2-dimensional steady waves generated by a submerged wing section are studied experimentally to make clear the mechanism of the sub-breaking wave. The sub-breaking wave is a kind of a turbulent free-surface flow taking place around wave-crests. It takes place after a sudden increase of the wave slope. Its appearance brings forth a velocity-defected layer with a significant turbulence intensity beneath the free-surface. The condition for its appearance is derived based on the instability analysis. It is found, for a constant-curvature-wave, that the sub-breaking takes place when the circumferential force is greater than the gravity acceleration ; in other words, the pressure gradient in the vertical direction is positive. Breakings observed in experiments are discussed through this criterion.

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The lateral force and the resistance that are caused by wave generation acting on the body advancing with steady drift angle were discussed by the asymptotic expansion method under the assumptions, F_n<<1 and β<<1, where F_n is the Froude number and β the drift angle. The technique of the Low Speed Wave Making Theory was applied to represent the flow field around the body. Lateral force and resistance are obtained by using the amplitude functions of the free wave derived by the both of the Approximation in x-Integral Method and in y-Integral Method those were identified. The coefficients of the lateral force and the resistance were calculated for not so slender floating prolate spheroids and vertical elliptic cylinder. It was shown that the first approximation of the coefficient of the lateral force, which acts opposite to the lift caused by the separated vortices in the case of bluff bodies, are proportional to βF_n⁶ and second one to βF_n⁷ sin (1/F_n²+π/4).

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A numerical analysis is tried how the “waves” and “boundary layer-wake” interacts. External potential flow around a hull is modeled by modified Guilloton method. Viscous flow is modeled by integral boundary layer-wake method. The displacement thickness concept is used to match the viscid-inviscid calculations. Results are compared with experiments and followings are obtained. Stern wave generation and boundary layer-wake growth depend on Froude number. The displacement thickness aft of the stern end increases and the wave resistance reduction due to the boundary layer-wake is remarkable at the speed from hollow to hump.

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A higher-order accurate finite-difference solution method is developed for three-dimensional incompressible viscous flows. The Navier-Stokes equations in rotational form are solved in boundary-fitted coordinates. Fourth-order compact scheme is used for the space differencing in order to have adequate degree of accuracy for viscous flow problems. A viscous flow around a circular cylinder is solved at R=100 and 1000. The simulated twin vortices and secondary twin vortices show fairly good agreement with experimental results.

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The direct formulation of boundary element method (BEM) based on the thick wing theory, which is expected to be a more accurate method than lifting surface theory, to the analysis of three-dimensional flow around the marine propeller in uniform flow has been presented at the 1st report for the need of more accurate prediction of pressure distribution acting on the surface of the propeller blade.
In the present paper, BEM formulation is extended to the marine propeller in steady ship's wake. The present method is applied to the analysis of flowfields around conventional propeller and highly skewed propeller. The result is compared with that of the lifting surface theory (LST), and the usefulness of the present method for the problem of marine propeller in steady ship's wake is verified.

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In the first report the authors discussed about the analysis in uniform flow. Using the same discrete model, the analysis for the present report was performed for the oblique case. In addition to the effect of boss, propeller slipstream asymmetry was also incorporated into the model. Experiments were performed by inclining the propeller shaft with respect to the flow direction in the cavitation tunnel. Predicted cavity extents had been found to agree relatively well with the observed ones when the predicted values were advanced by sixty degrees. In the calculation of pressure distribution on the blade, it had been found that there was a considerable drop in pressure at about 60% chord position of the blade near the boss and this position had been found to agree very well with the observed position of root cavitation erosion.

