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Re: [lammps-users] Poisuille flow
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Re: [lammps-users] Poisuille flow

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Fri, 6 Oct 2017 15:26:58 -0400

On Fri, Oct 6, 2017 at 2:58 PM, m n <mnnfean@...16...> wrote:
Dear Axel,

According to your last comment, in order to simulate a steady flow at a given velocity, I initialized the flow with a velocity command and added a small force, to compensate for the dissipation of energy through interaction with the walls:

velocity      flow set 1.0 0.0 0.0
fix    1 flow addforce 0.01 0.0 0.0 

In order to define "temperature" for the flowing medium, I used "compute temp/com" command to exclude the kinetic energy of the center of mass of the flowing medium: 

compute hot upper temp
compute flow argon temp/com
compute                   cold lower temp

Moreover, for controlling the temperature of the walls I have used the following commands:

fix hot upper nvt temp 150 150 0.01
fix cold lower nvt temp 90 90 0.01
fix nve flow nve

The temperature of the flow region decreased after I used the "compute temp/com" from 1250 to 840 but there are still some biases.

I would really appreciate if you could help me to figure it out.

​sorry, i don't have the time to debug everybody's inputs and figure out for them how they need to do their research.
i have outlined the problems and explained how you can approach individual steps. if this doesn't work, you have to do what everybody has to do: turn off features (e.g. the heated walls) one by one until your input is so simple, that everything works as expected or you can tell what is the problem and how to address it.

this really isn't a LAMMPS issue anymore, but a question of how to do research.




Dr. Axel Kohlmeyer  akohlmey@...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.