In the entry/reentry operation of the flexible marine riser, the operators are required to connect its lower end to the blowout preventer at the seabed quickly with both its top connected angle and its deformation controlled. Because of the hydrodynamical force and the flexibility of the riser, it is very difficult for them to operate it correctly. In the paper, we consider the entry/reentry control problem of the flexible marine riser. Firstly, the governing equation of the flexible marine riser is formulated and transformed to the finite dimensional equation by the mode expansion method. Secondly, for the control problem, we apply LPV (Linear Parameter Varying) technique taking the varying parameter as its upper end velocity which determines the hydrodynamical damping force. Finally, the effectiveness of the LPV technique is shown by numerical simulations, compared with the results by the LTI (Linear Time Invariant) H_∞ control

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Sugi bark sorbent (SBS), which is recycled waste, is comparable to commonly used petroleum products in performance and cost and has lower environmental loads. It has been commercially produced since 2001. For the purpose of reducing total environmental loads in the oil recovery, we investigated biodegradation disposal of SBS after use (after adsorbing oil), instead of incineration disposal. It was confirmed that the oil content was reduced from 14,300±1,600ppm to 1,500±500ppm after 164 days-period (36m³ site), and reduced from 8,600±900ppm to 1,400±400ppm after 170 days-period (100m³ site) in a biodegradation experiment using Bunker C in the bark compost (background : 430±140ppm).

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A database was newly constructed for the purpose of investigating winds and waves around Japan. The database is based on numerical forecast data for 10 years. The forecast data were composed of significant wave height, significant wave period, peak wave direction, mean wind speed and mean wind direction. They were calculated at intervals of two minutes in space and twelve hours in time.
In this paper, the statistical characteristics of the database are compared with several existing databases and their features are clarified in two sea areas, one is facing the Pacific Ocean and the other is in Japan Sea as a closed sea area. Using the advantage of high spatial resolution and a large number of data in the database, the detailed distributions of winds and waves in an average and in extreme conditions around Japan are also examined. In addition to the examination, evaluation of statistical characteristics among Japanese navigation areas is carried out.

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A numerical scheme was developed to simulate the Vortex Induced Vibration (VIV) of a flexible riser. To validate the accuracy of this numerical scheme, some experiments were carried out. In experiments, the top end of a hanging riser model was forced to oscillate periodically or irregularly in an uniform flow. The three-dimensional motion of the model was measured four times at every experimental condition in order to analyze and discuss the stability of the VIV. Good agreements between the amplitudes and frequencies of VIV are confirmed in those comparisons.

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The paper is concerned with an automatic position adjustable elevator to realize easy and safe passage between a workboat and a floating structure or an ocean platform. The elevator attached to the workboat is controlled to reduce the relative displacement between the workboat and the structures. The displacement is measured by image processing technique and is sent to the controller of the elevator. Model experiments were carried out to verify the performance of the system and successful results are shown. In addition, robustness of the image processing system is discussed.

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The reentry operators of the flexible marine riser are required to connect its bottom end to the blowout preventer at the seabed with both its top connected angle and its deformation controlled. Because of the hydrodynamical drag forces and the flexibility of the riser, it is very difficult for them to operate it correctly. In the previous paper, for the problem, we have applied LPV (Linear Parameter Varying) control techniques and shown its effectiveness through numerical simulations. In the paper, we carry out the reentry experiment in the towing tank at the Research Institute for Applied Mechanics, Kyushu University. We control the upper end of the riser model which is made of polyethylene and Teflon (PTRE) using parallel mechanism type forced oscillator in order to move the bottom end of the riser to the target point. In the experiment, the riser model motion can be captured by 14 CCD cameras. These motion data are analyzed using image analyzer software ”HALCON”. Finally, the experimental results can certify the good effectiveness of the LPV techniques for the reentry operation, copmpared with the LTI (Linear Time Invarinat) control.

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This paper propose the new method called “Random Pattern Refractometry Technique” which is possible to measure the unsteady density fields in stratified flows. In this method, the gradient vector fields of the refractive index can be derived from measured displacements of random pattern between two pictures captured before and after density distribution changed. And density fields can be reproduced by integration of gradient vector field. It is mathematically equal to reconstruction of the surface height from the gradient field problem. We can solve this problem by composing the Poisson equation using measured gradient vectors in experiments. To solve this equation, the source term had been computed from the divergence of measured gradient vectors and discretized by finite difference method or Fourier transform in previous studies. But these solutions have a common problem that the errors of reconstructed results further increase by constituting the source term from the differential of gradient vector with the measurement error. In this paper, we propose a new idea using derived solution of the Poisson equation that source term is assumed as unknown function from potential theory. The derived solution of Poisson equation shows that the surface height can be obtained if strength of each source in the field is determined. Since the number of gradient values is twice as that of source intensities, we can determine their strength by making overdetermined linear systems from the condition that gradient vectors from the derived solution corresponds to measured ones. And, we can expect an effect to reduce the impact of measuring errors when solving these overdetermined linear systems with least squares method. We validate this method by applying to simulated data and observation data from a lock-exchange flow.

