Vassilopoulos and Mandel 



the errors shown to exist in the Korvin-Kroukovsky procedure using Grim's 

 section added mass and damping are large. This remains to be further investi- 

 gated however. 



RECOMMENDATIONS 



While the present report represents a start, much more can be done to as- 

 sess the reliability and usefulness of an improved strip theory. The following 

 list of recommendations cover suggestions for correcting the work already ac- 

 complished as well as suggestions for future work. 



1. There is a strong need for phase angles to be uniformly and unambigu- 

 ously defined. There are essentially three different ways for phase angles to be 

 presented: 



a. Amplitude positive throughout and phase angles from 0°-360°. 



b. Amplitude positive throughout and phase angles ±0-180°. 



c. Amplitude both positive and negative and phase angles from 0°-180°. 



The last was used by Vossers et al. [18,19] while the second way has been used 

 in this report and in Ref. [6]. It is believed that the first way is the least am- 

 biguous and that this should be used in the future. In the definition of phase, the 

 maxima of response amplitudes should be referred to the maxima of the wave 

 amplitude and not to the maxima of the wave slope as was done by Korvin- 

 Kroukovsky. Furthermore, the reference point should be the mid-section of the 

 ship or model rather than the longitudinal center of gravity since the former 

 can be readily and precisely located. 



2. The importance of the neglect of surge in the theory remains to be de- 

 termined. The current work of Shen Wang at M.I.T. will help with the formula- 

 tion of a system with the needed three degrees of freedom. 



3. The assumption of wall sidedness as far as damping, added mass, and 

 wave excitation is concerned is an important possible source of unrealism in 

 the strip theory. The current work of Parissis [16] is important in this regard. 

 Unfortunately, while success in coping with this problem should improve corre- 

 lation between theory and experiment in regular waves, it will not be possible to 

 incorporate this refinement in the prediction of statistical responses in random 

 seas. The latter is strongly tied to a completely linear system. 



4. Further refinements of strip theory should include the use of Porter [32] 

 for computing section damping and added mass. 



5. Correlations between the strip techniques and other theories for predict- 

 ing ship motions should continue. For example. Fig. 73 shows a comparison 

 between the non-dimensional pitch and heave amplitudes for a Cg = 0.60, Series 

 60 model at zero speed using Grim's three-dimensional theory [55] and those 

 predicted for Model D at zero speed by the program of Ref. [6]. It is seen that 



346 



