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Re: [ff3d-users] a question about improving accuracy in ff3d

From: Wei Huang
Subject: Re: [ff3d-users] a question about improving accuracy in ff3d
Date: Sat, 20 Jan 2007 00:38:21 -0500

Now I see. The numbers specified are the number of *vertices*, not number of sections in each direction. Thanks!


--On Saturday, January 20, 2007 1:58 AM +0100 Stephane Del Pino <address@hidden> wrote:

Hello Wei.

Le vendredi 19 janvier 2007 17:09, Wei Huang a écrit :
Thank you Stephane! This does work!
I am curious on how to choose the right mesh size (for
example, why use (9,9,5),(17,17,5),(33,33,5), not
others?) I tried a few others such as (34,34,5), and saw
relatively big deviation from the exact result.
In fact, according to your geometry, the "center" part is
and your total domain is
So, if you use a 4*4 uniform mesh, the 4 middle cells
will describe *exactly*  the "center" zone, the other 12
cells will describe the remaining part of the  domain :
there is *no* jump of the conductivity *inside* any cell
of this  mesh.

If you want a good approximation, you need to respect
this rule. If you do  not, it will converge well, but not
very well near the conductivity jump.  This is mainly due
to the quadrature formulae which assume that the solution
integrated function is smooth in each cell...

Since in ff3d, mesh refinement of structured meshes are
defined using  vertices, the smallest mesh describing
*exactly* your geometry is defined by         n=(5,5,2)
To get finer mesh in x and z directions you can use the
meshes:         n=(4*n1+1,4*n2+1,n3+1)
where n1,n2 and n3 are integers bigger than 1.

Is that more clear?

Best regards,

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