Recently some researchers made attempts to make clear the effect of shapes of frame lines on wave making resistance. It is obvious that we can not obtain any informations about it from the Michell's thin ship theory.
Then, the authors developed a method to estimate approximate source distribution over the hull surface by making use of the slender body theory, and show that the result obtained by this method, for the model of Series 60 (C_b=0.60), agrees with the three dimensional solution calculated by J. L. Hess and A. M. O. Smith. They also calculate the wave making resistance of the ship represented by this source distribution, and the stream lines around a ship hull, which are compared with the experimental results.
In this procedure each transverse sections of the ship is approximately represented by Three-Parameter sections.

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The wave resistance and amplitude spectrum of two geosim-models (L_pp= 4 m and 7.5m) and their actual ship (L_pp=130m), were directly determined by means of the longitudinal parallel cut of their wave patterns, which has been developed by Newman and Sharma.
Through this investigation, the authors discuss the following problems to be solved for the practical application of the newly developed experiments.
The effect of the transverse location of the measuring probe on the results of the experiments, was mainly caused by the error due to local disturbance in the vicinity of the model and also due to the truncation of the records of wave pattern. The authors show that the truncation error is far more significant factor than the other and that it is mainly governed by the ratio of Y/M, in which M and Y are the length of records and the distance of the measuring probe from the center line of the towing tank, respectively.If the wave resistances were determined in the same condition for the ratio of Y/M, the scale effect of the wave resistance seems to be minor factor.
Some experiences in the experiments on determination of wave resistance of the ship, are also briefly explained.

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We can examine the validity of the wave-making resistance theory by the method of wave analysis. In order to investigate the discrepancy between the theoretical and experimental free wave spectrum, wave analysis was carried out for three Inuids, M-6, M-7 and M-8, at the speeds K₀L=14, 12, 10, 8 and its results were compared with theory. These Inuids were calculated from source distributions which were of the same form but different source strength. Therefore assuming linear theory they must generate free waves with the same form and linear relation between each other.
As for the free wave spectrum of M-6 (B/L=0.08), M-7 (B/L=0.13), linear relation generally held but agreement was very poor between the phase and the amplitude at small θ of linear theory and experiment.
Then the equivalent source distributions which gave the same free wave spectrum with the one obtained from wave analysis were calculated and compared with the theory.

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造波抵抗理論が船型計画に役立つためには, 造波のメカニズムがあきらかにされねばならない。その手段として, 波形解析があることは周知の通りであるが, この場合, 粘性影響が介入しない船首波を単独に抽出することが必要である。前回の報告では, 実測船首波系のradial cut profileと, 船首自由波に対する漸近展開式を対応させ, これより船首波の“実測”振幅関数を求めるプロセスについて述べ, かつWigley船型に対する適用例を示した。
前回は, その予備的な性格から, 模型船もありあわせを使用したため, その長さ (2.5m) も東大水槽の幅 (3.5m) に対してはやや過大であり, 船型と特異点の対応もMichell近似をそのまま使用し, また波紋の理論計算においても, 局部波を省略したり, 自由波をSin波のみで代用 (ただし+0.06Lの位相前進量を見込む) するなど, いくつかの粗い取扱いをおこなつている。
次のステップとして, このような欠点を改良しながら般首波に重点をおいた波形解析を, 基礎的な問題にまで立戻つて系統的に実施することは, 当然必要なことと考えられる。現在このような見地に立つた研究が, 東大をはじめ, 九大・船研などで共同的・平行的に進められているが, 以下はそのうち東大水槽で, 過去1年間に分担実施されたシリーズに関する第1報である。

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Mitsubishi Experimental Tank has been noticing the unstable phenomenon sometimes observed in the self-propulsion test of full ship models and endeavoring to make clear this phenomenon since several years ago.
It was found recently that the velocity field at stern of such a model showing the unstable phenomenon varies distinctively with the action of propeller.
The velocity field at stern of such a model in the case of self-propulsion test is remarkably influenced by the propeller loading and it tends to the velocity field in the case of resistance test as the propeller loading is decreased to zero.
It is not clear yet whether such a phenomenon exists on an actual ship as well. However, from another study made by Mitsubishi Experimental Tank, it is probable that the phenomenon is peculiar to model due to insufficient Reynolds number, even if a seven meter model is used. Then the meaning of model test becomes questionable and the study on ship-model correlation becomes to be burdened with another difficulty.
In order to design a superior ship form in such circumstances, it is the wisest way to have as many reliable data as possible on the ship-model correlation of full big ships and to advance the study of better ship forms recognizing the existence of such an unstable phenomenon.

