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Problem with tetrahedral-mesh (salome)

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Old   March 13, 2012, 14:02
Default Problem with tetrahedral-mesh (salome)
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Hello everybody,

I'm new to OpenFOAM and I want to use CAD-Data meshed with Salome in OpenFOAM. For learning how to use OpenFOAM with structural mechanics I used a simple model. It is a simple beam, which is fixed at the bottom and displaced (0.04m in y-direction) at the upper part.

I tried the import (ideasUnvToFoam) of a hexahedral and a tetrahedral mesh with the complete same case. The hex-mesh worked fine and with the tet-mesh I get really strange results which I can't explain (see pics). checkMesh does not complain after the import of the tet-mesh.
Unfortunaley the mesh-size is to big, so i could not upload it.

I would be very thankful if someone could help me!

Best regards
Matthias
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File Type: jpg balkenHex_fineMesh50k.jpg (44.9 KB, 49 views)
File Type: jpg balkenTet_fineMesh41k.jpg (50.1 KB, 41 views)
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Old   March 14, 2012, 07:38
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Hello all,

is there anybody out there, who had a comparable problem or has anybody an idea where I can start searching.
I already checked my mesh with checkMesh and the solver converged as well.


Another question I have is:
one of my boundary conditions is a displacement of 0.04m:
oben
{
type fixedValue
value uniform (0 0.04 0)
}

Now I want that the motion in x- and z-direction is not "0" but changes, so that the boundary "oben" isn't anymore parallel to its initial position. Is there an easy way to do this?.

With best regards
Matthias
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Old   March 15, 2012, 19:20
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Hi,
I've had a similar issue in fluid dynamics in laminar pipe flow of non-Newtonian fluids. With hex meshes developed using blockMesh I get converged solutions which agree very well for the pressure drop with the analytical values. With tet meshes with viscous layers developed in Salome, the pressure drop is about 5% too high even though the solutions are well converged. I'm working through some possible issues with mesh quality and choice of discretisation schemes etc. Perhaps these will help. I want to move to more complex gemetries so I need to validate the meshing.
Not sure if I have helped, but perhaps there is an issue.
Regards,
Lachlan
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Old   March 19, 2012, 06:23
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Hello Lachlan,

thank you for your reply! Until now I haven't found a solution for my problem. But I'm still working on it. As alternativity I'm testing snappyHexMesh, because I want to move to more complex geometries, too.

Best regards
Matthias
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Old   March 20, 2012, 11:59
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Eric Patterson gives some good recommendations for discretization choices for unstructured grids in this Thread (post #5).

http://www.cfd-online.com/Forums/ope...red-grids.html

It might improve your solution.
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Old   March 20, 2012, 16:52
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Hi kmooney,

thank you for the link. It sounds interesting and I will try it!

Best regards
Matthias
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