The purpose of the present paper is to simulate numerically the 2-dimensional sub-breaking waves which are generated by a submerged hydrofoil. Experimental investigations are carried out first to find out a turbulence model by relating the turbulence quantities to the averaged velocity. Then the numerical simulation is carried out by solving the Reynolds-averaged equations with a turbulence model.
The experimental results showed that the flow fields near the wave crest where the sub-breaking is appearing have velocity defects and are similar to those in the turbulent boundary layer developed on the solid surface. The free-surface boundary condition is investigated including the Reynolds stress. A 0-equation turbulence model is proposed as the simplest model. The k-equation model is modified under the assumption that the turbulence intensity is almost isotropic.
Numerical simulations of sub-breaking waves are carried out by making use of both the O-equation and the k-equation models under the free-surface boundary condition where the Reynolds stress components are taken into account. Through the comparisons with the measured data, it is found that the inclusion of the Reynolds stress terms is important.

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A boundary element method is developed for the 3-D non-linear water wave problems. Triangular panels are used which can represent general 3-D shapes easily and accurately. All the variables are linearly approximated on each panel. The non-linear free surface conditions are satisfied by finite difference approximation. The finite difference calculation is carried out in a mesh system which is finer than that used for the boundary element calculation. A new condition for the downstream open boundary is proposed. After several pilot computations for accuracy analysis, the waves and forces of a submerged sphere and a submerged ship-like body are calculated. Through the comparisons of the results with the analytical solution and those of experiment, it is found that the present method is accurate and efficient.

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The primary stage of the transition to turbulence is numerically simulated by the full Navier-Stokes solutions in a multi-grid system. The grid spacing is about 3 viscous unit and only very subtle disturbance is given to the flow. It is simulated that firstly streamwise vortices are generated, secondly they amalgamate to form vortex strips and thirdly three vortex components interact in a very complicated manner, resulting in the initiation of the lift-up of vortices of larger scale. It is also simulated that riblets are likely to suppress torsional motion of the streamwise vortices, which presumably leads to the reduction of vortex development and lift-up motion.

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The development of the separated shear flows about rectangular and circular cylinders is investigated in the Reynolds number range 3000 ≤R 9000 by means of flow visualization with hydrogen bubbles and velocity measurement with a hot-film anemometer. The results elucidate some interesting features of the three-dimensional flow in the nonlinear stage of the transition to turbulence. The small-scale spanwise vortices formed in the separated flow undergo strong distortion and merge into a large-scale Strouhal vortex. The interaction between spanwise vortices is closely associated with the spectral properties of velocity fluctuations. The pair of the counter-rotating streamwise vortices are detected between the large-scale spanwise vortices in the near wake of the cylinder.

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PBCF (Propeller Boss Cap Fins) was devised to enhance the efficiency of a ship's screw propeller by reducing the energy loss due to the propeller hub vortex and this was proposed in the paper presented to the Journal of the Society of Naval Architects of Japan, Vol. 163 (1988). The concept of PBCF is that the same number of small fins as that of the propeller blades are attached to the boss cap (hub cone) and that they rotate together with the propeller blades. The hub vortex is considerably weakened and the kinetic energy from the rotating flow around the boss cap is recovered by the fins and accordingly the propeller efficiency is significantly increased.
Following the previous PBCF paper, research into the PBCF effect was carried out through the measurement of the flow behind the propeller by 3D-LDV, the force measurement of PBCF and the cavitation test in a propeller slipstream. The following points were clarified from the results of experiments :
…Decrease of rotational flow velocities and acceleration of the flow of fore and aft direction behind the PBCF are confirmed quantitatively.
…PBCF generates torque reduction and also makes a main propeller increase thrust.
…The hub Vortex cavitation is eliminated by PBCF.
As for the PBCF effect on actual ships, 4.3 % of the efficiency gains on average from the analysis of the data from eleven sea trials of various kinds of ships, and a significant efficiency gain from the analysis of actual voyage data were obtained. The certain scale effect between the model and the actual ship is considered to explain the difference in the efficiency gain.
These results lead us to believe that PBCF is an excellent and practical energy-saving device because of its simple concept and the reliable efficiency gain of about 4 %.