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Wave excitation has been calculated by Grim based on the diffraction potential for two dimensional bodies of Lewis form sections.
On the other hand, it has been suggested by Newman making use of Haskind relation that wave excitation could be induced from the radiation potential for which many works have been done by Ursell, Tasai and Porter on two dimensional bodies of Lewis form sections.
In this paper, the author deals with the wave excitation due to beam seas on two dimensional ships of arbitrary sections making use of singularity distributions on the ship surface. The radiation potential induced by such singularity distribution was calculated, and the wave excitations for heave resolved into in-phase and out-of-phase components were obtained making use of the Kochin function.
The author also extended the same technique into calculation of wave excitation in oblique waves including head seas.
The calculation on wave-excitationless ship forms was performed, which showed satisfactory agreement with model experimental results. The calculation on three dimensional wave-excitationless ship forms was also done by means of the Strip Method. The results were in good coincidence with model experiment data.

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A simplified calculation is carried out to solve non-linear, non-symmetric rolling of ship in relation to the critical conditions of ship capsize.
Non-linear heeling moment due to the coexistence of non-zero average rolling angle and relative heaving is taken into consideration and its significance to ship stability is fully recognized by the calculation.
An example of this calculation to estimate the critical wind velocity and the wave height of a cylindrical model shows fairly good accordance with experiment.

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This paper deals with the effectiveness of U-tube type anti-rolling tanks paying particular attention to the following four points :
1) Effect of the vertical position of the tank from the center of gravity of a ship.
2) Effect of saturation i. e., performance of a tank when the tank water hits the top of the tank and is prevented its motion.
3) Effect of non-linearity of ship motion as well as tank water movement.
4) Effectiveness of tanks in transient states.
For 1), the author showed a simplified form of expression for the effect of the vertical position and showed that the effective strength factor of a tank was evaluated by multiplying (1-ω²_s/ω²_st) to the strength factor of the tank where ω_s is the natural frequency of the ship and ω_st is the de-coupling frequency of the tank.
For 2), the author showed that the effect of saturation caused not only the reduction of tank moment but a phase lag resulting in considerable decrease of tank effectiveness.
For 3), the author discussed the tank effectiveness introducing nonlinear terms.
For 4), the author showed that a tank was not sufficiently effective for transient stages.

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Considering the possibilities of solving the non-linear equations of motion numerically on a digital computer, the author contrived a method for numerical calculation of the steered motion of ships in uniform wind and flow.
The aerodynamic forces and moments and the longitudinal hydrodynamic force were taken in as the intermittent functions of relative wind direction and the Froude number respectively, and were interpolated at need. The so-called rotary derivatives were decided by a least-squares method, up to the third order of transverse velocity, turning rate and rudder angle, from the tested points at various values of the parameters.The equations of motion were described on the absolute motion of ship, and the external and intertia forces and moments caused by the relative motions were calculated at every small time intervals and integrated.
As an example, calculations were carried out on a mammoth tanker regarding the required lowest speed and the course stability in a straight course and the turning behaviours in wind and flow. Results of the calculation on the turning characteristics in calm sea were compared with the tested results on a free-running model and on the actual ship.
The following conclusions were obtained concerning the method of the calculation and the calculated results on the steered motions of a ship in wind and flow.
(1) The non-linear equations of the un-steady motion of a ship can be calculated numerically on a digital computer.
(2) The required minimum speed and the course stability on a straight course within the limits of definite rudder and drift angles can be calculated.
(3) In some cases the course stability index has a periodic solution.
(4) At the above-mentioned minimum speed, the ship tends to be course-unstable mainly in case of heading flow and of following wind, though the stability is improved by the higher ship speed.
(5) The effect of wind and flow change remarkably according to the loading condition of ship.
(6) The average direction of the macroscopic “drift” of the steadily turning ship does not necessarily coincide with that of the uniform wind or flow, and the average speed of the “drift” is smaller than that of wind or flow.

