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Re: [lammps-users] How do I model Couette Flow in a NVT system with a void space
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Re: [lammps-users] How do I model Couette Flow in a NVT system with a void space


From: "罗爽" <luoshuang@...7337...>
Date: Sat, 14 Apr 2018 11:06:36 +0800

Dear Axel,

After some thinking, I realized that this system was a little unrealistic.   I decided to obtain the linear velocity profile of the fluid by dragging a wall (similar to the case in the Flow subfile).  Meanwhile, I want to keep water molecules at constant temperature.  Will the fix NVT command still work for a flowing fluid?  Do I need to modify the temperature-controlling command?
Thank you for your reply.

LUO



----------------
 


---------- Origin message ----------
>From:"Axel Kohlmeyer" <akohlmey@...24...>
>To:"罗爽" <luoshuang@...7337...>
>Subject:Re: [lammps-users] How do I model Couette Flow in a NVT system with a void space
>Date:2018-04-13 20:58:00
On Fri, Apr 13, 2018 at 8:40 AM, 罗爽 <luoshuang@...7337...> wrote:

> Dear Giacomo,
> Thanks for your apply
> Pls see the attached PNG file. In my system, one face of the water system
> is exposed to the vacuum, the other side is exposed to a rigid surface.


please note, that the correct term is "immobile" not "rigid".



> A periodic boundary condition is used at three directions. The
> dimension of the simulation cell in the direction perpendicular to the
> surface is suffcientlly large to avoid unnecessary interactions due to the
> PBC.


please explain, what is supposed to be inducing the flow here?

axel.



>
>
> LUO
> ----------------
>
>
>
> ---------- Origin message ----------
> >From:"Giacomo Fiorin" <giacomo.fiorin@...24...>
> >To:"罗爽" <luoshuang@...7337...>
> >Subject:Re: [lammps-users] How do I model Couette Flow in a NVT system
> with a void space
> >Date:2018-04-13 19:49:02
>
> If I understand correctly, you are modeling an air/water interface, where
> one face of the water film is exposed to the vacuum. The water film will
> inevitably deform to minimize its total surface energy.
>
> If that's not the correct interpretation, can you explain more clearly what
> you're trying to model?
>
> Giacomo
>
> On Fri, Apr 13, 2018 at 1:22 AM, 罗爽 <luoshuang@...7337...> wrote:
>
> > Dear Lammps users
> >
> > The simulation system contains a rigid surface and a water film of 5-7
> > layers molecules sitting on the surface. To avoid unnecessary
> > water-surface interactions caused by PBCs, a void space above the water
> is
> > used. I am looking a way to model the Couette flow of water in this
> > system. I know that the linear velocity profile of the fluid can be
> > obtained by dragging a wall or used fix nvt/slood and fix deform
> commands.
> > But I don't want my box be deformed and I also don't want the water
> > confined in a channel. I tried to add a velocity paralleling to the
> > surface to water molecules in the upper-most layers. However, the volume
> > of the water is changed due to the void space. Thus, it's difficult to
> > define the water molecules in the upper most layer. How can I do to get
> > the couette flow in this system?
> >
> > Any help will be highly appreciated
> >
> > Thank you all very much
> >
> > Luo
> >
> >
> > ------------------------------------------------------------
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> >
> >
>
>
> --
> Giacomo Fiorin
> Associate Professor of Research, Temple University, Philadelphia, PA
> Contractor, National Institutes of Health, Bethesda, MD
> http://goo.gl/Q3TBQU
> https://github.com/giacomofiorin
>
>
>
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> ------------------
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>


--
Dr. Axel Kohlmeyer akohlmey@...24... http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.