Estimation of the extreme values of wave-induced ship motions and accelerations for the First Nuclear Ship in Japan

Abstract

For the purpose of predicting extreme values of ship motions and accelerations induced by waves on the First Nuclear Ship in Japan, a model test in the Ship Research Institute's experimental basin as well as theoretical computations were carried out. Firstly, the response character of the ship in regular waves was obtained and the influences of wave directions as well as ship speed upon the responses were investigated. Secondly, the power spectrum and the cumulative energy density of the responses in certain given irregular waves were obtained by two kinds of methods, the one experimental and the other theoretical. The short-term probability distribution of the ship responses in various sea states were determined and the extreme values expected to be encountered in the most severe sea state were estimated. Finally, the long-term distribution of the responses was calculated by using the short-term probability distributions of the above mentioned responses and the statistical probability of occurrence of sea state in the northern North Atlantic Ocean, from which the extreme values expected to encounter for long periods of time as one year or all her life could be estimated. The estimated extreme values were compared with those obtained by various methods already derived. As a result, it is recognized that the probable extreme values of accelerations and ship motions are within the design standard of safety for the nuclear ship.