in which ½ is the density of water (kg/m3), r is the volume of displacement of the body (m3), Fh is the hydromechanical force in the z-direction (N) and Fw is the exciting wave force in the z-direction (N).
This superposition will be explained in more detail for a circular cylinder, boating in still water with its center line in the vertical direction, as shown in figure 3.8.