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Article type: Cover
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Cover1-
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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Article type: Appendix
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App1-
Published: September 25, 1994
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Article type: Index
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Toc1-
Published: September 25, 1994
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Article type: Index
Pages
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Published: September 25, 1994
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Hisao TANAKA, Yasuyuki TODA, Aiji FUJITA, Yoichiro SUZUKI
Article type: Article
Pages
1-10
Published: September 25, 1994
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The authors presented a new integral method for thick boundary layer in the previous paper. Viscid stern flow field around fine ship is predicted well by this method. In this paper, the authors show two examples in which the method is applied to practical ship hull form. One is flow around fine practical ship (Series 60, C_B=0.6) with free surface, and the other is flow around full practical ship (SR196 Series). Comparing with experimental data, difference of Froude number or ship hull shape are reflected well in the obtained results. It is possible to select the good hull form based on the calculated results.
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Takeshi OSHSIMA, Shigeru NISHIO, Yoshiho IKEDA, Taketoshi OKUNO
Article type: Article
Pages
11-16
Published: September 25, 1994
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An image measurement system for wave height distribution has been developed. The system was applied to the wave measurement behind high speed craft. A number of small bubbles in water causes difference of light scattering between air and water. When a sheet laser illumination was given from the bottom of tank, the free surface is observed as the boundary of bright and dark area on the visualized image. The differential of the image data gives the position of free surface on the sheet illumination. The wave height distribution is obtained by changing the relative position of model and sheet illumination. Wave patterns around high-speed craft with several trim angles and sinkages are obtained. The wave patterns show that the undulation of free surface becomes gentle according to the decrease of sinkage in same trim angle. The difference of wave pattern with the trim angle is small in the present measurement range.
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Takashi OHTSUKA, Kazuki YABUSHITA, Katsuo SUZUKI
Article type: Article
Pages
17-23
Published: September 25, 1994
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A test for high-speed boat forms is conducted by using a trim-fixed type of dynamometer which was devised by the authors. Three boat models are used, the mother boat is the so-called deep omega plane form of torpedo boat the bottom of which is flat in longitudinal direction, the other ones have longitudinally cambered (concave and convex) bottom. The characteristics of resistance, trim moment and rise of center of gravity are compared for the three boat models with trim fixed. The location of center of hydrodynamic force is obtained and the change of the point for the concave bottom boat is much less than the other boats. The performances of the boats towed with trim free are simulated by the data with trim fixed and they show a good agreement with the trim free resistance test. The trim angle of the concave bottom boat is about a half of the other ones and the resistance of the concave bottom boat with initial trim at 2° is less than ones of the others at high speed.
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Koji MAKINO, Yoji HIMENO, Jun-ichi HAMASAKI
Article type: Article
Pages
25-32
Published: September 25, 1994
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A variety of applications of nonlinear programming to ship form design have recently been made. The authors have also worked on shape optimization problem for minimizing viscous resistance of 2-dimensional body by combining Computational Fluid Dynamics and the nonlinear programming. This paper provides an improvement of the method of sensitivity analysis for obtaining the resistance variance due to the deformation of an original body shape, which is represented by using B-spline function. The point of the improvement is to evaluate an additional linear term in the expression of the resistance sensitivity with respect to the design variable, which has been neglected in the existing methods. The results of a few examples of the optimized shape and the detailed analysis on the distribution of the sensitivity coefficient components demonstrate the validity of the present method.
