As a result of the remarkable advancement of optical fiber technologies, a long-scale ocean measuring system, which has formerly been considered to be impossible to realize, seems to become possible to be developed. A optical fiber measuring system, in which the fiber is used as a sensor element and as a transmission line at the same time, is considered to have the most suitable for ocean measurements, because it enable us to perform the long-scale, continuous and distributed measurements. But the system (sensor) developed so far is only for the distributed temperature measurement in ocean. In ocean, the flow profile measurement is as important as the temperature one. But neither a proposal nor a trial has been presented up to now to apply the system for a long-scale, continuous and distributed ocean flow measurement.
In this paper the new concepts of both the flow sensor and the distributed flow sensor using a polarization maintaining optical fiber were introduced. The measuring principle is based on counting the vortex number per unit time (vortex shedding frequency) shedding from one side of a vortex generator using the photoelastic effect generated by the fluctuating lift which acts upon the optical fiber. In order to make clear the usability of the principle, the countability of vortex frequency by the optical fiber must be investigated. Therefore the authors executed preliminary test using city water, and then wind tunnel test to get experimental data in uniform flow. The diameter of the optical fiber used in the tests is 0.9 mm. As a result of the tests, it was clarified that the detection of the vortex shedding frequency of the flow rate was possible in case of the Reynolds number (fiber diameter) greater than 160, and that the flow rate could be calculated by using representative experimental equation derived by Roshko. And the possibility of flow profile measurement was made clear.
Thus the authors conclude that this paper gives a basis for development of ocean flow measuring system using a polarization maintaining optical fiber.

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A computational and experimental study on the flow around the strut-plate juncture with zero and 5° angle of attack is presented to make clear its flow characteristics. The separation lines on the surface of the plate and the strut being visualized, the flows are simulated by solving the Navier-Stokes equations for the two Reynolds numbers, 10³ and 10⁴. The computational results seem to agree with the visualized flows qualitatively. Characteristics of the junction flow are discussed by making use of the computational results. It is made clear that the effects of the Reynolds number and the angle of attack on the flow are noticeable. The estimated pressure and skin friction on the strut showed a strong three-dimensionality in spanwise. It can be concluded that such numerical studies can be an effective tool for the study of complicated flow.

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A finite-volume method is newly developed and applied to a flow about a ship. It employed an explicit time-marching procedure with the subgrid scale turbulence model without any wall function on the body surface. The curvilinear grid system is fitted not only the hull surface but also to the free-surface which is deformed with respect to the wave motion. Simulations are carried out for the HSVA tanker with and without free-surface as well as the Wigley's hull with free-surface. The comparisons between simulated and measured results show quite excellent agreement in the waves, pressure and wake distributions. The simulated results reveal the systematic formation of the longitudinal vortices, the flow separation from the hull surface, the generation of vortices in the vicinity of the free-surface and the complicated interaction of vortices near the after end of a ship.

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This paper deals with numerical computation on surface waves which are generated by a running pressure disturbance. The characteristics of this computation are that including viscosity terms, the three dimensional Navier-Stokes equations are treated and that the distribution of a pressure disturbance is arbitrary and this enables computational method to apply widely, for example to the complex waves behind a high-speed planing craft.
The validation of computational results is not so easy at present because there is few experimental reports and this time, for the convenience, it is compared with the results of analytical calculation by Standing's method.

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Hull form improvements of a fishing vessel fitted with non-protruding bow bulbs are presented in this paper. Non-protruding bulbs are developed by Calisal et al., who call them side bulbs, to overcome the situation that classical protruding bulbs are not suitable for the operation of seiner nets. In the present work, a fishing vessel used off the coast of Canadian pacific is improved under several design constraints by means of nonlinear programming, in which the stability constraint is included. In order to verify these improvements, towing tests and wave analyses are carried out for models of improved hull forms. In the process of these experimental verifications, a simplified estimation method of resistance is also shown with respect to improved hull forms, which is based on the correction of thin ship theory by using the resistance data of the parent hull form.

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In the previous paper (Part 1), the authors have showed that a monohull displacement-type vessel of abt. 10, 000M. T. can navigate 5, 000 nautical miles at 50 knots. This paper presents detailed study on her resistance and propulsive property.
As for a displacement-type high speed vessel, it is important how to minimize wave-making resistance and spray resistance. Reforming the Ovoid-Type hull form obtained by semi-submerged ship theory, the Improved-Ovoid-Type hull form has been developed by experimental and theoretical approaches. This sophisticated hull form shows the better performance concerning with the spray drag and the viscous resistance.
With regard to high speed propulsion systems, a conventional triple screw system with two pods has been applied. As the results of cavitation tests, it was revealed that the ship speed would be limited to 46 knots due to the thrust break down phenomena. This limitation, however, can be removed by equipping a contra-rotating propeller system.

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On the R & D of a displacement-type monohull vessel suitable for high speed navigation, seakeeping qualities in rough seas are one of the most important subjects to be investigated.
In high speed range up to 50 knots, there still remains uncertainty of the applicability of theoretical prediction methods such as Strip Method. Therefore, seakeeping model tests in head sea condition were carried out in regular and irregular waves for experimental studies. Frequency response functions and short-term responses in irregular waves were obtained about ship motion, acceleration, relative motion, and vertical wave loads.
As the results of comparison between theoretical calculations and experimental results, it is revealed that the Strip Method can roughly estimate ship motions and wave loads even at F_n =0.6. For the prediction of short-term responses in irregular waves, however, experimental value of frequency response functions should be used.
From the investigation of seaworthiness in irregular head waves of various sea states at various ship speeds, it is estimated that the displacement-type high speed ship has generally a good seakeeping quality on ship motions and vertical wave loads. However, vertical accelerations and relative motions at bow are estimated to be significant in high speed range in long-mean-period irregular waves.

