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Article type: Cover
Pages
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Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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Article type: Index
Pages
Toc1-
Published: September 25, 1992
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Article type: Index
Pages
Toc2-
Published: September 25, 1992
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M. W. C. OOSTERVELD, J. J. MUNTJEWERF
Article type: Article
Pages
1-14
Published: September 25, 1992
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The activities of MARIN were heavily influenced since the early seventies by the ever increasing use of electronic computers. Rigorous computer and mathematical simulation programs were developed to approach problems which where earlier impossible to penetrate. In first instance the programs were developed to better understand and explain observed phenomena, but this development stimulated on the other hand the demand for more advanced instrumentation and measuring systems for more detailed measurements of flow and loads on ships. Further, these developments increased the efficiency of testing programs considerably. Finally a wide range of special purpose software has been developed for supporting the design and analysis of all kinds of ships and of their optimization for operational conditions. The "added value" of the MARIN software lies in the fact that many years of experience and the results of advanced model and full-scale testing are sublimated in this software. Thus, only extensively validated programs are used and made available to the industry. The paper gives a review of recent progress in this field at MARIN.
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Kazuo TANIKAWA, Yoji HIMENO
Article type: Article
Pages
15-24
Published: September 25, 1992
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The present paper proposes a method of obtaining sensitivity coefficients of the viscous resistance of a body in two-dimensional uniform flow due to a slight deformation of the body shape. The sensitivity coefficients for the unit change of the variables in the shape function are directly solved by using a deformed Navier-Stokes equation and a prescribed body-shape function. The authors apply the method to a viscous resistance optimiazation problem in two-dimensional viscous flow by using a gradient method in nonlinear programming. It is found that the present method of computing directly the gradient of the resistance works fairly well compared with the one which obtains the gradient using a finite difference of the resistances. The method is applicable further to optimization problems of other hydordynamic forces, and to three-dimensional case.
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Kazuki YABUSHITA, Toshio SUZUKI
Article type: Article
Pages
25-28
Published: September 25, 1992
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The first report dealed with the numerical method in which the full implicit scheme was used to solve the Navier-Stokes equations and a continuity equation. This numerical solution agreed with the calculated results around a finite flat plate by Lin's analysis that is assumed the high frequency and small amplitude in surging motion. In this report, effects of nonlinear terms in N-S equations are treated at the large amplitude, medium and high frequency cases. In this case, the N-S equations and a continuity equation must be solved in the same time. Numerical solution give slightly fluctured shearing stress and pressure distribution, but it is possible to argue qualitatively but quantatively. The tendency of the time averaged value of shearing stress is very close to the Blasius solution near the leading edge, and decrease near the trailing edge. So, it is suggested that the resultant frictional drag of the flat plate in surging motion will be decreased.
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Shukai WU, Neil BOSE
Article type: Article
Pages
29-40
Published: September 25, 1992
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Difficulties with the calibration and operation of hot-film anemometers in water have prevented their widespread application for towing tank measurements. The potential advantages for measurements such as ship model wake surveys, in terms of their accuracy compared with pitot tubes and their low cost compared with laser-doppler anemometry, have yet to be fully exploited. To this end, a series of calibration experiments with several hot-film probes was done in a towing tank to investigate their calibration characteristics. A nominal wake survey experiment was conducted behind a model of a Newfoundland fishing vessel form by using a wedge-shaped single sensor hot-film probe. The experiment is described. Results obtained of the mean and turbulent axial velocity components within a half propeller disk are presented. The model was towed at a speed of 1.45m/s, which corresponded to a Froude number of 0.33 and full scale vessel speed of 6.4 knots. Techniques associated with use of hot-film probes for wake survey experiments are discussed. The present results indicate the feasibility and potential of hot-film anemometry as a practical, economical, and accurate tool for towing tank applications.
