Motora and Koyama 



10 fai 



02. 0.4 0£ 0.8 1.0 1.2 



1,6 IJd 2.0 2.2 



_J I I 1 I 



0.1 0.2 0.3 a4 0.5 OA 0.7 0.8 0.9 1.0 M., 



Fig. 14 - Heaving magnification factor of a fin type model 



becomes zero when the frequency coincides 

 with 



(9) 



Therefore, at the frequency ^^ , tank water 

 is practically solidified and the breadth of 

 the strut is practically Bj. 



Therefore, if the excitationless frequency 

 for Bj is denoted co^^, heaving force will 

 vanish at co^^. Thus, the heaving force will 

 vanish at two different frequencies a)^ , , and 



Fig. 15 - Geometry of dou- 

 ble caisson type models 



Experiments were conducted on a model 

 for which Bj, Bj, and H were chosen as 

 shown in Fig. 15. Results are as shown in 

 Fig. 16 in which three results for different 

 size of the holes are indicated. By Fig. 16, it will easily be seen that the heav- 

 ing force almost vanishes at predicted co^ ^ and ^o 2> 3J^d is very small in a fre- 



quency range founded by 



and 



5. THREE-DIMENSIONAL PROBLEMS 



5.1 A Sphere with Vertical Cylinder 



As a most simple three-dimensional case, let us consider a sphere with 

 vertical cylinder as shown in Fig. 17. As the Eq. (2) is applicable for a 



396 



