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Article type: Cover
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Cover1-
Published: March 25, 1996
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Article type: Appendix
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App1-
Published: March 25, 1996
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Article type: Index
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Toc1-
Published: March 25, 1996
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Article type: Index
Pages
Toc2-
Published: March 25, 1996
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Jun-ichi HAMASAKI, Yoji HIMENO, Yusuke TAHARA
Article type: Article
Pages
1-6
Published: March 25, 1996
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This paper describes an attempt of improving ship hull form, minimizing ship viscous resistance. The method adopted here represents the hull-from variation function using B-spline function, takes the coefficients of the B-spline as the design variables, and evaluates the viscous resistance value by Computational Fluid Dynamics (CFD) method, called NICE Code developed by Kodama. Then a feasible direction method is applied to the optimizing process including the above procedure of viscous resistance computation. It is found that the convergence of the iterative optimizing process is steady, and that the method is useful for practical initial design of ship forms, although it also leaves some aspects of improvement such as accuracy of the sensitivity coefficients.
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Yasunori IWASAKI, Tadao YAMANO
Article type: Article
Pages
7-13
Published: March 25, 1996
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In ocean going fine ships such as container ships with high power main engine, it seems almost impossible to improve their propulsive performance to a large extent so far as the conventional stern form is used. The reason is that severe design condition such as a draft restriction, TKM (transverse metacentric height) requirement and propeller tip clearance requirement, restrict the propeller diameter and the stern form modification to a narrow range. This paper describes the change with year of these restrictions and the influence of these restrictions on the propulsive performance mainly on TKM, and a new stern form developed by the authors.
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Hiroyoshi SUZUKI, Masahiko ICHIKAWA, Yasuyuki TODA, Toshio SUZUKI
Article type: Article
Pages
15-24
Published: March 25, 1996
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The viscous flow computation of flow fields around a rudder with and without rudder angle behind a propeller are presented through comparison with mean-flow measurements using 5 hole pitot probes. The steady flow field is computed by a viscous flow code coupled with a body-force distribution which represents the propeller. The momentum transport equations are discretized using the Finite Analytic Method on a staggerd grid system. The velocity-pressure coupling is accomplished based on the SIMPLER algorithm. Although the details of the flow field of the computational results is different because of the laminar flow computation with different Reynolds number and numerical treatment, the effect by taking rudder angle is shown clearly in computatinal results. Concerning to the comparison computational results with mean flow data, quantitive agreement is obtained except near the rudder surface. Those comparisons shows the conclusion that the present approach can simurate also the steady part of the flow field around a rudder with rudder angle in propeller slipstream.
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Tadao YAMANO, Yasuo SAITO, Yasunori IWASAKI, Isao FUNENO
Article type: Article
Pages
25-35
Published: March 25, 1996
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In the bow form design for fine ships, the stem form preferable for better propulsive performance is often incompatible with that for easier construction. How this point should be treated is considered in this paper.
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Seiko OGIWARA, Seiya YAMASHITA, Masazumi MIFUNE
Article type: Article
Pages
37-45
Published: March 25, 1996
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Physical considerations are made on characteristics of added resistance in regular waves of short wavelength through tank experiments and numerical computation. By improving measuring accuracy of added resistance, experimental investigations are made into the effect of amplitude of incident waves, ship speed and ship draft. Interesting finding is that added resistance of shallow draft condition is larger than that of deep draft condition, that can not be prospected by a conventional theory. In order to find out the cause of resistance increase in short wavelength, pressure distribution is measured over the hull surface and evaluated combining with numerical simulation by CFD method. It is revealed that resistance due to diffraction on the bow is atributed to pressure increase on very narrow area of hull surface along the wave profile in steady state. Some recommendations are made to theoretical method to be improved by taking into account the exact boundary condition. Further, availability is discussed for a conventional theoy of added resistance due to wave diffraction addressing applicability of the theory to obtaining water plane geometry of minimum added resistance due to wave diffraction.
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Hiroyoshi SUZUKI, Kazuki YABUSHITA, Yasuyuki TODA, Toshio SUZUKI, Hide ...
Article type: Article
Pages
47-56
Published: March 25, 1996
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A turbulence boundary layer on a flat plate with a longitudinal vortex generated from a blade tip is measured by a triple sensor hot wire in the wind tunnel. Detailed profiles of mean-velocity and turbulence quantities which are analyzed from the time history data of the fluctuated three component velocities are presented. The magnitude of the measured turbulence shear-stress is compared with those which are predicted from the measured mean velocity or turbulence kinetic energy by two turbulence models to evaluate those models Repeatability of the measurement is also investigated to calculate standard deviations of the mean velocities and turbulence stresses measured at same interval.