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A surface panel method for the hydrodynamic analysis of a propeller operating in steady flow is described. The surface of propeller blade and hub is approximated by a number of small hyperboloidal quadrilateral panels with constant source and doublet distributions. The surface of trailing vortex sheet is also represented by hyperboloidal quadrilateral panels with a constant doublet distribution. The strength of source and doublet is determined by solving the boundary value problem at control point on each panel surface. Special emphasis was put on the Kutta condition of equal pressure on upper and lower surfaces at the trailing edge.
Pressure distributions on the blade calculated by the present method are in good agreement with the experimental data. A better agreement of pressure distributions near the hub is observed when compared with those of a conventional lifting surface method. Open-water characteristics of propeller calculated by the present method are also in good agreement with experimental data.

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Contrarotating propellers (CRP) became one of the most hopeful propulsion systems from a energy saving point of view owing to the development of reliable shafting systems. The efficiency of CRP in open water is superior to a conventional propeller. However, it is very important to investigate other properties such as propulsive efficiency, cavitation characteristics and propeller induced pressure fluctuations.
Although several experimental studies concerned with these items were conducted in these twenty years, there was a lack of hydrodynamic considerations in this area. The author intends to describe the essential differences between CRP and conventional propellers on the basis of previous studies which were pursued by the author et al.. As a result of experimental and theoretical studies on contrarotating propellers, advantages of contrarotating propellers over a conventional propeller in propulsive efficiency, propeller cavitation and pressure fluctuations are revealed.

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Recently many researchers have performed the pressure measurement on propeller models to obtain reliable data for validating propeller theories. This paper describes the new experimental techniques and the results of the measurement of pressure distribution on the blade of propeller models. In the present measurement, two kinds of propeller models were used ; a conventional propeller and a highly skewed propeller. In order to measure the pressure not only under the non-cavitating condition but also the cavitating condition accurately, “Helmholtz chamber-type waterproof pressure transducers with high sensitivity” were employed.
In earlier measurements, the measured pressure in some locations on the blades were greatly affected by the tortional or bending deformation of propeller blades. To remove such a detrimental effect, a special care has been taken of the attachment of pressure transducers to the propeller blades. In this paper, the pressure measurement performed by the improved procedure are described on two large propeller models working not only in uniform flow but in non-uniform flow. The present technique has the major advantage of the ability to measure unsteady pressure with high accuracy and no disruption to the measuring surface. The disadvantage is that the pressure transducers are very costly and specially fine techniques to install each pressure gauge in a chamber are demanded.
Finally this paper discusses the comparison of pressure distribution between the measured results and computational results given by the existing propeller lifting surface theory on two types of propellers, both in uniform flow and in non-uniform flow produced by the wire mesh screen, respectively. On the conventional propeller, good agreements between the computation and the measurement in the pressure distribution on the back side were observed, while the theory presented higher pressure values on the face side at any advance ratios in the present measurement. On the other hand, in the case of the highly skewed propeller, wavy profiles of the pressure distribution on the back side were obtained under the respective advance ratios probably due to viscous effects. The discrepancy between the theory and the measurements for the highly skewed propeller is the same as that for the conventsonal propeller, except near the tip region of propeller blades.
These discrpancies between the ewperiment and the theory should be attributed to the incomplete ness of the ewisting propeller lifting surface theory, that is, the two dimensional treatmdnt for thickness effects, the deformation of propeller blades and the neglect of viscous flow separation around the propeller blades.

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At present it is usual that the propeller cavitation noise characteristics are evaluated from the measured results at the cavitation tunnel through the scaling laws. However, the test section boundary of the cavitation tunnel is made of plural materials such as stainless steel and acrylic observation window. From this fact, it is predicted that the reflection effect of the boundary is significant and should be removed before the scaling-up to the fullscale. As the first step to this goal, the sound pressure distribution inside the cavitation tunnel was measured and compared with the calculated results by the two-dimensional Boundary Element Method (BEM) in order to argue the effectiveness of BEM for predicting the acoustic field inside the cavitation tunnel.
The measurement was carried out using monotone sound to evaluate the acoustic field purely. The sound pressure emitted from a B&K 8100 hydrophone was received by a B&K 8103 hydrophone array.
The sound pressure distribution in the transverse section was calculated by a two-dimensional BEM to argue the possibility of BEM application to the theoretical prediction of the tunnel acoustic field. Since the distance attenuation of the sound pressure in the experiment is three-dimensional, the comparison of the sound pressure level is not meaningful. However, since the reflection at the side boundary is considered dominant because of the tunnel test section configuration and the interaction of the sound pressure is mainly determined by the distance (phase) difference, it is considered that the calculated pattern of the sound pressure distribution, i. e. positions of the peaks, can be compared with the experiment. In the research, it was particularly examined what kind of boundary conditions should be given at the tunnel walls.
The results obtained were as follows :
(1) The measured sound pressure distribution in both the transverse and longitudinal sections showed some loops and nodes. This result showed that the reflection effect of test section boundary was very significant. This effect increased with frequency.
(2) The comparison with the experiment showed that calculated pattern of the sound pressure distribution agreed well if we adopted the boundary condition where the loops and nodes of the sound pressure amplitude respectively appeared at the boundaries between the water and the stainless steel and between the acrylic window and the air. This result could be elucidated from the acoustic impedance values of water, stainless steel, acrylic resin and air. It is concluded from this result that BEM is an effective procedure to predict the acoustic field inside the cavitation tunnel theoretically if the precise boundary condition is adopted.