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Shigeru NISHIO, Taketoshi OKUNO
Article type: Article
Pages
41-45
Published: September 25, 1992
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A spatio-temporal derivative method with higher order approximation is described. The spatio-temporal derivative method for flow field image measurement is well known as a high spatial resolution technique. Its governing equations are derived using Lagrange derivative, assuming that the visualized particle image pattern varies smoothly almost everywhere. Examining the formulation of governing equation and the brightness function of the flow image in detail, the authors try to extend this technique to the theory with higher order approximation. The obtained equation can be applied to the case that illumination intensity is not uniform in measurement area. An example of non-uniform illumination intensity was shown in the case of point illumination for flow around circular cylinder. The effects of illumination non-uniformity can be considered with some additional terms in governing equation. The effects of the higher order terms on the velocity field was also investigated, and it is found that the higher order approximation method gives good results when the control area is small.
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Shigeyuki OGINO, Yoshitaka HASHIMOTO, Ichiro TANAKA, Yasuyuki TODA
Article type: Article
Pages
47-53
Published: September 25, 1992
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The influence of the propeller suction on the flow field at the stern is investigated for a ship with asymmetric stern. The inflow rotation into propeller disk is shown to be considerably strengthened at the propeller suction from the velocity field measurement with and without propeller. This phenomenon is fairly well predicted by use of the proposed modified Huang et al.'s method. Based on the above, the discussion is made for the new self-propulsion analysis method applied for this kind of vessel, and also for the energy saving mechanism due to inflow rotation.
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Yusuke TAHARA
Article type: Article
Pages
55-67
Published: September 25, 1992
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The free-surface flows around a yawed ship in steady motion are analyzed by the boundary-element method. The solution is obtained by a distribution of singularities on the ship surface and on the undisturbed free surface. The total velocity potential is divided into two parts, i.e., the double-model lifting-flow potential and the free-surface-flow potential. The double-model lifting-flow potential is expressed by source and doublet distributions, and determined with a Dirichlet-type boundary condition. The free-surface-flow potential is expressed by a simple Rankine-type singularity and determined with linearized boundary conditions applied on the free surface. An overview is given for the present approach, and numerical results are presented for the Wigley hull, including comparisons with available experimental data.
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Masatoshi BESSHO, Shun SAKUMA
Article type: Article
Pages
69-78
Published: September 25, 1992
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When a ship cruises in a high speed, she trims and sinks balancing her displacement weight and moment with the water forces. Suzuki et al. studied it on the case of two-dimensional gliding plate in which the wetted length changes to balance the force and moment. This report deals with a case of a two-dimensional shallow draft ship in which the wetted length does not change but satisfies Kutta condition at the stern. For this purpose, it must be introduced a source singularity which may represents a vertical stem and is known as a line-integral singularity in the theory. As a result, such ship has an upper limit speed at which her cruises safety and cannot over this speed in normal state. Trim, sinkage and resistence are also calculated and especially components other than wave resistance are calculated.
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Masatoshi BESSHO, Shun SAKUMA
Article type: Article
Pages
79-91
Published: September 25, 1992
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A flat plate or prism gliding on a water surface can be represented by pressure distributions on a water plane in the linear theory of wave resistance. In general, the water plane varies as the speed changes so as to satisfy Kutta condition at the aft end. On the other hand, an ordinary ship with transom stern does not vary the water plane as the speed, so that it cannot satisfy Kutta condition at the stern. This is detoured by introduction of a source singularity around the forward periphery of the ship. The present report is a numerical verifications of this theory for a gliding flat plate and a prismatic column. This results show a good correspondence with experimental ones.
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Susumu HIRANO, Yoji HIMENO, Kazuhiro KITAGAWA, Toshiro TAKAHASHI
Article type: Article
Pages
93-99
Published: September 25, 1992
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The objective of the present research is to offer a hydro-dynamic view point to the design of high speed planing hull forms. The present paper describes the experimental results of wave-pattern measurement of a plaining hull form, running at high speed. In the experiment, a plaining plate of wedge form of deadrise angle of 13 deg. is used. The experimental items are 1) taking photograph of wave pattern, and 2) measurement of longitudinal cut wave profile. The process of the analysis are 1) to wright out distribution map of wave crest lines, 2) to take correspondence between 1) and logitudinal cut wave pattern, 3) to write out distribution figure of wave hight and wave profile, and 4) to estimate wave making resistance. It is found that the pressure resistance component consist of wave-making resistance and spray resistance.
