This paper reports the development of a new body-force model for the rotating propeller within viscous flow code and its application to uniform flow and propeller advancing with the angle of attack. A simplified quasi-steady blade element theory with the infinite-bladed propeller model (time averaged propeller induced velocity field) is coupled with the Reynolds averaged Navier-Stokes (RANS) code to determine the thrust and the torque distributions. The present effort aims to reduce the computational effort while keeping the effect of ship with motion in quasi-steady manner for propeller. The solid-surface effect on the propeller loading and power is also studied. Open-water validation simulations are done for the Methodical-AU type fixed-pitch propeller.Reported results show fair predictive agreement between the new body-force model and the experimental data.

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In the present studies, hydrodynamic phenomena with vortex flow around the bow of a blunt ship are simulated by using various CFD (Computational Fluid Dynamics) codes. In the conventional experimental studies, some flow properties in front of the blunt bow beneath the free surface have been found out and reported; for example, a necklace vortex based on the wave breaking phenomena is the typical one. In CFD simulations, however, reliable results have not been obtained yet. The authors pay attention to the free surface boundary conditions to carry out the numerical simulations by NS (Navier-Stokes) solvers in CFD codes. As NS solvers with the different free surface boundary conditions, two phase flow and double model flow solvers in OpenFOAM prepared as CFD tools box of open sources and one phase flow solvers of SURF, NEPTUNE developed by NMRI (National Maritime Research Institute) are used. As the results of two phase flow solver included in OpenFOAM above mentioned some flow properties with vortex flows can be obtained. Influences of the free surface boundary conditions to the vortex flow phenomena around the blunt bow are discussed in comparison with various results based on other NS solvers and experiments.

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This paper shows a thin ship theory of the wave making resistance considering an effect of the gradient of hull form in the depth direction based on linear approximation, which is made by modifying the original Michell's thin thip formulation and by using Havelock's Green function. Some computing applications of wave resistance by both Havelock's formula and pressure integration on the centerplane of the ship are shown to compare with other researchers' results. The effects of vertical gradient of the hull on wave resistance are the phase shift in Froude number domain and the decreasing amplitudes of humps and hollows in comparison with Michell's integral. We control the added depth gradient term to affect in low Froude number range by a condition. The present method must be improved further to enhance quality and reliability.

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To reduce fuel oil costs and emission of greenhouse gases of ships in operation, application of Contra-Rotating Propellers (CRP) will be one of the solutions, which have high propulsive efficiency. Although several estimation methods of predicting open water characteristics of CRP have been developed in the past, few methods treat accurately with trailing wake geometry, which influences much on estimate accuracy. CRP makes the flow around the propellers more complicated compared with conventional single propeller because aft and forward propeller of CRP interacts each other strongly. In order to improve estimate accuracy, more rigorous treatment of the trailing wake geometry is desirable. This paper presents a calculation method, taking deformation of trailing wake accurately into account. The method is based on a simplified surface panel method "SQCM" which satisfies the Kutta condition easily. The SQCM consists of Hess and Smith type source panels on the propeller surface and discrete vortices on the camber surface according to Lan's QCM (Quasi-Continuous vortex lattice Method). The wake vortex lines are arranged in accordance with the direction of the flow including induced velocity by both propellers. We show some calculated results and validate them by comparing experiments in this paper. It is found that thrust and torque of the aft propeller differ considerably depending on which the deformation of trailing wake is taken into account or not. The calculated results with deformed wake agrees very well with the experiment, while the calculated results without deformed wake always overestimate the thrust and torque of the aft propeller.

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This paper concerns results of model tests and full scale measurements of the propeller designed for inland ship (749 GT chemical tanker) aiming 1% increase of propulsive efficiency comparing with 1st retrofit small blade area NHV (Non Hub-Vortex)propeller.It was shown in the 1st report that the 1st retrofit propeller, of which blade area was decreased by 20% from the original propeller, reduced 4% of the engine output without any problem of the ship vibration and cavitation erosion.SBA-NHV propeller (Smallest Blade Area NHV propeller), of which the diameter was increased by 3.3% and the blade area was decreased by 10% from the 1st retrofit propeller, was designed and towing tank tests (propeller open water test and self propulsion test) and cavitation tests (cavitation observation, erosion paint test and fluctuating pressure measurement) were carried out. The model test results showed that the propulsive efficiency of the SBA-NHV propeller is about 1.5% higher than that of the 1st retrofit propeller and the risk of cavitation erosion and the fluctuating pressure of both propellers are almost equivalent.Finally, sea trial test of 749 GT chemical tanker was performed with the SBA-NHV propeller which was manufactured as the second retrofit propeller. The sea trial test results demonstrated about 2.5% deduction of engine output without any problem of the ship vibration comparing with the 1st retrofit propeller. And it was confirmed that the turning and stopping abilities of the SBA-NHV propeller were equivalent and a little worse respectively comparing with those of the original propeller.

