The present paper describes a hull form improvement of innovative low-speed Ultra Large Block coefficient Ship (ULBS). A hull form optimization method for reducing wave-making resistance and wave-breaking at the bow using nonlinear programming method (NLP) based on the Rankine source method is discussed. In the optimization process, wave-making resistance coefficient,surface integrals of the square of free surface elevations and free surface disturbance function D(x,y)-values are selected as the objective functions. Bow-body shape is optimized under the prescribed design constraints based on the present method. Numerical examples are given for unconventional ULBS. The three improved hull forms for the corresponding objective functions are obtained by optimal designs which indicate that the objective functions are reduced distinctly. In order to verify the present optimization method based on the potential solver, the flow characteristics around the initial and bow optimized hull forms are analyzed by using Computational Fluid Dynamics (CFD) analysis based on the Navier-Stokes (NS) solver. Comparisons of the computed resistance coefficients, pressure and velocity distributions of the initial and bow optimized hull forms are presented. It is confirmed that simulation results based on the viscous flow solver show reasonable agreements with the numerical results based on the Rankine source method for the bow optimized hull forms.

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In this paper, unsteady flow field around a 2-D oscillating wing is analyzed by vortex layer distribution method. We proposed some calculating formulae of induced velocity caused by trailing vortices. Calculated unsteady lift using by the vortex distribution that has been solved discretely well explained the experimental results.Flow simulation at the time-dependent is performed, and flow vectors are visualized. Then, flow field of the induced velocity is separated by bound vortex and trailing vortex. As a result, we showed the dependence of the frequency and amplitude to flow vector around oscillating wing. And, the generation process of trailing vortex has been elucidated.

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This is the first report of preliminary hull form planning for Non-Ballast Water Ship (NOBS) and Minimal Ballast Water Ship(MIBS). Ships having large block coefficient(C_B) like crude oil tankers and bulk carriers need huge amount of water ballast to keep proper propeller immersion and forward draught to operate in rough sea condition. Ballast water is necessary and useful for the safety operation, whereas it makes ship heavier and inferior in propulsion performance. And ballast water will need to be cleaned by the ballast water treatment system which is approved in accordance with IMO's guideline in the near future. A reduction of water ballast is also desirable to prevent ocean pollution. NOBS/MIBS has a unique hull form having V-shaped/convex bottom, and can keep sufficient draught to navigate safely on empty cargo condition even in rough sea without/with less water ballast. As a result of unique hull form, NOBS/MIBS has a very small midship coefficient in comparison to that of a conventional ship. Such unique principal particulars bring difficulties to investigate preliminary design of principal particulars for NOBS/MIBS.In this paper, the author proposes some simple procedures to estimate propulsive performance for NOBS/MIBS using neural network and measured data fitting. As the accuracy of these procedures and results are confirmed in the projects of NOBS/MIBS development, it can be the same level as that for conventional ships.

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This paper proposes a method that identifies ship motion parameters needed to a control system for an autopilot. The autopilot has the function of heading control and tracking control. In order to realize the function by automatic control, it is essential to identify parameters of dynamics of yaw and sway. The proposed method consists of ship motion models, identification models, evaluations of identified values, and identification algorithm. The ship motion models adopt first-order models that approximated second-order models derived from coupled motion between the yaw and the sway. The identification models have constructions based on the ship motion models and can apply practically. The identification algorithm uses a method that focused on minimum problem of multivariate function. Because the ship models have model error explicitly, the identified values are evaluated by the following response errors and the closed-loop stability. Finally, the proposed method verifies the validity by simulatins and full-scale experimental data.

