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Article type: Cover
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Cover1-
Published: September 25, 1996
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Article type: Appendix
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App1-
Published: September 25, 1996
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Article type: Index
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Toc1-
Published: September 25, 1996
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Article type: Index
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Published: September 25, 1996
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Yasunori IWASAKI, Tadao YAMANO, Takeshi UEDA
Article type: Article
Pages
1-6
Published: September 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. The authors developed a new stern form which has better propulsive performance under the above described design restrictions. This paper describes seakeeping ability and maneuverability of the ship with the new stern form.
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Osamu KINOSHITA, Kazuki YABUSITA, Katuo SUZUKI
Article type: Article
Pages
7-13
Published: September 25, 1996
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Experiment of wave analysis is performed in circulating water channel by using three high-speed boat models with trim fixed. An apparatus of making a wave height meter traverse in parallel direction to a ship model is deviced and wave measuring system is developed. In order to reduce amplitude of steady waves and inclination of mean water surface of the channel wave supressor and water level are controled by making use of reserve tank. The measured wave configuration caused by the model is subtracted by the one measured without the model to cancell the diverging waves caused from the unevenness of the channel side wall. The results of wave analysis are very well in comparison with total resistance measured by trim fixed type of dynamometer and the wave pattern resistance is almost one third of the total resistance at planning Froude numbers higher than 0.4. The component of diverging wave resistance which is dominant at high Froude number and is noticed as coastal nuisance is calculated from the wave analysis results and it is expanded in terms of bottom cambers of models and running trims. It is concluded that the concave curved bottom boat is better than the others and the control of running trim is moreover important from a view point of reducing the diverging wave resistance.
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Jun-ichi HAMASAKI, Yoji HIMENO, Yusuke TAHARA
Article type: Article
Pages
15-21
Published: September 25, 1996
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This paper presents an application of Computational Fluid Dynamics to ship hull optimization, which is based on the nonlinear programming approach developed by Hamasaki et al. The hull forms are first expressed by the offsets table and variation function using the B-spline functions, whose coefficients are used as the design variables. Then the fully-elliptic Reynolds-averaged Navier-Stokes and continuity equations are solved with zero-equation turbulence model to provide viscous resistance and stern flow information. The aft part of hull is optimized so as to minimize the viscous resistance and the value of wake at the top of propeller disc. The affine scaling interior method is used in the present multi-objective optimization procedure. The present iterative optimization procedure yields steady convergence of the solutions and appeared to be capable for practical ship form design. An overview is given of the present numerical method, and results are presented and discussed for the Series60 CB=0.8 as an initial form including comparison with available experimental data. In addition, requirements for improvements of the present approach are described regarding accuracy in computing the sensitivity coefficients.
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Tomoo HANAWA, Yoshito FUKUSHIMA, Satoru KUGIMIYA, Hitoshi NISHIMOTO
Article type: Article
Pages
23-34
Published: September 25, 1996
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Experimental study on the hull form at speed of Fn=0.35-0.45, for improving the high speed ability with added singularities on midship part is described in the presented thesis. There are two indispensable items for reducing the hull resistance under the influence of added singularities. 1. uniformity of pressure distribution on the hull surface. 2. reciprocal interference among bow waves midship waves and stern waves. The authors introduced above two indispenbable items into the designing new type hull form, so-calledHybrid・mark 2 Catamran Stern based on the simulant calculations, and clarified the design problems involved owning to the results of experiment. As a result, the valuable effects for reducing the hull resistance have been proved. It was confirmed that this new type hull form is expected the speed up of 1.5 knots with same output, or the fuel saving of 30% with same displacement and same service speed, as compared with ordinary hull form.
