Calibration Templates

This section introduces the calibration templates implemented in Aspherix® Calibration. Each template corresponds to a DEM simulation setup, the settings of which can be changed by the user via a set of parameters. These parameters are divided into three groups: material parameters, general settings and specific settings.

The material parameters must be defined in the input script as fixed or calibrated parameters. As the name suggests, they provide information regarding the properties of the particle and the wall materials, like density, Young’s modulus and friction coefficients. The general settings are parameters shared by all the templates which define, for example, the contact model employed by the template, the ratio between particle size and geometry, the output time interval and the number of processors. The specific settings are parameters that are unique to some templates and they are used to control some specific behaviours. Both the general and the specific settings have default values which can be overridden using the parameter_overrides keyword in the calibration_case command.

CFDEM®coupling templates 

Calibration templates for each contact model 

The following table contains a partial list of the contact models that are supported by the calibration templates. Information on the individual contact models can be found in the solver’s list of contact models.

cohesion adaptive : bulkDensityTest granuDrum inclinedWall rotaryKiln rotatingDrum shearCellSchulzePeriodic slumpTest soilCalibration tillageCalibration uniaxialCompression
cohesion asphalt : oscillatoryRheometerBurgers
cohesion bond : electrodeCalendaring solidDeformationWithBonds
cohesion jkr/general : shearCellSchulzePeriodic slumpTest
cohesion off : rotaryKiln rotatingDrum
cohesion sjkr : bulkDensityTest granuDrum inclinedWall rotaryKiln rotatingDrum shearCellSchulzePeriodic slumpTest
cohesion sjkr/powder : uniaxialCompression
cohesion sjkr2 : bulkDensityTest inclinedWall rotaryKiln rotatingDrum shearCellSchulzePeriodic slumpTest
epsd2 : soilCalibration tillageCalibration wear
hertz, : heatTransferRadiation wear
history : heatTransferRadiation
history, : wear
normal : heatTransferRadiation wear
normal adhesive_elasto_plastic : uniaxialCompression
normal thornton_ning : electrodeCalendaring
rolling_friction : wear
rolling_friction cdt : granuDrum inclinedWall staticAngleOfRepose
rolling_friction epsd : bulkDensityTest granuDrum inclinedWall rotaryKiln rotatingDrum slumpTest staticAngleOfRepose
rolling_friction epsd2 : bulkDensityTest inclinedWall rotaryKiln rotatingDrum shearCellSchulzePeriodic slumpTest uniaxialCompression
rolling_friction off : rotaryKiln rotatingDrum
tangential : heatTransferRadiation wear
tangential adhesive_elasto_plastic : uniaxialCompression
tangential burgers_asphalt : oscillatoryRheometerBurgers
tangential history : bulkDensityTest granuDrum inclinedWall rotaryKiln rotatingDrum shearCellSchulzePeriodic slumpTest soilCalibration tillageCalibration uniaxialCompression
tangential no_history : bulkDensityTest granuDrum inclinedWall rotaryKiln rotatingDrum shearCellSchulzePeriodic slumpTest uniaxialCompression

Particle Shapes 

All calibration templates support particle shape sphere, and some also support multisphere. Below is a list of calibration templates that support a certain particle shape. No other shapes are currently supported in Aspherix® Calibration.

Material parameters 

The following table contains the material parameters that are generally required to run calibrations with Aspherix® Calibration. For parameters ending with _x, the replacements are either _p for the particle value and _w for the wall value. For parameters ending with _xx, the replacements are either _pp for the particle-particle value and _pw for the particle-wall value. Parameter names prefixed with CFD_ are only used/needed for CFD-DEM coupled cases.

General param.	Meaning
rho_p	Particle’s density $[kg/m^3]$
Y_x	Young’s modulus $[Pa]$
poissonsR_x	Poisson’s ratio $[-]$
charVel	Characteristic velocity $[m/s^2]$ (see normal model Hooke)
c_rest_xx	Coefficient of restitution $[-]$
coarsegraining	Coarse-graining factor $[-]$ (see coarsegraining command)

Friction param.	Meaning
c_frict_xx	Coefficient of friction $[-]$ (see tangential model history)
c_rollFrict_xx	Coefficient of rolling friction $[-]$ (see e.g. rolling_friction model epsd2)
c_rollViscDamp_xx	Coefficient of rolling viscous damping $[-]$ (see rolling_friction model epsd)

Cohesion param.	Meaning
initCohStress_xx	Initial cohesive stress $[Pa]$ (see cohesion model adaptive)
maxCohStress_xx	Maximum cohesive stress $[Pa]$ (see cohesion model adaptive)
cohStrength_xx	Ratio between the normal and the cohesive force $[-]$ (see cohesion model adaptive)
cohEnSurfDens_xx	Cohesive surface energy density $[J/m^2]$ (see normal model jkr/general)
t0_bond	Time-step at which bonds are created $[-]$ (see normal model jkr/general)
cohEnDens_xx	Cohesion energy density $[J/m^3]$ (see cohesion model sjkr and cohesion model sjkr/powder)
cohesionVariation	Coefficient quantifying the change of cohesion energy density as a function of the compression level $[-]$ (see cohesion model sjkr/powder)

Powder compaction param.	Meaning
alpha_min	Minimum compression density $[-]$ (see fix powder/update command)
compressibility	Proneness of a particle to compression $[-]$
dilatability	Coefficient determining how much a particle dilates $[-]$
hardening	Coefficient for modifying the compressibility for compacted particles $[-]$
compression_exponent	Exponent for the non-linear hardening model $[-]$

Edinburgh model param.	Meaning
f_0	Constant pull of force (usually negative) $[force]$
delta_gamma_xx	Contact adhesion energy $[energy/length^2]$ (see normal model adhesive_elasto_plastic)
alpha_xx	Stiffness ratio $k_2/k_1$ $[-]$
powern_xx	Power value for loading and unloading springs $[-]$
xval_xx	Power value for adhesion branch $[-]$
ktm_xx	Factor relating the normal and tangential stiffnesses $[-]$ (see tangential model adhesive_elasto_plastic
mu_sl_xx	The coefficient of sliding friction acting between two materials $[-]$

CFD param.	Meaning
CFD_fluidDensity	Fluid density $[kg/m^3]$
CFD_fluidVisc	Kinematic viscosity of the fluid $[m^2/s]$
CFD_scaleDrag	Correction factor for particle-fluid drag $[-]$ (see Di Felice drag model)
CFD_volFracScale	Correcting factor for the particle volume to account for porosity or agglomerations $[-]$ (see divided voidfraction model)

Note

This table does not include all possible material parameters required by a template. Please, refer to the template individual documentations for more information.

General settings 

Most calibration templates share the following standard parameters, although they might have different default values.

Parameter	Meaning
scaleweight	weigthing factor of the quality function (effective only if multiple cases are run at the same time using the run single command)
pairGranModel	name of the granular contact model
pairTangential	name of the tangential model
pairCohesion	cohesion model name
pairRollingFriction	rolling friction model name
pairSurface	surface model name
NPROC	number of MPI processes to use
dumpT	time interval for simulation data dumps
dump	0: no dumps; 1: old csv-style dumps; 2: new vtk dumps
G_D_RATIO	ratio between a characteristic geometry length (i.e., plate diameter) and the maximum particle diameter
nChunks	number of chunks for a simulation (cluster mode only)
coresPerChunk	number of cores per chunk (cluster mode only)
useLoadBalancing	the simulations are run with (1) or without (0) load balancing

Specific settings 

The specific settings are discussed more in details in each individual template documentation.

Calibration Templates

Aspherix® templates

CFDEM®coupling templates