.dy1 pStructVelocity.dy1);
integrationMethod AdamsBashforth2; // integration method
writeFormat ascii; // data writting format (ascii or binary)
timersReport Yes; // report timers (Yes or No)
timersReportInterval 0.01; // time interval for reporting timers
Running the case
The solver for this simulation is sphereGranFlow. Type the following command in a terminal. Depending on your computer's computation power, it may take from a few minutes to a few hours to complete.
> sphereGranFlow
Post processing
When the simulation is finished, you can render the results in Paraview. To convert the results to VTK format, just type the following command in a terminal. This will convert all results (particles and geometry) to VTK format and save them in the folder VTK/.
> pFlowToVTK