A finite-difference method is developed for a viscous flow about a body of arbitrary configuration. The no-slip body boundary conditions are approximately implemented in the framework of a rectangular grid system. Three examples of simulation, that is, a flow about a car, a flow past two bridges and a flow about a cylinder in waves, demonstrate that this method is useful for the simulation of a viscous flow about a body of complex geometry to which a boundary-fitted coordinate system finds difficulties in the generation.

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A finite-volume method for a flow about a ship-like body is developed in generalized curvilinear coordinate systems. The conservation of mass and momentum is implemented in generalized coordinate systems with sufficient robustness. The numerical dissipation term of the fourth-derivative form and the sub-grid scale turbulence model are incorporated. Simulation results are presented for a flow about a Wigley hull at the Reynolds number 4 × 10⁶.

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A finite-difference method for a separating flow past a 3D body of arbitrary geometry is developed in the framework of rectangular coordinate systems. No-slip body boundary conditions are approximately implemented in the boundary cells making use of two kinds of porosity parameters. The availability of the method is demonstrated by the simulation of a flow past a sphere at the Reynolds number 1000. The complete 3D vortex shedding motion is well simulated.

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A boundary element method is developed for the simulation of 3-D non-linear water waves created by a submerged lifting body. Triangular panels are used to represent general 3-D shapes. All the variables are linearly approximated on each panel. The double mesh method is introduced to solve the non-linear free-surface equations and the Laplace equation with high efficiency and accuracy. On the down-stream boundary a new condition is used which is different from the commonly used Sommerfeld condition and proved effective for wave problems. A new implementation of the Kutta condition for the lifting body is proposed where the directions of wake are determined by an iterative procedure so as to satisfy the equal pressure condition at the trailing edge. The unbounded flow around a ship-like body with two wings is first calculated and then the free-surface flows and the hydrodynamic forces for the body are calculated. The computed results are compared with the measured ones. Discussions are made about the validity of the numerical method.

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In this paper an iterative method is proposed, combining an integral method based on 3-D boundary layer theory with Rankine-source method and considering the head loss due to viscosity in the equation of boundary condition on the free surface. The numerical calculation is carried out by using the Wigley models. The results of pressure distributions on the hull surface, wave profiles along the hull side, velocity distributions in the boundary layer and resistance components have been shown in comparison with measurements. They display good results to some extent. And the method has also been applied to the practical ship model Series 60 (C_d =0.6).

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A numerical method has developed to analyze unsteady hydrodynamic forces of 3D lifting surfaces of arbitrary planform, in which velocity potential is expressed by the doublet distribution over wing surface and the wake. The wing surface is divided into a number of meshes and the strength of the doublet on each mesh is assumed to be constant which makes numerical calculation simple. The wake is also divided into strips of semi-infinite length and the strength of the velocity potential within the strip is assumed to vary with x downstream. Velocity potential on wing surface is obtained by the solution of a set of simultaneous equations. Comparison of lift coefficients with existing theories show good agreement in steady and unsteady problems.
Experiments for some rectangular and triangular wings were carried out, where the steady lift with angle of attack and unsteady lift in heaving oscillation were measured. Triangular wing of aspect-ratio of 2 shows good lift characteristics in wide range of angle of attack. Unsteady lifts for whole wings generally show good agreements with linear theories within present experiments, but some nonlinear effects due to dependence of the velocity of uniform flow appeared in added-mass coefficients at low reduced frequency.

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The flow of an oil layer around an advancing skimming vessel has been investigated theoretically under the following assumptions : (1) the oil layer is so thin that the velocity distribution is uniform over the depth ; (2) there is no shear and tension at the oil-water interface ; and (3) the density difference between oil and water is so small that the elevation of the air-oil interface is negligible. The results of the investigation have showed that the oil layer flow is replaced by a supercritical flow in a shallow open-channel which is characterized by the densimetric Froude number in the ideal case of inviscid fluids with no interfacial tension. The other factors which have been neglected in the theoretical model, namely the nature of viscosity and interfacial tension, are investigated and the effect of them on the theoretical model is quantitatively evaluated. It is shown that the effect will only appear on small model ships.
Tank tests have been carried out to verify the theoretical model and its law of similarity of an oil layer flow, using geosim models of a mono-hull vessel. The geosim models with different entrance angles have been tested, at varying ship speeds and oil layer thicknesses. Furthermore, models having different hull-form with the geosim models have been tested to investigate the effect of hull-form on the theoretical model. The test results show that the theoretical model and the law of similarity are valid at lower densimetric Froude numbers, and the effect of the Froude number appears at higher densimetric Froude numbers. And the flow is characterized only by the entrance angles independent of the form of section and draft of vessels.