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Recently the amount of trade between China and Japan has been increasing. The trade value has grown by about 920% from 18.2 billion dollar in 1990 to 168 billion dollar in 2004. This paper presents a ship design procedure and implementation to integrate the logistic trends of the future and vessel design between China and Japan. To estimate the future logistic trends, authors made regression equation for trade value on per capita GDP of China and Japan. Several types of fleets were designed by a method which calculates the most efficient specifications depending on the travel speed, and were evaluated by the net present value of each fleet. Authors designed fleet between China and Japan, especially between Shanghai and Tokyo. And under some assumptions, the system provided a result that the fleet with four 25-knot ships offers the highest value of investment.

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We propose a new navigation system to decrease fuel oil consumption and CO₂ emission from ship. To decrease them it is important to avoid rough seas and to reduce the speed of ship. Therefore the system provides not only an optimum route but also an optimum speed of the ship. On the other hand schedule of voyage is generally constrained, so that weather forecast and ship responses must be considered in the system.
In this paper, simulations on a container liner in trans-Pacific route are demonstrated using the system. Concerning the schedule keeping, accuracy of weather forecast must be examined. The influence on the system is evaluated using two types of weather data; one is the forecast at departure and the other is the weather data set extracted from the sequential forecasts of every 24 hours. From the simulations it is found that the fluctuation of fuel oil consumption caused by updating the weather forecast is much smaller than the reduction of the fuel using the system. However, from the viewpoint of ship safety, it is necessary to execute the system again whenever the weather forecast updated.

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Tramper allocation is important and difficult work operation because it affects heavily on transport efficiency and stability although a lot of factors must be considered carefully and properly. Some information technologies are partially used in data collection, display and editing, but planning itself is done by human resources. Provided that high performance tramper allocation plan be generated automatically by using computer program, it is very useful not only for labor saving but also for seeking further enterprise-level efficiency and rationalization through various analysis. Notwithstanding above benefits, transport system dealt with real business is so complicated and large in scale that it is highly difficult to replace tramper allocation operation with computer algorithm and solve it within the time suitable for practical use.
In this paper authors tries to mitigate above difficulties by using Genetic Algorithm (GA), one of heuristic methods, and by using logistics simulator to evaluate each chromosome's score (fitness) precisely. First, we develop allocation algorithm and analysis system, secondly we apply it for a small model to observe its attribution, and lastly apply it to transport system modeled with real ship operator and assess the feasibility of our approach. We could conclude that our approach is applicable, and introducing heuristic database is useful and sometimes indispensable.

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Transpacific trade grows 10% per year and shipping companies have to consider the introduction of new transportation systems to adapt to this rapidly changing business environment. The changes of the freight flow and the competitiveness of the new business are major concerns when the new transportation system is introduced. Therefore, in this paper, we establish a discrete simulation model that the cargoes' choice of transportation route is expressed in logit model to evaluate the effect of new transportation system. The parameters of the model are estimated by the PIERS data of August 1999. The simulation result is compared with the PIERS data and it is shown that our model reproduces the real situation of freight flow well. The case that the new liner connects nonstop from Hong Kong to Los Angeles / Long Beach in the shortest time is discussed, and our simulation model proves that new service is competitive.

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As the wind power is now considered as one of the most promising renewable energy resources, the total amount of electricity produced worldwide by wind-power generators is increasing quite rapidly. In Japan, since land spaces suitable for wind-power generations are quite limited, the feasibility of wind-power generations in offshore areas is now being studied extensively. Among various possible types of offshore wind-power generations, a floating wind farm, which consists of large floating structures and an array of wind-power generators mounted on each of the floating structures is considered to be an adequate type for Japan because the water depth tends to become large steeply even in the close proximity of shores. It is known that, in such a floating offshore wind farm, the construction cost of the floating structures, on which an array of wind-power generators are to be mounted, accounts for a major part of the total construction cost. It is therefore quite vital for the reduction of the power-generation cost that the number of wind-power generators mounted on a unit area of a floating structure could be increased. On the other hand, however, a larger number of wind-power generators per unit area of a floating structure usually results in the lower amount of average power produced by each generator, because the wind speed incident to power-generating blades tends to be reduced due to the shielding effects among the congregated wind-power generators.
In the present study, the shielding effects among the generators in an offshore floating wind farm are investigated through extensive experiments and the trade-off effects on the generation cost due to the increase of the number of generators mounted on a unit area of a floating body and the increase of the shielding effects among generators are quantified. It has been found out through the experiments that the interaction effects between adjacent wind-power generators when they are placed side-by-side against wind direction are much smaller than generally conceived, and thus wind-power generators could be mounted in an offshore wind farm with significantly higher density than that of conventional wind farms.
Finally, an offshore floating wind farm free from the shielding effects among the mounted generators is proposed.

