A small saury fishing vessel (19GT-type) is newly developed and evaluated the total performance in order to increase profits and to attract the younger generation of fishermen. On the basis of inquiring surveys to fisheries unions, ship-owners and shipbuilders, problems and needs of saury fishing vessels are analyzed. Then, the performance of conventional fishing vessels is evaluated through model resistance tests in a circulating water channel. The hull form design for the fore-body is improved by the use of wave-making resistance theory. The aft-body is improved by the use of the Eulerian scheme with the Lagrangian particles. The general arrangement of the hull form improved vessel is developed to upgrade the habitability and fishing performance. The newly developed and advanced small saury fishing vessel can reduce the fuel consumption by half compared to the conventional vessels. An actual 19 GT saury fishing vessel, constructed based on the results of this study by using the present design method, demonstrates the superiority of performance.

The fixed net fishery is essential, because the quantity of catch is the second in Japan. And it is said that this fishery consumes very little oil and is friendly to the ocean environment. But researching fixed net fishing vessels has not been done at all for a long time. Under these backgrounds, study on a fixed net fishing vessel is carried out. Subjects on a vessel are cleared through field survey, so that hull form, hull construction, the difference of loading conditions and sea speed at between departing from the port and the fixed net and so on. Improving hull form is tried to 19 gross ton type, and the performance is evaluated through a model resistance test in a circulating water channel (cwc). The hull form design for fore body is improved by the use of wave making resistance theory, and one for aft body is enhanced by the use of the Eulerian scheme with the Lagrangian particles. The fixed net fishing vessel is defined as low fuel consumption. But the level of hull resistance is not very good, so the fact is cleared of that improving of hull form and decrease speed is necessary for saving energy and for getting up profit. Through present study, the truth is cleared that the cwc experiments are very useful for inducing the projects on developing hull form and there is the difference of view point to cwc experiments on between general merchant ships and special small ships including fishing vessels.

Evaluations of ship performance in actual seas based on onboard monitoring data have been widely conducted recently. Performance in a calm sea is important for estimating performance in actual seas. In order to estimate performance in a calm sea, onboard monitoring data should be filtered by certain items and criteria. This filtering procedure is important and difficult because the data depend on the filtering items and criteria, and the appropriate items and criteria will be different depending on the ambient condition and ship size. To solve this problem, this paper proposes a filtering method called the Resistance Criteria Method (RCM) using the estimated added resistance in actual seas. The method was validated with a tanker (VLCC) and compared with other filtering methods.

The wind forces acting on a ship are normalized using the air density, the projected area of the ship and the representative wind velocity. In this regard, the authors have presented that the use of height average wind velocities (HAWV) can reduce the effect of differences in wind profiles on wind force coefficients. In this study, the results of wind forces calculations carried out by several companies and institutes using flow solvers available for each participant on two types of ships were compared, and show the effectiveness of HAWV. The CFD calculations were performed with different wind profiles depending on the participants of the calculation. Although the difference of calculation conditions of each simulation causes the difference of profiles of inflow velocity and the wind forces acting on the ship, the HAWV have been proposed as an appropriate, representative wind velocities for the normalization which can reduce the influence of the difference of the wind profiles by considering the concept of kinetic energy. The normalization with the HAWV provides flexibility in CFD calculation settings and in the same in modeling wind profile demanded for estimation of the wind forces. This approach also expands the possibilities of available CFD tools. In addition, the calculation results with various configurations, such as differences in boundary conditions set in computational domain, mesh types and considerations of flow unsteadiness, were non-dimensionalized by HAWV method with enough accuracy for practical use. It indicates that the above variations might be the options for the computation set up.

Dead ships in rough sea make strong drifting motions and sometimes cause the significant accidents such as grounding or destroying offshore structures. For the prediction of such drift motion, it is necessary that the suitable mathematical model should be provided. Although many mathematical models for the conventional maneuvering ship motion are proposed and widely used, most of them are limited within the conventional maneuvering motion. They cannot be used for the large drift angle such as 90° including the zero-ship speed turning. It is very difficult for the conventional mathematical model to express the hull forces in such drift motion. One of the authors tried to make them using crossflow drag model^{1),2),4),5),6)}. However, the above models include the longitudinal integral terms, which makes the difficulties when using for real-time simulators or system identifications.

In this paper, the authors have developed a simple mathematical model that has the almost equivalent hydrodynamic force characteristics for conventional crossflow model instead of using the integral terms. The new model can also express the hydrodynamic forces with large drift and turning motion including zero ship speed condition. In order to validate the mathematical model, the drift tests in the uniform wind were carried out and the simulated results were compared with the measured data. From the comparison between experimental results and simulated them, it is found that the proposed mathematical model as well as the original crossflow drag model make it possible to predict the wide range of drift motion. Furthermore, the parameters in the proposed mathematical model can be easily obtained from the principal particulars of ship based on the regression analysis. Then the drifting simulations become very easy by using the proposed simple mathematical model and the empirical formulas of the parameters.