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A forced Mathieu type capsize equation is examined numerically on the basis of the nonlinear dynamical systems theory. It is shown that the capsize boundary in the control parameter plane, which consists of the forcing amplitude and the forcing frequency, is varied in a complicated and fractal like way as the amplitude of the parametric excitation increases. It is also shown that the Mathieu's first (principal) unstable region is formed from a part of the second (fundamental) unstable region and is developed as the parametric excitation increases. The capsize boundaries in the other control parameter planes and the variation of the safe basin in the initial value plane are also examined.
Qualitative characteristics of the solution are examined by means of the bifurcation diagrams, which are obtained by slowly increasing one of the parameters, the forcing amplitude in this paper. It is clarified that there are two kinds of the period bifurcation in the Mathieu type capsize equation. One is the ordinary type, which leads to the capsize through a cascade of the period bifurcation including the chaos. In this case the period bifurcation and the chaos should be regarded as the precursor of the imminent danger of the capsize. Another is the parametric type period bifurcation, which appears suddenly as a period doubling bifurcation and sometimes goes to the period quadrupling bifurcation but goes back to the fundamental solution of the period one as the forcing amplitude increases. In the latter case the period bifurcation never leads to the capsize as far as judging from the bifurcation diagram. Therefore the parametric type period bifurcation can not be regarded as the precursor of the capsize, though it is confirmed that the Mathieu's first unstable region is dangerous if the parametric excitation is large enough.
Some examples of the solution including the superharmonics and super-subharmonics, which appear in the third and sixth unstable regions, are illustrated in the form of the time histories and the phase portraits. By these numerical examinations some aspects of the solution of the forced Mathieu type capsize equation are clarified.
In order to clarify the totality of the global and local characteristics of the solution of the forced Mathieu type capsize equation, further numerical as well as analytical examinations should be continued.

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An analytical and experimental study of the side force and yaw moment on a ship model towed in severe quartering waves has been conducted. In order to investigate the side force on the ship with heave and pitch motions in a very low encounter frequency, extensive model tests have been carried out. The side force is divided into Froude-Krylov force, diffraction force and lift, and discussed in detail. The effects of heave and pitch motions to side force on the ship are investigated by taking into account the change of submerged sectional area. Comparisons of the experimentally determined force on the model and a theoretical prediction are presented.

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Results of numerical and experimental study are presented of the wave forces acting on a blunt ship advancing in oblique waves. A 3-D panel method using a new numerical scheme proposed one of the present authors for evaluating the Green function was applied to numerical estimation of wave forces in short waves provided that the line integral and the steady disturbance on the body surface can be neglected, and the numerical results are compared with the experimental ones in full detail.
The effect of the number of discretized panels on the body surface is investigated by increasing the number of panels from about 400 to 1600 and it is confirmed that the number of panels affects significantly accuracy of computed second order steady forces but the effect is not so remarkable on the first order wave forces.
Two different descriptions of the wave term of the Green function, one is the monopole type and the other is the panel type obtained by integrating analytically the monopole over the panel, are also investigated. We confirm that as large number of panels as the monopole type is necessary to obtain the accurate solutions even if the panel type estimation is adopted.
The present study confirmed that 3-D panel method is useful to predict the wave forces comparative-ly in long waves, while in short waves it does not give such accurate solutions as be in good agreement with experiments even if the large number of panels is used.

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This paper presents a concept about activating and optimizing procedures of an activated anti-rolling tank system. The concept consist of utilizing a numerical method of analyzing a feedback control system of ship roll motion in waves by a U-section anti-rolling tank and of utilizing an orthodox analytical method (U-tube theory). The computer program of the numerical method is newly remade for fluid dynamic motion in the tank on the basis of the SOLA-SURF scheme.
A series of numerical computation are executed for six anti-rolling tanks by using the newly-remade computer algorithm, and the damping characteristics of fluid tank and the period of natural oscillation of fluid in the tanks are estimated by means of analyzing the numerical results. And, several problems are discussed for activating and optimizing procedures of the fluid tank system for ship stabilization.

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When we investigate the flow around a bluff body such as a circular cylinder, we have to consider hydrodynamic forces induced by an unsteady vortex shedding. The shed vortex sheet is supposed to be deformed three dimensionally or sometimes has an irregular structure, even in case of two dimensional cylinder.
It is well known that the lift force (transverse force perpendicular to the oscillating direction) occurs even for a symmetrical circular cylinder and the magnitude of the force is the same order as that of the in-line force. Furthermore it has been confirmed that the lift force varies irregularly. Those characteristics of hydrodynamic forces have not become clear yet. Forces may act on the circular cylinder with a periodic structure called as the correlation length along the direction of an axis, and that under some conditions lift forces are surprisingly varied three dimensionally as the behaviors of lift forces are unperiodic or chaotic. Now it is strongly required how the lift force is estimated for designers of marine structures.
We have reported experimental results of hydrodynamic forces acting on a vertical circular cylinder oscillating sinusoidally at low frequencies in the still water, to examine the flow around a circular cylinder, particularly the three dimensionality and the irregularity of lift forces at low Keulegan-Carpenter number (Kc), From those results it was shown that three dimensionality of the lift force is remarkable and the value of the correlation length along the direction of an axis might be the same order as a diameter of the cylinder. However, roughness of the cylinder, which means the slits between each test section of six-divided model, has much effect on the flow including three dimensionality. For that reason we could not estimate the value of the correlation length by using the six-divided model, the test section of which consists of six slices of cylinders.
In this study, to investigate the flow around a cylinder, especially the three dimensionality of the flow with reducing effects of roughness in more detail, we measured forces with the same methods with four kinds of cylinders. Each cylinder has a value of the length-to-diameter ratio L/D (L : length of test section, D : diameter= 12 cm) of a test section (one-body model), L/D=1, 2, 3 and 4. The reduction rate of C_Lrms due to three dimensionality was obtained. Furthermore the behavior of the lift force was examined from a viewpoint of chaos. It was shown that the correlation dimension is a good index representing the characteristics of the forces.

