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Article type: Cover
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Published: September 30, 1984
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Article type: Index
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Published: September 30, 1984
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Article type: Appendix
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Published: September 30, 1984
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Shoichi HARA, Michiaki IGAI, Sadahiro NAMIE
Article type: Article
Pages
1-6
Published: September 30, 1984
Released on J-STAGE: March 30, 2018
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In case of accidents of tankers and seaside oil refineries, oil control barriers are usually set on the sea surface to prevent spilled oil from spreading, and many types of the barriers ware developed so far. However, the existing oil control devices are not always effective for containing oil slicks on the actual sea surface. Hence, the improvement in the performance of barriers has been required especially for the high values of current velocity, wave height and wind velocity. Authors have examined the air-bubble curtain that means two-dimensional water flow induced by rising air-bubbles as a new type of the oil control barriers. The velocity distribution, the momentum and the width of the induced water jet were obtained. The analytical results of the plume trajectory in the tidal current were also obtained and compared with the experimental results. In the report, the hydrodynamical performance of the plume is examined. Observing the oil leakage through the plume fundamentally by using the grain of polyethylene and also by using actual oil films, the critical velocity of current under which the air-bubbles curtain can prevent spilled oil from spreading is investigated in the co-existence of waves and current. Furthermore, the vertical distribution of water velocity behind the plume in the current and waves, and the performance of breaking waves by the plume are examined.
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Kimio YOKOTA, Takehiko KUROKAWA, Eiji MIYOSHI, Hiroshi YAMAMOTO
Article type: Article
Pages
7-14
Published: September 30, 1984
Released on J-STAGE: March 30, 2018
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Deep submergence research vehicle, on which batteries are installed as DC power source, requires inverter systems to drive AC electric motors and to supply AC power to electronic equipments. Oil-filled and pressure compensated transistor inverter, which is suitable to 6,000m class deep submersibles, is just developed, having characteristics of small size, light weight and high efficiency. Principal items of inverter unit manufactured as trial are as follows. ・Rated input voltage 108 VDC ・Output power more than 8 kVA, 3φ ・Rated output voltage more than 80 VAC ・Rated output frequency 120 Hz ・Maximum operating pressure 625 kgf/cm^2 This unit has been tested under the pressure conditions of 0∼938kgf/cm^2 (1.5 times of the pressure of 6,000m depth), and its good performance has been confirmed as reported in this paper.
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Hitoshi HOTTA, Takeaki MIYAZAKI, Yukihisa WASHIO, You AOKI
Article type: Article
Pages
15-23
Published: September 30, 1984
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We reported in 1st paper that the wave absorption efficiency of the air turbine (oscillating water column) type wave power generator was increased by phase control for air-flow in waves that period is longer than heaving natural period of the water column, and the optimum timing of phase control was found. But its experiment model was effected by 3 dimensional phenomenon, and the calculation method did not reappear with physical exactitude. So we performed some experiments by 2 dimensional air-chamber model in the same manner, and exact calculation to simulate the motion of the water column and the air power. Further we proposed the convencient calculation method in order to estimate the air power qualitatively. Results are, 1) Even in 2 dimensional condition, wave absorption efficiency increases by phase control for air-flow, but it does not exceed 50% because of the device absorbing by only heaving motion of the water column. 2) During the period when the valve is closed, we treate that the external force acts on the water column is due to air pressure in the air-chamber which is compressed and depressed by the motion of the water column. Results calculated by such simulation method reappears the motion of the water column and the air pressure. 3) Calculated value does not coincide experimental value, if the effect by unsteady phenomenon is not considered. 4) In oder to estimate the air power qualitatively, frequency response function method used equivalent sinusoidal force method is effective. 5) Value of optimum valve open timing obtained by 2 dimensional model is almost same as its value abtained by 3 dimensional model.
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Shigeru NAITO, Shoichi NAKAMURA, Haruo FURUKAWA
Article type: Article
Pages
25-31
Published: September 30, 1984
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The optimal conditions for complete absorption of wave energy in regular waves are well known. However, to establish the system of wave energy absorption in irregular waves it is necessary to consider the problem on the basis of time domain analysis, because the optimal condition depends on wave frequency and irregular waves contain many component waves having different frequencies. In this paper, the theory of optimal control system for absorbing the energy of irregular waves is studied. For this purpose, a system in which the incident irregular waves are measured at a certain distance in front of the floating body and the external mechanism attached to the floating body for wave energy absorption is controlled with high efficiency instantaneously by using the measured wave data, called "Feedforward Control System for Wave Energy Absorption", is proposed. Furthermore, the law of causation in the characteristics of wave propagation is discussed from the viewpoint of practical approach, because the kernel function of wave propagation does not usually satisfy the law of causation.
