Help meshing hollow region 1

[DrBwts]

So with the help of Mustaine3 I managed to create a merged solid geometry of a sphere encapsulated in a cube & maintained the inner boundary.

My problem is now that however I mesh it I keep getting a hollow sphere whereas, I am after the spheres surface partitioning the geometry not cutting it. The sphere & the cube are merged, its just that I cant select the spherical region to mesh just the outer region.

I was hoping that I could use this in the same way as a partition but so far no luck.

 

[Mustaine3]

It looks like you chose "cut" instead of "merge".

 

[DrBwts]

Yeah that's what I thought but when I check the geometry is solid

 

[Mustaine3]

Both results are solids.

With merge you keep the inner geometry, but you get separate cells for inner and outer regions.
With cut you remove the inner geometry and you have a hollow sphere.

 

[DrBwts]

Sorry I meant that the merged part is solid with no hole in it.

I've gone through it a number of times now, always the same result after meshing.

 

[DrBwts]

OK have attached it with parts 1, 2 & the merged part 3, if anyone gets time to look at it.

 

[Mustaine3]

What do you want to have finally?

 

[DrBwts]

I'd like both regions meshed with a continuous mesh and 2 sets, one with all the elements within the sphere & another with all the elements outside of the sphere.

 

[Mustaine3]

Your Part-3 is what you want. One part consisting of the two cells. When you mesh that part (or instance) wou'll get elements in each cell with common nodes at the interface. So everything is ok.

You just have to hide one cell and put the displayed elements into a set. Repeat that with the other cell. Then you'll have your two element sets.

 

[IceBreakerSours]

Given the nature of your questions, I suggest taking the time to go through a few relevant chapters in the CAE User's Guide to get more comfortable with a whole host of features. While it will take a day (or a few days), the skills gained will help in many ways for a long time.

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[DrBwts]

Mustaine3: the problem is that I dont get 2 cells. So whilst the partition is visible in graphics window there is no reference to it in the side plane. Event though I have merged the sphere & the block the mesher doesnt treat the spherical region as a solid, either that or there is no way of selecting that region that I can find.

IceBreakerSours: I have been doing just that, this is why I have opened up the question here. I have tried a number of different approaches, seed part, seed edge, mesh part, mesh region..... but I still get the hollow sphere.

 

[DrBwts]

Workflow,

I've tried to partitioning the volume in various ways & tried bottom up meshing but to no avail, I just cant seem to select the spherical region.

eg.

 

[Mustaine3]

Your mistake is on image 4.
You've just clicked on the outer cell to assign a tet mesh shape. The inner region is unseleted, so it should be a hex mesh, which is not possible for a ball and so not mesh is created.

Assign a tet mesh and select all cells by using a drag box.

 

[DrBwts]

Aaaaaaaaaaah thankyou, so simple in the end, that was driving me nuts.

I much appreciate your help in all of this, do you prefer chocolates or flowers?

 

[Mustaine3]

A check

 

[IceBreakerSours]

By the way, hex meshing a ball is not difficult, if you help the mesher by splitting the geometry appropriately.

http://www.truegrid.com/QualityMesh.html

Scroll down and see Best Quality for 3D.

Take a look at the hex meshes in the link below:

http://www.truegrid.com/GalleryHome.html

*********************************************************
Are you new to this forum? If so, please read these FAQs:

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http://www.eng-tips.com/faqs.cfm?fid=1083

 

[Mustaine3]

Practically there are two easy ways to make a ball hex meshable with partitioning:

1. Split the ball on his 3 global planes into 8 pieces. This should be structured meshable now (green).

2. Cut out a cylinder and then split everything once more. The two halfs of the cylinder are sweep meshable (yellow) along their axial direction. The outer region of the ball is sweep meshable along the circumference.