The perturbed complex potentials representing flows around a vertical plate semi-submerged in a uniform stream are derived in analytical forms by the reduction method. They are composed from the regular solution and the weak singular eigen solutions. The linear combinations of them represent some flows such as regular flow, zero-vertical flux flow, flow satisfying Kutta condition and wave-free flow. The wave resistances of the flows are also obtaied in analytical forms. The analytical solution obtained by Bessho-Mizuno(1962) has a possibility that it dose not satisfy the boundary condition on the plate.

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The authors propose a practical method to estimate the reduction rate of propeller-induced pressure fluctuations due to the backward rake around the blade tip. The designed geometrical shape of propeller blades decisively affects the propeller performance and the cavitation characteristics as well. The propeller designers try to reflect positive effects of the geometrical parameters to propeller design to enhance the propeller performance and to reduce the negative effects of cavitation behavior. In the present study, the cavitation tests and the measurement of pressure fluctuations induced by the respective propellers with five kinds of backward tip rake distribution working in the wake distribution behind an inland ship are performed systematically. The effects of the backward rake distribution on the pressure fluctuation signals are clearly demonstrated. The systematic analysis of the measured pressure fluctuations derives a practical formula to estimate the reduction rate of the pressure fluct uations due to the effective backward tip rake. Finally this formula is applied to the measured results of pressure fluctuations on other backward tip raked propellers working in the wake of a large low-speed ship to confirm its effectiveness. The results show that the present simple and practical method is promising but further validation is encouraged through the practical applications.

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Oblique towing test and circular motion test with changing heel angle were carried out to capture the hydrodynamic forces acting on ship models of container ship, pure car carrier and ferry. Based on the measured forces, the hydrodynamic derivatives with respect to lateral velocity (υ), yaw rate (γ) and heel angle (φ) were obtained for surge force, lateral force, yawing moment and roll moment. Using the derivatives obtained, ship maneuverability traveling in heeled condition was discussed based on a linear theory presented in this paper. As a result, we made clear the maneuvering characteristics of heeled ships. When the ship travels in heeled condition to starboard side, she turns to port side. Such characteristic depends on the order of magnitude and the plus(minus) sign of the hydrodynamic derivatives with respect to heel angle, Y'_φ and N'_φ. In case of the ferry, the turning strength per unit heel angle was about 1/3 comparing with that per unit rudder angle.There is a trend that the turning performance improves with increasing the heel angle. This is due to the course instability appears with increasing the heel angle. The course stability is deeply related to nonlinear derivatives with respect to heel angle, such as Y' _υφφ, Y' _γφφ, N' _υφφand N' _γφφ.

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In this paper, variational principles related to motions of an elastic plate in waves considering wave radiation condition at infinity, which are very important in calculations of the elastic response of the pontoon- type floating structure, are discussed. First, Sommerfeld radiation condition at infinity is extended to treat a case with an incident wave. Second, four kinds of variational principles related to motions of the elastic floating plate considering the incident and radiated waves are proposed and clarified the mutual relationship of these variational principles. Third, numerical results for elastic response of a floating plate of rectangular plan geometry in waves, which are obtained by using proposed variational principles, are shown.

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Securing the survivability under flooding condition is one of the most important subjects in ship design. For realizing rational and advanced assessment of damage stability, a numerical simulation method is developed for damaged ships by combining the moving particle semi-implicit method (MPS method) and the strip method based on potential flow theory. In this method, the flow field around the damaged part including damaged compartments is computed by the MPS method and that around the intact part is done by the strip method, separately. In order to validate the proposed method, model experiments are conducted for a damaged pure car and truck carrier. Then comparisons of the ship motion and the water flooding into the damaged compartment are conducted. As a result, it is confirmed that the proposed simulation method has good potential for the prediction of dynamic behaviours of damaged ships under flooding condition.

