8.6 KiB
Simulating a screw conveyor
Problem definition
The problem is to simulate a screw conveyorwith the diameter 0.2 m and the length 1 m and 20 cm pitch. It is filled with 30,000 4-mm spherical particles. The timestep for integration is 0.00001 s.
Setting up the case
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 the commands should be entered in the terminal while the current working directory is the simulation case folder (at the top of the caseSetup and settings).
Creating particles
Open the file settings/particlesDict. Two dictionaries, positionParticles and setFields position particles and set the field values for the particles.
In dictionary positionParticles, the positioning method is positionOrdered, which position particles in order in the space defined by box. box space is defined by two corner points min and max. In dictionary positionOrderedInfo, numPoints defines number of particles; diameter, the distance between two adjacent particles, and axisOrder defines the axis order for filling the space by particles.
positionParticles
{
method empty; // creates the required fields with zero particles (empty).
maxNumberOfParticles 50000; // maximum number of particles in the simulation
mortonSorting Yes; // perform initial sorting based on morton code?
}
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 lightSphere; // 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 rotatingAxisMotion;
.
.
.
rotatingAxisMotionInfo
{
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 the surfaces (shell) 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 helix, material name prop1, motion component none is defined. helix define plane helix at center of cylindrical shell, material name prop1 and motion component rotAxis.
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
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 prosperities 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 neighbor list for particle-particle contacts and wallMapping shows how particles are mapped onto walls for finding neighbor list for particle-wall contacts. updateFrequency sets the frequency for updating neighbor list and sizeRatio sets the size of enlarged cells (with respect to particle diameter) for finding neighbor list. Larger sizeRatio include more particles in the neighbor list and you require to update it less frequent.
contactSearch
{
method NBS; // method for broad search particle-particle
wallMapping cellMapping; // method for broad search particle-wall
NBSInfo
{
updateFrequency 10; // each 20 timesteps, update neighbor list
sizeRatio 1.1; // bounding box size to particle diameter (max)
}
cellMappingInfo
{
updateFrequency 10; // each 20 timesteps, update neighbor list
cellExtent 0.6; // bounding box for particle-wall search (> 0.5)
}
}
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 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 0.0001; // 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 AdamsBashforth3; // 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