Different elements using different mesh generation

Moderator: GiD Team

Post Reply
wangqing
Posts: 2
Joined: Sat Oct 15, 2016 7:01 am

Different elements using different mesh generation

Post by wangqing »

Hello,
I want to build a hexahedron,placing a sphere in the hexahedral inside,I want them on the grids of different sizes to split.But I found I always can not grasp the relationship between cube and sphere.I tried to use ‘the Geometry->Edit->Volume Boolean op.->substract and intersect’.but it will make the hexahedron and ball as a whole,so that i can not use the ‘Unstructured->Assign sizes on volumes’.how can it be resolved?
Thank you!
User avatar
escolano
Posts: 1918
Joined: Sun Sep 05, 1982 10:51 pm

Re: Different elements using different mesh generation

Post by escolano »

Your explanation is not clear, I am not sure when are you talking about 'mesh elements' or 'geometric entities'
It seems that you have created a geometry of a single volume with the shape of a brick with a hole.
But then you can assign to the volume the mesh size you want with Unstructured->Assign sizes on volumes !!

Maybe do you mean that do you want really two volumes? the holed brick and the sphere that fill this hole
Then you simply must create the second spheric volume, creating a volume selecting the surfaces of the sphere to define it.

Then both volumes will be connected ,because are sharing the same surfaces, and its mesh will be also connected.
If do you want to isolated volumes must duplicate the surfaces (and its lines and points) of the hole and use them for the second volume.
Note: you can use 'Geometry->Edit->Uncollapse->Volumes' to obtain this duplication
wangqing
Posts: 2
Joined: Sat Oct 15, 2016 7:01 am

Re: Different elements using different mesh generation

Post by wangqing »

I'm sorry for so long to reply to you, I have solved this problem, and now, I have a new problem. I want the grids from the center of model(0,0,99800) to outside gradually become sparse. but at the points of the four corners of the middle cube, the grids is not encrypted. how to achieve it.
Attachments
example.gid.zip
this my model
(517.93 KiB) Downloaded 282 times
User avatar
escolano
Posts: 1918
Joined: Sun Sep 05, 1982 10:51 pm

Re: Different elements using different mesh generation

Post by escolano »

Force a small size in the interior of a surface or volume is difficult.

You can somehow split your geometry in several parts to have, to have some points and lines to assign them your desired sizes and then have more control on the mesh sizes.
And do you have a thin volume that force small sizes of its tetrahedra.
I attach your model modified concentrating some elements near the center (after divide some lines and assign them mesh sizes)
concentrating_near_center.png
concentrating_near_center.png (134.35 KiB) Viewed 4174 times
example_2.zip
(2.58 MiB) Downloaded 288 times
For simple shapes you can also try structured (6-sided volumes) or semi-structured meshes (prismatic volumes)
Post Reply