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In the present report, we carry out an experiment in acoustic radiation problem with the 2-dimensional full submerged circular cylindrical shell, and compare its results with the theoretical solutions which were calculated in the preceeding report.
In order to compare with the 2-dimensional theoretical solutions, we separate the experimental cylinder model into 3 parts to exclude the 3-dimensional effects, put an exciter in the middle part of the model with watertight condition.
We could get a clear vibrational mode of the cylinder in the low frequency experiment, and measure the radiational sound pressure accurately.
Prior to the experiment in the anechoic tank, we carried out the vibration experiment in air, verified the eigenfrequency and the shape of vibration mode of the cylinder.

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In the prdvious papers, the authors examined the surf-riding phenomenon of a ship in the regular following waves by the self-running model tests and reported that the surf-riding phenomenon seemed to occur at the moment when the ship speed including the oscillating component due to the surging motion reached the phase velocity of the wave. They also tried to explain the occurrence of the surf-riding by analysing the equation of surging motion, and showed that once the ship speed reached the phase velocity of the wave, then the ship was caught in a state of the statical equilibrium of the longitudinal force, and therefore after that the ship speed could not change from the wave speed. The above explanation, however, was not very clear, because the equation of surging motion was characterized by the non-linear term of the exciting force and its analytical solution could not be obtained, and it was pointed out by the discusser that the confirmation by the numerical simulation should be done about the critical condition for the occurrence of the surf-riding.
In the present paper, the authors derive the expedient expression of the non-liner equation of surging motion and carry out the calculation of the numerical simulation. As the result the above critical condition for the occurrence of the surf-riding proves to be correct and the unsymmetrical periodic surging motion with a large amplitude, the behavior of the occurrence of the surf-riding, and the stable or unstable behavior of the surf-riding can be simulated. As regards the unsymmetrical surging velocity, some examples of the model tests are presented to show the qualitative agreement with the simulation. It is also clarified that in some small range of the ship speed close to the critical speed for surf-riding, the occurrence of the surf-riding or the periodic surging motion depends on the initial condition about the ship position and the surging velocity of the ship.
Since the critical condition itself proves to be correct, the simple method proposed previously to estimate the critical wave height and critical ship speed need not be corrected as a guidline to avoid the dangerous surf-riding.

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In the interest of brevity, practical equations for ship motion and capsizing in following seas are derived. Simulations of capsizing are carried out by using Tasai's and Inoue's practical formulas for the hydrodynamic coefficients. Finally a material to discuss safety against capsizing is presented for novelty.

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Recently the techniques of generating short crested waves with arbitrary directional spectrum are developed, and some experiments are conducted in such waves. However, ship towing or running tests in such waves are not conducted yet, because sufficiently uniform experimental area could not be obtained. This paper reports ship motion test in towed condition (Froude numbers are 0.2 and 0.275) in a long tank by generating uniform irregular waves with arbitrary directional spectrum, and describe the comparison between analyzed results and theoretically estimated results. The compared results show relatively good agreement.
For this experiment, a snake type wave maker was newly developed and installed at the end of the long tank of Yokohama National University.
For the analysis of directional wave spectrum, we adopted so called Maximum Likelyhood Method.
Theoretical estimation is made by using analyzed directional wave spectrum as input wave and also by using directional motion transfer functions calculated by so called New Strip Method.

