coarsegraining command¶
Syntax¶
coarsegraining cg_factor args
cg_factor = coarse-graining factor to be applied (dimensionless)
args = model_check
model_check = error or warn
Examples¶
coarsegraining 2.0
Description¶
Coarsegraining is a methodology to reduce the computational effort of a DEM calculation by scaling up the particle size by a coarse-graining factor (cg_factor). Thereby, the model size decreases by factor cg-factor^3.
However, changing particle size will change the physics of the model. On the particle scale, this change is obviously inevitable. However, in many cases model constants can be adapted so that on the bulk scale the change of the physics caused by the coarse-graining model is acceptable. See e.g. (Radl) and (Bierwisch) for details.
Some of the models in LIGGGHTS support scaling of the model constants to counteract this change in physics on the bulk scale. Moreover, some commands (such as insertion commands or the neighbor command) re-scale some of their length scales. Using model_check = error will throw an error if a model/command does not yield consistent results with coarse-graining. Using model_check = warn will issue a warning if a model/command does not yield consistent results with coarse-graining.
Model overview:
This table provides an overview of how different models behave when coarsegraining is used. Some models scale length-scales, other models scale model parameters to make results more coarse-graining consistent. Models that are not mentioned here are not affected by using the coarsegraining command
not supported |
||
not supported / inconsistent |
||
not supported / inconsistent |
||
fix dragforce |
downscaling of A, Re; upscaling of dragforce |
|
not supported / inconsistent |
||
not supported / inconsistent |
||
Finnie wear model |
inherently compatible |
|
radius -> cg_factor*radius |
||
radius -> cg_factor*radius |
||
not supported / inconsistent |
||
not supported / inconsistent |
||
not supported / inconsistent |
||
not supported / inconsistent |
||
skin -> cg_factor*skin |
||
any cohesion or rolling friction model |
not supported / inconsistent |
|
base model |
inherently compatible |
|
base model |
inherently compatible |
|
base model |
inherently compatible |
|
not supported / inconsistent |
||
base model with damp_massflag=0 |
kn -> cg_factor*kn, gamman -> cg_factor^2*gamman |
|
base model with damp_massflag=1 |
kn -> cg_factor*kn, gamman -> gamman/cg_factor |
|
base model with damp_massflag=0 |
kn -> cg_factor*kn, gamman -> cg_factor^2*gamman |
|
base model with damp_massflag=1 |
kn -> cg_factor*kn, gamman -> gamman/cg_factor |
|
diameter -> cg_factor*diameter |
Warning
Even if a model does not support proper coarse graining, in many cases it will still be possible to calibrate the model constant manually to capture the bulk scale physics with a coarse-grained model.
Restrictions¶
General warning: Coarse graining is an approximative method and will _never_ deliver exactly the same results than a fine-grained simulation.
One natural restriction is that the ratio of geometry length scale to particle length scale should be >> 1 when coarse graining is applied.
See description above the fact that not all LIGGGHTS models will deliver consistent results with coarse-graining ratios > 1.
Related commands: see table above
Default: cg_factor = 1 (no coarse-graining applied)
(Radl) S. Radl et. al., PARCEL-BASED APPROACH FOR THE SIMULATION OF GAS-PARTICLE FLOWS, Proc. 8th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries, 2011
(Bierwisch) Journal of the Mechanics and Physics of Solids, Volume 57, Issue 1, January 2009, Pages 10ff