Injecting air at the ship bottom to create a mixed layer of seawater and air bubbles between the hull surface and seawater is well known as an efficient energy saving technique to reduce the frictional drag of ships. Various studies have been conducted to promote the efficiency of frictional drag reduction by bubbles. In contrast to the extensive studies on frictional drag reduction involving bubbles, very little attention has been given to the influence of bubbles on the self-propulsion factor. However, the self-propulsion factor is one of the major ship performance parameters. The purpose of this study was to investigate the influence mechanism between a hull covered by air bubbles and propeller open water characteristics. A numerical simulation approach that can be applied to a self-propelled ship with air bubbles around the hull was used for this purpose. It was found that air bubbles around the hull could increase the inflow velocity to the propeller. It was also found that bubbles around the stern could affect the viscous pressure resistance and that the effect could be strongly affected by the propeller. Furthermore, the results showed that air bubbles could reduce the hull resistance and increase the inflow velocity to the propeller, which in turn could reduce the thrust loading coefficient and improve the propeller efficiency. In conclusion, the results indicated that air bubbles around the hull could influence the self-propulsion factors (the wake fraction and thrust reduction fraction) and propeller operating conditions. This suggests that these factors should be considered when improving the energy efficiency of air lubrication ships.

　In this study, the stability and operability of Japanese and Vietnamese purse seiners are analyzed. Three purse seiners (135GT, 199GT, and VNM) were tested through a series of experiments involving transient waves to determine their transfer functions and capsize experiments in irregular waves with fishing gear load.

　A stability limiting boundary was developed to assess the risk of capsizing based on operability calculations and determine the maximum significant wave height at which the vessel can safely operate. The stability limiting boundary take into account the effect of fishing gear load and back rowing forces, as well as the direction of the wave. This stability limiting boundary can be used by fishermen to predict the wave conditions under which their vessels can operate safely. The relationship between the operability limiting boundary and the stability limiting boundary is presented. The study also compares the risk of capsizing in traditional and Japanese-style fishing methods.

　Results show that 135GT is less stable compared to the other two ships, while the Vietnamese purse seiner VNM has good stability but poor operability, even in average weather conditions.

　In recent years, risk of dragging anchor is increasing by typhoon that is becoming stronger. Evacuation advisory for the typhoon is announced in each harbor. However, this is for large vessels and not for the small vessels that are not correspond to the criteria. These vessels need to moor at suitable area in the harbor. Counterplan of the dragging anchor for the small vessel needs to be established immediately. The slewing motion is specific motion under the initial stage of the dragging anchor. By stabilizing the motion, the risk of the dragging anchor is decreased.

　From these backgrounds, construction of the high accuracy simulation model for the slew motion is paid attention. Numbers of research about the slewing motion are conducted until now. However, those focus only wind load as the environmental load and are constructed by the maneuvering equation. In this research, wind and wave load were considered by using the Cummins equation that was the basic linear equation for seakeeping in time domain simulation. The linear and non-linear maneuvering effect were simulated by adding on the model as the external forces. The models were constructed for coastal tanker and ferry. Model tests were conducted to evaluate the accuracy of this model and parametric simulations were also conducted to evaluate the impact force acting at top of the mooring line.

　From the model test, the accuracy of the model was confirmed by comparing the trajectory of center of the gravity. Line top tension was also compared and confirmed the accuracy. Moreover, cause of top tension’s two peaks in yawing half period were studied by evaluating of cross-correlation function between the top tension and motional parameter. As a result, it is found that the main cause of first peak is multiple of the sway velocity and yaw rate. Additionally, the second peak’s cause is also found that the position of the moored ship. These knowledges are believed to be useful to reduce the top tension and the dragging anchor’s risk.

　Through the parametric simulation, the impact force ratio that is the value between the maximum value of the horizontal mooring force and frontal wind load was evaluated using the single anchored tanker and the ferry model. The simulations were conducted by changing the wave height, the maximum instantaneous wind velocity. From the result, it was shown that increasing of wave height under the condition of low wind velocity induce an increase the ratio. Moreover, the value greatly exceeded the usual ratio got by the frontal wind load. These knowledges also are believed to be useful to estimate the anchor holding power.

　In this paper, we derive a nonlinear state space equation of a floating point-absorber wave energy converter (FPAWEC) and apply a nonlinear model predictive control (NMPC) to the FPAWEC. To consider motion constraints in float velocities and a configuration constraint in the pitch angle between the float and spar, we used Kane’s equation to obtain the motion equation of the FPAWEC. The generalized coordinates and generalized speeds were selected to ease the formulation of the optimization problem. The accuracy of the state space equation was validated with measured results of the motion of the FPAWEC. To reduce the order of the state space equation used in the NMPC controller, radiation forces and moments that have marginal effects on the FPAWEC motion were neglected. The motion, control force, and power production characteristics of the NMPC were numerically investigated and compared with those of conventional control strategies.

