On the Long-Term Distributions of Ship Responses Considering Ship Operation

Abstract

In the design of a ship it is very important to estimate the maximum responses over the life of the ship on a given sea. For this purpose the long-term statistical predictions by an electronic computer have been developed to give the long-term probabilities of the ship responses exceeding a particular level value. The procedure of this calculation involves three steps: (1) ship responses in regular waves by the Ordinary Strip Method (2) short-term statistical values of the ship responses in irregular seas by means of the linear superposition principle (3) long-term statistical values of the ship responses using the long-term statistical wave data on a given sea In this report the authors have attempted to extend this procedure to calculate the long-term distribution considering the effect of ship operation defined by the speed drop and course change in rough seas. Numerical results by this method on the North Pacific Ocean are compared with those by the usual method and it is shown that the effect of ship operation is considerably large.