Accurate estimation of added resistance in waves is very important for evaluation of ship performance in actual seas. However, most estimation methods do not treat the influence of roll motion on added resistance in waves.

In this paper, a practical correction method for added resistance considering the influence of roll motion is proposed, and the proposed method is investigated by tank tests. In this estimation method, the roll component is extracted from the equation for added resistance in waves in accordance with the concept of Gerritsma & Beukelman’s method. This study demonstrated that adding the roll component to the estimation equations improves the accuracy of estimations of added resistance in oblique waves. A sensitivity analysis was also performed using the proposed method in order to discuss the effect of roll motion on fuel consumption in actual seas.

Model propellers used in cavitation tunnel test are smaller than actual ship propellers. Therefore cavitation occurred on model propellers tends to be unstable. As a countermeasure, a method of applying roughness on the leading edge of the model propeller blade to turbulent its surface is used. However, this method may be affected CFD analysis because the cross section of the propeller blades is different from the design. Furthermore, the influence on the measurement results due to the difference in the design and model of the wing cross section. In this study, stable cavitation generation have been made possible by generating hydrogen bubbles from the wire-mesh screen that upstream side of the propeller and flowing them into the propeller as the nuclei for cavitation. The authors have conducted a cavitation tunnel test of a model propeller using this device in a large cavitation tunnel of NMRI, and confirmed the stability of cavitation with this device and its usefulness.

The development of the evaluation method of life cycle fuel consumption from a ship as for a main engine is the aim of the project OCTARVIA: Project for Evaluation of Ship Performance in Actual Seas. The project had been conducted as the 3-years collaborative research of Japanese companies and organizations in a maritime cluster. The packaged GUI program has been prepared, which applied the developed method for external effects due to waves and winds in consideration of fouling and aging. For the evaluation of life cycle performance from an objective perspective, a standard operational model has been proposed and incorporated in the evaluation method and the program. The evaluation method and the applied standard model are described and the result of the evaluation of the life cycle fuel consumption for a ship is considered in the paper.

Over the years, shipping has been played on one of the most used transportation methods and marine trading is increasing more and more these days. As a result, the shipbuilders are trying to design and construct an efficient and enormous ship to be economical. On the other hand, the environmental awareness to eliminate greenhouse gas emission is rising due to the effect of global warming. Such factors make the various types of energy-saving devices (ESDs) to be developed reliably without affecting other functions. This paper characterizes the performance of the rudder bulb-fins system (RBF) fixed behind the propeller in wave. In this study, the analysis of dynamics forces and velocity fields around the stern which are crucial in evaluating the performance of ESDs were implemented using CFDShip-Iowa V4.5. The effect of the ESD on ship’s motion was analyzed by performing motions analysis in various regular head waves. The computational results were validated with the experiments conducted in the towing tank of Osaka University. The calculations were done for three cases of rudder conditions: the ship without a rudder, the ship with conventional rudder, and the ship with RBF. The predicted results and measured data reveal that the currently designed RBF can diminish the hub vortex strength and improve the hull efficiency due to the increase of thrust and wake gain without any adverse conditions. It can be confirmed that the computational simulations predicted and followed the trend of experimentally measured data well.

The shape of double optical fiber probe and analysis method for measuring bubbles near wall in turbulent boundary layer are proposed. The spanwise position of the probe is made to coincide, and it is tilted upward in order to enable the measurement of small bubbles and the measurement near wall. The measured data are filtered using a histogram, velocity ratio at the upstream and downstream sides of the bubble, and velocity gradient to eliminate the effects of bubble mismatching and deformation. The effectiveness of this method is confirmed in comparison with the result by Shadowgraphy. The bubble exists only near the wall and the bubble interface velocity near the wall is high when the friction drag is increased. The bubble interface velocity near the center of the channel is accelerated with increasing void fraction when the friction drag is reduced. The acceleration rate is on the same order as the rate of change of the drag reduction effect.

