Motora and Koyama 

 TO MR. FRANK'S DISCUSSION 



The authors appreciate Mr. Frank's discussion showing results of his fine 

 calculation at DTMB. It is quite encouraging to see the agreement between his 

 results and the authors' measurements. There are some discrepancies between 

 the theory and the measurement at higher frequencies, and the authors are in- 

 terested in checking their measurement at those points. 



In comparing Fig. 3 of the paper to Mr. Frank's Fig. D4, there are some 

 discrepancies between the authors' approximation and the exact solution given 

 by Mr. Frank for greater strut width. The authors hope that those results will 

 give valuable information to refine their approximation. 



TO MR. MILGRAM'S DISCUSSION 



Mr. Milgram showed that heaving excitationless phenomena can be ex- 

 plained by a simple theory neglecting the wave diffraction. 



It is very interesting to know that the Froude-Krylov force itself has nega- 

 tive sign to the wave elevation when a body is entirely submerged. This means 

 that the correction factor 73 in the authors' theory is less than they have esti- 

 mated, and therefore the excitationless frequency will shift toward a lower fre- 

 quency. 



For example, let us take a body shown by Mr. Milgram (Sketch 2). 



The Froude-Krylov force is 



FK = /ogh 



-kT 



KVe" 



(1) 



where notations are as given in Mr. Milgram' s 

 discussion. 



Inertia force induced by wave diffraction is 



I = -/pgh7ik^KV. (2) 



Therefore, total force is 



FK- I = /ogh 



Aje-'^'""- KVCe-'^^+Tik^) 



(3) 



The excitationless wave number k„ is 



Sketch 2 



A.e-^o" 



VCe-l^f + 7ikJ 



Comparing this with Mr. Milgram' s theory 



(4) 



412 



