巨大船に働らく波浪曲げモーメントの長期分布について

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There are proposed, in this paper, the theoretical methods predicting long-term distributions of wave-induced bending moments on ship hulls, and presented the predicted results for gigantic tankers. Predictions are made entirely based upon the theoretical methods as follows; (a) There are computed the response operators of wave-induced bending moment on a ship in regular waves, based upon a extended strip theory, for a range of ship speeds, headings and wave lengths. (b) The modified Pierson-Moskowitz wave spectrum is adopted in order to describe a short-term irregular seaway by the significant wave height and the average wave period. The short crestedness of sea waves is introduced by (cosine)^2 distribution for the directional spectral density. (c) The values of standard deviation of wave bending moment "R", which is the short-term parameter of wave bending moment, are computed based upon a linear superposition method by availing the calculated response operators and the assumed wave spectra, as functions of the significant wave height and the average wave period for given ship speeds and headings. (d) Long-term probabilities of exceedance for given values of wave bending moment are computed by availing the calculated short-term R-values and the wave statistics on the North Atlantic, where are given the long-term frequencies of sea waves defined by the significant wave height and the average wave period, assuming that the Rayleigh's law may be applicable for short-term distributions of wave bending moment amplitudes. According to those methods, there have been predicted the long-term distributions of midship wave bending moments on a series of tankers having different principal dimension ratios and different lengths. Then, the dimensionless values of wave bending moment and the corresponding effective wave heights, which were predicted with the exceeding probability of 10^<-8> in the North Atlantic, were derived as functions of ship length with parameters of principal dimension ratio and ship speed. And, the following trends of long-term wave bending moments were deduced; (1) Effective wave height (predicted with the exceeding probability of 10^<-8> in the North Atlantic) holds approximately constant for geometrically similar tankers longer than 350 meters independent on their lengths. (2) Long-term wave bending moments on large tankers tend to decrease with increase of ship speed at a range of usual speeds. (3) The larger length/breadth ratio of tanker ship form gives generally the larger effective wave height, and the effect of length/draught ratio on effective wave height is not uniform. However, the principal dimension ratios have not so significant effect on the effective wave height.
社団法人日本船舶海洋工学会の論文
1967-07-30

巨大船に働らく波浪曲げモーメントの長期分布について

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