A numerical technique to simulate breaking waves in front of an advancing floating body is developed. It is based on the TUMMAC-V method of the first report and the computational procedure for the wave motion near the free surface is remarkably modified. The method simulates the time-evolutional process of nonlinear bow waves from the steepening to the generation of necklace and horseshoe vortices. The simulated results of spilling breakers are in very good qualitative agreement with the experiment in terms of the dynamic motion of free surface flow, the steep velocity slope, the intense vortical motion and the high pressure due to breaking. The complicated evolution of ship waves with both dispersion and dissipation is also discussed.

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This paper describes a numerical method to solve nonlinear free surface wave problem for two-dimensional submerged bodies. The velocity potential is expressed as a sum of the basic velocity potential of double model flow and the perturbed wavy potential. The author previously showed the practical method to solve the wavy potential by using Rankine sources under the linearized free surface condition based on the double model flow.
In this paper, he presents a iterative method for solving the wavy potential under the nonlinear free surface condition using the linear solution as the first approximation. The method of numerical solution is examined on the steady waves around a two-dimensional submerged elliptic cylinder and the stability of numerical solution is discussed.
Further, the measurements of wave profiles and flow field beneath the free surface are carried out using the elliptic cylinder and nonlinearity of wave form are experimentally investigated. The calculations of the steady waves and velocity distribution around the elliptic cylinder are performed and good agreement with the experimental results is obtained. Finally, the simplified method for solving Rankine source distribution is proposed. It has been found from the view point of practical use that the numerical results of the simplified method agree well with that of the original method.

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An attempt was made to obtain a surface-piercing vertical strut with minimum total resistance by means of nonlinear programming under the constraints that the beam and water plane area of the strut were kept constant. The objective function in the nonlinear programming is the sum of wave-making resistance calculated by Michell's integral and viscous resistance calculated by a higher order boundary layer theory taking the longitudinal curvature effect into consideration.
In the minimization process, the strut form with minimum wave-making resistance was used as an initial form. It is a characteristic that the strut form of minimum total resistance has a fine shape near the trailing edge and the fore body has a similar shape as that of the body of minimum wave-making resistance. In the minimization process, it is shown that the viscous pressure resistance is reduced largely whereas the wave-making resistance is increased a little and frictional resistance is kept almost unchanged.

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This paper deals with the experimental analyses on the relationship between viscous pressure resistance due to flow separation and turbulent boundary layer development over a two-dimensional elliptic cylinder from the viewpoint of the scale effect. The experiments were carried out i) by attaching a roughness on the hull surface to control the boundary layer development and ii) by installing a pair of rotating cylinders inside the hull surface to control the separation point.
It was clarified through the experiments using a surface roughness that the contribution of the location of separation point and the displacement thickness near it to the scale effect of the viscous pressure resistance due to flow separation is significant. Of those parameters, the effect of the former is predominant for ship-like form with blunt stern.
The increase of the rotational speed of a pair of rotating cylinders made the separation point move downstream and the shape factor of the boundary layer be constant near the stern.

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Assuming Navier-Stokes equation of motion of viscous fluid as non-homogeneous one of Oseen's linear equation, the author derives reciprocal theorems, representations of flow field by following Oseen's scheme.
Then he introduces a variational principle of the boundary value problem, establishes approximate Rayleigh-Ritz or Galerkin method and tries to formulate minimum condition of the viscous resistance.
Numerical results show this theory to be a powerful tool to analyse viscous flow.
For example, he obtains frictional resistance of a flat plate of about 95% accuracy compared to Blasius one's by the second approximation.

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The pressure distribution on the propeller blade is usually predicted in Japan by using the lifting surface theory and Sugai's concept of the equivalent two-dimensional wing. Though the method is admitted to be useful through comparison between experiment and calculation, the effectiveness of the concept is not seemed to be garanteed by the theoretical calculations. Then we, as the first step, show that the concept is accurate enough for practical usage by comparing the pressure distributions which are obtained by the thick wing theory and the above-described method applied for the three-dimensional wings with several plan forms and wing sections. Conclusions are as follows. 1) The concept of equivalent 2-D wing predicts fairly well the pressure distribution on the 3-D wing, which is obtained by the thick wing theory. 2) The pressure distribution on the equivalent 2-D wing has a tendency to deviate from the one on the 3-D wing in case of thick wing or small aspect ratio wing or the swept wing and in case the section approaches the wing tip. 3) The shape of wing section does not affect the agreement of pressure distributions obtained by two methods. 4) The equivalent camber and angle of attack change considerably along the span and are different from those of the actual 3-D wing.

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The highly loaded marine propeller is affected seriously by non-linear effects of propeller race and hydrodynamic lift. The vortex lattice lifting surface model proposed by Kerwin seems to be the most suitable to deal with such non-linear effects. This Kerwin's model has been applied to develop the theoretical method for calcu lating the unsteady characteristics of a propeller in the harmonic wake in the previous paper by a part of the authors and another researcher. In the present paper the same methodology is employed and extended to a more general form for theoretical analysis of unsteady propeller characteristics in ship's wake, and some numerical results by this method are compared with those of other linearized theory and with experiments.

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A new theory on a cavitating propeller is proposed, treating the cavitation threedimensionally, and using a lifting surface theory. A numerical method has also been developed based on this theory, appying the vortex lattice method and replacing the cavitation and the blade thickness by source elements, for a cavitating propeller operating in a uniform flow.
To evaluate the present method, the calculations are carried out for a model propeller and compared with other prediction methods and the model test results.
It is confirmed that the present method gives considerable improvements, in comparison with the conventional methods, on the evaluation of the cavity thickness due to the three-dimensional flow, and on the elimination of the instability of the solution caused by the two-dimensional theory.