Fatigue tests under the condition of stress ratio ＝ -0.3 are conducted for three types of welded joints (as-weld, grinding treatment, and HFMI (High Frequency Mechanical Impact) treatment.), and the fatigue strength of these welded joints are obtained experimentally. By comparing the present results with the results by Iwata et al., the fatigue strength improvement effect of HFMI treatment under the condition of negative stress ratio is discussed. The stress concentration factor of the HFMI-treated welded joint increases as the plate thickness increases, and the weld toe may be yielded in compression when the plate thickness exceeds 40 mm. The fatigue strength of the HFMI-treated welded joint decreases when the plate thickness exceeds 40 mm. However, even when the weld toe of the HFMItreated welded joints is compressively yielded, a significant decrease in fatigue strength is not observed. In addition, the modified MILHDBK- 5 method is applied to all experimental data, which includes differences in stress ratio. By the equivalent stress based on the modified MIL-HDBK-5 method, a good correlation between the fatigue test results is achieved regardless of joint type, plate thickness, and stress ratio.

Floating wind turbine facilities installed in deep sea areas play an essential role in carbon dioxide emissions reduction.One of the problems associated with the commercialization of these facilities is the maintenance cost for mooring chains.Therefore,it is necessary to establish a quantitative wear evaluation method for mooring chains.Wear coefficient measured by wear tests is one of the essential physical parameters to evaluate the wear performance of metals.The pin-on-disk wear test is generally performed for obtaining wear coefficient.However, wear coefficient measured by this method had significant variation in our past study.Additionally, it has difficulty to use the heat-treated surface of the mooring chain under high pressure in fully immersed wet condition.To reproduce the actual situation,new wear test machine was designed and wear tests were implemented to validate the accuracy.As a result,it is confirmed that the proposed wear test method is possible to obtain the wear coefficient with significantly small variation compared with the conventional pin-on-disk wear test.

To ensure structural safety of large container ships, advanced application of monitoring data is pursued in the structural health monitoring project. In this study, we estimated statistical sea state that the ship actually encountered using Bayesian updating of the sea state data estimated from the measured hull stresses. To achieve reliable real-time short-term statistical estimation of the sea state, we introduced forgetting rate to the past data in the Bayesian model. In addition, abrupt change of the sea state due to the ship operation was detected by Bayesian analysis of the data to obtain probable time history of the sea state by Bayesian update. As a result, good tracking performance of the real time sea state was demonstrated.

In this paper, the estimation accuracy of hydrodynamic force acting on the fuselage of an open frame type AUV by CFD analysis was investigated. The hydrodynamic force acting on the fuselage was examined in case that the fuselage is stationary state including oblique and trim angle and the forced oscillation state including pure heave and pure pitch motion. Using the result of computation of pure pitch motion, the hydrodynamic derivatives are calculated by using harmonic analysis. These results were compared with the measured values obtained by experiment in the circulating water channel at Tokyo University of Marine Science and Technology using the experimental model made from the same CAD data which used as the numerical model for CFD.

From these results, the followings are revealed. The prediction accuracy of the hydrodynamic force is greatly affected by the computational domain, Spalart-Allmaras turbulence model and SST k-ω turbulence model have similar estimation accuracy for hydrodynamic force, There is a possibility that the flow prediction accuracy is insufficient inside the fuselage, the hydrodynamic force derivative calculated from the result of numerical PMM test can almost explain that of experimental PMM test.

This paper deals with numerical simulations using the nonlinear model predictive control (NMPC) for the route tracking problem of an autonomous underwater vehicle (AUV) in two-dimensional space. The NMPC algorithm minimizes the errors of the target heading angle or the target cruising speed. At the same time, the NMPC changes control signals in multiple constraints, such as maximum propeller speed and rudder angle. The Otsuka's continuation/generalized minimal residual (C/GMRES) algorithm, a kind of the NMPC, was introduced here to carry out the optimization calculation in short sampling period. Firstly, the computation speed of the NMPC was measured and it was verified that this algorithm is effective for the use of an on-board computer. Secondly, traveling routes and control signals using the NMPC and the PI control were compared. It was clarified that the AUV using the NMPC algorithm followed the target velocity with less fluctuation of the propeller thrust. In the numerical simulations, it was demonstrated that the NMPC method is useful for controlling AUVs.

