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Article type: Cover
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Published: March 25, 1991
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Article type: Index
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Toc1-
Published: March 25, 1991
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Article type: Index
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Published: March 25, 1991
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Masatoshi BESSHO, Tetsuya KUDO, Tohru NISHIMOTO
Article type: Article
Pages
1-10
Published: March 25, 1991
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This is a study to search optimum ship forms in a range covering Froude number from 0.4 to 1.4 with respect to their wave-making resistance of displacement type ships by the so-called thin ship theory. As well known the thin ship theory predicts fairly well the wave-making resistance of displacement type ships in the neighbourhood of last hump speed. Numerical studyes minimizing the wave-making resistance are carried out on three types of ship. The first type is a wall-sided model and its solution is stable and gradually joins to the foregoing theorectical result. The second type is Maier form model and this solution is also fairly stable and the wave resistance is somewhat larger than the above. The last case is a bulbous bow type ship forms. Is this case, the more the number of terms representing its half breadth, the less its wave resistance becomes. However, it happens that its half breadth curve has a negative value, so that the number of terms might be confined in small with regard to the speed and draught.
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Masatoshi BESSHO, Kazuaki YAMAGATA, Suehiro IMAIZUMI
Article type: Article
Pages
11-18
Published: March 25, 1991
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Following the first report, this is a study to search optimum ship forms of shallow draft ship represented by the surface pressure distribution in high Froude number range. At first, the case in which the pressure distributes on a rectangle are considered. If the pressure vanishes around the periphery, there is free from the splash by the linearized theory. In this case also, the more complex the distribution, the less the wave resistance becomes, so that the distribution may be taken simpler. The splash-free type seems to be optimum, have little dynamical buoyancy and may be said a displacement ship. Secondly, the yacht type which is a combination of a thin ship and a flat ship are calculated but the result is not favourable. Lastly, the cases in which the distribution plane is not a rectangle or symmetrical are considered and it is found that the wave resistance increases considerably in such cases.
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Zhi-qing YU, Ichiro TANAKA
Article type: Article
Pages
19-34
Published: March 25, 1991
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An attempt to obtain influence functions is described. These functions show the relationships between the change in shape of a body of revolution and the variation of frictional resistance, viscous pressure resistance, respectively. For this purpose an integral method of higher order boundary layer theory is applied. For reducing viscous resistance, a procedure reforming body shape besed on these influence functions is proposed. The results of calculation show if the body is subjected to a constant volume, optimum shape has a concave part near the tail whether the initial shape does or not. If the body is subjected to a constant volume and maximum diameter, optimum shape has a parallel part whether the initial shape does or not.
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Kyuichi YAMAMOTO, Nobuhiro BABA, Yoji HIMENO, Tetsu WADA
Article type: Article
Pages
35-44
Published: March 25, 1991
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Three-dimensional separation in unsteady flows when the vortex shedding occurs from a cylinder is investigated using the finite-difference solution of the incompressible Navier-Stokes equation. The diameter of the cylinder model is varied sinusoidally in the spanwise direction. The computed velocity field adjacent to the cylinder surface is analyzed by the phase-space theory to detect and classify critical points on the surface. The flow pattern of the three-dimensional separation becomes quite complicated and surprisingly changes in time as the large-scale vortices are shed from the alternate side of the cylinder. The nodal and saddle points move along the circumferential lines where the cylinder diameter is maximum or minimum, and the separation and reattachment lines wind accordingly. The focal points also appear, move, and disappear along the separation line, and as a result, the topology of the flow pattern changes in a drastic manner.
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Susumu HIRANO, Yoji HIMENO, Takahiro NAKAGAWA, Kazuhiro KITAGAWA
Article type: Article
Pages
45-51
Published: March 25, 1991
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The present report describes results of wave pattern resistance measurement for two models of prismatic planing hull forms. The resistance is analysed by Newman-Sharma's method. Discussion is also made on the separation of resistance components of the models, using the results of previous experiments, which were 3-component-force test, measurement of bottom pressure distribution, measurement of spray flux distribution, and the present measurement of wave-pattern resistance. An attempt of the separation of resistance components has resulted : (1) Frictional resistance due to Shoenherr's formula for an equivalent flat plate, added to the pressure obtained by integrating the measured hull pressure, turns out to be almost equal to the measured value of the total resistance. (2) The pressure resistance can be resolved into two components, i.e., the spray resistance which is derived from the measured momentum loss, and the wave pattern resistance which is also measured by removing the spray. It is found that the frictional resistance, the spray resistance and the wave-pattern resistance are almost of the same order, any of which may not be neglected.