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In this paper，the effects of hull attitude change，ship speed，metacentric height GM and stern appendages such as rudder，shaft bracket，bossing and propeller shaft on maneuverability of a high speed vessel are investigated. Range of Froude number of the studied ship is from 0.6 to 1.0. The hydrodynamic force characteristics are captured by a Circular Motion Test in Hiroshima University Towing Tank. Using the hydrodynamic derivatives，maneuverability indices are calculated. As a result，the following knowledge is obtained through the study: by inclusion of ship attitude change，Y'_υ increases，N'_γ slightly decreases，Y'_γ -m'_χ and N'_υ significantlyincrease. The effect of the attitude change is not negligible. Inclusion of the attitude change improves the course stability due to contribution of Y' _γ and -m'_χ and N'_υ. When ship speed increases and GM decreases,the course stability becomes worse in general although the turning performance is improved. This tendency is the same for displacement typed ships. The bare hull ship becomes unstable for course keeping in any Froude numbers,although the ship with stern appendages is stable. Thus，the effect of stern appendages on the course stability is considerably large. This is mainly due to the increase of absolute values of Y'_υ and N'_γ by the stern appendages.

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When the tsunami attacks in harbors, the vessels moored at a wharf may be unable to be evacuated. For example, it may happen the situations that the vessel is under cargo handling, the vessel has no crew or only foreign crew without knowledge of tsunami. In such a case, the following damages are assumed; breaking the mooring tether, grounding on a wharf, drifting to land areas and destroying buildings. This present paper describes the tsunami simulation and the motion analysis of vessel moored at a wharf using the MPS method (Moving Particle Semi-implicit method).In this research, the 3D-MPS method is applied. The chart of break of mooring tethers was created. The wave height of tsunami, draft of vessels and the relation of the break of the mooring tether were shown by the chart of break of mooring tethers. Then, the chart of break of mooring tethers is proposed for various scale of tsunami including the effect of incident angle of the mooring tether can be easily estimated against to the scale of tsunami and mooring system.

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The reduction of air pollutants, such as green house gas,NOx and SOx,is required in recent years. Regulation against emission gas from vessels has been also strengthened sequentially in conformity with the MARPOL73/78 ANNEX VI. Under such conditions,the superiority of natural gas attracts attention,and an early introduction of LNG-fueled ships is expected. Safety standard for LNG-fueled ship and its required equipment are now discussed in IMO and ISO,but unfortunately,the discussion does not refer to any safety evaluation method for the transfer of LNG fuel between vessels.In the previous year, the Ministry of Land,Infrastructure, Transport and Tourism started a project for early introduction of LNG-fueled ship, and published a safety manual and operative guidelines on LNG transfer.In that project, we took charge of safety evaluation of Ship-to-Ship transfer of LNG fuel using a flexible hose.In order to prepare operative guidelines on LNG transfer between a bunker ship and a LNG-fueled ship,we have proposed anew safety evaluation process. Following the process, we have examined the limiting environmental conditions of LNG transfer based on the results of numerical calculations of motions of two moored vessels and the LNG transfer hose, respectively. This paper presents the results of the above-mentioned safety evaluation.

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A primary conversion efficiency of a floating OWC-type wave energy converter "Backward Bent Duct Buoy (BBDB)" in regular waves is investigated in 2D and 3D wave tank tests. Firstly, the amplitude and phase difference between the internal wave height and motions are investigated. In a 3D tank test, surge, heave and pitch become in-phase at efficiency become maximum. The phase of internal wave height is close to motion. Secondary, the efficiency of duct-extended buoy is investigated in 2D test. Efficiency is reduced because the pitch becomes small by duct extension. Thirdly, the effect of a moment of inertia is investigated. In case of total mass and draft is constant, frequency band of high-efficiency increases as the moment of inertia become large. Fourthly, the effect of the shape of the air chamber is also investigated.