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船の操縦運動を論ずるとき, 非線型性を考慮する必要性が痛感される。そこで静水中の操縦運動について流体力 (モーメント) および操舵装置の非線型性を考慮して考察する。本論文において取扱う運動を (擬) ステップ応答と周期運動に限定して, 運動方程式を導き, この運動方程式を近似的に解く。

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A set of four characteristic figures-K, T₁, T₂ and T₃-provides a full description of the response behaviour of a ship to steering [ref. 1]. Although a simplified analysis based upon this idea (so-called K-T analysis) has a wide popularity to measure and to assess manoeuvrability of ships, the four constants above-mentioned should be called upon to describe the response perfectly in the analysis and synthesis of steering control of a ship, taking an automatic steering device and/ora human operator into account [2].
This paper relates to a new procedure of defining these four characteristic constants using a radio-controlled, free-sailing model. This is also adoptable to a full-size experiment in principle.The procedure employs two kinds of manoeuvres ; a parallel shifting of ship's path and periodic steering with a fixed amplitude and a number of frequencies. Both manoeuvres can be performed in a conventional towing basin. The periodic steering results and harmonic analysis of the parallel shift manoeuvre give an enough information to assess the transfer function (frequency response function) of a ship, which, in turn, yields the characteristic constants K, T₁, T₂ and T₃.
These constants are composed of the eight stability derivatives (coefficients of the linear equation of motion), so that we can define these derivatives through the present procedure if four of these derivatives are given by any other sources, for example, oblique towing test.
The data involved were obtained at the Osaka University Experiment Tank (80 mx7mx 3. 6m) employing two 4. 5m models out of Todd's 60 series.

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To calculate the absorbed energy by the flacture of ship's structure in case of collision, it is necessary to estimate accurately the added mass of striken ships.
Minorsky has proposed in his famous paper to use 0.4 for the added mass coefficient of striken ships. In this paper, the authors tried to obtain an exact expression of the hydrodynamic force which will act on ships during a collision by theoretical calculations and series of model experiments on the first atomic-powered ship of Japan were conducted.
As a result, the authors have shown that the ratio of external force to the acceleration of the striken ship varies with the time elapsed during the collision : i. e., the added mass of the ship is not constant during the collision. From this result, the authors introduced an equivalent added mass which, dividing the external force by it, will give an acceleration equal to the exact value of acceleration at the end of the collision.
It was also shown that this equivalent added mass changes its value with the “duration” of the collision. If the duration is infinitely small, the equivalent added mass is equal to the added mass for infinite high frequency. This agrees with Minorsky's assumption. However, if the duration is finite, the equivalent added mass becomes larger as the duration increases.
Since the duration is only related to the initial speed of the striking ship and the amount of penetration, and lower the initial speed or deeper the penetration the longer the duration, the equivalent added mass coefficient will be much greater than 0.4 in the case when a soft structured ship is striken by a low speed ship resulting in a considerable amount of penetration.

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At first, in order to obtain the manoeuvrability and response to wind, waves and oblique current, various experiments on a 1.3m self-propelled model of passenger ship were carried out in the circulating water channel. Utilizing these values, the optimal control system of this model, which reduces the following integral to a minimum, was analysed.
I=∫^t_t0 {γ₁ (Δη) ²+γ₂ (Δθ) ²+δ²} dt
where
Δη : trajectory error
Δθ : azimuth error
δ : helm angle
γ₁, γ₂ : coefficients
t : time
Moreover, the experiments of optimal automatic navigation on settled route with this ship model were performed by use of above calculated value in calm water, wind, waves and oblique current, in circulating water channel.