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Existing theoretical investigations on oscillating foil propulsion have rarely treated a foil which has chordwise flexibility. However, an experimental investigation showed that propulsion performance of a partially elastic oscillating foil Is better than that of a rigid one.
In this paper, the authors propose a theory for partially elastic oscillating foils, where the deformation of the elastic part is treated by incorporating the equation of elastic curve in the small amplitude linearized oscillating foil theory. Using this theory, theoretical analysis of propulsion performance were made in detail for both elastic and rigid foils.
The following results were obtained.
(1) It was shown that propulsion performance of an oscillating foil is decided by three parameters of foil motion, namely, reduced frequency, phase difference between heaving and pitching motion and modified heaving to pitching amplitude ratio.
(2) Under the same conditions of motion, compared to a rigid foil, an elastic foil produces less thrust but at a higher efficiency.
(3) To obtain the same thrust, an elastic foil is more efficient compared to a rigid one.
(4) To produce a given thrust at the highest efficiency, the conditions of motion, namely, heaving and pitching, is not so much affected by the variation in reduced frequency in case of an elastic foil compared to that of a rigid one. This fact is desirable from practical operating conditions.

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In a previous paper, the authors analyzed partially elastic oscillating foils by a linearized theory and idenfied its various characteristics.
In this paper, the authors propose here a nonlinear theory using singularity distribution method. In this theory, Hess & Smith's method is extended in order to treat unsteady foil motion and wake distortion is taken into account by discrete vortices. In the case of partially elastic oscillating foil, the solution is obtained by satisfying also the equation of motion which can be derived from the equation of elastic curve.
The results obtained by the present theory was found to be in good agreement with experimental ones using a large amplitude rigid oscillating foil. From this fact, it can be said that this calculation method is effective for quantitative analyses of oscillating foil propulsors.
Some simple oscillating foil propulsors were designed for practical application to ships. The results showed that adequate thrust force can be achieved and efficiencies as high as 65% can be envisaged in case of elastic foils.

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In the previous report, thrust generation through absorption of wave energy by a passive-type hydrofoil propulsor was verified experimentally. Some theoretical studies are also conducted on the basis of Wu's theory for an unsteady hydrofoil in a wave
. In the previous report, the experiments were conducted in a rather short wave range. So, the experimental apparatus and model have been improved, and the experiments in a long wave range are conducted in the present report. The experimental results are compared, more widely than in the previous report, with the theoretical ones obtained by the above mentioned theory.
An application of the theory to cases where the foil draft is very small as in the present study may be doubtful, since the theory neglect the free surface effect completely. The theory, nevertheless, gives a correlation with the experiment better than expected, when the advance speed is not small.
Effects of foil draft, heave and pitch springs and an auxiliary float are also investigated theoretically by applying the theory.
Effects of wave making damping on thrust and motion of a foil are also studied. by introducing wave making damping terms into equations of foil motion approximately.

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Experimental results of nonlinear wave loads acting on submerged cylinders by using fairly large models are presented. Nonlinear effects of the incident wave amplitude, the cylinder submergence and the cross-sectional geometries are studied. Those results are compared with the numerical calculations to the second-order. The calculation method is based on the regular perturbation theory and the wave loads are obtained by the integration of hydrodynamic pressure over the body surface. The fluid is assumed inviscid, incompressible, homogeneous and infinitely deep.
Consequently, when the cylinder is placed appropriately deep, the second-order theory agrees well with the experiments. However, when the cylinder is close to the free surface, the theory would overestimate the wave loads obtained by the experiments. In this case, the nonlinear such as wave breaking would be significant.

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A calculation method for predicting the interference effect between two circular cylinders in tandem arrangement in harmonically oscillating flow is developed using a discrete vortex method. The flow is assumed to be symmetrical in order to reduce the computer time. Since the zero-shear point and the strength of the shedding-vortex are determined by an unsteady boundary layer theory, no experimental information is required to carry out the simulation.
The simulation results reveal some different kinds of viscous interference effects according to different behaviours of shedding-vortex movements. The drag coefficient of a cylinder decreases and the inertia coefficient of it increases with decreasing the distance between the cylinders.

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An experiment has been conducted to clarify the nature of ship motions and wave impact phenomena in bi-directional wave conditions. Irregular and regular waves traveling at a sharp angle have been generated simultaneously using two kinds of wave maker, one of which is capable of making snake motion to generate arbitrary waves in oblique direction. Discussions are made on the relationship between wave formations and the ship motions and the occurrence of slamming or green sea impact. It is concluded that bi-directional waves at a sharp angle could be dangerous if it encounters the ship in bow wave condition and that wave height distributions and motion amplitude distributions can be approximated by Quasi-Rayleigh distribution more appropriately than Rayleigh distribution in the bi-directional waves stated here.

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It is supposed that wave loads exerted on a ship advancing in large amplitude waves show quite different from those in small amplitude waves due to the fact that the submerged portion of ships hull varies remarkably with time, and coupling phenomena between longitudinal and horizontal hydrodynamic forces may occur, and etc.
To develop a theoretical, but practical, method of predicting wave loads caused by large amplitude waves, and of clarifying the nonlinear characteristics is the most important goal of the present study. In this paper, 1st report, wave loads acting on a ship fixed in large amplitude waves is treated. All the results of the wave loads computed by the present method show good agreement with experimental ones in predicting the peak values of wave loads as well as their time dependent nonlinear behaviour.
The main advantage of present method based on the conventional Ordinary Strip Method is that estimation of nonlinear wave loads in large amplitude waves can be easily performed with sufficient accuracy without solving three-dimensional and/or higher order potential problem.

