# Help !

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 March 9, 2011, 16:35 Help ! #1 Member   William Tougeron Join Date: Jan 2011 Location: Czech Republic Posts: 51 Rep Power: 8 Sponsored Links Hello, First, I would like to thank everybody who will spend time reading this post. So, that's it : for the second time I tried to make a calculation with a coarse mesh and nothing wrong happened. Then I tried with a finer mesh and I had this kind of error at the first iteration: Code: ```Starting time loop Time = 0.450001 Courant Number mean: 0.000114088 max: 0.141285 DILUPBiCG: Solving for Ux, Initial residual = 4.08431e-07, Final residual = 4.08431e-07, No Iterations 0 DILUPBiCG: Solving for Uy, Initial residual = 5.36397e-07, Final residual = 5.36397e-07, No Iterations 0 DILUPBiCG: Solving for Uz, Initial residual = 1.92053e-06, Final residual = 1.92053e-06, No Iterations 0 DICPCG: Solving for p, Initial residual = 0.994395, Final residual = 0.0949762, No Iterations 10 time step continuity errors : sum local = 7.27923e-09, global = -2.19507e-11, cumulative = -2.19507e-11 DICPCG: Solving for p, Initial residual = 0.0759985, Final residual = 9.46632e-07, No Iterations 142 time step continuity errors : sum local = 1.55001e-13, global = 5.68589e-15, cumulative = -2.1945e-11 #0 Foam::error::printStack(Foam::Ostream&) in "/opt/openfoam171/lib/linuxGccDPOpt/libOpenFOAM.so" #1 Foam::sigFpe::sigFpeHandler(int) in "/opt/openfoam171/lib/linuxGccDPOpt/libOpenFOAM.so" #2 Uninterpreted: #3 Foam::divide(Foam::Field&, Foam::UList const&, Foam::UList const&) in "/opt/openfoam171/lib/linuxGccDPOpt/libOpenFOAM.so" #4 void Foam::divide(Foam::GeometricField&, Foam::GeometricField const&, Foam::GeometricField const&) in "/opt/openfoam171/lib/linuxGccDPOpt/libincompressibleRASModels.so" #5 Foam::tmp > Foam::operator/(Foam::tmp > const&, Foam::GeometricField const&) in "/opt/openfoam171/lib/linuxGccDPOpt/libincompressibleRASModels.so" #6 Foam::incompressible::RASModels::kEpsilon::correct() in "/opt/openfoam171/lib/linuxGccDPOpt/libincompressibleRASModels.so" #7 in "/opt/openfoam171/applications/bin/linuxGccDPOpt/pisoFoam" #8 __libc_start_main in "/lib/libc.so.6" #9 in "/opt/openfoam171/applications/bin/linuxGccDPOpt/pisoFoam"``` I really don't know what to do. This is my case: (You can click to enlarge the pictures) I wanted to use pisoFoam with a k-epsilon turbulence model. This is my first mesh (around 50 000 cells): ...and the result of the first calculation: I found this result good, so I did a finer mesh (around 500 000 cells): ... and I made a "mapField" onto it from the coarse mesh: But the story ends here... My fvSchemes : Code: ```// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // ddtSchemes { default Euler; } gradSchemes { default Gauss linear; grad(p) Gauss linear; grad(U) Gauss linear; } divSchemes { default none; div(phi,U) Gauss limitedLinearV 1; div(phi,k) Gauss limitedLinear 1; div(phi,epsilon) Gauss limitedLinear 1; div(phi,R) Gauss limitedLinear 1; div(R) Gauss linear; div(phi,nuTilda) Gauss limitedLinear 1; div((nuEff*dev(grad(U).T()))) Gauss linear; } laplacianSchemes { default none; laplacian(nuEff,U) Gauss linear corrected; laplacian((1|A(U)),p) Gauss linear corrected; laplacian(DkEff,k) Gauss linear corrected; laplacian(DepsilonEff,epsilon) Gauss linear corrected; laplacian(DREff,R) Gauss linear corrected; laplacian(DnuTildaEff,nuTilda) Gauss linear corrected; } interpolationSchemes { default linear; interpolate(U) linear; } snGradSchemes { default corrected; } fluxRequired { default no; p ; } // ************************************************************************* //``` ... and my fvSolution: Code: ```// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { p { solver PCG; preconditioner DIC; tolerance 1e-06; relTol 0.1; } pFinal { solver PCG; preconditioner DIC; tolerance 1e-06; relTol 0; } U { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } k { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } epsilon { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } R { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } nuTilda { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } } PISO { nCorrectors 2; nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; } // ************************************************************************* //``` I would be very grateful to the one who can teach me what I did wrong ! Very sincerely,

 April 22, 2011, 07:27 #2 New Member   Daniel Cebrián Join Date: Nov 2010 Posts: 8 Rep Power: 8 Hello William. I think you used a fine mesh near the surface the body, this is good, but there is a problem with the change of cell´s size. I think the solution maybe not to make big change of size between cells. I don´t know why you are using triangular cells. Square cells are better. I´m doing a case similar to yours. I simulate a flat plate with pisoFoam, if you want we could talk about it. I calculate the forces in the bluff body and the aerodynamic coef. My name is Daniel and my email is: danielcebrianr@gmail.com

 April 22, 2011, 07:50 #3 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,749 Rep Power: 29 Hello William The error message tells you that you are dividing by 0 within the k-epsilon equations. Are you sure that you have not changed the boundary conditions/internal values for either k or epsilon from the coarse to the fine mesh? Neither property most be 0, but should take a finite value. Good luck Niels

 April 24, 2011, 16:19 #5 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,749 Rep Power: 29 Hi William Sure, here is a small explanation. I have always interpreted the numbering as a kind of unwinding of the error, essentially like an onion, where the inner part, the actual problem is given "#0", and then you can trace back from there. So: #2: (SIGFPE) You can always try wiki, however, this error tells you that you have performed an illegal arithmetic operation. #3: This tells you that the SIGFPE reported in #2 originates from a divide operator, meaning that the denominator is numerically taken as zero. #6: Those in #4 and #5 tells something about the fields, which cause the error, and this part of the error tells you that it occurs in kEpsilon.correct(). Therefore find the place in this method in the object kEpsilon, where you divide by zero. The reason for my suggestion to the origin of the error is: 1. It is the very first encounter with a solution to either k or epsilon after the start of the simulation, because the top of what you have reported states "starting time loop". 2. I have seen questions about this error so many times on this forum during the last 3-4 years. (I know it does not help you, though ) I hope my suggestions have solved your problem. Happy Easter - Niels

 December 27, 2011, 21:38 #6 Member   张德胜 Join Date: Oct 2011 Posts: 71 Rep Power: 7 Hi,friend,i got the same error when i calculated my case.Did you solve your question? Can you give me some advice? Thanks a lot .My e-mail is :zhangdesheng0068@126.com.Please contact me,ok?

 December 28, 2011, 02:59 #7 Member   William Tougeron Join Date: Jan 2011 Location: Czech Republic Posts: 51 Rep Power: 8 Dear hei@ge, Unfortunatelly, I didn't solved this problem and won't use OpenFoam before a while I think (no time). If you are like me using a coarser and a finer mesh, you can maybe take a look to the danielcebrian or ngj advices below (cells too much different between coarse and fine meshes or a change in the k-epsilon boundary or initial conditions) ? In each case, have a happy new year ! Best regards,

 December 28, 2011, 03:50 #8 Member   张德胜 Join Date: Oct 2011 Posts: 71 Rep Power: 7 Thanks for your reply.I think i should discuss it with my boss.Happy new year.

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