This article and accompanying files (provided below) are meant to help Abaqus users new to Discrete Element Method (DEM) get started. The two DEM models obtained (with and without Particle Generator) after following the step-by-step instructions below can be modified by the user (geometry/material/interactions) to meet their specific model requirement. Brief descriptions of the modeling steps are also provided.
DEM is a versatile tool for modeling particulate material behavior in pharmaceutical, chemical, food, ceramic, metallurgical, mining, and other industries. It is not meant for modeling deformation of a continuum (like SPH), but can be used together with finite elements for modeling discrete particles interacting with deformable continua or other rigid bodies. Further information on DEM in Abaqus is available in the Abaqus documentation and the ‘Analysis of Geotechnical Problems with Abaqus’ SIMULIA training course.
The accompanying CAE file (DEM_GetStart.cae) has two models ‘WithParticleGenerator’ and ‘WithoutParticleGenerator’ where the geometry of a simple conveyor transfer chute has been defined. In addition to that, ‘WithParticleGenerator’ has a flat surface (part ‘Particle1’) that is later used as the source for the particle generator, and ‘WithoutParticleGenerator’ has a cube (part ‘Particle1’) that is converted to DEM particles using the accompanying script (solidtodem.py – modification of script available in QA00000019285 that creates an SPH mesh).
Step-by-step instructions to set up a DEM analysis in Abaqus of a simple conveyor transfer chute with and without using the ‘Particle Generator’ tool in Abaqus are provided below.
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A. DEM analysis using the ‘Particle Generator’ tool
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IMAGE: DEM analysis using the ‘Particle Generator’ tool
VIDEO: DEM analysis using the ‘Particle Generator’ tool
Step 1:
Open DEM_GetStart.cae and write the input file for the job named WPG (for the model ‘WithParticleGenerator’). Make a copy of this file and rename it to WPG_DEM.
Step 2:
Open WPG_DEM in a text editor and add the following lines after ‘*Part, name=Particle1’:
*************************************************************************************
*Particle Generator, name=dem1, type=PD3D,
Maximum Number of Particles=1000
*Particle Generator Inlet, surface=inlet1
*Particle Generator Mixture
dem1,
*Discrete Section, elset=dem1, density=0.25, alpha=7.0
PDF1,
*Discrete Elasticity
2.0E+10, 0.25
*Probability Density Function, name=PDF1, TYPE=DISCRETE
0.2, 1.0
*************************************************************************************
Description: Addition of these lines defines the particle generation and properties of the particles. They have to be manually added to the input file as these keywords are not supported in Abaqus/CAE 2016. The surface ‘inlet1’ refers to the surface already defined in the CAE file.
Step 3:
Add the following lines after ‘*Rigid Body, ref node=_PickedSet17, elset=b_Set-2’:
*************************************************************************************
*Surface, name=dem1
Particle1-1.dem1,
*************************************************************************************
Description: Addition of these lines defines the surface of the particles that is later used for contact definition.
Step 4:
Add the following lines after ‘*End Assembly’:
*************************************************************************************
*Amplitude, name=FlowSpeed
0., 0.0,
1., 0.0
*Amplitude, name=MassFlow
0., 1.5,
0.6, 1.5,
0.61, 0.0,
1., 0.0
*************************************************************************************
Description: Addition of these lines defines the amplitude for the particle flow speed at the generator inlet and for the mass flow rate per unit inlet area.
Step 5:
Change the pressure-overclosure type for the surface interaction ‘P11’ between the DEM particles from ‘LINEAR’ to ‘HERTZ’.
Description: This modification defines a hertz-type normal elastic contact between the particles to allow DEM results to match Hertz contact behavior between deformable spheres.
Step 6:
Modify the lines:
*Dynamic, Explicit
, 1.
To:
*************************************************************************************
*Dynamic, Explicit, direct user control
5e-06, 1.0
*************************************************************************************
Description: Since there is no deformable element available in the model (the chute has a rigid body constraint applied) to control the stable time increment, this modification defines a direct time incrementation to perform the analysis at a user specified time increment.
