In the first paper, the authors pointed out that a new mode of capsizing, which accompanied the period doubling bifurcation phenomenon, had been observed and that about 25 % of the total capsizing had been classified into such a new capsizing mode. Since the period doubling bifurcation phenomenon was regarded as a precursor of the chaos in the nonlinear dynamical systems, and the chaos was regarded as a precursor of the unconditional capsizing, which was equivalent to the blue sky catastrophe or the boundary crisis in the softening spring system, the chaos and fractal in the symmetrical capsize equation was examined in the authors' second paper. Although the mysterious nonlinear phenomena appeared in the symmetrical capsize equation were examined numerically, a cascade of the period bifurcations was not observed in the numerical study.
In the present paper, the authors have examined the asymmetrical capsize equation as well as the symmetrical one. As a result, the cascade of the Feigenbaum bifurcation, which begins from the period doubling bifurcation and ends at the unconditional capsizing through the chaos, has been observed for both asymmetrical and symmetrical capsize equations. Further it has been clarified that in the symmetrical equation the cascade of the period bifurcations begins after the break of the symmetry of solution, and that the period bifurcation with the distinct difference of the adjoining amplitude, such as observed in the model tests, appears only in the asymmetrical equation. The differences of the fractal capsize boundaries in the initial value plane and the control space between the symmetrical and asymmetrical equations have been also examined, and the danger of the biased ship is emphasized by the numerical results. In the examination of the safe basin in the initial value plane, a cell-to-cell mapping method developed by Hsu has been atempted to confirm its effectiveness and accuracy. A numerical analysis of the fold bifurcation which approximates the capsizing boundary in the control space, and also a numerical Melnikov analysis which approximates the beginning of the fractal metamorphosis in the safe basin in the initial value plane have been carried out. An approximate analytical expression for the flip bifurcation is obtained.
The idea that the appearance of the period bifurcation in the roll motion of a ship implies the imminent danger of the capsizing has proved to be correct.

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This study presents a theoretical method for calculating probabilities of capsizing due to pure loss of stability for a ship running in short crested waves and fluctuating wind. The aim was to develop stability criteria of a ship in quartering seas making use of the risk analysis. We divide the ship motions into the stationary motions and the unstationary motions. Then we integrate the probability density function, which is given by the stationary random process theory, on the safe domain that is determined by separatorices of the unstationary dynamical system. The reduction of restoring moment when a wave crest moves into the center of gravity of the ship is fully considered by Grim's effective wave concept.
Numerical examples for a coastal trawler indicate that the probability of capsizing in quartering seas is larger than that in following or beam seas when the wind velocity is 10 m/sec. However, they also indicate that the probability of capsizing in beam seas is larger than that in following or quartering seas when the wind velocity is 20 m/sec.
Furthermore, we concluded that the present method is effective for developing stability criteria, because the capsizing probabilities predicted by the present method are slightly larger than those given by the Monte Carlo simulation in time domain.

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A new grid generation method is proposed. The geometrical method has been modified to produce the present implicit geometrical method. An iteration to modify initial grid is regarded as time integration, and an explicit time differencing operator is replaced by an implicit Padè time differencing. Four requirements, i. e. orthogonality, smoothing, clustering, and minimum spacing are imposed to obtain a convergent grid. 2D grids are shown as examples and extension to 3D to generate grids around a practical ship hull form is explained.

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A hybrid method is under development to measure 3-dimensional velocity fields where the image processing of visualized flow and numerical computations are used. The 3-dimensional velocity is computed from several scanned plane flows which have been obtained by the flow visualization and image processing. It is necessary to analyze the plane flow fields as accurately as possible, for they are used as boundary conditions in computations for the 3-dimensional reproduction.
The present paper proposes a new method to determine the plane flow velocity accurately. The method is to analyze the intensity distribution profiles of visualized streaklines rather than the discrete images of tracers. The velocity is determined from the movement of the profiles at three successive times. The zero crossing points are invoked to characterize the profiles whose identification is much easier than the tracer method because of its 1-dimensional identification along the streakline. The use of the distribution of the intensity rather than the binary data makes the results accurate where the results do not depend on the slice level. Because the intensity distribution profile carries much information than discrete binary data, amendment for higher accuracy can be done by making use of the correlation function and so on.
The method is applied to analyze the uniform flow and the plane flow around the stern of Wigley model. Although several points are still left to be improved for higher accuracy, the present method provides much better plane flows than those obtained by the particle-trace method. It is expected to be used for the computation of 3-dimensional flow reproduction.

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A simple method to predict the resistance of SES (Surface Effect Ship) operated in calm sea is presented in this paper for the use of initial design of SES. Total resistance of SES is broken down into individual components ; sidehull frictional drag, seal frictional drag, cushion pressure wave making drag, aerodynamic drag, appendage drag, residual drag and waterjet inlet drag. To estimate each component, results of model tests and theoretical calculation are utilized. Among them it is shown that the estimation of wetted area of sidehulls and seal and trim angle is of critical importance. Predicted resistance of 30 ton type SES experimental craft shows good agreement with that of full scale trials data. Further study will be necessary to refine the method, especially regarding the residual resistance component.

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A resistance test program of a high-speed semi-displacement craft was performed by sixteen towing tanks (including one circulating water channel) in Japan and it involved thirteen geosim models of 0.4 to 4 meters in length. This work forms a part of the tasks of the High-Speed Marine Vehicle Committee of the 19th ITTC.
Analyzing sixty three data sets, the following conclusions are obtained. The scale effect is not found in the wave resistance, and on the other hand, it appears in trim and spray ation. The form factor of frictional resistance can be determined even at high Froude numbers, by the method suggested by Hughes as a function of Froude number. The application of turbulence stimulator is necessary in resistance tests even for larger models at high-speed. Appropriate turbulence stimulator for semidisplacement hull forms should be developed.
The characteristics of semi-displacement hull forms in the range of medium Froude numbers (Fn < 1.3) are similar to those of displacement hull forms in many points. This means that the ITTC 1978 power prediction method, with partial modifications, would be applicable to this type of high-speed craft.

