船の応答の非線型性と高次元スペクトラム : バイスペクトラムの応用

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When the ship's response in waves is non-linear, the ordinary power spectrum of the response process is not enough and sometimes even misleading to show the statistical character of the ship's response. One of the authors has attacked this problem^<1), 3)> and computed theoretically the effect of weak-non-linearity of known types of ship's rolling on the apparent power spectrum, through a perturbation method, and also introduced^<2), 3)> the multi-input spectrum analysis method to analyse a certain type of non-linearity of a ship's response. However these ways resulted to be not enough to show directly the existence of non-linearity and its character, and he has pointed out the necessity to introduce the higher order spectrum in the analysis of ship's responce in waves. At present stage however, very few works have been published on the higher order spectrum, and its physical interpretation is not fully explained, and even the practical computational procedure are still left uncertain and unclear. Here the authors firstly considered the physical meaning of the higher order spectrum, its relations with the character of the non-linearity of response process, on the basis of comparison with the ordinary power spectrum, and tried to make clear the necessity of higher order spectrum analysis in the study of ship's response in waves. Secondly, taking the Bispectrum and Trispectrum, the 2nd and the 3rd order spectrum as the most basic and important higher order spectra, the authors tried to do the same thing, relating with the skewness and peakedness of the response process, and then showed examples of Bispectrum, analysed from the ship's oscillations in waves. Thirdly, to check the above mentioned thoughts, an analogue simulation of the weak non linear rolling was tried by analogue computer. A white compulsory input was feeded to the simulator which is weakly non-linear, and the record of output was analysed and the Bispectra were obtained. The results are not fully satisfactory ones in some points, however, as the first step of introduction of the higher order spectrum method in the study of ship's response, expecting to proceed into the Cross-Bispectra or cross higher order spectra in near future, and to make up the deficiency of published materials on these problems, the authors wished to present these results. As Appendices, the F.F.T. program, which is very effective in the computation of higher
社団法人日本船舶海洋工学会の論文

船の応答の非線型性と高次元スペクトラム : バイスペクトラムの応用

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