Kim and Mevoiev 



on the inertial force (proportional to z), they appear to have neglect- 

 ed its effect on the vertical wave -induced force. For non-cylindrical 

 floats, such as shown in the sketch, the inclusion of added mass ef- 

 fects is still more significant. 



The added mass wave force results because the flow is un- 

 steady and the presence of the body does modify the fluid acceleration 

 patterns (contrary to the Froude-Krylov assumption) resulting in a 

 pressure force in phase with the vertical wave acceleration. The add- 

 ed mass may be associated with two principal sources, the primary 

 one being the enlarged attenuator at the lower end of the float. Extern- 

 ally-attached damping devices will also have associated added masses. 

 The effective added mass from the primary source, the enlarge at- 

 tenuator, may be estimated by assuming that the attenuator is similar 

 to a prolate spheroid with a ratio of semi-major to semi-minor dia- 

 meter, a/b equal to L & /2R a . Lamb [39] gives theoretical added 

 mass coefficients for translation "end-on" that can be expressed as 



K - |f*Hs (35) 



where kj can be taken from Table 14. 



It has been found, of course, that the ideal fluid theory added 

 mass is insufficient for slender craft such as airships and surface 

 ships in monotonic rectilinear motion,presumably because of boundary 

 layer influences (cf. Thompson and Kirschbaum [40] and Smith [4l] ). 

 The reasons for the differences between theory and experience for 

 these craft may not be relevant to the float-attenuator in the wave flow 

 field so the tabulated theoretical values are recommended for use 

 pending more complete experimental results. The wave acceleration 

 can be evaluated at an effective depth, z Q = T - L /2. 



The added mass associated with the damping devices, which 

 probably would be attached to the float at the upper end of the conical 

 transition above the attenuator (see sketch), is not derivable from 

 familiar simplified cases. The interaction of the flow about the damp- 

 ing "collar" with the flow about the cylinder may be important and 

 ought to be studied experimentally. Fot the purposes of the present 

 analysis , the added mass of damping devices will be assumed to be a 

 fraction of the added mass of the attenuator 



m\ = c'm' (36) 



d a 



where approrpiate values of c 1 should be obtained experimentally or 

 simply assumed. The value of z e to be used for evaluating the wave 



824 



