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Article type: Cover
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Cover1-
Published: June 30, 1986
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Article type: Index
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Toc1-
Published: June 30, 1986
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Article type: Appendix
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App1-
Published: June 30, 1986
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Jun OBOKATA, Yasuo YOSHIMURA, Matsuji SUGITA, Jitsuro NAGASHIMA
Article type: Article
Pages
1-6
Published: June 30, 1986
Released on J-STAGE: April 01, 2018
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For the numerical simulations of manoeuvring slip motions or the slow oscillations of single moored ships, it is necessary to specify the hydrodynamic coefficients in the equation of motion at low frequency. Recently, computer analysis has become to be practical to obtain added mass and other coefficients. However, so-called Motora's chart, which was presented by Motora about twenty years ago, is still available to estimate added mass coefficients because of the simple and practical use of it. Meanwhile, as Motora's chart was produced based on the experiments with conventional type ships of those days, added mass of ships with unconventional dimensions such as recent ultra wide beam ships can not be obtained from the chart. In this report, added mass of several such particular ships are measured by a new model test so-called CAT (Constant Accelerating Test), and the chart is extended to those ships confirming by both model tests and the computer calculations based on three dimensional sourse distribution method. Throught our study, it is found that Motora's chart is still available for such particular ships by means of extrapolating the chart. Also, measured added mass from CAT shows that the added mass at decelerating condition is smaller than that of accelerating condition, which suggests that the different values of added mass have to be used when ship motion is simulated.
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Norihiro MATSUMOTO, Keiji SUEMITSU, Yoshitane KUSAKAWA
Article type: Article
Pages
7-17
Published: June 30, 1986
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The interference effects among hull, propeller and rudder have not been studied enough to establish the MMG type mathematical model for maneuvering motion of ships. An interference factor in the MMG model concerning inflow velocity to a propeller is calculated by applying the thrust identity method to measured propeller thrust under captive model tests. On the other hand, a factor concerning inflow velocity to a rudder is also calculated by applying the normal rudder force identity method to measured rudder force. In some published papers about the MMG model up to this time, the inflow velocity to a propeller under starboard side turning is different from one under port side turning whose turning rate is the same as the former's in an absolute value. And it is also shown that the inflow velocity to a propeller becomes increased by removing a rudder from an after body. Above mentioned facts seem so unreasonable that the following measures were taken. (1) Rotating fluid velocity around the longitudinal axis at a propeller disc which is generated around an after body under maneuvering motion is added to driving propller's revolution as increasing or decreasing relative propeller's revolution. (2) In order to derive the inflow velocity to a propeller before a rudder behind a ship, the K_T-J curve of a propeller with a rudder is used in applying the thrust identity method. Furthermore, in the latter part of this paper, measured velocity distribution at a propeller and a rudder are shown, and the characteristics of flow field in stern's neighborhood under maneuvering motion are described clearly.
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Osamu YAMAMOTO
Article type: Article
Pages
19-29
Published: June 30, 1986
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A theoretical prediction method for calculating the resistance increase of a ship in oblique regular waves is investigated in this paper. Two kinds of approximate formula on second-order steady-state forces are derived by using the momentum principle, and two kinds of approximate expressions on resistance increase are obtained from these approximate formula. Furthermore, numerical calculations on resistance increase are carried out using a container ship (SL175) and a bulk carrier. The results of the calculations are compared with the results of model experiments which were done at the Tsu Ship Model Basin. It is confirmed from the comparison that the resistance increase in a regular following or quarter wave can be predicted accurately enough for practical use. This is accomplished by the first approximate expression. Also, the resistance increase in a regular head or bow wave can be predicted accurately enough for practical use by the second approximate expression.
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Taketoshi OKUNO, Hiroshi SAKAUE, Yoji HIMENO
Article type: Article
Pages
31-41
Published: June 30, 1986
Released on J-STAGE: April 01, 2018
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Three-dimensional turbulent boundary layer on several ship hulls, of which the stern forms are changed systematically, is calculated by a simple integral-type prediction method with small crossflow assumption, and is measured by three-hole Pitot tube in a circulating water channel. The viscous resistance components due to streamwise momentum loss in the boundary layer and stern bilge vortices are evaluated by Himeno's method. The usefulness of the estimation method of viscous resistance is examined in stern-form design problem. A change of the frameline shape at stern affects not only the crossflow in the boundary layer and the strength of the longitudinal vortices, but also the streamwise momentum loss. The viscous resistance becomes small by reducing the fullness of stern shoulder.
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Yoji HIMENO, Huai-Xin CHANG, Takeo OHISHI
Article type: Article
Pages
43-52
Published: June 30, 1986
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In order to clarify the characteristics of the unsteady wake of a ship in waves, the velocity distributions at a stern section of a ship model in forced pitching motion or in incident head wave are measured by use of a propeller-type velocimeter. It is found that the variation of the time-mean velocity in pitching motion increases near the propeller position and decreases near the bottom and the water line region. The profiles of time-mean velocity in unsteady flow are similar to those of steady boundary layers. The oscillating velocity component is found to be comparable to the unsteady Stokes' solution for an oscillating flat plat, although the theoretical values are slightly different from the measured one in case of pitching motion. The result of the measurement, however, indicates that the viscous effect of the unsteady wake velocity is restricted within the region of the steady boundary layer along the hull.
