Spilled oil from stranded ship pollutes the ocean environment, and it also damages the regional economics. In order to prevent such damages from expanding, we are developing an autonomous buoy system. This paper is the second report on the development of this system. When the ship accident occurs, several buoys are dropped into the sea from a ship or a helicopter. These buoys are expected to inform us the meteorological and oceanographic data around it in real time. We envisage that the buoys will drift along with spilled oil for the most part. However, it may happen that the buoys are apart from spilled oil by accidents. To overcome this problem, the buoys must be capable of chasing spilled oil. In this research, we developed the algorithm to chase the given target point. In real situation, such target point means the center of an area of spilled oil detected by sensor. Then, we carried out some chasing control experiment using a new buoy model. The buoy went toward the given target point by controlling its buoyancy and two pairs of wing angles. Experimental results show that the buoy could chase the target point even if it is moving.

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The estimation of the high resolution wind speed distribution is required for the potential evaluation for the wind power generation over the sea. In this paper an algorithm is presented which enables high-resolution sea surface wind fields to be retrieved from the advanced synthetic aperture radar (ASAR) data acquired by European remote sensing satellite ENVISAT. The wind speeds are compared with the normalized radar cross section (NRCS) around the coast of Amami-Oshima Island. As a result, there is a high correlation (r=0.97) in NRCS derived from ASAR and the in-situ sea surface wind speed. The estimation RMSE of the ASAR wind speed is about 1.2 m/s. Thus, if the ENVISAT ASAR data is used, we can estimate the sea surface wind speed distribution with a resolution of about 125m.

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Technologies enhancing primary production are expected to promote CO₂ absorption by marine ecosystem. When we evaluate the effectiveness of these technologies, ecosystem models are valuable tools for evaluating the amount of CO₂ absorption. To evaluate the amount of CO₂ absorption by marine ecosystem, we made an ecosystem model, which has detailed decomposition process of particulate organic matter. In addition, the model can simulate both carbon cycle and nitrogen cycle, to consider the CO₂ flux between atmosphere and ocean. As a result, the model suggested that detailed biodegradation process improves the accuracy. Then we embedded the ecosystem in the three-dimensional physical model and tested the effectiveness of the coupled mode by comparing the simulation with observation of the coastal sea area of Nagasaki. Finally, we suggested that the carbon budget between atmosphere and ocean would fluctuate with the variation of the vertical profile of C/N ratio.

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The wave data collection method and the wave characteristic in Indonesian domestic seas using the satellite altimeter data in this research were discussed. For the estimation of long-term probability distribution of wave height and wave period, P(H,T), the satellite TOPEX/POSEIDON wave height data for five years from 1997 to 2000 and the JWA (Japan Weather Association) wave hind-casting data in 2000 were used. As a result, the characteristics of long-term P(H,T) distributions in the four small sea divisions of Indonesian domestic seas were cleared. It was confirmed that the satellite altimeter data was very effective tool for the wave data collection in the seas.

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We have been developing an autonomous underwater vehicle (AUV) with a manipulator aiming at underwater operations using AUVs.At first, we describe an underwater manipulator which is designed based on motion control simulation and the modular concept. From the results of simulation, the specifications of the manipulator such as maximum torque and velocity are decided.As the waterproof mechanism of the manipulator, we introduced the magnet coupling structure to transfer motor torque from inside motor to outside gear. And the modular concept is introduced to realize reliability and good maintenance. Each link of manipulator has the same structure and includes a motor and a motor driver inside. Multi degree of freedom manipulator can be realized by combining same link modules. The modular concept is introduced into the AUV design, such that a functional device can be plugged into a matherboard to be less-wiring. Finally, the experimental results using an AUV with a manipulator are discussed.

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Precise motion control without mechanical noises is a technical issue on the operations of research vessels and underwater vehicles in order to observe creatures in actual. As a solution for the problem, we pay attentions to bio-mechanisms of underwater creatures, especially undulately fins being used for attitude control. Bio-mechanisms of creatures are adapted to environment as a result of evolution. If the motor control mechanisms of the creatures can be introduced into underwater robots, there is a possibility to realize a high performance actuator. In this research, we have been trying to develop a bio-inspired underwater actuator instead of screw propellers. As the material of the actuator, electroconductive polymer is used as an artificial muscle. We describe the concept of the developing actuator, behavior of water creatures and development of electroconductive polymer and the results of performance evaluation test of the developing electro conductive polymer.

