problem in velocity profile

LAMMPS LAMMPS Mailing List Mirror
1 
I want to simulate  a pois flow  between two parallel  walls .when I calculate the velocity profile (I used 

dump velocity),I find that the velocity profile  is not similar to **parabolic** and my velocity profile is 

completely flat.I attach the velocity profile in below.  what is wrong with my input script file?

# 2-d LJ flow simulation

dimension	2
boundary	p s p

atom_style	atomic
neighbor	0.3 bin
neigh_modify	delay 5

# create geometry

lattice		hex 0.7
region		box block 0 20 0 10 -0.25 0.25
create_box	3 box
create_atoms	1 box

mass		1 1.0
mass		2 1.0
mass		3 1.0

# LJ potentials

pair_style	lj/cut 1.12246
pair_coeff	* * 1.0 1.0 1.12246

# define groups

region	     1 block INF INF INF 1.25 INF INF
group	     lower region 1
region	     2 block INF INF 8.75 INF INF INF
group	     upper region 2
group	     boundary union lower upper
group	     flow subtract all boundary

set	     group lower type 2
set	     group upper type 3

# initial velocities

compute	     mobile flow temp
velocity     flow create 1.0 482748 temp mobile
fix	     1 all nve
fix	     2 flow temp/rescale 200 1.0 1.0 0.02 1.0
fix_modify   2 temp mobile

# Poiseuille flow

velocity     boundary set 0.0 0.0 0.0
fix	     3 lower setforce 0.0 0.0 0.0
fix	     4 upper setforce 0.0 0.0 0.0
fix	     6 flow addforce 0.5 0.0 0.0
fix	     7 all enforce2d

# Run

timestep	0.003
thermo		500
thermo_modify	temp mobile

dump            1 all custom 10000 traj_nvt.lammpstrj y vx

dump  3 all image 10000 image.*.PPM type type zoom 1.6 adiam 1.5

run		100000
2

Hi, You used a big force (fix 6 flow addforce 0.5 0.0 0.0) , you can use this command:

fix	     6 flow addforce 0.05 0.0 0.0

Good Luck
3



Sent from Yahoo Mail for iPad |

4

why repost a question for which you already received an answer and without any discussion of that suggestion?

please note, that your inquiry is not really a question about LAMMPS, but rather about the science you are doing. this is something that you should first and foremost discuss with your adviser or whoever is consulting you on doing good and correct MD simulations. the focus of the mailing list is to solve LAMMPS specific problems, e.g. where LAMMPS is not working correctly.

thanks for your understanding,
axel.