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In order to provide a tool, which is useful for synthesizing hull forms leading to superior seakeeping performance in the early stages of high-speed craft design, the authors propose some regression equations to evaluate the seakeeping performance of high-speed crafts of a hard-chine type, by means of some simple hull form parameters.
Several years ago, one of the authors and Prof. M. Fujino developed a practical method for calculating vertical motions and wave loads of a high-speed craft travelling in head sea, and verified its validity by comparing the computed results with those of model tests. In this paper, the above-stated method is applied to calculate the vertical motions of 20 hard-chine-type data base hulls in head sea, and the obtained motion responses are classified into several groups by using correlation analysis. Then following Bales' procedure, a number of seakeeping performance ranks connected with these groups of motion responses are found. Finally, the relations between these performance ranks and hull form parameters are established by using regression analysis. Through the present rank equations, the effect of hull form parameters are clarified and the guidelines for improvement of seakeeping performance are also presented. Furthermore, the influence of ship speeds are also discussed.

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Added resistance can be usually calculated by a method of the pressure integral on the wetted surface of a body or the momentum relation of the control volume. In our previous study, the values of Maruo's formula based on the latter for a surface-piercing body with linearized condition (so-called Neumann-Kelvin problem) was not in good agreement with the results of the former.
In this study, inconsistancy of the Neumann-Kelvin problem is considered as a reason of its disagreement. For the validation of added resistance by the upper two methods, new terms in Maruo's formula need to be considered which are caused by the inconsistency in the rate of change of momentum and energy flux arising from the intersection in the surface-piercing body with forward velocity. Diffraction problem of a vertical circular cylinder which is a column of ocean structure is taken as an example, and first order fluid force and added resistance in regular waves are calculated. With respect to the added resistance, the result of modified formula based on Maruo's momentum theory in Neumann-Kelvin problem agrees well with that of the pressure integral method.
The calculated result is compared with the measured one. First order fluid forces agree well. The results of added resistance generally show good agreement, but the accuracy of results needs to be improved as Froude number increases.

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Hydrodynamic forces acting on three dimensional circular cylinders in an oscillating flow are investigated experimentally. Forced surge tests were carried out on the finite length circular cylinders of which the ratios of the length to the diameter are varied from 1 to 10. The drag coefficient, the added mass coefficient and the lift coefficient were obtained. They were compared with those of two dimensional circular cylinders. The experiments showed that these coefficients of three dimensional circular cylinders are much smaller than those of two dimensional circular cylinder.

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Free running model tests on turning characteristics using scaled SES models varying L/B and rudder area were conducted. L/B series tests were carried out on 2.14 and 4.39 L_c/B_c models and rudder area series tests were performed on 3 rudders employing a 2.53 L_c/B_c model.
As a result, effects of L/B and rudder area on SES turning characteristics, i. e. turning diameter, trim and heel and so on, were made clear.

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It seems that ride control is an important technology in order to develop a high performance SES. This paper describes a basic design method of ride control system (RCS) based on classic control theory (PID) and optimal control theory (OR), and then the RCS tests results in waves for 30 ton SES test craft.
The PID gains were determined by the root locus method using experimentally obtained frequency response characteristics of each component of the closed loop system. The OR gains were obtained based on an optimal regulator algorithm employing a mathematical model of longitudinal motions and experimentally determined hydrodynamic coefficients.
The test results showed that the RCS can reduce SES motions in waves effectively, and the RCS proved to be applicable to this type of ship.

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This paper proposes new concepts of configuration and attitude control of underwater towed vehicle to perform operation in both vertical and horizontal axis with stable attitude.
The principal configuration composed of fuselage, main wing, horizontal tail, vertical canard, upper and lower vertical tails designed taking into account stability and manoeuvrability in vertical and horizontal planes. The manoeuvrability was estimated by use of lamped mass method for equilibrium equations of motion of towed cable and vehicle. The dynamic stability was analysed by use of eigenvalue analysis based on linear equations of motion.
CCV (Control Configured Vehicle) technology was adopted to perform the attitude control. Three types of decoupled mode were considered, i) pitch angle and vertical velocity, ii) pitch angular velocity and vertical velocity, iii) roll angle, yaw angle and side slip velocity. Fuzzy algorithm was applied to CCV attitude control.
The effect of motion of towing mother ship in waves was simulated numerically based on non-linear equations of motion of cable and vehicle to examine the effectiveness of attitude control in vertical axis. Not only drifts of velocity components and pitch angle, but also oscillation of pitch angle are remarkably suppressed.
The effect of tidal current was simulated numerically to examine the attitude control in horizontal axis. Oscillations of side slip velocity, roll angle and yaw angle are almost eliminated.

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The automatic position and the attitude control for the underwater vehicle staying still or moving at dead slow speed becomes non-linear, because the acceleration or the deceleration motion must be applied using thrusters, while the linear control system can be applied to the underwater vehicle cruising at high speed.
In the previous paper, the linear approxmation of this non-linear system and a linear design method were proposed.
This paper describes the results of the sea tests of the experimental underwater vehicle, and the evaluations made by the test results which proved the thory and the design method proposed in the previous paper to be applicable to the control of these underwater vehicles.

