the mean waterline and the last term is a line integral along the 

 line defined by the intersection of the hull and the mean free 

 surface. This term accounts for the variation of the wetted sur- 

 face at the waterline due to run-up of the wave and vertical dis- 

 placement of the hull. 



The direct integration of the pressure has several advanta- 

 ages over the integral momentum equation formulation. Firstly, 

 all six components of the drift-force can be obtained through 

 this procedure and secondly, it appears that it may be possible 

 to extend the basic development to compute the complete low- 

 frequency second-order forces and moments. The complete second- 

 order force involves the second-order potential, and while the de- 

 termination of this may be feasible in principle the overall task 

 appears somewhat overwhelming from the viewpoint of computer time. 

 The computation of the low-frequency part of the second-order 

 force is much more within the realm of the attainable since it is 

 strictly dependent only on first-order potentials and motions. 



5. CONCLUSIONS, COMMENTS AND RECOMMENDATIONS 



1. The hydrodynamic coefficients can be computed fairly efficient- 

 ly for three-dimensional bodies using the distributed source 

 (Green's function) technique. The available experimental data 

 agrees quite closely with calculations using linear theory except 

 in certain cases where the damping coefficients are rather small. 

 In such cases it is suspected the viscous effects become relative- 

 ly significant and in order to deal with such cases, some effort 

 should be directed toward development of a "viscous correction" 

 for the damping coefficients which is appropriate for barge-like 

 shapes. 



2. Because of the frequency-dependency of the coefficients in the 

 -equations of motion of a floating body, superposition of the mo- 

 tion resulting from each component of an incident wave system be- 

 comes questionable. 



3. Two methods of evaluating the mean drift-forces and moments 

 have been outlined. The pressure integral technique has the ad- 

 vantage over the momentum equation formulation of providing all 

 six components of the load which may be of value in certain cases. 



4. It appears that it may be possible to evaluate the complete 

 slowly- varying drift-force using the pressure integral formula- 

 tion. This could provide a basis for a time-domain simulation 

 of the slowly-rvarying drift motion of a moored vessel with the 

 high-frequency wave^induced motion superimposed on this motion. 



52 



