It is important to predict the unsteady cavity shape in order to calculate the pressure fluctuation induced by cavitating propeller. For the purpose of this, we had already developed the calculation method for unsteady cavitation on a marine propeller using a simplified surface panel method "SQCM" and presented the reasonable results with respect to the cavity volume and the cavity shape.In this paper, we present a calculation method for pressure fluctuation on a hull surface induced by cavitating propeller. In the present method, first, the variation of unsteady cavity shape is calculated. Next, hull surface flow and propeller flow are calculated simultaneously in order to calculate the pressure fluctuation on the hull surface including the interaction between hull and cavitating propeller. At that time, we change the cavity shape on blade section at each time step using calculated cavity shape. The boundary condition is zero normal velocity condition on not only the wetted surface but also the cavity surface. Namely, we deal with the cavity surface as the rigid surface and regard the variations of cavity shape as the variations of blade section.The calculated results of the fluctuating pressure, the amplitude and the phase are shown about two kinds of propellers and we compare the results with experimental data. Qualitative agreements are obtained between the calculated results and the experimental data about low order blade frequency component.

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Navigating in two layers is a common case for ships. It's reported the rigid bed of shallow water areas, such as ports, navigation channels, harbors and river estuaries, is often covered by a mud layer which consists of a dense mixture of water and particles of sand, clay and etc¹⁾. Additionally, it's well known the density stratification occurs in Norwegian fiords and ice-rimmed seas. It's due to the variation in salinity and temperature with depth. When navigating at a low speed in such sites, a ship accidentally experiences the large drag mainly due to the wave-making on the interface. Understanding the ship hydrodynamics in two layers is a must for her safe navigation. However there apparently has been not so many experimental and theoretical works so far.This paper proposes a new method to solve the ship steady wave-making problem in two layers. A Green function which satisfies the linearized interface condition and the rigid bottom surface condition was newly derived and used for the expression of the velocity potentials. In this method, the hull shape and the interaction between the free surface and the interface can be considered more exactly so that the ship wave-making in two layers can be discussed more correctly. First, the wave patterns generated by a single source and the wave-making resistance of a submerged spheroid were calculated to prove the validity of the proposed method. Second, Wigley hull was used for calculations and it was numerically confirmed that the sharp increase of the wave-making resistance occurred when navigating close at the critical velocity of the internal waves. The proposed method succeeded to capture the waves both on the free surface and interface properly through a series of calulations.

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The flow in a two-dimensional cavity with a free surface and a bottom opening on a channel stream is numerically calculated.The calculated results are compared with experimental data measured in the vertical openings of ship models. The calculations are performed using GSMAC-FEM. The arbitrary Lagrangian-Eulerian formulation is applied to deal with the free surface motion. To test the algorithm used in the present calculation, three cases of the fluid problem are examined: normal cavity flow, free oscillation of water in a tank, and the run up height of a solitary wave on a tank wall. In the three cases, the calculation results show good agreements with previously published data. Using the present calculation algorithm, the flow in a cavity with a free surface and a bottom opening to a channel flow is calculated and the following conclusions are obtained: (1) Vertical oscillations of the free surface in the cavities are observed in the numerical calculation when there are two vertical cavities with the free surface on the upper wall of a channel flow. (2) The stream velocities of the free surface motion in the numerical calculation are the same as those of the experimental results measured in the vertical opening of ship models at the dimensionless speed, 2U/(Lω0) or 1/(πSt).

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The effect of the Reynolds number on propeller performance in open water was investigated through numerical simulations at Reynolds numbers ranging from model scale to full scale. The comparisons of computational results with experimental data suggested that large part of the boundary layer on the blade surface is laminar at the model scale Reynolds number. On the other hand, it was shown that the dependencies of the thrust and torque coefficients on the Reynolds number is rather simple when the Reynolds number is sufficiently large. This result indicates that correction based on the skin friction coefficient can be applied to the extrapolation of the thrust and torque coefficients at the full scale.

