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Article type: Cover
Pages
Cover1-
Published: March 25, 1990
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Article type: Index
Pages
Toc1-
Published: March 25, 1990
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Article type: Index
Pages
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Published: March 25, 1990
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Shoichi OHTANI
Article type: Article
Pages
1-5
Published: March 25, 1990
Released on J-STAGE: April 01, 2018
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A trial to concentrate Navigation informations on CRT display is carried out in Europe but very rare in Japan. And Navigation system based on Antieollision radar (ARPA)is used popularly, but other navigation informations are not concentrated yet. On the other hand, officers onboard ship are decreasing. From this view point, it is necessary to concentrate many kinds of informations at one place compactly likely as an airplane cockpit. Navigation informations containing Navigation instruments, chart, ship's tracks etc., reach much volume. Therefore, many graphics are required to display these informations on CRT. To use these graphics effectively, we propose "Navigation Information System" able to change graphics on CRT rapibly as necessarily.
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Susumu HIRANO, Suguru UCHIDA, Yoji HIMENO
Article type: Article
Pages
7-12
Published: March 25, 1990
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Bottom-hull pressure measurements were carried out for two prismatic planing hull forms. The models have v-shaped bottom with rise angle 13 degree and vertical-side chines with breadth 200 and 400mm. The hull pressures at the planing speed condition were measured on 465 points at the bottom of the 200mm breadth model, and 765 points for 400mm.The pressure distribution shows a strong peek around the spray root line, relatively low positive values in the pressure area, and undulations in transverse direction. The pressure integrated values associated with wall friction effect are compared with the lift, the drag and the moment which were also measured.
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Rituo SHIGEHIRO
Article type: Article
Pages
13-20
Published: March 25, 1990
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The paper presents results of free running test of a windmill boat with an air propeller coupled to a water propeller. The windmil is 4-blades, 2.0m diameter. The length of boat is 3.0m, and the breadth is 1.0m. The basic mechanical layout consists of windmill which can be rotated on a vertical axis to face any direction, mounted on the top of the mast. It drives via a bevel gear, a vertical shaft inside the mast, which in turn drives the water propeller shaft via another set of gears at the base of the mast. The two set of the gear in the drive result in a 1:2.5 ratio so that the water propeller rotats two and half as fast as the windmill. The performance of windmill is calculated out by linear lifting line model. The resistance of hull and performance of water propeller are carried out tank test. The simulation study is carried out to make the comparison between calculation model and experiment. In addition, the simulation results are in good agreement with experiment results.
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Ken TAKAGI
Article type: Article
Pages
21-29
Published: March 25, 1990
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Rankine Source Method is applied for unsteady free surface flows in this paper. In order to clarify the radiation condition of Rankine Source Method, eigen values and eigen vectors of the matrix obtained from a discrete boundary integral equation are investigated. And it is found that the radiation condition is satisfied by introducing a small variable ε which is equivalent to the artifice due to Rayleigh. For a examination of the new radiation condition, a wave field induced by a periodic source under the free surface is calculated. Calculated results are in good agreement with analytical ones. Wave forces acting on a virtical circlar cylinder with forward speed are also calculated. Results suggest that the present method is applicable to the calculation of the 3-dimensional unsteady free surface flow around a ship with forward speed.
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Shigeru NAITO, Jian-min ZHANG
Article type: Article
Pages
31-43
Published: March 25, 1990
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It is well known that when a ship moves in waves, unsteady waves are generated and the resistance acting on the ship increases as compared with its corresponding value in still water. Analysis of unsteady wave field is very important for the study on seakeeping performance of ships, because many unsteady phenomena can be made clear by knowing the characteristics of wave field. In this report, we will show some investigated results on the approximate calculation method (stationary phase method) for the unsteady wave field which is given by the linear theory. By using the method we can know about the asymptotic behavior of the unsteady waves at far field. The unsteady wave pattern analysis method developed by Ohkusu is a very effective one for the study of generated diffraction and radiation waves by ships with advance velocity in incident waves. His method is that the analytical line, so to speak the cut line of unsteady wave field, is parallel to the ship moving direction, so, it is named as a longitudinal cut method. We propose a transverse cut analysis method of unsteady wave pattern as a pair of the longitudinal cut one. Experiments to obtain the Kotchin function have been carried out, and the effectiveness of the proposed method has been confirmed.
