This paper describes the hull form optimization method of an icebreaker. In this optimization method, hull forms are generated by the original method we develop. The objective functions to be minimized are ice resistance in level ice and wave making resistance in open water. A multi-objective genetic algorithm is adopted as a numerical optimizer. We optimize a hull form which has the same hull form parameters as the preliminarily designed hull form for an application example. The optimization result provides many hull forms which have different balances of both objective functions as the Pareto solutions. It is found that some hull forms have better performance both in ice and open water conditions than the preliminarily designed hull form. We can develop an icebreaker hull form efficiently using the present optimization method.

Ship propellers made of Carbon Fiber Reinforced Plastic (CFRP) is expected to be beneficial for the propulsion plant operation in waves. This is because the elastic modulus of the CFRP is lower than that of bronze alloys of a conventional propeller, thus in the condition of varying load in waves, the pitch of the propeller made of the CFRP slightly changes reducing the load fluctuation of a propulsion engine. In response, the engine control system also reduces the correction of fuel amount required to keep the shaft rotation speed constant. In this respect, the engine combustion process takes place in a relatively stable condition favoring better fuel efficiency of the propulsion plant. In this study, the propulsion performance of a ship with the CFRP propeller in waves is investigated experimentally and numerically. The ship's performance with the CFRP propeller is evaluated by comparing it with that of the conventional propeller. The ship with the conventional propeller is designed to correspond to such ship with the CFRP propeller. The propulsion engine characteristics are represented by the Hybrid-CMV model of the diesel engine. This engine model is able to explicitly introduce the fuel-combustion process in the framework of the Cycle-Mean Value approach. A time-series calculation methodology for the ship speed and the engine states in waves is explained in the first place, that is the propeller thrust and torque models in waves are coupled to the Hybrid-CMV engine model. Secondly, the proposed calculation method is validated through experimental results of the free-running model test in regular head waves, using the Marine Diesel Engine Simulator (MDES). The MDES is the self-propulsion device of the propeller model, which utilizes the engine response model. In the model tests, the model of the CFRP propeller, made of chloroethylene-resin which is chosen to correspond the elastic modulus to in full-scale, was taken. The experimental results are also compared with those obtained using the conventional propeller. Thirdly, with the validated calculation methodology, the propulsion performance in waves of the ship with the CFRP propeller is investigated through the numerical speed-trial test in regular head waves. With the focus on the characteristics of fuel consumption, it was confirmed that the CFRP propeller contributes to better engine fuel efficiency when operating in waves.

International Maritime Organization has adopted the initial IMO strategy on reduction of GHG emissions from ships at 2018. Achieving the strategy requires technical innovations on ship design and operation. Recently the utilization of natural energy source in operation is expected as a measure to reduce GHG emissions from ships and specifically wind is expected as a factor to enhance ship performance in actual seas.

This paper focuses to a rotor ship as a ship with wind propulsion. A rotor ship can obtain an additional thrust by winds based on Magnus effect and consequently fuel oil consumption of the ship can be reduced. For an effective use of wind propulsion, fuel saving due to rotors should be accurately evaluated. In this paper, the author addresses a panamax bulk carrier having one rotor. Wind force and moment acting on the bulk carrier is estimated and provided to performance prediction in specific conditions. Based on results of the performance prediction and occurrence probability of winds and waves, an evaluation of fuel saving of a rotor ship in actual seas is conducted and reported in this paper.

