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local mesh refinement
  • admin March 2009
    Hi,
    I'm trying to generate a mesh with engrid for a a few simple geometries.
    Now I got two questions:
    Is it already possible to refine the mesh locally working with the
    snapshot release? And I can't open the meshing options, is that because
    it's only a snapshot?
    Best regards,

    Julian
  • admin March 2009
    Hello,

    Currently it is not possible to refine the grid locally. What exactly do
    you have in mind? Specifying the mesh resolution on the surface mesh,
    adapting the grid according to a prior solution, or defining regions in
    the volume that should have a better resolution than the surroundings?

    The meshing options dialogue doesn't exist yet; it will be written soon,
    though (next 2 weeks). There will be options to control the smoothing
    process for the boundary layers.

    Thanks for your interest,
    Oliver
  • admin March 2009
    Hello Oliver,
    thanks for the qick answer. I'd like to refine the volume mesh in the
    regions close to the prismatic boundary layer around a profile. So
    defining regions in the volume with a better resolution than the
    surroundings would be the point. Is there maybe a way to do this,
    because I saw this kind of refinement looking at the examples (launch
    vehicle) on the engrid hompage.
    Best regards,
    Julian
  • admin March 2009
    Unfortunately that feature doesn't exist yet, but what you can do is the
    following:

    (1) create a first volume grid with boundary layer "create prismatic
    boundary layer"
    (2) re-create the tetrahedral part of the grid "create/improve volume
    mesh (NETGEN)"

    Re-creating the tetra grid will compute a mesh density on the original
    grid and use that as input for the tetra mesher. This will lead to
    generally smoother transitions which means more elements as well. It
    might be useful to run this re-creation two or three times -- just have
    a look at your grid. Of course the mesh density very much depends on the
    density of the original surface grid. What do you use for surface meshing?
  • admin March 2009
    Hi Oliver,

    for the surface meshing I use the gmsh tool. But I haven't found a way
    how to refine the surface mesh locally with the gsmh tool. Do you know
    if this is possible?
  • admin March 2009
    Hi Julian,

    strictly speaking that should go to the Gmsh list -- which I have never
    been able to post to ...

    However, I use Gmsh as well and Gmsh allows you to specify the mesh
    density (characteristic length) per point of your geometry. One,
    somewhat tedious solution, that I have used in the past is to create the
    geometry in a way that you have a point in the region where you want a
    fine surface grid (e.g. split a cylinder in the middle and reconnect it
    -- as a result you might, depends on the CAD software, end up with
    additional points that can be used to specify the mesh density). That is
    a really annoying process at times which is one of the reasons why we
    want to add surface meshing capabilities to Engrid. Surface meshing,
    starting from STL geometries, is number one on the list of new
    developments (apart from minor things like the options dialogue and
    proper OpenFOAM export).

    Oliver
  • admin March 2009
    Hi Oliver,
    thanks. I will try the refinement as you explained by adding points on
    the edge.
    Regards,

    Julian