In the previous paper I showed some applications of periodic source theory by taking appropriate distributions of sources on the boundary surfaces.
In this paper, (a) the heaving forces of two-dimensional ships among incoming waves and (b) the disturbances of incoming waves by fixed flat bottom ships are discussed. The methods of calculations are the same to that of the previous paper, and the results are shown in table 1 and figure 5.

抄録全体を表示

The resistance of a ship among waves is discussed by means of the energy analysis. The result proves that the increase of wave-making resistance is the origin of the additional resistance due to the seaway. The resistance in irregular waves can be defined only by the statistical sense. It is expressed in terms of the resistance in regular waves.

抄録全体を表示

In order to investigate the effect of sinkage and trim on form factor, resistance tests were condducted on two sets of geometrically similar models with keeping their trim and sinkage constant. The results of these experiments show that sinkage and trim have important effects on form factor of resistance and that form factor is nearly constant independent of ship's speed if the trim and sinkage in her runs were kept constant.

抄録全体を表示

In recent years, oil tankers which are newly built are getting large every year, and most of trial courses near the shipyards in Japan have become too shallow in relation to their dimensions.
In Hitachi Shipbuilding & Engineering Co., too, the drop of speed due to the effect of shallow water has become more important, when the speed trials of large tankers are carried out at the trial course off Yuge Island.
In this paper, some trial data of large tankers at the trial course off Yuge Island and some other places were analized refferring to the results of model experiment for a D. W. 47, 000T tanker, and following relations between the increase of resistance and the relative depth of sea were deduced.
(1) As for the frictional resistance,
α=191.4 (√A_??_/H-0.32) ²+16.57 (√A_??_/H-0.32)
where, α=Rate of increse of frictional resistance in %
A_??_ Area of midship section in M²
H= Depth of sea in M
(2) As for the wavemaking resistance, the effect of shallow water can be neglected in this case.
(3) Consequently, the upper limit of relative depth where the effect of shallow water upon the resistance of large tankers does not appear is =0.32 in ordinary speed for them.
This analysis was done by Dr. Hughes' new method, and it is concluded that, in practical use, Dr. Hughes' method is better than the old one using the Schoenherr line or I. T. T. C. 1957 Model-Ship correlation line as far as the problem of frictional resistance of large tankers.

抄録全体を表示

Some years ago the systematic model experiments on fishing boat forms were carried out at the experimental tank of Tokyo University.
Since that time there have been major changes in model testing technique, and the analysis of model resistance results, which have made earlier data unreliable.
Accordingly, on four typical models among the former series, resistance tests with turbulence producing devices were carried out in three draft conditions, and the results obtained are compared with the earlier data. Specially, the effect of hull forms on form factors are investigated.

抄録全体を表示

As to the wave-interference phenomena connected with the bulb there have been presented two kinds of explanations : one being theoretical, and the other practical.
Following the theoretical explanation, which is largely indebted to Havelock and Wigley, we may assume that the wave-making characterististics of the bulbous bow can be safely represented by an isolated point doublet. If admitted, this goes at once to the conclusion that the free wave patterns due to the fitted bulb can be intentionally put just in inverse phase or with strictly half wave-length difference against the main hull waves. This is nothing but the most desirable situation for us in view of promoting the maximum interfering merits of the bulb.
On the contrary, the other explanation enforces, rather practically, too much importance of the virtual increment in the wave-making length of the hull which is caused by the bulb waves. In this way, it has long been believed that the reduced wave-making resistance accompanying the bulbous bow has much to do with its increased “effective wave-making length”. From this standpoint of view, it is suggested that, when any amount of bulb merit observed, the bulb waves must proceed by some intermediate fraction between 1/41/2 of ship wave length against the main hull waves. This means that from the bulbous bow we can expect only an incomplete interfering merit at the best.
This report is aimed for the experimental determination of the existing conflict, mentioned above, with regard to the 'actual' phase-difference between the bulb waves and the hull waves. The wave analysis procedure is applied for the first time. The conclusion is that the theoretical treatment of the bulb which is introduced by Havelock and Wigley can be practically approved. A few remarks are also made on the two different phases of the hydrodynamical characteristics of the bulbous bow. Its corresponding system of singularities is represented by the combination of an isolated doublet with a continuous source distribution.
The former has a positive and therefore the same sense with the latter in hull form characteristics, but has a negative and therefore the reverse sense in wave-making characteristics. This is the true reason why the wavemaking resistance is sometimes reduced remarkably with the bulbous form whose displacement is larger by its bulb than the original form.

