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Article type: Cover
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Published: September 30, 1986
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Article type: Index
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Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Seiji TAKEZAWA, Toshiaki AOYAGI
Article type: Article
Pages
1-11
Published: September 30, 1986
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The previous report (KSR No.198) dealt mainly with the wave slope characteristics and wave steepness statistics of irregular deep water waves. This paper investigates in details the saturation shape of frequency spectrum of wave elevation and wave slope etc. by the experiments of artificial irregular water waves. Moreover, extreme high steepness irregular waves including many breaking individual waves are generated in the long tank, and the statistical characteristics and the limiting frequency spectrum etc. are researched. The Half-Cycle Counting Method (HACYM), recently suggested to use in the analysis of irregular phenomena, was applied to clarify the details of statistical character on nonlinear irregular water waves with large wave slope. Consequently, non-dimensional value 0.8 x 10^<-2> given by Longuet-Higgins as the saturation range constant of frequency spectrum is best fit for our experiment. Furthermore, non-dimensional value 3.0 x 10^<-2> is obtained as an example of the extra-ordinary unstable constant of rapidly growing high steepness irregular water waves. Those extreme high irregular waves can be artificially generated only in the near field of the wave-maker.
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Hisaaki MAEDA, Akio KASAHARA
Article type: Article
Pages
13-21
Published: September 30, 1986
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In order to simulate irregular waves with directional spectrum in a model basin, the authors studied the characteristics of directional waves generated in a model basin numerically and experimentally, They found out that the power spectrum of directional waves which consist of component waves with same frequencies as ones of one another direction is non-stationary-in-position. They proposed to use stationary-in-position directional waves in a model basin which consist of component waves with different frequencies from ones of one another direction. They also discussed three methods of analysing directional spectrum, those are, Maximum Liklihood Method (M.L.M.), Direct Integral Method (D.I.M.) and Fourier Series Expansion Method (F.S.E.M.). By using of these three methods, They derived numericaly directional spectrum from cross spectrum calculated directly from designed directional spectrum and they also derived directional spectrum from numerical time-histories of irregular waves with designed dierectional spectrum. They concluded that M.L.M. is on of the best analytical methods but it is not alway the best in any case.
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Shigeru NAITO, Hiroshi ISSHIKI, Keisuke FUJIMOTO
Article type: Article
Pages
23-28
Published: September 30, 1986
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This is a study of thrust generation of a fin attached to a ship in waves. A high aspect ratio fin which is holded by a spring system is placed horizontally in front of the bow. This can generate big thrust due to its vertical motion and wave orbital velocities. Resistance increase in waves can be reduced, since that a fin has a effect of the reduction of the ship motion. In the present paper, ship and fin motion, resistance increase of a main hull, and thrust generation by a fin are calculated. Important relationships between thrust generation and some factors such as fin location is clarified.
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Yoshikazu KASAHARA
Article type: Article
Pages
29-37
Published: September 30, 1986
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The influence of the flow field at the stern due to the operating propeller was investigated experimentally by using a full form ship model. The velocities in front of the propeller and the hull surface pressures with and without a propeller in operation were measured in the towing tank. The potential flow calculation taking into account the propeller-hull inter-action and the 3-dimensional boundary layer calculation were carried out. And, the reliability of the calculation method was examined by comparing it with the results of the measurements. The main results obtained are as follows. (1) The total velocity distribution including the longitudinal vortices was measured in front of the operating propeller. The low pressure region near the bilge part at the stern was hardly affected due to the operating propeller. It was confirmed experimentally that there is a close connection between them. (2) The region of strong velocity gradients in the direction of the propeller radius was influenced more considerably due to the operating propeller than the high wake region. (3) The calculated results of the changes in the hull surface pressure due to the operating propeller explain the measured results fairly well.