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Shotaro UTO
Article type: Article
Pages
33-39
Published: September 25, 1994
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This paper describes the mechanism of the scale effect on the viscous flow around a marine propeller, which are regarded as a very important problem from engineering point of view due to its close relation to the full-scale powering estimation using the model-scale experiment data. Using Reynolds Averaged Navier-Stokes code developed by the author, a series of turbulent flow computations are made around a three-bladed marine propeller at four Reynolds Numbers in the range between a model and a full scale condition. The computed results show the thrust coefficient (K_T) tends to increase as Reynolds number higher and vice versa for the torque coefficient. The mechanism of the scale effect on K_T is further investigated by decomposing it into pressure (K_<TP>) and friction component (K_<TF>). The scale effect on K_<TP> is shown to have the same order as that of K_<TF> and it reveals the importance of the scale effect on K_<TP>, which are neglected in the method of powering estimation used at the design process. By comparing the computed results of surface pressure and displacement thickness distributions at model and full scale Reynolds number, the mechanism of the scale effect on K_<TP> is understood as the increase of the effective camber of the blade section due to the decrease of the displacement thickness as Reynolds number higher. Decomposition of K_<TP> into the spanwise direction shows the magnitude of the scale effect is much larger at the tip than at mid-span sections, which suggests the close relation with three-dimensionality of the flow structure. Improvement of turbulence modelling including transition and surface roughness effect is thought indispensable for the quantitative estimation of tha scale effect on this important problem.
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Kun MA, Ichiro TANAKA
Article type: Article
Pages
41-47
Published: September 25, 1994
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This paper is the second report of the method for obtaining an optimum ship form of low resistance. The Basic procedure is the same as the first report, i.e., the objective function is the sum of wave-making resistance and viscous resistance and SUMT method is used for optimization. Only difference between this and previous paper is that, in this paper, a correction of bulb size, especially at the stern, is made according to separation prediction by using a method devised previously. As initial hulls, Wigley hull and Series 60 with Cb 0.6 are used. The results of optimization are confirmed by resistance experiments in towing tank.
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Tetsuo NGAMATSU, Fumio KURE
Article type: Article
Pages
49-56
Published: September 25, 1994
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In order to grasp the aerodynamic characteristics of Power-Augmented-Ram Wing-in-Ground (PAR-WIG), measurements of lift, drag and moment acting on a low aspect wing were carried out by use of the towing tank of Mitsubishi Heavy Industries Ltd. A pair of model propellers were arranged in front of the wing. Reynolds number was about 3×10^5. It is shown that lift and drag of the wing increase remarkably due to PAR effect when the wing is close to the water surface. The lift drag ratio decreases considerably. The trailing edge flap works to increase PAR effect significantly. The position of center of lift moves rearward due to PAR effect. The lift gradient versus angle of attack becomes negative value at large angle of attack. Further studies such as flow visualization test and pressure measurement on the wing surface are necessary to understand the mechanism of PAR effect.
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Masatoshi BESSHO, Shun SAKUMA
Article type: Article
Pages
57-64
Published: September 25, 1994
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When we design high speed displacement type ships, it is the most important to reduce her resistance. The faster a ship cruises, the larger wave making resistance becomes. This is the reason why designers want to search hull forms which give small wave making resistance. Moreover spray resistance is also large at high speed. And it is known from recent studies there is water head resistance in a ship which has a vertical stem and a transom stern. Hull forms which give minimum resistance components are studied, but obtained forms are strange and unrealistic. This report represents improvement of such strange forms and application for practical hull forms. The obtained hull form has small spray at the bow. And this form is enough to be realized.
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Huai-xin CHANG, Ying-zhong LIU, Guo-ping MIAO
Article type: Article
Pages
65-72
Published: September 25, 1994
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In order to clarify basic features of the free-surface effects on the ship frictional resistance, analysis of the laminar boundary layer along a surface-piercing flat-plate are attempted. The laminar boundary layer equation is expanded with the assumption of small-amplitude waves, the second order equations, which describe the effects of free-surface, are solved by a simplified integral method. The ship frictional resistance decreases due to free-surface are calculated. The results explicitly indicate the dependence of ship viscous resistance on Froude number.