　The main purpose of this paper is to develop a new intrusive method to replace the traditional non-intrusive methods, such as Monte Carlo Simulation (MCS). By using the proposed method, the estimation of the stochastic response surface does not require time consuming multiple simulations, but the uncertainties in wave parameter can be estimated by optimizing the stochastic objective function only once. This study discusses the uncertainty in wave parameters estimated by using the present method when both the transfer function and the measurement data contain uncertainties. The validity of the present method is discussed by comparing its results to the results of uncertainty analyses through the MCS in which solutions of the deterministic problems are collected.

　A new response-based wave estimation method is proposed for addressing problems of uncertainty in wave parameters associated with uncertainty in the transfer function. The present Principal Component Analysis-based Stochastic Wave Spectra Estimation (SWSE-PCA) method utilizes the Principal Component Analysis (PCA) for representing the uncertainty in transfer functions of wave-induced responses. Using the SWSE-PCA method, the stochastic response surface estimation does not require time-consuming multiple simulations, but the uncertainty in wave parameters can be evaluated by optimizing the stochastic objective function only once. The validity of the present method is discussed by comparing the SWSE-PCA results to the results of uncertainty analyses based on the Monte Carlo Simulation (MCS) in which solutions of the deterministic problems are collected, by referring to numerical simulations and full-scale measurements.

　This paper examines bending and torsional testing methods specific to hydro-structural ship models. The methods examined include testing on land and water. The on-land testing uses supports that are designed not to damage the soft hull. Meanwhile, the on-water testing gives vertical bending or torsional moments to a floating ship model by moving ballast weights. The ship model is naturally twisted with respect to the shear center, which is a significant advantage of on-water torsional testing. Bending and torsional tests based on the proposed methods were performed using a hydro-structural bulk carrier model composed of GFRP (Glass Fiber Reinforced Plastics) sandwich panels. The test results validated these proposed test methods except for the on-land torsional test, where it is difficult to provide accurate bilaterally symmetric constraint conditions at the supports. In addition, these test results are used to discuss the influences of the adhesive and ambient temperature variations on FBG (Fiber Bragg Gratings) strain sensor outputs.

　The two-dimensional wave spectrum obtained by the hindcast are fitted on the function of the Ochi-Hubble spectrum and Mitsuyasu directional distribution namely 4-parameter spectrum and analyzes the trend of the spectrum shape in the actual sea area in the North Atlantic. The effect on the vertical bending moment(VBM) of a container ship are evaluated. A method to get the long-term maximum expected value utilizing the shape parameters of spectrums is proposed.

　The occurrence probability of multi-peak spectra tends to be low in sea conditions with high significant wave heights in which occur the maximum wave load. The long-term maximum expected value by using the 4-parameter spectrum was estimated to be larger than the value by using 2-parameter Pierson-Moskowitz spectrum, and contributed to approaching the true value gained directly using the hindcast wave spectrum. A method for efficiently estimating the long-term maximum expected value by using the shape parameters(λ, s) was presented. There is a higher possibility of estimating a larger load when using the realistic shape parameters than when using the IACS2023 spectrum.

　This study focuses on the flow field around a rotating cylinder and describes the effect of the rotation of the cylinder on the velocity distribution as part of the clarification of the hydrodynamic forces acting on a rotating cylinder in flow. A water tank experiment was conducted to measure the velocity distribution around a rotating cylinder. The measurement conditions were roughly divided into two groups: the side where the flow is decelerating and the side where the flow is increasing due to rotation.

　On the side where the flow is slowed down by the rotation of the cylinder, the Reynolds stress increases due to the effect of the cylinder rotation, and the apparent viscosity increases. This makes it more difficult for the fluid to flow, leading to an overall decrease in the velocity distribution. On the side where the flow increases due to the rotation of the cylinder, the flow from the decelerating side is added, leading to an increase in the overall velocity distribution. In addition, a layer of highly turbulent flow due to the effect of cylinder rotation is formed near the surface of the cylinder, and flow from the decelerating side does not flow into the inside of this layer. As a result, the flow velocity distribution is consistent with the linear superposition of the flow velocity distribution around a rotating cylinder in a uniform flow and a stationary fluid.

　Accurate dynamic models of wave energy converters are essential for the design of these devices. To create an accurate model, it is necessary to consider not only the free surface effects of water but also the mechanical friction forces and cogging forces of the power takeoff system. Nevertheless, these are hard to calculate theoretically. Consequently, this study addresses the development of a nonparametric dynamic model that can consider complicated forces, such as mechanical friction forces and cogging forces of a power take-off system. A regression model using a Gaussian regression process was developed to estimate the heaving displacement and velocity of a wave energy converter based on the data measured in tank tests. This regression model predicted the generated output power more accurately than a numerical simulation model based on the system identification. Additionally, it was shown that the accuracy of the regression model does not decrease significantly as the observed noise in the training data increases. An accurate dynamic model of wave energy converters based on measured data can be used for a wide range of applications, including the development of new control methods, evaluation of power production, and estimation of the maximum displacement of wave energy converters.