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The surface force, which is a cause of ship hull vibration, is due to oscillating pressure on the hull induced by a propeller. In the present paper analytical investigation has been performed into characteristics of oscillating pressure on a horizontal plane fixed in the space above a propeller. At first the general formulation of the pressure field around a propeller has been made as the general solution of the Poisson equation. The well-known expression by loading and thickness effects has been deduced by linearized approximation of the solution. The relation between the integral equation of Ishida's theory and the general solution has been explained. It has been pointed out that the relative position of the calculation point to back or face sides of propeller blades is an important factor to control the characteristics of the pressure distribution. Numerical examples have been made for a uniform flow and two nonuniform harmonic wake flows, cos 2θ and cos 5θ wake distributions. The calculated results for a five-bladed propeller have shown the normal distribution of oscillating pressure in case of a uniform flow and cos 2θ wake flow but an abnormal distribution in case of cos 5θ wake flow. Such calculations have been in good agreement with the measured results by experiments in the towing tank.

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A new type propeller derived from “winglets” was investigated. This propeller is also fitted small blades at the blade tips likely to “winglets”, so we named it “bladelets”. These are for the purpose of reducing induced drag from tip vorteces. This paper, as the first report, mainly presents the results of the series tests which are concerned with the arrangement of these small blades. Propeller open test, flow visualization and flow velocity measurements were performed, and one of the best arrangement of “bladelets” were found out. The results looks 1 or 4% better compared the efficiency of “bladelet propeller” with that of the original one within the bound of real working condition.

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At first, the fundamental equation of the energy distribution in the flow field around a propeller and fins are derived. Next, the theoretical and experimental studies on the recovery of the rotational energy in the propeller slipstream show the following results :
a) In the propeller slipstream between 0.125 D and 2.0 D behind propellers (D ; propeller diameter), the dissipation of the rotational energy is very weak and the rotational flow is same at every cross sections.
b) The fins after propellers decrease the rotational energy in the propeller slipstream and convert the most of the energy into the work done by fin thrust.
c) With increasing the number of blades, fin improve the rotational energy recovery. The increase of fin drag, however, makes the optimum blade number finite. It mainly depend on propeller loading conditions and fin chord length.
d) The rudder with fins recovers the rotational energy more efficiently than without fins.

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From several years ago, the free propeller (vane wheel), which is fitted at the rear of the main propeller, is going to be put to practical use for the purpose of the energy saving. The authors had a chance to measure the effect and the strength of the free propeller in both conditions before fitted and after fitted on the same full-scaled ship. From this data, it is found that ;
a) the number of revolutions of the free propeller is 37.5% of that of the main propeller, b) the thrust force by the free propeller accounts for1417% of the total thrust force, c) on the blade stress of the free propeller, the mean value is 2.6 kg/mm2 and the peak-to-peak value is 8.8 kg/mm², and this value is permissible, d) the blade frequency components of the pressure fluctuations induced by the main propeller are reduced to 80% and the level of the hull vibrations is also reduced consequently.

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The cavitation minimization of the waterjet inlet is an important matter in designing the inlet configuration for high speed SES (Surface Effect Ship). For this purpose it is necessary to know the pressures on the inlet surface. However it takes much effort to calculate the pressure distribution in 3-D flow even when it is inviscid. On the other hand, the 2-D potential flow calculation is expected to be an useful design tool.
From the point of view, the author surveys and finds the optimum inlet configuration in cavitation minimization by calculating the 2-D potential flows of many kinds of flush type inlet configuration. In order to examine the performance of this optimum inlet, a model test of the inlet is carried out in the wind tunnel and the pressures are measured. The result shows that the inlet has the possibility of high performance in cavitation avoidance.

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A theoretical method is proposed for computing the wave forces on a ship running in the following oblique waves with very low encounter frequency. It incorporates, in addition to the Froude-Krylov forces, all the terms up to the lowest order of magnitude with respect to the disturbance of the incident waves. They include the interaction effect between the stationary waves generated when the ship running on a calm water and the disturbed incident waves.
Several examples of numerical results by the method are presented to test its validity, for example, for predicting the wave yaw moment which was found by Motora et al. to bring about broaching-to phenomenon when it exceeds the course keeping ability of the ship given by the rudder action. The results show that the method proposed is better than the Froude-Krylov assumption for describing the relation between the wave force magnitude and the location of the incident waves relative to the hull.

