A structure optimization for the initial design stage using FEM of ship is under consideration in this paper. General bulk carrier is selected as the object of the optimization. Both the size and the plate thickness of the bottom structure of the ship are taken as design variable simultaneously for the weight minimum optimization problem. The individual mesh-subdivision technique and the multi-point constraint method are used for change the bottom shape in this paper. Five design variables for the shape and thirty-one design variables for the plate thickness are considered for the optimization of ship structure. The yield stress constraint conditions for each element and buckling stress constraint conditions for each buckling plate on the bottom plate, the inner bottom plate, the girder plate, the floor plate, and the bilge hopper plate are considered. The optimal calculations are performed with several conditions of the types of design variable and constraint condition, and the designs obtained in the calculations are coMPared. It is shown that the Structural optimization with shape and plate thickness design variables can reduce the weight of ship structure effectively. Genetic algorithm is used for the optimal calculation since the design variables are discrete resulting in a combination optimization problem.

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Strength and deformability of steel plates for marine use are studied from the viewpoint of geometry of corrosion pits. In the present study, the effect of actual pit shapes has been investigated by the non-linear, large deformation and three-dimensional finite element analyses for simulated corrosion surfaces generated by a probabilistic model of corrosion process. The tensile strength of corroded plates with semi-ellipsoidal pits is found to be estimated by the empirical formula obtained from that with conical pits,where the estimation is based on the minimum cross sectional area of the plate. The deformability of the corroded plates subjected to uniaxial tension could be estimated by the surface roughness represented by the difference of averaged plate thickness and that at the section of minimum cross sectional area. This study also shows that the reduction of the bending strength due to semi-ellipsoidal pitting corrosion is higher than that of compressive/shear/tensile strength. An empirical formula for the reduction of bending strength due to semi-ellipsoidal pits is proposed which can be a useful tool for condition assessment of aged marine structures.

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Fracture accidents are often caused by fatigue, and these fractures start from the sites of structural discontinuities such as notches, holes, sharp corners, and weld defects which may induce the considerable local stress concentrations. In order to investigate the effects of plate thickness on fatigue strength, semi-elliptical side notches in plates and two types of welded joints of different plate thickness are studied in the present paper.An empirical formula is used to calculate the stress intensity factors of semi-elliptical side notches in plates so that the thickness effect on fatigue strength can easily been investigated for a variety of geometrical parameters. In the welded joints combined analytical and numerical calculation is performed for the evaluation of stress intensity factors of shallow cracks, and the rest of the calculations are carried out by the finite element method. From this study, the transition point, at which the magnitude of stress intensity factor is reversed has been identified, and the results are contrasted with the 1/4 power law based on the S-N approach.

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Low frequency response to normal wave loads and high frequency response due to wave-induced vibrations coexist in the ship's structural loads. This paper addresses the effect of the wave-induced vibrations on long-term fatigue damage in various types of ships. A bulk carrier, a VLCC, and a container carrier are employed as subject ships. A weakly nonlinear method proposed by one of the authors is employed for evaluating the load effects. Slamming loads are separately implemented by using momentum theory.The whole ship is represented by using shell FE model. The calculations are performed for various short-term sea states. Stress cycles are counted by using Rainflow counting method. Then, long-term fatigue damage is evaluated by using the Palmgren-Miner rule. A series of sensitivity analysis is also performed to clarify the characteristics of the fatigue damage by the wave-induced vibrations in oblique seas as well as in head seas. It is shown that the amount of the increase in fatigue damage depends on the wave load characteristics of the ships in waves as well as the structural properties such as natural frequencies of flexible mode.

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The strip yield model is known as one of numerical models for the estimation of the crack opening displacement and the plastic zone ahead of a crack tip. This model, however, is not able to allow the consideration of the work hardening effect of materials because this model is based on the elastic-perfect plastic material behavior.Authors developed the strip yield model allowing the consideration of work hardening effects beyond the small scale yielding.This model incorporates a nonuniform cohesive stress, which is a function of the material work hardening coefficient (the second modulus or the strain hardening exponent). The relationship between the crack opening displacement over a fictitious crack obtained by the strip yield model and the plastic strain distribution in the vicinity of a crack tip by the elastic-plastic finite element analyses is investigated. The model proposed with the weight function technique is applicable to the estimation of crack opening displacement for arbitrary two-dimensional crack problem.

