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Sphere meshing

Posted: Tue May 15, 2018 12:31 pm
by Lau
Hi all,

I'm new to this forum and using GID 10.0.9 recently.

I'm working on a model regarding a structure with spherical voids. Now i'm wondering if there's a way to mesh parts of this model with a structured mesh. see the following figure and the attached GID file
structure.JPG
structure.JPG (275.08 KiB) Viewed 2636 times
,
sphere_meshtest.gid.rar
(1.22 MiB) Downloaded 121 times


According to what I have read til now, spheres can be meshed by tetrahedra's only. My goal is to create a mesh aproaching the given mesh in the following figure (created with another FEM package) where a structured mesh is used outside the area with the spherical voids
mesh_goal.JPG
mesh_goal.JPG (53.38 KiB) Viewed 2636 times
.

Kind regards

Laurens

Re: Sphere meshing

Posted: Tue May 15, 2018 2:30 pm
by abelcs
Hello,

you can mesh volumes with hexahedra using structured or semi-structured mesh. Structured volume meshes must correspond to 6-faces volumes, and semi-structured meshes must be applied to topologically prismatic volumes, this is, a volume where it can be recognized two 'top surfaces', and lateral surfaces going from one top to the other.
To reach this requirements, you may work a little bit on your geometry, splitting some volume so as all the volumes can fit into structured or semi-structured mesh.

Re: Sphere meshing

Posted: Tue May 15, 2018 2:55 pm
by Lau
Hi, thanks for the quick response. I'm still wondering how the connection between the 'unstructured' part with spherical voids can be made with the structured or semi-structured part with hexahedra elements. In the attached image the two volumes (4 and 5) are given wherein surface '2' is shared. When the hexahedra type is choses for the prismatic part (volume 5) an error, regarding incompatibility is given.
structure_2.JPG
structure_2.JPG (129.3 KiB) Viewed 2629 times


Thanks, Laurens

Re: Sphere meshing

Posted: Tue May 15, 2018 3:45 pm
by escolano
It is possible to create and mesh with GiD a geometry like your first image, but split the volume around the sphere hole into structured (6 faces block-like) could be hard to do.

I attach the zipped GiD example
StructuredSphereHoledCube.zip
(77.82 KiB) Downloaded 153 times
of this picture
StructuredSphereHoledCube2.png
StructuredSphereHoledCube2.png (12.18 KiB) Viewed 2625 times
(some hexas were deleted to see the interior)

But it is not possible to do the same for the model of your second image.
This is because structured meshes are not used for complicated geometries. Unstructured meshes of triangles/tetrahedra are much powerful.

Re: Sphere meshing

Posted: Tue May 15, 2018 3:50 pm
by escolano
About your last questions, GiD doesn't allow to create the mixed mesh of unstructured tetras and structured hexas because as you pointed are not compatibles in the shared surface (one has triangular faces and another quadrilaterals!!).

You can do all unstructured, or at least force the structured mesh to be automatically splitted in tetrahedra.
Mesh->Element type->Tetrahedra
and select the structured volume.

Then the whole mesh will be of tetrahedra.

Re: Sphere meshing

Posted: Tue May 15, 2018 4:22 pm
by Lau
Thanks! this is very helpful!

Re: Sphere meshing

Posted: Wed May 16, 2018 7:38 am
by abelcs
Just another way of splitting your geometry to reach hexas:

Kind regards,

Re: Sphere meshing

Posted: Thu May 24, 2018 12:12 pm
by Lau
Thnx!