Step 7:
After:
‘*Bulk Viscosity
0.06, 1.2’
Add:
*************************************************************************************
*Particle Generator Flow, generator=Particle1-1.dem1
FlowSpeed, MassFlow
**
*Contact
*Contact Controls Assignment, rotational terms=STRUCTURAL
*Contact Inclusions
dem1, ChuteInnerSurface
dem1, dem1
*Contact Property Assignment
dem1, ChuteInnerSurface, P1F
dem1, dem1, P11
*************************************************************************************
Description: Addition of these lines defines the particle flow (keyword not supported in Abaqus/CAE) and the contact interactions between the particles, and the particles and the chute.
Step 8:
Modify the line ‘, GRAV, 9800., 0., -1., 0.’
To
Particle1-1.dem1, GRAV, 9800., 0., -1., 0.
Description: This modification causes the gravity load to be applied only to the particles.
Step 9:
Run this input file and visualize the results. Select the displacement magnitude as the primary variable and make ‘Feature edges’ as the Visible Edges (Option>Common…). Either ‘Apply Translucency’ (Option>Common…>Other), or use the ‘View Cut Manager’ (Tools>View Cut>Manager…) to apply a Z-Plane view cut (adjust the plane position using the slider so that only the front face of the chute is not displayed). Plot contours on the deformed shape and animate the results.
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B. DEM analysis without using the ‘Particle Generator’ tool
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IMAGE: DEM analysis without using the ‘Particle Generator’ tool
VIDEO: DEM analysis without using the ‘Particle Generator’ tool
Step 1:
Open DEM_GetStart.cae and write the input file for the job named WOPG (for the model ‘WithoutParticleGenerator’). Make a copy of this file and rename it to WOPG_DEM.
Step 2:
The accompanying script solidtodem.py has the following usage and options:
USAGE: abq python solidtodem.py -inp -elem -part
OPTIONS:
-inp Required argument to provide the solid mesh input deck for processing
-elem Optional argument to prefix DEM elements with a given integer
-part Option to specify if the input deck is of parts/instances format. Script may not work correctly if this option is not used with parts/instances based input deck.
To convert the cube (part ‘Particle1’) to DEM particles, run the accompanying script (solidtodem.py) using the following command:
abaqus python solidtodem.py -inp WOPG_DEM.inp -part
The script will write the DEM mesh corresponding to the cube (part ‘Particle1’) in a new input file dem_WOPG_DEM.inp. Copy the entire contents of this new input file and replace all the C3D8R element definitions (total of 353 lines: *Element followed by 352 data lines) for the part ‘Particle1’ in WOPG_DEM.inp with it.
Description: A solid part of any shape and dimension can be defined in the CAE model to be converted to a DEM mesh following this procedure. DEM particles are generated at every node of the solid part mesh. Thus the refinement of the solid mesh can be varied to vary the density of the DEM particles generated.
Step 3:
Right after the DEM mesh added in the previous step, add the following lines:
*************************************************************************************
*Discrete Section, elset=dem1, density=2.5, alpha=7.0
0.2
*Discrete Elasticity
2.0E+10, 0.25
*************************************************************************************
Description: Addition of these lines defines the properties of the particles.
Step 4:
Add the following lines right BEFORE the line ‘** Constraint: Constraint-1’:
*************************************************************************************
*Surface, name=dem1
particle1-1.dem1,
*************************************************************************************
Description: Addition of these lines defines the surface of the particles that is later used for contact definition.
Steps 5 - 6:
Same as those listed previously for DEM analysis using the ‘Particle Generator’ tool.
Step 7:
After:
‘*Bulk Viscosity
0.06, 1.2’
Add:
*************************************************************************************
*Contact
*Contact Controls Assignment, rotational terms=STRUCTURAL
*Contact Inclusions
DEM1, DEM1
DEM1, ChuteInnerSurface
*Contact Property Assignment
DEM1, ChuteInnerSurface, P1F
DEM1, DEM1, P11
*************************************************************************************
Description: Addition of these lines defines the contact interactions between the particles, and the particles and the chute.
Steps 8 - 9:
Same as those listed previously for DEM analysis using the ‘Particle Generator’ tool.
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Note: This work uses fictitious geometries and material properties, and is meant for demonstration purposes only.
ACCOMPANYING FILES (CAE model and python script):
