The general equation of flow near the free surface is derived by considering up to the 2nd order terms of velocity components. It is given by the non-linear 2nd partial differential equation, whose mathematical type is classified by the sign of its discriminant.
By solving the discriminant approximately, clear explanation of the breakdown of bow wave in deep water, which is important for a full hull form, can be given. The assumptions used in the calculation are supported by the model experiments of Inuid Model S. 201.
According to the above test results the law of conservation of energy is maintained by the occurrence of vorticity with lateral axis during the breakdown of bow wave. Thus the mechanism of the occurrence of the wave breaking resistance becomes clear.

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In order that the wave-making theory should be applied successfully to the hull form design, it is of primary importance that the theory can reproduce the actual wave-making phenomena of ships as exactly as possible.
Here an attempt is made to obtain the effective wave-making source of a ship from the measurement of hull-side wave profiles rather than from that of the free wave patterns in the rear of a ship.
The integral equation of the source distribution function is simplified and solved numerically under the specific limitation, (a) rectangular, vertical central source distribution plane, and (b) draughtwise uniform.
Two Inuid models M 20 (B/L=0.0746) and M 21 (B/L=0.1184), whose hull-generating sources are optimized to give the minimum wave resistance at K₀L=12 (Fn=0.2887), are wave-analyzed.
The obtained source distribution shows a clear discrepancy from the hull-generating source.
Then the correction function α (ξ) is introduced in a form of the ratio of wave-analyzed source to hull-generating source. The general tendency of the correction function α (ξ) of the wider model M 21 is found as quite similar to the previously proposed μ-correction.
By adopting α (ξ), the calculation shows remarkable agreement with experiment in (a) wave profiles, (b) wave patterns, and (c) wave-making resistance.
As an example of practical application, an asymmetry Inuid model M 21-M is designed so as to minimize the wave resistance under the same restraint conditions as M 21 except that α (ξ) of M 21 is taken into account in the design procedure of M 21-M. From the tank test of M 21-M, it is clarified that almost 40 percent of the wave resistance is reduced, which may suggests that such design procedure is significant.
To investigate the theoretical basis of the correction function α (ξ), the second order contributions are calculated approximately with respect to the two boundary conditions, namely (a) hull-surface condition, and (b) free-surface condition. It is found, however, that the second order terms do not give sufficiently the theoretical basis for the correction function α (ξ), which may suggests the importance of the hull's sheltering effect.

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A method to apply wave pattern analysis to the ship form improvement is proposed. The principle of the method is to find a thin ship which is added to a given basic hull form so as to reduce wave-making resistance. The wave pattern of the thin ship is calculated theoretically and superposed linearly on the measured wave pattern of the basic hull form. To find the wave-making characteristics of the basic hull form, Hogner's idea of influence function is employed. The influence functions are calculated from measured wave data instead of theoretical calculation. Therefore they inform more realistic values of modifications than those by a pure theory only. Further, a method of empirical correction for the finite breadth effect of the given ship on the thin ship has been developed. Taking an example of ship form improvement, it is demonstrated how the present method works effectively in reducing wave-making resistance under appropriate design constraints such as constant beam and displacement.

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The objective of this paper is to afford a more rational procedure for finding an optimum singularity distribution which will generate a practical ship form with a flat bottom as well as low wave-making resistance. The effects of singularity generated flat bottom on wave pattern are discussed both theoretically and experimentally. Measurements are made of wave pattern and total resistance of two Pienoids. One of them has a flat bottom, while the other has a curved keel line. The difference in the wave patterns measured of the models indicates a remarkable discrepancy between the liner theory and the experiments of the surface disturbances due to the singularities for flattening bottom. An optimum source distribution is then modified with consideration of this discrepancy. The modified singularity distribution is found to give a ship form with lower wave-making resistance than the un-modified.

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In order to investigate the interference between surface waves and a frictional wake of a ship, a simple mathematical model, such as a current of uniform width and uniform velocity in the surrounding still water upon which a regular train of waves propagates, is considered. The analysis is based on the assumption that the fluid is inviscid and the motion is irrotational except on the boundary of the wake or current. The result of calculation shows a remarkable change of the incident wave when it propagates accross the boundary of the wake. When the direction of the incident wave is parallel to the wake belt, a considerable attenuation of the wave height is resulted. An experiment in a circulating water channel is conducted to observe the transfiguration of waves inside the wake, and a qualitative agreement with the theoretical result is obtained.

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There are many kinds of fishing boats in Japan, and fairly amount of them have bad resistance characteristics. The tendency is getting hard especially in these few years.
To improve the circumstances, simple estimation methods of EHP values for any fishing boat at any speed in the initial design step are necessary. FAO has published a equation to estimate the total resistance coefficient C_R16 of fishing boats by statistical regression analysis of tank tests in 1969. But, as it is not convenient enough when the displacement and speed are given but the water line length is varied, new analysis is tried for the same samples after the re-arrangement of them, which are as follows :
(1) Total resistance coefficient r=R_t/ (1/2ρ·∇^2/3·V²) is used.
(2) The r values of each model test are corrected by the ITTC 1957 model ship correlation line to those of Δ=300t.
(3) Froude number F_n∇=V/√∇^1/3·g is used.
(4) Hull form parameter L/∇^1/3 is used instead of L/B.
(5) The values of hull form parameters are normalized by using modification factor to reduce the estimation error for those which exist at fewer samples' zones.
(6) Samples having quite different hull forms are excluded.
After the analysis, new regression equation is introduced which has almost enough accuracy for practical use, and is put into the computer program for the initial design of fishing boats. By the program, a improvement of traditional tuna long liner is tried, and after the tank tests, about 40 % of EHP reduction is confirmed. This method will be used for improving the other kinds of fishing boats in Japan.

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Semi-empirical formulas previously proposed by the present author to estimate the characteristics of the peripheral jet of ACV_s are re-examined for wider range of operating conditions and jet discharge angles and it has turned out that the proposed method is applicable with slight corrections. Numerical calculations are made for possible cases in the practical operation and the results are given in tabular forms.

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The hydrodynamic characteristics of a marine propeller in uniform flow are evaluated in relation with the geometry and the working condition. The problem is reduced to a two-dimensional integral equation by means of the lifting surface theory. The calculating method, developed by Dr. Hanaoka for solving the equation, is used in the present paper. Numerical examples, illustrated in the present paper, verify the usefullness of his method. As for the lift distribution near the tip of a blade, however, the examples show the difficulty in accurate evaluation.

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Cavitation is one of the most important problems in the field of ship hydrodynamics. It is almost unavoidable phenomena for heavily loaded screw propellers. In spite of many investigations that have been carried out for a long time, there are many problems left to be pursued. Especially quantitative explanations of cavitation are lacking or left vague.
An experimental research on the steady state cavitation on a two-dimensional hydrofoil was undertaken at the cavitation tunnel of Tokyo University. We have aimed at adding some experimental data, emphasizing the importance of pressure distribution itself rather than the total force or moment acting on a hydrofoil. To this end local pressures at four points on the suction side of the profile were measured and compared with calculation.
Conclusions obtained are as follows.
1) A complicated type of cavitation named “activated sheet cavitation” occurs and plays a significant part as far as a two-dimensional hydrofoil at high angle of attack is concerned.
2) Pressure distributions in the wetted area are scarcely affected by the presence of partial cavitation that covers the fore surface of a hydrofoil.
3) The pressure at the rear end of cavity does not reach the stagnation pressure, and the reduction of C_P is less than 20 percent of the non-cavitating C_P.
4) Mathematical model of cavity that the rear part of cavity is represented by a distribution of weak sink shows fairly good agreement with experiment.

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Unsteady cavitation that results from the non-uniformity of the flow field renders evil influences on marine propellers. It has been a general experiment for the investigation on such problems to observe unsteady cavitation in a flow field analogous to a wake pattern. At the time being, however, quantitative information cannot be derived from such kinds of experiment, and explanations of unsteady cavitation are likely to be qualitative, which can sometimes give us erroneous conclusions.
The most basic and fruitful quantity for the study of cavitation is the pressure distribution on a unsteady hydrofoil in non-cavitating condition. With this quantity we can clarify unsteady cavitation more rigorously.
This paper deals with two-dimensional hydrofoils pitching simple-harmonically. With this simplification pressure distributions can be directly measured, and can be calculated by the use of unsteady wing theory. These pressure characteristics have intimate relations with the real cavitation phenomena that were observed by high-speed motion pictures.
Principal conclusions obtained are as follows.
1) The oscillatory flat-plate-wing theory shows good agreements with experiments when a rigorous correction is made for the steady component.
2) Characteristics of cavitation on a pitching hydrofoil can be explained by the time-dependent pressure distribution calculated by the unsteady wing theory.
3) Unsteadiness of pressure field strongly affects the process of the collapse of cavity. Increase of unsteadiness will lead to serious erosion.
4) Maximum length of unsteady cavitation on two-dimensional pitching hydrofoils tends to be shortened with the increase of reduced frequency up to 1.0.

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This paper gives a general description of a new ship model experiment tank, “Mitaka No. 3 Ship Model Experiment Tank”, built at the Ship Research Institute. The principal dimensions of the tank are 150 m×7. 5 m×3. 5 m.
The main features of the tank are as follows :
1. towing carriage of box girders convenient to perform various kinds of experiments, not only on ship models but also on ocean structures.
2. strong tank wall and special apparatus, which enable the accurate tests in shallow water.
3. sub-carriage carrying a small wind tunnel to perform the tests in waves with wind.
4. wave maker of plunger type whose vertical position can be varied corresponding to the water level.
5. easy control of the towing carriage any one can drive.

