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-   -   [ICEM] Mesh stretching with tetrahedras (http://www.cfd-online.com/Forums/ansys-meshing/95175-mesh-stretching-tetrahedras.html)

MrAnderson December 8, 2011 07:52

Mesh stretching with tetrahedras
 
Dear All,

Is there anyone who knows how to perform stretching of tetrahedral mesh. I have a simple case where the fluid is supposed to flow past a rectangular beam in a rectangular channel. Basically, I want have a dense mesh just behind the beam and then gradually coarsen towards the outlet of the channel. I did try the function under Edit Mesh -> Adjust Mesh Density, however this function did not yield a gradual change of the mesh.

I am looking forward to any kind of help.

Regards!

PSYMN December 9, 2011 10:03

Delaunay generates a smoother mesh...
 
If you just want a more gradual change from a refined area to a coarse area, you should probably use a density region to refine the fine area and replace your octree mesh with delaunay. By definition, Octree mesh needs to change sizes in powers of 2. But if you start with an Ocree mesh and then smooth the surface mesh, and then go back to generate mesh and switch to "Delaunay" "From existing surface mesh" you can generate the smoother transitioning mesh you are looking for. Don't forget to add the density box to control the max size int he volume of interest.

If you are looking for stretched (anisotripic) tet, ICEM CFD generates only isotropic meshes. One way around this is the squish and stretch... You scale the geometry in one or two dimensions to squish it... Then you mesh it. Then you scale the geometry and mesh back to the original dimensions to stretch it back out again... But this gives a uniform stretch to the entire mesh...

MrAnderson December 28, 2011 06:49

Delaunay for a smoother mesh
 
Dear Sir,

Many thanks for your guide!

If I follow the first part of your description, does it mean that I only need to add the density region at the back surface of the beam.
Actually I did this, however, by doing this I only can get refinement at the proximity of the beam. That is, I would like to have a much more slowly coarsening mesh all the way to the outlet, since in my case the mesh gets coarsen already after a short distance behind the beam and then is completely uniform.

Do I have to perhaps add a density region at the walls of the fluid-domain as well??

MrAnderson December 29, 2011 03:52

Hi again,
 
1 Attachment(s)
Here I attach a cut of the computational domain consisting of the beam at a distance of 4D from the inlet. As you can see, I can manage the high density region at the proximity of the beam. Also, the transition from the high-density region to low-density region is quite smooth. This has been done by utilizing the 'Create Mesh Density' button under the 'Mesh' tab in the main menu. The back surface of the beam was chosen as the density location.

Nevertheless, what I actually would like to be able to do is to perform a more gradual coarsening of the mesh from the back of the beam to the outlet of the channel. As it is now, I have a constant high-density region from the back of the beam to a certain distance in the channel, then a smooth transition from the high- to low-density region, and then again a constant low-density region. My actual purpose is basically to perform a continuous coarsening of the mesh from the beam towards the outlet and the side-walls of the channel.

If anyone knows how to perform this for unstructured tetrahedral mesh, please let me know.
A detailed guide would be appreciated since I am a beginner with ICEM.


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