コンテナ船あめりか丸による北太平洋航海性能試験(第3報)

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This is the last report in series ones on the seakeeping test in the 25th voyage of a container ship "America-maru" of Mitsui-O.S.K. Lines Ltd. on the North Pacific Ocean. As we mentioned in the former reports on this voyage, roll, pitch, yaw, lateral and vertical accelerations at F.P., longitudinal acceleration at the navigation bridge and rudder angle were measured and recorded on a magnetic analogue data recorder. After these data were converted into digital ones by an A-D converter, firstly we examined the analysis what we called "statistical analysis", namely the fitting to the Rayleigh distribution of amplitude frequencies and mean periods in their time variant records. Secondly we analyzed them applying ordinary "power spectra" method. Finally we tried to apply the well known "multiple input analysis" introduced by L.J Tick, H. Akaike, Y.Yamauchi and others. In this analysis, we mainly took aim at the yaw and the lateral acceleration at F.P as the output of system. These data processing and various calculations were executed almost automatically on a digital computer. We can summarize the analyzed results as follows. (1) In order to avoid a heavy roll in a rough sea, it is very effective to reduce speed or to alternate course to some moderate value. (2) An anti-rolling tank (A.R.T) is effective, but users must use it with due regard to the ship's encountering period with waves. (3) The radius of gyration of roll is estimated to be (0.67〜0.70)B/2. Where B denotes the breadth of this ship. (4) The frequency distribution of full amplitudes of the vertical acceleration at F.P may be approximated to the Rayleigh distribution. And also, we can obtain natural period of pitch from its distribution. (5) The londitudinal at the navigation bridge in a head sea condition becomes about 0.3 times as much as the vertical one at F.P.. (6) In the so-called statistical analysis, we can estimate the natural period of pitch, but not of roll. (7) The record of pitch represents the encountering state better than the other modes of motions. (8) On navigation using an auto-pilot, frequent full amplitude of rudder angle is nearly about 10 degress in a rough sea and 2-3 degrees in a moderate sea, but even in the former case, the maximum full amplitude does not exceed 20 degress, (9) Generally, the setting value of auto-pilot has indirect influence to the yaw angle. (10) The relation between the standard deviation of power spectrum and the mean full amplitude H^^- may correspond approximately to that of the Rayleigh distribution. (11) In order to represent the mean period of zero crossing, T_<02s>, which is obtained from the second order moment of spectrum, is suitable, though T_<01s>, from the first order moment, does not make so much difference, (12) According to the multiple input analysis with regard to the lateral acceleration at F.P. and yaw as the outputs, the assumed linear relations between inputs and outputs are vert strong at the neighbour of the peaks of power spectra. (13) The roll contributes strongly to the lateral acceleration, whether the anti-rolling tank actes on or not. (14) If we put the effect of the feedback loop between rudder angle and yaw out of consideration, it can be said that the rudder angle contributes most strongly to the yaw.
独立行政法人海上技術安全研究所の論文
1972-05-31

コンテナ船あめりか丸による北太平洋航海性能試験(第3報)

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