This paper describes the life cycle assessment of sorbent (oil absorbent) in estimation of CO2 emissions produced throughout the life cycle for each scenario of sorbent ; Sugi Bark Product and Anaerobic/Aerobic Biodegradation Disposal (Scenario A/B), Sugi Bark Product and Incineration Disposal (Scenario C) and Polypropylene Product and Incineration Disposal (Scenario D). CO2 emission is the highest in disposal stage in all scenarios. In comparison of LCA of SBS (Sugi Bark Sorbent; scenario A, B, C), CO2 emission is lower in biodegradation disposal than in incineration disposal. Biodegradation disposal has more advantage in CO2 emission than incineration disposal, when the oil content of recovered substance is lower. The ratio of total CO2 emission of SBS and Polypropylene is 1:3 at most; the replacement of Polypropylene sorbent with SBS can reduce 8.3t-CO2 emission in recovering 1t of Bunker C oil.
CO2 sequestration will be one of the effective options for the mitigation of the global warming, and its technology development is underway widely in the world. In spite of number of benefits of the technology, there are also risks, i.e. local impact on deep-water environments. In order to implement this technology, public acceptance is inevitable, even though the impact is proved to be trivial. In this study, a questionnaire survey was conducted to obtain the correlations of possible factors to the public acceptance by the covariance structure analysis and to estimate marginal willingness to pay for this technology by the conjoint analysis. The results show that the outreach of information increases the acceptance and that the people who make much of its benefits have tendency to accept but those who consider the use of deep ocean ethically are concerned about its risks. In addition, we carried out risk communication via Internet, where the logic analysis of the discussions in its BBS site reveals that field experiment and adaptive management are important.
In recent years, the congested tanker route and abnormal weather unfortunately raise the possibility of sea accidents. Spilled oil from a stranded ship pollutes the ocean environment and also does damage to the regional economics. Therefore, in order to prevent damages spreading, it is very important for us to take adequate measures as soon as possible. Under the circumstances, we are developing an autonomous buoy, which is dropped into the sea and chases spilled oil autonomously when the ship accident occurs. This buoy is expected to inform us in real time of the location of the spilled oil and meteorological and oceanographic data around it. This paper is the first report on the development of a spilled oil chasing autonomous buoy system. This paper firstly introduces the total system of a spilled oil chasing buoy, and secondly shows the experimental and numerical results of maneuverability of the buoy model."
The authors are planning to develop an 'underwater glider with independently controllable main wings' for the use of oceanographic survey, monitoring of marine environment, fisheries, ocean exploration, and marine sports / leisure activities. Underwater glider has no propulsive machinery, and so this silent and safe vehicle can be maintained with relative ease and is easy on environment and many forms of life in the sea. The first report deals with development of an experimental underwater glider. The glider was designed for much of a high performance of motion. Main wings, upper rudder, diving rudder, movable balance weight, and vent - blow valves can be remotely operated by using the 6-ch-radio-controlled system. Three-component-force test has been conducted in a circulating flow channel so as to obtain hydrodynamic characteristics of the glider. Motion performance of the glider was also observed in a towing tank and a diving training pool. Various kinds of experiments leads to the conclusion that the 'underwater glider with independently controllable main wings' had an admirable motion capability as compared with conventional 'underwater gliders with fixed main wings', and therefore practicability of the proposed glider was demonstrated.
The Darrieus turbine is one of the suitable water turbine for tidal power generation, because of the high performance by making use of the lift generated by rotating wings around the vertical axis, therefore, no directivity to tidal current, and the structural simplicity with the straight wings. Torque generated by one, two and three rotating wings was measured by the dynamometer in the circulating water tank. Power coefficients of the turbines with two wing sections of NACA0018 with/without the camber were measured in the experiments. Power coefficient change by the wing attaching angles to the rotor was also studied. Torque around the axis of the Darrieus turbine is estimated by the single stream tube theory and the results of the starting torque are discussed in comparison with measurements.
