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Old   March 11, 2013, 22:04
Default Surface orientations
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Thomas Kudla
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Hello,

I am new to EnGrid v 1.4 - I like it since it is somewhat familiar to what I have been using commercially.

I have tried to export an *.stl from salome with the surface mesh, import into EnGrid. Everything imports, passes mesh checks.

I have a box farfield, and a sphere solid wall. When I try to set the mesh orientation, the 'outside' of the farfield domain and the 'outside' of the solid sphere wall are always different colors. I tried to change just one surface, but to no avail, it always changes both to opposite. I cannot grow my volume mesh until I can figure this out. When I goto edit BC, I cannot choose green or yellow like in the tutorial. All I have is A >> or << B as an option... does anyone have any ideas? Should I try v 1.2 or 1.3 instead?

Thank you for the help,

Tom
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Old   March 14, 2013, 08:17
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Thomas Kudla
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Ok, so it is necessary to re-orient the faces in your surface mesh program (in my case SALOME) before importing into EnGrid, at least this is my experience. After that it works o.k., except there is a prism mesh cell limit which is easily changed in the source.
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Old   March 15, 2013, 11:05
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Oliver Gloth
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Hi,

A >> or << B is the equivalent of green or yellow; it got changed in order to make it configurable for people with a red green deficiency.

Where did you find a prism limit in the the source code?

Cheers,
Oliver
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Old   March 15, 2013, 20:42
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Thomas Kudla
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Thank you,

In: /engrid/src/libengrid/octree.cpp

Original:
Code:
while (N2 > 0);
  N2 = m_Cells.size();
  if (N2 + 8*N1 > m_MaxCells) {
    QString num;
    QString msg = "maximal number of cells exceeded\n";
    num.setNum(N2 + 8*N1);
    msg += num += " requested and ";
    num.setNum(m_MaxCells);
    msg += num + " allowed";
    EG_ERR_RETURN(msg);


To:


Code:
while (N2 > 0);
  N2 = m_Cells.size();
  if (N2 + 8*N1 > 10000*m_MaxCells) {
    QString num;
    QString msg = "maximal number of cells exceeded\n";
    num.setNum(N2 + 8*N1);
    msg += num += " requested and ";
    num.setNum(m_MaxCells);
    msg += num + " allowed";
    EG_ERR_RETURN(msg);

I did not look for m_MaxCells, just wanted it to run so I brute forced it.

Best,

Tom
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Old   March 17, 2013, 12:05
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Oliver Gloth
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Hi Tom,

that limit is not related to the number of prisms but to the size of the geometric search tree. This tree is used to find triangles of the underlying geometry if surface nodes need to be projected onto the surface. This is mainly used for the surface meshing algorithm but also sometimes during the boundary layer meshing. I think I will simply make this limit configurable.

Did you try to create the surface mesh directly within enGrid, instead of importing a surface mesh from a different mesher?

Cheers,
Oliver
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Old   March 21, 2013, 21:52
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Thomas Kudla
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Hi Oliver,

I tried creating a surface mesh within Engrid, and it works better than trying to import it from Salome.

One last question, is there any way to create "density zones", or areas of concentrated tetra volumes? Maybe by specifying 8 points, and a 'max' cell size?

I think this is a great unstructured mesh tool.

Best,

Tom
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Old   March 22, 2013, 15:09
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Oliver Gloth
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Hello Tom,

yes you can define "density zones"; it happens in the same dialogue where the surface rules are specified (see picture). These zone apply to the surface and volume mesh.

'hope this helps!

Cheers,
Oliver
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Old   March 24, 2013, 18:29
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Thomas Kudla
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Thanks Oliver, I am now able to specify density zones.

Best,

Tom
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