The purpose of this study is to propose the propulsive performance estimation method for high-speed planing craft with outboard engine. In order to understand the characteristics of propulsion, a fully captive model test with propulsion is carried out. Based on the results, an estimation method taking the self-propulsion factors, which are the changes of hydrodynamic forces acting on hull with lower-hull of outboard engine caused by propeller action, the effective wake fraction and the relative rotative efficiency, is proposed. Using the proposed method, running attitude, thrust (or THP), crank shaft torque (or BHP), maximum forward speed and fuel consumption of a real craft are estimated. As the results, it is found that the effective wake fraction and the relative rotative efficiency of the self-propulsion factors are significant to estimate maximum forward speed of the craft.

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In this study, the characteristics of rolling in head waves for a vessel with nonlinear GZ-curve, which includes parametric rolling, are investigated. Rolling is measured for systematically changed wave length and height under the same forward speed, which is service speed in heavy weather. As the results, the range of Te/Tø(Te and Tø are encounter wave period and roll natural period),when periodic rolling occurs, is wider than one of previous results by Taguchi et al¹⁾, and the range spreads out wider range of Te/Tø>0.5. Especially, in the range of Te/Tø>0.5, roll amplitude becomes large, and a periodic rolling occurs at large wave height.It is supposed that the result is caused by the effects of roll amplitude on roll natural period. Then, numerical simulations₂₎ are carried out for some variation of GZ-curves to confirm the measured results. Additionally, roll measurements in superposed waves of two different wave periods and in the irregular wave with Pierson-Moskowitz spectrum are also carried out.

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Greenhouse gas should be reduced for our future. For the shipping sector technical and operational measures as improving the energy efficiency have been established in the international frameworks. Evaluation of the ship performance in actual seas is important for the superior design of ships and energy efficient operation of ships, as well. For the purpose of establish the ship performance index in actual sea a research project has been carried out in Japan. In this paper following contents examined by the project are reported. 1) comparison between tank tests in short waves using a bulk carrier and a tanker model, 2) comparison of the calculation method and 3) verification of the calculation method through onboard measurement. The results of the examination is 1) the tank test in short waves is practically satisfied the enough accuracy and it is found the robustness of the measurement, 2) according to the calculation method, it is clear that there is no practical problem in using the present approximation of the calculation method and 3) onboard measured data have good corresponding with the onboard measured data, so that the usefulness of the calculation method is confirmed.

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For the estimation of ship speed in actual seas, it is important to calculate external forces acted on a ship hull with accuracy. In National Maritime Research Institute, a calculation method for ship speed in actual seas on a constant engine output has been developed and validated by onboard measurements with the cooperation of the Ministry of Land, Infrastructure, Transport and Tourism, Japan, the Ministry of Environment, Japan and the relevant shipping and ship building companies. The results of onboard measurements for the pure car carriers, the tanker, and the bulk carrier have been reported.In this paper, the results of onboard measurements for the container ship of about 280 meter long are reported in terms of the verification of the calculation method of ship speed in actual seas. Moreover the influence of container load condition related to ship performance in actual seas is studied by the calculation and the onboard measurement.

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Estimation of ship speed in actual seas is very important to evaluate the comprehensive performance in her life. Estimation of the added resistance in ballast condition is more difficult than that in full load condition due to the complicated phenomena around the bulbous bow. The proposed method, which combines tank tests with calculation, shows the estimation of added resistance in ballast condition accurate for a Panamax bulk carrier.In this paper, the proposed method is applied to a handy-size bulk carrier (approximately 160m length) equipped with cranes in both ballast and full load conditions, and its accuracy is confirmed by model tests and onboard measurements. Moreover the difference of resistance components due to winds and waves is discussed in terms of load condition toward the improvement of evaluation of performance in actual seas for handy-size bulk carriers equipped with cranes.