Environmental issues have been very much concerned recently. In addition, there has been a growing awareness that rising cost of fuel is inevitable. For reducing fuel consumption of a ship, an intelligent navigation system is one of possible approaches. In the previous paper, the authors have proposed a new navigation system for coastal shipping to decrease fuel consumption and CO2 emission from a ship. The navigation system, called WAN-CS, optimizes engine revolutions with constraint of the voyage schedule. Combined the WAN-CS with a weather information system and a navigation information system, an onboard experiment has been carried out. The ship used for the experiment was a domestic cement carrier "Shin-ei Maru". The route was selected the Ube- Nagoya route, which was one of the main routes of the ship. The experiment result showed that the system saved 10% fuel and arrived on schedule, though it was depend upon the weather condition and scheduled time. Consequently the system was validated by the onboard experiment. From an economic viewpoint the system also retained its superior performance in cost.
Recently, the amount of international maritime container-cargo movement has seen a dramatic increase, especially in East Asia. In response, shipping companies have formed strategic alliances and have attempted to upgrade their service to attract more cargo. As well, very large container ships have been introduced and voyage routes have been optimized to improve transportation efficiency. In this study, a Genetic Algorithm (GA) is applied to develop a design method to further optimize the maritime container-cargo network. In this method, not only the sea routes of the container ships but also detailed information regarding cargo flow, such as which cargo is transshipped to which ship at which port, etc., is considered. Thus, an effective design of the transportation network can be achieved. From a case study in which the scale of the cargo volume for a virtual alliance was assumed, a pendulum route between Europe and East Asia was obtained as an optimum solution. Also, another case study, in which the value reduction of the cargo due to the increase of transit time is considered, showed that direct voyage routes, by which the minimum transit time and no transship are realized, are effective. These results provide very useful information to the stakeholders of maritime transportation.
This paper deals with the effect of phase transformation on the transverse shrinkage by comparing experimental data and numerical results of transverse shrinkage generated by welding. Both mild steel with non-transformation effect and 3.5Ni-steel with transformation effect were welded by laser welding. The transverse shrinkage of 3.5 Ni steel was almost equal to that of mild steel. This reason is the following two causes:(1) the transformation expansion on cooling process makes the transverse shrinkage small and (2) thermal shrinkage of austenite phase before martensite transformation on cooling process makes the transverse shrinkage large. The total shrinkage obtained from above two reciprocal causes on cooling process is not affected very much by phase transformation.
The factor that influences the residual stress distribution generated by a quenching process was clarified and an analysis technique for estimating the residual stress distribution was established accurately even if the diameter of the cylinder is changed. First of all, a method of the numerical analysis was established through the comparative study of the experimental and the numerical analysis values of the residual stress distribution by using the steel material where the phase transformation is not generated during a quenching process. Next, using the established method of the numerical analysis, the influences of material constants and mechanical properties on the residual stress distribution were examined followed by clarifying the factor to estimate the residual stress distribution when the diameter of the cylindrical material is changed. Non-dimensional heat dissipation 'H' is important as for the factor of temperature, and each temperature dependency of linear expansion coefficient, Young's modulus and yield stress are important as for the factor of materials to analyze the residual stress distribution. It was confirmed that the residual stress distribution was able to be predicted by using Non-dimensional heat dissipation 'H' provided that the material was fixed and the diameter of cylinder was changed.
It's getting more important to transfer knowledge from elder experts to young engineers especially in shipbuilding industry in Japan. We proposed a method to support knowledge transfer and developed a system based on workflow concept. From the case study in our prior report, the method and the system were proved to be useful for knowledge acquisition in design department. At the same moment, several problems are found during the case study. To resolve these problems, a formal process description method using semantic web technology is introduced and developed. The newly proposed method for formal process description and the developed system are evaluated in experimental use for CAD operation.