抄録全体を表示

This is the second paper on the “Waveless Hull Form” which has been developed at the Tokyo University Tank during last two years.
In the first paper the tank experiments on the bulbous bow have conclusively proved that the wave-making characteristics of the bulb can be practically represented by an isolated point doublet. The free wave due to a point doublet has just the inverse phase against the wave due to a continuous source distributian. The latter singularity corresponds to a main hull, and the waves arise exclusively at the bow and the stern.
Therefore, if the waves due to the bulbs fitted at the bow and the stern most effectively interfere with the waves due to the main hull, the situation of the “Waveless Hull Form” is to be realized. That is perfectly possible with the combination of the bulbs and the main hull, best adapted to the designed speed. Thus we can realize the ideal of the “Waveless Hull Form”, which means the “Wave-Making-Resi stanceless Hull Form”.
The present author began with the investigation on the characteristics of the phase and the amplitude of the waves due to the bow bulbs with the newly designed mathematical hull forms, and attained to the “Waveless Bow” with the two models : one being a fine model C-101F and waveless at the speed of Froude's number 0.26, and the other a full model C-201 F2 and at F. n. 0.27.

抄録全体を表示

This is the third paper connected with the “Waveless Hull Form” which has been developed at the Tokyo University Tank during last two years. By the first paper, it has been ascertained experimentally that the wave-making characteristics of the bulbous bow is actually represented by an isolated point doublet, and that we can expect to realize the “Waveless Hull Form” by fitting two suitable bulbs at the bow and stern, respectively, of the carefully pre-designed main hull form. The second paper, presented by Prof. Takahei, deals with the problem of the “Waveless bow”.
While this third paper deals with the “Waveless Stern” from the above-mentioned standpoint of view. Unlike the bow wave, the stern wave is affected by the boundary layer, growing thicker and unstable near the stern. So it is not so simple to work out the problem theoretically as in the bow wave. With these effects of viscousty it redouble difficulty that the stern bulb is connected with the problem of the propulsion. Before proceeding to design the bulbs, we must know the starting point and amplitude function of the stern wave system. However, we have only poor informations about the behaviour of the wave near the stern. These must be determined almost experimentally.
As the first step, it is desirable that the bow wave system is canceled already and the stern wave system is sin term only, because the wave of the bulb also has sin term. Resistance tests were carried on the bow-waveless mathematical models, C-101 F and C-201 F, fitted with the various stern bulbs. Thus, by trial and error method, we pursued the optimum bulb for the designed speed.
Through the above tests, we may conclude that the “Waveless Hull Form” has been almost completed in C-201 F2 × A4 (see Fig. 7, 8, 9) at F = 0.28.

抄録全体を表示

Regarding the utilization of the energy of propeller race by Contra-Rudder to the propulsive perfomance, the author cleared the currrent-pattern of propeller-race and handled this problem on the basis of the lifting line theory, to examine, from the viewpoint of velocity field of propeller-race, the propriety of the propeller theory that has hitherto been advocated.
This report deals only with the fundamental theoretical calculations and three important results induced therefrom ; and the contrasting of the fundamental calculations with the experimental results produced by various counting methods will be described in a succeeding report.
The items which were cleared up in this theoretical counting, and the matters wherein the errors in the theory hitherto advocated were amended are reported as follows :
i) The time average value of induced velocity of the propeller-race by a finite number of blades is equivalent to the values secured on the assumption of an infinite number of blades when circulation distribution is given.
ii) The element-value of propeller-radius-direction in the induced velocity on the propeller disk by free vortices is not a half of the value in the ultimate wake.
iii) The average value of element of propeller-revolving diredion in the induced velocity by bound vortices is equivalent to the value on propeller disk by free vortices, and the former coming over the latter, the velocity becomes zero in front of the propeller and the definite induced velocity regulated by the circulation is given in the race.

抄録全体を表示

The author once pointed out that the face-cavitation around 0. 7 R might occur at the lowest number of rotations in the four-bladed propeller with ogival section, and emphasized at the same time that the blade-section around 0. 7 R should be designed perfectly to be an aerofoil section. Afterwards, the erosion that grows on the face around 0. 8 R in five-bladed propeller has frequently become an issue for discussion. The author, however, is of the opinion this is chiefly because the danger-section around O. 7 R in four-bladed propeller has slipped nearby to 0. 8 R which holds an almost perfect ogival section in five-bladed propeller.
In planning cavitation free propeller it is insufficient to consider only 0. 9 R or other specific sections ; the author is of the opinion that the growth of cavitation all over the propeller should further be studied. For this purpose, it is necessary to make the pressure distribution of wing section in each radius quite clear. The author has made a surveying experiment on the pressure distribution, of the blade sections of Troost's type propeller and Kármán-Trefftz profiles with circular arc camber line, and wishes to report on the result of his experimentations.

抄録全体を表示

Theoretical methods in planning the wake adapted propeller and the cavitation free propeller are being suggested in foreign lands nowadays. Almost all of these methods are to design the optimum propeller by the lifting-line theory and to amend the camber ratio and pitch ratio by the theory of wide-bladed propeller advocated by Ludwieg & Ginzel and Lerbs. The theory of the wide-bladed propellers has been published also by Strscheletzky, Yamasaki and others, in addition to the above stated three. However, there are defects in those theories, theoretical and practical, and the counting methods are very much complicated. The author has developed a new theory of the wide-bladed propellers by applying De Young's theory of the low aspect ratio wings of arbitrary plan forms to propellers.