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This paper describes some hydrodynamic mechanisms of PBCF (Propeller Boss Cap Fins) behind a propeller derived by computational fluid-dynamics method (Finite Volume method).Ouchi¹⁾ makes it appear that in his experimental method (inverted propeller open test), more effective propeller performances by installing PBCF are obtained. It is the fact that thrust of propeller system with PBCF is higher and torque is lower than without PBCF, as a result, efficiency of propeller with PBCF is higher than without PBCF. Unfortunately, as it is very difficult to obtain effective quantities showing physical phenomena as velocity, pressure, and vorticity, because of a propeller as rotational wings, the detailed information in order to explain the mechanisms cannot be investigated in the experiments easily.The purpose of this paper is to clear the hydrodynamics mechanisms of PBCF shown by 3 kinds of experimental results (higher pressure on boss cap, higher thrust working on blade and against torque working on PBCF). As a result, we obtain that increased pressure around boss cap by damming flow before PBCF will prevent generation of hub vortex.

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Finnish-Swedish ice class rules (FSICR) requests resistance estimation of ship navigation in a brash ice channel with a certain condition. We develop numerical estimation method of the above situation on the basis of physically-based modeling, and apply this method to the model-scale simulations of ship navigation in channels filled with small ice pieces. Real-scale resistances are estimated using the above results with cubic law. Results of the numerical simulation show that our simulator can handle simulation under condition with more than 65000 ice pieces. Estimated resistances are about twice as large as that of FSICR rule formula, but tendencies of differences with two bows are consistent each other. Effects of channel length, the size of ice pieces, fluid force and other parameters are discussed.

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In this study, the occurrence of parametric rolling in head seas for high speed trimaran is experimentally investigated. First, in order to check the conditions where parametric rolling occurs, a towing tank test is carried out. A model of trimaran is a stabilized slender mono-hull type high-speed craft, and its distributions of displacement for main-hull and side-hulls are decided by based on a real high speed vehicle-passenger trimaran ferry. Next, in order to investigate dominant reasons of the variation of roll restoring moment as a cause of occurrence of parametric rolling, a captive model test with heave and pitch free conditions is carried out. In the test, the position of side-hulls is systematically changed. And the results indicate that the variation is mainly caused by side-hulls. Moreover, it was confirmed that the occurrence of parametric rolling estimated with the measured roll restoring moment and the calculated roll damping by the estimation method proposed in previous our study¹⁾, are consistent with the measured results.

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Since parametric roll is well known as one of the most dangerous phenomena which could lead to serious accidents due to large amplitude roll motion, a new Intact Stability code, which is under development at IMO, is required to cover this phenomena. To realize quantitative prediction of parametric roll, systematic forced roll motion tests were conducted to measure roll restoring variation and roll damping with relevant roll angle/amplitude up to 30 degrees. Then, a 3DOF numerical model based on nonlinear strip method is developed and compared with model experiment to validate its prediction accuracy and applicability as a direct assessment method towards the new Intact Stability code.

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A "Resonance-Free SWATH (RFS)" ship is introduced as an example of the oceangoing large fast ship. Because of the extraordinary small water plane area, the restoring moments of the RFS are negative, which leads to resonance-free in the motion responses. 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 towing tank and theoretical calculations based on the strip theory are carried out to examine hydrodynamic forces and motion responses in waves. The results are compared with those of various hull forms, i.e. mono-hull, ordinary SWATH and trimaran. The predominance of the RFS regarding seaworthiness will be pointed out in the conclusion.

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The paper describes the computational method for motion responses on a Resonance-Free SWATH (RFS), which has extremely small water-plane area and it leads to the feature close to the resonance-free in the motion responses.Theoretical calculations based on the strip theory are carried out and compared with experimental results in regular head waves. The influence of forward speed on lift due to hydrofoils and lower hulls are large and numerically modeled well. Hydrodynamic interaction between twin hulls is well computed through the introduction of a practical manner.

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In order to increase ship performance in actual navigation conditions, a definite evaluation method of the performance should be established. For that purpose, a design index, 10 mode Index for Ships, is developed. The index consists of ship speed in ten kinds of weather conditions as well as ship speed in calm seas.The present paper prescribes a calculation method for the 10 mode Index for Ships. To obtain the ship speed in actual seas,equilibrium equations of external forces acting on a ship are calculated. Selected as the external forces acting on a ship are resistance in still water, propeller thrust, and resistance due to drift, steering, winds and waves. In calculating these forces, accuracy should be kept for resistance due to waves. Therefore, the calculation is developed based on the hybrid type procedure, which combines the model tests with the numerical calculation. In addition to this, a package program to calculate the index is developed.In the paper following verifications are carried out; 1) comparing calculations on added resistance in regular waves with other programs, 2) comparing tests of a container ship model in several ship model basins and 3) full scale measurement of a pure car carrier. From the verifications it is clarified that the hybrid calculation is robust to evaluate ship speed in actual seas.

