This paper describes the attempts made in Nagasaki Experimental Tank to improve the accuracy of flow measurement in high wake region of single screw ships. Noticing strong downward velocity in the high wake region preliminary approach was made by modifying analysis method with extension of calibration range and by inclining the probe towards flow direction. The results indicated that the normal use of a 5-hole pitot probe (set in horizontal direction) does not yield accurate data of downward velocity component.
As a next step an 8-hole pitot probe was developed incorporating a 'normal' and an 'inclined' probe, and it proved to be convenient for measurement of the flow at the propeller plane.
Effect of wake peak values on propeller vibratory forces is examined and significance of choosing accurate measurement data is discussed.

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Methods for calculating the hydrodynamic load distribution on the blade of marine propllers are discussed.
The numerical solutions of the existing lifting surface theories do not converge at the parabolic wing tip on account of the singularity. The restriction in the existing theories can be removed by using the new integral equation presented by Dr. Hanaoka¹¹⁾ .
Employing the new integral equation, a numerical procedure is developed for the steady propeller. In the present method, the range of validity of propeller lifting surface theory is extended to include the tip of blade.
The method is applied to an usual broad bladed propeller and to a highly broad bladed propeller. The result is compared with the calculations by the existing mode function method⁴⁾ and by the new doublet-lattice method¹⁶⁾ . The new doublet-lattice method is the method devised to give the accurate solution near the leading edge.
Following facts are revealed by the results of the numerical investigation. (1) Accurate solutions for the hydrodynamic load distribution near the tip of blades are obtained by the present method. (2) For the case of a highly broad bladed propeller, the existing mode function method is invalid and the present method should be used. (3) The present method is useful for the calculation of cavitation. (4) For the case of an usual broad bladed propeller, the existing mode function method is valid in wide range up to 0.9 radius. The method is useful for the calculation of propeller forces. (5) The new doublet-lattice method gives the converged chordwise load distribution. The method is supposed to give the accurate solution near the leading edge and to be useful for the calculation of cavitation.

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In this second report the optimization of rudders is studied from resistance and propulsion point of views, where a synthetic, rather than analytic, method of approach is applied in contrast with the first report.
Based upon Kumano's (1960-61) finding that the ship's rudder occupies near optimum position as stern bulb which is aimed at stern wave cancellation, several types of unconventional rudder configuration are examined both by towing test and by wave analysis. Possible improvement of self-propulsion factors is also pursued by propulsion test.
Obtained increment of propulsive performance reaches up to 7 percent, which is mainly attributable to stern wave cancellation.
Viscous scale effects upon the main hull stern wave system both in towing and self-propulsion condition are studied by two geosim models of L=2.5m and 10m.

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By utilizing propeller-rudder system with the absence of the ship body, the author conducted experiments concerning characteristics of a rudder behind the propeller in oblique flows in order to make clear flow-straightening effect of the propeller itself. The tests were performed by varying drift angle of the propeller axis, rudder angle and propeller loading systematically. Through these tests, propeller flow direction at the rudder position was obtained from the rudder direction in which normal force did not act on the rudder. The results were represented in the form of a coefficient of flow-straightening effect.
Principal conclusions obtained through the studies are as follows :
1) It was confirmed from experiments that the coefficient of flow-straightening effect is constant regardless of drift angle.
2) The coefficient estimated from direction of the resultant velocity from drifting velocity of a propeller and increased axial velocity of the slipstream agrees with the actually measured value fairly well.
3) Influence of propeller loading on the effect is remarkable. This fact is related with the problem of model-ship correlation for maneuverability.
4) This paper suggests an idea which may be called flow-straightening effect identity as a method to obtain the effect of a ship's hull using that of the propeller itself.

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The local non-linear free surface effects acting upon hull generating elementary waves are surveyed. Through the simplification of the exact free surface condition, the basis of the non-linear theory, the low speed theory and the linear theory is characterized.
A non-linear wave theory developed as an extension of the geometrical optics is presented. The propagation of elementary waves generated on the hull from bow through stern is numerically traced. The non-linear effects integrated along the passage of waves in the non-uniform double body flow are discussed.
Based upon the asymptotical expression for free waves far rear the ship where the remained non-linear effects are taken into account, wave resistance is evaluated for an Inuid model. Less prominent humps and hollows of the calculated wave resistance coincide fairly well with the towing test results within the moderate Froude numbers.

