Learning Forum

[gao.1571]

As the title, how can i get hex mesh for a rectangular box with a spherical void inside? i know the multi-zone method can be used to get hex mesh for a sphere but it doesn't work for this geometry. 

The mesher is the default one when the mesh component from workbench is launched. 

The geometry is shown in the image, 

[NickFL]

Multizone tries to break things down into sweepable/mappable portions, meaning they have the same cross-sectional profile along a path. Because there are no points on your sphere, the software becomes confused and wants to mesh it with tets. So here are three approaches that I see:

1. Use the meshing in SpaceClaim. Setting up the blocking there is pretty straightforward and there are many videos on YouTube that do similar problem but with more complexity. You can use those as a guide. (see below for simple example)
   
2. Use DesignModeler or SpaceClaim to decompose the domain into the sweepable block bodies. Then combine these into a multibody part so they share the nodes between the “bodies”. Here you will basically to project a cube “inside” of your sphere onto your sphere surface. It will look kinda of like a beach ball. Look at examples of O-Grids for a good starting point (there it is basically a 2d version of what we want–again see below).
3. This is the least elegant and I really should not recommend. But you could use virtual topology in ANSYS Meshing to decompose the faces. The problem here is you don’t have full control of exactly wher the points are on the sphere surface (based on mouse clicks) and changing anything like the geometry would likely require to start over from stratch.

 

 

[gao.1571]

Thanks very much. i appreciate if you can help me further. 

1. it looks like the sphere is projected to a outside box (the center small one)?
2. what software do you use to get the mesh above? 

[NickFL]

I used ANSYS SpaceClaim to create the geometry and the mesh.

In SpaceClaim there is a built-in meshing tool. I would recommend you look at couple of videos on YouTube for examples. One in particular by MECSO ANSYS is very good (search for tworzenie siatki w ANSYS SCDM, it is the one with the 90° elbow).

What I did below (basically following the first few steps of the video mentioned above), is 1. create a "Bounding Box" Blocking element for the body with all quads and, if I assume correctly that this is a CFD model, linear elements. The key will be to see that this is a Mapped Block.

2. Then I simply sliced it two times in each direction creating 27 Mapped blocks.

3. Next, I went thru the tree and found the block for the center and deleted it.

That is all that is required as if your splits are near the sphere surface it will to the association (this means projecting the block face onto the geometry surface) automatically. Now if you wanted a longer downstream section I would create a blocking for that too.

[gao.1571]

Thanks. The videos are great. I have some experience in using ICEM and now I understand why Ansys stop puting efforts into that software.  

[gao.1571]

Thanks very much. i appreciate if you can help me further. 

1. it looks like the sphere is projected to a outside box (the center small one)?
2. what software do you use to get the mesh above?