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Koji YOKOMIZO, Yoshiho IKEDA
Article type: Article
Pages
101-110
Published: September 25, 1992
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In the present paper, the authors propose a method to assess the performance of a high-speed semi-planing craft using a database of the measured three-component hydrodynamic forces (drag, lift and moment) acting on the model by towing test. A computer program to simulate its running attitude and resistance using the database is developed. The simulated results are in good agreement with the experimental results. Using the present method the effects of the length/beam ratio, hull shape, loading condition and appendage of the craft on the attitude and resistance, and the scale effect between a ship and its scale model are investigated. On the basis of the present study it is safely said that the present simulation procedure will offer much more useful information than a conventional resistance test in the design stage of a high-speed craft.
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Yoshiho IKEDA, Tatsuya ISHIBE, Naoya UMEDA, Junichi HAMASAKI
Article type: Article
Pages
111-120
Published: September 25, 1992
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Hydrodynamic forces (the drag, lift and trim moment) acting on scale models of high-speed semi-planing craft are measured to know the characteristics of them. Nine models whose hull shape are systematically varied are chosen, and the trim and sinkage of them are systematically changed in the test. The models are fixed to a towing carriage by a three-component load cell to measure the hydrodynamic forces. It is found that the residual resistance is proportional to the square of the displacement and is not so sensitive to the hull form, trim angle or sinkage. It is also found that the lift force acting on a hard-chine craft is almost proportional to the square of the beam of model at high speed region and is not so sensitive to the hull form. Finally, the characteristics of the trim moment at high speed are investigated.
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Katsuo SUZUKI
Article type: Article
Pages
121-132
Published: September 25, 1992
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Rowing a shell eight boat is analysed by means of the technological approach from its basic principles to the actual styles of rowing. An evaluation method for strong oarsmen and a rule of selecting oars appropriate for the crew and the speed are obtained. The motion of a boat and oars are dynamically analysed and are numerically simulated. A rational definition of propulsive efficiency for rowing boats is introduced. By using the technological concept of the propulsive efficiency the optimal style of rowing is proposed through the simulations performed under various conditions relating to rowings. The important results obtained from the analysis and the simulations are as the followings: the fluctuations of boat speed in a stroke of rowing are mainly due to the moving of the center of weight of the crew sitting on sliding sheets, schemes of decreasing the speed fluctuation are effective for reducing the boat resistance and attaining a gain of fast boat speed, the main part of the thrust generated by an oar is due to the lift acted on the blade surface, the obtained optimal propulsive efficiency achieves 75 to 80%, shortening the race record muchmore demands the drastic horse power augumentation of the crew, the delicate difference of the moving of crew's weight, the angle of oar and the timing at the catch have a great effect on the propulsive efficiency.
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Toshio SUZUKI, Yasuyuki TODA, Junji HAMAZUMI, Hideki OKA
Article type: Article
Pages
133-143
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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The laminar shear flow at the junction of a wing with a flat plate is considered. The simplest case, the flow past a symmetric foil on a flat surface at zero incidence to a uniform flow, is selected. A numerical method for the solution of the Navier-Stokes equations has been employed to calculate the flow around this simple model geometry with the objective of studying flow phenomena associated with junctions in practical configurations. The computed results for two foils are presented. Computed streaklines and limiting streamlines are shown as well as pressure and velocity distributions to visualize the flow fields.
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Tetsuo NAGAMATSU, Tetsuji HOSHINO, Fumio KURE, Toru IIZUKA, Akio MIYOS ...
Article type: Article
Pages
145-152
Published: September 25, 1992
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In order to grasp the aerodynamic characteristics of wings in ground effect, measurements of lift and drag were carried out for two kinds of airfoils with low aspect ratio by use of the towing tank of Mitsubishi Heavy Industries, Ltd. Theoretical calculations were also made for the same airfoils by a 3-dimensional panel method assuming that the free surface is rigid wall. It is shown that lift and lift-drag ratio increase, in general, with decrease of the trailing edge clearance, but the feature is considerably dependent on the shape of airfoil section, angle of attack, aspect ratio and so on. Comparisons between measurements and calculations show a fairly good agreement each other but further study remains to reduce quantitative discrepancy between them.