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In the previous papers, the authors presented a method for evaluating the seakeeping performance of ships at sea in the initial ship design stage.
They introduced 'mission effectiveness' concept as a measure which gave the effect of seakeeping performance on ship system and her missions, and showed it was effective for evaluating the seakeeping performance of ships. They showed too that the short-term mission effectiveness gave the ship's inherent seakeeping performance, and that the long-term mission effectiveness was important to obtain informations for cost/performance trade-off which ship designers as well as ship owners must evaluate in the initial ship planning and design.
In the present paper, the authors present a method for estimating the long-term mission effectiveness of ship system, which is to be operated under a mission composed of several different duties, as a function of long-term conditional probability. The long-term mission effectiveness obtained by the present method is compared with that estimated by the simulation method previously. A method for cost/performance evaluation is presented, which gives the mission effectiveness in a broad sense. The present method is applied for the same patrol boats which were used for the numerical examples in the previous papers.

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The previous paper, the first report, described a new method to calculate the hydrodynamic lateral forces acting on a ship during manoeuvring motions on the free surface. As an application of this method, the hydrodynamic lateral forces on a flat plate piercing the free surface were calculated, and it was found that the predicted values of linear stability derivatives were in good agreement with the experimental results.
In this paper, the hydrodynamic lateral forces on a Wigley model, which is a substitute for a ship model with realistic hull form, are calculated and compared with experimental results obtained by the authors and Kashiwagi, independently. Although the present method is not completely satisfactory, it can predict well the effects of hull form, ship's foward speed and the frequency of manoeuvring motions on the linear stability derivatives.
Hence, it is supposed that the present method may be valid for estimating the linear stability derivatives of a ship with more general hull form.

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In restricted waters such as harbour, bay or cannal, it is necessary to know the precise manoeuvring characteristics of ship including the effects of water depth, channel bank or the another ships from viewpoint of safety of navigation. In narrow waterways, specially, the effects of channel bank and hydrodynamic interactions between ships are fairly significant.
This paper examines hydrodynamic behavior of ships during meeting and passing in narrow water channel, by using slender body theory. Furthermore, ship motions with rudder control during passing in channel by using these hydrodynamic forces are discussed. This paper concludes as follows.
(1) During passing, the interaction forces, such as lateral force and yaw moment, between two ships are affected by the differences of ship speed and ship length, and by lateral distance between ships.
(2) Lateral force and yaw moment acting on the ship are significant when the another larger ship passes nearby this ship.
(3) By simulation study of ship motions, some problems on two way traffic in channel are noted.

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In order to clarify shallow water effects on the various parameters necessary to predict the rudder normal force during manoeuvring motions, which are called rudder-effectiveness parameters in this paper, different kinds of captive model tests were extensively carried out for a particular ship. As a result, it is found that the rudder-effectiveness parameters are remarkably dependent on the water depth, and that intimate knowledge of those parameters at a certain water depth is essential for predicting manoeuvring motions at that depth with accuracy. In particular, both κ value and δ_R versus β relationship, which denote the increase of rudder inflow velocity and effective rudder inflow angle respectively, are most important.
Prediction of rudder normal force in transient state during manoeuvring motions is not satisfactorily accurate especially in shallow water, although the steady turning characteristics may be predicted well by means of the mathematical model used in this paper.
Lastly, it is shown that the full-scale manoeuvring motion can be successfully estimated from the results of model tests by taking account of the scale effects on the total resistance and the effective wake fraction.

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The authors have already proposed the new mathematical model of ships' maneuvering motions at low speeds. Combining the mathematical model with results of captive model tests in shallow-water conditions, ships' maneuvering motions in harbours are simulated at ease. In the present paper, an attempt is done to make a safety assessment of harbour maneuvers of some VLCC, utilizing the above simulation technique.
To assess the safety in the harbour maneuvers, it is necessary to make plans of approaching to the berth and departing from it by skillful pilots, being based on the informations on the harbour, traffic rules, environmental conditions, ship's specifications and so on. Next, to verify the plans, basic maneuvering abilities in course keeping, course changing, decelerating, turning and so on are checked by the numerical simulations. These results are very useful for the improvement of the maneuvering plans. Real-time simulations of approaching and departing maneuvers conducted by skillful pilots are also beneficial for the total judgement of the safety. After investigating systematically on the above three steps, the final conclusions are achieved, taking the experts' opinions into consideration.
It is concluded that the above procedure is very useful for designing ships and harbours and for improving the methods to handle ships in harbours as well as for making safety assessments.

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In congested waters, traffic control will be necessary to avoid collisions. The time and speed of each ship at waterway intersections should be specified by the traffic control center.
The acceleration and deceleration characteristics of ships are non-linear, and ship's speed slows down when turning. These factors make it difficult to control the propeller speed to meet both the specified time and ship velocity at waterway intersections.
Fuzzy control theory is very useful to control a system with multiple objectives like this. No mathematical model of the system is necessary in fuzzy control. The knowledge of experienced human operators expressed like “If the ship velocity is high, then the propeller speed should be reduced.” are translated directly into fuzzy control laws.
In this paper, the fuzzy control laws of propeller speed to adjust the ship time and velocity at waterway intersections are developed. The control laws are composed of 3 categories which are the time adjusting mode, the speed adjusting mode and the mode transfer. Each control law was built up rather intuitionally.
Computer simulations were carried out to show that both ship time and speed were adjusted with good accuracy by these controls. It was also shown that fuzzy control was helpful to increase the smoothness of changes in propeller speed.