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Hydrodynamic interaction between hull and foils is one of the important aspects for performance prediction of high speed craft lifted up partially by sumberged foils. In order to investigate such interaction, measurements were made of the lift of foils, trim and elevation of a craft model in the towing tank. It was found that the elevation of the model is smaller than that estimated from the measured lift of the foils. This suggests that there exists lift loss due to additional sinkage force acting on the hull as a result of hydrodynamic interaction. Then, numerical calculation was carried out to clarify such hydrodynamic interaction. As expected, it was found that negative pressure is induced by the foil on the bottom of the hull just above the foil, and results in the sinkage force as observed in experiments.

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A semi-submersible displacement-type high-speed ship with wings is studied on its stability control by flaps.
The vehicle, called HSV (High-speed Semi-submersible Vehicle with wings) here, is consisting of a main hull, main and tail wings with flaps, and a strut to support the super-structure. The HSV floats at a certain draft like a conventional ship while it is still, and it submerges when it moves forward due to a downward lift force induced by the main wings. HSV cannot have enough upright moment as conventional ships because of its small waterplane area. HSV is expected to be stable by an active control of flaps.
Experiments are carried out to study about the possibility of the stability control by the flaps of the main and tail wings. An automatic control system is developed under which HSV is towed with the heaving, rolling, pitching and yawing motions free. The angles of attack of flaps are controlled after the measured ship motion in order to stabilize the motion.
It is concluded that, although the control is not perfect due to the mechanical limitation of the used system, HSV can run stably by the active control of the flaps. The experiments among regular waves made clear that waves could not be a serious factor for the stability of HSV.

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The procedure for predicting the second-order biharmonic response and tether forces of a tension-leg platform in regular waves is presented. This consists of evaluating the second-order wave exciting forces based on the second-order wave diffraction theory, and solution of the equation of motion including the effect of the second-order mooring tether forces. Model tests are carried out to measure the wave exciting forces on the fixed circular dock, as well as the response and tether forces of the tension-moored circular dock. Satisfactory agreement is observed between the theoretical and experimental predictions, confirming the validity of the proposed method. The conclusions arising from the present study are summarised as follows :
1) The vertical-plane motion and tether forces of the tension-leg platform in regular waves include the second-order biharmonic components which are comparable in magnitude with the first-order wave-frequency components.
2) The nonlinear sum-frequency wave exciting forces provide an important source of excitation of such oscillation. These exciting forces can be predicted accurately based on the second-order wave diffraction theory.
3) The contribution of the second-order velocity potential to the second-order wave exciting force is significant, in particular to the heave and pitch exciting forces. The simplified method neglecting this contribution is found to underestimate the forces drastically.
4) The theoretical method proposed in this study provides an effective means for predicting the second-order sum-frequency response and tether forces of the tension-leg platform.

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We carried out experiments of wave focusing by two kinds of Fresnel lenses, which are 20m long and consist of a horizontally submerged flat plate and an array of submerged circular cylinders, in a wave tank of 30m × 50m × 2.4m. The results show that the circular cylinder type produces higher wave power magnification at a focal point than the flat plate type in both regular and irregular waves, but that the magnification is affected by the lens' shape and nonlinearity of a free surface.
The three dimensional singularity distribution method demonstrates that a Fresnel lens significantly reduces the predicted wave height magnification by slender ship theory and that a convex lens hardly does that even when its slenderness is relatively large.
It is shown by experiments in a narrow wave tank that the breaking limit of waves passing over a submerged plate and an array of submerged circular cylinders is given by the ratio of the wave height of incident waves to the submerged depth and independent of wave frequencies and the number of cylinders.
Nonlinear effects of a free surface of one dimensional concentration of transient waves agree with those of two dimensional wave focusing very well. Furthermore, an approximated nonlinear wave theory estimates the nonlinear effects with increase of wave slope around a focal point.

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Estimation of directional frequency transfer functions of floating offshore structures is important to estimate their behaviours in realistic short crested irregular waves (such waves are called as directional spectrum waves)
Of course, there are some theoretical calculation methods for such directional response functions, but it seems that there are not so many experimental results confirming such theoretical ones. For that purpose, square basins are needed.
In the first report, the authors showed the method of inverse estimation of directional transfer functions of a floating offshore structure only using results of a few experiments in directional spectrum waves in a long towing tank.
In this paper, this method is improved for the estimation of wide range of directional response fuctions. The precisions of estimated directional frequency response functions are confirmed by experiments.

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The at-sea experiment of the moored floating platform “POSEIDON” has been carried out at Japan Sea since 1986 for four years. In this experiment, three ultra-sonic type wave probes were installed as a line array at the sea bottom of the test area, and the directional wave spectra were obtained using measured three time series of water surface elevation by Maximum Likelihood Method (MLM). Also, the six components of motions of POSEIDON were measured by accelerometer and vertical/directional gyro.
In this paper, the authors tried to estimate the directional frequency response functions in wave frequency range using these field data. The results estimated by present method were compared with the theoretical response functions and it was found that we need many experimental runs of various wave directions for obtaining fairly good response functions.

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New concepts of hull forms with characteristics of low motions in waves, a big displacement and simple hull structure have been developed. They are most ideal for the floating production, storage and offloading units (FPSO). Two new concepts, a mono-column type (MC type) and a double moon pool type (DM type) were introduced in the former paper read at OMAE (1989).
This paper will introduce the design of MC type FPSO and the model test in waves for the improved mono-column hull, which has more displacement and keeps the motion in waves almost same as the former model.
The MC type FPSO has a low frequency response for pitching motion as a semi-submersible has. Such a pitching motion was reduced by the open type anti-pitching tank.
The pitching motions in waves of the MC type FPSO and semi-submersible type floating production facility (FPF) were calculated in the typical oil fields in the world and the performances were compared through a year. It was confirmed that the MC type FPSO will be operated even in the North Sea with the same performance as the semi-submersible type FPF.
The MC type FPSO will be most suitable for the production testing, early production and production for small oil fields.