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Masakazu KAJI, Tadao YAMANO
Article type: Article
Pages
153-161
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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This paper presents the theory of the wave making resistance and the induced drag of a hydrofoil catamaran whose weight is supported by both the buoyancy of the side hull and the lift of the hydrofoil mounted between the side hulls. There are a lot of studies about the wave making resistance of a catamaran without hydrofoils and the induced drag of a hydrofoil only. But few studies have been made about the resistance of a hydrofoil catamaran in consideration of interference of the hull and the hydrofoil. Therefore we present the theory of estimating the resistance of the hydrofoil catamaran and examine the validity of the theory by comparing experimental and calculated values.
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Qian Wenhao, Zhao Hanhun, Cai Yuejin
Article type: Article
Pages
163-169
Published: September 25, 1992
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The fore-propeller hydrodynamical fin sector (FPHFS) is a new type of energy-saving device developed by MARIC recently. It is composed of 2 or 3 radially placed hydrodynamical fins of aerofoil section and installed at an appropriate position before propeller. The inflow state of propeller and the propulsive efficiency of ship may be improved through the installation of FPHFS. In this paper, model tests and trial results of two versions of 1942kW twin screw river pusher, Version I with reduction gear and Version II without are presented. Within the service speed range, the trial results are quite close to the predicted energy-saving rate (ESR) obtained from model tests. With the installation of FPHFS, the ESRs form Version I pushing a total of 13,000 dwt bargeload plus 4,000t lightship weigh varies from 3.4% at 14km/h to 6,4% at 12km/h ; and those for Version II, pushing 12,000 dwt bargeload plus 4,000t lightship weight from 3.8% at 13km/h to 7.0% at 11km/h, both with derated engine power by reducing an average of 2.3% in rpm. In case when the main engine rpm were kept unchanged, speed increase from 0.15 to 0.35km/h were recorded, which means more trips per year are possible provided the operational schedule be modified accordingly. FPHFS may be easily installed on both new-built and existing inland ships, tugs and pushers. The energy-saving rates are found to be satisfactory. It is estimated that the total cost of model research and FPHFS installation will be covered within a few months for a fleet of 10 sister ships.
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Shotaro UTO, Yoshiaki KODAMA
Article type: Article
Pages
171-180
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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This paper shows an application of CFD (Computational Fluid Dynamics) to the flow computation around a marine propeller, i.e. grid generation and inviscid flow computation. New grid generation system around a marine propeller is developed using Implicit Geometrical Method. This system consists of two parts, i.e. surface grid and three-dimensional grid generation and is possible to generate a grid system around a marine propeller with practical configuration. A series of inviscid flow computations are made using Euler equations and continuity equation with pseudo-compressibility. Finite-Volume, cell-centered, 3rd order upwind, and Implicit Approximate Factorization (IAF) scheme is adopted in order to simulate a flow around a propeller at the open test condition with high accuracy and efficiency. Computations are made modifying propeller pitch ratio larger (P=10,5,2) than original value (P=0.95). Computed results are compared with those by Lifing Surface Method, and good agreement is shown for chordwise load distribution, thrust and torque coefficient (K_T and K_Q). It is also shown that grid skewness may deteriorate accuracy of the computed results, especially of pressure distribution near the leading edge, when pitch ratio small (P=2). "Multi-block" type grid system, which is possible to keep grid skewness small at small pitch ratio, is thought to be one of the probable method for successful simulation around a marine propeller with practical configuration.
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Katsuo Suzuki
Article type: Article
Pages
181-191
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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Two types of formulae are proposed for the peak suction pressure, its distribution and the duration time which are of vital importance for determination of the critical speed of ships cruising over the shallow water area. One of the formulae, related to the added mass of the ships, are deduced from the results of the numerical calculation using the double model flow and the other formula are empirically deduced by analysing the measured peak suctions. The present formulae are shown to be satisfactorily available by comparing with the measured values but the old ones are not for practical use.
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Matao TAKAGI
Article type: Article
Pages
193-201
Published: September 25, 1992
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Succeeding to the first report the present paper gives the mathematical proof the equality of the integral representations to the multipole expansions (series representations) of the velocity potentials in ship motion theory in the case of 3D problems (with forward speed). The coefficients of the series are represented in terms of the source distributions in the integral representation. In order to show the usefulness of the series representations some applications of them to ship motion problems are discussed.