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Shigeru NAITO, Sumitoshi MIZOGUCHI, Kazuhiko KAGAWA
Article type: Article
Pages
45-50
Published: March 25, 1990
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We have many experimental and calculated results on the added resistance in head waves. In case of oblique wave conditions, there is not so many, and there is few data on three steady forces-added resistance, lateral force and turning moment. For knowing behaviors of ships in oblique wave conditions, it needs to obtain them. We can calculate the added resistance in oblique waves by Maruo's and Hosoda's theories. But, we have not the theory to obtain the steady lateral force and the turning moment acting on ships with advance velocity. The authors had calculated the added resistance of the blunt bow ship in short waves by the ray theory. By extendinng this method, other two steady forces can be got easily. Results of comparison is shown between calculations and experiments which are carried out in the recutangular basin with the wave maker.
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Yoshiho IKEDA, Hiroshi TAKATA, Norio TANAKA
Article type: Article
Pages
51-56
Published: March 25, 1990
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The roll dapming characteristics of a car ferry with split-stern hull (twin skeg hull) are experimentally investigated. The experimental results show that the roll damping is increased by the twin skeg at zero forward speed and at high speed. The increase at zero forward speed is caused by the generation of large eddies at the twin skegs, and that at high speed is caused by the lift force increase due to the skegs. The bilge keel component of the roll damping, however, decreases at high speed over F_n=0.25 because of the low aspect ratio. In order to increase the roll damping, a system of bilge keels and fixed fins of large aspect ratio is designed, and its effect is experimentally investigated. The results show that the roll damping per unit area due to the fixed fins is about 12 times that due to the bilge keels at F_n=0.3 which is the cruising speed of the ship.
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Yoshiho IKEDA, Naoya UMEDA
Article type: Article
Pages
57-62
Published: March 25, 1990
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A prediction method of the roll damping of a hardchine boat at zero forward speed is deduced on the basis of experimental results of the roll damping for two dimensional section cylinders. In the prediction method, the roll damping is divided into three components, the wave damping, the eddy damping of the hull and the skeg damping components, and these components are individually predicted. The frictional damping is ignored in the method. The predicted results are in fairly good agreement with measured one for fishing boat models.
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Naoya UMEDA, Tamotsu KOHYAMA
Article type: Article
Pages
63-74
Published: March 25, 1990
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This paper discusses critical conditions of surf-riding of a ship in regular following seas. The authors carried out time domains simulations of ship longitudinal motion in regular following seas and presented those results as phase trajectories. The ordinate of the phase plane is instantaneous velocity of the ship and the abscissa is relative position of the ship to wave. The phase trajectories showed three different patterns of the motion. The trajectories with a periodic attractor represent "perlodic surging motion". Those with point attractors represent "surf-riding under any initial conditions". And those with both point attractors and a perlodic attractor represent "surf-riding under certain initial conditions". Further those trajectories indicate that a ship self-propelled with constant revolution in regular seas does not suffer the surf-riding under certain initial conditions". The critical velocity of the "surf-riding under any initial conditions" predicted by separatrices on the phase plane agreed with that measured by free running model experiments. In the ligtht of the separatrices, we can easily recognize that the critical condition proposed by Grim is identical to that by Kan and valid for "surf-riding under any initial conditions." In addition, we pointed out that surf-riding remarkably reduces rudder force as propeller advance coefficient increases.