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This paper presents a practical simulation model for ship launching taking the dynamic coupling effect of trim angle change and vertical motion into account. The motion equations were derived in three stages of sliding, lift by stern and afloat modes in launching. By solving the motion equations in three stages continuously, ship speed change, trim angle change, traveling distance, pivoting load, etc. during launching can be calculated. To obtain the validation data of the simulation method, a fullscale test was carried out to measure the ship motions during launching by a Kinematic GPS (KGPS) system. Then, three antennas for KGPS were arranged on a Chip Carrier with 191.5 m in ship length. Some parameters needed for the simulation were determined by comparing with the fullscale test result. The present simulation method is useful for capturing th ship launching behavior.

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Roll-coupling effect on ship maneuvering motions is not negligible for high speed vessels, large container ships, passenger ships and so on. To perceive the roll-coupling effect on the ship maneuverability, in this paper, approximate formulas for course stability criterion, steady turning index and the response time until reaching to steady turning (time constant) in the framework of the linear motion theory were derived on the assumption where the depthwise acting point of lateral force with respect to roll moment is constant even in any modes such as oblique moving, turning, rolling and steered conditions. Using the hydrodynamic derivatives measured in tank tests for 3 ship models, the roll-coupling effect on the ship maneuverability is discussed. The course stability becomes worse with increase of Froude number of the ship and/or decrease of metercentric height in general, and the turning performance is improved and the time constant becomes long. The approximate formulas have sufficient calculation accuracy and the formulas are useful for conventionally checking the ship maneuverability.

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This paper describes the application of weight function method for the calculation of stress intensity factors in a surface crack and an embedded crack under complex two-dimensional loading conditions. The crack shape is approximated by an ellipse.Improved formulation of the point load weight functions are proposed based on the properties of weight functions and the available weight functions for two-dimensional cracks proposed by Wang and Glinka. For a surface crack and an embedded crack of any aspect ratio, the unknown parameters in the general form can be determined from one reference stress intensity factor solution obtained by the finite element analysis with J integral method. The derived weight functions are then validated against available stress intensity factor solutions for several linear and non-linear stress distributions. The derived weight functions are particularly useful for the fatigue crack growth analysis of a planer surface crack and an embedded crack subjected to fluctuating non-linear stress.

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Fatigue crack propagation behaviour under superposed loading histories which contain two different frequency components is highlighted. Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Retensile Plastic zone Generating) stress criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history. The critical value of the plastic hysteresis for the stress versus strain relationship occurring in the vicinity of a crack tip is defined as the control parameter for extracting the effective loading history. Comparison of fatigue crack propagation curves obtained from the improved numerical simulations with the measurements under the superposed loading histories is performed. These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superposed loading history containing different frequencies. Besides, the insufficiency of S-N curves approach with the cumulative damage law for the superposed loading history condition containing different frequency components is conducted.

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In this research, the numerical analysis method which can predict the residual stress distribution after tempering with sufficient accuracy was established. First, residual stress distribution of the cylinders test material after quenching and tempering was measured. Next, the creep test was done using the material after quenching, and the formula which predicts the creep strain of each material was clarified. Finally, comparison and examination of the experimental and numerical analysis value of the residual stress distribution after tempering were performed using the formula which predicts creep strain drawn from the experiment. By using the linear expansion coefficient, the yield stress of heating and cooling process of tempering, and the formula which predicts the creep strain, the residual stress distribution after tempering can be predicted with sufficient accuracy by numerical analysis. Moreover, reduction of the stress by tempering has the great influence by the fall of yield stress and creep strain, and the influence of strain resulting from a deposit of the carbide which arises in the heating process of tempering hardly affects residual stress distribution. Key words : quenching, tempering, residual stress, creep, finite element method

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Welded joints are often applied to ships and ocean structures. Fatigue strength evaluation for the welded joints is important for assessing structural integrity of welded structures. In recent years, effective computational techniques for analyzing fracture mechanics problems and the crack propagation simulations have been proposed. In addition, the simulation for complex shaped geometry is easy to handle for the development of computational power. In this study, fatigue strength evaluation based on the crack propagation is examined. In the numerical examples, crack propagation analyses of surface crack in T-shaped welded joints are carried out for employing the computational techniques. Mk factors, crack paths and fatigue cycles are evaluated and are compablack with existing techniques. Effectiveness of the fatigue strength evaluation based on the new techniques is discussed.