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Gokasho Bay in Mie Prefecture is a typical enclosed sea, and has some problems with water pollution, such as red tide, blue tide and hypoxic water at the bottom layer. The Marino-Forum 21 installed a density current generator in 1997, to restore the water quality by the improvement of vertical water exchange. The purpose of this study is to clarify a long-term environmental restoration effect of the apparatus by surveying sea bottom quality and seaweed bed distribution. The results of the field surveys showed that the conditions of both bottom quality and seaweed habitat in the test area installed with the apparatus are much better than those in the neighboring area surveyed for reference. This suggests that the apparatus works effectively for the long-term restoration of marine environments.

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A water surface wave observation method to use Doppler velocity of the microwave backscattering from water surface has been proposed. Water surface waves were observed by using a X-band CW microwave Doppler radar in an experimental basin. The observed waves by the radar were compared with the waves measured by an electric capacitance type wave gauge. There was very high correlation between the wave shapes measured by the wave gauge and observed by the radar. The results verified that the water surface wave observation method to use Doppler velocity of the microwave backscattering from water surface is useful for observation of a water surface wave. The ratio of a microwave irradiation width on water surface and a wavelength of water surface wave, and the orbital velocity of a water surface wave are important parameters to determine the wave height accuracy on water surface wave observation by a radar. The orbital velocity of a water surface wave becomes faster, and the wavelength becomes larger than the microwave irradiation width on water surface, the observation accuracy of wave height by a radar is improved. When an angle of direction that is an angle between the direction of microwave radiation and the direction of wave propagation changes, the phase difference between the waves observed by radar with disregarding the angle of direction and measured by wave gauge changes. By use the relation between an angle of direction and a phase difference of waves observed by a radar and measured by a wave gauge, wave direction can be determined.

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To optimize sea transportation system, two models are used in cooperation, namely continuous model and discrete model. Discrete model takes each container and each ship as discrete variables and simulates in time domain and can get accurate container flow in the specific transportation system, while continuous model takes container flow of each ship during 1 week as continuous variables and can get container flow more quickly. To improve the continuous model the detention cost and distribution cost are taken into account and it was shown that these 2 factors improve the accuracy. By GLS methods and continuous model, candidates of the optimal route are obtained, and by discrete simulation the optimal route is selected.

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Present situation surrounding occupational accident in shipyard is described that number of occupational accident is shifting from approximately flat to increase, and these are related with increase of ship construction in Japanese shipyard in recent years. Harmful occupational accidents are not only great loss to workers and companies, but also social and economic loss. And advancement of occupational health and safety represents an important issue in progress of ship industry. The falling type accident is deal in this paper mainly, because this type of accident is happen 30% of all approximately 130 cases of occupational accident per year and is situated in the top order of all categories of occupational accidents in shipyard. This feature of fall accident is contained fall from high place such as scaffolding and many cases of fall from lower place such as ladder only from one or two meters height and this is also characteristic of all construction industries. So, database about falling type accident has been constructed by use of published reports of occupational accident by the Shipbuilders' Association of Japan. And an introducing mode to falling accident is analyzed through risk matrix method by constructed database, and evaluation of walking environment on harmful introducing mode is considered by experiment on transferring platform mock-up. A trial calculating methodology for body burden on walking is proposed through the construction of human model on walking, the development of instrument of floor reaction force from foot and the motion capture technique.

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AIS(Automatic Identification System) is a communication system that enables a ship to get information about other ships and navigation status, such as their position, course, speed, name etc. automatically by VHF radio. The system is expected to contribute the improvement of marine traffic control and safety. In some congested waterways overloaded/conflict transmission of AIS is a potential problem from the planning stage. In this study, a simulation system has been developed for predicting AIS communication in real or simulated marine traffic flow considering the movement of each ship. This system can even evaluate the conflict state and the garble state of duplicate messages on the same slot in the actual navigation environment as real as possible.

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To make BRM training scenario design more objective and reasonable, it is necessary to understand the characteristics of training scenarios. In this paper, simulation analysis is applied to BRM simulator training scenario. The simulation model is composed of cognitive model of bridge crew and task network model which predicts watchkeeping performance of bridge team. By using of the simulation, training scenarios designed by some experts are analyzed in two ways, visualization of scenario progression as Gantt chart and evaluation of the crew size change effect on watch keeping performance. These analysis and evaluation are applied to three training scenarios and useful knowledge to quantify and control scenario difficulty is obtained.