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Ballast water for vessels is significant to prevent their stability and propulsion performance losses, which are caused by their light-draught. However, the International Maritime Organization (IMO) adopted International Convention for the Control and Management of Ships' Ballast Water and Sediments in 2004, because of avoiding its environmental impact.Then, in order to solve this problem, new hull forms are being designed, which use a small amount of ballast water or don't need ballast water. For example, one of new designed hull has shallow draught and wide breadth. Such a type of hull may show different roll characteristics from the conventional vessels.In this study, for a wide breadth and shallow draft vessel, its roll characteristics seas are investigated experimentally. The results show that its roll natural period is changed by its roll amplitude and its roll resonance occurs in different wave period for different wave height. Then the adaptation of the estimation methods of roll amplitude in resonance wave, which are proposed by International code on Intact Stability 2008 of IMO (2008 IS code), for this shallow draft vessel is also investigated. As the results,it is indicated that the parameter identification technique (PIT), which is one of recommendations, is better method to understand roll response of the object hull form.

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In order to guarantee the safety of vessels, it is very important to understand the characteristics of roll damping and to estimate it accurately. Because it affects the occurrence of parametric rolling and its amplitude significantly. However, it is very complicated to calculate roll damping theoretically, because of significant viscous components caused by vortex shedding. It is well-known that there is a prediction method of roll damping proposed by Ikeda for conventional displacement type mono-hull vessels, barge ships and small hard chine fishing boats. It has been developed based on theoretical and experimental backgrounds for regular roll motion. Therefore, it is difficult to apply it to computer simulation of transitional or irregular roll motion (i.e. roll motion and parametric rolling in irregular waves, broaching to capsize etc).The purpose of this study is to investigate the characteristics of drag force acting on a flat plate under transitional and irregular oscillation as a basic study, and to develop an estimation method of bilge-keel roll damping in time domain. First, under transitional motion, the characteristic of drag coefficient of flat plate at low Kc number is investigated experimentally. Second,using a forced sway motion device, the characteristic of drag coefficient of flat plate under transitional regular sway motion is investigated. Finally, based on the measured results, an estimation method of drag force of flat plate in time domain is proposed.

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Manoeuvring prediction is indispensable for the designing stage of ship. It becomes a serious concern that the manoeuvring performance complies with the IMO standard. For medium speed merchant ships such as container ship and PCC, they have the tendency that the advance and tactical diameter become larger by the course-keeping quality too stable, and have a possibility not to comply with the standard. Particularly, at the ballast condition with large trim by the stern, the above tendency becomes stronger. As for fishing vessels, C_b is around 0.6 that is similar to the above merchant ships because of the high Froude number, and has an initial trim in addition to the conventional baseline trim. It becomes very important to precisely evaluate the manoeuvring hydrodynamic forces against the trim.Based on the above background, the authors have made the database of manoeuvring hydrodynamic coefficients for medium speed merchant ship and fishing vessels with one propeller and one rudder system. Then, the regression models which properly presume hydrodynamic coefficients are introduced based on this database.The concluding remarks are summarized below. 1. The linear hydrodynamic derivatives of hull can be well predicted even in the large trimmed condition by correcting Kijima's model that had been predicting a turning circle excessively large.2. The interactive coefficients which have been modeled as functions of principal dimensions of ship are not so affected by them.Particularly, k_x, x'_H and l'_R can be modeled as almost constant. a_H and γ_R are slightly affected by the parameter C_b/(L/B), however the effects are too smaller than conventional models.3. Using the presented new regression models, turning motion and z-manoeuvr are simulated and compared with conventional Kijima's model. As the result, the prediction errors can be reduced to 1/2-1/3 of conventional model.

