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-   -   Increasing Square Cavity mesh to 100x100 causes crash. Why? (http://www.cfd-online.com/Forums/openfoam-solving/138513-increasing-square-cavity-mesh-100x100-causes-crash-why.html)

Tom717 July 5, 2014 06:13

Increasing Square Cavity mesh to 100x100 causes crash. Why?
 
Hi, I am a beginner with OpenFOAM and CFD in general.

I am experimenting with the first tutorial, the square cavity. For my first modifications I edited the mesh size. Changing from 20x20 to 40x40 caused no problem. However if I edit blockmeshdict to give me a 100x100 mesh then icoFoam crashes.

I get this:

Code:

Courant Number mean: 5.32474e+87 max: 2.58355e+89
#0  Foam::error::printStack(Foam::Ostream&) at ??:?
#1  Foam::sigFpe::sigHandler(int) at ??:?
#2  in "/lib/x86_64-linux-gnu/libc.so.6"
#3  Foam::symGaussSeidelSmoother::smooth(Foam::word const&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::Field<double> const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, unsigned char, int) at ??:?
#4  Foam::symGaussSeidelSmoother::smooth(Foam::Field<double>&, Foam::Field<double> const&, unsigned char, int) const at ??:?
#5  Foam::smoothSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#6 
 at ??:?
#7 
 at ??:?
#8 
 at ??:?
#9 
 at ??:?
#10  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#11 
 at ??:?
Floating point exception (core dumped)

Can someone explain what is going wrong?


Tom

wyldckat July 6, 2014 05:23

Greetings Tom,

Notice this at the top of the output you've given?
Quote:

Originally Posted by Tom717 (Post 500185)
Code:

Courant Number mean: 5.32474e+87 max: 2.58355e+89

The Courant Number should not go over 1.0, otherwise it will likely lead to a divergence and eventually crash.

I strongly suggest that you read the User Guide more carefully and take notes, because in the User Guide, section "2.1.6.2 Changing time and time step" it explains how the mesh resolution relates to the Courant Number and how the "deltaT" value should be adapted to the new mesh resolution.

If you did take this into account, you should have indicated what calculations you made and the "deltaT" value you used ;)

Best regards,
Bruno


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