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Article type: Cover
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Cover1-
Published: March 25, 1997
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Article type: Appendix
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App1-
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Article type: Index
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Toc1-
Published: March 25, 1997
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Article type: Index
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Published: March 25, 1997
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Article type: Bibliography
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Misc1-
Published: March 25, 1997
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Makoto UCHIDA, Kefeng HU, Takanori NIMSHIJIMA
Article type: Article
Pages
1-6
Published: March 25, 1997
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The load fluctuation acting on a propeller blade in the condition that the propeller blade exposes partially over the water surface had been investigated experimentally. The experiment has made clear the interesting phenomenon that the negative torque acts on the blade at the moment when it passes through the water surface from water to air. And the former report proposed the hypothesis that the negative torque is due to the force caused by the change of the added mass of the blade along the rotational direction. In order to confirm the above hypothesis, the forces acting on a horizontal cylinder passing throught the water surface are experimentally investigated in this report. The experimental results are compared with the calculated results. The calculation is carried out according to the theory that the test cylinder is acted by a force system of 5 component, that is, the inertial force of real mass, the inertial force of added mass, the drag, the buoyancy and the force caused by the change of added mass. The last component acts in the same direction with the cylinder motion from water to air. It is called here a negative force. The calculated results are in approximate agreement with experimental results. The existence of the negative force component is confirmed.
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Yusuke TAHARA, Yasunori IWASAKI
Article type: Article
Pages
7-19
Published: March 25, 1997
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This paper presents a study of free-surface flow near the transom stern by the two-dimensional experimental and computational models. The experiments were performed at towing tank with main emphasis placed on free-surface and pressure measurements. The computational approach is based on Reynolds-averaged Navier-Stokes equations, and computational grids are fitted to body as well as free surfaces. Nonlinear free-surface boundary conditions are satisfied at the exact location of free surface, which is obtained as part of solution. The present computational model approximately includes breaking wave effects, such that the breaking wave is expressed as the reversed flow region under the free surface which is assumed continuous. Numerical results are presented for three transom sterns, including detailed comparison with experimental data. Discussions are made regarding influences of geometrical differences of transom stern and Froude and Reynolds numbers on the free surface flows as well as frictional and pressure drags acting on the body surface. Satisfactory agreements are demonstrated between the computations and measurements, and the present two-dimensional models appears to be capable to analyze hydrodynamic factors of generation of breaking wave near the transom stern, which are found to be related to boundary layer flow near the stern associated with wave-induced pressure gradients.
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Hassan GHASSEMI, Mitsuhisa IKEHATA, Hisashi YAMASAKI
Article type: Article
Pages
21-27
Published: March 25, 1997
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In this paper, a verification of cavity model for the analysis of partially cavitating for two dimensional hydrofoil by using a potential surface panel method is presented. A type of cavitation that is applied for calculation is sheet cavitation. Using the Green's theorem, the normal dipoles and sources distributions on surfaces of the foil and cavity may constitute the perturbation velocity potential. The source singularity plays an important role in the cavity surface and is determined by an iterative process. We verified a various cavity models in the transition zone and it is concluded that a closed type model is approvable to physical phenomenon. The effect of hydrofoil thickness on the cavity shape is investigated. That is the bigger hydrofoil thickness generates the shorter cavity volume. As for a closed type model, some quantities, for example, cavity shapes, surface pressure distribution and other hydrodynamics characteristics have been calculated. The calculated results are in good agreements with other numerical calculations.
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Hiroyoshi SUZUKI, Toshio SUZUKI, Satoshi MIYAZAKI
Article type: Article
Pages
29-40
Published: March 25, 1997
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A ship stern turbulent flow field of a double model (Series 60, C_B=0.6) was measured by triple-sensor hot wire system in the wind tunnel. The mean velocities and turbulent quantities were analyzed from the time history data of the fluctuated velocities, and detailed stern flow database was obtained. CFD calculations of RANS equation around the ship hull were carried out using k-ε turbulence model and tuned k-ε turbulence model. The results of computation were compared with measured velocities and Reynolds stresses distributions. The long period phenomena of the stern flow field at the Propeller plane were analyzed using the data of another set of triple-sensor hot wire system fixed in the flow field. The period of the motion of a longitudinal vortices in the model ship stern flow field was specified.
