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Re: [ESPResSo-users] lbboundary
From: |
Stefan Kesselheim |
Subject: |
Re: [ESPResSo-users] lbboundary |
Date: |
Thu, 4 Dec 2014 20:25:35 +0100 |
Hi Roya,
On Dec 4, 2014, at 8:04 PM, roya moghaddasi <address@hidden> wrote:
> Hi Espresso users,
>
> I want to use a cylinder boundary for my lbfluid. I want to ask some
> questions:
> 1. can I use penetrable or direction or reflecting for this boundary?
> 2. If I use "reflecting 2", will the boundary condition be bounce-back
> condition which is nice for a lbboundary? What is your suggestion?
Both options exist only for constraints and not for lbboundaries.
> 3. Espresso manual says "This has important implications for the location of
> hydrodynamic boundaries which are generally considered to be halfway between
> two nodes to first order". my main cylinder which contains all the particles
> has a radius of 25 and I want my lbboundary to have the same radius. Do you
> see any contradictions of this and the Espresso manual statement?
lbboundaries use the "link bounce back" method, that is described a lot in the
LB literature. If you create an lbboundary cylinder with a certain radius
around a certain point all nodes inside this cylinder will be flagged "wall".
If the walls were plane, The the hydrodynamic boundary appears halfway between
the outermost "fluid" and the innermost "wall" node. The lbboundary node
positions are half-integer, i.e. 0.5, 1.5, 2.5 …
Thus, if you make e.g. a cylinder with radius 10 around position x=15, node
x=4.5 will be "wall", and node x=5.5 will be "fluid". The hydrodynamic
boundary will be at 5, thus you get what you expect. You should, however, check
the results i.e. by applying a pressure gradient against the analytical
solution. From you other mail, I see you might be using a viscosity that is not
suited for using the link bounce back method because it is too high.
Note that in most soft matter applications, the absolute value of the viscosity
does not matter anyways, because the fluid is described by the linear Stokes
equation and changing the viscosity only changes the absolute timescale, but
that can be corrected for at the end.
Cheers and good luck
Stefan
- [ESPResSo-users] lbboundary, roya moghaddasi, 2014/12/04
- Re: [ESPResSo-users] lbboundary,
Stefan Kesselheim <=
- Re: [ESPResSo-users] lbboundary, roya moghaddasi, 2014/12/05
- Re: [ESPResSo-users] lbboundary, roya moghaddasi, 2014/12/05
- Re: [ESPResSo-users] lbboundary, Ulf Schiller, 2014/12/05
- [ESPResSo-users] LBM, speed of sound, stability, Ivan Cimrak, 2014/12/17
- Re: [ESPResSo-users] LBM, speed of sound, stability, Ulf Schiller, 2014/12/17
- Re: [ESPResSo-users] LBM, speed of sound, stability, Vincent Ustach, 2014/12/17
- Re: [ESPResSo-users] LBM, speed of sound, stability, Ulf Schiller, 2014/12/18
- Message not available
- Re: [ESPResSo-users] LBM, speed of sound, stability, Ulf Schiller, 2014/12/18
- Re: [ESPResSo-users] LBM, speed of sound, stability, Wink, Markus, 2014/12/18
- Re: [ESPResSo-users] LBM, speed of sound, stability, Ulf Schiller, 2014/12/18