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In 2010, National Maritime Research Institute (NMRI) had developed an integrated design support system,called "Harmonic Design Tool", to construct offshore platforms that harmonize with safety, economical aspects, and environmental matters. Using this tool in the basic design phase of platform, we are able to propose, in consideration of its operation plan, an optimum hull size and the specification of equipment such as mooring system and DPS,and to roughly estimate construction cost and other expenses. The safety of mooring system and DPS can be also evaluated with the tool.In this paper, we discuss the position-keeping ability of a ship type platform designed in 2009 for mining of SMS (Seafloor Massive Sulfides), and evaluate the safety of its DPS (Dynamic Positioning System) using the "Harmonic Design Tool". At the same time, based on the model test carried out under complicated environmental conditions at Ocean Engineering Basin in NMRI, we evaluate DPS capability of the platform, and the accuracy of the "Harmonic Design Tool" is also verified. Because these evaluations revealed that our basic design of the platform could be materialized, we report the results in this paper.

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The paper describes the boundary element analysis method for the water impact of an arbitrarily shaped section.Computational method for the nonlinear solution, which is the initial condition of the free surface for the simulation of the fully-nonlinear wave-body interactions, is proposed. For stable computation on the water impact problem, the time-step division and the element length are decided in a practical manner. Computational treatment of the intersection of the free surface with the body is discussed and the numerical technique is proposed for the simulation of nonviscous flow separation.

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The paper describes the simulation method for the wave impact pressure acting on a bow section, where the boundary element analysis on a two-dimensional water impact problem is applied. Computed results are compared with those by the MPS method, a kind of particle methods. Good agreement is recognized in both the free surface flow and the time histories of pressure. The numerical description using the boundary element is properly-validated in the water entry, the water exit, the jetting, the nonviscous flow separation, the trapped air, and so on.

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Viscous flow simulation of flow field around ships for manoeuvrability prediction has become a highly sought after issue now-a-days among the ship hydrodynamicists. As potential flow theory still lacks the versatility to consider the viscosity and flow separation effects in calculation, RANS simulation has gained its popularity in calculating detailed pressure and shear force distributions around drifting ships. The objective of this research work is to investigate the patter of flow around a manoeuvring tanker. An in-house code using unstructured grid based RANS solver has been developed to investigate the behavior of a ship in drifting motion. For unstructured grid the oscillations caused by the adoption of second order differencing scheme have been minimized through the implementation of a slope limiter algorithm in discretizing the diffusion term of the Navier-Stokes equation. A double hull model has been implemented in the manoeuvring simulation instead of considering the free surface flow.This approximation is justified when the ship speed is considered to be quite low (Fr<0.2) during drifting motion.

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A time domain simulation method for wave-induced motions of tow and towed ships in head seas is presented. The present method uses a 2D lumped mass method for expressing the dynamics of towline, and so can take into consideration the effects of self-weight and deformation of towline and the fluid resistance acting on it. The present method can calculate not only wave-induced motions of tow and towed ships but also tension acting on a towing point in time domain. In order to validate the present method, using a ship model with twin podded propellers as tow ship and SR108 container ship model as towed ship, the simulations of wave-induced motions of tow and towed ships and tension acting on a towing point were made in various wave lengths and the calculated results were compared with the model test results. As a result, although there is some room for improvement, the present method can roughly capture the wave-induced motions of tow and towed ships and tension behavior during towing in head seas.

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To capture the ship performances of a catamaran with asymmetric demi-hulls, tank tests were carried out such as resistance test in still water, measurement test of wave height of wash, seakeeping test in regular head waves and captive test for measuring hydrodynamic forces on maneuvering using a scaled model with 2.036m in length. To investigate the effect of clearance of the demi-hulls on the performances, the clearance was changed in the tests as W/B = 2.55, 2.90 and 3.25, where W denotes the breadth overall and B the breadth of the demi-hull. Also, two ship models with different load water line tendencies were used: one is the inside flat and outside round type (IF-type) and the other the outside flat and inside round type (OF-type). The test results obtained are as follows: Residual resistance coefficient of W/B = 2.90 in IF-type is the smallest at the design speed corresponding to Froude number Fn = 0.44 and that of W/B = 2.55 in OF-type is secondary small. In the maximum wave height of the wash, OF-type is almost 30% smaller than IF-type in any demi-hull clearances.In both performances of heave and pitch motions, and added resistance in head waves, OF-type is superior to IF-type near the design speed. Smaller demi-hull clearance and IF-type are better in course keeping performance. The course keeping and turning performances are suitable in any conditions of the catamaran.

