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-   -   [blockMesh] How to define the interpolation points of "arc"? (https://www.cfd-online.com/Forums/openfoam-meshing/151308-how-define-interpolation-points-arc.html)

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

I want to create a quadrisected cylinder with blockMesh, like this:
http://s23.postimg.org/mpd0hrfmj/image1.jpg

What I've done so far is that I created a block with fewer than 8 vortices:
http://s13.postimg.org/jsoca35rr/Scr...8_15_39_21.png
http://s13.postimg.org/6pspqtfjr/Scr...8_15_39_44.png

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
(
);

// ************************************************************************* //
http://www.cfd-online.com/Forums/<a ...upf/image1.jpg

alexB April 8, 2015 16:45
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

Harak April 9, 2015 09:54
Quote:
Originally Posted by alexB (Post 540636)
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 (http://www.cfd-online.com/Forums/ope...blockmesh.html) but didn't get it neither.

I appreciate your help! :)

amod_kumar April 9, 2015 11:57
Re: How to define the interpolation points of "arc"?
 
1 Attachment(s)
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,

Harak April 9, 2015 12:25
Quote:
Originally Posted by Harak (Post 540822)
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 (http://www.cfd-online.com/Forums/ope...blockmesh.html) 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! :o

Thank you sooo much! :)

alexB April 9, 2015 16:52
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

amod_kumar April 10, 2015 05:40
How to define the interpolation points of "arc"? Reply to Thread
 
2 Attachment(s)
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

Harak April 10, 2015 06:55
Quote:
Originally Posted by amod_kumar (Post 541004)
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 ;)

dinesh1700 September 26, 2018 05:58
how to define interpolation points in arc ?
 
1 Attachment(s)
i am facing problem in defining arc in wedge type of problem. without the arc option the mesh is running fine but as i include an arc mesh problem arises
blockmeshdict file is as follows:

Attachment 65759

amod_kumar September 29, 2018 10:59
Hello Dinesh,
Can you attached your blockMeshDict as txt file?

dinesh1700 October 5, 2018 07:38
blockMesh dict file is attached below
 
1 Attachment(s)
sir the blockMesh file is attached i am struggling with this from last 2 weeks still not able to find the error in arc syntax.

thanks

amod_kumar October 5, 2018 22:49
Hello Dinesh,
I do not think there is any issue with the arc. The wedge is such a small angle 1.5 [deg] that is looks a straight line. If you zoom very closely in ParaView, the arc is visible. Try changing

hex ( 0 1 5 4 0 1 2 3) (400 50 2) SimpleGrading (1 0.2 1)

to

hex ( 0 1 5 4 0 1 2 3) (400 50 8) SimpleGrading (1 0.2 1)

and then check.

I also realized that the blockMesh does not work if wedge angle is > 15 [deg].

Regards,
Amod

dinesh1700 October 6, 2018 00:59
4 Attachment(s)
the problem i am solving is laminar flow in a pipe , but i am getting same velocity profile everywhere. i am attaching other files.


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