Journal of the Japan Society of Naval Architects and Ocean Engineers
Online ISSN : 1881-1760
Print ISSN : 1880-3717
ISSN-L : 1880-3717
Volume 12
Displaying 1-27 of 27 articles from this issue
  • Yuki Kawahara, Ikeda Yoshiho, Nihei Yasunori
    2010 Volume 12 Pages 1-7
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    Design of the ship-compartments arrangement in the initial design stage of a ship is one of the most important and troublesome steps to determine the loading capacity and the safety level of the ship. Since the ship's damage stability is strongly related to the safety level of the ship, the maximization of her survivability is a primary recommendation for the designer, especially in view of recent changes of the damage stability regulations towards more stringent requirement. Moreover, the optimum design which is satisfied with both sides of the loading capacity and the ship building cost guaranteeing the adequate safety is requested the designer by the ship owner.In the present study, a multi-objective optimization method of ship-compartments arrangement by using genetic algorithm is developed for the purpose of the reduction of the designer's load and the increase of the design efficiency. The objectives of this optimization problem are herein the maximization of the Attained Subdivision Index as a safety level and the maximization of the total lanes lengths. The effectiveness of the proposed method for optimizing ship-compartments arrangement is demonstrated through applying this methodology to a practical design of ship-compartments arrangements.
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  • Naoto Sogihara, Masaru Tsujimoto, Yasuo Ichinose, Yoshimasa Minami, No ...
    2010 Volume 12 Pages 9-15
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    On prediction of ship performance in actual seas, it is important to estimate external forces acting on a ship. The predominant factor is added resistance in waves which reduces ship speed. Therefore, added resistance in waves is required to be calculated with accuracy. In addition, since a ship sails with a drift motion due to winds and waves, it is required to estimate hydrodynamic forces and moment due to drift motion.As ocean waves is characterized their irregularity which contains various frequency and direction component, it is required to estimate added resistance in oblique waves as well as in heading waves. In this paper, it is investigated by tank tests whether the calculation method on added resistance in heading waves is applied to that in oblique waves. Furthermore, hydrodynamic forces and moment due to drift motion is calculated with appending a term of drag for wing of a small aspect ratio. The effectiveness of the calculation methods is shown by estimating decrease of ship speed in actual seas.
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  • Naoto Sogihara, Michio Ueno, Kunihiro Hoshino, Masaru Tsujimoto, Noriy ...
    2010 Volume 12 Pages 17-24
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    For building and promoting low greenhouse gas emission ships, a design index of ship performance in actual seas is required to be developed. On a project for 10 mode at sea, a calculation method of ship performance in actual seas has been developed. The method can calculate added resistance in short waves with engineering accuracy in terms of correction factors based on tank test results.Onboard measurement is carried out for the purpose of verification of the calculation method. As for onboard measurement, it is difficult to observe encountered waves with accuracy. To avoid the difficulty, wave radar measurement system is applied and measured results are compared with those by other wave measurement systems and the accuracy of wave measurement is discussed.Thereafter, a comparison of calculated ship speeds is made with measured ones with correction by the displacement, engine output,and weather. A procedure for correcting the measured data is described at some length. As a result, it is clarified that the results of onboard measurement show effectiveness of the calculation method.
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  • Naoto Sogihara, Michio Ueno, Toshifumi Fujiwara, Masaru Tsujimoto, Nor ...
    2010 Volume 12 Pages 25-31
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    For reduction of Greenhouse Gas (GHG) emission from shipping sector, low GHG emission ships are required to be built and promoted. On a project for 10mode at sea, a calculation method on decrease of ship speed has been developed. The calculation method has confirmed by tank tests.Full-scale onboard measurements have been conducted for four kinds of ocean-going ships in operation; pure car carrier, very large crude oil carrier, container ship and bulk carrier, with a view to attesting the reliability of the method for evaluating ship performance in actual seas. In this paper, results of onboard measurements for a pure car carrier and a very large crude oil carrier which data accumulate for whole four seasons are reported. The measured and calculated data matched well, showing sufficient reliability of performance estimation for both a fine and a blunt ship type.The results of onboard measurement for the two ships show good agreement with those of the calculation. These results confirmed that the calculation method can be accurately applied to both a fine and a blunt ship type.