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Model tests of a semi-submersible have been conducted in directional spectra waves generated by the new snake type wave maker installed in the towing tank of Yokohama National University.
In various kinds of short-crested irregular waves which have specified power spectra and directional distribution functions, motion responses of the moored semi-submersible ITTC model were measured.
The 1st-order motion responses in wave frequency range were estimated by the linear superposition theory using directional wave spectra and transfer functions in oblique waves. Successful agreement between measured and estimated responses was obtained even in wide spreading waves as well as in narrow spreading waves.
The influence of directional spreading function and principal wave direction on the short-term prediction of motions was also investigated and some examples are presented.

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Slender-ship theory is applied to develop a new method of calculating with quantitatively good accuracy the effects of side-wall interference on the added-mass and damping coefficients of a ship in a waterway. The present paper is restricted to the radiation problem of heave and pitch motions with zero forward speed, but it may be easily possible to extend to the forward-speed case and the diffraction problem.
In the outer region, 3-D Green function satisfying the boundary condition on the side walls is placed along the ship's centerline on the free surface to describe the outer solution. The side-wall boundary condition is satisfied by considering an infinite number of image ships, and then the summation of the resultant infinite series is analytically obtained in a closed form.
In the inner region, the radiation condition and side walls are absent, and thus the inner solution is identical to that of Newman's unified theory : the strip-theory solution plus a homogeneous solution multiplied by a three-dimensional interaction coefficient. This interaction coefficient is determined by the compatibility requirement of the inner and outer solutions in an overlap region. Therefore through this coefficient, the side-wall effects are incorporated in the inner solution.
Computations of the added-mass and damping coefficients are performed for a floating spheroid of length-beam ratio L/B=8 in a channel of breadth ratio B _T/B=16, and of L/B in a channel of B _T/B = 5. Numerical results are in virtually perfect agreement with the results by a newly-developed 3-D panel method. This suggests that the theory proposed can be quite effectively used also in estimating the tank-wall effects on the results of experiments in a towing tank with limited width.

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Following the first report on the problem of the wave force reduction at lowK_c number region in regular waves, the problem in irregular waves are experimentally investigated in the present paper.
Measurements of wave forces acting on circular, square and lowerhull cylinders horizontally submerged in irregular waves show a reduction of inertia forces at the moment of high wave amplitude. An existence of a circulating flow round a cylinder is confirmed by flow visualization as same as in regular waves.
The reduction of the inertia forces has a similar dependency on K_c number to that in regular waves if a K_c number are defined in terms of each amplitude of water particle. A prediction method of the wave forces acting on a cylinder in irregular waves is proposed.

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To carry out a reliable design of the ocean project and same thing for observation of marine science, it is essential to survey the ocean environment extend over a long time and continuously. Japan Marine Science and Technology Center (JAMSTEC) proposes to construct an ocean stable laboratory (OSL) in order to enable the long term continuous research and to contribute the development of the deep ocean area far from the shore.
The proposed OSL is planned to be a kind of tension leg platform (TLP) which suppresses its vertical motion (heave, surge, sway) by the leg tension and it is stable and removable. The principal particulars of OSL are length of 77 m, breadth of 77 m and depth of 70 m and to be set in a deep ocean area of about 800 m water depth. This OSL equips various kinds of facilities for experiment and research works, the support systems for undersea work, the measuring and monitoring systems, the telecommunication network, the accommodation facilities, etc. Around this OSL, the undersea habitation, the underwater shuttle boat, etc. are also arranged in the plan to perform the research works.
JAMSTEC have been performing fundemental studies of the TLP and also performed the sea test of TLP in 1986 and 1987 at Yura, Yamagata prefecture and confirmed its availability and safety. Based on the results of the above, design procedure of the optimum hull form of the OSL is developed in this study. The model experiment using 1/100 sacle model is also performed to confirm the motion characteristics and varying tensions of the tendons in waves. This paper discusses the design procedure of an optimum hull form of the OSL and the results of the model test.