抄録全体を表示

The paper records the result of experiments with a systematic series of modified AU-type four-bladed propeller models.
Charts of the series are shown by so called √B_pδ design diagrams.

抄録全体を表示

This paper reports on the new electric-type torsion meter, designed and developed by Mitsubishi Nagasaki Experimental Tank, for the measurement of the torque of the propeller shaft of the high speed naval craft.
The special features of the new torsion meter are as follows.
1) The mechanical parts are designed to be as compact and light as possible, in order to be fitted to the small and high speed propeller shaft.
2) The electronic measurement part consists of the “inductance-variation-type” transducer for the measurement of the relative angular displacement of the two sections of the propeller shaft, and is very stable and convenient for use.
3) The mean value of the fairly steady torque can be measured by zero-method with high accuracy, and continuous recordings for varying torque are also possible.
The data for design and construction of our new torsion meter, the method of calibration and our experiences of the measurements, are reported with some examples of ship trials.

抄録全体を表示

It is needful in design of the freeing ports to know discharge coefficients of them. Results of experimental studies now conducted are as follows.
1. The fundamental coefficients for full-sized ports (Fig. 1), standing and upright, are shown in Figs. 2-5.
2. The coefficient, when ports, small-sized, are standing and upright, is approximately independent of arrangement of deck houses.
3. If ports roll, the coefficient will be somewhat decreased at a high water-head and moderately increased at a low head, so long as the ports are situated on the both sides of a well. Of ports along side passages, this tendency will be feeble.
4. Orbital motion of a ship does not affect so much to the coefficient.
5. We can use in some allowance the coefficient for an uprightly standing port.
6. Continuous ports on the both sides of a well, found on cargo ships etc., will discharge water between the top of the bulwark and the upper edge of the port within one period of rolling. A port along a side passage will show the same capacity, if it has an area required by the “Free-board Rule”.
7. Deducing the size of port, the coefficient get larger.
8. A slant port (Fig. 20), bored in an inclined plane inside a bulwark lest the port-door may open and patter with ship's rolling or by wind, proves some increment even in discharge.

抄録全体を表示

We usually assume a constant wind moment or a cos²-ly varing one. But these are not wellfounded.
Wind force and its centre of application were ever experimented by Mr. okada and the centre of water pressure which resisted to steady drifting on a still water by one of the present anthors. With these results the wind moment on a ship is most stong at nearly upright position and decreases somewhat rapidly with her list, wind-wards or lee-wards. Work done by the wind moment during one swing of the ship is considerably less than that by an assumed constant moment.
This suggests that effects of shipping sea, shifting of goods and so on upon a ship in a confused sea, which were not ostensibly taken in usual calculations related to the dynamic stability, for example, in the stability standards, stand comparison with wind and waves.
These data, especially the centre of water pressure, however, may be affected by encountered waves and associated rolling. Experiments were conducted with model-ships, for this time, under actions of wind and regular waves in the experimental tank, and it was cleared that the wind moment among waves also was computable approximately with above data modified suitably.

抄録全体を表示

An attempt of measuring the rolling and heaving, and observing the shipping water of ship models on the regular short-crested waves was made to see the behaviours of the small crafts floating on the seaway, and the following results were obtained :
(i) The rolling of a ship is easier on the short-crested waves than that experienced on the long-crested waves.
(ii) On the top of the short-crested waves, the shorter the ship is the heavier the heaving becomes.
(iii) The ship floating on the short-crested waves has more occasions of shipping water in spite of her reduced angles of roll.

抄録全体を表示

Spectral distribution of oscillation of a ship has, in general, two peaks, which originate the resonances of pitching or heaving and rolling.
This phenomena increase the irregularity of motion compared with the case when they are completely isolated with each other, and furthermore, also freqnency distribution of amplitude hastwo peaks, the larger portion of which is due to combined oscillation.
According to Rice's theory of envelope, letting R be the amplitude of envelope, which is irregular, P, Q be rolling and pitching, which are supposed to be regular, then the probability density which lies between R and r+dR is
p (R) = R∫^∞₀rJ₀ (Pr) J ₀ (Qr) J₀ (Pr) e ^{- (ψ₀/2) r2}dr.
This integral can be developed further as follows :
R/ψ₀exp [-1/2ψ₀ (P²+Q²+R²)] · {I₀ (PR/ψ₀) I₀ (QR/ψ₀) I₀ (PQ/ψ₀) +2∞Σm=1I_m (PR/ψ₀) I₀ (QR/ψ₀) I_m (PQ/ψ_m)}
where ψ₀ is mean square of forced oscillation components.
This distribution becomes
R>>0.p (R) _??_I₀ (PQ/ψ₀) /2π√PQexp [-1/2ψ₀ (R-P-Q) ²]
and when there is only one resonance
Q=0. p (R) =R/ψ₀exp [-1/2ψ₀ (P²+R²)] ·I₀ (PR/ψ₀) _??_1/√2πψ₀ [-1/2ψ₀ (R-P) ²]
so that the maximum frequency shifts from R=P to R=P+Q, namely at the amplitude of sum, of P and Q.
So that combined resonance oscillation sometimes causes extraordinary large amplitude.
Letting circular frequencies be p andq for the amplitudes P and Q, irregularity reaches at the extreme value when :
Pq=Qq

抄録全体を表示

A ship, which is directionally unstable on straight course, can turn against the rudder in a certain range of rather small rudder angle. This singular phenomenon was first pointed out by P. Contensou.
The present writer discusses this phenomenon mathematically by assuming that the resistance derivatives are linear functions of the curvature of ship's path. He assumes, for simplicity, that C_Yβ=C_Yβ₀ (1+kΩ), and descrives the motion of ship by nonlinear differential equations. Then the stability of the steady turning of an unstable ship can be tested topologically on a phase plane.

