CFD Online Logo CFD Online URL
Home > Forums > General Forums > Main CFD Forum

Multigrid on non-uniform grids

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Display Modes
Old   July 7, 2000, 12:58
Default Multigrid on non-uniform grids
Posts: n/a

Are there any multigrid methods for a Poisson equation which have a good convergence rate on highly stretched grids (about two orders of magnitude between the largest and smallest cells)?. The stretch is in both dimensions. Whilst algebraic multigrid seems very effective for a u niform grid, it rapidly becomes very slow, until it constantly diverges after the stretch is about a single order of magnitude.

Thanks. This could save me many headaches. Jude
  Reply With Quote

Old   July 7, 2000, 13:32
Default Re: Multigrid on non-uniform grids
Posts: n/a
I have had similar problems. Although I have not tried them, I have a feeling that the multigrid techniques with semi-coarsening might help.

Good luck
  Reply With Quote

Old   July 8, 2000, 10:34
Default Re: Multigrid on non-uniform grids
John C. Chien
Posts: n/a
(1). I am not using Multi-grid, so I can't comment on it. (2). But based on your message, the process diverges when the mesh stretching is high. (3). So, in this area, I would suggest that you keep the cell-to-cell size stretching ratio to 1.2 or smaller. (4). The high stretching (cell-to-cell) of mesh will generate higher errors in your numerical scheme. In addition to this truncation error, you also have a source term. The form and the distribution of this source term also will have great impact on the solution stability. (5). So, Just use more grid points, and let the computer do the hard work.
  Reply With Quote

Old   July 10, 2000, 05:29
Default Re: Multigrid on non-uniform grids
franck bertagnolio
Posts: n/a
Hi. I deal with highly stretched grids as well. I have found that there are several factors that can greatly influence the convergence rate, and/or cause divergence. These are: 1) the choice of the restriction and prolongation operators 2) the type of smoother used at each grid level (I use ADI-type solver on the finest grid and Gauss-Seidel and the coarser ones) 3) I found that sometimes it is not so good to have too many grid levels (that could cause divergence). Finally, I have been told (but never tried myself) that the Bi-CGStab method with multigrid as a preconditionner is very efficient.

Hope this helps. Franck
  Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
chtMultiRegionSimpleFoam javad814 OpenFOAM 1 September 26, 2011 13:30
Need help with boundary conditions: open to atmosphere Wolle OpenFOAM 2 April 11, 2011 07:32
turbulent jet simulation antonio_ing OpenFOAM Running, Solving & CFD 5 September 16, 2010 02:31
rhoSimpleFoam claco OpenFOAM 7 April 20, 2010 04:32
RasInterFoam STRANGE RESULTS AT BOUNDARY kumar2 OpenFOAM Running, Solving & CFD 8 March 24, 2008 19:38

All times are GMT -4. The time now is 03:10.