The paper presents an unified approach to scheduling problems on ship-building lines based on discrete event-driven system theory. The dynamics of the production lines are mathematically described using linear system representations based on Max-Plus algebra, which makes it possible to solve the problems to strictly keep delivery dates by model-predictive control theory adjusting arriving times of parts or materials. Specifically, for a dock of tandem-type, the dock process consisting of building up blocks, rigging and painting is succesfully modeled by a Max-Plus-algebra-based linear system representation which determines the cyclic delivery dates for the block-assembling process. The process is consisting of making-up blocks ('Oo-gumi'), stocking them and gathering several bolocks ('Sou-gumi') is also modeled by another Max-Plus-algebra-based linear system representation.Simulation results show that arriving times of parts to the block-assembling process can be determinded by 1-step-ahead or 2-step-ahead model-predictive control methods. Futhermore, it is shown that the problem reducing stock periods can be formulated into linear programing problem.
Recently, in domestic shipping, a shortage of crew members resulting from the severe labor environment and the aging of members are serious problems, and there is concern about stable transportation becoming difficult because of this. The hiring of younger crew members by improving the labor environment and reducing the labor load is therefore an important target. The automatic mooring is one means of mitigating the labor load of standby operations. If the shift of the mooring tension induced by tide level change and the draft change while loading can be prevented, and moreover, if the hull position can be kept automatic within the allowable limit, the labor load can be reduced. In this research, a simulator which calculates mooring tensions and ship motions was built first, and calculation accuracy was checked by model experiments. The controller was then designed using the simulator and the performance was verified by tank tests. Successful results are shown.
In this study, we conducted tank experiment to measure ship responses to the Freak wave, Quasi Freak waves were generated utilizing focusing wave packet superposed on a regular wave train. Motion of the wave maker was determined in reference to wave simulations by our fully nonlinear numerical wave tank, NWT2D. An elastic model of a container ship was used to measure ship motions and whipping response. A time domain nonlinear strip method, SRSLAM, was used to simulate ship responses in the same incident waves. In this paper, the experimental and numerical results are presented and ship responses to the Freak wave are discussed
A practical method for simulating both ship maneuvering and wave-induced motions is presented. Separating the basic motion equations into 2 groups where one is for high frequency wave-induced motion problem and the other is for low frequency maneuvering problem, we derive the total 10 motion equations which are composed of 6DOF equations for high frequency problem and 4DOF (surge, sway, roll and yaw) equations for low frequency problem. New Strip Method was used for estimating the hydrodynamic force components such as added mass, wave damping and wave exciting forces for high frequency problem. The present method coincides with the time domain strip method when dealing with a ship straight moving problem. And when the wave height is set to be zero, the method coincides with the maneuvering simulation method in still water, so-called MMG model. Wave-induced motions for SR108 container ship model in turning condition were predicted using the present method. The predicted results are compared with the free-running model test results. The results roughly agree with the test results. The present method can capture the overall tendency of the wave-induced motions of the turning ship in time domain.
In order to capture the ship turning performance in waves, free-running model tests were carried out in regular and irregular waves using SR108 container ship model. The model tests were conducted at Seakeeping and Maneuvering Basin, Nagasaki R & D Center, MHI. The regular wave tests were carried out in various wave lengths in heading and beam waves. As the irregular wave conditions, long and short crested irregular waves are selected corresponding to sea state 4 and 5. Simulation results of the turning motions in waves are also presented in this paper together with the model test results. A practical simulation method which takes only wave drift forces into account to usual maneuvering simulation model in still water was used. The simulation method can predict the turning motions in regular and irregular waves with the practical accuracy, although there is some room for improvement in short wave length region such as wave length ratio 0.5.
A simulation method for the maneuvering motion of a towed ship in still water is presented. A 2D lumped mass method is employed for expressing the dynamics of the towing cable. The motion equations of the towed ship and the cable are derived under the assumption that the motions are defined in the horizontal plane. Motion of a towing ship is assumed to be given. As a calculation example, a towing barge with/without skegs is selected. The captive model test is carried out to capture the hydrodynamic force characteristics of the barge. Using the force characteristics, simulations are made for various towing speeds, towing cable lengths and so on. The calculated results are compared with the model test results conducted in the towing tank. The results of the slewing motion frequency, changes of heading angle and yaw rate in time domain agree well with the experiments. The present method is useful for predicting the slewing motion of towed ship.
