The purposes of this study are to propose a procedure for accurate calculation of the flow field around a prismatic planing surface by using an existing commercial CFD cord (Star-CCM+), and investigate the scale effects of its hydrodynamic phenomena. First, according to ITTC Recommended Procedure³⁾⁴⁾, the hydrodynamic forces acting on a prismatic planing surface are calculated and compared with the measured results. As a result, it is found that the calculation accuracy of the frictional force is poor by appearance of numerical ventilation. In order to obtain highly accurate calculation, the resolution of the partial mesh around stagnation line are made higher and the surface tension model is included, moreover, un-steady calculation is applied. The above-mentioned mesh generation procedure is applied for the 10 times large prismatic planing surface and the scale effects of hydrodynamic phenomena are investigated, and it is shown that the pressure coefficients acting on the wetted surface area are same regardless of model size and the frictional resistance coefficients acting on the wetted surface and spray area are near the turbulent frictional coefficient line of the equivalent flat plate. On the other hand, the pressure coefficients acting on the spray area has the scale effects if model size is too small because of the surface tension effects.

In recent years, high-speed vessels such as passenger ships, fishing boats, and pleasure boats, have been operated in various applications. In Japan, the method of towing test, the characteristics of hydrodynamic forces acting on the hull, and the kinetic characteristics during running in waves have been studied on many occasions particularly for high-speed planing vessels and semi-planing vessels. However, in foreign countries, high-speed rectangular-shaped vessels that have a large flap at the fore part of hull, such as Expeditionary Fighting Vehicles (EFV, hereafter), have been researched in addition to vessels used for business and leisure applications. Unlike in general high-speed vessels that have been actively studied so far, various assignments are left unclarified in the research of EFV, for example, the kinetic characteristics during high-speed running, the characteristics of hydrodynamic forces acting on the hull, and so on.

The purpose of this study is to evaluate with numerical simulation the kinetic performance of a high-speed planing vehicle such as EFV that surfaces due to lift force caused by the large flap. Our report focused on the straight running of a high-speed vehicle. We obtained data by measuring resistance and motion in the free towing tests and measuring the hydrodynamic forces acting on the hull in the captive towing tests. These data would contribute to future numerical simulations. Furthermore, we evaluated the kinetic characteristics of the high-speed planing vehicle running in waves with numerical simulation applying the maneuvering motion model used for general ships. This paper presents results of the above-mentioned investigations.

This study describes mechanism of motion reduction effects of a pontoon type floating structure with moonpools. Characteristics of hydrodynamic forces, and motion responses of such as the floating body were clarified by model experiments and linear potential theory based calculations. Forced oscillation tests of heave and model fixed tests were carried out using a 1/100 scaled experimental model. As a result, the forced oscillation tests found negative added-mass and almost wave-less frequency in wide frequency range were found. At the same time wave exciting forces on heave and pitch were reduced very much in wide frequency range. The prediction method reproduced behaviors of hydrodynamic forces and motion responses except peak frequencies due to resonance of water within the moonpools.

It is necessary to obtain actual wind state at the sea area where offshore wind farm will be constructed to realize its profitability and safety. Our research group has been investigating methods to reduce motion of floating platform caused by wave, wind, current for offshore wind observations by Doppler Lidar, and has proposed a spar-buoy with ring-fin motion stabilizer. However, the spar-buoy is not small, therefore it requires high installation cost. As another method, in this study, a controlled rigid body swing as a motion stabilized platform to place on floating structure is investigated numerically. First, a single pendulum type motion stabilized platform on a spar-buoy type floating plat form with a tension-moored is proposed, and its motion mechanism is clarified. Based on the results, a counter-weight type motion stabilized platform is proposed, which is an improvement of the single pendulum type, and the effectiveness in reducing motion is confirmed. Furthermore, the counter-weight type motion stabilized platform is adjusted so that it has no restoring moment, and further motion reduction is confirmed by using skyhook spring. Finally, it is confirmed that the motion reduction effects are also sufficient when the motion stabilized platform is mounted on a discus-type floating platform.

A technical challenge in deploying a floating offshore wind turbine in shallow water is dissolution of the poor performance of a catenary mooring system due to the decreased absorbable potential energy. It is common practice to improve mooring performance by using buoys and sinkers to enhance the potential energy absorbed by the mooring system. In this research, a tower-shaped buoy (tower-buoy) is proposed which is a buoy and a sinker integrated structure. In this design, a relatively large buoy and the sinker are connected by a column, and a chain subject to large tension by connecting the buoy and the sinker is removed. A mooring configuration is also proposed to maximize the effect of the tower-buoy.