　In this paper, to calculate the offshore installation cost more precisely during the development stage, a model is proposed to estimate the offshore installation time of floating offshore wind farm. The concept of this model is based on the CBS (Cost Breakdown Structure). It entails dividing offshore installation processes into seven main processes and their respective subprocesses. Thus, the total installation time can be estimated by summing up the operational time of seven processes. This estimation is achieved by determining eight model parameters which represent the efficiency of the installation process. Using the actual installation data from Japan and Europe projects, the model parameters of each project are analyzed and compared. To achieve the efficiency level of current European FOWT installation, the loading time, and the total time of pre-installation and ultimate holding force verification, both per mooring line, should be improved by twenty and five times, respectively, from the present levels. The velocity of cable trenching, and the time for connecting one-side of dynamic cable to the floater, should be improved by six and eight times from the present levels, respectively. Comparing the results of model parameters from actual installation data in Japan and Europe projects with that obtained from the model, the proposed model is validated in view of reproducing the process of offshore installation of floating offshore wind farms.

　The Kuroshio current flowing near the coastal areas of Japan is one of the strongest ocean currents in the world. In addition, it is expected to be a stable power source of renewable energy from the ocean. Recently various ideas are studied to utilize the Kuroshio current for power generation by researchers worldwide. But there has hardly ever been report on demonstration tests in actual sea areas and stress measurement of the demonstration machine.

　We are developing a floating-type ocean current turbine system to utilize the Kuroshio current for power generation supported by NEDO. In this paper, we report the result of demonstration tests in the actual sea area. Especially the power curve was obtained from the measurement in the demonstration test and we confirmed that the estimated capacity factor using the power curve fulfills our initial expectation.

　As a result of the stress measurement, good agreement was observed in general between the measured stresses and the FEM results. However, it was confirmed that with the turbine rotating, the hull may vibrate significantly with the frequencies corresponding to the multiples of the turbine rotation. This is considered to be a resonance of the hull at those frequencies, and although the absolute amplitude of the vibration is small and does not pose a problem for this demonstration test machine, it may become a design issue for future large-scale commercial machines.

　The safety assurance of autonomous vessels is a major issue for their implementation, and it is necessary to prove their equivalent safety compared to the existing vessels. Two “model-based approaches” are important to identify and quantify the risks of such complex systems: systemic risk analysis using descriptive models, and system simulation using numerical models. This paper proposes a method for defining test scenarios from risk assessment in the design phase of the autonomous vessel and shows the flow of simulation-based verification and validation (V&V) using model-based simulation. Specifically, we extended the System-Theoretic Process Analysis (STPA) and extracted specific risk-based critical scenarios. Then we picked up a specific scenario for the short-range voyage planning function and presented a simulation-based verification flow using a ship avoidance maneuvering simulator. The results of this study are expected to be utilized in discussions regarding the verification and certification process of autonomous systems and the functional requirements of the simulators for verification.

　The efficiency of the ballast water drainage system affects the profitability of shipping companies when loading and unloading. Moreover, the arrangement of the ballast system is closely related to the tank structure, which affects the component production and structural strength of ship. However, there is no mature design and evaluation method to balance the relationship between drainage efficiency and tank structure.

　This study utilizes hydraulic experiments and computational fluid dynamics (CFD) methods to verify the flow phenomenon during the drainage process in the ballast tank, so as to discuss the drainage efficiency. The model designed for the experiment data collection is a part of ballast tanks of a typical bulk carrier with the scale of 1:10. The experimental results are then validated and verified by conducting a two-phase flow model based on the volume of fluid (VOF) simulation. The research follows the order from simple to complex, starting from the single-arranged small-scale tank, and gradually expanding to the complex large-scale model. Therefore, the VOF method has been recognized in the ballast tank drainage simulation, and based on the simulation results, the drain course to improve the drainage efficiency is proposed. The results provide the reference for the design and improvement of the ballast system.

　The performance of ballast water drainage systems has a significant impact on the profitability of shipping companies. Furthermore, the arrangement of the ballast system is closely related to the tank structure, affecting the production of ship components and structural strength. However, the current state is that the design knowledge and assessment method are mainly based on the experience of the designer, and the ambiguity of design factors makes it difficult to make definite design principle.

　This study uses hydraulic model experiments to analyze the complex flow phenomena in ballast tanks to provide design strategy for improving the drainage efficiency. The tank model design refers to a part of the ballast tank of a Panamax bulk carrier at a 1/10th scale, and some detailed structures are appropriately simplified. The hydraulic experiments are carried out from the small-scale ballast tank to clarify the flow phenomena between compartments, and further analysis for the impact of the drainage path on the drainage efficiency. Based on this study, a design policy for the drain course is established and verified in the hydraulic experiments based on the multi-compartment ballast tank model. The experiment results are compared with the case of the ballast tank model applying conventional design methods, and the effectiveness of the drain course is confirmed. This study provides the reference for the design and improvement of the ballast tanks design.