How to distinguish solid from fluid zone
 

Hi

I am very much new in handling Fluent and I have just started my journey with Ansys Fluent.
I wish to make a hydrodynamic analysis of a ship hull (you may think it as a circular cylinder) in shallow water. So how can I distinguish the solid (ship hull or cylinder) from the surrounding fluid zone......The solid body is in 3D...Can anyone please help me....
thank you in advance.......