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Yoshiho IKEDA, Toru KATAYAMA, Yuji HASEGAWA, Masayuki SEGAWA
Article type: Article
Pages
73-81
Published: September 25, 1994
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The roll damping plays a very important role for large amplitude roll motion in resonance, and the lack of the damping sometimes causes capsizing of a ship. Since the viscous damping components are usually dominant in the roll damping, the theoretical calculation is difficult for predicting it. One of the authors proposed a prediction method of the roll damping of a conventional cargo ship, and the method is widely used. In the present paper, some problems which occur when the prediction method of the roll damping of a conventional cargo ship is applied to a high speed slender vessel are experimentally revealed, and some modifications of the method to improve the accuracy are proposed.
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Kazuhiko HASEGAWA, Keisuke SUZUKI
Article type: Article
Pages
83-90
Published: September 25, 1994
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Image analysis is a technique to sense and/or extract appropriate physical features from an image. The authors have investigated a method to extract ship position and motion using a pair of VTR views taken from two CCD cameras. In this report, several methods already proposed for this purpose are reviewed, and a new direct image analysis method is proposed. Two case studies are made using the proposed method; turning tests of a tanker and a hydro-foil. Although extraction of ship image and measurement of turning trajectory is satisfactorily done in both cases, detection of heading angle is rather difficult in the case of small model ships such as a hydrofoil. Further improvement is to be planned in the following reports.
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Sigeru NAITO, Syuichi NAGATA, Seijiro MIYAKE, Hisafumi YOSHIDA
Article type: Article
Pages
91-96
Published: September 25, 1994
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The time history of hydrodynamic pressure acting on ship's side near by waterplane is cut because of exposure of a point of ship's side to the air. The method of long-term prediction of such a hydrodynamic pressure that is non-linear is not established yet. In this paper, the method of dealing of the cut time history of the sinusoidal or random hydrodynamic pressure is developed and the result of long-term prediction for hydrodynamic pressure by using the proposed method is described.
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Ken TAKAGI
Article type: Article
Pages
97-106
Published: September 25, 1994
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The two dimensional wedge entry problem with the hydro-elasticity effect is discussed in this paper. The bottom plate of wedge is treated as an elastic beam but the effect of air trapping is ignored. The theory is based on the matched asymptotic expansion method which was applied to the hydrodynamic impact problem recently. An experiment of wedge entry with elastic bottom also has been carried out. Results show that the agreement between the theory and the experiment is pretty good and the effect of hydro-elasticity is very important for the estimation of the strain of the wedge bottom plate.
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Akinori YUMURO
Article type: Article
Pages
107-115
Published: September 25, 1994
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In order to provide basic data needed to predict maneuvering motions in shallow water, the author carried out some experiments concerning propeller-rudder interaction in water of finite depth. The tests were conducted by utilizing propeller-rudder system with the absence of the ship body. Normal forces on a rudder were measured by changing drift angle, propeller loading and water depth. Adopting the so-called MMG Mathematical Model describing maneuvering motions, a theoretical calculation of rudder normal forces in shallow water is made. The shallow water effect is evaluated through infinite images which are arranged below the fluid bottom and above the free surface. Calculated values of the rudder forces agree fiarly well with the experimental results, when the rudder is set in open water. On the other hand, regarding the rudder behind propeller, both agree qualitatively. Additionally, coefficients of flow-straightening caused by the propeller are obtained from measured results of the rudder forces in oblique flows. As a result, it is found that the water depth has a considerable influence on the flow-straightening effect. The values of the coefficient will increase as the depth of water decreases.
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Hiroshi ISSHIKI
Article type: Article
Pages
117-123
Published: September 25, 1994
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It is long since trafic safety of ships in congested waters has become a big problem. The potential needs for systems, which makes a ship avoid running on rocks and colliding to other ships, may be said very big. Extensive researches have been conducted on the collision avoidance of ships in 1980s since Japanese Ship Research Program on hi-tech ships. They are expert systems which realize authorized rules such as collision avoidance law and skills of well trained seaman. Some of them are based on AI, and some of them on fuzzy inference. The technology developed by Japanes Ship Research Program was proved by a test using a training ship "Shioji-Maru" in Tokyo Bay. The collision avoidance system consists of monitor of the environments and collision avoiding manoeuver. In the present paper, the environmental informations are assumed to be given by radars, and the discussion is focussed on algorithm for collision avoidance. The algorithm for collision avoidance should be simple to assure rapid computation. If the computation is not fast enough, the system may not correspond sufficiently to the changing environments. On the other hand, the ship must avoid collision certainly in any situations. In the present paper, fuzzy inference is used for the former purpose, and virtual topography method for the latter purpose. The idea of virtual topography may also be used for avoiding real obstacles such as islands and coasts and guiding a ship to its goal.
