[overture] Re: on multigridding

  • From: Bill Henshaw <henshaw@xxxxxxxx>
  • To: "overture@xxxxxxxxxxxxx" <overture@xxxxxxxxxxxxx>
  • Date: Sun, 13 Jun 2010 15:53:33 -0700

Hi Joel,

I am not sure why the multigrid solver would work with twoDrops but not with your version. It might have something to do with the boundary conditions. Multigrid does not handle a singular pressure equation (so you need to set the level of the
pressure somehow such as with an outflow BC).

I have been working on the multigrid solver lately and the next version should
be better.

To change the multigrid coarse grid solver look for "Oges parameters" under the "multigrid parameters" option -- Ogmg uses Oges to solve the coarse grid equations.

Regards,
 Bill.

Hi I have some questions regarding the multigrid solver,

I have been using the multigrid solver for a while  and so far it works fine 
(for moving and fixed bodies).  Now I am trying to use it with the rigid body 
motion solver, but I am getting totally different results to those that I get 
when using  petsc.   I am getting these results with a modified version of the 
rigid body motion solver, which I already validated with other results and I 
obtained a quite good agreement using petsc, but when using the multigrid 
solver the solution is totally different.  Any clue of what could be the 
problem?.   I also ran the twodrops case using petsc and multigrid and I got 
the same solution for both solvers, so I guess the error could be something 
related to the modified version.

The second question is how do I change the solver for the coarser grids?.  I am 
always getting the same solver, I already tried to changed it by setting the 
desired solver in oges parameters but I always get the YALE solver, which does 
not perform well for the grid I am using (something about 5 millions points in 
the finest mg level)


Regards,

Joel






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