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  • Hiroshi Arai, Doi Yasuaki, Nakashima Takuji, Mutsuda Hidemi
    2010 Volume 12 Pages 33-41
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    The objective of the present study is to investigate the flow mechanism of delaying stall by use of a wavy leading edge on rectangular wing. Flows around rectangular wings with wavy leading edge were simulated by large eddy simulation with the Dynamic Smagorinsky Model (DSM). The Reynolds number based on the chord length of the wing and the uniform-flow velocity was 1:38X105. The predicted lift and drag coefficients for poststall condition agreed qualitatively with experimental data by using DSM, moreover those for prestall condition were in very good agreement with the experimental data. The mechanism of delaying stall was revealed by the flow simulation. The predicted flows around the wavy leading edge indicated existence of longitudinal vortices and the flows around wavy leading edge remained attached at poststall angle of attack. The longtiudinal vortices were carried to wing tips and the flow separation was suppressed in the area from the protuberances to the wing tips.
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  • Chiharu Kawakita, Shinichi Takano, Yoichiro Kodan, Shuji Mizokam
    2010 Volume 12 Pages 43-50
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    In recent years, air lubrication system has been attracting attention as a method of reducing carbon dioxide from ship. This method can reduce the frictional resistance through the injected air bubbles on ship bottom, and save energy for propulsion. The authors have investigated the behavior of bubbly flow on the ship bottom and the propeller performance in bubbly flow mainly using the model tests in order to apply the air lubrication system to ship. From the experimental results for module carrier ahead in calm sea, the bubbly flow can cover a wide range of ship bottom, the volume of bubbles flowed into propeller is small and the increase of propeller pressure fluctuation is negligible. However, if the ship is running in oblique flows or in waves, bubbles may flow slightly into the top of propeller and the propeller pressure fluctuation is increased as a result.
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  • Toru Katayama, Tomoki Taniguchi, Takuya Sato
    2010 Volume 12 Pages 51-59
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    The purpose of this study is to develop a simulation method of porpoising for real scaled planing craft with outboard engine. At first, in order to check the conditions where porpoising occurs, a free running attitude towing tank test is carried out. In the test,longitudinal position of the center of gravity and ship's weight are systematically changed. And in order to investigate the effects of outboard engine on occurrence of porpoising, the same test is also carried out for the models with and without lower hull of outboard engine. From the measured results, it is found that lower hull of outboard engine can reduce the occurrence of porpoising.In the simulation, measured three components hydrodynamic forces acting on fully captured model are used. In order to simulate porpoising for real scaled planing craft, the scale effects on the hydrodynamic forces are taken into account. As the results, it is found that the condition of porpoising occurrence for a real scaled craft is slightly different from the model scaled craft, because of difference of running attitude between them affected scale effects. Finally, a simulation method of porpoising for real scaled planing craft is developed and a method for avoiding porpoising is proposed.
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  • Hiroshi Kagemoto, Takafumi Kawamura, Yoshiaki Akutsu, Takayoshi Kato, ...
    2010 Volume 12 Pages 61-68
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    As the second report on the same subject, the shielding effects of wind among wind turbines deployed in a wind farm are further investigated. In the first report 1) , the shielding effects among wind turbines were investigated by varying the spacing and the wind direction systematically. In this second report, models of different scale (two times the size of the models used in the first report) are used in order to examine the scale effect, especially the effect of Reynolds number. The effects of the power coefficient of wind turbines on the shielding effects are also investigated.As in the study reported in the first report, the experiments are conducted while using circular disks with holes, which are not geometrically similar to real wind turbines. Besides, the experiments are conducted in a wave tank instead of in a wind tunnel. The justifications of these ambiguities are examined in this study by comparing with other existing experimental results and also by comparing with the results of CFD (Computational Fluid Dynamics) calculations..
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  • Shuji Mizokami, Chiharu Kawakita, Youichiro Kodan, Shinichi Takano, Se ...
    2010 Volume 12 Pages 69-77
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    In late years, a demand for the carbon dioxide discharge reduction from a ship and the reduction of the operation cost has been risen more and more. According to these backgrounds, the authors are grappling with establishment of the frictional resistance reduction technology of the ship by means of the air lubrication methods. In the present paper, we carried out confirmation of the air blow condition with a mock-up examination, examination at the wharf, and the numerical computation for investigation of the valve opening rate when air lubrication method is applied to large shallow water ship. After that, we confirmed the energy saving though sea trial test. When the ship was in a horizontal state we confirmed that air was blown uniformly from each small hole, by means of mock-up examination and full-scale examination by use of actual ship at wharf. In addition, through the wharf examination, we confirmed that air was almost uniformly distributed to each branch piping in heeling condition under adequate valve opening. The analytical result of the distribution of flow rate by use of MelTHERFY almost coincides with the estimated flow rate in the heeling condition. Therefore, this method is effective as an analytical technique. Thereafter, when we used air lubrication system at the speed trial test, we confirm an energy saving effect of 12% at the maximum, and the fuel consumption is reduced at the same time.
