coarsegraining command
Note
This command is supported by Aspherix GPU.Syntax
coarsegraining cg_factor(s) keyword value
cg_factor = coarse-graining factor to be applied (dimensionless), if more than one factor
is defined, material type specific coarsegraining is used
General keywords:
Keywords |
Description |
|---|---|
available options:
error, warn, offdefault:
error |
Examples
coarsegraining 2.0
coarsegraining 4. 2.
coarsegraining 3 model_check warn
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.
If more than one coarse-graining factor is entered, type-specific coarse- graining is activated. So every material type in the simulation may have a different coarse-graining factor. The coarse-graining factors must be stated in the order of the defined materials (see the materials command) with custom materials as last entries in the list.
Some of the models in Aspherix® 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_check = off will
suppress all warnings and is only intended for long CFDEMcoupling simulations.
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
create_atoms (legacy!) |
not supported, Use create_particles instead |
|
not supported / inconsistent |
||
not supported / inconsistent |
||
downscaling of A, Re; upscaling of dragforce |
||
not supported / inconsistent |
||
Finnie wear model |
inherently compatible |
|
radius -> cg_factor*radius |
||
radius -> cg_factor*radius |
||
particle_size -> cg_factor*particle_size |
||
particle_size -> cg_factor*particle_size |
||
particle_size -> cg_factor*particle_size |
||
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 |
|
kn -> cg_factor*kn, gamman -> gamman/cg_factor^2 |
||
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 Aspherix® models will deliver consistent results with coarse-graining ratios > 1.
The coarsegraining command needs to be at the beginning of an input-script. It needs to be defined before any fixes or the definition of a simulation box.