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This paper deals with i) the roles of floating wave power plant in the control of environment of coastal waters for coastal fisheries, ii) experimental investigation of physical characteristics, i. e. waves and wave induced nearshore current around a model of the floating wave power plant on inclined bottom comparing with those around a model of detached breakwater from the viewpoints of creation of calm water areas and water exchange. The results of this paper are summarized as follows.
(1) The floating wave power plant can be utilized from the viewpoints of environmental conservation and progress of coastal fisheries for creation of calm sea areas, improvement of water quality and control of nearshore current, and power for aeration and dipping out of bottom waters.
(2) The calm water area behind the floating power plant model where wave transmission ratio is less then 0.5 in three dimensional condition is almost the same as behind the detached breakwater.
(3) The above mentioned calm water area becomes wider near the shore line as the bottom slope becomes more gentle.
(4) The reflected wave height at the front of the floating power plant model is much smaller than the detached breakwater.
(5) Circulating current on free surface from the center of the model to outer side in the case of floating power plant model is dominant near water surface, on the contrary, it is dominant from outer side to the center of the model in the case of detached breakwater. In particular, strong current toward shore line just behind the floating wave power plant model was observed.
(6) Water exchange near the floating wave power plant model is larger than the detached breakwater. It becomes larger as the bottom slope becomes more gentle for both models.

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Calm sea area is necessary for nursery, marine leisure, renewal of harbour, and so on. For those purposes, floating breakwaters have been taken interest from the view of cost, preservation of water, etc. Especially, reasonable-sized ones suited to waves of long period are desired.
In this study, the floating breakwaters utilizing inside water are treated. A proper design of the mode of water behavior is expected effective to reduce the transmitted waves. It is because the radiation waves from body are interactive with relative motion of the body and inside water. At first, a theoretical method is developed to evaluate the breakwater performance. Its validity is confirmed by comparison with experimental results. Secondly, in order to extend the efficient range of wave period, a novel idea of the mechanism for additional mode of water behavior is introduced into the existing concept of floating breakwater. That is, inside winding flow mode with controlled long natural period affects the sway-roll motion in the vicinity of the matched wave period. Finally, a proto-type is designed by the use of the theoretical method, and good performance of the newly developed floating breakwater is confirmed for longer wave period.

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An optical fiber distributed temperature sensor has been developed for the purpose of continuous measurements of vertical temperature profile in the ocean. The sensor uses essentially OTDR (Optical Time Domain Reflectometry). The fiber was encapsulated in metallic tube. The fiber with total length of 1000 m was duplicated with the result that the sensor can measure the temperature twice at the same depth, which affords us means to make the sensor more reliable.
Comparison measurements in the ocean were conducted using the CTD and XBT as standard instruments during about 15 days, summer 1990, in the Toyama Bay. Temperature differences at successive depth with spatial inverval of lm were analyzed. We found,
(1) The proposed temperature correction method for the fiber sensor worked well in the whole 17 cases analyzed.
(2) Mean spatial temperature difference between the fiber sensor and CTD decrease about 14 % in average, and about 20 % in the case of XBT when we applied the proposed correction technique.
(3) The temperature difference in the case of CTD is 0.64°C in maximum and 0.51°C in average, and these in the case of XBT are 0.99°C and 0.73°C, respectively.
These values are nearly the same as them obtained on the laboratory experiments in temperature chamber.
We could demonstrate the usefulness of the optical fiber distributed temperature sensor, to monitor the spatial temperature distribution in the ocean.

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Global problems have been raised by the fact of an environmental warming due to the green house effect of an increased carbon dioxide (CO₂) and basic researches have been under conducting by many countries' laboratories including the governmental authorities with an international cooperation.
In the near future international agreement for the regulations against worldwide CO₂ emission is expected to be discussed.
In this papers CO₂ recovered from the fossil fuel was taken up as the most influential gas quantitatively, and discussed the disposal of the solid CO₂ (SCO₂) into the deep ocean thermo-physically utilizing the vast storage capacity of CO₂ dissolution in the deep ocean. Spherical solid CO₂ is disposed into the sea water allowing a free settling with sublimation and melting from SCO₂ in a water.Settling velocity of CO₂ and heat transfer coefficient between SCO₂ and water was obtained taking a transpiration effect and mass reduction effect into consideration from empirical data. After landing on a sea bottom surfacial melting will occur and diffusion follows it in a sea water having a steady horizontal velocity. Melting and transient diffusion processes were calculated as a thermal and diffusion problem with an hypothetical eddy diffusion coefficient and water velocities.
As conclusions viewing from a thermo-physical analysis a certain amount of SCO₂ will sublimate and melt during settling toward sea bottom, most of it, however, remain unmelt and reach on the sea bottom. Following diffusion are so rapid that a high concentration area of CO₂ will be so limited and within a short period of time.

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For the purpose of establishing the crack propagation law we make a consideration about the small change of compliance for a cracked body under cyclic loadings. From the consideration, it becomes clear that the load just when re-tensile plastic zone generates at a crack tip under loading process is little higher than crack opening load. In this loading range, the cracked body shows fully elastic and then it is expected that no damage occures in the vicinity of the crack tip.
From the fact, we propose effective stress intensity factor range corresponding to the terms of appearing re-tensile plastic zone (ΔK_RP) in place of ΔK_eff proposed by Elber as for a fatigue crack propagation parameter.
Moreover for the purpose of measuring the re-tensile plastic zone's generating load (RPG load), a subtraction circuit which can measure the small change of compliance during fatigue test is developed and automatic controlled system which can controll the adequate value of resistances in the circuit and the output voltage range from strain amplifiers for minimizing relative noize level is also developed.
CT test results by using the newly developed system show that RPG load is higher than crack opening load but is lower than crack closing load.

