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Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

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Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by Rouven Mayer at June 25. 2019

Hi!

I'd like to generate a structured mesh around a prolate spheroid (6:1) to run flow simulations with OpenFoam. Running some Salome tutorials and getting familiar with the geometry and the mesh module, I've been able to mesh all the edges and faces. However, the "Extrusion 3D" algorithm produces an error (OCC exception. Standard_NoSuchObject: NCollection_DataMap::Find) when I try to mesh the volume.

 

 

The structure of the mesh:

Due to symmetry reasons, I consider only half of the prolate spheroid. The farfield is a sphere. Using “Partition”, I’ve divided the sphere into 4 spherical pieces.

 

Some more pictures of the mesh:

https://ibb.co/nbqcbSc

https://ibb.co/cFLvxFm

https://ibb.co/hWKpHF7

https://ibb.co/chgh3ZR

https://ibb.co/stXhyXm

 

https://ibb.co/RNs80dS

 

The odd thing is: when I build up the geometry with only 1/8 of the sphere (one single spherical piece) I’m able to generate a volume mesh with the “Extrusion 3D” algorithm.

Can anyone help?

Thank you very much in advance...!

Attachments

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by Saint Michael at June 26. 2019

Hi

Having consrtuced 3D mesh on 1/8 of your geometry, you can get mesh of the whole geometry using Transformation > Symmetry operation.

St.Michael

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by Rouven Mayer at June 27. 2019
Thank you very much for the reply!
 
Indeed, I've been able to construct the whole mesh by using the transformation option. However, the prolate spheroid is only the first step and for the future, it might most probably not be feasible to use the transformation option.
 
As the case of the prolate spheroid is really simple, I'd like to understand what is the issue because I'm pretty sure that it is a user's problem and not a software issue...

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by Saint Michael at June 27. 2019

Can you share your case with the prolate spheroi (sudy file or Python dump file)?

St.Michael

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by Rouven Mayer at June 28. 2019

Of course! Here's the .hdf file of the case...

 

https://gofile.io/?c=IvZGpK

 

Everything works (all submeshes etc.) except of the final generation of the volume grid.

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by SMESH expert at July 01. 2019

Hello

The issue is connected to some geometry inconsistency due to STEP import. The issue disappears if I apply Partition to your geometry and make a mesh of a Partition result.

I have added a protection for such a case (commit https://git.salome-platform.org/gitweb/?p=modules/smesh.git;a=commit;h=b718a7cc45afdc2f1e8d06862f1e043402d2ea19)

Best regards

Edward

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by Rouven Mayer at July 02. 2019

Hi Edward!

Thank you very much for your comment!

I had indeed some problems generating the geometry. Especially the partition sometimes failed, meaning that after partitioning some faces were missing (?!). I will outline shortly what I did and I would highly appreciate your comments on my approach…

  1. Generate a sphere of radius 1
  2. Scale the sphere by x:y:z = 6:1:1 to generate the prolate spheroid
  3. Generate a sphere of radius 150 (for the farfield)
  4. Cut out the prolate spheroid from the farfield sphere
  5. Cut off half of the resulting sphere (by using a large block) to consider only one half of the problem (for symmetry reasons)
  6. Generate two disks and use these disks to partition the half sphere into 4 spherical pieces
  7. Explode the resulting geometry to get all faces and edges

While the explode function works perfectly fine for the faces, it seems to generate more edges than necessary. In fact, some edges are generated which seem not to exist (meaning they are not visible even if I use ‘show only’ and ‘fit all’). Is that a bug or a feature?

Due to this issue, I exported the geometry to a STEP file and then imported it again. Don’t know if that makes sense but obviously it didn’t solve the problem…

However, in the meantime I think I found the problem: the OCC error seems to come from a geometric progression I applied to all the internal edges to generate a proper boundary layer. With this hypothesis, I’m not able to generate the volume mesh (OCC exception error). However, when I change the hypothesis to e.g. a scaled distribution, everything works perfectly fine. I read the user guide section about the geometric progression and searched this forum but didn’t come up with a satisfying answer for this issue. Do you have any idea, why geometric progression does not work? For me it is the most convenient way to define a boundary layer (define first cell height, e.g. 1e-5 and growth ration, e.g. 1.2)…

 

case-file: https://gofile.io/?c=kuGspg

picture of the case: https://ibb.co/bBRSFT3 

 

Best regards,

Rouven

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by SMESH expert at July 10. 2019

Hello Rouven,

About geometry construction: I'd use a plane instead of disk to partition the half sphere into 4 spherical pieces, to be sure.

Indeed, Geometric progression causes a problem. I'll check it later. Thank you for reporting this issue.

Best regards

Edward

 

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by Edward AGAPOV at August 05. 2019

Hello Rouven,

Geometric progression issue is solved with the following commit

https://git.salome-platform.org/gitweb/?p=modules/smesh.git;a=commit;h=0146a69d8258d1264247a2970627f89e514fc6f6

Best regards

Edward

Re: Structured grid for prolate spheroid: Extrusion 3D causes OCC exception error

Posted by Rouven Mayer at August 13. 2019

Hello Edward,

thank you very much!

Best regards,

Rouven

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