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It is often experienced that the resistance of a catamaran hull form is more than the twice of that of the demihull. To investigate the reason for this resistance increase, the velocity components around a symmetrical catamaran form were measured and compared with those around the demihull. Further, the wake survey and wave pattern measurements were carried out.
As a result the wake resistance determined by means of wake survey was found to be more than the twice of that of the demihull. In the lower speed range this resistance increment is simply attributed to the increase of viscous resistance by the velocity augmentation around the catamaran. In the higher speed range, on the other hand, a resistance component due to the breaking waves is added further. Asymmetrical property of the velocity field around each demihull of the catamaran is relatively small and is considered to have less influence on resistance when comparing with the mean velocity augmentation from the demihull condition.

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An observation of the flow around the oscillating flat plate shows that the flow separates at the edge, and the vortices are shed into the fluid. The effect of the viscosity seems dominant only in shedding the vortices, so that such an unsteady problem may be tractable with the potential flow theory by assuming that (1) the fluid is incompressible and irrotational except a vortex sheet, and (2) the behavior of the vortex sheet can be approximated by that of a system of discrete vortices. In the frame work of the potential flow theory it is evident that the hydrodynamic force coefficient does not depend upon the frequency but upon the amplitude of the oscillation, which is consistent with the experimental facts. In this paper an attempt is made to utilize such assumptions in order to investigate the nonlinear characteristics of the hydrodynamic forces acting on the flat plate oscillating normally to its plane.
A new method providing the mechanism of shedding and growth of the nascent vortices is proposed for the elimination of the disposable parameter which has usually been introduced for meeting to the uncertainty of the simultaneous determination both of the circulation and of the position of the new vortex born. The method is proved to be useful in the starting problem and in the oscillating problem with a rather small amplitude.

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In the previous papers, ship's responses among waves were investigated theoretically taking account of nonlinear hydrodynamic pressure. As an example, the bottom slamming and whipping of a tanker in a ballast condition were calculated, and the pressure history was compared with a model test, which shows good agreement.
In the present paper, the bow-flare slamming is investigated along the same line of thought; it may become very important for a fast container ship from the structural point of view, because it may results in a serious damage in the fore body. Assuming that the heading angle is nearly 180°, the longitudinal vertical bending moment in a container ship is investigated theoretically, ignoring rolling motion.
Results obtained are as follows : 1) As for a container ship, whipping is largely influenced by the interaction of bow-flare and bottom slamming. If the time difference of these two kinds of slamming is of order of the ship's natural period of vibration, serious whipping motions may occur. 2) Whipping vibration is enlarged in case of higher wave. 3) Reduction of the ship's speed decreases the maximum whipping moment. 4) As far as the ship's rolling motion can be ignored, the maximum whipping moment is independent of the direction of waves.

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Motions of a floating structure which consists of two or three blocks with rigid or pin joints are investigated experimentally and theoretically. Barge and semi-submergible type are adopted as floating structures. The motions in head waves represent heave, pitch, relative angles between blocks, and the internal shearing force and bending moment at the joint part. The strip method is used for the numerical calculations.
From the experiments, the following deductions may be drawn : 1) The rigid joint gives smaller amplitudes of the heave and pitch motions than the pin joint does, on the contrary the amplitudes of the shear force and bending moment get smaller in the pin joint than in the rigid joint. 2) The semi-submergible type obtains smaller amplitudes of the shear force and bending moment than the barge type does, while the amplitudes of heave, pitch and relative angle depend on the length of the incident waves and are the functions of the type of a model, that is to say, in the case of λ/L₀<2.0 the semi-submergible model gets smaller amplitudes than the barge model and in the case of λ/L₀>2.0 the barge model obtains smaller amplitudes than the semi-sub does. 3) With regard to the relative angle, the three blocks model gets larger amplitude than the two blocks model does.
The comparison of the experimental results with calculated results indicates that the strip method is successful for barge models, even for the three blocks model with the pin joints, however, it shows also that one has to take into account of the effect of the viscous damping of the sectional heave mode, if the corresponding wave making damping is very small and the expected frequency range contains the wave free frequency.

