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Re: [ESPResSo-users] Simulation of fluid using LB-method


From: Wink, Markus
Subject: Re: [ESPResSo-users] Simulation of fluid using LB-method
Date: Thu, 30 Jan 2014 17:20:35 +0000

Hi everybody,

I am quite sure, that the solution has converged. Attached you will find a 
figure showing the maximum velocity as a function of the integration steps. For 
me, it looks at is has converged. What do you say.

Just to be clear: if I want a channel width of 50 with a_grid=1, I put the 
walls at positions 1 and 51 having a box length of 52?

Greetings Markus
________________________________________
Von: address@hidden address@hidden" im Auftrag von "Stefan Kesselheim 
address@hidden
Gesendet: Donnerstag, 30. Januar 2014 14:57
An: address@hidden List
Betreff: Re: [ESPResSo-users] Simulation of fluid using LB-method

Hi everybody,
please forgive me, but is it clear that the solution is converged? Markus, have 
you tried running for twice (or half) as many steps, and checked that you get 
exactly the same results?
Because near the boundary the curvature looks perfect and closer to the center 
I'm not sure.

Let me make one thing clear. With our staggered grid the position of the node 
(m,n,o) is at m+0.5, n+0.5, o+0.5. This means if you lbboundary is located at 
z=1, it means there is a layer of wall nodes at x=*, y=*, z=0.5. For not too 
high viscosities (should be in the He formula as well) no measurable slip 
should appear and the hydrodynamic boundary should be located mid-grid, thus at 
z=1.
If you place a boundary at - say - 0.8, the hydrodynamic boundary of course is 
still at 1.

I'm not sure, Markus, if you put these parameters correctly into you 
theoretical curve. We introduced the staggered grid some time after Georg's 
bachelor thesis to allow for using a nonzero skin with LB.

Cheers
Stefan

On Jan 30, 2014, at 2:47 PM, Ulf Schiller <address@hidden> wrote:

> On 01/30/2014 02:33 PM, Georg Rempfer wrote:
>> Hey all,
>>
>> I remember that we fixed the issue with the missing 0.5*h*F some years
>> ago. For a flat bounce-back wall aligned with the lattice axis, the
>> actual hydrodynamic no-slip wall is positioned in the middle between the
>> last fluid node and the first wall node.
>
> There is still a viscosity dependent slip velocity, cf. Eq. (20) in [He et 
> al. (1997), J. Stat. Phys. 87, 115].
>
> Cheers,
> Ulf
>
> --
> Dr. Ulf D. Schiller                        Building 04.16, Room 3006
> Institute of Complex Systems (ICS-2)       Phone:   +49 2461 61-6144
> Forschungszentrum J├╝lich, Germany          Fax:     +49 2461 61-3180
>


Attachment: saturation.png
Description: saturation.png


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