What is thsuitable meshing method for bottom face?
 

For a cylindrical 3D geometry, it can be generated in Gambit by extruding a cycle face.

Now, my question is:

How to meshing "the cycle face" using unstructed mesh method (like Tri)? If choosing small number of intervals, the edge arc seems not to be indluded or is cut-off. So,is it necessary to combine of reactangular mech and trianglemesh together? If yes, how?

Please suggest your ideas.