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[ff3d-users] mesh adaptation with ff3d

From: Stephane Del Pino
Subject: [ff3d-users] mesh adaptation with ff3d
Date: Fri, 16 Feb 2007 13:04:11 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.6) Gecko/20050319

Hello Emilio.

Emilio Melero García wrote:
The variables are local now. So far i have not tried to refine the mesh so it is not clear to me now how this should be done... How does it help the variables being local??

Well. Local variables are a more standard behavior regarding to other programming languages. It is a bit technical, but before, variables were created once for all: even if the variable was declared in a loop. This introduced a major problem for femfunction variables since they were always defined on the same mesh. This means that the variable always leaved on the mesh used for their creation. And this made refinement not possible.

Shortly just considere that previously changing a variable mesh was not possible, now it is...

And i would like to take the opportunity to raise a question...What is the best approach to improve the numerical accuracy of ff3d computations?. Is it always to use a finer mesh (larger computing cost)?
Well, in fact, to get a better solution you need to have a fine mesh where it is needed or to have a better approximation. If I remember your case, if it is possible for you to define new meshes that are finer near gradients with gmsh, it could be a good starting point. I am not a specialist of gmsh, but, if it can generate meshes based on a metric definition it should work with ff3d. The computational loop would look like :

generate a first mesh with your favorite mesher

do {
  load the mesh
  solve the problem on the mesh
  get some adaptation criterion (gradient,...)
  re-generate the mesh with your mesher using the adaptation criterion
} while(...);

I will have time next week to work on ff3d, I will try to do such a procedure ...

After proceeding to some research on the web, I am not sure that gmsh or netgen can do dynamic mesh adaptation, does anyone have information on that ? Maybe Benoit ?

Best regards,

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