抄録全体を表示

Previously the author defined the hull forms by the expression of U, M, V. (Cf. the Journal, Vol. 106)
The author calculated the hydro-static characteristic of 36U, M, V combinations of after and fore bodies by the Simplified Non-dimensional Hydro-static Calculation method, (Cf. the Journal, Vol. 107) and compared the hydro-static numerals by the non-dimensional expression.

抄録全体を表示

As the results of theoretical calculations about a uniformly loaded rectangular plate with supported edges we find as follows,
1. The bending moment at midspan can not be reached the plastic hinge moment, therefore the plastic hinge does not appear.
2. The elastic region diminishes rapidly with the increase of the load after the yielding of outer fiber of tension side at the midspan.

抄録全体を表示

In this report, following the preceding paper, the large plastic deformations of the corrugated bulkhead are discussed under transverse impact at center such as considered inelastic imapct when all edges of the bulkhead are clamped.
We are first concerned about both maximum deflections and deformations, in the case of plate material having ideal characteristics of plastic bending moment M_p (θ) such as expressed by M_p0γ₁ (1+γ₂θ) and keeping the ratio of two plastic moments due to bending or twisting, independent of angular velocity θ. Then the criterion of fracture for the impulsive load to the plate is given applying the theory of the propagation of plastic strain along the longitudinal axis of corrugated bulkhead. In theoretical analysis, the shape of impulsive load is assumed rectangular between impact duration 2T.

抄録全体を表示

This is the 6th (final) report of the studies on the orthogonally stiffened plate. In this report, it is given the solution of the orthogonally stiffened box type structure, while the experiment of large scaled box structure is carried out.
Comparing the observed deflections and stresses with the values derived from this theory, it is shown that orthogonally stiffened box type structure can be also expressed by this theory as concluded in the preceding reports.

抄録全体を表示

In the case of circular cylindrical shells reinforced by frames a certin part of shell plating cooperates with frames. The neutral axis of reinforced shells can be determined assuming the shell of breadth equal to the effective breadth B_F for normal forces as a part frame. The effective moment of inertia is given by the sum of the moment of inertia of the assumed frame and (B_M-B_F) t³/12, where t is thickness of shells and B_M is the effective breadth for bending moments. These two kinds of effective breadth are determined by means of a simplified theory of shells. B_F is of order of thickness of shells.
On the othe hand, B_M may be of order of radius in the case where frame space is large enough.

抄録全体を表示

Collapse of ring-stiffened thin cylindrical shell under external pressure can be divided into two kinds, one “Shell Collapse”, the other “Bodily Collapse”.
The “Bodily Collapse” was named and proposed by Tokugawa as the originator in this study of the world, but subsequently it is called “General Collapse” in the United States. As for “Shell Collapse”, researches were made by both Tokugawa and Windenburg, and are sufficiently practical in respect of Mild Steel. But, since High Tension Steel with superior weldability came out in public sales, we carried out experiments to obtain its characteristic qualities.
Regarding “Bodily Collapse” there are two Theories in Elasticity, one by Tokugawa, the other by Kendrick, but they have not been put into actual use yet. Formulae, either by Levy or by Lame, which are now adopted in actual designs, show considerable discrepancies, as far as their definite length are concerned, when compared with the experimental results. Therefore, we aimed at putting Tokugawa's Theory of Elasticity into actual design, this time.
Now, let us take :
ψ=P_K·D/2S (1+σ_YF/σ_YS·F/l'S) ·σ_YS, B=σ_YS· (1+σ_YE/σ_YS·F/l'S) /E· (D/L) (S/D) ^1.5· (I/l'S³/12) ^3/4
considering, ψ is “Mean Pressure Factor” and B is “Bodily Factor”. The relation of ψ and B is shown in Fig 9.
When calculating moment of inertia of stiffener, the effective breadth can be adopted with three (3) S in case of inner stiffener, and one (1) S in case of outer stiffener.
If ±10% of tolerance is permitted, Fig 9 may be used in the actual design as they are, regardless whether they are Mild Steel or High Tension Steel.

抄録全体を表示

The paper on the stress measurements of the transverse members of three actual tankers were already reported by the author, and after them, similar experiments were carried out on the two tankers under the auspices of the 38th. Research Committee of the Shipbuilding Research Association of Japan.
In this paper, were described an approximate calculation method on the transverse strength of tanker by use of Slope-deflection method and the examples of the calculations to be compared with some data of the experiments.