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Since the response of a panel to moving impact pressure has been shown to differ widely from that to stationary uniform impact pressure. Therefore, before we can clarify the dynamic effect of slamming pressure upon the bottom plate of a high speed craft, a more thoughtful investigation into slamming pressure must be performed, not only the peak values but also the spatial distribution and temporal variation of the water pressure on bottom while travelling in waves.
In this paper, a series of test in waves was carried out to measure heave and pitch, acceleration at C. G. and bow, and water pressure at 17 points located on the bottom of a hard chine type model. The time histories of water pressure recorded were compared to the results of the theoretical simulation, which is principally based on a nonlinear strip synthesis. Although the agreement of peak values of impact pressure is less satisfactory, the present theory was confirmed to be a useful method to obtain an overall description of the spatial distribution and temporal variation of the water pressure acting on the bottom of a high speed craft in head sea.

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Fatigue analysis becomes more important recently at structural design stage of large ships, such as VLCC and large bulk carrier. In fatigue analysis of a ship, it is necessary to know precisely how the distribution of dynamic pressure on the hull is and how much the amplitude of the pressure or resulting stress is. Hydrodynamic pressures on the hull of a ship in waves usually consist of the following two components ; outer pressure due to incident waves and resulting ship motions, and inner pressure due to the acceleration of the liquid cargo and/or ballast water. As for the former one, there exists a big problem in nowadays design stage, that is ; pressure acting on the side shell between actual wave surface and still water line cannot be calculated by linear theories. On the other hand, there are two types of assumption are adopted so far in order to estimate the inner pressure. Under one assumption, the point of zero-pressure is taken to be on the wall where the acceleration is negative, while the point is on the center of the tank under another assumption. Although the validation of these two assumptions is not easy, it is necessary to know how much the difference in the results is. Moreover, phase differences of these outer and inner pressures are important in fatigue analysis.
In the present paper, hydrodynamic pressures of large ships in waves are investigated for fatigue analysis. Considering the abovementioned problems, the characteristics of the outer and inner pressures are clarified.

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In this paper, a three-dimensional (3D) numerical simulation based on the Marker-and-cell (MAC) method is used for the study of sloshing phenomena in marine vehicles. In order to develop a practical method to predict impact load on tank ceiling, emphasis is given to the numerical treatment of the impact boundary condition on tank ceiling. At first, two-dimensional (2D) numerical simulations are conducted, and the results are compared with the corresponding experimental ones to investigate the parameters which affect the impact load simulation. The same parameters are used in the next step in 3D simulations. The influences of submerged internal structures are also analysed. The results of 3D impact load simulations and experimental data are found to be in good agreement. The comparison of the response amplitude operators of the dynamic pressure by the present numerical simulation, linear theory and the model experiment shows non-linear effect and emphasises the importance of 3D simulation for the analysis of sloshing.

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Wave forces acting on a test cylinder fixed to an offshore platform were measured to determine the nature of the hydrodynamic force exerted on a structure in random waves. Forces were measured by two dynamometers, wave height and direction were determined using a wave height meter array, and information on the orbital velocity was collected by a three-component current meter set near the test cylinder to confirm the accuracy of the phase and amplitude of this velocity calculated from the height meter array data. The inertia coefficient (C_M) and the drag coefficient (C_D) of the test cylinder in irregular waves were obtained, and laboratory studies developed a method of data analysis. The following was found :
(a) Constant values of C_D and C_M obtained from least square fit of the complete force time series are well ordered as a function of significant value of K_C numbers while the values determined from least squares fit on a wave-by-wave basis are widely scattered with no apparent meaningful tendency.
(b) Ocean wave forces exerted on the cylinder are represented well by Morison's formula ; the difference between the measured and predicted force by the formula is 10% and was very stable throughout the field experiments.
(c) Transverse forces acting on the cylinder when it is fixed in irregular waves are weaker than those impacting when the cylinder is fixed in regular waves.

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To measure a response, such as wave induced bending stress, for about 20-30 minutes is usual in full scale measurement, while in the case of measurement by scratch extreme stress gauge duration of it is 4 hours. In the latter case, they have never studied theoretically the type of distribution of extremal value of stress measured by the gauge.
Authors study the problem from theoretical base. At first, authors pay attention to the group of peak value of stress measured for such longer time. The measured stress probability distribution consists of several group of distribution each of which is approximated by a Rayleigh distribution. By numerical analysis, it is found that the extremal distribution for such group is approximated by the Rayleigh distribution that have the largest parameter among the distributions. It means that an extreme distribution of the parameter has a significant effect on the long-term distribution of extreme values of a response.
Usually the value of the parameter of the Rayleigh distribution, R, have a significant effect on the adjacent value of R. This means that a sample distribution of R is regarded as a distribution of samples drawn from a group, member of which subjects to a Markov chain. Authors make clear that the extreme distribution of R is approximated by a Weibull distribution by numerical simulation.
It follows that a long-term distribution of extreme value of response is also expressed by a Weibull distribution approximately. By authors study, it is concluded that a result of measurement for such longer times is to be regarded as a sample from a population having a Weibull distribution.

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In the first report the authors presented a numerical simulation method on the falling motion of a freefall lifeboat with experimental verification and proposed, as its application, tentative criteria on geometries of the freefall lifesaving system for the safe entry into the water.
In the present report they develop further a numerical method to simulate the falling motion of a freefall lifeboat from a cradle on a ship oscillating in the vertical plane. The method is verified through an experiment where a wooden block slides off from a slope on a swinging frame. In the discussion of the results they deal with the interaction between motions of the wooden block and frame. They calculate, using the method, the effect of the ship motion on the entry attitudes of the boat. The followings are concluded from the calculation :
(1) The present method is of practical use for predicting the falling motion of a freefall lifeboat from a cradle on an oscillating ship in waves.
(2) The angular motion of the cradle does not effect so much on the entry attitudes of the boat in the practical ranges of amplitude and period of pitching motion of the ship.
(3) The surging motion of the cradle effects more on the entry attitudes of the boat than the heaving motion of same amplitude.
(4) The combination of phases releasing the boat in surging and heaving motion brings about changes in the entry attitude from the stationary cradle. It is roughly assumed, however, that the simple superposition of those independent motions gives a general tendency of the changes.
(5) A combination of those releasing phases makes a zone of the safer entry than the entry from the stationary cradle. A zone of particular combination of phases can lead to the dangerous entry.
(6) The real ship motion concerned is sufficiently described on a “ship motion phase line”, which is defined in the present paper, when the ship and incident waves are given. The entry attitude calculated along this line provides useful information for the design and usage of the freefall lifesaving system for the ship.