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Since International Maritime Organization (IMO) has adopted "The Standards of Ship Manoeuvrability" as IMO Resolution MSC.137(76), the ship manoeuvrability is evaluated under this standard. Therefore, ship designers have to know the accurate ship manoeuvring characteristics at the initial design stage. One of the estimation methods for ship manoeuvring characteristics is a computational simulation. Some papers have proposed approximate formulas for hydrodynamic derivatives based on the model ship tests, so we can simulate the ship manoeuvring motion with the hydrodynamic derivatives.However recent full ships aren't included in the range of ship types on the papers. We need to adjust the formulas for hydrodynamic derivatives, so as to simulate the manoeuvring motion of recent full ships.In this paper, we propose the method to revise the approximate formulas for hydrodynamic derivatives of full ships. We confirm the effectiveness of the practical prediction method using proposed formulas. It will be expected that this method is very useful to estimate the manoeuvring characteristics of recent full ships at the initial design stage.

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price of fuel, in order to keep and improve the management of fishing. As for the balance of income from fishing, the technology of the saving energy should be achieved by low cost and it is desirable to be adopted not only new vessels but also existing vessels.There are usually anode protections on a ship hull, bilge keels and a rudder to protect them from electric reactions from a propeller and seawater. The rudder is behind the propeller, and the inflow velocity of rudder becomes large. On a rudder, small objects like anode protections would increase resistance and reduce the lift force. The authors researched the situation of anode protections on approximately twenty Japanese fishing vessels. It is clear that the arrangement is various and there is no single confirmed way though the front positions on a rudder would be effective for the prevention from electric reactions. This study reports the hydrodynamic characteristics of a rudder with anode protections and the influence to the propulsion and the maneuvering performance of a ship. And appropriate positions of anode protections on a rudder for the energy saving are considered.This first paper reports the drag and lift characteristics of a rudder with anode protections at different cord length from leading edge and at different directions against the flow having different thickness or conditions. By model experiments in the uniformed flow and in the flow behind a propeller, this paper concludes that anode protections become resistance and reduce the lift force. And the front positions, the positions against the flow and large thickness increase the drag force and reduce the lift force. In the next paper, the detail influence to the propulsion and maneuvering performance of a ship will be reported.

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Using a ship model with azimuthing propellers (PODs) which are arranged in parallel at stern part, captive model tests were carried out to investigate the effect of POD strut profile area and the effect of stern fins on the hydrodynamic force characteristics related to ship maneuvering. The subject ship was unstable for course keeping.With increasing the strut area, ship control forces due to POD steering increase and the course stability of the ship was improved. Thus, the strut area is important for the performances of both ship control force and course stability.Stern fins were also useful for improving the course stability. However, effective control forces were reduced about 15% by attaching the stern fins. This is due to decrease of additional lateral force component acting on the hull induced by POD steering. Improvement of the course stability of the subject ship was insufficient by enlarging the strut profile area and attaching the stern fins. Further investigations are needed.

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For identifying possible danger of a trimaran running in following and quartering waves, numerical simulation in the time domain was systematically conducted. Here a surge-sway-yaw-roll manoeuvring model with a PD autopilot was used. The manoeuvring forces, the roll restoring moment and the wave-exciting forces are calculated for the trimaran with hydrodynamic interaction among three hulls taken into account. As a result, as well as harmonic motions and stable surf-riding, repeated broaching within one wavelength at higher speed and sub-harmonic yaw motions with large amplitude at lower speed are found. This repeated broaching could be chaotic via period doubling. These phenomena do not result in capsizing thanks to large restoring arm due to side-hulls but are threats to safe manoeuvring. They can be prevented by increasing the magnitude of differential gain for the auto pilot.

