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Article type: Cover
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Published: March 25, 1994
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Article type: Appendix
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Published: March 25, 1994
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Article type: Index
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Published: March 25, 1994
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Article type: Index
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Published: March 25, 1994
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Masatoshi BESSHO, Shun SAKUMA
Article type: Article
Pages
1-7
Published: March 25, 1994
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When we design a high-speed ship, it is the most important to reduce her resistance. We must reduce her residual resistance, because it occupies the great part of her total resistance at high speed. Then, how can we desigh her hull form? There are many studies, but there are few papers on the method of reducing them. This report deals with such a method theoretically. As the first step, we think the residual resistance consists of spray resistance, wave-making resistance and head resistance. In their optimization, we think all components shoud be minimum. When we tested in fixed condition, the bow spray was diminished.
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Kun MA, Ichiro TANAKA
Article type: Article
Pages
9-15
Published: March 25, 1994
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This paper describes a method for obtaining the optimum ship form of low resistance and its validation including the prediction of separation by model experiment. Wigley form is used as the parent model. Based on Michell's wave resistance theory and considering viscous resistance, nonlinear optimization techinique, SUMT method, is applied for two cased, one for bow form optimization and the other for overall optimization. Occurrence of separation is checked by a newly devised, simple prediction method of separation. Model experiments are made to investigate the comparison between the theory and experimental results.
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Hisao TANAKA, Yasuyuki TODA, Toshio SUZUKI
Article type: Article
Pages
17-23
Published: March 25, 1994
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An integral method of three-dimensional boundary layer with small cross flow assumption is used for predicting axial velocity distribution around ship stern of a fine practical ship form (Series 60, C_B=0.6 model ship). Potential streamlines on the hull surface and in the flow field are used for coordinate system suitable for small cross flow method. The flow fields can be obtained to the propeller plane without any divergence of the solution. The results are compared with available experimental data. The comparison show that the present method is promising because of the simple computational method although it has some discrepancy.
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Tadao YAMANO, Yasunori IWASAKI, Kazunori TAGUCHI, Naoki MAEDA
Article type: Article
Pages
25-33
Published: March 25, 1994
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In ocean going fine ships such as recent container ships with high power main engine, it seems almost impossible further to improve their propulsive performance to a large extent so far as the convetional stern form is used. The reason is that severe design conditions such as a draft restriction, a large TKM (transverse metacentric height) requirement and an enough propeller tip clearance requirement restrict the propeller diameter and the stern form modification to a narrow range. The authors have tried to break through this wall and, as a result, have developed a new stern form, "Kawasaki SCS (Sophisticated Concave Stern)" (patent pending). This paper describes the development of the stern form.
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Yukihiko OKAMOTO
Article type: Article
Pages
35-41
Published: March 25, 1994
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Six propellers with different skew angle distributions and constant pitch distributions are selected in order to clarify the skew effects on unsteady cavitation characteristics of marine propeller in non-uniform flow fields. Using these propellers, the effects of the skew angle and the skew distributions on characteristics of propeller cavitation were investigated experimentally. Cavitation observations, hull pressure measurements above the propeller, cavity thickness measurements, paint tests and noise measurements were carried out in two different wake fields. One is a model wake distribution of a car carrier which had been adopted in comparative erosion tests of 17th ITTC, the other is the estimated ship wake distribution by Sasajima and Tanaka's method. The results of the experiments show the reduction of the hull pressure amplitude as the increase of skew angle, while the cavity volume increases in proportion to the increase of skew angle. The effect of increase in skew angle seems to reduce the extent and weaken the impulsive pressure of the cloud cavitation which occures when unsteady cavity collapses. This is supported by the results of paint tests and cavitation noise measurements. The falling off area of the paint on suction side of propeller blades and the sound pressure level are reduced as the increse of skew angle.