抄録全体を表示

In order to measure the deflection in long span dynamically, a new type deflection gage was designed.
The gage is made up of eleven steel pipes placed in one row, ten connecting pieces (pickups) and two end pieces. The pickup contains four electric resistance strain gages and the output voltage is in proportion to the angle change between adjacent pipes. The sensitivity is 0.3 mv per 1/1, 000 radian. (0.06 degree) The accuracy of deflection over 66 ft. span is 1/50 in., and maximum measurable deflection is 10 in. in same span.
Satisfactory results were obtained in experimental voyages of four wooden ships in rough sea, and the influence of hull deflection upon the bending of shafting was explained.

抄録全体を表示

Previous reports of this series of article concern the impact force of a ship receives from the quay-wall when the ship contacts it. This paper discuss the stress and deflection in outside plate of ships subjected to the impact force.
Various possible conditions of contact between quay-wall and a ship are considered. A model experiment is given. Numerical results presented in the form of graphs showing the maximum speed not induced the damage in the ship.

抄録全体を表示

To study the fatigue behaviour of ship structural steels, in high stress ranges far beyond the elastic limit, the author conducted the cantilever rotatory bending tests of circular rod specimen with semicircular circumferencial notch on some kinds of steels.
The time strength diagrams of low cycle fatigue, with in both logarithmic scales, are straight lines for each material. The stress ratio of the bending stress to the ultimate tensile strength is the best standard to estimate the time strength diagram of unknown material.
The depth of the circumferencial crack in the ruptured section increases with the increasing number of cycles to rupture N, or the decreasing bending stress σ. We can estimate the value of N and σ from the depth of crack c. The ratio of the nominal maximum bending stress at the root of crack in the ruptured section to the breaking stress on the final area, takes a constant value unrelated with the number of cycles to rupture.

抄録全体を表示

Several vessels have recently been fitted with Bipod type masts, which compries two legs, inclined towards each other, and connected at the top by an outrigger.
The authors attained the formulas of calculations, by the “Slope deflection method”, for these mast structures built up with the outrigger of various rigidities. These results were confirmed by the experiments for the model.

抄録全体を表示

This paper describes, firstly, an analytical method of computing the eigenvalues of vertical vibration of ships taking into account the distribution of mass, the effect of variable section and the effect of shear deflection and rotary inertia. The fundamental equation is solved by Galerkin's method in the form of numerical integration.
For 2 node vertical vibration, the virtual added mass is calculated by Lewis' or Taylor's method and by using it the computed natural frequencies are usually in good agreement with the, observed frequencies. For more than 3 node vertical vibration, however, the virtual added mass calculated by Lewis' or Taylor's method results in considerable discrepancy between the computed and observed frequencies.
To explain this discrepancy the author examins the effect of local vibration of ship's bottom on the virtual added mass and obtains a reasonable correction factor for the virtual added mass.
Applying the above described method, an analysis of the vertical vibration of two actual cargo ships is shown, and the computed natural frequencies are in good agreement with the observed frequencies for 2 and 3 node vertical vibration.

抄録全体を表示

In my previous paper, the estimation of the natural frequencies of hull has been made with the intention of avoiding the resonance with the service rpm of main engine. However, as a Diesel engine is practically selected from the existing types, it is occasionally impossible to keep clear of any resonance.
In this paper, allowable exciting force or moment at resonant point is investigated in the case where the acceleration due to hull vibration is restricted to a limitted value.
The procedure is as follows,
1) Allowable acceleration in accommodation (a) to be determined principally from a view-point of human sensibility.
2) The force at the ship's end causing the acceleration a (Fe) to be estimated.
3) The force at the ship's end of the primary order due to the production errors etc. of propeller and engine (Fp) to be deduced from the analyses of measured data.
4) The allowable force at the ship's end of main engine derived as the difference of Fe and Fp to be transformed to the force or moment at the position of main engine.
Allowable exciting force or moment can be considered to be approximately proportional to L² and L³ respectively.

抄録全体を表示

The present paper shows the three-dimensional correction factors for the virtual inertia coefficient and the correction for the rotatory inertia of the virtual added mass of water for horizontal vibration of a ship, including higher modes. Special consideration is given to the three-dimensional correction factors obtained from the theoretical study on the three-dimensional calculation of the virtual mass of water on a half-immersed circuler cylinder of finite length which vibrates on water. In calculating the kinetic energies for the horizontal vibration of the ship and the entrained water, the rotatory energy of the hull and the corresponding virtual rotatory energy of the water are taken into account. In addition the experimental determination of the virtual mass has been carried out on a wooden model of a tanker and the theoretical results are confirmed.

抄録全体を表示

A study is made of the three-dimensional virtual mass moment of inertia on the torsional vibration of an elliptical cylinder of finite length vibrating on the water with half-immersed draught. By taking the ratio of the three-dimensional virtual mass moment of inertia to the two-dimensional one on the torsional vibration of the elliptical cylinder, the correction factors are obtained in zero-node to three-node modes of the torsional vibrations of the elliptical cylinder. The computed results are applied to the correction factors for the torsional vibrations of a ship including higher modes, taking into account the beam-draught ratio and the length-draught ratio as parameters.