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FOWTs, i.e. Floating Offshore Wind Turbines, are recently planned to be set in the offshore, where bottom-mounted type's one is not feasible, to generate natural resource electricity. One of the ways for FOWTs' application is that a wind turbine facility is mounted on a slender column type floater to keep buoyancy and stability in the sea, that is called as Spar type. In this case, the characteristic of VIM, i.e. Vortex Induced Motion, on the column type floater is concerned about to keep mooring safety of the FOWT. Then VIM characteristic on the column type floater was investigated using a huge experimental model in supper critical Reynolds number at the large towing tank in the National Maritime Research Institute, Japan. The results of the experiment were compared with ones of small similar figure models under lower Reynolds number, and the VIM amplitudes against reduced velocity parameter were clearly understood. Using these results the amplitude distribution relating to duration time for the huge experimental model is investigated having the effect on fatigue damage of mooring lines. These unique and precious results on the column type floater have important role for safety assessment on FOWT mooring lines.

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After the Tohoku earthquake tsunami in Japan, many evacuating options from a huge tsunami, e.g. tsunami tower, large building,moving onto hill, stronger breakwater, underground shelter and small lifeboat, have been proposed in recent years. In this paper, we have proposed and developed one kind of a large-sized tsunami shelter with mooring that is capable of accommodating at least one hundred people or more to evacuate from a run-up tsunami. The optimization for the shape of the tsunami shelter was also examined using Particle method, Smoothed Particle Hydrodynamics. The tsunami force acting on the desired shape was compared with that on the basic shape, e.g. a rectangular shape. The proposed tsunami shelter could be one of useful options for evacuating from a huge tsunami attacking near coastal area.

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The free-running model ship test is one of effective measures to estimate ship performance and response in various situations.However, since Reynolds numbers are quite different between model and full-scale ships, phenomena of model ship especially those concerning propeller load are not necessarily similar to those of full-scale. The authors developed an auxiliary thruster to assist a free-running model ships’ propeller. The auxiliary thruster consists of a duct fan, a signal amplifier, a load cell, and a PC. The PC can control the longitudinal force of the duct fan arbitrarily using feed-back data of the force measured by the load cell and instantaneous model ship speed. A prototype confirms through verification test basic capabilities and adequacy of the authors' design of the auxiliary thruster.

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Influence of side hulls arrangement for wave loads acting on cross deck of trimaran is investigated. We developed the prediction method for wave loads acting on cross deck of trimaran. The present method is based on strip method (STF method) and is not considering hydrodynamic interaction between main hull and side hull. And we carried out the experiment measured wave loads acting on cross deck of trimaran in head seas with side hulls position changes. Results show the vertical shearing force on cross deck increases and pitch connected moment decreases with shifting side hulls forward. And, it is confirmed that the present method can evaluate qualitatively influence of the side hull arrangement for wave loads acting on cross deck of trimaran in head seas.

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We developed the prediction method for ship motions of trimaran in oblique waves. Present method is based on STF method, and is not considering hydrodynamic interaction between main hull and side hull. To validate the present method, we carried out tank test measuring ship motions of trimaran in oblique waves. Results show that the present method gives good agreement with experiments in the case of zero ship speed, and that it can capture ship motions in the case of non-zero ship speed qualitatively.

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Duration of calm wave state or harsh wave state is an important factor for planning and designing offshore operation. The statistical characteristics of wave state duration, such as three days calmness ratio, is studied using long term reanalysis data. The spatial distribution of duration statistics for sea around Japan is illustrated through data analysis. We also attempt to reproduce the duration statistics by assuming a Markov process. Our assumption is verified by Markov Chain simulation. After considering multistage and high order Markov processes, a simple first order 2-state Markov process, provided the transition matrix is defined monthly, is found to be efficient to describe the desired duration statistics. The simplified stochastic process allows us to generate synthetic data of various lengths for further consideration.

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This paper discusses power cable loads for a floating ocean current turbine. The floating ocean current turbine is supposed to have unique motion characteristics, which causes unknown loads to the power cable. In this study, two severe situations and three candidates of cable configuration have been considered. In one of these situations, the cable shows unique motion due to bend & torsion moment. To confirm the accuracy of numerical calculation in this situation, calculation by two methods and an experiment are performed. In addition, theoretical analysis is performed to interpret the reason of the motion. The results show that the FEM analysis agrees well with the experiment, and that the cable motion is interpreted as energy shift from bending to torsion energy.Therefore, full scale calculation is performed using the FEM program. The results show that floater style with vertical connector is the most suitable cable configuration for the floating ocean current turbine and the maximum loads do not exceed 15% of allowable loads of the power cable even in the severe situations.

