Re: Fluid dynamics

*To*: mathgroup at smc.vnet.net*Subject*: [mg44530] Re: Fluid dynamics*From*: Paul Abbott <paul at physics.uwa.edu.au>*Date*: Thu, 13 Nov 2003 05:57:49 -0500 (EST)*Organization*: The University of Western Australia*References*: <boif5j$oau$1@smc.vnet.net> <bopc55$olh$1@smc.vnet.net> <botced$chd$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

In article <botced$chd$1 at smc.vnet.net>, Jens-Peer Kuska <kuska at informatik.uni-leipzig.de> wrote: > oh with > > "why not _start_ with a > cellular automata, modeling the > microscopic behavior of fluid molecules" > > you can also make a cow from the beef ? For an intelligent person, Jens, it seems you have missed the whole point of NKS. > The Naver-Stokes equation is an approximation, > a numerical model is an approximation to this > approximation and a CA is an approximation to this > approximation. No, No, No ... > And now tell me why the approximation, > of the approximation, of a approximation is a good > starting point to describe the *real* process without > an approximation. Because this is _not_ what NKS is proposing. > Where is the source of all the information that is > lost in during the various approximations if you start > not with the original ? But what is the original? It is not, as you describe it, the Navier-Stokes equation. > In a real collision the scattering take not place > on a hexagonal grid, and the scattering directions are > not bounded on a grid. Agreed. The CA model on a hexagonal grid is an approximation. > The *only* reason to use a CA is, that a CA has excelent > properties for massive parallel computing. This is _not_ the only reason to use CA. > And it is realy surprising that such a lausy model has still some > (qualitative) features of the real process. However, > in the most cases the quatitative computed features, like > pressure differ significant from the measured ones or from > the computed values obtained by a FE solution. > > Starting with a CA and use it for the real process is like to take > the a photograph of an image of a painted apple and eat it. It seems like you are still stuck in the world of continuum models ... Anyway, http://forum.wolframscience.com is probably a better place to discuss this topic. Cheers, Paul -- Paul Abbott Phone: +61 8 9380 2734 School of Physics, M013 Fax: +61 8 9380 1014 The University of Western Australia (CRICOS Provider No 00126G) 35 Stirling Highway Crawley WA 6009 mailto:paul at physics.uwa.edu.au AUSTRALIA http://physics.uwa.edu.au/~paul