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Yukiharu NEKADO, Akihisa KOKUMAI, Hiroshi ISSHIKI, Masanori SUGIURA, T ...
Article type: Article
Pages
1-9
Published: June 30, 1980
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Floating breakwaters are required to protect offshore structures and fish breeding facilities on the coast from the damage due to heavy sea. In order to meet this requirement, a study has been conducted to develop a new breaking-water system of better performance. The new system is based on the principle shown by Bessho, "which utilizes the interaction of the diffracted and radiated waves through a proper contol of the motion of the floating body to attenuate the transmitted wave." The air-controlled floating breakwater shown in this paper adapts a method which, instead of controlling the motion of the floating breakwater itself, regulates the motion of the water mass in the tank of the air bell type by controlling the pneumatic pressure which acts on the free surface of the water mass. Tank tests with small scale models were carried out in order to confirm the effectiveness of the system. In the tests with fixed models, the influence, on the breakwater performance, of dimensionalratios such as the beam draft ratio etc., the opening degree of valves that serve to regulate the air flow, and so on were investigated by varying these parameters. It has been shown through these experiments that the air-controlled floating breakwater can well attenuate the transmitted wave as compared with the pontoon type floating breakwater of the similar size. In the tests with floating models, the tests were carried out by varying the mooring conditions to investigate their effect on the breaking-water performances and to evaluate the tension of the mooring lines. Thus it has been clarified that the tension-leg mooring system has difficulties from a practical point of view because of the too big tension of the mooring lines, and a small transmission coefficient is obtained for incident waves of the considerably long wave-length even in the case of slack moorring. A full-scale field test was carried out on a sea surface off Uwajima City, Ehime Prefecture. Through measurements of the incident and transmitted waves, the wave transmission coefficient for irregular waves was obtained. Also the tension on the mooring chain was measured. These results are reported in this paper.
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Kazuhiro FUKUDA, Osamu KISHIMOTO, Tatsuzo IWATA, Mitsuhiro ABE
Article type: Article
Pages
11-19
Published: June 30, 1980
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Self-propulsion tests are frequently carried out to estimate the required power of ships. However, it's very difficult to settle the propeller revolution speed at a self-propulsion condition, because to control a model ship on a constant towing force is troublesome. A new self-propulsion system which can be automatically controlled by feedback mechanism was developed by the Akishima Laboratory of Mitsui Engineering and Shipbuilding Co., Ltd. In this system a model ship is towed by a self-balancing resistance dynamometer. Then, the propeller revolution speed is controlled through an electrical feedback loop connected with the resistance dynamometer, which measures the difference between the actual thrust and the identical model ship resistance at the self-propulsion point. This paper shows the outline of this automatic self-propulsion system, and also describes several results of simulation study by an analogue computer and actual model experiments by using this system.
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Kiyoshi TAKASHIRO
Article type: Article
Pages
21-35
Published: June 30, 1980
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The aim of this paper is to get comparatively reliable speed-horse power curves at primary stage of the basic design of the ship having L between 30^m and 400^m. The author improved the classic method of EHP prediction based on the Yamagata resistance chart, adding residuary resistance coefficients for C_b>0.80 and changing values of B/d_<mld> correction into half. For modern bulbous bow, the author introduced the new correction factor in accordance with C_b. Also for the stern form, the author added the correction factor in relation to the wake fraction. For twin screw ships, the author adopted the correction of the frictional resistance coefficient in stead of adding some percents to the residuary resistance coefficient according to Lap's opinion. With regard to the wetted surface, the author gave modified Todd's formula. As to the thrust deduction factor t and the wake fraction w, the author investigated many model experimental data and gave the new curves of t and w. By using above-mentioned new method, the author believes comparatively reliable calculation results of BHP or SHP for the speed will be expected for the ship of full loaded condition or vicinity.