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Block construction method is generally used in modern shipyards. In this method, interim products are built by assembling parts, and the ship is built from these interim products. This process can be referred as "Assembling Hierarchy" in this paper. In order to construct the ship effectively, an appropriate Assembling Hierarchy plan which considering the configurations of interim products is required. So in this paper, an optimization system of ship Assembling Hierarchy using Genetic Algorithms (GA) and Product Model is discussed. In order to realize the optimization using GA, it is necessary to define the chromosomes and to examine the GA operations. Therefore, Joint Hierarchy Chromosome is newly introduced. Joint hierarchy chromosome is genotype or encoded solution of Assembling Hierarchy. In this chromosome, the level of Assembling Hierarchy on each joint is set as design variable. By using this chromosome, various plans of ship Assembling Hierarchy can be generated. Effective GA operations such as selection, crossover and mutation are also shown. Moreover, proposed system is integrated with Product Model. Therefore, fitness with penalty of the plan is calculated by the use of Product Model data. Finally, an example of the optimization is shown in the paper to confirm the validity of the developed method.

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The correlation between the quenching crack and the tensile stress was clarified and the quantitative evaluation method of the quenching crack generated by quenching was established. First of all, the influence of the dimension of cylinders test material on the quenching crack was clarified by using the steel material which shows the martensitic transformation in quenching process. Next, it was shown that the residual stress distribution of the small cylinder test piece used for the quenching crack experiment was able to analyze accuracy good. Finally, the correlation between the transient tensile stress generated in the quenching process by numerical analysis and the quenching crack presence was examined followed by the clarification of criterion for the stress that causes the quenching crack was clarified. The quenching crack occurs on the side wall of the cylinder test piece because of circumferential stress when the ratio of the diameter size to axially length of the cylinder is adjusted to 1:3. Moreover, the quenching crack presence can be evaluated by both the quenching crack test results when the diameter size of cylinder is changed and the maximum circumferential tensile stress of the transient stress in quenching process. Thus, the stress which causes quenching crack in the martensitic structure can be clarified.

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It's getting more important to transfer knowledge from elder experts to young engineers especially in shipbuilding industry in Japan. We proposed a method to analyze design process for knowledge transfer support. Design process is represented by workflow and related documents using newly developed document management system. Proposed method defines difficulty and importance of each task through questionnaires and structured interviews, and proposes direction of knowledge transfer .The method is evaluated in design department of a shipbuilding company. The experiment proves that tacit knowledge about some tasks can be represented in workflows and documents. By representing some of tacit knowledge for efficient knowledge transfer, costly training like on-the-job training focuses on only difficult and important tasks.

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A high-speed optimization system, which can be connected to user-friendly evaluating design candidates system, is developed here in order for handling a large number of de`sign variables with aim of supporting ship design. There are many design variables and complicated constraint conditions in ship structure design. Moreover, their relations are so complicated and some of them rely on the designer's tacit knowledge. In order to solve such problems, design process of ship structural design is analyzed by the use of DSM and PPM, and optimization system which can generate actual solutions of designer is developed. In the system, Microsoft Excel is used for handling complicated constraints. However, connecting an Excel file to an optimization engine as an external module makes computational time tremendously large in optimization process. In order to overcome this drawback, a program source file is created from an Excel file automatically and connected with a main part of optimization system. DLL file system, which makes dynamic linkage possible, resulting that any designer can solve optimization problems easily, is also used here. Mid-ship section is designed by not only the proposed optimization system but also a commercial optimization system. The proposed optimization system can give the same design with only 3% of computational time used for commercial optimization system.

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This paper proposes a framework of transferring knowledge of parametric design. The software provided in the framework records input/output data of each calculation executed repeatedly in an engineer's try-and-error process. Design knowledge and know-how are acquired by visualizing the computation data and by interviewing the design engineer. The framework also proposes a set of standardized questions for structured interview based on recorded data. The proposed framework is applied to marine propeller design process. The result illustrates the effectiveness of design knowledge transfer. Moreover, it is considered that the system can be introduced to organizations with low cost and few man hours.

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Realization of a large floating structure is considered to be effective for ocean space utilization in Japan. As examples of ocean space utilization, floating airport, container terminal and offshore wind farm are proposed and there are many researches for its realization. To realize the large scale floating structure, an establishment of maintenance technology after construction is important as well as comprehension of elastic response characteristics and structural response characteristics. Identification of damaged area in a short time is meaningful when the large scale structure is damaged in-service. Therefore, it is significant to establish a wide-range damage detection method which can comprehend a structural health of vast region. In the present study, a new method of damage detection of large floating structure is proposed based on elastic wave tomography. To verify and confirm the availability of the proposed method, basic model experiment and numerical simulation were carried out with flat plate. Then the same approach was carried out with box model consisting of flat plate and the damage was detected successfully.

