Rami,
In Mechanica you can apply a global temperature to the part, which will
require a reference temperature.
This is how you would apply the delta T associated with the cooling process.
Apply constraints to the
outer diameter of your lens. If the material of your lens is more
complicated, you can apply orthotropic
material properties.
I don't fully understand question #2, however the paragraph above should
give you a good start on
your simulation.
Good luck,
Stephen Seymour, P.E.
Principal Engineer
Seymour Engineering & Consulting Group, LLC
3600 NW 138th Street
Suite #102
Oklahoma City, OK 73134