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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: Axel Kohlmeyer <akohlmey@...24...>
Date: Fri, 13 Apr 2018 23:21:01 -0400

On Fri, Apr 13, 2018 at 11:06 PM, 罗爽 <luoshuang@...7337...> wrote:
> 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?

you need to subtract out the bias from the induced flow. start reading
here: http://lammps.sandia.gov/doc/Section_howto.html#howto-16

axel.

> 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@...7553....> 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
>> >
>> >
>> > ------------------------------------------------------------
>> > ------------------
>> > Check out the vibrant tech community on one of the world's most
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>> > lammps-users@lists.sourceforge.net
>> > https://lists.sourceforge.net/lists/listinfo/lammps-users
>> >
>> >
>>
>>
>> --
>> 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
>>
>>
>>
>> ------------------------------------------------------------
>> ------------------
>> Check out the vibrant tech community on one of the world's most
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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.
>



-- 
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.