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Michio TAKAI
Article type: Article
Pages
35-41
Published: September 25, 1996
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The CFD technique for the viscous flow field around a ship has been developed and enabled us to stably acquire the solution with high accuracy. However, in the case of taking wave-making resistance into consideration, there still exists many problems. As for the CFD technique, the importance of the time discretization tends to be undervalued, while there are lots of discussions concerning how spatial discretization, i.e. grids system, influences the computational results. In this paper, a numerical investigation concerning the time increment for the computation of the viscous flow with waves around a ship has been conducted. Some examples of application of newly developed method to several ship configurations like VLCC and high-speed ship are to be shown.
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Munehiko HINATSU
Article type: Article
Pages
43-48
Published: September 25, 1996
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In order to clarify turbulent flows precisely, we develop an LES code and verify it through a simple channel flow simulation. We use a dynamic SGS model as a eddy viscosity model, which is one of the promising models in the engineering turbulece studies. The numerical scheme is based on a finite difference method. Computational results are compared with the experiment data and thus the present method can evalaute the turbulence properties well. We think that the present method can be applied to simulate flows around drag reduction devices such as LEBU (Large Eddy Break-up Device).
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Takanori HINO
Article type: Article
Pages
49-54
Published: September 25, 1996
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The shape optimization using CFD (Computational Fluid Dynamics) is expected to be a powerful design tool, because CFD can simulate inviscid as well as viscous flow fields around a body of complex geometry. In the present paper, the gradient based optimization methods are applied to the shape optimization of a two-dimensional body in which the fluid dynamic objective function is minimized. Flow fields are computed by a finite-volume Navier-Stokes solver. Sensitivity analysis which gives the gradients of the objective function and the constraints is carried out by the adjoint variable method. The numerical procedure is described together with the results of several applications.
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Shigeru NISHIO, Shigeki NAKAO, Taketoshi OKUNO
Article type: Article
Pages
55-61
Published: September 25, 1996
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A measurement system for were height distribution using visualized image has been developed and applied in towing tank. When a laser sheet illumination is given from the bottom of the tank, the free surface is visualized as the boundary of bright and dark area on the image. The high contrast image is obtained by large light scattering in water. Combining the visualization and a image processing technique, present image measurement system has been developed by the authors, and is modified so as to apply on the measurement in towing tank. High power laser is needed to obtain a enough contrast on the visualized image in large size towing tank, and the simple coordinate transformation should be considered to make up a practical system. Two camera system is used to obtain a wide range distribution in same spatial resolution. The measured result shows that the present system can be applied on the wave measurement around not only a high speed craft but also a ordinary displacement type ship model.
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Yusuke TAHARA
Article type: Article
Pages
63-76
Published: September 25, 1996
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A multi-domain method is set forth for calculating boundary-layer and wake flows around the International America's Cup Class (IACC) sailing yacht. The physical domain is divided into two parts, i.e., the port- and starboard-side domains, where those centerplane (matching) boundaries include keel and rudder surfaces. 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. An overview is given of the present approach, and numerical results are presented and discussed for an IACC yacht for zero and nonzero yaw angles, including the comparisons with the canoe body solutions in order to evaluate influences of keel and rudder on boundary-layer flow near the hull surface. The present approach appears to be capable for the detailed study of the flow fields around the entire boat as well as the drag and lifting forces acting on it. Lastly, some concluding remarks are made concerning requirements for future work of the present study.
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Yoshiho IKEDA, Gen NISHIDA, Toru KATAYAMA, Yoshinori YAMAGUCHI, Jiro N ...
Article type: Article
Pages
77-84
Published: September 25, 1996
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In the 1st report, the authors reported the development of an experimental system to measure hydrodynamic forces acting on fully captive models of planing craft at high speed (maximun speed=15m/s). Following this report, three-component hydrodynamic forces acting on series models towed by the system are measured to know fundmental characteristics of them with high speed up to Fn=6.0. It is shown that the residual resistance coefficient in terms of the displacement is not so sensitive to the hull form in very high speed. A simulation of the attitude and resistance of a craft using a database of measured hydrodynamic forces is also carried out to be compared with experimental results of a conventional resistance test. The comparison shows that the simulation results are in fairly good agreement with the experimental results at high speed.
