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Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions
From: |
Ulf Schiller |
Subject: |
Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions |
Date: |
Tue, 02 Dec 2014 12:52:16 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 |
Hi Markus,
I tried another thing and replaced the boundaries by plane walls normal
to the x and z direction. With that, I do not see any peculiarities.
This suggests that the issue is related to the more complex boundaries
in your system. I'll have a look at your boundaries.tcl tonight.
Cheers,
Ulf
On 01/12/14 17:08, Wink, Markus wrote:
> Hello everybody,
>
>
>
> I performed simulations as Ulf proposed to help to track the problem
> down. In detail three different simulations are performed, graphs on
> that can be found attached:
>
> 1) I removed the boundaries, putting a particle with an initial
> velocity v_0y. I can see the exponential decrease of the velocity in
> y-direction (as expected). The z-position is pretty stable, nevertheless
> I see an (uncorrelated (?)) change of the velocity in z direction. It
> seems to be directed towards the –z direction, although it is very small
> (of the orders of 1E-24 ), so I guess it is an numerical artifact (?).
> Nevertheless I don’t see the jump in the z-position nor in the z-velocity.
>
> 2) A simulation as in 1), in addition the particle has an initial
> velocity in the +z direction (of the order I got for the lift force). I
> still see the exponential decrease in both the z- and y-velocity. No
> jumps of the z-position at the boundaries can be found.
>
> 3) The same as simulation 1), but this time with boundaries. I see
> the migration towards the middle of the channel as expected (notice,
> that this time, the initial z-velocity of the particle is set to zero).
> Neither a jump in the z-velocity nor in the z-position can be seen.
>
>
>
> In combination of the first script I posted (which was the same as in
> simulation 3 here, but furthermore an external force is exerted to the
> fluid) I see the jump in the z-component of the position and the
> z-component of the velocity only if there is a combination of boundaries
> and an external force acting on the fluid. What is missing is a
> simulation with no boundaries and an external force acting on the fluid.
>
>
>
> I furthermore played around with the friction coefficient. If I lower it
> by three orders of magnitude, I still notice a jump in the z-component
> of the velocity, although it is not as steep as before. I am not sure
> what this means.
>
>
>
> I hope this helps to isolate the problem.
>
>
>
> Kind regards
>
>
>
> Markus
>
>
>
>
>
>
>
> -----Ursprüngliche Nachricht-----
> Von: Ulf Schiller [mailto:address@hidden
> Gesendet: Montag, 1. Dezember 2014 16:41
> An: address@hidden
> Cc: Joost de Graaf; Wink, Markus
> Betreff: Re: [ESPResSo-users] Particle in Fluid, periodic boundary
> conditions
>
>
>
> Hi Joost, Markus, all,
>
>
>
> after a quick inspection I can't see any relevant changes to the
> coupling on that branch (I've not gone through the CUDA implementation
> though). After merging and running the script Markus provided, I'm
> afraid the issue persists. I don't have time to track this down, but
> according to my experience it is likely to be due to one of the following:
>
> - problem with pos-lattice mapping (less likely since only halo affected)
>
> - halo not up-to-date
>
> - forces missing in halo upon redef of fluid momentum
>
>
>
> Note that this bug potentially affects any system with particle-fluid
> coupling and periodic boundary conditions.
>
>
>
> Cheers,
>
> Ulf
>
>
>
> On 28/11/14 15:27, Joost de Graaf wrote:
>
>> Dear Markus,
>
>>
>
>> Sorry about that. The ENGINE branch on hmenke's git account
>
>>
>
>> https://github.com/hmenke/espresso/tree/engine
>
>>
>
>> has a fix for the bug. As I said, I recalled seeing something like it,
>
>> and at that time we apparently fixed the problem (which I cannot
>
>> remember doing). We are still working on one last testcase for the
>
>> ENGINE branch, before we have it pulled into the Master, which will
>
>> take about a week. Then a lot of the LB bugs should be fixed.
>
>>
>
>> Kind Regards, Joost
>
>>
>
>> On 28 November 2014 at 16:24, Joost de Graaf <address@hidden
>
>> <mailto:address@hidden>> wrote:
>
>>
>
>> Dear Markus,
>
>>
>
>>
>
>>
>
>> On 24 November 2014 at 21:24, Joost de Graaf
>
>> <address@hidden <mailto:address@hidden
> <mailto:address@hidden:address@hidden>>>
> wrote:
>
>>
>
>> Dear Markus,
>
>>
>
>> I remember spotting something like this in one of the older
>
>> versions of the master, but I tried to find it and could not
>
>> reproduce the bug with the latest version, which one are you
> using?
>
>>
>
>> KR, Joost
>
>>
>
>> On 24 November 2014 at 19:35, Ulf Schiller <address@hidden
>
>> <mailto:address@hidden>> wrote:
>
>>
>
>> Hi Markus,
>
>>
>
>> On 24/11/14 18:12, Wink, Markus wrote:
>
>> > can explain it to me? It seems, that the periodic
> boundary condition in
>
>> > the LB Fluid doesn’t work. If I remove the fluid I don’t
> see that.
>
>>
>
>> Yes, looks like something is at odds with the periodicity
>
>> here. Can you
>
>> plot the z-velocity over x-position? That may point towards
>
>> what is
>
>> going wrong.
>
>>
>
>> Cheers,
>
>> Ulf
>
>
>
> --
>
> Dr Ulf D Schiller
>
> Centre for Computational Science
>
> University College London
>
> 20 Gordon Street
>
> London WC1H 0AJ
>
> United Kingdom
>
>
>
> Phone: +44 (0)20 7679 5300
>
>
>
--
Dr Ulf D Schiller
Centre for Computational Science
University College London
20 Gordon Street
London WC1H 0AJ
United Kingdom
Phone: +44 (0)20 7679 5300
- Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions, Ulf Schiller, 2014/12/01
- Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions, Wink, Markus, 2014/12/01
- Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions,
Ulf Schiller <=
- Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions, Ulf Schiller, 2014/12/02
- Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions, Wink, Markus, 2014/12/02
- Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions, Ulf Schiller, 2014/12/02
Re: [ESPResSo-users] Particle in Fluid, periodic boundary conditions, Joost de Graaf, 2014/12/01