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Conceptual designs and initial planning of systems which are extremely subjective to the decision maker's discretionary powers, require a methodology of overall decision making, to perform the balancing act in a multi-criteria objective situation. A method of breaking down the decision making process into different analytical models and their proper evaluation using the fuzzy theory was established in the first report.
However, the model forces the perpetual threat of an inexperienced decision maker super imposing the same item more than once during the decision making process and thus degrading the actual purpose of the model. The same situation arises even when the decision maker fails to achieve the best trade-offs available in a particular situation.
This paper tries to correlate the different items and establish the degree of agreement between the interacting factors, to find a process of regenerating the proper judgements through a repeated decision making process. The evaluation problem of an intercity transportation system is taken as an example to demonstrate the applicability of the present method.

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Since exact controls of heat and moisture states in enclosed environments are necessary to make the enclosed spaces such as cabins comfortable, it needs to consider the heat and moisture released or absorbed from surrounding walls as well as those from inner air. Moreover, it is too complex to solve the states as a three-dimensional problem accurately and the method of considering conduction of heat and moisture across the surrounding walls only by means of average thermal conductivity is not fully reliable.
In order to deal with the heat and moisture released or absorbed from the surrounding walls, we introduce new concepts-heat penetrating rate and moisture penetrating rate, based on which a mathematical model for the control of space states is established. Furthermore, results of simulations carried out by using the present model and those of experiments are compared with each other to justify the validity of the present mathematical model.

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This paper deals with a new digital type of marine engine governor which can regulate fluctuations of not only propeller revolution but also torque. The basic models for predicting their fluctuations are a control type of multi-variate auto regressive model which is fitted by minimum AIC estimate procedure. Using these models, the authors designed two types of marine engine governor. Actual on-board experiments are carried out by using a small type of training ship with a controllable pitch propeller.
In this paper, the authors report on the results of the actual experiments and make clear that the newly proposed engine governor can regulate the propeller rpm and the torque at the same time.

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It has been discussed some time that in optimal design of plate with thickness as design variable, many thin ribs appear and optimal solution is very mesh sensitive. To prevent this difficulty, the expansion (relaxation) of the solution space is done so as to include microstructure, and structural optimization can be carried out as the optimal distribution problem of the microstructure, which include layout optimization as well as shape optimization.
Formulation of plate equation for the plate with rapidly varying thickness is derived using homogenization theory, under the assumption of Y-periodicity. The optimization is formulated as minimize mean compliance under constraint on the total volume of material to be used.
Using this method, the optimal shape and layout of plate structures were obtained and it was shown that in statically indeterminate plate structures the hinge lines appear in the optimal solutions, which is distinct in plate structures.

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In general, ship basic design is based on design-spiral approach where variable design parameters are defined through repetition of trial and error. This kind of approach is a process of satisfying a lot of complicated design criteria empirically, rather than optimizing some object function. However, in order to realize optimum or rational design for a new type of structural concept with complicated design criteria, it is necessary to model the design problem as strictly as possible and accomplish more highly numerical optimization.
As for ship structural optimization, the object function (hull steel weight or total cost including material, fabrication and paint cost) is closely related to principal dimensions and general arrangement. Therefore, in order to obtain better design in the optimization process, it is desirable to search broader design space with many design variables such as principal dimensions, arrangement, frame spaces, stiffener spaces, scantlings and material.
This type of optimization is considered as a combinatorial optimization problem, and such optimization method that is robust and quickly converging to global optimum is required. In this paper the authors apply the genetic algorithm which simulates the law of the survival of the fittest to structural optimization problems.
At first, the authors apply the genetic algorithm to minimum weight problem of a hatch cover with 6 independent variables, and compare several approaches to the genetic algorithm through numerical experiments. As a result of the examination the authors propose the genetic algorithm which attaches importance to vicinity search as the method appropriate for structural optimization problems.
Then, the authors apply the genetic algorithm to the optimum design problem of a double hull tanker with 40 independent variables. It is shown that the proposed method is effective for the optimization with a variety of independent variables of different types. Using this method it is possible to obtain more accurate optimum design of ship structure by enhancing the accuracy of the estimation of object functions and many appropriate constraints.

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A new buckling design formula of plate panels subjected to combined loads, which is available in the elastic and/or elasto-plastic ranges is proposed. The effect of lateral loads and residual stresses is included. The proposed equation is compared to existing theoretical solutions and other results obtained using design codes of classification societies such as ABS, DnV and LR. A good correlation between the present solution and the other results is shown.

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Dynamic instability behaviour of thin shell structures subjected to follower forces are governed by several geometric and physical factors like curvature, boundary conditions, loading, disturbances and so on, contributing to the overall possibility of a dynamic failure at intervals of its deformation history. However, an actual threat to the ultimate stability or the static critical points may not be posed, unless and until when the pertinent damping forces are overcome. Disturbance forces of various types, which are omnipresent in a marine environment, may be the single most serious factor that could undermine all the other considerations and lead the structure to exhibit dynamic instabilities at a much earlier stage than that could be predicted by a static stability criterion.
In the previous paper, we proposed a general governing equation in monoclinically convected coordinates to deal with shell deformations and validified the applicability of the method of small disturbances to unravel the problems of shell instabilities, in general, through analyzing the natural frequencies of deflected shells at subsequent disturbed equilibrium states. Here, the proposed method is used extensively to investigate the same problem in more detail and reached at some generalisations for singly and doubly curved shells. Also, a discretized approximate equation is proposed to get an insight into the total problem in a much simplified way.

