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-   -   can anyone explian the logic behind defining the vertices (http://www.cfd-online.com/Forums/openfoam/81926-can-anyone-explian-logic-behind-defining-vertices.html)

gandesk November 10, 2010 14:39

can anyone explian the logic behind defining the vertices
 
I am not able to figure out the direction chosen for defining the vertices in the example figure 5.6 explained in this following link.

http://www.openfoam.com/docs/user/blockMesh.php

may be they have not defined the lengths of the edges and now am not able to figure out the lengths from the vertices definition.

Thanks for the help
Sandeep

marupio November 10, 2010 16:33

Hi Sandeep,

Your question isn't very clear. I'm not sure what you are asking...

If it's about finding the length of the edges, then look at example blockMeshDict files. The points are listed first. The order in which they appear is their number.
Code:

    (0 0 0)        // point 0
    (0 0.1 0)    // point 1
    (0.1 0.1 0)    // point 2
    (0.1 0 0)    // point 3

Then when the blocks are defined, they are done according to the numbering in the figure you pointed out. CCW around the bottom, then CCW around the top, as seen from above. You can infer the length of each side by the points list above.

Lastly, you should pay attention to the axis directions defined (shown as x1, x2 and x3 in the diagram). The simpleGrading or edgeGrading lists are based on these axes, not a global coordinate system.

Is that what you wanted to know?

gandesk November 10, 2010 18:08

Quote:

Originally Posted by marupio (Post 282995)
Hi Sandeep,

Your question isn't very clear. I'm not sure what you are asking...

If it's about finding the length of the edges, then look at example blockMeshDict files. The points are listed first. The order in which they appear is their number.
Code:

    (0 0 0)        // point 0
    (0 0.1 0)    // point 1
    (0.1 0.1 0)    // point 2
    (0.1 0 0)    // point 3

Then when the blocks are defined, they are done according to the numbering in the figure you pointed out. CCW around the bottom, then CCW around the top, as seen from above. You can infer the length of each side by the points list above.

Lastly, you should pay attention to the axis directions defined (shown as x1, x2 and x3 in the diagram). The simpleGrading or edgeGrading lists are based on these axes, not a global coordinate system.

Is that what you wanted to know?


Hi david,


Thanks for the reply. Its my bad that i am not clear in my question. My question is that vertices for the figure 5.6(single block) are mentioned under the section 5.3.1.1 at 'the vertices' in the link i have sent. Now that am not able to visualize the same figure with the defined vertices. Also there are no lengths defined in the figure 5.6 and how the vertices were defined by taking 0.1 in one direction and 1 in another direction etc. Also for some vertices he has taken -ve value which looks impossible for the figure.

the vertices you have sent do not match with the list in the link. i wonder if you are refering to the same figure??

Also i want to know the x y and z directions are same as x1, x2 and x3 directions in the figure 5.6?

Thanks and regards
sandeep

nakul November 11, 2010 00:18

Hi,

The vertices that have been defined in the link are defined correctly.

x1, x2 and x3 can be assumed as x,y,z directions respectively.

The lengths are arbitary here as this is just an illustration of defining vertices in blockMeshDict. In an actual case the choice of vertices would be detrmined by the dimensions of your domain. Besides that figure is not an exact representation of those vertices.

You can safely assume the figure to be a representation to understand the procedure. If you are having trouble visualising these vertices try making your own rough figure on paper.


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