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In order to design cable-body towed system, dynamic analysis of the system, especially body dynamics, is indispensable. For the purpose of the analysis, hydrodynamic characteristics of a cable and a body must be made clear first of all, then steady state theory and dynamic theory of cable-body system must be developed.
In this report, firstly, resistance and vibrational characteristics of typical cables and hydrodynamic characteristics of a hypothetical body, each of which were obtained experimentally, were shown. Secondary, utilizing above experimental results and steady state cable-body equations which were derived by deviding a cable into inextensible finite elements, steady state configulations of the cable and the hypothetical body trim towed at constant speed were calculated. As the result, the effect of parameter values in the equations on the cable configurations were made clear.

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According to a linear theory, the probability density function of the maxima of response whose spectrum is narrow banded can be expressed by the Rayleigh probability density function. However, this function does not reflect the asymmetrical characteristics with regard to maxima (positive amplitudes) and minima (negative amplitudes) which are seen in the experimental results. Especially in the case of relative motion (one of the most important factors in the safety operations of semi-submersibles), the linear theory tends to underestimate results relative to the experimental data. In order to obtain better results, the second order theory must be considered.
Starting from the functional polynomial method, Vinje derived a method to calculate the nonlinear distribution using both time domain and frequency domain representations of the system. However, he did not show the calculated results of the density or distribution.
In the present work, the frequency domain method proposed by Vinje is applied to calculate the probability distribution and density of the relative motion of a semi-submersible.
At first, the distribution of irregular wave elevation was calculated and compared with experimental data.
After ascertaining the effectiveness of the present method, a calculation of the relative motion was carried out as the second step. The calculated results agree fairly well with the experimental results.

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For analysis of intact and damage stability of semisubmersible type rig, it is important to estimate the magnitude of steady environmental forces such as wind and current forces and moments. Since it is difficult to get the theoretical calculations of these forces and the test techniques need special apparatus, only few researches have been done in these fields.
In this paper an attempt to clarify the contribution of various elements of semisubmersible to total force and moment using 1/100 and 1/150 scale test models is made, and the validity of wind tunnel tests in a water channel with wind tunnel facility is discussed.
Although the difficulty to simulate the boundary layer on water surface exists, the wind velocity profile required by rules of classification societies was done with success and 6 component forces and moments were measured in this environmental condition.
In order to obtain the total force and overturning moment the towing tank test of under water part was carried out, and lift effect on lower hull was observed.
Finally the comparison of experimental results and the corresponding calculations obtained from ABS and DnV rules was done and the accuracy of these calculation methods is discussed.

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In the previous paper, the authors discussed the larger angle of steady tilt can be induced by the wave-induced vertical steady forces on the lower hulls when the semi-submersible platform is moored in regular waves having short period. This curious phenomenon is considered to be dangerous to introduce the capsizing of the platform in violent seaway. However, as many existing rules concerning the platform stability requires the consideration of wind heeling moment for the design of the platform, this wind effects on the steady tilt must be taken into consideration as the another possibility of capsizing phenomenon of the semi-sub-mersible platform.
This second report deals with an investigation of the magnitude of some environmental loadings on a eight-column twin hull semi-submersible platform for finding the possibility of larger steady tilt as well as the platform behaviors in such loading conditions. The timedomain simulation which was introduced in the previous report is used and some of the results are compared with experimental records for the purpose of their validity. Furthermore, the behavior of the semi-submersible platform in the combined environmental factors were studied by the simulation. As a result of study, the following conclusions are made.
1. The magnitude of current and wind induced loadings are comparable as well as that of the resultant steady tilt.
2. The wave-induced drift force and moment can be the same magnitude as other environmental steady forces and moments.
3. The magnitude of the moment due to the wave-induced vertical steady force may be the same order or more comparing with others depending on the submergence of lower hulls.
4. The results obtained by the computer simulation are agreeable with the experimental ones.
5. Concerning with the steady tilt in the combined loading condition, the effects of the wave-induced vertical steady forces on the lower hulls cannot be disregarded in the region where the larger wave-induced drift force arises.

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Japan Marine Sience and Technology Center is putting into practice th e Kaimei project Phase II. The targets of this plan mainly include the field test of the turbine and generator, and the establishment of the phase control technique. The wave power device Kaimei is classified as the floating attenuator type using the air turbine and the generator. The performance of this device seems to depend on the arrangement of the air chambers and the buoyancy rooms, and also on the external loads. This study as a part of the project aims to extablish the design procedure of the optimal device form by predicting the power output and estimating the feasibility at the identified site and sea condition.
In this paper the hydrodynamic forces are calculated by the singular distribution method and the performance is estimated by changing the fundamental form parameters. The results are following.
(1) The wave power absorbing performance of the Kaimei type device is almost proportional to the areal ratio of the air chambers in an optimal external load condition.
(2) By making the breadth of the device wide, we can expect the increasing performance.
Further in order to assure the design procedure, the model experiment was made and compared with the analysis. Both agree well as a whole. However, the heaving and pitching motions of the floating device are made clear to badly affect on the performance. The author recommends the device form hard to move, or with the performance not susceptible of the motion of the floating device.

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In this paper, the system simulation of a fixed O. W. C. type wave energy absorber is proposed, which takes into consideration the interaction between the O. W. C. and the turbine.
In the present simulation, the coefficients of turbine system show a nonlinear characteristic against the flow velocity and the revolutions per minute of turbine, so that a time stepping procedure is applied to the analysis. Both equations of motion of O. W. C. and the turbine are solved simultaneously. The turbine reaction and the generated powe are obtained.

