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Published: March 30, 1980
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Akira TANAKA, Yoshio YAMAGAMI, Yasuki YAMASHITA, Etsumi MISUMI
Article type: Article
Pages
1-10
Published: March 30, 1980
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Conventionally, the upper limit of wind velocity at which a ship is manoeuvrable is estimated by solving equilibrium equations of steady motion of a ship. However, this method is not realistic because the actual steered motion of a ship in wind is unsteady. In this report, the authors investigate the manoeuvrability of a ship in wind not only by solving non-linear equations of motion numerically on a digital computer, but also by carrying out a steering test with a manoeuvring simulator. From this investigation, a more realistic upper limit of wind velocity is obtained. And by comparison of this value with the one estimated by equilibrium equations, the relation is made clear that, in the beam and quarter wind severest in ship manoeuvring, the realistic upper limit of wind velocity obtained as above is nearly equal to the one estimated by the equilibrium equations of steady motion of a ship whose rudder angle is kept at 15 degrees. By using this relation, the upper limit of wind velocity for many kinds of ships are shown in Fig.24. Moreover, this report describes effects of shallow water, rudder area, waves, uniform current and fluctuated wind on the upper limit of wind velocity.
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Norihiro MATSUMOTO, Keiji SUEMITSU
Article type: Article
Pages
11-22
Published: March 30, 1980
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It is necessary to predict ship's manoeuvrability, in order to prepare a manoeuvring manual for crew of a new ship at a ship design department of a ship builder. We proposed the new mathematical model describing manoeuvring motion of a ship, and then have established the method of a series of captive model tests in a towing tank and the analysis method to predict this performace accurately. With the object of confirming the methods, we made experiments following the proposed sequence, and obtained a group of hydrodynamic coefficients. Putting these coefficients into the mathmatical model, we calculated the simulation of various manoeuvring motions. After comparison between the simulation and the results of free running tests using the same model, these proposals were certified.
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Tetsuo TAGORI, Hisashi OKAMOTO
Article type: Article
Pages
23-29
Published: March 30, 1980
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It was supposed that the origin of unstable phenomena during self propulsion test was the reverse flow and down flow induced by propeller near the upper and fore part of propeller aparture. The side force measurement and flow observation on a Lpp 2 m ship model were carried out in the circulating water channel, using the rotor or suction at propeller position induced the similar reverse flow and down flow, in order to confirm this supposition. As the result, the rotor or suction at propeller position made the similar flow and characteristics to unstable phenomena of self propulsion test. Therefore, it is thought that the origin of this unstable phenomena is the reverse flow and down flow induced by propeller, and the unsymmetrical effect of propeller is not necessary for the inception of this unstable phenomena.
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Yoshiho IKEDA, Masafumi ISHIKAWA, Norio TANAKA
Article type: Article
Pages
31-39
Published: March 30, 1980
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This paper deals with the viscous effects on forces and moments acting on a ship in sway and roll motion at zero forward speed. Through the forced swaying tests, it is found that the sway damping of a ship with bilge keels in moderate sway amplitude may be estimated well by the potential-flow theory. The roll damping and coupling terms in velocity-phase of roll into sway and of sway into roll, however, are affected considerably by the viscosity of fluid. A method for estimating the roll damping was proposed in our previous papers. In the present paper, the methods for predicting the coupling terms in velocity-phase of sway into roll and of roll into sway are obtained on almost the same assumptions as those that we used in deriving the prediction method of roll damping of ships. The values predicted by the present methods are in fairly good agreement with the experimental ones.
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Iwao FUJII, Tsutomu KOBAYASHI
Article type: Article
Pages
41-50
Published: March 30, 1980
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Small FRP fishing boats have recently been built extensively and most of them have hull forms of high speed type with hard chine. In order to clarify scale effect on this type of boats, FRP Hull Form Development Committee carried out full-scale and model tests for two fishing boats. This paper deals with the test results and their analysis. Two actual boats tested are Nikko-maru and Koshin-maru. Both of them are 11m FRP fishing boats with hard chine. Nikko-maru has skegs and Koshin-maru has not. For two actual ships, 2.9 m wooden model ship and corresponding model propellers were manufactured. Model tests were performed in No.2 Tank of the Shipbuilding Research Centre of Japan. Principal results obtained from the above tests are as follows ; (1) Although scale ratio of the models to the actual boats is only about 1/4, values of wake fraction are a little different between the actual boat and the model. (2) Roughness allowance ΔC_F obtained on a base of Schoenherr's method is quite large and decreases with the increase of ship speed. (3) Expressing resistance argumentation due to wind and wave by ΔC_F', ΔC_F'≒1.7×10^<-3>. This value was obtained from the full scale experiment of Nikko-maru in waves and Koshin-maru is calm sea. Therefore, some other effects than wind and waves may be included in this value. (4) If there is no scale effect on wake fraction, ΔC_F based on Schoenherr's friction line will be about 1.2×10^<-3>. (5) The total resistance coefficient of the actual ships, which were obtained assuming that thrust deduction coefficient does not vary between the ship and model, crosses with that of the models at Fn≒0.88, and is higher at the lower Fn. (6) Running trim is nearly the same between the ship and model.
