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-   -   Volume mesh with layers (http://www.cfd-online.com/Forums/ansa/114410-volume-mesh-layers.html)

AndyZ March 10, 2013 19:18

Volume mesh with layers
 
Hello,
I'm new at using ANSA for CFD meshing. I'm getting a good quality surface mesh for a car model and the road and tunnel walls, but then I'm having some difficulties with the volume mesh.

In the ANSA tutorial for external aero, they are using a structured layers mesh only for the road. Since I'm interested in capturing the air speed gradient at the surface of the car, I assume these layers are also supposed to be generated from the car surface. The problem is that afterwards the VOLUME>DEFINE function doesn't recognize the rest of the tunnel volume (without the car and the newly created layers), why is that? There is an autodetected volume, but when I select it nothing gets highlighted.

Also, once I do the layers operation, the side walls are reported as unmeshed, although I can still see the mesh grid on them.. Is it a problem if they remain like this?

vangelis March 11, 2013 04:18

Hi Andy,

Which ANSA version are you using?

In the external aero tutorial layers are grown from both car wind tunnel road.

Now coming to your exact problem.

When ANSA grows layers it connect to the side mesh of the windtunnel.
To do that it uses ELEMENTs>RELEASE on the four sides where it connects.
By RELEASE the elements are de-associated from the geometry and ANSA
is free to reconstruct the mesh, create the quad imprint of the layers and connected the layers. As the mesh is RELEASED, these Macros become
unmeshed. In order to avoid accidental remeshing (and hence duplicate mesh)
These Macros become also Frozen. Play around with the visibility flag buttons for FE-mod and Macros and you will see what I mean.

Finally about the problem of Volume detection.

Do you have any layer collapsed areas?
Open the property list and use Show Only to see if ANSA has collapsed
some areas from layers.

To perform the DETECT process follow these steps.

Check in the VOLUMEs>LIST what volumes you have.
You should only have one volume for layers in fact.
You can use Show Only on a volume to inspect it.
Delete any unecessary volume.

Press ALL
Ensure Macros and FE-mod mesh flags are active!
In the SETs button if there is a SET called
Do Not include in Detect
Select it and make it Hide.

Now press DETECT.

Does it work?

Best regards

Vangelis

AndyZ March 11, 2013 06:12

Hello,
Thank you for your reply

I am using v.13.2.2

You are right about the layers, I read the tutorial more carefully and now I have the whole volume meshed. One question though : I also had a set with collapsed areas, I put that in hide along with the "do not include....." set, is that ok or should I keep the collapsed set visible?

Thanks again,
Andy

vangelis March 11, 2013 06:36

Hi Andy,

The collapsed areas are marked with duplicate FE-mod shell elements
on top of the original surface mesh of the Macros, on the areas of the problems.
Just before DETECT, these shells must be visible,

The SET "Do not include in Detect" contains the original surface mesh of the
macros from which the layers were grown.
As Now you have the TOP_CAP_Fluid_Layers and the Collapsed Areas FE-mod
shells, these original Macros are set to Hide, so that DETECT can work
without finding duplicate shells.

It is a bit complicated but I hope it is clear

cheers

Vangelis

AndyZ March 11, 2013 12:46

Hey,

Thanks for your help, it's clearer to me know. I'll try to run my FLUENT analysis tonight with this ANSA mesh, hopefully it's good enough.

Volume info is this:
According to FLUENT Skewness
Average TETRA Quality : 0.259 WORST : 0.9922488
0.00 - 0.10: 350161 15.454 %
0.10 - 0.20: 505417 22.306 %
0.20 - 0.30: 572581 25.270 %
0.30 - 0.40: 446563 19.709 %
0.40 - 0.50: 235915 10.412 %
0.50 - 0.60: 115061 5.078 %
0.60 - 0.70: 34922 1.541 %
0.70 - 0.80: 4223 0.186 %
0.80 - 0.90: 946 0.042 %
Worst than 0.90: 44 0.002 %

This is after FIX QUALITY command. Any chance it can be improved?

And one more thing, I don't know of your experiece with FLUENT, but.. I have imported my mesh into FLUENT (new "Mesh" element in the project, import my mesh there, then drag it over the Mesh in the FLUENT case). In the FLUENT setup, I see that my surfaces "road" and "car" are not found in the Boundary Conditions, I can't specify which boundary to use for drag/lift/moment calculation... What am I missing?

Thanks,
Andy

vangelis March 12, 2013 03:04

Hi Andy,

If you do not see all the zones in Fluent it may be that not the whole
model was visible when you output from ANSA.

Go back to ANSA.
Press ALL
Ensure that FE-mod, Macros and Volumes flag are all active.

(I assume that you start ANSA in CFD setup so all quality criteria
are predefined for CFD)
Press VOLUMEs>IMPROVE>FIX QUAL Visible

Check the Volume Stats again, they should be better now.

Finally use Fluent output with everything visible.

Hope this helps

Best regards

Vangelis

AndyZ March 13, 2013 01:06

Hello,


It works, thanks! :)

vangelis March 13, 2013 03:18

You are welcome!

cfdivan August 15, 2013 08:37

Hi all,

I am facing the same problem and I already tried yours sugestion but when I do DETECT i only have fluid_layers. It looks like there is no volume of fluid. Do you have any clue how can I fix this?

Thanks!

vangelis August 19, 2013 03:34

Hi cfdivan,

What message do you get in the text window when you press DETECT?
Have you followed the steps described above:

"The collapsed areas are marked with duplicate FE-mod shell elements
on top of the original surface mesh of the Macros, on the areas of the problems.
Just before DETECT, these shells must be visible,

The SET "Do not include in Detect" contains the original surface mesh of the
macros from which the layers were grown.
As Now you have the TOP_CAP_Fluid_Layers and the Collapsed Areas FE-mod
shells, these original Macros are set to Hide, so that DETECT can work
without finding duplicate shells"

Can you upload an image of the model?

cfdivan August 27, 2013 15:50

Hi Vangelis,

I already tried all the steps but i am still struggling with it. The "BL" mesh is created but by doing autodetec no additional mesh is detected (only "BL" mesh is present). Do you have any clue of what I am doing wrong?

Thank you very much for your help.

http://s14.postimg.org/gu2wyru3h/fluid_layers.jpg

http://s14.postimg.org/rutgq1wyl/flu..._show_only.jpg

http://s17.postimg.org/s019d5yvf/do_..._show_only.jpg

http://s23.postimg.org/sy3a9okxz/Volume_auto_detect.jpg

http://s21.postimg.org/tuevtaw1f/volume_detected.jpg

vangelis August 28, 2013 01:54

Hi cfdivan,

Can you tell me what ANSA reports in the text window at the bottom left
when you press DETECT?
Might it report some duplicate elements?


Also, prior to DETECT can you set in MESH menu
SHADOW OFF
WIRE OFF
BOUNDS ON

so that ANSA displays in red the free edges and in cyan the triple ones?

Can you check if there is a opening in the volume or something like that?

Vangelis

cfdivan September 14, 2013 10:07

Hi Vangelis,

I am so sorry to give you a feedbcak too late. Meanwhile I was away from this project.
I already checked the geometry and there is a very small hole in the geometry. Very likely is what messing all up. I already fixed the problem and I'll give a try again.

Thk u very much for your very usefull help.
Regards,

vangelis September 15, 2013 16:27

you are welcome cfdivan

i am sure it will work now!


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