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It is well known that if numerical time domain simulations are performed with the equations of sway-yaw-roll motions of a ship in oblique waves, the solutions of sway and/or yaw motions are drifting in process of time steps. Because of the coupling effects of the equations, this drifting affects other modes of motions badly, and the steady state solutions cannot be obtained even in the case of regular waves. This fact is emphasized in calculations of wave loads.
When the nonlinearity of the fluid forces acting on a ship's hull is to be taken into account, numerical simulations in time domain are inevitable and a special care is necessary to perform such simulations because of abovementioned drifting. Since this drifting is not physical one but purely numerical one, which is dominated by the eigenvalues of the equations of motions, it would be necessary to eliminate the drifting solutions from numerical simulations.
In the present paper, a scheme, in which the digital filter technique is applied, is proposed to eliminate drifting solutions and obtain steady state solutions in the process of numerical simulations of nonlinear ship motions and wave loads in regular oblique waves. Example calculations are performed for a high-speed container ship using this scheme. Calculated results show that the proposed scheme is effective to obtain stable solutions in the calculation of ship motions and wave loads in regular oblique waves.

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Model tests on capsizing of a container ship running in quartering seas were performed using a radio-controlled model. The model tests were carried out for the one P-M type irregular wave and various regular waves in the 80 m square tank of the Ship Research Institute. The parameters of the experiment were the GM value, the model speed and the encounter angle with the wave for the irregular wave, and also the model speed, the encounter angle, the wave length and the wave height for the regular waves. The encounter angle was varied precisely every 10 degrees from 0° (following wave) to 90° (beam wave) by using the auto-pilot steering system in order to specify the dangerous range. The Froude number of the model speed was varied every 0.01 to clarify the critical speed for the capsizing. The wave length and wave height of the regular wave were also varied in a fine intervals to examine the tendency of the capsizing for the various waves. Among 763 runs in the irregular and regular waves, 225 capsizings were observed. From these results three characteristic features were clarified. Firstly, most capsizings occurred in the range of the encounter angle of 20° to 40°, and the range was spread to 0° to 50° as ship speed increased. Secondly, as ship speed decreased, the capsizing decreased, and there existed a critical ship speed below which the capsizing never occurred. Thirdly the direction of the capsizing was always to the leeside.
On the basis of the above results, a hypothesis is presented that such capsizing may be explained fundamentally as a simple static one which occurs because the capsizing moment of the wave exceeds statically the restoring moment decreased in the quartering wave in the above dangerous range of the encounter angle. The reason why the capsizing occurs only in the high speed range and only to the leeside direction is also explained in connection with the surf-riding motion or asymmetric nonlinear surging motion with a large amplitude.
The capsizing due to the parametric oscillation, which had been regarded as one of the typical mode of the dynamical capsizing, was never observed in the present experiment. Instead, a number of the new mode of the dynamical capsizing accompanied with the phenomenon of the period doubling bifurcation which was regarded as the foreboding of the chaos were observed.

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In recent research works on capsizing in beam sea conditions it is reported by some authors that the model ships were capsized by breaking waves which gave them a large overturning moment due to the direct attack of high speed wave fronts. But the model shapes were different from the ones of small ships those are mainly reported in the record of maritime accidents to have capsized.
This paper deals with the capsizing of a small fishing boat and shows the different patterns of capsizing phenomena from other papers. Many capsizing could be seen in concentric transient waves with two successive crests, which excited a large rolling amplitude beyond the stability vanishing angle of the vessel. The model ship was of about 1/6 scale of an actual fishing boat and set free-floating abeam in the model basin. The GM values were varied in a wide range so that critical GM values could be determined. The effect of the initial heeling angle and the initial position of the model was also investigated. The maximum wave height was about the same order as the model breadth.
As for the mechanism of capsizing it is concluded that the model ship was capsized not by the impulsive moment of breaking waves directly but the loss of stability due to a large rolling motion developed by the transient large waves. The breakers played a significant roll to change the conditions of encountering the next critical waves.

