This paper presents a theoretical investigation of the frictional resistance of ship by three dimensional boundary layer theory. The stream lines and pressure distributions are found from the linearized potential theory.
The momentum equation of the three dimensional turbulent boundary layer used by streamline coodinate and entrainment equation introduced by Cumpsty-Head are integrated numerically along the stream line to determine the momentum thickness, shape parameter and the angle of boundary layer flow to the outer flow.
The results of computation for Inuid S-401 and tanker ship form are presented. And the results are compared with the approximate calculation by two-dimensional boundary layer theory.

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The wave-making resistance could not be calculated quantitatively at present, though the excellent qualitative results have been obtained and one can design the ship form of minimum wave-making resistance through the wave-making resistance theory. Some points of the theory to be improved has been pointed out and by applying perturbation method the precise constructions of thin ship theory and slender ship theory have been devised, but the definite directions not yet found. The problems of a moving body which causes waves on the water surface might be very intricate and highly delicate. Recently T. F. Ogilvie paid attention to the composite properties of the problem, pointed out the defects of usual perturbation method and proposed a new method. Following him the author tries to explain the properties of ship wave in low speed range and to find out the points to be improved in the wave-making resistance theory by introducing an expansion of the solution appropriate to the characteristics of wave and ship motion. As a result, he asserts that usual linear theories can be applied only in high speed range and that the effect of finiteness of ship-breadth and the effect of wave diffraction have to be taken account into the boundary condition in low speed range. This conclusion confirms theoretical back-ground of some recent attempts to make satisfy the boundary condition exactly on the ship hull surface.

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In this paper the resistance of a floating body in a uniform stream of a viscous fluid is obtained theoretically to Oseen's approximation. It is shown that the total resistance is expressed as the sum of two components, namely the wave making resistance and the viscous resistance. The former is determined by the source and Oseenlet distributed over the hull surface, while the latter is proportional to the total strength of the Oseenlet. The effect of the Oseenlet on the waves and the pressure is turned out to be the same as that of the source.
The authors tried to apply these results to the actual ship resistance problem, and found that there exists a new component of the wave making resistance which is proportional to the skin friction coefficient C_f.

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The ship form of finite draft, which minimizes the wave-resistance for a given displacement, is calculated by the aid of the electronic computer. The ship is assumed to be wall-sided. The result gives the optimum distribution of doublets over the center-plane, which replace the ship hull. After a slight modification of the curve of distribution at both ends, the doublet distribution determines the curve of sectional area, so as to minimize the wave resistance. It determines also the optimum coefficient of fineness, e. g. prismatic coefficient, as a function of Froude number. Another calculation is made to minimize the wave-resistance, when the moment of inertia of the water plane with respect to the transverse axis through the mid-ship section is fixed. The result gives the optimum curve of sectional area, when the coefficient of fineness is different from the optimum value.

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Velocity distributions were measured by 5 hole pitot tubes at the section about 1. 1 D before the propeller on a ship and the models, as shown in Fig. 3. The lengths of the ship and models are 167 m, 8. 267 m and 4. 5 m respectively. The smaller model was used for the preliminary tests to plan the full-scale measurements.
The measured results are shown in Figs. 7 to 12 both for the ship and models. Principal conclusions obtained are as follows ;
(1) Velocity distributions in the boundary layer does not follow the 1/n law and shows the tendency of seperation, at the measured section, which is more remarkable on the models than on the ship, as shown in Fig. 13.
(2) The pattern of V_X/ V and the vector of V_YZ/ V are coincided well in tendency between the ship and models except the region near the hull at the shaft center line.
(3) So-called stern vortex is affected by Reynolds no., and the vortex of the ship is shrinked by more than the ratio of thicknesses of the boundary layers between the ship and model.
(4) According to the three dimensional expression of the flow around the stern, shown in Fig. 18, the flow before the propeller attains to the propeller disc, keeping the general tendency constant, including the complicated flow of vortex. This fact will give a hint to obtain the better estimation for wake values of the ships.
(5) The values of (1-w_s) / (1-w_M) calculated by various methods are shown in Table 2.