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When estimating the construction cost of ship structure in early design stag e, it is important to decide roughly the arrangement and scantling of structural member of mid ship section in a short examination time. The technique for determining the optimal structure of midship section using a genetic algorithm etc. has begun to be a pplied in actual design. However, these optimization techniques seem not to be able to obtain the optimal structure within practical computation time.Moreover, CSR (Common Structural Rule), which is published in April 2006 by IACS, requires FEM calculation for estimating the stress of double bottom member, such as bottom plate, inner bottom plate, transverse webs, and girders . If including FEM analysis directly in an optimal structural calculating program, it will require great computation time. In this research, FEM calculations for typical scantling of above members were performed and the response surface for estimating the stress of above members is produced. By including this response surface in the optimal design calculation using a genetic algorithm, the optimal structural calculation for the midship section was realized within a practical computation time. The availability of optimal calculation for structural members in mid ship section is presented by showing calculation results for Handy max bulk carrier.

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Fatigue crack propagation behavior under superimposed loading histories with several mean stress conditions is highlighted.Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) stress criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history for fatigue crack propagation. The parameter, which is based on the plastic hysteresis consuming in the vicinity of a crack tip,is applied to extract the effective loading for fatigue crack propagation and implemented into the numerical simulation code of fatigue crack propagation. Fatigue crack propagation tests under various superimposed loading conditions, which contain several constants and variable mean stress, are performed and comparison of fatigue crack propagation histories obtained from the improved numerical simulations with the measurements is performed. These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superimposed loading histories with different frequencies. Subsequently, practical fatigue strength evaluation based on the linear cumulative fatigue damage parameter were conducted to investigate the tendency of fatigue damage value affected by mean stresses.

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Recently, the risk of the brittle fracture is increasing because of expansion of the use of structure in low temperature, such as LNG pipe, ships in ice sea, and use of thick plate with upsizing of container ship. Although, CTOD design curve by WES 2805 in Japan and FAD by BS 7910 in United Kingdom are used as fracture evaluation of brittle fracture, unified and reliable criteria are needed in international community. For this reason, new fracture assessment criteria, CTOD-FAD, with feature of CTOD design curve and FAD is proposed in this study. CTOD-FAD is analytically and experimentally generated and verified for structure model with through thickness crack in this paper. As a result, it is proved that it is possible to evaluate more accurately by using CTOD-FAD compared with existing criteria for many types of structure.

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FEM analysis using fine-mesh shell models has been increasingly applied to the ultimate longitudinal strength analysis of ship's hull girder. However, the cost and elapsed time necessary for FEM analyses including FE modelling are still large for the design stage. Therefore, it is a common procedure to apply the Smith's method and to evaluate approximately the maximum longitudinal bending strength of a specified cross section. In this case, the effect of shear and warping stresses, which is significant in very large container ships, is not considered.The objective of this study is to propose a method of the analysis of ultimate hull girder strength under combined bending and torsion. The hull girder is modelled by a series of thin-walled beam elements and the average stress-average strain relationship of plate and stiffened panel segments under axial loads considering the effect of shear stress is implemented in the beam elements. The shift of instantaneous neutral axis and shear center can be automatically considered by introducing axial degree of freedom as well as the bending ones in the beam elements, and keeping the zero axial load condition. The proposed simplified method is applied to the test model explained in the 1st report. First, bending and torsional moment is applied to the beam model for a whole model within the elastic range. Then, the ultimate bending strength of cross sections is calculated applying the Smith's method to a beam element considering the warping and shear stresses. On the other hand, nonlinear explicit finite element analyses are adopted for analysis of the test model by using LS-DYNA. The effectiveness of present simplified analysis method of ultimate hull girder strength under combined loads is discussed comparing with the results of experiments and LS-DYNA analyses.