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Mitsunori MURAKAMI, Yusuke TAHARA, Yoji HIMENO, Shigeya MIZUNO
Article type: Article
Pages
57-65
Published: March 25, 1996
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Study on the unsteady pressure distribution in case of oscillating and non-oscillating flat plate in uniform flow is discussed by Vortex Shedding Panel Method (VSPM), in which the unknowns of both vortex and source densities on the surface are signified, comparing with the observable facts. This paper also shows the comparison on the calculated results between VSPM and another calculation method (Finte-Analytical Method based on N-S equation) in order to evaluate the theoretical treatment on this kind of problem with the separation flow.
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Shigeru NISHIO, Taketoshi OKUNO
Article type: Article
Pages
67-74
Published: March 25, 1996
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An measurement technique by means of statistical analysis of visualized images have been developed by the authors. The technique is based on the fact that the probability of the particle passing is proportional to the flow speed if the particle concentration is uniform through the measurement area. In the present, the governing equation for the measurement is formed using Lagrange's differentiation. The process of forming the equation is similar to it of the so-called spatio-temporal derivative method. The stream-line coordinate system has been introduced on it in order to obtain the general form so as to apply this technique to the flow field where the particle concentration is not uniform. The new governing equation gives also an idea to measure the velocity component. The image temporal derivative gives the velocity component normal to the particle edge. Therefore the velocity vectors can be obtained through the ensemble average of the product of temporal and spatial derivatives. The principles of the measurement is explained in the case of both one-and two-dimension. The result of a numerical simulation in two-dimensional case shows that the time-mean velocity vector can be obtained directory from the visualized image data.
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Yusuke TAHARA, Yoji HIMENO
Article type: Article
Pages
75-91
Published: March 25, 1996
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This paper presents applications of isotropic and anisotropic turbulence models in computation of ship boundary-layer and wake flows. The fully-elliptic Reynolds-averaged Navier-Stokes and continuity equations are solved with several kinds of turbulence models, using a regular grid, finite-analytic discretization, and a PISO-type velocity-pressure coupling algorithm. An overview is given of the present numerical method, and results are presented and discussed of the SR196a tanker form, including detailed comparisons with available experimental data. Lastly, some concluding remarks are made concerning limitations, requirements and prognosis for improvements of the present turbulence models.
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Yusuke TAHARA, Satoshi MITARAI, Yoji HIMENO
Article type: Article
Pages
93-105
Published: March 25, 1996
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This paper presents a computational study of three-dimensional laminar separation on a prolate spheroid at incidence. The fully-elliptic Navier-Stokes and continuity equations are solved using the regular grid, finite-analytic discretization, a PISO-type velocity-pressure coupling algorithm, and method of lines. An O-O-type body-conforming grid, which is suitable for the detailed study of the present problem, is used in the computation. An overview is give of the present approach, and numerical results are presented and discussed for a 6:1 prolate spheroid for several angles of attack. The latter includes comparisons with available experimental data. The present computational results display detailed flow structures in the post-separation region and near wake, such as the generation and development of the girthwise and longitudinal vortices or the separation patterns which can not be classified by the conventional open- and closed-type separation models.
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Yoshifumi TAKAISHI, Kenji WATANABE, Naoya UMEDA, Koichi MASUDA
Article type: Article
Pages
107-114
Published: March 25, 1996
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The feature of encounter waves a ship will experience when navigation in following and quartering seas is investigated by tank experiments and numerical simulations. The energy spectrum of encounter waves becomes narrow-banded shape with a high peak on the encounter frequency domain, when the ship speed-wave period ratio is within a certain range. This shape of spectrum connects closely with the specific feature of encounter waves that a ship will be attacked by a series of very high waves which sometimes causes danger of capsizing. This is named as "Dangerous encounter wave grouping phenomena" and the authors propose that any model experiment of ships in following and quartering seas should include this dangerous encounter wave grouping zone determinable on the "V/T diagram" for test conditions and to conduct the test in highest wave group in irregular waves.
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Keiichi KARASUNO, Tomoaki YASUNAGA, Kazuyoshi MAEKAWA, Kouichirou TAKA ...
Article type: Article
Pages
115-124
Published: March 25, 1996
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This paper describes a very compact CMT apparatus (2.00m W × 1.00m D ×1.00m H) and its application for captive test of oblique, pure turning, pure sway and pure yaw motion. The paper presents the measured results of hydrodynamic forces acting on a block-typed ship in oblique or tough turning motion using CMT apparatus only, and in tender turning motion using both of CMT apparatus and towing carriage in the ordinary towing tank. Here our intention is to contrive the new method of convenient experiment-systems instead of huge CMT apparatus and huge amount of time for experiments.