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Takae YAMAMORI, Mitsuyasu NAGAHAMA
Article type: Article
Pages
41-46
Published: March 25, 1997
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Comparing with experimental results, the rudder resistance calculated by NICE-code is overestimated in self propulsion condition particularly. This causes bad influence upon the accuracy of calculated self propulsion factors, for example 1-t etc. In this study, the arrangement of grid near the leading edge is studied to calculate the rudder resistance accurately. First, the viscous flow field around a two-dimensional Joukowski aerofoil is computed with H-type grid. As suggested by the potential theory, fine grids are needed near the leading edge to follow numerically the very steep pressure gradient there. Secondly, the fine grids are applied to compute the viscous flow field around the rudder behind ship. As the result, estimated rudder resistance with finer grid, shows better agreement with experimental results.
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Akihiko MATSUDA, Naoya UMEDA, Shiro SUZUKI
Article type: Article
Pages
47-55
Published: March 25, 1997
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Heave and pitch motions of a ship model running in following and quartering seas with zero and very low encounter frequency were measured in a seakeeping and manoeuvring basin. Considering that 2D added mass tends to infinity at zero encounter frequency, new formulae to evaluate heave and pitch motions at zero encounter frequency were presented as a limit of a solution set of a strip theory. By comparison of the experiment and some theoretical predictions, it was concluded that, when the ship meets danger for capsizing in following and quartering seas, heave and pitch motions can be approximated by simply tracing their static equilibria. The prediction as the limit of the solution set of the strip theory at zero encounter frequency shows better agreements with the experimental values than the prediction based on the Froude-Krylov assumption. Further, up to the steepness 1/10 the heave and pitch motion with very low encounter frequency can be regarded as linear with respect of wave steepness.
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Shoichi HARA, Kenji YAMAKAWA, Kentaroh KOKUBUN, Masami IWAI
Article type: Article
Pages
57-70
Published: March 25, 1997
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One of the box-shaped floating structures of the Technological Research Association of Mega-Float has been towed about 700 km from Mizushima, Okayama prefecture to installation site Oppama, Kanagawa prefecture. Its dimension is 100 m in length, 20 m in breadth, and 2 m in depth with 0.5 m draft. The full-scale measurement of the strain along the center line on the upper-deck, towline tension and the motion of the floating unit have been done. The wave condition during towing was 2 m significant wave height at maximum. The transfer function of the wave bending moment has been compared with the theoretical calculation and the model experimental data. The dynamic towline tension in waves has also been measured and the extreme maxima distribution has been shown. The model experiment using scaled elastic stiffness has also been carried out to investigate the wave bending moment, towing force, motion of the floating unit in both head and following waves. The theoretical calculation using pressure distribution method agree well with the experimental results concerning wave bending moment.
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Toru KATAYAMA, Yoshiho IKEDA, Koji OTSUKA
Article type: Article
Pages
71-78
Published: March 25, 1997
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Following the first report in which the porpoising motion of a planing craft in calm water is measured and discussed, an experimental investigation on hydrodynamic forces acting on the hull is carried out in the present report. Captive model tests are carried out to find the influence of the restoring forces on the dynamic instability. The results show that there are significant nonlinear effects of motion amplitudes on the restoring forces, and that the coupled heave restoring coefficient from pitch motion decreases with advance speed and becomes negative at high advance speed. The negative coefficient is in the same order as other coefficients. This result suggests that there is a possibility of occurrence of parametric excitation due to the energy exchange between heave and pitch motions. Forced motion tests are carried out to reveal the influence of the added mass and the damping on the dynamic instability, The results show significant nonlinear effects of motion amplitudes appear on the added mass and the damping as well as the restoring coefficient. The measured hydrodynamic forces are compared with the calculated ones using a non-linear prediction method based on a strip method. The results show that the calculated results are not in good agreement with the experimental one
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Ritsuo SHIGEHIRO, Kohei UEDA, Toshihiko ARII
Article type: Article
Pages
79-87
Published: March 25, 1997
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The high-speed-towed fish preserve is a new type vessel about 15.6m long with a fish preserve capacity of 200m^3. The ship is supposed to be towed efficiently with a lighter draft (about 0.8m) at a maximum speed of about 10 knots (Fn=0.42). The course stability of the ship might be affected by the ship's speed, trims and towline's positions. It is important to clear the relation between ship's speed and course stability. In this paper, we present the course stability characteristics of the towed fish preserve in high-speed range. We discuss the effect of the trims and towline's positions. We conducted the model experiment tests using l/25^<th> scale(0.624m) models in a circular tank. Also we performed the simulation studies to investigate the course stability for our models. The results of our experiments and simulation studies are described and discussed.