The goal of this study is to simulate the mechanical strength of the methane-hydrate bearing sand layers in a microscale computational domain filled with sand particles, hydrate, and water using the discrete element method. For this purpose, we have developed a cement-type coupling model in which methane hydrate intervenes between sand particles. A computational domain was prepared for the tri-axial compression test of a cylindrical specimen, and the specimen domain was filled with glass beads so as to match the particle size distribution used in the experiment in the literature with a porosity of 0.4. The specimen was compressed by moving the wall surface installed above and below the specimen. The stress was calculated for various methane hydrate saturation. At all restraint pressures, the axial stress increases with almost the same slope after the start of compression. The larger the restraining pressure, the larger the peak of the axial stress. The axial stress, which was initially 1 MPa, peaked and then decreased sharply, exhibiting marked strain softening. The calculated results are in good agreement with the experiments, and it was found that this model can simulate the experiment well at different confining pressures and methane hydrate saturation.

The ocean absorbs heat and carbon dioxide from the atmosphere and serves to mitigate rapid climate change caused by human activities. The ocean also has the function of maintaining natural cycles such as the oceanic general circulation, carbon cycle and providing us with fishery resources. A healthy, pollution-free marine environment is essential for the sustainable development of human society. However, global warming, ocean acidification, oxygen depletion, and accumulation of marine plastic waste are now facing serious threats to marine ecosystems. In order to conserve the abundant sea, it is very important to have a correct understanding of the ocean environment and marine ecosystem conditions over a long term and wide area. In this research, the authors assume the underwater glider with independently controllable main wings, SOARER developed at Osaka Prefecture University, and propose a threedimensional wide-area ocean observation strategy for Japan's Exclusive Economic Zone (EEZ). Several cases of underwater cruise simulation with swarm intelligent autonomous underwater gliders were carried out to estimate the required number of underwater gliders which cover the Japan's EEZ and to consider its validity and effectiveness.

By developing Automatic Identification System (AIS), vessel positioning and detailed movement can be understood in real time. Although vessel movement data including AIS have been conventionally utilized in suspicious vessel detection, collision avoidance, and vessel trajectory analysis, etc., this study focuses on the new application fields of vessel movement data including logistics, shipping, shipbuilding, environment, and cruise industry. In this paper, description of AIS data and literature review of each field are first summarized, then the results of the questionnaire survey to the industry and application service of AIS data are analyzed. Finally, the future prospects of research and application to the industry in the fields that the authors focus are summarized.

Just after inevitable Nankai Trough earthquake in Japan huge amount of emergency relief supplies must be transported rapidly. Truck transportation is supposed to be the main means but there is a non-negligible possibility that its capacity becomes heavily insufficient because of road network damage and shortage of available number of truck resources and so on. In this paper we propose major-scale ferry/roro fleet transportation in Japan Sea for "push-type" transportation period as a redundant means. We discuss the necessity of the proposed transportation system and show its qualitative merits and quantitative performance by using variety of numerical backbone transportation simulations between cargo origin and logistics hub of the destination area.

Many collisions are caused by human factors and are often attributed to errors in situational awareness, such as inadequate lookout. It is therefore necessary to investigate the situational awareness at the time of the accident to analyze the accident, but there has been no evaluation of the validity of the results of this awareness. The National Maritime Research Institute (NMRI) has developed a method of assessing situational awareness using OZT in previous studies for accident analysis. However, since OZT is expressed as positional information, it is not easy to determine collision risk between own ship and a target ship from the OZT positional variation at any given time. In this study, the author developed a method to quantify collision risk from OZT information to apply to collision risk assessment. The collision risk by OZT was based on arrival time to reach the OZT considering the ship's length and speed which is defined as the unsafe rate. And the OZT was calculated by a weighted average which the unsafe rate times a pre- defined weight coefficient against ship's course. To show the validity of the method, it was applied to an example of actual collision accident. The result showed that it could be available to the applicability to validation for cognitive behavior for risk of collision at the accident.

Although 3D-CAD has been used in the shipbuilding industry for a long time, effective use of 3D data in the production and new initial design based on the 3D model are not advanced compared with the expectation. Moreover, it is difficult for a ship owner and a classification society to use the 3D model effectively because CADs and the security policies are different according to the shipyard.