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Hiroyuki SADAKANE, Kunihiro YAMAMOTO
Article type: Article
Pages
33-42
Published: September 30, 1984
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The following equation of rolling motion is treated to study a capsizing condition. θ_a+2K_eθ_a+ω_0^^2f(θa)=(γπH/λ)ω^2 sin ωt where f(θ_a)=θ_a+β_3θ_a^^3+…+β_<2n+1> θ_a^<2n+1>, θa:apparent rolling angle, K_e:damping coefficient, ω_0:natural frequency, γ:coefficient of effective wave sloap, πH/λ:angle of maximum wave sloap, ω:wave frequency, t:time, and :differenciating with respect to t, β:non-linear factors and n:natural number. The swings capsizing from weather side to lee side are taken out. Under some assumptions, the most severe capsizing condition in these swings is approximately obtained as follows, [numerical formula] where [munerical formula] θ_υ:vanishing angle of stability, ν:ω/ω_0, A:(∣θ_<awm>∣+θ_υ)/2, and θ_<awm>:minimum heel angle in weather side to induce the capsizing. The relation between the ship stability and the capsizing is able to discuss by using critical lines calculated by the above equation. Results of the discussion are examined through numerical simulations and experiments used in three type models without shipping Water.
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Norio TANAKA, Yoji HIMENO, Shinichi SAKAGUCHI
Article type: Article
Pages
43-52
Published: September 30, 1984
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The authors have recently been working on the problem of the motion and the stability in waves of Japanese fishing vessel. In the preceding papers, the nonlinear roll damping of models and actual ships, the effects of hull form and appendages on the motion, and a method of solving the nonlinear equation of motion were discussed. The present work concerns with the hydrodynamic effects of the over-hung deck, which is commonly adopted in small fishing vessels in Japan. Through the measurements of the radiation forces, wave-exciting forces, and the lateral motions in regular beam waves, it is found that the over-hung deck is not so effective for reducing the ship motions in moderate sea as has widely been expected.
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Akinori YUMURO
Article type: Article
Pages
53-64
Published: September 30, 1984
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By utilizing propeller-rudder system with the absence of the ship body, we conducted experiments concerning normal force acting on a single rudder behind twin propellers. The tests were performed by varying gap between propeller axes, rudder angle, propeller loading and drift angle systematically. From these experimental results, increment of rudder nomal force caused by propeller stream and flow direction in the rudder position are discussed. On the basis of slipstream velocity given by the propeller momentum theory, a simple calculation is made for the normal force on the rudder in non-uniform flow with step velocity profile by using the linear lifting surface theory. An attempt is made in this report to determine values of the correction factor included in the formula giving slipstream velocity, comparing the experimental results with the calculated ones. This consideration yields the following results:when gap between propeller axes is kept constant, the ratio of increase of the normal force due to slipstream may be estimated by adopting constant values as the correction factor regardless of rudder angle. There is a tendency for the correction-factor value to decrease with increase in distance from the propeller to the rudder. According to results of the propeller race measurement, it can be understood that the tendency results from contraction of propeller stream.
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Masashi KASHIWAGI, Kazuya HATTA
Article type: Article
Pages
65-74
Published: September 30, 1984
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The strip method is in common use for predicting the hydrodynamic forces on ships oscillating in sway and yaw motions. However, as well known, it breaks down in the high-speed regime. On the other hand, Chapman's numerical method is known as a powerful method, but it is not applicable to bodies of arbitrary shape. Therefore it is essential to establish the new procedure which can be applied to ships of general shape and can also account for the forward-speed effect correctly in the high-speed range. In this paper a theoretical method using Fourier transform technique is presented. This method is considered to be an extension of Chapman's method, and the relationship of this method to the strip method can be shown analytically. Computational results are presented for uniform slender bodies with the cross section of general shape. The influences of the cross-sectional forms on the hydrodynamic sway force and yaw moment are investigated. Furthermore, the relations between the forward-speed effect and the cross-sectional forms are also discussed.