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Air pollution caused by the generated metallic fume during the progress of welding in a fabrication shop is one of unavoidable issues for labor health. Especially, a worker is likely to be exposed to high concentration of welding fume in semi-enclosed spaces such as cubic blocks under construction. For setting to cope with the pollution-control, it is necessary to take suitable measures considering the diffusing aspect of welding fume in a cubic block. However, this issue has the problem in which a ventilating way for purging fume should not disturb the welding arc and the shielding gas.
In collaboration with the measurements of distributional concentration of welding fume during manufacture of cubic block, the turbulent diffusing aspect of fume is numerically analyzed using the viscous eddy model in the condition of various ventilation systems and the way of low fume generation. Then, the effect of the measures for decreasing fume concentration on the working site in cubic block is investigated evidently on the base of calculated results.

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A methodology to apply the Design Irregular Wave to ship structural design was studied in the present paper. The Design Irregular Wave is an irregular wave train which is comprised of intentionally superposed regular waves to realize a maximum of a certain ship response in a given short-term sea condition. In order to apply the Design Irregular Wave to ship structural design, a design short-term sea condition has to be fixed firstly. The regular wave components of Design Irregular Wave is extracted from the wave spectrum of the given short-term sea condition. Frequency range and the phase angle of the regular wave components are fixed based on the linear response calculations. Simulating the nonlinear ship response in the Design Irregular Wave, the maximum response can be estimated. Problems in producing the Design Irregular Wave were discussed in the present paper; that is, how to determine the significant wave height and the mean wave period of short-tem sea condition, and how to confine the number of regular wave component. Example calculations were performed on vertical wave bending moment of S175 container ship. Simulating linear and nonlinear ship responses in Design Irregular Wave, maximum wave bending moments were estimated. The results were compared with the bending moment of 10^-8 and 10^-6 occurrence probability obtained by long-term predictions and also the design values provided by IACS unified rule. It was found that vertical wave bending moments relevant to a design value can be estimated by using Design Irregular Wave.

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It's getting more important to transfer knowledge from elder experts to young engineers especially in shipbuilding industry in Japan. We developed knowledge transfer system based on UT-ESS (University of Tokyo Educational Software for Shipbuilding) and proposed a method to acquire knowledge of elder experts using the developed system. The system describes design process as workflows and design documents are associated with tasks in workflows. The association between design process and design documents is described by metadata based on semantic web technology. The proposed method is evaluated through a case study of knowledge acquisition in basic design department in four shipbuilding companies.

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In a hot season with skylight, the storage of body heat during an operation at an exposed working place causes the deteriorating work efficiency and the physiological defect. Therefore, it is necessary to keep the suitable working environment by taking measures for the exclusion of heat storage of worker's body corresponding to the magnitude of working load.
In first report, the formula on heat storage of human body considering the effect of sunshine was established. And this report describes that the thermal criterion of working environment is defined by merging thermal environment factors, in order to judge the allowable threshold of work and to settle on the thermal-control measures. Moreover, the contour line of thermal storage is proposed for the estimate of effects on heat-measures of every sort.

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The residual deformation induced by welding processes becomes a cause of repair work at the subsequent process. Therefore it is necessary to manage the assembly of welded structures by estimating accurately the welding deformation considering welding conditions, welding length, and structural dimension, etc. Until now, theoretical, experimental and practical studies have been carried out widely, and then the prediction of the welding deformation can be done accurately by using FEM analysis now. However, technical knowledge is required for the analysis, and long hours are necessary to calculate the deformation, because thermal elasto-plasticity FEM analysis is usually required in order to ensure the accuracy of the estimation.
Though the elastic analysis is applied generally in order to predict the welding deformation easily and practically, in this study simplification of the prediction was done using neural network model. At first, thermal elasto-plasticity FEM analysis was carried out for the fillet welding of a T-type build-up structure, and the relationship between welding conditions and welding deformations (transverse shrinkage and angular distortion) was studied. Next the neural network by back propagation method was programmed by C language, and the FEM analysis results were given into the program as the teacher data. Then, the transverse shrinkage and angular distortion can be output by this program, if the welding conditions and member dimensions are input. This program would be able to estimate the welding distortion of joints with different dimensions and welding conditions in a simple manner.