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  • Motoki Yoshida, Masakazu kaji, Hajime Kihara, Hidetsugu Iwashita, Take ...
    2010 Volume 12 Pages 79-88
    Published: 2010
    Released on J-STAGE: October 25, 2012
    JOURNAL FREE ACCESS
    Motion control system using small fins is necessary for Resonance-Free SWATH (RFS) which has negative pitch restoring moment. Theoretical estimation method regarding Bode plot which determines the stability of PD control system and motion equation including PD control system is developed. In the theory, the time lag of fin lift generation and the interaction among fins and lower hulls of RFS are taken into account. Also, experiments using RFS model with movable fins are carried out to validate the theoretical estimation. As the result, the maximum stable gain constants for PD control of RFS motions are determined and motion responses of RFS are significantly reduced. Furthermore, non-linear VSS control system is introduced to make a good use of negative restoring moment of RFS. Sliding mode control and the effect of VSS system are discussed.
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  • Motoki Yoshida, Hidetsugu Iwashita, Hajime Kihara, Takeshi Kinoshita
    2010 Volume 12 Pages 89-99
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    A "Resonance-Free SWATH (RFS)" as the oceangoing large fast ship has the negative restoring moments, which leads to resonance-free in the motion responses, because of the extraordinary small water plane area. The RFS is designed to cross 4,800 nautical miles of Pacific Ocean in 5 days punctually at a high speed of 40 knots, with the good seaworthiness such as no speed reduction or absolutely no slamming even in the rough sea. To verify the seaworthiness of the RFS, experiments in model basin and theoretical predictions are carried out to examine the lowest limit of motion responses in waves. The results in regular and irregular head waves are compared with those of various hull forms, such as mono-hull, ordinary SWATH or trimaran. The predominance of the RFS regarding seaworthiness will be pointed out in the conclusion. For example, by using PD control action, heave motion responses of the RFS is reduced to about 1/40 compared with those of mono-hull or trimaran, and pitch motion responses of the RFS become about 1/8.
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  • Mitsuhiro Masuda, Koichi Masuda, Tomoki Ikoma, Kuniaki Shoji
    2010 Volume 12 Pages 101-106
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    The present paper describes the collision forces induced by the floating structures washed onto the apron by tsunamis using the MPS method (Moving Particle Semi-implicit method). The effectiveness of application is also verified.The two dimensional MPS method is used in this paper. It explains the governing equations and the modeling of behavior of floating body in the MPS method in the beginning. Afterwards, the spatial resolutions and the collision forces are examined. The spatial resolutions are examined by adjusting the inter-particle distance. The collision forces are examined by comparing between the numerical results and the experimental results. From the comparison between the numerical results and the experimental results, the applicability of the MPS method is discussed.
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  • Kouji kakizoe, Tsugukiyo Hirayama, Yoshiaki Hirakawa, Takehiko Takayam ...
    2010 Volume 12 Pages 107-114
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    This paper proposes "Vertical Weight Stabilizer (VWS)" which is a new type of stabilizer. VWS is composed of a weight which can be shifted vertically by a servo motor. The weight gives to the ship two kinds of effects. The first one is an anti rolling moment given by the Corioli's force. The moment reduces the roll motion given by the wind and wave etc. Another one is change the moment of inertia of the ship. Roll of the ship is reduced when the difference between natural roll period and wave period is increased. Actual ship experiment was done at Lake Biwa by the VWS research group. The study intended to do experiments on still water and irregular waves. However, only still water condition was able to be done because of the weather.The experimental results show a reduction of the roll movement caused mainly by the dissipation of motion energy by Corioli's effect. It was observed that VWS reduce significant value of about 50% in free roll trial
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  • Takero Yoshida, Chang-Kyu Rheem, Kimihiro Ano
    2010 Volume 12 Pages 115-123
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    In order to improve the measurements of the sea surface by active microwave remote sensing, it is necessary to understand the mechanism of microwave backscattering from the sea surface. The phenomenon of microwave scattering at the sea surface is complicated and not clarified enough. The purpose of the present research is developing time domain numerical simulation technique to clarify backscattering mechanisms and evaluate sea surface observation methods. In the simulation,backscattering coefficients and Doppler spectra can be obtained. Physical optics approximation is applied to calculate scattering electric fields. The validity of the simulation has shown by comparing with the results of the experimental basin.Microwave backscattering has been simulated under the same condition as the experiment. The results indicate that the simulation technique is effective to calculate microwave backscattering from the water surface changing in time.As an application of the simulation, we have simulated microwave backscattering with a pulse Doppler radar. Radar images of backscattering coefficient and Doppler velocity have been generated. The results show that radar images of Doppler velocity are more effective than images of backscattering coefficient for sea surface observation.