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Yoshiaki KODAMA
Article type: Article
Pages
85-90
Published: September 25, 1996
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A method is shown to generate a surface grid on a ship hull with bow and stern bulbs and stern overhang. The hull geometry is represented by a set of offset data defined at constant x-sections. A spline net which consists of horizontal and vertical splines, is defined based on the offset data. The spline net is modified iteratively using the implicit geometrical method which imposes orthogonality, smoothing, and clustering requirements. A new reclustering method is shown, which produces grids much better than the original reclustering algorithm.
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Shigeru NAITO, Norihisa KODAN, Ken TAKAGI, Koichiro MATSUMOTO
Article type: Article
Pages
91-98
Published: September 25, 1996
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Two types of above-water bow shapes have been developed for the reduction of the added resistance in waves. The new shapes are named the pelican type and the beak type respectively. Series measurements of the added resistance in regular waves have been carried out with variation models of the above mentioned two types. The experimental results showed that the pelican type could not reduce the added resistance, on the contrary, the beak type could reduce it. Some explanations are presented on the mechanism of the reduction of the added resistance in waves with the variation of the above-water bow shape. From the practical viewpoint, the potential candidate of the above-water bow shape for the reduction of the added resistance in waves is discussed.
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Tsugukiyo HIRAYAMA, Takehiko TAKAYAMA, Kiyoshi MIYAKAWA, Ning MA
Article type: Article
Pages
99-105
Published: September 25, 1996
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We had already proposed a long-life type floating airport composed of removable floating units. About this type of airport, we studied on the elastic effect on the function of airport. On the other hand, it will be preferable to be equipped with active controlling system for elastic deformation by the lack of units or wave forces. For this purpose, we developed a pneumatic type attitude control system and examined by model tests.
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Roby KAMBISSERI, Yoshiho IKEDA
Article type: Article
Pages
107-116
Published: September 25, 1996
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The present Deterministic and Probabilistic damage stability rules for ships, their drawbacks and a concept of a new approach are discussed in this paper. In the proposed approach, safety level is varied using a survivable damage opening size. All the damages causable by damage openings of sizes upto this survivable damage opening size should be survived by a ship in the maximum sea state it has to operate. The survivability criteria should also take into account the static and dynamic effects of flooded/trapped water. The survivable damage opening size varies with the degree of safety, damage statistics, structural strength of ship, etc.
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Hideo SHIRAZAWA, Yoshiho IKEDA
Article type: Article
Pages
117-126
Published: September 25, 1996
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Experimental investigations on ship motions are carried out for models of high-speed passenger ships in regular head and following waves, and vomiting ratios of passengers on the ships are estimated on the basis ofthe experiments. It is found that the heaving and pitching motions in regular head wave decrease with increasing advanced speed, and that this tendency is different from the theoretical results by a Strip Method. Even in head seas, the rolling motion occurs in high speed due to reduction of the restoring moment. It is demonstrated that evaluation of seakeeping performance of high-speed passenger ships have to be done in terms of vomiting ratio, because the distribution of vomiting ratio is different from that of the vertical acceleration due to the frequency effect on vomiting.
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Toru KATAYAMA, Yoshiho IKEDA
Article type: Article
Pages
127-134
Published: September 25, 1996
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An experimental investigation was done on the calm water longitudinal dynamic instability at high advance speeds of a planing craft. Free attitude tests were used to detect the conditions causing porpoising and the motions involved. Experiments were done by systematically changing ship's weight, position of center of gravity and towing speed. It was found that porpoising is caused by heave and pitch coupling when their periods were the same and the porpoising limits varies with longitudinal center of gravity and ship's weight. By captive model tests, the influence of hydrodynamic forces on porpoising was studied. Experiments were done systematically changing angle of trim, draft and towing speed. From measured hydrodynamic forces, restoring forces of heave and pitch were calculated. It was found that the coefficients of heave induced pitch restoring forces are negative at high advance speeds. As a result, there is a possibility for parametric excitation due to transfer of energy between heave and pitch motions. Stability analysis was done, using Routh-Hurwitz stability criterion, to predict the porpoising limits. But, the results did not agree with the experiment.
