> Looks like the model generate a lot of small radius
> overlapping vertex.

There's basically two kinds of refinement that happens when the mesh gets created - the underlying surface gets broken down into quads, and then apart from that trim curves get broken down into some little edges as well.

In the pieces here where you've got a surface cut at like a 45 degree angle, some of the vertices from underlying surface quad refinement are really close to the vertices from the trim edge refinement - something along those lines anyway.

- Michael