how to reset the position of atoms

Dear,users
I’m simulating atom’s flow with obstacle in 3D dimension. and boundary p f f

The way of atom’s flow is from left to right(see the pic.)
The area atoms not exists is obstacle.

image2.jpeg

image3.jpeg

Dear,users
I’m simulating atom’s flow with obstacle in 3D dimension. and boundary
p f f

The way of atom’s flow is from left to right(see the pic.)
The area atoms not exists is obstacle.

Next, the problem is the atoms avoided obstacles moves just as it is.
So, the area like cylinder occurs .

To me, and with the very limited amount of details, it seems that is
exactly what should happen.

I want reset the position of atoms when they through the periodic
boundary.

What should I use command to deal with this problem?

Thanks all
Ryota

I don't see any physical reason that would support resetting atoms
position at periodic boundaries... So what the point of using periodicity?

The only problem here: what do you want to simulate? Is your simulation
setup correct?

Best,
Julien

I want to simulate about plane’s wing.
I regard the obstacle as a wing and I want to check movements of atoms around wing.

And I use “fix addforce command” to make flow.
I added the velocity for only x way.
Because of that, atoms avoided wing moves only x way.
And then, the area like a cylinder occurs.
image1.jpeg

2019/02/04 19:33、Julien Guénolé <[email protected]…5809…>のメール:

you had reported this behavior before, when your input had serious problems.
how did fix those problems. from what you describe here, you didn’t.
so bogus input is producing bogus output (or GI-GO for short).

without the input, nobody can give meaningful advice.

axel.

image1.jpeg

I want to simulate about plane’s wing.
I regard the obstacle as a wing and I want to check movements of atoms around wing.

Although it’s possible you have some errors in your input file (haven’t read, sorry), the main issue does not appear to be related to LAMMPS, but a physics problem. Your system is in the wrong regime.
Specifically, your wing appears to be too small. From your pictures, the system you are simulating looks like it might even be smaller than the mean free path of the particles in your simulation. It is also likely that your drift velocity (due to “fix addforce”) is unrealistically large compared to your thermal velocity (temperature). (Did you remember to include a thermostat?)
This means that the gas molecules surrounding the wing might behave ballistically during the short time it takes for them to pass over the surface of the obstacle (due to the small system size and their high drift velocity). In this case, the gas will not behave like a continuum fluid. It will not satisfy the Navier-Stokes equations. This is one possible reason why the gas does not fill the space after passing the obstacle.
If you have not done this yet, look at how other people have simulated computational fluid dynamics using LAMMPS. Here are some random links:

https://www.google.com/search?
q=LAMMPS+CFD&oq=LAMMPS+CFD&aqs=chrome…69i57.2876j0j1&sourceid=chrome&ie=UTF-8

https://www.cfdem.com/liggghts-open-source-discrete-element-method-particle-simulation-code

https://www.cfdem.com/forums/coupling-lammps-and-openfoam

and links to some non-LAMMPS software:
https://www.researchgate.net/post/wich_is_the_best_software_to_realize_Computational_fluid_dynamics_CFD

I don’t know if this helps at all. Forgive me if these aren’t the best links. (CFD is not my area.) Good luck.

Andrew
P.S. Thanks for including pictures with your question. They are helpful.

image1.jpeg

Thanks for reply.

Velocity of atoms by “addforce command” resulted the problem.
So I adjusted them and found the basis of problem.
I’m sorry to ask you foolish question.

Thank you very much.

Ryota

2019/02/05 7:50、Andrew Jewett <[email protected]…24…>のメール: