A hull form improvement method is presented using Genetic Algorithm in conjunction with Rankine source method based on a wave resistance theory for modified hull. By means of the present method, improvement of fore ship form is introduced for Series 60 (C_b =0.6) hull. As a result, the wave resistance is reduced about 25% at F_n=0.3 by modifying the original form to bulb-like bow shape. We found that GA improves the estimation accuracy of the optimum hull form.

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The Projected light distribution method is applied to measure the unsteady wave pattern generated by ship oscillating with advance speed on calm water. The merit of this method is that the unsteady wave pattern can be evaluated two-dimensionally. In this method the unsteady wave patterns are projected onto a screen as to the brightness distribution which is proportional to the second derivative of the unsteady wave elevation. The projected brightness distributions on the screen are recorded by CCD video recorder digitally. Transverse cut method introduced by Naito is applied to evaluate Kochin function. The obtained Kochin functions are compared with the results from theoretical prediction and the results from the longitudinal cut method proposed by Ohkusu respectively. For Fn = 0.25 the results show good agreement in the smaller angle region of elementary waves.

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This paper presents a calculation method for the 3-D steady cavitating hydrofoil problem. The method is based on a simplified surface panel method “SQCM” which satisfies the Kutta condition at a time even for the 3-D problem. Hess and Smith type source panels are distributed on the hydrofoil and cavity surface. Discrete vortices are distributed on the camber surface according to Lan's QCM (Quasi-Continuous vortex lattice Method). The boundary conditions to determine these singularities are the constant pressure condition on the cavity surface and the zero normal velocity condition on the hydrofoil and camber surfaces. The cavity shape in each spanwise section is determined so that the zero normal velocity condition is satisfied.
In the present method, a cavity length for each spanwise section is given first. Then the singularities, the cavitation number and the cavity shapes are determined. These steps are repeated until the cavity shapes are unchanged. Next, the cavity length is corrected by comparing the obtained cavitation number with the objective cavitation number in each section. By using the corrected cavity length, the calculation is restarted from the beginning. Above described procedure is repeated until the obtained cavitation number is converged to the objective cavitation number in each section. Cavity shapes, pressure distributions and forces acting on hydrofoils are calculated for four kinds of hydrofoils. Good agreements are obtained between the calculated results and the experimental data.

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Regression analysis and neural network were applied to evaluate the contribution of major factors of propeller geometry, wake distribution and attack angle variation to propeller induced pressure fluctuations and surface force on the basis of a large volume of data stored through the cavitation tunnel tests conducted at the Shipbuilding Research Centre of Japan during these two decades.
The measured and designated quantities in each case of the test and propeller geometry were readjusted as explanatory variables with properly non-dimensional expression taking into account of theoretical considerations. Not only 1st blade rate components of pressure fluctuation but also 2nd and 3rd components were examined as the target including characteristics of distribution and phase variations. Both multiple linear regression analysis and method of reconstruction learning of the layered neural network were applied.
Major results obtained are
(1) both cavitation number and tip clearance given as test conditions have significant effect on pressure fluctuations, as expected,
(2) effect of attack angle variation and wake distribution suggested by cavitation theory is also confirmed being significant,
(3) effect of propeller geometry is relatively less than that of hydrodynamic factors mentioned above, and
(4) regarding the characteristics of pressure fluctuation distribution, much influence of cavitation number is shown as a new finding together with marked effect of tip clearance as expected.

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The present paper proposes a theoretical design method for a transcavitating propeller. This method determines circulation distribution using a lifting line theory and a blade section using a lifting surface theory. The designed propeller has non-cavitating section near the root and supercavitating section near the tip, which are connected smoothly to each other. Eight propellers were designed and tested in a cavitation tunnel. The result showed that the present method designs a transcavitating propeller mostly within 5% accuracy of thrust.

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This paper describes an extensive experimental evaluation of eleven marine propeller models for a large high-speed inland ferry with a shallow draft. Six propellers were designed at 30.6 knots and the others were designed at 35.0 knots under each normal continuous output. Most of the suction side of the propeller blades was covered with cavitation and significant thrust breakdown was revealed; this is called the trans-cavitating condition. In each case, the design of the propeller was made by not only current methods but also a newly developed method which can theoretically control sheet cavitation on the propeller blades so as to satisfy a given thrust with optimum efficiency. The propellers designed by the former method and the latter one are called conventional propellers (CP) and trans-cavitating propellers (TCP), respectively.
First of all, this paper proposes a method to evaluate the propeller efficiency working behind a ship model under the trans-cavitating condition and a given propeller load condition. Secondly, experimental evaluation of TCPs was made in the SRI large cavitation tunnel with respect to the propeller thrust, propeller efficiency, pressure fluctuations and erosion. For the 30 knot case, conventional propellers still kept the same level of efficiency and lower pressure fluctuations than the TCPs, while for the 35 knot case, some TCPs showed better performance not only for the efficiency but also for the pressure fluctuations.
The present paper concludes that the TCP is promising for highly loaded propellers working behind a high-speed ship with a shallow-draft. Further investigations on the design of the transcavitating propeller and experimental techniques at low cavitation number are needed to improve the propeller performance with respect to the efficiency and pressure fluctuations.

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Existing theories for 2-dimensional foil sections can predict foil performance in noncavitating condition or sheet cavitation condition, but cannot predict foil performance in bubble/streak cavitation condition. In this study, the authors developed a new method to predict foil performance in bubble cavitation condition theoretically. Displacement thickness due to bubble cavity is calculated by solving Reyleigh-Plesset equation in an iterative method, and pressure distribution around the “displacement body” is computed.
Experiments are performed in a cavitation tunnel in order to verify the accuracy of new prediction theory. The calculated results by the new theory agreed well with the experimental results on foil performance. It is still difficult to predict foil performance when sheet cavitation turns into bubble cavitation.

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By applying an optimization method to supercavitating foil section design, the authors developed a new method to design super cavitating foil section automatically. Using this method, we designed 150 foils as a series foil sections. Then polynomial expressions were obtained by a method of least-squares for foil shapes and foil performance such as lift/drag ratio. By using these polynomials, one can obtain foil shape and estimate hydrodynamic performance for a set of a few design parameters including design lift coefficient and strength requirement. A trans-cavitating propeller (which adopted supercavitating-blade sections near the tip and noncavitating ones near the root) was designed using these series foil sections, and has realized high performance.

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In the 1 st report, a new technique for reducing frictional drag using a super water repellent surface and air-injection (SWR & A method) was proposed, and its effectiveness for two-dimensional flow was confirmed by carrying out pressure loss tests in a rectangular tube and resistance tests on a horizontal flat plate.
This paper presents the results of resistance tests applying the new technique to a tanker model of 7.2 m long and a high length-to-beam-ratio ship model of 12 m long. The results of these tests show that the new technique can significantly reduce frictional drag of the tanker model and the high length-to-beam-ratio ship model, and that frictional drag on the SWR surface of the 12.0 m high length-to-beam-ratio ship model was reduced by 75% at a speed of 6 m/sec, which is the same reduction rate obtained with the flat plate.

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Precipitation of dissolved materials during the mixing by a gravity current is investigated in the laboratory. The experiment includes the physical process as well as the chemical process of two miscible fluids of slightly different density. Ammonium carbonate and calcium chloride solutions are used for these fluids, and sodium chloride is also dissolved into the former solution to control the density difference between these fluids accurately. When these solutions are mixed during the physical process of the advancement of a gravity current generated by lock-exchange flows, the chemical reaction takes place to make calcium carbonate which hardly dissolves in water to be visible as white substance. The behavior of this visible suspended substance is analyzed by digital image processing.
The results show that the white substance made by the mixing of the two fluids appears most clearly in the upper region of the current head. The substance remains stationary and elongated downstream along the density interface. After a while it collects in masses of clouds in a three-dimensional way, and eventually sinks to the bottom. It is found that this chemical process depends on the dynamics of the gravity current, and that the chemical reaction is suppressed with increasing density difference.

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A numerical simulation method of the motion of a rowing race boat is developed in order to evaluate the performance of oar size and rowing pattern. The driving force of blade is measured experimentally. The resistance of the boat is referred to the experimental result carried out in a towing tank. The motion of crew, which is most important in the simulation, is evaluated from the equation of a boat motion where the other terms are experimentally measured. These measured external forces are modeled by Fourier series or polynominal expressions. The equation of a boat motion is numerically solved by use of Runge-Kutta method.
The Simulated boat velocity and force acting on blade are compared with the measured ones. The experiment was carried out in cooperation with the crew at Hiroshima University. Good agreement with the simulated results and measured ones shows that the present simulation method has merit to evaluate the rowing performance. Through the present simulation method, outboard length, blade area, stroke rage and phase of catch are evaluated.

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It has been suggested that the wave making resistance of a submerged body is reduced by downward lifting force. In the present study, it is focused to make more clear the characteristics of resistance of three-dimensional rectangular hydrofoils which generate downward lifting force. Measurements of drag and lifting force are carried out together with numerical simulations. The boundary element method is used for the simulation where an attached wake and the nonlinear free-surface conditions are invoked. The study is carried out by decomposing the total pressure resistance into the wave making resistance and the induced resistance components. The former is determined by the wave pattern analysis method for the computed wave patterns while the latter is by the subtraction of the wave making resistance component from the total resistance.
The numerical simulations, which have been validated in the beginning compared with the measured, show that the wave making resistance is reduced by the downward lifting force. It is also made clear that the wave making resistance has a minimal value of almost zero at a certain lifting force which can be related to the buoyancy force.
Effects of the submergence depth, Froude number and the volume and the aspect ratio of the hydrofoil are discussed.

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The direct parameter estimation algorithm is applied to the simple equation of rolling motions. The algorithm is composed of the IIR (Infinite Impulse Response) digital filters and RLS (Recursive Least Squares) algorithm. The IIR digital filters are introduced to avoid taking direct derivatives and to reduce the effects of measurement noise. Furthermore, the digital filters are free from the initial condition problem and the accumulation problem of integration error.
In order to discuss the quantitative accuracy, the authors carried out model experiments. At the first, the present method is applied to the time history data of free rolling motion tests in the still water. Next, the method is applied to the random rolling motion data in irregular waves. In both cases, there is satisfactory agreement of the dynamic rolling motion parameters identified by the present method and the previously measured parameters. This concludes that the present method is a powerful tool for on-line identification of dynamic rolling motion parameters. Finally, in order to verify the practical usefulness, we also carried out on board tests. The results of these tests are shown and problems encountered on applying are reported.

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Sailing yachts has been experienced extensively in the past years, generating very fast yachts. However, the search for speed has lead to very similar boats, with similar performance and, frequently, with poor behavior in rough water. The study of performance of sailing yacht in waves, experienced in heeled and yawed condition has been conducted, as well as the prediction of its motion in order to generate more data and provide tools to better design yachts for rough water. A deeper study of influence of the lateral force generated by the keel was done, testing the model with a normal fin keel and a pole keel (that did not generate lift). The free-running technique was applied in order to allow the model freedom for heeling and yawing. The resistance due to the attitude was obtained as an additional result. The conclusions are very interesting and intriguing and indicate the strong influence of the keel over the added resistance in waves, but the mechanism that rules that influence is not clear yet.

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The long term characteristics of mean added wave resistance (AWR) is very important from the view point of long term ship operation and ship design. Today, the short term prediction of AWR can be made through theoretical calculation. So, by using the long-term ocean wave data, we can carry out long term prediction of AWR. Here we carried out long term prediction, and found that the mean AWR follows the so called log-normal distribution. Furthermore, we investigated into the effect of wave data and ship form on that distribution. As wave data, we adopted the database of North Pacific Ocean by SRI and by BMT (GWS). As ship type, we adopted the bulk carrier with large B/d ratio.

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This paper describes a new concept for launching free-fall lifeboats proposed by Yokohama National University. Using the conventional single-skid free-fall system, as the fall height of the lifeboat increases, the potential for increasing incidence of dangerous lifeboat motions, in which the lifeboat moves backward or stumbles on the surface after entering the water, has been pointed out. One of the principal causes of this undesirable motion is rotation of the lifeboat during its restricted fall at the edge of the launching skid. Thus a new “double- skid” launching concept is proposed to effectively eliminate the rotation of the lifeboat at the skid end and to enable the lifeboat to move smoothly after entering the water. In order to confirm the performance of the proposed method a series of numerical simulations and model experiments are carried out in which two lifeboat models with overall lengths of 1 meter and 6 meters are used. The effects of design parameters such as skid angle, skid height, etc., are investigated and an example of the implementation of this new system at the stern of a large merchant ship is illustrated.

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When a large-sized ship, like a cargo ship or tanker, encountered a marine disaster and lost its ability to cruise, she must be towed immediately to a safe place to avoid a secondary calamity. In such a case, the course stability of tow and towed vessels would become a very important aspect from the viewpoint of safety for ship manoeuvring motion. An exact estimation of the hydrodynamic forces acting on tow and towed vessels is needed in order to predict accurately the course stability of tow and towed vessels by means of numerical simulation. However, any theoretical method estimating the hydrodynamic forces acting on towed vessels has not yet been established, particularly on the damaged vessels with a trim or heel angle. There are very few papers dealing with the hydrodynamic forces acting on capsized vessels with such a posture change as trim or heel angle. Therefore, an accurate estimation of the characteristics of hydrodynamic forces acting on capsized vessels with a large posture change is fundamentally necessary from the viewpoint of the safety in towing vessels.
The hydrodynamic forces acting on a capsized model ship with a geometrical configuration and its characteristics have been investigated. The numerical simulation by using the measured hydrodynamic forces acting on the model ship has also been done in order to examine the manoeuvring motion and course stability of the towed capsized vessel.

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This paper concerns an investigation of wave influences on viscous flow around a ship in steady yaw motion, which is based on detailed analysis of numerical solutions of Reynolds-averaged Navier-Stokes (RaNS) equations. The present numerical method solves the unsteady RaNS and continuity equations for mean-velocity and pressure and wave fields with exact nonlinear kinematic and approximate dynamic free-surface boundary conditions. In the following, an overview is given of the present numerical approach, and results are presented for the Series 60 C_B=0.6 at yaw angle 10°for with/without-wave cases, including wherever possible comparison with experimental data. Then discussions are focused on identification of salient feature of wave-included effects on the mean-velocity and pressure fields, body surface pressure and frictional streamlines, and hydrodynamic forces acting on the hull. Lastly, some specific aspects of flow for wave breaking and wave-induced vortices are described.

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An efficient hull form design needs to incorporate some prediction methods which will be able to predict the influence of hull form modification on the ship performance. This paper presents a new and simple prediction method for the form factor which relates directly to the hull form. Six flow-field parameters which have influences on the form factor are proposed on the basis of the result of double-model flow calculation and 3-dimensional boundary layer calculation around the hull form. A regression equation to predict the form factor is made by using 7 parameters (6 flow-field parameters and displacement-length ratio) and model test results in a towing tank. In order to adopt the minimum Akaike Information Criterion (AIC) estimate method in a regression analysis, 7 parameters are selected among many variations.
Predicted results for the form factor of full form ship at full load condition by the present regression equation show good agreement within 2% with tank test results. At ballast condition, predicted results show good agreement within 3%. Since flow-field parameters in the present regression equation act as intermediary between actual hull form and ship performance, a designer can easily obtain an information of how to modify the hull form according to the flow-field parameter in order to improve ship performance.

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For free surface flow computations with an unstructured grid, an interface capturing method using a level set function which is the signed distance from the interface has been developed. The level set equation is discretized by the finite volume method on an unstructured grid with the Euler backward scheme for the time integration. This procedure is coupled with the unstructured Navier-Stokes solver discretized in the similar manner. Due to the special extrapolation procedure to satisfy free surface boundary conditions, only the water portion of a flow domain needs to be solved. Numerical results for free surface flows around a hydrofoil and around a ship demonstrate the capability of the present solver.

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This paper describes a numerical method to calculate viscous ship flow with the overset composite grid approach based on fortified solution algorithm concept. Communication among the grids is achieved by interpolation based on small volume elements. In the present computation, the composite grid consists of three component grids. The primary grid is constructed with respect to the ship hull, and the subsidiary grids are generated about propeller and rudder. Propeller effect is considered using equivalent body force distribution in propeller grid. The individual grids overset and, once combined, cover the entire computational domain. This feature allows computational grids to be generated quickly and easily. The hydrodynamic force characteristics on a tanker [ESSO OSAKA], moving with constant rudder angle, agree well with the model experiments. It is shown that the present method can be an effective CFD tool for complex body configurations.

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In recent years, Very Large Floating Structures (VLFS) such as floating airport have been planned for effective utilization of ocean space. The VLFS is some times sheltered by breakwater depending on the situation. This paper presents an effective scheme for calculating the wave-induced hydroelastic response of VLFS including the effect of breakwater.
Part 1 report, at first, presented an effective calculation method of the diffracted wave field due to the existence of breakwater. And then it showed an approximate calculation method of the response of VLFS in that deformed wave field by the breakwater. In that method the mutual interaction between breakwater and floating structure was neglected.
This part 2 report presents an exact calculation method of the response including the effect of the mutual interaction. And it shows some numerical results paying special attention on the resonance phenomena which occur depending on the relation of incident wave length and clearance between breakwater and floating structure.

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A real elastic motion of a very large floating structure is complicated because a field that a VLFS will be installed is random sea area. Then, it is important to predict horizontal motions too, because slowly varying drift motion may occur in irregular waves. So, the motion responses must be investigated in irregular waves.
In this paper, one method in order to calculate a time series of wave drift forces is shown. The validity of that method and the estimation method of wave drift forces is confirmed by comparing with the corresponding experimental results. Then, the time histories of vertical and horizontal displacements are compared. And, this paper proposes the some examinations on the estimation method of the wave drift force. They are the effect of an interaction among directional angles of incident waves and the necessary term in order to predict it.

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Most studies on responses of a very large floating structure have been investigated in regular waves. So, estimation methods were validated in a frequency domain. However, it is important for validation with better accuracy and understanding the characteristics of responses to measure responses of VLFS in irregular waves. And, they must be measured exactly in order to compare with corresponding theoretical results in time domain.
Authors measured some responses by model tests, which can be compared with time series of theoretical results of responses in two-directional irregular waves. The present paper shows the measurement method of the responses of an elastic body, and proposes some results of the responses in not only uni-directional irregular waves but also two-directional irregular waves. Then, angles of incident waves were not only head or beam sea conditions but also oblique waves.

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The modal analysis method is very useful for the numerical calculation on elastic oscillation of a very large floating structure, while we have not discussed yet the applicability of modal analysis for the numerical calculation of sea shock response of a very large floating structure. Therefore, we introduce the direct calculation method which is a kind of the influence function method, and comparing both methods with each other.
The conclusions obtained by the present paper are that the calculation results of the modal analysis for elastic oscillation of a very large floating structure due to sea shock forces is not in good agreement with the direct calculation method which is more reliable. In addition, characteristics of sea shock response of a very large flexible floating structure in shallow water based on the direct calculation method are almost the same as the vibration of sea bottom and very close to those of a rigid structure.

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Nowadays the hydroelastic responses of very large floating structures have been predictable for regular waves. From viewpoint of practical use, the study on responses to irregular waves, arbitrary external loads and actual sea loads including validations by model experiments becomes indispensable. Furthermore, the reduction of response using certain adequate control devices to meet the motion criterion is also needed. Therefore, the development of a precise and practical numerical simulation method in time domain, and investigations through model experiments should be done further.
In this study, the experimental results of hydroelastic response and attitude control by using newly improved pneumatic pressure type actuators in long crested head regular and irregular waves are shown. Numerical simulations in time domain are performed and the results are compared with the experiments. The calculation results agree with experiments generally well for both regular and irregular waves in control and no control conditions. Moreover, the results of active control indicate that it is possible to suppress the deflection of a very large floating structure by using air actuator for waves of various frequencies.

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It is important to estimate slowly varying drift forces on very large floating structures (VLFS), since it may be happen that slowly varying drift forces would have frequencies close to eigen frequencies of VLFS-mooring systems. Considering with real seas, we should estimate slowly varying drift forces in multidirectional seas and, to carry out such estimations numerically, we may need large effort because of hydroelastic behaviors of VLFS. This is our first report to propose a method to evaluate slowly varying drift forces rather easily even in multidirectional seas. We showed that it is possible to neglect contributions from bottom slopes of VLFS to slowly varying drift forces when deflections of VLFS are small comparing with wave amplitudes. We validated the present method with model tests in long crested irregular waves.

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A new method is developed to evaluate radiation force acting on a large-scale platform that is composed of many floating elements. The order of the size of the platform is almost equal to the one of topographical feature change. Mild slope equation is used in order to taking into the influence of the topographical effect. The interaction between floating elements is also taken into consideration. Energy absorption at the seashore is modeled by two methods. Added-mass and damping derived by this coastal model is compared with those of flat bottom.

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Recently certain resonant phenomena in an array of cylinders in waves have been reported. At some specific frequencies, wave surface elevations between adjacent cylinders or pressures acting on each cylinder become very large. This resonant phenomenon is called trapped mode. In this paper, to investigate trapped mode, the diffraction problem of an array of rigidly fixed plates on shallow water in waves is studied. The effects of the number and space of the plates on the resonant frequencies are shown. The relationship among transmitted wave amplitude and the resonant frequencies is also shown. Considering the diffraction problem of two plates in waves, some prediction formula for trapped mode zone are proposed.

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Tsunami is brought about an earthquake in the bottom of the sea. Tsunami's wave height becomes higher in shallower sea. Under that condition, Tsunami is considered as shallow water long period wave. Wave load from Tsunami has much influenced to the motions and mooring tensions of a floating structure in offshore area. For this reason, wave load from Tsunami is essential to planning protection against calamities. Since, an estimation method on Tsunami wave exciting forces in the stage of basic design of floating structure has been presented in this study. Summaries of this study are shown as follows;
1) A concept of solitary wave corresponding to Tsunami has been proposed. Tsunami wave exciting forces can be calculated with lessor labor.
2) The effects of Tsunami wave loads have been made clear comparing two kinds of calculation results. The former is calculation results with Tsunami, the latter is calculation results with wind waves.

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A group of university researchers and Technological Research Association of Mega-Float made continuous measurement of temperature and salinity of the sea water around Mega-Float model, moored off Oppama, from August 1996 till December 1998. The purpose of the measurement was to examine the impacts of Mega-Float on surrounding marine environment and it was found that the effects were very small. In the meantime, these observation data is very useful for the verification of the results of numerical simulations which is thought to be one of the useful tools for environmental impact assessment. So we calculated the current flow, water temperature and salinity in the summer of 1996 in Tokyo Bay. In numerical simulation, to compare the results of numerical simulation with observation data directly, we use the observed field data such as the amount of solar radiation, wind velocity and direction, etc. as boundary conditions. Additionally, the effects of boundary conditions on the results of numerical simulations were also examined. It was clarified that the variations of water temperature and salinity were predicted well quantitatively and the simulation results are affected by the boundary conditions such as extinction coefficient of sunlight and wind velocity.

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When the phenomena in a bay are calculated, the open boundary is often located around the mouth of the bay. On the other hand, the effect of physical conditions of outer ocean is essential for such phenomena as thermohaline front or intrusion of warm water mass into the bay. However, it is difficult to elucidate the mechanism of such phenomena if the constant conditions are applied for the open boundary. In the present study, the influences of outer ocean state on the phenomena in the bay were investigated by numerical simulations. At first, the effects of fresh water discharge, surface cooling and outer ocean condition on the structure of thermohaline front was examined for an idealized model basin. Next, the numerical simulations were carried out for Tokyo Bay and the influence of water temperature distribution of Sagami bay was discussed. In the calculation considering the effects of outer bay region, the satellite remote sensing data was used for determining the sea surface temperature.

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A nonlinear simulation is carried out for the motion of the inviscid, incompressible fluid in a two-dimensional tank of barge for extraction of lithium from seawater that is subjected to forced oscillations. According to a conceptual design of the barge, seawater flows into the tank from suction valves on the inner bottom of the barge, then passes through the piled granulated absorbent and it is discharged out of the tank by drain pumps on the side hull of the barge. In order to solve the problem associated with the inhomogeneous domain of seawater and granulated absorbent, the basic boundary element method (BEM) is extended. From the numerical results obtained by the present method, the effect of forced oscillations on the fluid motion in the tank has been shown. The validity of the present method is confirmed by comparing with other publications for the special case of the problem. One is the sloshing of a two-dimensional tank which was studied by Nakayama et al. and the other is the fluid motions passing through the granulated absorbent with the steady flow from the bottom which was studied by Nobukawa et al.. It is confirmed that the calculated results agree well with others.

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While FSA of formal safety assessment is in marine terms still in its infancy, it is believed that such research will adopt a holistic approach to the design, operation and human aspects needed to make ships safer.
The generalized methodology of FSA is published as a guidelines, leaving detailed methods undetermined.
In the guide lines, human elements issues should be systematically treated within FSA framework, only with the words “appropriate techniques for incorporating human factors should be used”. For the problem of human elements introduction, the author proposed the methodology of the introduction in the same ring with structure issues.
To define recommendation for decision making, as a result of FSA, assessment should be made for potential risk control measures, options and cost benefit. The basic principle of the assessment is ALARP (as low as reasonably practicable).
In this paper, the author investigated detailed method and algorism to determine risk control measures with cost benefit. The risk control measures are always multiple variables. For example, these for an accident are route control, navigation apparatus and hull structure. The problem is how to determine the degrees of improvements for each measure. The method and algorism in this paper is, mathematically, the optimization of a function with discrete multiple variables, including author's human element introduction method.
The validity of the method is confirmed for some actual collision and grounding accidents.

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To verify the effectiveness of Minorsky's formula that is used in the current regulation of ship with anti-collision structure, the simplified analysis based on the rigid-plastic analysis is developed. The collision of test ship with T2 tanker and Suezmax class tanker is analyzed, and it was shown that the Minorsky's formula, which assumes same collapse length for striking and struck ship, gives incorrect estimation of the energy balance when the strength of ship bow and side has big difference. Also, the results are compared with those by dynamic FEM analysis, and good agreements are observed. It was shown that the simplified analysis method is an effective tool in the early design stage.

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This report is concerned with statistical analysis on long-term distribution of wave induced load. The relation between the statistical property of supposed wave condition and the long term distribution of wave induced load is studied. For long term distribution, authors examine which factor gives influence by load revel, such as significant wave height, average wave period of supposed wave condition and relative angle between ship course and wave direction. The analysis method is that the long term distribution is decomposed into every these factor and contribution rate of these factor in each load revel is introduced. The method is applied for the long term deck stress data measured by 2 destroyers and for the numerical estimation of long term distributions of double bottom stress of a bulk carrier. As the result, whether wave condition (significant wave height, and average wave period) and the navigation condition decide the distribution shape of the long term distribution can be made clear and whether wave condition and the navigation condition determine the maximum value of the stress in the vicinity of the probability of exceedance 10^-8 can be specified by using the proposed analysis method.

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This paper describes results of investigation on examples of hull damage relating to hull monitoring and examination of stress and acceleration of a large bulk carrier corresponding to condition of shipping seas and apparent slip ratio of propeller at rough seas using data through onboard tests.
Typical hull damage relating to cargo and ballast operation and hull damage relating to ship handling at rough seas were extracted and studied from a view point of hull monitoring.
Condition of shipping seas based on log book was used in the examination and the results show that deck longitudinal stress at midship well correspond to condition of shipping seas. It is also found that vertical acceleration at bow well correspond to condition of shipping seas as same as longitudinal stress.
Apparent slip ratio of propeller was obtained using mean value of ship speed and propeller revolution. The results show that deck longitudinal stress at midship well correspond to apparent slip ratio of propeller in head and bow wave. It is also found that vertical acceleration at bow fairly correspond to apparent slip ratio in head and bow waves.

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There are many unknown variables at the initial stage of ship design. Since the computational time of finite element analysis including modeling is large, it is not appropriate to use finite element method at this stage of ship design. In this paper, structural analysis by transfer matrix method for longitudinal and transverse strength is implemented for container ship design. Genetic algorithm is used for an optimization method, since discrete design variables can be handled easily. The method also has advantage that globally optimized solution can be obtained. The objective function of cost minimization is considered, and its result is compared with real ship.

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In this paper, the theory of fuzzy set is introduced to the optimization of engine room structure considering the dynamic response constraints. Two ways of solving the fuzzy optimization are investigated. Firstly, the constraints of static stresses and dynamic response to the external excitation are handled by the fuzzy set theory. By this approach, a family of optimal designs under different degrees of satisfaction with constraints for the structure can be obtained. Secondly, the objective is also considered to be a fuzzy variable with its own membership function. Through maximizing the degree of membership to the fuzzy decision, a crisp solution can be provided to designers. A Genetic Algorithm (GA) is applied to do the optimization. The optimum results for the numerical example are presented and it is shown that the proposed method for the dynamic response optimization is applicable.

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The concern of the paper is the transient behaviors of a VLFS (Very Large Floating Structure) subjected to dynamic load induced by airplane landing/taking-off. A series of weight dropping test and a series of car running test have been carried out in SRI using a scale model, VL-10, which was designed similar to the Mega-float prototype VLFS. These kinds of dynamic behavior are regarded as most essential phenomena in airplane landing/taking-off. Elastic response of the structure to vertical or horizontal transient load has been investigated through experiments and calculations, then the characteristics of the behavior of VLFS will be discussed focussing on the hydroelastic effects.
A time-domain analysis method which can be applicable to the hydroelasticity problems for VLFS has been developed. The method is based on FEM scheme to treat structure and Wilson's θ method to pursuit time step procedure taking advantage of the memory effect function for hydrodynamic effects. The present calculation method has been applied to the analysis of the tests. The effectiveness of the method has been verified through comparing the calculated results with the tests.

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This paper deals with progressive collapse behavior of mooring system of very large floating structure. We have studied progressive collapse behavior of mooring system of barge type floating structure which is installed in calm sea, moored by dolphin mooring, and protected by break water. In this report, floating structure installed in open sea is considered. The wave condition may be so strong that semisubmersible type is reasonable rather than barge type. The water depth may be so large that it should be moored by inclined tension legs.
Time series program which models in-plane elastic response as a beam and anti-plane elastic response based on the theory of plates is made and progressive collapse behavior is simulated.
An experiment was made on collapse behavior under regular and irregular wave using 1/333 scale model of semisubmersible type floating structure moored by inclined tension legs. Mooring rope is set to be cut off from floating structure when the load on the rope is over preset value.

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Response characteristics of semi-submersible type VLFS are discussed for optimization of the structural configuration. In this paper column diameter, column spacing, deck rigidity etc. are treated as components consisting the structural configuration. The problem is qualitatively discussed by use of results derived from simple analytical method and quantitatively estimated by numerical analysis. Semi-submersible type VLFS which is supported on many columns of large diameter is rationalized for large scale use such as air-port application from the view point of response characteristics through parametric studies and tank test.
We also discuss design methodology of semi-submersible type VLFS. The most dominant parameter governing its response characteristics was proved to be column configuration, that is, the ratio of column diameter to length between columns, which is related to restoring force.

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When a drilling riser is operated, tension is applied to maintain configuration of the riser and protect it from collapse. In the emergency condition, for example drift off or drive off of drilling vessel, the riser is disconnected at top of the BOP which is placed on the sea floor. When disconnected, the riser starts to lift and recoil, and if the tension is not properly reduced the riser hits the vessel and destroy both the vessel and riser. If the tension is reduced too fast, riser can not reach the vessel and riser drops on to the sea floor and destroyed. An anti-recoil system is necessary to protect the riser and vessel from destruction and make the catching successful.
In this research response prediction system of disconnected riser is developed considering coupled response of riser and dynamic response of internal and external fluid. Vessel heave motion prediction system is also developed. An algorithm is developed to search catching timing from the both predictions of riser motion and vessel heave motion. To achieve successful catching, the catching timing must satisfy catching condition of no relative displacement, velocity and acceleration. Once the catching timing is found, riser disconnection timing is determined from the predicted riser motion. Feedback control is employed at the final stage of catching to adjust and absorb modeling errors and prediction errors and secure successful catching. Effectiveness of the developed algorithm is verified by simulation calculation.

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In this paper, a stress sensor using piezoelectric element is developed to monitor the feature of stress history of structural member. The sensor is a rectangular box (90mm long, 60mm width and 25mm thick) made of thin aluminum plate, in which piezoelectric element, electric circuit including integrating circuit, button type battery, make and break switch, stress level meter using light emitting diodes (LED) and stress level cross counter are facilitated. The stress level meter can turn on and off different color diodes according to the change of stress level. The stress level cross counter can display the number of cycles which exceeds a specific stress level during a monitoring period. The sensor is bonded onto the structural member by using adhesive agent. The monitoring period can be determined by the attached switch.
In order to see the influence of the installation method on the performance of the sensor, experiments are carried out using a fatigue testing machine. The sensor is bonded onto a smooth specimen and multiple repeated stresses are applied to the specimen. The output signals of the sensor are investigated by changing wave shape, stress amplitude and frequency. Followings are made clear from the experiments.
1) The thickness of the sensor box influences on the measuring performance of the sensor.
2) The sensor can operate until the yield point of the mild steel. Upper limit of the measuring by using piezoelectric element is about 260 JVIPa or 1200 micro strain.
3) It is shown the possibility to measure stress of structures which have curved surface by using piezoelectric film (PVDF).