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In the previous report, failures of hull structures in ships registered with Nippon Kaiji Kyokai, such as cracks in ship bottom transverses due to ship vibration, cracks due to improper local design and excessive corrosions etc. in hull structure, found by ship surveyors on occasion of annual surveys are analysed statistically and their occurrences are approximated by series of Weibull's distribution functions.
This report presents a statistical theory of predicting the occurrences of failures in ships of several types and ages under an assumption of two probability density functions which have been obtained from the failure databank, i. e., an exponential distribution indicating the number of failed structural components in individual ship and a function indicating distribution of failures in the fleet.
The predicted number of failures to be found by annual surveys are compared with observation in actual ships in cases of failures caused by vibration, improper local design, mishandling of cargo gear and heavy corrosions, respectively.
Furthermore, a method of prediction of the rate of scrapped ships due to excessive corrosion in a fleet is proposed in this paper.

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Dynamic stress response of the double bottom structure of a bulk carrier to wave loadings was investigated by the stochastic method. Wave-induced loads on the double bottom, as well as the hull girder vertical wave bending moment, were calculated by the new strip method for the ship motion analysis. The phase differences and the correlation coefficients between the dynamic sea pressure and the cargo inertia force were evaluated and it was found that these two loads act generally in the opposite direction. Stress response functions of the double bottom structure were obtained by the quasi-static structural analysis of a 3-dimensional model for the entire hold part. The short-term and the long-term predictions of stresses in irregular seaways were made based on the random response theory for linear systems.
Special attention is given to the longitudinal stresses in the bottom shell platings for which the superposition of stresses of longitudinal and transverse strength is necessary. Correlation coefficients between the hull girder vertical wave bending stresses and the alternating double bottom bending stresses were investigated in the short-term long crested irregular seas. An approximate formula is presented for the superposition of these two kinds of stresses in terms of long-term predicted values. Based on the above results, considerations were made on the selection of the design criteria for the double bottom strength in waves.

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The strength of ship structures in collision is an important matter in terms of saving life, preventing pollution and from an economic point of view, especially in the case of hazardous cargo carriers, oil tankers and so on. So far, several analysis methods or formulae have been presented to estimate the collision strength of such ships. However, there are few papers in which the accuracy of the methods have been verified.
In this paper, the collision strength of a typical double hulled structure was examined. The types of collisions were classified into five groups from a geometric view point between a colliding bow and a hull. Two kinds of experiment (which were considered to be more critical than others among those five groups), were carried out using large scale models. The first was an experiment in which a stem collided against the ship's side and in the other a bulbous bow collided against it. In both cases, the bow models were assumed to be rigid.
A simplified method to analyse the damage of double hulled structures in collision was developed on the basis of the results from the experiments. As far as this method, is concerned, a double hulled structure is considered to consist of three main structural members, the side shell, trans web frames and side stringers. The side shell is modelled into plastic membrane plates, and trans webs and side stringers are assumed to support the side shell rigidly and buckle when critical load is imposed.
The method was formulated in matrix form, where triangular membrane elements and buckling elements are used to model a double hulled structure.
The accuracy of the analysis method was then examined by comparing the calculated values with the experimental ones. From these, a strong correlation emerged.

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In this paper, two types of slamming impact load are investigated both theoretically and experimentally, assuming that the water entry speed is constant and gravitational effects are negligible. One is of the water impact of a wedge and the other is of the impact caused by trapped air layer between a flat bottom and a water surface.
For the impact of a wedge, numerical calculation is conducted by means of the Boundary Element Method taking the splash into consideration. The results are in good agreement with Wagner's theoretical ones.
In case of the impact of a flat bottom, it is clarified from the experimental results that the impulsive phenomenon is composed of two stages. The phenomenon of the first stage is one of before contact of the bottom with a water surface and the second stage is one of after the contact. For the impact during the fist stage, numerical calculation is conducted by means of the characteristic curve method assuming that the flow of the air layer is onedimensional compressible one. For the second stage, the impact pressure is obtained by solving a system that is composed of the bottom, the a!r spring and the added mass. The numerical results and experimental ones agree precisely in the first stage, but in the second stage the calculated values are higher than the experimental ones.

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Water impact of a wedge is a very primitive but an essential phenomenon to wave impact loads on ships in waves.
Investigations have been carried out extensively on water impact loads on ships and so many features are known today on water impact on wedges and ships.
But, a few aspect is lack in them. It is a scaling law of water impact pressure. In reality, Froude scaling law is applied to utilize the model test results for full scale ships, implicitly or explicitly.
On the other hand, many test results put a question to the appropriateness of Froude scaling law for the water impact pressure.
Response of a panel to the water impact pressure is another problem. Some papers and reports proposed methods to estimate the impact pressure on full-scale ships and to calculate the response of structures to the impact pressure, in which impact pressure is applied to the structure as a stationary uniform impact load.
But, actual impact pressure on a wedge moves on the surface of the wedge at very high velocity.
The response of the structure to the different two types of loads must be different.
In this context, Water impact test of a wedge was carried out to study the scaling law of water impact pressure and to study the response of a panel to the water impact pressure.
The test result showed that non-dimensional peak pressure is affected by the distance between the pressure gage and the keel of the wedge. The farther and farther the distance is, the larger and larger the peak value is. But, there seems to be an upper bound to them, which is almost equal to Wagner's theoretical impact pressure for the wedge.
This implies that the water impact pressure for a wedge might obey Wagner's theory, but a pressure gage might modify it. A simulation of a pressure gage by finite element analysis with Wagner's theoretical impact pressure indicates that the impact pressure is modified by the pressure gage to be an analogous one to the test results. The result of this analysis explains well the tendency of the test results. The effect of a pressure gage on the peak pressure depends on the ratio of the diameter of the pressure gage to the distance between the pressure gage and the keel of the wedge.
A finite element analysis of the panel with Wagner's theoretical impact pressure as external loads, gave results which showed very good agreements with the test results.
Furthermore, the analysis indicated that the response of the panel to the moving impact pressure, as is the actual one, is about one half or one-third of that to the stationary uniform impact pressure.