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In this paper, a relationship between nonlinear dynamical system and statistical model is considered, and it is clarified that a second order nonlinear dynamical system is approximated by a Bi-variate Time Varying AutoRegressive (BTVAR) model with respect to a displacement or a rotation angle component and a velocity or a angular velocity component which is a kind of time series models.This obtained finding is applied to a stability judgment system of ships. That is, to monitor characteristic roots of the characteristic equation associated with a BTVAR operator online, the judgment for stability of ships is carried out. In this case, BTVAR coefficients are estimated by using an algorism of Kalman Filter. The verification of this idea is carried out based on numerical experiments. From the comparison of the proposed procedure and a Scalar Time Varying AutoRegressive (SVAR) modeling procedure with respect to a goodness of fit to the data of the model based on Akaike Information Criterion (AIC), it is confirmed that the proposed procedure is better than the SVAR modeling procedure from the view point of AIC.

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This paper reports on the improvements of a simulation model for ship motions in following and quartering waves. The authors use a wave-piercing tumblehome vessel as a subject ship. The existing 4-DoF (degrees of freedom) model shows some limitation in its capability for predicting broaching of this vessel. In a free-running model experiment for the vessel, we observed rudder and propeller emersion from the water leading to broaching. This rudder and propeller emersions can significantly reduce steering performance. To express these rudder and propeller emersions, we should take account of not only roll but also pitch and heave.Therefore the authors develop a 6-DoF model. With the heave and pitch motion, we can calculate the local draft variation for calculating wave exiting forces and moments. Roll restoring variations are one of the important factors to estimate roll motions.Therefore we theoretically estimate restoring variations in wave then we found the tendency of variation dramatically changes due to the roll angle. Submergence of superstructure can be important for that variation. We also consider the variation of maneuvering coefficients and rudder forces in waves which are relevant to broaching. To estimate these variations, we conduct PMM tests, straight-line tests and rudder angle tests in waves using a scale model of subject ship. With some of these improvements, we obtain better agreements with experimental results than existing 4-DoF model.

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The present paper proposes a numerical method for calculating the coupled ship motions and sloshing in time-domain. In the present method, strip theory is used to solve the ship motion problem and a finite difference method is used for the sloshing problem; both problems are calculated in time domain. To verify the computational results, first the calculated force due to sloshing was compared to experimental data and good agreement was found. Next, the authors compared the numerical and experimental results for ship motions, and the accuracy of numerical computation was confirmed. Finally, the wave height at certain position in the tank was compared. Even near the natural frequency of the tank, the numerical results based on the present method showed good agreement with the experimental ones. Moreover, a special case when tank is fully filled with liquid was discussed, and both experimental and computational results showed that the influence of liquid cargo is different from the solid one although the tank is completely filled.

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The present paper provides the results of an investigation on STEP (Spray Tearing Plate) for reducing the added resistance in waves.The research has been started to develop a device for suppressing spray; thin wave like a film that is generated around the bow above the waterline when a ship runs in waves. The effect of STEP is examined through tank tests with a model of 2500TEU container ship equipped with bolsters for anchors. The optimum shape of STEP reduces the added resistance in waves by 10% at designed speed under the condition of summer full load in short head waves of 3 meter height. The 3% reduction of CO₂ emission is indicated by the tank test results and calculation for ship performance in head waves and winds of Beaufort scale 6.

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In order to design a floating OWC (Oscillating Water Column)-type wave energy converter such as Backward Bent Duct Buoy (BBDB), it is necessary to develop a numerical method to make clear an optimal hull shape which maximizes the generating electrical energy.In this paper, a two-dimensional numerical method to estimate the primary conversion efficiency of a floating OWC-type wave energy converter with arbitrary cross section in frequency domain is proposed. The fluid motion in water waves is calculated by using boundary element method based on velocity potential theory. For the air flow in air chamber, an equation of state,conservation of mass and energy with the assumption of air being the perfect gas are used. From these equations, motions of floating body, air pressure in air chamber, transmission and reflection coefficient of water waves and primary conversion efficiency etc. are calculated. Wave tank tests are also carried out for BBDB in regular waves. Numerical results are compared with experimental results.

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The present paper describes tests performed with models inside centrifuge apparatus as a special tool for analysis and design of foundation elements applied in offshore structures. By using wireless smart sensors technology in physical model test inside centrifuges, significant improvements in the parameters determination will be possible for first time in Brazil. The centrifuge modeling has been used to address geotechnical problems in offshore engineering area, in order to avoid misinterpreting results commonly observed in reduced model tests. Herein it is also presented a modeling example of a special type of anchor known as"turtle anchor", developed by CENPES-PETROBRAS, which has already been used in real cases. A comprehensive series of tests in conventional scale has been performed on turtle anchors; however, the results did not bring numerical information about contact stress between soil and anchor, due to difficulties in evaluating the bearing capacity and deformation.