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Masakazu KAJI, Naoki MAEDA, Tadao YAMANO
Article type: Article
Pages
53-60
Published: March 25, 1991
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A hydrofoil catamaran whose weight is supported by both buoyancy and lift has come to our attention as one of high performance vessels. A lot of study on resistance has been made but few papers have cleared the characteristics of each resistance of the hull, the foil and these interaction. And so this paper clears these characteristics experimentally to understand the resistance characteristics of the hydrofoil catamaran very well. As a result of our study, it has been cleared that interaction forces between the fore foil and the hull are very small but that interaction forces between the aft foil and the hull are significant values. And it has also been cleared that providing spray rails and lessening the stem angle to the water line are very useful to decrease the resistance because the spray resistance is large for such high speed vessels.
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Shotaro UTO, Yoshiaki KODAMA
Article type: Article
Pages
61-67
Published: March 25, 1991
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Recently, the application of CFD (Computational Fluid Dynamics) method to the incompressible viscous flow problem has been developed remarkably. Nevertherless, difficulties of grid generation has restricted so far the application of CFD method to the problems with geometrically simple flow regions. In order to overcome such difficulties, present study shows computations of the two-dimensional incompressible viscous flow with composite grid method, by which a grid system around a geometrically complicated shape of body such as a practical hull form or a marine propeller can be generated easily and effectively. Composite grid scheme is based on cell-centered, finite-volume, upwind scheme with global conservation property, which was developed by one of the authors. The zonal boundary condition is derived from momentum and mass flux conservation law and introduced into this scheme. To evaluate the robustness and accuracy of composite grid scheme, computations of the low Reynolds number flow around a two-dimensional circular cylinder are made for 7 cases with varing the location of the zonal boundary and discontinuity condition of a grid system. Finally, computations of the two-dimensional laminar flow around a wing section in cascade are made to show the applicability of the present method to the problem with geometrically complicated flow region.
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Taketoshi OKUNO, Jun NAKAOKA
Article type: Article
Pages
69-74
Published: March 25, 1991
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Recent developement of flow velocity field measurements using visualized flow pictures has been advanced remarkablely. Although many of these techniques have great possibility a practical universal method is not found yet. The user of the image measurement system must choose a suitable analysis method coresponding to the flow characteristics. This paper describes the spatio-temporal derivative method, which is known as a high spatial resolution technique. The several measuremed results have shown and discussed the problems and possibilities. The flow field of necklace vortex in front of full hull model, which can not be measured by the Pitot tube or the hot film, has been shown at first. The unsteady separated vortex region behind a two-dimensional aerofoil and the flow around circular cylinder in regular wave are measured.
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Mitsuru KAWAKATSU, Ryouzou HIRAKU, Toshio SUZUKI
Article type: Article
Pages
75-79
Published: March 25, 1991
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Tracer pathline images of flow field give us a great deal of information about the flow field, and several methods were developed to obtain the velocity vectors from these pictures. However, the techniques mainly give us 2-dimensional velocity components because they use a 2-dimensional slit light sheet to observe the flow field. In this paper, a new technique is proposed to obtain the 3-dimensional velocity components from a pair of stereoscopic photographs of the flow field which is lighted by slightly thick slit light sheet. The summary is as follows. 1) The new technique was formed by combining the stereoscopic photograph with the correlation method. 2) The technique makes it easy to analyse the stereoscopic photograph which contains highly dense particles. 3) The technique is applied to measure the 3-dimensional velocity components of the flow field around a circular cylinder in the uniform flow and reasonable results are obtained.
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Shigeyuki OGINO, Yoshitaka HASHIMOTO, Toshio DOI, Isao SUZUKI, Masamit ...