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The correlogram method through a discrete auto regressive (DAR) model is powerful to estimate a damping coefficient and a natural frequency of ship's rolling and pitching motions using the sampled time series of their motions under navigation. But it is difficult to extend the method to a coupled motion, a nonlinear one of ship's oscillation, an input-output motion like maneuvering one and so on. However, nowadays, the development of stochastic identification technique of model is remarkable.
In this paper, we propose a new stochastic approach using a continuous auto regressive (CAR) model not only to gain more precise linear parameters of ship's oscillating equation representing roll and pitch under navigation but also to extend the model to the above mentioned more complicated problems in future.
The new approach begins with a transform of the equation representing a ship's oscillating motion to a CAR model which will be transformed in the last step to a state space model in accordance with the Kalman's frame work. The likelihood value is calculated by the Kalman filter using information square-root algorithm and the parameters are searched so that the likelihood value takes numerically the maximum value, using the Davidon-Fletcher-Powell optimization technique. The goodness of the model is evaluated by using AIC (Akaike's Informaton Criterion) of the model.
The data fitted in this paper are two sets of the roll's and pitch's records which were observed by a container ship under the PNW route in winter. One of them has a single peak and the other one has multiple spectral peaks due to strong rough sea.
According to the results, the CAR model proposed here fits well to the actual rolling and pitching data than the conventional method using the correlogram in the viewpoint of the AIC. The estimated natural frequncies of the ship's roll and pitch motion are fairly well but the damping coefficients by a low order's model are not stable especially in the data under rough sea conditions.

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A numerical procedure is described for predicting wave exciting forces and motions of multiple three-dimensional bodies of arbitrary shape freely floating in waves. The developed numerical approach is based on combination of a three-dimensional source distribution method and interaction theory which is exact within the context of linear potential theory. The method presented is applicable to an arbitrary number of three-dimentional bodies having any geometrical arrangement and individual body geometries. Numerical results of wave exciting forces and motions of two freely floating bodies in shallow water are compared with those obtained in the literature. The results of comparison confirmed the validity of the proposed approach. Finally, the interaction effects are examined in the case of an array of 40 (4 by 10) freely floating rectangular bodies in shallow water.

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In Japan, space utilization of the ocean has been considered as one of the most important subjects. Therefore we thought out a new type structure for ocean space utilization which can be installed in the ocean of water depth 3070m. This structure is composed of a semisubmersible type ring-like structure and supporting foundations. For the sake of investigation of structural feasibility of this ring-like structure, the steps of procedure taken in this paper are as follows ;
(1) concept design of a new type structure,
(2) setting of natural environmental conditions (wind, current, wave, earthquake) and designcriteria,
(3) initial structural design,
(4) evaluation of external forces using wind tunnel tests and a source distribution method,
(5) structural response analysis using FEM.

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Wooden ships up to around 55 m in length have been so far designed and built with hulls of double skin planking which consists of each single layer of longitudinal planking and diagonal planking crossing with an angle of 45°. Based on successful operation of these ships, large-scaled wooden ships of around 70 m are recently under consideration adopting hulls of triple skin planking. The triple skin planking consists of the outer skin of a single layer of longitudinal planking and the inner skin of double layers of diagonal planking wihch cross the longitudinal planks with angles (θ) of ±45°.
Experiments and theoretical investigation as listed in the followings have been made in order to establish design formulae for the longitudinal bending and shear strength of hulls of the triple skin planking :
(1) Simplified formulae are induced for calculating the rigidities and the stresses of the triple skin planking, and the practical methods are shown on the longitudinal and shear strength of hulls.
(2) The results of the structural loading tests of the box-shaped ship model sizing 6.54 × 0.9 × 1.04 m are compared with the structural analyses by the three-dimensional (3D) truss model. The structural members of the test model are in 1/2 scale of those of a prototype ship except the overall dimensions.
(3) The results of the same kind of 3D truss analyses made for the whole hull of the prototype ship are compared with the calculations by simplified formulae.
It is concluded as follows :
·The 3D truss model reasonably represents the behaviour of the triple skin planking.
The simplified calculation methods can be applied to actual ship design.
·The effectiveness of the diagonal planking on the longitudinal bending strenth is 25 % theoretically when θ= ±45°, and a practical value of 20 % is proposed.
·The inner skin of two layers of diagonal planking predominantly carries shear forces. The axial stresses of diagonal planks are simply obtained by doubling the shear stresses when θ= ±45°.
·Longitudinal members such as gunwale, chine and keel contribute to the shear strength of a hull by their sectional areas multiplied by a factor of 4G/E theoretically when the rotations of the sections are restrained by neighbouring members. The actual degree of contribution is subject to further investigation.