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An active mass damper has been developed to reduce the vibration occured in ships especially in the superstructures.
Active mass damper was designed so as to reduce effectively the vibration of fluctuating frequency and amplitude induced by several vibration sources such as main engine and propeller as well as the steady vibration of single frequency and amplitude.
Vibration characteristics were confirmed by the experiment with the aid of model structure. Then the active mass damper was applied to 150, 000 DWT tanker to verify the efficiency of reducing vibrations, and obtained satisfactory results. In this paper,
(1) The active mass damper reduced the vibration of the superstructure of the 150, 000 DWT tanker especially in the resonance peak area. The vibration due to unbalanced moment decreased to one sixth of its original level, vibration derived from propeller exciting force to one half and vibration induced by main engine exciting force to one fifth, simultaneously.
(2) The active mass damper can be applied to not only the vibration of superstructure of ship but local vibrations of various part.

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This paper describes a method for structural optimization considering the elastoplastic structural behaviour. The proposed method consists of three parts : elastoplastic incremental structural analysis, elastoplastic sensitivity analysis, and optimization. The structural analysis and sensitivity analysis are performed using the incremental finite element method. For structural optimization, the Sequential Unconstrained Minimization Technique (SUMT) is used.
In the optimization process, reanalysis is performed using the elastoplastic sensitivities. To get rational reanalysis solutions, some limitations should be imposed on the magnitude of changes in design variables. The maximum allowable changes in design variables are automatically evaluated by applying repeated sensitivity analysis during the optimization process.
After verifying the accuracy of the reanalysis solution based on repeated sensitivity analysis, a three-bar and a ten-bar plane trusses are analyzed taking the cross-sectional areas as design variables. Comparison of the results shows that the proposed method gives very good results.

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The present study is concerned with the refinement of the previously proposed 'shifted integration technique' for the plastic collapse analysis of framed structures using the linear Timoshenko beam element or the cubic beam element based on the Bernoulli-Euler hypothesis. In the newly proposed 'adaptively shifted integration technique', numerical integration points are automatically shifted immediately after the occurrence of plastic hinges according to the previously established relations between the locations of numerical integration points and those of plastic hinges. By using the adaptively shifted integration technique, sufficiently accurate solutions can be obtained in the nonlinear frame analysis by two linear element or only one cubic element idealization for each structural member. The present technique can be easily implemented with a minimum effort into the existing finite element codes utilizing the linear and the cubic beam element.

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The author's research group developed Plastic Node Method (P. N. M.) and has demonstrated the efficiency of this method in analyzing the material nonlinear behavior of many kinds of structures, such as ships, offshore structures. While, for analysis of elastic large deflection (geometrical nonlinear behavior) of structural elements, such as beam-columns, rectangular plates, some analytical methods are effective.
In this paper, these two methods are combined for an accurate and efficient analysis of elasto-plastic large deflection of these elements. The work of this paper will be summarized as follows.
1) The original plastic node method is modified in such a way that condensed nodal plastic displacements are redistributed in the element for evaluation of elasto-plastic stiffness with large deflection.By this treatment, an accurate analysis becomes possible for elasto-plastic large deflection of the elements, including at post-ultimate strength state.
2) A simple and accurate deformation function for each type of the elements is selected.
3) Appropriate locations and number of checking points for plasticity are proposed. To take account of intermediate state between initial plasticity and full plasticity, an appropriate size of plastic zone at each checking point is assumed.
This method is applied to several examples, and its usefulness and validity is demonstrated by comparing with the results of the finite element analysis. Necessary computer time for the example analysis by this new method was found to be 1/601/100 by F. E. M.

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In the framework of the Idealized Structural Unit Method (ISUM), a rectangular plate element has been developed. This element takes account of buckling, post-buckling behavior and ultimate strength of the plate. After ultimate strength, the element predicts a constant carrying capacity in contrast with the decreasing carrying capacity of actual plates after they reach their ultimate strength.
In the ultimate strength analysis of redundant structures, such as ships, highly loaded plate panels may reach their ultimate strength and exhibit considerable plastic deformation, thus losing a portion of their carrying capacity, before the whole structure reaches its ultimate strength.
In this paper, an improved element is presented in which the effectiveness of the plate after buckling is expressed as a function of the total strain, and a new concept of strain hardening is introduced in evaluating the post-ultimate strength elastic-plastic stiffness matrix. In this way, after the element reaches its ultimate strength the reduction of plate strength with the increase of inplane displacement can be evaluated. Comparison of results of analysis by this improved element with those by the Finite Element Method indicates good accuracy of the new element in practical use.

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Among the trends of revolution for ship structures, the use of high tensile steels in many parts of the structures has been tried by many organizations concerned. With high tensile steels, ship structures will be generally thinner than those with conventional mild steel, taking account of higher yield strength of the material. This, in turn, will lead to lower buckling strength. This fact may suggest to accept buckling of such structures in order to utilize the advantage of high yield strength of the material.
Allowing buckling in ship structures will bring out several problems. This paper discusses some of these problems, namely : the maximum stress, ultimate strength and fatigue strength under regular and random loads. A design philosophy on buckling accepted design is proposed. Design criteria, design methods and related design graphs are presented in connection with the new design philosophy.

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Recently, a conceptual design study of the displacement-type high speed ship has been presented. For a new type ship, a serious problem may very possibly occur in relation to the ship hull strength, especially, on the longitudinal one which is the most fundamental hull strength.
The elastic backbone model tests and the numerical analyses have been carried out in order to investigate the longitudinal strength of the ship, especially, in the high speed condition.
Based on the above mentioned investigation, both the problem at high speed and the safety in the rough sea of the longitudinal strength of this ship have been discussed.

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Durability in the ocean environment is one of the most important problems to be considered, in designing offshore structures. One solution of the problem has found in using concrete. The advantage of concrete structure is its corrosion resistance. However, the structure has disadvantages in heavy structural weight and long building time. The concepts of steel/concrete hybrid and assembling precasted blocks are thought to make up for these weak points of concrete structures.
In this paper, the longitudinal strength of steel/prestressed concrete hybrid barge is dealt with, experimentally. The test model, about 1/4 in scale, was produced by assembling three precasted blocks and prestressing in the longitudinal direction. Three points bending test was performed on the model. The test results showed that the structure has enough strength for bending moment, but has narrow margin of cracking due to shear force in the towing condition.