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Water impact of wedges and cones is a very essential phenomenon to wave impact loads on ships. For many years, invesigations on water impact pressure on wedges and other models such as ships have been carried out extensively, and today some methods are proposed to predict wave impact loads on ships, whose application might be limited.
But, we still have problems about water impact pressure, one of which is scaling law of water impact pressure. It has been pointed out that there might be discrepancy between test data and the scaling law.
The author carried out water impact test of a wedge to study scaling law of water impact pressure. The test result implies (1) Water impact pressure may obey Wagner's water impact theory of wedges, (2) The test data might be modulated by pressure gages.
Accoding to the assumption that impact pressure obeys Wagner's theory, response of pressure gage was analyzed. The response of pressure gage showed very good agreement with the test data. This means the assumption is true, but to assure it, it must be recognized for, other test data.
The purpose of this paper is to show that the same assumption can be applied successfully to other test results.
S. L. Chuang performed investigations on water impact of wedges and cones. He compared the test data with theories on the basis of the velocity at the moment when the model touched the water surface.
In order to compare the test data with theories rigorously, the velocity at the moment when the pressure gage comes across the water surface must be used.
Therfore, in this paper, equation of motion of falling body must be solved with reaction forces given by the impact theory to get actual impact velocity which is the velocity at the moment when the pressure gage comes across the water surface.
Water impact theories are given by H. Wagner for wedges, and also given by S. L. Chuang for cones.
Characteristics of pressure gages are very simple in this case. The natural frequency is more than 200 kHz, and the diaphragm is thought rigid. The output of the gage can be assumed to be proportional to the forces acting on the diaphragm.
At first, impact peak pressures are given by the theory using actual impact velocity, then they are modified by characteristics of the pressure gage. The results correspond to the measured data in water impact tests.
The comparison between the test data and the calculated data under the assumption showed very good agreement for all impact angles and impact velocities but very small impact angles.
Now, we may be able to conclude that the water impact pressure on wedges and cones obeys the theory by Wagner or Chuang.

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The present paper concerns with the ultimate behavior of the simply-supported rectangular plates loaded biaxially in compression. The plates under consideration are part of columns, pontoons and deck structures of offshore platforms or double bottoms of ships.
Existing simplified biaxial interactions are examined based on the results by the finite element nonlinear analysis. It is clarified that loading conditions employed in the previous researches result in an unsafe biaxial interaction.
Several empirical formulas are newly presented for estimation of ultimate strength of rectangular plates.

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When local buckles or dents occur in a submarine pipeline, these local damages may change into a longitudinal buckle and propagate along the pipeline by the action of external pressure alone.
The lowest pressure required to maintain the propagating buckle is called “propagation pressure” and is a characteristic pressure of the pipe.
In this paper a simple analytical method is proposed for evaluating the propagation pressure based on a rigid-linear strain hardening hinge model considering large deformation.
For greater applicability, parametric analysis is made using the proposed method and an attempt is made to fit a single formula to them, the resulting formula is :
p_p/σ_Y=π (t/D)²(1+1.9E_t/σ_Y
t/D)
The maximum difference between this formula and the actual values from the above mentioned method is less than 0.5%.
The proposed formula is checked with available published test data and other formulae. The following conclusions are obtained.
1) Relatively good agreement are found compared with the experimental data.
2) Considerable increasses may be expected of the propagation pressure for thick pipe by considering material strain hardening.

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In designing offshore structures and ships including LNG carrieres, it is very important to accurately predict the buckling strength and collapse strength of stringer stiffened cylinders under axial compression, expecially with initial imperfections.
Some researches have been reported with respect to the elastic buckling strength of stringer stiffened cylinders with initial imperfections, but there still remain unknowns because the characteristic of buckling strength is much affected by many shape parameters for example Batdorf parameter Z, the size of stiffeners and the eccentricity of applied load.
Moreover, there are few systematical numerical researches in the plastic range.
This paper introduces the resultant force method (FEM), which was developed by authors, to the elasto-plastic analysis of stringer stiffened shells, and moreover investigates effects of the initial imperfections on the collapse strength of stringer stiffened cylinders under axial compression.
Main conclusions obtained from this study are as follows :
(1) The usefulness and accuracy of the resultant force method are confirmed by comparison with the experimental results and other numerical results.
(2) Effects of initial imperfections on the buckling strength of stringer stiffened cylinders, not only in the elastic range but also in the plastic range, have been presented.
(3) In the elastic range, the stiffened cylinders with Z>75 when A_s/d_st=0.1 or with Z>200 when A_s/d_st=0.2 are very sensitive to imperfections and buckle with asymmetric mode.
On the other hand, the heavy stiffened cylinders with short length are not so sensitive to imperfections and buckle with axisymmetric mode.
(4) In the plastic range, the more plastically the stiffened cylinders collapse, the smaller the effects of the imperfections on the collapse load become.

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Offshore structures are always subjected to periodic forces by waves and winds. Therefore, it is essential for the persuit of safety to conduct studies of the behavior of deformation and fatigue strength of structural member under compressive and tensile loads.
Experiments were performed on the behavior of deformation of a column with rectangular cross section, which was the simplest structural member, under compressive and tensile loads, and on the fatigue strength in repeated loading.
Also, a simple combined perfectly elastic analysis and perfectly plastic analysis was made, as well as an elasto-plastic analysis. Good agreements were shown between the results of these analyses and ones of experiments for the relation between loads and deflections of a column. Especially, the latter analysis is able to take the effect of residual stress into consideration, and its effect on the maximum compressive loads was shown.
Furthermore, in fatigue test of a column, it was found the results of this study agreed with the results of standard uniaxial fatigue test.