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It was already reported that the fatigue fracture surface for TMCP steels with large SI_max. value has a lot of micro-separations which distribute with each length of 0.010.02 mm and with their direction parallel to their plate surface. These micro-separations can be supposed to generate between the boundary of ferrite and pearite structures in the vicinity of a crack tip as a crack propagates.
In this report, we investigate the effect of existence of micro-separations on the fatigue crack propagation life and the change of crack contour line by using model test specimens with edge notches parallel to loading axis in which the fatigue crack goes through the passage between their notches in semi-elliptical quasi-surface crack. Moreover we investigate the density and the length distribution of ferrite-pearite structures which are supposed to be the generation parts of micro-separations and then propose an estimation method of the fatigue crack propagation life for steels in which micro-separations are generated as a fatigue crack grows in accordance with above investigated structures distribution.
This estimation method shows the good agreement with experimental change of aspect ratio for surface crack and experimental crack propagation life for thickness direction.

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An experimental study was made on the fatigue strength of non-load-carrying fillet welded joints performed with KE36 (TMCP) steel. Both residual stress measurement and fatigue tests were carried out on specimens of which plate thickness, plate width and heat input for each pass were varied as parameters. In order to examine the effects of residual stress directly, specimens given PWHT (Post Weld Heat Treatment) were also prepared.
As a result, plate width had no effect on the fatigue strength of joints, because of the slight effect of plate width on the transverse residual stresses at weld toe. On the other hand, heat input for each pass influenced the transverse residual stresses at weld toe, causing a significant difference in fatigue strength (especially in the high cycle region such as N≥10⁶).
It was also found that PWHT removed almost all the residual stresses at weld toe, improving the fatigue strength of joints drastically.
In this study, the values of stress concentration factor K_t were estimated by Tsuji's equation. From analyses using those values, it was concluded that the effect of plate thickness was an combined effect of both stress concentration and residual stress, and the contribution of the latter was relatively significant in the high cycle region such as N≥10⁶.
Finally, two equations were newly proposed in order to estimate the fatigue strength of joints at 5 ×10⁵ cycles and 2×10⁶ cycles respectively. It was shown that both effects of stress concentration and residual stress could be quantitatively taken into consideration using the equations.

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HAZ CTOD tests have been carried out using two types of CTOD specimen, a through-thickness notched type and a surface notched type, extracted from multipass welds of HT50 steel for offshore structural use. The surface notch tends to sample one HAZ region at the crack tip, whereas the through-thickness notch intersects several regions in the HAZ. However, the surface notched specimen shows complicate fracture behavior especially when a stable crack growth occurs, which makes it difficult to measure the toughness of HAZ-microstructure at the fatigue precrack tip. By contrast, with the through-thickness notched specimen, the fracture toughness of the CGHAZ is evaluated practically because the initiation of cleavage fracture is controlled by the CGHAZ intersected by the crack tip. Critical CTOD of the HAZ-notched CTOD specimen decreases with increasing the total size of the CGHAZ along the crack front, which can be explained in terms of the weakest link effect of the CGHAZ. Bearing this size effect of CGHAZ in mind, the through-thickness notched specimen is more useful for the evaluation of the CGHAZ toughness of welds.

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The thickness effect of fatigue strength was investigated on welded steel joints with thicknesses ranging from 10 to 80 mm. As-welded cruciform joints and Tee joints were tested under pulsating tension and pulsating bending, respectively. The combination of main plate thickness and welded attachment size was varied systematically.
As a result, it was revealed that thickness effect is clearly influenced by the combination of main plate thickness and attachment size. A series of joints with attachment proportional to main plate thickness showed the greatest thickness effect. Another series of joints with constant main plate thickness and increasing attachment size was second. It was followed by the series of joints with constant attachment size.
As for the other influencing factors, pulsating bending has shown a greater thickness effect than pulsating tension. This means that the thickness effect in proportional joints under bending stress is very large. The thickness effect for crack initiation was largest, and it was followed by failure life and then by crack propagation life. This was confirmed by finite element analysis. It was also clarified that the longer the fatigue life, the greater the thickness effect.

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In this study, the thickness effect was investigated by systematic experiments on welded steel joints with thicknesses ranging from 10 to 80mm. Cruciform joints and Tee joints with improved weld by overall profiling or toe-grinding were tested under pulsating tension and under pulsating bending, respectively.
These experimental results were analyzed together with the previous results of as-welded joints. As a result, it was concluded that the thickness effect exponents for various conditions may be classified into three categories according to the combination of joint type and loading mode. As-welded joints under bending stress have the greatest thickness effect exponent of -1/3, while as-welded joints under tension having an exponent of -1/5. If the weld profile is improved by grinding, the thickness effect becomes much milder to an exponent of -1/10. The as-welded joints with constant-sized attachments also have an exponent of -1/10. Furthermore, thickness effect dependency on fatigue life was investigated.
Based on these results, a new evaluation criterion for design purposes has been proposed in this study.

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In design of a large marine structure, the assessment of fatigue strength is one of major design considerations. In evaluation of fatigue strength of welded toes, it is important to analyze the “hot spot stress” due to structural discontinuity accurately but in a single way.
The hot spot stress will be defined as a conventional stress at an intersection of plates where fatigue crack is possibly expected to occur.
For plate type structures, it is not clear how to define the hot spot stress.
In this paper, using the experimental data of the model tests carried out by SR202 committee of Shipbuilding Research Association of Japan, a definition of the hot spot stress and S-N diagram for fatigue design of plate type structures were proposed.
The hot spot stress for plate type structure is defined by linear extrapolation of measured strains with the location at distances of two points to the welded toe. The two points are 1.57⁴/√ (T³) and 4.9⁴√ (T³), where design S-N diagram in term of the hot spot stress is newly defined named as SRF curve.