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  • =Shigeru Akiyama, Shinobu Sugasawa, Michio Ushijima
    2010 Volume 12 Pages 125-132
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    We developed a novel recycling system for discharged FRP (Fiber reinforced plastics) of disused FRP boats, and demonstrated that the product manufactured by the system is available for the burning process in cement plant. In this system,the recycled products are manufactured as follows: at first, FRP fine particles of the size of about 3 mm or less are made by crushing discharged FRP, the particles made are mixed with the used polyethylene sheets in agriculture, and are bound together with the polyethylene sheets melted by frictional heat of a twist mill. The dusts arising when FRP is crushed are prevented from scattering in the air by water shower. In cement plants, since there is a limit value of the concentration of chlorine due to the problem of dioxin, urethane foam containing a lot of chlorines that is used as a structural material in FRP boat is removed from FRP particles by making floated on water. Recycled products of non-dust-scattering type for the cement burning were experimentally manufactured by this recycling system and the cement burning test was done using the recycled products of size from about 3 to 8 mm. As a result, it was confirmed that the products were effective in the cement burning process.
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  • Tomohiro Yuzui, Makoto Arai, Fujio Kaneko
    2010 Volume 12 Pages 133-141
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    In recent years, the necessity of risk assessment is rising in various study fields and in the industry. It is the same in the maritime field. The environmental risk assessment is especially important because the damage for marine environment is serious once the accident of the oil tanker occurs. However the environmental risk assessment is more complex than the safety risk assessment because many things must be considered. The study of the method for assessing the pollution by oil spill from tankers has st arted in IMO, the volume of spilled oil was adopted as its basic index. On the other hand, Inclusive Impact Index (Triple I) has been proposed by the IMPACT Research Committee in The Japan Society of Naval Architects and Ocean Engineers. Triple-I is defined and calculated based on the ecological footprint, ecological risk, human risk, cost, and benefit. By using this index, we can objectively discuss the societal importance of the risk control option from both environmental and economical viewpoints. In this paper we try to apply Triple-I to the environmental risk assessment in the maritime field, and evaluate the risk of the oil tanker and disuss whether Triple-I can be used for the cost effectiveness assessment.
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  • Ken Takagi, Hiroyuki Osawa
    2010 Volume 12 Pages 143-148
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    Reduction of a 25% in greenhouse gas emission by 2020 is written in Japanese basic acts against global warming. Utilization of ocean renewable energy starts getting attention. A preliminary consideration on the expansion of ocean renewable energy utilization is shown in this paper. The obtained energy in a year per unit area for various ocean renewable energy devices is estimated. The required area is one of important indexes for evaluating the possibility of renewable energy devices. Other indexes such as the energy profit ratio, the cost and the typical weight of devices are also estimated, and the possibility on expansion of ocean energy utilization is discussed. Summarizing these results, it is found that Japanese exclusive economic zone has a considerable potential for ocean renewable energy. A closed system of an ocean renewable energy generation for the fishery industry in a remote island is proposed as for the first stage of deployment of the devices. In addition, further expansion of the ocean renewable energy utilization is discussed.
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  • - Estimate of Interaction Effect and Proposal of a Mono-hull Type -
    Ken Takagi, Takuro Hiramatsu
    2010 Volume 12 Pages 149-155
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    The National Institute for Environmental Studies Japan proposed a twin-hull type concept of floating wind power plant, which has no mooring system but moves with sails and thrusters. The mobility of the structure is a key of this concept. We estimate maneuverability coefficient by using the lifting line theory in which interaction effect among many struts is considered. The result suggests that the twin-hull type is not efficient for inducing the lift force because of the interaction effect. A mono-hull type VLMOS is thus proposed, and structural strength and the maneuverability of the mono-hull type are investigated. The results show that the mono-hull type VLMOS has enough structural strength and maneuverability. In addition, the power supply cost becomes 10% cheaper.