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Naoya UMEDA
Article type: Article
Pages
75-80
Published: March 25, 1990
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This study deals with probabilities of surf-riding of a ship in irregular following seas to develop stability criteria against broaching-to. Because, the surf-riding is a prerequisite for the broaching-to to happen. The author presented a theoretical method to calculate probabilities of surf-riding for a ship self-propelled with constant revolution in irregular seas. This theory is based on an assumption that a spectrum of the waves is narrow-banded. Probabilities of the "surf-riding under any initial conditions" are calculated by means of joint density of local wave height and period because this surf-riding depends on only a wave that the ship is situated on. For probabilities of the "surf-riding under certain initial conditions", we must consider both the wave and the preceding motion of the ship by means of joint density of wave height, phase and those derivatives. Calculated results showed that the probabilities of the "surf-riding under certain initial conditions " are not so small. This means that the "surf-riding under certain initial conditions" does not occur in regular seas but does in irregular seas. In addition, the calculated results quantitatively confirmed that a reduction of propeller revolution is one of effective measures to prevent surf-riding.
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Shigeru NAITO, Daidou NAGANO, Tomohiro ARII
Article type: Article
Pages
81-88
Published: March 25, 1990
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It is required for shipping companies to reduce the number of crews against high operation cost of ships. If high technology, super computer, remote sensing technique, new materials are fully applied to a ship for operating in the ocean, automatic ship operation without crews will be realized. For this purpose, it is necessary to plan the system which can make a ship avoid the danger automatically in rough seas, for example in typhoon. We focus our intention on the short time operation. In very rough seas, mission of the first priority is to keep crews and cargoes safe for avoiding the danger of ship. In this paper, two subjects are studied for the purpose. (1) The Automatic Rough Sea Avoidance System [ARSAS], which has two systems, works when the ship runs in rough sea. They are named "Judge system on dangerous degree" and "Operating system to auoid danger". In the former system, the dangerous degree on a ship is defined by the method with integrating many research results on seakeeping performance, which has proposed by the authors, and in the later system, the captain's knowledge about the operating performance of the ship and the data of weather condition are summarized. We propose the concept on the systems by making use of AI (Artificial Intelligence) procedure. (2) Exact information on environmental conditions becomes needed for an accuracy improvement of weather routing. An improvement of the prediction accuracy is hoped. However, an enormous cost is needed to raise prediction accuracy of information on environmental conditions. We make clear, with analytical method and simulation, the effects of the accuracy of typhoon information on the estimation accuracy of ship route, ship speed and fuel oil consumption etc.
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Takashi IIDA
Article type: Article
Pages
89-96
Published: March 25, 1990
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Dynamic positioning system (DPS) is the system to maintain vessels on a specified position and at a desired heading. The controller in DPS has been conventionally designed by PID control theory. The control gain of PID-based DPS is fixed, so it is necessary to tune the gain manually according to the change of wind, wave and current directions. In this paper, a self-tuning regulator (STR), one of adaptive control theories, is applied to DPS. The STR identifies the characteristics of a vessel's motion and determines the optimal control gain according to the result of the identification. The simulations are carried out for a semi-submersible platform in calm water to certify the performances of the designed DPS and to determine the system parameters. The results of simulations are satisfactorily acceptable compared with those of a conventional PID-based DPS.
