I am using the lastest LAMMPS to simulate a 3D couette flow, however, I could not
get the classic linear velocity profile. I created my script mostly from the 2D couette flow example.
I used fix nvt command to do NVT simulation and used fix ave/spatial to
get the averaged atoms velocity profile. The results are very strange for the vx
Any suggestion? Thanks a million
in.script
3-d LJ flow simulation
echo screen
dimension 3
boundary p p s
atom_style atomic
units lj
neighbor 0.3 bin
neigh_modify delay 5
create geometry
lattice fcc 0.81
region box block 0 10 0 10 0 12
create_box 3 box
create_atoms 2 box
mass 1 1.0
mass 2 1.0
mass 3 1.0
LJ potentials
pair_style lj/cut 2.5
pair_coeff * * 1.0 1.0 2.5
define groups
region 1 block INF INF INF INF INF 1
group lower region 1
region 2 block INF INF INF INF 11 INF
group upper region 2
group boundary union lower upper
group flow subtract all boundary
set group lower type 1
set group upper type 3
initial velocities
#compute mobile flow temp
compute mobile flow temp/partial 0 1 1
velocity flow create 1.0 482748 temp mobile
fix 2 flow nvt 1.0 1.0 1.0 drag 0.5
fix_modify 2 temp mobile
Couette flow
thermo 100
thermo_modify temp mobile
velocity lower set 0.0 0.0 0.0
velocity upper set 0.0 0.0 0.0
fix 3 boundary setforce 0.0 0.0 0.0
Run
dump 1 all atom 5 dump.flow
run 5000
timestep 0.005
velocity upper set 2.0 0.0 0.0
velocity lower set -2.0 0.0 0.0
run 60000
fix 4 flow ave/spatial 100 10 2000 z 0.0 3.0 vx ave running file vel.profile
run 40000