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nCellsInCoarsestLevel

Hey All!

While running a calculation on 48processors on 8 machines i get the following error when exectuting potentialFoam:

Code:

Calculating potential flow

[0] 

[0] 

[0] --> FOAM FATAL ERROR: 

[0] No coarse levels created, either matrix too small for GAMG or nCellsInCoarsestLevel too large.

    Either choose another solver of reduce nCellsInCoarsestLevel.

[0] 

[0]     From function GAMGSolver::GAMGSolver(const word& fieldName,const lduMatrix& matrix,const FieldField<Field, scalar>& interfaceBouCoeffs,const FieldField<Field, scalar>& interfaceIntCoeffs,const lduInterfaceFieldPtrsList& interfaces,const dictionary& solverControls)

[0]     in file matrices/lduMatrix/solvers/GAMG/GAMGSolver.C at line 116.

[0] 

FOAM parallel run exiting

[0]

what is nCellsInCoarsestLevel?

i set it to 1 instead of 10 and now at least potentialFoam works. ...but simpleFoam does not konvergate. It even aborts after 3 timesteps. The case runs perfectly when calculated with only 4 processors.

but what did i change with that?

greets
Christian

Read about multigrid methods. During the solution the grid is coarsened, and this parameter tells the algorithm when to stop. 10 is already a very low value, so I have the feeling you are wasting resources running this problem on 48 CPUs. Does your domain have less than 100 000 cells?

Oh Ok!

Thanks!! that was the problem!

Quote:

Originally Posted by ChrisPro (Post 340407)

Oh Ok!

Thanks!! that was the problem!

Sorry to bring up an old thread, but what did you do to resolve this? I am getting the same error. My case has some processor directories which contain no mesh due to the complexity of its shape. Is this an issue?

Edit: I realized that having empty processor directories was the issue, and remedied this by changing my how my mesh was decomposed (in decomposeParDict).

So have you solved your problem? :)

Either take less processors or use a finer mesh

greets
Christian