This paper describes the relationship between an arrangement of Point Absorber Wave Energy Converter (PA-WEC) and power generation. In an array of PA-WECs, complex hydrodynamic interaction occurs. The interaction affects both increase and decrease of wave power density among PA-WECs. When aiming to maximize the generated electric power, it is necessary to appropriately select the control force of the generator in consideration of the positive effect of hydrodynamic interaction. This paper presents a numerical solution of the control force parameter for maximizing the generated electric power of the multi PA-WECs, taking into account the hydrodynamic interaction among PA-WECs in both diffraction and radiation problems. Then, numerical studies are carried based on the proposed method. From these results, the effects of the distance between PA-WECs and the number of PA-WECs in a linear arrangement on the generated electric power are discussed. In addition, the sensitivity of the arrangement of PA-WECs to the generated electric power is considered.

This paper describes an analytical solution on the optimal control force for maximizing power generation of Point Absorber Wave Energy Converter (PA-WEC) in irregular waves. The response and optimum control force on a PA-WEC in regular waves achiving a maximum electric power generation has been already developed taking into account the energy loss in the electric circuit in frequency domain and in regular waves. On the other hand, in irregular waves, to obtain the best control force in timely has been difficult, because the control force act on the instantaneous power generation rate and the whole later heaving response of the PA-WEC. This means that whether the decided control force is the best or not is difficult to judge. Actually, in the previous researches, the researchers applied a lot of way to decide the control force. But the generated electric power in irregular waves ratio to the expected generated power obtained from the wave spectrum is up to almost from 0.3 to 0.7. This paper presents an analytical solution of the control force parameter for maximizing the generated electric power in irregular waves on a PA-WEC in time domain. Then, numerical studies are carried based on the proposed method. From these results, it is shown that the proposed method achieves the generated electric power to the expected generated power obtained from the wave spectrum

It is important for the safety of ship in waves to understand its roll characteristics at the design stage. However, it is not easy to estimate roll accurately, because the viscous effects on roll damping affect significantly roll near its resonance frequency. For that purpose, it is significant to estimate roll damping accurately. As one of prediction methods of the viscous effects, Ikeda’s method is well-known. However, it is pointed out by Tanaka et al. (1981) that the method overestimates the roll damping when the method is applied to a ship with shallow draught. On the other hand, with the recent enlargement and specialization of merchant ship, its breadth has increased compared to the hull form at the time when Ikeda's method was developed, and its height of the center of gravity has increased relative to draft. Therefore, when Ikeda's method is applied to such hull form, there is a concern that the estimation accuracy will deteriorate.

In this study, the characteristics of roll damping for two hull types (PCC: Pure Car Carrier and LNGC: Liquefied Natural Gas Carrier) with shallower draft and higher center of gravity compared to the ships which existed when Ikeda's method was developed, are investigated experimentally. The measured results are compared with the results of Ikeda’s method to confirm the estimation accuracy and its characteristics, and the results of investigating the difference of them are reported.

International Energy Agency (IEA) predicts an increase of 62 % over that of 2008 in the demand for natural gas in 2035. For the stable supply of natural gas, construction of the Floating LNG (FLNG) is now being discussed worldwide as one of the promising ways to exploit undeveloped gas fields.

The Ship-to-Ship (StS) transfer using flexible hoses is one of the methods to transfer LNG from FLNG to LNG carrier in the ocean. In 2011, the Society of International Gas Tanker and Terminal Operators (SIGTTO) published an operative guideline for the StS transfer of LNG, but it did not refer to the safety and workability evaluation in the StS transfer.

During the StS transfer operation, water level has been reported to rises to the height equivalent to several times as much as incident wave amplitude in the gap (so called gap resonance) between the side-by-side moored vessels. The flexible hoses are frequently beaten by waves because of the gap resonance during the operation, resulted in an injury to the hoses or in hitting against the ship hull. Thus, the gap resonance causes an important problem because such unfavorable conditions directly affect the safety and workability characteristics during the StS transfer operation.

In this paper, we investigated an evaluation method of the gap resonance during the StS transfer. We estimated the wave resonance behavior in the gap between FLNG and LNG carrier moored by side-by-side configuration using the boundary element method with parameters such as loading conditions, wave period and wave incident angle. In addition, we tested a tendency of the gap resonance using the 1/140 scale models at Ocean Engineering Basin in National Maritime Research Institute (NMRI). We confirmed that the result of estimation based on the boundary element method coincided well with that of the actually measured gap resonance behavior.