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Shoichi HARA
Article type: Article
Pages
135-151
Published: September 25, 1996
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The towline tension during towing in waves has to be estimated concerning constant tension and fluctuating tension induced on the towline. The relative motion especially surge motion between tug and tow causes the dynamic towline tension due to cross-flow drag which is proportional with the square of velocity of the towline induced by the towline movement in water. This frequently has both the high frequency component of wave elevation and the low frequency component due to slow drift motion. The towline tension becomes exponentially large in case the distance between tug and tow becomes extremely large during towing. The dynamic towline tension has been composed of the cross-flow drag force and nonlinear restoring force. The nonlinear model using those force terms has been proposed in order to simulate the dynamic towline tension during towing. The effect of the inertia force term on the dynamic towline tension has also been evaluated. The probability density function, expected mean upcrossing frequency and expected largest value of the dynamic towline tension have been obtained. The theoretical calculation of the dynamic towline tension has been validated by the results of the numerical simulation.
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Hajime KIHARA, Yohsuke SHIRAKURA, Shigeru NAITO
Article type: Article
Pages
153-161
Published: September 25, 1996
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The experimental investigation was carried out with two frigate models whose above water bow forms were different respectively. The investigation consists of three tests including restrained in still water, forced oscillation in still water and restrained in regular waves. For visualizing the free surface the illuminating wetted surface method is introduced and unsteady wave profiles as well as steady ones are measured as image data. Moreover, the data are transformed into time histories of wave height at each Station. A harmonic analysis is carried out to analyze time histories data. The effect of above water bow form is recognized as the difference of wave height.
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Kazuhiko HASWGAWA, Hidenobu FUKUDA, Futoshi TANIZAKI
Article type: Article
Pages
163-168
Published: September 25, 1996
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Strategy for multi-ship encounter problem is not yet established in automatic collision avoidance system. In SAFFS (Ship Auto-navigation Fuzzy Expert System) proposed by the first author and others, it is treated to avoid one-by-one for the most dangerous ship among other ships each reasoning moment. Some dangerous or wasteful manoeuvre may occur at certain occasions. To improve this a new concept of avoiding a group of ships is proposed. The principle ideas of defining "group" and strategies for avoiding groups are dealt with. On the other hand, in SAFES, there is no feature of improving the rules, degree and timing of avoiding. This may be called the learning feature. As an idea of this feature, a simple random-walk optimization is proposed and validated by simulation. Although as a goal of ship automatic navigation system, both features should be included to compensate each other, as a first step, they are independently treated in this paper.
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Takashi TSUBOGO, Thomas GEORGE, Hiroo OKADA
Article type: Article
Pages
169-176
Published: September 25, 1996
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This paper deals with the dynamic buckling strength of columns and cylindrical shells used in marine space structures, which are subjected to axial impact forces due to water waves or seaquakes. The dynamic buckling strength of initially curved columns subjected to axial impact forces is investigated through a parametric analysis which has brought out the dynamic relationship between the reduced slenderness ratio and the buckling strength. Similar analyses are made for the axi-symmetrical and local buckling strength of cylindrical shells with initial local deflections. From these results the effects of shape factor, degree of impact velocity, and initial deflections on the buckling strength of columns and cylindrical shells are evaluated. Results obtained in this study are summarized as follows: (1)The dynamic buckling strength of columns and cylindrical shells with initial deflections subjected to slowly varying loads such as water wave or seaquake induced impact loads is nearly equal to the static strength. On the other hand, the dynamic buckling strength under rapidly varying loads is larger than their static strengths. (2)The axi-symmetrical buckling strength of locally deflected shells decreases with increasing initial deflections. The degree of decrease of dynamic buckling strength is more remarkable than that of static strength due to the inertia effect. (3)The possibility of axi-symmetrical and local buckling failure of steel columns supporting the elevated structures which have undergone extensive damage during the Great Hanshin-Awaji Earth-quake of 1995 is also discussed using the above results.