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This paper presents an automatic design method for pipe arrangement. A pipe arrangement design problem is proposed for a space in which many pipes and objects co-exist. This problem includes large-scale numerical optimization and combinatorial optimization problems, as well as two criteria. For these reasons, it is difficult to optimize the problem using usual optimization techniques such as Random Search. Therefore, multi-objective genetic algorithms (GAs) suitable for this problem are developed.
A pipe is characterized by both a pattern of generation and numerical parameters. The former describes the way the pipe bends and the latter details the length of the straight parts. For this reason, a combination of the pattern of generation and the numerical parameters is used for the solution representation and a new method of crossover is proposed that takes into account interference with obstacles. As the number of pipes increases, it becomes rapidly more difficult to find feasible solutions where pipes do not interfere with each other. Therefore, two modification operators that transform infeasible solution candidates into feasible ones are introduced. One operator modifies the pipe having a lot of interferences with other pipes so that it will not interfere with them, and the other is related with the operation that modifies the pipe that travels through obstacles. Although there are cases in which pipes cannot completely avoid obstacles in practical designs, this situation is taken into consideration by this design process. The proposed method for optimizing a pipe arrangement efficiently is demonstrated through several experiments, and remarks are provided for applying this methodology to a practical pipe arrangement design.

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The ship hull form fairing is one of costly tasks in ship hull design stage. Because the fairing task operators must be trained for a long time to acquire the skills and it is done with manual procedure even though the 3D CAD system is implemented. The present study investigates an automatic fairing method for ship hull surface which is created with the combined Coons patch. In past researches concerned with the automatic surface fairing technique, the fairing is carried out by minimizing the unfairness function of the surface with optimization method. The unfairness function is usually defined by using physical property of surface such as strain energy or by using geometrical property represented by surface curvature. However, it would appear that minimizing the strain energy of the surface sometimes changes the hull form characteristics which should be maintained. On the other hand, most of existing unfairness functions based on surface geometrical property are defined for the surface which have continuous curvature in whole area and are not applicable for the combined Coons patch surface which we use for hull surface creation, because Coons patch surface do not have continuous curvature on the boundary of the patches. Therefore the present study defines several unfairness functions with geometrical property of the surface which can be applicable to combined Coons patch surface and minimize it to obtain a faired hull surface. The present method is applied to the fairing at aft part of tanker type ship. The obtained hull surface after the fairing is smoothened compared with before the fairing and it is considered that the rough fairing is carried out successfully through the present method.

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The authors have established an accurate good analysis technique for presuming the experimental value of the stress and the deformation caused by phase transformation through the finite element method. Because it is necessarily method to prevent from the quenching crack which is dominated by stress and deformation caused by phase transformation accompanied with the heat treatment. By using the steel transforming to fully martensite during the quenching, the experiment of heat cycle, residual stress and transformation were carried out, followed by the comparative study of the experimental and the numerical analysis value concerned with the residual stress and the deformation. Consequently the notable factors were made clear on the numerical analysis. As a result, the following conclusion was obtained. The accurate good analysis of the temperature change, the linear expansion coefficient by considering the phase transformation strain and the yield stress of each phase during quenching process are important to analyze the phase transformation stress and the deformation by the numerical analysis.

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In previous papers ^{1, 2, 3, 4, 5)}, the author demonstrated the application of the learning feed-forward control (LFFC) system for multivariable systems and the effectiveness of the LFFC system by on-board experimental results. The LFFC system was thus confirmed to be suitable for use as the control system since it followed the desired values and compensated for continuous variations in wind disturbance.
In this paper, focusing on the approach and berthing control, which is one of the most difficult problems in automatic maneuvering, the author attempts to design an approach and berthing control system which can act as the ship operation support system. The feasibility and the problems of this control system are discussed based on computer simulation. If considered from the viewpoint of control, then it can be thought that approach maneuvering is a tracking control problem, whereas berthing maneuvering is a set-point control problem. Accordingly, it is appropriate for the control method to be changed at each maneuvering stage. The author herein discusses whether or not the LFFC system is suitable for use as the automatic approach and berthing control system, by itself.
The computer simulation results show that the automatic approach and berthing control system based on the LFFC system is adaptive for changes in the dynamic characteristics of the object ship at each maneuvering stage, however, it is necessary for further improvements to be made in the wind compensation system.

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Influence of outrigger position of a high speed trimaran on the wave-induced motion was investigated. The trimaran is composed of the center hull with L/B = 8.0 and B/T = 3.57 where L, B and T denote the length, breadth and draft respectively, and the outriggers with l/L = 0.375 where l denotes the outrigger length. Using the trimaran model with 2.0m in ship length, tank test was carried out to capture the ship motions in regular head waves. The wave-induced motions of the trimaran, as a whole, become larger than those of the center hull which is regarded as a monohull ship. With shifting the outriggers rearward, the motion amplitude increases in the long wave-length range and decreases in the short wave-length range. Strip method excluding the hydrodynamic interactions between center hull and outriggers can capture qualitatively the change of the wave-induced motions with the outrigger position changes.