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The present study shows an automatic ship hull form fairing method using an optimization technique. The hull form fairing is carried out by minimizing unfairness function represented with design parameters which define a hull surface form. In the actual hull form fairing task, a fair hull surface is obtained by fairing all cross-sectional curves such as frame lines, water lines and buttock lines. Therefore, in this study, a new unfairness function not for the hull surface but for the cross-sectional curves is defined. This new unfairness function for curves is defined with "Porcupine" distribution which is used as a guidance to detect the unfairness in the actual fairing task. Obtained frame line by minimizing the present unfairness function is fairer than one obtained by minimizing the curve strain energy which is commonly used for unfairness function. The unfairness function for whole hull surface is organized by summing the unfairness function of each cross-sectional curve with a weighting function. The faired hull surface obtained by present method has appropriate fairness for practical use.

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In a ship DPS equipped with azimuth thrusters, desired forces and moment are realized by means of thrust allocation or control allocation (CA) of determining magnitudes of thrusts and directions of thrusters. The most popular method of thrust allocation is well known as Lagrange multiplier method in the case that thrusters can turn around in all directions to reduce the fuel consumption. Recently thrust allocation problems under constraints on thruster performance are discussed, but almost every solving scheme need heavy computational load for iterative calculations to get an optimal solution. Therefore, a new algorithm solving such a problem in real time is required certainly in the navigation field. In the paper, we propose thrust allocation algorithms that handle the bases in the kernel space of a CA matrix which represents the relationship between the azimuth thrusts and control forces. The proposed algorithms satisfy the azimuth thruster angle constraints and make the real-time calculation possible in a reasonable sampling time. Numerical results are given to show the effectiveness of the proposed method, compared with the conventional Lagrange multiplier method.

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Thrust allocation is one of the most important problems for the motion control of a ship with rotatable azimuth thrusters. The conventional method optimizes only the fuel consumption, which makes the control performance poor because azimuth thrusters cannot realize the allocation commands instantly. Recently, several studies have been made on the allocation method in consideration of both fuel consumption and limitation of thrusters' angular velocities. However, each solution scheme needs an iterative optimization in the online calculation and it makes the implementation difficult. On the other hand, Ohtsubo et al. have proposed the allocation method under the constraints on azimuth thrusters' angles, which needs no online optimizing calculation while the energetic efficiency is poor compared with some conventional methods. Koterayama et al. have improved the allocation method via linear approximation and verified the performance through model experiments. However the approximation method cannot always satisfy angle constraints and achieve the optimality. In the paper, we present the thrust allocation method under the constraints on azimuth thrusters' angles using piecewise linear interpolation and verify that the algorithm satisfies angle constraints strictly and achieves the optimality through numerical simulations.

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It is presented how to calculate the efficiency of wave power absorption by oscillating water column type wave power devices installed to breakwaters. Experimental results and theoretical calculation results on amplitude of pressure and water lever in air chambers are shown. The theoretical calculation results, in which the compressibility of air is taken account and the pressure surface condition on water surface is strictly satisfied within the range of liner theory, are good agreement with experimental ones in the case when the period of incoming wave is long. In the case of wave length being short, the agreements are improved by taking the energy loss due to vortex shedding under the edge of curtain wall into consideration. The energy absorption characteristics of the chamber partitioned into two regions by a vertical or horizontal plate are shown. Such cambers have two resonant period corresponding with the dimensions of each partitioned region . The wave power device partitioned by a vertical plate is considered to have more applicable characteristics of wave power absorption as compared with the one by a horizontal plate.

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Recent systematic model experiments demonstrate that pure loss of stability, broaching, and bow-diving are major causes of ship capsizing in following and quartering seas. Once these dangerous phenomena happen, even a ship complying with the current Intact Stability Code (IS Code) of the IMO could capsize. In this research, we propose a wing-type appendage attached to the ship bow above the water line as a new capsizing prevention device. If a ship heels, the wing-type appendage is submerged into water. Then a ship obtains additional restoring moment induced by lift force acting on a submerged wing. Since broaching and bow-diving are associated with surf-riding where a ship is accelerated by a wave up to wave celerity, ship forward velocity is enough high to obtain sufficient lift force. The submerged wing also induces additional resistance due to drag force, which helps a ship to escape from surf-riding condition and violent yaw motion. We conducted free running model experiment to examine the effectiveness of the proposed wing-type appendage to prevent ship capsizing in severe astern waves. As a result, no capsizing was observed with the wing-type appendage while capsizing due to broaching and bow-diving was observed without the wings under the same wave condition and control parameters.

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Recently, the author reported a new method to estimate and evaluate long term ship performance in actual seas, including fouling and aging effect of hull, propeller and main engine. In the present paper, previous works are reviewed, concerning time depending effect in surface roughness of hull and propeller as well as log book analysis to verify for the method to be quantitatively reasonable as compare with these results. The calculation using the new method is carried out for five ships with different particulars of hull and propeller, to evaluate the influence of ship type and size on the fall of ship performance due to fouling, aging effect and sea condition.

