Water Tight unv Mesh to Volume Mesh

swaraj

I have been searching ways to create volume Mesh from Stl Surface Mesh. I tried to convert stl mesh to solid using freecad but still the exported CAD model contains only shell. How to convert surface mesh to volume mesh.

disla

You can mesh a stl surface mesh to volumetric mesh directly from Mecway with the "auto mesh 3D" tool.
You need a water tight surface.
Give a try with the attached one.

To be sure your volume is not empty I recomend to checq with the Mecway cutting tool.

swaraj

Hey @disla,
I tried that option but Mecway failed to import it without error message, so i converted stl mesh to .unv and i got an error, attached is the image. I am also attaching my .stl hollow file, in case you find whats wrong with it.

swaraj

Hey @disla
I repaired some errors in meshlab and imported the new stl file into mecway but it gives the same error as before. Attached is the new stl file

disla

ERROR: TRIG 27982 has 5 neighbours!!!!
ERROR: TRIG 29503 has 2 neighbours!!!!
ERROR: TRIG 29512 has 5 neighbours!!!!
ERROR: TRIG 29515 has 2 neighbours!!!!
ERROR: TRIG 29516 has 2 neighbours!!!!
ERROR: TRIG 29519 has 2 neighbours!!!!
ERROR: ++++++++++++++++++++

ERROR: 8 wrong oriented neighbourtriangles found!


Netgen has an Stl Doctor.
https://ngsolve.org/files/windows/

Hope it helps.

Victor

Since this is so thin, I think you should extrude the old surface mesh (Mesh tools -> Extrude) instead of using Automesh to create a volume mesh. By extruding, you'll get prism elements which are a little better than tetrahedra from Automesh 3D.

This STL file isn't watertight, at least not after importing. That will prevent it from meshing. You can find the faults with Tools -> Labs -> Find non-manifold shells which selects the bad edges. If the Labs menu isn't there, turn it on with Tools -> Options -> General -> Labs.

swaraj

Hey,
Yeah I fixed the stl file and it got meshed, during solving elements got converted to C3D6L.
On solving i got this error:
*ERROR in cascade: zero coefficient on the
dependent side of an equation
dependent node: 135750 direction: 3
I am attaching my limil file. The error was shown in the node having both fixed constraint and in master surface of contact

Victor

The problem is in the the teeth part and their fixed support, but not the contact. I'm a bit surprised at that and it even happens when I delete the entire mesh except for a single element. But some elements are OK even though the look just as reasonable.

It avoids that error if you replace fixed support with 3 displacement constraints (x,y, and z). That might be the way to go, but it's still strange why it didn't work. I'll have to investigate that.

swaraj

Hey,
3D automesh problem started in another stl. I cleaned the stl file. I am attaching that stl file. Can someone tell me whats exactly wrong with it?

Victor

I didn't have a problem meshing that with the default settings. Though with quadratic elements, turning off Fit midside nodes to geometry prevents some badly shaped elements appearing.

swaraj

It didnt work in my system. Ngmesh stopped working. Can you send me the 3D mesh of the sent stl file

Victor

It turns out that it fails if you open the file as millimeters but works OK as meters! That's pretty surprising. It seems like Netgen prefers bigger coordinate values (60 mm is sent to Netgen as 0.06).

Here's the mesh I made anyway - you'll have to scale it by 1/1000 if it should have been mm.

NARAIN

Sir, the problem took placed in my model too. How to do I scale to 1/1000 sir ?

Victor

If you're opening a .stl file, you can choose units when you open the file and that will scale it.

If it's already in Mecway, ensure no nodes, faces or element are selected, then use Mesh tools -> Scale to scale it.

NARAIN

Sir, but when i import the STL file in mm means, the mechanical property shifts to shell and membrane module and not able to mesh.
while importing the STL file in meters means, i am able to mesh and simulate..

Now I need to scale the imported STL file sir..

Victor

I see, sorry about this inability to mesh small-scale meshes. You'll have to scale it up using Mesh tools -> Scale before meshing. You can then scale it back to the correct size afterwards.

NARAIN

ok sir, i will look into it...

NARAIN

sir, i scaled the STL file which is imported in millimeters to 1000 times in all axis, and then i meshed it. The mesh got completed. And then, i scaled down the developed mesh to the original size by 1/1000 times in all axis. At that time, the mesh disappears and it states an error "The shape is too badly developed which is marked in X".....

disla

i scaled down the developed mesh

¿Are you sure your selected all the nodes and not surfaces or maybe only the visible surface nodes?

You can go to Edit--> Select all (Be sure you are in the nodes selection option.

NARAIN

ok sir, i will check and let u know

NARAIN

NO SIR, THEN ALSO IT DISAPPEARS WHILE SCALING IN A REDUCTION RATIO

NARAIN

WARNING: File has normal vectors which differ extremly from geometry->correct with stldoctor!!!

DURING VOLUME MESHING

WHAT SHOULD I DO SIR ?

NARAIN

PLEASE LET ME THE PROCEDURE FOR MESHING THE STL FILE SIR

Victor

All I can think of is either you scaled only some of the nodes as @disla suggested or scaled them to 0 in at least on dimension. Could you post the model or email it to me?

NARAIN

your email id sir ?

NARAIN

if possible let me know the procedure for meshing stl file sir ?

Victor

My email is the one in the top-right corner of the page

It sounds like you've already used the procedure for meshing an STL file in the normal case where it works correctly - File -> Open then Mesh tools -> Automesh 3D.

NARAIN

SENT THE MAIL SIR...

NARAIN

Sir, while meshing the stl file, i am not able to choose the type of mesher

disla

Manual page 34.

5.4 Gmsh


https://gmsh.info/bin/Windows/gmsh-4.11.1-Windows64.zip

NARAIN

ok mam, I will look into it.