When disabled ship accidents occur, optimum towing operation for safety is important to prevent secondary accident such as collision and grounding, which induce oil spill leakage after drifting. Optimum Towing Support System (OTSS) is a simulation program, which has been developing by the National Maritime Research Institute to calculate towing condition of tow and towed ships under waves, wind and current. OTSS can predict drifting motion of disabled ship, trajectory of tow and towed ships, towline tension and so on. In order to investigate applicability of OTSS to the actual ship on the sea, towing test by using patrol vessels of the Japan Coast Guard was carried out. The results of straight and turn towing in calm and rough seas are compared with the calculated results by OTSS, and performance for OTSS is evaluated. These results demonstrate that predicted results of towing motion in wave by OTSS are in a good agreement with the measured results rather than those in calm sea. Based on experimental results of towing test in turning, turning characteristics of tow and towed ships during towing are clarified. Moreover, influence of towing on turning performance of tow ship is indicated in comparison with turning test results of a single ship. These results obtained by towing tests show that OTSS is available for the prediction of towing condition in rough sea.
Broaching is a phenomenon whereby a ship cannot keep a constant course in severe following and quartering seas with relatively high speed. Once this dangerous phenomenon happens, even a ship complying with the current Intact Stability Code (IS Code) of the International Maritime Organization(IMO) could capsize. This paper focuses on broaching of slender vessels with twin screw propellers and twin rudders because they are often operated in high speed range which make susceptible to broach. First, existing experimental results at the Haslar basin were explained by a mathematical modelling proposed by the authors and extended here to predict broaching of high-speed slender ships in severe following and quartering seas. Second, we discussed the effect of the fin-stabilizer (anti-rolling fin) with which high speed vessels are often equipped, on broaching. Then, we identified an optimal control gains to reduce danger of capsizing due to broaching. Effects of the fin size and its aspect ratio as well as the area of rudder were also investigated. The above results are expected to be used for designing high-speed slender ships with a fin-stabilizer set for avoiding dangerous broaching at seas
This paper presents a numerical simulation method to predict the wetted surface area and hydrodynamic forces acting on a planing ship running in a fixed condition. The flow field around a planing ship under the potential flow assumption is determined by solving two integral equations with unknown boundary. The one is well-known lifting surface integral equation and the other one is an integral equation which imposes water surface condition along the wetted surface boundary so called spray root line. The second integral equation is shown by Matsumura et al. and they solved equations under the high aspect ratio approximation. In this study, the integral equations without approximations based on high or low aspect ratio assumptions are solved numerically and it is applied for practical planing ship flow calculation in fixed condition. The obtained wetted surface area and pressure distribution on hull surface are agreed well with experimental results.
The present study developed a CFD based hydrodynamic shape optimization system which contains CAD based shape representation module and high performance optimization module. The sequential quadratic programming (SQP) is employed for the optimization algorism and the adjoint variable method adopted for the sensitivity analysis. The sensitivity analysis with the adjoint variable method shortens the much amount of computation time for the optimization compared with finite difference based sensitivity analysis; additionally the results of the sensitivity analysis with adjoint variable method have less grid dependency than that with finite difference based sensitivity analysis. This optimization system is applied for the optimization problem to maximize the lift-drag ratio of a two-dimensional foil shape which is represented with 12 control points under the constrained condition that foil sectional area is constant. The lift-drag ratio of the optimal foil shape is more than 50% larger than initial foil shape and all the constrained conditions are maintained. The influence of the initial shape on the optimal shape is also investigated. The initial value dependency is not so heavy and similar solutions are obtained. By this means the present optimization system is considered useful for the hydrodynamic shape design.
