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Article type: Cover
Pages
Cover1-
Published: September 25, 1995
Released on J-STAGE: April 01, 2018
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Article type: Appendix
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App1-
Published: September 25, 1995
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Article type: Index
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Toc1-
Published: September 25, 1995
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Article type: Index
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Published: September 25, 1995
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Yusuke TAHARA
Article type: Article
Pages
1-11
Published: September 25, 1995
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A numerical method is developed for calculating boundary-layer and wake flows around the International America's Cup Class (IACC) sailing yacht for zero Froude number. The Reynolds-averaged Navier-Stokes and continuity equations are solved with the Baldwin-Lomax turbulence model, using a body conforming grid, finite-analytic discretization, and a PISO-type velocity-pressure coupling algorithm. The computational domain includes both port and starboard sides of the hull in order to account for the ship flow with yaw angle. An overview is given for the present approach, and numerical results are presented and discussed for the canoe body of IACC sailing yacht for zero and nonzero yaw angles. Lastly, some concluding remarks are made, including the requirements and prognosis for extension of the present method for the complete hull geometry with keel and rudder.
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Jun-ichi HAMASAKI, Yoji HIMENO, Masatoshi BESSHO
Article type: Article
Pages
13-19
Published: September 25, 1995
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This paper describes an attempt of improving ship hull from, minimizing ship wave resistance. The method adopted here represents the variation function by use of B-spline function, takes the coefficients of the B-spline as the design variables, and evaluates the wave resistance value by Rankine source method. Then a feasible direction method is applied to the optimizing process including the above procedure of wave 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 total resistance and variation function.
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Michio TAKAI
Article type: Article
Pages
21-26
Published: September 25, 1995
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This paper discusses the practical application of Computational Fluid Dynamics, CFD in ship design. In recent years, CFD has made a great advance in naval hydrodynamics as well as in various other fields. We can estimate the resistance and self-propulsion factors of the limited ship. However, there are some problems to apply the CFD in practical use. The reduction of time of grid generation and computation must be carried out. And actual ships must be represented with calculation grid precisely. The paper describes the method of grid generation that represents a hull from correctly in a short time by the hull surface data in segment form. Then resistance and self-propulsion factors were computed with the double model assumption about VLCC hulls that are actually designed and build in our ship yards. The results of computation with free surface are also discussed.
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Shigeru NISHIO, Taketoshi OKUNO, Nobuaki KIMOTO
Article type: Article
Pages
27-34
Published: September 25, 1995
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An image measurement system by means of statistical analysis has been developed. The number of tracer particle passing in a time is proportionate to the speed when the concentration of particle is uniform through the flow field. The present image measurement method evaluates the flow speed by means of the probability of the tracer particle passing which can be measured through the probability of tracer-edge passing. The difference function of binarized image data gives two pulse-like signal in a particle edge, and the interval and period of the signal are inversely proportional to the flow speed, and that form is depend on only the shutter time. The mean of the absolute value of difference function obtained from binarized image data is used as the measure of flow speed, and is estimated by means of the ensemble average of the measured data. The absolute value of flow velocity can be obtained through the present developed system, and it is suitable for the measurement of time-mean velocity. Measurement of rotating speed of particle patterned disk and wake distribution of circular cylinder in low Reynolds number has been made. A correction method considering the difference of particle concentration has been proposed, and applied on a rotating disk which has two area of different particle pattern concentration. Present measurement system can be applied not only the 2-D flow field but also 3-D, and will decrease the measurement time of wake distribution compare with the ordinary devices.
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Yukihiko OKAMOTO
Article type: Article
Pages
35-41
Published: September 25, 1995
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This paper deals with a calculation method to obtain the shape of unsteady cavity sectional geometry on a propeller blade operating in non-uniform wake field. The method make use of calculated cavity geometry by a quasi-steady calculation. This method is based on the consideration about a non-uniform flow field around a propeller blade section operating in non-uniform wake field. A calculation result based on present method show the suppression of cavity length and volume in cavity growing process, the phase delay of the maximum cavity volume and the acceleration of cavity collapse. This means that the hysterisys of the cavity length which was pointed out by Tulin could be expressed by present method. However, the decrease of the total cavity volume compared to the quasi-stady calculation result could not be clearly obtained. Moreover the detail geometry of cavity on the propeller blade does not coinside with the model scale expermantal results precisely. Further improvements are needed on these points.
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Yoshitaka OGAWA, Iwao WATANABE
Article type: Article
Pages
43-52
Published: September 25, 1995
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When estimating an expectation value of ship response, a long term prediction is commonly made under the assumption that a ship speed is constant with equally distributed encounter angle to waves. But in severe sea states, a ship speed is naturally reduced and shipmasters often change the speed and the course of ships to avert hull damage and to ease a ship motion. Since ship responses are sensitive to the encounter angle and to the ship speed, it is important to account for the effect of ship handling, speed reduction and course change, on the long term prediction. The present paper describes at first the statistical characteristics of ship's navigation in real seas, based on weather reports by ships in operation. Distribution of mean value and variation of ship speed in some routes are discussed. Then an empirical model to describe navigational behavior is presented by fitting simple formula. Several ship types are chosen as examples. Finally, a new method for the long term prediction is proposed to take in the effect of the ships handling in real sea. Example calculation is made for wave-induced midship bending moment and relative wave motion at the bow. Comparisons with results by conventional prediction method are made.