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Keiichi KARASUNO, Kunisaburo YONETA, Shunji JANUMA
Article type: Article
Pages
97-107
Published: March 25, 1990
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When advancing slowly, a ship's motion is largely affected by any existing external forces, for example wind force, resulting in drifting at angles which vary from small to large. Accordingly, when simulating ship maneuvering motion in wind, the hydrodynamic lateral force Y, the yaw moment N and the longitudinal force X, varying largely with the ship's drift angle, and also the aerodynamic forces varying with wind direction, should be describable by simple and accurate mathematical models covering all ranges of drift angle or wind direction. Furthermore it is desirable for the mathematical model to be a physical model based on hydro or aerodynamics. This paper separates fluid from ideal force (Munk moment), lift and induced drag forces due to viscosity, cross flow drag force, and frictional drag force. As the result, logitudinal force X, lateral force Y and yaw moment N of the fluid dynamic force acting on ship are described by the following mathematical model. [numerical formula] where [numerical formula] and U: fluid speed β: drift angle S_w: wetted surface area S: lateral projected area C_<f0>: frictional resistance's coefficient of flat plate k_e: form factor x',d': longitudinal position and draft of ship's section u': longitudinal speed(=u/U=cosβ) v': lateral speed(=v/U=-sinβ) m_x・m_y: added mass coefficients C_<D90>: cross flow drag coefficient at β=90° 1/2ρ・S・U^2: nondimensionalizing factor of forces C'_L: derivative of lift force C'_<Di>: derivative of induced drag force ΔC'_L,ΔC'_<Di>: coefficients of stall
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Takasi NAGAI, Koichi MASUDSA
Article type: Article
Pages
109-114
Published: March 25, 1990
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The present paper is concerned with the development of retional method for calculating second-order low frequency wave forces on floating structures in shallow water. The boundary value problem for the slow potential is formulated by the multiple scale perturbation method and is solved numerically by a boundary inteqral equation method. The numerical results of second-order low frequency waves on a floating circular cylinder are compared with the analytical results, so that the accuracy of the numerical method is comfirmed. Further, the numerical results are compared with the experimental results for the case wtere the envelope of the incident wave train is a sine function and the usefuiness of the present method are discussed.
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Kimio SAITO, Hisafumi YOSHIDA, Takashi IMAI
Article type: Article
Pages
115-120
Published: March 25, 1990
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In order to investigate the damping increase of a moored multi-hull platform during low-frequency motions in waves, free oscillation tests were conducted both in still water and regular waves. It is found that the estimation method for the damping increase of a mono-hull platform gives a relatively good results for a multi-hull platform. For a more precise prediction, further study on the evaluation of the wave drift force of a multi-hull platform is needed.
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Noriyuki TAKASUGI, Takuya TANIUTI, Fumiaki MATSUMOTO, Yohzoh SHIBATA, ...
Article type: Article
Pages
121-128
Published: March 25, 1990
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The tethered Remotely Operated Vehicle (ROV) has recently come to have the potential to tolerably perform as the underwater surveyor or work vessel in the slowest current. In the offshore current, however, it is very difficult to accurately control it's position and attitude only by the operator's maneuver for its various motions caused by current, reaction of the manipulator, drag force of tether cable, etc.; unless any adequate automatic maneuvering system is developed, ROV cannot be put to practical use at an underwater work site. By using the dynamic position control technique, we have developed a precise 3-demensioal automatic maneuvering ROV which is greately improved in the capability. The control system is based on the dual closed loops of feedback control, that is rate control and position control, besides feedforward control is applied for attitude adjustment. The 3-dimensional graphic display to give a visual information has been also developed and arranged on operator's console. This ROV was tested in the Osaka bay. The results indicated its excellent performance in the automatic maneuvering including hovering, translation and manual override control modes. This paper describes the systcm configuration of the maneuvering system, and some of the test results.
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Tetsuo OKADA, Isao NEKI
Article type: Article
Pages
129-135
Published: March 25, 1990
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In this paper the authors apply two types of adaptive mesh refinement procedure to a transverse ring of a tanker. One is the method to generate boundary fitted coordinate systems using biharmonics on appropreate boundary conditions, which are adaptively optimized for each problem. The other is the h-method, in which a quadrilateral element exposed to high error estimate is simply divided into four quadrilateral elements. We compare effciency of various meshes created by the two methods and investigate advantage and disadvantage of each method. It is shown that these methods are effective and practical when they are applied to ship structure analysis.
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Hajimu MANO, Hiroshi KAWABE, Kouji MASAOKA
Article type: Article
Pages
137-143
Published: March 25, 1990
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This report is concerned with optimum configuration of a hole from the standpoint of the minimum stress concentration in an infinity elastic plate under biaxial loading. Investigating the fundamental property of tangential stress distribution around a hole, we clarify the optimum stress distribution around a hole which have the minimum value of stress concentration ratio must be stepwise distrbution corresponding to the loading condition. We employ the conformal mapping technique in obtaining the optimum configuration of a hole having that of stress distribution. As the result of investigation, the relation between aspect ratio of hole and the minimum stress concentration ratio are shown for various biaxial loading condition. For practical use of design of a hole, we propose the simple mathematical description of hole whose stress concentration ratio is closer to the minimum value.
