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Published: June 30, 1982
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Takeji ADACHI, Toshihiko ARAKI, Toshihiko KAN
Article type: Article
Pages
1-7
Published: June 30, 1982
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Various aspects of initial design of a semi-submerged catamaran are reviewed basing on the experience of S.S.C. "OHTORI" which is in service since March, 1981. "OHTORI" is a Government owned survey vessel of coastal service, 27m long, high speed diesel driven, with steel main structure and with fixed fins. Decision of length, beam and general arrangement, hydrostatic features, subdivision, resistance, seakeeping characteristics, etc. are reviewed in comparison with conventional catamaran and mono-hull ship.
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Yoshihiro NAKAI, Hiromasa TAMAI
Article type: Article
Pages
9-20
Published: June 30, 1982
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Recently a keen attention has begun to be paid to what is called "SWATH" because of its highly valued seakeeping and high speed performances. Instead of its high degree of design freedom to be expected, the SWATH desing is liable to be governed by the choice of power generation and transmission system and the wave resistance which is the main resistance component in the high Froude number (Fn) region. Besides, its transport efficiency is not so high, therefore the so-called "Optimum desing procedure" should be especially needed. For that purpose, it is essential to grasp the hydrodynamic performances in still water. As the SWATH, on the other hand, becomes unstable in the high Froude number region, the motion control system with fins is indispensable. And for the desing of this system, it is necessery to get the characteristics of fins to be acted under the effects of free surface, hull, etc. This paper shows the results of investigation of resistance and propulsion performances of a high speed type of SWATH, including its fin lift characteristics.
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Munehiko HINATSU, Hiroyuki ADACHI
Article type: Article
Pages
21-29
Published: June 30, 1982
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The interaction of the boundary layer with the ship wave resistance is treated in this paper. Previously the effect of the wave flow on the formation of the boundary layer was investigated. Reversely the effect of the boundary layer on the wave generation is investigated here. Calculations have been made for a thin ship model and also comparison with experiments is made. Although the boundary layer measurements were not performed, the wave making characteristics such as wave spectra and wave pressure on the hull calculated including the effect of the boundary layer are compared with the experiments.
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Yoji HIMENO, Yoshinao KINOSHITA
Article type: Article
Pages
31-37
Published: June 30, 1982
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The present paper concerns with the nonlinear liting-flow phenomenon associated with a thick symmetric two-dimensional body with a large trailing edge angle. For such a body or an airfoil, the lift coefficient has a negative slope near zero angle of attack under some conditions. In the previous report, the existence of the phenomenon was confirmed by the experiments using small airfoil models. In this paper the authors attempt to make a physical explanation for the nonlinear phenomenon that it is caused by a viscid-inviscid interaction effect of a thick streamlined body. Results of the experiment with a large airfoil model are also discussed.
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Yasuyuki TODA, Ichiro TANAKA, Yoshihiko IWASAKI
Article type: Article
Pages
39-48
Published: June 30, 1982
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The distorsion of axisymmetric boundary layer due to propeller suction is investigated experimentally by means of measurement of velocity distribution ahead of and at the propeller location. It is found that the difference between velocity distribution with propeller and without propeller is approximately expressed by the change of boundary layer integral parameters. The prediction of propeller-suction effect on the boundary layer velocity distribution is made theoretically by use of the integral method for the axisymmetric boundary layer. A close agreement is obtained between the measured and predicted velocity distribution upstream of a propelle. The notion of the effective velocity distribution is also discussed.
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Masami HAMAMOTO, Naoya UMEDA, Ritsuo SHIGEHIRO, Yoshitaka NISHIMURA
Article type: Article
Pages
49-56
Published: June 30, 1982
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Transverse stability of small fishing boats in following sea are investigated both theoretically and experimentally. A ship model is towed with the same velocity as the celarity of a wave train generated by means of a wave-generating screen board that is attached beneath the towing carriage. The relative position of ship model to wave is fixed at several different positions. The ship model has a given angle of heel and is free with sinkage and trim. The righting moment, ship resistance, lateral force and moment acting on the model are measured with a 4-component dynamometer. On the other hand, a calculation based on Froude-Krylov Hypothesis are made to compare the experimental results. The calculation is carried out for both cases in which the effect of wave orbital velocity is taken into account and neglected.