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To evaluate vibration fatigue life of SES flexible seal materials, medium size water-jet flagellator which can simulate the actual vibration of SES flexible seals was made and various types of the flexible seal materials were tested. CR or U on double mesh weave nylon, CR on special weave nylon and Thermo Plastic Polyester Elastomer showed good fatigue life among the tested materials.
Then, Thermo Plastic Polyester Elastomer was chosen as SES flexible seals, in order to obtain the data of durability of bow seal for 30 ton SES test craft and to study the relationships between flagellation test and bow seal's vibration test, both tests were conducted.
As the results of the tests, it was proved that the maximum acceleration of the lowest part of the bow seal went up to 70 g, the mean frequency of the seals was about 60 Hz, and also the effectiveness of the flagellation test as a accelerated fatigue life test of seal materials was made clear.

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The proper choices of analytical methods, design specifications, machinery selection and their layout during the ship equipment design stage, are generally made of a number of possible alternatives. The problem of reaching at a final decision that is balanced in an overall perspective is extremely vital, especially when the decision is to be taken based upon multi-criteria objectives which may be mutually exclusive, and again, when there are alternate approaches to various decision making methods. In such problems, which are extremely subjective to personal likes and dislikes, and highly dependent upon conceptual variations, the fundamental nature of alternate objectives attain an amount of fuzziness, leading to discretionary difficulties. As a result of which, instances of making use of the experience and ingenuity of engineers and specialists, are common.
The analytical process of this evaluation problem is broken down here into a hierarchy model, an impact model and an evaluation decision model. In order to postulate the conceptual, qualitative and fuzzy-quantitative elements, an analytical evaluation method based upon these models, is proposed through a multi-criteria analysis using the fuzzy theory.
The choosing problem of liquid level measuring instruments for oil/ballast tanks, and the problem of proper selection of a comfortability index and then the evaluation of thermally comfortable room environments in accommodation spaces, are presented here as two typical applications of the proposed method.

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As ocean going vessels and floating offshore structures with huge size and with various shape have been so developed as to meet the highly advanced demands in the sea, their experimental validation has been placed a higher value on for the purpose of rational design. In some cases, the use of an elastic scale model is indispensable because the interaction between its structural rigidity and hydrodynamic effects plays a significant role.
The main concern of the paper is to derive fundamental laws of similitude which regulate the hydro-elasticity problems. An equation of torsional vibration has been developed by modifying Timoshenko equation which was derived for a rectangular plate model by Kumai. The laws have been derived through analyses of free vibration for vertical bending and torsion. The characteristics of floating structures have been represented, assuming the similarity in the fluid action on the basis of Froude number, in terms of six non-dimensional parameters in which vertical bending rigidity, torsional rigidity and shear rigidity are included as the representative of structural elastic properties. The laws which precisely realize the similitude for all the parameters, under the assumption that the geometrical similarity is perfectly retained not only in overall configuration but also in detail members, are found to be unified to a single equation which describes the relation between the supporting fluid and the elastic modulus.
Though the law is simple, its realization is quite difficult. The actual alternative to that is to hold the similitude only in dominant parameters disregarding other minor ones. The contribution of all the parameters has been evaluated through sensitivity analyses of natural frequencies. That leads to the conclusions. In the case of huge shallow structures :
1) The similitude on static restoring effects goes first in the range of lower order vibration mode, but the role of the elastic properties grows in the higher order range.In the case of rigid structures like ship hulls :
2) The priority of the similitude should be placed first on the bending rigidity and second on the shear rigidity for vertical bending, and first on the shear rigidity and second on the torsional rigidity for torsional action.
3) The contribution of the similitude on shear rigidity should be emphasized especially when their higher order vibrations are concerned.

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A small and short impulsive load yields relatively small deformation and large stress on structural elements, but large and long one does large deformation. Then a sharp impulsive load may cause brittle fracture or fatigue on such structural parts as subjected to high stress concentration, and a large impulsive load also brings about ductile fracture or collapse.
The response of structural elements to an impulsive load can be obtained by the dynamic analysis of continuous model or spring-mass approximation. The recent progress of computer makes possible to calculate dynamic response of actual structures. However, impact tests are important to obtain impulsive load and structural response in actual structures.
In this paper, simply supported T-section beams, clampped square plates and restricted stiffened plates were tested by using drop weight testing apparatus. The characteristics of impulsive load measured on long size impact bars used as the drop weight, deflection and strain of specimens were ascertained. Based on the test results and the elastic calculation using beam and plate/shell Finite Element Methods, simple methods with impact energy and impulse were proposed to estimate the impulsive load and deflection of structural elements.

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The Boundary Element Method based on perturbation is applied to sloshing analysis. In usual sloshing analysis by the Boundary Element Method, a flow field is solved at each time step, assembling the matrix corresponding to the boundary integral equations for the deformed domain. At this time, if an analysis for the deformed field is carried out approximately with the Boundary Element Method based on perturbation, it is not necessary to re-assemble equations and therefore the calculation time would be decreased. For example, the calculation time is decreased to 1/280 in a problem which has 40 D. O. F.. The reduction ratio of the calculation time improves with an increase in the number of D. O. F..

