Simulation of granular particles on an inclined plane

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1

I am a new user of LAMMPS. I am using its latest version. And I am
unable to find out the problem in my code.
I am trying to simulate a flow of granular particles on an inclined
plane of angle 14 degrees, however I have initially used 60 degrees to
stabilize the flow. Since, I am unable to install the granular
package, I am currently simulating the flow by using atom_style
sphere. These are the following problems I am facing:

1. Seeing the visual on VMD, the size of the box that I have used for
simulation is continuously increasing.
2. The temperature values are coming out very high.
3. E_ pair is coming out to be zero every time.

LAMMPS Code:

# Defining properties of the particles
units si
dimension 3
boundary p m p
newton off

atom_style sphere
atom_modify sort 50 0.5
neighbor 0.005 bin
neigh_modify delay 0
communicate multi vel yes

# Creating Geometry
lattice fcc 1.0
region box block 0 0.05 0 0.02 0 0.05 # 5cm x 2cm x 5cm
create_box 1 box
create_atoms 1 random 8000 453 box

group flow type 1
set group flow type 1 diameter 0.002

# Particle Interactions
pair_style gran/hooke 200200 NULL 0 0 0.0005 0
pair_coeff * *

# Initial Velocities
velocity all set 0.0 0.0 0.0

fix 1 all nve/sphere
fix 2 flow gravity 9.81 vector 0.866 -0.5 0
fix 3 all wall/gran 20020 NULL 0.005 0.003 0.0005 0 yplane -0.000002 NULL

# Run
timestep 0.00003
thermo 400
dump 1 all custom 100 dump.flow id x y z vx vy vz
run 5000 upto

fix 2 flow gravity 9.81 vector 0.24 -0.907 0
dump_modify 1 append yes every 100
run 10000 upto

2

Since, I am unable to install the granular
package, I am currently simulating the flow by using atom_style
sphere.

Your script below is using a granular pair style. So what
do you mean that you can't install the package?

I suggest you run both the examples in example/pour to
start with, to insure you can viz them and interpret the
output correctly.

Steve

3

I can only tell you what I see that is wrong with your simulations.
First, remember that temperature is some what meaningless for athermal
granular systems. A more common measure is granular temperature or
T_gran=2*E_kin/3*N_p*m. Another suggestion would be to just scale
your problem rather than using physical units. I don't believe that
you will get an energy per pair for granular models. At any rate
it doesn't matter because (I reiterate) thermal output is meaningless
for granular problems. You WILL need to do your own post processing.

I also suggest reading up on these flows, since there is ample
literature. Particularly, papers by Leo Silbert, I suggest his paper
in PRE VOLUME 64, 051302. You will find that flows at 60 degrees are
unstable. In addition, without normal damping you likely will not get
a stable granular temperature if you are inputting
energy(gravitational) using nve integration.