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With the aid of the boundary element method, this paper presents an efficient design and evaluation tool of the impressed-current cathodic protection (ICCP) system for a ship hull. Desirable working state of ICCP system is obtained by the control of anode current, monitoring the potential of reference electrode. Converting impressed-current anodes to concentrated internal point sources, the Poisson's equation becomes available to express electric behavior in cell. In the present approach, not only potential and current densities on boundary but also the electric current from anode points and the set potential of the reference electrode can be calculated. The proposed methodology is applied to a practical container ship protected by an ICCP system. Based on the results of analysis, rational design of ICCP system for ship hull becomes possible.

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Experimental studies were carried out to examine the influence of undercut depth at the weld toe on the fatigue strength. Non-load carrying cruciform and T fillet welded joints were tested and quantitative life reductions due to undercut were obtained. Test results and life estimation procedure were reported in the previous paper.
In this report, the fatigue strengths for 2 × 10⁶ cycles were studied and were compared with each other. Adding to 16 test series joints concerning to undercuts, 40 test joints having various fillet shapes were also analysed. The equivalent fatigue strengths for 2 × 10⁶ cycles were calculated from each failure life of test data, referring to the estimated S·N relations of these joints. The joint strengths were evaluated through the mean and the standard deviation of these equivalent strengths. The influence of the undercut depth and the bead toe shapes could quantitatively be discussed considering the undercut dependence of estimated strength as well as the scatter of equivalent strength data. These results led to the draft of the acceptance level that the allowable maximum undercut depth is 0.3 mm for the special members of offshore structures.

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It is essential to predict precisely the welding deformation of hull structures at assembly stage, to built accurately ship blocks and to increase productivity through mechanization/automation effectively.
At a first step of the studies, a practical system applied for production engineering was proposed to simulate in-plane deformation of one side automatic welding of the panel, with an analytical model using finite element method solving unsteady heat conduction problem and thermal elastic-plastic behavior.
Some parametric studies were carried out using this numerical simulation system and also experimental measurements :
(1) The distribution of the shrinkage across the butt weld is affected mainly by residual stresses due to tack welding, fitting of tab plate and so on.
(2) Some countermeasures to prevent end cracking in one side welding, such as local heating in the vicinity of the plate edge and changing of welding sequence, affect also the distribution of the shrinkage, while pitch of tack weld beads, type of tab plate and root gap have less effect.

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In the plate bending process by line-heating, the decisions on which part of the plate should be heated and in which direction are usually made by skillful workers. However, the number of skilled worker is reducing rapidly and this becomes a serious problem in shipyard today. To solve this, the authors proposed a method to make these decisions based on theoretical analyses focussed on inherent strain in the previous report. The potential usefulness of the method was demonstrated through example problems dealing with mathematical ideal geometry. In this report, comparison between the theoretical prediction and the real practice in the shipyard to form curved members of ship hull are made and it is attempted to visualize the knowledge of skilled workers, which was unvisible, using computer graphic images showing inherent strain. Further, it is demonstrated that the same idea can be applied not only to make decisions on line-heating process but also to design the total plate bending process including those using the bending roller and the press machine.

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The purpose of this paper is to make clear the influence of yield stress on the fatigue strength of non-load-carrying fillet welded joints. First of all, brief descriptions about relations between the actual maximum stress considering weld residual stress and the stress range are given, and the combined effect of stress ratio and residual stress is shown. Then, using published fatigue test results, the effect of yield stress on the fatigue strength is studied.
In the first step, the results, whose actual maximum stresses are inferred to reach yield stress, are dealt with, and an expression of fatigue strength is obtained. Then, in the next step, the whole data are treated. Finally, the fatigue strength is expressed as follows :
Δσ= 33680·σ_r^-0.2282·N_F^-0.3071 +47.76·σ_r^-0.5508·N_F^-0.1249· (σ_r-σ_max')
where Δσ is the stress range in MPa, σ_r is the yield stress in MPa, N_F is the number of cycles to failure and σ_max' is the actual maximum stress considering residual stress in MPa.
Based on the equation above mentioned, the effect of yield stress on the fatigue strength of welded joints is discussed. The most important finding is ; that, in the case of high tensile residual stress, the fatigue strength of welded joints tends to decrease with increase in yield stress.

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Two-dimensional FE-analysis has been conducted to investigate the stress-strain fields in the vicinity of M-A constituents corresponding to local hard zones (LHZ) in the weld HAZ. Existence of the LHZ elevates considerably the stress in the LHZ and causes very inhomogeneous deformation around the LHZ. Stress distribution in the LHZ is strongly affected by the shape of the LHZ : In the slender LHZ almost all region in the LHZ is exposed to elevated stress, whereas in the blocky LHZ only the edge region sustains high stress. The increase in the strength of the LHZ results in remarkable elevation of the stress level in the LHZ. This implies that the slender LHZ is cracked at a lower load level than the blocky LHZ, and that the crack nucleation in the LHZ is promoted by increasing the strength of the LHZ. The shape of the LHZ affects also the plastic deformation in the vicinity of the LHZ : Slender LHZ encourages the accumulation of plastic strain in the matrix region adjacent to the LHZ. Significant difference in deformation of the matrix and the LHZ will induce the fracture along the LHZ/matrix boundary. These analytical results suggest that the heterogeneous material including slender LHZ has lower fracture resistance than that with blocky LHZ. This finding was confirmed by the HAZ-notched CTOD test on high strength steel welds : The coarse grained HAZ including elongated M-A constituents fractured at an apparently lower critical CTOD value than that with massive one. Accordingly, it is necessary to control the shape of M-A constituents for toughness improvement of the weld HAZ.

