Please read the doc about the mesh settings, use feed mesh points an tweak the "Size" node (and add related size nodes to your mesh node) You could mesh first the edges (or some) with edge mesh and a dimension sub node Meshing is almost an art more than a science to get it smooth, it requires some training and experiences (testing) so it comes with the use of the tool (any FEM tool by the way). You will gain too by following the excellent training courses on meshing given by COMSOL, and to come to the mini-seminars at the COMSOL conferences, that is where you can do your training and maintenance learning.

Thank you very much for your kind information.

You did not mention your COMSOL version, so I assume it is 4.4.

It appears you have a geometry with edge and/or face features too small to properly mesh. I assume it can happen with COMSOL's geometry features.

First check the geometry to see if it has an improper mating or other cause of small faces. If unsuccessful in finding or correcting this, try one of the Defeaturing and Repair operations in the geometry node, or perhaps one of the Virtual Operations. You may apply trial and error to find the operation that did the trick.