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A floating offshore airport, a floating offshore city, etc. are giant marine structures supported by a great number of floating bodies as never been experienced in the past. Because of limitations in scale and ability of an experimental tank and a model, it very difficult to experimentally estimate the wave exciting forces and the drifting forces acting on these structures. It is necessary to establish a theoretical method for their accurate and practical estimation.
For this purpose, we adopt, as a floating element, a semi-submersible circular dock with a cylinder type footing (Fig. 1) which will be actualized as a column of marine structures as mentioned above, and derive a theoretical formula from the velocity potentials for determining the wave exciting forces and the drifting forces acting on the floating elements which are arrayed in many rows and an infinite number of columns.
In development of the theory, we divide a fluid domain into three parts, assume the velocity potentials in each part to be infinite series expansion of eigenfunction in each part, and take only the diverging waves interaction into account between rows and columns of floating element.
A feature of this theoretical formula is that an interaction effect between rows can be explicity obtained.
The numerical values obtained from this formula are in good agreement with those obtained by experiment.

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The nonlinear programming is now used in the field of structural design in general, but it has possibilities of application to other engineering problems. In this paper, the authors apply the SUMT (Sequential Unconstrained Minimization Technique) method to the hull form design so as to make the resistance minimum under several kinds of the constraints. The total resistance is expressed by the sum of the Michell integral and the plank friction both of which are multiplied by suitable weighting factors. Series 60 model is employed as the basis of a numerical example. The fore body shape is improved by the present technique.

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This paper deals with the design criteria for the mooring systems of offshore floating structures.
The design criteria, presented in this paper, is based on the fundamental research works conducted by the author, and is applied for the basic designs of actual structures which are built at IHI. The diagram to predict the slowly varying oscillations of moored structures is also presented as shown in Fig. 4.
By way of example, the design of mooring system of floating breakwater is introduced.

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A 220m long and 45m wide square Plant Barge was towed for about three months from Japan to Brazil covering the distance of 13, 000 sea miles.
During this towing, some of the items concering motions and strength of the abrge were measured for 40 minutes per day. Observations of environmental conditions were made simultaneously, and, in some cases, wave heigths were measured using throw-in type wave meters.
The measured results were analyzed by means of statistical analysis and spectral analysis.
The feature of short term responses was investigated, and the spectral form thus obtained was compared with that of Pierson-Moskowiz type wave spectrum.
As for the frequency response function of motions, the calculated values obtained by using the measured power spectra of wave heigth were compared with the measured ones and experimental results in model test basin, and a good agreement was found between the measured values and experimental results, and also the calculated values indicated to agree fairly well with the measured ones.

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In the previous papers by the present authors^{2), 3)} a new discrete method of analysis was proposed on the dynamic collapse of beams and plates subjected to transverse impulsive loads. In the present paper, this method is applied to the dynamic collapse analysis of clamped beams and rectangular plates under distributed impulsive loading. Numerical results obtained are compared with the experimental ones by N. Jones⁷⁾¹⁰⁾ in order to verify the validity of the present method.

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One numerical method of Variational Difference using random grid points is proposed. This method belongs to finite difference method, but is based on the variational principle.
Stresses, energy and etc. are estimated at each line which connects two of their grid points. These features which are very different from finite element method increase the accuracy of stress and make comparison between plastic line with slip line easier. Furthermore the concept of joint element in FEM can be naturally introduced.

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The present paper proposes a methed for the elastic-plastic analysis of plate bending problems using the finite element method. In the present method plastic deformations are idealized according to the concept of plastic hinge lines, while the conventional finite element procedure is employed before yielding occurs. Morley's plate bending element is used herein because of its simplicity. Plastic analysis is based on the assumption that plastic bending deformations are concentrated in plastic hinges along the element boundaries. In order to decrease dependancy of calculated results on mesh idealization, simple automatic mesh re-subdivision is implemented in the procedure.
This method overcomes the following two difficulties in the ordinary finite element method; time consuming numerical integration of stiffness matrix along plate thickness and overestimation of stiffness due to shape functions with too strong compatibility conditions for localized plastic deformations.
Basic numerical examples are studied to verify the validity of the present method.

