Geometry Disappearing when Meshing

mmccann · March 6, 2018, 10:13pm

Hello!

I have been trying to do a full car simulation for an FSAE car for a while now. At first I had to fix my geometry, because I had weird surfaces when the file was exported. I have since fixed my geometry, and now when I create the mesh I lose parts of my rear wing, front wind and sidepod end plate. It also looks as if the air guide inside the sidepod has also lost some surfaces.

I have made sure that all of the faces I required in my mesh were selected, and this result still happened.
Why is this happening? / How can I fix it?

Project: https://www.simscale.com/projects/mmccann/full_car_try_1/
Geometry: R6 (Fixed FW Surfaces)
Mesh: Copy of (Fixed FW Surface) Mesh - Changed Symmetry Plane

Geometry after creating the mesh:

Geometry before creating mesh:

Geometry from CAD:

dheiny · March 6, 2018, 10:38pm

Hi @mmccann - I took a quick look, indeed nothing obviously wrong with the geometry. I filed a ticket for the CAD/Mesh team to take a closer look at it. Will get back to you once I know more.

mmccann · March 6, 2018, 10:41pm

@dheiny,

Thank you very much! If there is anything I can do to be of help, please let me know.

mmccann · March 7, 2018, 4:32pm

Good morning @dheiny,

I have tried to make the mesh again with the automesh feature. The same problem occurred. I know you already submitted the ticket, however I’m just trying to provide as much information as possible.

mmccann · March 13, 2018, 10:19pm

Hello @dheiny,

I was wondering if anyone has taken a loot at the ticket? I really need to get this simulation going so I can prepare my design binder for competition. If no one has gotten back about the ticket, is there a chance you could try to take the geometry and make a mesh and see if I was just doing something wrong?

Thank you!

Morgan McCann

jousefm · March 13, 2018, 10:40pm

Hi @mmccann and sorry for the delayed response!

For the geometry you mentioned in the first post it seems that there are some intersections and the geometry is not watertight at all. Has this been fixed somewhere? Makes things definitely harder! @dheiny will get back to you asap!

All the best!

Jousef

mmccann · March 14, 2018, 12:58am

Hello @jousefm,

I think I am confused on the term water tight. How could I turn the geometry into a water tight model?

I understand how to do it for an internal flow, something like if I were analysing an intake. However, for external flow I am confused.

Thank you!

jousefm · March 14, 2018, 5:51am

Hi @mmccann!

You have to close open holes and make sure that there are no gaps that would make the fluid “go inside” the vehicle. You can do that with a CAD software of your choice.

Best,

Jousef

mmccann · March 14, 2018, 4:06pm

Hello @jousefm,

I am confused where I have open spots in the model, in Solidworks the whole model is all solids. I think I may have an issue with how my file is being exported from CAD or imported into SimScale platform. When the model gets imported into SimScale, it adds “faces” for each side, and then turn the model into a hollow model when a mesh is created.

How do I fix this?

Would you like me to share the Solidworks Assembly with you?

Thank you!

Morgan McCann

jousefm · March 14, 2018, 6:57pm

Hi @mmccann!

Although you use solids it can still be that there are holes inside the geometries causing this issue. Just to make clear what watertightness means here a good post by @dheiny: SnappyHexMesh - Watertightness. Make sure that the inside of the geometry can not be “flooded” if you wanna put it like that.

Cheers!

Jousef

mmccann · March 15, 2018, 6:48pm

@jousefm,

Thank you for your quick reply.
That post did help clear that up, however that still doesn’t explain why the geometry is getting “eaten” up when meshed. Unless my material paint could be messing it up?

If I export my model as a different format it will import into SimScale only as “Solid 0” with no faces attached or anything, however if I use an IGES I get faces in SimScale.

jousefm · March 15, 2018, 8:02pm

Hi @mmccann!

The information with the material point was just a side note - this determines if you are performing an external or internal flow analysis. Having a single solid won’t help you much as you will run into trouble with boundary layer creation for your vehicle so splitting the surfaces will be an essential part of the pre-processing.

Maybe some of our @PowerUsers_CFD have some good tips on how to improve your geometry. @pfernandez, any input from you here?

Cheers!

Jousef

pfernandez · March 17, 2018, 9:03am

I managed to mesh and run the case. What I did was download the step geometry and mesh it locally into a STL file that I then uploaded again.

I then ran the case for about 500 iterations in order to check that everything was OK.

You may see the case here: https://www.simscale.com/workbench/?pid=6671105432443116453

Figure 1: automatic STEP to STL conversion.

Figure 2: manual STEP to STL conversion.

The only issue though is that in my case some of the PIDs merged (maybe when importing the CAD due to similar names) and I didn’t realize 'till I was setting up the simulation. But that’s something I could fix easily.

In short: try converting your CAD into STL and upload that instead of a STEP file.

mmccann · March 17, 2018, 1:38pm

@pfernandez,

Thank you for doing that.

I know that when I was trying to upload as a STL, the online platform was never able to process my file. Maybe there is something messed up with my version of Solidworks. I’ll have to try exporting on a school computer. Did you convert it in SimScale or using a CAD program?

jousefm · March 17, 2018, 3:04pm

Thanks a lot for jumping in @pfernandez!

Didn’t you run into issues with the watertightness or did you fix them before conversion? Just wondering as the basic geometry was not closed.

Cheers and thanks!

Jousef

pfernandez · March 17, 2018, 5:02pm

@mmcann @jousefm

Did see any leakage in the file when I did the conversion in a CAD program in my PC.

When uploading the STL to SimScale, make sure that it is in ASCII format an below 300 MB to avoid any issues.

mmccann · March 22, 2018, 4:03am

@pfernandez,

What software did you use to convert the IGES to STL?

I would like to perform a similar simulation/mesh on the car without an aero package, to show how it works.

When I tried, it was definately less than 300 MB however I am not sure of the format. I will have to try again.

Thank you for your help!

pfernandez · March 22, 2018, 9:57pm

Hi @mmccann,

I guess you can use your own CAD software to do the conversion. As per the format, there are to possibilities: ASCII and binary. The former is human readable so to speak, while the latter is binary data only readable by computers. Might be binary is OK; but I usually had less issues with ASCII.

mmccann · March 23, 2018, 5:19pm

@pfernandez,

Thank you!!! I was exporting my STL’s in Binary, switching to ASCII fixed my importing issues. That was one of my issues!

mmccann · March 25, 2018, 9:44pm

@pfernandez,

So it turns out I was actually wrong. That did not fix my issue. I had downloaded your STL and accidentally uploaded that when I was trying to test mine.

Now my problem is how the platform is importing the STL. With your STL I could select individual assemblies (rear wing, front wing…) When I create one the whole assembly turns into one part.

Please see the pictures below. How do I fix this?

Thank you!