WAVE EXCITATIONLESS SHIP FORMS 



Seizo Motora and Takeo Koyama 



University of Tokyo 



Tokyo, Japan 



INTRODUCTION 



It has been deduced theoretically by Ursell (1) and Hishida (2) that prisms 

 of certain sectional shapes create no waves when they roll in a still water sur- 

 face, and experimental check has also been made by McLeod and Hsieh (3). 

 Bessho has extended this theme into motions of six degree of freedom and de- 

 veloped the theory of 'Wave-free distributions" (4). 



In addition, Newman (5) has shown, on the basis of Haskind relation, that 

 the amplitude of radiated wave by an oscillating body in a free surface is di- 

 rectly related to the exciting force acting on the same body in waves. 



These results indicate that there must be bodies which are free from ex- 

 citing forces in waves. 



The authors, being interested in the possible existence of such wave- 

 excitationless bodies, have been carrying out experimental research for such 

 bodies, and have found that there were a group of bodies which are free from 

 wave- induced heaving force in waves of specified frequencies. 



1. APPROXIMATE FORMULA OF HEAVING FORCE 



Froude-Krylov hypothesis has long been used in estimating wave-induced 

 heaving force until body- wave interaction was clarified in recent years. Ac- 

 cording to the Froude-Krylov hypothesis, heaving force becomes nil only when 

 the waterplane area is zero. However, the authors were aware that the body- 

 wave interaction is reverse in sign of that of Froude-Krylov force and that 

 there must be a possibility that a body could be designed to have greater body- 

 wave interaction in relation to the Froude-Krylov force so that they will cancel 

 each other. 



As Motora has shown (6), the heaving force is expressed approximately as 

 a summation of an inertia term, a damping term, and a buoyancy term as shown 

 in Eq. (1). 



Zw 



7ik^p VZw + 72NZ Zw + 73/:'gAZw , (1) 



383 