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This paper reports the results of manoeuvrability experiments (spiral and zig-zag tests) of three small tankers, which are course-unstable. Experiment were carried out those with or without skeg, and with single or twin rudders.
The major conclusions obtained are :
1. The effect of skeg is notable. The skeg of which area is about Ld/45 reduces the spiral loop width from 910° to 12°.
2. The difference between single rudder and twin rudders is not so larger, as far as the results of experiments concerned. However, the ship with twin screws and twin rudders is better than other ships, when steering near the wharf.
3. Even if an unstable loop exists in γ'δ curve, steering ship is not always difficult, and 23°is allowable in the case of these examples withV/L=0.090.1 (1/sec).
But steering ship becomes difficult when the spiral loop width is over than 910°
4. In conclusion, ships of these types with twin screws, twin rudders and skeg are best in steering.

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Coupled vibration of ship hull with bottom has been treated theoretically and the equation of motion has been derived where the main hull is simulated as Timoshenko Beam and the bottom as orthotropic plate. The numerical solution of the equation has been coded in the digital computer. The results of test calculation agree with those derived by Prof. Yamakoshi and Mr. Ohnuma.
Qualitative investigation, including the examination of the effect of the transverse bulkheads, has been made on a box beam model whose particular such as rigidities and weights of hull and bottom are nearly equal to those of the midship part of 20, 000 tons D. W. bulk barrier. It is found that the vibration characteristics become very complex in the higher modes due to the effect of coupled vibration and the deviation from the beam theory is quite prominent. The transverse bulkheads make significant influence on the frequency and mode of the vibration.

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The vibration of a container ship has been studied with a chief attention to the horizontal and the torsional vibrations. Some checks on the problems of structural behaviour and of the added virtual mass of water have been made. Centre of virtual mass of water is calculated for the Lewis form sections. The model experiment has been carried out to check the behaviour of coupled vibration. At the last the experiments in a full scale container ship have been made, using the vibration generator and in the sea trials. It is found that the problem is pretty complicated and many investigations are necessary in order to clarify the mechanism of coupled vibration and the rigidities in the torsional vibration. Horizontal vibration, though it is complicated due to the coupling with torsional vibration, is more accessible. The characteristics of the vertical vibration of the container ship are qualitatively the same as those of conventional types of ships. The bottom vibration is significant in the vertical vibration of higher modes which is likely to reduce the natural frequency of the vertical vibration.

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From the standpoint of the transverse strength of ships the joint probability distribution (short term) of the hydrodynamic pressure on the ship side and on the bottom in irregular seas was discussed. For typical cargo ship and oil tanker in long-crested irregular head seas, correlation coefficient of the pressure on the side and on the bottom and regression coefficient of the pressure of the ship side were calculated by means of the linear superposition principle.

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The study on elasto-plastic analysis of framed structures based on the plastic hinge concept has been greatly developed by use of matrix method, and on the elasto-plastic in-plane instability problem of columns with pretty high axial force, a great deal of work has been done experimentally and also analytically, especially by CDC method. As to the elasto-plastic instability problem of columns subjected to high axial force and also hi-axial bending moments, several kinds of analytical method have been published. However, in most work, the kind of applied load is limited to eccentrically axial loading and more over the computation is complicated. In this paper, simplifying theory by neglected torsion effect and adopting a new concept with respect to bending stiffness of a section, a unified method for computing the elasto-plastic behaviour of columns subjected to axial force and also to bi-axial moments is proposed. Many kinds of column problems will be able to be solved by use of this method, for example, a column with initial deflection, bi-axial eccentricity and a column with loading-program.
The computation results were compared with the experiments of four H-section columns with loading-program, and it showed that this method is useful to predict column behaviour in elasto-plastic range.

