Overlaying Mesh for Complex Urban Geometries


#1

Hi everyone!

Back again with another annoying problem. I’ve been attempting to mesh a large complex urban environment and it has been relatively problem free with the exception of this problem. The project link is here. The mesh basically creates strange deformations as if it is overlaying each other causing the cells to be very skewed and when a simulation is attempted, instability will occur resulting eventually in an error. Below are examples of where these occur, but they do occur everywhere within the geometry.

Sample Area Overview 1

Sample Area 1 Zoom

Sample Area Overview 2

Sample Area 2 Zoom

Normally if I were out of ideas I would re-mesh it while tuning the refinements to get it right but if you look into the project itself it is very costly to always re-mesh such a geometry, hence any help would be much appreciated!

Cheers.

Regards,
Barry


#2

Hi @Get_Barried,

can you share the project / the originating CAD file?

Best,

David


#3

Hi David!

Sorry I forgot to insert the link into the post. It is up now.

Thank you!

Regards,
Barry


#4

Hi everyone,

I’ve discovered something a little peculiar in that geometries on the lower ground do not have this meshing issue as you can see in the figures below.

Area of interest with blue being the lower ground and not having the meshing issues, red vice versa

Close up of mesh, blue being lower ground and not having the meshing issues, red vice versa

I’ve tried removing the surface refinement at the floor containing the elevated ground where the problematic area is along with increasing surface refinement of the individual buildings but the problem still persists.

Cheers.

Regards,
Barry


#5

Hi everyone,

Another peculiar problem that might actually be the cause of the issue. As seen in the two figures taken from identical angles, the floor elevation consisting of a sloped gradient has disappeared in the meshing phase.

Original Model before meshing

After meshing (Red is the elevated flat floor)

Any ideas on what might be causing the floor to disappear? I suspect once this is fixed, the meshing issues will be resolved.

Cheers.

Regards,
Barry


Error without explanation (simulation)
#6

Hi Barry,

unfortunately never had this issue before. Darren (@1318980), did you encounter such issues before?

Cheers!

Jousef


#7

Hi, @Get_Barried and @jousefm,

I have had this issue when both an internal and an external mesh is created on a face. Maybe it would be worth creating a solid geometry to ensure this doesn’t happen, for me the geometry had holes, but if the bounding box doesn’t properly intersect your floor, this might also cause it.

Hope this helps,
Darren


#8

Hi Darren & Jousef,

The geometry is open due to the nature of the case but it should work. Good suggestion on making the section giving problems a solid I will try to see if i can do that. Making the geometry entirely solid is another issue all together, any suggestions on how to do so? Do i need to enclose the bottom surface first?

The geometry also has lower floors at the same level or even lower than that of the elevated/sloped floors and it didn’t have problems so it is rather strange.

Cheers everyone!

Regards,
Barry


#9

Hi Barry,

Yes, what I would do is bring the model into CAD maybe as an STL, convert it to faces, fill the bottom and hopefully it will be enclosed and can, therefore, be converted to a solid. If some of the floors are level with the bottom maybe extend the bottom to ensure that a solid floor is present. If you cannot enclose, you might need to do some CAD cleanup.

I presume you have tried just raising the bottom of the bounding box a bit and meshing?

Kind regards,
Darren


#10

Hi Darren,

Thanks for the great input as always. I’m currently attempting to do as you suggested and its meshing at the moment so we’ll see how it goes.

Accuracy is an important factor so I aim to keep the geometry as original as possible since this is a validation case. So no I have not slightly raised the floor bounding box, but that is an excellent suggestion to raise it just enough to see what happens to the mesh. Will attempt it if the previous suggestion dosen’t work.

Thanks again! Will update once its done.

Cheers Darren & @jousefm!

Regards,
Barry

Edit:
The rough run is done and apparently it seems like the issues are not there anymore! Will re-run this geometry with the full details to see if it actually holds up.

Edit 2:
Simulation does hold up! Thanks Darren for the solutions!


#11

Hi Barry!

Saw that you fixed the issue. Did you just use a CAD tool for that ?

Cheers!

Jousef


#12

Hey @jousefm!

Yup! Used OnShape to do it! The fill function is brilliant and as long as you have a proper clean geometry that is made up of solids (at least at the critical areas) then the meshing process should be relatively painless.

Cheers!

Regards,
Barry


#13

Awesome Barry!

I think that’s a nice tip for other users who are struggling with problems like these! Good tip from Darren here!

Cheers!

Jousef