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In research on cavitation, it is well known that the incipient cavitation number σ_inc is less than or equal to the desinent cavitation number σ_des. This condition is called “Cavitation Histeresis”. Authors observed how this condition could be affected by the time-dependent change of the system pressure. This test is named “the transient cavitation”. The delay time of cavitation after stepwise pressure drop, is concidered mainly affected by gas nuclei. From the experiments which is made under sinusoidal oscillation of the system pressure, it is revealed that in the region of lower velocity and higher frequency the incipient cavitation number was larger than the desinent cavitation number.
However, this rather strange result is only tentative and quantitative, clearly indicating the need of further careful experimentation and analysis.

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The unsteady phenomena of the flow around the hull of ships have begun to come into question as their forms become fuller and fuller. For example, we know unstable phenomenon in the self-propulsion test of full ship models discovered by Watanabe, the problem about remarkably great irregular vibrating propeller forces, unsteady propeller cavitation problem and so forth. These phenomena are likely to be related to the turbulence in the flow field of ships or model ones. Townsin and Boes pointed out that the turbulence in flow is not negligible in the field of ship hydrodynamics.
The authors attempted in the present work to obtain empirical informations about the turbulence in the wake of a model ship at first and, next, to estimate its influence on unsteady propeller forces. The measurement of velocity of the flow behind the model ship of a full form was carried out in the towing tank. The three dimensional components of velocity were measured employing 5-hole Pitot tube device, whose pressure output was detected by the electronic pressure transducer responsive to rapid change of pressure. The analyzed results have shown that the intensity of the turbulent flow is more than 50 % of mean velocity in the region of strong wake near the central vertical plane, and that the low frequency components below 10 Hz are powerful in the power spectra of the turbulence.
The influence of the turbulence in the flow on a propeller forces was estimated applying the unsteady airfoil theory for the case that the tested model ship was equipped by a 5-bladed propeller. This estimation has revealed that the irregular noise part due to the turbulence in the flow occupies 80 % of power of the total fluctuation of unsteady thrust and torque. The irregular variations of unsteady lift, thrust and torque were simulated by the computor, the results of which are similar to some experimental data measured by Kumai and others.

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The maneuverability of ships in a seaway may be considered from various aspects which include small and favorable wave motion. Especially, it is well known that the most dangerous condition of a ship at sea developed when the ship is in a following sea or quartering sea.
In order to investigate the directional stability of ships under such circumstances, in this paper the linearized equations of motion of ship are carried out taking into account the hydrodynamic forces which act on the ship due to the presences of waves. These hydrodynamic forces are calculated using the Froude-Kriloff hypothesis and according to the conception of simple flow theory of the slender body and the quasi-static theory and the assumption that width and draft of the ships are of the small in camparison with the wave length. So as to consider stationary condition of the surging motion, herein the ship travels with the propagating velocity of waves at any position of the ship relative to the waves.
On the other hand, a method is shown that these hydrodynamic derivatives of the model ship are experimentally measured by operating the planar motion mechamism behind the wave making board realizing stationary following sea conditions.

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The 'auto-piloting' system is usually used with ships which navigate in a seaway. It is considered that the system has some connection with ship responce to wave and the rudder, and with wave spectrum and precision of gyros.
So the authors design the new auto-piloting system which minimizes the criterion function
J=∫TN0 (θ2+λδ2) dt
where θ : course error, δ : rudder angle
λ, TN : constant value, t : time accounting with above three elements. And the experiment with the automatic pilot was conducted.
Then they suggest that the new 'auto-piloting' system is not only theorctically valuable to show the optimal 'weather adjustment' in auto-piloting system, but practical indeed.

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Forced oscillation test, wave exciting forces test with the restrained model and ship model motion experiment are the well known experiment techniques to obtain the hydrodynamical forces acted on a ship with forward speed and it's motions in waves.
The authors carried out three kinds of experiments as follows, mainly using transient input signals (transient forced heave and transient water wave), and also did with sinusoidal signals to check it's property.
(a) Transient forced pure heave test in still water
(b) Wave exciting force test in transient water wave
(c) Ship model motion experiment in transient water wave
Moreover, the comparison between the experimental values and the calculated values by Ordinary-Strip Method was made in detail.
The authors could come to the next conclusions from the above test results.
(1) Within the limit of linearity, the frequency transfer functions in respect to Exp. (a) and (b) are given as the stationary responses from the transient responses.
(2) Calculated heave amplitudes by experimental values Exp. (a) and (b) coincide fairly good with the measured values Exp. (c).
(3) Oscillating forces, wave exciting forces, ship motion and etc. also coincide with the calculated values by O. S. M. with a practical accuracy.
Then it is certified under the linearity that the transient response method is the useful one for research on ship's behaviors in waves.
Concerning about the experiment techniques, transient forced oscillation test, wave exciting force test and ship model motion experiment in transient water wave were proved to be the useful practical methods.
The authors hope that testing ship models by transient response method will be put to practical use in model basins.