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For the vibration analysis of floating structures, fluid-structure coupled analysis method which combine the added mass matrix into FEM has been used since many years ago. However, this method has some problems.To solve those problems, reduced added mass matrix method was proposed and this method needed the rotation vector for vibration analysis of higher order modes.
In this paper, the method of extracting rotation vector in experiment is used by MCE (Modal Coordinate Expansion) method. The modal structural modification analysis is done by using the eigenvectors in 6 directions which contain the extracted rotation vector. This calculation is compared with the experiment in water condition, and the importance of eigenvector on fluid-structure coupled vibration analysis is shown.

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The outstanding obstacle to estimate vibration level is that the precise damping of fluid and structure can not be estimated because the mechanism of the damping has not been explicated. Recently, the damping matrix based on dissipation energy caused by fluid viscosity has been obtained, and the damping matrix is expressed more rationally by introducing modulus of velocity distribution β_w as a parameter to estimate the influence of the water depth. We developed a method to obtain β_w both in the shallow water and in the deep water, by using experimental data in the air. But it is generally impossible to make an experiment using a real ship in the air.
In this paper, we propose a method to obtain β_w by using only data in different water depths. Concretely, authors incorporate reduced added matrices into transfer function by means of modal structural modification analysis, and formulate the partial differential iteration method by using the transfer function. The formulation and the results are described.

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In the optimization of the complicated structure, the computational cost increases rapidly as the number of design variables increases. And we need a great amount of calculation and time on problems of modified dynamic characteristics of large and complicated structures. In this paper, the multi-level optimization is used, which decreases computational time and cost.
The multi-level optimization methods used in this study are as follows : In the first step, the dynamic characteristics is controlled for the simplified two-dimensional model of stiffened plate by sensitivity analysis and quasi-least squares methods. In the second step, the cross-section of the stiffener is decided so that the weight is minimized under needed constraints. In the third step, the three-dimensional model is made based on the results of the first step and the second step, and then confirmation calculation of the dynamic characteristics is carried out.
The vibration characteristics of the stiffened plate is examined, and some main vibration modes are studied. The simplified equation for the main vibration mode of stiffened plate is proposed. In the multi-level optimization, the dynamic characteristics of the stiffened plate is changed by the proposed simplified equation and the effectiveness of the method is examined. It is shown that the results are effective in the optimum modification for dynamic characteristics of the stiffened plate.

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The some model tests on pressure loads induced by granular cargo were carried out. This paper describes the properties of static and dynamic pressure distributions measured on panels of the tank model. And a simplified method to estimate the pressure loads applied by granular cargo to the bottom plates and side walls of cargo holds is proposed.
The findings obtained from the present investigation are as follows :
(1) The new measuring method without soil pressure gage was useful for measuring the granular cargo pressure.
(2) The static component of granular cargo pressure acting on side walls and bottom plates of hold increases according to tightening of granular cargo, but the dynamic component of the pressure caused by vertical or horizontal acceleration decreases in tightened condition.
(3) The formulation based on the Janssen's theory which estimates both static and dynamic granular cargo pressure distributions adequately was proposed.
(4) The pressure loads estimation has been performed for the simple full-scale hold loading granular cargo, and the validity and usefulness of the proposed method have been demonstrated through the comparison with the measured value of Kuramoto's full-scale tests and the estimated value of ABS SAFEHULL method.

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In this study, an effect of residual stresses on brittle fracture initiation for a structural steel is investigated on the basis of the Local Approach. Compressive residual stress is introduced by pre-loading at a room temperature and the subsequent fracture test is conducted at low temperatures (-75°C and -40°C) with a high strength steel of 780 MPa class. It is shown that the pre-loading apparently elevates the critical load and critical CTOD at the onset of brittle fracture initiation. This is explained in terms of the effect of a compressive stress field near the crack tip. This paper employs the Weibull stress fracture criterion to evaluate the brittle fracture resistance of the pre-loaded specimen. The assertion is that the critical Weibull stress at brittle fracture initiation is a material property independent of test conditions with and without pre-loading. Using the Weibull stress fracture criterion, the critical CTOD of the pre-loaded specimen can be predicted from fracture test results of the specimen without pre-loading.

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This paper employs the Local Approach for the evaluation of the fracture performance of a large structural component. The material used is a high strength steel of 490MPa class for steel-framed structures. Hollow-section beam specimens are constructed, where shallow V-notches are introduced at the edge of the flange. Conventional fracture mechanics procedures can not be directly applied to the notched component, because they have a basis on a crack or a crack-like defect. Three-dimensional FE-analysis demonstrates that the shallow V-notched component holds a considerably relaxed stress field compared to the fracture toughness specimen with a deep crack. This is due to a large difference in the near crack/notch tip constraint between the component and toughness specimen. This study insists that the Weibull stress, an integrated stress over the fracture process zone, is a measure of the fracture driving force of both notched and cracked specimens. The fracture load and fracture strain for the hollow-section beam with shallow V-notches can be predicted from the fracture toughness test results based on the Weibull stress criterion ; the critical Weibull stress at brittle fracture initiation is a material property regardless of the type of a notch/crack.

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