agreement is due to the fact that the longitudinal ship motion amplitudes at 

 high and very low frequency ranges are insignificant. But in case of spring- 

 ing and mooring problems, where the high and very low frequencies are involved 

 respectively, this kind of engineering approach may not be satisfactory. 



Use of the Haskind-Newman relationship in calculating the wave exciting 

 forces is a useful method so far as avoiding the solution of the diffraction 

 problem, while calculating the forces and moments created by the diffraction 

 of waves. So the approach is, in a way, equivalent to the solution of the 

 wave diffraction problem. The main difference is due to the evaluation of 

 the Haskind-Newman relationship. The original approach requires that in the 

 evaluation of diffraction force (moment) the perturbation potential <^ is the 

 three-dimensional potential satisfying the same state equations and radiation 

 condition as the diffraction potential, whereas in "strip theory" only the 

 two-dimensional potential is available which satisfied different state equa- 

 tions and radiation condition. 



Newman [42], however, proved that for the high-frequency range this 

 difference does not cause any significant error. 



For longer waves McCreight [43] recently developed a relationship similar 

 to that of Haskind-Newman for the computation of wave exciting forces. 



As the numerical evaluation of the wave excitation by the Haskind- 

 Newman relationship is not difficult, this approach should be preferred in- 

 stead of the previous approach as it eliminates the somewhat arbitrary choice 

 on the relative motion between the ship and the waves. 



It should, however, be mentioned that this approach also fails in very 

 long waves because of the breakdown of the strip theory. For such long waves 

 the approach adopted by [11] is preferrable as it includes the effect of wave 

 deformation in an approximate way. 



69 



