On the Non-Linearity of Ship's Response and the Higher Order Spectrum
On the Non-Linearity of Ship's Response and the Higher Order Spectrum
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船舶响应的非线性和高阶谱
DOI：
10.2534/jjasnaoe1968.1972.115
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发表时间：
1972
期刊：
影响因子：
--
通讯作者：
K. Ohtsu
中科院分区：
文献类型：
--
作者：
Y. Yamanouchi;K. Ohtsu
针对船舶在波浪中的响应为非线性时，其响应过程的一般功率谱不足以反映船舶响应的统计特性，有时甚至具有误导性的问题，采用摄动法从理论上计算了已知类型船舶横摇的弱非线性对视功率谱的影响，并引入多输入谱分析方法来分析某类船舶响应的非线性。但这些方法还不足以直观地反映非线性的存在及其性质，并指出在分析船舶在波浪中的响应时引入高阶谱的必要性。然而，现阶段关于高阶谱的研究成果很少，对其物理意义的解释也不是很充分，甚至实际的计算过程也是不确定和不清楚的。在与普通功率谱进行比较的基础上，首先考虑了高阶谱的物理意义及其与响应过程的非线性特征的关系，并试图阐明高阶谱分析在船舶波浪响应研究中的必要性。其次，将双谱和三阶谱、二阶和三阶谱作为最基本、最重要的高阶谱，结合响应过程的偏度和峰度，给出了双谱的算例，并从船舶在波浪中的振动进行了分析。最后，用模拟计算机对弱非线性横摇进行了模拟。对弱非线性的模拟器输入白色强制输入，分析了输出的记录，得到了双谱。然而，作为将高阶谱方法引入船舶响应研究的第一步，作为在不久的将来进入交叉双谱或交叉高阶谱的第一步，作者希望给出这些结果，以弥补已发表的关于这些问题的资料的不足。作为附录，对于高阶谱的计算和普通谱的计算，非常有效的F.F.T.程序。作为附录，作者希望给出这些结果。并总结了通过傅里叶变换获得双谱的程序。
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 and computed theoretically the effect of weak-non-linearity of known types of ship's roiling on the apparent power spectrum, through a perturbation method, and also introduced 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 2 nd and the 3 rd 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 ih tne computation of higher order spectrum, as well as in ordinary spectrum, and the program to get the Bispectrum through F. F. T. are summarised.