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Akio ITO, Sumitoshi MIZOGUCHI
Article type: Article
Pages
125-132
Published: September 25, 1994
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Results of numerical and experimental study on hydrodynamic pressure on a full ship in oblique short waves are presented. Ship length of VLCC is long compared with wave length in sea. Hydrodynamic pressure on a full ship in oblique short waves are measured to investigate the wave loads of VLCC. The hydrodynamic pressure which are predicted with New Strip Method (NSM) are compared with the measured ones. The predicted results with NSM are not in good agreement with the measured ones in oblique short waves. One cause for the error is the inexact body boundary condition in short waves. The other is not to consider the effect of the diffraction wave from bow, stern and bottom. The modified method for the diffraction wave term of NSM which is calculated with the exact two dimensional body boundary condition and considered the effect of the diffraction wave from bow, stern and bottom is developed. Symmetric term of diffraction pressure is used the velocity potential for wave frequency ω_0. The pressure distributions with this modified method for NSM are in good agreement with the measured ones in oblique short waves.
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Shogo MIYAJIMA, Hyojae JO, Hisaaki MAEDA
Article type: Article
Pages
133-140
Published: September 25, 1994
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It is very important to estimate exactly low frequency motions in directional waves in order to design rationally mooring systems of floating offshore structures, as the real sea consists of directional waves. We have developed the numerical simulation method of the moored body motions in multi-directional waves with low frequency motions. However, we have not yet clarified the sufficient number of directions of incident multi-directional waves for estimating the low frequency motions in directional waves. In this paper, we carry out the numerical simulation of motions of a moored semi-submersible structure in 1,3,5 and 7 directional waves and discuss the mean and significant amplitudes of the low frequency surge and sway motions. From the results, it became clear that the low frequency motions in directional waves can estimate using the motion simulation in 7 directional waves. Furthermore, very important characteristics of low frequency motions in directional waves were cleared that the low frequency sway motions in directional waves the principal direction of which is that of head seas are larger than the low frequency surge motions in the same waves.
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Yoshiho IKEDA, Hideo SHIRAZAWA
Article type: Article
Pages
141-147
Published: September 25, 1994
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In order to evaluate the method for assessing a seakeeping performance of a passenger ship on the basis of vomiting ratio of the passenger proposed in the 1st report, measurements of ship motions and vomiting ratio of passengers on ships are carried out for two passenger/car ferries and a fast passenger ferry operating domestic services in Japan. The results demonstrate that the vertical acceleration which significantly affects on seasickness depends on hull form and advanced speed, and that the relation between the measured vomiting ratio of passengers and vertical acceleration (amplitude and frequency) is in good agreement with the experimental results by O'Hanlon et al.
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Makoto ARAI, Reaz H. Khondoker
Article type: Article
Pages
149-154
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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Prediction of the behaviour of free fall bodies during water entry is very important in the field of naval architecture and ocean engineering. Motions of free fall life boats and dropping pipes from offshore platforms are typical examples of this phenomenon. In this study the analytical technique for predicting the falling motion of the cylindrical bodies including water impact on them has been presented by solving the motion differential equations in the time domain. A computer program has been developed to simulate the submerged trajectory of such bodies and verified the accuracy of the program with experimental results. Trajectory simulations have been conducted using simple body shapes, like circular and rhomboidal cylinders, for different dropping and environmental conditions. Several numerical studies have been carried out to determine the key parameters which influence the trajectory and motion of the falling bodies.
