Re: [ESPResSo-devel] Lattice Boltzmann - Grid Spacing

[Ulf Schiller]

Zitat von Kai Grass <address@hidden>:
> To whom it may concern,
>
> I ran several tests on the current Lattice Boltzmann implementations
> (D3Q18 and D3Q19). From my results, I conclude that there is a bug in
> the implementation with regards to the lattice spacing (a). According
> to the theory, the single particle diffusion (D) should decrease with
> increasing lattice spacing (see paper by Ahlrichs et al 1999).  Exactly
> the opposite is observed, but I didn't yet delve into the  code, to
> find out where the error arises from. For a grid spacing of  1, the
> results agree with the prediction, therefore it is safe to  assume,
> that for this specific grid spacing the code works fine.

For grid spacing 1.0, also the properties of a single polymer chain  
were verified extensively and compared with Brownian dynamics  
simulations. For other grid spacings, it may well be that there was a  
factor missing somewhere (most likely in the fluctuating part). I  
don't have the time to search for it and the fluctuating part has been  
replaced by a corrected implementation anyway (obeying FDT at the  
microscopic level, see recent PRE).

Regards,
Ulf

--
Ulf D. Schiller   *   Room 1.404   *   Phone +49 6131 379-481
Max Planck Institute for Polymer Research
Theory Group
D-55128 Mainz, Germany


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