'exploding'/instable simulation

Dear lammps users,

I am trying to model a 2d rotating drum… so far, I think I have gathered all the code I need in order to produce a simulation.

But, the simulation seems unstable (as you can see in the attachments).

Below is my code

=== initializing ===

units si
atom_style sphere
dimension 2
boundary f f p
newton off
communicate single vel yes

==== Defining the region ====

lattice sq 0.5

region BLOCK2 cylinder z 0 0 100 -0.5 0.5
region BLOCK4 block -100 100 -100 -50 -0.5 0.5
region HALF intersect 2 BLOCK2 BLOCK4

create_box 1 BLOCK2
create_atoms 1 region HALF

group ATOM region HALF
region HALF delete

pair_style gran/hooke 2.0e5 NULL 50.0 NULL 0.5 0
pair_coeff * *

==== Fixes ====

timestep 0.001

fix f1 ATOM nve/sphere
fix f2 ATOM enforce2d
fix f3 ATOM gravity 9.81 vector 0.0 -1.0 0.0
fix f4 ATOM wall/gran 10000.0 0.0 64.0 64.0 0.5 1 zcylinder 100 shear x 20

compute 1 ATOM erotate/sphere
dump myDump all image 3 dump.*.jpg type type

==== Run it ====

run 10

can anyone see what is going wrong?
I tried different timesteps… but this did not help. Besides that, I also have the vague idea that my fix f4 is being ignored by the particles… Since, when I decrease the radius of this fix, the particles do not interact with the wall.

Thanks in advance!






If the motion (dump files) of the particles don’t change
when you comment in/out the fix wall/gran command,
then it isn’t doing what you hope. You should experiment
(debug) with what is happening.