9-noded quadrilateral FE mesh

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jtong
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Location: Australia

9-noded quadrilateral FE mesh

Postby jtong » Wed Jul 25, 2012 7:04 pm

I am working with a small 2-D (x-z) finite element code for fluid dynamics modelling over ocean topography on my pc.
(I have full control on output data formats).

I am looking for a plotting package to produce some plots.

The only plots I want to make are the following:
1) vector plots for flow current
2) contour plots for turbulence or fluid density
3) both vector and contour together
and of course there will need to be an outline of the bottom ocean topography.

The finite element mesh I am using consists of 9-noded quadrilaterals (4 nodes at the corners, 4 nodes at the side centerpoints and 1 node in the center).
Sometimes the quadrilaterals are rectangular/square and in some regions they can be squashed so that they resemble a triangle (2 sides becomes linear with each other, but still a "quadrilateral" with 9 nodes).

I have been reading about tecplot and see that basic grids can be handled like the 4 noded quadrilateral.

I am interested to know are 9-noded quadrilaterals as I have described above able to be handled in tecplot?

You help is much appreciated.
Thankyou.

Chris Idso
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Location: Bellevue, WA
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Re: 9-noded quadrilateral FE mesh

Postby Chris Idso » Thu Jul 26, 2012 8:26 am

Hello,

Tecplot can make the plots you want, but it does not handle 9 noded quadrilateral elements. Tecplot understands the following node-based elements:

triangle (2d three nodes)
quadrilateral (2d four nodes)
tetrahedron (3d four nodes)
brick (3d 8 nodes)

It also understands two face-based elements:

polygons (2d)
polyhhedrons (3d)
Chris


Christopher Idso

Tech Support Lead
Tecplot, Inc

jtong
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Posts: 3
Joined: Wed Jul 25, 2012 6:37 am
Location: Australia

Re: 9-noded quadrilateral FE mesh

Postby jtong » Thu Jul 26, 2012 6:34 pm

Thanks Chris.

I just had a look at the dataformat.pdf to try and work out how I would need to organise my input data. My understanding is that I will need to follow the format (eg. velocities and temperature variable):

VARIABLES = "X", "Y", "U", "W", "T"
ZONE NODES=#, ELEMENTS=#, DATAPACKING=POINT, ZONETYPE=FEQUADRILATERAL
# # # # #
# # # # # coordinates and variable values (Part 1)
# # # # #
..............
# # # #
# # # # connectivity of the nodes (Part 2)
# # # #
............

By Using FEQUADRILATERAL, I would be basically splitting my 9-noded element into 4 4-noded elements. So I end up with 4 times as many elements. Is this the easiest way do you think to produce vector/contour plots?

Alternatively, if I used FEPOLYGON, entering all node data exactly as in Part 1 above, but this time for the connectivity (Part 2), only connected the 8 nodes around the element boundary which would give me the correct number of elements (not 4 times)...would this work? The 9th node would be isolated in the center of the element with no connected lines (as it is in the model).

Would the output appearance be different between the 2 methods?

At first glimpse, I don't think cell centered data is for me, as I have to have data at node corners too.....I could be wrong.

Thanks,
Judy.

Chris Idso
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Posts: 249
Joined: Mon Jan 15, 2007 10:07 am
Location: Bellevue, WA
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Re: 9-noded quadrilateral FE mesh

Postby Chris Idso » Fri Aug 10, 2012 1:38 pm

Sounds like you do need your data to be node-centered.

The format you described will work fine for FE Quad elements, which is much easier to do than FE Polygons. It will not work for FE Polygon elements as those are face based, and so have a more complex format, with some extra parameters in the header of the file, and a few more sections below the data itself.

If you were able to define your FE Polygons correctly the resulting plot should look just like the plot you would get with FE Quads.
Chris





Christopher Idso



Tech Support Lead

Tecplot, Inc

Syed Moez
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Joined: Tue Apr 14, 2015 5:32 pm
Location: USA

Re: 9-noded quadrilateral FE mesh

Postby Syed Moez » Tue Apr 14, 2015 6:12 pm

Hi,
I have a similar problem. I am using an FE mesh for eight node quadrilaterals and I don't understand how I can mesh it in Tecplot. i.e. how do I create an eight node quadrilateral in tecplot. Please help!.


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