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1. In the present paper, a numerical method of getting differential coefficients of high order is presented.
A continuously differentable function ƒ is approximated by the linear combination of pyramid-shaped base function {Φi} and coefficients {αi} as
ƒ≈∑iαiΦi
Then, nth derivated function ∂nƒ/∂xk, …∂xlis also approximated with {Φi} and other coefficients {α∂xk, …∂xli} Using theory of distribution, coefficients {α∂xk, …∂xli} is expressed in terms of {αi} After all, nth derivated function is approximated by following form.
∂n/∂xk, …∂xlƒ≈∑iα∂xk, …∂xliΦi=∑ijαjN∂xk, …∂xlijΦi
α∂xk, …∂xli=∑jN∂xk, …∂xlijαj
2. The method is applicated for forced vibration of a beam.
Partial differential equations of beam vibration contain two differentials of 2nd order and 4th order ; ∂²/∂t² and ∂⁴/∂x⁴. Though it is said to be difficult to build a space-time element applicable for such problem, it is quite easy to apply a space-time element for FEM analysis using the present method.

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For the analysis on the distribution of gas concentration during gas-purging in oil tank of a tanker, it is necessary to determine quantitatively the dispersion coefficient and the interception rate of gas-purging caused by existance of circulated gas flow and dead zones in tank.
In this paper, the values of dispersion coefficients are calculated by use of the distribution of flow velocity and the interception rate ξ by stagnated flow is introduced in analytical method for one dimensional model. Besides, two dimensional analyses by finite element method are carried out to investigate the variation of distribution of flow velocity and gas concentration in tank using various conditions of decisive factors governing gas diffusion, i. e. position of inlet and outlet, volume of supplied gas and tank geometry. By the results of analyses, the relations between above-mentioned factors and dispersion coefficient or interception rate ξ are clarified.
The actual values of dispersion coefficient and interception rate ξ are obtained from measured values of gas concentration in a 250, 000 DWT oil tanker by means of one dimensional analysis.

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Many researches have been carried out on sloshing forces of liquid in a ship tank. But most of them have focused on sloshing phenomena of a tank which has considerably large gas space. And only a few results have been reported about nearly fully loaded tanks. This may come from the fact that there are some internal structural members in usual tank tops which prevent the occurrence of large impulsive pressure. But in the case of a tank which has a large flat tank top without any internal members, it is considered important to predict the magnitude of impulsive pressure.
In this report, authors present the results of model experiments focused on impulsive pressure of a nearly fully loaded tank. The experiments were carried out under the following conditions :
Filling ratio : 90-98% tank depth
Kind of ship motion : Pitch, Roll, Surge and Sway
Mode of motion : Regular and Irregular
Results are summarized as follows :
(1) Even in the case of a tank filled up to more than 90%, considerably large impulsive pressure occurs at marginal part of tank top.
(2) Considerably large impulsive pressure occurs in long period range in pitching and rolling.
(3) Large impulsive pressure occurs in a very small area at each moment.
(4) Pressure increases proportionally to the amplitude of motion in some cases, but it shows saturation in many other cases.
(5) It is considered that the probability density function of impulsive pressure shows a distribution close to Rayleigh's and truncated exponential distributions in the case of regular motion.

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The object of this research is to clarify the stiffening effect of a hat-shaped stiffener on a FRP single-skin panel. In the previous report, the bending deformation of a single stiffener model was described. However the ultimate tensile and compressive strength of FRP laminates are approximately equal to the yield strength of mild steel, the Young's modulus of them is generally only one tenth to one twentieth of that of steel, so that a problem of elastic instability is not less serious than that of bending.
In this report, the buckling deformation is analyzed on a simply supported orthotropic plate with a single hat-shaped longitudinal stiffener under uniaxial compression. An instability may occur in the form of local or overall buckling in such a fundamental plate structure considered, so that three analytical models are proposed to modelize the stiffening effect of a hat-shaped stiffener, that is, Euler buckling, local wrinkling and the rotational spring model proposed in the previous report. They are compared with detailed finite strip analyses and experimental results on plastic models.
It is shown that a simple model considering the rotational spring constant of a stiffener web gives a good explanation of the local buckling mode as well as the bending deformation as shown in the previous report. The difference between buckling deformation mechanisms of hat-shaped and T-shaped stiffeners is also demonstrated based on these results.

