Problems with loading my Discovery Mesh into Fluent

[thore.schmid]

Hey, 

I'm working on a project where I need to simulate the air flow in bronchia. I have created a suitable 3D model in a previous software, here I have already labeled all the significant surfaces like inlet, outlets and the wall. I now wnat to load the model into discovery to create a volume body and optimize the STL file. The problems I'm facing are the following: 

1) If I optimize my mesh in Discovery it seems like a second surface is created over the original STL which leads to problems in the following software (Ansys Fluent)

2) All the tutorials I have watched have a 3D model which is not seperated into tiny STL triangles but is rather consisting of 'normal' surfaces which is also a problem I can't seem to fix, do I just need to tweak my view mode or is there indeed no continous surface? 

3) I feel like because of the afore mentioned problems I cannot load my STL from Discovery to Fluent properly, I always get errors when trying to do the capping step in the Fault Tolerant workflow as there seems to be a problem with the outlines of my defined outlets/inlets 

I don't know if this is enough information to go on but I would appreciate some help and will provide further information if necessary. 

Kind regards

Schmid

[NickFL]

I have not had much experience with STLs in Discovery (I still use SpaceClaim to work with them). You mention that you create labels in another software, those are not saved in the STL, correct? 

    0. Have you tried ANSYS Fluent Meshing? You can read in the STL and remesh the surface directly in Fluent. Here is a an example from an ANSYS channel partner that may be useful https://www.leapaust.com.au/blog/cfd/how-to-shrink-wrap-a-biomedical-stl-file-in-fluent-meshing/

1. To your point 1, the STL surface is treated like a CAD surface. When creating a mesh a volume is then created not using this, but remeshing the CAD surface and using that for your Volume Mesh. However when you export this to Fluent, Fluent can also read the STL mesh (see above), therefore you can suppress the STL-surface in Discovery so it does not get sent. 
2. You can create smooth CAD surfaces from the STL by using the skin command. The user peteroznewman has put together some great videos on Youtube. Check them out. This one may be of particular interest: https://www.youtube.com/watch?v=Gj3bTd0aN8I
3. If you using the FTM in Fluent, is the reason why you are using Discovery is to clear up any errors in the STL? The first link above shows the basic process going directly from STL to Fluent Meshing and using the shrinkwrap tool in Fluent Meshing. This is similar to the tools that you are likely using in Discovery. It may be easier to not put in an intermediate step (Discovery), I do not know how "dirty" your geometry is.

There are also some free non-ANSYS products that may be useful. One is FEBioStudio (https://youtu.be/Xh87eOrC8mU?feature=shared) which was created by the National Institute of Health (it may be without further developments because--me trying to keep in apolitical--the current US Adminstration).

STL files are difficult to work with, it is the nature of the beast. But without working with your geometry and knowing your reasons for simulation, it is difficult to say what the best approach is. You mentioned that you want to "optimize the STL". Are you trying to optimize the outer surface and then save this as an STL? That bit is unclear. 

 

[Rob]

Thanks Nick, and thanks for keeping it non-political! 

If you're extracting the geometry from scan data have a look in that tool for options. Both Materialise Magics and Synopsys Simpleware (Ansys are now part of Synopsys) are often available to the scanner team and can create surface/volume meshes for Fluent.