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An object-oriented data model for the finite element method is described in this paper. In the data model, which is based on the Entity-Relationship model, a finite element is treated as an object.
The proposed data model is applied to the h-version adaptive mesh technique. In the h-version adaptive mesh technique, an element is divided into 2 or 4 elements recursively to reduce the error norm for the whole analysis domain. The present mesh refinement system is constructed using the C+ + object-oriented programming language for the implimentation of the data model. To verify the mesh refinement system, we have chosen some 2-dimensional stress concentration and singularity problems. The results show that the newly proposed data model is very useful for the h-version adaptive mesh technique. Moreover, the data model shows great promise for the integrated FEM systems.

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This report proposes the iterative method for the dynamic thermo-plastic-elastic stress analysis by the finite element method (FEM), of which scheme satisfies the condition that the stress point must move on the yield surface during plastic deformation. The common engineering condition of a von Mises, isotropic hardening model and the constitutive equatin expressed as a function of a strain rate-temperature parameter R are used in this FEM program. As a example of calculation using by this FEM, we show the strain and temperature distribution around a hole for a plate loaded in the uni-axial direction.

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Initial imperfections such as residual stress and deflection are inevitable for steel structures fabricated by welding. The estimation of the magnitude of these imperfections and their effect on the strength of structures are indispensable to rational design.
Firstly, the magnitudes of initial imperfections both in panels and in stiffeners are estimated according to and modifying Sato's empirical formula.
Secondly, a refined method of analysis is introduced, in which the original method is so improved as to take into account arbitrary mode of imperfections in a stiffener.
Finally, the effects of initial imperfections on the reduction of ultimate strength of stiffened plates are discussed by comparing the calculated results.
Conclusions obtained in this study are :
(1) A simple but useful method to predict residual stresses and initial deflections both in panels and in stiffeners due to heat input is introduced, and it is found to give satisfactory results as compared to the data obtained from scale models and existing structures.
(2) The refined calculation method to derive the ultimate strength on the basis of elastic large deflection analysis and plastic analysis are used in a parametric study and the results are validated by comparing with FEM analysis. It is shown that the effect of residual stress is underestimated and that of initial deflection a little over emphasized.
(3) The reduction of ultimate strength caused by initial deflection in stiffeners is significant in the region of β<2, but the effect of residual stress in stiffeners is little in almost all the region of β.

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In order to make a system safety and reliability assessment of ship structures in the longitudinal strength point of view, it is essential to analyze ultimate longitudinal strength of ship's hull girder under sagging or hogging bending moment. In the previous report, the author formulated an idealized plate element using idealized structural unit method and the developed method was then applied to ultimate longitudinal strength analysis of unstiffened hull structure as an example, concluding that the method is useful for ultimate collapse strength analysis of plate structure.
In this study, an attempt is made to analyze ultimate longitudinal strength of stiffened hull structure by using idealized structural unit method. For this purpose, an idealized stiffened plate element subjected to biaxial load is developed taking account of the influence of initial imperfections as well as the interaction effect between local and global failure in the structure. The developed method is then applied to ultimate longitudinal strength analysis of Suezmax-sized double skin hull girder as an example for the intact and the damaged condition in the event of accidents of grounding and collision. A new deterministic measure of safety based on the absorbed energy capacity is proposed. Based on the obtained results, ultimate longitudinal strength-based safety and reliability assessment is made using the proposed measure of safety in addition to the conventional one, concluding that the objective hull structure has relatively sufficient safety and the present procedure is useful when ultimate longitudinal strength-based safety assessment or optimization is made in the structural design stage for a new type of hull structure.

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Extending the basic theory of Plastic Node Method (PNM), a new method of elastic-plastic analysis of framed structures considering combined strain-hardening effects is developed. The proposed method is applied to two and three-dimensional frames under cyclic loads. In the PNM, a generalized hinge mechanism (plastic node) based on the flow theory of plasticity is introduced at a node of beam-column elements. A strain-hardening rate for the plastic node is obtained by equating a plastic work done at the plastic node with that evaluated in the actual elastic-plastic stress distribution in the element. The resulting elastic-plastic stiffness matrix can be derived simply by matrix calculation. The numerical results are compared with those calculated by FEM program MARC. It was shown that the proposed. method provides very accurate results in a short computation time.

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This paper describes a procedure to predict the elasto-plastic responses of structures within the framework of the finite element method when design variables are changed. Reanalysis technique was used applying the Taylor Series Expansion Method with the results of sensitivity analysis. In the incremental finite element analysis, the load magnification factor is usually introduced to control the load increments so that yielding of individual elements takes place exactly. In sensitivity analysis, sensitivity of the load magnification factor with respect to the design variable was newly derived. In this connection, the sensitivity of elasto-plastic responses with respect to the yield stress of the material was also derived.
Some sample calculations were performed on plane truss, plane frame and plane stress problems. The results proved the rationality of the proposed method. The reanalysis solution was much improved by considering the sensitivity of the load magnification factor although the computational time for sensitivity analysis increases. The limit of changes in design variables was also discussed to get rational reanalysis solutions.

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This paper presents a fitting-adaptive approach to importance sampling, in which a fitting density function is introduced to calculate the failure probability instead of the importance sampling density function. The approach improves the accuracy of the importance sampling technique when the sample size is relatively small. Therefore, it is very useful to problems that have high reliability and consume much CPU time in a single Monte Carlo run. Furthermore, the adaptive operation is performed if the fitting density function is not satisfactory. When the design point is used, the proposed approach yields even better results. Numerical examples demonstrate that a significant reduction in variance of the failure probability can be achieved by use of this approach.

