120 lines
6.4 KiB
HTML
120 lines
6.4 KiB
HTML
<HTML>
|
|
<CENTER><A HREF = "http://www.cfdem.com">LIGGGHTS WWW Site</A> - <A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LIGGGHTS Documentation</A> - <A HREF = "Section_commands.html#comm">LIGGGHTS Commands</A>
|
|
</CENTER>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
<H3>coarsegraining command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>coarsegraining cg_factor args
|
|
</PRE>
|
|
<UL><LI>cg_factor = coarse-graining factor to be applied (dimensionless)
|
|
|
|
<LI>args = <I>model_check</I>
|
|
|
|
<PRE> <I>model_check</I> = error or warn
|
|
</PRE>
|
|
|
|
</UL>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>coarsegraining 2.0
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>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.
|
|
</P>
|
|
<P>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. <A HREF = "#Radl">(Radl)</A> and <A HREF = "#Bierwisch">(Bierwisch)</A> for details.
|
|
</P>
|
|
<P>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 <I>model_check</I> = error will throw an error
|
|
if a model/command does not yield constistent results with coarse-graining.
|
|
Using <I>model_check</I> = warn will issue a warning if a model/command does not
|
|
yield constistent results with coarse-graining.
|
|
</P>
|
|
<P><B>Model overview:</B>
|
|
</P>
|
|
<P>This table provides an overview of how different models behave when
|
|
coarsegraining is used. Some models scale lengthscales, 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
|
|
</P>
|
|
<DIV ALIGN=center><TABLE BORDER=1 >
|
|
<TR><TD ><A HREF = "create_atoms.html">create_atoms</A> </TD><TD > </TD><TD > not supported </TD></TR>
|
|
<TR><TD ><A HREF = "fix_addforce.html">fix addforce</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "fix_drag.html">fix drag</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD >fix dragforce </TD><TD > </TD><TD > downscaling of A, Re; upscaling of dragforce </TD></TR>
|
|
<TR><TD ><A HREF = "fix_efield.html">fix efield</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "fix_heat_gran_conduction.html">fix heat/gran/conduction</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "fix_mesh_surface_stress.html">fix mesh/surface/stress</A> </TD><TD > Finnie wear model </TD><TD > inherently compatible </TD></TR>
|
|
<TR><TD ><A HREF = "fix_particletemplate_sphere.html">fix particletemplate/sphere</A> </TD><TD > </TD><TD > radius -> cg_factor*radius </TD></TR>
|
|
<TR><TD ><A HREF = "fix_particletemplate_multisphere.html">fix particletemplate/multisphere</A> </TD><TD > </TD><TD > radius -> cg_factor*radius </TD></TR>
|
|
<TR><TD ><A HREF = "fix_spring.html">fix spring</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "fix_spring_rg.html">fix spring/rg</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "fix_spring_self.html">fix spring/self</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "fix_viscous.html">fix viscous</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "read_data.html">neighbor</A> </TD><TD > </TD><TD > skin -> cg_factor*skin </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/*</A> </TD><TD > any cohesion or rolling friction model </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/hertz/history</A> </TD><TD > base model </TD><TD > inherently compatible </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/hooke/history base model</A> </TD><TD > base model </TD><TD > inherently compatible </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/hooke base model</A> </TD><TD > base model </TD><TD > inherently compatible </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/hertz/history/stiffness</A> </TD><TD > </TD><TD > not supported / inconsistent </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/hooke/history/stiffness</A> </TD><TD > base model with damp_massflag=0 </TD><TD > kn -> cg_factor*kn, gamman -> cg_factor^2*gamman </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/hooke/history/stiffness</A> </TD><TD > base model with damp_massflag=1 </TD><TD > kn -> cg_factor*kn, gamman -> gamman/cg_factor </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/hooke/stiffness</A> </TD><TD > base model with damp_massflag=0 </TD><TD > kn -> cg_factor*kn, gamman -> cg_factor^2*gamman </TD></TR>
|
|
<TR><TD ><A HREF = "pair_gran.html">pair gran/hooke/stiffness</A> </TD><TD > base model with damp_massflag=1 </TD><TD > kn -> cg_factor*kn, gamman -> gamman/cg_factor </TD></TR>
|
|
<TR><TD ><A HREF = "set.html">set</A> </TD><TD > </TD><TD > diameter -> cg_factor*diameter
|
|
</TD></TR></TABLE></DIV>
|
|
|
|
<P>IMPORTANT NOTE: 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.
|
|
</P>
|
|
<P><B>Restrictions:</B>
|
|
</P>
|
|
<P>General warning: Coarse graining is an approximative method and
|
|
will _never_ deliver exactly the same results than a fine-grained
|
|
simulation.
|
|
</P>
|
|
<P>One natural restriction is that the ratio of geometry length scale to
|
|
particle length scale should be >> 1 when coarse graining is applied.
|
|
</P>
|
|
<P>See description above the fact that not all LIGGGHTS models will
|
|
deliver consistent results with coarse-graining ratios > 1.
|
|
</P>
|
|
<P><B>Related commands:</B>
|
|
see table above
|
|
</P>
|
|
<P><B>Default:</B>
|
|
cg_factor = 1 (no coarse-graining applied)
|
|
</P>
|
|
<HR>
|
|
|
|
<A NAME = "Radl"></A>
|
|
|
|
<P><B>(Radl)</B> 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
|
|
</P>
|
|
<A NAME = "Bierwisch"></A>
|
|
|
|
<P><B>(Bierwisch)</B> Journal of the Mechanics and Physics of Solids, Volume 57, Issue 1, January 2009, Pages 10ff
|
|
</P>
|
|
</HTML>
|