The authors carried out the experiment on ride comfort of a high-speed catamaran plying the Bay of Osaka, and proposed a new evaluating method with a 'ride comfort index' RCI, introducing the concept of Weber-Fechner's law. It was demonstrated that the resultant RCI combining effects of vertical and lateral acceleration could estimate well ride comfort of a high-speed craft. Another experiment has also conducted on board a car ferry running across the Tsugaru-Straits in North Japan. The purpose of this study is to verify the index by applying it to a conventional displacement-type car ferry, and to establish a method for evaluating ride quality of passenger ships. Ship motion was measured at the navigation bridge, and a questionnaire survey was carried out so as to obtain passengers' physiological and psychological responses. The first report deals with a questionnaire survey for revealing the relationship between ship motion and passengers' subjective evaluation of ride quality. Motion sickness was quantified by indices of 'illness rating' and 'symptom score'. Various kinds of consideration leads to the conclusion that the resultant RCI combining lateral and vertical motions can be a useful index for estimating ride quality of a displacement-type passenger ship as well.
A new method to estimate and evaluate ship performance in actual seas is investigated from the viewpoint of long term estimation including time depending influence such as fouling and aging effects of hull, propeller and main engine as well as resistance increase due to waves and winds and so on. In order to verify the present method, simulation is carried out. The result shows that the present method gives better estimation for the ship performance such as increase of sea margin, decrease of ship speed and change of the revolution number of propeller, compared with the previous work. The present method should be useful for ship designers to design a ship hull, a propeller and to choose a suitable main engine at the initial design stage under the condition of the deadweight, ship speed and sea condition given by a charter party.
An analytical method in so-called Neumann-Kelvin problem is proposed to represent 2-D flow about semi-displacement type ship having blunt stem and transom stern. At first, the usual Neumann-Kelvin solution, complex potential, is deduced from Green's integral formula by using the boundary conditions on the linearized free surface and on the exact body surface and is represented by the velocity distribution along the body surface and by wave sources located at the fore and aft cross points. This new representation shows explicitly the non-uniqueness of Neumann-Kelvin solutions. Next, the transom wall is removed and the representation is reduced to the sum of integration along the body surface, the unknown being the velocity differences, and the wave source located at the fore cross point. The resulting boundary integral equation has two unkowns which are determined from planning conditions, Kutta velocity condition and the other wave height condition at the transom point. The numerically obtained solutions show good flows around the body with blunt stem and transom stern. It is reported to be able to assess the Froude number when planing starts by combining wave breaker indices, the values of resistance, lift and trim moment when the rise of center of gravity and the trim are varied and the Froude number when heave and pitch are unstable. It is also shown that a concave camber over the bottom of planing hull makes a profit for attitude and resistance. At last, a possibility is suggested to obtain a good evalution of resistance for body with transom stern by using high-speed approximation of inverse mirror solution.
With the increase of the size of container ship, the number of container stack on deck is increasing up to 8 high. The multi high stack containers are secured with the use of securing system such as twistlock or lashing rod; however, incidences of container loss due to stack failure have been reported in recent years. In the present paper, behaviors of a container stack on deck were analyzed by a motion simulation software of complex mechanical assemblies. The container is assumed to be rigid and modeled in a column-plate structure. The twistlock and the lashing rod are also model in a rope. The dominant ship motion to container stack failure was clarified firstly, and the effectiveness and limitation of the use of twistlock and/or lashing rod were investigated. The securing system with the use of twistlock and the lashing rod were discussed based on the simulation results.
A methodology to apply the Design Irregular Wave and the Direct Loading Analysis Method to estimate a maximum local stress in 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 state. On the other hand, the Direct Loading Analysis Method is a calculation method of time-varying stress in a whole ship structure by using FEM. Example calculations were performed on the local stress of a 6,200 TEU over Panamax container ship. Stress transfer functions were calculated using the Direct Loading Analysis Method firstly, and the maximum local stress was estimated by means of the Design Irregular Wave with the use of the stress transfer function. An alternative method to estimate the maximum stress was investigated with the use of load transfer function, instead of the stress transfer function. Significant wave height and the mean wave period in design short-term sea state, the ship encounter angle to wave, and the phase information of the Design Irregular Wave were discussed based on the calculated maximum stress.