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Influence of outrigger position of a high speed trimaran on the maneuverability was investigated. The trimaran is composed of the center hull with L/B = 8.0 and B/T = 3.57 where L, B and T denote the length, breadth and draft respectively, and the outriggers with l/L = 0.375 where l denotes the outrigger length. The captive model tests were conducted at F_n = 0.35 in towing tank of Hiroshima University to capture the hydrodynamic force characteristics of the trimaran with 3 different outrigger positions. Baesd on the force characteristics, maneuvering simulations were carried out. We found that with shifting the outrigger position rearward, the turning circle becomes large and the course-keeping ability is improved. The change comes from increase of lateral resistance at the stern part.

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The authors have elaborated an evaluation method of ride quality using facial expression. They introduced the concept of Fourier Descriptor (FD) to characterise the outline of facial factors such as eyes and mouth. Two facial-expression analysis models were proposed so as to relate one's facial expression with his/her psychological state as fundamental emotions. One was modelled for estimating subjects' own emotion from their facial expression. The discriminant analysis was applied to classify facial expressions into the six fundamental emotions, and the optimised model with a comparatively small number of FDs could discriminate them with a high discrimination rate. The other was modelled for estimating emotions by other people from subjects' facial expression. Fuzzy measure theory was here introduced to model human ambiguous judgement in evaluation. In this paper, these facial-expression analysis models were applied to subjects' facial expressions who actually felt sick in motion-exposure experiments using a ship-motion simulator and in a high-speed passenger craft. To conclude, facial expression can be an objective physiological index of motion sickness and the proposed models were found to be useful to evaluate ride comfort from facial expression.

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The purpose of this study is to establish an evaluation method of ride comfort of high-speed passenger craft. For the conventional displacement-type ships, vertical acceleration was used to be analysed so as to estimate ride quality of vessels or the motion sickness incidence (MSI) which represents the percentage of a group who will vomit during the voyage. This is because the principal vertical motion of most ships is close to 0.2 Hz where motion sickness sensitivity is considered to be at a maximum. Various types of stabilizer have been designed to reduce the rolling motions of ships. However, it is pointed out that lateral acceleration cannot be negligible for evaluating ride comfort of especially high-speed catamaran. Effect of vertical motion might be rather small because oscillatory frequencies of vertical motion are somewhat higher. Sway motion of high-speed crafts therefore comes to be a research subject overseas too. The authors have conducted experiment on ride comfort of a high-speed craft. Ship motion and subjects' psychological and physiological responses were measured in a high-speed craft running across the Bay of Osaka. The present paper deals with analysis of ship motion and proposes an evaluation method introducing the concept of the “frequency weighting” defined in ISO 2631-1 (1997).

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A time-domain hybrid method developed by authors is applied to estimate motions and added wave resistance of ships advancing in waves. The fluid domain around a ship is decomposed into the near field and the far field, and the Rankine panel method and the Green function method are applied in each field. Combining both solutions on the artificial surface makes it possible to satisfy the radiation condition exactly and to take the nonlinearities of ship motions and the free-surface into account. The estimation accuracy of the method has been already confirmed in regard to hydrodynamic forces and wave fields in the previous studies.
In this paper, we apply the method to simulate ship motions in regular head waves and also to estimate added wave resistance for four ships; two modified Wigley models, Series-60 (C_b = 0.6) and Series-60 (C_b = 0.8). The computed results are compared with experimental results and another numerical results by the strip method and the enhanced unified theory. Through the comparison, it is confirmed that the present hybrid method can estimate ship motions and added wave resistance with high accuracy for any cases.

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Wake wash is one of the serious problems for high speed ships, because it may cause damage on the coastal aquaculture using rafts or nets. Since some important parts of high speed ships are catamaran, a CFD code for the catamaran ship is developed. It can properly evaluate wave resistance of both symmetric and asymmetric demi-hulls with consideration on wake wash. The code is applied to the development of a catamaran type commuter ship operated for domestic services. Wave resistance and wake wash characteristics are demonstrated to be improved by the numerical simulation. The towing tank experiment for the evaluation of wave resistance and wake wash is carried out for the verification. It is clarified that the improved hull form shows lower resistance with smaller wake wash at higher Froude number when the displacement is reduced by 30%.

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Recent huge amount of CO₂ discharge and the diffusion of detrimental substances by the excessive use of petroleum resources have brought the serious problem of an earth scale such as the global warming. It has been the world common subject for every work of the future to take account of the preserving natural environments. There are several solutions for taking place the petroleum energy. One of them is the wind energy. In 1980's when the petroleum price jumped up with the twice oil crises, the use of wind power was re-examined. Many kind of modern sailing rigs and new concepts of sail-equipped ships were proposed. These researches are summarized in the international symposiums by RINA^{1), 2)}, and some of them were successful projects among them.
Although the purpose of such sail-equipped ship is obviously the use of the above-mentioned wind energy, it is also empirically known as a secondary effect that the rolling of ship can be reduced by the sail. This comes from the air damping force of sail since the inflow angle of the sail changes with the rolling and this change acts on the direction which decreases the rolling. From this fact, the rolling can be more reduced if the angle of a sail is well controlled against the rolling.
In this paper, the roll-damping mechanism is solved based upon the aero and hydrodynamics, and then the control technique of sail angle for decreasing the rolling for various wind directions is proposed, where the sail angle: Δδs is simply controlled as Δδs = kφ, but the polarity of control gain: k must be changed with the wind direction and average sail angle. According to this method, the validity and use of this control have been checked by the model experiments. As the results, it is found that the rolling angle can be remarkably decreased when the ship is sailing against the oblique wind and wave.

