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hsieh July 1, 2008 10:13

HI, I am trying to split th

I am trying to split this block into smaller bricks with contrains on all 6 faces. I can only add additional nodes inside the block. Can someone shed some light on this?

(all 6 sides are fixed - cannot add more nodes).



bengtsson July 2, 2008 10:00

That is impossible, because se
That is impossible, because several of the surface faces can never be part of a closed hexahedron, if you don't want to subdivide them. (Any four quadriliterals, mutually connected to a quad strip by disjoint edges, would have to form a closed strip, but they don't.)

If you numbered your patches I could explain this in more detail.

What do you mean by "bricks with contrains on all 6 faces", why can you only add nodes inside the block, and why don't you use general polyhedrons?


hsieh July 2, 2008 18:52

Hi, Ole, Thanks for the rep
Hi, Ole,

Thanks for the reply!

This block is part of a much bigger mesh. I am using this block to transition to other blocks with "already" fixed number of nodes. All the nodes on the 6 outer faces of this block are fixed.

The problem is that, this is only an initial mesh. I cannot have polyhedrons in the mesh, only Hex elements are allowed.

I am hoping this is not impossible (but, maybe this is really impossible). I am still giving this much more thoughts. I will post some examples later.


bengtsson July 2, 2008 19:38

Hi Pei! I still don't underst
Hi Pei!
I still don't understand why you impose unnecessary constraints which make a solution impossible. Do you want to use blockmesh independent from Openfoam with a solver which is limited to hex elements?
Any CFD tool that I know, including Openfoam, can easily mesh your structure, if you either
- allow additional nodes on the surface (can be easiliy propagated outside) or
- allow more general elements (a tet mesh is trivial, but requires much more than the minimal 4 elements.)

Maybe you shouldn't ask how to do what you have in mind, but instead ask how to find a solution to your problem. Of course we don't know the problem, so I'm afraid we can't help.


hsieh July 3, 2008 10:25

Hi, Ole, I really appreciat
Hi, Ole,

I really appreciate your help.

Unfortunately, life sometimes is tough. In this project, I am constrained to all hex elements (no tet, no polyhedrons). Also, this is a block using to transition from dense mesh to coarse mesh, hence, all nodes on all 6 sides are fixed (so that the nodes match with its neighbors). Only adding nodes inside the block is allowed. This is where the challenge comes from.

Below are two examples similar to what I am trying to achieve.


bengtsson July 3, 2008 11:51

>This is where the challenge c
>This is where the challenge comes from.

I guess people call it positive thinking if you have no unsolvable problems, but a few challenges instead.

Have fun!

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