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Re: [ESPResSo-users] Any limit of the lattice Boltzmann grid number?

From: Florian Fahrenberger
Subject: Re: [ESPResSo-users] Any limit of the lattice Boltzmann grid number?
Date: Mon, 02 May 2011 07:17:14 +0200
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; de; rv: Gecko/20101207 Thunderbird/3.1.7

Hallo Chunda,

> My current box length is 690. And I want to have LB grid size at 0.004
> (0.004x100nm).

Wow! Just a quick calculation with a D3Q19 implementation of Lattice
Boltzmann for this system:
(690/0.004)^3 * 19 = 9.7526e+16
This means you would need 100000000 GBytes of RAM just to store your
fluid in single precision!!! I don't think this is a senseful number for
whatever system you want to calculate.

Even your second try with 690 cells per dimension will leave you with 10
GBytes of memory and is probably too much. Depending on what kind of
system you want to do your simulation on.

Usual system sizes for LB are around 32^3 or 64^3 cells, maybe slightly
bigger if necessary.

So, to answer your question: There is no hard implemented limit for the
number of cells in LB, but it obviously depends on how much RAM your
system has, and you seem to be running out there. Your first try might
even have been caused by the problem that the cells could not be
numbered because your computer ran out of integers. :o)

What kind of system do you want to simulate anyways, with such a huge
amount of LB cells?



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