[prabhumechebet]

Hi,
I am new to openFoam, I am trying to solve tutorial problems icofoam Cavity model its solved completely.(Blockmesh to define polymesh)
But, when i made the geomentry in ansys and import mesh file into openFoam its not solving and showing error. (Ansys mesh file to define polymesh).

Same model same template, same tutorial but error is coming like this:
Time = 0.005

Courant Number mean: 11047.338 max: 25960.852
#0 Foam::error:rintStack(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<d ouble>&, 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 ? in "/opt/openfoam8/platforms/linux64GccDPInt32Opt/bin/icoFoam"
#7 ? in "/opt/openfoam8/platforms/linux64GccDPInt32Opt/bin/icoFoam"
#8 ? in "/opt/openfoam8/platforms/linux64GccDPInt32Opt/bin/icoFoam"
#9 ? in "/opt/openfoam8/platforms/linux64GccDPInt32Opt/bin/icoFoam"
#10 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#11 ? in "/opt/openfoam8/platforms/linux64GccDPInt32Opt/bin/icoFoam"

Can anyone help me to solve this problem.???
Thanks in Advance.
Prabhu M

[Tobi]

Hey,

Well this is a bit tricky to debug as there is too less information. Did you check your converted mesh? Commonly, the dimensions are wrong if you convert a Fluent Mesh to a foam format.

The error however gives an indication regarding too high Courant number. Maybe you are using wrong numerical schemes as block Mesh products pure hexahedron meshes.

There is no information which volume cell types you have.

[prabhumechebet]

Hi,
I attached the working file here.
1. 04_cavity_simple : Its an tutorial model, we can run blockmesh and solve using icofoam solver.
2. m_model_mesh : I attached the mesh file in this. we want to do mesh extract and do the icofoam solver.

Once you run this problem you can find the issues what i am facing.

Please guide me to solve this problem,
Thanks in Advance,
Prabhu M.

[Tobi]

Okay, ... solution and remarks

• Cases are not identical
• Cases are set-up wrong (both) -> empty patches are for 2D or 1D analysis - should not be applied here, not sure why the FOAM mesh still runs and that checkMesh does not give any error here.
• Schemes for time-derivatives are different
• However the main difference is the scale of the mesh. The FOAM mesh has dimensions of 1 meter and the other one of 0.5 mm, hence the velocity boundary is same (1 m/s) the courant number is completely different. The solver explodes as you get Co >> 1 which is fatal for icoFoam and pisoFoam

To resolve your problem:

• Change your empty patches
• Change the time steop for the smaller scale to e.g., 1e-8;

Happy foaming,

[prabhumechebet]

1.Change your empty patches
If i change the empty patches name means the tutorial is not solving.
2.Change the time step for the smaller scale to e.g., 1e-8
This step i tried and its solved the problem. This solved the error which i got in my older running.

Now another problem arises:
04_cavity_simple : For this model i got pressure value as 0.72
m_model_mesh : For this model I got pressure value as 2300.

By comparing this two i got a huge differences in results, I dont know where i did wrong. I am new to this openFoam so i cant able to figure out the problem.
-------------------------------------------------------------------------------
Once more query
you mentioned (The FOAM mesh has dimensions of 1 meter and the other one of 0.5 mm) I cant find out this one. Can you specify where to find this one.
-------------------------------------------------------------------------------
Final Query
How to specify the start and end time and deltaT. If we give deltaT as e-8 the time to get the results also taking too long time. Can we reduce the end time? If yes means how much.
-------------------------------------------------------------------------------
Thank you so much for your time Tobi
Waiting for your reply.

[Tobi]

Originally Posted by prabhumechebet

1.Change your empty patches
If i change the empty patches name means the tutorial is not solving.

• You have to change the empty patches in the boundary files (0/*) and in the constant/polyMesh/boundaries file
• As you have a mesh that contains more cells in each Cartesian coordinate direction, the wedge condition is wrong.

2.Change the time step for the smaller scale to e.g., 1e-8
This step i tried and its solved the problem. This solved the error which i got in my older running.

• That's clear, as - otherwise - you don't take care about restrictions e.g., the Courant number. By the way, icoFoam is a very limited solver.

Now another problem arises:
04_cavity_simple : For this model i got pressure value as 0.72
m_model_mesh : For this model I got pressure value as 2300.

By comparing this two i got a huge differences in results, I dont know where i did wrong. I am new to this openFoam so i cant able to figure out the problem.

• Already answered. Your cases are dimensionally not equal. One box has 1 m x 1 m x 1 m and the other does have 0.001 m x 0.001 m x 0.001 m. So please read what I wrote. As the dimensions are different, it is obvious that the results are different.

-------------------------------------------------------------------------------
Once more query
you mentioned (The FOAM mesh has dimensions of 1 meter and the other one of 0.5 mm) I cant find out this one. Can you specify where to find this one.
-------------------------------------------------------------------------------

• Use the application checkMesh
• I suggest to read the OpenFOAM user-guide

Final Query
How to specify the start and end time and deltaT. If we give deltaT as e-8 the time to get the results also taking too long time. Can we reduce the end time? If yes means how much.

That is a trivial question. Depending on the length scale of your domain, you should change the end-time respectively. That means, in the second case (dt = 1e-8) it should be converged almost after 1e-6 s. However, icoFoam does not let you control the time step based on the Courant number. Peronally, I would use pisoFoam or pimpleFoam. Here, one can control the time step based on the Courant number and you can add residual control (solver stops after the user input is reached).

• It seems that your are new to CFD, hence, I highly recommend to read some books regarding this topic - it will help a lot and it will save time
• I know, testing is nice but in most cases it lead to frustration

[prabhumechebet]

Hi,
I corrected all those possible things which i noted and i run both the tutorial model and mesh model (3D-Mesh created from Ansys and imported here).

Both model runs completely. But, both shown result values as different. I check all possible things but can't sort out the problem. I attached the file here just check it once and give some solution for me.

Thanks in Advance,
Prabhu M.

[Tobi]

You are not reading what I am writing, right?

• First of all. You use »empty« patches that are used for 2D or 1D calculations
  Your mesh is 3D as you have more than 1 element in each direction (x,y,z)

• The mesh density is different so expect to have different results

But the main difference is:

• The tutorial case mesh is of size 1 m x 1 m x 1 m
• Your fluent mesh is a box of 0.001 m x 0.001 m x 0.001 m

Furthermore, you just attached the cases to your post. No run script nothing. Should we all know which commands you are executing to run your case? You should have all information why things went wrong.

1. Wrong boundary conditions as you are not calculating a 2D case
2. Wrong scales, one case is 1m large, the other has a scale factor of 1000
3. Different cell densities

[prabhumechebet]

Hi Tobi,
Thank you so much for your support, I found the mesh size is different and I correct those dimensions now its fine. Answer is not correct may be due to 2D and 3D meshes. But some how we got some close results.

Did you know how to give porous conditions in 3D models. For example If i am generating model in 3D and meshing using Ansys means how i give the porous zone?