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A new type wave maker without water on back side was developed and installed in the Seakeeping and Manoeuvring Basin of Nagasaki Technical Institute, M.H.I. The design theory of this new type wave maker, construction device of the gap of the flap ends assuring water tightness as well as no disturbance on wave making and the system design are described, followed by a description of the new type wave maker of the Basin.

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The wave exciting force and moment for a ship advancing in regular waves have been calculated by the so-called ordinary strip method (O. S. M.) proposed by Prof. Watanabe and Prof. Tasai. Many comparisons between computed values obtained by O. S. M. and experimental data have shown fairly good agreement in case of a ship advancing in head seas.
On the contrary, the computed values for oblique waves have been scarcely compared with experimental data from lack of the testing facilities available for measuring the wave exciting force and moment in oblique waves.
In this paper, the experimental data of the wave exciting force and moment in oblique waves which were measured at the New Seakeeping Basin of Tokyo University are reported and compared with the theoretical values.
The theoretical calculations were carried out by the two different methods, that is to say the ordinary strip method and S. T. F. method. Comparisons between the theoretical values themselves by these two methods are also made.
In consequence of comparison between the experimental data and the computed values, the fairly good agreement for practical purpose was shown with respect to the five components of the wave exciting force and moment except the roll-moment.

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Model tests of two container ships in oblique regular and irregular waves were carried out at the seakeeping tank of S. R. I., and the relative wave elevations at various positions of the models' hull were measured by means of capacitance wave probes attached on the hull.
The relative wave elevation induced by combined ship motions as pitch, heave and roll and the wave elevation can be calculated by the strip method. The deformation of the wave surface near the hull which is induced by hydrodynamic interaction between ship's body and wave is estimated by the Tasai's two dimensional theory, and it is added to the above-mentioned relative wave elevation.
The comparison of the test results with the computed values shows that :
a) calculations including the hydrodynamic interactions show good agreement with the experiment, generally speaking, in head and bow seas, b) the measured values in beam sea lie between calculated values including and excluding hydrodynamic interactions, c) disagreement between measured and calculated values is most remarkable in quartering sea, except one for the stem provided that the estimation is made excluding hydrodynamic interactions, d) the amplitude distributions of the relative wave elevations measured in irregular waves show good agreement with the estimated one by the linear superposition of the response amplitude operator and sea spectrum.

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The effect of advance speed on ship rolling characteristics has been a problem to which many researchers have had their interest for a long time. In line with the speed-up of cargo liners, the speed range of experimental investigations of this problem was extended as high as 0. 7 in Froude number in the recent studies by Obrastsov, Ferguson and Conn and so on.
The authors have examined carefully the results of these experiments including their own experimental data and obtained an empirical formula for calculating GM under forward motion. A consideration based on the theorem of moment of momentum was made to get some dynamical concepts.
In addition, an experiment was carried to estimate the augmentation of frictional resistance for rolling due to ship advance speed.
It is found that the augmentation is a linear function of λ=V/σL (V : ship speed, L : ship length, σ : circular frequency of rolling) and the frictional resistance can be considered small irrespective of advance speed even in case of small model ships of 2 m long.

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The authors carried out theoretical investigations into the impulsive pressure acting on elastic structures.
In the paper, the following two items are mainly discussed;
(1) On the distribution of impulsive pressure acting on elastic structures induced by compression of fluid.
(2) On the possibility of calculation of the deformation of elastic structures using simple dynamic model without considering the strict dynamic behavior of the impulsive pressure.
The following conclusions were obtained :
(1) When the impulse on the fluid is cushioned by the likes of a spring, the impulsive pressure is distributed uniformly except some special cases. On the other hand, when the impulse is not cushioned, the pressure is not distributed uniformly by the occurence of pressure of sound wave.
(2) When the natural period of the structure is less than the duration of the impulsive pressure, the reasonable elastic deformation can be estimated by an proper approximate method.

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In the third report, the author presented the results of his comparison between the growth rate and amount of ice accreted on patrol boats obtained from icing experiments conducted at sea and the rate and amount of ice estimated by the theories of forced convection of heat developed in the first and second reports.
It is also advanced that the growth rate and amount of ice accreted on any vessels, can be estimated approximately under any ambient air temperature, wind velocity and duration of icing at sea through the results of these studies.
This paper describes some materials for ambient air temperatures and relative wind velocities during icing on ships, which have been collected through questionnaires entrusted to various types of patrol boats in the northern waters around our country over several years.
The weather condition of the growth of ice accreted on ship has been made considerably clearer by these investigations.
Therefore, assuming conditional ambient air temperature, wind velocity and duration of icing on ships from the abovementioned materials, and picking up four vessels, whose navigations are scheduled in the northern waters, the amounts and heights of centres of gravity of ice accreted on them are estimated, and the change of ships' stability between before and after icing is also presented.
It is also indicated that the centre of gravity of ice accreted on ship can be estimated satisfactorily by these theories.
Finally, the author has made a comparison of the two kinds of amounts and centres of gravity of ice accreted on various types of patrol boats and two fishing vessels estimated by these theories and by the USSR icing norms respectively.
It is pointed out through the results of the comparison that the USSR icing norms contain some defects basically and new icing norms are proposed by the author on the basis of the already reported investigations and studies.

