# fmg!?!?!?

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 November 12, 2009, 16:43 fmg!?!?!? #1 New Member   Michelle Join Date: Nov 2009 Posts: 5 Rep Power: 9 My FMG completes level 4, but when it goes to level 3, it says: Normalized Residual = 1.#QNAN So what happened between level 4 and 3? at level 4, it says: FMG: FAS reached maximum iterations. Normalized residual = 729.568 FMG: Interpolate solution on next level...end then it begins the messed up level 3. The 1.#QNANs continue through levels 2 and 1. Finally, it ends with: Primitive Error at Node 7: Floating point exception ->1.->2.->3.->4.->5.<<<<< What does all this mean? And how do I fix it? Thanks! Michelle

November 12, 2009, 19:00
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Chris
Join Date: Jul 2009
Location: Ohio, USA
Posts: 169
Rep Power: 10
Quote:
 Originally Posted by psigcochair My FMG completes level 4, but when it goes to level 3, it says: Normalized Residual = 1.#QNAN So what happened between level 4 and 3? at level 4, it says: FMG: FAS reached maximum iterations. Normalized residual = 729.568 FMG: Interpolate solution on next level...end then it begins the messed up level 3. The 1.#QNANs continue through levels 2 and 1. Finally, it ends with: Primitive Error at Node 7: Floating point exception ->1.->2.->3.->4.->5.<<<<< What does all this mean? And how do I fix it? Thanks! Michelle
The residual are increasing, meaning that the simulation is diverging. Assuming that you have a good grid, you could try lowering the CFL number used in the fmg initialization. To do this, in the text user interface type "solve/initialize/set-fmg" and work through the text menu until you you get to the CFL number. The default is 0.75.

If that doesn't work, you could try increasing the number of multigrid levels, increasing the number of iterations performed on course multigrid levels, or lowering the residual threshold on the course multigrid levels.

You should also make sure that your boundary conditions, grid, and case setup are all ok first. Does your simulation bomb if you run it without fmg?

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