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A new method to estimate longitudinal and lateral wind forces, and yaw and heel moments for ships is presented in this paper. The proposed estimation procedure is based on physical component models of the wind loads acting on ships. It is assumed that the wind forces consist of longitudinal- and cross-flow drags, and lift and induced drags. The wind moments are obtained by crossing the moment lever to the lateral wind force. Each term of the components in the estimation equations is decided by the regression analysis using many wind tunnel experimental data. This estimation method has the same accuracy level to the authors' previous method, which was more accurate than the earlier reported prediction methods, and has more rational and simple forms of estimation rather than the previous one.

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From economical and safety aspects the assessment of steady-state cruising performance of ships under heavy wind loading is very important. A large passenger ship and a PCC with a very large hull and superstructures above sea level, which are greatly affected by wind, are treated in this paper. The assessment of the ship performance is conducted using a computational calculation method. The steady-state equations are formulated based on the MMG model for ship manoeuvring simulation to obtain the steady ship conditions like drift, heel and rudder angles. The wind loads on those ships used in the calculation, including the effect of boundary layer profiles of wind and the heel effect of the ships, are estimated by the method that the authors proposed. As a result, some important characteristics of the resistance increase in steady running condition in heavy wind for the ships are clearly revealed.

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The cavitation phenomena, such as tip vortex cavitation, leading edge vortex cavitation or sheet cavitation on a propeller increase vibration and noise. In order to reduce vibration and noise, the extent and the collapsing behavior of cavitation should be controlled. In this paper, three types of propellers were designed; a standard propeller, a straight leading edge propeller (SLEP), and a backward tip rake propeller (BTRP) having the tip rake to the pressure side. With these model propellers, open water test, the observation of cavitation by means of a high speed video camera, and the measurement of the pressure fluctuations were conducted. For all three cases, sheet cavitation was involved into tip vortex cavitation around the blade tip and for the case of SLEP, sheet cavitation was separated on the blade surface. For the cases of SLEP and BTRP, the blade surface was attacked by cloudy sheet cavitation connected with tip vortex cavitation and this area was eroded. And the propeller open efficiency of SLEP was better than that of the standard propeller and the pressure fluctuations of BTRP were lower than those of the standard propeller.

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Modern large passenger ships usually have a buttock-flow hull shape with flat stern and large bow flare. Such shapes cause significant variations of the stability in waves. In the present study, measurements of roll motion of a scale model of a large passenger ship of 110,000 GT with such a hull shape in beam regular waves are carried out in a towing tank. The results demonstrate that when the ship has no bilge keels, large parametric rolling with 27 degrees of maximum amplitude appears at about half period of the natural roll period in 5m of wave height. The effects of wave height and roll damping on appearance and magnitude of the parametric rolling in beam seas are experimentally investigated.

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The PID control theory is very often used in practice in the field of shipbuilding; it is not an exaggeration to say that the use of other control theories is rare. Even though the theory possesses a defect in that it is not able to rationally design a multivariable control system, it nevertheless offers many advantages.
In contrast, the optimal control theory has rarely been utilized for designing the ship-maneuvering control system. The main reason for this is that the relation between gains and responses in optimal control is not clear despite the many advantages provided by state-variable feedback; thus, it is very difficult to finely tune the gains. From the viewpoint of practical use, it is important that the relation between gains and responses is crystal clear.
In this paper, the feedback-gain setting for control of a single input-output system that operates the heading angle by the rudder is discussed on the basis of the root-locus technique. The system is attached to three state-variable feedback loops similar to the optimal regulator, and the relation between gains, response speeds and ship speeds can be derived. Consequently, it is now possible for the gains designed for a linear time-invariant system to be applied to a time-varying system.

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Corrosion of structural members of ships is one of the main problems for ship safety.
In this report effect of grooving on static strength of corroded fillet welded joints for ship structure is investigated with experimental result and FEM analysis. Four points bending (4PB) test was conducted with T-shape specimen (TSS) without bracket plate against lateral deflection of web plate and the test result was compared with 4PB test result using a half size model specimen of hold frame of Cape-size bulk carrier (SMS). It is mainly obtained that in case of grooving in compressive stress region applied by bending moment, at fillet welded joint, maximum load occurs at lateral deflection of web plate and grooving width and grooving depth effects maximum load. There is no precise difference between 4PB test result with TSS and that with SMS. There is precise effect of inclined angle (20°) on the maximum load and is a little effect of Face-shape on it.