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Hideaki MIYATA, Yeun Junn LIN, Takanori HINO, Shigetomo FUJITA
Article type: Article
Pages
37-50
Published: June 30, 1980
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The optimization of hull forms of the aft-part of fine hull forms is pursued following the optimization of overall performance of rudders. The investigations on the optimization of rudder configurations and on the development of the Stern-End-Bulb suggest that the aft-part of hull forms of merchant ships has broad possibility to be improved. The main aims are to clarify the potential interactions between a hull and a propeller by theoretical and experimental researches and to develope a new method of designing the aft-part with available theoretical tools. In this first report, two ways of theoretical approach and some experimental results are presented. Firstly, a method of calculating thrust deduction is developed with the double model flow theory, Lagalley's theorem and pressure integration. This method is applied to a container model ship and a modified hull form is designed. Calculations and experiments on the original and modified model ships indicate the simultaneous improvements of thrust deduction and wake fraction. They also clarify the components of thrust deduction. Secondly, a new method of calculating the inviscid resistance of propelling ships is developed. This method is based on the linear wave making theory in which singularities are distributed on the hull surface together with the propeller disk plane. It is verified with extensive experiments that this method is excellently effective for the theoretical explanation of thrust deduction and for the calculation of inviscid resistance of propelling ships. The effect of waves cannot be neglected in the evaluation of thrust deduction for moderate and high speed ships.
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Michio NAKATO, Kimiaki KUDO, Ryuichi KATO
Article type: Article
Pages
51-58
Published: June 30, 1980
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The results of model basin experiments on rectangular flat plates near temporary wall are presented. The experiments simulated the condition of a rudder operating near stern-bottom with finite gaps. Tests were carried out on two flat plates having aspect ratios of 1.0 and 1.35. The open water tests were also carried out for each and/or double aspect ratio flat plate which is equal to the limiting case of infinity and/or zero gap-to-span ratio. Results are presented for each rectangular flat plate as normal force coefficients. The leading edge was sharpened in every case. In case of aspect ratio 1.0 the results are compared with Winter's experiments. Both agreed very we11, so that we are able to be assured of our measuring system. When the gap ratio becomes less than about 0.1, the normal force coefficient tends to be equal to that of double aspect ratio flat plate. However, the effect of increasing aspect ratio seems to advance the stall at the leading edge. The theoretical calculations were also made and compared with the experimental results. The linear lifting surface theory gives lower normal force coefficients but predicts higher effect of gap than the experiments. The strip method for the nonlinear lifting surface was applied to this problem. Assuming that the free vortex shedding angle Θ is equal to the angle of attack α, this method compares well with the experimental results.
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Akinori YUMURO
Article type: Article
Pages
59-68
Published: June 30, 1980
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This paper deals with a simplified method of calculating normal force of a rudder whose height differs from propeller diameter. This paper limits the problem to the accuracy for the calculating method of the normal force for a case in which inflow velocity to the rudder is not uniform along the span. The values obtained by the simplified equations are compared with a solution of an integral equation.It is shown that as long as velocity increment due to propeller slipstream is not high and ratio of propeller diameter to rudder height is not remarkably small, the approximate equations in this paper provide the values permissibly similar to the value obtained by the integral equation. Further, it is indicated that an approximate equation based on an elliptical circulation distribution can explain the tendency of influence of propeller arrangement in the rudder height direction on normal force of the rudder.
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Nobuo NAGAMATSU
Article type: Article
Pages
69-74
Published: June 30, 1980
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The purpose of this paper is to present the characteristics of pressure distribution on the blade surface of a highly skewed propeller (HSP) compared with the corresponding conventional propeller (CP). Measurements and theoretical calculations of the pressure distribution for CP and HSP (with 60 degrees skew) are carried out in the uniform and non-uniform flow. The results obtained are as follows. (1) In uniform flow, skew (60゜, 66.7% for 4-blades propeller) has little effect on the pressure distribution. (2) In non-uniform flow, skew has little effect on the amplitude of the pressure fluctuation but causes phase lag corresponding to skew angle.