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It is generally difficult to calculate the wave excitation forces for three dimensional bodies, so strip method is usually applied to the bodies that have sufficiently long parallel parts, but it can't be applied to axi-symmetrical bodies, circular docks with or without footing, for instance.
In this paper, authors deal with the wave excitation forces upon axi-symmetrical bodies by means of the variational method making use of source singularities along symmetrical axis, and give good approximate solutions. At this time, we calculated added masses and damping coefficients for heaving spheroids, circular docks and circular docks with sperical footing by means of the variational method, and then we derived wave excitation forces and amplitude ratio of radiation waves from damping coefficient by the aid of Haskind-Newman's relation, and from these results we showed that three dimensional wave-excitationless forms existed and that they had the same character as two dimensional wave-excitationless forms.
The variational method employed here has been developed by Professor M. Bessho.
The results show the good agreement with model experiments, and calculations of Havelock and W. D. Kim.

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As a step of improvement of the calculation of lateral motion (sway, yaw and roll) of a ship in waves, the coefficients of equations of motion were determined by the forced oscillation technique. Experiments made it possible to know the effects of frequency, advance speed and bilge keels on ship motions.
The experimental values were compared with the calculated values by the strip method. For the main terms of sway, yaw or roll, except roll damping term, the results show a fairly good agreement.
For the coupling terms of sway-yaw, yaw-roll or roll-sway, there are fair correspondences.
For the prediction of the roll damping term, a proper method of approximation which includes the effects of viscous damping, advance speed, bilge keels and frequency of motion should be developed.

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This is the second report of the subject on which the author reported at the Spring Meeting of the Society in 1971.
The previous report deals with the studies on icing on cylinders under the following assumptions :
(1) Heat conductivity of ice is so small that conductive heat loss might be neglected in treating icing over a long time ;
(2) Ice accumulation on ship occurs at ambient air temperature lower than 0°C and furthermore in the vicinity of sea surface. Therefore saturated vapour pressure is low and evapolation or sublimation from ice surface might be hard to occur;
(3) From these points of view, it is considered that all the latent heat quantity of fusion of ice accreted is removed only due to forced convection; and a plenty of water droplets supercooled as low as ambient air temperature are always in uniform suspension in air stream, in which a cylinder is placed.
This paper describes theoretical and experimental studies on icing on plate parallel to or perpendicular to air streamline, in which a plate is placed, under the same assumptions as those for cylinder. Theoretical studies on the “collection efficiency” of plate perpendicular to an air flow, assuming two dimensional potential and continuous stream is also dealt in this paper.

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The theories and experiments of static peripheral jet in proximity to the ground with application to air cushion vehicles have been investigated in detail for a long time. It is, however, not too much to say that arguments about the influence of forward speed on lift force of A. C. V. (i. e. dynamical theory) have not been made sufficiently.
In this paper, the influence of forward speed on lift force of A. C. V. was investigated using a two-dimensional wind tunnel model, and a simple method of theoretical calculation was presented, getting a fairly good agreement with experimental results. The followings are the main conclusions :
1) Total lift force of an A. C. V. is divided into two parts ; lift on upper surface C_Lu and that on lower surface C_Ll. They can be considered independently of each other.
2) The pressure distribution on the upper surface is independent on the height over the ground and also the type of blowing, C_Lu is in proportion to jet momentum of blowing air.
3) The pressure distribution on the lower surface is regarded as almost uniform except the both ends of the model.
4) C_Ll on lower surface of the model can be calculated by using the simple theory presented in the present paper.
5) When jet momentum coefficient C_μ takes small values, both two types of blowing-the A. C. V. type and the jet flap type-give almost same values of C_Ll. As the value of C_μ is increased, the C_Ll of A. C. V. type is increased with C_μ, but C_Ll of the jet flap type reaches the maximum and then it is reduced gradually.
6) From the view point of the effective lift for the constant horse power, the jet flap type blowing is considered to have some merits to the A. C. V. type in the case of small C_μ. On the other hand, the A. C. V. type has more merit when the value of C_μ is large. The border line of merit is a straight line passing through the origin proportional to h/D.