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The course stability of a ship is a difficult task to be determined from the quantity of the performance in the initial design stage.Most of newly-designed ships' maneuver abilities are examined by the model tests in a towing tank. Although, the drawback of this experimental method is that it will have high running costs to investigate the course stability. In the present state, it is too costly to conduct the experiments of maneuvering motions with a fishing vessel in the towing tank. The authors have proposed the simple evaluation method of the course stability by using a circulating water channel. However, the model of the ship is too small to mount its power motor and propeller. The simple evaluation method neglected the influence of propeller race on the course stability.In this paper, the simple evaluation method is improved and takes into account the influence of propeller race on slewing motions in a circulating water channel. As the towing point moves forward at a constant speed, the amplitude of slewing motion decreases and its period gets longer. The index of evaluation (aT) is represented by the point of towing from the center of gravity. Accordingly, the influence of propeller race (ΔaT) is the difference between the index of evaluation on a propeller working and the one of a dummy boss. The results are checked and compared with the course stability of sea trials. By using the present method, new fishingvessels can be designed to achieve the improvement of course stability.

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The unsteady hydrodynamic forces acting on a berthing ship model was examined, and an procedure for the analysis of measured result in towing tank was considered. The blockage effect could be a problem if we execute the large attack angle lateral force measurement in towing tank, and it will be much serious in the case of shallow water. The authors proposed an experimental procedure, which enables us to carry out the test in towing tank. The proposal employ the normal size model ship with the resistance test, and the blockage effect was avoided by towing the model normal to the tank length. The additional problems in connection with the side wall of towing tank was considered as well. The refected waves affect on the measurement, and it causes unstediness. The authors consider the analysis process on that factor, and they proposed practical solution to extract steady component.

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A container ship with much larger structure above sea than the hull volume under water is strongly affected from wind at sea. It is important to estimate wind effect exactly for assessing navigational performance of the ship. Ordinary, specification of a ship external form does not change without considering the main hull's thickness that means the height from sea level to main hull deck top. On the other hand, the container ships have many kinds of on-deck forms depended on the number of containers. Under these situation, it is difficult to reflect individual shape influence on the deck of a container ship in the estimation method, since the method is basically proposed using fully loaded or ballast ships' experimental results and only uses the simple ship external form parameter, that is total projected area, center potion of the projected area for lateral area above sea etc. In the present, there is no estimation method to calculate the wind effect easily by the external ship form specification including the lack influence of the containers at some parts on deck. Then, the authors carried out the wind tunnel experiments of a container ship for the many kinds of stowage of containers on deck in order to grasp the aerodynamics specifications of them. Using the experimental results, authors propose a new estimation method for wind forces on no fully loaded container ships. This new method is able to estimate the longitudinal and lateral forces and yaw moment on wind load for several kinds of container ship forms more exactly rather than the previous estimation method.

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This paper presents crack propagation analyses using the wavelet finite element method. The wavelet finite element method is a new methodology to solve partial differential equations. In the authors' previous studies, solid/structural mechanics analyses without cracks were performed. In the wavelet finite element analysis, the scaling functions are placed throughout the domain of analysis and it is divided by equally spaced structured cells to integrate the stiffness matrices. To improve the accuracy, wavelet functions are superposed on the scaling functions within the regions of high stress concentration, such as the vicinities of hole edge, crack tip, etc.However, since all the basis functions in the wavelet finite element method are assumed to be continuous, there are difficulties in treating displacement jumps across the crack face. In present research, we propose that the discontinuous displacement functions and crack tip asymptotic solution are introduced based on the concept of X-FEM. The proposed method can perform the crack propagation analysis without any remeshings. In this paper, the mathematical formulations of the wavelet finite element method for the crack propagation analysis and its numerical implementations are described. Then, some two dimensional crack propagation analyses are presented for illustrative purposes.

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This paper presents the methodology of the CTOD fracture toughness correction for wide plates' welded joints from lower to upper ductile-brittle transition temperature region. Tensile plastic zone size criterion is adopted in lower transition region. The equivalent CTOD ratio, β r , is adopted in ductile-brittle transition and upper transition region. The equivalent CTOD ratio is defined as the ratio of CTOD in a standard fracture toughness specimen to CTOD in a wide plate with welding residual stress at the same level of the Weibull stress. Fracture assessments for "After Weld Notch" and "Before Weld Notch" type welded joints have been conducted by applying the toughness correction methodology. It has been found that an excessive conservatism observed in the conventional procedure is reasonably reduced by applying the proposed methodology.