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In this paper, a new method to determine the manoeuvrability of ships by using some kinds of phase portraits is introduced.
When we want to determine the stability indices T₁T₂/K and (T₁+T₂) /K by Bech's method, it is much necessary to assess the derivative ψ=ψ (dψ/dψ) with enough accuracy. However, it is difficult to do so because the yaw rate signal measured on the board containes many noises. On the contrary, this new method makes good use of the areas of limit cycles on the phase portraits instead of the time derivatives (ψ, ψ, ψ), at certain instants.
The validity of this method is verified by some trials on the analogue simulator. Moreover this method is applied to the analysis of the modified zigzag manoeuvres of a certain real ship and is proved to be very useful.

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Derectional stability and steering control of a ship can not be concluded merely by defining the dynamic behaviour of a ship itself; rather, it is the problem of the dynamics of a closed-loop feed-back system which is composed of a ship, steering gear and a human or mechanical helmsman.
The control behaviour of human helmsmen is highly complicated and its modelling is not an easy matter, yet the closed-loop analysis on steering control under manual steering is of great interest, since every ship is operated in that manner in narrow and crowded water where steering control is of vital importance.
In this aspect, the introduction of a real-time, analogue simulator will be useful. The present paper relates to this kind of simulator studies with particular emphasis on course-keeping performance of dynamically unstable ships under manual steering.
Some of the results are discussed, including the “limit-cycle” steering which appears unavoidably in course-keeping of unstable ships and the effect of the time scale factor L/V on the ease of steering of unstable ships, where L denotes ship length and V, ship speed. A brief description of the facilities is also given.

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In order to manoeuvre a gigantic ship easily, some devices such as auto-pilots and yaw rate indicators have been equipped on board to keep and/or alter ship's course. Also, for the abovementioned purpose, there are some studies concerned with a time optimal control to alter ship's course [1, 2, 4] and an improvement of ship's manoeuvrability by means of a subsidary automatic device [5, 10].
This paper deals with a subsidary automatic control system which is a kind of the time optimal steering for ship's steady turning. The proposed control system has a yaw rate input instead of a rudder angle which is given by helmsman through a steering wheel, and has a feed back loop of yaw rate and can improve the quick responsibility of a ship to almost maximum degree without destroying turning ability. It is, therefore, expected that the helmsman can control easily and quickly even for a ship whose course stability is unstable.
In this paper, the required time to set the ship's turning steady by the automatic control system is compared with the times by the time optimal steering and the ordinary steering by using of the digital computer simulation of ship's manoeuvre.

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It has been shown in the previous paper, that the extreme value in the long-term distribution of wave bending moment expected to be exceeded with the probability of 10^-8 or near order is ruled by only probability of encounter of one or at most several severe wave conditions. This is caused by the composition of the long-term distribution of it. The distribution is composed by various short-term distributions which are described by the Rayleigh distribution.
In this paper, it is shown that the extreme values in the long-term distributions of such various random variables as wave shearing force, various wave loads, pitching and rolling angles, heaving amplitude, various accelerations caused by ship motions etc., which have the same composition as that of wave bending moment, have the same character. And a new simplified method of estimating the extreme values with high accuracy is suggested.
The method not only simplifies the calculation, but also can be applied to the analysis of relation between the extreme values and various factors which have influences on the values. As examples of the application of the method, the influences of operating conditions such as change of course or ship speed in rough seas, etc., and wave conditions, on the extreme values are analyzed in detail. Judging from the foregoing studies, it is concluded that the extreme values are to be estimated on assumed operating condition that the ship sails always heading sea course at very low speed (heave to condition) in short crest irregular waves.

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Hitherto, the Coulomb theory based on the theory of rupture surface has been adopted to estimate the ore pressure in a hold of an ore carrier. It introduces an approximate method for determining the stability of foundations, walls and slopes. As is indicated by experimental studies, this theory is inadequate for the present purpose.
Granular media compacted in a closed space show the elastic property accompanied with well-known characteristics as the dilatancy, and the elastic behaviors should be taken into consideration for the estimation of ore pressure.
Since Boussinesq, several authors have suggested constitutive equations for granular media by modifying Hooke's law. But these equations cannot be derived from elastic potentials, so that they cannot describe elastic deformations of granular media.
In this paper, the authors propose a nonlinear constitutive equation which shows the dilatancy phenomena. By choosing coefficients adequately, this equation is in comformity with the results of the triaxial compression test in a wide range. On the basis of this constitutive equation, stress distributions can be calculated easily by the finite element method. An experiment was performed with granular media in a cylindar subjected to non-uniform axial compression and the pressure distributions can be predicted approximately by the elastic theory.
For the precise determination of behaviors of ore, the elastic-plastic theory should be introduced, and the present constitutive equation may easily be applied with the aid of the Drucker-Prager theory of plasticity.