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Hideyuki SHURI, Kouhei MATSUMOTO, Hiroshige KOBAYASHI
Article type: Article
Pages
89-94
Published: March 25, 1997
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The noise prediction using SEA(Statistical Energy Analysis) method in high-speed boats such as patrol boats, passenger boats, has been investigated theoretically and experimentally. In the development of the SEA model for a high-speed boat, it is important to define subsystems containing the engine-girder structure which vibration energy is transmitted through. It is also important to divide the system into physical components which have enough modes in the frequency band of interest at low frequency range. And it is useful way to apply the Power Flow Analysis using FEM to determination of main subsystems in the SEA model. Finally in order to improve the precision of the noise prediction, it is necessary to evaluate the average power flow between ship structural components and cabin interior components, to combine the SEA method and the Acoustic Radiation method.
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Yasumitsu TOMITA, Kiyoshi HASIHMOTO, Naoki OSAWA, Katsuya HIROSE
Article type: Article
Pages
95-107
Published: March 25, 1997
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We have to acquire knowledge about the microscopic deformation mechanisms under cyclic loading condition in order to improve a prediction method of the crack initiation or failure life. In such studies, it is helpful to compare the simulated macroscopic deformation behavior derived from the dislocation models and stress-strain relation of real materials obtained in fatigue tests. We have been developing a crystalline elastic-plastic FEM code which can calculate macroscopic stress-strain response under cyclic loading conditions. In this report, a FEM code for cyclic plastic deformation which can consider lattice rotation and rate-dependency is developed. Using this code, the ununiform deformation behavior of a f.c.c. cubic single crystal under cyclic loading condition is investigated. Results of the analyses are summarized as follows. 1) Although it is assumed that the strain hardening of slip systems depends only on back stress (that is, fully kinematic hardening is assumed), the deformation modes under tension and compression loading are different. 2) The deformation mode changes during loading history. There is a tendency that the local plastic strain intensity becomes more obviously as the number of cycles increases. It is assumed that this mechanism is connected with the generation of P.S.B (persistent slip band), which is the birthplace of fatigue cracks.
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Masahiro MORI, Yukio KANEKO, Naoto MORITA, Sigehiro TERAYAMA, Kentarou ...
Article type: Article
Pages
109-118
Published: March 25, 1997
Released on J-STAGE: April 01, 2018
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Once a great natural disaster occurred, traffic systems and life-lines in land would be cut everywhere. So it would be difficult to run and reach by land to the place where the disaster had occurred. Our country, Japan, is surrounded by the sea. It seems, therefore, to be reasonable to run and reach by sea for rescue activity. We carried out feasibility planning of the "Disaster Rescue Supporting Fleet". Our fleet is constituted of a command ship with reconnaissance boats and helicopters, a car-landing ship and heavy car carriers, a heli-port ship, and so on. Bases of the fleets should be set at the places from where the fleets would be able to reach to any one of the representative cities in Japan, within 6/12 hours by the speed of 20 knots. Our fleet must be operated by the specialists, both in the fields of operations and of rescue activities. To maintain such the specialists in groups for emergency, we propose "registering system for the specialists" both in the public and in the official. We do hope that this concept should be discussed among all of the Japanesea and would be studied further by those who have some interests.
