[Gmsh] 1D mesh size

[walter steffe]

hello

I have noticed that, in order to define the 1D mesh size there are two
possibilities depending on the setting of "lcFromCurvature" flag.
In case it is set (lcFromCurvature=1) the parameter "minCircPoints"
defines the mesh size on a curved surface. This is an isotropic
refinement so that with a cylindrical surface it is done in both
circumferential and axial direction. In my opinion this is not a good
strategy because on a long cylinder characterized by a small radius
(like a thin wire) it produces an excessive (and not useful) refinement
in the axial direction. The situation becomes even worse in the meshing
of a solid with rounded edges having small radius. In this case the two
curves which limit the rounding region are divided in a big number of
small edges (dictated by the small radius radius) and than, in the
following 2D meshing process, the high refinement is propagated to the
triangles of the adjacent faces. So in the end a small detail (the
rounding of a corner) which should have a negligible impact on the
numerical simulations (I am considering electromagnetic problems but
this general considerations should remain valid also in other
applications) produces a very bug change in the global mesh. The number
of triangles can increase of a big factor and the numerical simulation
can easily become unfeasible.
I think that all these problems would be avoided by a simple change of
the 1D meshing with a mesh size that depends only on the linear
curvature of the underlying geometrical curve and does not depend on the
surface curvature in the orthogonal direction.

Walter Steffè