Regarding the proposed tower-buoy mooring, a static mooring performance analysis method was formulated, and static tension-displacement relation of the tower-buoy mooring is calculated and compared with the performance of conventional catenary mooring. It was shown that the tension of the mooring line of the tower-buoy can be significantly reduced compared with the catenary mooring. In addition, a wave tank experiment was carried out to investigate dynamic effect with a 1/35 scale model of a actual mooring deployed at a shallow water with depth of 50 m using φ 132 mm chain. The experimental results were compared with static analysis obtained by the formulated analysis, static and dynamic analysis by Orcaflex. The expected decrease in tension of mooring line is confirmed. Noticeable dynamic effects was also observed and cause was considered.

Cable-driven parallel robots are mechanisms that control the position and attitude of an object using multiple cables. Typical cable-driven parallel robots have been studied for use on land, but not for use in water. This is because the position and attitude control of object and motion analysis become difficult underwater due to the large deformation of cables caused by fluid forces. In this paper, we propose an underwater cable-driven parallel robot consisting of multiple on-water robots and derive a dynamics model that considers the cable dynamics underwater. Then, we proposed a position and attitude control system for the suspended object based on the inverse kinematics problem for the suspended object and studied its effectiveness by simulation by using the planar two degrees-of-freedom underwater cable-driven parallel robot.

Bending fatigue tests with stress ratio R = -1 and R = 0 of as welded (AW) and stress relieved (SR) root-failed plug weld (PW) specimens and toe-failed out-of-plane gusset weld (GW) and T-joint (TJ) specimens are performed. The welding residual stress (WRS) at the root notch and the weld toe of AW and SR specimens are measured by XRD method. The mean stress effect of the fatigue test results are analyzed by using modified MIL-HDBK-5D equivalent stress σ_eq based on hot spot stress (HSS) and 'root local stress (RLS)' determined by two-points stress extrapolation. It is found that all fatigue test results can be approximated by a single S-N curve regardless of failure mode, joint type, stress ratio of the external load and SR treatment when RLS can be determined so that the root-failed AW fatigue test results can be approximated by HSS S-N curve. As an alternative means for the root-failed cases where HSS-based σ_eq is inapplicable, 'EPLSC method', in which σ_eq is determined from the elastic-plastic local stress cycle (EPLSC) calculated by welding and cyclic loading thermal elastic plastic FE analyses with very fine FE mesh, is proposed. The fatigue test results of AW PW and GW specimens with various external stress ratio can be approximated by a single S-N curve when σ_eq is determined by EPLSC method. It can be considered that the proposed EPLSC method is effective in a large number of root-failure cases.

In Europe and Japan, various types of floating wind farms are being constructed. In recent years, the size of wind turbines has been increasing, and the floating structures have also been getting larger. The types of floating structures are generally classified into a semi-submersible, spar, and barge types. The advantages and disadvantages of each type are depending on the construction cost, response characteristics in wind and waves, and water depth (depending on the draft of the floating structure). The semi-submersible type is generally more expensive to build but has a smaller installation depth and a larger installation area, while the spar type is less expensive to build than the semi-submersible type but has a larger draft and a limited installation area. For the construction of a spar type floating structure, deep and calm waters, like fjord are necessary and for the installation, deep waters are also necessary. However, it is said that such area is not so large near Japanese shore. In this study, the installation potential of 2 types of floating structure in the vicinity of Japan was estimated by using GIS (Geographic Information System) software based on the results of the basic design of floating structures, assuming the installation of large (10 MW to 20 MW) wind turbines. The author clarified that the installation potential of semi-submersible FOWTs is larger than one of Spar type FOWTs and the shallow water area has enough potential for installation of FOWTs to achieve Japanese Government's target. The 1st step of a strategy to achieve the goal is the installation of 20 MW turbines on semi-submersible FOWTs to a shallow water area with 50 ~ 100 m water depth. Furthermore, the effect of a sharing anchor system is estimated, and the results show that the cost reduction effect of the anchor sharing is about twice of the one of the normal moorings, depending on the turbine arrangement.

