yade-users team mailing list archive

["Chen, Feng" <fchen3@xxxxxxx>]

Hi, Chris:

Thanks for your answer, I would like to share my experience on the issues below:

Btw: Is it correct that Yade is based on a shared memory approach?

///Vaclav has answered that problem, the performance increase on the parallel issue using OpenMP seems to be limited.

>1. FVM size/particle size

The simulations I did so far were with particle diameter in the same order of
magnitude or smaller than the grid spacing.
I did not extensively test particles that are much larger than the grid size because my flow problems did not involve such cases. 
But to my knowledge, this would lead to a) convergence issues and b)
possibly malpredictions of the dragforce by standard drag correlations 
(Gidaspow, DiFelice,...)
My maximum ratio cell spacing/particle diameter was ~1/1 which converged and
matched the validation experiments well

///As I know the minimum FVM size must be larger than the particle size, when the FVM size is close to particle size, will lead to porosity value singularity, which will in turn, cause instability in N-S continuity solution (This is also mentioned in PFC2D fluid option's manual)


>2. The maximum particle number possible on a cluster

It depends on what cluster you have :-)
If you look at http://lammps.sandia.gov/bench.html#chute
you fill find the rightmost dot in the left figure corresponding
to 2 BILLION PARTICLES!

///In my thesis I used 8200 particles on a workstation, I wish I could use at 10^6 level.


>3. The parallel mechanism

We are using MPI because we think that the code should be portable to
clusters.
We have a small cluster (~150 proc.) at our Institute, so for me it is a
huge speed-up 
switching from my workstation to the cluster

///Same answer as the "shared memory", I met the "bottle neck".


>4. What kind of problem/type of flow you use in your problem?

Typical problems that we are using or intending to use CFD-DEM for is
pneumatic conveying,
fluidized bed, hopper discharge and die filling.

///I use this in the chromatography column packing, stress-strain caused by fluid drag, sheet pile, seepage in dam


>5. Is it easy to change/create new particle constitution laws for the solid
phase?

Yes, LAMMPS is written in the intention to be easily modified. A whole
section of the documentation is dedicated to this:
http://lammps.sandia.gov/doc/Section_modify.html
I must admit that currently, LAMMPS is missing a feature to import granular walls from
CAD. But I am working on this...

///I ask this because I am working on visco-elastic model (Burgers, Maxwell etc which can be used in asphalt concrete) and some other non-linear models


>6. Effect of different drag equations

I must admit that I did not extensively test that. Afaik, Gidaspow could
lead to convergence problems as it is discontinuous in one point. Thus I also used
DiFelice but did not find much difference

///I used Ergun's (1952) equation, there is a more detailed comparison in MFix about different drag equations

I should add that the simulation experience I am talking about was with a EDEm-FLUENT coupling that I wrote myself. The "LammpsFoam" is now in beta, and this fluidized bed configuration http://lammps.sandia.gov/movies/gran_openfoam.avi
is the only case that we calculated with "LammpsFoam" so far.

///YADE-OpenFOAM has also been in an "alpha-beta" status for a long time, some portion of the code (especially coupling part) is so crappy that I even feel shame to release it:-P, although I have been working on this for 2 more years, hehe :-)