Article type: Article
Pages
81-87
Published: March 25, 1991
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The manoeuvrability was studied for the ship with this newly developed asymmetrical stern which contributes much to energy saving in propulsion. Two models were used for the typical manoeuvring tests, one was this new stern ship and the other was its parent ship having usual stern. The adoption of asymmetrical section rudder to this new stern was also studied and its effect was examined. The results show this new stern has good manoeuvrability as well as the parent usual stern and the adoption of asymmetrical rudder is effective.
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Yasushi HIGO, Mun-Keun HA
Article type: Article
Pages
89-95
Published: March 25, 1991
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Three-dimensional source distribution method is used to represent the disturbed potential by a surface piercing body travelling in regular wave. It is analytically proved under the assumption based on the Ursell's least singular solution that the singularity where field point P(x,y,z) approaches source point Q(x',y',z') on z=0 disappears and the potential at this point has a finite value. In numerical computation, the panel method in which the green function is analytically handled in source panel produced good results than the monopole method, at least in the panel that has contact with free surface. Moreover, the solution of integral equation varies easily with the size of this panel.
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Sunao MURASHIGE, Takeshi KINOSHITA
Article type: Article
Pages
97-101
Published: March 25, 1991
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Kato et al. reported that a wave height of a symmetrical component and an antisymmetrical component of scattered waves is exactly one half of that of incident waves, that is, "equally energy splitting law", and that in two dimensional diffraction problems this law does not require symmetry of a body geometry. It gives us valuable information as an invariant property. In the present note, however, we show that it is invalid in the case of an asymmetrical body, although it is reviewed as valid by Kan.
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Hisafumi YOSHIDA, Kimio SAITO, Matao TAKAGI
Article type: Article
Pages
103-111
Published: March 25, 1991
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Following the previous papers, the second-order currents and changes in local mean surface level induced by two-dimensional mono- and bi-chromatic radiation waves in an experimental flume are discussed. In this paper, particularly, the comparison between the results obtained from a paddle type wave-maker and heaving motion of a rectangular body is investigated. It is found that the second-order currents and changes in local mean surface level are almost same when they are non-dimensionalized in terms of the amplitude of the first-order radiation waves.
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Hisaaki MAEDA, Hyo Jae JO, Shyogo MIYAJIMA
Article type: Article
Pages
113-121
Published: March 25, 1991
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Newly amended Code of Mobil Offshore Drilling Units doesn't consider the short crested wave effect on the responses in the stability of the structure. Therefore, in this paper, it will be cleared up how the directionality of the wave affects on each mode of the motion. We developed a simulation program in the time domain and a spectral analysis program for the short crested waves. The latter would save large computational efforts. We compared each result of numerical calculations and we found that the spectral analysis can be used to expect the responses of the structures in the short crested waves. And the accuracy of the numerical calculation programs was validated by the corresponding experimental results in the square towing tank which can generate the bi-directional waves. The experiments were carried out for semi-submersible rig model with eight columms and two lower hulls, which was moored horizontally by four soft linear springs. From the numerical and experimental results, we can find that in the short crested waves, the amplitudes of the motions in the principal direction of wave propagation are smaller and the amplitudes of the motions in other directions are larger than those in the long crested waves. Thus we can conclude that the directionality of the wave has an influence on the each mode of motion.
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Zhi YU, Hisaaki MAEDA
Article type: Article
Pages
123-128
Published: March 25, 1991
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Considering the nonlinear characteristics of the Wells turbine and random and irregular characteristics of ocean waves, a mathematical model of OWC wave power system in time domain is more useful. The model currently used in time domain is written in the form of a differential-integral equation by using impulse response function, which is not convenient for the research of control problem especially when modern control methods are applied in the research. So, a state space model is useful for the study of OWC wave power system. In this paper, system realization techniques are applied to establish a state space model for OWC wave power system from the impulse response function. The integral term of the differential-integral equation is replaced by a linear part system whose output is equal to the integral term and the motion velocity of OWC is looked as the input of the system. System parameters of the part system are optimally determined by using Gauss-Newton least square method. Two fixed terminator type OWC wave power devices are considered as calculation examples. Simulating results show that the state space model is in good agreement with the impulse response function model. Besides OWC wave power system, the modeling techniques proposed in the paper can also be used in the modeling of other ocean dynamic systems.
