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harman79 November 30, 2009 05:46

3D Meshing Discontinous Shapes
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Hi guys,

I am trying to mesh the geometry included in the picture below. This is the diverging part of a nozzle, which then ends up onto a larger cylinder. The black coloured face on which the "cone" is attached is a wall. The intersection is where the air flows..

My problem is that when I create the ogrid I get a thin diamond shaped block at the interface of the cone-cylinder.. The resulting cells in this region are of zero quality as they are compressed to virtually no width.. I've tried projecting the vertices on the appropriate face or merging the diamond block with the big cylinder block but no luck...

Please shed some light.. Is my ogrid approach correct or do I require a different strategy?

Thanks for your time,

PSYMN December 12, 2009 23:52

Where do you want the OGrid to go? I am not sure what you did here, but I know what you should do.

I can do it in a couple minutes for you if you want to send me the model.

But I will try to describe the process in words...

1) Start with one big rectangle... The initial block.

2) DO an OGrid first. (There are two main uses for OGrid, you need it at the end for boundary layer, but you can also use an OGrid early for capturing topology. Cylindrical models have a basic OGrid topology, so start with the OGrid.

3) Rescale the OGrid so that the box fits inside the circle on the small end of your model. This will be your core.

4) Now split (across x) to separate the cylinder from the cone.

5) Associate the edges on the outside of the cylinder with the curves. If you associate while the model is simpler, everything is simpler.

6) At the middle index (Between the cylinder and the cone), split the OGrid index.

7) Associate these new edges with the curves at the ends of the cone.

8) Delete the 4 Ogrid blocks outside of the cone. (Not permanently, we really just want to send these to the VORFN region)
Tada. At this point, you could be happy and done. Your mesh follows the walls of the model and you can adjust your mesh distribution to suite your needs… You may also want to widen the core at the opening of the cylinder in order to reduce the bunching. However, if the step down were a wall instead of an opening, you may want to add the second type of OGrid…

9) Go to OGrid and Select all the blocks in the model. For Faces, select all the opening faces. Apply.

That’s it.

Best regards,


harman79 December 14, 2009 03:04


thanks a lot for describing the correct process so comprehensively...

I managed to mesh the model by breaking it in parts and then merging the meshes but as I am still in the learning process I understand that your approach is the most appropriate and I will try it ASAP.

very much appreciated,

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