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How to define the interpolation points of "arc"?

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Old   April 8, 2015, 09:59
Default How to define the interpolation points of "arc"?
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Hey,

I want to create a quadrisected cylinder with blockMesh, like this:


What I've done so far is that I created a block with fewer than 8 vortices:



My question is, based on what do I have to define the 3 values in arc in the brackets, for example, arc 3 6 (? ? ?).

Thanks!

This is my blockMeshDict:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | foam-extend: Open Source CFD                    |
|  \\    /   O peration     | Version:     3.1                                |
|   \\  /    A nd           | Web:         http://www.extend-project.de       |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

convertToMeters 1;

vertices
(
    (0 0 0)
    (1 0 0)
    (0 1 0)
    (1 1 0)
    (0 0 1)
    (1 0 1)
    (0 1 1)
    (1 1 1)
);

blocks
(
    hex (1 1 3 3 4 5 7 6) (10 10 10) simpleGrading (1 1 1)
);

edges
(
    //arc 3 6 (? ? ?)
    //arc 1 4 (? ? ?)

);

patches
(
    empty frontAndBackPlanes
    (
        (1 3 3 1)
    )
);

mergePatchPairs
(
);

// ************************************************************************* //
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Old   April 8, 2015, 16:45
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Alexander Bartel
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Hi Harak,

first off all, does your blockmeshdict run well?
As written in the UserGuide ( http://cfd.direct/openfoam/user-guide/blockMesh/ ) you shouldn't let collapse thethe first defined vertices of your block, because they also define your coordinate system. Perhaps that never will be a problem while running your case.

Now to your posted problem.
For simple geometries as yours I would propose to just use a calculator to determine the interpolation point.
You want to describe an arc in the x-z-plane.
Many arcs are possible to connect Point 3 and 6.
With the interpolation point you chose one specific arc.
With an interpolation point in the x-z-plane that also contain 3 and 6 you choose an arc in this plane.
To make it short:
take ( sin(45) 1 cos(45) )

regards
Alex
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Old   April 9, 2015, 09:54
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Quote:
Originally Posted by alexB View Post
Hi Harak,

first off all, does your blockmeshdict run well?
As written in the UserGuide ( http://cfd.direct/openfoam/user-guide/blockMesh/ ) you shouldn't let collapse thethe first defined vertices of your block, because they also define your coordinate system. Perhaps that never will be a problem while running your case.

Now to your posted problem.
For simple geometries as yours I would propose to just use a calculator to determine the interpolation point.
You want to describe an arc in the x-z-plane.
Many arcs are possible to connect Point 3 and 6.
With the interpolation point you chose one specific arc.
With an interpolation point in the x-z-plane that also contain 3 and 6 you choose an arc in this plane.
To make it short:
take ( sin(45) 1 cos(45) )

regards
Alex
Hi Alex,

thanks for your reply!

Yes, my blockMeshDict is working well without any errors.
I tried
Code:
arc 3 6 (0.70710678 1 0.70710678)
arc 1 4 (0.70710678 1 0.70710678)
but unfortunately it seems that nothing happened.

Can you please explain what the rule of defining these three values is?
I've already read through this thread (defining and connecting two circular pipes using blockMesh) but didn't get it neither.

I appreciate your help!
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Old   April 9, 2015, 11:57
Default Re: How to define the interpolation points of "arc"?
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Amod Kumar
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Hi,

I corrected
arc 3 6 (0.70710678 1 0.70710678)
arc 1 4 (0.70710678 1 0.70710678)

to
arc 3 6 (0.70710678 1 0.70710678)
arc 1 4 (0.70710678 0 0.70710678) //vertices 1 & 4 are at y=0

It created arc and generated the mesh but highly skewed. You may like to review the co-ordinates to define the arc. The mesh is attached.

Regards,
Attached Images
File Type: png QudriSected_Cylinder.png (13.3 KB, 9 views)
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Old   April 9, 2015, 12:25
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Quote:
Originally Posted by Harak View Post
Hi Alex,

thanks for your reply!

Yes, my blockMeshDict is working well without any errors.
I tried
Code:
arc 3 6 (0.70710678 1 0.70710678)
arc 1 4 (0.70710678 1 0.70710678)
but unfortunately it seems that nothing happened.

Can you please explain what the rule of defining these three values is?
I've already read through this thread (defining and connecting two circular pipes using blockMesh) but didn't get it neither.

I appreciate your help!
Nevermind, just solved the problem.
The reason it didn't work was because of what you said here:
Quote:
you shouldn't let collapse thethe first defined vertices of your block, because they also define your coordinate system
My origin was my 0-vertice, so I just changed the numbering so that my first defined vertice does not collapse anymore!

Thank you sooo much!
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Old   April 9, 2015, 16:52
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Alexander Bartel
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You are welcome Harak,

the rule behind the definition of an arc is simple.
The three values are the x,y and z coordinates of one additional point on the arc.

Because an arc is defined completely by three different points on this arc.
Just imagine two arbitrary points in 3-dimensional space.
If its clear that the connecting line is an arc, every additional point defines another arc.

@amod:
I suggest you just helped Harak and are not hung at the same point.

regards
Alex
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Old   April 10, 2015, 05:40
Default How to define the interpolation points of "arc"? Reply to Thread
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Amod Kumar
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Hello,
Out of curiosity, I tried
hex (0 4 1 1 2 6 3 3) (10 10 10) simpleGrading (1 1 1)

It generated the correct geometry and mesh. Though I would recommend to use Y-block and further divide the sector into 3 sub-sector as shown below. I will not only eliminate the need of collapsed blocks but a high-quality mesh can also be generated with ease.

Regards,
Amod
Attached Images
File Type: png OF1.png (23.2 KB, 10 views)
File Type: png 1_8th_Sector_3_Blocks.png (9.8 KB, 14 views)
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Old   April 10, 2015, 06:55
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Quote:
Originally Posted by amod_kumar View Post
Hello,
Out of curiosity, I tried
hex (0 4 1 1 2 6 3 3) (10 10 10) simpleGrading (1 1 1)

It generated the correct geometry and mesh. Though I would recommend to use Y-block and further divide the sector into 3 sub-sector as shown below. I will not only eliminate the need of collapsed blocks but a high-quality mesh can also be generated with ease.

Regards,
Amod
Your idea sounds pretty smart, though my configuration fits my case well enough
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