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To enhance performance of a ship in waves, improvement of its geometry appears to be important and should be treated properly. For this purpose, a practical integrated optimization method is developed to acquire improved ship geometry. Namely the Enhanced Unified Theory (EUT) and the Binary-Coded Genetic Algorithm (BCGA) are integrated together to optimize the ship hull geometry of a basis hull through its Sectional Area Curve (SAC). A modified Wigley model is firstly employed as a basis hull and optimized for some wavelength regions. From the obtained results, the added resistance of modified Wigley model decreases in large amount at the desired wavelength region. Furthermore, optimization with an actual ship e.g. SR-108 is also performed with the aim of illustrating effectiveness of the present method for practical purposes. The obtained results show a large reduction of the added resistance while discrepancy in the steady wave resistance is negligible and the total resistance is confirmed to diminish accordingly.

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The primary objective of the present paper is to obtain an irregular wave train inducing the most likely nonlinear response at an arbitrary probability level in a short term sea state. The target response includes nonlinear combined load, e.g., von Mises stress, and cumulative elasto-plastic behavior of hull girder after the ultimate strength. To this end, FORM (First Order Reliability Method) is adopted following the works by Jensen, JJ. Then, the irregular wave train could be obtained as design points on limit state function by FORM. Once such an irregular wave train is obtained, the most likely response could be estimated easily either by simulation or experiment under the specified wave train. It is shown that such an irregular wave train could be specified for nonlinear response such as the combined load and the cumulative collapse behavior. It is observed that the irregular wave train which induces the most likely collapse behavior is characterized by one extreme peak.

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Generally, the finite element method is used in the initial design stage of large-scale structures such as ships. These FEM models tend to be made by shell element because they are usually composed by plate members. However, actually, the stress distribution at the joint of structural components is quite different from the stress distribution which can be obtained by shell element. Therefore, it is desired that 3-dimensional solid elements are used for the joint. However, it is difficult to use solid element for FEM models with fine mesh in the initial design stage because it costs a lot of time in modeling and analyzing. Then, it aims to obtain the complex stress distribution of the joint of structural components at the cost equivalent to the analysis by beam and shell elements. In this study, the new elements which enable to evaluate the stress of the joint of structural components were created with low calculation cost. Then, the good results were veried when these elements were applied to some examples.

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In the present study, three-dimensional cleavage crack path prediction model is proposed. The model is based on the local fracture stress criterion in which three candidates for a cleavage plane in a computational element is assumed and the one which has maximum value of normal stress divided by local fracture stress is selected. In this model, normal stress acting on each plane is obtained by local stress intensity factor which is calculated by combination of approximate solutions where crack front non-straightness, crack surface irregularity and crack closing force acting at ridges between crack planes are considered. The model also incorporates multiaxial stress field and non-uniform toughness distribution. Therefore, this model is applied to welded joint of ESSO test where welding residual stress and non-uniform toughness distribution exist, and the predicted results of crack paths show a general agreement with the test results. Parametric study is also conducted in order to discuss the effects of applied stress, welding residual stress, toughness distribution and type of welding groove on brittle crack path behavior.

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A numerical model to evaluate brittle crack branching initiation in steels is proposed. First, we experimentally investigated macroscopic as well as microscopic crack branching initiation phenomena in steels with different crystallographic anisotropy by three point bend tests. From the tests, we observed microscopic process of crack branching initiation. In the crack branching, one of the microscopic branched cracks propagates through the thickness, leading to macroscopic crack branching initiation. This observation accords with prior researches. We assumed that micro branched cracks are initiated by a process that directions of cleavage planes at a crack tip are concentrated in two directions. We developed a model using this assumption with a further assumption that one of the three {100} planes having highest normal stress is selected as a cleavage plane in a grain. Normal stress on the {100} planes is calculated by a crack tip stress field and crystal orientation distribution.The crack tip stress field is obtained by analytical elastodynamic solution. The crystal orientation distribution is obtained by EBSD measurement. So the model reflects both of a mechanical condition and a material texture. We applied the model to the three point bending tests and evaluated crack branching initiation probabilities. Calculated results show good agreement with the experimental results.

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A structure optimization of mid-ship section is under consideration in this paper. A double hull oil tanker is selected for the target of optimization. Since there are many design variables in the mid-ship section, usually, design variables are divided into some groups in the viewpoints of designing and the manufacturing. When the classification of design variables is not proper, there is a problem that the optimal solution cannot be obtained. In order to overcome this drawback, a classification method of design variables is proposed here. Influences of design variables to constraint conditions are estimated based on principle component analysis and used for classifying design variables. The classification of design variables obtained by the proposed method is different from a conventional group. The selected problems by use of the proposed method are solved, and it is shown that the proposed method can give us a better solution than the conventional method.