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The authors have developed a new composite steel-concrete structure for the strength members of huge offshore structures, where concrete is placed between steel plates.
In the previous papers, a series of experiments under static loading and theoretical analyses using the nonlinear finite element method were carried out. It was clarified that the composite has various excellent properties and the nonlinear analyses accurately represented the behavior of the composite.
In the present paper, the authors carried out experiments under repeated loadings. The effect of the repeated loading on the strength of the composite was clarified. Experimental and theoretical investigations were also carried out on the strength of the composite structure with a girder plate. It was found that the composite with the girder is very effective for shear force.

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The authors have investigated the detailed behaviors of a stiffened plate and first maintained the concept of the minimum stiffness ratio of the stiffener, γ^U_min for the ultimate strength in the first paper. Sequently, in the second paper, the authors described the result of investigation into the ultimate strength of a both-sided stiffened plate and γ^U_min, for the plate.
In this paper, a theoretical investigation into the ultimate strength of one-sided stiffened plate and the minimum stiffness ratio, γ^U_min, against the ultimate strength are carried out. Firstly, the elastic-plastic large deflection analysis by the finite element method is performed and the behaviors of one-sided stiffened plates are devided into three different types according to the stiffness of the stiffener. These are, (1) overall failure after overall buckling, (2) overall failure after local buckling and (3) local failure after local buckling. Secondly, as a simpler analysis, a theoretical elastic large deflection analysis is also performed considering the effect of the plastification of the stiffener in a simplifying way. In order to determine the ultimate strength of a one-sided stiffened plate by the simpler analysis, simple criteria are proposed after both theoretical results are compared. The prediction by this method is accurate enough for the practical purposes. Applying this method, the minimum stiffness ratio, γ^U_min of one-sided stiffener is defined as the stiffness ratio which guarantees approximately the maximum ultimate strength. A simple analytical method is also proposed to determine γ^U_min as the intersection of overall buckling strength curve and the maximum ultimate strength curve of the plate. This method is also applied to one-sided stiffened plate with several stiffeners, and γ^U_min for more general cases are calculated.
The effect of initial deflection and welding residual stresses are also discussed, and the effective minimum stiffness ratio, _effr^U_min is difined for the cases with these initial imperfections.

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It is difficult to estimate reduced buckling length of struts which are main structural members in a wingtank of a ship, because they are tightly connected with the transverse girder and have variable cross sections at the ends. The author and others have suggested through numerical calculations^{7) '8)} that strut-end structures give a great influence upon the buckling strength of struts.
In this paper, approximate calculation of reduced buckling length of struts under compression is suggested, in which strut-end structures are treated as a spring supporting face-bars. The results of the calculation show fine agreement with ones of FEM buckling calculation and suggest how much reduction of flexural rigidity of face-bars should be taken into account at round corner.
It is also investigated how much restraining effect is given on buckling strength of struts by tripping brackets. The results show that tripping brackets are most effective against buckling of struts when they are straightly connected with face-bars at the ends of round corners and they lose the effect rapidly as the connected points are rotated along the round corner, consequently the boundary condition of face-bars is regarded as fixed at θ=0° (see Fig. 7) while it is regarded as simply supported at θ=90°.

