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-   -   Surface orientations (http://www.cfd-online.com/Forums/engrid/114478-surface-orientations.html)

mlotek March 11, 2013 22:04

Surface orientations
 
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

mlotek March 14, 2013 08:17

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.

ogloth March 15, 2013 11:05

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

mlotek March 15, 2013 20:42

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

ogloth March 17, 2013 12:05

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

mlotek March 21, 2013 21:52

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

ogloth March 22, 2013 15:09

1 Attachment(s)
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

mlotek March 24, 2013 18:29

Thanks Oliver, I am now able to specify density zones.

Best,

Tom


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