Motora and Koyama 



02 0.4 0.6 0.8 1.0 1.2 1.4 16 1.8 2.0 2.2 2.4 2.6 <%i. 



0.1 



0.2 



0.3 0.4 



06 



as 



T< 



Fig. 12 - Heaving magnification factor 

 of circular cylinder type models 



As far as the wave damping is concerned, it seems hopeless to decrease the 

 heaving amplitude. However, it should be noted that eddy damping or artificial 

 damping are not included in Haskind-Newman relation. 



Therefore, eddy-making damping or artificial damping such as by a passive 

 tank are given to a wave-excitationless body, it will be possible to minimize the 

 heaving. 



Heaving of an ellipse (a/b= 2) with a strut is measured as shown in Fig. 13(a) 

 in which less heaving amplitude will be recognized than the case of a circular 

 cylinder due to eddy damping. Thinner ellipse (a/b= 4) with a strut is also tested 

 as shown in Fig. 13(b). Remarkable decrease of heaving due to eddy damping will 

 be noted. 



Heaving of a body with fins as described in Section 2.3 is also tested. Re- 

 sults are as shown in Fig. 14. Though the magnification factor diagram looks 

 like that of critical damping, actual damping is about one-third the critical 

 damping. Apparent critical damping of the magnification factor diagram is due 

 to rapid decrease of the exciting force as the frequency approaches co^. 



4. A TRIAL TO ELIMINATE WAVE EXCITATION 

 IN WIDER RANGE OF FREQUENCY 



According to the above described method, the exciting force is eliminated at 

 only one specified frequency. The following is a trial to eliminate the exciting 

 force at two or more frequencies. 



394 