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Toshihiko FUNAKI, Tomohide NAKANO, Jun KAWAYANAGI
Article type: Article
Pages
155-160
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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In order to analize the dynamic responses of the structures, we must know the time-histories of the acting forces and the vibration characteristics of the structures, such as vibration modes, frequencies and damping coefficients. In this paper, we obtained the damping coefficients from parametric experiments using beam structures. Recognizing the response by various impact force on the structure as the summation of the responses by many impulsive forces on the structure, we think up a damping models on Euler's equation in linear system between force, structure and response, considering T,K,Caughey's model. And we could reproduce impact response on beam structure by calculation very well.
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Mitsuyasu NAGAHAMA
Article type: Article
Pages
161-165
Published: September 25, 1994
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It has been clarified that sloshing motions in ship tanks can be estimated by numerical calculations such as MAC method. But, even now, it is not easy to evaluate the magnitude of impact pressures. In this study, to clarify the characteristic of calculated impact pressures, the mechanism how impact pressures are obtained in the numerical procedure is investigated as one dimensional problem. And, impact pressures obtained from 3 dimensional calculations are compared with above results. As a result, the following characteristics are clarified. 1) When incompressibility is assumed, the magnitude of calculated impact pressures is in inverse proportion to numerical time step, but the impulse is unchanged. 2) When pseudocompressibility is introduced, the magnitude of calculated impact pressures converges to a constant value in case very small numerical time step is used.
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Yukio UEDA, Hidekazu MURAKAWA, Masayuki TANIGAWA, Naohiro YONEDA, Mine ...
Article type: Article
Pages
167-172
Published: September 25, 1994
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In the collision of VLCC, prediction of energy consumed by plastic deformation of ship hull structures before their destruction is important to evaluate oil flow from cargo hold. In the prediction of consumed energy, behavior of large deformation must be analyzed with practical accuracy under appropriate rupture condition. The authors tried to simulate the experiment of ship side collision model destructed with static indentation load by using a nonlinear structural analysis code ABAQUS and investigated behaviors of deformation, reaction force and strain concentration. And rupture condition was also examined.
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Noriyuki KAMOI, Tomokazu TANIGUCHI, Makoto UNNO, Tatuya MOTOI, Masato ...
Article type: Article
Pages
173-181
Published: September 25, 1994
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Connection structures between longitudinals and floor structures (i.e. slot structure) are one of the most fundamental structural elements in ships. The authors have developed a new type slot (APPLE SLOT) for the above connection structure, and already reported non-linear behaviors of the floor structure with the new type slot under a pure compressive load. In this paper, the authors have investigated the elasto-plastic large deflection behavior of the floor structure with the slots under "combined" loads, using non-linear FEM analyses and large structural model experiments. As results, characteristics of the behavior of the structure are revealed and the accuacy of non-linear FEM analysis under "combined" loads is verified.
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Takahito TAKAHASHI, Takeshi FUWA
Article type: Article
Pages
183-190
Published: September 25, 1994
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A wing flying in proximity to a surface experiences a reduction in induced drag and an increase in lift. Wing-In-Surface-Effect-Ship (WISES), which make used of such phenomena, are being studied with interest as a future type of high speed craft. At the Ship Research Institute a safety assessment is cosidered necessary for the operation of WISES. Safety is closely connected to the nature of ground effects and the shape of the craft so a conceptual design will show the important design objectives and lead to greater understanding of the Ground Effect phenomena. This paper studies the design methods for WISES and shows an example. Fundamental elements of the design of the airplane are the wing that supports body and the control surfaces that help provide stability. Design methods for airplanes are used as a basic approach and characteristics of WISES are added and unnecessary elements are eliminated. The CAD tools used in this report consist of the following : ISAAC (a program for the basic design of airplanes), DATCOM (a program for predicting stability and control parameters of airplanes) and other stability and control programs developed specifically for use in ground effect. By using the CAD tools for wing and horizontal tails the nature of ground effects could be studied with regards to safety and design aspects. Even though this study is preliminary, it will highlight some important design aspects for WISES.