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This paper deals with a method of the theoretical calculation of the lateral wave loads (i. e. shear force, bending moment, and torsional moment) acting on ship's hull in oblique regular waves.
The strip theory utilizing the hydrodynamic coefficient obtained by Tasai's theory is applied to this method, and a correction is made on the viscous roll-damping coefficient.
In the calculation of torsional moment, the effect of shear center height is considered.
The longitudinal distributions of lateral wave loads exerting on a typical ship model are shown herein. Then comparisons are made between the calculated values and the data of experiments carried out at several model basins.
The calculated and measured values of the lateral wave loads-especially, of the lateral shear force and lateral bending moment-are in good agreement with each other. However, the calculated values of the torsional moment are, in some cases, slightly different from the measured values.
This calculation method seems to be practical in predicting the lateral wave loads as a preliminary design stage routine, though it is necessary to obtain more accurate evaluation of distribution of roll-damping moment and transverse moment of inertia along the ship's longitudinal axis.

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In order to obtain the collapse strength data on the spherical shells suitable to the pressure capsule of DSSV, collapsing tests were conducted using spherical shell models by means of MHI 1, 200 kg/cm² hydrostatic tank. These models were made from several kinds of materials including ultra-high yield strength steels such as 18% Ni maraging steel, 10% Ni dual-strengthened steels etc., and machined into near-perfect spherical shape or spheres with initial imperfection of various, thicknesses.
From these experiments the following conclusions are obtained :
(1) Collapse pressure of relatively thick shells (h_a/R₁₀≥0.03) agrees to the theoretical inelastic buckling pressure by Gerard et al.
(2) The effect of initial imperfections are evaluated by local radius in case of relatively thick shells. But for thinner shells, this method is not sufficient and nonlinear elasto-plastic analysis will be required.
(3) Present results will not always agree with Krenzke's data, especially in thinner shells with flat spot.
(4) Fracture appearance of collapsed shells are closely related to the fracture toughness of materials.

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The most ship structures are composed of plate elements. When appropriate stiffeners are furnished on plates, the buckling strength of the plates increase effectively, as well as their bending rigidities.
The finite element method has been expanded to analyse the buckling strength of ship structures. While the finite element method is very useful, the size of equations obtained by the method is extremely large.
In the paper, a powerful eigenvalue economizer technique was introduced, which reduces the degrees of stability problems. As a basic example of the application, the accuracy of the solution by the technique using the finite element method was examined for several kinds of stiffened plates in relation to the number of degrees of freedom. The authors discussed mathematical meaning of the eigenvalue economizer technique. Variable informations are obtained on variables which are eliminated from the characteristic equation.
Finally, the buckling strength of transverse ring of large tanker was analysed, varying the location of stiffeners. It was found that the ship structure without any stiffener buckles under applied load. While, the structure with horizontal and diagonal stiffeners was found not to buckle under the load.

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The research on the analysis of plate structures has a long history and a number of kinds of method for analysis have been proposed. The Finite Element Method, which is characterized by its systematic analytical process and generality for application, may be the most powerful method among them.
However, it has disadvantages that the number of unknowns becomes large and that a relatively long computing time is needed for good accuracy. In a case where shapes of main plate elements composing plate structures are simple and moreover they are orientated in one direction, these features may be seen in many actual plate structures, it is one way to adopt the Finite Strip Method which has been developed successfully for bending or vibration problems of plate structures by Y. K. Cheung and others.
In this paper, it is treated how to deal with stiffener elements in the Finite Strip Method. It is assumed here that stiffeners are not so deep that they can be treated as beams, which implies that the section do not deform. In addition to longitudinal stiffeners mentioned roughly in the previous paper on the buckling analysis of plate structuers, transvers stiffeners with arbitrary section properties and locations are treated.
It is presumed that the basic concept on transverse stiffeners may extend applicability of the Finite Strip Method up to considerably wide range. Besides check calculations, the computed results were compared with the experiments for the several kinds of simple plate structuers and the accordance of them was satisfactory.

