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Old   March 4, 2014, 18:33
Unhappy Floating Point Exception Error
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Muhammad Hassan
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Hello. I have been doing combustion simulations on Star CCM+ and have to do combustion of C12H26 fuel with oxygen. The version of star CCM+ is 8.02 and operating system is Windows 8. I created an automatic surface mesh and tetrahedral volume mesh on the fluid volume of a burner and have also set up appropriate physics, soultion control, initial conditions and boundary condition options. Now, whenever I try to run simulations I get the following error message:

'A floating point exception has occurred: floating point exception [Invalid operation]. The specific cause cannot be identified. Please refer to the troubleshooting section of the User's Guide.'

What kind of error is this and how to solve this issue? Has anybody ever encountered this kind of error before? Thank you.
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Old   March 5, 2014, 05:54
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Oliver Lauer
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This is a quite general error that could happen nearly everywhere.
Very often this is a 'division by zero'.

Do you have any report annotations? For us this error appeared as these reports were run before first iteration and therefore before having any results. One of these reports had an uninitialized division.
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Old   March 5, 2014, 09:02
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Muhammad Hassan
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Thanks for your reply. No, I don't think I had any repot annotations. My question is that what might have gone wrong with my settings? How to solve this problem, I have tried different number of boundary conditions and solver settings settings but am still facing the same problem. Should I do meshing again from scratch? I have followed all the steps of problem set up prescribed in the user manual, but don't know whats going wrong. Where I might be making a mistake in your opinion?
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Old   March 5, 2014, 09:15
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Oliver Lauer
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Did you check your cell quality (Remove Invalid Cells), do you have unconnected regions?
Does your model run with more simple physics?

It is something I demanded for a long time: error messages in CCM+ are most often not very helpful
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Old   March 8, 2014, 00:34
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Does it blow up without doing any iterations? Most likely one of your reports or field functions divides by zero.

If that's not the case, there is a BC or initial condition issue.

Why are you using a tet grid? A poly grid will give you a better answer with fewer cells, and will generally be higher quality.
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Old   March 9, 2014, 19:08
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Muhammad Hassan
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Hello. I just checked on another forum and I found out these two main reasons of floating point error in star ccm+:

- Running correctly set up simulation that contains difficult physics with poor initial conditions.

- fundamental problem with the set-up of the simulation. Common problems that cause a simulation to diverge are: incorrect boundary conditions; poor quality mesh; incorrect set-up of physics models.

I think my problem belongs to the first category, I changed some initial conditions and also lowered the under rerlaxation factor from 0.9 to 0.5 and this seems to have solved the problem and I am getting the results now.

@ me3840: I am trying to do a comparison of Ansys Fluent simulations with Star CCM+ simulations, the test case which I have is using tetrahedral meshing instead of polyhedral meshing technique, so I have to use tet grid as well, in future simulations I will use poly grid. A questions for you: Is polyhedral grid always the best grid to use for most of the CFD simulations if you want good results?

@ olauer: My model was also not working with simple physics as well, but now I think since I have lowered under relaxation factor now so simulation is giving results.

Thanks for your help, I appreciate it.
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Old   March 10, 2014, 10:38
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The poly grid is not necessarily better. Your grip topology should be chosen based on the flow physics. Polyhedrons are good for highly swirling or rotating flows, or flows that are chaotic. Other flows may demand different topologies. However, I don't think there's an instance where one would want to use a tet grid over a poly grid.
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Old   November 17, 2015, 00:27
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Ahmad Jabbar
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@ Muhammad Hassan!
I am also facing the same problem with comb simulations, while using radial nozzle in nozzle arrangment for fuel and combustion air in non premixed Combustion. (But when I use up down nozzle arrangment the issue is resolved, well i need to use nozzle in nozzle arrangment)
Would u please share, which relaxation factors have u reduced to 0.5.
Cheers !
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