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The estimation of distritization error in the finite element method is considered in this paper. The proposed method can estimate error of solutions obtained by the finite element method for 2-dimensional elastic problems with 4-node elements. Because quadratic term is expected to dominate the error field, an 8-node element is utilized in the estimation. Even though the 8-node element is used, the proposed method does not require a large memory or long computing time since error is estimated element by element. Not only rectangular elements but also any shape 4-node elements can be used in this method for estimating the error in the finite element computation with high accuracy. An error norm is computed in the paper which can indicate an element-wise relative error. The finite element solutions are also improved drastically by adding the estimated errors onto the original solutions. The proposed method can be utilized for any type of linear problem if an isoparametric finite element method is used.

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Most of offshore structures for oil exploitation are composed of deck and legs (pipe framed structure). The local failure of the leg may lead to overall collapse of the structure. Accordingly, it is very important to clarify the ultimate strength of the leg.
For the analysis of the strength of the leg, an investigation on the strength of a joint has to be performed previously. However, the studies carried out so far are limited to the joints of which chord and braces exist in the same plane, such as Y (T) -joint and K (TY) -joint. While the loading condition of the K (TY) -joint is limited to brace-axial force.
In the actual structures, most of joints are constructed three-dimensionally. The loads acting from the brace to the chord are not only brace-axial force but also in-plane and out-of-plane bending moments. The mechanical behavior of such three-dimensional joint may differ from the one of two-dimensional joint.
In this study, simple (unstiffened) V-joint is investigated as one of three-dimensional joints, of which two braces exist in the plane perpendicular to the axis of the chord. The mechanical behavior under various loads (normal force and bending moment) are analyzed by PNM (Plastic Node Method) which is one of the very efficient and accurate FEM for elastic-plastic analysis.
Based on the results, the characteristics of the stiffness and strength of the V-joint are clarified, comparing with those of the T-joint which has the same dimensions. The mechanisms which vary the stiffness and strength depending upon the loading condition are shown. One of the most important result is that the stiffness and strength of V-joint is reduced to 70 % of those of T-joint in severe loading condition. So the reinforce method by using a stiffener is discussed.

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Perturbation analyses for slightly non-colinear and quasi-static crack extension were first performed by Banichuk (1970), and Goldstein and Salganik (1970, 1974) with the use of Muskhelishvili's complex potentials. Having obtained a rather simple expression of stress intensity factors, Cotterell and Rice (1980) examine the crack growth path of a semi-infinite crack in an infinitely extended plane. First order perturbation analyses are made by Sumi et al. (1981, 1986) for a straight crack in a finite body with the slightly branched and curved extension. The shape of branched and curved extension is approximated by a continuous function with three parameters, and the approximate stress intensity factors at the extended crack tip are obtained in terms of these shape parameters and the near tip stress field parameters ahead of the crack tip prior to its extension, where the effects of the geometry of the domain are also taken into account.
In the present paper we extend our perturbation analysis from the first order to the second order with respect to the shape of the non-collinear crack path. An approximate description of the stress intensity factors is obtained at the kinked-curved crack tip, where the cracked body is subjected to an arbitrary far field boundary condition. A kind of a matched asymptotic expansion method is introduced in order to construct the solution, where the effects of the geometry of the domain are taken into account by alternately matching the far field asymptotic behavior and the near tip field asymptotic behavior in an ascending order of the square root of the crack extensional length. If we consider the smooth crack curving which confirms the continuity of the first derivative along the curved trajectory, the second order perturbation solution thus obtained gives the exact asymptotic property of the solution.
The elastic energy release rate, which corresponds to the non-collinear crack growth, can be calculated by using Irwin's formula. As far as homogeneous materials are concerned, both the maximum energy release rate and the local symmetry critria predict the same crack growth direction within the second order approximation. Considering material inhomogeneity such as degradation zone, a crack may be branched and curved due to the spatial variation of the fracture toughness. The energy criterion is relevant to predict this type of behavior, which cannot be properly examined by simple stress or strain criteria.

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A method is proposed for estimation of the probability distribution of fatigue crack growth life and reliability assessment of structures by simulating material resistance to fatigue crack growth along a crack path. The data for the simulation can be obtained from a few fatigue tests. The material resistance is treated as a spatial non-Gaussian (eventually Weibull, in this report) stochastic process. Therefore, a non-Gaussian stochastic fields simulation method proposed by Shinozuka, et al. is applied with statistical data obtained experimentally. The statistical analysis of the material resistance is performed with the data obtained by stress intensity factor control tests. The main results obtained are : (1) This method is useful to estimate the probability distribution of fatigue crack growth life ; (2) the material resistance seems to follow a 3-parameter-Weibull distribution ; (3) this method is useful for simulation of rather long fatigue crack ; (4) using this method, the probability distribution of fatigue crack growth life can be estimated from very few fatigue tests ; (5) the smallest life can be determined ; and (6) stress intensity factor control test is preferable for the statistical analysis.