In this study, the authors proposed explicit formulae of the surge, heave, and pitch motion of ship in regular waves expressed as the explicit function of principal hull-form parameters and extracted dominant hull-form parameters of those for simple estimation of the wave loads for the ship structural design. In order to develop the estimation formulae which have enough accuracy and wide range of applicability, the theoretical approach was adopted based on the linear seakeeping theory. In the process of deriving formulae, the equations of motion were simplified based on the relationship of the fluid forces that cancel out each other and the approximation that the ship speed is slow. For both surge and pitch motion, 1-DOF model, in which interaction effects were ignored, was applicable and the dominant parameters were successfully extracted. On contrast, heave motion in head sea was significantly affected by pitch motion especially for full loading conditions. Although the mechanism of interaction effect and the factor were clarified, it was difficult to express simple form and extract dominant parameters. However, in beam sea, the heave motion can be expressed as the 1-DOF model, and the dominant parameter was extracted straightforwardly. By using the extracted dominant parameters, the approximated formulae of peak value of the response amplitude operators of the vertical motion were proposed. It was confirmed that the proposed formulae have enough accuracy regardless of ship size and ship type through validation compared with numerical calculation by using actual hull-forms of 77 ships × 2 loading conditions.

Marine renewable energy is expected to replace fossil fuels as an energy source. Wave energy is one of these marine renewable energy sources. A floating point-absorber wave energy converter (PA-WEC) is a wave energy generation system that is expected to be utilized because of its low mechanical loss and lack of wave directionality. Many studies have been conducted to maximize the power generation of PA-WECs, and theoretical solutions have been presented for the maximum expected value of power generation and its control in regular waves and known irregular waves. However, the components of the incoming irregular waves are not known when the system is actually installed on the ocean. Therefore, in this study, a basic investigation of the possibility of applying AI to predict and determine the control power to maximize the power generation of PAWEC is conducted. In this investigation, we have narrowed down the focus to the possibility of estimating the optimal control power from time to time, and investigated and discussed the effective combination of training data sets based on theoretical situations in known waves.

In this paper, we derive the equations of longitudinal motion for a floating point absorber type wave energy converter (FPAWEC) by Kane's equation. Since FPAWECs have a nonholonomic constraint, we selected Kane's equation which is based on the principle of virtual power. The time-domain motion equations of the FPAWEC with several control strategies were developed and its motion evaluations were conducted in regular and irregular waves. The motion evaluation results were reasonably consistent with the measured ones, both in regular and irregular waves. The dominant pitch motion in irregular waves was observed around pitch natural frequency. Using the derived equations, we investigated the pitch moment components and found that the pitch moment on the float had the largest contributions to pitching motion with the pitch natural frequency.

It is important for the design of the safe hull structure to grasp the hull structural response in waves. A seakeeping test by using a flexible ship model is carried out to clarify hull structural response in waves. But it is difficult to design and deal with a flexible ship model. In this study, the estimation method available to a rigid ship model for hull structural response is proposed. First, hydrodynamic pressure in the hull surface is measured by conducting a seakeeping test. Next, the hydrodynamic pressure is interpolated in the whole hull surface considering the hydrodynamic pressure distribution near the draft. Finally, the hydrodynamic pressure distribution is used as load and finite element analysis (FEA) is carried out. Inertial force is considered by using the inertia relief method. The hull structural response in waves can be obtained from FEA results. In this 1^st report, a seakeeping test is carried out, and the vertical bending moment (VBM) is estimated by using the proposed method. An acrylic flexible ship model is used in the test to measure the hydrodynamic pressure on the hull outer surface and hull strains at many points by using the fiber Bragg gratings sensors. VBM obtained by the proposed method is good agreement with one obtained by the measured strains.

A numerical simulation is conducted to investigate movement of iron ore fines by ship's rolling motion under saturated condition using the microscopic fluid coupling scheme devised in the Discrete Element Method. The scheme solves pore water pressure in particle assemblies by change of void spaces and flows between them. Updated pore water pressure is applied to related particles around void spaces. The result shows liquefaction, that is, pore water pressure increases, as rolling motion begins, the effective stress decreases on the other hand. Relative motion between particles increases upper area of the assembly, also particles on surface moves laterally as rolling motion proceeds, such that, the surface tilts from the lateral direction during motion. Further analysis with changing parameters, such as water content is needed for safe carriage of iron ore fines.