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Non-linearity in structural Analysis is caused in most cases by two factors ; one is plastification of material and another is finite deformation. These two factors usually make the analysis so complicated that it is difficult to obtain the exact analytical solutions. Therefore, numerical analysis is used to get approximate solutions. In this paper, as a first step for solving square plates subject to lateral pressure, one approximate numerical procedure is used for solving the same kind of problem of strip plates. This procedure is based on linearization of non-linear equations by the concept of small increment and on solving these linearized equations by finite difference method.
From the fact that analysis of strip plates can be regarded with good accuracy as the analysis of square plates subject to lateral pressure, provided that their aspect ratios are over about 3, the strip plates have been investigated by several researchers analytically and experimentally. The comparison showed that the computed load-deflection curve by the procedure in this paper coincided with the experimental ones published previously with fairly good accuracy. Another results of this paper is estimation of the effect of end restraints of strip plates. The behaviour of strip plates with linear and non-linear end restraints were investigated.

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Since the famous paper on the postbuckling behavior of an elastic rectangular plate was published by von Kármán, much work has been done on the various geometrically nonlinear problems such as large deflection, postbuckling, snap-through and dynamic stability of elastic plates due to lateral as well as inplane loadings. Most of these studies are based on the Energy method proposed by E. Trefftz, K. Marguerre and others in which solution can be found by the stationary condition of the total potential energy of a given plate whose deflection is assumed in the form of known functional series with unknown coefficients. Numerical calculation in this method, however, is so laborious that problems of simple plate shapes, boundary conditions as well as loading conditions were only considered before high-speed digital computers became available.
A practical method of solution on the general nonlinear problem of elastic plates with arbitrary shape, boundary and loading conditions is proposed in this paper by extending the method proposed by K. Marguerre, E. Trefftz and others.
Displacement functions used are constructed by combined use of the finite element method and Rayleigh-Ritz's procedure.

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As continuation of studies on the matrix method of analysis of ship structures, displacement method of analysis was applied to study the vibration as well as buckling characteristics of framed structures and the basis for development of computer program was established with some experimental verification in this paper.

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In the previous paper, the authors developed the general form of the stiffness matrix of elastic-plastic members of one-dimension based on the plastic flow theory and presented the new method of analysis on framed structures using the matrix method.
The method was developed on the assumptions that loadings on structures are to be applied proportionally and there is no yielded section where unloading occurs under proportional loading.
In actual cases, however, it is very important to investigate the behaviors of structures under general loadings. Furthermore, the proportional loading does not always assure no unloading at yielded sections of elastic-plastic behavior of structures. This implies that unloading at yielded sections should be examined at each step of loadings. To this end, a judging method for unloading is required to be established.
In the previous paper, a quantity, A which indicates the magnitude of plastic deformation at a yielded section is assumed positive for the following step of the analysis. This quantity is however, not always positive and when it is negative, the deformation is considered to be elastic. Accordingly, unloading at a yielded section is inspected by the condition
λ<0
and loading is continued at a yielded section, when
λ≥0
In this report, furthermore, the effect of large deformation is taken into consideration and the method is expanded for the analysis on elastic-plastic behaviour of structures with large deformation and instability. In this case, unloading at a yielded section is also examined by the same condition as mentioned above.

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It is the final purpose of the study to establish a method of analysis on general nonlinear behaviors of plates……material and geometrical nonlinearitis….
In this paper, these nonlinear behaviors are separately investigated. For the behaviors of plates under incremental loading, the fundamental equilibrium equations are developed for each step of load increment which is sill of nonlinear form with respect to the resulting deformations. To eliminate difficulties in solving the above equations, higher order terms in the equations are neglected and linear fundamental equations are obtained, since the increment of loads at each step is to be kept so small that the effect of the higher order terms is estimated negligibly small on the results. Based on these linear equations, analytical methods are proposed for each nonlinear behavior, and several examples are solved by the methods with the aid of Galarkin's method.
The examples for material nonlinearlity are on elastic-plastic behavior of simply supported rectangular plates under uniform pressure and for geometrical nonlineality large deformation of simply supported rectangular plates subjected to compression, and shear at the edges with consideration of the effect of initial imperfection.
The results of the analysis verified the usefulness of the methods and assured the possibility of analysis on general nonlinear behaviors of plates.

