When sailing in level ice fields, an icebreaker moves forward with breaking ice and pushing down/away the broken ice pieces along the hull surface. The broken ice pieces make hull resistance and cause propeller-ice interaction. Therefore, evaluating the flow of ice pieces around a hull surface is important to hull form development. When taking ice tank tests, we observe the flow of ice pieces around a model ship using observation windows on the floor of the ice tank. However, visual observation is limited to qualitative analysis. Therefore, we developed quantitative analysis method for the flow of ice pieces from bottom-view movie using the image analysis techniques. In this paper, ice concentration and the motion of ice pieces on a hull surface were analyzed for the flow of ice pieces.

　Ice concentration is analyzed by extracting ice pieces from the original movie using “Otsu's method”. The distribution of ice concentration on a hull surface is analyzed by projecting the coordinate points of hull surface onto the movie, considering the positional relationship between the hull and the camera. The motion of ice pieces is analyzed using CSR-DCF tracking method. The three-dimensional position of ice pieces are estimated by projecting tracking results onto the hull surface based on the assumption that ice pieces move on the hull surface.

　The accuracy of these analysis methods was verified using a simplified model test in the ice tank. As a result, the distribution of ice concentration was almost the same as the true distribution although it tended to be overestimated. Moreover, the error in the position of an ice piece on the simplified model was less than 10mm at the model scale. We analyzed the flow of ice pieces of the new “Arctic Research Vessel” of Japan. As the result, it was confirmed that the ice pieces moved sideways along with they moved from the fore to aft area, and that the motion of the ice pieces became linear as the ship’s speed increased. By using these analysis methods, the flow of ice pieces on a hull surface can be analyzed quantitatively. Moreover, the analysis results of the flow of ice pieces can be used for validation to develop more accurately simulation methods for icebreakers.

　One of the energy-saving technologies for ships is a duct-type energy-saving device for the purpose of improving propulsion performance. With the tightening of GHG (Greenhouse Gas) emission regulations, it is necessary to improve the effectiveness of the energy-saving devices. In order to understand the flow field for the purpose of enhancing the effect of the duct type energy-saving device, the flow field around the duct is measured by PIV (Particle Image Velocimetry). However, the measurement is limited to the outside of the duct because the laser sheet does not reach the inside of the duct.

　In this research, we are developing a method to measure the flow field inside the duct by the refractive index matching method using a transparent model close to the refractive index of fresh water. Since we discovered a model material (CYTOP) with a refractive index of 1.34 in the previous research, we measured the flow field in the duct using CYTOP. From the measurement results, it was found that the difference was within 4% compared with the 2-hole Pitot tube and CFD (Computational Fluid Dynamics). Therefore, CYTOP may be used for measuring the flow field inside the duct using the refractive index matching method in fresh water.

　SK-Bow is a characteristic bow flare shape and developed to reduce the added wave resistance. It is important to obtain the distribution of added pressure on SK-Bow to clarify the reduction mechanism of the added resistance and consider its required structural strength. For this purpose, we use FBG pressure sensors to compare distributions of the added pressure between SK-Bow and conventional bow flare shape. Through experiments, we found that SK-Bow can reduce the added pressure particularly around the steady ship-side wave profile and hence the added resistance. In other words, we can reduce the added resistance if we could reduce the added pressure around the steady ship-side wave profile by an energy saving device. For about structural strength, we need to consider not only the average pressure but also the amplitude of unsteady pressure on the flare part of SK-Bow.

　In order to achieve a head-out mooring, instead of a head-in mooring ordinarily conducted in larger ships, as a countermeasure of a quick evacuation for large ships against a great earthquake and tsunami, it is important to investigate and obtain a property of yaw moment acting on the ship in shallow water during a turning short around assisted by tugs. From several pure yaw rotating tests conducted in this study, it is found that the yaw moment is increased rapidly in a shallow water where the ratio(h/d) of water depth(h) and draft(d) is less than 2.0, and that during accelerated situation is larger than that during the steady situation. The yaw moment has a steady value during the turning, which corresponds to the rotating angular velocity, at h/d ≧ 2.0, and is also significantly influenced and varied by the attitude of the ship in the turning basin at the shallow water; h/d < 2.0.