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Masahiko MORI
Article type: Article
Pages
75-81
Published: June 30, 1980
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Potential theory of the pressure distribution on a wing section shall always give the values bigger than the ones obtained from the experiments in a viscous flow. It comes from the viscous effect due to the boundary layer around a wing section. The boundary layer on the suction side of a wing section grows thicker than the one on the pressure side, when the wing section has some angle of attack against a viscous flow. Such unequality in the boundary layer thickness hydrodynamically brings the virtual reduction of the attack angle as well as the camber ratio of a wing section due to the decline of the nose-tail line, or effectively distorts the section shape so that the trailing edge should be slightly raised up from the original. The author proposes a practical method to form the distorted wing section, in which the experimental slope of lift curve is utilized, and by which the pressure distribution can be computed for a wing section in a real flow. The pressure distribution thus computed for an exemplified wing section is in rather good agreement with the experimental result.
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Kimiaki KUDO, Atsushi KINOSHITA, Michio NAKATO
Article type: Article
Pages
83-90
Published: June 30, 1980
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This study aims at making clear of the advantageous performance of the rectangular cylinder over the circular one as the lower hull of the offshore floating structure. This paper presents the results of the experiments for the hydrodynamic forces acting on the oscillating rectangular cylinders. Tests were carried out on the cylinders having cross-sectional aspect-ratio 0.1 to 0.8. Results are presented for each cylinder as added mass coefficient C_a and damping coefficient C_d. These coefficients are correlated with the amplitude ratio πa/b. When the added mass and damping coefficients of the rectangular cylinders are compared with those of the plate and cylinder obtained by Keulegan et al, the following conclusions are derived; 1) When the aspect-ratio d/B equals to 0.1 or 0.2, the hydrodynamic coefficients C_a and C_d agree with those of flat plate. 2) As d/B becomes greater than about 0.4, C_d reduces nearly half of flat plate at the moderate amplitude ratio. However, C_a shows a constant tendency. 3) Comparing with the coefficients of the circular cylinder, both C_d and C_a are considerably great. Therefore, it can be seen that the rectangular cylinder yields the greater resistance against the exciting oscillations than the circular cylinder.
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Yasuyuki HOMMA, Yoshio IWATSUKA
Article type: Article
Pages
91-98
Published: June 30, 1980
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In the previous paper, present authors investigated two techniques, which were named tentatively the linearization of constraint and the multi-step optimization, with the purpose of improving SUMT, and shown that those techniques had a good convergence property and a computational efficiency. In this paper the following technique is studied to make SUMT more efficient. The gradients of the constraint ∇g_j (x), which is necessary to make the constraint into the linear form, is derived by differentiating the stiffeness matrix of structure or the eigen value equation for buckling with respect to the design variables. Using this technique, the number of the structural analyses can be decreased. The extent to be applied the linearized constraint is reduced as the searching point approaches to the optimum. The computational efficiency can be improved in this way. The present technique combined with finite element method is applied to the minimum weight designs of the local structures of ship (transring strut and transring corner) with the constraints on allowable stresses and the perforated plates with buckling constraint.
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Masatoshi BESSHO, Hiroshi KAWABE
Article type: Article
Pages
99-106
Published: June 30, 1980
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Betti's formula in the theory of elasticity which describes displacements by their boundary values and external forces acting on the boundary surface of the elastic body permits us to solve the boundary value problems by taking its boundary value as the integral equations and recently some authors report the usefulness of this method in numerical analysis. In the present report, in the same aim as the predecessor, authors develope various representation of the stress field, try numerical comutation and compare its usefulness with othor methods, especially with the finite element one in the plane stress problems. Conciudingly, this method is very much usefull especially for stress concentrasion problems making use of the proposed representation of the stress function.