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The purpose of this research project is to establish a method of evaluating the effect of pitting corrosion with a circular cone shape on local strength of hold frames of bulk carriers. In the present study, an empirical formula is proposed based on the tensile test results conducted in the previous study. In the formula, tensile strength reduction due to pitting corrosion is expressed as a function of DOP (degree of pitting intensity), pit diameter and original thickness of pitted plates. It has been shown that tensile strength of relatively small plates with pitting can be well predicted by the formula. In order to check the applicability of the formula to wide plates, a series of tensile test with wide specimens having artificial pits has been performed. It has been found that when diameter of all the pits is the same, prediction results of the tensile strength of wide specimens with artificial pits are conservative, and when pits with different diameter coexist, prediction of the tensile strength using average pit diameter give a little optimistic (non-conservative) results.

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The aim of this research project is to establish a method of evaluating the effect of pitting corrosion with a circular cone shape on local strength of hold frames of bulk carriers. In the present study, an empirical formula for predicting ultimate strength of plates with pitting corrosion is proposed based on the results of FE analyses with pitted plates under uni-axial compression. In the formula, equivalent thickness for ultimate strength of pitted plates is expressed as a function of DOP (degree of pitting intensity), pit diameter and original thickness of pitted plates. Equivalent thickness predicted by the proposed formula has been compared with the results of FE analyses with pitted plates under various loading conditions and it has been revealed that the proposed formula could well predict the equivalent thickness for ultimate strength of pitted plates under uni-axial compression, shear, bi-axial compression, combined uni-axial compression and shear, combined bi-axial compression and shear, in-plane bend and combined in-plane bend and compression.

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In this paper, emphasis on physical meanings of hysteresis loops denoting a relationship between loads and strains near the fatigue crack tip, variations of the tensile plastic load zone in loading and the compressive plastic load zone in unloading are studied respectively under various test conditions, and the effects on acceleration, delayed retardation and non-propagation during fatigue crack propagation are also studied. It can be speculated that the compressive plastic zone at the crack tip has some effects on fatigue crack propagation. Furthermore, it is known that the crack closure phenomenon ends after the compressive plastic zone appears but before the minimum load. Therefore, a parameter P_CF called the crack closure finish load is presented for evaluating behavior of fatigue crack propagation.

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In ship structures, fatigue cracks may initiate at the intersection between face plates of the longitudinals and web stiffeners attached to the transverse girders. These cracks may propagate in web plates of the longitudinals and may penetrate inner or outer skin plates, which have a possibility to cause the loss of oil and/or water tightness of critical compartment boundaries. Therefore, cracks must be detected by inspections before they reach the critical length. In the present paper, a simulation program is developed for multiple cracks propagating in a 3-dimensional stiffened panel structure. The simulation program can predict fatigue crack lives and paths taking into account the interaction of multiple cracks, load shedding during crack propagation and welding residual stress. The characteristics of fatigue crack propagations of ship structures are investigated by using the developed numerical simulation program and experiments. It is found that the crack propagation behavior in the ship structures may significantly change depending on the loading conditions, structural details and residual stress distributions.

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Due to the accuracy and the efficiency of hexahedral elements, automatic hexahedral mesh generation has a growing demand for finite element analysis. For this problem, several algorithms have been proposed by many researchers. However, reliable automatic hexahedral mesh generation has not been established yet. In this paper, a new strategy of fully automatic hexahedral mesh generation is proposed. In this strategy, the prerequisite for generating hexahedral is quadrilateral surface mesh. From the given surface mesh, combinatorial dual cycles (whisker sheet loops for whisker weaving algorithm) are generated to produce hexahedral mesh. Since generating good quality hexahedral mesh does not depend only on the quality of quadrilaterals of the surface mesh but also on the quality of the dual cycles generated from it, the method to remove self-intersections from dual cycles is proposed. The surface mesh modification procedure of the proposed method has three basic steps. These steps are (a) face collapsing, (b) new face generation and (c) template application. Next, automatic hexahedral mesh generator by the improved whisker-weaving algorithm has been developed in this paper. By introducing nodal placement technique, it becomes possible to generate hexahedral mesh with fewer bad-quality elements. Several examples will be presented to show the validity of the proposed mesh generation strategy.