　In this study, the characteristics of thrust and rudder force caused by an outboard engine attached to a small boat at low speed are investigated based on the measured data by fully captive oblique towing model test with outboard engine and its required experimental conditions to obtain them sufficiently are proposed. The range of experimental conditions in propeller advance coefficient, rudder angle and drift angle of boat are determined according to the measured data for a real boat at berthing maneuvers.

　From the results of the oblique towing test with outboard engine being in operation, it is confirmed that the test with forward speed should be conducted for several inflow angle for outboard engine which is sum of drift angle and rudder angle and propeller advance coefficient within the range of motion of a real boat at berthing maneuvers. On the other hand, the test with backward speed should be conducted for several combinations of drift angle and rudder angle in addition for the conditions of the test with forward speed. However, the measured thrusts and rudder forces for the two conditions which are line symmetry in the longitudinal direction of towing tank are almost same, therefore one of them can be omitted. Moreover, from the comparison the results of oblique towing tests with outboard engine in being operation and not, it is found that the effects of the operation on rudder force is small, then the rudder force can be obtained from the test with outboard engine not in .

　Dynamic response characteristics of a floating support structure of a Floating Offshore Wind Turbines (FOWT) with low rigidity characterized by guywire supported tower and single-point mooring was investigated through wave tank experiments and numerical simulation using analysis code UTWind. The results of the wave tank experiments showed that the motion has a nonlinearity to wave height mostly at resonance condition due to the viscous effect and a waveless response was observed at a specific wave period. Meanwhile, the elastic deformation increases in two wave periods, the peak at longer wave period is caused by the inertial force of motion of RNA and tower, and the peak at shorter wave period is caused by sagging-hogging elastic response of the floater. The comparison of the results from the tank experiment and UTWind simulation confirmed that the calculation is accurate except for the resonance period, as the viscous effect has a significant effect on the response where careful selection of drag coefficient is required. Additionally, the numerical method revealed that upwind guywire is affected by Pitch and Heave, while the downwind guywire is affected by Pitch and Roll. The comparison of results with slightly different incident wave angles revealed that the amplitude of the bending moment significantly changes due to small variations in wave period and incident wave angle at short wave period. Moreover, the study found that Heave motion varies depending on whether the wave comes from front or back of the floater. These findings are crucial for the design of FOWT.

　In this study, a parametric study was conducted to investigate the optimization of floating structure and blade pitch control settings for a semi-submersible floating offshore wind turbine. For the floating structure, a total of 11 different floating structures were assumed with varying column diameters or lower hull lengths. For the blade pitch control, we focused on the saturated control, called peak shaving, and six settings were assumed. The blade pitch control settings are a trade-off between the amount of power generated and the tower base load. Evaluation using the construction cost of the floating structure relative to lifetime revenue and the fatigue damage equivalent load on the tower base showed that the most efficient case was when the lower hull was slightly shortened, and the coefficient a that characterizes peak shaving was set around 0.9.

　The semi-closed flexible fish cage (SCFFC) is a new concept that is supposed to be an alternative to conventional net cages as an important part of the next-generation aquaculture system. In this study, the dynamic responses and sloshing of SCFFC in regular waves are studied by experiments. A 1:30 physical model is made and set with several accelerometers, wave gauges, and cameras in a water flume. Waves with different periods and heights are made, and the dynamic responses and water levels inside and outside SCFFC are measured. The surge, heave, and pitch of SCFFC increase as the period of the incident wave increases. Its dynamic responses are similar to that of a semi-closed rigid cage, but the magnitude of the motions is much smaller. The bag is deformed and shows strong non-linear responses under some wave conditions, which should be attributed to the complex interactions between sloshing, wave field, and bag’s deformation. The filling level of inner water has a great influence on pitch, which might be attributed to the interactions between the moving inner water mass and deforming bag.

　At the 79th Marine Environment Protection Committee in December 2022, it was discussed to combine regulatory measures and market-based measures (MBMs) for decarbonization in the international maritime transport. In this study, the evaluation of Feebate is focused on, which is an MBM proposed by Japan. This institute has the challenge that the carbon dioxide (CO₂) emissions to be reduced are not definitive, and it is not easy to make accurate future projections by top-down simulation. In this study, therefore, future CO₂ emissions from the international maritime transport with Feebate are simulated by multi-agent simulation to help the policy maker effectively reduce the emissions. Furthermore, it is analyzed what kind of agent behavior affects the CO₂ emissions. The simulator developed in this study is a multi-agent simulator that uses multiple agents to imitate the decision-making processes of real shipping companies. Feebate is modeled as the differences of fuel prices among heavy fuel oil (HFO), liquified natural gas (LNG) and ammonia, and as the ratio of fuel consumptions among these fuels. Case studies are conducted by varying the degree of the fee for the fossil fuels, and the starting year of Feebate. The simulation results suggests that Feebate encourages shipping companies to switch from HFO-fueled vessels and LNG-fueled vessels to ammonia-fueled vessels, and the slow start of Feebate makes it difficult to reduce CO₂ emissions, even with a stronger fee, which causes unnecessarily cut into shipping companies’ profits.