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Hitherto, in the studies of the plastic design of steel structures, it bases on the concept of plastic hinges to determine the maximum strength of structures, or, recently in the case of high axial loaded beam-columns, the maximum load is obtained by using the method of Column Deflection Curves developed at Lehigh University.
In the present paper, the finite element method is developed for large deflection and elastic-plastic analysis of frame works by using stationary potential energy of structure.
Material and geometrical nonlinearlity are linearized by the incremental load procedure. This method of analysis is possibly used to determine the maximum strength of elastic-plastic frames, taking into account instability of frames and pursuing the spreading of the plastic region in each member of structures.
As numerical examples, the authors calculated elastic buckling of columns with eccentric loads, beam-columns under high axial loads and moments, instability of portal frames, and sidesway failure of three-story frames. It was conclusively found that the calculated results showed a fair agreement with the experimental results.

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近年の船舶の超大型化は, トランスリングのウエブ等を相対的に薄肉化し, また各種開口を有するのが通例であるが, そのために従来それ程大きな問題とはならなかつた開口部の強度が問題とされるに至つた。従つて巨大船の船体横強度, または局部強度を検討する際には, 開口を有するウエブの座屈強度を算定し, ウエブで起る座屈損傷を防止することが極めて重要である。
本報告では, 隅に矩形切欠を有する平板の圧縮座屈, 及び, 従来の円形開口板の座屈問題がすべて弾性領を扱つており, 板内に塑性領域も存在する実際の場合を説明できないことから, 偏心円開口を有する平板の弾性圧縮座屈も研究したので, それらの結果を報告する。なお, 解析は前回の報告で指摘した方法, 即ち数値解法より応力分布を知り, たわみ形を適当に選んでエネルギ法を用い, 座屈値を近似的に求めるという方法を用いた

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There are presented in this paper the results of tests on the ultimate strength of beams subjected to combined bending and axial compression. They are compared with the collapse solutions based on simple plastic theory, to determine the correlation curves of the beams relating applied bending moment and axial compression.
For ease of computations, is developed the FORTRAN PROGRAM LIST for the interaction curves of the beams with arbitrary I-section including hybrid beams.
On the basis of the interaction curves, the hybrid beams, in the flanges of which high strength steel is used, are discussed from the viewpoint of cost performance.

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In the previous report, the authors developed a particular computer program based on the finite element method for theoretical analyses on buckling of web plates with slots for longitudinals. The authors also conducted several kinds of experiments and compared the results with those analyzed by the computer program. Quite good agreement was recognized between them.
Subsequent to the previous report, the authors carried out systematic calculations on the buckling strength of web plates with slots for longitudinals and investigated the effect of reinforcement with collar plates, face plates around slots, horizontal stiffeners on web plates or partially increased thickness of web plates on shear buckling of web plates with slots.
As the results, sufficient informations were obtained on the buckling strength of web plates.
Finally, many design charts of the buckling strength of web plates with slots for longitudinals were made and presented here; they are considered to be very valuable for the design of such web plates.
Furthermore, analyses with the design charts were conducted on buckling failures of web plates of transverse rings in an oil tanker. In the study, loading conditions in which actual failures in web plates possibly occured were examined and theoretical conditions in which the failures occured were ascertained.

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In the previous report, the authors reported the results of experimental study on the effective breadth of the face plate and the skin plate of a curved girder such as bilge parts of a tanker structure.
They showed that the effective breadth of a curved plate is considerably small owing to the hang down deformation of the plate, and that it is necessary to attach many brackets to the face plate and longitudinals to the skin plates for recovering the effectiveness of each plate.
In this report, two theoretical methods, energy method and finite element method, are introduced to calculate the influence of brackets and longitudinals on the effective breadth of a curved plate and compared with the test results which were reported in the previous report.
Theoretical results show good coincidence with the test results.
Design curves, from which the effective breadth of the face plate reinforced by brackets can be obtained easily, are given.
In case of skin plates, it is showed by the results of calculation by finite element method that the stiffness of longitudinals has influence on the effectiveness breadth of skin plates.