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The hawser used to moor a floating structure to an articulated column generates nonlinear restoring force for the angular displacement of articulated column. The nonlinear restoring force causes an oscillation with a period of several times the period of oscillatory exciting force, that is to say, a subharmonic oscillation. The present report deals with the conditions necessary for the subharmonic oscillation to occur when an articulated column placed in regular waves is provided with nonlinear restoring force. As the result of numerical analysis, it is clarified that the magnitude of nonlinear hydrodynamic drag force coefficient as well as wave period, wave amplitude and nonlinear spring constant are deeply associated with the occurrence of subharmonic oscillation.
In particular, the role of drag force coefficient is important; as the drag force coefficient increases, the possibility of occurrence of subharmonic oscillation is reduced. Besides, the subharmonic oscillation does not occur in waves of an arbitrary period, but does occur in a particular range of wave period which is determined by the oscillatory characteristics of an articulated column.

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As a sequel to our previous reports on tank testing results of ship motions in directional spectrum waves this paper discusses the applicability of motion test results to estimate transfer functions of motions for various wave encounter angles. As we have observed in our previous reports that in many cases, especially in head sea condition, theoretical estimation of motion spectra do not agree so well with experimental results, estimation of true magnitude of transfer functions becomes a necessity. In the present study a practical method of estimation has been discussed and short term prediction of motions over various range of wave periods has been carried out with the estimated transfer functions. The prediction shows good agreement with experimental results. Results of long term prediction in Winter North Atlantic have also been presented.
This paper also discusses the possibility to extend Maximum Likelihood Method (MLM) to estimate directional encounter wave spectra analyses of which is necessary for reverse calculation of transfer functions of motions.

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The at-sea experiment of the moored floating structure, which is called POSEIDON, has been done at the Japan sea since september in 1986.
This paper deals with the characteristics of wind speeds measured at the test field. Especially, we concentrate upon varying wind speed spectrum, 1/nth highest expected values, and gust factors.
As an anemometer, a sonic anemometer was used and it was installed at the top of mast of POSEIDON, at which is the position of 19.5 m height above sea surface.
The main results are as follows.
i) A new formula of varying wind speed spectrum is developed under physical considerations. The presented spectrum can be determined by two parameters, i. e. the peak frequency and the power, those are prescribed by the friction coefficient between air and sea surface.
The measured spectra do not agree with the well-known spectra (Davenport's and Hino's spectra) but accord with the presented spectra.
ii) 1/nth highest expected values and gust factors can be estimated by using the well-known statistical estimation theory (i. e. Longuet-Higgins theory) and the presented spectrum.

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Dynamics is studied of long and flexible line structures, such as a riser pipe and a cold water pipe for OTEC hanging down from a floating platform on the sea surface into the water. A mathematical model widely used is shown to be capable of describing general features of the behaviours observed at forced motion tests of a pipe model in model basin. Among them lateral motion induced by axial forced motion is a little unusual. This is caused by parametric excitation of Mathieu type. We propose a method to predict magnitude of this limit cycle type of motion.
Theoretical prediction of this parametrically excited motion by the analytical model is not completely satisfactory. Numerical analysis admitting finite amplitude effect of motion is shown to predict this motion with complete accuracy. Other interesting behaviours of 3D motion of line structures in the water predicted by the numerical analysis are presented and the finite amplitude effect is discussed.