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Makoto OHKUSU
Article type: Article
Pages
39-42
Published: September 30, 1986
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A formula is proposed of predicting added resistance of a ship due to the diffraction of short waves. Wave length is assumed very short compared with the length scale for changes in the stationary and non-uniform flow prominent in the vicinity of the ship. Incident waves are refracted in this non-uniform flow and reflected on the hull surface. This process induces wave pressure on the ship to give the added resistance.
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Hiroshi ONOGI, Michio NAKATO
Article type: Article
Pages
43-51
Published: September 30, 1986
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The paper deals with the new attempt to find the relationship between the roughened surfaces configuration and it's roughness function. In order to research, two ideas are introduced. One is the roughness height corrected by k/L and other is the roughness Reynolds number described by k^2/Lin place of k, where k is measured roughness height and L is spacing between roughness elements or apparent wave length. The new roughness functions are calculated in two cases, the elementary roughness type and the painted roughness type, using several experimental data which include authors' experimental results for roughened pipe flow. These are fairly convergent compared to the previous method. Further, a fitting approximation is introduced on the roughness function of painted surfaces, and finary, as an application the increase of frictional resistance of a newly built ships and the speed loss of ships in service are calculated using above approximate roughness function.
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Tokio OHNISHI, Hajime KAWAKAMI, Naoyuki TAKATSU, Tadashi TANIZAWA
Article type: Article
Pages
53-66
Published: September 30, 1986
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The dynamic behavior of mooring lines has not been regarded as an important factor of the practical design. But, it has gained increasing interest recently, and a large number of papers have been written about methods for analyzing the dynamic response of mooring lines. In this paper, dynamic behaviors of mooring lines are analyzed in order to investigate the strength of mooring lines of the 10MWe OTEC Plant. An analytical procedure is developed for time domain analysis so as to simulate the nonlinear behavior exactly, and a computer simulation program is developed to estimate the dynamic tension of mooring line excited by the motion of platform due to wave. Firstly, the dynamic analysis of the above mooring line is carried out and the effect of the nonlinear behavior on the dynamic tension force is studied. Secondly, for estimating the maximum tension force of mooring line in 100 year storm, the static analysis to compute the dynamic neutral position of platform and mooring lines, motion analysis of platform, and time domain analysis of mooring lines are carried out. Considering the displacement of the connecting point of the platform and mooring line to be the forced displacement, the mooring line is oscillated at the upper end by that displacement. The maximum tension force occurs at the upper end of the mooring line, and it is found to be smaller than the breaking force. Thirdly, the procedure to evaluate the fatigue strength of mooring line is presented by using the results of frequency domain analysis or time domain analysis. An example of the 20-year's fatigue damage calculation of the above mentioned mooring line is shown, by using the results of frequency domain analysis. In this case, the accumulated damage by the fatigue is pretty smaller than 1.0.
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Syohei YOSHIDA, Kazuo NOZAWA, Tsuneyuki YAGI, Kiyoshi NEMA, Hiroshi IK ...
Article type: Article
Pages
67-79
Published: September 30, 1986
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To study characteristics of ice loads acting on offshore structures, we carried out various model tests in a small ice tank installed in a low temperature experimental room. First, ice modeling test on urea doped ice was conducted, and mechanical properties of the model ice were investigated. Then, penetration tests were conducted using cone models of various inclination angles and circular pile models of various diameters. To study the relation between global ice load and local ice load, penetration tests were also carried out using a divisible model consisting of five flat plates. From this study, we could grasp characteristics of global ice loads acting on cone type and circular pile type structures, and ice failure modes of respective structures. The measured values agreed well with the calculation results by the plastic limit analysis method by Ralston and the experimental data by other investigators. This shows that even model tests in a small ice tank can provide effective experimental results. The test results further made it clear that normalized local ice load is larger than normal-ized global ice load and, therefore, that grasping local ice load is important especially in wide structures having vertical walls.
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Ryotaro OGIWARA, Noriyuki KAMOI, Masatoh NAKAMURA, Tsutomu HARADA, Aki ...