抄録全体を表示

When side walls of a rectangular tank, which is filled with water, is vibrating, the inside water will also make vibratory motion. This motion of water lowers considerably the natural frequency of vibration of the side walls of the tank. This effect is conveniently expressed by “Virtual Mass” of water. In the previous report, the author has made a theoretical study on the value of “virtual mass” of water, restricting ourselves to the case in which two opposite side-walls (among the six walls) are vibrating. The present report is an outcome of continuation of this study, and treats the case in which four walls of the tank vibrate. An approximate formulae for natural frequency of vibration for whole system consisting of four walls and the inside water, is also given.
The calculation throughout is made, regarding the water to be an incompressible, non-viscous fluid, and the amplitude of vibration to be infinitesimally small.

抄録全体を表示

As a testing method to obtain critical temperature-stress curve for propagation of brittle crack, the author proposes a notch tensile test of cross welded steel plate. An experiment has been carried out for the quenched and tempered steel “2 H”, having high notch toughness and high tensile strength, such as, 60 kg/mm², and the test result was compared with those of ESSO test and of double tension test with each gradient and flat temperature distribution. The result obtained by the test was very similar to that of double tension test with flat temperature distribution. (cf. Fig. 7)
The distinctive features of this test are summarized as follows :
1) The cross welded specimen, having a sharp notch in its high tensile residual stress field, may cause single stage complete fracture under lower applied stress than yield stress.
2) When a brittle transverse weld metal is provided at the location of notch, running crack may propagate to the base metal at the temperature above critical temperature for crack propagation without gradient temperature destribution on the specimen. Therefore, it is easy to apply this test for the steel of excellent notch toughness.
3) By adjusting the length of brittle transverse welded joint, sufficient speed of running crack may be obtained.
4) Fracture stress level of the specimen may be adjustable by preloading at the temperature above critical temperature of crack initiation under low applied stress level.
Further investigations should be performed about stress destributions at the propagation field under various loading conditions and also about stress re-destribution during crack propagation.

抄録全体を表示

The authors have investigated in their experiments the effects of residual stresses due to welding upon the initiation of brittle fracture in welded structures from the several points of view.
As one of these series of their tests, an experiment was carried out to investigate the effect of notch shape, such as, length of notch and radius of notch root, on brittle fracture strength of welded steel plate, by conducting the notch tensile tests on wide longitudinal welded specimens and base metal specimens.
The main results obtained are summarized as follows :
1) Providing the location of the notch root to the un-affected zone of base metal apart from the weld heat affected zone, wide longitudinal welded specimens caused brittle fracture under lower applied stress levels than yield stress at the temperature range below nil ductility transition temperature of the notch root, while the fracture strength of the base metal specimen, having same shape of notch, reached to high stress level as high as yield stress at the same low temperature range. (cf. Fig. 5 and Fig. 6) The exhaustion of ductility in steel at the root of notch is, of course, one of the reasons. why brittle fracture initiates as Mylonas pointed out. Although the exhaustion of ductility in steel may be a necessary condition for initiation of brittle fracture, it might not be a sufficient condition for low stress fracture,
2) In order to investigate the effect of notch length on brittle fracture in residual stress field, wide longitudinal specimens with different length of notch but constant radius of O. 1 mm were tested at the temperature of -30°C. Fracture test on the base metal was also conducted with different length of the notch. As the results seen from Fig. 9, the fracture strength of base metal decreases with the length of notch, while the fracture strength of welded specimens increases with the length of notch except the length below 36 mm. For the case of specimens with notch less than 36 mm the fracture strength increases as notch length decreases. This is mainly due to the higher initiation strength of weld metal. The reason why the fracture strength of welded specimens increases with the length of the notch is due to the reduction in residual stresses while the stress concentration factor at the root of the notch remains constant because of the same sharpness of the notch. This is a strong evidence of the effect of residual stress upon the initiation of brittle fracture.
3) Effect of notch radius on the brittle fracture strength of welded joint was clearly confirmed as shown in Fig. 10. The radius of notch was varied from 0.1 mm to 1.0 mm for base metal and welded specimens respectively. If the radius of notch is greater than 0.3 mm, the reduction in fracture strength due to residual stress seems to diminish except extremly low test temperature. Therefore, it is concluded that the effect of residual stresses on brittle fracture can be evaluated only if the sharp notch exists in the residual stress field.

