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Published: September 30, 1981
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Yoshihiro OHASHI, Naomi KATO
Article type: Article
Pages
1-10
Published: September 30, 1981
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A procedure of preliminary design of semi-submerged catamaran (SSC) is presented, treating the investigation of both characteristics of motions in waves and of resistance as a process of design, the former of which plays a more important role on the design of SSC than on the design of conventional ship. The principal dimensions (breadth of strut, distance between two demihulls) are determined from the survey of the natural periods which lead with little probability to resonant conditions in a seaway, while the dimension and the configuration of lowerhull are given beforehand so that the lowerhull has charge of the required displacement under the restriction of draft. After the determination of the principal dimensions, the shape of strut is determined so as to minimize the wave making resistance caused by the strut and the lowerhull by the use of linear theory of wave making resistance. The motions in regular waves and the resistance are measured with the models which are designed with the procedure proposed here. The interaction between both characteristics of motions in waves and of resistance is shown by changing the principal dimensions. The effect of asymmetric lowerhull with respect to vertical and lateral directions on resistance performance is examined with resistance test. The effect on the flow field near bow is also investigated through the observation of limiting streamline.
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Norio JINGU
Article type: Article
Pages
11-19
Published: September 30, 1981
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Small Waterplane-Area Twin-Hull Shlp is superior to conventional ships from a viewpoint of wave making resistance and seakeeping characteristics, so it is given attention as one of the new type of ships. Recently, two types of SWATH have been investigated, one is single strut type and the other twin struts type. In this study, the model tests on the later type of SWATH were carried out and were compared with the theoretical calculation by using the strip theory that neglected the interaction between catamaran hulls. Consequently, it is certified that the strip theory is usefull to predict the longitudinal motion of SWATH in head seas.
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Hiroyuki MATSUMURA, Takao YOSHIKAWA, Shigetomo NAKAGAWA, Hiroshi KAMOT ...
Article type: Article
Pages
21-28
Published: September 30, 1981
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Synthetic Ice with various compressive strength for Propeller-Ice interaction test has been studied. Compressive strength, about 1.0∼20kg/cm^2 of synthetic ice prepared from NaCl+CMC aqueous solution was required. The production process of synthetic saline ice with large thickness in short time has been carriedout. The synthetic ice were availably used for Propeller-Ice interaction test and satisfactory experimental results has been obtained. This report mainly describes details of production process and mechanical properties of the synthetic saline ice to be used in the model ice load test for arctic marine propeller.
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Mitsuhisa IKEHATA
Article type: Article
Pages
29-37
Published: September 30, 1981
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The author has intended to obtain the self-propulsive performances of a ship of full size directly from the data of the self-propulsion test of the ship model, in order to investigate the scale effects on self-propulsion factors. It is necessary to reduce the excess wake of the model down to that of the ship as well as to supply the model with skin friction correction. Then, the author has had the idea that the method similar to the water jet propulsion would be available to this purpose. The idea has been realized by the apparatus illustrated in Fig. 4. The water jet spouted from the nozzle located at S.S. 13/4 on the flat bottom flows into the propeller disk to accelerate the velocity of wake stream. Thus, the wake of the model in the propeller disk becomes narrow nearly close to the feature of the ship wake. Total flux of jet is then controlled by the valve to generate the thrust corresponding to skin friction correction. On the selfpropulsion test the sum of two thrust forces generated by the propeller and by the water jet counterbalances the resistance of the hull of the model. This balancing condition is inspected by the zero towing force of the resistance dynamometer. As shown in Fig. 10, the results of one example as for 4 meters long model of 240 meters long full bulk carrier, C_B=0.8, have given some interesting conclsions that, in the condition of with-jet, the effective wake factor (1-w) has been raised 15∼20% higher while the thrust deduction factor (1-t) has got 3∼6% up and the relative rotative efficiency (ηr) 2∼3% up. Those gains of self-propulsion factors are thought corresponding to their scale effects. The calculation by the author's method based on the modified blade elements theory has also given almost same results as those of with-jet. It proves the validity of this calculation method. It has been shown in comparison with the results of the test with jet that the wake factor has been estimated to about 10% higher value by 1978 ITTC performance prediction method.