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Recently, structural design of a ship considering various risks in the lifecycle of the ship has become more and more important.In the committee IV.1 (Design Principle and Criteria) of the International Ship and Offshore Structural Congress (ISSC), it is discussed that sustainability of ships and marine structures should be evaluated when the structure is constructed based on assessment of "holistic risk" which includes assessment of safety, environment, social responsibility and etc. Based on the concept of holistic risk evaluation, we carried out lifecycle structural optimization of mid-ship section of a double hull tanker in this study. For the evaluation of environmental risk, the method of life cycle assessment (LCA) is introduced to evaluate the CO2 emission. Also, evaluation of environmental pollution is carried out by using oil outflow calculation shown in the MARPOL. For the evaluation of the risk of failure, we carried out structural reliability analysis of longitudinal strength of the ship. Then, we carried out the following five optimization problems, (1) Minimization of construction cost, (2) Maximization of life cycle benefit (LCB) considering the risk of oil outflow, (3) Maximization of LCB considering the risk of CO2 emission, (4) Maximization of LCB considering the risk of failure, and (5) Maximization of LCB considering the holistic risk. Finally, the optimum solutions of these five problems are compared to discuss about the advantage of the design of ship structures based on the holistic risk evaluation.

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A geometrical nonlinear formulation is presented to simulate buckling/post-buckling behaviors of panels in ship structure employing meshfree approach. Reproducing kernel is adopted in the meshfree approximation. The author's previous study,a meshfree flat shell formulation, was developed based on Mindlin-Reissener theory. However, there were difficulties in introducing initial imperfection to the flat panel. In this study, convected coordinate system is applied to the meshfree shell formulation to reproduce complicated initial imperfection, e.g., thin-horse mode. To verify the proposed approach,buckling/post-buckling behaviors of panels are simulated using total and updated Lagrangian formulations and the results are examined.

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Arrestability of brittle cracks is extremely important in the structural integrity of welded joints of heavy gauge steel plates used in large container ships. Recently, a great attention has been focused on potential crack propagation along welds made with large heat input.In this study, a T-joint is applied to the strength deck structure of container ships to enhance crack arrestability. Material crack arrest toughnesses, Kca, of some steel plates are varied. The ESSO tests of T-joint components showed that a brittle crack is arrested at the T-joint if the steel plate used in the flange has a high Kca value in the range from 4900 to 7300 N/mm^3/2.FE-analyses of the stress intensity factor K indicated that brittle crack propagation is arrested under the condition that the K-value at the running crack tip is less than the Kca of the material. It is noted in the T-joint that the K-value at the deepest point of the crack decreases and is finally below the Kca of the flange plate when a brittle crack rapidly penetrates the flange plate to a depth of 30-40mm. These phenomena show the advantage of the T-joint in brittle crack arrestability in the flange plate of the strength deck structure.

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In this study the stochastic properties of the response of a square steel plate under in-plane compressive load subject to random initial distortions have been characterized using Polynomial Chaos Expansions (PCE). At first the random characteristics of maximum initial distortions of a steel plate have been approximated using PCE. Subsequently an analytical procedure has been developed based on elastic large deflection analysis which can be used to predict the stochastic characteristics of the plate response. A significant feature of the proposed method is the avoidance of the generally time-consuming Monte Carlo Simulation for evaluation of response statistics. Moreover, this methodology requires knowledge about the governing equations of the physical system. It is also theoretically reasonable as it has a strong mathematical basis. It has been found that the proposed formulation can predict the statistical characteristics of the plate response with sufficient accuracy, when compared to those obtained from Monte Carlo Simulation.

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As described in this paper, we investigated the effect of interfacial tension on the spread of oil under an ice sheet after an oil spill accident in an icy region. We measured the interfacial tension of oil and water, the contact angle of ice, water, and the oil interface with an interface tension measurement technique called Axisymmetric Drop Shape Analysis. The contact angle was about 180 degrees. Results suggest that a thin water film forms between the oil and ice. A simple but accurate model formula was produced based on the result. The oil slick radius predicted using this model formula agrees well with oil spill experiment results. Additionally, we proposed an application method for the model to an oil spread problem under an ice sheet with an irregular bottom face. The method described herein can estimate the oil slick spread region created by an oil spill accident.

