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## Re: [ESPResSo-users] LB Boundary

 From: Georg Rempfer Subject: Re: [ESPResSo-users] LB Boundary Date: Wed, 17 Jul 2013 09:22:15 +0200

```Hello Vincent,

another hint: the lbfluid grid's origin is located at (agrid/2,
agrid/2, agrid/2). So to create a cubic boundary that contains the
lbnode at (x+agrid/2, y+agrid/2, z+agrid/2) use pos = (x, y, z) and a
= (agrid, 0 , 0), b = (0, agrid, 0), and c = (0, 0, agrid), where x,
y, and z are integers ranging from 0 to box_l - 1 (in the respective
direction).

Greetings,
Georg

2013/7/17 Georg Rempfer <address@hidden>:
> Hello Vincent,
>
> the pos argument is used to define any of the corners and the
> arguments a, b, and c are meant to define three edges adjacent to the
> corner given by pos. You can imagine this as a tripod consisting of
> three vectors (a,b, and c) originating at pos. In other terms, pos
> gives the coordinates of one of the corners and a, b, and c give the
> difference vectors of three neighboring corners and pos.
>
> I remember we recently used lbboundaries in that fashion to do a
> similar thing. A minor problem that occurred was that with the
> creation of every individual boundary, the whole boundary grid got
> reinitialized, which made the initialization very slow when we used
> hundreds of boundaries. I am not sure that this is going to happen for
> you as well, as it might have been caused by code not present in the
> current master / release versions. If it does happen, please just
> notify us using this mailing list. This should be easy to fix.
>
> Greetings,
> Georg
>
> 2013/7/17 Vincent Ustach <address@hidden>:
>> Hello all,
>>
>> I have a complex geometry made of walls of particles with LJ and coulomb
>> potentials to simulate roughness and charge, respectively.
>>
>> These simulate a thin membrane with a pore. The pore shape is square
>> pyramidal.
>>
>> I also need hydrodynamic boundaries and I believe some of these can be
>> modeled using several "lbboundary rhomboid" constraints that will follow the
>> shape of the walls of particles. If not, I will look into augmenting the C
>> code to allow for flagging of individual boundaries.
>>
>> My question is regarding the shape args of the lbboundary rhomboid. If "pos
>> [3]" is the coordinates of one corner, are a and b and c the other three
>> corners?
>>
>> Thanks,
>>
>> --Vincent Ustach

```

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