W.L 1.0 



Motora and Koyama 

 then 



f(t) 



t + ih 



+ K lof 



t + ih 



(12) 



-2.0 



-3.0 



Fig. 24 - Typical 

 stream lines of two- 

 dimensional wave- 

 free distributions 



Stream lines given by this function are as shown 

 in Fig. 24. As seen in Fig. 24, one of them is 

 similar to the circular cylinder type model of the 

 present paper. It is quite interesting to see that 

 two different approaches reached similar results. 



An experiment was conducted to measure the 

 heaving force for such a body. Results are as 

 shown in Fig. 25 where heaving force for a circu- 

 lar cylinder type is also shown for comparison. 

 From Fig. 25 it will be noticed that the wave-free 

 body shows quite similar heaving force vs fre- 

 quency curve compared with the circular cylinder 

 type model. 



CONCLUSIONS 



1. The Froude-Krylov buoyancy and the 

 inertia force which is induced by the added 

 mass effect are reverse in sign. Therefore, it is possible to make them 

 cancel each other so that wave excitation is reduced. 



2. At a frequency at which the absolute value of the inertia force is equal to 

 that of buoyancy, the heaving force becomes exactly zero theoretically, and is 

 proved experimentally to be almost zero. 



Fig. 25 - Comparison between the heaving force of a wave-free body 

 obtained by Bessho and that of the circular cylinder type model 



402 



