Testing Ship Models in Transient Waves 



expected to describe a circle if plotted in the velocity phase plane as suggested 

 by Mr. Laitone, and furthermore, the departure from such a circle would shed 

 no light as to the nature of the problem. A better understanding of the problem 

 can be obtained by separating the effects of added mass, damping, cross cou- 

 pling and hydrodynamic memory by use of the integro-differential equations of 

 motion developed by Dr. Cummins. This information, along with knowledge of 

 the wave excitation, should provide us with information as to why a ship per- 

 forms the way it does as well as possible changes in design to improve her sea- 

 keeping qualities. 



We would like to apologize to Dr. Leo Tick" if we have in any way contrib- 

 uted to his confusion. We are also very grateful for his pedagogical dissertation 

 on the basic philosophy of testing. Of special note is his recollection of pro- 

 found personal conversations (with someone whose name he can't quite remem- 

 ber). Apparently the choice of a suitable test function is not clear to him. This 

 is understandable. The choice of a test function or procedure depends upon 

 many factors. We may be less philosophical and more pragmatic; this choice in 

 the final analysis depends upon whether or not it serves the purpose intended, 

 i.e., to provide an efficient and economical means of obtaining a reliable meas- 

 urement of the transfer functions. We believe that the transient test technique 

 meets these objectives. We have provided both theoretical and experimental 

 evidence to support our claims. It is anyone's prerogative to accept or reject 

 them. 



'■'See discussion by Tick (p. 457) on paper by Smith and Cummins, 



543 