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Kazuyoshi MAEKAWA, Keiichi KARASUNO, Yoshiharu ORITO, Amerudin THAMBY, ...
Article type: Article
Pages
125-131
Published: March 25, 1996
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It is important to know the motion characteristics of speed boat, because the resistance of the boat is affected by running posture remarkably. But it is difficult to carry out easily the full-scale sea trial of a small boat due to the limitation of the deck space for device installation on board. This paper is intended to investigate measuring system of full-scale sea trial on small speed boat. We carried out straight course running and turning tests of a trimaran high-speed fishing boat with water-jet propulsion and tried to measure running bow elevation, trim, speed and trajectory in the sea.
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Akinori YUMURO
Article type: Article
Pages
133-139
Published: March 25, 1996
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This report deals with a simplified method for calculating maneuvering hydrodynamic forces on a ship taking off-centerline course in a narrow water channel. In this report, calculation is made by using infinite images with respect to the side walls and the water bottom. The ship body is replaced by sources and vortices distributed in the center plane. The source strength is proportional to the slope of a distribution curve of ship width. The hydrodynamic forces are evaluated on the basis of the linear lifting surface theory. Numerical calculation is made by changing channel width, water depth and off-centerline displacement systematically. Calculated values are compared with the experimental results presented by Prof.Fujino. As a result, it is indicated that the calculated values agree qualitatively with the experimental results. It is clarified that the value of the correction factor, which is introduced to provide effective width of the channel, is almost constant regardless of ship form, channel width and water depth.
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Toru KATAYAMA, Yoshiho IKEDA
Article type: Article
Pages
141-148
Published: March 25, 1996
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In this study, an investigation on the dynamic instability of unstable rolling induced by pitching of a planing craft, at high advance speeds, is carried out. Using a database, of measured three-component hydrodynamic forces acting on a fixed model, the nonlinear pitch-excited rolling of the craft is simulated, using the fourth order Runge-Kutta method, varying inertia moment, roll damping, amplitude of pitching and the height of center of gravity. The results show that the period of rolling induced by pitching has no relation with the period of pitching and is almost constant and unstable rolling occurs when the period of pitching is a multiple of half the period of induced of induced rolling. The critical range of instability and the minimum roll damping to prevent unstable rolling increase with the increase of the inertia moment, the increase of the amplitude of pitch and the decrease of the height of center of gravity.
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Nobuyuki SHIMIZU, K. ROBY, Yoshiho IKEDA
Article type: Article
Pages
149-156
Published: March 25, 1996
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Authors have done experiments with a model of a RORO car ferry with opening at the bow, instead of a bow door. The model was run into regular head waves, allowing only heave and pitch motions. The flooding of the car deck increased with the increase of bow opening size, wave height and Froude number, and the peak is around λ/L=1. The motions changed with the flooding, which ranges from 0 to full volume, of the car deck. Theoretical calculations revealed that there is heavy loss of (static) righting moment due to the shift of water on desk. This study suggests that a ship should be slowed down or stopped, on damage, to reduce or avoid further flooding.
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Shigeru NAITO, Kenji TAKAGISI
Article type: Article
Pages
157-166
Published: March 25, 1996
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In this paper authors propose the practical method to estimate the mutual relation between the added resistance in short crested irregular waves and the horizontal bow form of full ships. The simplified estimated method of the mean added resistance is proposed based on the short wave length assumption and the new representation of bow form of full ships is introduced with Bezier curve. The mutual reration between the new representation of bow form and added resistance in short crested irregular waves is expressed. By using the Bezier curve and the pressure integration on the hull, side force and turning moment are obtained by the same method as added resistance. The consideration on optimum bow water line form of full ships is shown with this method.
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Toshimasa SAITOH, Yoshitaka OGAWA, Hideo YAO, Shuji MURATA
Article type: Article
Pages
167-174
Published: March 25, 1996
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This paper examines impulsive force given to a hull at the time of underwater explosions and transient vibration response of a hull when this impulsive force is given to a hull. We divided the hull by several sections in its length direction and calculated impulsive force against each divided section as a time history function. As for transient vibration, we applied impulsive force calculated in advance, as forced power, to a calculation model of substituting hull structure to lumped mass and variable cross sectional beam. As for impulsive force, we calculated by setting 9 condisions as charge weight (TNT) as 1,000kgs and explosive and hull's distance as a parameter. We clarified transient vibration character against these 9 condisions.