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Masao MORIKAWA, Yutaka YAMAUCHI, Kuniteru ISHIKAWA, Norihisa KODAN, Ha ...
Article type: Article
Pages
129-136
Published: March 25, 1991
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Research and development of new concept of TLP (Tension Leg Platform) which has very long prefabricated tendon, a mooring system capable of diver-less installation and stable gravity template have been performed under the "OffShore Oil & Gas Production Platform Project" promoted by the Ministry of International Trade and Industry Japan (MITI) and supported by Japan Ocean Industries Association (JOIA). In this project, the tendons are planed to be fabricated and assembled on the land in an overall length and they will be horizontally towed to the site. After that, they will be upended there. This type tendon needs to investigate a behavior and strength on not only the working condition but also the towing and upending condition. The towing and upending procedures, however, have not been established theoretically nor empirically. This paper presents the validity of a simulation method in comparison with experimental and theoretical studies on the towing and upending condition of tendon and also presents a consideration of actual upending method on site. At first, the tank tests were performed to verify a simulation method using the 1/20 scale model made from polycarbonate resin. The bending strains were measured and analyzed on towing and upending tests. In the towing tests, the horizontally towed model using some floats in the regular waves were examined. In the upending tests, the tendon was freely dropped under the conditionthat the one end was supported by pin joint. Afterward, the simulation analysis was performed using time domain and non-linear FEM program. The results of simulation analysis were compared with the experimental ones. Both results coincide qualitatively and quantitatively. Parametric studies on actual upending method were performed varying mass of lower connector. It is possible to evaluate safety of long prefabricated tendon actual upending condition using the proposed simulation method.
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Tetsuya YAO, NIKOLOV Plamen Ivanov
Article type: Article
Pages
137-146
Published: March 25, 1991
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To use the High Tensile Steel effectively for a ship's hull, the plate thickness becomes thin so that plate buckling may take place in some cases. In these cases a precise estimation of plate's behaviour after buckling is necessary, and nonlinear analysis of isolated and stiffened plates is required for structural system analysis. In this connection, this paper dicusses stiffeness and strength criteria of plates after bucking. A simple elastic large deflection analysis of isolated plates with initial deflection and welding residual stresses subjected to bi-axial compression and lateral load is performed. Four fondamental boundary conditions along the sides are assumed. Simple expressions are derived to evaluate the effective width and the initial yielding strength of plates under these boundary conditions. Some sample calculations are performed to demonstrate the validity and the usefulness of the presented method of analysis.
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Kiyotaka UNO, Kuniteru ISHIKAWA
Article type: Article
Pages
147-153
Published: March 25, 1991
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This paper described the application of reliability method of the level-2 method for two modes of failure. Firstly, safety factor for initial yielding and cumulative fatigue damage for fatigue failure were evaluated by ordinary methods. Secondly, safety indexes for same two failure modes were evaluated by the level-2 method on condition that the same demand and the same capacity. Thirdly, the safety factor and the cumulative fatigue damage factor were compared with the safety indexes, and the relationship between the ordinary methods and the level-2 method were presented. Lastly, three design curves based on structural reliability analysis are proposed and the design formula for the estimation of failure probability in fatigue is proposed.
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Masakazu YAMAMOTO, Katsuo TANAKA, Jyo HANAZAKI, Kazuhisa SAEKI
Article type: Article
Pages
155-161
Published: March 25, 1991
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For the first time in Japan, a Turbo Compound System (TCS) and a Renk Constant Frequency system (RCF), were applied to KAWASAKI-MAN B&W 6S80MCE main diesel engine for a 182,000 DWT bulk carrier in order to obtain the overall operating economy. After carrying out a number of detailed examinations and tests, the vessel was delivered on Feb.28, 1989 and more than one year has passed with satisfactory operating results. This paper outlines the main features of the TCS & RCF systems and gives the test results and the effects of the systems on the vessel performance.
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Article type: Appendix
Pages
App1-
Published: March 25, 1991
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Article type: Cover
Pages
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Published: March 25, 1991
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