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Norio ISHII, Kazuo ARAI, Hiroshi TOMARU, Kazuo MASUYAMA, Ken SHIMIZU
Article type: Article
Pages
43-48
Published: March 25, 1994
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This paper presents a numerical method for predicting the hydrodynamic and cavitation performance of a submerged hydrofoil. The numerical model of a hydrofoil is constructed with a hydrofoil and center and side struts. It is also taken account of the effect of the controll of flaps. The method represents a hydrofoil and struts by discrete vortices and line sources located on the camber surface of the hydrofoil and strut. The effect of the water surface is considered approximately by the image system in the present method. A three-dimensional theoretical procedure is used to calculate partial-and super-cavitation occurring on the hydrofoil surface. In order to verify the validity of the method, the lift and drag acting on the hydrofoil and the extent of the cavity occurring on the back or face surface of the hydrofoil were calculated and compared with the test results which was carried out in the cavitation tunnel of Akishima Laboratories (MITSUI ZOSEN) Inc. The comparisons show that the present method becomes a very useful tool for designing the hydrofoils of a high speed craft.
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Toshihiko KAWASHIMA
Article type: Article
Pages
49-62
Published: March 25, 1994
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To improve the accuracy of model tests, fluid dynamical problems of circulating water channel are considered by surveying the free surface inclination. Fundamental characteristics of the free surface inclination are studied by systematically controlling the water volume and the setting angle of the plate of the wave suppressor. From the practical viewpoint, the evidence is shown that the effects on the free surface inclination is unchangeable regardless of changing the water volume and the plate angle. A practical correction method is proposed that of diminishing the influence of the steady wave and the free surface inclination from results of measured resistance by traversing model to longitudinal direction. The reasonability and reproducibility about the conventional driving method is investigated, that of keeping the minimum condition on the steady wave height by adjusting the water volume and the plate angle.
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Mitsunori MURAKAMI, Yoji HIMENO
Article type: Article
Pages
63-69
Published: March 25, 1994
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Study on the calculation method of wind forces on a 2-dimensional body is made to propose a more reasonable one in theoretical treatment, based on the Discrete Vortex Method (DVM) which is considered to be useful in calculation because of its simplicity. The general theory based on a Fredholm type integral equation of the 2nd kind is introduced into the problem, in which the unknows of both vortex and source distributions on the body surface are signified simunltaneously, and this problem leads to the so-called well-posed problem differing from the usual DVM. Furthermore, another calculation method of the pressure distribution on the body surface is proposed considering with the unsteadiness of vortex shedding. Numerical calculations are carried out for simple cases and compared with the experimental data in order to confirm validity of this method.
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Makoto ARAI, Satoshi SASAKI, Yoshiyuki INOUE
Article type: Article
Pages
71-76
Published: March 25, 1994
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In this paper, a new open boundary treatment technique on the probrem of irregular wave simulation in numerical wave tanks is proposed. A neurl network model is applied in the present study to set up an open boundary where outgoing waves can pass it smoothly without affecting the solution inside the computational domain. An artificial velocity reduction zone is also installed adjacent to the open boundary to assist the treatment at the boundary. By comparison of the performance of the tanks with the alternative techniques, the advantage of the proposed one is shown.
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Setsuo TAKEZAWA, Hiroshi TAMAMA, Kazumi SUGAWARA, Koichi KONDO, Shuhei ...
Article type: Article
Pages
77-82
Published: March 25, 1994
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The sea trials of the world's first prototype experimental ship with super-conducting electro magneto-hydrodynamic propulsion, "YAMATO 1" were carried out in Kobe harbour in 1992 and the performance was proven to be as designed. This report shows the comparison the results of the sea trials and the calculation by the estimation method for propulsive performance which was developed through the reseach and deveropement project for "YAMATO 1" and evaluates the calculation method.
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Iwao WATANABE
Article type: Article
Pages
83-89
Published: March 25, 1994
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A new method calculating diffraction pressure over a ship running in oblique waves is presented. The method is constructed based upon the same assumption as convetional strip theory (NSM) except for exact formulation on body boundary condition and inclusion of x-derivative term of the velocity potential in the free surface condition. Through the boy boundary condition effect of the variation of the wave orbital velocity along the body surface is taken into account whereas most of conventional strip method calculation fail. Numerical scheme is presented following Ursell-Tasai method. Results obtained by the present method are compared with experimental results to show that they are in good agreement for most of running and incident conditions in waves.
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Kimio SAITO, Masaru TSUJIMOTO
Article type: Article
Pages
91-95
Published: March 25, 1994
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Based on the nonlinear optimization technique with constraints, the optimum hull forms from the hydrodynamic aspects have been investigated. The design system used in the paper to find an optimum hull form consists of three models ; (1) Shape definition model, in which the spline curves are used to define the underwater shape of a ship, (2) Hydrodynamic model, in which the wave exciting forces and haeve damping coefficient are concerned, (3) Optimization model, in which the so-called GRG method is used. Two examples are illustrated. One is the optimum hull form Which minimizes is wave exciting forces and another is the one which minimizes ship motions in waves.