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Structural elements of actual structures usually have several kinds of imperfections ; initial deflections, residual stresses, unexpected discontinuities of structural components and so on. These imperfections may severely weaken the strength of structures designed based on the ideal states of structures.
It is necessary to clarify the effects of imperfections not only qualitatively but also quantitatively. The theoretical analysis of the structures with imperfections, however, will not so easy in many cases partly because linear problems will become non-linear ones and in some cases two dimensional problems will become three dimensional ones and partly because it will be difficult to consider a suitable analytical models for so small amount of imperfections.
In this paper, the effects of initial deflections of columns on the compressive maximum loads are investigated where columns are assumed to be under the combined states of axial compression and one-dimensional bending.
The compression tests of 20 rectangular section columns and 8 H-type section columns with sine half wave type initial deflections were conducted.
The analytical solutions were computed by using incremental Finite Element technique. The accordance of both results was satisfactory.
Moreover, the maximum compressive loads of columns with irregular type initial deflections or with rotationally restrained ends were obtained theoretically.

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This paper presents the results of experimental test on the transverse strength of 120, 000 DWT, class bulk carrier built by MHI in September 1970.
The test was carried out under light loaded afloat condition by filling sea water into the cargo hold/water ballast tank, and the measurements were made on the stresses of double bottom structure, hopper tank, topside tank and side frames as well as the deformation of the hold.
On the other hand, theoretical analysis was made by using a 3-dimensional frame structure model. Furthermore, in order to examine more accurately the stress distribution of the members in hopper tank and topside tank, calculation was carried out by finite element method.
The general conclusions obtained from this investigation are as follows :
(1) In general, theoretical predictions show a fairly good agreement with the experimental results. Accordingly, it is concluded that the reasonable estimation on the transverse strength of bulk carriers can be made by this analytical method of 3-dimensional frame structure model.
(2) Comparatively high stress consentrations were observed at the ends of longitudinal girders and floors.
(3) Hopper tank is very effective for the strength of double bottom structure in this test condition. Boundary condition of the double bottom seems near to fixed one.
(4) Almost of the shear force in floor plate flows into the sloping transverse member of hopper tank.
(5) The degree of the end fixity of the hold frames connected to balancing brackets is about seventy-five percent of those connected to transverse rings.

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Dynamic collapsing of side structures of an ore carrier under non-impulsive wave pressure is investigated theoretically and experimentally. The damages due to impulsive wave pressure are restricted to local ones such as dents of shell plates, because the duration of peak pressure is very short and consequently the momentum is small in spite of its high peak value. On the other hand, non-impulsive wave pressure may cause serious damages in side structures widely because of its long duration and its large momentum, though it has comparatively small maximum value.
In the present paper, the following items are clarified :
(1) Non-impulsive wave pressure may yield vital damages in an ore carrier, if it goes beyond the maximum strength of the wing tank structures.
(2) The amount of deflection of the side shell caused by non-impulsive wave is almost two times as much as that calculated by the statical analysis.
Dynamic response of side structures in oil tankers may be studied along the same line of thought.

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In regard to oil tankers of apploximately 130250 thousand ton deadweight, optimum design of longitudinal strength members is undertaken. Ship size, main proportion, transverse web space and so forth are varied. Rule requirement specified by the ship classification society of Japan is adopted as standard for design. A kind of nonlinear programming techniques, SUMT is used for numerical search. By some numerical results obtained, trends of optimum longitudinal frame space, frame area and plate thickness are examined. Furthermore the influence of using high tensile steel combined with mild steel and that of taking account of fabrication cost are studied.
Main conclusions are as follows :
I In comparison with actual design, optimum longitudinal frame space, frame area and bottom plate thickness are larger, hence steel weight of midship section decreases by 13%.
II As ship size increases, both longitudinal member size and steel weight of midship section increases, however steel weight per cargo space decreases.
III When 50 kg/mm² high tensile steel is used combined with mild steel, steel weight decreases by about 12%, while steel cost remains almost unchanged.

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Stress fields near crack tips in elastic body can be specified by the stress intensity factors which are closely related to the stress singularities arising from the crack tips. These singularities, however, cannot be represented exactly by conventional finite-element models. A new method for the analysis of stress intensity factors in cracked plates is proposed in this paper on the basis of the superposition of analytical and finite-element solutions. This method is applied to several two-dimensional problems whose solutions are obtained analytically, and it is shown that their numerical results are in excellent coincidence with analytical ones. Sufficiently accurate results can be obtained by the conventional finite-element analyses with rather coarse mesh subdivision. Computational efforts are then considerably reduced compared with other methods.