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In our previous papers, some theoretical investigations on the strength of container ships were reported.
But, last year, the torsional strength test on the actual container ship “Hakone Maru” was carried out in order to confirm the reliability of the above torsional strength theory.
In this paper, the results of the above experimental test are described. And the following results are obtained.
1) The torsional distortion of hatch opening can be estimated by the theoretical calculation which was introduced in our previous papers.
2) The position of shear center of the vessel is considered to be at the near the base line of ship.
3) The stress distribution of hatch corner can be estimated theoretically based on four elemental stresses due to torsional distortion of hatch, longitudinal bending and horizontal bending of upper deck and axial force of cross deck, respectively.

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There have been many theoretical calculations around the holes in the first boundary condition : or the perfect rigid bodies in the second boundary conditions in a plate. Extending these studies, the author has carried out stress analysis around an inclusion with different properties in a plate. He has studied on some fundamental problems of stress concentration in the combined boundary condition.

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A new evidence for the relationship between plastic strain range and cycles to failure under strain controlled cycling condition was reported in the previous paper. It was a divergence from Manson's linear relationship.
In the present investigation analyses are undertaken from the various points of view, such as geometry of the specimen, hysteresis loop, dynamic strain hardening exponent, structural change of material and fractographic aspect.
Following test conditions were used smooth and hour glass shaped specimen, completely reversed strain controlled condition, and triangular wave form.
It was realized so far that the shape of hysteresis loop should be considered rather than accumulated plastic hysteresis energy to evaluate the low cycle fatigue life of high strength steel.
The stress concentration factor of specimen and the phase transformation of material during fatigue test don't seem to be important factors in dealing with this phenomena.

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Assuming a fatigue crack propagation mechanism, the effect of characteristics of randomized load sequences on fatigue life was discussed using numerical simulation with the aid of the electronic digital computer.
Fatigue lives under independent random load sequences were longer and showed smaller coefficient of variation than those under correlated random load sequences.
The effect of truncation of the probability density function was remarkable, the larger the minimum load, the longer the fatigue life.
The number of possible load levels, when load level is assumed discrete, should be large enough to obtain a good estimate of life.
To simplify testing method a selected load may be applied several times and changed to another one. Such simplification, however, may give shorter life than the actual.

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In this paper, for the purpose of reproducing brittle fracture at low stress levels in the welded joints of 80kg/mm² high strength steel, we have carried out a systematic investigation on fracture load conditions of surface notched wide tension test specimens, continued from the previous report about 60kg/mm² high strength steel.
Further, we considered to obtain a substantiation of fracture conditions, and suggestions for the prevention of similar troubles in future, by application of fracture mechanics for various experimental fracture conditions.
The main results obtained are summarized as follows.
(1) Brittle fracture in the welded joint of 80kg/mm² high strength steel was reproduced below yield stress levels in practical service temperature regions, by the superposition of various actual stress concentration factors such as a surface notch, angular distortion of the welded joint, welding residual stress, etc.
(2) Stress concentration factors are severer, the fracture transition region and stress transition region in wide tension test specimens are closer to each other.
(3) By application of Irwin's fracture mechanics it was possible to analyse the experimental results approximately, although the brittle fracture initiation was in a considerably high temperature region.
(4) Even when various stress concentration factors are present in superposition, it is possible to prevent the fracture initiation of the welded structure under low loading condition by mechanical stress relieving such as preloading in the higher-temperature region than the service temperature.

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Previously the authors investigated that the effect of low cycle fatigue on the brittle fracture propagation-arrest characteristics and brittle fracture initiation from fatigue crack in ordinary ship steels.
This paper concerns with some fundamental aspects of brittle fracture initiation from fatigue crack and fatigued plate in 60kg/mm² class high strength steels.
The followings have been obtained conclusively : The material deterioration due to repeated plastic straining seems to be relatively slight. The specimens with low cycle fatigue crack showed higher toughness than that of the virgin plate specimen with machined notch, for which the tilting of fatigue crack and the residual compression stress developed in crack tip zone seemed to be responsible. On the other hand the same degree of fracture toughness is observed in the specimen with high cycle fatigue crack where the above two factors are almost absent.