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The main portion of a ship structure is usually composed of stiffened plates. Between girders and floors, stiffeners are furnished to plates in one direction, usually the longitudinal direction. Under various loads applied to a ship, such as those due to waves, these stiffened plates are subjected to combined in-plane and lateral loads.
In this report, buckling, ultimate and fully plastic strength interaction relations of plates and unidirectional stiffened plates subjected to in-plane biaxial and shearing forces, are derived and expressed in explicit forms based on the result of theoretical investigation of the nonlinear behaviour of plates and stiffened plates.
The accuracy of the interaction relations is confirmed comparing with the result of analysis by other methods.
With the aid of these interaction relations, buckling load and ultimate strength, or fully plastic strength of this type of stiffened plates subjected to in-plane loads may be predicted by hand calculation.

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In order to analyze the nonlinear behaviour of large sized structures such as ships, composed of many stiffened plates, the “rectangular plate unit” and the “stiffened plate unit” are developed in the framework of the Idealized Structural Unit Method which has been developed by the authors. For each unit, the nonlinear behaviour is idealized, failure conditions and stiffness matrices corresponding to the respective failures are formulated.
A computer program has been completed and the accuracy of the new units is confirmed in comparison with the results of analysis by the finite element method. The behaviour until ultimate strength of a large example structure is analyzed using the new units.
The units are found to be very effective since very short computing time is necessary for the analysis.

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The lateral energy absorbing characteristics of axially loaded structural members were investigated from a qualitative point of view based on the energy balance equations of the inelastic column model with single degree of freedom, and its stability and response characteristics were discussed in the general. Furthermore the limitations of the method of rigidplastic analysis for the present problem were studied by the comparison of the rigid-plastic solutions with the elasto-plastic solutions. The obtained results are summarized as follows :
(1) The equations of the elastic critical energy and the stable critical energy were derived and the stability diagrams were presented.
(2) The equations of the elastic maximum displacement and the elasto-plastic maximum displacement were derived and the response diagrams were presented.
(3) It was shown that the accuracy of the rigid-plastic solutions is determined by the ratio of the axial load to the elastic buckling load (p/q) by the comparison of the solutions with respect to the critical energy and the maximum displacement response.

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Despite every means available at the time of construction applied to prevent vibration, violent vibrations were reported on two ocean-going tugboats constructed by IHI, of size that places them among the world's largest. Measurements made of the vibration of aft part including nozzles and analysis of measured data revealed that the vibrations of nozzles : -
-were constant in frequency, irrespective of propeller or engine revolution, and attained values of acceleration reaching 8, 000 Gal;
-were generated only under certain conditions of operation, and diminished to very low levels under all other conditions ;
-corresponded to what is known as flow-induced vibration, and were closely associated with the water flow around the nozzles.
Two possibly ascribable mechanisms were considered as cause of the self-excited vibration.
(1) Locked-in vibration induced by Karman's vortex street ;
(2) Occurrence of negative damping (known as “galloping”).
Neither of these two mechanisms have so far proved conclusively assignable as cause : (1) Karman's vortex streets on account of uncertainty in estimating the exciting force under lock-in condition, and (2) galloping for lack of definite tendency of the negative slope of nozzle lift vs. attack angle curve.
The vibrations observed being of such amplitude as to permit no delay in remedial action, measures were taken to counteract both the mechanisms considered above : (1) Karman's vortex streets by attaching fins to the nozzles to decrease their trailing edge thickness, and hence to modify the shedding frequency of the vortex streets, and avoid resonance ; (2) galloping by strutting the two nozzles together so as to constrain them to in-phase vibration mode, which was considered from observation of the damping behavior to be conductive to marked modification of the structural and mass damping performance, and consequently convert the damping to positive value.
Vibration measurements reperformed after applying the above measures proved. the violent vibrations to have been completely eliminated, evidencing ample effec tiveness of the measures adopted. Further token of the effectiveness of the measures is provided by the complete absence of reports from either tugboat on violent vibrations, throughout the two years that have since elapsed, during which the tugboats have each marked over 4, 000 hours of active service.

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A method is proposed to analyze the vibration of jack-up rig using a model made by replacing its legs and platform with equivalent beams and rigid body, respectively, and connecting them by equivalent springs. The transfer matrix method is applied to analyze the natural vibration of the above mentioned model. The accuracy of this method is studied by comparing the results calculated by this method with those calculated by the detailed method assuming legs as space frames and platform as plane grid structure and also with the measured data obtained by the full scale measurement, and it has become clear that the method in this paper gives practically sufficient results in shorter computer time compared with the detailed method. Thus, this method seems to be very useful not only for the analysis of natural frequency and mode but also for the analysis of forced vibration by waves.

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Researches in finite element analyses in the area of two dimensional field problems and elastic-plastic problems under the plane stress and plane strain conditions have been vastly dealt with. However, in order to understand the phenomenon of, out-of-plane deformation resulting from welding or gas heating, it is necessary to clearly define the three dimensional temperature distributions around the moving heat source and the three dimensional thermal stress and strain distributions in the plates.
In this paper, as the first step of three dimensional finite element analyses, unstationary heat conduction problems are formulated using a simple tetrahedral element. After the development of the computer program, the present method is applied to some practical examples, and the calculated results are compared with the experimental ones to confirm the usefulness of this method.

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It is essential to adopt the welding fabrication which assures high level of soundness of the welded joint in welding high performance structures such as submersible vessel made of steels with both high toughness and high tensile strength. In that case, it is important to prevent weld cracking which affects the soundness of welded joint.
Therefore, the authors carried out various weld cracking tests for butt joint and fillet joint of steels with high toughness and high tensile strength to be used for pressure hull of submersible vessel, and investigated the effect of water content in flux of electrode and ambient humidity on the weld cracking behavior from the viewpoint of welding fabrication. On the basis of the investigation, the conditions for preventing weld cracking were established.