抄録全体を表示

In construction of hulls, the most of weld crackings are originated in fillet joints, and also many toe crackings which are remained almost unknown on their initiating process, are frequently included in them.
In this respect, author has studied on the cause and effect of the toe crack initiation in a full penetrated T type fillet joint of thick plates and obtained the conclusions as follows :
1. The cracking of this kind was prevailing on the toe of the backingpass-side weld and originated from the notch root suffered large weld strain by the thermal and strain cycles in the finishing-pass-side welding.
2. In these thermal and strain cycles, above 90% of the strain were proceeded below 550°C and the strain cycles worked mostly as contraction on the notch root.
3. In the case of the sum of the absolute value of the weld strain on the notch root exceeding 12%, the toe cracking initiated in further straining.
On this critical value of the strain, same results are obtained as retained ductility of the mechanical prestrained specimen in bending.
4. As factors increasing the weld strain, there were the depth of back-chipping, the larger diameter of welding electrode and the sharpness of the notch root. On this account, for the prevention of the cracking, the welding should be carried out in controlled conditions on these factors.

抄録全体を表示

The stress distribution and the amount of crack-open-up are calculated on an extending crack : with a certain constant velocity under uniform tensile stress at infinity, and the effect of crack velocity on the stress distribution and strain energy release rate is studied.
The conclusions are as follows :
(1) The stress distribution on the crack path is not disturbed beyound the point where the longitudinal stress wave reaches at that moment, and in the disturbed region stress becomes partially lower than the uniform stress at infinity. The minimum stress appears at the point where Rayleigh wave reaches.
(2) As in the static problem, the released elastic strain energy is proportional to the square of the crack length and the strain energy release rate is proportional to the crack length. The effect of crack velocity to them is little while the velocity is not so high (α < 0.2), but when the crack propagates at the higher velocity they increases rapidly, and at the velocity of Rayleigh wave they becomes indefinite.

抄録全体を表示

Adopting the idea of double tension test developed at University of Tokyo, the author investigated the behaviours of steel plates to propagation of brittle crack under the similar condition to the service. Critical temperatures for crack propagation defined on the double tension transition curves by the same stress level as the design stress were found to be closely correlated to the 50 %crystallinity transition temperatures of the pressed-notch Charpy test. Acceptance criterion on the pressed-notch Charpy specimen derived systematically from the present experiments was well corresponding to the minimum Charpy requirements by the Lloyd's Register of Shipping and the Nippon Kaiji Kyokai, for the hull structural steel plates.

抄録全体を表示

Mechanical properties of high strength steel in the plastic range are of fundamental importance especially when it is applied to the plastically designed structures. The structure may fail because. of various types of buckling : column buckling of the bending type, torsional or local buckling. Often the failure is due to a combination of these different types of buckling. In order to be able to solve these problems theoretically it is necessary to know the relationship between increments of stress and strain after the material has been loaded and deformed up to a certain state and along a prescribed loading path.
For the case of flange buckling of wide flange sections the resistance against buckling depends. almost completely on the relationship between additional shear-stresses and strains following a given amonnt of axial compression.
The tests described in this report were an sttempt to measure the tangent shear modulus G_t directly. Round bar specimens machined from the plates of high strength steel were axially loaded up to the strain-hardening range. Keeping the axial load constant, the torsional moments were applied next. By means of a specially made foil gage for the measurement of plastic strain both axial and torsional strains were measured.
Initially the value of G_t approached the elastic value G=8, 000 kg/mm²but dropped rapidly with_ increasing values of shear strain γ. For γ=1. 02. 0× 10^-3 it is found that G_t=2, 5001, 500 kg/ mm². From there on G_t decreased slowly with increasing γ, and for γ=5× 10^-3, G_t=1, 000 kg/mm².
Thus it can be concluded that the flow theory of plasticity which predicts G_t=G (elastic) is true, but only for very small shear strains. Due to unavoidable initial imperfections the initial. behavior for small shear strains cannot be of determing influence. The above finding value of G_t ≈2, 000kg/mm² may be used for the prediction of lateral-torsional buckling of high strength steel structures. The theoretical analysis on G_tbased on the flow theory of plasticity was confirmed by the test results.

抄録全体を表示

In order to investigate the ductility of stainless clad steel with various clad ratios and clad arrangements, eight tests for the notch sensitivity of steel were performed, and clad ratios were varied in five stages, zero (mild steel), 1/7, 1/3, 1 and infinite (stainless steel) and clad arrengements were varied in three types, single type, double type and sandwich type. Effect of clad ratio and clad arrangement on various transition temperature can be seen in Table 3 and 4.
In all tests performed, clad ratio and clad arrangement affects the ductility of stainless clad steel and higher clad ratio indicated more ductility and sandwich type clad steel had highest ductility in the three clad arrangement.

抄録全体を表示

In the tests on brittle fracture of longitudinally welded wide plate specimens or welded spherical containers it was frequently observed that the propagating brittle crack in the direction oblique to the weld line changed its direction when the brittle crack approached to the welded joint, or the brittle crack initiated from the weld flaw was branched off and arrested by the base metal. The similar phenomenon was also observed in the brittle fracture of welded structures in a service condition.
Consequently it may be considered that the residual stresses due to welding affect considerably the propagation of brittle fracture as in the case of initiation of brittle fracture. In order to study these effects of residual stresses on brittle fracture propagation, especially on the direction of propagation, the tests were conducted by using several types of welded plate specimens having an unsymmetrically placed longitudinal joint, adjacent two joints parallel to each other, or a diagonally placed oblique joint. The test specimen with a trapezoidally impressed artificial notch was fractured by applying impact under the temperature lower than the arresting temperature.
The principal stresses in the welded specimens were measured in order to analyse the direction of brittle fracture.
It may be concluded from the test results that the brittle crack propagates in the direction perpendicular to that of the maximum tensile stress resulting from the residual stresses due to welding and the applied stress, and the direction of brittle crack becomes unstable in the compression region of the resultant stress field.