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Fatigue tests were conducted on plate with wrap around weld. And the effect of stress ratio of the weldment on fatigue strengths was obtained experimentally. Despite cracking was observed in most of the compressive tests, no specimen reached complete failure. And the results for tensile (R=0) and compressive (R =-∞) fatigue strength for crack initiation life were compared. The fatigue strength for initiation life of compressive stressing at high cycle range exceeded that for the tensile (R =0) stressing by a factor of two.
Analytical estimation for failure life was conducted for tensile specimens. Crack initiation, Nc of the tensile specimen was estimated using the relation between the crack initiation and the local stress range at weld toe. And the crack propagation life, N_p utilizing the two dimensional stress distribution obtained from the FE solid model analysis. Comparison of the estimated life Nf=Nc+NP with the experiment showed a good agreement.
A qualitative analysis for the fatigue crack arrest was conducted under compressive loading condition (R =∞). By obtaining the weld residual stress, the stress intensity factor due to the weld residual stress k_res was calculated. Taking into account of the K_res, crack arrest conditions for different applied stress levels were formulated using the crack closure concept. A fair agreement for the length of the arrested crack was obtained between the analysis and the experiment. Application of the test results in evaluation of the side longitudinal element in a large ship structure is also discussed. It is stated that the stress at location of attached plate in L₂ longitudinal is magnified by a considerable amount due to the out-of-plane deformation of the web. This was experimentally observed in the measured stress distribution on the face plate of the structure model.
A reference stress S_t is proposed, which is a unified stress for evaluating the fatigue strength, for the element with a wrap-around weld in a structure with attachment. The proposed S_t is the stress at a distance t (plate thickness) from the weld toe.

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An experimental study was made on the fatigue behavior of A5083P-O aluminum alloy under various types of superposed random strain waves. Each random strain wave was generated by superposing a Gaussian random process having a specified power spectral density with the peak frequency of 2.42 Hz, on a constant amplitude pulsating trapezoidal wave with the frequency of 0.25 Hz.
In all the fatigue tests, including the constant amplitude tests, drastic hardenings of the material were observed. In order to handle them quantitatively, the mean hysteresis energy per cycle was calculated for each specimen. Then it was found the rapidity of the hardening process increased as the RMS value of the Gaussian process, E2RMS, increased. And it was also found the initial value of the mean hysteresis energy was a good parameter to relate the random fatigue test data to the constant amplitude test data, resulting in a fairly good estimation of the fatigue lives.
Meanwhile different five types of wave count methods were comparatively examined, namely, range count, hysteresis loop count, rain flow count and two types of peak count (named peak 1 and peak 2 respectively), combined to the modified Miner's law. As a result, the rain flow count method gave the most consistent and acceptable results among all, though the estimations fell on the dangerous side owing to its incapability of estimating the life-reducing effect by the superposition of random waves.
Finally, it is to be noted that the above-mentioned life estimation with the initial value of the mean hysteresis energy was still more superior to the one by the rain flow count method and the modified Miner's law.

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Japan Welding Engineering Society (JWES) standard WES2805, which is based on an elastic-plastic fracture mechanics (CTOD design curve approach), has been widely used to evaluate fracture safety of structures. And work on revision to the standard is now underway so that it can take into account the recent advances in fracture mechanics treatments.
On the other hand, U. K. CEGB R6 approach has lately attracted considerable attention. The notable feature of the R6 is that the approach interpolates between two criteria, that is, LEFM failure and plastic collapse. Although the basis of the approach can be formulated by an elastic-plastic J analysis, it simply needs stress intensity factor and limit load in an assessment, and this point is considered as an advantage for its application.
In this study, the validity and accuracy of the fracture assessment of JWES and R6 for the situation where brittle fracture occurs from a defect at a structural stress concentration are investigated. These two approaches are applied to four types of structural model test which were carried out in Japan. The investigation includes examination of conservatism and discussion on the relation of the two methods.

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Japan Welding Engineering Society (WES) standard WES 2805 and British Standard Institution (BSI) standard BSI PD6493 were established in 1980. Since then, these standards have been widely used to evaluate fracture safety of structures. They are based on elastic-plastic fracture mechanics (CTOD criterion), because most brittle fracture may occur from defect at structural stress concentration where plastic zone size generally seems to be larger than the defect size.
Work on revision to these standards are underway in U. K. and Japan. The BSI are going to provide a new defect assessment. The fracture sections of the revised document will take three levels of assessment. Level 1 is essentially consistent with the PD6493-1980 and treated as a preliminary evaluation. In Level 2 and 3 assessments, brittle fracture and plastic collapse are taken into account by use of a failure assessment diagram (FAD) similar to that proposed originally in CEGB R-6 procedure.
In Japan, research on the validity of WES 2805 has been carried out and a modified CTOD design curve and a new method for estimating local strain at stress concentrator were proposed. Work on revisions to WES 2805 has been in progress by taking into account the recent advances in fracture mechanics treatment.
In this paper, critical evaluation was carried out for fracture assessment of CTOD and FAD. Wide plate tests with cracks emanating from a hole were carried out and the fracture strength was evaluated by means of WES CTOD and FAD approaches. The FAD analysis based on the WES CTOD was also investigated. The assessment results were almost the same between those two approaches. However, it is said that the WES CTOD method is more practical, because this method is based on the relation between CTOD and local strain. In some practical cases, only the local strain near the region where defect is discovered, is available. The FAD approach is required the global stress condition (plastic collapse load) for fracture evaluation.

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In designing a large marine structures, assessment of fatigue strength is one of major design considerations. In the evaluation of fatigue strength of weld toes, it is important to analyze fatigue strength data of structural model in terms of “hot spot stress” due to structural discontinuity, in a simple way but as accurate as possible.
In the first report, the authors defined the “hot spot stress” based on fatigue tests for plate type structural components by linear extrapolation of measured strain at two specified points differently distant from welded toe. In the second report, use of peak strain instead of hot spot stress was attempted to seek the practical method.
In this report, the authors have attempted to evaluate the applicability of simplified finite element analysis to estimate hot spot stress on the basis of its practicality. For five structural models, several different computations were made to compare each other in order to obtain an acceptable and appropriate modelling method using shell element. The proposed method gives about 10 % conservative estimate of stress for fatigue assessment.

