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[ICEM] Effect of globle mesh size and mesh independency

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Old   February 26, 2013, 08:57
Default Effect of globle mesh size and mesh independency
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Dear All,

My geometry is similar to water tank with inlet at top and outlet at bottom (both at off center) along the central axis.

For Meshing i am using smaller size at inlet and outlet (Max size 4 mm) through part mesh setting and for rest region through Global mesh size (Max Size).

With fixed max mesh size for inlet and outlet (Max 4 mm) , I am setting global mesh size. The change in total elements and nodes are as below,

Global Mesh Size (Max) Total Element Nodes
64 mm 414383 72421
32 mm 461344 80527
16 mm 841709 145118


How total element/nodes depend on Global mesh size? Please guide to select mesh size for mesh in-dependency.

Thanks,

Sujay Patil
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Old   February 26, 2013, 12:38
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Quote:
Originally Posted by sujay View Post
Dear All,

My geometry is similar to water tank with inlet at top and outlet at bottom (both at off center) along the central axis.

For Meshing i am using smaller size at inlet and outlet (Max size 4 mm) through part mesh setting and for rest region through Global mesh size (Max Size).

With fixed max mesh size for inlet and outlet (Max 4 mm) , I am setting global mesh size. The change in total elements and nodes are as below,

Global Mesh Size (Max) Total Element Nodes
64 mm 414383 72421
32 mm 461344 80527
16 mm 841709 145118


How total element/nodes depend on Global mesh size? Please guide to select mesh size for mesh in-dependency.

Thanks,

Sujay Patil

global scale factor means grow ratio in x,y,z direction.

e.g, you have a mesh with 100.000 elements and want to achieve a 300.000 elements mesh. You need an total grow ratio of three, which simply means cube root of three and you have approx. your global scale factor (not absolutely exact, but very close).
you can also scale spacing, but be aware: it's only enlarged up to 33%

speaking for turbomachinery, I normally goes in my example for 100k, 300k and 900k
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Old   February 26, 2013, 12:46
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Quote:
Originally Posted by energy382 View Post
global scale factor means grow ratio in x,y,z direction.

e.g, you have a mesh with 100.000 elements and want to achieve a 300.000 elements mesh. You need an total grow ratio of three, which simply means cube root of three and you have approx. your global scale factor (not absolutely exact, but very close).
you can also scale spacing, but be aware: it's only enlarged up to 33%

speaking for turbomachinery, I normally goes in my example for 100k, 300k and 900k
btw: i was speaking about hexa
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Old   February 27, 2013, 01:55
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Quote:
Originally Posted by energy382 View Post
btw: i was speaking about hexa
Dear Chirstoph,

Thanks.

Meshing Details :

Shell Meshing: Patch dependent with Quad dominant Mesh
Volume Meshing : Tetra/mixed with Robust(Octree)

Can you please guide for tetra mesh.

Sujay Patil
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Old   February 27, 2013, 04:38
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Hey,

it's better to ask someone more experienced (with tetra), as I usually use hex mesh for my simulation, sorry.
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Old   February 28, 2013, 15:01
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I would guess that this has to do with "powers of 2" and the octree process.

Do a search and you will find lots of other posts with details about how this works.

It appears to be seeing your 64 and 32 mm as the same basic size. Then when you go down to 16, it subdivides again. The Octree algorithms uses logic to decide if it should subdivide down to the next level or not. The solution is in your setup.

If you can post your tetin file with the 32 bit setting, I could take a quick look.
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Old   March 1, 2013, 01:56
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Old   March 1, 2013, 02:05
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Dear Sir,

Please find the tin file.

Inlet, outlet, pipe submerged and pipe top assigned with smaller size while rest with 32 mm.

During the meshing i am not at all used the shell meshing, directly volume meshed.

Please clarify on the mesh quality also. Regarding the single edges, multiple edges and delauncy violation for the geometry.

Thanks,

Sujay Patil
Attached Files
File Type: zip Normal 32.zip (15.5 KB, 8 views)
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Old   March 1, 2013, 02:06
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Quote:
Originally Posted by PSYMN View Post
I would guess that this has to do with "powers of 2" and the octree process.

Do a search and you will find lots of other posts with details about how this works.

It appears to be seeing your 64 and 32 mm as the same basic size. Then when you go down to 16, it subdivides again. The Octree algorithms uses logic to decide if it should subdivide down to the next level or not. The solution is in your setup.

If you can post your tetin file with the 32 bit setting, I could take a quick look.
tin file added
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Old   March 1, 2013, 02:42
Default Meshing of IC engine
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hello frnds
I am working on cfd simulation of in-cylinder flow in SI engine, for which i am using dynamic mesh(layering and smoothing method) for movement of piston and valves. I have done full tetra meshing which is giving negative volume during compression. therefore it is required to have hybrid meshing i.e. tetra along with hex. Hex is required mainly at regions which is deforming eg engine cylinder. But, i am not able to mesh both hex and tetra on same geometry for some region. So can anyone help me in this case? how to mesh tetra and hex both in one geometry?
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Old   March 3, 2013, 15:52
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Played with global scale factor (kept every thing else same, surface mesh from octree and volume mesh from denauly)

a) 1 >>>> fine mesh (500,000 nodes)
b) 2 >>>> Coarse mesh (250,000 nodes)


Coarse mesh:





Fine mesh:









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Old   March 3, 2013, 18:28
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Hey Far, Did you figure out what he did wrong, or did you just leave the size alone and play with the scale factor?
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Old   March 3, 2013, 23:38
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I just played with scale factor.

I did steps in following manner:

1. Surface sizing through part mesh setup.

2. Density box at few locations

3. Gave tetra width and ratio

Once above parameters were set (though were random, may be he requires some different settings), then I played with scale factor : 1 and 2.

For scale factor 1, I had the fine mesh (double size) ~500,000
and for scale factor 2, mesh was coarse ~ 250,000
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Old   March 4, 2013, 03:07
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Quote:
Originally Posted by Far View Post
I just played with scale factor.

I did steps in following manner:

1. Surface sizing through part mesh setup.

2. Density box at few locations

3. Gave tetra width and ratio

Once above parameters were set (though were random, may be he requires some different settings), then I played with scale factor : 1 and 2.

For scale factor 1, I had the fine mesh (double size) ~500,000
and for scale factor 2, mesh was coarse ~ 250,000
Dear Sir,

Thanks.

can you show these steps with snaps in ICEM

1. Surface sizing through part mesh setup.

2. Density box at few locations

3. Gave tetra width and ratio

Sujay Patil
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