Vassilopoulos and Mandel 



0.5 



(.0 



2.0 



8, NONDIMENSIONAL FREQUENCY 



Fig. 2 - Waveheight ratio A 

 for Models 4, 5, and 5G 



DISCUSSION A 



THE INFLUENCE OF THE ADDED MASS FORMULATION 

 UPON THE COMPUTER MOTION PREDICTIONS 



Peter A. Gale 

 Bureau of Ships 

 Washington, D.C. 



To this discusser's knowledge, the significant differences between the Bu- 

 reau of Ships computer program and the author's Massachusetts Institute of 

 Technology (M.I.T.) program as of January 1964, are: first, the Bureau of Ships 

 program is based upon ten station spaces while the M.I.T. program is flexible 

 in this respect and it is believed that twenty station spaces are commonly used; 

 second, the Bureau of Ships computer program uses the Prohaska added mass 

 coefficients with Ursell's free surface corrections as presented in Davidson 

 Laboratory Report No. 791 while the M.I.T. program uses Grim's 1959 added 

 mass coefficients. Both programs use Grim's 1959 damping coefficients. 



In order to assess the influence of the added mass formulation upon the 

 predicted ship motions, the motions of the DD 710 (this discusser's ship "A") 

 were computed using both the Bureau of Ships program and the M.I.T. program 

 with ten station spaces. The resulting motion predictions are plotted in Fig. 1 

 for a wave length to ship length ratio of 1.25. This figure gives an indication of 

 the influence of the change in added mass formulation described above for a 

 particular set of conditions. For other wave length to ship length ratios the in- 

 fluence was found to be of the same or a lesser order of magnitude. 



366 