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Yasumitsu TOMITA, Kiyoshi HASHIMOTO, Naoki OSAWA, Taira OZAKI
Article type: Article
Pages
177-184
Published: September 25, 1996
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In this report, we analyze cyclic plastic 3-dimensional deformation of f.c.c. polycrystalline by infinitesimal deformation FEM analysis, and evaluate the assumption on the characteristics of dislocation movement under cyclic loading condition, which was obtained by the 2-dimensional FEM analysis in the previous report by the authors. Furthermore, we investigate the effect of grain size on the local deformation of polycrystallines. Results of the analysis are summarized as follows. 1)As in the 2-dimensional analysis, it is possible to represent cyclic plastic behavior of real materials qualitatively if c.r.s.s. mainly raise by long-range stress field by dislocation structures, or the increment of c.r.s.s. vanishes during unloading and backward loading process. Most of dislocation movement model for cyclic plastic deformation under fatigue process meet the requirements mentioned above. 2)As in the 2-dimensional analysis, there exists plastic strain localization on free surface of the FEM model. The ratio of maximum localized plastic strain to mean plastic strain is more than 15 on the beginning of plastic deformation, but it reduces to an asymptotic value of 3 to 5 as plastic deformation develops. It shows that there exists stress level where finite local strain occurs but not observed as macroscopic plastic deformation, and it is assumed that such stress level corresponds to the fatigue limit. 3)In the cases calculated in this report, there is a tendency that a model of which grain size is larger shows higher maximum and mean plastic strain.
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Yoshiyuki INOUE, SEIF Mohammad Saeed
Article type: Article
Pages
185-191
Published: September 25, 1996
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The need for vehicles transportation among Japanese islands is very important, and many large fixed bridges have been constructed across the rivers as well as seas. But, the concept of a floating bridge takes advantage of natural law of buoyancy of water to support the dead and live loads on the bridge. In addition, there is no need for conventional piers and foundation. However, there is not so many data base on such structures, and a direct design should be employed for each case. Therefore, it is important to evaluate their overall behavior in preliminary design stages. In the present study, a method has been developed to evaluate hydrodynamic loads on floating parts of the bridge and to analyze the dynamic behavior of the structure by using FEM. The proposed method takes into account the hydrodynamic interaction among the floating parts and nonlinear effects such as drag forces. Furthermore, based on numerical results, effects of wave conditions on the dynamic behavior of the bridge are investigated.
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Naoki NAKATANI, Taketoshi OKUNO, Koji OTSUKA
Article type: Article
Pages
193-199
Published: September 25, 1996
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The water quality in an inner part of a gulf encircled big cities is chronically bad, because the pollution load is very high. It is known that the so-called UTSURO, an artifitial lagoon using rubble-mounted breakwater, has water purification functions for such an enclosed sea area. In this research, the mathematical model is constructed using ecosystem models. The result of numerical simulation shows good agreement with measured values, and also shows the system is effective for purification of water quality.
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Shigeru NAITO, Kazuo TOMITA, Takao NAKAMURA, Haruaki SAKASHITA
Article type: Article
Pages
201-210
Published: September 25, 1996
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When we conduct higher order experiment in wave basins, we must consider the following three points. One is related to a configuration of wave basin, second is a control of towing carriage and third is a control of absorbing wavemakers. A configuration of wave basins is usually rectangular and the wave basin has a wavemaker at the end of it. It can not be cleared whether this configuration and wavemakers are adequate or not for wave basins. This paper describes theories, experiments and simulations mentioned above by cotrolling absorbing wavemakers, the advancing ship model, which trajectory is also controlled, can encounter the given waves at the expected position and time in proposed new wave basins, which configurations are circular, ellipse and convex polygon.
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Article type: Appendix
Pages
App2-
Published: September 25, 1996
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Article type: Cover
Pages
Cover2-
Published: September 25, 1996
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