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An integrated performance of ships is evaluated by using all the performance information of resistance, propulsion, seakeeping, maneuvering and others. One of the evaluation indices is a power increase of ships in actual seas. In this report, detail estimation methods of the power increase by using model experiment data are shown, and the estimated results are presented. These methods include the resistance not only due to waves but also due to winds and weather helm. Based on the results of power increase, it is possible to get significant performance information on the ship as speed drop, ratio of power increase, increase of fuel consumption and cost increase of it. Discussions and proposals are performed to make more advance procedure on this subject.

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An azimuthing podded drive system is established as one of the most promising technologies for the improvement of propulsive efficiency and maneuverability. The system is also useful for fishing vessels to control the power of generators during the draw in fishing gears for a long time in low speed. Although, the drawback to a fishing vessel with this system is that it will be a worry to the course stability in the voyage. A large number of studies have been made on maneuverability of conventional ships. What seems to be lacking, however, is the course stability of the fishing vessel with the azimuthing podded drive system. In this paper, a new evaluation method of course stability is proposed on the basis of experimental study that is conducted in a circulating water channel on survey of slewing motion in a towed condition. As a towing point moves to forward in a constant speed, the amplitude of slewing motion (a) decreases and its period (T) is getting longer. Accordingly, the index of evaluation is represented by the point of towing from the center of gravity of ship and the value of the amplitude divided by the period (2πa/T). The results are checked that compared with the course stability criterions by means of derivatives of hydrodynamic forces and moments. By using the present method, newly fishing vessels can be designed to achieve the improvement of propulsive efficiency and maneuverability.

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This paper concerns investigation on effective turbulence models for predicting tanker stern flows. Objectives of the present work are twofold: i.e., (1) perform detailed evaluation of two equation models that are, at present, most widely accepted in numerical ship hydrodynamics; and (2) investigate feasibility in extending the models for more accurate and efficient mathematical forms. The ad-hoc approach on simple zero or one equation model is not of interest in the present work. Instead, effort will be fully focused on models that offer consistency with flow physics and possibly universal validity. The CFD code used in the present study is FLOWPACK version 2006, which was developed by the authors and its capability has been validated through detailed studies in past years. In particular, three turbulence models are investigated in the present study, i.e., the blending k-ω/k-ε model, the Shear-Stress Transport model, and the near-wall (or low-Reynolds number) modification model. In the following, an overview is given of the present numerical method, and results are presented and discussed for SR196 series tanker and KVLCC2M tanker hull forms including detailed comparisons with available experimental data. Lastly, some concluding remarks are made concerning limitations, requirements, and prognosis for improvements of the present turbulence models.

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Backward Bent Duct Buoy (BBDB) is a kind of oscillating water column type wave energy converter invented by Masuda.BBDB is said that it has superior primary conversion efficiency and the mooring cost is small. However, some problems are left to be made clear, for example the relationship between body shape and its motions, and the relationship between primary conversion efficiency and its motions. A number of physical tests for motions of five different BBDB models were carried out in this research.From the experimental results, the effects of BBDB body shape to the primary conversion efficiency are obtained. In addition, the measurement of incident wave height is very important to estimate an accurate performance of wave energy converter.But, it is not so easy to take an accurate measurement of the incident wave height because of the existence of reflected wave in wave basin.So some methods to measure wave and motions of BBDB in this basin are shown in this research.

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Many analytical methods have been proposed to calculate hydroelastic responses of a very large pontoon type structure in waves. In relation to the elastic response of such pontoon type structure in waves, Isshiki and Nagata proposed four kinds of variational principles related to motions of the elastic plate floating on a water surface and clarified the mutual relationship of these variational principles. "Modified Hamilton-Dirichlet's Principle 2" which is expressed using the velocity potential is one of four kinds of variational principles and has expressed the motions of the fluid and plate. In this paper, in order to calculate the wave-induced responses of an elastic floating plate in waves, a new method is proposed which uses the "Modified Hamilton-Dirichlet's Principle 2" and the "eigenfunction expansion method for fluid motion". The velocity potentials in regions with and without the plate are expanded by eigenfunctions in vertical mode which satisfy the governing equations and free-surface conditions, taking into account the presence of the plate in the same manner as Kim and Ertekin. In this method, "Modified Hamilton-Dirichlet's Principle 2" is finally reduced to a variational equation which corresponds to boundary conditions on the plate's edge and is applicable to the plate with arbitrary horizontal shape. This proposed method has the expression which can be applied to the floating plate with arbitrary horizontal shape. However, in this paper, as a 1st step, the calculated results of two kinds of rectangular horizontal plates are compared with the experimental results.