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Matao TAKAGKI, Kimio SAITO
Article type: Article
Pages
39-48
Published: September 30, 1981
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Concerning the study of non-harmonic wave problems, the hydrodynamic responses, memory effect functions, generated by an impulse in oscillating velocity of a body are required. To deal with practical problems, the calculation method which gives these functions from the wave amplitude rations in the frequency domain is a useful tool. The wave amplitude ratios for all frequencies are obtained by connecting the exact values of the wave amplitude ratio in a medium frequency range with the asymptotic values in a high frequency range. In this paper, firstly, the authors investigate a more rational method of calculation for the asymtotic values of the wave amplitude ratio in a high frequency range. These values for forced swaying and rolling cylinder on a calm water are presented by extending the Ursell method for forced heaving circular cylinder. Secondly, numerical calculations of the memory effect functions are carried out for three Lewis form sections.
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Matao TAKAGI, Kenichi SAWAYAMA, Eizoh YAMAGUCHI
Article type: Article
Pages
49-54
Published: September 30, 1981
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In order to extract the wave power, the floating cylinder has to satisfy the condition of being wave-free on one side when it is forced to oscillate in a given mode. In this paper the authors show the method of determing the contours which satisfy the above condition. Numerical calculations were carried out for the case of heaving and rolling mode, and these results show that the obtained contours have good performances for wave power absorption. The calculated results were confermed by the experiments for heaving mode.
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Eijiro TAKAGI, Ichiro INO, Yoshio MISHIRO, Tadashi SANO, Masumi KAWAHA ...
Article type: Article
Pages
55-64
Published: September 30, 1981
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There are some cases where the pressure hull of a submersible includes a partial outer pressure tank within two concentric cylinders. In this paper, the strength was calculated by two methods-FEM and some approximate theories. The calculated results were compared with the results of stress measurements made on an actual submersible. The measurements were made to find out the most accurate and efficient method of analysis for this type of structure. The FEM analysis was done in two steps. In the first step, the analysis of the whole structure model was tried in order to understand the behavior of the structure as a whole. A suitable method of partial (local) modeling was investigated to increase the efficiency of the FEM analysis. In the second step, the analysis using the partial (local) structure model made clear the stress and deformation of the structure in detail. The approximate theories, the analyses using theories by W.Hovgaard, K.Okuda and others, were also tried. From the results of these analyses and the stress measurements, the following main conclusions were reached. 1) The deformation and stress distribution for the section of this structure was nonuniform. 2) On the inner shell in the concentric cylinder area, particulary near the partial single hull, peak stress was generated. 3) The stress calculated by FEM analysis closely coincided with the measurements. 4) Concerning the location where the critical stress was generated, the results from the approximate theories (W.Hovgaard, K.Okuda, and others) underestimated the measurements, and were not within acceptable tolerance.
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Kin-ichi NAGAI, Mitsumasa IWATA, Sung-won KANG
Article type: Article
Pages
65-71
Published: September 30, 1981
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In this report is studied the method predicting the fatigue crack initiation life, Nc, with probability of failure, P, in welded structure members of mild steel. As a result, it is shown that the P-ΔS-Nc curve in weld toe of structure members could be estimated using the P-Δε-Nc curve in mild steel and the expectation and variance of logarithm of elastic stress concentration factor, ln (K_t^^w), in weld toe. The propriety of the P-ΔS-Nc curve in the transverse strength members of ship hull construction is confirmed by the comparison with the results of fatigue test on the model of the various transverse strength members, and it is clarified that the ΔS-Nc curve at P=5% is available as the design curve for high cycle fatigue more than 10^4 cycles.
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Shozo KAZAKI, Kiyoshi HASEGAWA
Article type: Article
Pages
73-81
Published: September 30, 1981
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In marine carburized gears, it is especially important to determine the optimum carburizing conditions for tooth bending fatigue strength. So it has been conducted the inplane or rotating fatigue tests using the test pieces and determined the optimum conditions experimentally. This report presents the results of pulsating bending fatigue tests of carburized gears under the optimum conditions obtained by test pieces, in order to know whether the optimum of test piece could be applied to gear. The gears used for the test are of 20゜ pressure angle with 34 teeth and 8 module. The results are as follows: (1) In case of gears, the fatigue strength is the highest at 1.1 mm of effective case depth (h). This result is almost similar to that obtained by test pieces. (2) The fatigue strength of gears almost corresponds to that of test pieces, arranging them by not only the value of h but also the ratio of h to the thickness of gear tooth or test piece. It seems to be still difficult to determine the optimum effective case depth by the value or the ratio. (3) Estimating fatigue limits by hardness and residual stress distributions, the experimental values are about 60 to 70% of estimated values in case of both gears and test pieces. The difference seems to be caused by the fact that the relation between fatigue limits and hardness used in the estimation is the results obtained by rotating bending fatigue tests.
