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Article type: Cover
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Published: December 30, 1987
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Article type: Index
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Published: December 30, 1987
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Article type: Appendix
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App1-
Published: December 30, 1987
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Matao TAKAGI, Kimio SAITO, Yutaka OOKAWA, Tsukasa KYOE
Article type: Article
Pages
1-10
Published: December 30, 1987
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A survey of computer simulation results of slow drift oscillations on a moored semi-submersible in regular wave groups and irregular waves is presented. Calculation methods used by each participant for the second order wave forces, damping as well as the first order hydrodynamic forces on a semi-submersible are examind. Fifteen different results are compared and it is found that the correlation between the computed results and the measured ones is kept within the acceptable bounds when the appropriate value of viscous damping is taken into accounts in the computation.
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Hideaki MIYATA, Hisashi KAJITANI, Ming ZHU, Takeshi KAWANO, Michio TAK ...
Article type: Article
Pages
11-23
Published: December 30, 1987
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The finite-difference method TUMMAC-Vbk developed for 2D breaking waves is improved so that higher-Order accuracy is achieved in a variable mesh system. This numerical tool is used to investigate into two wave breaking problems, i.e., wave breaking on a shallowly submerged obstacle and on a bump. The comparison of the simulated results with experiments shows good agreement.
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Shigeru NAITO, Jun HUANG, Shoichi NAKAMURA
Article type: Article
Pages
25-32
Published: December 30, 1987
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With the development of the interest of exploiting ocean sources, experiments carried out on real sea wave conditions are playing a more and more important role in ocean engineering field. When experiments are carried out, reflective waves from a tank termination or a test floating body would make experiments unreliable. In order to eliminate reflective waves, theoretical and experimental approches on wave absorb-makers have been tried over the past few years. Many of them are concerned with the characteristics of wave absorb-makers in regular waves. Practically more interest must be focused on the problem in irregular waves. A new wave absorb-maker (WAM) is developed, which is installed on a two dimensional water wave tank. The new wave absorb-maker consists of a buoy, a measurement instrument, a motor activator, a control unit and an operational unit. External force for wave absorption can be calculated in the control unit by use of velocity and displacement of the buoy. The activator drives the buoy such that force measured by the force detector installed on the buoy is a close approximation to calculated force. To absorb and make waves simultaneously, we add a wave-making signal to the signal of the external force for absorption. The optimum condition for complete absorption of regular waves is well known and is easy to realize. However, the optimum condition in irregular waves can't be realized physically, because it does not satisfy the causality. Two systems, one is called "Causal System" and the other is called "Constant Coefficient System" are proposed. Both systems are described in detail in this paper. Our research is concerned with theoretical and experimental investigations on wave absorbing and wave absorb-making performace of device.
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Ken TAKAGI, Akihiro NIIMI, Shigeru NAITO
Article type: Article
Pages
33-43
Published: December 30, 1987
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A theoretical study of the phenomenon for deck wetness is presented. And the optimum flare angle is discussed. It is shown that the 2-dimensional self-similar flow is aplicable to the analysis of deck wetness on the assumption of the long wave length and high Froude number. The 2-dimensional self-similar flow which includs effects of the deck is caluculated by the analytical method. Calculated results are compared with experimental ones which are obtained at the limit of long wave length, i.e., in still water. Using calculated results, the optimum flare angle is discussed. And an attempt to determine the Optimum flare angle is presented.
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Shigeru NISHIO, Ichiro TANAKA, Yoshinori NORITAKE, Tomoyoshi NISHIKAWA
Article type: Article
Pages
45-52
Published: December 30, 1987
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The separated flow field around prolate spheroid at incidence is investigated. The characteristics of flow field are investigated experimentally by the measurement of surface pressure distribution, the measurement of velocity distribution by use of 5-hole pitot tube and the flow visualization. Based on these results, the relationship between characteristics of separated flow field and surface pressure distribution is discussed. Vortex layer configuration and surface pressure distribution are calculated numerically by considering the shedding of vortex sheet, based on a slender body approximation. The agreement between measured vorticity distribution and calculated vortex layer configuration is relatively good. The comparison between the calculated pressure distribution and the measured one shows, however, the consideration of secondary separation as well as viscous diffusion and dissipation is necessary to obtain the agreement between them.
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Yasuhiro SAKOH, Yoji HIMENO, Masatoshi BESSHO
Article type: Article
Pages
53-62
Published: December 30, 1987
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The present paper deals with an inverse problem for obtaining optimum body profiles with minimum viscous drag. In the preceding first paper the authors applied the inverse procedure for drag optimization developed by Bessho to two-dimensional Oseen flow, and obtained symmetric optimum profiles about the origin. The present work is an extension of the method to fore-aft asymmetric profiles with minimum drag under some restrictions. Numerical results and discussions on the optimum profiles are made. The procedure to find optimum profiles is an iterative scheme. The flow quantities for a given profile are firstly determined by integral equations using Oseen kernel functions. Then the optimum deformation is determined so that the drag is minimized. And the body profile is deformed to obtain a new profile. These processes are iterated until a convergence is reached.