In recent years, under the tightening of environmental regulations by the International Maritime Organization (IMO), attention has been focused on the superiority of LNG fuel and LNG fueled ships that can reduce CO₂ emissions in addition to SOX. Over 129 LNG fueled ships are already in service worldwide, and the movement for introducing LNG fueled ships is gradually increasing in Japan.

One of the authors previously demonstrated a method of safety evaluation for LNG bunkering in Ship-to-Ship configuration using a LNG transfer hose, and examined based on the proposed method the limit of environmental conditions in LNG transfer operation. The use of a cryogenic composite hose is typical to transfer LNG fuel in Ship-to-Ship bunkering for LNG fueled ships. However, there is a problem of icing around the composite hose because of LNG transfer at extremely low temperatures. Another problem is that contact occurs between the hose and the ship hull or the hose and the sea surface during bunkering operation.

In this study, we investigated the use of a flexible metal hose provided with a heat insulation layer and an outer sheath in order to avoid these problems during Ship-to-Ship bunkering. We compared results of calculation with those of actual test using a newly manufactured 1/3 scale LNG transfer hose, and verified the accuracy of the calculation in terms of the end load of the hose and the minimum bending radius. In addition, we evaluated the safety of LNG bunkering in Ship-to-Ship configuration using the validated simulation model. Necessary requirements for applying the flexible metal hose to Ship-to-Ship bunkering were also investigated in this paper.

The recent increase in the size of container ships has resulted in lower natural frequency of the hull girder vertical bending and torsional vibrations; this has caused great concern regarding excessive whipping in these responses to incident waves. To accurately account for whipping in ship design, it is important to understand the relationship between the whipping response and sea states in which the ship operates. However, this specific topic has been reported little to date. In this study, we quantitatively analyze the influence of various sea states and navigational conditions on the whipping response in hull girder bending vibration and torsional vibration based on full-scale measurement. Moreover, a simple estimation method is proposed for fatigue damage using the relationship between whipping and sea states/navigational conditions. By providing quantitative analysis of the relationship between whipping and sea states/navigational conditions, our study will contribute to future ship design to ensure better operation safety and longer hull life.

Osawa et al. (2016) developed a two-dimensional cellular automaton (CA) for under-film corrosion analysis and succeeded in consistent analysis of coating film deterioration and corrosion depletion. In this CA analysis, the CA parameters for coating performance and metallic corrosion are given by random number fields without spatial covariance structures. In this report, a corrosion test of coated steel panels with double scribes was performed, showing non-uniformity in corrosion surface profiles. The under-film corrosion simulations of double scribed coated panels were carried out by using the improved CA in which CA parameters were given by lognormal random number fields with spatial covariance structures. As the result, the probability that the non-symmetric corrosion surface profile in the experiment could be reproduced by simulation was improved by 10.5 times by considering the covariance structures. Based on this result, the effectiveness of the developed analysis method was verified.

Aiming at developing underwater battery recharging system, we have been researching on automatic docking of an underwater robot using dual-eyes-based visual servoing and 3D marker without emission of light (passive 3D marker). In our previous researches, we conducted docking experiments in seaarea, having verified the effectiveness in the day time in an environment with less turbid water condition. Given the situation that the docking aims for battery recharging in deep sea bottom, pitch-dark and turbid environment should be considered as inevitable condition. Since lighting passive 3Dmarker from vehicle in turbid water environment results in the images taken by video cameras set on the vehicle being looked wholly white, some new idea seems to be required. Our proposal to overcome this difficulty is to introduce a lighting 3D marker (active 3D marker) that has LEDs inside. Inthis paper, recognition performances using active and passive 3D marker are compared, having confirmed that the new active marker with no-lighting from a vehicle could be recognizable in dark and turbid environment than the passive marker lighted from the vehicle. This has contributed to the actualsea docking in pitch-dark real sea environment.

An index that can mutually evaluate the navigation performance of ships of different sizes will promote an introduction of vessels with excellent navigation efficiency. In this study, the Energy Efficiency of Navigational Indicator (EENI) and the energy efficiency of propulsion indicator (Kn) were introduced to compare the operating performance of coastal vessels with each other. A methodology using the bootstrap was introduced to accurately identify curves of these indicators even with a small sample, because the number of coastal vessels is small. This methodology was applied to the results of sea trials of 16 coastal cement and limestone ships, and the relationship between ship energy efficiency and displacement was clarified.