A process simulation based on a multi-agent system for shipbuilding is developed. The works in the shipbuilding are precisely modeled including supplemental tasks. In many conventional studies, the work time is estimated by dividing a total workload by the work efficiency observed on the shop floor. On the other hand, shipbuilding work consists of many supplemental works as workers work under the constraints of three-dimensional space. Therefore, this paper proposes a modeling method for shipbuilding tasks that can represent supplemental works as well. The shipbuilding task is represented as a combination of elemental tasks, and each elemental task is an executable function that can consider a path in three-dimensional space. The ship simulator considers a virtual shipbuilding factory as an environment and workers as multi-agent. By comparing the results of the simulation in a sub-assembly process with the actual work in a real shipyard, it was confirmed that the simulator can properly approximate the time of each task including supplemental works. Also, it was shown that the proposed method enables precise examination and reduces the non-value-added time.

Floating offshore wind turbines (FOWTs) have been attracting a lot of attention as a main energy source for a carbon-neutral society. Although it is said that the costs of commercialization of FOWTs are still high, many studies have been conducted to rationalize costs. The main cost is construction of the floating structure, and now many novel FOWTs concepts have been proposed to reduce it. The unique shape and structure of one of those FOWTs, which consist of a steel tower and concrete lower hulls with wires holding them rigid, make it difficult to evaluate their safety using existing numerical analysis methods. In this study, we investigated a multi body dynamics analysis method for the novel floater. The analysis method was employed to reproduce the behavior in regular waves, considering the elastic response of the floating body. A model test was also carried out to verify the accuracy of the analysis method. In the model test, a special large-size scale model was used, which was manufactured in the same way as the actual model. Comparison of both results, i.e., the analysis and the model test, showed good agreement in floater motions, mooring tensions, and wire tensions. On the other hand, differences were also observed between them for some wave period conditions. It is possible that the asymmetry of the floating structure and its columns that penetrate the water surface at an angle caused the differences in the estimation of the fluid force acting on the columns. Through the analysis, the effectiveness of the FOWTs concept on reduction its tower base load was also confirmed.

Bezaisen, a Japanese typical wooden vessel of Edo era, is characterized by its single large sail supported by one set of huge mast. On the installation procedure of the mast, some references are available such as the record prepared by Armand Paris who was a lieutenant of French navy visiting Japan in early Meiji era. But those did not cover the procedure in detail to get overall picture. In this paper, the procedure is studied based on some calculations considering shapes, sizes, weights and center of gravities of the sail and mast on the reconstructed Bezaisen “Naniwa-maru" as well as its construction records.

Schooner Heda was constructed in the bay of Heda at the end of Tokugawa Shogunate. There are many evidence showing this construction and Schooner Heda was authorized as one of Ship Heritages of Japan. Concerning to this ship there are drawings of body plan and profile, but there is no sign that this is the drawings of the ship Heda. In this paper, the author tris to show those drawings are that of the ship Heda, comparing with similar ship called as Schooner Kimisawa.

Long-term expected value of vertical bending moment (VBM) and fatigue damage at mid-ship deck are estimated utilizing the two-dimensional wave spectrum found by hindcast and the response function obtained by the strip method.

The estimated value using the two-dimensional spectrum is about 6% larger in long-term value and about 20% larger in fatigue damage than in case of using the wave spectrum which IACS recommend. It did not act in the direction of filling the gap between the value of the on-board measurement and the value based on the numerical calculation. On the other hand, it is able to be said that the selection of the spectrum does not bring much difference to the long-term prediction as long as the representative wave direction, the significant wave height and the average zero-up crossing wave period are matched.

It was confirmed that the higher the significant wave height, the greater the concentration of the hindcast spectrum than the IACS recommended value (λ=1). The difference between the two (R_Hindcast -R_IACS) is that if the peak frequency of the wave spectrum match with the frequency at which the response is maximum, R_Hindcast with a higher degree of concentration is larger. However, if this does not match, the relationship may be reversed.

Automatic collision avoidance is of significant importance to prevent maritime collisions. Although many studies have been conducted in recent years, autonomous system has not completely replaced human captains since it is still difficult to imitate their complicated decisions. Thus, the present paper tries to investigate and imitate experienced captains' maneuver using maximum entropy inverse reinforcement learning (MaxEnt IRL). We firstly verify that MaxEnt IRL can reproduce appropriate reward function from demonstrative trajectories. Afterwards, we conduct an experiment on a simulator where well-experienced captains maneuver in congested sea and estimate reward from the trajectories. Searching the route which maximizes the obtained reward, finally, we demonstrate the optimized route can avoid collision against multiple ships in compliance with the International Regulations for Preventing Collisions at Sea (COLREGs).