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Shin-ichi ARAI
Article type: Article
Pages
75-84
Published: September 30, 1984
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The fact that the sway motion of moored vessel is not symmetrical about the mean position is shown in this paper. For the design of mooring system, it is of great importance to study such an asymmetrical phenomenon because the sway motion affects mooring forces strongly. The vessel is moored at sea with a linear spring. Wave forces are calculated by the pressure integration over the wetted surface up to the wave surface. Then the sway, which consists of wave period motion due to 1st order wave force and slow drift motion due to 2nd order one, is simulated numerically. Statistical property of time history of sway is investigated. The following emerge: (1) The degree of asymmetry of the motion is affected by hardness of the spring and magnitude of the hydrodynamic damping force. (2) When the slow drift motion is the same order with the wave period motion, the degree of asymmetry becomes large. (3) When the slow drift motion becomes fairly large comparing with the wave period motion, the asymmetry vanishes and the maximum of sway becomes smaller than the theoretical extream value for Gaussian process.
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Yasushi HIGO, Yasuo MOCHIOKA, Ichiro NAKAMURA
Article type: Article
Pages
85-93
Published: September 30, 1984
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This paper provides a numerical calculation method for the first-second-and third-order hydrodynamic forces acting on two-dimensional floating body heaving with large amplitude. The procedure of the calculations is based on the theory in which it is assumed that the free surface elevation are small and that the interval of impulsive motions are small enough too but the amplitude of the oscillation is so large. So that the non-linear hydrodynamic problem can be formulated using the impulse response function and the problem can be solved by memory effect function which is given from the wave amplitude ratios in the frequency domain. Numerical calculations are made for a circular cylinder and the results are compared with Yamashita's experiments and the numerical results which are calculated by Chapman's method. It is observed that the calculated value are in fairly good agreement with those experiments.
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Hiroshi DOI, Osamu KIKUCHI
Article type: Article
Pages
95-101
Published: September 30, 1984
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Five roughness models that were found on the hull surfaces of ships in service were prepared on the test plates. Frictional resistance coefficient (C_F) of these test plates were measured in the circulating water channel and following results were deduced. (1) A painted surface which was carefully applied with airless spraying had 40μm in BSRA roughness but its C_F value was as same as that of smooth surface of glass plate. (2) The C_F of orange peel surface of antifouling paint was bigger than that of the shallow eroded surface in spite of BSRA roughness values of the two were almost same. (3) Three roughness models in this experiment can be said as sand roughness by their curves in frictional resistance test and it is difficult to say that BSRA roughness of these roughness models are mutually related to their equivalent sand roughness by their k_S/k_<BSRA> values. (4) Ship speed reduction deduced from frictional resistance values of roughness models was 0.2-2 knot in low-speed, blunt ship and 0.3-3 knot in high-speed, fine ship.
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Shoichi NAKAMURA, Shigeru NAITO, Akira NISHIGUCHI
Article type: Article
Pages
103-109
Published: September 30, 1984
Released on J-STAGE: March 30, 2018
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In the field of seakeeping, it is very important to know the characteristics of waves generated by a ship in the far field. An experimental method to analyse the wave pattern generated by a ship in waves, Unsteady Wave Pattern Analysis, has been proposed by Ohkusu. In this method, the following two problems should be examined. (1) Correction for the truncation of measured wave records to avoid the effect of reflection wave from tank wall. (Truncation correction) (2) Effect of the distance of wave probe from the model center line. (Y effect) In this paper these two problems in the unsteady wave pattern analysis are studied by the experiments with blunt bow ship model and the informations on wave pattern due to pulsating source with forward velocity.
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Osamu YAMAMOTO, Akira NISHIGUCHI
Article type: Article
Pages
111-117
Published: September 30, 1984
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The effects of two propeller types and various main engine rates on the propulsive performance of a ship in waves, are investigated in consideration of economical ship speeds and minimum fuel oil consumption in waves. A 86,000 DWT bulk carrier on a Japan∼North America route was chosen for the investigation. The load condition of the ship is a full load and the encounter angle between the ship and irregular waves is assumed to be head-on. Sea states which may occur during a voyage are estimated by using the long term wave frequency data. The results of the theoretical calculations show that the minimum fuel oil consumption of the ship when equiped with a CPP is 6% lower in the winter and 2% lower for a one year period than that of the ship when equiped with a FPP. Furthermore it is shown that the minimum fuel oil consumption of the ship equiped with a CPP is 5% lower, even for a one year period, than that of a FPP in the case that the frictional resistance coefficient is increased by 1×10^<-3> due to the fouling of the hull surface. Finally, it is shown in the case of the ship equiped with a CPP that the minimum fuel oil consumption of the ship when equiped with a main engine of MCR=12,000ps is about 5% higher than that of the ship when equiped with a main engine of MCR=14,200ps.