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As the new project of a deep submergence research vehicle following “SHINKAI 2000”, 6000 m vehicle is now under contemplation in Japan. One of the essential themes for a 6000 m vehicle is how to reduce the weight of the vehicle in order to achieve excellent maneuverability and operational efficiency. A pressure hull material with a high strength to density ratio is indispensable for this application.
Some of the authors of this paper have been studying the material properties and fabrication procedure for both ultra-high strrength steel (10 Ni-8 Co Steel) and titanium alloy (6 Al4 VELI). As to 10 Ni-8 Co steel, the pressure hull fabrication procedure have already been established. As to titanium alloy, it was utilized for the small pressure vessels of SHINKAI 2000.
In this paper, the authors have constructed the full-scale model of a titanium alloy (6 Al4 VELI) pressure hull, and established the fabrication procedure of the titanium alloy pressure hull.

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Recently, it has been very active to develop various types of marine structure and ice breaking vessels in order to exploit energy resources in ice fields. These steel structures are to be operated in severe environments of low temperature in the arctic area. Expecially, ice breaking vessels are required to navigate smoothly with breaking ice floe, thus the side shell and the deck structure should be fabricated of heavy plating with a good notch toughness.
To obtain excellent notch toughness and mechanical properties, the authors introduced the new steel manufacturing process, namely CLC process and have successfully developed 50 kgf/mm² class high tensile strength steel of heavy thickness.
Then, experiments associated with fabrication, welding procedure and joint performance were carried out for this newly developed heavy section steel to study its applicability to hull structures of ice breaking vessel. It was consequently made clear that this steel could be welded by conventional welding procedure and showed a satisfactory performance which could assure the safety to be required for ice breaking vessel.

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To improve the effectiveness in ship performance, more and more high tensile steel has come to be employed than hitherto.
One of the problems to be addressed when using the high tensile steel for the ship hull is that of fatigue strength. For with the high tensile steel, compared with mild steel, its fa tigue strength does not improve so much as its tensile strength when used in the ship hull.
The authors studied the high tensile steel K factor based on relevant literatures and, to in crease the fatigue strength of high tensile steel structure, explored the possibility of fabrication process improvement by the TIG dressing, as well as of structural improvement by modifying, for example, the vertical frame bottom end and the slot in the transverse ring. In this connection, test was conducted, which was a basic model test using a simple specimen fabricated by fillet welding two adjoining attachment to a flat plate.
The studies showed that although the high tensile steel structure would exhibit almost no appreciable improvement in fatigue strength at the welded joints of high stress concentration as compared with the mild steel structure, this shortcoming could be dealt with by slightly modifying the detail structure. It was also found that the TIG dressing would not raise but reduce the structural strength when the fillet welded joints were located very close to each other.

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The strain-controlled fatigue tests were carried out on SM5OB steel under bending and axial loading condition to investigate the correlation between these fatigue properties. By use of a cyclic hysteresis energy concept, the possibility of fatigue life prediction under bending from axial load fatigue data was discussed.
The relation formula between nominal bending stress σ_b and actual stress σ_n was derived as follows :
σ_b/σ_n=(1-u₀)/(1+n)(2+n) (1+ζ) [1+n+u₀-(1-u₀)ζ-{(2+n)u₀-(1-u₀)ζ}(ζ/1+ζ)¹⁺ⁿ]+(ζ/1+ζ)ⁿ·u₀²,
where u₀ : ε_y/ε_t0, ε_y : yield strain, ε_t0 : bending total strain amplitude on a specimen's surface, n : strain hardening coefficient, ζ : α/ε_p0, α : material constant in cyclic stress-straincurve, and ε_p0 : bending plastic strain amplitude on a specimen's surface.
Using this equation and the equivalent cyclic hysteresis energy ΔW_eq proposed in this study, which has a functional form to predict the mean stress effect, fatigue lives under bending were well coincident with those estimated from axial load data with R_ε=-1.
It can be considered that crack initiation lives under bending are the same as those under axial loading, if the stress-strain behavior under bending on a specimen's surface can be ex actly estimated and the mean stress effect can be considered by use of the equivalent cyclic hysteresis energy.

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Cyclic stress-strain curves, strain-life curves, and notch evaluation procedure are the basic features of the local strain concept which allows predictions of initiation lives for fatigue cracks of an engineering size of the order of 0.5 mm1 mm. For variable amplitude loading situations, the cumulative damage rule has also to be adopted mostly being a linear damage rule because of a lack of known shortcomings. Under constant amplitude loading and particularly for variable amplitude loading histories following a stress-strain path on a cycle-bycycle basis, hysteresis loop with varying values of mean stress and mean strain have to be evaluated with respect to their damage contribution based on an appropriate strain-life curve.
In common practice, this is carried out by use of the damage parameters. In this report, the capability and accuracy of several damage parameters to predict the mean stress effect on fatigue life of smooth specimens are evaluated using the results of strain controlled fatigue tests with and without mean strains and mean stresses. By combining two proposals from the literature, an improved damage parameter is obtaind and presented.

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The hysteresis loop obtained in the course of low cycle fatigue test is to be the most important key to conjecture the process which is going on in the material. However, the information which the hysteresis loop possesses has hardly been utilized, except hysteresis energy in the case of hysteresis energy accumulation criterion for failure.
In the present paper, the author proposed a rheological model that the material consists of elements with linear strain hardening properties. By using the model, the author interpreted stress-strain relation, or hysteresis loop, analysed hysteresis energy, and discussed hysteresis energy accumulation criterion in terms of effective hysteresis energy.

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