I am trying to simulate the flow of a precessing cylinder in the cylinder frame of reference. I have got some additional terms in the incompressible Navier-stokes equation which are velocity dependent. 

(1) How do I add these additional terms to the incompressible Navier-stokes equation?

(2) When I create a mesh in Gmsh and try to convert it into the .xml file format, how do I identify the composites corresponding to the global boundaries?

I am new to this framework. So, any help will be largely appreciated.