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When a plate structure is externally loaded, it is considered that structural elements such as stiffened plate and panel are usually subjected to combined stresses. In order to estimate the ultimate strength of these structural elements, as a basic study, a square plate subjected to compression and shear is treated in this paper. As a practical example of such elements in ship structure, horizontal girders, a part of longitudinal bulkhead and so on can be cited.
In the previous papers, the authors proposed a new analytical method for evaluating the ultimate strength of a stiffened plate subjected to compression. This simplified method in which numerical and experimental results were taken into consideration was proved to be fairly efficient.
In this paper, this method is extended for a problem of estimating the ultimate strength of a square plate under compression and shear. This extended method consists of two parts. The first one is elastic analysis in which Galerkin's method is adopted. The second one is plastic analysis in which collapse mechanism is assumed. In both of them large deformation theory is considered.
The analyses were carried out for a problem of a plate subjected to various combinations of compressive and shear loading. In addition, the influence of initial imperfections on the ultimate strength was clarified.
The following conclusions are obtained.
1) For a plate whose edges are kept straight under pure shear, it can be said that the maximum shear stress which corresponds to ultimate strength equals to τ_Y.
2) The ultimate strength of thick plate without initial distortion is not influended by types of load in combination. With the decreasing thickness of plate, in the range where compressive load is dominant, the ultimate strength becomes smaller.
3) On the other hand, the influence of initial deformations on the ultimate strength becomes remarkable with the increase of plate thickness and share of compressive load.

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The authors have already proposed the general principles in measurement of residual stresses. In this paper, the authors developed a new method for selection of observing positions of strains to ensure highly accurate measurement by using the theory of inherent strain, which is based on one of these principles.
By this selection method, it is seen that the more number of measurements ensures the better average accuracy of estimated values. However, there are many positions where observed values scarcely influence the accuracy of measurement. These positions can be excluded from the measurements for reasons of economy and comparatively small number of observing positions can be selected by the present theory, which still secures a high accuracy of measurement.
Furthermore, in order to measure three dimensional residual stresses in multipass welded joint, the proposed measuring method can be simplified by using the characteristics of the distribution of its inherent strains. According to this theory, three dimensional inherent strains can be divided into the components of inherent strains contained in the sliced cross section of the weld line and the longitudinal inherent strains contained in sliced plates parallel to the surface of the joint, and the measurement of three dimensional welding residual stresses has become practically possible.
By this theory, the distributions of residual stresses and longitudinal inherent strains in multipass welded joint have been measured for the first time. And the estimated residual stresses show a good coincidence with the directly observed stresses on its surfaces.
This implies that the present theory is reliable and applicable to measure such complex internal residual stresses.

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The welded joint is prepared to have a certain value of deformability as well as load-carrying capacity. Appreciable deformation of the structural component will be realized in the general yielding stage. In order to evaluate welded joint properties from the standpoint of engineering assessment for selecting materials, it is important to consider the criterion and deformability in unstable general yielding fracture of welded joint with defects. In the present report, attention is paid to the COD-criterion as the onset of unstable fracture beyond general yield, and deformation behaviors in the vicinity of notch tip of notched plate are studied in taking account of COD-gloval applied strain ε_∞. (overall strain in sufficient large gauge length). It is made a clear that the COD-concept can be adopted as the engineering fracture criterion for onset of fracture beyond general yield in the range that plastic constraint factor is not larger than unity. According to non-linear fracture mechanics approach in homogeneous materials, COD is proportional to the overall strain, and the proportional constant N is a function of specimen geometry and strain hardening exponent, n. In wide plate, N-value is almost equal to 1 and 2 for low strength C-Mn steel and high strength steel such as HT 80, respectively. In welded joint, the deformation behaviors is affected by the mechanical heterogeneity, and the COD vs. overall strain relation is not linear and mainly depends on the strain hardening exponent ratio.

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In this paper, the authors deal with the possibility of nonlinear excitation in “Tension Leg Platform” (TLP) which is categorized into vertically moored floating platform. The authors formulate the governing equation of sway and surge motions of TLP in which case TLP was modeled for mass-spring system with the consideration of geometric stiffeness effect, and carried out the fundamental test using one taut moored floater model.
Principal findings are as follows;
1) The motions of TLP generated by wave are expressed with Mathieu type differential equation.
2) Parametric excitation suggested from theoretical consideration was qualitatively confirmed from fundamental tests.
3) For the more plactical estimation of stability range and steady-state amplitude, more detail examination of hydrodynamic force are necessary.

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