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Article type: Cover
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Cover1-
Published: December 30, 1984
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Article type: Index
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Toc1-
Published: December 30, 1984
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Article type: Appendix
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Published: December 30, 1984
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Seiji TAKEZAWA, Akio KASAHARA
Article type: Article
Pages
1-15
Published: December 30, 1984
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Various statistical characteristics of long crested artificial irregular water waves generated in long experimental tanks have been particularly investigated in this study. As that results, the statistical properties on wave heights, wave amplitudes (maxima and minima), wave periods and wave steepness of artificial irregular water waves were widely obtained. The relations between the statistical characteristics by the direct statistical analysis of measured timehistories those estimated properties by the spectral analysis were also clearly shown. Moreover various new knowledges were obtained for following important items, those are probability distribution of wave periods, joint probability of wave heights and wave periods, statistical characteristics of wave steepness and the vertical asymmetry on hidh irregular waves. Finally authors point out, it is considered that the major part of obtained results of this investigation consist not only in the artificial irregular waves but also in the real ocean waves.
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Masashi KASHIWAGI
Article type: Article
Pages
17-27
Published: December 30, 1984
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As for the calculation of hydrodynamic derivatives for sway and yaw of high-speed ships, Chapman's theory is known as a powerful method. It is also recognized, however, that his method can not be applied to the usual ship-like body, because his numerical procedure is based on the finite difference method. Therefore it is necessary to consider an extension of Chapman's method to the usual ship-like body. In the previous paper, a new method using Fourier transform technique was described and computational results were also presented. Furthermore, the relations between the cross-sectional forms and the forward-speed effect on hydrodynamic forces were investigated. In this paper the author presents the integral equation method which is considered to be an extension of Chapman's method. The integral equation method is applicable to the usual ship-like body and coincides with Fourier transform method for the case of the uniform cylindrical body. These facts may be confirmed by the computational results. Through the comparison of theoretical calculations with experiments of a Wigley ship model, the usefulness of the integral equation method is discussed
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Sumitoshi MIZOGUCHI
Article type: Article
Pages
29-37
Published: December 30, 1984
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Flow around model ships of a container carrier and a tanker with a small angle of yaw are observed by the dye tracer method and the vorticity distributions at some sections are also measured. From the observed results, the vorticities in the lee side of the aft body are allowed to roll up and form a concentrated vortex and the vorticities from the bow bilges of the tanker flow down and along the bottom. The flow around ships are calculated by the invisid strip method with a number of vortex-lines which are emanated from the separation points at each section and extend down stream along a stream line. The calculated vortex positions are compared with the observed results. The calculated side force distributions and hydrodynamic forces acting on a ship are also compared with the measured ones and it is concluded that the leading and trailing edge effects must be taken into account to calculate the side force distributions and hydrodynamic forces by the strip method.
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Minoru SAITO, Matao TAKAGI, Kimio SAITO
Article type: Article
Pages
39-49
Published: December 30, 1984
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In this paper, the author investigate the applicability of the multipole expansion method (MEM) to the three-dimensional radiation problems. The calculation results for the ellipsoids are compared with the boundary integral equation method (BIEM) and the satisfactory agreement is shown. In the comparisons of the computing time, it is revealed that the MEM's time is one fifth of the BIEM's.
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Kimio SAITO, Matao TKAGI, Hiroshi OKUBO, Mitsuo HIRASHIMA
Article type: Article
Pages
51-59
Published: December 30, 1984
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The damping forces play an important role in the estimation of the low-frequency motion of a moored body. Wichers et al. 9) 10) proposed a kind of added damping force due the drift of the body among the waves, which was referred to as "wave damping". On the contrary Kato and Kinoshita 4) showed an increase of the decay of the low-frequency motion coupled with the wave induced motions due to the nonlinear viscous damping forces. In this paper, the authors investigate the above two damping mechanisms experimentally and theoretically. The results show that in the sway motion both "wave damping" and "nonlinear viscous damping" play an important role while the latter is less effective in the surge motion.
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Hiraku TANAKA, Hiroyiki ADACHI, Munehiko HINATSU, Hisashi KAJITANI, Ma ...
Article type: Article
Pages
61-70
Published: December 30, 1984
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The 17th ITTC Resistance Committee has organized the Cooperative Experimental Program. The object of the program was to be produced a comprehensive data base concerning resistance components and flow around hull for a Wigley parabolic hull form, series 60 hull form and others. The authors have joined the program and have presented the "global data" comprising total resistance as well as wave, viscous and pressure resistance components on geosim Wigley models composed of 2.5m, 4m and 6m in length of the models. Taking this opportunity, the authors planed to evaluate the scale effect of resistance components in view of not only the geosim model tests but also study on the 3-dimensional boundary layer theories. This paper is the first among four serial ones, in which the scale effect of the resistance components obtained in the cooperative experiment are mainly discussed. The authors showed the form factor of viscous resistance as a function of Froude Number and the length of models.
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Hisashi KAJITANI, Masaaki NAMIMATSU, Seikoo OGIWARA, Hiraku TANAKA, Mu ...
