How do i know if my mesh is good or not?

I export my surface from CAD and load it into netgen. Mesh Options depends on your geomitry size and the number of curved areas. For a simple hopper with 20m x 15m I use min size 1000 and max size 8000.
After meshing make sure the triangles are not too small (much bigger than r_particle min) and does not have a range over the whole geometry (parralization becomes bad in this case bc. every core needs to store the contact history for the large triangle), also try to have equilateral triangles, they have a good curvature.
After meshing, export to ASCII-STL.
Good Luck,
Christian