Hi
I’m trying to simulate a channel flow (with perscribed inlet bulk velocity in the x direction) in LAMMPS.
However, as I understand it, if I use “velocity inlet set”, I would just get a homogeneous movement of atoms. Also, if I were to use “velocity inlet create” and then “velocity inlet set 1 NULL NULL” I don’t think I would get a fair representation of atomic motion either.
Would it be possible to create the thermal velocity field and then add an x-component velocity so that the bulk velocity would have the non-random x-directed component? And how would I go about doing that? (I haven’t found a way to ‘add’ a velocity to the existing value).
Best regards,
Steph
Hi
I'm trying to simulate a channel flow (with perscribed inlet bulk velocity
in the x direction) in LAMMPS.
However, as I understand it, if I use "velocity inlet set", I would just get
a homogeneous movement of atoms. Also, if I were to use "velocity inlet
create" and then "velocity inlet set 1 NULL NULL" I don't think I would get
a fair representation of atomic motion either.
Would it be possible to create the thermal velocity field and then add an
x-component velocity so that the bulk velocity would have the non-random
x-directed component? And how would I go about doing that? (I haven't found
a way to 'add' a velocity to the existing value).
you can use velocity set with atom style variables. you can define one
of those to compute to the current velocity plus a fixed value.
for details, please see the documentation.
axel.
It looks like it. Please read this:
http://lammps.sandia.gov/doc/velocity.html,
especially the part about the “bias” keyword.
I think it would be possible with a combination of velocity set (to first set the centre-of-mass to the desired velocity), then define a compute temp/com on the group, then use velocity create with bias and temp to make sure the centre-of-mass velocity is used as the bias velocity.
Note that this only sets the initial velocities to what you want, I am not sure how to keep the flow going indefinitely, that depends on your model I guess.
You can also create the thermal velocity field by using velocity create, then add the x-component velocity on top of the thermal velocity by using the “sum yes” keyword.
Ray