Article type: Article
Pages
71-79
Published: December 30, 1984
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Viscous effects at low Froude numbers exerted on Wigley Geosim Models (2.5^m:Univ. of Tokyo, 4^m:SRI, 6^m:IHI) in the 17th ITTC cooperative works are analyzed. Double model flows are assumed and 3-D boundary layer equations of integral method are applied to evaluate frictional resistance as well as viscous pressure resistance, sinkage force and trim moment. Through the analysis, it is concluded that; 1. 3-D boundary layer calculation based upon small crossflow assumption is valid for thin mathematical forms of Wigley models. Displacement thickness, momentum thickness and hull surface pressure are well reproduced on the computation. Results coincide well with measured. 2. Scale effect on form factors worked out experimentally are also firmed through the calculation of viscous pressure resistance. Reynolds number effect exists regarding pressure on hulls at the stern which can be visualized as the small difference of wave profiles.
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Yoshiho IKEDA
Article type: Article
Pages
81-87
Published: December 30, 1984
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The asymmetrical flow pattern around a circular cylinder in harmonically oscillating flow is calculated by a discrete vortex method. The obtained vortex-shedding frequency shows a good agreement with experimental results. The Pressure, in-line force and lift force acting on the cylinder are calculated.
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Junkichi YAGI, Toshihiko FUNAKI, Naoki TAKAHASHI
Article type: Article
Pages
89-93
Published: December 30, 1984
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The catamaran ship has twin hulls and a connecting deck. When a catamaran ship is in the oblique waves, the connecting deck is subjected to forces and moments due to relative motions of the twin hulls. In the 1st report, the motions of the twin hulls in the various waves were analysed theoretically and it was found that the wave loads in the deck became largest in the transverse waves and the effect of hydrodynamic interaction between twin hulls could not be neglected. Therefore, in this report, considering hydrodynamic interaction between twin hulls, the motions of the hulls in the transverse and oblique waves were analysed. And the effect of variations of the scantling and the stiffness of the deck structure on the relative motions of the twin hulls and the wave loads in the deck were investigated.
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Yoshisada MUROTSU, Mitsuo KISHI, Hiroo OKADA, Yoshiho IKEDA, Satoshi M ...
Article type: Article
Pages
95-106
Published: December 30, 1984
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This paper is concerned with probabilistic analysis of ultimate strength for jacket-type offshore platforms due to extreme wave induced loads. Morison's formula and finite amplitude wave theory are applied to probabilistic modeling of the loads together with the first-order-second-moment method. Probabilistic collapse analysis is performed by taking into account of the combined effect of the bendig moment and axial force and by systematically generating stochastically dominant failure modes. Numerical examples are provided to demonstrate the validity of the proposed method.
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Yoichiro OKAMURA, Hiroo OKADA, Ken-ichi KITAURA
Article type: Article
Pages
107-112
Published: December 30, 1984
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In this study, the repeated tensile loading fatigue tests for SS41 and SM50A steel plates are carried out on smooth specimens and the two kinds of notched specimens with similar form and different sizes (scale is 1/8 and plate thickness is constant), i.e., stress concentration factor K_t=2.9 and 6.2. And from the results on the fatigue strength based on crack initiation life N_c in intermediate cycle range, the relation between the fatigue strength and K_t and the elastic stress gradient G, is discussed. At the same time, the size effect of notched plates on tensile fatigue strength is also discussed from a viewpoint of the stress gradient G. The results obtained in this study are summarized as follows: (1) Results of above tests show that the fatigue strength of notched plates depends on not only K_t but also G for each material and that there exists the size effect. (2) The ratio of the fatigue strength of notched specimens at notch root K_tσ_<max> for that of smooth specimens σ_<max0>, K_tσ_<max>/σ_<max0>=K_t/K_f (K_f=the fatigue strength reduction factor), is obtained as a function of G independent of K_t in the both materials. (3) From above results, the empirical formula giving the fatigue strength reduction factor of N_c-basis, K_f, is obtained in the following form: K_f=(K_t/(1+a_1G^<b1>))N_c^a_2G^b_2(K_f≧1) where a_1, a_2=constants, b_1,b_2=exponents (see Eq.(7)). This formula shows good agreement with the results of other researchers in comparatively high cycle range. (4) The size effect factor showing degree of the size effect of notched plates, K_s, is also obtained as a function of G, i.e., K_s=K_t/K_f(K_s≦K_t).
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[in Japanese]
Article type: Article
Pages
113-116
Published: December 30, 1984
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[in Japanese], [in Japanese]
Article type: Article
Pages
117-121
Published: December 30, 1984
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Article type: Appendix
Pages
123-125
Published: December 30, 1984
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Article type: Appendix
Pages
App2-
Published: December 30, 1984
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Article type: Appendix
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App3-
Published: December 30, 1984
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Article type: Appendix
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App4-
Published: December 30, 1984
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Article type: Appendix
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App5-
Published: December 30, 1984
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Article type: Appendix
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App6-
Published: December 30, 1984
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Article type: Appendix
Pages
App7-
Published: December 30, 1984
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Article type: Cover
Pages
Cover2-
Published: December 30, 1984
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Article type: Cover
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Published: December 30, 1984
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