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Hiroo OKADA, Keiji UEYAMA, Minoru HARADA
Article type: Article
Pages
145-151
Published: March 25, 1990
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This paper is concerned with ultimate strength analysis of ship bottom platings, which are modelled as plane frames and subjected to combined in-plane compression and lateral pressure. Ultimate strength of the structure is evaluated by using a linearized plasticity condition of the section of the spatial structural element under the combined effect of biaxial bending moments, shearing forces and axial force to generate the safety margins of structural collapse modes, using a matrix method and a plastic node method. Dominant collapse modes are selected by aiding the socalled branch-and-bound method. The above methods are applied to a typical plate structure having orthogonal stiffeners. Through numerical examples and comparison with previous researches, the applicability of the proposed methods is demonstrated.
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Hiroo OKADA, Hidehiko TSUZUKI, Atsushi SANO
Article type: Article
Pages
153-159
Published: March 25, 1990
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This paper proposes a method for the probabilistic analysis on the strength and natural vibration of slender and composite offshore structures for large water depth. The composite structure is dealt as a simple tower model made by replacing its tower frameworks and platform etc. with the beam-columns with equivalent stiffness and strength. At first, the reliability assessment of the structures under the quasi-static extreme wave loads is performed by using the system developed for spatial frame structures based on ultimate strength analysis. Probabilistic properties of quasi-static extreme wave loads are estimated by using Stokes wave theory and Morison's formula. Collapse strength of structures under the notional extreme sea-state is evaluated by using a matrix method combined with a plastic node method. Probailistically dominant failure modes are selected by applying the so-called branch-and-bound method. Next, a study of the effect of structural parameter uncertainty on the natural vibration is also conveniently done by use of reliability methods. Finally, the applicability of the proposed method is demonstrated through the numerical example for 450m guyed tower.
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Yoshitaka MAENO, Hirofumi HANAZAKI, Toshihiko FUNAKI
Article type: Article
Pages
161-167
Published: March 25, 1990
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It has become common works in the shipbuilding yards, to analize precisely the vibration characteristics of the ship structures by the numerical method such as the Finite Element Method, in order to avoid excessive response of ship vibration. We developed a new approach method to know the characteristics of the ship vibration, considering its energy distribution and parametric sensitivities of the structures. The results of our study show that this method is very useful to understand the vibration phenomena and make it easy to find effective countermeasures for remedy of structures to prevent harmful ship vibration.
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Takayuki NAKAMURA
Article type: Article
Pages
169-176
Published: March 25, 1990
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Taking into consideration of the damping characteristics of wake vortex, a numerical simulation method for separated flow around a large horizontal cylinder with sharp edges in waves was newly developed based on the combined diffraction theory and discrete vortex model. A damping vortex model was proposed semi-empirically and used in order to simulate the steady-state vortex flow pattern around the body in waves, which is observed in the real flow. Vortex patterns around a vertical thin-walled barrier, i.e. a curtain-walled breakwater, in waves were examined experimentally and compared with the numerical simulation results to check the validity of the analytical model. It was confirmed that the proposed numerical simulation method is very useful for obtaining the steady-state vortex flow patterns around the curtain-walled breakwater in waves. Based on the calculated results on the vortex flow, it was seen that the wave energy loss caused by the curtain-walled breakwater increases with increasing the wave period because larger vortices are formed around it.
