Estimation of the Long-term Maximum Expected Value of Vertical Bending Moment taking the Shape of Directional Wave Spectra into account

Abstract

　The two-dimensional wave spectrum obtained by the hindcast are fitted on the function of the Ochi-Hubble spectrum and Mitsuyasu directional distribution namely 4-parameter spectrum and analyzes the trend of the spectrum shape in the actual sea area in the North Atlantic. The effect on the vertical bending moment(VBM) of a container ship are evaluated. A method to get the long-term maximum expected value utilizing the shape parameters of spectrums is proposed.

　The occurrence probability of multi-peak spectra tends to be low in sea conditions with high significant wave heights in which occur the maximum wave load. The long-term maximum expected value by using the 4-parameter spectrum was estimated to be larger than the value by using 2-parameter Pierson-Moskowitz spectrum, and contributed to approaching the true value gained directly using the hindcast wave spectrum. A method for efficiently estimating the long-term maximum expected value by using the shape parameters(λ, s) was presented. There is a higher possibility of estimating a larger load when using the realistic shape parameters than when using the IACS2023 spectrum.