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At start-up operation of hot dip galvanizing baths to galvanize steel products, several leakage accidents of liquid zinc due to the damage at the vicinity of welded parts between side and bottom plates have been reported. Among those accidents, it is found that transferred liquid zinc solidified in the bath heated inadequately. In another paper, the authors investigate stress levels and directions at corners of the bath to clarify the cause of the damage applying unsteady heat conduction analysis, elastic and elastic-plastic analysis for solidified zinc inside of the bath as mechanical approaches. However, they have not studied the direction of the crack, that is, it starts from the vicinity of a welded part at the bottom plate and propagates downward vertically or 45 degrees toward outside of side plate, then changes its direction to be parallel to the bottom plate.This paper investigates the cause of the direction change of crack, which propagates downward then horizontally, at the corner of the bottom plate from mechanical and material aspect.

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At start-up operation of hot dip galvanizing baths to galvanize steel products, several leakage accidents of liquid zinc due to the damage at the vicinity of welded parts between side and bottom plates have been reported... The authors reported in the previous paper that the material of bottom plate of the damaged bath were examined by metal structure observation, SEM observation, EPMA analysis, hardness measurement and tensile test and it was concluded no problems were found in the material... In addition, they guessed the effect of liquefied metal soaking into grain boundary of the metal as a cause of the damage because lead and zinc were found inside of the crack... This paper, following previous one,reports that the heat affected zone of applied material at the damaged part does not have any peculiarity according to the results of Charpy impact test and maximum hardness test for a heat affected zone of the new sample of the same virgin material. .. Further it specifies the part where crack occurs by examining crack profile of newly taken sample and the sample applied in the previous paper.

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At a fatigue crack tip, the occurrence of opening-closure behavior is already known. The opening-closure behavior of a fatigue crack tip is caused by cyclic elasto-plastic deformation of the crack tip. Fatigue strength ( S - N curve ) and fatigue crack propagation rate ( da/dN- K ) have been evaluated only in mechanical environment, and they have not been evaluated by comparison with mechanical environment and the limits of material characteristic as other fracture phenomenon.The present paper proposes a numerical simulation method using comparison with mechanical environment of crack tip and the limits of material characteristic for consideration with delayed propagation of fatigue crack. In the proposed simulation method, tensile fracture elongation after compressive plastic deformation of a mild steel have been used. In this paper, the results of the case of constant amplitude loading, block loading, and constant amplitude loading with spike load are shown.

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In recent year, the extremely thick plate becomes used in the deck plate of the large ships. To prevent the brittle fracture it is important to detect and measure the inner defects. If the defect sizing can be accurately measured during the in-service period, the estimation of the residual life becomes possible. Ultrasonic Testing is used in order to inspect the inner defects in a thick plate, and it is necessary to select adequately the probe frequency, size, refraction angle, or another condition to evaluate the defect size accurately. The estimation of the defect size in vertical direction to plate surface is important from the viewpoint of fatigue strength. But the vertical defect size and also the inclined defect size are hardly to be estimated accurately.In this study, the simulation program based on the superposition technique of points sound source was developed to estimate the inner defects in the deck plate precisely by authors. Moreover, the effectivity was clarified by simulation using FEM and experimentation using the test specimens including artificial defects.

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The internal pressure of liquid cargo or ballast water in a hold of a ship is the major load for the ship structure, as well as the external pressure due to waves. Although the sloshing phenomenon in a partially filled tank has been extensively investigated so far,not so much attentions were paid to the liquid pressure of a fully filled tank. As the magnitude of the internal liquid pressure of a fully filled tank is comparable to the external wave pressure, a precise estimation of the internal pressure is very important in the ship structural design. In the present paper, the internal liquid pressure in a fully-filled rectangular tank is investigated in the case where the tank is in heaving, swaying and rolling motion by analyzing the forced oscillation test results, and a simplified formula to estimate the internal liquid pressure of the fully filled tank of rectangular cross-section is proposed.