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Toshimasa KAWANISHI, Wataru KATOH
Article type: Article
Pages
83-90
Published: September 30, 1981
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The tension leg platform is a type of moored stable platform whose buoyancy exceeds the weight. The supplementary equilibriating downward force is supplied by tensioned vertical anchor wires. For such a platform, heave, roll and pitch motions will be suppressed. In order to design a reliable anchoring system, it is necessary to accurately predict the forces in the mooring legs induced by earthquake action and the platform motions. This paper presents an model test of the response of a tension-leg single buoy mooring system subjected to earthquake excitation. Based on the results of the test, it can be confirmed that for the purpose of the design of T.L.P. the vertical component of earthquake must be sufficiently taken into consideration.
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Masayosi YOKOMACHI, Hidenobu TANAKA, Mitsunori MURAKAMI, Hiroshi ISSHI ...
Article type: Article
Pages
91-102
Published: September 30, 1981
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Cavitation is usually generated on propeller blades rotating in a ship wake, and it can dramatically increase the fluctuating pressure on the hull surface. So, it is important to estimate pressure corrctly. In the present paper, the following three methods are used to make a quasi-steady estimation of the cavitation: (1) A two-dimensional linearized cavity flow theory is applied to the equivalent hydrofoil section determined by Hanaoka-Koyama's unsteady propeller theory. (2) The cavity extent is given by measured cavity pattern on propeller blades. (3) The cavity extent is obtained by the so-called "Lift Equivalent Method" which is based on the pressure distribution determined by Hanaoka-Koyama's unsteady propeller theory and Moriya's two-dimensional hydrofoil theory. In the method (2) and (3), the cavity shape is determined by using the cavity shape-extent relation for the steady cavity which is derived by the above-mentioned two-dimensional cavity theory. And, on Huse's theory, fluctuating hull surface pressure in cavitating state is obtained based on these different estimation methods for cavitation, and the mutual comparisons are made. The "Lift Equivalent Method" seems to give more promissing fluctuating pressure than the linearized cavity flow theory.
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Michio OHTA, Sakito KAMEI
Article type: Article
Pages
103-110
Published: September 30, 1981
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In this paper, vibrations of the separate typed superstructure of which accmmodation quarter is separated from engine casing are investigated theoretically. Qualitative investigations of them are carried out using shear beams of uniform section on elastic foundation. Main conclusions are as follows: 1) When engine casing is connected to the accommodation quarter, coupled frequencies of them do not obey the law of so-called "spring-off". Namely, the 1st coupled frequency dose not become lower than the lower uncoupled frequency. It comes between two uncoupled frequencies. And the 2nd becomes higher than the higher one. 2) Coupled effect depend on mainly the ratio of the uncoupled frequency of accommodation to the one of engine casing. 3) Coupled effect for accommodation quarter of actual ships is about 5∼10%.
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Kohei MATSUMOTO, Toshimasa SAITOH
Article type: Article
Pages
111-121
Published: September 30, 1981
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Bossing vibration for a twin screw ship was discussed theoretically. Coupled effect of two bossings and shell plating of after part of ship was investigated using a simple mathematical model. The main conclusions obtained from this study are as follows; (1) Natural frequency for symmetrical and asymmetrical mode shape of two bossings depends upon rigidity of bossing and shell plating and distance between two bossings. (2) For a twin screw container ship, the lowest natural frequency indicates asymmetrical mode shape and the second lowest symmetrical mode shape, and for a twin screw roll-on/roll-off ship vice versa. (3) The added mass for symmetrical mode shape becomes two times that for asymmetrical mode shape. (4) It was found that calculated natural frequency obtained from the present theory agrees very well with the experimental value for the roll-on/roll-off ship.
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[in Japanese]
Article type: Article
Pages
123-136
Published: September 30, 1981
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[in Japanese]
Article type: Article
Pages
137-141
Published: September 30, 1981
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Article type: Appendix
Pages
143-144
Published: September 30, 1981
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Article type: Appendix
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Article type: Cover
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