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Hydrodynamic forces acting on vertical circular cylinders forced to surge in low frequencies in regular short waves are measured. Hydrodynamic forces acting on the cylinder forced to surge in combined two harmonic motions in low and high frequencies are also measured. Hydrodynamic coefficients for the slow and fast motions are obtained respectively. These experimental investigations have been done in order to study on the viscous damping force acting on a moored ocean structure in the slow drifting oscillation in irregular waves. Experiments show that the drag coefficients of the cylinder oscillating in low frequencies in waves are quite different from those of the cylinder oscillating in low frequencies in a still water.

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An exact second order solution is presented for the slowly varying drift overturning moment on an articulated column in irregular waves. The wave diffraction problem is formulated and solved correctly to second order in wave amplitude by application of Green's second identity and Haskind's reciprocal relations. The approach allows the evaluation of the second order excitation force due to the second order wave without knowing the second order pressure distribution over the body surface. All the contributions to the total drift moment are thus evaluated only from the solution to the first order diffraction problem, for which explicit analytical results are available. As illustration of the theory, results are presented for the quadratic transfer functions of the drift overturning moment, which are then used to investigate the slow drift motion of the articulated column under typical sea conditions. The present exact results are also compared with those from different simplified solutions. Conclusions arising from these numerical results may be summarised as follows : a) In short to moderate seas with high wave frequencies, the total drift moment is dominated by the force components arising from products of first order quantities. In this frequency range, the slowly varying drift moment may be predicted fairly well with the knowledge of the mean drift moment in regular waves ; b) In extreme seas with longer wave frequencies, the component from the second order locked wave dominates the total slowly varying drift moment. In such low frequency range, diffraction effects due to the first order wave are so small that the contribution of the second order wave may be calculated most accurately by means of the proposed approximate method neglecting these effects ; c) The conventional method using data of the mean drift moment in regular waves gives accurate results for the slowly varying moment in short to moderate seas, but tends to underestimate the responses in extreme sea state with longer mean wave period.

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Japan Marine Science and Technology Center plans to execute TLP sea test in this and next years. The site is 40 m deep and 3 km off Yura harbor, Yamagata prefecture. An outline of the TLP and the basic design results are described in the 2 nd report. In the tension mooring system, the rubber-chain which is a chain filled and covered with an elastomer, will be applied in order to absorb the shock loads, and prevent the mooring line from locally abrasing.
This paper presents the fundamental test results of the rubber and the detail design and 1/3 model tests results of the rubber-chain. The tension elasticity of the rubber-chain is widely disposable with rubber hardness and the allowance ratio which is defined as the ratio of the rubber parts got between the chain links to the total rubber-chain length.
In this design, the rubber hardness 50 and the allowance 26 mm are finally selected for the 10 m long and φ 50 grade IV chain.

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An approximate method is proposed to calculate the statistical distributions of the maxima and minima of a weakly nonlinear response in irregular waves. Different from the previous method which dealt with the same problem, the present formulation includes the effect of the band width of the response spectrum. Therefore, the present approximation is even applicable to the response whose spectrum is not narrow banded but arbitrarily wide banded, as may be frequently experienced in most seakeeping problems.
First, the formulation for the quadratic nonlinear response is derived in the form expressed by the Hermite polynomial.
Second, calculations are carried out on the probability density and the 1/n th highest expected amplitude of wave elevation. The comparisons of the calculated results with simulated time domain results as well as experimental ones suggest that the present method may be useful from an engineering point of view.

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Recent development of underwater acoustic devices causes a need to study the underwater sound radiated from the ship.
Such underwater sound has two sources, the one is mechanical due to the vibration of main or auxiliary engines and the other is hydrodynamical due to the propeller cavitations and flow noise.
In the present report, we deal with the former one, that is, the sound radiation problem in which the vibration of engines is transmitted to the ship hull and then its hull vibration is radiated into the water as sound. In order to study the fundamental characteristics, as an example, we solve a two dimensional circular cylindrical shell floating on the free surface which vibrates periodically and show the mutual interaction between the shell vibration and the acoustic field of the surrounding water especially its far field property.