抄録全体を表示

Pressed and aged notches were employed to large tension specimens for propagation tests of brittle crack. Shapes and conditions of specimens which were determined by several preliminary tests showed excellent ability for crack initiation.
Following the similar method to the ESSO test, only one-tenth of impact energy was required in this test to initiate the brittle crack, as compared to the one necessitated in the ESSO test and the condition of crack initiation was insured even at lower stress level or at higher temperature range in spite of very low impact energy.
Only by applying the impact without any tensile stress, the brittle crack could initiate and propagate, so the propagation characteristics of target steels could be estimated by wedge impact test on smaller specimens.
The specimens with no impact showed crack initiation at about two-thirds of stress level of yielding stress.

抄録全体を表示

In order to protect carbon steel in sea water cathodically, it is necessary to polarize it less noble than-0.77 V (referred to saturated calomel electrode).
In the case of cathodic protection of the ship, -0.77 V is usually applied as the protective potential.
And in most the protective effect of this application has been decided with measuring the hull potential of stationary ship.
But it is very doubtful from the view point of the polarization characteristics whether the potential of ship hull is kept in equal without in active state or in stationary state or not.
So that, foundamental study was conducted on the relationship with the sea velocity and the natural electrode potential or protective current of mild steel.
Furthermore the influence of the speed of ship (destroyer) on the hull potential was investigated under the auspices of the Japan Defence Agency.

抄録全体を表示

The use of the zinc anodes having superior character is the simplest and most effective method for the corrosion protection of ship hulls. In order to find the anodes, we carried out some experiments with various zinc anodes containing different kinds of elements. From the experiments, it is found that the performances of zinc alloy anodes which contain Hg, Cd, or Al exceed far that of other zinc anodes containing Mg, Mn, Te, Ge, or K etc.

抄録全体を表示

The corrosion rate of tank depends mainly upon the service condition of the tank, but the relation between the corrosion and the condition of the tank have not been unclarified in delails. We carried out several corrosion test of tank compartment in their different conditions. The corrosion rate of test pieces installed in tanks which were alternately filled with crude oil and kept empty (not filled with sea water) was 0.0720.23 mm/yr. and was severer than that have expected.
In the case of tanks which was alternately filled with crude oil and dirty ballast sea water, the corrosion rate was slightly severer than that of the empty tanks. The tanks filled with clean ballast sea water was corroded as much as 0.240.36 mm/yr. and these values were several folds of the corrosion in the empty tanks.

抄録全体を表示

Authors investigated the effect of the amount of prestrain at high temperatures on the retained ductility, fracture stress and flow stress curve of killed mild steel.
As the result, it was revealed that the retained ductility of steel was fairly affected by both temperatures and amounts of prestrain and generally reduced more conspicuously by prestraining in tension at high temperatures than at room temperature. It was also indicated that the ductility retained after prestraining at 200°C and 500°C exhibited the lowest values, and that in the range of much prestrain, total ductilities obtained after prestraining at these high temperatures became about 60% of those obtained after prestraining at room temperatures. Moreover, it was observed that the fracture stress was fairly reduced by prestraining in tension at the temperature higher than 400°C (cf. Figs. 7 and 8).
On the contrary, the conclusions were led to be rather different when compressively prestrained. In this case, it was found that in the range of prestraining up to about 60%, the retained ductility was hardly reduced at any prestraining temperatures and consequently that the total ductility rather increased with larger amount of prestrain, beyond which the retained ductility began to be apparently reduced as after tensile prestraining. As a whole, it appeared that the retained ductility was less reduced after prestraining in compression than in tension. Similar results were obtained regarding the fracture stress in the same range of pre-compression (cf. Figs. 12 and 13).

抄録全体を表示

After scrutinizing both the contents and quantity of work carried out in the Shipbuilding Plate Shop, we adopted a renovated production system by using conveyors, whereby the steel materials are not only carried on the conveyors but at the same time processed thereon.
The result proved so fine that the layout of the new shop became neat and systematic as is illustrated in Fig. 7, the production efficiency was improved by more than 30 percent, and the production capacity per unit area was nearly doubled.

抄録全体を表示

It is a well recognized fact that the arc-air gouging process is more advantageous than the pneumatic chipping method in point of economy. In carring out the gouging in Japanese shipyards there arises an important problem because their electric source is of alternating current whereas the arc-air gouging should be of direct current.
Considering this special situation of Japanese shipyards, authors have made different types of carbon electrodes for arc-air gouging in order to investigate their applicabilities and ascertained the usefulness of carbon electrode for use with alternating current in shipyards.

抄録全体を表示