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Ken SUGIMOTO, Noritsugu SHIMOYAMA
Article type: Article
Pages
51-58
Published: March 30, 1980
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In this paper, authors present a numerical calculation method using boundary layer approximation to predict the velocity distribution of a ship wake which has ordinarily the complicated shape infulenced by the existence of bilge vortices. The procedure of this method for obtaining the velocity distribution consists of the following steps ; 1) The secondary flow velocity is evaluated by solving 3-D boundary layer equations using Okuno's integral method. 2) The shear stress in the boundary layer is assumed to obey Boussinesq's eddy viscosity conception, using the equivalent kinetic viscosity approximated by the quartic equation. 3) The differential equation for the streamwise flow velocity is derived by substituting these secondary flow velocity and shear stress for boundary layer equation. 4) Solving this differential equation numerically, the velocity distribution in the boundary layer is obtained. The wake distribution near the propeller disk of two ship models are calculated by this method and compared with the measured ones. The result is that the method adopted here to obtain the velocity distributions might to predict the wake distribution, the shape of which has the similarity to that of the measured wake distribution.
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Satoki MISHIMA, Masayoshi HIRANO, Hiroyuki ODA, Mitsumasa KATAGIRI
Article type: Article
Pages
59-70
Published: March 30, 1980
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This paper presents a new method to construct statistically a practical estimate formula for the form factor. Many formulae are available to estimate the form factor being based upon principal particulars and hull geometries. The rusults of application of those formalae to our hull forms have not necessarily shown satisfactory accuracy. Therefore an attempt to obtain mora accurate and reasonable estimate formula was made by utilizing the statistical approch. Applying the minimum AIC estimate method, the parameters which consist of the estimate formula were selected under the explicit criteria of selection. Three kinds of formulae were made, namely for full ships, fine ships, and all kinds of ships respectively. The estimated results of the form factor by the formulae obtained in this paper show fairly good agreement with the measured quantities.
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Akikazu NAKAMURA, Ryotaro OGIWARA, Seiji MIYAZAKI, Noriyuki KAMOI, Tom ...
Article type: Article
Pages
71-77
Published: March 30, 1980
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Kawasaki Heavy Industries, Ltd. carried out a stress measurement of Moss type spherical LNG tank of their first LNG carrier which was also the first LNG ship in Japan. The measurement was carried out on No.3 LNG tank during interaction test and hydro-pneumatic test. The test conditions were as follows : (1) Interaction test A longitudinal vertical bending moment of 500,000 T-M was introduced to the hull. This moment is about half of the maximum design bending moment (M_s+M_w of Q=10^<-8>). (2) Hydro-pneumatic test Fresh water of 70 % volume and air pressure of 1.25 kg/cm^2 G were applied to the tank. The weight of the fresh water corresponds to the weight of 100% LNG with the maximum vertical acceleration due to wave induced ship motion. The measured stresses were compared with the calculated ones. The agreement was found very good. The interaction stresses were negligibly small and the stresses due to 70% fresh water and 1.25 kg/cm^2G air pressure were all moderate as designed. This stress measurement proved the reliability of the design of the spherical LNG tank system.
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Masakatsu MATSUISHI, Setsuo IWATA
Article type: Article
Pages
79-84
Published: March 30, 1980
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It was confirmed through preliminary studies that composite concrete-steel structures are best fitted for the strength members of huge offshore structures, due to the high strength and ductility, and good weldability of steel and due to the low ratio of cost to the weight and excellent durability of concrete. A new prestressed concrete-steel structural module hase been developed for the strength members of offshore structures. The composite structural module is composed of biaxially prestressed concrete and a steel frame surrounding the concrete. The prefabricated composite structural modules are joined together to bild the main structure by welding the steel frames. The joint between composite modules is simpler and more reliable than those of conventional concrete structures. In the paper, the authors carried out both experimental and theoreticai investigations into the stresses and deformation of the composite modules during prestressing. Experiments were carried out by fabricating a prototype composite module ; a full scale model, and a floating break water. Theoretical analyses were carried out on stress distribution and bending deformation during prestressing. A comparison of calculated and observed results shows good agreement. Based on this comparison, the fundamental properties of the composite were clarified.
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Kouhei MATSUMOTO, Hiroaki KADO, Kenji ARIMA
Article type: Article
Pages
85-91
Published: March 30, 1980
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The paper deals with the coupled effect between a fore-and-aft vibration of super-structure and a longitudinal vibration of ship's hull. Characteristics of the coupled vibration were discussed by using the two-beam model. The present theory was found to explain well the coupled vibration of actual ship. Main conclusions are as follows : 1) Coupled effect depends on two parameters. One is a mass ratio of superstructure to ship's hull. The other is an uncoupled natural frequency ratio. 2) Natural frequencies of the coupled vibration obey the law of so-called "spring-off". : When uncoupled natural frequencies coincide with each other, coupled ones spring off in the largest amount. 3) Coupled natural frequency is estimated by multiplying the uncoupled one by the correction factor.
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Yoshikazu MATSUURA, Hiroyuki ZENJAKU
Article type: Article
Pages
93-104
Published: March 30, 1980
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It is difficult to calculate correctly the natural frequencies of vertical vibration of ships with deck errections such as superstructures or deck-houses. At present, applicable calculation methods are the one proposed by Johnson and Ayling and the one by one of the present authors, Matsuura. In these calculation methods, ships with deck errections are treated as beams having effective bending rigidity derived from statical strength calculation which is made in order to allow for the presence of deck errections. Although the calculated frequencies by these methods are approximately correct in the lower modes, the accuracy of those in the higher modes is questionable. In this paper, the ships with deck errections are treated as the so-called Bleich's model. Dynamical analysis is made for the vertical vibration of this mathematical model taking into account the coupling effect of main hull and deck errection. Transfer matrix method is used in the actual computation. Experimental investigations on the model ships are also made. The results show good agreement with the theoretical results.
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[in Japanese]
Article type: Article
Pages
105-109
Published: March 30, 1980
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Article type: Appendix
Pages
111-112
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Article type: Appendix
Pages
113-117
Published: March 30, 1980
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Article type: Appendix
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Article type: Cover
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