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The purpose of the present investigation is to examine the effect of plate thickness on the ductile fracture toughness values experimentally and numerically. Considerable attention is paid to the stress, strain and deformation in the vicinity of the crack tip in order to analyze the fracture behavior.
Fracture toughness tests are performed for center cracked specimens (CCS) of SUS430 stainless steel and compact tension specimens (CTS) of SS41 mild steel. The thicknesses of CCS are 0.4, 0.7 and 1.2 mm and those of CTS are 1, 2, 5, 10 and 19 mm. The deformation, stress and strain in the vicinity of the crack tip of CCS are obtained numerically by using 3-dimensional elastic-plastic Finite Element Method.
In addition, the authors propose the method to evaluate the critical J-integral value at the onset of crack extension by using the numerical results of equivalent plastic strain in the vicinity of the crack tip. The results in this study are summarized as follows :
1) At thinner plate thickness than 5 mm, the ductile fracture toughness (J_i) values decrease with in an decreasing plate thickness for the metallic materials used in this study.
2) Even very thin plate thickness, the stress condition at the crack tip becomes high triaxiality due to plastic constraint.
3) Estimated values of J_i, which are evaluated by using the equivalent plastic strains, displayed good agreement with the experimental results. Then, it is considered that the critical value of the equivalent plastic strain is one of the fracture parameters of ductile metals at the crack initiation.

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A new DC motor drive release was designed, built, and tested at sea. The conventional motor drive release was worked by DC motor driving a detent attached on the shaft. In this composition, the frictional force between detent and lever increased according as the water pressure increased in the deep ocean. Therefore, an accident which the release did not work occasionally happened and it was unreliable. A new release is worked by DC motor driving a pin connected to the nut along the axis of the screw inward the pressure hull using a sending screw. In the new composition, water pressure works effectively to release. A ball screw is used in order to decrease frictional force as the sending screw. A frictional brake is also used to hold the hook with a pin and for itself not to move by water pressure. The release is worked by acoustic command.

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The concept of the extraction system of uranium from sea water using sea water current and wave power by the application of sphrical fiber adsorbents is presented in this paper. The adsorbent bed system consists of thin disk cartridges enclosed in nets and arranged below the sea surface in horizontal layers by suspending ropes hung from a cylindrical buoy with a hole in the centre. These cartridges filled with the adsorbents are transferred from the ships hold to the buoy by the ship board crane and are fixed to the suspended ropes. The ropes are the unwound through the center hole so as to place the adsorbent beds in the sea water current which enables the current to pass through the adsorbent beds. The exchange of sea water around the adsorbents is improved by the heaving motion of the buoy due to waves. After about 40 days, the adsorbent beds are recovered using the same process, the cartridges are transferred into a tank for the elution process. Throughout the above processes, the adsorbents are not taken out of the cartridges.
The model tests of a cylindrical buoy with adsorbent beds are carried out in uniform flow as well as in regular waves. The displacements of the adsorbent beds in the flow and the heave motion of the buoy with adsorbent beds suspended from it are analysed.
Furthermore, numerical simulation of this system was carried out for practical operation in the ocean and the production cost of uranium extraction was calculated to be 41, 800 yen/kg, where adsorptive ratio is assumed to be 3.2mg/g. 40days.

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Following the previous reports, dealt with in this report is the strength of crankshafts of long stroke marine diesel engines.
The authors propose a new method which evaluates the strain of crank pin fillets of an engine under its operating condition, by introducing a new concept 'Response Factor'. The response factor, which is defined as the ratio of strain response to external concentrated force, is classified to 9 types according to kinds of the applied load and positions. The every response factor is obtained effectively by the calculation using F. E. M. zooming model of the pin fillet, and then the strain is calculated through summation of each response produced by the external forces which are evaluated by matrix calculation.
Moreover, measurements were carried out on two kinds of long stroke engines to know the stress condition of the crankshaft of such type engines while running. The results show that the pin fillet's strain along radial direction has much effect of the constrained moment from the adjacent throws and the axial vibration.
The fact that calculation results by the new method corresponds to measured ones fairly well shows the high reliability and great effectiveness of the method.

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