3D meshing with tetrahedrons

Hey, thanks for reading.

I am trying to mesh a closed brep volume with tetrahedrons, for the purpose of finite element analysis.

Two options I thought of were,

1) meshing it in Grasshopper. Though I can't find a plugin that does it. Meshedit says it offers volume meshing but I can't seem to find the component that does that.

2) meshing it outside with for example gmsh. Problem is, once I export it (as iges, or step) the geometry is interpreted as a polysurface, and not a solid. So 2D meshing works but there is no actual volume.

Anyone else had the same issue? or have solutions for it?

Thanks a bunch,

Tim

Replies to This Discussion

Permalink Reply by Tim Chen on November 12, 2014 at 8:40am

Sorry for bumping my own post.

I managed to mesh the geometries externally with Gmsh (through a cmd call in rhino python). Though I am still at a loss for finding a component that meshes 3d breps within grasshopper.

I am looking for a "simply" Delaunay triangulation that goes from the surface mesh into the 3d mesh.

Any ideas would be greatly appreciated.

Tim

Permalink Reply by djordje on November 12, 2014 at 2:44pm

Hi Tim.

Such grasshopper component does not exist, at least not currently. It would have to be custom written.
What you have read about Mesh Edit is that it offers mesh volume analysis (meaning: calculating mesh volume and mesh centroid) not 3d meshing.

Permalink Reply by Tim Chen on November 12, 2014 at 3:45pm

Thanks for clearing that up! Also good to know that it doesn't exist.

Permalink Reply by Arend on November 12, 2014 at 1:45pm

any example of what you need? Is it similar to a convex hull?

Permalink Reply by Tim Chen on November 12, 2014 at 2:50pm

An example from Gmsh is shown here.

The result should include a list of nodal id, and corresponding coordinates, and a second list including all the tetrahedron elements, with the corresponding nodal id.

From what I could do within grasshopper, the closest thing I found was to populate a brep with points, and use voronoi 3d. But then, the resulting cells aren't necessarily tetrahedrons. There isn't a "split" component available..to my knowledge either.

Permalink Reply by Oliver Tessin on July 2, 2015 at 6:42am

Hi Tim,

Im also searching a way to make a 3d delaunay mesh (volumetric mesh). Did you find a solution?

I tried something by making a structure by using the voronoi 3D centroids and faces, if you want to have a look.

Permalink Reply by Tim Chen on March 9, 2016 at 3:13am

Sorry, haven't been active on here for a while.

I tried that as well. Delaunay is great for making a truss structure though the bounding box are by definition not "filled". Voronoi fills the bounding box but isn't a truss (no tetrahedrons), I fixed that by connecting each voronoi cell's vertices to its centroid. It works, but the resulting elements may be sliver-like.

Permalink Reply by WT4 on March 9, 2016 at 11:59am

You can export the surface mesh as an STL file and providing the mesh is ok ie no high aspect ratio elements, you can import it into a free program called LS Prepost from the www.lstc.com website. This allows you to generate a tet mesh subject to the above criterion. If you need some help with this software, I can give you some help.

Permalink Reply by Nik Willmore on March 9, 2016 at 1:37pm