不規則波中における係留浮体の水平面内の長周期運動の統計的予測法について

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This paper deals with the probability distribution and the distribution of maxima of the horizontal motions including slow drift motion of a moored floating offshore structure. If the motions can be described in two term Volterra functional series, the probability distribution of the motions can be solved exactly by use of the statistical value of quadratic form. The distribution of maxima can be found by the joint probability density function between the motion displacement and the motion velocity under Powell's assumptions in the field of structural dynamics. In this paper, the authors propose the new method which can be obtained by matching between finite Gram-Charlier expansion and the asymptotic form derived from the exact solution of the probability distribution. Furthermore the relationship between the statistical values of the probability distribution and the characteristics of the motion responses including the nonlinear response are found. The approximate solution for the distribution of maxima is discussed by introducing the assumptions which the motion displacement and the motion velocity are independent and which the motion velocity is Gaussian process with zero mean in addition to Powell's assumptions. In order to confirm the applicability of the present method, the measurements of wave elevation and horizontal motions in long duration have been carried out in the long tank, the characteristics of the first and the second order transfer functions of the motion have been found through cross spectrum and cross bispectrum analyses, the experimental results are compared with the results of the present method. As the results, the following items have been found : 1) Pinkster's approximation is applicable to the second order transfer function of motion. Further the linear transfer function can be estimated by the usual linear motion prediction method. 2) The present method can be applied to the estimation of the probability distribution and the distribution of maxima of the horizontal motions including slow drift motion.
社団法人日本船舶海洋工学会の論文

不規則波中における係留浮体の水平面内の長周期運動の統計的予測法について

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