Mesh around an opening and other mesh-related queries

[Hamed]

Hi Escolano,

I hope this message finds you well.

I have a cube with holes in one of its faces that goes all the way to the opposite face of the cube (images 1 and 2). As you can see in this image, I have a semi-structured hexahedral mesh. I want to concentrate the meshes along the edge of the holes but I can’t do it using the semi-structured hexahedral mesh. Now my questions are:

1- Correct me if I am wrong that meshes cannot be concentrated around the hole using the semi-structured mesh. The other option is to use tetrahedral meshes which allows for unstructured meshes and mesh concentration nearby a point or line. But the tetrahedral mesh has fewer integral points than the hexahedral mesh and if it is possible, I prefer the hexahedral mesh.


3- Regardless of the capabilities of GID, what is your software recommendation to generate very complex meshes and then import them into GID? How can I make meshes like this (see image 3)? I have gone through the manual but the meshing section guidelines doesn’t seem to work for my model

4- My 4th question is irrelevant to the above ones; how can one mesh a circle like any of the below images this in GID? (images 3-7)


5- How can one improve meshing in the surface of a cylinder? (see image 8). Make it Radial like the images above (image 3-7)

I am Using GID 16.0.6. Images are attached in a .rar file. Many thanks for Your time, support and kind consideration.

Best regards,
Hamed Sadaghian

[escolano]

1- you are wrong. In a semi-structured volume you can concentrate mesh sizes in the surface normal to the extrusion direction, but off course must do the same concentration in both linked tops.

e.g. I have assigned a number of divisions=8 to the lines of the holes of the tops (can also assign a mesh size, but I prefer in this case a number of divisions to ensure the same mesh in the master and slave surfaces)
Note: it is better to set a number even, because a mesh of quadrilaterals is topologically imposible is the sum of edges of its boundary is odd

semistructured_hexa-concentrating-8-divisions-holes.png (49.76 KiB) Viewed 15730 times

I attach also my GiD model (i used the one of your question 8633 joining again the volumes, surfaces and lines in a single volume)

semi-structured-volume-concentrate-elements.gid.zip

(66.34 KiB) Downloaded 431 times

3- Use an external mesher (e.g. gmsh) probably won't be a good solution, because for this problemype Atena there are usually extra requirements, like create contact elements, have hexahedra when possible, attach more boundary conditions...

4- generate a mesh of a ring of 4.png is simple, e.g. divide the surface in 2 halfs that can be meshed structured
If it has the center is not possible because all elements will degenerate on this center, then can use the same approach of 5.png (b), dividing the circle inserting an square, ant then do you have five structured surfaces with a meshing pattern that won't degenerate in a rotation center.
patterns of 6.png and 7.png do not seems very good in my opinion

5- the mesh of the cylinder of your image 8.png seems perfect for my. It show hexahedra with good angles, and concentrated a little in the boundary.
As I've said a revolution mesh will be bad solution, because of the degeneracy of the faces on the revolution axis.

[Hamed]

Dear Escolano,

Hi, I hope this message finds you well and thanks for the responses you have kindly provided.
Now, I have a new problem.

I have a 40-mm 3D-printed cube with a filament width of 20 mm and layer height of 10 mm, after validating my model with 8 rectangular cross-sections replicating filaments in GID 16.0.6, I have filleted the corners with a radius of 1 mm. Now, I do not know how to mesh them properly, I can’t mesh them with structured hexahedral meshes, and I have to go with semi-structured hexahedral meshes. Doing so, the cross-section of the filaments is not meshed properly unless I use a very fine mesh which is computationally ineffective and I am sure is wrong.

I would be really grateful if you guided me how to mesh my model properly and more importantly, how to mesh structures that cannot be meshed with structured hexahedral meshes, either because of not having 6 sides or having a curved geometry.

I will have to mesh trapezoids, 6 sided- and 8-sided polygons as well. I think I will have to go with the semi-structured option, right?

I have attached my cube model for your kind consideration. Thanks for your time and support in advance.

Best regards,
Hamed