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Freefall lifeboat systems were developed in 1970s by Scandinavian countries as a life saving system which ensured safe and quick evacuation from a wrecked ship even in adverse weather conditions. The international regulation requires that the system launches a lifeboat into water wituhout any harmful acceleration to occupants and effectively clears the ship. Before studying these important matters for safety, the attitude of the boat must be defined at the water entry. The falling motion of the boat is a pure dynamic phenomenon in the air and then a mathematical model should be useful for describing it. No theoretical investigation, however, has been presented yet about the falling motion.
In this paper the authors present a numerical simulation method on the falling motion of freefall lifeboats. After validating the method through experiments, they discuss the relation between the attitude and launching conditions, i. e. geometries of the boat and cradle, friction between the boat and cradle, starting position and fall height, H, of the boat, etc. They further propose tentative criterion for the safety entry of freefall lifeboats as an application of the method.
The followings are some of the conclusions from the discussions :
(1) The present method is of practical use for predicting the attitude of freefall lifeboats at the water entry and providing the criterion of safety entry for given boat and cradle geometries.
(2) There is a range of launching angle where the attitude of the boat at the water entry dose not change seriously.
(3) The friction of the boat and cradle is negligible in the practical range of rolling friction. They are warned, however, against unexpected stumbling on the cradle which increases the rotational motion of the boat.
(4) In practical ranges of the radius of gyration and height of C. G. of the boat, their changes give no serious influence on the attitude.
(5) The plunging speed is assumed in practice to be √2gH when the F. P. of the boat is close to the lower end of the cradle at the starting position.
(6) The length of guide rails after C. G. of the boat is one of the most important factors for defining the falling motion and it is, to some extent, possible to control the attitude by changing the length.

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A method is proposed for estimating and evaluating the service performance of ships at the initial design stage.
The defects involved in the so called “seamargin” that has been used at the initial design stage of ships for many years are pointed out. To improve those defects, the authors introduce the probabilistic approach to estimate and evaluate the seamargin.
The method proposed here is applied to evaluate the commonly used seamargin of an exsisting ore carrier engaged in the service between Japan and Australia.

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The purpose of the present study is to develop the economical finite element analysis program for the collapse simulation of framed structures and to verify the validity of the developed code through the comparisons of the numerical results with the test results. In the first report, the details of the incremental formulations were described, in which the linear Timoshenko beam element was employed with the variable location technique of the numerical integration point and the elasto-plastic constitutive equation expressed in terms of resultant forces. In this second report, the finite element results by the updated Lagrangian formulation are compared with the crush test results conducted for beams, columns and space frames. The strain hardening and the frictional contact are taken into account in the present analysis. The obtained results can be summarized as follows :
(1) From the results for beams and columns, it can be seen that the present analysis method gives sufficiently accurate solutions for the crush problem accompanied by large strains and large displacements, except for the cases that local deformations as shells are obvious
(2) From the results for space frames, it can be seen that the developed code is sufficientlyeconomical and accurate from a practical point of view, however, some trial-and-error analyses are necessary for the crush behaviors in which friction and contact play important roles.

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Adaptive mesh generation using a posteriori error estimation has recently attracted great interest. This paper proposes a new r-method of adaptive mesh generation for the finite element method. The objective function of this method is to minimize the error norm of the whole computational domain. It is very impotant for the adaptive mesh generation to estimate the numerical error accurately. The discretization error in the finite element method is estimated using the computer code ERRAND-FEW developed by the authors.
In order to verify the newly proposed adaptive method, we have chosen two 2-dimensional stress concentration and singularity problems. The results show the validity and the effectiveness of this method. Since this method is very simple and flexible, it is quite possible to extend it to any other problems, such as shell problems or solid problems.

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The mass, the damping and the stiffeness matrices in the equation of vibration are called as the characteristic matrices of a vibration system. In this paper, a new method to identify the characteristic matrices from the response of the vibration system (transfer function) is proposed. In this method, the initial value of characteristic matrices are estimated by the 1st report of Ookuma and Nagamatu, and modified so as to minimize the error between the actual and the estimated transfer function. This modification is iterated, and stopped when the error becomes minimum or the curve fit of the transfer function is sufficient.
In order to confirm the accuracy of the proposed method, the transfer function is calculated using the given characteristic matrices, and from its transfer function the characteristic matrices are again identified. The identified characteristic matrices are compared with the original ones, and a good agreement can be seen between them when the transfer function contains sufficient information about the vibration system. When the transfer function containing insufficient information about the vibration system is used for identification, the fitness of transfer function is found be good. However the identified characteristic matrices are considerably different from true matrices.