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Koichi OSHIMA, Hiroo OKADA, Yoshio FUKUMOTO
Article type: Article
Pages
107-115
Published: June 30, 1980
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As a basic study on the buckling and compressive strength of a ship's bottom plating, authors had already studied buckling strength of plates (rectangular plates of aspect ratio α=2, 3 and 4 and infinitely long plate of α=∞) under increasing compression and constant hydrostatic pressure. Further, by using results of these studies, they had also studied the compressive strength of simply supported long rectangular plates (α=3 and 4) under such combined loads. In this paper, the compressive strength of simply supported plates (α=1, 2 and ∞) is theoretically clarified following the previous studies. Calculations are performed by means of the method assuming that the plate behaves elastically up to the collapse, and it collapses when the plate will satisfy the condition of plastic collapse based on plastic analysis in which collapse mechanism is assumed and large deformation theory is considered. From these results including those for plates of α=3 and 4, the effect of aspect ratio of plates on the compressive strength of simply supported plates under such combined loads, is also discussed.
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Junkichi YAGI, Yasumitsu TOMITA, Yukio FUJIMOTO, Osamu MURAYAMA
Article type: Article
Pages
117-130
Published: June 30, 1980
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In order to estimate crack initiation life of structural members, it is necessary to know relation between nominal stress, stress concentrated factors and local strain at the place where fatigue crack will initiate. For this purpose, step tests were carried out for notched specimens of several types and cyclic nominal stress-local strain curves were obtained. To calculate local strain at notched part, Neuber's equation and modified Stowell's equation, etc. have been employed, but the calculated strain does not always agree with measured strain accurately. Using Neuber's equation, relation between K_ε/K_t and S_a・K_t/σ_y^' is expressed by the equation K_ε/K_t=f[(S_a・K_ι)/σ'_y] But this equation does not give accurate results as mentioned above, the following modified equation was proposed K_ε/K_t=f[(S_a・K_t)/(σ'_y)-((ε'^^_y)/(ε'_y)-1)] where K_ε ; strain concentration factor (at stress concentrated region) K_t ; elastic stress concentration factor (at stress concentrated region) S_a ; nominal stress amplitude σ_y^', ε_y^' ; cyclic yield stress and cyclic yield strain at uniform strain field <ε_y^'>^^^- ; cyclic yield strain at non-uniform strain field The above modified Neuber's equation was applied to two kind of materials of SM41B and A5083 Al Alloy, and calculated local cyclic strain amplitude at stress concentrated part agrees to the measured one with good accuracy.
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Kiyoshi KONDO, Masatsugu TOYOFUKU
Article type: Article
Pages
131-138
Published: June 30, 1980
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The proper design estimate of stiffened plates is very important because they are one of the most basic structural elements of a ship hull. Since stiffened plates such as walls in a tank are immersed in water or other kinds of liquid, their natural frequencies tend to decrease and often become resonant with the exciting force due to a propeller or a main engine. In many cases, the scantlings of stiffened plates are increased to avoid resonant vibrations. In the previous paper, we developed a computer program for the vibration analysis of rectangular stiffened plates in water, and we obtained a good agreement between calculations and experiments. According to those results and adding some other calculations, we are discussing here a simple method to estimate the virtual mass of immersed stiffened plates. We performed a vibration analysis of aft-peak tank floor using NASTRAN as an example. The result showed a possibility of large reduction in natural frequency for the floor vibrating in water.
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Hiroshi ISSHIKI
Article type: Article
Pages
139-144
Published: June 30, 1980
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Wave motions on a circular membrane and in a circular water tank due to an unsteady rotating external force are discussed. The response function and the condition of resonance are derived. In the case of a constant rotating force, the resonance is observed when the angular velocity of the rotating force coincides with any of the phase angular velocities of the rotating free waves on a circular membrane or in a water tank. The above mentioned wave motions may in a sense be considered to be similar to the wave phenomena observed on a disk of a rotating machine such as a centrifugal compressor, on a tyre of an automobile and on an ocean as tidal wave etc., from a mathematical point of view.
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[in Japanese]
Article type: Article
Pages
145-149
Published: June 30, 1980
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[in Japanese]
Article type: Article
Pages
151-154
Published: June 30, 1980
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Article type: Appendix
Pages
155-157
Published: June 30, 1980
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Article type: Appendix
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Published: June 30, 1980
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Article type: Cover
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Article type: Cover
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