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Masaru TSUJIMOTO, Kimio SAITO
Article type: Article
Pages
53-58
Published: September 25, 1995
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In the previous paper, the authors discussed a method to obtain the optimum hull forms which minimize ship motions in waves by using an approximate method for hydrodynamic forces. In this paper, therefore, the same problem to find the optimum hull forms is discussed by using more precise hydrodynamic forces and wave exciting forces, in which the so-called Ursell-Tasai's method is used for Lewis form cross sections. Furthermore, the wave making resistance still water is also considered as the constraints in the optimization method and the resistance is evaluated from Michell's formula. The numerical example of the present method is shown and discussed the results.
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Kouichirou TAKANO, Amerudin THAMBY, Keiichi KARASUNO, Kazuyoshi MAEKAW ...
Article type: Article
Pages
59-67
Published: September 25, 1995
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Previously, some experiment and analysis had been done on ship hydrodynamic forces acting on the block type ships moving oblique. As the analyzed results, the elements composing hydrodynamic forces showed a big different characteristics from ones of an ordinary fine ship, especially on the drag to lift ratio. On this case, it is considered that sharp corners sections at both ends of bow and stern, may cause a lot of induce drag existed in the motion. Then, in order to investigate the cause, several ship models transformed on bow or stern shape have been examined on ship hydrodynamic forces by means of oblique towing test. As the result, the characteristics of hydrodynamic forces show a great change and variation due to the transformation on the stern shape of the model.
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Akinori YUMURO
Article type: Article
Pages
69-76
Published: September 25, 1995
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Assuming that a ship hull can be replaced by a rectangular flat wing, a simplified method is examined for calculating the maneuvering hydrodynamic forces and shedding angles of the trailing vortices in shallow water. This method is based on the INOUE's method using infinite images with respect to bottom. This study takes into account bound vortices retained at the wing tip in shallow water condition. If the fluid behaves ideally, vortices bridging the gap must be distributed over the tip-clearance. In this report, influence of the vortices remaining in the gap on predicting the hydrodynamic forces and the shedding angles is discussed. As a result, it is indicated that the vortices distributed in the gap cause decrease in the shedding angles and the hydrodynamic forces. However, the changein the hydrodynamic forces is slight compared with that in the shedding angles. It may be concluded that taking account of the vortices in the gap is useful for obtaining better agreement between calculated values and experimental values for both the hydrodynamic forces and the shedding angles.
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Toru KATAYAMA, Yoshiho IKEDA
Article type: Article
Pages
77-85
Published: September 25, 1995
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In this study, experimental investigations on the high speed transverse stability loss and the dynamic instability of pitch-excited rolling are carried out for a planing craft, in calm water. Some types of unstable rolling phenomena are observed from free rolling test of a model which is also heave free. The restoring moment, the lift force and the transverse force acting on the model with zero degree of freedom are measured by towing tests, systematically changing towing speed, heel angle, trim angle and draft. As a result, it is found that the unstable phenomena observed by the free rolling tests are due to the influence of the advance speed on the roll restoring moment, and that the roll restoring moment of the craft depends significantly on its trim angle. Using a database, of the measured three-component hydrodynamic forces acting on the model, the nonlinear pitch-excited rolling of the craft is simulated, using the fourth order Runge-Kutta method. The results show that large rolling motion occurs when the period of pitching is half of the natural period of rolling.
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Yoshiho IKEDA, Hideo SHIRAZAWA
Article type: Article
Pages
87-93
Published: September 25, 1995
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The authors measured ship motions and the vomiting ratio of passengers on a crusise ship in one week voyage. The results demonstrate that it is possible to estimate the vomiting ration in fairly good accuracy by the author's estimation method on the bases of O'Hanlon's experimental data. However, when the passengers are exposed to severe ship motions more than one day, the estimated vomiting ratio after then show an overestimation due to the habituation effect. A decrease function of vomiting ratio with time which shows habituation effect is obtained from the results of the present experiment. The vomiting ratio estimated using the function is in fairly good agreement with the results of actual vomiting ratio.
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Shigeru NAITO, Hajime KIHARA, Naoaki NISHIMURA
Article type: Article
Pages
95-104
Published: September 25, 1995
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Recently it is reported that in spite of a small ship motion, the damage at the large ship's side shell near by free surface occured. It is considered that which is because of fatigue of the structual member in oblique short waves length. This hydrodynamic pressure acting on ship's side can be estimated by using strip method, however in the case of short waves length, an another simple theory can be proposed. When onsidering hydrodynamic pressure acting on the side shell near by free surface, the profile of hydrodynamic pressure is partially criped because of exposure of the point of the side shell to the air. The variance of load at this point is very different from the result analysed by liner theory which value effects on the fatigue strongly. Hence by using the liner theory, the short and long term prediction of load does not give valid result. This paper shows a simple method to estimate hydrodynamic pressure acting on the side shell near free surface, and that the way for treating non-linear loads like cripped profile is very important in considering hydrodynamic loads distribution.