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This paper presents a calculation method for the trailing wake geometries shedding from marine propeller in steady and unsteady flows. The method is based on a simplified surface panel method "SQCM". Hess and Smith type source panels are distributed on the propeller surface. Discrete vortices are distributed on the camber surface according to Lan's QCM ( Quasi-Continuous vortex lattice Method ). The boundary condition to determine these singularities are the zero normal velocity condition on the hydrofoil and camber surfaces ( except the trailing edge ). We consider the unsteady Kutta condition that the pressures must coincide with each other on the upper and lower surfaces at the trailing edge. Then we introduce the normal velocity at the trailing edge. This normal velocity is obtained by iteration for the equal pressure condition. In the present method, the wake vortex lines are removed from the previous position to the new position by inflow velocities first. Then induced velocities by singularities and trailing wake are calculated on the wake sheet. In order to prevent the numerical instability, induced velocities are evaluated at the center of the ring vortex defined by QCM. Next the wake vortex lines are corrected by using induced velocities. These steps are repeated until the wake sheet converges and then we move to next time step. This method is applied to steady flow, oblique flow and ship wake problems. We show some calculated results and validate them by comparing experiments and other numerical results.

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The Peaucelier Mechanism, that is one of straight-line motion mechanisms, and a parallel crank mechanism were combined, and the combined device was utilized in an oar motion mechanism of rowing boat for the aim of increasing the power of the oar blade. The comparison between the power of the oar blade of the conventional device and that of the improved device was discussed by obtaining force and velocity of the oar blade. It was found by the calculation that the improved device creates greater power of the oar almost around all range of oar angle, especially in the narrower angle or in the wider angle, than the conventional oar motion mechanisms. It is considered that the rowing angle of oar will be designed narrower, as possible, than 107 degrees.

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The present paper proposes a crew workload analysis method of berthing operation. The method helps identifying the cause of crew workload variation based on the analysis of multiple data obtained from berthing operation. It consists of mental workload analysis, crew behavior analysis and ship movement analysis. Mental workload is estimated from heart rate variability measured by physiological sensor. Crew behavior is recorded by handy and fixed video cameras to analyze frequency of behavior and response time. Ship movement is measured with two GPS receivers to calculate turning and distance to pier. Based on these data, mental workload is compared with other measures. The method is applied to three berthing operations and the causes of workload change during berthing operation are partly cleared.

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Large diameter and low rotational speed propellers have been applied for a number of merchant vessels to improve the propeller efficiency, while the propeller immersion has become small relatively. Air cavity ventilated from free surface can be easily formed on propeller blades due to small immersion and the bearing forces increase under a certain operational condition. There were several reports which investigated the bearing forces induced by air ventilation. In those research works, the observation of air ventilation was carried out by still pictures with stroboscope, and the air ventilation phenomena were classified into full ventilation and partial ventilation. There are many points at issue which must be made clear on the dynamical phenomena. In the present research work, the observation of dynamic cavity formation by using a high speed video camera and the measurement of bearing forces caused by air ventilated propellers are carried out synchronously. It is discussed in this paper that the partial ventilation can be classified into three modes of unstable ventilation, non-uniform ventilation and uniform ventilation, and the amplitude and the frequency characteristics of the bearing forces are closely related to the cavity formation on propeller blades.

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Recently, many incidents of parametric roll of container carriers and pure car carriers have been reported. For the prevention of parametric roll, installing an Anti-Rolling Tank (ART) is one of the most effective risk control options. To estimate the performance of ART, however, a damping coefficient of ART is required in a numerical simulation of parametric roll. For this purpose, a scaled model test of ART is normally executed while other coefficients related to the tank or coupling coefficients between the ART and the ship roll motion can be obtained from its dimensions. To overcome this drawback, we attempted to estimate the damping coefficient of ART by applying a MPS method (Moving-Particle-Semi-implicit method) and examined its applicability by comparing with the model experiment. As a result, the MPS method can estimate not only damping coefficient but also natural period of ART. By utilizing the obtained damping coefficient by the MPS method, numerical simulations of parametric rolling for a post-Panamax containership in regular head seas were conducted. Calculated results with help of the MPS method well reproduce parametric rolling observed in the model experiment. These comparisons show us the possibility of the design of an ART as a parametric rolling prevention device without any model experiments

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An analysis method is presented to know whether a towed ship is stable or not in the course stability in wind. The method is based on the linearized motion equations newly derived in this paper for the towed ship. The special feature is to take the effect of hull steady condition of the towed ship in wind into account. By means of the analysis method, the wind effects on the course stability of a towed barge were investigated. The course stability recovers in the range from beam to quartering wind even if the towed barge is unstable in no wind case. Namely, the barge is stably towed with keeping the certain heading/drift angle in the beam/quartering wind. On the contrary, the course stability reduces in head and following winds with higher speed even if the towed barge is stable. We found that the course stability of the towed ship is much affected by the hull steady condition in wind. The analysis results agreed well with the simulation results by a nonlinear time domain method. The present analysis method is useful for better understanding of the course stability of the towed ship in wind.