In this paper, a comparison of Life Cycle Cost (LCC) for steel structure of wharf which is constructed with steel piles with several types of protective coating and concrete deck is presented. The study focuses single pile strength as a basis of evaluation of whole structural strength, and proposes ultimate strength formulae derived from FEM analysis with combined beam-shell model that can cope with local buckling deformation of piles as well as their global deformation. The so-called modeling parameter that accounts for uncertainties in strength formulation is evaluated from a comparison of FEM results with existing test results. Failure mode of single member and whole structural system are studied and the probability of failure of whole system is evaluated. Then failure risk is added onto LCC. The results show that the failure risk of the considered wharf under horizontal seismic excitation is small compared to the total LCC. They also show rational anti-corrosion system for marine steel structures; i.e. cheap anti-rusting system such as epoxy coating for steel structure of wharf is generally economical but heavy duty epoxy coating or anti-corrosion metal coating system tend to be more economical with increase in service period.
The strength and deformability of corroded steel plates are of great interest for the proper evaluation of structural integrity of aged marine structures. In the present paper, the authors use a CAM system which numerically controls a desktop milling machine to reproduce the surface geometry of a corroded surface. Surface data may be generated by a CAD system by the assembly of simulated pits of certain shapes such as cone or partial spherical shapes, or by numerically simulated arbitrary surfaces. Also, corroded surfaces may be measured by scanned the plate by a laser displacement sensor, so that the surface data are stored in the CAD system to generate the input for the CAM system. In order to investigate the effects of surface pits, three kinds of periodically distributed surface pits are machined on the both sides of specimens, where geometrically similar specimens, whose sizes are a half and a quarter of the original ones, respectively, are also used to investigate the size effect to the strength and deformability of the specimens. It will be seen that the size effect can be disregarded so that valid data can be obtained by scaled model experiments. As a typical example of plates with general corrosion, surface geometries of a sample specimen taken from the bottom plate of MS Nakhodka are reproduced, and the corresponding tensile test are carried out. The results show a slight reduction of the tensile strength, while the plastic deformation is reduced considerably. In order to examine the extent of the corroded surface, test specimens having different size but the same thickness are tested, where the surface undulation is machined in the original scale.
Pitting corrosion is a great concern when the integrity of ship's hull structures is considered. Corrosion pits with a conical shape are typically observed on coated hold frames in way of cargo holds of bulk carriers which exclusively carry coal and iron ore. A series of tensile tests using specimens with randomly distributed pits has been conducted to investigate their effect on tensile strength. The stochastic model developed in the previous study has been employed to determine the random pit distribution for the tensile test specimens. It has been shown that tensile strength is little affected by the pitting pattern and total elongation is influenced by the pitting pattern in cases where the degree of pitting intensity (DOP) is the same. Following the experiment, the empirical formula, where DOP and pit diameter D are used to estimate the tensile strength of pitted steel plates, has been applied to the test results. It has been revealed that the tensile strength of randomly pitted steel plates could be predicted conservatively by replacing D with 0.8Dmax (Dmax: diameter of largest pit) in the formula.
The relation between the resistance of fatigue crack propagation and the cyclic softening characteristics in a ship structural steel is investigated numerically by using Crystalline-Elastic-Plastic F.E. (CPFE) analysis in order to clarify the microscopic mechanisms of the fatigue strength improvement of FCA steel developed by Konda et al. (2001). The degree of the resistance is evaluated by microscopic-crack closure level and Crack-Tip Opening Displacement(CTOD). The closure level is determined by detecting the load at which the stress changes from compression to tension near the crack tip. As results, followings are found; 1) The in-house CPFE code which has the capability to perform the fatigue crack closure analysis for a cyclic softening metallic material has been developed. 2) For conditions chosen, the accumulated sum of slip within the plastic wake in the cyclic softening material becomes larger than that in the ordinary material, and a lower stress region appears directly behind the the crack tip. 3) For conditions chosen, the maximum compressive stress on the crack surface plane at the minimum load appears in front of the crack tip in the ordinary material while it appears behind the crack tip in the cyclic softening material. The stress changes more steeply near the crack tip in the cyclic softening material than do that in the ordinary material. 4) For conditions chosen, it is found that the crack opening level increases and CTOD decreases when the cyclic softening occurs. This means that the propagation rate of a fatigue crack in the cyclic softening material becomes smaller considerably compared with that in the ordinary material.
