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-   -   Poitwise and Fluent, non positive elements (http://www.cfd-online.com/Forums/pointwise/81207-poitwise-fluent-non-positive-elements.html)

filipwa October 19, 2010 22:28

Poitwise and Fluent, non positive elements
 
Hi to you all.

Im am trying to learn how to use Pointwise in combination with Fluent. I have worked through all tutorials that comes with Pointwise and have successfully managed to export the mesh, so far so good.

The problems start when i try to read the cas file in Fluent, the grid check tells me that i have non positive elements. So im assuming that something is wrong with my mesh. How should I go about correcting this?

(The mesh i have been playing around with is the "2d airfoil" case which is the first tutorial that comes with Pointwise)

lachie October 20, 2010 20:32

what version of pointwise gridgen are your using?

if your reply me and i didn't know for a long time, please email: lachie.zhu@gmail.com and let me know.

filipwa October 20, 2010 23:42

Quote:

Originally Posted by lachie (Post 280057)
what version of pointwise gridgen are your using?

if your reply me and i didn't know for a long time, please email: lachie.zhu@gmail.com and let me know.

i am using Pointwise version 16.03R1, 64-bit version.

lachie October 21, 2010 00:57

Quote:

Originally Posted by filipwa (Post 280071)
i am using Pointwise version 16.03R1, 64-bit version.

that's it. my version is also V16.02R3, i have be confused by this problem for a long time. then i solved it.
if you generate a 2D grid, the software seems more tend to give you a negative area than 3D.
when you fish the grid, choose all the domain, click the "edit" on the Menu Bars,choose the "orient", click "I" or "J", then "apply". done
i am a freshbird, i don't know why the problem can be solved if i do so, certainly, the grid must not be too bad.
i also want the expert of pointwise to give me more details about this.
hope helps.

filipwa October 21, 2010 04:13

Quote:

Originally Posted by lachie (Post 280076)
that's it. my version is also V16.02R3, i have be confused by this problem for a long time. then i solved it.
if you generate a 2D grid, the software seems more tend to give you a negative area than 3D.
when you fish the grid, choose all the domain, click the "edit" on the Menu Bars,choose the "orient", click "I" or "J", then "apply". done
i am a freshbird, i don't know why the problem can be solved if i do so, certainly, the grid must not be too bad.
i also want the expert of pointwise to give me more details about this.
hope helps.

that worked perfectly! thanks a lot!

would be good to know the reason for this though :)

ganesh October 21, 2010 05:07

Dear Friends,

I had faced the same problem and solved it in a similar way, what I find by comparing the .cas files from Gridgen and that for the same mesh from GAMBIT are that the normals are differently oriented. The flip that was suggested essentially gets the .cas file from Pointwise to be consistent to what GAMBIT would have provided.

Regards,

Ganesh

jingmy October 27, 2010 09:44

i have the same problem in 2d case.and now i know how to fix it. all my thanks:D

lachie October 29, 2010 03:01

1 Attachment(s)
hi guys:
i think i have made more clear of this problem. i found an official explanation in the user manual of the Pointwise V 16.02.
On the page 4.34, you can see
"For 2D and 3D structured domains and blocks, the orientation can be changed with the commands in the Reverse and/or Swap frames. NOTE THAT THE GOAL FOR orienting structured domains and blocks for most cases is to make them RIGHT-HANDED. For 2D and 3D unstructured domains and blocks, the Reverse Normal command will flip the domains or block face normals in the opposite direction. For an unstructured block, it is desirable for the normals to point toward the interior of the block. "

So, if you build a multi block like me(2D), as you see in the picture, what you should do is to make ALL the domain RIGHT-HANDED. For more details, you can see the manual yourselves.:)

filipwa November 1, 2010 05:04

Quote:

Originally Posted by lachie (Post 281298)
hi guys:
i think i have made more clear of this problem. i found an official explanation in the user manual of the Pointwise V 16.02.
On the page 4.34, you can see
"For 2D and 3D structured domains and blocks, the orientation can be changed with the commands in the Reverse and/or Swap frames. NOTE THAT THE GOAL FOR orienting structured domains and blocks for most cases is to make them RIGHT-HANDED. For 2D and 3D unstructured domains and blocks, the Reverse Normal command will flip the domains or block face normals in the opposite direction. For an unstructured block, it is desirable for the normals to point toward the interior of the block. "

So, if you build a multi block like me(2D), as you see in the picture, what you should do is to make ALL the domain RIGHT-HANDED. For more details, you can see the manual yourselves.:)

Your "trick" worked well when i used the Extrude - Normal method of generating the mesh. However, dividing the grid in to different domains, as you have done in the picture above, still results in the same error.
How do you actually see if the grid is RIGHT HANDED? When i click the Reverse - Normal button there are now arrows or anything indicating in which direction the normals are oriented.

lachie November 1, 2010 10:37

Quote:

Originally Posted by filipwa (Post 281613)
Your "trick" worked well when i used the Extrude - Normal method of generating the mesh. However, dividing the grid in to different domains, as you have done in the picture above, still results in the same error.
How do you actually see if the grid is RIGHT HANDED? When i click the Reverse - Normal button there are now arrows or anything indicating in which direction the normals are oriented.

hi Filip:
first, if you do not know what is RIGHT HANDED exactly, you should review it in the math book.
second, when you in the ORIENT label of 2D STRUCTURED grid, you will see the domain you have choosed has connectors of two different colord, one stands for I, and the other J. what you should do is to make the position relationship between I and J like the one between X and Y in the globe coordinates. (I = X, J = Y)
In the multi block strctured grid generation this makes sense, and in the unstuctured one it can be more easier.
holp helps.

filipwa November 2, 2010 12:40

Quote:

Originally Posted by lachie (Post 281662)
hi Filip:
first, if you do not know what is RIGHT HANDED exactly, you should review it in the math book.
second, when you in the ORIENT label of 2D STRUCTURED grid, you will see the domain you have choosed has connectors of two different colord, one stands for I, and the other J. what you should do is to make the position relationship between I and J like the one between X and Y in the globe coordinates. (I = X, J = Y)
In the multi block strctured grid generation this makes sense, and in the unstuctured one it can be more easier.
holp helps.

Right and left haded normals just give the direction the normal is oriented in. However, i dont remember which is which right now but im pretty sure wikipedia has the answer... :) What i could not understand though was how it is indicated in the pointwise, but after posting i realized that changing the view the direction of the vector is seen. Was scratching my head way too long trying to figure out what those red dots were.. Changing view put an end to my queries...


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