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Old   September 19, 2013, 11:59
Arrow Engrid modify shape of stl
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James
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Hi Engrid users,

I am modifying the edge lenght and cell grow factor of a stl in Engrid. My goal is to obtain more density of triangles in order to obtain more tetrahedral elements in volume mesh. But in some kinds of geometries, I see that Engrid modifies the shape of stl file containing the geometry a big problem for me because stl file contains the info of all geometry, itīs more than the surface mesh for me and if it changes, the geometry and the later CFD computations change), making even the crash of volume meshing (yellow triangles indicate inside part I guess).

How can I avoid this?I thought that when I changed surface mesh I was only introduing more triangles but never changing the original shape...What about smoothing?Or more Delaunay steps?

I attach some pictures for ilustrate the problem better.

Thanks for all your help!
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File Type: jpg before.jpg (47.2 KB, 32 views)
File Type: jpg after.jpg (51.6 KB, 28 views)
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Old   September 21, 2013, 15:02
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Bruno Santos
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Greetings James,

From the (little) experience I have with enGrid, the idea is that you have to properly separate STL surfaces into independent boundary codes, so that enGrid is more easily able to ascertain which surfaces should be preserved.
In other words, whenever you have an edge that has to be preserved, you need to keep each adjacent triangle in their respective boundary code.

The other detail is regarding the refinement options you use for the surface mesh, as explained here: https://github.com/enGits/engrid/wik...e-surface-mesh

Best regards,
Bruno
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Old   September 26, 2013, 07:12
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Hi Bruno,

Thanks for the reply.

The images attached in the previous post were taken from he wall of my geometry, so first of all I set boundary codes correctly (and I assure that they are well assigned), but with surface meshing this is the result, the stl changes (and all of this triangles belong to the same boundary code).

Any other idea? Maybe using "fix CAD geometry" option or "store geometry for surface meshing", but I am not sure how this tools work...
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Old   October 1, 2013, 13:47
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James
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Oliver Gloth, please can you give some light over this issue? I guess you are the only one who can...

Can I refine my surface mesh from .stl file without modifying the shape of my geometry? If not, how can I refine volume mesh without changing surface mesh?

Thanks in advance.
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Old   October 5, 2013, 04:02
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Bruno Santos
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Hi James,

Can you provide a simple geometry example that we can use to create an example guide from it?

Best regards,
Bruno
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Old   October 5, 2013, 08:04
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Hi Bruno,

Sorry, I am not allowed to share geometries. My problem occurs when the geometry shows high sharp corners. The software remesh my stl file and breaks this corner in something like a shell, showing some triangles in green and some in yellow. I guess this make Engrid crash, because it is not able to understand wich triangles belongs to interior parts, and when I try the volume mesh it crashes ("Boundary meh is overlapping") and also my geometry has changed, which is not acceptable for the next CFD step.

Please help! S.O.S

Thanks Bruno for your interest. I am so sorry. Iīd like to share geometry but I canīt!
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Old   October 5, 2013, 08:12
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Hi James,

We do not need a geometry that reveals the nature of your project. We only need a simple geometry that reflects the kind of situations you are having.

As for sharing such a simple example geometry, ask for permission, after fully explaining what it's for.

I ask this because as you can see from this tutorial: https://github.com/enGits/engrid/wik...TL-geometry%29 - sharp edges are handled just fine by enGrid, as long as you properly identify each major surface with a boundary code.

Best regards,
Bruno
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