A problem which has yet to be solved satisfactorily is the heaving added 

 mass at very low frequencies. Although this may appear unimportant, in reality 

 this is not the case because in following waves such low frequencies of encounter 

 are highly probable. 



According to the present theory, the heaving added mass tends to infinity 

 as the frequency tends to zero and the ship response in this region is obtained 

 in practice, by extrapolation based on physical arguments. Ref [27] showed 

 that the heaving added mass for a circular cylinder in a finite depth of fluid 

 is finite when the frequency tends to zero, and compared their results with 

 others. This result suggests that a fictitious depth may be applied in order 

 to obtain useful result. 



Another problem in relation to the computation of fluid reactive forces 

 and moments arises at the intersection of the hull surface with the free sur- 

 face. It is necessary that the wetted surface of the ship should be smooth 

 but it also requires this to apply to the closed double-body formed by the 

 ship and its mirror image. But this condition is violated for almost all 

 vessels near the fore and aft ends, thereby necessitating an additional singu- 

 larity distribution at the intersection of the wetted surface and the undi- 

 sturbed water surface. 



In spite of the, above-mentioned limitations, predictions of the sectional 

 fluid reactive forces and moments by the strip theory have been quite success- 

 ful with the exception of roll damping which has been obtained recently with a 

 significant success by [28] which included additional roll damping moment 

 caused by appendages etc. 



Approximati on by Lewis Form 



A section contour of the foirward part of a hull can be approximated 

 reasonably well by Lewis-form but there exist considerable differences for 



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