Approximate Calculation of the Wave Force 



In the strip method, when calculating the diffraction force, one uses 

 approximations in which the orbital- velocity of the regular wave is represented 

 by the value in the mean draft. As to the circular cylinder subjected to trans- 

 verse waves, there is exact solution of [31] and [19] compared them with the 

 approximate solutions with reference to the force Z which is proportional to 

 the orbital acceleration of the wave and the force Z. which is proportional 

 to the orbital velocity. Fig. 9 shows the comparison whereas Fig. 10 shows 

 the similar calculation for a circular cylinder subjected to longitudinal waves. 



In case of transverse waves, there are considerable differences in the 

 regions of high frequency but in case of longitudinal waves there is no 

 noticeable difference. However, in case of longitudinal waves, final conclus- 

 ion cannot be drawn at present since it includes the problem of the three- 

 dimensional effect. 

 Critical Revi ew of Strip Theory 



It must be mentioned that the usefulness of the strip theory approach, 

 especially for longitudinal motions and associated predictions, has surpassed 

 the imagination of many theorists and engineers. 



Predictions for the transverse motions and the associated effects, how- 

 ever, were not so good because of the difficulties arising from the modeling 

 and computation of the roll associated parameters. But recent efforts of 

 [28] have been proven to be very successful. 



The difficulties in connection with the transom stem (or more generally 

 blunt-ended) ships have been removed by the inclusion of end effects. 



In utilizing the results of strip theory one should always remember 

 that this approach is valid as long as: 



1) The vessel is slender, smooth and the geometrical variations in 

 the longitudinal direction are gradual, and not abrupt. 



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