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The non-detective testing is usually applied for the inspection of defects of welded structures and casting parts of machines. The Ultrasonic testing (UT) is safer and more inexpensive compared to other non-detective methods such as the X-rays testing.Therefore, UT is gradually expanded the application region. But even now, when applying UT for complicated structure, it is very difficult no only to evaluate the defect size, shape, and location precisely but also to determine the proper probe position for detecting. It is because that we cannot observe how the ultrasonic wave is propagating in specimen and reflecting at defects and specimen boundary.In this study, the numerical simulation software of ultrasonic wave propagation has been developed to obtain the high performance of Ultrasonic Testing, and the Neural Network and Migration techniques have been examined to evaluate the defect properties.

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Heat input generated in plate by gas cutting process was determined quantitatively. And, the feature of distribution of heat input along the thickness was clarified. First of all, the heat input distribution of the preheating flame was examined. Next, about the gas cutting process, the method of predicting the heat input was proposed, and the predicted values were compared with the experimental values. Finally, the inherent strain distribution along the thickness was measured, and the heat input distribution along the thickness was examined. The main conclusions obtained were as the following: 1) It was able to explain the heat input distribution of the preheating flame as gaussian distribution. 2) It was shown that the proposed method of presuming the heat input in plate generated by gas cutting was appropriate. 3) The distribution of heat input by gas cutting along thickness is effected by preheating gas flame and dross.

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In this paper, an anti-vibration optimal design method for bridge wings of bulkers is proposed. In general,bridge wings have disadvantage for its vibration characteristic due to its cantilever like structure. To improve vibration characteristics of the bridge including wing structures, some structural optimization methods can be effective. The research is performed in following processes. First, vibration of the bridge is simulated using finite element method for frequency response problems. Next, based on the vibration analysis, the stiffness maximization optimization problem of wing structure is formulated to raise eigen-frequencies of bridge. Two types of topology optimizations are performed for the optimization problem. Based on the optimal results, two new structures of bridge wing are proposed based on the optimal result. Finally, we confirm the usefulness of the proposed method by vibration analysis of the new bridge wings.

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Stick-slip is critical problem for offshore drilling, especially scientific drilling, because it will cause crushing or grinding the layer.In order to repress stick-slip, first of all it is necessary to establish a model of the torsional motion of the drill bit and express the stick-slip phenomenon. Therefore, in this paper, the model of the torsional waves in a drill string is established by applying a neutral delay differential equation (NDDE), and then it leads to expression of stick-slip phenomenon for the friction models and a rotation speed that was applied on the uppermost part of the drill string. In addition, utilizing data acquired from the actual drilling operation,stick-slip phenomenon was analyzed and stick-slip level was discussed.

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The anxiety about the risk of international food shortages is getting larger in the face of population growth, climate change and other concerns. Especially, worldwide price increase and low self-sufficiency rate of our country are considered as significant problems in these days. To increase the production of fishing resources by means of ocean fertilization could become an effective option for solving the problem. Since it is quite difficult to know the stock abundance of fishing resources, the resource management is always accompanied by the uncertainty. In the present study, management method for the Japanese sardine (Sardinops melanosticus), whose stock abundance stays very low in recent years, is examined on the supposition that ocean fertilization technology is applied to increase the stock abundance. A VPA (Virtual Population Analysis) scheme is developed to predict the resource conditions of the fish under ocean fertilization. Some adaptive management schemes are proposed and examined through the VPA simulations. The results indicate that the adaptive management scheme using the information of VPA will produce better results than the conventional management schemes.

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Regarding ocean space utilization, many plans have been proposed for floating airport, container terminal, energy facilities and oil storage basis etc. from the viewpoint of their advantage of being earthquake free and away from an urban area. In case facilities are constructed independent from shore, the investigation on access facilities is dispensable. Bridges, landing piers and tunnels are constructed as access facilities, but they have own difficulties due to deep water, soft ground condition and ground subsidence. In case of passage way of airplane, there is severe restriction and requirement in inclination of passage, and has not been discussed specifically in this viewpoint. In this report, the required functions for floating access facilities are reported and technical countermeasure and applicability are considered.

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In first report, two of the authors presented a new concept of floating access facility, "a both-end supported lower-hull semi-submersible type facility", and discussed its applicability. For such new-type floating structure, the design procedure has not been established. In this report, both-end supported semi-submersible facility is designed for example. Further, dynamic response analysis in waves was carried out, and structural characteristics of response are discussed. Design flow, design ground in determination of principal dimensions obtained in the process of study is summarized and proposed.

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