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The brittle fracture initiation characteristics have successfully been investigated in terms of COD concept in these few years. The COD concept seems to be promising as one of the possible useful fracture criteria to assess the fracture behavior of steel structures. In order to clarify the significance of defects in structures and select the proper materials, it is very important for the fabricators to be able to obtain the critical COD value from small sized and simple test. The present authors have investigated the effectiveness and utility of COD bend test as one of the fundamental material tests. The bend test specimen can be made smaller and can fracture at lower load, so that it could be very useful testing method from the industrial point of view.
But one of the troubles associated with the measurement of critical COD on a bend specimen is that the notch tip COD is not so easily obtained for bend test as for tension test. So far a COD value is estimated from the clip gauge reading using “rotational factor”, on the assumption that a notched bend specimen rotates about a sort of “pivot”, the location of which in the specimen is dependent of applied load.
In this paper the method of determining COD value at notch tip in a bend specimen is disscussed on the basis of the results of experiment and calculation using the Dugdale-Barenblatt crack model in bending stress field and Finite Element Method. It is revealed that the critical COD value can be obtained only from fracture load of bend specimen.
The COD bend test were carried out with various specimen size and notch acuity for the purpose of clarifying the characteristics of critical COD value. It is confirmed that not only the critical COD value obtained from COD bend test compares well with that obtained from tension test but also it is independent of specimen geometry to a certain extent.
Finally the tentative method of COD bend test is proposed as a fundamental material test.

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In the soft welded joints having notches in the weld metal, plastic deformation at the notch tip will be held in check by the stronger base metals. In the present report, effect of plastic constraint caused due to mechanical heterogeneity on brittle fracture initiation is investigated. Notched wide plate with groove tensile tests (Groove Deep Notch Test) were carried out as a clue to elucidate effects of plastic constraint on plastic behaviors at crack tip and critical crack opening displacement, and deep notch test of soft welded joints which have saw cut notches in weld metal was carried out. The main results obtained are summarized as follows :
(1) As the plastic constraint factor becomes larger, the applied stress required to produce a constant crack opening displacement becomes larger (Fig. 9) and the critical crack opening displacement Φ_c becomes smaller (Fig. 10). The brittle fracture net stress is maximum at a certain value of plastic constraint factor (Figs. 3, 11).
(2) The relations between the applied stress and crack opening displacement for various values of plastic constraint factor can be calculated by considering increase of the general yield stress due to plastic constraint (Figs. 9, 16).
(3) In the practical soft welded joints, the brittle fracture strength is affected more considerably with fracture toughness than yield strength of weld metal.

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In the welded joints, it becomes a common idea that the strength of weld metal is equal to or higher than it of base metal from the viewpoints of efficiency of welded joints. Otherwise, it is effective to use the weld metal whose strength is lower than it of base metal in order to prevent the initiation of weld cracking. In this report, the static tensile behaviors of the welded joints having weld metal whose strength is lower than it of base metal --so called “Soft Welded Joints” --are investigated. The “all soft welded joint” in which all weld metal are soften metal and the “partial soft welded joint” in which only a part of weld metal is soften metal were made by metal-arc welding. The main results obtained are summarized as follows :
(1) The strength of the welded joints using soft weld metal whose strength is lower than it of base metal is much elevated from it of the soft weld metal itself. It is effective to use soft weld metal in a part of weld metal from the viewpoint of efficiency of strength.
(2) The two standard strengths are considered as the required strength σ_u of welded joint, or
(i) σ_u≥σ_u^B
(ii) σ_u≥ (guaranteed strength for design).
The “Soft Ratio” S_r of weld metal required to guarantee the standard strength and the elongation of welded joints are considered (Table 6). When S_r (=σ_u^W/σ_u^B) ≥0.93, ultimate tensile strength and elongation of all kinds of soft welded joints become almost equal to those of base metal.

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The characteristics of fatigue crack propagation from a surface flaw under cyclic bending stress are studied experimentally and the propagation rate is related to the stress intensity factor range.
Measurement of crack configuration is made using electric-resistance probe method. The stress intensity factor for semi-elliptical surface crack is calculated using stress intensity magnification factor proposed by Kobayashi et al.
It is concluded that the initial flaw size has little effect on fatigue crack propagation rate, but the range of applied load has considerable effect. This suggests that the maximum value of stress intensity factor should be taken into account as well as the stress intensity factor range.
Fatigue crack propagation rate in bending test is compared with that in tensile test. It is shown that the former is a little lower than the latter.

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A series of research for clarifying the brittle fracture initiation characteristics of narrowly spaced notches, has been carried out following the research reported previously (1st Report). Firstly, tensile tests were conducted at room temperature by using test specimens of 200 mm width, and thereby interaction effect of narrowly spaced notches were analysed by means of measuring the crack opening displacement by Moiré method. Secondly, brittle fracture tests were conducted at a low temperature (-160°C) by using test specimens of 400 mm width.
The above analyses and tests were respectively carried out for four kinds of neighboring notches, viz. equal length collinear notches, unequal length collinear notches, equal length parallel notches and equal length parallel staggered notches. Steel material tested was a 60 kg/mm² high strength steel.
The results of test were summarized as follows :
1) From crack opening displacement which is measured at room temperature by Moiré method, it is possible to estimate fracture stress of narrowly spaced notches.
2) Fracture stress of notches arranged in a straight line which is perpendicular to load direction, becomes lower in comparing with that of a single notch, and decreases with distance between notches.
3) Fracture stress of notches, which are arranged in parallel and perpendicularly to load direction, is higher in comparison with that of a single notch and increases with decreased distance between notches.
4) Fracture stress of equal length parallel staggered notches, having the characteristic which combines the equal length collinear notches and equal length parallel notches, varies complicatedly depending upon the location of notches.