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In order to extend a life of ageing ship, it is necessary to make a study on feasibility for extending her planned life. Such feasibility study consists of life assessment with a condition survey/assessment, life prediction technique and availability assessment. Nippon Kaiji Kyokai (NK) has made a basic study for developing life assessment system of ships and offshore structures. The logic of procedures for the life assessment is shown diagrammatically in the paper. On the life assessment, special attention shall be paid to fatigue strength as well as protection of corrosion. In the paper, studies on fatigue strength of hull structures and maintenance procedures for well protection of corrosion are briefly reviewed. A discussion is made on several technical aspects of the assessment of aging ships.

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Strength of the shell subject to external pressure is experimentally and theoretically studied for an about 70m long wooden ship with triple skin planking which consists of the longitudinal planking and the first and the second layers of diagonal planking tied by fixing bolts. The 1/2-scaled wooden model was subjected to the static pressure up to 2.0 kgf/cm² assumed as a probable maximum pressure, the 15, 000 times of low cycle fluctuating pressure between 0 and 2.0 kgf/cm², and the destructive pressure gradually increased up to 9.5 kgf/cm², followed by the three-dimensional (3D) frame analyses and some beam analyses to find a reasonable way of estimation.
The results are as follows :
(1) No damage was found at the static and the fluctuating load tests, confirming the structure has sufficient static and fatigue strength.
(2) No rapid collapse occurred in the range of the tested destructive pressure. Only slightly bent necks were found at a fairly large number of the fixing bolts when examined after the test.
(3) The deflections and stresses by the experiment are expressed fairly well by the 3D-frame model (3) which takes into account the elastic deformation of fixing bolts and also the lateral compression of frames within their width. Shear rigidity due to a group of fixing bolts is expressed by a bending beam element, of which the effect is found considerably large.
(4) The deflectional mechanism of the triple skin planking is well explained by the newly introduced diagonally-crossing continuous beams, and also by the single continuous beam which gives results equivalent to those by the former. These two models give results similar to those by the 3D-frame model (2) which is before adding the effect of fixing bolts to the model (3).

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A combined numerical and experimental study is conducted to investigate the failure behavior of bolted connections in vessel made of GFRP laminates. An incremental 3D FEM code, based on the progressive damage model, is developed for determining the stress distributions, damage propagation and ultimate bolted joint strengths of the FRP laminates with different stacking sequences and degrees of lateral clamping. Next, the bearing strength model test is performed to investigate the failure behavior of the S-500 glass/polyester laminate specimens. The results show that the stacking sequence significantly affects the interlaminar stress concentration on the hole boundary as well as the failure behavior of pin joint in GFRP laminate. Furthermore, the introduction of a suitable lateral clamping generally improves the normal interlaminar stress state at a bolted joint and also increases the initial delamination strength as well as the ultimate strength of bolted connections in GFRP laminates.

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In the previous study, the Self-Organizing Nerural-Net-Controller System (SONCS) was developed as an adaptive control system. In order to utilize this system more efficiently, it is important to investigate modelling ability and learning flexibility of the forward model networks. Under the everchanging environmental condition, the forward model should be able to express the complex dynamics of the controlled object and should be easily modified. In this study, the forward model network is improved by adding recurrent connections from the hidden layer to the input layer instead of recurrent connections in the input layer of the previous one. Characteristics of both the forward model networks are investigated using a simple nonlinear system as the modelled object. It is concluded that the frequency range the forward model can cover is spread by this improvement of the recurrent connections.
A small test-bed, which has been built to be used to test the control system in the real environment, is introduced.The new version of SONCS is tested using this test-bed through free-swimming tank tests. It is shown that the SONCS can appropriately generate and adjust the controller which is intended to let the vehicle swim at the desired depth.

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Quantitative description and recognition of underwater shape of ships are important problems in estimating and evaluating the performance of ships. For this purpose, a method is introduced using the Fourier Descriptors (FD's) which was developed for analyses and syntheses of plane closed curves. After examined the contribution of FD's on shape description and recognition for a plane closed curve, FD's are applied to describe and recognize various ship forms. It is understood that several terms of FD's are enough to recognize discriminate various ship forms.

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CIM for shipbuilding studied basically by SHIP & OCEAN FOUNDATION is one of the measures to continue shipbuilding industry under the circumstances that man power is decreasing year after year. This paper is one of the results of works for developing pilot system of CIM for shipbuilding.
The paper proposes the representation for the process of structural design by which the fundamental framework of knowledge-based structural design system can be establishied. “Panel to be Stiffened” as design process object is newly defined and the process of structural design can be represented as the process of generation and division of “Panel to be stiffened”. Knowledge of the process of structural design is defined as the description of method of generation and division of “Panel to be Stiffened”. The knowledge is classified to enable to use knowledge of structural engineering independent of the product.
Thus bottle neck of shallow knowledge acquisition dependent on specified ship type can be avoided. “Panel to be stiffened” is general representation of static state in process of structural design including plate, girder, stiffener and strut, which is easily converted into structural analysis model. On the basis of this representation, computer system that is a good assistant of designer to support design works excluding creative parts can be developed.

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In order to integrate information in design and manufacturing stage, System of Design and Assembling for Shipbuilding (SODAS) was developed in the report 1. In the report, design of bulk-carriers are mainly discussed on the concept of “UNIT”. In the report 2, activity model and facility model in assembling stage are introduced. As the result, it was shown that design of element parts is easily conducted by using the information of hull structure which was obtained in the report 1.
In this paper, design of oil-tanker model is again discussed. At first, it is shown that structures of oil-tanker can be parametricaly designed by using “plane type of UNIT”. And then it is also shown that it is very important to combine “box type of UNIT” for bulk-cariers and “plane type of UNIT” for oil-tankers in order to make ship model for any kind of ship. It is needless to say that the information of designed oil-tanker can be used in assembling stage prescribed in the report 2.

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