Hi everyone,
the case I am simulating consists of a bunch of particles stirred in a tank. The geometry of the stirrer is available in stl format.
I would like to calculate the torque exerted on the stirrer or the axle moving it, respectively. I've played around with fix mesh/gran/stressanalysis and its capabilities are almost what I need. Is there a way in liggghts to integrate the stresses such that I get the resulting torque on the axle?
Thanks for any comments.
Best regards,
Moritz
ckloss | Wed, 07/27/2011 - 09:55
Hi Moritz, the torque on the
Hi Moritz,
the torque on a mesh (such as the stirrer) is available directly as the output of the fix mesh/gran/stressanalysis command. Its doc says: This fix stores a global vector with 6 components for access by various output commands. The first 3 components are equal to the total force on the mesh, the last 3 components store the total torque on the body exerted by the particles.
Cheers,
Christoph
moritzhoefert | Wed, 07/27/2011 - 10:20
Hi Christoph, thanks for the
Hi Christoph,
thanks for the quick reply! ... wer lesen kann, ist klar im Vorteil.
Best regards,
Moritz
richti83 | Wed, 10/26/2011 - 11:31
how to dump total force and torque
Hi Christoph,
I've a similar problem to dump the total force and torque of a mesh.
I added stressanalysis to the import mesh fix
fix screw_pos all mesh/gran/stressanalysis stl/screw+x.stl 1 0.001 0. 0. 0. 0. 0. 0.
fix screw_neg all mesh/gran/stressanalysis stl/screw-x.stl 1 0.001 0. 0. 0. 0. 0. 0.
and I'm able to dump into vtk file this was:
dump dump_stress0 all mesh/gran/VTK 250 post/Stress_file-*.vtk stress screw_pos screw_neg
It seems the stress is assigned to the triangles of the mesh. But how can I dump the total values of the global vector you mentioned ?
I tried:
dump wall_stress all custom 100 post/wall_dump*.txt f_screw_pos to access the fix directly but got an error "Dump custom fix does not compute per-atom info"
thank you,
Christian
ckloss | Wed, 10/26/2011 - 11:42
you can use the fix print
you can use the fix print command for this - as mentioned above, the torque is a direct output of fix mesh/gran/stressanalysis
Christoph
richti83 | Wed, 10/26/2011 - 11:55
sorry ...
Finaly I got it,
to all who are interested in: use
fix force_pos all ave/time 1 1 250 f_screw_pos[1] f_screw_pos[2] f_screw_pos[3] f_screw_pos[4] f_screw_pos[5] f_screw_pos[6] file post/force_on_screw_pos.txt
fix force_neg all ave/time 1 1 250 f_screw_neg[1] f_screw_neg[2] f_screw_neg[3] f_screw_neg[4] f_screw_neg[5] f_screw_neg[6] file post/force_on_screw_neg.txt
to dump the vector at specific timesteps:-)
I was a little bit confused of dump and fix styles.
Have a nice day,
Christian