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Makoto ARAI, Liang-Yee CHENG
Article type: Article
Pages
119-125
Published: March 25, 1997
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In this paper, a design method for the optimization of hull geometry considering slamming characteristics is proposed. The momentum theory and the concept of added mass are utilized to determine the optimal sectional shapes that satisfy some different design criteria such as constant impact force, constant pressure, constant acceleration, etc. Numerical simulations are also carried out to confirm the validity of the analytical method shown in the paper.
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Kouji MOCHIZUKI, Hajime KIHARA, Ken TAKAGI, Shigeru NAITO
Article type: Article
Pages
127-136
Published: March 25, 1997
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Seaquake is generally distinguished from tsunami. In this paper, the effects of seaquake on the floating structure is studied. At first the compressibility of the water and the effect of the free surface are studied to deal with seaquake phenomenon. Secondly, the dynamic pressure acting on the floating structure by seaquake is investigated, and it shows that the resonance plays an important role. In numerical work, the boundary value problem is solved by using Green function method. After computing the radiation hydrodynamic force and the vertical exciting force by seaquake, the structure's heaving motion is discussed.
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Ken TAKAGI, Tetsuro IKEBUCHI, Akira KOUSAKA, Mari ISHIHARA, Shigeru NA ...
Article type: Article
Pages
137-144
Published: March 25, 1997
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To estimate the wave exciting forces and pressure acting on a pontoon type floating structure while it is towing to the installation site, some measurements on the bending moment, the shearing force and the acting on the bottom of the structure in regular and irregular waves are carried out. A simple theoretical method for the estimation of forces and motions which is based on the strip method is offered. The measured results in regular waves show that the theoretical method gives good estimations and the effect of the elasticity of the structure is important for the estimation. Other measurements in irregular waves show the importance of the nonlinear effect on the bending moment, shearing force and impact pressure.
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Yoshiyuki INOUE, Xuangang ZHANG
Article type: Article
Pages
145-153
Published: March 25, 1997
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Floating breakwater system to reduce high waves has been used in recent years because it has advantages of sea water circulation and lower cost especially in deep sea. Now, plans are proposed to construct very large offshore structures of floating type such as a floating airport. Therefore, the effectiveness and capability of wave protection of floating breakwater in oceans are investigated in this paper. A new multiple floating breakwater, which consists of several single floating breakwaters, is proposed in this paper. The separated region method is modified to calculate resulting wave reflection and transmission coefficients of the multiple floating breakwater. A mathematical model based on the separated region method is obtained to evaluate the performance. Numerical results based on the proposed method are compared with several previous numerical and analytical results. Good agreement is found between the present results and others. The transmission coefficients of the multiple floating breakwater are searched thoroughly, and interesting properties of the multiple floating breakwater have been obtained. These properties are very important in designing the multiple floating breakwater in ocean engineering.
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Koji OTSUKA
Article type: Article
Pages
155-167
Published: March 25, 1997
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In this Paper, an integrated OTEC/biomass system is proposed. This system consists of OTEC with optional 2nd stage desalination, deep water air conditioning, giant kelp cultivation utilizing nutrient-rich deep water, and marine biomass conversion (methane production by anaerobic digestion and gas turbine power generation). In order to determine the cost effectiveness of the integrated OTEC/biomass system, economic analysis was performed using input parameters taken from the literature. The results of an sensitivity alalysis show that the addition of a 2nd stage desalination system becomes cost effective only when the market value of fresh water is $0.9/m^3 or greater, and that the air conditioning co-product influences the overall cost only for small OTEC systems (< 10MW). The cost of electricity depends on the scale of the biomass conversion system, and this dependency is affected by the discount rate. In addition, we investigated the optimum distribution of electric power production between the OTEC and biomass conversion systems. When the total power production is small (< 10MW), the optimum distribution ratio is 100% OTEC for low discount rates (< 8%), and l00% biomass conversion for high discount rate (> 10%). For total electric power production of > 50MW, 68% OTEC and 32% biomass conversion becomes the optimum distribution ratio in some cases. When the discount rate is low (< 8%), the optimum system is competitive with fossil fuel power systems.
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Article type: Appendix
Pages
App2-
Published: March 25, 1997
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Article type: Cover
Pages
Cover2-
Published: March 25, 1997
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