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As material flaws have great influence on fatigue strength of cast or forged components, it is important to establish evaluation method of fatigue strength for a material with flaws. In the previous studies, fracture mechanics approach using “intrinsic crack model” was made to estimate fatigue strength of material with a round-shaped flaw and with a small flaw.
In this paper, evaluation method of fatigue strength was discussed for a material with clustered small flaws, and following results were obtained.
(1) Evaluation method of the fatigue strength for a material with clustered small flaws is proposed. This method is based on the fracture mechanics approach using “intrinsic crack model” and equivalent correction factor of nearness of flaws.
(2) Estimated fatigue limit by the proposed method agreed with fatigue test results on nodular graphite cast iron (JIS FCD 600) which have many micro-shrinkage cavities.
(3) Equivalent correction factor of nearness of the clustered small flaws can be obtained by brittle fracture test on a material which has similar clustered small flaws at an extremely low temperature.

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The effect of the notch depth on the critical CTOD value at cleavage fracture initiation was analysed by the local approach. Three-point bend CTOD specimens with different notch depth extracted from a high strength steel were tested at the lower shelf temperature. The critical CTOD values showed large dependence on the notch depth. Three-dimensional elastic-plastic finite element analyses were performed to investigate the crack tip stress fields for all specimen geometries. The numerical results showed that shallow and deep notch specimens exhibit very different near tip stress fields at the same CTOD level, which leads to the specimen geometry dependence of the fracture behaviour. The analysis of the notch depth dependence of CTOD results was conducted on the basis of two formulations of the local approach. In the first formulation, cleavage fracture was assumed to be controlled by the maximum principal stress. In the second formulation, the stress tensor ahead of the crack tip was fully described in terms of all principal stresses and cleavage fracture was assumed to be controlled by an equivalent stress for mode I loading. It was shown that both formulations of the local approach lead to geometry independent parameters, especially when the stress triaxiality effect is taken into account. Prediction of the notch depth dependence of CTOD results based on the local approach presented good agreement with the experimental data, particularly when stable crack growth prior to cleavage was not significant.

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Ocean waves have been observed with a wave height meter array and a three component current meter suspended from an ocean research platform. Directional spectra of measured waves are determined using the Maximum Likelyhood Method. The results obtained with these two sets of instruments were compared and investigations revealed the following;
(a) measured values of the characteristics regarding the angular spreading of wave energy obtained with the wave height meter array and three-component current meter showed good agreement.
(b) time series of wind speed, significant wave height and spreading parameter S_max at the peak frequency were in good mutual relation, and the value of S_max may be estimated practically from the significant wave height.
(c) representation of directional function due to Mitsuyasu et al., which was developed on the basis of the well developed wave data in mid-ocean, are in good agreement with that determined here from wave data collected near the coast and contained wide range of the development stage.

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Many plans to construct of very large offshore structures of floating type are proposed, such as floating cities, airports, and so on. The size of floating structures is expected to become larger and the natural frequencies of structural vibrations become lower. In these conditions, wave exciting force and moment induce structural vibration. The flexibility of structures must be considered in the phase of not only operation but also construction. Therefore, it is important to study the response including the structural deformation.
This paper deals with the experiments on the responses of very large floating offshore structures in directional spectrum waves. To clarify the structural response in waves, response functions of flexible models for experiments are estimated. For this purpose, the response function is divided into two transfer functions. One shows the relation between the wave height and the wave exciting force, and the other evaluates the structural deformation due to the wave exciting force in a modal space. The natural frequencies and mode shapes are evaluated by structure analysis program for simple models on the condition of floating. The two transfer functions are verified by experiments respectively and utilized to estimate the response function in waves. The estimated response functions show that the position in the structure differs the amplitude of response. So, there are some frequency regions in that the larger response causes at the lee side than the weather one. This characteristics are also shown in the results of experiments in transient water waves.
Three types of models are used for experiments in directional waves. Difference among the three models is only the structural flexibility. The structures are moored by a single buoy of a TLP type. The experiments are performed in many waves. The measured responses are displacements in the inertial coordinate, structural deformations and tensions of the mooring system. In the experiments, the most flexible structure is designed as follow. When the structural natural frequency is same as the wave one, a shape of the structural deformation agrees with the wave length. So the response of the large flexible offshore structures are easy to be affected by characteristics of waves, directional distributions and frequency properties. And, it is also shown that the characteristics of response for flexible structure is different from ones of rigid structures.

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The model experiments for three different single point mooring systems of an Articulated Column system, two Articulated Columns system and SALS system were carried out in wind, current and irregular waves.
The spectral responses are calculated by constraint matrix method in frequency and time domains and compared with those of the model experiments.
Theoretical analysis methods are verified by these comparison and frequency domain analysis is implied to be useful for the determination of design loads.

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The effect of the deflection due to the ununiformity of the temperature distribution caused by the natural environment conditions such as solar radiation cannot be neglected for the design stage of the huge floating offshore platform like a floating airport. In this report, the temperature of the upper structure of floating offshore platform 'POSEIDON' has been estimated although its size of the upper structure is not so large. Further, the distribution of both the deflection and the thermal stress have been obtained by the structural analysis using Finite Element Method (FEM).
The following results have been obtained.
1) The central part of the upperdeck has been deflected upward due to the temperature difference between upper and lower side of the box-girder and its deflection becomes largest at noon in a day.
2) The compressed stress occurs in the upper side of the upperdeck. The maximum longitudinal axial stress occurs in the central part of the upperdeck and that of transverse axial stress occurs in the box-girder.
3) The upper structure has been deflected due to the ununiformity of the temperature distribution between side walls even in the horizontal plane.
4) The estimation of the structural strain agrees well with measured results as for the upper side of the box-girder and that as for both side wall and lower side of the box-girder also does qualitatively.
5) The regression equation estimating the maximum and minimum temperature of the upperdeck in a day has been shown using the data of climatic elements in every 3 hours.

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