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This paper deals with the performance in the wave-energy absorption over a wide range of wave frequencies by using a rotating pendulumtype electric-power generator installed inside an asymmetric floating body. In the present model, an electric-power generator is supposed to be set at the center of a smaller cylinder which rotates without sliding on the interior circular surface with larger radius of an asymmetric floating body. The floating body responds in roll to the action of incident wave, and due to coupling effects between the floating body and smaller cylinder inside, the smaller cylinder rotates and then the electric-power generator installed in the smaller cylinder generates electricity.When only the roll motion is allowed for the floating body, the conditions for maximizing the wave-energy absorption efficiency can be derived analytically. It is also shown analytically that if an asymmetric floating body has a special feature that no wave generates on the lee side of the floating body,the maximum wave-energy absorption efficiency becomes 1.0 only with a single mode of roll motion. This result implies that the present device can absorb the wave power perfectly provided the special conditions are satisfied. Numerical computations are performed to confirm the results obtained analytically. It is also shown by numerical computations that the wave-energy absorption efficiency becomes higher around the two resonant frequencies in the swing motion of smaller cylinder and in the roll motion of floating body, and that the total wave power absorbed, which is the integrated value of the absorption efficiency over the wave frequency, can be large by tuning the geometric parameters of the device and the damping coefficient of an electric-power generator.

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A prototype of a 3000m-class underwater glider for virtual mooring is being developed by JAMSTEC (Japan Agency for Marine-Earth Science and Technology) with RIAM (Research Institute for Applied Mechanics) of Kyushu University. The vehicle houses an observation equipment and glides back and forth between the sea surface and the seabed collecting ocean data in a specific area (virtual mooring area) for more than one year. This paper summarizes our restudy on the hydrodynamic coefficients of the vehicle by constant acceleration tests and the simulated results of gliding angle control are compared with the experimental results carried out in a towing tank.

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Two new methods to estimate time values are suggested. The methods can estimate time values in sacrifice model with disaggregate data. With the methods, it becomes possible to treat data with no aggregation in which unit prices for same origins and destinations vary according to the lot size or other individual properties of each sample, which was impossible with the existing method for sacrifice models. In addition, the methods are faster than logit model based methods, and are more flexible at probability functions assumed in sacrifice models.

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A comprehensive understanding of traffic properties is necessary in evaluating and controlling the ship collision risks. AIS (Automatic Identification System) provides a quick and effective method to obtain ship behavior in a wide area, which facilitates gathering of ship traffic data not only in inland seas or restricted congested sea areas, but also in wide coastal sea areas. In this paper, the authors propose a method to utilize AIS data to develop a ship traffic model that represents traffic characteristics, especially focused on lateral direction, ship speed, and course. Nojimazaki area in Japan is taken as a case study. By introducing a definition of virtual gate lines located in the targeted area, and taking intersection points of trajectory with the gate lines, information on ship status at the points are extracted. Statistical analysis shows that speed and course distributions are bilaterally symmetric and distributed in narrow range, while lateral distribution is asymmetric and has a great concentration around the mode. To suit these characteristics, Gauss and gamma distributions are selected. Obtained model reproduced the observation result with reasonable accuracy.

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An innumerable number of buildings in the coastal part of the east side of Japan were devastated by the Great East Japan Earthquake and Tsunami. Medical institutions also suffered the damage caused by tsunami, and the function to carry out the medical act has been spoiled. And the disabled concentrated on the medical institution which avoided tsunami damage. Under such circumstances, assistance from the water area began three days after the earthquake disaster, and much support supplies reached the stricken area. It was revealed that the support from the water area including the river was extremely effective against the stricken area.And then, the Tokyo Inland Earthquake disaster was assumed, floating medical support system installed in the quay of Arakawa River in Tokyo was proposed. Floating medical support system is movable; furthermore, it is built in the structural system of having very high isolation characteristics. Therefore, feasibility study such as selection of suitable setting position of this floating structure on Arakawa River, floor planning and flow planning at the time of always and a disaster, facilities and storage of various material,structural strength of the floating base, and the effects of disaster risk reduction was carried out about floating medical support system.

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Recently, the natural gas is expected to be an environmentally friendlier energy and alternative to the nuclear energy. In the social situation, many oil and gas and engineering companies had studied FEEDs of the FLNG expected to be a new production system for offshore natural gas development in the near future. The FLNG system is no proven technology and there is no operation, which can make it difficult for us to design the FLNG. Furthermore, it is noted that the FLNG designers can't get enough information for the design and need the design standard.Gas explosion is the technical problems for the topside facilities of FLNG. Though it is so difficult for us to understand the gas explosion phenomenon, the FLNG designers have to evaluate the peak over pressure of gas explosion for the design of topside layout to prevent gas explosion from damaging the facilities. The objective of this paper is to study the gas explosion by the numerical simulation. We have conducted the gas explosion analysis for FLNG model by the numerical simulation program AutoReaGas which was developed by TNO and the Century Dynamics. The results show that the physical factors such as ignition location can make significant effects on the peak over pressure of gas explosion.

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