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In this paper, the Monte Carlo simulation is applied to reliability assessment of frame structures. Importance sampling technique is used to reduce the sample size that is necessarily large for small failure probability problems, and Neumann expansion method is adopted to decrease the computational effort in finite element analysis. Based on the analyses of numerical results, it is discussed how to select and check importance sampling distributions. Numerical examples show that the Monte Carlo simulation combined with importance sampling and Neumann expansion is much more advantageous than direct Monte Carlo simulation.

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Reliability-based design approaches are needed for novel ships whose design and operational experiences are few and which are subject to external loads of random nature such as wave-induced loads. This paper deals with reliability assessment of Semi-Submerged Catamaran (SSC), one of the novel ships. An SSC is modeled as a spatial framework to which side force under beam sea is applied. Structural systems reliability analysis is carried out by using the method in which probabilistic plastic collapse analysis and failure mode analysis are combined. Effects of some design alternations on systems reliability are also discussed.
Main conclusions are summarized as follows;
(1) Reliability assessment is necessary for a novel ship such as an SSC in order to realize a rational design of the structure.
(2) Systems reliability is indispensable because component reliability can not necessarily predict structural safety of the vessel.
(3) Important design parameters are clarified through parametric studies.
(4) Importance factor of members under damaged conditions is proposed.

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Wood is a material for which strength and elasticity vary greatly in relation to grain direction. To build wooden structures such as ships (which suffer from severe simultaneous bending and shear stresses), combining plankings of several directions has been found to be effective in providing inplane stiffness.
These patterns are called diagonal systems of planking and were the subject of intense research during the 1950s'. Diagonal systems of planking made it possible to build much lighter and stronger wooden ships than those which had been built of only longitudinal plankings.
Several problems remained unresolved by the earlier research projects :
(1) There was no method to determine the complicated stress distribution of shell plankings.
(2) There was no method to determine the reaction forces of joints.
(3) Breaking stresses and modes of failure of planking were not well understood. The purpose of this project was to develop a method to analyze these aspects of wooden ship structures.
Strength tests of shell structures were conducted by full scale partial models to investigate static behavior.
The shell stiffness was investigated by a detailed FEM analysis of the shell. Axial stresses of each layer were analyzed for a whole ship FEM model using the unidirectional stiffness plate method. Then the detailed FEM analysis of the shell was conducted again to investigate local planking stresses and joint reaction forces. Breaking tests of the shell were also conducted to investigate breaking strength. Its failure mechanism was also discussed.

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It is said that most of hull damages in old ships are caused by corrosion /wear because ships are closely related with corrosion in the sea condition. Accordingly, in assessing the remaining lives of those ships, it is important how to estimate the strength of corrosive members.
On the other hand it has ever been said that corrosive members often indicate the characteristics of brittleness even if they are mild steel in the room temperature. So the authors confirmed that corrosive members of mild steel, in some cases, shows the decrease in ductility, that is, elongation by the experiment. Furthermore, it has been examined that this phenomenon has been brought about by corrosive pits formed on their surfaces. And the effect of corrosive pits on static strength have been studied parametrically by the simulation test in which artificial pits are formed on the surfaces of the test specimens. Obtained main conclusions are as follows ;
(1) The characteristics of tensile strength in corrosive members are very similar with that of members with artificial pits on their surfaces. Then the tensile strength of corrosive members can be substituted by that of those with artificial pits.
(2) Elongation of members with pits varies with the density and depth of pits. That is, as the density becomes high and the depth ratio (d/t) becomes large, the value of elongation decreases.
(3) Ductile fracture of members with pits starts at the pits in the tensile test. And introducing the volume ratio V_p, the elongation can be represented as the following equation;
ε_e/ε_e0=1/1+k_pV_p (k_p : constant)
where k corresponds with the density of pits.
(4) Absorbed plastic energy of members with pits is the function of V_p as well as the case of elongation and can be represented as the hyperbolic relation;
W/W₀=1/1+k_pV_p (k_p : constant)

