The Author attempts to develop the method proposed in his last paper (this Journal Oct. 1947)to the general cases. Specially the Vibration of the rectangular plate stiffened with beams aredealed.

View full abstract

In this paper the vibration of the double bottom constructions of ship is investigated theoretically, using the method which was introduced by Dr. W. Schilling in his research of the strength of the double bottom and it is confirmed that the frequency functions presented in my last paper (this Journal May, 1946) are useful to describe the formulae concisely.

View full abstract

The torsional-and extentional-vibrations of plates are not so important as an ordinary vibration problem owing to their high frequencies, but in the case of impact, the duration of impact may be the same order as the periods of these vibrations of plates, so that the vibration of this type will be excited in plates.
On this standpoint, the auther investigated on the torsional-and extentional-vibrations of circular plates clamped at the periphery. In the first place, the free vibrations, and the second, the forced vibrations are studied analytically. as the results, the natural frequencies, the displacements, and the stresses are obtained in some cases.

View full abstract

The investigations on the transient phenomena of vibration of a strut due to axial impact load are scarcely known so far as the author is aware, and only the case of the strut under constant impact load is mathematically investigated1).
In the previous papers2), 3) the author explaned influence of the initial condition of vibrating strut upon the transient vibration and the case of buckling of the straight bar due to axial impact load.
The present writer deals with, as the third report, the case of transient vibration of the strut having initial deformation same as fundamental mode of vibration under axial impact load.
In the results of the present investigation, the author has been proposed a convenient solid curve to find the amplitude of the transient vibration in connection with the given magnitude of impact load and the duration of impact.
The model experiments which already explaned in the previous first paper were carried out and compared with results of theoretical calculations.

View full abstract

Vierendeel beams with longitudinal bars of different moment of inertia are treated. By the aid of the Slope-Deflection Method, the relation between the end-slopes of each members are represented in the forms of simulaneous difference equations. Solving these equations, the slopes of each members are to be determined, and the constants involved in the expressions of the slopes can be calculated in the both cases of the end-conditions of both ends fixed and both ends supported simply. By the use of the above determined values of the end-slopes of the each member, the bending moments, the shearing forces and end-displacements of each member are able to be obtained. Therefore, we can determine the strength and rigidity of the Vierendeel Träger at the same time.

View full abstract

The auther applied the sequential probability retio sampling test to some rule of “Kosenkozokitei” and “Kosenkisoku”. He calculated sampling number of test piece for material test, and tabulated result. And he proposes scientificallization of safety factor or factor of ignorance by using mathematical statistics. Last, he must say he is very obliged to Mr. A. Wald who devised that test plan.

View full abstract

Marine propellers, being operated in the wake of a vessel, are subjected to the forces and moments of every kind. This paper deals with the theoretical treatise of this probem with an approximation after the manner of Mr. H. Glauert. Consider a right handed propeller and choose the system of axes shown in Fig. 1, The xis of x is taken forward along the axis of rotation, the axis of y to the left, and the xis fz upwards. Let OP represent one blade of the propeller at an angle ψ from Oy, and let the speed of advance and the angular velocity of the propeller be V and Ω respectively, For a propeller of a twin-screw vessel, the flows as follows must be taken into account besides the uniform axial one.
(i) Velocity v along the axis of y......δΩ=usinψ/r, δV=0.
(ii) Non-uniform flow of the direction of the axis of x varying along the axis of y, h=w₂-w₁/2(1-w)V......δΩ=0, δV=hr/Rcosψ
(iii) circular flow around the axis of x, {rotational flow, ......δΩ=ω, irrotational flow, ......δΩ=f/r², where w₁ and w₂ are the wake fraction at ψ=0 and ψ=π respectively, w is the mean wake fraction over the propeller disc, and r=√y²+z², f=Γ/2π, Γ is the cyclic constants. Let the components of the inerements of the resultant force and moment experienced by the propeller be δX, δY, δZ and δL, δM, δN respectively, then these values may be expressed as shown in the following table. In this table T and Q are the thrust and torque of the propeller in uniform axial motion respectively, and R is the radius of the propeller.
Δ₁ and Δ₂ denote the differential operators defined by the equations Δ₁=1-1/2J∂/∂J, Δ²=J/2∂/∂J respectively, A₁ and A₂ are the coefficients expressed as
A₁=l_nπ²2+J²2/J²/1-J²/π²l_nπ²+J²/J², A₂=1/{21-J²/π²l_n (J²+π²/J²)}-J²/π²and J is speed coefficient.
The authors apply the above results to the case of a twin-screw vessel, and obtain the forces and moments experienced by the vessel. Furthermore, they make a numericalr calculation for the case of full speed sailing of the train ferry-steamer “Ishikari-Maru” of the Aomori-Hakodate line as an example.

View full abstract

The auther describes in this paper, about some characters and amount of forces acting to bodies among waves, and side forces and turning oments acting to ship passing athwart through wave crests; and then, solving the equation of motion under the action of periodic forces caused by the waves, referes to the general characters of yawing, especially about the relations with amplitude of yawing for period of waves, amplitude for direction of waves (rear or ahead), and amplitude for length of ship conpared with wave length,

View full abstract

In this paper a method of judging the stability of small sea-going vessels recently built in our country was studied. The standard condition selected for the research of stability is that in which a vessel sails in the direction of synchronism with waves under the action of her standard steady wind and centrifugal force and is suddenly struck by a squall when she is extremely inclined to the windward direction. New formulae were used to calculate the inclining couples due to the wind, centrifugal force and rudder pressure. For the unsymmetrical rolling among waves about the steady heel due to statical inclining couples the increase in the resistance to rolling under way and also in the apparent moment of inertia with the angle of roll was considered. When the vessel was struck by a squall, the angle of inclination was found by treating the new motion as composed of free rolling and forced rolling. A number of small vessels of all types with poor stability arms including several capsized ones were investigated by this new method and a critical line for stability was consequently obtained.

