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Solid HEX meshing

Hi All,

I am not very experienced in 3D meshes so please correct me if I am wrong.

Last time I met some problem with HEX mesh generation, I had to mesh quite simple object which was prismatic extusion but with holes drilled in direction perpendicular to the extrusion axis.

Is there any other way of meshing this than cutting the solid into prismatic solids and then mesh-mating them to get nice HEX mesh? Of course for the example is extremly easy to obtain good quality mesh. I just try to figure out easier approach for more complex geometries.

 

I work on NX 9.
See attached example.

Thanks ! Smiley Happy

4 REPLIES

Re: Solid HEX meshing

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Dear Tomek,

My suggestion is first to use command DIVIDE FACE to control the quality of the mesh around the holes using a 2-D SEED mesh, you need to set regular regions. You can do it in the IDEALIZED environment, OK?. (I run NX V10 but is valid for NX V9).

 

divide-face.png

 

Next use command SPLIT BODY to have at the end three bodies like in the picture (using option, for instance, "by plane"):

  • The key next is to perform the MESH MATING command to connect the three separated solid bodies and their associated 3-D mesh. You can activate this effect either in the SPLIT BODY command in the IDEALIZED environment, or later in the FEM environment, I prefer the last one.
  • Next mesh the surfaces around the holes using command 2D MAPPED MESH, this command is critical to create an structured mesh with exceptionally quality on faces of the solid body. Here you will need to learn how to play with DEFINE CORNERS in order to create good quality QUAD mesh in faces with "more than 4 edges", give it a try, OK?. Also, do not forgot to set OFF the option "EXPORT MESH TO SOLVER" in the 2D Mapped mesh command, please note this is a 2-D SEED mesh to guide the 3-D solid HEX mesh.

2d-seed-mesh.png

 

Next use command "3D SWEPT MESH", but with the option UNTIL TARGET. The step done previously using MESH MATING is critical to run correctly everything, this way NX HEX mesher knows that all solids are connected, and the mesh sizing will be the same.

  • Select the top 14 surfaces for the SOURCE.
  • Select the ONE surface in the bottom for the TARGET.
  • You will see that NX mesh the two bodies with holes at the same time.
  • Repeated for the other body

And you will arrive to a perfect mesh, with excellent quality and very small size, OK?. Enjoy!!.

 

hex-mesh.png

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

Re: Solid HEX meshing

Siemens Phenom Siemens Phenom
Siemens Phenom

That's a great answer from Blas. My only additional comment is that this should work with 2 solid bodies. The 2 bodies containing the holes can be combined into a single body. NX supports multiple faces defining a wall along the swept direction.

 

Regards,

Mark

 

 

Mark Lamping

Simulation Product Management

Simulation and Test Solutions

 

Siemens Industry Sector

Siemens Product Lifecycle Management Software Inc.

 

mark.lamping@siemens.com

www.siemens.com/plm

Re: Solid HEX meshing

Thanks Blas_Molero,

 

This is all true what you just wrote, however I just wanted to avoid cutting the master body into separate prismatic bodies. This solution you just presented is trully great but for more complex models (with many edge blends) is useless, because it requires huge number of separate bodies and sometimes it is just practically not doable.

As I can see below, methode of cuttitng bodies into sweepable sections was present in NX 7.5 and didn't it change since that moment ?

PS: is is available in NX 9 to check before, whether hex mesh is doable for particular body as it is shown in link below ?

 

NX 7.5 HEX Meshing

 

Thanks ! Smiley Happy

Re: Solid HEX meshing

Siemens Phenom Siemens Phenom
Siemens Phenom

The check for sweepable bodies shown in the video still exists in the product. It is available in the Split Body command while in Advanced Simulation.

 

SplitBodySimulationSettings.png

 

The check is fairly basic. It will try to find a source/target face pair, then check to see that all other faces are 4 sided in form (i.e. mapped meshable) to satisfy meshing of the swept walls. 

 

You are correct that swept meshing has not changed much since NX 7.5. Since then, we added the ability to sweep between faces from different bodies. In NX 10 we added mesh recipe support for sweep between meshes, so that they update as geometry and meshes update. The original version of sweep between produced an FE based mesh with no update ability.

 

Regards,

Mark