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hole in a mesh

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Old   June 23, 2012, 00:32
Default hole in a mesh
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hello everyone,

i am learning CFD using openfoam, and i am at the basic yet. i learnt some cases from the tutorial, and built a laminar incompressible flow in a channel, to see the parabolic velocity profile.
Now, i want to add holes to the mesh and observe the flow behavior. i have a superficial idea how this could be done, but they are not good ideas. in the "platehole" tutorial i could understand how the hole in the plate was made, but doing something similar in my case would be unpractical. i have a rectangular block and would like to add some (maybe many) small other little blocks, so that from a 2D perspective i could approach it to a porous media.
i have been playing with edges, but when i generate the mesh, it isn't shown.
what i have done so far was creating a small block inside, setting boundary conditions there...but that does no changes in the flow.

i would appreciate any reply.

thanks in advance and kind regards
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Old   June 23, 2012, 11:52
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seems like snappyhexmeshdict is the way to go.
i am testing a little sphere inside my rectangular block, but it lasts a while for building it, and it exits with different errors that i correct one by one, per time.
considering i have to set many very little spheres inside, is there a way to make it run faster?
there is no priority for refinement of the spheres or so, they may be rough...what matters is there being spheres. whatever mesh with holes inside would fit to my problem
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Old   June 23, 2012, 15:21
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Greetings wilker and welcome to the forum!

There are two plugins for Blender that might interest you:
These give you the ability to manipulate the geometrical boundaries for "blockMeshDict" and "snappyHexMeshDict" directly in Blender as if it were yet another geometry!

And given the complexity of your geometries, this might be the best solution.

Best regards,
Bruno
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Old   June 23, 2012, 15:45
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Thank you Bruno, for your reply. Let me write a new detail before starting your suggested approach. Maybe i am half way or almost there...

i created a small sphere using meshlab, and according to:
http://www.openfoam.org/docs/user/snappyHexMesh.php

there is shown an example, where its linked a .stl file to the snappyhexmeshdict file. i could check this procedure, by running the wigleyHull present in openFOAM 2.1.1 and noticed the "boat shell" is already there when i loaded the mesh.
i am trying to do something similar now.
i created a little sphere using meshlab software, and exported it as .stl. i linked it in my snappyhexmeshdict file this way:

geometry
{
kugel.stl
{
type triSurfaceMesh;
name kugel;
}
};

and when i run blockMesh and snappyMesh i get no errors. when i open parafoam to view the results, my block is the same rectangular block as before. also, the sphere won't be shown.
If i manage to add one sphere there, i could write a simple code in c++ to generate random coordinates in the interval of my mesh, generating as much spheres as i want.


i am skipping a lot in the geometry part, but i don't know if i need these parts, and honestly i haven't understood their objectives:

Code:
 regions 
          { 
              secondSolid             // Named region in the STL file 
              { 
                  name mySecondPatch; // User-defined patch name 
              }                       // otherwise given sphere.stl_secondSolid 
          } 
      } 
   
      box1x1x1  // User defined region name 
      { 
          type   searchableBox;       // region defined by bounding box 
          min    (1.5 1 -0.5); 
          max    (3.5 2 0.5); 
      } 
   
      sphere2  // User defined region name 
      { 
          type   searchableSphere;    // region defined by bounding sphere 
          centre (1.5 1.5 1.5); 
          radius 1.03; 
      }
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Old   June 23, 2012, 15:53
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Hi Wilker,

I'm tired, weekend and all... so I'll simply point you to an old tutorial: http://www.hydroniumion.de/general/s...mesh-tutorial/

Happy reading!
Bruno
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