1/2 

 When (mK) = coU/g = 0.25, there is a discontinuity in the computations. This 



1/2 

 singular behavior can be explained by the Green function. If (mK) approaches 



0.25, Equations (119) and (120) become logarithmic functions as shown in Reference 



15. 



Figures 9 and 10 show the results of excitation forces and moments for SWATH 

 6A and 6D, respectively. The heave forces for both configurations are slightly 

 larger than those from strip theory. The excitation moments are generally larger 

 also. For SWATH 6D, the results of strip theory for the heave force show better 

 agreement with experimental results than those from the unified slender-body theory. 

 The pitch moments of SWATH 6D are scattered between the results of the strip theory 

 and the experiment. 



The motion results for SWATH 6A are plotted in Figure 11. Heave amplitude 

 shows a similar discrepancy with experiment as with strip theory. When the en- 

 counter frequency becomes very small, the peak of the heave amplitude disappears; 

 this peak is shifted to the higher encounter frequencies. The plus points show the 

 results of the "mixed method," in which the added mass and damping coefficients are 

 computed by the unified slender-body theory and the excitation forces are computed 

 by the strip theory. When A/L is less than 2.5, heave amplitude, computed by this 

 method, agrees better with experimental results than with the results of either the 

 unified slender-body theory or the strip theory. However, when A/L is larger than 

 2.5, the results of the mixed method underpredict the experimental results and 

 those of both theories. 



Pitch amplitude shows the same tendency as heave. The peak is shifted to 

 higher A/L values. Pitch amplitude, computed by the mixed method, agrees well with 

 experiment for all A/L values. 



The motion results for SWATH 6C are given in Figure 12. The heave and pitch 

 amplitudes become very large as the encounter frequency becomes large. The results 

 of the strip theory are better than those of the unified slender-body theory and 

 the mixed method. From the results of the mixed method, we can conclude that the 

 added mass and damping coefficients computed by the unified slender-body theory in 

 Figure 7 are too large. 



40 