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Reverse simulation was proposed to specify the source of pollutant in closed water. One of the major problems of reverse simulation is the numerical instability of computation. This instability is caused by the high-frequency rounding errors. A Gaussian filter was used for the spatial distribution of pollutant or of the flux of pollutant to eliminate the instability. The effects of filtering operation were verified by comparing the results of forward and reverse simulations. Forward simulation was executed assuming that pollutant flows out from the west coast of Lake Biwa as an example of closed water. The final result of forward simulation was used as the initial condition of reverse simulation. The concentration of pollutant was solved inversely using the current velocity obtained in forward simulation. As a result, the instability of reverse simulation was suppressed by applying the Gaussian filter for the spatial distribution of pollutant, while the concentration of pollutant was more diffusive than that of forward simulation. When the Gaussian filter was applied to the special distribution of the flux of pollutant, the accuracy of reverse simulation was improved. This is because the high-frequency rounding errors were mainly suppressed by the fourth-order derivative term. The filter width is a key parameter to determine the accuracy of reverse simulation. It was relatively larger in the present study than that in the existing studies for simpler flows. This may be attributed to the numerical instability caused by complex topography and boundary condition. In addition, the distribution of the concentration of pollutant in reverse simulation was more circular than that in the forward simulation since the filtering operation was more effective where the spatial gradient of pollutant was larger. The filter width should be determined reasonably with examining the sources of the numerical instability as future studies.

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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 social acceptance for the ecological risk due to the development and the business feasibility for the decision making of investment are significantly important. In the present study, questionnaire survey was conducted about the environmental risks due to SMS development. The results show that the non-specialists feel greater environmental risks than the specialists, which indicates social acceptance could be improved by proper risk communication between them. The economic value of the ecosystem in the vicinity of SMS are also investigated by the questionnaire survey, the result of which is used to determine the scaling factor between ecological and economic values in the inclusive impact index. The environmental risk due to the development of SMS is quantified by analyzing the obtained experts' opinions by means of cross-impact method and species-area relationship. Then the sustainability of the development is investigated by using an inclusive impact index considering both the environmental and the economic factors. From the results, the requirements of the sustainable development are shown for the damaged area and the ratio of species extinction.

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This paper is aiming at investigating the effects of flexibility and chord-wise cross section of pectoral fins on the swimming performance of the biomimetic underwater vehicle PLATYPUS by designing and making new types of pectoral fins. Experiments using a mechanical pectoral fin device BIRDFIN fixed in uniform flow verify the advantage of fin flexibility in underwater robot control. Fundamental experiments using PLATYPUS investigate the roles of both fin flexibility and chord-wise cross section in propelling underwater vehicles and iterative computation of spanwise deformation between Finite Element software and wing theory analyze the hydrodynamic characteristics of these new pectoral fins. Finally PTP control tests in still water and water currents check the different performances of each fin in carrying out specific task, and at the meantime the fuzzy control rules are revised to find the most suitable one for each fin respectively. It is found that asymmetric flexible fin (harder) behaves best in PTP control in still water but symmetric rigid fin does best in PTP control in water currents.

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In Ocean development, many cylindrical shape structures are in use. These structures are subjected to many external forces, such as water current, waves and reaction force from the upper structure. Especially, the lift force induced by the shedding vortices cause the vibration of the structures. This phenomenon is called Vortex Induced Vibration, VIV. It is assumed that VIV causes fatigue damages on the structure because it contains high frequency component of vibration and it increases in drag force on the structure.One of the solutions to decrease VIV, the appendage such as splitter plates or fairings is used to be attached on the structures.However, it may happen that such appendages increase the amplitude of VIV in some situations. Meanwhile, for actual use, it must be considered not only the decreasing performance but also the ease of handling. If we use Computational Fluid Dynamics, it is easy to modify the shape of the appendage and simulate its performance in different circumstances. Before that, it is needed to reveal the influence of the motion and flow field around the structure with the appendages.In this study, a rigid circular cylinder with or without appendage was supported by coil springs in the circular tank. The motion and rotation of the cylinder were measured by tracking the markers attached on its cross section. In the same manner, those of the appendage were also measured. The flow field around the cylinder was visualized by PIV. Experimental results show that the appendage, such as splitter plate or fairing, sometimes can’t decrease the amplitude of VIV. They also show that the appendage which can shorten the distance between the shedding vortices near the cylinder can decrease VIV.

