Clarification about Mesh orthogonality
 

Hello everybody,

I have a question concerning the Mesh Orthogonality. The situation is as follows:

- I have a pipe where I have a sudden change in diameter. At one position I have an increase in diameter (from small to larger diameter) and at another position the opposite (from large to smaller diameter).

- At both locations I get cells with bad orthogonal quality. In the picture the location is displayed where the change from the large to smaller diameter happens.

The definition of Mesh orthogonality is clear and makes sense. My question is: Is it even possible to have cells with good orthogonal quality in regions like that? If yes how do you obtain them? :confused:

Thanks a lot for your answer and have a nice day!

This should probably be in the meshing forum. But anyways...
That looks like a step in diameter?

I would be using hex elements and mesh that larger volume like a hollow cylinder. A full structured mesh would have perfect orthogonality. I would slice it up into multiple cylinders of the same diameter, end to end, split where the change in diameter occurs. Then a hollow cylinder around the cylinder that should be larger. Use a structured mesh on all 4 bodies.

One approach, as Erik states, is to use a hex mesh in that region.

If you want to use a tet mesh over everything then you will probably need to make the element size smaller at the step to improve mesh quality. You only have 1 or 2 elements defining the step, if you made that 4 or 5 the quality will improve quite a bit, especially if you are using inflation layers.

First of all, thanks a lot Erik and Mr. Horrocks for your answers! (I know that should be in the meshing forum, but already posted it there and didn't get an answer)

@Erik: I'm not quit sure if I get your idea with the hollow cylinder. For clarification I made the following sketch (see attachement), where:
- black lines --> geometry
- red lines --> splitting lines
- green lines --> also splitting lines, with which the hollow cylinder is achieved

Is that what you meant?


@Mr. Horrocks: I'll definitely give it a try and compare it to the structured option.

Yes, that is what I meant.
I always slice up my geometry into regions where I can control the mesh easily, and get a good quality mesh. If you have a complex geometry, it is very difficult to control the mesh, so you slice it up into simple, easy to mesh shapes.

Thank you one more time and your picture made it even clearer.

Have a nice day!

Patrick