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When we consider the reliability of structural member group, we sometimes face the case of not being able to treat members as samples from the same population. For this case, reliability analysis becomes a very difficult one. In order to perform the analysis, we require subjective information which can describe the structure of member group and cover the shortage of objective probability data. The present paper deals with the problem of how to utilize effectively the subjective information in the structural reliability analysis. A method of utilizing pattern perception of human is presented. Expert's intuitions perceived from the insufficient objective data as well as his knowledge and experience are expressed by the “subjective distribution patterns” and utilized as the prior probability information in the reliability analysis. First, several patterns which can be the cause of objective data are generated by the expert's judgement. Second, in order to distinguish between probable distribution patterns and misdirected patterns, probabilistic analysis using likelihood function is carried out. The improvement of estimated pattern is also performed with the aid of Monte Carlo simulation. The effectiveness of this method is numerically examined through the problem of inspection maintenance of a structural member group with unevenly scattered fatigue deterioration.

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As material flaws have great influence on fatigue strength of cast materials components, it is important to establish fatigue strength evaluation method of cast materials with flaws.
In this study, concept of allowance rate was introduced to evaluate fatigue strength of cast steel with round-shaped flaws. The results obtained were summarized as follows :
(1) A fracture mechanics approach was made to estimate fatigue limit of cast steel with a round-shaped flaw, regarding the flaw as an elliptical notch having an intrinsic crack, which is material constant, at the root. By this method, the allowance rate of flawed body againtst cracked one can be estimated.
(2) The allowance rate can also be obtained experimentally by brittle fracture test of notched body at an extremely low temperature.
(3) The concept of allowance rate was verified by fatigue test of specimen with a notch and with an actual casting flaw.

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One of the recent advances in fracture mechanics is the crack path prediction whose need stems mainly from two reasons. One is the understanding of the micromechanical toughening mechanisms of non-metallic materials such as ceramics and advanced composites due to noncollinear crack extension, while the other is the growing concern of the critical assessment at fracture and the related fracture control of potentially dangerous engineering structures. Several computational methods have been proposed for crack path prediction based on the finite element methods and the boundary integral equation methods, respectively, combined with appropriate crack path criteria.
Considering a finite element approach, the step-by-step analysis requires mesh generation and nodal numbering at each incremental curved crack extension, which may be one of the most important procedures of the simulation method. In order to improve the computational efficiency and capability, an automated mesh generating method so called the modified quadtree method is applied to the computational crack path prediction proposed by the first author. In the method, the object of interest is first placed inside a square having an integer coordinate system. This square is subdivided into four quadrants, which are again subdivided into four subquadrants. This procedure is continued until the mesh density reaches some desired level, where the quadrants placed along the object boundaries are appropriately cut to approximate curved boundaries. After correcting the nodal location, the finite element mesh subdivision is completed. In order to apply this technique to crack problems, special treatments are introduced both for the identification of the two crack surfaces occupying same coordinates, and for the shape and size control of the mesh in the neighbourhood of a crack tip.
The present method is applied to crack path prediction along a butt-weld plate made of mild steel. Numerical simulations are performed by taking into account of the effects of applied stresses and residual stresses. Although the initial crack is located along the toe of weldment, once the crack begins to extend, it is sharply curved to the base metal due to the tensile residual stress, and it continues to propagate in the base metal. This kind of crack propagation behavior qualitatively agrees with experimental results observed by several researchers.

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It is well known that the TMCP steel rolled at the temperature of its intercritical region in steel production has high brittle crack arrestability. The cause is generally considered to be related with the generation of separations ahead the main brittle crack just in advance.
However it has been sometimes experienced that there are no observation of appearance of separations on the brittle fracture surface for TMCP steel plate with high K_ca.
Then in this study, we carried out not only double tensile tests but also COD tests and Charpy impact tests with various directions by using two TMCP steel plates, which are produced from same slab but are rolled at the different finishing temperature, thus leads to different maximum separation index. By analyzing these test results, it is understood that high K_ca value comes from zig-zag path of brittle crack which is caused by anisotropy of fracture toughness of steel plates.