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This paper describes circulation water tunnel tests for investigating the wind effects on the course stability of a towed barge. The tests on the slewing motion of the towed barge were carried out in various wind speeds and the directions. As a result, the followings were obtained: The course stability recovers in the range from beam to quartering wind even if the towed barge is unstable in no wind case. Namely, the barge is stably towed with keeping the certain heading/drift angle in the beam/quartering wind. The course stability of the towed ship is much affected by the hull steady condition in wind. The course stability reduces in head and following winds with higher speed even if the towed barge is stable. The features obtained in the experiments agreed well with the analysis results which have been presented in the previous paper. The measured results were used for validation of the simulation method presented by the authors. We confirmed that the prediction accuracy of the simulation method is sufficient in view of the practical use.

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A wave-piercing catamaran was developed in Australia, and has been increasing in size for these twenty years. The first largest 112m wave-piercing car-ferry was built in Australia, and introduced in Hakodate-Aomori route in September 2007. The ship is made of Aluminum alloy and much lighter than a conventional mono-hull ferry. The ratio of gross tonnage to displacement of the ship is about four times of the conventional one. This means that the ship has small displacement, shallow draft and large superstructure. This may cause different seakeeping characteristics of the ship from conventional mono-hull ships. In the present paper, the seakeeping performance of a 112m wave-piercing catamaran in heavy waves are experimentally investigated for all wave directions. The experimental results are compared with calculated results for conventional mono-hull ferries. The comparisons reveal that the ship motion performance of the wave-piercing catamaran in heavy waves is better than those of conventional mono-hulls, particularly in pitch and roll motions. The contribution of the unique center-bow of the catamaran to the seakeeping performance is also discussed.

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In order to make a plan of ship towing, it is necessary to investigate the towing performance of the tow ship, status of the towed ship, external force acting on the towed ship and sea conditions. The factors of the towing performance are derived from the towing gear and main engine power, which are evaluated by the bollard pull test in the case of the tugboat. When the general ship instead of the tugboat makes a towing operation, the towing performance with the main engine power is crucial. It is important to know the towing performance of the tow ship and tow force depending on the size of towed ships in several sea states in the emergency towing by the general ship.The bollard pull test and towing test in calm and rough seas have been carried out to investigate the tow force and tow power, critical tow force and the condition of safe towing. The towing safety factor is defined by the critical tow force divided by the maximum towline tension during towing. The factor less than 1 indicates the disability of towing. The critical condition is shown by the value between 1 and 2. Lastly its value larger than 2 indicates the safe towing. The towline tension is calculated by the Optimum Towing Support System developed by the National Maritime Research Institute. In this calculation, the patrol vessel as tow ship tows 5kinds of ships in several sea states. By using the ratio of critical tow force and calculated towline tension, the towing safety factor is estimated and the chart for the critical towing performance in several sea states using the displacement ratio between tow and towed ship has been shown. Even the operator of the general ship will be able to know the possibility of the safe emergency towing using the displacement of the towed ship in certain weather condition in this chart.

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This paper provides the reciprocal form on wave-drift-force and moment from momentum theory. In the 1st report we has transformed from the pressure integration on the wetted body surface oscillating in regular waves into the reciprocal form at near field, then transformed into the form at far field owing to Green's second identity, and transformed into Maruo's and Newman's formula. Therefore we underwent the cumbersome calculations using the method of stationary phase. But in this paper the start point is the momentum theory and the goal is the reciprocal form. The transformation is easy and simple. The obtained reciprocal form at far field can be transformed into the integration over the wetted floating body surface owing to Green's second identity.

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At the design stage of the large-scale steel structure, displacement and stress are generally analyzed by using the FEM. At the initial design stage, it is required for evaluating conditions of numerous design candidates. Therefore, it is not efficient to use FEM with fine mesh for analyzing the strength of structures in spite of requiring accuracy in the evaluation. In this paper, Neural Network System is developed for predicting displacement and stress based on a coarse mesh with the same accuracy of fine mesh. It is able to predict accurate displacement and stress at stiffened plate using FEM analytical results with coarse mesh as input factors for Neural Network System. In order to improve the approximation accuracy of Neural Network System, Multiple linear regression method is introduced for selecting input factors for a Neural Network System. This technique improves the accuracy of Neural Network System and reduce manpower used for structure design. The proposed Neural Network System is able to predict displacement and stress in spite of changing the load, plate thickness, and the number of stiffeners.

