granuDrum

Overview

Template Info

Target Parameters: c_frict_xx c_rollingFrict_xx maxCohesiveStress_pp cohesionStrength_pp cohesionEnergyDensity_pp
Contact Models: tangential no_history tangential history rolling_friction cdt rolling_friction epsd cohesion adaptive cohesion sjkr
Particle Shapes: sphere

This calibration template simulates the GranuDrum™, a rotating drum manifactured by Granutools™. The setup consists of a cylinder which is first filled with particles and then starts rotating around its axis, see figure below. After reaching a steady-state condition, images of the granular material are taken and used for the calibration.

This setup is designed to be sensitive to the particle-particle static/rolling friction and cohesion coefficients. Hence, one or more of these target parameters can be iteratively modified during the calibration process to achieve the optimal correspondence between simulation and reference results. To calibrate friction, set c_frict_pp and/or c_rollFrict_pp as target parameters. For cohesion, the adaptive and simplified jkr models are supported. To calibrate the former, use maxCohesiveStress_pp and cohesionStrength_pp as target parameters. For the latter, use cohesionEnergyDensity_pp. It is possible to calibrate cohesion and friction at the same time. Note that this will increase the parameter space and hence the number of simulations required to obtain a properly calibrated parameter set.

Note

when calibrating the simplified JKR model, make sure that the parameters maxCohesiveStress_pp and cohesionStrength_pp are either set to 0 (as param_fixed) or not set at all in your input script.

Simulation phases

Filling

During this phase, particles are inserted into the drum. The amount of particles depends on the desired filling level, which can specified through the fillLevel variable.

Settling

During this phase, the inserted particles settle down. The simulation stops when the total kinetic energy is below a certain threshold.

Rotation

During this phase, the rotation velocity of the drum increases linearly from zero to the desired value (specified through the RPMMeas variable) during a time interval specified via the simRampTime variable. After reaching the prescribed velocity, the system moves gradually to a steady-state condition during the time interval speciefied by the simEquilTime variable. After this time, the drum keeps rotating at the target velocity for another time interval (specified through the simMeasTime variable) during which images of the granular material are saved.

Quality function

The images of the granular material obtained during the rotation phase are used to calculate the average interface position and the interface fluctuations. From these two quantities, the simulated dynamic angle of repose and the dynamic cohesive index can be derived. The difference between the simulated and the reference output is quantified by the following quality function:

$f_q = (\alpha_{sim} - \alpha)^2 + (\sigma_{sim} - \sigma)^2$

where $\alpha_{sim}$ and $\alpha$ are the simulated and measured dynamic angle of repose, while $\sigma_{sim}$ and $\sigma$ are the simulated and measured dynamic cohesive index.

Measurement file

The text file containing the experimental measurements consists of two lines, in which the dynamic angle of repose and the dynamic cohesive index are specified. An example of measurment file is given below.

angle=62.34
cohesion_index=11.82

Template parameters

General settings

Parameter	Default
scaleweight	1
pairGranModel	hertz
pairTangential	history
pairCohesion	sjkr
pairRollingFriction	epsd
pairSurface	default
NPROC	4
dumpT	0.01 s
dump	0
nChunks	1
coresPerChunk	1

Specific settings

Variable	Default	Meaning
simRampTime	1	Interval of time [s] during which the drum increases its velocity linearly from zero to RPMMeas (see below).
simEquilTime	0.5	Interval of time [s] after reaching the prescribed. rotation velocity. Needs to be large enough for the system to reach an equilibrium state.
simMeasTime	2	Interval of time [s] during which the images of the granular material are taken.
RPMMeas	20	Rotations per minute used in the experiment
fillLevel	0.5	Fraction of the drum volume to be filled with particles. 0.5 corresponds to a half-full drum. Values higher than 0.5 are not recommended due to limitations of particle insertion. [-]