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Shigeru NAITO, Hideaki UEMATSU
Article type: Article
Pages
97-109
Published: March 25, 1994
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In the high speed marine transportation age, various kinds of transportation systems are proposed. As a ship speed becomes higher, it is important to reduce the wave making and viscous resistance particularly. One method is that ship body is put up in the air by the foil and the propulsion system is set up under the water. As this system has an instabiliity of motion in the takeoff condition, an investigation is necessary on how to take off. Considering these tendencies, the jet engine system which is for the aircaft and has a high reliability is proposed as the propulsion system in this paper. This idea is based on the following three reasons. 1. trouble avoidance by putting up the propulsion system in the air 2. high reliability of a jet engine and simplicity of a maintenance by putting up it in the air 3. motionless in waves When this system is studied, it is important for the motion in the takeoff to know the behaviors of thrust, resistance and the attack angle of the foil etc. at each instance, and also to think of the foil control, which foil does not stall and the ship body can rise up smoothly. The purpose of the paper is to solve the equations of motion in the takeoff condition, to investigate the effect of various parameters with the simulation and to get the useful data at the initial design stage.
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Toshifumi FUJIWARA, Yoshiho IKEDA, Naoya UMEDA
Article type: Article
Pages
111-116
Published: March 25, 1994
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The authors proposed a method to assess the stability quality of a ship by the risk analysis based on the capsizing probability of it in wind and waves. This method was already experimentally confirmed to be valid for hard-chine craft when experimental results of the roll damping and exciting moment of the craft were given. In the present paper, the method is applied to conventional cargo ships whose roll damping and exciting moment can be predicted by modern ship motion theories developed in these twenty years. The experimental work on the capsizing probability of cargo ships in waves are carried out to confirm the availability of the method. Six kinds of cargo ships in Japanese domestic service are chosen to calculate the capsizing probability for making the assessment of the stability quality of them in severe sea conditions. These results also show that the method is useful to decide the optimum GM value and the optimum size of bilge keels to keep the sufficient stability quality in design stage.
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Tsugukiyo HIRAYAMA, Kiyoshi MIYAKAWA, Takehiko TAKAYAMA
Article type: Article
Pages
117-122
Published: March 25, 1994
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Recent years, many ocean going sailng yachts are constructed. Among those yachts, there are types that have poor stability performance especially at the capsized condition. The light displacement sailing yachts belong to this type. Sooner or later, capsizing phenomena can not be avoided for ocean going small vessels when hitted by a large plunging type breaking waves. So the most important point is the restoring characteristics from capsized condition. This paper investigated into the capsizing process of a 47-feet sailing yacht in a breaking waves taking into account the real hazard occured in 1991 and also studied on the restoring process mainly by model experiments. Plunging breaker in deep water is difficult to be generated in the experimental tank, so we applied Transient Water Wave Technique for the generation of such waves. This technique was developed at Yokohama National University more than twenty years ago. As the results, the relation between breaking wave height ,mast length, wave encounter angle and capsizing are obtained. The relation between the amount of water immersion and self restoration is also obtained.
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Noriyuki KAMOI, Tomokazu TANIGUCHI, Takashi KISO, Kazuo KADA, Akira KO ...
Article type: Article
Pages
123-132
Published: March 25, 1994
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A new slot structure to ensure both structural safety and constructional easiness has been developed. By FEM analysis of its static strength in a 280,000 DWT double hull VLCC and by fatigue strength test using a model, practical use of this new structure has been studied. Further, based on the fatigue strength test results for its structural elements, a fatigue strength evaluation criteria that can directly evaluate its fatigue strength under working load and has a good conformity with past data has been made. Then, the fatigue strength of the new slot structure adopted for a double hull tanker has been evaluated according to this criteria. As a result, it has been ascertained that the new slot structure is superior to the conventional one in the static strength and the fatigue strength and is applicable to actual ships.