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Ocean current near Miyake Island was measured by an Acoustic Doppler Current Profiler equipped on a moored buoy system from March 2013 to March 2014 for an ocean current energy converter development project. Current variations associated with the Kuroshio,tide and wind,were found in the observed record and are described in the paper.Based on the Kuroshio axis location,periods with and without the Kuroshio intrusion into the island were identified. Spectral analysis of the current speed revealed that the diurnal variation is enhanced when the Kuroshio does not intrude.This enhancement of diurnal current variation is possibly related to the generation of the Island-Trapped Waves.By combining the fine-scale observation data and the long-term coarse-resolution Kuroshio axis data,inter-annual variability of the current power was estimated.The estimated current power is about three times larger than the one estimated from an ocean reanalysis.The result implies that coarse-resolution non-tidal numerical models possibly underestimate current power in coastal ocean.

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Recently, the movement of promoting renewable energy is increasingly growing in the world. In this paper, twin-rotor ocean current turbine is adopted as a new generation system by which Japan will be able to use strength of an island country. It is said that stable operation of ocean current turbine is possible basically because of the stability of ocean current. However, ocean current turbine may cause unstable motion at particular situations, while ocean current turbine is floating type and uses single mooring system.Therefore, the motions of the device at the transient state are estimated. As those states, time of startup, ocean current change, and accidents are selected. Especially, concerning the time of startup, a model experiment is conducted and the stable motion of the startup is demonstrated.

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Seafloor exploration and seabed resources development are important missions for solving international energy issues. The crawler driven ROV which is capable to do heavy works is considered as one of the probable systems for those missions and some have been developed already. It is well known that the movability of actual ROVs on the sea floor is worse compared with the terrestrial crawlers. Therefore it is important to make clear what conditions have to be satisfied for the stable running of a ROV on the sea bottom. The experimental investigation on the crawler based ROV's movability suggests that light weight ROVs are easy to run in bow up condition and sometimes turn over. The authors have shown the condition for the normal running of the ROV which moves on the horizontal and inclined flat water bottom by means of a simple dynamic model. In this paper, a method to estimate the ROVs' ability to climb up the bumps is shown and it is validated by model experiments. The ROV model has three sets of crawlers;the centered main crawlers are set horizontally, the fore and rear crawlers are movable just like the flipper of the pinball to climb up the bumps. The requirements for the design parameters of ROV to climb up the bumps such as crawler length, weight and displacement of ROV, location of gravity and buoyancy center, derived from present method agreed with the experimental results qualitatively.

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Recently, many subsea pipelines have been developed in busy port areas, including industrial ports, recreational areas, fishing areas, and other port facilities. Under busy ship traffic conditions, these subsea pipelines are likely to be exposed to the risk of damage by a dragged anchor or other dropped objects. In this paper, a model is proposed to estimate the dragged anchor accident frequency on subsea pipelines based on the concept introduced by Fujii. The proposed model is approached by estimating the number of dragged anchor candidates on subsea pipelines, Na, based on an analysis of the anchor stopping distance in a critical subsea pipeline area. The causation probability Pc is estimated using a Bayesian network method that is modified from the model of Det Norske Veritas (DNV) and Hanninen. Various factors are considered to estimate Pc, including the human factor, weather factor,technical factor, and support factor. Automatic Identification System (AIS) and Geographic Information System (GIS) data are combined to estimate the lateral probability distribution of the ship traffic around a subsea pipeline area. A case study of anchors dragging on the subsea pipeline in the Madura Strait of Indonesia is performed to demonstrate the implementation of the proposed model. The proposed model is validated by comparing the results for the estimated dragged anchor accident frequency on the subsea pipeline using the proposed model with the actual accidents recorded in the Madura Strait. The results of this validation analysis show that there is reasonable agreement.

