Re: [ESPResSo-devel] A bug in Espresso

[Axel Arnold]

On Friday 29 June 2012, Ivan Cimrak wrote:
> That could be the reason. Thanks very much for the explanation!
> 
> Just to be sure, you have shifted the lb lattice by a half grid point.
> Does that mean that if I set the fluid velocity by
> lbnode 0 0 0
> that it is set in the spatial point 0.5 0.5 0.5? Or at -0.5 -0.5 -0.5?

It is at +0.5, so that the lattice basically ranges from 0.5 till box_l - 0.5
in each direction.
 
> Also, if I set a wall constraint by
> constraint wall dist 0.5 normal 0 0 1
> should I set the lbboundary shifted? Do I need to set
> lbboundary wall dist 1.0 normal 0 0 1
> or
> lbboundary wall dist 0.0 normal 0 0 1
> ?

As far as I remember, the boundaries are set such that every grid point in the 
constraint is a wall. Therefore, you set the LB wall best at the same place as 
the real wall, that is, lbboundary wall dist 0.5 normal 0 0 1. That will be 
equivalent to lbboundary wall dist 0.0 normal 0 0 1 since 0.5 would the first 
grid point to be in the wall in both cases.

Axel

-- 
JP Dr. Axel Arnold      Tel: +49 711 685 67609
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