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Recently, R&D of marine renewable energy becomes very popular all over the world. In this paper, the contra-rotating turbines are adopted as an ocean current power generator. The contra-rotating turbine system is theoretically torque free, since the second blade counters the first blade torque. Therefore, small main body (pod) and low cost mooring might be achieved. In this paper, a conceptual design of the contra-rotating ocean current turbine is presented. A computer code, which represents motions of the pod and turbines with 6 degrees of freedom together with the non-linear mooring effect, is developed. The numerical results are compared with experiment in which a newly developed small size turbine-generator model is used. The results show that the current turbine is stably moored even when the flow direction is suddenly changed. An attempt to reduce the pod motion by controlling the blade pitch angle is also discussed and it is found that it could be possible to reduce both long and short period unsteady motions.Summarizing these results, it is concluded that the contra-rotating ocean current turbine has a technical merit from the perspective of motion characteristics.

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In order to consider how to strengthen and foster core ocean technologies, current state of ocean technology in Japan is reviewed. The framing of ocean technologies used in the offshore oil and gas development is investigated, and linkage between these technologies and ocean technologies necessary for the ocean renewable energy utilization, the sea floor mining and the methane hydrate development which are expected to be industrialized in Japanese exclusive economic zone (EEZ) in the future. The history of development of ocean technologies in Japan is reviewed to know strength and weakness of Japan's ocean technologies. Summarizing these results, it is found that there is strong linkage between ocean technologies used in the offshore oil and gas development and future projects deployed in Japanese EEZ, and it is important to invest governmental funds in a comprehensive and systematic fashion for developing those core technologies. It is also emphasized that it is important to apply the environment technology and IT to the ocean technology for strengthening Japan's core ocean technologies.

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AUV "REEF" was developed in Osaka University for monitoring environments in coastal sea areas. REEF is characterized as a surface piercing autonomous underwater vehicle using route tracking control in horizontal plane and pitch control in waves in longitudinal plane. Route tracking controller was designed using PID control method, and pitch control was designed using H_∞ control method. Route tracking control was evaluated through experiments both in still waters and in winds. Pitch control in waves was evaluated in irregular waves in water tank comparing with PID control.

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In this study, the concept of "vertically movable tension leg mooring system" is proposed for the purpose that an offshore floating body subject to comparatively large static horizontal loads for its scale, which is represented by floating wind power generator, ocean current power generator, etc., is moored so that the occupied plane area of the mooring system may become as small as possible. In the system, a gravity type template is hung from the floating body with vertical lines and the template is moored with relatively short catenary chains to seabed anchors. The advantages of the proposed system are discussed comparing mainly with the tension leg mooring, and the fundamental mooring characteristics are shown with model calculations.

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The development of seafloor massive sulfide (SMS) is eagerly investigated for its potential of abundant amount of metal resources in Japanese exclusive economic zone. In order to promote the development of SMS and create new ocean industry, the business feasibility for the decision making of investment are significantly important. In the present study, Monte Carlo DCF and real options valuation were applied to evaluate the business feasibility of a SMS development project. In the analysis, the uncertainty of environmental risk is taken into account by quantifying of experts' opinions. The results of Monte Carlo DCF analysis indicate that the SMS development project has large business risk due to the uncertainties. Then, real options valuations considering decision-making options of abandon and deferment were carried out for two development scenarios. It is clarified that the options values are significant for each scenario of the target project. It is also found that the project will be started easier when the baseline survey for environmental impacts is carried out in earlier stage of the project.