View full abstract

Under the present condition in which we are suffering from shortage of good qualified tallow, this system can be used for launching of large-type ships, without any tallow, by rolling steel balls between the rails of standing ways and sliding ways. It is far superior to the “Truck System” because of bigger allowable load and less friction, and is more advantageous than the “Roller System” due to the fact that balls can roll smoothly around any axis.
1) Diameter of ball is (90m/m±0.5m/m) and material is of high chrome steel. Each ball has 17 tons of allowable load and they are not effected by temperature like tallow.
2) Friction of this equipment may be expressed approximately by the following equation: F=μW F: Friction W: Launching weight μ: 0.01 in which μ shows ratio between friction and launching weight which is considered to be almost fixed.
3) This equipment can be used permanently and will cut down launching expenses considerably. Furthermore, it may be favorable for “Slip way” owing to merit of small friction.

View full abstract

Dichloro-Diphenyl-Trichloroethane is commonly called D.D.T. and it is a well known fact that its catalytic action has poisonous effect on insects.
With the presumption that the same effect may be seen on barnacles and seroula of algae, a soaking test has been performed with a test paint which has been mixed with D.D.T. to experiment of its utility value as shipbottom paint.
The first water test experiment was conducted on July 1947 at the quay in Yokohama Harbor by ship-bottom paint number one and nnishing it with paint containing 10% D.D.T. Kerosene Solution (as D.D.T. 0.5%). The result of the experiment showed that D.D.T. has some effect on barnacles during its breeding months of Summer. However, Since it was impossible to increase the compound ratio of the above percentage we were unable to obtain the final result.
The second test was performed in the Autumn of the same year, when seroula is plentiful, by increasing the mixture of kerosene solution from 5% to 40% with paint (as D.D.T. from 0.25% to 2.0%). But the result was not too favorable when compared to the test on barnacles. However, we learned that with the increase of D.D.T. contents it gradually became effective.
A similar test was further continued the following year with a 1% mixture of pure D.D.T. crystal, on a part of the bottom of the tug boat which runs within Yokohama Harbor. As a result of this test, it proved to verify our previous experiments that D.D.T. is very promising as poison to be used in shipbottom paint.
(1) The effect that D.D.T. has on barnacles is very promising and with a 10% mixture of D.D.T. it will completely stop the growth of barnacles for a long time. It can be recommended as a substitute for the heretofore used mercury commpound.
(2) D.D.T. has considerable effect on serpula but not quite so effective when compared to barnacles.
(3) The same could be said of in reference to“kokemushi”(Phylum molluscoidea-Class Bryozoa Gymuo aemats).
(4) D.D.T. alone will not serve a poison when used along with shipbottom paint. It is ideal to mix with inorganic poisonous matters such as copper compound which is effective to serpula and algae.

View full abstract

To determine the specifications for the strength of the anchor chain cables in cast steel, a series of experiments was done about the stud-links casted with different carbon-contents and heat-treated in different ways. As a result the empirical formula for the strength of links has been obtained as follcws:
W=0.446d²εt^0-25σt where W and d are breaking load in kg. and diameter in mm. of a link, σt and εr are ultimate strength in kg/mm² and elongation in % of the material of which the link is made.
Besides, the theoretical formulae for the strength have been obtained, considering plastic rupture of a link as a curved beam loaded by axial force and bending moment simaltaneously. Numerical calculations show that the theoretical values obtained by these formulae are agreed with the empirical values within the limits of experimental errors. Using these theoretical formulae, also the change process of distribution of stresses in cross sections of a link from no load to rupture can be shown evidently.

View full abstract

It is feared that the excessive thrust and torque of the shock type may act on the shafts of a vessel during starting, stopping or backing etc. and cause damages on the propeller blades, the thrust block, or the reduction gear in the case of a turbine steamer. But it is difficult to obtain a general conclusion because this phenomenon depends not only on the ship form, characteristics of the propellers and the propelling machineries but also on the operation of the machineries.
The authors prove the existence of the four “Humps and Hollows” of the characteristic curves of a screw propeller working under conditions of whole range of speed eoefricient J=v_a/nD=-∞ to+∞. And they give a thorough explanation theoretically on the three conspicuous fluctuations appeared on the “torque-time” curves plotted from the data of the backing trials of U.S. Destroyer Roe published by Comdr. P.D. Gold and of U.S. coast guard cutter Compbell by Comdr. Curry. The change of the thrust thus obtained theorectically can be used to calculate distance run, the speed of a vessel etc. during stopping or backing.
The train ferry-boats repeat arrival and departure time after time every day, and serve conditions of starting, stopping and backing on all such occasions as compared with ordinary large ships. The authors make a detailed numerical calculations after the above-mentioned theory about the train ferry-steamer “Ishikari Maru” of the Aomori-Hakodate line as an example.

View full abstract