Article type: Article
Pages
81-92
Published: September 30, 1986
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Authors developed an original insulation system named "KAWASAKI PANEL SYSTEM" for a LNG carrier with MOSS type spherical tanks and applied it to three LNG carriers successfully. This insulation system is composed of cellular plastic materials and metallic materials, whose properties are very complicated. The cellular plastic materials have temperature dependent and anisotropic properties. The metallic materials are wire net and very thin embossed aluminum sheet whose properties are dependent on the construction. This paper introduces FEM analysis which was carried out to clarify the behavior of such complicated composite insulation panel. In this analysis, Hill's yield criterion was applied to explain the failure of anisotropic polyurethane foam (PUF). Some tests including actual ship test were carried out to obtain back data for the FEM analysis. The results are as follows: (1) The FEM analysis is applicable to such complicated composite insulation panel which is composed of cellular plastic materials and metallic materials. The reliability of FEM was proved by experiments. (2) Hill's yield criterion can explain the failure of anisotropic PUF. (3) "KAWASAKI PANEL SYSTEM" has sufficient strength. (4) The design method using FEM can be utilized for the development of new insulation systems.
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Yasuo YOSHIDA, Shingo YAMAUCHI, Koji TANIDA, Makoto MAEDA
Article type: Article
Pages
93-105
Published: September 30, 1986
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This paper deals with the development of a centrifugal pendulum absorber to reduce ship superstructure vibration. The developped absorber has following characteristics. (a) The size is compact and easy to install on superstructure. (b) Vibration of any order caused by engine or propeller can be reduced. (c) Random variations of amplitude and phase can be automatically followed. (d) Any other structures are not excited by the absorber. The authors performed the theoretical analysis of the absorber and carried out the forced vibration experiment of a model structure by a test absorber and it's control system. The conclusions obtained are as follows. (1) This absorber was effective to reduce vibration of the structure as it was predicted by theoretical analysis. From the test of pendulum bearing endurance and control system simulation, we confirm this absorber can be applied to an actual ship. (2) In the absorber, pendulum tuning is most important. Mass ratio decides the permissible tuning error value. Small mass ratio requests the accurate tuning control. Resonance caused by tuning error larger than permissible value makes the absorber ineffective. (3) From the experiment, the amplitude of the structure was constant and independent from exciting force when pendulum tuning was perfect. This can be explained by the theoretical analysis of Coulomb damping acting on pendulums.
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Koji TANIDA, Minoru KUBOTA, Noboru HASEGAWA
Article type: Article
Pages
107-118
Published: September 30, 1986
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Recently there is a trend to install long stroke type diesel engines with a small number of cylinders on ships for saving energy and simpler maintenance, but the engines cause to increase ship vibration problems induced by shafting vibrations, due to less stiffness of crankshaft and increased exciting forces of diesel engine. For estimating coupled longitudinal and torsional vibration response of long stroke type crankshaft by conventional methods, problems for modelization have been still left to be solved. So, the authors carried out detailed static and dynamic analysis of total shaft system concerning IHI-SULZER 6RTA58 diesel engine, by the use of 3-dimensional finite element method with solid elements applying component mode synthesis and image element method to reduce a large amount of computer time. These calculated results have agreed well with tested results of longitudinal stiffness of actual crankshaft and with the results of vibration measurements of shafting on board ships, and have shown great improvements of accuracy especially for the coupling vibration characteristic between longitudinal and torsional vibrations compared with the conventional methods. From these studies, the authors also obtained improved simplified formula for estimating such as equivalent longitudinal stiffness, equivalent longitudinal exciting force converted from radial gass force.
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[in Japanese]
Article type: Article
Pages
119-130
Published: September 30, 1986
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[in Japanese]
Article type: Article
Pages
131-135
Published: September 30, 1986
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Article type: Appendix
Pages
137-138
Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Article type: Appendix
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Published: September 30, 1986
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Article type: Cover
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Published: September 30, 1986
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Article type: Cover
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Published: September 30, 1986
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