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Tidal current energy is one of the most important future energy, clean, renewable and predictable. We are studying the Darrieus turbine that has omnidirectional characteristic in the reciprocating tidal current in a narrow channel. To enhance the performance of the tidal turbine, we propose adding a pair of appendage structures near the turbine, because the power of the turbine is proportional to the cube of the current velocity.In this report, we first present the performance of the simple Darrieus turbine by model tests in a circulating water channel and CFD calculations. For the validation of CFD calculation, the torque variation and the power coefficient of Darrieus turbine are compared with experiments. For the determination of the shape of a pair of appendage, the CFD results for several shapes of the a pair of appendage are compared. It is found that the small difference in shape of a pair of appendage is not important for the final performance, so that we adopt the arc shape a pair of appendage. We compare the power coefficients of the Darrieus turbine with/without a pair of appendage by the experiments.

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Wind speed and wind power map around the Pacific side of Tohoku district are created by atmospheric model, and validated by various kinds of observation data including land and on the sea. In the downscaling calculation of wind filed from the coastal area to on the sea, it was found that the accuracy of the boundary condition had the more importance than the grid size and the quality of atmospheric model. Wind speed in coastal area showed the high correlation and small mean error less than 1 m/s with observation data.

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The evaluation process of the curved shell plates' accuracy carries great risks for no quantitative criteria, and great depending on implicit knowledge, the skill and experience of the workers. An accuracy evaluation method for the curved shell plates using laser scanners was proposed. The shape of the objects is obtained as point cloud data. In the system, the point cloud data and the design data are registered and the displacement errors are evaluated and visualized by a color map and histogram. Before the two input data's registration, the points of curved shell plates are extracted using region growing method. To extract the curved shell plates from the point cloud with noises, a new extraction algorithm which is more efficient and faster is proposed in this paper. And the ICP algorithm for registration of the design data and the point cloud data is also developed to automatize the registration operation. In practice stage, automation engine which can operate the scanner directly has been arranged. Also, the measurement and analysis flow has been totally automated for ease of use. By deploying the improved system to factory for about 5 months, the evaluating process was automatized, which lead directly to the immediate correction processing and obvious decrease of the error dispersion.

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To cope with the problems in the marine ecosystem caused by the ballast water from ships, the IMO adopted the International Convention for the Control and Management of Ships' Ballast Water and Sediments in 2004. In response to this legislation, ballast water treatment systems are being developed worldwide. The ballast-free ship concept proposed by Yokohama National University is aimed at solving this ballast water problem from a completely different standpoint. In the proposed system, seawater continuously passes through the buoyancy control tank to keep the contents of the water inside the tank the same as that outside the ship. A series of studies on this new concept has been carried out by the authors, including the analysis of seawater circulating performance inside the buoyancy control tanks, an examination of the increase in resistance caused by adding small appendages such as intake and exit gates on the ship bottom, a study of structural integrity of the system, and related work. In the present study, we used a scale model of an actual double bottom tank and carried out an experiment to examine the water exchange performance of the proposed system on the open sea. In the model experiment, the water inside the tank was set as fresh water initially, and as time passed, the water inside the tank changed to the seawater outside the tank. The water locality ratio inside the tank was evaluated based on the salinity change of the water inside the tank and the change of the numbers of phytoplankton cells inside the tank. Numerical results and experimental results were compared to examine the performance of the proposed ballast-free system.

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Recent developments with offshore terminals and floating liquefied natural gas production, storage and offloading (FLNG) applications have included the new requirement that the storage tanks be able to handle unrestricted filling with LNG. If membrane-type tanks are used in such new systems, the occurrence of sloshing in the half-load condition becomes one of the most important design issues. In this paper, we propose a simple anti-sloshing floating device to be installed inside a liquid cargo tank. By setting the device on the free surface of the liquid cargo, the original free surface is divided into two or more sub-surfaces, and resonant sloshing of the liquid can be avoided by changing the natural frequency of its motion. This floating device can follow the liquid height change in the tank during loading and unloading operations of the liquid cargo, a feature that is especially preferable in FLNG applications. We examine the performance of the proposed anti-sloshing device by a series of model experiments and numerical simulations, which indicate that the device's performance is very promising.

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