Dear users,
last week I posted about problems with my ball mill simulation. The problem was that the balls adhered underneath the lifting bar of the stl geometry. I was told to improve the mesh because of high skewness and aspect ratio.
After I've done it, the problem still remains! The balls still adhere to the bar!
I will attach the new mesh, so you can check it.
Please tell me what the real problem is and what do I have to do to solve it.
Thank you!
Kind regards,
Eugen
P.S. Why the high skewness and big (few) triangles/mesh elements are a problem at all?
| Attachment | Size |
|---|---|
 mesh_ball_mill.tar_.gz | 1.34 MB |
 in.Kugelmuehle_massrate.txt | 5.02 KB |
 Mill_01_03.PNG | 262.75 KB |
ckloss | Tue, 03/06/2012 - 18:38
I'll have a look. Can you
I'll have a look. Can you post the complete case + input script for this?
Thanks, Christoph
Sapsan | Thu, 03/08/2012 - 09:33
Hi Christoph! Thanks for
Hi Christoph!
Thanks for replying!
I have uploaded the input script and a picture, which shows a problem. This picture doesn't fit to the mesh, which is attached to this forum topic/post, it only shows the problem which is occuring with my ball mill simulation.
The problem is:
After filling the balls, the mill starts to rotate and then this problem emerges: the balls adhere to the lifting bar being located in the middle of the bar or under it. So it makes no sense physically.
Meanwhile I meshed the geometry with 3 Meshers, but the problem is still there!
I am modelling steel balls with a Young's Modulus (YM) of 200e9 GPa. It leads to a very small timestep.
I was told that I can reduce the YM by a order of magnitude of 2 or 3. Can you please give me some advice regarding some input parameters or in general?
Moreover, I would be very thankful if you could give me some links or pdf's which explain the functionality of LIGGGHTS and DEM in general, so I can understand what I am doing much better.
Thanks again!
Kind regards,
Eugen
Sapsan | Mon, 03/12/2012 - 14:58
Dear all, after changing the
Dear all,
after changing the coefficient of restitution from 0.28 to 0.8 (trial and error) the problem of ball adhesion disappeared (for the time being). The CoR for steel is abot 5/9. I hope there will be no problems with this value...
Regards,
Eugen
ckloss | Mon, 03/12/2012 - 15:15
Good to know. I assume it's a
Good to know.
I assume it's a round-off-error for high damping, probably due to inaccurate wall velocity calculation in the moving mesh case. We will re-write this part anyway in the next major release, so this should vanish in the next major release (2.0)
Christoph