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Old   July 6, 2010, 03:33
Default Problem with simpleFoam
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Daniele
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Hi
When I run my case with simpleFoam with a refine mesh, after some iteration I have this error message why? (my k and epsilon aren't zero)

time step continuity errors : sum local = 2.25645e+45, global = -2.2833e+38, cumulative = -2.2833e+38
#0 Foam::errorrintStack(Foam::Ostream&) in "/user/parolini/OpenFOAM/OpenFOAM-1.7.x/lib/linux64GccDPOpt/libOpenFOAM.so"
#1 Foam::sigFpe::sigFpeHandler(int) in "/user/OpenFOAM/OpenFOAM-1.7.x/lib/linux64GccDPOpt/libOpenFOAM.so"
#2 __restore_rt at sigaction.c:0
#3 Foam::PBiCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const in "/user/OpenFOAM/OpenFOAM-1.7.x/lib/linux64GccDPOpt/libOpenFOAM.so"
#4 Foam::fvMatrix<double>::solve(Foam::dictionary const&) in "/user/OpenFOAM/OpenFOAM-1.7.x/lib/linux64GccDPOpt/libfiniteVolume.so"
#5 Foam::lduMatrix::solverPerformance Foam::solve<double>(Foam::tmp<Foam::fvMatrix<doubl e> > const&) in "/user/OpenFOAM/OpenFOAM-1.7.x/lib/linux64GccDPOpt/libinc$
#6 Foam::incompressible::RASModels::kEpsilon::correct () in "/user/OpenFOAM/OpenFOAM-1.7.x/lib/linux64GccDPOpt/libincompressibleRASModels.so"
#7 main in "/user/OpenFOAM/OpenFOAM-1.7.x/applications/bin/linux64GccDPOpt/simpleFoam"
#8 __libc_start_main in "/lib64/libc.so.6"
#9 Foam::regIOobject::writeObject(Foam::IOstream::str eamFormat, Foam::IOstream::versionNumber, Foam::IOstream::compressionType) const in "/user/OpenFOAM/OpenFOAM$
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Old   July 6, 2010, 04:56
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Moritz Wied
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hi daniele,

time step continuity errors : sum local = 2.25645e+45

this seems to produce a floating point exception caused by too large numbers.

maybe check the velocity field of the last time step before divergence?
could be that a bc is not set correctly.

best,
moritz
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Old   July 8, 2010, 08:06
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Daniele
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Hi
Time step error explode when I refine mesh, i don't understand...
this is my case, is a atmospeheric bundary layer with a obstacle on the bottom
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Old   July 8, 2010, 08:10
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have you tried to change the relaxation factors for p and U?
and maybe initialize with some magnitude!
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Old   July 8, 2010, 08:15
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Initialize p and U in 0 dir?. U is initialized but p is set equal zero, I try to change it . How can change relaxation factor?

Thank you
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Old   July 8, 2010, 08:27
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Moritz Wied
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no, initializing U is enough . the relaxation factors are set in system/fvSolution like that:

relaxationFactors
{
U 0.3;
p 0.7;
}

they sould be 1 in sum. for the beginning 0.3 for U may be better, you might change it to 0.7 and p to 0.3 after a while.
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Old   July 8, 2010, 08:31
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And factors for k epsilon? 0,8 is good? What value can i use to initialize U?

Thanks
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Old   July 8, 2010, 08:40
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you can try to switch off turbulence in constant/RASProperties and calculate some laminar iterations. then you can start from there with turbulence switched on. i don't know which factors for k and eps to use, depends on your case, but you can start with 0.8 and decrease them if its diverging.
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Old   July 8, 2010, 09:04
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With the factor that you give me time step continuity error is ok! Thanks! You are very kind. My result now are better. Can I ask you another thing? This is my wall shear stress on bottom The obstacle has a step with a ricircularion bubble; and in my plot I have a overshooting. How can i try to eliminate it?
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Old   July 8, 2010, 09:43
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sorry i have no experience with that yet... maybe someone else .
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