Dear all,
I’m trying to simulate the displacement between two infinite blocks. Therefor I’m using the command velocity and style set in both blocks in oposite directions with the same velocity module. The problem is that when I plot the center of mass displacement from the lower block, I get a periodic function. Could you please tell me what this command really does? In the way I’m applying it, can it mask any interaction effect as adhesion, cristalline defects or vorticies if they are to appear?
The input is as follows:
"
2d friction simulation
dimension 2
boundary p s p
atom_style atomic
neighbor 0.3 bin
neigh_modify delay 5
units lj
create geometry
lattice hex 0.9
region box block 0 30 1.1 80 -0.25 0.25
create_box 4 box
mass 1 1.0
mass 2 1.0
mass 3 1.0
mass 4 1.0
atom regions
region lo-fixed block INF INF 1.1 3.1 INF INF
region lo-slab block INF INF 3.2 15.9 INF INF
region hi-fixed block INF INF 28 30 INF INF
region hi-slab block INF INF 16 27.9 INF INF
create 2 surfaces with asperities
create_atoms 1 region lo-slab
create_atoms 2 region hi-slab
create_atoms 3 region lo-fixed
create_atoms 4 region hi-fixed
LJ potentials
pair_style lj/cut 2.5
pair_coeff * * 1.0 1.0 2.5
define groups
group lo region lo-slab
group lo type 1
group hi region hi-slab
group hi type 2
group lo-fixed region lo-fixed
group hi-fixed region hi-fixed
group mobile union lo hi
group boundary union lo-fixed hi-fixed
group upper-group union hi-fixed hi
group lower-group union lo-fixed lo
set group lo-fixed type 3
set group hi-fixed type 4
initial velocities
compute temperatura boundary temp/partial 0 1 0
compute temperatura2 mobile temp/partial 0 1 0
compute 1 lo com
velocity all create 0.033 482748 temp temperatura
#Upper-group displacement
displace_atoms upper-group move 0 20.0 0 units box
#Fixes
fix 2 all nve
#Minimize
minimize 0.000001 0.001 1826000 1826000
run details
thermo 5000
timestep 0.0001
run_style verlet
dump 1 all atom 500 dump.p01
run 1826000
#move atoms back
displace_atoms upper-group move 0 -20.0 0 units box
write_restart restart.p01
run 20000
#main simulation
variable Temperatura atom “mass*(vy^2)/4”
unfix 2
fix 3 boundary nvt 0.033 0.033 0.75
fix_modify 3 temp temperatura
fix 4 mobile nve
fix 5 all ave/spatial 1 1 1000 y 0.0 0.6 v_Temperatura x y file temp.p01
#velocity command
velocity hi set 0.1095 0 0 sum no
velocity lo set -0.1095 0 0 sum no
thermo 5000
thermo_modify temp temperatura2
thermo_style custom step temp etotal c_1[1] c_1[2] c_1[3]
undump 1
dump 2 all atom 1000 dump.p01_a
dump 3 all xyz 1000 dump.p01..xyz
dump 4 all custom 1000 dump.p01_c. id type x y vx vy fx fy
timestep 0.0001
run 300000
"
Best regards,
Débora M M Marques