Considering the above discussions, Japan society of naval architects and ocean engineers set the project research committee and has examined the information platform named SPEEDS (Smart Platform of Enhanced Engineering Data for Shipping and Shipbuilding). SPEEDS aims to realize the sharing and exchange of various information on ships among the all maritime industries including shipyards, classification society, ship owner, operator and the marine equipment manufacturers. A simplified 3D geometry information and a variety of attribute information are described in the SPEEDS and the player in maritime industries can utilize these information promptly and effectively based on the various use cases of ship lifecycle.

In this paper, overview of SPEEDS is discussed with some examples intended for use cases in ship lifecycle.

The spray coating process in ship-building is strongly affecting the ship's lifetime. However, skill transfer of the coating operation to beginner learn by watching senior worker's coating work. To improve such a situation, we developed a training program for spray coating workers. The program consists of practical training and theoretical training and provides a systematic approach to the skill transfer. The practical training employs a 3D virtual reality (VR) spray coating simulator. The practical training is conducted safely by using the simulator. In addition, the simulator has functions to enhance the education effect such as a visualization of spray gun motion. We executed the training program actually and evaluated its effect quantitatively. By comparing the spray coating skill before and after the training, the education effect was validated. Also from an analysis of data obtained from the training, we found there is a strong correlation between spray gun-to-target distance and distribution of paint film thickness.

With the aim of introducing laser-arc hybrid welding (LAHW) into the field of large steel shipbuilding, a study was carried out to construct a T-shaped fully penetrating welded joint with a weld length of 3,000 mm in one pass. Tack welding for the installation of members, which is a preliminary step of LAHW, was carried out by CO2 gas shielded arc welding. Since the effect of the main welding by LAHW on the tack welding has not been sufficiently confirmed, preliminary investigations were also carried out. As a result of repeated preliminary experiments, a T-shaped fully penetrating welded joint with a weld length of 3,000 mm was completed by the arc welding before the laser irradiation, unlike previous studies. The performance of the joint was evaluated by Radiographic test and macroscopic observation of the weld line cross-section in accordance with the "Laser-Arc Hybrid Welding Guideline" published by the Nippon Kaiji Kyokai, (ClassNK) and it was confirmed that the T-shaped joint could be obtained within the acceptable range. Considering that fatigue is the main cause of damage in welded joints, the fatigue performance of the joints was also investigated. As a result, the fatigue strength of the T-joint by LAHW using flux-cored wire was superior to that of the joint by LAHW preceded by laser irradiation using solid wire. Furthermore, all the fatigue cracks, which were fluctuating in the previous study, were located at the weld toe on the back side of the flange in the method proposed in this study. This result is favorable or the maintenance of the joint because it reduces the number of monitoring positions for fatigue cracks. In addition, it was confirmed that the application of the Λ-shaped groove is promising as a method to increase the welding speed and to extend the range of possible thicknesses, which is a challenge for the LAHW method of welded joints in thick plates.

In this paper, the authors proposed simplified formulae of the long-term maximum wave-induced vertical motion (surge acceleration, heave acceleration, and pitch angle) of exceedance probability of 10^-8 expressed as the explicit function of dominant hullform parameters. First, the dominant factors of the long-term maximum response were identified in a general discussion that did not depend on the types of response, and the methodology for the development approach of simplified formulae was demonstrated. In the process, the ratio of long-term maximum response and peak value of response amplitude operator (RAO) was defined as “Equivalent Regular Wave height" H_ERW. Then, it was clarified that H_ERW was dominated by the kurtosis of nondimensional RAO and peakwavelength of RAO as scale-dependent parameter. Furthermore, it was confirmed that long-term maximum response can be expressed by only the peak value of RAO when the RAO has certain properties; “kurtosis-invariant" and “peak value and peak-wavelength compatibility". Based on those consideration, as concrete examples, simplified formulae of the long-term maximum response of the vertical motion were derived. The obtained results were verified by comparison with numerical analysis using actual 154 merchant ships. The proposed development approach of simplified formula is effective regardless of the ship type as well as type of response. However, it should be noted that the proposed method is based on linear theory and is verified only for low speeds. Consideration of speed effect in high-Froude number and nonlinearly should be discussed in future work.