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A general expression for the pressure distribution on the inclined flat rectangular bottom of a ship penetrating the water surface is derived by matched asymptotic expasion on the bases of the shallow draft and gravity free assumptions which are essentially equal to those made by Wagner in the 2-D theory. The flow field is divided into two regions, the outer region where the linearity assumption holds and the 3-D flat plate formulation is utilized to have the outer solution and the edge region where the impact phenomena occur and the solution is constructed by using its flow similarity to the 2-D planing plate case of which solution is known analytically. Both solutions are matched asymptotically to make them determinate and the composite solution valid in the entire region is derived. The calculated results are compared to the experiment which was conducted to measure the pressure distribution over the inclined box-shaped hypothetical ship. Some of the assumptions made in the present formulation such as uniform tranverse distribution and no pileups of the perturbed water are found to be satisfactory by comparison with the experiment. Agreements in the peak impact pressure are very good if considerations are made to the fact that the measured peak pressure has averaged value over the pressure gauge membrane.

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It has been proposed in some papers to apply statistics of extremes to prediction of the extreme value in a long-term distribution of such response as wave induced load from result of full scale measurement. But there is no discussion on the difference between the conventional extremal distribution and that of the largest value among peak values measured by the experiment.
Though a short-term distribution of peak values of the response is approximately described by the Rayleigh distribution, a distribution of the largest value is not equal to that of the Rayleigh distribution with a constant parameter. At first, authors study on it and clarify that it is described by the double exponential distribution, which has another character than that of the extremal distribution for the Rayleigh distribution.
The extremal distribution of the conventional theory puts the base on the result of random sampling. This sampling condition is not the same as that of measured peak values in the experiment. Considering the difference in sampling, authors lead equations, by which we can calculate the accurate extremal distribution. Supposing such a model which is a group of numberless Rayleigh distributions with parameters described by the Weibull distribution, authors investigate the characteristics of the extremal distribution. The following characters are find out by our study.
Speaking strictly, the distribution dose not fit to the double exponential distribution and the Weibull distribution except a limited condition. In general it is approximated by the latter.
The distribution varies with sample size of the largest values measured during the experiment. In the case when we predict the extreme value in a long-term distribution from result of a shorter period measurement, it is required to correct the distribution counting for the sample size.
Regarding the above result, authors propose two prediction methods which can estimate the value accurately.

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This paper describes summarized results of the analysis on hull response data of a pure car carrier in service which is obtained through on board test of hull strength monitoring system. The system is currently being developed by Nippon Kaiji Kyokai and the purpose of installing this system on board of ships is to provide the navigator with accurate information on hull response in heavy weather so that the ship master can make an appropriate judgement for ship operation and maneuvers.
Response data of deck stress, web frame stress and vertical acceleration at bow etc. is analyzed from view point of studying relation between hull response and deliberate loss of speed in rough seas. The results show that vertical acceleration at bow well correspond to deliberate loss of speed. It is also found that hull response is fairly influenced by wind direction and speed reduction is made mostly in head and bow wind. In full load condition speed reduction is made suddenly, on the other hand in ballast condition speed reduction is made gradually.
It is anticipated that the hull strength monitoring system developed by the society will make fair contribution to safe and economical operation of ships.

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This paper presents a probabilistic method of prediction of occurrence of fatigue failure in ship's structural members under external load during ship's life.
The considered kinds of load are irregular wave load during ship's life and quasi-constant load such as exciting force due to propeller.
For occurrence of fatigue crack, a lognormal distribution function is adopted.
Three stochastic variables are considered for fatigue crack in ship structure ; scatter of S-N curve, misalignment due to workmanship and distribution of applied stress level in a group of structural members such as in a row of bottom transverses in tanker.
The obtained distributions of number of failure against age of ship show good agreement with the observation in actual ship obtained on occasion of hull survey.
An approximate method on estimation of allowable hot spot stress including effect of welding bead is proposed.

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This paper is concerned with reliability assessment of ship transverse structures, which are modeled as relatively rigid frame and subjected to quasi-static extreme loads, based on plastic collapse analysis. Plastic collapse is evaluated by using a linearized plasticity condition of the section under the combined effect of bending moment, shearing force and axial force to generate the safety margins, using a matrix method. Probabilistically dominant collapse modes are selected by applying the so-called branch-and-bound method. The above method is successfully applied to the transverse structures of large and medium size tankers and an ore carrier under some notional load conditions. Through the numerical examples, probabilistic properties of plastic collapse of ship transverse frame structures are investigated.

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In the present paper a nonlinear finite element code based on the updated Lagrangian approach will be developed for the analysis of the crushing behavior of structural elements and some numerical examples will be presented in order to show the validity of the present algorithm. Several features of the developed code are :
1. The bilinear degenerate shell element with reduced integration is employed.
2. The hourglass control stiffness proposed by Flanagan and Belytschko and in-plane rotational stiffness due to Kanok-Nukulchai are added to the element stiffness.
3. The virtual work equation is expressed in terms of the updated Green strains and the updated Kirchhoff stresses and the calculated Kirchhoff stress increments are transformed into the Jaumann stress increments at each incremental step. In this transformation the normal strain in the thickness direction is determined so as to maintain the plane stress condition.
In numerical examples the post-buckling behavior of axially loaded elastic and elasto-plastic columns are analized and the calculated load-deflection curves are checked against the exact solution and experimental results. The crushing behavior of axially compressed circular cylindrical shells is also calculated, and the obtained results are compared with experimental results.

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The concept of “effective width” of plates subjected mainly to uniaxial compression is widely used in design of plate structures.
In this paper, an analytical expression for effective width of rectangular plates subjected to uniaxial compression is derived taking account of initial deflection and welding residual stresses. In order to verify the validity of this expression, it is used to evaluate the ultimate strength of compressed plates. This is then compared with experimental results presented by Ueda et al. and Dwight et al and found to be in good agreement.
An expression is also derived to evaluate the effective width of rectangular plates subjected to biaxial compression and shear taking initial deflection and welding residual stresses into consideration.
Comparisons with available results of finite element analysis and experimental results exhibits the accuracy and reliability of this expression.

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In this paper, formulation of an elastic-plastic large displacement theory of the “Idealized Rectangular Plate Element” and the “Idealized Stiffened Plate Element” is carried out. In this formulation, local (inter-unit) nonlinearities (large deflection, buckling and plasticity) as well as overall nonlinearities are taken into account. On the local level, behaviour of plates and stiffened plates is idealized according to the techniques of the Idealized Structural Unit Method.
On the global level, plates and stiffened plates are treated as membranes neglecting their out-of-plane bending contribution to the global structure in comparison with their inplane contribution and the contribution of primary supporting members. Out-of-plane as well as inplane large displacements of the global structure are taken into account.
The process of the formulation is presented and the validity of this approach is theoretically demonstrated. The problem of coupled local and global buckling of box columns is demonstrated through results of analysis of an example box column. Results of analysis of coupled web buckling and lateral buckling of I girder are also presented.

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In general, a deck plate of a ship hull is subjected to inplane tensile and/or compressive load due to longitudinal bending. When the strength of a deck plate is considered, the contribution of the plate elements subdivided by stiffeners and girders are very important, and the accurate evaluation of their compressive strength is essential.
In this report, based on the results obtained in this series of research, the authors have developed a simple estimation method of the ultimate strength with a limited amount of information on the kind of steel, sizes of deck plate, welding condition, etc., which does not require complex calculation such as FEM.
The main results obtained in this study are as follows.
(1) A simple estimating method of welding deformation and residual stresses produced in a deck plate is proposed. The calculation can be performed by using the yield stress of material, welding condition, etc.. The estimation is very accurate compared with the actual measurement.
(2) In order to describe the influence of actual complex initial deflection, the effective coefficient of initial deflection is theoretically determined for the standard initial deflection which was idealized from the actually measured initial deflection. The maximum initial deflection influences the ultimate strength fully for thick plates and less than a half for thin plates.
(3) The ultimate strength is evaluated from the ultimate strength formulae proposed in the previous report, taking into account of the effective coefficient of initial deflection. The estimated ones are very accurate in the comparison with those obtained by direct FEM calculation to the actual panel.

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The jack-up rig is composed by the platform for drilling operation and legs supporting it. About 400 of approximately total 700 mobile offshore drilling units (MODU) under operation in the world in 1984 are the jack-up rigs, namely the majority of MODU is the jack-up rigs because they have high maneuverbility for movement and operating performance under harsh environment. Since the structural strength is the main subject for the safety of operation, the various kinds of methods for structural analysis have been presented until now. But the development of methods for simplified practical structural analysis has been delayed due to less experiences in comparison with ships because it has been studied in only about thirty years after the first jack-up rig has been built. The author has developed and presented the simplified practical methods 1), 2), 3), 4) for strength and vibration analysis with high accuracy that is assured by the precise calculations using detail models and experiments for full scaled or 1/45 scaled, models.
In this paper, the effects of water depth, jack spring, sea bed spring, wind incident angle, wave height and period to the structural characteristics of jack-up rig are studied by the results of parametric calculations with methods mentioned above for strength and vibration analysis and some design points are discussed.

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Recently there is a trend to install engines with a small number of cylinders on ships in order to save energy and space and to gain simpler maintenance. But the engines with a small number of cylinders which have long piston stroke and run slowly have a tendency to cause serious vibration problems. Particulary some observations of fore-and-aft vibration of an engine frame, which are not found in the engines with a large number of cylinders, have been reported.
The fore-and-aft engine vibration is excited by the longitudinal vibration of a shaft system and the fluctuation of propeller thrust. In this report, dynamic response of shaft systems with 4-, 5- and 6-cylinder engines is studied in order to see it's effect on the fore-and-aft engine vibration. Main conclusions obtained are as follows :
1) A significant longitudinal displacement of the shaft arises due to coupling between torsional and longitudinal vibrations when the shaft diameter is increased to make the natural frequency of the torsional 1-node vibration higher than the exciting frequency.
2) The shaft of decreased diameter with the 5-or 6-cylinder engine induces little longitudinal displacement at the thrust bearing due to torsional vibration.
3) When the diameter of shaft is increased to avoid resonance of the torsional 1-node vibration, more significant exciting force of the for-and-aft engine vibration is induced in the 5- cylinder engine than in the 4-cylinder engine. The following two reasons may be considered : a) The crank shaft of the 5-cylinder engine induces larger longitudinal displacement associated with torsion. b) The shaft system with the 5-cylinder engine has usually closer natural frequency of the torsional 1-node vibration to the exciting frequency.

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In stiffened plate structures, cracks are often formed at the intersections of the stiffeners, where severe local stress concentrations and welding residual stresses exist. Since the local stress distribution is rather complicated along the crack trajectory, crack curving is one of the essential features of this type of problems. Cracks initiated and growing in the stiffened plate structures are difficult being detected by small leakage of fluid, and the crack arrest design concept which is different from the leak before break (LBB) concept could be introduced in preventing the catastrophic failure of such structures.
A computational scheme has been developed for the crack path prediction, which is performed by the step-by-step stress analysis ahead of the crack tip and the prediction of a curved increment of the crack growth by the use of analytically expressed asymptotic crack path in the neighbourhood of the crack tip. As a fracture criterion we use the locally symmetric condition which requires the Mode II stress intensity factor vanishing along the crack path.
In this paper, holes are considered as crack arresters and their capability is examined by computational crack path prediction and experiments. We consider the case where a crack is approaching a circular hole. When the crack tip approaches in the neighbourhood of the hole, where the shortest distance between the crack tip and edge of the hole is within the radius of the hole, they attract with each other and the crack penetrates into the circular hole resulting arrest at the hole.