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This paper provides a new approach to the buckling analysis of plate structuers whose section are not varied along the longitudinal axis, for example, stiffened plates with one directional stiffeners, corrugated plates, polygonal tubes, sandwich plates with corrugated cores and so on.
In this approach, the prebuckling stresses are assumed to be normal stresses in the longitudinal direction only, however the distribution pattern may be arbitrary.
The foundamental concepts of this method are as follows. The plate elements which compose the section of the plate structures are divided into the narrow strip elements and then the stiffeness matrixes of these strip elements are derived by assuming the displacement functions and using the energy theorems. In the subsequent processes, the usual techniques of matrix method can be applied and then bucklig load is computed as the lowest eigen value. Several kinds of plate structures were analized by this method and experiments were also conducted. The coincedence was fairly good.

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This paper presents a generalized method of analysis of large-deformed elastic-plastic plate problems. The nonlinear geometric and material problems are solved by the incremental load procedure (step-by-step method).
The method of solution is outlined as follows.
(A) Plastic analysis is based on the flow theory of plasticity. The method of initial strains is applied considering the following characteristic feature. Structures can be treated by this method as if they had elastic stiffness and the effect of plastic deformation is transformed into the equivalent additional external force. So this method makes it possible for us to apply the principle of stationary potential energy of elastic plate with initial strains.
(B) Finite deformation analysis is performed at the respective loading steps in the following way.
(1) Incremental deflection Δw is expanded in a series of functions with unknown coefficients ΔC _[m] .
(2) Inplane incremental displacement Δu_e is expressed in terms of ΔC _[m] , considering inplane equilibrium condition. The finite element method for plane stress problems can be used in this process.
(3) ΔC _[m] are determined to satisfy inplane and out-of-plane equilibrium conditions.
This method has a special merit to require only a short computing time owing to expantion of Δw in a series of functions. Whole application of the finite element method would result in untolerable time-and core-consuming troubles.
As numerical examples, two problems are studied with regards to the simply-supported square plates and the perforated square plates.
(1) Laterally loaded plate
(2) Ultimate compressive strength of the plates with various thickness and initial deflection.
A few experiments were performed to investigate the applicability of the method of solution.

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Many papers concerning with thermal stress problems have been published. Recently, the finite element method having widely been developed, the application of the method to thermal stress problems seems to be practical. However, there are some difficulties in welding thermal stress problems due to the fact that temperature dependence of material properties must be taken into consideration as the material is subjected to high temperature.
In this paper, special regards are paid to the fact that Young's modulus and coefficient of thermal expansion in elastic region and yield stress in plastic region are temperature dependent. And a general method to solve the thermal elastic-plastic problems is shown by using the incremental technique. In elastic range, stress-strain relation in which temperature dependence of material properties is considerd, can be obtained by taking derivative of the generalized Hooke's law with respect to time. In plastic range, stress-strain relation in which temperature dependence of yield stress is taken into consideration, can also be obtained and the relation coincides with the so-called D^p matrix shown by Prof. Yamada.
As numerical examples, some typical thermal elastic-plastic problems are solved by the above-mentioned method and the results obtained are quite satisfactory.

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The recent development of the finite element method has been giving a favor to analysis of complex subjects in structural engineering.
In this paper, the method is applied to analyze the stress and strain history during welding as the thermo-elasto-plastic problem of bilinear strain hardening orthotropic plate.
Though the plate has not only in-plane but also out-of-plane rigidities, the latter is neglected in this study because of the secondary importance in most welding problems.
The approach in this problem is based on the Mises yield criterion and the Prandtl-Reuss flow rule in conjunction with anisotropic parameters of elasticity and plasticity.
As a basic example of the application, the history of deformations and stresses under welding are analyzed in case of a rectangular plate.
The results indicate qualitatively the usefulness of the method.