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Hitoshi TOBITA, Masayuki TANIGAWA, Shin-ichi NAGAHAMA
Article type: Article
Pages
175-180
Published: March 25, 1996
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In membrane type LNG carriers, impact pressure arises due to sloshing. High pressure is calculated by sloshing analysis assuming tank wall to be rigid. However, it is known that flexibility of a tank wall structure would mitigate this high pressure. In this paper mitigation effect of slosing pressure was investigated by using dynamic analysis code MSC/DYTRAN. In the first, to simulate and evaluate basic behaviors of fluid-structure interaction, 1-dimensional models which consisit of a fluid-part and a structural-part were analyzed. From these analyses it was found that mitigation effect could be simulated. Then, this analysis method was applied to an insulation structure of LNG tank. As a result, impact pressure was mitigated to about a half level due to flexibility of the insulation structure compared with rigid wall.
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Yasushi ASHIDA, Teruhisa ISHIHARA, Hirohiko FUJIHARA, Hitoshi TOBITA
Article type: Article
Pages
181-185
Published: March 25, 1996
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Mainly because of the complicate loading pattern, the recent estimation of fatigue crack growth in ship structures is still insufficient. So, the accurate and efficient measurement of crack length under the complicate loading pattern are needed. In the present study, a measurement system for fatigue crack length in a dynamic state, applied a D.C. electrical potential difference method (EPD method) was developed. Using this system, some crack length measuring were carried out under a dynamic loading condition. Usually, the measurment of crack length using EPD method are held under a static state or a quasi-static state, avoiding effects of the crack tip openning and closing, the plastic zone generation at the crack tip etc.. However, it was found that the crack length measurement in a dynamic state is possible with sufficient accuracy even under a condition in which the delayed retardation effects appear.
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Toshihiko FUNAKI, Shigehiro HAYASHI, Hiroshi TERADA
Article type: Article
Pages
187-193
Published: March 25, 1996
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It is important to identify the power flow path in dynamically loaded structure. Statistical energy analysis (SEA) is a method used to solve energy flow problems only in the high frequency domain. This paper presents a method for the calculation of power flow and structural intensity in low frequency band by using FEM.
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Toshiya UCHIBORI, Yuichi TAMURA, Toyofumi TANAKA
Article type: Article
Pages
195-200
Published: March 25, 1996
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Shiphulls made of Al-Mg alloy have a tendency to have pitting corrosion in anchorage. Cathodic protection systems using galvanic anodes have been applied to prevent such pitting corrosion. To clarify problematic points on application of cathodic protection, such as optimum protection potential, over-protection potential ranges and the most suitable galvanic anode, some experiments were conducted for bare and welded metal of Al-Mg alloy (JIS A-5083) in artificial sea water. Following results were obtained. A galvanic anode of Al-Zn-Mg-In-Si alloy was the most suitable from the view point of cost performance and protection efficiency. Optimum protection potentials were in the range of -950 ∼ -1000 mV refer to a saturated calomel electrode for the welded metal and -1000 mV for the base metal. Repassivation potential of the base metal measured in deaerated artificial sea water of pH 10 at 25℃ showed good coincidence with the optimum protection potential.
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Yasumitsu TOMITA, Kiyoshi HASHIMOTO, Naoki OSAWA, Youichi INADA
Article type: Article
Pages
201-208
Published: March 25, 1996
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In order to improve an estimation method of fatigue strength, the fatigue strength is related to stress-strain response under cyclic loading conditions. The materials used in this study were both three kinds of base metals (mild steel, conventional high tensile steel and thermo mechanical controlled process steel) and those synthetic heat-treated metals whic are heated with simulated actual weld heating process. Static tension and axial cyclic loading tests were performed on hourglass type specimens in order to obtain the characteristics of stress-strain response such as hardening, softening, hysterisis energy, Baushinger effect and fatigue strength. The relationship between the parameters of stress-strain response and fatigue strength was examined. The main results obtained in this study are as follows. 1. The characteristics of stress-strain response vary as the number of loading cycle proceeds, and differ from those under static loading condition. 2. The elastic limit stress (yield stress) under cyclic loading conditions is lower than under satic tension test for each materials, that is to say, the softening appears during cyclic loading. 3. There is a close correlation between 0.2% proof stress under cyclic loading condition and the fatigue strength of mother metals, while the fatigue strength of synthetic heat-treated metals does not increase being proportional to the increase of 0.2% proof stress. 4.The hysterisis energy per cycle during cyclick loading can be considered to be a useful parameter for an estimation of fatigue strength.