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Isao NEKI, Hideaki TATAMI
Article type: Article
Pages
63-68
Published: December 30, 1987
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Many papers and applications about the boundary element method (BEM) were reported on the various fields, because of its easiness in the modeling and the economy on the calculation cost. The authors have already published new applications of BEM for the stress analysis and applied in practice. On the other hand, it is genallary said that the higher-order elements show the good accuracy, but there are few detail research for them. In this paper, the authors investigated the accuracy of the constant, linear, quadratic and those hybrid boundary elements on the added mass of vibration, and confirmed the super-parametric hybrid elements give the good results.
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Tamotsu SHINOHARA, Shin-ichi TAKAGAWA, Kimio YOKOTA, Hideyuki MORIHANA ...
Article type: Article
Pages
69-80
Published: December 30, 1987
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The 6500m Deep Submergence Research Vehicle is now under construction in Japan. In order to obtain high maneuverability, the Vehicle should be compact in size and light in weight as possible. For this purpose, titanium alloy (Ti-6AI-4VELI) is adapted for the material of the pressure spherical hull. From the viewpoint of weight-strength ratio, titanium alloy is the best candidate for the pressure hull at the present stage, which was already adapted for the pressure vessels of subsidiary use in the 2000m Deep Submergence Research Vehicle "SHINKAI 2000". For a main pressure hull made of titanium alloy, the fabrication procedure was investigated by building a full scale model since there was no prior experience in electron beam welding fabrication so far. The material characteristics before and after fabrication were fully examined and it was confirmed that the fabrication procedure was satisfactory for the present purpose. Collapse behaviour has been examined by the collapsing test using three models of 500mm in diameter made of titanium alloy as described in the first report. Based on these investigation, titanium alloy has been proved to be applicable for the actual structure of the main pressure hull. The collapsing test was carried out with a 1/2.86 scaled model of 700mm in diameter, which was designed after the actual main hull and fabrication following the Procedure described above. The test consisted of two stages; (1) 1500 cyclic pressurization up to 680kgf/cm^2 corresponding to the cyclic submergence to 6500m deep sea within the Vessel's whole life, and (2) collapsing test following ordinary procedure. As a result, it is shown that such cyclic pressurization has no influence on the collapse behaviour, and that the shell fails after the occurence of considerable plastic deformation.
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Hajimu MANO, Hiroshi KAWABE
Article type: Article
Pages
81-89
Published: December 30, 1987
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In the first and second report, authors studied the optimum configuration of hole with minimum stress concentration in an infinite elastic plate under uniform loading. However, when we analize the stress distribution around hole arranged on a deck, such as hatch opening, we have to take the finite boundary condition into consideration. Also, holes are continuously arranged more than one. In this report we studied the optimum configuration of continuous holes with minimum stress concentration in a rectangular elastic plate under uniform loading. For the expression of the configulation of hole, we employ the mathematical descriptions which were proposed in the first report. At first step, we examine the single hole problem in a rectangular plate. As the result of investigation, the optimum configuration of hole depends on the ratio of the plate breadth to the hole breadth, The narrower the plate breadth becomes, the lower the stress concentration ratio drops and the optimum configuration of hole forms more rectanglelike shape than that of infinite plate. In the case of continuous hole problem, the distanse between holes affects optimum configuration of holes. The property of configuration and stress concentration of hole at both ends are similer to that of single hole. The other middle hole configurations have a small radius at corner and are more rectanglelike shape than end holes.
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[in Japanese], [in Japanese], [in Japanese], [in Japanese]
Article type: Article
Pages
91-96
Published: December 30, 1987
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[in Japanese]
Article type: Article
Pages
97-100
Published: December 30, 1987
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[in Japanese]
Article type: Article
Pages
101-104
Published: December 30, 1987
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[in Japanese]
Article type: Article
Pages
105-106
Published: December 30, 1987
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[in Japanese]
Article type: Article
Pages
107-108
Published: December 30, 1987
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[in Japanese]
Article type: Article
Pages
109-
Published: December 30, 1987
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Article type: Appendix
Pages
111-115
Published: December 30, 1987
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Article type: Appendix
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Published: December 30, 1987
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Article type: Appendix
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Published: December 30, 1987
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Article type: Appendix
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Published: December 30, 1987
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Article type: Appendix
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App5-
Published: December 30, 1987
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Article type: Appendix
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App6-
Published: December 30, 1987
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Article type: Cover
Pages
Cover2-
Published: December 30, 1987
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Article type: Cover
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Published: December 30, 1987
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