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The brittle fracture initiation from the surface crack in the large diameter pipe subjected to inner pressure is treated from the practical point of view. The crack opening stretch model is applied to the surface crack and the ligament of the crack is subjected for the crack closure force.
The hydrostatic tests are carried out for two kinds of pipes. One is a heavy wall and large diameter pipe, API 5 L X 70 grade, 940 mm in outer diameter and 39. 2 mm in wall thickness. Another is a relatively thin wall and small diameter pipe, API 5 L X 65 grade, 508 mm in outer diameter and 12. 7 mm in wall thickness. The test pipes have various notches, which are ma. chined by electrical discharge. And the crack closure force is experimentally determined from the notch tip COD, which is directly measured by the clip gage installed on the center of the notch tip, by use of the Dugdale Model with regard to the bulging factor for the pipes.
Consequently crack tip COD of the surface crack center is calculated by the proposed crack opening stretch model. And corresponding to the defect size, the required fracture toughness to prevent the brittle fracture initiation from the surface crack of the pipes subjected to inner pressure is estimated.

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Side notch type CTOD tests with various specimen thicknesses including full thickness were carried out by using a narrow gap welded joint with plate thickness of 200 mm to ensure the effect of specimen thickness on critical CTOD for as-weld joint. All the specimens were intended to have a fatigue pre-cracked notch at HAZ. After completion of CTOD tests, notch location was checked for each specimen. At the same time, the peak temperature of welding thermal cycle at each point was analyzed from the macro structure of the welded joint and the part in the vicinity of the weld metal was classified approximately according to metallography due to estimated peak temperature, such as simple coarse grain region, coarse grain region with island martensite (C+M^*), simple island martensite region, simple fine grain region etc., It was investigated what kinds of region were cut across by the front line of the fatigue pre-crack and their crossing length for each specimen.
As a result, it becomes clear that brittle fracture initiated from the most locally embrittle zone which was suggested by thermal cycle calculation. Moreover critical CTOD's were converted to those for full thickness CTOD specimens by using equations which represents the mathematical effect of specimen thickness on critical CTOD and was confirmed by experiments using base metals with various strength levels. From the result of the relation between a maximum crossing length of a fatigue pre-crack front for the most local brittel zone and the converted critical CTOD, it becomes clear that the critical CTOD for full thickness CTOD specimen can be estimated by using small size CTOD specimen sampled adequately from the joint.

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Fracture toughness values obtained are considerably affected by specimen thickness. Two plausible explanations for such thickness effect are given as follows : (1) Plastic constraint increases as plate thickness increases. And (2) Possibility that the embrittled structure zone exists along crack front increases with increase in plate thickness.
In the present paper, probabilistic considerations have been carried out by using various kinds of data obtained in order to clarify the applicability of the weakest link model for evaluating fracture toughness with respect to thickness effect. Moreover, to obtain the data for the above probabilistic analysis, a new statistical method has been studied for determining population of fracture toughness distribution with taking the temperature dependency of fracture toughness into account. Statistical method proposed newly in the present study is sufficiently applicable.
In both steel plate and its welds with heterogeneity in fracture toughness, thickness effect in fracture toughness results from a statistical effect and the weakest link model can be adopted to evaluate the thickness effect.

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Investigations have been conducted on crack growth and crack-tip strain characteristic of stable fibrous crack. Double edge-cracked tension specimens of mild steel have been prepared for both monotonic loading and constant loading tests. After unloading test, the measurements of crack-tip profile, COD at moving crack tip (CTOD) and crack-tip strain distribution of mid-cross section of specimens have been carried out.
When COD at initial crack tip (δ) is determined, fibrous crack length, crack-tip profiles, CTOD, and crack-tip strain distribution are uniquely evaluated regardless of loading history. A. critical COD δ_iis a required displacement for initiation of slow crack growth regardless of loading history. CTOD abruptly decreases as fibrous crack length increases. Moreover, crack-tip strain increases as COD at initial crack tip or fibrous crack length increases. Crack-tip strain fields under both loadings have HRR-singularities.