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In many cases, composite construction is adopted in FRP ship's hull incorporating plastic foams or woods, in order to compensate the low rigidity of the material. In such cases, the structural behaviour of the hull is very complicated for its structural anisotropy and heterogenity. The other factors to prevent the exact structural analysis of the hull are in the fact that the effectiveness of various members is rather ambiguous for the effects of the shear and the local deformation are large compared to the steel hull.
For this reason, seven kinds of the simplified FRP composite structural models are fabricated and tested. The bending behaviour of these models is discussed from the view-point of the structural effectiveness. Simplified analyses are made on the effects of the shear deflection, the incomplete interaction of the stiffeners and the main beam, and the fall of effectiveness of the compression-side flange due to local deflection. Finally, the test-results of these models are compared and discussed, defining the structural efficiency as the ratio of the so-called structural Young's modulus and the material's one.

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A 1/50 scale model of side tanks of a tanker is used in this experiment to know effects of rolling on the heat transfer from shell walls. Results of the experiment are as follow.
(1) The temperature of oil in the tank becomes uniforrn when rolling occurs.
(2) The heat transfer coefficient increases almost linear according to the angle and frequency of rolling.
(3) Fin effect of stiffeners is little, then their size and material affects little the heat transfer from stiffeners. They work mainly as mixers of oil in tanks.
Empirical equations for increments in the heat transfer coefficient by rolling are given as,
ΔN_u=0.0160 R_e^0.942P_r^1/3……for side shell
ΔN_u=0.0155 R_e^0.910P_r^1/3……for bottom shell where ΔN_u=Δαl/λ and R_e=2πbθl/ (Tν).
(Δα : increment in heat transfer coefficient, l : stiffener space, λ : thermal conductivity, θ : rolling angle, b : half breadth of tank, T : rolling period, ν : kinematic viscosity.)

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This paper describes a theoretical and experimental investigation aimed at measuring ship's speed to the ground by means of the Doppler effect of underwater ultrasonics.
Measurable quantity of the Doppler effect of underwater ultrasonics is thought to be influenced by the distribution of flow velocity, temperature, and salinity of the water. Assorting to the computational formula of the aftereffect obtained by theoretical consideration, calculated speed to the ground is failed within 1% of the real speed to the ground in a numerical example of the aftereffect. It is suggested that the error in calculation of the speed to the ground may be corrected by measuring the Doppler shift frequency in two direction (θ₁ (0<θ₁<90°) and 180°θ₁). An experimental apparatus is introduced in order that output signal of frequency Δf may emerge from input signal of frequency f₀+ Δf and f₀-Δf. The spectrum of the output signal in the experimental towing tank is analysed by the frequency analyser, and it is shown that it has a steep peak. Error of velocity measurement is, as a result, shown to be 0.97≤Δf_DC/Δf_T<1.01 and0.97<Δf_PSΔf_T <1.02, where Δf_DC, Δf_ps and Δf_T are the digital counted, the spectral peak, and the theoretical frequency, respectively.

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The line heating method is extensively applied to the bending of steel plate and the amending of distortion of welded members in fabrication of structures such as ships and bridges. Generally, in process of line heating, the surface of steel plate heated is quenched by water immediately after heating. Although there have been reported many papers concerning this line heating method, very few papers are dealing with the effect of water cooling on angular distortion.
The authors carried out the experiments on the effect of water cooling on angular distortion in line heating of steel plate and performed the calculation of plastic behaviours of the plate being subjected to water cooling or air cooling subsequent to line heating by the using of total strain theory. In this investigation the following facts are clarified;
1) The quantity of angular distortion finally obtained in case of water cooling of the heated surface was less than that obtained in case of air cooling.
2) When the reverse side of heated surface was cooled by water after the temperature became distributed uniformly through section, the quantity of final angular distortion was more than that obtained in case of air cooling.
The results of calculation used on total strain theory gave the rather reasonable explanation to the behavior of the plate line heated in the experiment.

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