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Hiroshi SASAJIMA
Article type: Article
Pages
105-109
Published: September 25, 1995
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Singular Point Method was reported by author of its usefulness and accuracy in using structural vibration problem contacted with fluid. Accuracy of Singular Point Method is confirmed in the fluid pressure problem which is solved theoretically, however it is necessary to estimate error of fluid pressure calcuration in case of no theoretical and experimental value. In this paper, auther shows the method for error estimation of fluid pressure by using Singular Point Method. 1. Different method shold to be used to estimate the error in case of Source and Doublet. 2. In the case of calcuration model which can be estimated theoreticaly, good accuracy can be estimated however check of actual structure was not doe in this paper. Application of this error estimation method shall be investigated in future.
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Toshihiko FUNAKI, Shigehiro HAYASHI, Naoki OHYABE, Masaki FUJITA
Article type: Article
Pages
111-120
Published: September 25, 1995
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Because of the increase of superstructure height, natural frequency of its rocking vibration have been lower to the blade frequency. Then some problem caused by fore-aft vibration of superstructure have often occurred. Therefore the natural frequency of rocking vibration must be estimated accurately in the design stage, to decrease such vibration and problems. The authors have studied to apply model analysis to such vibration. In this paper, examples on the application of mode synthesis method and its structural modification method to model ship and actual ship are described.
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Yasumitsu TOMITA, Kiyoshi HASHIMOTO, Naoki OSAWA, Yanao FUKUDA, Yoshio ...
Article type: Article
Pages
121-130
Published: September 25, 1995
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The line-heating method is applied to the bending work of hull steel plate. These processes have been dependent on skilled worker's hand-working based on mainly experience. However, it has become necessary to mechanize the line heating working and establish the forming technology, because the skilled workers have recently been decreased. In order to solve these problems, we have two approaches; one is to analyze physical phenomena theoretically, and the other is systematization of the skillful workers' knowledge. In this paper, an expert system of plate bending by line heating is developed. By interviewing skillful workers to construct production rules, an expert system is built on "Nexpert Object"; the knowledge base development system of Neuron Data Inc. The system is easy to maintain rules, and it has user-friendly interfaces. Its validity is examined through an application of the system to processing of actual plates in a shipyard.
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Yasushi HIGO, Teruaki INO, Hideki UENO
Article type: Article
Pages
131-137
Published: September 25, 1995
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In this paper, a research about scattering problem by two-dimensional bodies in shallow water is reported. Most studies of under water sound propagation have investigated at relatively long ranges, because they have been carried out with a view-point of underwater sound technology as a means of transmitting information. However, the sound field in shallow water at short ranges becomes more complicated than the field at long ranges. This paper presents the theory and the numerical calculating method of sound scattering in shallow water at relatively short ranges. In order to investigate the effect of water-surface and sea-bottom on the scattering character, some numerical results are compared with the results in free sound field.
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Naoki KIMURA, Nobuhiro BABA
Article type: Article
Pages
139-145
Published: September 25, 1995
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Effects of density stratification on the three-dimensional structure of an isolated vortex with the vertical axis in the process of decaying in a non-rotating system are investigated by numerical experiments based on the finite volume solution of the Navier-Stokes equation for inhomogeneous fluid, the continuity equation and the transport equation of density variation. A circular vortex is embedded in stratified fluid with the constant density gradient, and the computation in the time-marching procedure gives the velocity and vorticity distributions, the dissipation of total kinetic energy and the radius of vortex core in the decaying process. The results show that the convergence flow in the bottom boundary layer causes the upwelling flow in the vortex, and both form the vertical circulation in the vortex. When dense fluid on the bottom is raised by the upwelling flow ,the density interface appears in the form of a circular corn between this dense fluid and above stratified fluid, which confines the main part of the vertical circulation below it and weakens the three-dimensional motion of the upper flow. Hence the density stratification reduces the dissipation rate of kinetic energy and it elongates the life of voretx.
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Nobuhiro BABA, Shotaro HANADA, Naoki KIMURA, Ken-ichiro TAKAMATSU
Article type: Article
Pages
147-152
Published: September 25, 1995
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Mixing in a stratified cavity flow and its associated flow structure are investigated by numerical experiments. The computational method for stratified flows developed in the previous paper is extended to the three-dimensional cases and applied to the phenomena in which a density interface is formed by erosion of the region with density gradient and it descends by the mixing. In the two-dimensional computation the mixed layer develops slower than in the experiment, while the result in the three-dimensional computation is in good agreement with the experiment. It is found that the flow structure of streamwise vortices as observed in the visualization experiment is formed near a density interface in the computation and it enhances the mixing across the density interface by deforming the interface to the wave shape.
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Article type: Appendix
Pages
App2-
Published: September 25, 1995
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Article type: Cover
Pages
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Published: September 25, 1995
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