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Yasumitsu TOMITA, Kiyosi HASHIMOTO, Naoki OSAWA, Taira OZAKI
Article type: Article
Pages
209-218
Published: March 25, 1996
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In order to improve a prediction method of the crack initiation or failure life, it is needed to develop a simulation method which estimate macroscopic deformation behavior from microstructural models. In this report, we analyze ununiform deformation of f.c.c. pollycrystalline using 2-Dimentioal FEM model, and evaluate propriety of models for movement and interaction of dislocations. Results of the analyses are summarized as follows: 1) It is possible to represent cyclic plastic behavior of real materials if dislocation structures generated during plastic deformation raise c.r.s.s. only by long-range stress or these structures disappear during unloading. 2) There is concentration of plastic strain on grain boundary of a crystal which faces free surface and is next to crystals with small plastic deformation. It is supposed that PSB (persistent slip band), which cause fatigue failure, appear in such regions.
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Yutaka MASUYAMA, Kouji KUROKAWA, Akihisa YAMADA, Mitsumasa TAMAMURA
Article type: Article
Pages
219-227
Published: March 25, 1996
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Since solar energy produces no by-products and consumes no natural resources, it is the from of energy that provides the greatest potential for the future. So far in the history, There are no records whatsoever on the use of solar energy as a source of power for marine vehicles. Moreover, there is only a handful of documented accounts where such an attempt has been made. The purpose of this research is to present the design of a solar boat with the aim of increasing its practicality. In particular, considerations on the optimal design and performance testing of the solar boat are presented. Furthermore, the use of solar cells and battery as a power source, the design of a body with minimum resistance, and the design of a propeller with low loading and high efficiency is investigated and tested in detail. At the end, putting together the various crucial factors as mentioned above, the overall performance of the solar boat is evaluated.
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Kazuyasu HIRAO, Nobuhiro BABA, Ken-ichiro TAKAMATSU, Shotaro HANADA
Article type: Article
Pages
229-238
Published: March 25, 1996
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Vortex shedding from a sinusoidally oscillating horizontal circular cylinder in a stratified fluid with constant density gradient is studied by numerical experiment based on finite-volume solution of the Navier-Stokes equation for a heterogeneous fluid, the continuity equation and the transport equation for solute. To validate the computational method to the flow field with small density fluctuation we perform the computation at Kc=1 at which the amplitude of the oscillation is relatively small and compare the result with the linear theory of the internal gravity wave with small amplitude. The computed results show that the internal waves are generated with the conditions and the direction of propagation identical with those predicted by the theory. We also perform the experiment at Kc=5 in the range of Fn=2.0 ∼ 0.2 to examine the effects of density stratification on vortex shedding which would occur in a homogeneous fluid at this Kc number. For the range of Fn >__- 0.6 the stratification weakens the rotational motion as well as the diffusion of vorticity so that it prevents the process of the generation, movement and shedding of vortex and as a result both in-line and lift forces decrease with the Froude number decreasing. For The range of Fn <__- 0.4 vortex shedding does not occur but vorticity is generated away from the cylinder as well, and such a relatively wide distribution of strong vorticity leads to the increase of drag force.
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Shotaro HANADA, Nobuhiro BABA, Ken-ichiro TAKAMATSU, Kazuyasu HIRAO
Article type: Article
Pages
239-248
Published: March 25, 1996
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The interaction of a horizontal circular cylinder and a density interface when the cylinder penetrates the interface is investigated by numerical experiments based on the finite volume solution of the Navier-Stokes equations for a heterogeneous fluid. The location of the density interface is determined from a time-dependent numerical solution of the transport equation for relative density deviation using the general curvilinear coordinate system fitted to the cylinder but not to the interface. The interaction process includes the stretching of the interface with being thinner along the cylinder surface, the splitting into two to the sides of the cylinder, the splashing, the breaking and their reconnecting behind the cylinder. Such a process is affected by the twin vortices attached to the cylinder to an extent strongly dependent on the Froude number. For low Froude numbers the supply of vorticity from the cylinder surface is interrupted by the sharp interface so that the twin vortices are shed and convected upward with the interface reconnected behind the cylinder. For high Froude numbers the cylinder draws relatively a large mass of upper less dense fluid behind it so that the reconnected interface confines this fluid below it. It is concluded that when a body penetrates a density interface the interaction of the separated vortices from the body with the interface is an important process which has great effects on the entire flow field around the body.
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Article type: Appendix
Pages
App2-
Published: March 25, 1996
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Article type: Cover
Pages
Cover2-
Published: March 25, 1996
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