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Recent steel manufacturing produces 9 % Ni steels with high toughness through minimizing steel impurities and improving heat treatment. These 9 % Ni steels show ductile fracture and absorbed energy more than 20 kgfim in V-Charpy impact test at -196°C, which indicates V-Charpy impact test being insufficient for the material selection. It has become difficult to know the arrestability of these 9 % Ni steels through surface-notched double tension test using LN₂ (-196°C) as refrigerant. The method was developed to get brittle crack propagation-arrest toughness for high toughness material. In this paper crack arrestability of 9 %Ni steels which varies in toughness is examined by means of surface-notched double tension test and Charpy impact test of two specimen types. Surface-notched double tension test is conducted to check Kca values and Charpy impact test is conducted at temperature ranging -100-269°C in order to clarify the effect of specimen notch shape on ductile/brittle transition phenomenon of high toughness 9 %Ni steels and crack initiation and propagation energies. The following conclusions are obtained.
(1) 3-surfaces slitted Charpy impact test is available for the material selection of recent 9 %Ni steels because transition temperature of this method rises 4584°C higher than that of V-notched one.
(2) Crack arrestabilily of 9 %Ni steels can be estimated based on transition temperature and propagation energy of 3-surfaces slitted Charpy impact test.

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In order to extend the applicable range from the parallel parts to the non-parallel parts of hull structures, a new CAM system for the arc-welding robot has recently been developed.
When automatic arc-welding is extended to all the non-parallel hull part workpieces of different shapes, the new CAM system is required to respond flexibly to the alterations of production order, shapes and the laying positions of related workpieces, without taking much time for programming. Satisfying these needs, the following means has been studied for the new system.
(1) The new CAM system supplies a task level welding program to the robot controller, which, simultaneously generates every robot motion. Consequently, when it becomes necessary to alter the laying positions of workpieces due to the change of the production order, the robot can react freely to the alterations.
(2) For saving programming time and for simplifying the operation, the system of a human interface with an interactive mode is adopted using graphic displays. Operation guides of the system and those commands for selection are both shown on the graphic displays.
(3) For saving time and avoiding errors, the data-base of the hull structures is used for programming.
(4) A micro computer is provided at the control room in the sub-assembly shop for editing, alterating and maintaining the welding programs.
This new function enables the system to react flexibly to the alterations of design and production order.
It is estimated that utilization of the new CAM system reduces programming time by 2/3.
Experimental calcurations on the economy of the robot based on the actual record of programming and welding time has confirmed that it is possible to maintain an economical advantage even in the case of the robot being applied to workpieces of various shapes.
The arc-welding robot for hull sub-assemblies can be effectively used on non-parallel parts of hull structures by employing the new CAM system.
This new system offers full automation potential for every welding activity on the sub-assembly line of hull structures.

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In the previous report, we derived extensible catenary equations and discussed the fundamental characteristics of catenary. We also descrived the ways to solve the equations under various boundary conditions.
In this paper, we introduce a program package based on the extensible catenary theory. Next, a simplified dynamic analysis method is shown. The accuracy of calculation by the program package is verified by comparing with the results of tank tests or calculations with other programs. Finally, initial design method of underwater line structures using the program package is shown and typical line structures such as mooring lines, towing lines and flexible marine risers are designed easily applying this method.

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To realize the construction of huge floating offshore platform, the investigations of upper-structure deformation and stress distribution caused by the non-uniform thermal distribution of solar radiation are indispensable.
This paper deals with the measured data obtained through at-sea experiment of the test sturucture “POSEIDON”. Long continuous data concerning of temprature and strains of steel at various points of the box-girder of upper-structure were obtained as well as the records of solar radiation, air temperature and wind speed etc.
In the fields of meteorology, architecture and air conditioning, there are some estimation methods of solar radiation and thermal distribution of the structure. In this paper, the measured data of solar radiation and thermal distribution were compared with the values estimated by those methods, and their applicabilities were discussed.
The results are as follows.
As for the estimation of total solar radiation in any plane, it can be said that the present method is a practical method and also has a good accuracy. Furthermore, the present method can also predict the thermal distribution in the box-girder due to solar radiation.
Using the present method, it is confirmed that the thermal distribution remarkably changes due to the external disturbances, e. g. wind speed, atmospheric temperature, air temperature in the box-girder and relative humidity etc., and the effect of wind speed is the largest in these disturbances.

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