Regarding wall particle inelastic collision

Dear All,

I am using Yukawa interaction among particles in the simulation.

I want a wall in simulation which interacts with particles inelastically.

Can it is possible in LAMMPS ?.

Thanks in advance.

Dear All,
I am using Yukawa interaction among particles in the simulation.
I want a wall in simulation which interacts with particles inelastically.
Can it is possible in LAMMPS ?.

yes.

I am using wall/reflect. Is it correct?

I am using wall/reflect. Is it correct?

What does the documentation say?

In the documentation of fix wall/reflect it is written that if an atom moves outside
the wall on a timestep by a distance delta (e.g. due to fix nve), then it is
put back inside the face by the same delta, and the sign of the corresponding
component of its velocity is flipped.
From above lines i understand that there is no change in kinetic energy of particles
that means it is elastic collision.
For inelastic collision with wall, i have read about fix wall/gran but it requires

pair style granular. I am using pair style Yukawa. How i can use fix wall/gran?

Actually fix wall/gran does not require a granular

pair style, at least in the most current LAMMPS.

However that is the typical use case, i.e. granular

systems. You might be able to set the tangential

interactions for fix wall/gran … hooke … to

zero, and only use the normal interaction which

will include a damping term (i.e. inelastic). You’d

need to look at the pair_style granular doc page

to see the formulas. Note that you would also need

finite-size particles (atom_style sphere) to use

with fix wall/gran, which is also probably not what

you are using with pair yukawa.

So I’m not sure if this will give the inelastic behavior

you want. Maybe Axel was thinking of some other

option.

Steve

Actually fix wall/gran does not require a granular
pair style, at least in the most current LAMMPS.
However that is the typical use case, i.e. granular
systems. You might be able to set the tangential
interactions for fix wall/gran ... hooke ... to
zero, and only use the normal interaction which
will include a damping term (i.e. inelastic). You'd
need to look at the pair_style granular doc page
to see the formulas. Note that you would also need
finite-size particles (atom_style sphere) to use
with fix wall/gran, which is also probably not what
you are using with pair yukawa.

So I'm not sure if this will give the inelastic behavior
you want. Maybe Axel was thinking of some other
option.

no, i primarily wanted to demonstrate to sandeep how frustrating and
irritating it is to have people asking vague, imprecise questions in a
fashion that expects other people to do his thinking for him without
having sufficient information. in fact, it looks to me as if this
requires some more thinking and research before it is even worth
asking on the mailing list. i've provided accurate yet, equally vague
and incomplete replies to his unspecific questions. he's been asking
in this style for an extended period and i've pointed out the problems
with his approach before. so i thought it was time for a little
demonstration instead.

axel.

Thanks for your reply.

Now, i am using finite size particles with fix wall/gran but getting an
Error: Expected floating point parameter in input script or data file (…/fix_wall_gran.cpp:57).

When i comment fix wall/gran command simulation run properly.

What improvement required in the input script can you suggest to me?.

Input script is given below-

Variables

variable m equal 1e-27
variable lu equal 0.418e-3
variable cutf equal 15.0*{lu} variable dia equal {lu}
variable neigh equal 0.1*${cutf}

#Initialization
units si
atom_style sphere
dimension 2
boundary f p p

#Atom definition
lattice sq 0.418e-3
region reg block 0 50 0 200 -0.25 0.25

Box

create_box 1 reg
create_atoms 1 random 8000 13356798 reg

Thanks for your reply.
Now, i am using finite size particles with fix wall/gran but getting an
Error: Expected floating point parameter in input script or data file
(../fix_wall_gran.cpp:57).
When i comment fix wall/gran command simulation run properly.
What improvement required in the input script can you suggest to me?.

please pay attention to the specific wording of steve's suggestion:

"Actually fix wall/gran does not require a granular
pair style, at least in the most current LAMMPS."

so are you running the most current version of LAMMPS?

axel.

Thanks for reply.
Yes, i am using LAMMPS’s 30 Sep 2016 version.
LAMMPS (30 Sep 2016)
Lattice spacing in x,y,z = 0.000418 0.000418 0.000418
Created orthogonal box = (0 0 -0.0001045) to (0.0209 0.0836 0.0001045)
2 by 11 by 1 MPI processor grid
Created 3183 atoms
Setting atom values …
3183 settings made for mass
Setting atom values …
3183 settings made for diameter
ERROR: Expected floating point parameter in input script or data file (…/fix_wall_gran.cpp:97)

please look at the documentation and the given examples very
carefully. i am certain, you are making a mistake with the syntax of
fix wall/gran.

axel.