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Osamu YAMAMOTO, Yasuhiro KITAMURA
Article type: Article
Pages
203-208
Published: September 25, 1992
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Non-linearity of hydrodynamic forces acting on a small volume hull form above water plane is studied experimentally. Nonlinearity of vertical radiation force and moment can not be clarified because rated capacity of a forced oscillation device is insufficient for high frequency oscillation of large amplitude. Both wave exciting heave force and pitch moment show typical tendency of saturation against wave amplitudes. Applicability of the linear superposition on radiation forces and wave exciting force is studied by conducting forced oscillation test in regular head waves. It is recognized from results of the experiment that the linear superposition can not be applicable when phase lag between forced heave motion and incident wave motion becomes greater than 90 degrees.
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Shigeru NAITO, Naoto YAMAMA, Takeo SETO
Article type: Article
Pages
209-214
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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It is important to know the characteristics of unsteady wave field for the study on seakeeping of ships. There are much information in unsteady waves generated by ships running with a constant forward velocity in waves. Unsteady wave pattern analysis was proposed as a method for extracting the information. The contents are to measure and analysis diffraction and radiation waves around ships and to derive added resistance and wave damping force due to waves directly from the mesured wave pattern. There are two methods in unsteady wave pattern analysis. The one is longitudinal cut method proposed by Ohkusu, that the analytical line is parallel to ship running direction. The other is the transverse cut method proposed by us that it is transverse to the ship moving direction. In the former method, the wave probes can be set up at the fixed point in space and the truncated correction is necessary, because of a restricted water tank correction. This facility is a small-scale. In the later method, as the wave probes must be set up at the moving coordinate with ships, and the method does not need the correction, because the wave elevation gets almost to zero very rapidly near the edge of unsteady wave field. This equipment is a large-scale. As both of two methods have a merit and a demerit respectively, we had better sellect a method to serve our purpose. We carried out the experiments of wave pattern analysis by the transverse cut method with new equipment which is on the moving coordinate with ships and has a small carriage with five wave probes moving perpendicular to ship's course. Finally, we got the wave amplitude function, namely Kochin function. In order to confirm validity of this analysis, we compared with the wave amplitude functions derived from the measured wave patterns and calculated ones. As the mutual relation between unstady wave field and added resistance, wave damping force exists, we also compared with the wave damping force coefficient derived from the measured Kochin function and the radiation tests. And also compared with the added resistance derived from the wave pattern analysis and the calculated one. Good agreement is obtained. We found that validity of the analysis is complete and the new equipment is useful.
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Yoshiho IKEDA, Yukie KAWAHARA, Koji YOKOMIZO
Article type: Article
Pages
215-227
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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In the present study the roll characteristics of a small hard-chine craft whose length between perpendiculars is smaller than 12m are experimentally investigated. Three kinds of crafts are chosen to measure the roll damping, wave exciting forces and ship motions in regular beam seas. Through the experimental works in measuring the roll damping moment, it is confirmed that the roll damping can be predicted in enough accuracy by using a potential flow theory for the wave component and the prediction method for the viscous component proposed by one of the authors. The wave exciting moment acting on the hull in beam seas are measured by two different ways, the first one is the measurement of the roll moment acting on a fixed model in waves and the another one is that acting on it in free condition of sway and heave motions in waves. The agreements between measured exciting moment by former way and calculated one depend on the hull shape of a craft. The measured ones by the latter way are much smaller than the calculated Froude-Krylov force. From the comparison between calculated and measured roll resonant angle, it is found that the calculated roll resonant angle by OSM can be much larger than experimental one and that the difference is caused by the error in prediction of the cross-couping moments from sway to roll in addition to the disagreement in the wave exciting roll moment and sway force. Finally the prediction method to estimate the roll resonant angle of such a small craft in the Japanese Stability Standard is discussed.
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Iwao FUJII, Akira ARAI
Article type: Article
Pages
229-234
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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A great number of small ships have been built in every year, however, only a few studies have been made on the problem of rolling performance for the ships. The authors performed free-rolling tests using five model ships with different hull forms. From results of the tests including 39 different test conditions, we could obtain new approximate formulae of extinction coefficient N.
