In Part I, the authors treat the problem of the trimming moment caused by wave-making of. a surface vessel or a submerged body moving through a deep or a shallow water. General expressions are obtained for the trimming moment in each of the above-mentioned cases from Prof. Michell's method as well as from Prof. Havelock's one. The results of numerical calculation carried out for the cases of a yessel of mathematical form and a submerged prolate spheroid show good coincidence with the experimental results qualitatively. In Part II, general expressions are obtained for the wave resistance of a vessel of twin hulls. The results of numerical calculation show that the total effective horsepower can be reduced for a wide range of Froude's number by dividing into twin hulls keeping length, draught and displacement of a vessel constant, provided the distance between hulls is chosen suitably.
The author discusses the motion of water due to the oscillating body below the water surface with uniform advancing velocity, and obtains the free surface effects, such as wave making effect to the virtual mass and the damping for of the body.
In order to investigate fundamental properties of turning motion of a ship, movements of an elliptic cylinder were dealt theoretically with, when the cylinder in advance was steered suddenly in the perfect fluid. The resultant force on the cylinder in the direction of its long axis is a resistance in a case of stern rudder, while in bow rudder it becomes a negative resistance. But they are small and neglegible. The resultant force on the cylinder in the direction of its short axis is smaller than the lift of the rudder due to steering and acts in the contrary direction. Then the cylinder is on the bodily movement in the direction of the lift of the rudder. The resultant moment due to fluid pressure on the surface of the cylinder is smaller than the turning moment of the rudder and has the contrary sense. Then the turning motion of the cylinder is delayed. These effects is varied in accordance with the shape of the ellipse. The narrow form is effective, that is, it has better directional stability than the broadish one.
The Ship forms, especially those of small fishing vessels are to be determined from the point of view not only of propulsive performance but also of dynamical properties on the ocean. As the first step in the direction of researches, the author has performed the resistance -& rolling-tests about the 5 ship forms (a steel ship type, a wooden ship type & 3 intermediate types) of small seine-fishing vessels. This paper is reported about the results of these tests.
The Author has studied the “Course Stability of Ships” since last year. In this paper, he describes some results-specially the effect of cut-ups of stem & stern, - and calculates the motion of a ship after she was acted by some external forces.
The problems of lateral vibrations of rotating bars are very important with respect to the tur bine blades, and other revolving parts of high speed machine. The author has tried to solve the fundamental equation by means of the combination of Shrödinger's perturbation method and Baker Cowley-Levy's method. Namely the deflection was expanded in the double series of the square of angular velocity ω, and of the eigenvalues λ. Thus the frequency equations were obtained from the boundary conditions, and the frequencies of variable cross sectional bars were calculated with sufficient accracy.
In this article, we investigated the forced vibrations of clamped elastic circular plates under any eccentric forces, and the behaviours of elastic shock waves transmitted in the plates due to any eccentric shocks. We solved the problem by means of the forces or shocks expanded in the normal functions with the initial conditions; w=0, dw/dt=0 at t=0. As the particular cases, the distribution of forces or shocks were (i) uniform in the circle with radius a0 and eccentricity ε. (ii) concentrated at the point having eccentricity ε. and their time factor were (i) t/β for 0≤t≤β, 2β-t/β for β≤t≤2β, 0 for t≥2β or t≤0 (single trigonometric shock) (ii) e-ptsin(ωt-mk) for mk≤t≤mk+π/ω 0 for mk+π/ω≤t≤(m+1)k (continous shock) (iii) sinωt Thus we had the deflection of the plate and the bending moment at any time.
For investigation of the stress concentration around the notch or crack of a plate, by using the hypotrochoidal co-ordinate x=a(2eαcosβ+re-2αcos2β) y=a(2eαsinβ-re-2αsin2β) namely, by using a triangular-shaped hole with sharp or roundish corner, how much stresses decrease due to the roundness of corner was discussed. The author investigated the following items. (1) The effect of stress around a hole due to the change of roundness of corner, under uniform tension, simple shear and simple bending. (2) The stress distribution of plate at neighbourhood of sharp corner under uniform tension at right angle to the corner. (3) Above case, infeering the effect of stress distribution of plate on the line of corner owing to its roundness, some hints for strengthening the plate having sharp-corner was gaind.
In this paper, the authors deal with the problem of the torsional rigidity of plane skeleton girders, which consist of two longitudinally parallel rods in the same plane and transverse rods fixed on them. In the 1st chapter, the approximate expression of the torsional rigidity is obtained theoretically by means of the principle of virtual work. In the 2nd chapter, the experimental method is stated and results are compared with the theoretical values. In the 3rd chapter, they show one example of the application of this theory to the design of the girders.
Separate the strength of timber scarf joints to three elements of (1) frictional resistance between contact surface, (2) keys or hooked shapes and (3) steel bolts, the author experimentally investigated the characteristics of their independent actions and the relations between these elements. The conclusions are; (1) the actions of bolts and keys or hooked shapes are fundamentally similar ones and are compressions between timbers and those elements. (2) the strength of joints connected by more than two bolts or keys are not proportional to the number of elements. (3) the resistances of keys and hooked shapes are proportional to their sizes. (4) the frictional resistances should not be taken into joint strength. (5) the joint efficiencies are decreased as the deformation advances.
As I described in the Journal of Zosen Kiokai vol. 76., in the case that we drive nails in tim bers, the relation of slip and load of a point has a proportional limit when the bearing pressuce about nail-holes attains the proportional limit of bearing of timbers. Aad this time we shall describe how to design the lap points of timbers using this theory.
By applying the results of the experimental research of the nails, which the Auther reported at the last lecture meeting, he has contrived a methode of the design of the nails in double butt joint of wood, using metal splice plates, and has compared it with Mr. Trayer's methode. Then he has found that two are both based upon the nearly sinular thoughts. So using Mr Trayer's table, he has made out a table, by which one will find the proportional limit of hearing of any wood. And further he gave to finis of the paper the charts showing the safety load of the nails being acted by single shearing force.
Applying Prof. Havelock's method of analysis the author studies the relative importance of the transverse- and diverging-wave systems which are produced by a ship of Michell's type. Special reference is given to the effects of the depth or the width of a water upon the wave resistance, and the numerical calculations are made for the three cases: (a) deep water (h=∞, b=∞), (b) shallow water (h=finite, b=∞), (c) restricted water (h=finite, b=finite), where h denotes the depth of water, b the width. The main results obtained are as follows: 1°. In (a), the contribution from the diverging wave system to the total wave resistance is lound as given by a steppedly increasing function of Froude number, with each step taking place at the hollows on the curve of the transverse wave resistance. 2°. In (b), the resistance component due to the transverse waves attains its maximum at the speed just lower than the critical speed or the solitary wave velocity V=√gh, while the diverging wave resistance has its peak just at the critical speed. 3°. In the case (c), the side-walls are found as affecting inverse effects upon the two contributions of the wave resistance : the transverse wave resistance being augmented, while the diverging wave resistance being reduced, in comparison with the case (b).