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Yusaku KYOZUKA, Kenji NAGAMACHI
Article type: Article
Pages
133-141
Published: March 25, 1994
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Mass transport in water waves is a nonlinear phenomenon and it plays important role in the environmental problems in the ocean such as the propagation of oil spills and the diffusion of contaminated materials. Mass transport induced by a wave maker in the shallow wave tank is theoretically and experimentally studied. Viscous effects on free-surface and water bottom are considered by the boundary layer theory with the basis of Longuet-Higgins' thoery. Contributions by local waves in front of a wave maker are exactly taken into account by the eigen function expansions. Stream lines and velocity vectors are presented graphically and they are validated in comparison with measurements measurements in a wave flume.
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Hisaaki MAEDA, Koichi MASUDA, Shogo MIYAJIMA, Yasuaki TOTSUKA
Article type: Article
Pages
143-149
Published: March 25, 1994
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We have developed the numerical calculation method to simulate the short crested wave fields. In this paper, we compare the simulated multi-directional waves with the measured waves in experiments using directional wave spectrum, as the results we confirm that this simulator of multi-directional waves is useful to express the short crested wave field. On the other hand, because this simulator uses the linear summation method of regular waves, the simulated waves may have very large wave steepness as breaking in real sea state. To have reality the simulated waves, we contain the algorithm of numerical estimation of breaking wave fields. The algorithm has the wave height limitation of breaking wave using the acceleration of water surface elevation. We compare the simulated multi-directional waves using the breaking wave estimation with the measured waves in experiments with breaking waves. As the results, we confirm that the algorithm of breaking wave estimation is useful to simulate the wave heights including breaking waves.
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Tsugukiyo HIRAYAMA, Seiya UENO, Takuya KATOH, Kiyoshi MIYAKAWA, Takehi ...
Article type: Article
Pages
151-157
Published: March 25, 1994
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It is important to make a research on directional spectrum waves, because it can characterize the ocean waves. Recently, we manage to control the generation of the directional spectrum waves that has an arbitrary directional distribution in a longitudinal towing tank. By that way, we are able to study the characteristics of real ocean waves. Since it is difficult to measure directly the local wave slope with precision, there are not so much researches available in this matter. For that reason, this report deals with the characteristics of the local wave slope of the directional spectrum waves measured by the laser beams. Further, the relationship between the wave slope and wave height spectrums and the criteria of breaking waves are also investigated.
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Yo-ichi TACHIBANA, Yoshiho IKEDA, Koji OTSUKA, Taketoshi OKUNO
Article type: Article
Pages
159-164
Published: March 25, 1994
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Motions of a discus buoy which is generally used in a fast current are relatively large in waves. In this study, the effects of a ring-shaped damper on the motion of a discus buoy in waves are experimentally and theoretically investigated. Hydrodynamic forces on the buoy and the ring-shaped damper are experimentally and theoretically investigated in order to obtain the coefficients of the equation of motion. The results show that the forces on the ring-shaped damper significantly depend on the aspect ratio, which is defined by the ratio of the ring height H to the ring diameter D, and that the hydrodynamical interaction between the buoy and the damper is negligibly small. The motions of the buoy obtained by calculating the non-linear equation of motion in time domain are in good agreement with experimental ones. From these results, it is found that the optimum aspect ratio of the damper exists to reduce the motion in waves.
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Shoichi HARA, Kenji YAMAKAWA, Hideki MARUYAMA, Ryoji TAKAHASHI
Article type: Article
Pages
165-175
Published: March 25, 1994
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There have been many marine accidents around Japan Recently. About 270 ships have actually been towed by the patrol boats in 1991. The towing operation is a very important role in the rescue mission of the patrol boats of Maritime Safety Agency in Japan. Maritime Safety Agency carried out the preparatory towing experiment using patrol boats first in the calm sea. After investigating the procedures of experiment, Full-scale measurement during towing has been carried out using 3 patrol boats offshore of Chiba prefecture. The main purpose of at-sea experiment is the estimation of towing force and the maneuverability in wind and waves. The following remarks have been demonstrated in this experiment. The average towing force during towing using synthetic fiber ropes agreed well with the estimation. However, the estimation of the extreme towline tension is quite important under rough sea conditions. The Characteristics of the turning toward the windward direction of the towed ship have to be understood during towing especially in the case of towing of PCC. The standard estimation of 1 ton per 100 PS decreases drastically in waves.
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Article type: Appendix
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Published: March 25, 1994
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Article type: Cover
Pages
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Published: March 25, 1994
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