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Makoto UCHIDA, Shigeru NAITO
Article type: Article
Pages
235-241
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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The load fluctuation acting on a propeller blade in wave have investigated experimentally using the device to measure the load acting on a blade and reported. In this report, the load fluctuation acting on a blade under the condition that the propeller blade rises partially to the water surface have investigated experimentally using the same apparatus. The tank tests were carried out on the condition that the open propeller boat was restrained and the propeller revolution was controlled at a constant rate in the sti11 water to make the fundamental characteristic of the blade load fluctuation clear. And the experimental results were examined with the simplified estimation model. The followings were obtained. 1) On the condition that a blade rises partially to water surface, the load acting on the blade fluctuates terribly. It can be inferred that the torque acting on the blade is negative. 2) The reason of this result is considered that the force caused by the change of the added mass periodically through water surface acts on the blade along the rotational direction. 3) The effects of the change of the added mass upon the blade thrust is small. So, the thrust acting on the blade is positive even the blade pass through water surface.
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Ritsuo SHIGEHIRO
Article type: Article
Pages
243-253
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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The author is investigating consequent motion sickness of a 60 feet long motor yacht passengers. It is well known that the natural frequencies of rolling and pitching motions of motor yachts are higher than those of ocean going cruise ships. At present, it is not feasible to estimate the probability of motion sickness for small ships like motor yachts at the initial design stage. The estimation formula presented in this paper is composed with vertical acceleration and lateral acceleration, and the frequencies and amplitudes of accelerations are also taken into account. The results of estimation by this formula is compared to the results of questionnaire to passengers which consists of three-choice questions on feeling of motion sickness. We can mention that the results of this method agree with the questionnaire well.
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Katsuji TANIZAWA, Dick K. P. Yue
Article type: Article
Pages
255-262
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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Numerical simulations of the plunging wave impact on a vertical plane wall were performed. The trapped air impact was mainly considered. For the simulation, BEM based on Cauchy's integral theorem was used to solve the governing equation of water and the mixed Eulerian-Lagrangian method was used to update the free-surface profile. The internal free-surface bounding on the trapped air was also updated in the same manner. To compute the air impact pressure, adiabatic and uniform air compression was assumed. To simulate the wave impact with air trapping, the vertical wall must be located within the wave breaking region. Three different wall locations within this region were selected to study the influence of wall location to the impact pressure. The scale of the trapped air impact is defined by the ratio of the characteristic air pressure to the characteristic hydrostatic pressure. Successful simulations with four different ratios for each wall location were done and the peak air impact pressures for each combination of the ratio and wall location were obtained. The reliability of the simulations was checked by comparison between experiment of Chan & Melville and the simulation. With these numerical results, the scaling law of the trapped-air impact pressure was discussed and the practical formula of the peak air impact pressure and its rise time was presented.
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Hidekazu MURAKAWA, Yukio UEDA, Shouji YAMAGATA, Kazuya NAGI
Article type: Article
Pages
263-274
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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The fundamental philosophy of structural design can be divided into two according to the criterion which defines the failure of a structure. One is the allowable stress design based on the initial failure of individual member. The other is the design based on the ultimate strength of a structure. The design or the assessment of the safety of the structure can be further divided into deterministic and probabilistic approaches. However, regardless of these differences, the general goal of the design is an optimization of the structure with maintaining sufficient reliability. The authors studied optimum designs of truss structures based on the deterministic and the probabilistic estimation of the strength for both the initial failure and the ultimate failure criteria. Especially, a new probabilistic optimization method based on the ultimate strength is proposed. It employs the idea of optimum distribution of safety indices for each failure mode. Further, the significance of the optimum design based on the reliability is discussed through the comparison with deterministic approaches.