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  • Hirofumi Sumoto, Satoru Yamaguchi
    2010 Volume 12 Pages 157-163
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    The authors involved in developing fish type robots using artificial muscle for several years. The authors have developed small sized fish type robot in the length of 20cm. These robots mimic the motion of actual fish such as transient swimming motions and phototaxis. But the limitation of payload becomes problem to develop a practical robot. To address this problem, the authors attempted to scale-up the fish type robot. The actuators for the up-scaled robots need to overcome the rigidity of their body and fluid force produced by moving their caudal fins. The present paper proposes a control method of artificial muscle for the fish type robots using "Segmented Binary Control (SBC)". This method uses several artificial muscles connected in series, instead of using one artificial muscle of the same overall length. Each artificial muscle is individually activated to produce displacement. The authors developed an artificial muscle unit and examined its performance. Newly developed artificial muscle unit shows same displacement regardless to load, produces tip displacement in step, and the tip displacement of the unit is not affected by ambient water temperature. With these results, proposing control method of artificial muscle is effective for the up-scaled fish type robots.
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  • Masahiko Nakamura, Hyakudome Tadahiro, Hiroshi Yoshida, Shojiro Ishiba ...
    2010 Volume 12 Pages 165-173
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    A small AUV "MR-X1" was developed in 2000 for detailed investigation of the seafloor and marine organisms at JAMSTEC (Japan Agency for Marine-Earth Science and Technology). In order to assure high maneuverability under low-speed cruising and good hovering performance, the motion of the vehicle is controlled by five thrusters. When the vehicle was built, PID control was implemented, but in order to improve control performance, renovation of the vehicle operating system has been ongoing since 2007, and a model based control (LQI control) is due to be adopted when this is complete.This paper summarizes the design method of the motion controller to cruise along an observation line in the current, and shows successful simulated results.
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  • Hiroshi Matsukura, Michelle C. Buen-Tumilba, Hiroyuki Yamato
    2010 Volume 12 Pages 175-184
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    A maritime transportation planning without concern of delay risks is not robust against disturbances. Once delay happens it is likely to be amplified in the subsequent activities and its influence is serious since transportation amount is huge. This paper proposes a basic planning procedure that can provide maritime inter-factory short-term transportation plans using a logistics simulator to mitigate the difficulty. A multi-national shipbuilding company with supply ports in Japan and a shipyard in a foreign country is taken as an example and applicability and effectiveness of the procedure is demonstrated through various analyses.
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  • Hiromichi Akimoto, Shoji Takechi, Hisaho Nozawa
    2010 Volume 12 Pages 185-191
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    To cope with the highly volatile market of freight rate in recent years, both shipping and shipbuilding companies require a tool for designing the structure of fleet that satisfy the economic demand. The authors use a numerical simulation of bulk carriers to evaluate the optimal portfolio of ships by their size and routes. In this study, we simulate the transportation network of iron ore carriers using multi agent approach. It shows the operation cost, shortage risk of iron ore stocks in steel manufacturing companies. We also discusses the economical benefit of combination trade and remedy operation for the congestion of ships in a port caused by accidental breakdown of its loading functions.
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  • -case to use only GPS-
    Daisuke Terada, Genshiro Kitagawa, Shintaro Miyoshi
    2010 Volume 12 Pages 193-199
    Published: 2010
    Released on J-STAGE: March 25, 2011
    JOURNAL FREE ACCESS
    In this paper, a new technique for an estimation of a ship's position is introduced. In the past, an estimation method of a ship's position by using Kalman Filter (KF) has been already proposed. However, when an observed position signal with GPS has a large noise component, the accuracy of the estimated position by using KF is wrong because the probability density function of the observation noise does not satisfy the assumption of Gaussian sequence. In order to solve this problem, we introduce sequential data assimilation by using Monte Carlo Filter (MCF). Moreover, in this study, we assume Cauchy distribution as the probability density function of the observation noise. The verification of the proposed procedure is carried out by numerical experiments and onboard experiments. From the comparison of the proposed procedure and the procedure by using KF, it is confirmed that the proposed procedure can remove the influence of the large noise component.