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The failure of ship structures usually causes serious disaster such as human loss or oil spill from tankers that may cause catastrophic environmental destruction by the pollution of the sea. To avoid such casualties and disasters, it might be necessary to make a proper maintenance plan for the ship by rationally evaluating the condition of the ship structures. However at present, the strategy of maintenance of a ship structures varies by different ship-owners. Some ship-owners may well maintain the ship structures and operate it over a long duration. Whereas other ship owners may leave a ship in bad structural condition without any repair action in order to reduce the maintenance cost from the economical viewpoint. From the rational point of view, it is possible to say that the strategy of the maintenance of a ship must be decided by considering both the allowable level of the safety and the cost of the maintenance. To overcome this problem, we propose a new method for rational decision-making of maintenance plan for an individual ship. In the proposed method, the Remaining Life Benefit (RLB) is computed considering the survey results and the risk of failure of the ship. Then, a proper maintenance plan can be selected by maximizing the RLB. In this paper, the formulation for evaluation of the cost and the risk is firstly presented. Secondly, calculation of the risk of failure based on the reliability analysis for hull girder strength is described in which deterioration of the structure by corrosion and fatigue is accounted for. Finally, examples of calculated RLB for a bulk carrier is displayed to show the validity of the proposed method.

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Recently, plate thickness in mega container ships has reached the very heavy thickness range, exceeding 70mm, not common in shipbuilding. The most important requirement for ensuring structural reliability of such ships is the prevention of brittle fracture. Behavior of brittle crack propagation is, therefore, a matter of renewed concern today. Influence of applied stress, residual stress and toughness of welded joint on brittle crack propagation, is analyzed based on a fracture mechanics model developed by the authors. This model assumes that a crack propagates along the cleavage plane with the highest tensile normal stress among the cleavage planes in a grain. Results of numerical simulation are compared with the experimental results which were carried out in the SR 147 research committee of the Shipbuilding Research Association of Japan. Discussions about the influence of the above parameters on crack propagation behavior are done, and the model used in this study can explain the experimental results.

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This paper describes numerical simulations and experimental results of dynamic response of a cylindrical floating structure subjected to an underwater explosion. An explosion was generated by wire explosion method under the center of bottom plate. Responses of the cylinder were recorded in the experiments with three different offset conditions. Nonlinear explicit finite element method and finite volume method were used for the structural analysis and the fluid analysis respectively. Compressibility of fluid and fluid structure interaction were taken into account in the numerical simulation. Explosion bubble shape was observed with a high speed camera and were compared with the numerical simulation results. Experimental results of time histories of bottom surface pressures and displacement of the bottom plate were also compared with the numerical simulation results. Numerical simulation results regarding to dynamic response of the cylinder corresponded well with experimental results. Discussions are given to boundary effects on behavior of explosion bubble and offset distance effects on response of the cylinder.

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The impedance and phase characteristic of a magnetic thin film changes when a magnetic field is applied. The high-frequency-carrier magnetic field sensor, also called a GMI sensor, employs this phenomenon as its principle. We directed our attention to the chThe relation between the fatigue crack propagation behavior and the microscopic characteristics (the morphology, distribution, hardness of the 2nd phase) of Ferrite / Martensite Dual Phase steel is investigated numerically by using Crystalline-Elastic-Plastic F.E. (CPFE) analysis. As results, followings are found; 1) Under the conditions chosen, the crack closure level increases and CTOD decreases as a crack tip approaches the martensitic phase (M-phase) boundary. These changes become more pronounced when the hardness of M-phase becomes higher. 2) Under the conditions chosen, the J-integral of a crooked crack becomes nearly equal to that of a straight crack when the initial crack tip is located adjacent to the M-phase border. 3) Under the conditions chosen, the driving force of crack propagation of a fatigue crack which propagates in a narrow ferrite slit in M-phase is equal to or greater than that of a crack which propagates in a wide ferrite phase. 4) The calculation results lead us to a prediction that the crack growth rate of a Ferrite / Martensite Dual Phase steel with polygonal and banded M-phase becomes much higher than that with flattened (elongated) and banded M-phase because cracks can slip through M-phase when there exist narrow ferrite slits. The experimental results obtained by Nakashima et al. (2003) agree approximately with this prediction. This demonstrates the validity of the CPFE theory employed in this research.

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