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Koji OTSUKA, Yoshiho IKEDA
Article type: Article
Pages
177-186
Published: March 25, 1990
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In the present paper, wave forces acting on a horizontal circular cylinder are investigated. The results of experiments in regular waves demonstrate that a circulating flow exists around the cylinder and causes the force orthgonal to incident velocity of fluid particles. This force always reduces the inertia force. The results of a simulation of the vortex shedding flow around the cylinder demonstrate that much larger scale of vortex shedding that in plane oscilatory fiow occures in regular waves even in low Kc number, and the shed vortices create the circulating flow around the cylinder. From results of experiments in irregular waves, it is found that the reduction of inertia forces in each wave cycle seems to be greatly affected by the amplitude of the previous cycle. The memory effect on the circulating flow is comfirmed by the simulation of the vortex shedding flow in irregular waves.
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Teruhiko KIDA, Tomoya NAKAJIMA
Article type: Article
Pages
187-195
Published: March 25, 1990
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The vortex methods are applied to various complicated problems of high Reynolds number flows of inviscid incompressible flows. These numerical simulations have been proved to be reasonable in point of view of the features of flow behavior, comparing with experiments or results given by other numerical methods. In the point vortex method, the local induced velocities are permitted to be arbitray large. To avoid them, the idea of using a finite vortex core has been proposed and a large number of successful simulations of two-dimensional flow problems have been carried out. However, in the practical numerical simulations, there are many choices such as time step, smoothing function, setting additional condition at the boundary, and simulation model on the viscous effect, and numerical results seem to be sensitive to the choice of paramenters mentioned above. From these circumstances, in the present paper, we pick up some analytical works which the present authors are interesting in and we survey the theoretical analysis of the vortex method of a two-dimensional fluid flow in order to know the theoretical background of the vortex methods.
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Kenjirou HAYASHI, Yousou OGIHARA, Kouji FUJIMA, Toshiyuki SHIGEMURA, N ...
Article type: Article
Pages
197-202
Published: March 25, 1990
Released on J-STAGE: April 01, 2018
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This paper describes an experimental investigation into the non-linear vortex-excited vibration of a cylinder in plannar oscillatory flow with emphasis being placed on the fluid-structure interaction. The experiments were carried out using a water tank which has an internal dimension of 1.0m long, 0.5m wide and 0.5m deep, and is oscillated in true harmonic horizontal motion. The deferences between the vortex patterns around the vortex-excited cylinder in rezonace condition and those around the rigidly mounted cylinder are clarified in the range of Keulegan-Carpenter number 5 to 8.4 by using the flow visualization. In this range of KC number, the amplification of the fluid forces acting on a vortex-excited. cylinder are large.
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Yoshiho IKEDA, Akihiro FUJIWARA
Article type: Article
Pages
203-209
Published: March 25, 1990
Released on J-STAGE: April 01, 2018
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Low-frequency viscous damping force acting on a circular cylinder, a lowerhull-section cylinder of a semisubmersible and a flat plate is experimentally investigated. Flow visualization of an oscillating cylinder in combined motion of high-frequency and low-frequency oscillation, reveals that the low-frequency viscous damping force is caused by the deformation of the shedding vortices in each swing of the high-frequency oscillation by the low-frequency oscillation. On the basis of experimental results, a prediction method of the damping force is proposed. In the method, an experimental drag coefficient, which depends on the shape of models and the Keulegan-Carpenter, is needed. The drag coefficient is determined by exper imental results for each cylinder. The memory effect on the drag coefficient due to vortices created in the previous swing is discussed.
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Yutaka UNNO, Kenji ISHIDA
Article type: Article
Pages
211-213
Published: March 25, 1990
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On the 27th February 1984, a weather satelite took a beautiful photograph of the Karman votexes under the lee side of Cheju Island. We surveyed geographical features of the island and meteological data of the day. The hydrodynamic conditions of the occurence of votexes were examined and also compared with the surveyed results. The Karman votexes possibly occured hourly on the one side when the wind of velocity 18∼22m/s blew from NNW to the island higher than 1,000m above the sea level.
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Article type: Appendix
Pages
App1-
Published: March 25, 1990
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Article type: Cover
Pages
Cover2-
Published: March 25, 1990
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