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This report is concerned with the development of an analytical system for calculating thermal stresses during welding and resulting residual stresses.
The present analysis concerns only longitudinal stresses, that is, stresses in the direction parallel to the weld line. Computer programs developed in this study calculate both temperature and stress distribution during welding. Using these programs, an analysis was made of effects of welding parameters on thermal stresses during bead-on-plate welding of ASTM 2219-0 aluminum alloy.
Important results are :
(a) The maximum stress at the weld center is little affected parameters. However, the width of tensile residual stress zone is significantly affected by welding parameters, especially heat input. With an increased heat input, a wider residual stress zone is formed.
(b) However, when a weld is made with very low heat input, considerably high tensile stresses are produced in area just behind the arc.
(c) Fairly high compressive stresses occur in area ahead of the welding arc.
Experiments were conducted. Temperature and strain changes were recorded during bead-on-plate welding of 2219-0 aluminum alloy plate, 30 inches long, 18 inches wide, and 1/4 inch thick.
Measured temperature changes coincide well with calculated ones by assuming the arc efficiency, η, to be 0.7. As far as the general trend is concerned, measured longitudinal strains coincide fairly well with calculated ones. However, transverse strains and shearing strains reach considerable amounts in area near the welding arc. The current analysis is not adequate for studying complex stress changes in area near the welding arc.

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Stress distributions around a crack in a plate is specified by the stress intensity factor which is closely related to the singularity of stress at the tip of the crack. A new method for calculation of the stress intensity factor is proposed in this paper, and it is based on superposition of analytical and finite-element solutions. Stresses have an singularity at the tip of a crack ; they cannot be obtained exactly by the finite element technique, but they can be expressed analytically near the tip of a crack. Stresses in the whole plate can be expressed with the sum of such an analytical part and a residual part which is regular everywhere and can be calculated accurately by the finite element technique. The singuarity of stress can be determined from the analytical part of the solution, and it yields the stress intensity factor.
The present technique is applied to several problems. In the case of rectangular plates with cracks, the numerical results are in good coincidence with those obtained analytically by the former authors. Computations for the present method can be performed without fine element subdivision, and computer time is economized compared with other methods. The stress intensity factors for cracks in a complicated structures, such as stiffened plates, are obtained by the present method, and some results are shown in this paper.

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This paper presents the results of theoretical and experimental investigations on the torsional strength of large container ships having large hatch openings. Especially the effect of the double hull structure on the strength was studied.
The feature of the method of calculation is that the ship structure is treated as a beam shell having multi-cell structure and the effect of the double hull is directly developed.
Further, the influence of cross decks between hatch openings is studied.
A series of experiments was carried out and it was confirmed that calculated results obtained through this method are in good agreement with experimental results.
Also, the double hull structure and cross decks were found to increase the torsional strength of ships.

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As one approach towards the optimization of ship structures, such stiffened structures as bulk-heads, side and bottom shells are considered. Stiffened structures are transposed into flat grillages composed of straight orthogonal beams laterally loaded and their optimum design analyses are conducted by using framed structure analysis and nonlinear programming. The relationships between loaded area, beam number and optimum arrangements of beam sections in both simplified grillages and the bottom grillages of oil tankers are discussed. Conclusions obtained are as follows :
I. The combination of matrix force method for framed structure analysis and nonlinear programming (here, SUMT method in corporating DFP method is used) can be successfully applied to the optimum design of grillages.
II. In design of grillages, as the number of beams increases, the weight of grillages increases.Furthermore, the weight in case of grillages is larger than that in case of single beam structure.
III. Optimum arrangements of beam sections in simplified grillages are such that shorter beams with large sectional area hang longer beams with small sectional area, still more in case where total load is applied only shorter beams, longer beams are not necessary.
IV. Optimum arrangements in the bottom grillages of a center tank of oil tankers are a little different from in case of simplified grillages because of bottom platings working as a part of longitudinal and transverse girders and of difference in allowable stress between longitudinal and transverse girders.

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The pressure distribution on hold wall of ore-slurry carrier was experimentally studied under the following conditions :
(1) Ore slurry to be taken on board at slurry consistency of 60% through 75% by weight
(2) Ore slurry to be subjected to the acceleration of 0. 02 g through 0. 3 g corresponding to the ship's vibration and motion.
The investigation shows that
(1) Ore slurry shows the behavior of homogeneous liquid during loading.
(2) After loading, are gradually precipitates, and consolidates within a certain limit of acceleration of ship's motion and vibration and shows soil characteristics.
(3) But so called phenomenon of liquefaction, that is, it loses shear strength and becomes in a state of liquid, is clearly observed above some acceleration limit.
The conclusion reaches that the ore slurry should be treated as homogeneous liquid when calculating the pressure distribution on hold wall and examining the ship's stability.