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Norio JINGU
Article type: Article
Pages
191-196
Published: September 25, 1994
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It is very economically important for the planner of the submarine pipeline construction to estimate the required days for the construction. In generally speaking, the offshore constructions as the laying submarine pipeline are strongly affected by the waves. Therefore, it is important for estimating the workability of the submarine pipeline construction to predict the combined behavior of the pipe laying barge, pipeline and stingers in waves. In this paper, the theoretical predicting method and the model test conducted to verify such predicting method are shown. The predicting method, described in the 1st report, is the finite element method and the equations of motions were directly solved in the frequency domain. The predicted results were compared with those obtained from experiments. Consequently, it is shown that the prediction method in this paper can be practicaly used to plan for the pipeline construction.
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Minoru INOUE, Nobuhiro BABA, Kenichiro TAKAMATSU
Article type: Article
Pages
197-202
Published: September 25, 1994
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The interaction of the viscous flows with the free surface waves may make the nonlinear fluid motion more complicated. In this paper the vortex shedding from an oscillatory circular cylinder vertically piercing a free surface is investigated by the numerical experiments. The three-dimensional finite volume method using the free surface fitted coordinate system is used for solving the incompressible viscous flow field with a free surface. The numerical results about the viscous flow field around an oscillatory circular cylinder piercing a free surface are shown the effect of the free surface waves on the vortex shedding from the cylinder. The vortex structure shedded from the cylinder is changed in the circular arc-shape in the vicinity of the free surface by the waves. The effect of the free surface waves is discussed by the comparison with the other numerical results about the viscous flow field around a circular cylinder in the oscillatory shear flow field.
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Tsugukiyo HIRAYAMA, Takuya KATOH, Kiyoshi MIYAKAWA, Takehiko TAKAYAMA
Article type: Article
Pages
203-209
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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Generation of freak waves in an experimental tank are occasionally necessary for the investigation of the responses of floating structures in case of capsizing, impact pressure of waves and so on. For the long crested freak waves, there are so many researches available. However, there are not successful research on the generation of freak waves by utilizing Multi-Directional Transient Water Waves. For this reason, one point-concentrated freak wave is generated and it's criteria is investigated, where a directional spectrum wave generator is used in a longitudinal towing tank.
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Shoichi HARA, Kenji YAMAKAWA, Hyunkyoung SHIN
Article type: Article
Pages
211-218
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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As for the towline tension during towing, the behavior of the oscillating towline in current has generally to be investigated. This problem has been treated on the assumption that the superposition of the drag force in current and the dynamic towline tension in still water can be applicable. The authors have investigated the oscillating towline behavior in still water experimentally and theoretically. However, there were few experiments concerning this plroblem in current. This paper deals with the forced oscillation test in current in order to validate the assumption. The sway oscillation test has been carried out to investigate the dynamic towline tension as well as the surge oscillation test. Furthermore, the low frequency oscillation mode superposed on the high frequency oscillation mode has been tested considering the slow drift motion in waves. The comparison with the theoretical calculation using the three dimensional Lumped Mass Method has been done.
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Makoto ARAI, Yoshiyuki INOUE, Shingo ADACHI
Article type: Article
Pages
219-223
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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In this paper a numerical simulation method to predict the behaviour of spilled oil over the surface of the sea is proposed. On the basis of the shallow water assumption, dispersion of the oil slick is efficiently solved by a finite difference method. The simulation method is verified by comparison with experimental data obtained from scale model tests and tests at actual seas. The followings are main conclusions from this study: (1) From the discussions shown in the paper, the present method is effective to simulate the early stage of oil spill phenomena (i.e., gravity-inertial and gravity-viscous regimes). Especially, the accuracy of the numerical simulation is excellent in the gravity-inertial regime. In the gravity-viscous regime our numerical simulation slightly over estimates the area of spreading oil. However, this estimation is considered to be on the safe side. (2) The present method has the advantage of treating the arbitrary shaped boundary conditions such as ship hulls and oil fences and therefore it can be used to simulate actual tanker accidents. The method is also applicable to a wide range of related studies ; assessment of the performance of oil skimming vessels, investigation into the set-up strategy of oil fences around wrecked tankers, etc.