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In order to investigate the low-cycle fatigue performance of plates under hydrostatic pressure, four cubic boxes with 600 mm of each side were fabricated from 20 mm thick plates of Q & T high tensile strength steel (HT 70), and internally pressurized cyclically at peak nominal stresses comparable to the yield strength of the material.
From these experiments the following conclusions are obtained : -
(1) Cracks initiate at the toe of weldment of corner joints inside of the box, at about 1, 500-4, 000 cycles.
(2) Number of cycles for crack initiation and average crack propagation rates are related to total strain range.
(3) Weld contouring on the corner joints by grinding has little effect on the cycles for crack initiation, however, reduces the possibility of crack initiation.
(4) Boxes made from high notch-tough materials begin to leak when cracks propagate through the plate thickness, and no unstable fracture will occur.

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As a part of labor saving design of ship's hull, usefullness of the straight type structure were investigated.
In the Western and the Northern Europe, the ships having straight type structure members have been built. But this type is not generally used, especially in large ships.
One of the reason is that the fatigue strength related with the stress intensity of the detailed structural part is not yet known clearly.
As for the former research on the straight type structure members, preliminary analysis of the stress and man hour were done at the 110 th division of Japan Ship Research Association and Mitsubishi Heavy Industries, Ltd..
As the result of the research, on type of the structure was picked up as the type of practical use.
Our research is composed of Program Fatigue Tests and analysis of the results based on the Linear Fracture Mechanics, and purpose of the research is to estimate the safety of the straight type bracket.
The experimental models are 1/2.5 reduced scale of 200, 000 ton tanker's bilge corner and strut end.
From the experimental facts and the analytical studies, we may anticipate the practical application of the straight type structure without fatal damages.

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An investigation has been carried out to realize commercial application of welding of 9% Ni steel using ferritic filler metal having chemical composition similar to that of base steel, which was developed by the authors.
The weldments having excellent notch impact properties and superior strength were obtained by gas metal arc welding.
And the brittle fracture initiation characteristics before general yielding of the weldment was surveyed both experimentally by three kinds of the large scale type tests such as Welded Wide Plate Tension Tests, W-I Type Notched and Welded Wide Plate Tension Test and Deep Notch Test and theoretically based on the fracture mechanics.
The safety to brittle fracture before general yielding was confirmed especially at LNG temperature.

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The MCF (Mitsubishi Cupro-Ferrous alloy) which can be used as the new material for marine propellers in place of conventional copper alloys has been developed.
Although the static tensile strength of MCF is not so high, the alloy has the excellent corrosion and erosion resistance to sea water, and has the corrosion fatigue strength larger than or almost equal to that of nickel aluminium bronze.
The MCF has the material features just appropriate for propellers which are used in polluted sea water, in which conventional copper alloy propellers may be deteriorated due to the sulphur attack, and the MCF will present a great contribution to the prevention against troubles concerning surface damage unavoidable in copper alloy propellers.

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The bend parts of high pressure pipings by using high frequency induction heating are to be heat treated for stress relieving in compliance with many application standard, the requirements of the rules and regulations of classification societies and the power plant engineering standard for example.
The new bending technique was developed in order to do away with heat treatment of the bend parts of steel pipings, which are satisfactory and adequate in mechanical property and change in wall thickness and shape of the bend parts.

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To the forming of curved shells of ships, the line heating method is extensively applied. However, the line heating method is not suitable for automatic operation.
The authors investigated a new system of plate bending, which is composed of a universal press with multiple piston heads. The universal press with multiple piston heads is quite suitable for numerically controled operation. Yet, there exist many problems which must be solved before the universal press is in practical use.
In the paper, the authors conducted experimental investigation of plate bending by small press with a solid head (10 ton) and large universal press with multiple piston heads (500 ton). Various informations are obtained on the reproduceability of the results, the fairness of curved plate after bending, the amount of spring back after bending, the effect of pitch of multiple piston heads, etc.
The authors also carried out theoretical investigations into the deformation of plates and proposed valuable empirical formulae.
In the next paper, the authors will discuss the results of investigation into the various problems which arises from the numerically controled operation of the universal press with multiple piston heads.

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This paper describes primarily progress during the last two years in the areas of wave induced motions and loads, finite element technique, and propeller induced loads and propeller design. Various examples are given to reflect applications to hull as well as machinery structures.

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