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-   -   Mesh resolution to capture thin solid regions (https://www.cfd-online.com/Forums/flow-3d/127746-mesh-resolution-capture-thin-solid-regions.html)

Akshay December 19, 2013 01:38

Mesh resolution to capture thin solid regions
 
Hey Guys

I have a solid region with a small thickness. How do i make sure that the mesh captures these thin regions. Interestingly even when I have a super fine mesh(order of 10 mil), it does not capture these solids. Is there any special way?

Thanks

JBurnham December 22, 2013 02:57

There are three ways:

1) make the mesh cells small enough that there are 3 cells across the thinnest region.

2) if the region is too thin for (1), then consider using a baffle (which is 2-D, and lies on the grid lines) instead of a component (which is 3-D, and needs to be resolved by cells). Note that because baffles snap to the nearest gridline, they will make stair-steps if they're angled diagonal to the mesh. Complex baffles can be imported from .stl files in v10.1 and later.

3) if possible, consider making the regions thicker in CAD. For example, extrude topography surfaces downward. Make sure to re-check and fix the .stl file after you export it, like maybe with netfabb Studio.

Akshay December 23, 2013 01:29

1 Attachment(s)
Thanks Burnham but....

The baffles option will not work for me because my model is a moving object. And I don't think I can increase the thickness considering my case. So the only option left is to resolve it through a finer mesh.
I've attached an image(notice it has a small thickness). Now how can I setup mesh planes(grid points) for such a geometry so that I can capture the entire model. Is there any quick way for such situations?

Akshay

Akshay December 23, 2013 01:31

MultiBlocks!!?? One block contained in another? Will that work?

JBurnham December 23, 2013 13:35

Yes, you can nest finer blocks inside larger blocks. FLOW-3D will change the boundary condition in the nested block to "inter-block" type automatically. However, the nested blocks do not move, so they can't follow the moving object. Good luck.

Akshay December 24, 2013 08:54

I'll let you know what happens. And..
What is the usual cell count for complex meshes/physics used in Flow3D?

JBurnham December 31, 2013 12:38

Cell count depends on how much memory you have. In general:

cell counts in the hundreds will run in seconds
cell counts in the thousands will run in minutes
hundreds of thousands of cells run in hours or days
millions of cells take days or weeks to run

jyoen November 2, 2016 02:53

about the boundary condition in the nested block
 
Quote:

Originally Posted by JBurnham (Post 467448)
Yes, you can nest finer blocks inside larger blocks. FLOW-3D will change the boundary condition in the nested block to "inter-block" type automatically. However, the nested blocks do not move, so they can't follow the moving object. Good luck.

FLOW-3D will change the boundary condition in the nested block to "inter-block" type automatically.:confused:So we needn't set the boundary condition of nested block?

hanif pourshahbaz November 2, 2016 05:54

Quote:

Originally Posted by jyoen (Post 623759)
FLOW-3D will change the boundary condition in the nested block to "inter-block" type automatically.:confused:So we needn't set the boundary condition of nested block?

Hi

it depends on your problem
but in most cases you can simply use symmetry for boundary conditions

Regards
Hanif

jyoen November 2, 2016 23:52

Hi

Yeah, I also think so.

For example, if the inter-block doesn't have superposition boundaries with outer-block , we can just choose the symmetry for inner-block. But if it has, I think maybe the superposition boundary conditions should be the same as the outer-block's. I will do experiments to text and verify it .

Thank you very much. It's important for my research.

Best

Jyoen

hanif pourshahbaz November 3, 2016 07:12

Quote:

Originally Posted by jyoen (Post 623910)
Hi

Yeah, I also think so.

For example, if the inter-block doesn't have superposition boundaries with outer-block , we can just choose the symmetry for inner-block. But if it has, I think maybe the superposition boundary conditions should be the same as the outer-block's. I will do experiments to text and verify it .

Thank you very much. It's important for my research.

Best

Jyoen

you are exactly right
and we have done this part in our work
you get my point

Regards,
Hanif

jyoen November 3, 2016 10:34

Dear Hanif,

It's cool! Thanks for your reply. It helps me save much time to verify it.

Best

Jyoen

hanif pourshahbaz November 3, 2016 11:48

Quote:

Originally Posted by jyoen (Post 623994)
Dear Hanif,

It's cool! Thanks for your reply. It helps me save much time to verify it.

Best

Jyoen

your wellcome

Regards,
Hanif


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