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Kazuhiro FUKUDA
Article type: Article
Pages
53-64
Published: June 30, 1986
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A singly-nonorthogonal coordinate system for Reynolds equations is derived in order to perform the calculation of the flows around ship hulls precisely and economically. In this coordinate system, i) the angle between X^1 and X^2 axes on the body surface or ii) the angle between X^1 axis on the body surface and X^3 axis taken as the distance from the surface, need not to be orthogonal, but the others are perpendicular to each other. Using this coordinate system, boundary layer calculations are performed around a ship model which hull form is represented mathematically, and these results are compared with experimental data.
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Masatoshi NAKAZAKI, Hironao KUBO, Sinsaku SAINO, Joji OMORI
Article type: Article
Pages
65-78
Published: June 30, 1986
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It is well known that the reduction of a blade area ratio and a number of blades are the effective means for improvement of propeller efficiency. On the other hand, the reduction of a blade area ratio and a number of blades cause problems such as a severe cavitation and a excessive propeller surface force. Due to these problems, it is not general for a merchant ship to have a three bladed propeller with smaller blade area ratio. The authors designed the prototypes of three bladed propeller with smaller blade area ratio (expanded area ratio of 0.25) by the new design method which can take into consideration of the variations of effective attack angle in a wake to make pressure distributions on blade surface desirable in view of cavitation. Model experiments were also carried out for the purpose of comparison between a newly designed propeller (SBA type) and a conventional propeller (MAU type). The results this time indicate that the new design method is useful to control and reduce a cavitation and a hull surface pressure of the propeller. The results in the research are summarized below. (1) The propeller efficiency of the newly designed three bladed propeller with smaller blade area ratio (SBA3-25) was improved by about 5% at Reynolds number R_<nD>=6.0 x 10^5 in comparison with the conventional four bladed propeller (MAU4-46). (2) Cavity extent on propeller blade surface for the new propeller (SBA3-25) was remarkably reduced to about a half of the case for the MAU type (MAU3-25). The fluctuating pressure on the stern hull for the SBA3-25 was reduced by about 20% as compared with the MAU3-25. This pressure was almost the same level as that in non-cavitating condition and same as that of the MAU4-46. (3) The characteristics of a smaller blade area propeller was found to be much influenced by the Reynolds number in model propeller open test. (4) It is necessary to make further study because the strength was not exactly considered in this investigation and the self propulsion test behind model ship was not performed. The evaluation of the performances for this kind of propeller should be investigated at full scale in future.
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Yoshiho IKEDA, Takashi NOMURA, Norio TANAKA
Article type: Article
Pages
79-89
Published: June 30, 1986
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Viscous hydrodynamic forces acting on an oscillating circular cylinder and an oscillating flat plate in steady flow are experimentally investigated. The steady-drag, oscillating-drag, added-mass and lift coefficients obtained from measured forces show significant effects of the oscillating flow and the steady flow. The simulation results by a discrete vortex method demonstrate that it is partly because the separated vortices grow much bigger than those for a purely oscillation mode, and that a modified Keulegan-Carpenter number based on the relative displacement of the fluid governs the flow field around an oscillating cylinder in steady flow, The experimental results also show that the increase or the relative velocity on the cylinder surface due to the added steady flow causes the increase of the drag coefficients, and that the time history effect due to the separated vortices generated in previous cycles is significant particularly at low modified K_c number.
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Munehiko HINATSU, Yoshiaki KODAMA
Article type: Article
Pages
91-100
Published: June 30, 1986
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This paper presents a numerical calculation scheme of a flow affected by electromagnetic force and some examples of simulations of flows controlled by MHD (magnetohydrodynamic) effect. An Implicit Factored Scheme, which is a finite difference scheme to solve the Navier-Stokes equations, is used to simulate the flow. In this paper, the problems are limited to the 2-D laminar flow. First, in order to check the scheme and the computer program, the Hartmann flow, which has analytical solution, is simulated. The numerical result agreed well with its exact solution. Then, as the application of flow control using MHD effect, an internal duct flow and an external flow past an elliptic cylinder are simulated. The possibility to control a flow by the MHD effect is thus shown.
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Takeshi KINOSHITA, Kazuhito TAKAIWA
Article type: Article
Pages
101-108
Published: June 30, 1986
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Conserning restoring force and dynamic reaction of slack chain mooring, a linear theory developed by Shimada et al. assuming infinitesimal displacement from catenary is well known to show good agreement with experimental results. In this paper this linear theory is extended to a case of slack chain mooring in current assuming that sectional added mass coefficient and drag coefficient are not changed in current. Experimental results of forced oscillation test in current show good agreement with theoretical evaluation.
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[in Japanese]
Article type: Article
Pages
109-126
Published: June 30, 1986
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[in Japanese]
Article type: Article
Pages
127-133
Published: June 30, 1986
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[in Japanese]
Article type: Article
Pages
135-138
Published: June 30, 1986
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[in Japanese], [in Japanese]
Article type: Article
Pages
139-144
Published: June 30, 1986
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Article type: Appendix
Pages
145-147
Published: June 30, 1986
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Article type: Appendix
Pages
App2-
Published: June 30, 1986
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Article type: Appendix
Pages
App3-
Published: June 30, 1986
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Article type: Appendix
Pages
App4-
Published: June 30, 1986
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Article type: Appendix
Pages
App5-
Published: June 30, 1986
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Article type: Cover
Pages
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Published: June 30, 1986
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Article type: Cover
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Published: June 30, 1986
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