phasicFlow/tutorials/sphereGranFlow/screwConveyor

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.

a view of rotating drum

---

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.

in settings/particlesDict file

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.

in settings/geometryDict file

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.

in settings/geometryDict file

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.

in caseSetup/interaction file

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.

in caseSetup/interaction file

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.

in caseSetup/sphereShape file

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.

in settings/settingsDict file

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