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  • Naoki Osawa, Junji Sawamura, Shota Okada, Kei Shigeta, Tomohide Tsuji
    2010 Volume 12 Pages 201-208
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    It is necessary to calculate the Stress Intensity Factor (SIF) of surface cracks in welded joint in order to carry out fatigue assessment based on fracture mechanics approach. The SIF of a surface crack in weld can be calculated by using Influence Factor Method (IFM) developed by Shiratori et al. (1986). Influence Factor (IF) database is needed to be prepared in order to carry out IFM calculations. Only the database for cracks in flat plates had been prepared. The use of this IF database in the SIF calculation of cracks in welds leads to calculation error because the size and shape of a structure with a weld differs from that of a flat plate. The degree of this error can be examined by comparing IF values of cracks in a weld and that of cracks in a flat plate. However, reports of such comparative study have apparently not been published yet.In this study, a full-automated IF calculation software system is developed. The validity of the developed system is examined by comparing SIFs of a crack in a flat plate derived from the IF database constructed by the developed system with that assessed by Newman-Raju's formula. The IF values for flat plates and welds are compared by using the developed IF calculation system. As results, the followings are found:(1) The developed system reduces dramatically the man-hours needed to construct an IF database.(2) The SIF of a crack in a flat plate derived from the IF database constructed by the developed system agrees very well with the Newman-Raju's solution. The SIF of a crack in a fillet weld derived from the IF database constructed by the developed system agrees well with the direct FE analysis result. These show the validity of the developed system.(3) IFs have significant values only in the vicinity of SIF calculation point while those at far-off nodes are negligible.(4) IFs in the vicinity of the crack mouth for a fillet weld become up to 15% smaller than those for a flat plate. However, the difference in IFs in the vicinity of the crack bottom of cracks in flat plates and welds is negligible.(5) The SIF of a crack at the crack mouth in a fillet weld is overestimated when the IF database for flat plates is used in IFM calculation while the estimation error is negligible for the SIF at the crack bottom.
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  • Junichi Katsuta, Satoshi Kubo, Noboru Konda, Shuhei Koga, Shinichi Ush ...
    2010 Volume 12 Pages 209-217
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    It is clarified that fatigue crack propagation rate of the optimum ferrite-bainite (F/B) steel shows superior resistance in comparison with conventional ferrite-pearlite (F/P) steel. In this study, fatigue crack propagation properties of both F/P steel and the F/B steel are investigated in consideration of opening/closure of fatigue crack tip. Fatigue crack propagation tests have been carried out under various loading conditions ( constant amplitude cyclic loading, block amplitude cyclic loading and constant amplitude cyclic loading and a few static large spike loads ) for acceleration, retardation and non-propagation of crack growth rate. From the results of this study, fatigue crack propagation phenomena are shown in hysteresis loop for fatigue crack tip, and fatigue crack growth retardation and non-propagation bring long tail of hysteresis loop for fatigue crack tip. And effects of retardation in the F/B steel are larger than that in F/P steel.
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  • Makoto Toyoda, Tomoki Sakurai, Yukitaka Yasuzawa
    2010 Volume 12 Pages 219-228
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    In this study, vibration characteristics of a rectangular tank with a horizontal plate to divide inside liquid are examined by model test and FE analysis. The plate in the tank has an opening at the center, which allows fluid in the tank to pass through it up and down.Vibration tests are performed with the change of water level and opening size and acceleration responses of the tank walls are measured. The effect of opening size, position of openings and number of openings are also examined using FE analysis. Main conclusions are as follows.(1) With the increase of water level, natural frequency of the tank drastically drops when water level passes up the divider plate,especially when the area of hole on the plate is small.(2) Damping ratio of 1st mode increases as the ratio of the area of hole of a divider plate decreases.(3) Natural frequency of a tank is dependent on the size, position and number of openings. The size of an opening has most significant effect on natural frequency.(4) Tank design method to avoid resonance can be newly developed making use of the vibration characteristics shown above.
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  • Shinya Suzuki, Makoto Arai
    2010 Volume 12 Pages 229-236
    Published: 2010
    Released on J-STAGE: March 25, 2011
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    Ballast water discharged at each port is accounted to help spreading marine organisms and to cause damage to the marine ecological system. At present, the International Maritime Organization is preparing to take effect 'International Convention for the control and management of Ships'Ballast Water and Sediments, 2004' to solve this issue. Responding to the convention various type of ballast water treatment systems are under developing worldwide. The present ballast-free system is based on a completely different concept compared to those ballast water treatment systems. The present system utilizes the flow around a moving ship to generate water circulation inside the ship's tanks. Thus the water inside the tanks is always exchanged with the sea water outside the ship to keep the contents of water inside the tank to be identical to those of the sea water outside the ship. In order to design suitable vent shapes that can generate effective water circulation in the tanks numerical simulations and model tests were carried out to analyze the flow around the vents and estimate the increase of the ship resistance.
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