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Nobuhiro BABA, Shigeru KIMURA, Yoshiyuki IKEDA, Kenichi MARUNO, Susumu ...
Article type: Article
Pages
225-230
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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The mixing process in stratified fluid in the closed region of the ocean by the recirculating flow induced by wind is modelled in the laboratory using the lid-driven cavity flow. The deepening of a mixed layer into a region of constant density gradient is examined and the three-dimensional features of flow structures near a density interface is investigated by visualization experiments. The characteristics of the mixed layer and the stratified layer are determined using a conductivity probe. The flow pattern of a primary circulation formed in the top downstream corner, growing gradually, but bounded by a stratified fluid beneath as it were a wall is quite different from that of homogeneous fluid. The density interface formed by erosion of the basic density gradient is distorted by the primary circulation and at the same time it is subject to the three-dimensional instability in the initial stage of the formation. Then the interface is of a wave shape in the spanwise direction, sharper near the crests and flatter in troughs, the wave length of which increases as the interface descends. It is shown that this is caused by the existence of the vortical structure which consists of the pairs of counter-rotating wise stream vortices in the strong shear layer near the interface. The considerable amount of the spanwise distortion of the interface indicates that the three-dimensional structure possibly makes a significant contribution to the mixing across the density interface along with the primary circulation in the upper layer.
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Nobuhiro BABA, Minoru INOUE, Junko ISIZAKI
Article type: Article
Pages
231-237
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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The formation process of three-dimensional vortical structure beneath a free surface by wind waves is investigated by numerical experiments. The full Navier-Stokes equation with the nonlinear free-surface condition is solved by the finite volume method. The flow field is assumed to be periodic in both wind and lateral directions. The surface shear layer with the velocity profile of an exponential function of depth and the free surface waves of small amplitude propagating in the same direction induced by wind are incorporated in the numerical model as a initial state. The model shows that the transition to three-dimensionality of flow field occurs when laterally periodic disturbance is imposed on the shear layer. Then the waves are deformed by the shear layer with the wave amplitude increasing in low speed region while the vorticity component in the wind direction is amplified by the waves propagating over it. It is shown that this interaction of the shear layer and the waves causes the formation of three-dimensional vortical structure which consists of a parallel system of counter-rotating vortices aligned with the wind. It is also confirmed that the structure has the same qualitative features as the observation of Langmuir Circulation. These results indicate that the presence of the surface shear layer and the free surface waves with small lateral anomaly is sufficient for the formation of Langmuir Circulation.
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BARROS Ettore A. de, Fumihiro SUZUKI, Shogo MIYAJIMA, Hiroyuki YAMATO, ...
Article type: Article
Pages
239-246
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
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The control system of a towing carriage was adapted for permitting variable speed control in both longitudinal and transversal directions. Using the automatic pursuing system aimed originally to experiments with free running ship models, and attaching underwater acoustic sensors to the carriage, a robotic system was achieved allowing automatic guidance in collision avoidance experiments. Such system can be used as a test bed for a preliminary debugging of real-time control programs of autonomous underwater vehicles, without the expenses of building, and using the actual vehicles. Another possible application include experiments on berthing systems for ships. First tests were concerned with the investigation of sonar mapping and collision avoidance tasks performed by a decentralized control system based on parallel distributed computing.
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Article type: Appendix
Pages
App2-
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
CONFERENCE PROCEEDINGS
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Article type: Cover
Pages
Cover2-
Published: September 25, 1994
Released on J-STAGE: April 01, 2018
CONFERENCE PROCEEDINGS
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