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We still have experienced cargo oil spill from a struck D/H(double hull) tanker like the accident case of “Baltic Carrier (at Denmark in 2001)”. “Buffer Bow” has come to be considered as an innovative strategy following after D/H system to prevent marine environmental pollution. The mission expected to buffer bow is “minimizing the damage on the struck ship” and thus “decreasing the risk of oil outflow from struck D/H tankers” when it encounters collision accidents. This performance is supposed to be realized by such structural characteristics as “to be crushable” and “to have high energy capacity in the internal mechanics”. As the measures to represent the performance level of buffer bow the critical striking velocity (V_B,cr) and the critical collision angle (θ_cr) are proposed. Those critical events are defined as the threshold where the inner hull of struck tanker is ruptured or not.
As it has been confirmed in the preliminary investigation that the bulb structure is most threatening to struck ships, buffer bow design considered is focused on bulb structure. The buffer bow design items which are supposed to be effective are (1) blunt shaped configuration, (2) transverse stiffening system and (3) adopting minimum shell thickness. The advantage expected to those design items are the fact that no special equipments nor special materials are needed. Their contributions have been evaluated through a series of FEM simulation analyses adopting a VLCC as the model struck ship, and VLCC's and container ships as the threatening striking ships. The effectiveness of buffer bow is confirmed by comparing the performance of the critical striking velocity and the critical collision angle between buffer bows and standard bows.
At the final stage the effect of buffer bow is evaluated by focusing on the performance that how much the risk of oil outflow is decreased. “The mean oil outflow” is derived based on probabilistic procedure considering dangerous collision scenarios. The case study has shown that the probabilistic oil outflow is decreased by about 80% if buffer bow design is adopted to VLCC.

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Welded built-up steel structures in service encounter many accidents caused by fatigue, and it is important for maintenance of social foundations and safeness to estimate their fatigue lives quantitatively.
By considering that fatigue cracks cannot grow without the accumulation of alternating tensile / compressional plastic strain, one of authors identified that the effective stress intensity factor range ΔK_RPG based on the Re-tensile Plastic zone Generating (RPG) load which represents the fatigue crack driving forces, and suggests that ΔK_RPG should be applied as the parameter in order to describe the fatigue crack growth behavior. For predicting fatigue crack initiation and propagation, numerical simulation code “FLARP” based on ΔK_RPG was developed.
In this paper, it is confirmed that fatigue life estimation by FLARP gives accurate results by comparing the estimated fatigue crack growth curves with the experimental results for in-plane gusset welded joints which are used in many welded steel structures. Moreover, the effect of induced bending moment due to misalignment for the fatigue strength is investigated by the numerical simulations.

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The deformation and dynamic behavior mechanism of submerged thin shell structures are in principle of a non-conservative nature as circulatory system, because the working load is the follower type as hydrostatic pressure that works vertically to its deformed surface at all times. The disturbance forces of various types, existing in marine environment, lead the complicated dynamic behaviors of the thin shell in the circulatory system of load-deflection. The dynamic behavior of a thin shell undergoing large deflections with small disturbances should be clarified for critical analysis.
This paper deals with the correlation dimensions corresponding to dynamic behaviors of a thin shell subjected to follower forces with small disturbances. For that purpose, the finite deformation and dynamic behavior of the thin shell are numerically analyzed by the governing equations in a mono-clinically particle coordinates description. Then, the correlation dimensions and Poincare sections are calculated corresponding to dynamic behaviors of a thin shell. By the results of these studies, it is clarified that the correlation dimension related to dynamic behaviors gives an aim of changing from quasi-oscillatory motion to non-periodic motion. Moreover, the correlation dimension makes clear that the difference of the route going to unstable state between two scenarios as “Self-organization type” instability and “Self-assembly type” instability.

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Finite element method is a powerful tool for predicting welding distortion. However, the mechanical phenomena in welding are strong non-linear transient problems and thermal-elastic-plastic FE analysis requires very long computational times. To overcome this problem, an interactive substructure method is developed as a method to reduce the computational time in three-dimensional analysis. In this paper, by comparing with commercial software, the calculation accuracy and speed of this method is discussed. In order to confirm calculation efficiency for a large scale problem, calculation of the model with 670,000 degree of freedoms is performed. Further, calculation of the rotational distortion in FSW is performed and its applicability for practical problems is demonstrated.

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The authors proposed a set of closed-form simple formulae to estimate the ultimate strength of a continuous stiffened panel under combined biaxial thrust and lateral pressure. This paper extends the application of the formulae to biaxial compression/tension stress field based on a series of elastoplastic large deflection FE analyses. It was found from the FEM results that the effect of tensile load on the ultimate strength is not so significant when compressive stress is large and the collapse mode is similar to buckling mode. On the other hand, ultimate strength interaction curve can be approximated by Von-mises yield function as a safe-side estimation when compressive stress is very small and the collapse mode is similar to plastic collapse mode. FE analysis for typical stiffened panels with consideration of in-plane shear has been also performed to examine its effect on the ultimate strength of a continuous stiffened panel. Based on the observed FEM results, a set of simple ultimate strength formulae for a continuous stiffened panel under combined loads has been derived. The validity of the proposed simple formula has been confirmed through a comparison with the FEM results and the estimated strengths obtained by some existing methods.

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