In a design stage of marine structures, the S-N approach is commonly used for fatigue strength evaluation, where fatigue failure is often considered as the penetration of the plate-thickness of structural members. It is sometimes observed that the cracks having penetrated the plate-thickness of ship structural members exhibit relatively slow growth rates, which may be due to the high structural redundancy and/or the compressive residual stress. Therefore, it is important to predict the crack propagation when it is detected during in-service inspections, which can give us the proper maintenance schedules of marine structures. From the viewpoint of such aspects, the authors have developed a simulation program, "CP-System", for multiple cracks propagating in a three-dimensional stiffened panel structure. It can predict fatigue crack lives and paths, where through-the-thickness crack propagation is formulated as a two-dimensional in-plane problem, and the crack propagation behavior is simulated by step-by-step finite element analyses. In order to accurately evaluate the fatigue lives of ship structures, it is necessary to take into account wave-induced load histories, which are generally a kind of clustered loading with variable stress range. In the present paper, a new crack opening/closing simulation method is developed utilizing the crack tip stress field parameters evaluated by finite element analyses, and the effective stress intensity range, ΔKRP, which precisely correspond to the tensile plastic deformation ahead of the crack tip, is obtained by taking into account of the plastic wake induced by fatigue crack propagation. The usefulness of the developed method is demonstrated by the simulation of fatigue crack propagation in a ship structure under a wave load sequence.
There have been many correlations between Charpy test results and fracture toughness test results such as CTOD test results.However, these correlations are not based on the theoretical model but quite empirical. Therefore, the current empirical correlations between both test results, that is especially the brittle-to-ductile transition temperatures, would not be necessarily applicable to the structural steels with various properties. In this study, an analytical evaluation model to correlate Charpy transition temperature with CTOD transition temperature is proposed only after applying the following new ideas with aiming at the effect of steel properties on the transition temperature difference. One is the definition of fracture transition temperature where brittle fracture coincides with ductile crack initiation in both Charpy and CTOD testing. Another one is employing "local plastic strain criterion" for ductile cracking and "Weibull stress criterion" for brittle fracture initiation. This proposed evaluation model provides fracture transition temperature difference ΔTi (= TiCharpy - Ti CTOD) between Charpy transition temperature TiCharpy and CTOD transition temperature TiCharpy, and on effect of steel properties quantitatively. It is analyzed that strength level and work hardening as well as toughness and ductility level of steels can influence transition temperature difference ΔTi. A higher strength and a higher ductility of steels decreases ΔTi, on the contrary, a higher work hardening and a higher toughness increases ΔTi. The effects of these mechanical properties on ΔTi can be interpreted by strain rate and temperature effects on flow stress of steels.
Pitting corrosion is a great concern when the integrity of ship's hull structures such as the hold frames in way of cargo holds of bulk carriers which exclusively carry coal and iron ore is considered. The strength of actual pitting corroded member is depending on the pitting corroded surface condition which varies according to the progress of pitting corrosion. In order to investigate the practical strength evaluation method, a serial strength evaluation for various pitting corroded conditions is necessary. However it is difficult to obtain pitting corroded members which meet the purpose of analysis from existing ships. Therefore the strength analysis of simulated pitting corroded members is an alternative procedure. In this case, simulated pitting corrosion surface must well represent an actual pitting corrosion condition. In this paper, the investigation on the pitting corroded surface condition of the hold frames in way of cargo holds of bulk carriers is made to comprehend the statistical nature of pitting corroded surface. Then the simulation procedure is proposed to generate an optional pitting corroded surface. It is confirmed that the simulated pitting corrosion condition is similar to the actual condition.