8.0 KiB
Simulating a screw conveyor
Problem definition
The problem is to simulate a screw conveyor with a diameter of 0.2 m, a length of 1 m and a pitch of 20 cm. It is filled with 30,000 4 mm spherical particles. The integration time step 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 empty; // other options: ordered and random
maxNumberOfParticles 50000; // maximum number of particles in the simulation
regionType box; // other options: cylinder and sphere
boxInfo // box for positioning particles
{
min (-0.1 -0.08 0.015); // lower corner point of the box
max (0.1 0.0 0.098); // upper corner point of the box
}
}
Enter the following command in the terminal to create the particles and store them in 0 folder.
> particlesPhasicFlow
Creating geometry
In the settings/geometryDict file you can provide information for creating geometry. Each simulation should have a motionModel which defines a model for moving the surfaces in the simulation. The rotatingAxisMotion' model defines a fixed axis that rotates around itself. The dictionary rotAxisdefines a motion component withp1andp2as the end points of the axis andomega` as the speed of rotation in rad/s. You can define more than one motion component in a simulation.
motionModel rotatingAxis;
.
.
.
rotatingAxisInfo
{
rotAxis
{
p1 (1.09635 0.2010556 0.22313511); // first point for the axis of rotation
p2 (0.0957492 0.201556 0.22313511); // second point for the axis of rotation
omega 3; // rotation speed (rad/s)
startTime 5;
endTime 30;
}
}
In the dictionary surfaces you can define all surfaces (shell) 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 helix, material name prop1, motion component none is defined. In helix we define a plane helix at the center of the cylindrical shell, material name prop1 and motion component rotAxis. rotAxis is used for the helix because it is rotating and none is used for the shell because it is not moving.
surfaces
{
helix
{
type stlWall; // type of the wall
file helix.stl; // file name in stl folder
material prop1; // material name of this wall
motion rotAxis; // motion component name
}
shell
{
type stlWall; // type of the wall
file shell.stl; // file name in stl folder
material prop1; // material name of this wall
motion none; // motion component name
}
}
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]
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
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 No;
}
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 (0.01); // diameter of shapes
materials (prop1); // material names for shapes
Other settings for the simulation can be set in the settings/settingsDict file. The `domain' dictionary defines a rectangular bounding box with two corner points for the simulation. Any particle that leaves this box will be automatically deleted.
dt 0.0001; // time step for integration (s)
startTime 0; // start time for simulation
endTime 20; // end time for simulation
saveInterval 0.05; // 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 (0.0 -0.06 0.001);
max (1.2 1 0.5);
}
integrationMethod AdamsBashforth2; // integration method
timersReport Yes; // report timers?
timersReportInterval 0.01; // time interval for reporting timers
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