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Tank containers are usually used for the transportation of the liquid cargo by the ship. In late years the new method by the container which loaded with liquid bag which filled with liquid was applied. And most of the liquid bags are made of thin resin.Therefore, hydrostatic pressure of the filled liquid is supported on the walls of the container. In this paper, author discussed an experimental study of the load acting on the walls of the container laden with liquid bag with a scale model which made the walls with acrylic board. From this study the shape of the bag which filled a liquid and relations of the load were considered. And then the deterrent effect for the sloshing of the bag was observed with transport experiment by the towing carriage.

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In the present study, a vessel collision model between two ships based on NDM model was developed by combined approach of fault tree, event tree and matrix description, which illustrates the navigator's situation (observation, cognition, planning and action),in order to determine success or failure of collision avoidance. Applying a frequency index of human error to this collision model resulted in the same order of magnitude as conventional geometric models. This result suggests that the model based on NDM model has an accuracy equivalent to geometric models. Therefore, the failure probability of collision avoidance at vessel's encounter can be derived by only employing the frequency index of human error for the vessel collision model. Subsequently, for the purpose of confirming the feasibility of the evaluation of risk control options by use of the model based on NDM model, we examined the effect of the five risk control options for vessel collision, which are applicable to general vessels. The examination implied that "boarding (embarkation of) a coast pilot" and "on-board VHF radio telephone" are the most effective risk control options. Furthermore, these two options are also effective for vessels which are not required to be equipped with by legislations,since this model does not depend on the size of vessels. This paper shows that the vessel collision avoidance model based on NDM model is useful not only to discern the impact of vessel collision caused by human error but also to assess the effect of risk control options.

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Nowadays, the pipe arrangement has been enabled to be more efficient and economical by development and spread of CAD(Computer-Aided Design). However, it is difficult to design a piping layout automatically because there are many regulations and functional design rules which must be satisfied. We propose an automatic routing method for simple pipes including elbows and bends. In a practical design of a piping layout, there are many bends connecting straight eccentric pipes which have gaps within the pipes' diameter. However, no precedence automatic piping algorithm has been taken into account pipelines with such bends. The proposed method finds piping routes making use of not only elbows but the bends in order to minimize costs of the path connecting start point to goal point, while avoiding obstacles such as structures, equipments and the other circuits. In our approach, we regard the piping route design problem as a routing problem in a directed and weighted graph. Note that the nodes in the proposed graph have state variables not only locations but directions of the pipes. This graph can easily express the bends as simple edges, and then the routing algorithm can easily handle the bends. In addition, the presented method has specifications that the sizes of each cell, which is generated by decomposing of a free space, are not restricted within the diameter of the pipe. The routing algorithm uses Dijkstra's method to provide candidate paths. The efficiency of the proposed method is demonstrated through several experiments

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At the IMO (International Maritime Organization), new generation intact stability criteria are now under development. Here it is essential to establish a physics-based method for quantifying probability of capsizing for intact ships in beam wind and waves. For this purpose, the authors herewith propose an updated methodology for calculating the capsizing probability based on piece-wise linear approximation of restoring arm curve. Although its earlier version had been reported so far, the current version was newly formulated with more rigorous theoretical modelling on roll properties at the moment of outcrossing of roll angle. For validating this new method, a Monte Carlo simulation using a time-domain model was executed with its confidence interval analyses. As a result, it was obtained reasonably good agreement between the new theoretical method and the relevant Monte Carlo simulation. It was also confirmed that the computational time of new theoretical method is much shorter than that of Monte Carlo simulation. Therefore, the new theoretical method can be recommended as a reliable and feasible element of new generation intact stability criteria.

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