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The lateral vibration of deep girder in water has been treated in this report since the fatigue due to vibration is supposed to be one of the principal causes of the fractures in the local structures in the cargo tanks. The inertia of surrounding water is calculated by two-dimensional FEM using distributed sources and sinks, and taking account of three-dimensional correction.
The effect of both the structure and the hydrodynamic inertia on the lateral vibration is examined theoretically where the latter is expressed in term of kinetic energy for the linear combination of the elastic modes. The effect of the face plate upon the pressure distribution and upon the frequency is shown to be large in water.
The model experiments have been carried out and the results fairly agreed with that of calculation.
The calculated natural frequency agrees with that obtained on board a large tanker with about 10% of errors and it is shown that the present calculation method is applicable to the actual structures and that the frequencies of this type of structures immersed in water may be lowered enough to cause the resonance with the blade frequency component of the exciting forces.

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It is well known that there could be many, more or less, mis-aligned members in ship structures. In oder to evaluate ship strength, it is necessary to know the behavior and its strength of such mis-aligned structures.
In this report, as the first step of such investigation, mis-aligned I section joints are subjected to tensile load and their static tensile stength as well as fatigue strength are studied, concluding that these mis-aligned joints may be adequately strengthened by increasing the leg length of fillet weld.
However, more systematic and detailed experiments are needed to refine to design and the construction of ships by taking into account of the effect of mis-aligned members.

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This paper deals with the results of the low cycle fatigue tests on hour-glass type and round notched specimens of SM 41 A. Strain-controlled and load-controlled low cycle fatigue tests at ambient temperature were carried out to investigate the notch effect on the fatigue strength reduction factor.
The following conclusions were obtained :
1) A visible crack of 0.2 to 0. 5 mm in length will be initiated on the notch root of a notched specimen with any shape factor at an approximately same number of cycles, if the same equivalent strain at the root of a notch is used as the measure of evaluating strain amplitude.
2) A concept was proposed on low cycle fatigue strength reduction factor. The fatigue strength reduction factor K_f, _{_??_} which is calculated from the results of strain-controlled low cycle fatigue tests on smooth and notched specimens, would be equal to the dynamic strain concentration factor. In case that no low cycle fatigue tests would be carried out, the fatigue strength reduction factor may be obtained from the result of dynamic strain analysis.
3) “A” factor for a carbon steel, which is given in the Fig. D-201 in the Nuclear Piping Code (USAS B 31. 7 1969), is found to give lower and higher value than the K_f, _{_??_} value depending on an applied stress amplitude. It is also revealed that “A” factor in the Nuclear Power Piping Code is much lower than that obtained by the Method proposed by S. W. Tagart for the material used in the present test.

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Structural members of ship in seaway are subjected to the repeated stress due to the hogging and sagging bending moment, or the difference of water pressure due to the change of draught. In rough sea, the impulsive forces due to the wave are added to the above repeated stress. Moreover, the ship is always in the environment of corrosion due to sea water. The combined action of these three factors-repeated stress, impulsive force and corrosion-may lead to failure of ship in stormy sea. Nevertheless, the strength of materials, such as steel or aluminium alloys, under such conditions has not yet been studied.
In the present investigation, a simple method was used to obtain the effect of combined action of the above three factors on the strength of 60 kg/mm² high-tensile steel, mild steel and corrosion-resistant aluminum alloy.
Fatigue testing machine of a rotating canti-lever type was used. The range of testing is restricted up to about N= 5×10⁵, as the number of repetitions of stress are 3. 5 per minute. Corrodant used is the artificial sea water which is dripped on the test section of the specimen. Impulsive force is applied on the point of loading of the rotating machine by a dropped hammer per 4, 10 or 30 repetitions of repeated stress. Impact energy can be adjusted by the change of the weight of hammer.
The results obtained are as follows :
(1) Considerable decrease in fatigue life was observed under the simultaneous action of intermittent impact and corrosion-fatigue compared with the corrosion-fatigue life.
(2) The larger the impulsive energy (e. i. stress induced by impact) the shorter the fatigue life. In mild steel and aluminum alloy, the rate of decrease in life under an impulsive stress is nearly constant in spite of the change of repeated stress, but in the high-tensile steel, under a constant impulsive stress, the smaller the repeated stress, the larger the reduction in life.