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Seikoo OGIWARA, Akira MASUKO, Ryuichi SATO, Takayuki TSUTSUMI
Article type: Article
Pages
119-131
Published: September 30, 1984
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This is a report on experimental study of wave breaking phenomena in front of ship bows. To make clear the flow characteristics of bow near field with wave breaking, the authors conducted the following experiments by using two types of model ship with a blunt and a sharp bow; 1) Observation and measurement of bow wave profiles 2) Measurement of flow field beneath the free surface 3) Visualization of vortices in front of the bows 4) Observation of limiting streamlines on the surface of the bows 5) Measurement of pressure distribution on the surface of the bows. On the basis of experimental results, several considerations are made on free surface flow related to the bow wave breaking. Further, the effect of a bow wing on wave breaking is experimentally investigated. It has been found that the bow wing reduces ship wave resistance by decreasing the turbulence on the free surface of breaking waves. The measurements of the flow field around the bow wing proves that leading edge vortices exist above the wing, which can be observed on swept wings at large angle of attack. A bow wing is attached to a model of a fishing boat, and it is confirmed that the bow wing is also effective for reduction of wave resistance of the practical hull form.
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Yoshikazu KASAHARA, Yukihiko OKAMOTO
Article type: Article
Pages
133-148
Published: September 30, 1984
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The scale effect on the wake distribution at the propeller plane has an important influence on the prediction of the shaft horsepower, the designing of the propeller and the ship vibration excited by the propeller. The authors have two purposes mainly in this study. One is the experimental investigation of scale effects on wake distributions by use of geometrically similar models of fine form and full form ship. So the authors examine the problems of various methods for estimation of wake distrubutions within the range of the Reynolds numbers at these experiments. The other is the investigation of the influence of the methods to estimate the full scale wake distribution on the theoretical prediction of propeller excitation forces. It confirms experimentally that the peak values of the wake fraction decrease as the dimensions of the models become larger in both full form and fine form ship models. This scale effect can not be explained by Sasajima-Tanaka's method, but can be represented by Tanaka's and Himeno's method. Calculated bearing forces, moments and pressure fluctuations induced by a cavitating propeller are strongly influenced by the estimated wake distribution of a ship. Their predicted values in the estimated wake distrubution by Sasajima-Tanaka's method are higher than by Tanaka's and Himeno's method.
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Tokio OHNISHI, Wataru YASUKAWA, Hajime KAWAKAMI, Naoyuki TAKATSU, Tada ...
Article type: Article
Pages
149-156
Published: September 30, 1984
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To analyze the dynamic response of mooring line, it is necessary to take into account the non-linear phenomena such as large deflection (geometrical stiffeness), contact problem at the bottom of the sea and drag force. The time domain analysis is used to treat such non-linear phenomena, but it takes much time in computation. In this paper, the modal method in the frequency domain analysis has been studied, by using finite element model of mooring line and equivalent linealization method of drag force. Further, the method to reduce the error caused by neglecting the higher modes has been also investigated. The calculation results by this method are compared with those by the non-linear time domain analysis, there by a good agreement of both has been confirmed. It is shown that this method has good accuracy and takes less time in computation.
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Norio FUKIAGE, Shoichi HARA, Kenji TAGA
Article type: Article
Pages
157-162
Published: September 30, 1984
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The FRP plate has good properties on resistance to corrosion and strength. Furthermore, sandwich structure with the core of plastic foam material and light wood have been recently developed because of its low modulus of elasticity, about 1/20 of steel. In this report, bending test about 5 kinds of core such as high rigidity, medium one and almost zero one are carried out in order to investigate the sandwich plate strength and the effect of the core. There are two fracture mode about sandwich plate. One is fracture of RRP part due to tension or compression, and the other is that of core fracture due to interlaminer shear or crush. It is desirable to set the sandwich composition in order that sandwich plate can be fractured by the maximum bending moment, the fracture bending moment is lower when interlaminer shear or crush in the core part occurs. It is better to raise the strength of core in the thickness direction without reducing the thickness of sandwich plate. 4 kinds of core out of 5 satisfy this condition and turned out to be utilized as the core of sandwich plate for ship hull.
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Article type: Appendix
Pages
163-164
Published: September 30, 1984
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Article type: Appendix
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Article type: Appendix
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Published: September 30, 1984
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Article type: Appendix
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Published: September 30, 1984
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Article type: Appendix
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Published: September 30, 1984
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Article type: Appendix
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Published: September 30, 1984
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Article type: Appendix
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Published: September 30, 1984
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Article type: Appendix
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Published: September 30, 1984
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Article type: Appendix
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Article type: Cover
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Published: September 30, 1984
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Article type: Cover
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