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The author proposed "vertically movable tension leg mooring system" in the previous paper for the purpose that an offshore floating body subject to comparatively large static horizontal loads for its scale is moored so that the occupied plane area of the mooring system may become as small as possible. And its static mooring characteristics were discussed with model calculations to demonstrate the advantages compared with the conventional tension leg mooring or the catenary mooring. In this paper, the response of the floating body and the mooring system to waves is studied to investigate the dynamic effect of the massive template hung from the floating body in the proposed system. As a result, it is demonstrated that the dynamic effect of the mooring system on the wave exciting motions of the floating body is quite small when the system is properly designed. And it is found that the tension fluctuation could generate the slack and taut repetition in the windward side mooring chain which connects the sea floor anchor and the template hung from the floating body. Finally, some guidelines to reduce such phenomenon are shown based on the parametric case study.

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In order to mitigate the global warming, reduction of CO₂ emissions has become a great concern in the world. Carbon dioxide Capture and Storage (CCS) is a possible measure to curtail CO₂ emissions to the air while using fossil fuel energy, and is now broadly expected as an enabler for the coexistence of the existing energy supply chain and the deep reduction of CO₂ emission. The author et al. proposed 'CO₂ shuttle shipping and direct injection from the ship' for applying offshore CCS to Japan, whose advantages are mitigating the necessity of source-sink matching, the deep water application outside the coastal zone, the avoidance of large offshore facilities, etc. In this paper, the margin of the transport system in a large-scale integrated project is discussed. The intermediate buffer capacity at the connection to the plant on land, the additional capability of ship transport, etc. as the necessary margins are preliminarily estimated considering the realistic wave data in the sea near Japan.

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The paper is concerned with a just-in-time scheduling problem of block-assembly lines conveyorized for tandem construction of a pair of ships in a shipyard. The blocks fabricated are stocked for pre-fitting and painting works and they are provided to pre-election area. It is not easy to schedule the block-assembly lines in order to avoid the stock overflow and to realize the just-in-time arrivals to the pre-election area. In a conventional scheduling of push type, there are many idling days in the stocking period. Therefore the problem can be formulated as minimizing these idling days such that constraints of conveyor plates and stockyard capacities are satisfied under a dispatching rule for assembled order. In the paper, a new method to solve the problem is proposed, which requires a linear inequality represented by Max-Plus algebra. A pull-type scheduling is obtained as its maximal solution. Based on the scheduling results applied to the shipyard, the effectiveness and limitations are discussed.

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During the ship design, designers have to deal with all pipe-routes in order to generate practical piping layouts composed by the minimum cost value (i.e. interference with obstacles, the length of each pipe-parts, etc.). However, the routing task requires huge work hours because there are many regulations and functional design rules in the field. In this paper, we propose an automatic routing system for multiple pipe-routes. The proposed system aims to solve the complicated multiple routing problems and to improve the design work efficiency. In the routing problem for pipes, there are two major factors having the significant influence to final routing designs: the order of routing search and the selection from candidates of pipe-routes. The routing system is capable of handling these two factors by adopting Touch and Cross method and simulated annealing method. Touch and Cross method is routing algorithm to find candidates including no interference with each path. Simulated annealing method is one of the optimization methods to find a global optimum of a given function in a large search space. By combining these two methods, the routing system can reduce the influence of the search order and the selection problem. Therefore, it is able to find suitable pipe-routes automatically though there are no guarantees to find the best layouts. The routing system also uses Dijkstra's method as a routing method to find the optimal route efficiently. The performance of the system is demonstrated through several simulations.

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The performance of the product and the design time are influenced by the design process. Therefore, it is very important to advance the design in an appropriate design process. However, the design process generally relies on the experiences of the designer and it is difficult to examine their characteristics. In this study, design process of ship principal particulars is optimized by using the optimization technique. Moreover, the features of the optimized design processes are examined. Characteristics of this paper are following points; ・ The optimum design process is generated by using the Wildcard Genetic Algorithm which can deal with the uncertainty of product information. ・ By executing the optimization, two kinds of design processes are generated i.e. performance valuing process and feasibility valuing process. ・ Characteristics of the optimized design processes are analyzed by using our design support system in which dependency of the information and changes in the variation range of constraints and objective functions according to the progress of the design are visualized. In this paper, optimization method of design process and the results of the optimization are shown. Moreover, overview of our design support system and features of the optimized design process are discussed. As a result, effectiveness of the proposed system is confirmed.

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