The development of FOWTs (Floating Offshore Wind Turbines) is going into the commercial stage from the demonstration one. One of the key issues for success in the commercial stage is how to reduce the construction cost. For example, watertight bulkheads in narrow space of FOWTs become obstacles to the cost reduction from the perspective of structural complexity and manufacturing. On the other hand, new IEC TS 61400-3-2 standard describes the unnecessity of the damage stability requirement under certain conditions. To secure the sufficient safety without the damage stability requirement according to the IEC TS 61400-3-2, an examination method with a probability theory and the FEM analysis is proposed in this paper. The probability of collision with cruising ships, P1, around a FOWT is estimated to use by the AIS data, and the probability of structural total loss, P2, due to the ship collision is indicated according to the total loss curve which is delivered from the FEM collision analysis. The joint probability which is represented by the product of P1 and P2 is compared to the target damage probability, 10^-4 per year. The detailed information about this method and the results of trial analyses for the FOWT off the coast of Nagasaki Prefecture are also introduced in this paper.

First of all, the paper focuses the problem to construct a scheduling model of the stockyard in a shipyard in Japan, which should be verified by comparing the actual usage of facilities. Secondly it discusses the problem to apply the model to determine appropriate starting dates for block fabrication in assembly lines in order to achieve leveling of working hours. It is shown that these problems are formulated into RCPSP (Resource Constraint Project Scheduling Problem) and solved successfully using a software OptSeq (TM) developed by Prof. M. Kubo based on an RCPSP solver developed by Prof. K. Nonobe and Prof. T. Ibaraki.

The current power generation or the tidal power generation is considered to have high possibility for utilization of ocean renewable energy since the current speed or tidal speed is steady. Authors carried out scale model experiments of floating type horizontal axis tidal turbine for the study on safety assessment technology. The scale model consisted of 2 rotors on 1 crossbeam moored by 2 wires. The rotor thrust load, the rotor torque, the crossbeam load and mooring tension, and the floater motion was measured. The load conditions for the experiments were decided considering typical situation in actual sea, that is, the power generation condition, the standby condition and the accidental conditions. In the accidental conditions, a stop of a rotor, error of blade pitch angle, a loss of a blade, and a break of 1 mooring line were considered.

Numerical calculations were also carried out and the accuracy of BEM (blade element & momentum method) and CFD calculations were confirmed through the comparison with the tank test results.

This paper proposes a simulation model to evaluate an effectiveness of GHG reduction on ship transportation. Our model is extended INFINIT model, which is generalized multi-commodity network model and applicable for ship transportation system. The model makes it possible to evaluate the system with GHG emission, operating cost, and opportunity loss if the system’s capacity is short. Moreover, the method shows the detailed flow of ships, cargos, and fuels on the transportation network. As a case study, the method was applied for international transportation of iron ore. The case study demonstrates that the method can support decision-making by comparison of multiple scenarios to reduce GHG emission in shipping. Especially, it is useful in that it can evaluate those scenarios from the perspectives of not only transportation performance but also required bunkering infrastructures.

The authors (Toyosada and Niwa, 2001) proposed to evaluate the Elastic-Plastic Fracture Mechanics (EPFM) parameters of edge and surface cracks by applying a crack face traction to a center-cracked infinite plate so that the relation between the crack length and SIF (α-K relation) is reproduced. This crack face traction is called Equivalent Distributed Stress (EDS). An EDS determination technique based on spline interpolation and generalized matrix inversion has been developed. Three numerical procedures for cohesive force's EDS determination, Fictitious crack face Loading Method (FLM), Yield stress Loading Method (YLM) and Whole crack face Loading Method (WLM) are proposed. A computation system which carries out EDS determination and fracture mechanics analysis, EDSGI, is developed. Crack Cohesive Force (CCF) model analyses based on FLM, YLM and WLM are performed by EDSGI. The validity of EDSGI is examined by comparing the edge crack's EPFM parameters calculated by FLM, YLM and WLM with the reference solutions evaluated by a direct CCF model analysis. It is found that the EPFM parameters evaluated by FLM agree well with the reference solutions, while YLM overestimates the plastic zone size for large applied stress, and WLM underestimates both plastic zone size and CTOD under the conditions chosen.

This paper presents a deep reinforcement learning control method to maximize output energy for a point absorber type wave energy converter (WEC) with a linear generator. Conventional control methods require the dynamic model of the WEC. Modeling errors of the dynamic model, however, make energy absorption smaller and cause incorrect control. The proposed method, which is a model-free control method learns the optimal damping and stiffness coefficients based on experiences. In the proposed control method, damping and stiffness coefficients are able to vary in time-domain depending on the incident waves by deep reinforcement learning. The performance of the proposed control method is investigated through numerical simulation in both regular and irregular waves. Compared with the conventional control method, averaged output power increased, and the power fluctuation decreased without the dynamic model. It is understood that the proposed method is more effective than the conventional control method.