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Tongxi SHEN
Article type: Article
Pages
275-280
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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In view of the fact that certain new regulations concerning international conventions are going into effect, the matter of stability has become one of the keys in the design of double-bottom and double-skin oil tankers. Should the conventional method still be adopted to check the stability of the double-bottom and double-skin tankers, the result would be that stability would not meet the above-metioned new regulations so that we would face the following unpleasant situation : either alter the cargo tank arrangement or exert the limits on the load. The author has found out in his practice of design that it is not quite resonable to apply the conventional calculation method to the check of the stability of double-bottom and double-skin oil tankers. Therefore, the stability calculation method for such oil tankers has been probed into, and a corresponding calculation method has been worked out.
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Yusaku KYOZUKA, Hiroshi IKEDA
Article type: Article
Pages
281-288
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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Reflected wave coefficients of sloping beaches are obtained in experiments in regular waves. Three straight beaches consist of 1/10, 1/3 and 1/2 sloping angles. A simple linearized model which replaces breaking wave zone with hypothetical semi-infinite fluid domain of constant depth is proposed for calculation of reflected waves. The constant depth of hypothetical domain is varied proportional to the incident wave height. The linearized model is solved numerically by the boundary integral equations, and the results are compared with measurements. For 1/10 slope, calculated reflected wave coefficients agree well with measurements both in the amplitude and the phase. As an application of this model, wave-exciting force/moment of a floating structure near beach are compared in two cases, with or without sloping beach. Those results are presented graphically.
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Takashi KIKU, Koji OTSUKA, Yoshiho IKEDA
Article type: Article
Pages
289-299
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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In order to predict low-frequency viscous forces acting on a semisubmersible moving with large amplitude and low frequency, it is necessary to know the viscous forces acting on cylindrical members of it. To get fundamental information on the viscous forces, force measurements of a lowerhull cylinder and a circular cylinder slowly oscillating in regular waves, and a circular cylinder oscillating with two different frequencies are carried out. The results show that the low-frequency hydrodynamic coefficients significantly depend on two parameters, K_c=U_LT_W/D and U_W/U_L, where U,T and D are maximum fluid velocity, period and representative diameter of the cylinders respectively. The subscripts W and L denate wave-and low-frequency components respectively.
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Chen XIAOHONG, Huang XIANGLU
Article type: Article
Pages
301-305
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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Dynamics of an oscillating mooring line are commonly calculated by using the traditional numerical method as FEM and FDM. In this paper another approach is proposed which is based on the linearization of the dynamic equations of the mooring line, and the method of the inversion from frequency domain to time domain. By using the perturbation method, the nonlinear dynamic equations of an oscillating mooring line were linearized, and transformed into frequency domain. This Frequency domain equations were solved by using Goodman-Lance method. The impulse response functions were then obtained by the inverse Fourier transform of such frequency domain solutions. The time history of the tension induced by the oscillation of upper end of a mooring line then can be calculated by a convolution integral along the time axis with the corresponding impulse function and the oscillation velocity. This method has the merits of less time required and more stable compared with other numerical methods as FEM and FDM. In order to verify the validity of the proposed method an oscillating experiment of a model mooring line was conducted in a water flume by an oscillating apparatus. Comparison between the calculated results and measured results show that in the frequency of interesting this method gives good coincidence with measured results.
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Wataru KOTERAYAMA, Naoyuki TAKATSU, Tomoo NISHINO, Tsutomu HORI, Masah ...
Article type: Article
Pages
307-313
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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An experimental study on the dynamics of floating ocean platform for the research on the air-sea interaction was carried out. The motions of a platform model in regular waves were measured by using the technic of image processing, which was newly developed for the experiment on a very small model in this study. The experimental study showed that the accuracy of the measuring system is very good and the motions of the model in regular waves are small.
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Masahiko NAKAMURA, Wataru KOTERAYAMA
Article type: Article
Pages
315-323
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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Cable vibration caused by vortex shedding is an undesirable phenomenon in the design of a towed vehicle system. Sever vibrations cause fatigue fracture or a great increase in the drag coefficient of the cable. Cable fairing can reduce the drag force acting on a cable. In this paper, an experimental study is carried out on airfoil and several other types of fairing. Normal and tangent drag coefficients, lift coefficients and strouhal numbers were obtained for inclined faired cables, and their performances were compared.
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Article type: Appendix
Pages
App1-
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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Article type: Cover
Pages
Cover2-
Published: September 25, 1992
Released on J-STAGE: April 01, 2018
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