Kim and Mevciev 



where T = the maximum draft of the two bodies. The subscripts 



S,H,R indicate swaying and heaving forces and rolling 

 moment, respectively. 



The hydrodynamic force has real and imaginery parts, for 

 instance 



F< T) - F< T) + i*^ (22) 



In the radiation problem, the real part of the hydrodynamic force 

 (moment) is called the inertia force (moment while the imaginary part 

 corresponds to a hydrodynamic damping force (moment). In the dif- 

 fraction problem, the complex force defines the amplitude and phase 

 of the wave-exciting force relative to the passage of the crest of the 

 incident wave by the origin . The hydrodynamic moment arms also 

 consist of inertial and damping parts in the radiation problem. In the 

 diffraction problem, however, the moment arms of the real and imag- 

 inary components are identical because the force and moment maxima 

 occur at the same instant. 



Force and Moment Coefficients 



Hydrodynamic interactions affect the pressure distributions 

 and forces acting on the individual bodies. Certain components of 

 these resultant forces and moments may be considered as internal 

 forces for the evaluation of dynamic structural loading on rigidly con- 

 nected cylinders. The hydrodynamic forces on individual bodies are 

 useful and the individual bodies when they are elastically coupled or 

 unconnected. 



Table 6 defines the various force and moment components, in 

 accordance with Eq.(20), and their corresponding dimensionless coef- 

 ficients. 



The first subscript denotes the mode of motion (in place of the 

 parenthetical superscript used previously ; the forces, moments, and 

 coefficients do, however, depend on the details of the modes and 

 phases of motions), while the second subscript denotes the components 

 of force (moment). For example, 



2 „ 



co m q = roll hydrodynamic inertial moment induced by swaying 



motion of unit amplitude of displacement 



coN = the heave damping force induced by rolling motion of 



unit amplitude of displacement 



812 