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A small AUV "MR-X1" is being developed for detailed investigations of the seafloor and marine organisms at JAMSTEC (Japan Agency for Marine-Earth Science and Technology). The motion of the vehicle is controlled by five thrusters. In order to improve control performance, digital implementation of a model based controller (LQI controller) was begun in 2009, and field experiments were carried out in the sea area near the volcano "Teishi Kaikyuu" in Sagami Bay on February 8, 2010.In this paper, the results of field experiments on direction control of the vehicle are summarized, and the motion equations of the vehicle required for a model based controller (LQI controller) are modified by using the results of the field experiments.

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The purpose of this study is to improve the FPED (Flexible Poiezoelectric Device) which we have developed and also to propose an elastic floating unit with a hanging structure using the FPED (EFHAS).The FPED consisting of piezo-electric polymer film (PVDF) is a way of harvesting electrical energy from the ocean power, e.g. tide, current, wave, breaking wave and vortex. In this study, we performed vibration tests of the FPED with a bluff body having a specific gravity in water.We found that the electric power of the FPED with the bluff body is larger than that of the FPED without it. To investigate a mooring type with the FPED generating a maximum electric power, we also compared a floating type with a submerged type. We revealed that the floating type is better than the submerged one. We have developed the EFHAS with the improved FPED to obtain the electric power from ocean energy.

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It is important to evaluate whether the ship can arrive on time by using the weather routing (WR hereafter) in order to discuss the impact of the use of WR against the maritime industry. Not only the reduction of the mean time of the navigation (i.e. how fast the ship can get to the destination) but also the reduction of the variance (i.e. how precise the ship can arrive) should we consider. In this research, we simulated and analyzed the large amount of navigation data, and examined the shape of the distribution of it. We demonstrated that we can decrease the variance of the navigation hours by adopting the WR. Along with the precise arrival of the ships, (i) we can reduce the delay risk against the same estimated time to arrival, (ii) we can have enough time for shipping, and (iii) we can decrease the offshore waiting time. We have evaluated these results quantitatively.

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Automatic designing of piping layout is challenging since it is composed of several numerical and/or combinational optimization problems, e.g., routing problems of pipes including branches, and arrangement problems of equipments. This paper presents a new approach based on a simple idea that the branches of pipes are considered to be a variety of equipment. Accordingly, the pipe routing problems are fairly simplified by removing the branches, and it derives a lot of efficient algorithms to solve the pipe arrangement problems. One is a multi-objective genetic algorithm (MOGA) in which the gene represents both the locations of the equipments and the arrangement of the pipes. And a new simple and efficient crossover operation which appropriately merges two different piping layouts (but of course the PID is the same) is proposed. In order to provide a fairly good initial population for the MOGA, a new heuristics making use of self-organization techniques to arrange equipments is proposed. The efficiency of the proposed approach is demonstrated through two experiments, one is a designing problem including five valves, one pump, and five branches, and the other includes seven valves, one pump, and six branches. The objective of the optimization in the experiments is to minimize the length of the pipes, the number of elbows, and the valve operability cost. The algorithms are programmed using Java language. Although the automatic arrangement system used in the experiments is academic, the concept of the proposed approach will be accepted in practical systems.

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A new simple and accurate shell FE-based structural Hot Spot Stress (HSS) determination method for web-stiffened cruciform joints has been proposed. Local stress of welded joints in full-scale BC lower stool models subject to bending and pressure loadings are examined. HSSs determined by the proposed method are compared with those derived by Lotsberg's method (Lotsberg et al., 2007) and the conventional 0.5t-1.5t extrapolation. It is shown that the local stress of full-scale BC lower stool models with various stool angle and plate thickness can be calculated accurately solely from shell FE results by following the proposed method. HSSs of welded joints in BC lower stool models subject to pressure loadings derived by the proposed method show good agreement with the target HSSs. This demonstrates the validity of the proposed method for actual ship structures under the real load. The proposed HSS determination method has advantage over Lotsberg's method in the accuracy and application range.

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