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how to save mesh data with engrid
  • rvs September 2012
    Good day!
    I have two questions.
    1) As I know from tutorials engrid can construct the layer of prisms from triangulated boundary. For my problem of research I need the mesh in which I have the layer of triangle prisms at one boundary and the tetrahedral grid in the other part of complex domain. To merge these grids the mesher must construct the layer of pyramids.
    Can I do hybrid grid (tetrahedra, prism, pyramids) with engrid?

    2) I ask you to tell me please, is it possible to save the grid data (points, edges, faces, elements (tetrahedron, hexahedron, pyramids, prisms)) after I have contructed the mesh with the edgrid. I mean *ele, *.faces, *.edges, *.node files, as it can be done for example with Tetgen by Hang Si. I need this information because I am writing my own program for flow calculations and I am not really use any solver.
    May be you can advise me some program or converter where I can get information that I need.
    Very hope on your answer,
    Thank you.
  • Oliver September 2012
    Hi,

    1) To connect prisms and tets you do not need any pyramids, they are mainly required to connected hexes and tets. The process which is outlined in the tutorial (damper in a duct) should give you a hybrid grid with tets and prisms.

    2) The native format of enGrid is the VTK *.vtu format. You could easily link your code to VTK and use the VTK reader classes to import the mesh. Alternatively, and maybe better, is to use the Gmsh2 format which is sufficiently documented in order to write your own reader for it. The last option would be to invent your own format and write an export function/plugin for enGrid.

    Cheers,
    Oliver
  • rvs September 2012
    Dear Oliver.

    Thank you very much for your quick reply. I am agree with you that to connect prisms end tets I do not need any pyramids, but only if I connect them from triangular faces of prisms. But in my case I need to connect prisms with tets from one of the quadrangular faces of prisms. Excuse me I couldnt formulate it in previous mail. For example, I have the volume the top and bottom faces of which are hexagons and side faces are quadrangles. This volume can be devided into six triangular prisms. Then I need to connect this volume with the domain constructed with tets. So it can be made with pyramids only I guess. Can I construct such a mesh type with engrid?
    Now I begin to study Gmsh2 and VTK files format in order to write my own reader and writer for it.

    Thank you very much again,
    Cheers,
    Roman
  • Oliver September 2012
    Roman,

    this would not work out of the box. Also, I am not sure I understand the motivation behind this. Could you maybe post a few pictures somewhere? Are you talking about isotropic prisms or an-isotropic prisms?

    Cheers,
    Oliver
  • rvs September 2012
    Dear Oliver,

    I load the file with the domain in this place: http://files.mail.ru/PI7OBL. As you can see from this picture the green domain (internal volume) must be devided by triangular prisms (each element of this internal volume can be devided by six triangular prisms). The other part of the box shape volume must be devided by tets. So the quadrangular faces of prisms must be connected to tets and it is nesessary to build pyramids to connect these two meshs.

    Cheers,
    Roman
  • rvs September 2012
    Dear Oliver,
    Sorry, the previous link to the file does not work. You can download picture from this place: http://files.mail.ru/TWVNOY.
    Thank you,
    Roman
  • rvs September 2012
    Dear Oliver,

    I would be very greatful if you can answer on my last post as soon as it will be possible.

    Thank you in advance,
    Roman
  • Oliver September 2012
    Roman,

    as I said, it will not work without tweaking the code.

    What is the motivation for the prismatic cells? What are you trying to simulate with this mesh?

    Would it be possible to have a triangular mesh in both zones, as long as the "interface" is respected? This kind of mesh should work with the current release of enGrid.

    Cheers,
    Oliver

    P.S. If you use JPEG instead of BMP, your image files will be a lot smaller.
  • rvs September 2012
    Dear Oliver

    Such a grid is widely used in areas where it is necessary to take into account the fluid flow in thin capillaries. Such is the case in the calculation of blood flow in thin capillaries. Their walls are not completely impermeable, and the flow through the walls typically occurs in the radial direction. The same is the case in the calculation of the various drainage systems and as I know the flow to oil wells. In this case, to account for such a radial flow (relative to the axis of the capillary) is required is the same grid to which I referred. Using a different network (only tetrahedra or others) is difficult due to the geometry of the inflow. Therefore required a hybrid grid.

    In principle, the same problem arises when stitching a grid of parallelepipeds with mesh of tetrahedra, as in this case also raises the pyramid. If, engrid is able to combine grid of parallelepipeds with tetrahedral mesh, the prisms should not be the serious problem, I think.

    It is the task of mesh from the two surfaces, one of which is given by the quadrangles, and the other with triangles. Such a function of engrid package significantly expand its functionality (which is already quite widely), especially in the use of hybrid meshs. But I know that a greate motivation have to exist to do it.
    Thank you the valuable disscussion

    Cheers,
    Roman




  • rvs September 2012
    Oliver,
    May be you can advise me, please, another program which makes such a mixed grid (triangular prisms, pyramids, tets)?

    Cheers,
    Roman