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As the continuation of the last report, program fatigue tests were carried out on the structural models of member joints in ship's hull structures. The main purposes of these tests were to estimate the fatigue strength of this part and to find a most effective method of reinforcements therefore.
In this investigation we treated the oblique type corner where the tank top plate and the sloping plate of a hopper tank top plate are jointed together in π/4 and/or π/6 angle as is usually found in a bulk carrier.
The experimental models were made on a deduced scale, and loads to be applied on the models were determined on the basis of the results of transverse strength calculations and the load program consisted of 2 mean loads, one corresponding to full-load condition and the other corresfonding to ballast condition, each with fluctuating loads of 5 stages.
On the analysis, in addition to the consideration on the experimental data, we are also planning to carry out some preliminary calculation based on the fracture mechanics.

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The Double Tension Test or the ESSO Test with temperature gradient has been carried out to estimate the brittle fracture propagation arrest characteristics of the steel used in the welded structures. However the effects of specimen size and loading condition on these tests have been considered vaguely.
In this report, the authors have investigated these effects by the statical elastic analysis using the simple spring model and by the systematical experiments. In fact they have been carried out for the 5 test series changing the parameter of the loading condition and the aspect ratio of the test specimen, the distance of pin-to-pin to the specimen breadth.
In the test results these effects have been found as was expected and explained by the above-mentioned analysis satisfactorily.
Then the one of the experimental methods to avoid these effects in the test of the brittle fracture propagation arrest are proposed.

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The operation of ship on the sea, which is too large and full of energy to compare with the ship, does really require bravery and also comprehensive judgment on the state of surroundings and of ship herself, so much so that it must necessarily be too difficult to explain or define simply the way of operation in rough seas. This fact simultaneously explains the difficulty of defining the dynamic sea load carried on the ship's hull.
However, in the long run of history, the strength of hull and the way of operation may well be said to have been understood to be interrelated each other, even though it was in a implicit way, and if the hull design is going to be more theoretical in future, the relation with the operation must be more clarified.
Before that, however, the usual way of operation in rough seas in the past is tried to be shown by reviewing the various observations and studies made by many predecessors, hoping that the interrelation might come to be more clearly recognized in the future.

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The design of Gas-Freeing system for optimum performance requires much more information on the flow velocity and gas concentration distribution occurring between the obstructive baffles and the structural members in a cargo tank during gas-freeing. In the above point of view, tests were carried out to investigate flow velocity and gas concentration change at the various positions in the scale model tanks which correspond to 1/10 th and 1/50 th of wing tank for a existing 150, 000 D/W ton crude oil tanker.
At first, flow patterns were observed using transparent and colored water which visualize the flow behaviors in 1/50 th scale model as shown in photo-3. In next, using CO₂ and air, which are to represent crude oil vapor and vent gas respectively, gas-gas system was studied varying systematically vent air flow rate and initially filled gas concentration.
The followings were proved :
(a) Three paticular flow fields were observed in the tank from vent air inlet to exit as follows : (1) Jet stream zone. (2) Recirculating stream zone, where the fluid flows induced by jet. (3) Slow stream zone not affected by jet. The last zone which is usually widest of three and involves difficulties of gas-freeing was especially focussed in the thesis.
(b) In this zone, vent air stream which flows penetratingly through residual gas causes to deteriorate gas-freeing performance.
(c) Densimetric FROUDE number Fr' has significant influence on the gas concentration distribution especially in the third flow field and is proved to be most important criterion in similarity of gas-freeing.
(d) A few investigations carrid out with actual gas-freeing in large tankers revealed that the temparature difference between air and initially filled gas, which is sometimes affected by tank washing with hot water, also has considerable influence on the performance of gas-freeing.

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Scientific industrial service in marine technology is dealt with. For the various aspects of this subject the activities of the Netherlands Ship Model Basin are taken as an explanatory example.
Due attention is paid to the hydrodynamics of ship hulls and ship propulsion, the oldest domains of industrial service of ship model basins. This includes research on hull forms with high block coefficients, different aspects of ship propulsion with regard to cavitation and propeller induced dynamic loads.
Motivations for building special purpose laboratories for specific problem areas are given. Especially for solving the problems of offshore technology, special purpose laboratories such as a seakeeping laboratory, a restricted waterdepth channel, a wave and current laboratory and a manoeuvring simulator are needed.
Some examples of industrial service in the field of computer aided ship design, shipyard production and shipowner operations are included.
In conclusion some considerations will be given about the initiative of designing and building a depressurized towing tank (Vacutank).

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