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To supply data needed for a rational fatigue design of structures subject to random load there must be some appropriate testing methods which are able to reproduce a specified time history of the random variable such as load, stress, strain and stress intensity factor and also must be inexpensive to be popular ones.
With a small micro computer system alone, it is very difficult to perform exact experiments considering the dynamic characters of the test system varying as the fatigue damage accumulates in the specimen. In this report, two Micro Processing Units are used to perform experiments with or without response compensation by FFT. Stationary Gaussian random processes are generated with a large computer and data are packed into special forms to be sent through TSS within a reasonable time.
The developed soft and hardware are satisfactory and fatige crack growth tests under a stationary random stress intensity factor showed the effect of the compensation and indicated the possibility of a simplified and less time consuming test method without response compensation.

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From a microscopic point of view, composite materials generally contain innumerable defects in itself, but even if they have some defects, many of them are sometimes almost harmless depending upon types, locations and applied conditions. On the other hand, in a stress concentrated region, even a very minute defect often causes a crack growth and then arrives at a fatal size. So it is impossible to estimate the strength reliability of composite materials until the extent that every type of defect takes part in a catastrophic fracture is predicted and examined.
For this purpose, the present paper aims at estimating the strength reliability of composite materials containing defects in itself on the basis of a stochastic tensile failure process simulation of unidirectional fiber reinforced composites which was described in the previous report. Each type of defect modes of composite materials has been classified and modelized systematically, and the damage tolerance has been examined as follows : a goodness of fit has been investigated for statistical distributions on each type of defect mode, which gives the difference in goodness of fit due to the number of included defects or the sample size. As for a decrease in the strength reliability due to defects, the effect of fiber and matrix defects has been examined in detail. And finally, a comparison has been tried among each type of defect modes by means of the PDF curve, which has been shown to be useful to a certain extent in discriminating a defect mode.

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Rigid PUF (polyurethane foam) is one of materials for in-ground LNG storage tanks which have been successfully constructed since 1970. For LNG carriers, however, it is necessary to use a material having sufficient strength to withstand cyclic load and impact load caused by hull motion in waves and hull deformation etc., and having excellent resistance to crack propagation as well. To meet this requirement, reinforced PUF consisting of continuous glassfiber uniformly dispersed in rigid PUF has been developed especially for TGZ Mark III cargo containment system.
The present paper aims at making a quantitative evaluation of the reinforcing effect of glassfiber in reinforced PUF from a viewpoint of increased crack resistance performance. In this report, crack extension behavior and fracture toughness of reinforced PUF have been examined in detail in comparison with those of rigid PUF under a three-point bending test on notched beam specimens at room temperature. Acoustic emission analyses and finite element simulations have been shown to be successful in comparing the fracture behavior of reinforced PUF with that of rigid PUF.

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A rare kind of structural vibration induced by flow was experienced on sea chests of high speed ships. Model experiments in cavitation tunnel revealed the cause of vibration and the mechanism of excitation. The results showed that the free shear layers flowed into the cavity of sea chest were rolled up periodically into vortices and the vortex excitation resonated with the natural frequency of the vibration system composed of the sea chest structure and the water involved in it. Countermeasures reducing the excitation were also obtained by the model test.
Energy method was applied for the estimation of the natural frequency of sea chest vibration system. The calculated results by this method were verified to correlate well with the results of vibration test on sea chest model, together with the measured results on actual ship.

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In this paper, the statical holding power and forms of the tandem type anchors on dry sand are investigated theoretically and experimentally.
Tandem type anchor consist of a considerable number of small unit anchors, these small unit anchor has some flukes around shank and be connected tandem.
The results of experiment on dry sand are compared with those of calculation.

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