　A duct-type energy saving device is one of the effective devices for ships. Most of the kind of ducts are attached to the front of the propeller, which is widely used in actual ships. National Maritime Research Institute has also developed an energy saving duct, and it has been empirically found that the effect tends to be greater in the ballast condition than in the laden condition. The authors tried to clarify the mechanism of energy saving effect by using the data of nominal wake distribution and surface pressure distribution of a ship, because the flow field around the hull changes when the draft or trim varies depending on the loading conditions. As a result, we conclude that the thrust deduction coefficient and the wake coefficient of the self-propulsion factors change depending on the loading conditions, which are caused by the variation of the position of the vortex flowing into the duct.

　The purpose of this study is to propose a procedure for accurate calculations of the flow field around prismatic stepped planing surfaces by using an existing commercial CFD code (STAR-CCM+), and investigate the characteristics of hydrodynamic phenomena including their scale effects. In the previous studies³⁾, it is shown that high resolution of partial mesh around stagnation line and application of surface tension model are significant to obtain highly accurate calculation results. The same procedure is also applied for prismatic stepped planing surfaces with one step or two steps, and the hydrodynamic forces acting on prismatic stepped planing surfaces are calculated and the calculated results are compared with measured results. The characteristics of the flow field on the hull behind step are investigated, and the frictional resistance coefficient is obtained for each hull. The calculated coefficients for Reynolds number using average length of each wetted surface as representative length are near the turbulent frictional coefficient line of the equivalent flat plate. In addition, the 10 times large prismatic stepped planing surface with one step is calculated to investigate the scale effects on the wetted surface and its frictional resistance coefficient. As the result, the wetted surface area behind step has the scale effects that is nondimensional value of large hull is smaller than model hull caused by the difference of frictional force which comes from R_n differences on the wetted surface in front of the step.

　Ship maneuverability is a crucial aspect of safety, requiring thorough evaluation before construction. The Maneuvering Modeling Group (MMG) model offers a simulation-based approach to estimate this performance. Hydrodynamic derivatives play a pivotal role in the MMG model. To acquire these parameters, towing tank tests are essential, and two common methods are the Oblique Towing Test (OTT) / Circular Motion Test (CMT) and the Planar Motion Mechanism (PMM) test. The PMM test allows for acquiring hydrodynamic derivatives with fewer tests than OTT/CMT. The results of the PMM test are influenced by the motion frequency given in the tests, and test conditions must be carefully considered. While it is known keeping the frequency sufficiently low in PMM test reduces frequency effects on hydrodynamic derivatives, the relationship between coefficients obtained through PMM and OTT/CMT has not been thoroughly explored.

　In this paper, the relationship between the results of the low-frequency PMM tests and OTT/CMT has been investigated. Consequently, this study identifies that the hydrodynamic derivatives obtained from low-frequency PMM tests are equivalent to those obtained from OTT/CMT.

　Wet-tow transportation of floating offshore wind turbines (FOWTs) is affected by weather and sea conditions and may become a bottleneck in the supply chain. However, there has been no accumulated knowledge on the towing of FOWTs, and the impact on the supply chain has not been clarified. In this study, dynamic analyses are conducted for three different semi-submersible floating designs, and the towing performance of each design is examined. Furthermore, the influence of the towing performance on the overall construction flow is examined using data of actual sea conditions. The results show that when the lower-hull is exposed on the water surface due to de-ballasting, the pitch and roll natural periods are shortened, which causes large motions depending on the wave period and wave direction. It causes an increase in the waiting time before the departure of towing in winter and an increase in uncertainty. When towed with the lower-hull submerged, the motion is small and FOWTs can be towed throughout the year. Depending on the design of the floating body, more towing force is required to maintain sufficient towing speed when the lower-full is submerged, and a trade-off occurs between the steadiness of construction and the cost of transportation.