434 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 62.5 



English version in TMB Transl. 225, May 1949 



(2) Prohaska, C. W., "Vibration Verticales du 

 Navire (Vertical Vibrations of the Ship)," 

 ATMA, 1947, Vol. 46, pp. 171-219; abstracted in 

 EngUsh in SBMEB, Oct 1947, pp. 542-546 and 

 Nov 1947, pp. 593-599; complete English trans- 

 lation (unpubUshed in 1956) available in TMB 

 library. A list of 21 references appears on pp. 

 214-215 of the original paper. 



(3) Prohaska, C. W., discussion of paper entitled 

 "Ship Vibration," by F. H. Todd and W. J. 

 Marwood, NECI, 1947-1948, Vol. 64, pp. 

 D119-D123, plus authors' reply on p. D127 



(4) Marwood, W. J., and Johnson, A. J., "Vibra- 

 tion Tests on an Up River Colher with Special 

 Reference to the Influence of Depth of Water," 

 NECI, 1953-1954, Vol. 70, pp. 193-216, D103- 

 DUO. 



Koch's data in (1) were obtained by tests in 

 a 2-diinl electrolytic tank, using the methods 

 described in Sec. 42.13. The tank represented a 

 horizontal half of a rectangular-section channel, 

 with half of the underwater body of a rectangular- 

 section ship in the center of the channel. The 

 half-breadth of the channel was about 7 times 

 the half-beam of the ship. This was considered by 

 Koch to be the equivalent of a channel of infinite 

 width. 



Figs. 62.J and 62.K, adapted from Figs. 8 and 

 1 1 of the Koch reference, give data for determin- 

 ing the added mass of the entrained liquid around 

 a floating 2-diml body of rectangular section, for 

 a combination of variables involving the beam 

 B, the draft H, and the bed clearance h-H (in the 

 notation of the present book) between the bottom 



3 " 4 5 



Beam B 

 S(Bed Clearance) 



Fig. 62.J Added-Liquid-Mass Data of Koch for a 

 Rectangular-Section Surface Ship, Vibrating 

 ■ Vertically in Shallow Water 



of the ship and the bed of the channel. Fig. 62. J 

 gives these data for vertical vibration; Fig. 62. K 

 for horizontal vibration. 



For one who studies the papers of either Koch 

 or Prohaska, it is important to remember that 

 the "added mass factor" (phi bar) of Koch's 

 paper (TMB Transl. 225) and the "coefficient" 

 C of Prohaska's paper, although non-dimensional 

 in both cases, are based upon the masses of two 

 different transverse shapes of underwater body. 

 This factor and this coefficient are therefore only 

 shape factors for the bodies in question, to be 

 defined presently. They are not true added-mass 

 or inertia coefficients. 



The reference body of Koch is a buoyant one 



Fig. 62.K Added-Liquid-Mass Data of Koch for a Rectangular-Section Surface Ship, Vibrating 

 Horizontally in Shallow Water 



