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Fallback tessellation for CAD

6 REPLIES 6
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Message 1 of 7
xusho
375 Views, 6 Replies

Fallback tessellation for CAD

When meshing CAD models, we may see this message in mesh log:

 

First attempt:
Encountered problem when meshing face 130.
Second attempt:

Trying to recover from previous error(s).
Retrying the mesh process using a fallback tessellation method.
Mesh density defined on faces will not be used by this approach.

 

For the "First attempt", we try to generate mesh by a normal algorithm for CAD models.

This process may fail when CAD model has defects. If it cannot be meshed by this step, we will try "Second attempt".

 

For the "Second attempt", we convert the CAD model into STL and generate mesh by a simple tesselation plus remesh.

Because STL models are not very good, the geenrated mesh are not ideal.

 

The reason we provide this result is it can be used as a clue to find defects based on mesh. 

We would not suggest to run analyses with this fallback mesh. Not worth to repair this mesh.

 

Instead, it is suggested to fix the CAD model and generate mesh again, until "Second attempt" does not appear.

 

Shoudong Xu

Moldflow Meshing Team

 

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com
6 REPLIES 6
Message 2 of 7
sabarinathan1021
in reply to: xusho

Hello Shoudong Xu,

 

Thank you for the info,

 

Yes fallback tessellation method wont create a satisfactory quality mesh,

Always do meshing in Moldflow for a solid parts which doesnt have any surface defects or Try using a third party softwares for better mesh creating.

 

 

Regards
Sabarinathan. S
Core Engineering Specialist - Plastic, Auburn HIlls, USA
eMail : sabi1021@gmail.com
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Message 3 of 7
harald_goetz
in reply to: xusho

Regarding Fallback Tesselation:

This happens also with CAD Models that seemed to be clean.

 

1st I try to analyse and repair the geometry in CAD

2nd I try to mesh external

3rd - mesh the geometrie as STL external, even the good old Autocad Mechanical has some nice options.

 

The 3rd points opens the question why the Fallback Tesselation is so coarse? This is for my feeling the biggest issue with it.

Why not offering an option if Fallback Tesselation takes place?

 

Regards

Harald

Message 4 of 7
xusho
in reply to: harald_goetz

Hi Harald,

 

Thanks for your feedbacks.

Could you please provide more details:

 

RE: "Why not offering an option if Fallback Tesselation takes place?"

What option do you expect?

Do you want an option on UI, so that you can choose to use fallback or skip it?

 

RE: "why the Fallback Tesselation is so coarse?"

Did you try to change global edge length?

 

In general, it is recommended to fix CAD models when fallback happens. You can use the fallback mesh as a clue to find where the problem is.

Also, you can use Cad Dr. to check you model.

 

Alternatively, you can send your models to me. I will keep them confidential. Feel free to contact me.

 

Shoudong Xu

Moldflow Meshing

Shoudong.Xu@autodesk.com

 

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com
Message 5 of 7
harald_goetz
in reply to: xusho

Shoudong,

I might expect something like a stop:

"Now Fallbacktesselation takes place...- what paramters for meshing would you like (i.e. coarse, middle, fine or parameters like in the meshing dialog)

 

So far I didn´t retry with other global length when it came to Fallbacktesselation, but I´ll look into that. Thanks for pointing that out.

I really appreciate what you share about meshing in Moldflow.

 

Why I mention the STL mesh option?

I´m also a user of Cadmould, which converts every mesh or CAD Model to STL then mesh it internally (very similar to Dual Domain in Moldflow, but different anyway).

Cadmould often meshes CAD geometry that shows problems in Moldflow.

That doens´t mean it´s good or better, just more "tolerant" it seems.

 

I find myself often using external mesher, but I´m not sure what do I have to consider with these.

Like:

- Geoemtry of tris, where I choose equilateral tris over rectangular ones.

- Avoiding "patterns" - but how? Usually patterns are what makes a mesher good, right?

 

So how compare external meshes to moldflow internal ones (for 3D meshes only) in regard to precison, warp result and calculation speed as well as necessary "repair" work.

Another issue: When transfering fiber orientation and you have used the Skin mesh from FEM you´ll have the exact same space for mapping!

 

So what are the advantages on the moldflow meshing side?

- It´s already there, no extra cost

- It´s better suited to the needs of the MF simulation purpose(?)

- It´s the only way for DD meshing(?)

 

Do you have more insights here for me?

 

Best regards

Harald

Message 6 of 7
xusho
in reply to: harald_goetz

Hi Harald,

 

Thanks for the information.

 

RE:  "advantages on the moldflow meshing"

We apply imprinting on surface meshes, so that nodes/triangles are aligned on opposite sides of the same body. This is important for Dual Domain analysis.

 

You can use other products to create DD meshes. But just be aware that surface matching can not be garantteed in geenral.

 

 

RE: " STL mesh option"

When CAD meshing fails, I would suggest to fix CAD model, instead of meshing it as STL.

STL is not ideal. 

 

Shoudong

Moldflow Meshing

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com
Message 7 of 7
xusho
in reply to: harald_goetz

(Continued:)

 

RE: " coarse, middle, fine"

It is NOT recommended to use the fallback mesh for analysis, even if mesh density is fine.

Instead, you can use the fallback mesh as a clue to find problems on CAD model.

 

 

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com

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