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Shin-ichi ARAI
Article type: Article
Pages
57-66
Published: June 30, 1982
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A method to reduce the slow drift oscillation of moored vessels due to winds and waves was considered. A sliding block on a sea-bed is connected by a spring with the moored vessel. Coulomb friction between the block and the sea-bed is expected to reduce the vessel motion. Experimental tests of an idealized model excited by sinusoidal forces were carried out. And numerical simulations by Runge-Kutta-Gill method,availability of which had been confirmed for the case of the experiments, ware done for an actual model excited by irregular wind forces. The following conclusions were obtained. (1) The effect of reducing the vessel motion due to this method exists surely, and it is remarkable one. (2) The reducing effect is influenced by not the mass of block,but the friction and the connecting spring. (3) There is the optimum ratio of friction force to exciting force to minimize the vessel motion.
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Yoshiyuki INOUE, Kouji KADOMATU, Yutaka OHKAWA
Article type: Article
Pages
67-78
Published: June 30, 1982
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The box shaped floating body which is one of the basic shapes for various offshore structures has a low length-breadth ratio, which is nearly 1. Because of this, it is necessary to consider the three-dimensional effect for prediction of hydrodynamic forces acting on them. The three-dimensional method of calculation being very complex, it is not rational to apply it to box shaped bodies. In this paper, we compared the hydrodynamic coefficients obtained from both two-dimensional potential continuation method and three-dimensional source method. From this, we found out the length-breadth ratio below which the three-dimensional method of calculation is necessary. We performed motion tests in regular waves by use of two box shaped bodies which were supposed to have three-dimensional effects, and these results were compared with the calculation results from both two and three-dimensional methods. From these comparisons, it can be said that the responses of transverse motion as estimated by the ordinary strip method (OSM) using the two-dimensional hydrodynamic coefficients is sufficiently accurate. It was also found that for the longitudinal motion, the inversed strip method, in which the length is replaced by the width of the body, is also effective. In case of the drifting force, we obtained negative values in low frequency range.
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Shoichi NAKAMURA, Shigeru NAITO, Keizo KOGANEYA
Article type: Article
Pages
79-86
Published: June 30, 1982
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Absorbed wave power in irregular waves obtained by generating system which is composed of floating body and external mechanism has two components, one is steady component and the other is fluctuating one. From the viewpoint of practical purpose, the fluctuating component is not desirable, so it is necessary to devise the method of smoothing. In this study, formulation of the probability density function and the spectrum of absorbed wave power in irregular waves extracting by generating system is derived. Digital simulation and experiments with a two-dimensional model of floating type wave absorber in irregular waves are carried out to confirm the validity of this formulation, and the agreement among them is clarified. By using this results, the suitable method to array the multi-floating bodies to reduce the fluctuation of the absorbed wave power is proposed.
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Akinori YUMURO
Article type: Article
Pages
87-95
Published: June 30, 1982
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This report deals with a practical method for the estimation of the steering quality indices of a full-size ship from zig-zag maneuver tests of the ship model. This method is based on a new procedure to analyze maneuvering motions. In this procedure, the response behaviour of a ship to rudder force is employed instead of the response to steering rudder angle in the conventional one. Through the procedure, the coefficients in the first-order equation with respect to yaw angular velocity are determined separately from the influence of rudder force caused by maneuvering motions. In this report, it is confirmed that the estimation method of steering quality indices is useful for both a tanker and liner type ship. As an additional attempt the author modifies the method, taking account of the effect of interaction between hull and rudder on the hydrodynamic force acting on the ship body. Then, it is indicated that more accurate estimations are given by using the method improved in this report.
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Hisayoshi TATANO, Takayuki SASAKI, Kiyotaka TANAKA
Article type: Article
Pages
97-105
Published: June 30, 1982
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For improving the performance of a sailing yacht, it is desired very eagerly to investigate the hydrodynamic forces and moments acting on a yacht hull. This paper deals with the lateral force and the yawing moment of fin-keel yacht hulls in oblique sailing and shows a procedure to estimate them by theoretical calculation. The outline of the procedure is as follows: l) The lateral force of the bare hull is calculated by means of the slender-body theory. 2) Assuming that the hull be an infinite length cylinder, the lateral force of the fin-keel including the hull-to-fin interference is calculated by mens of the vortex wing theory. The fin-to-hull interference force is also obtained by the same assumption. 3) The lateral force of the rudder and it's interference to the hull are calculated by means of the wing theory, taking account of the down-wash by vortex sheets shed from the trailing edge of the fin-keel as well as the frictional wake caused by the hull and the fin-keel. 4) The total lateral force of the whole under-water body is obtained by summing up all these forces. The center of lateral resistance, CLR, is also obtained similarly. The procadure works well to interprete model test results. It will be usefull to predict the full scale performance of a yacht hull together with a scale-effect correction.
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Yutaka MASUYAMA, Hisayoshi TATANO
Article type: Article
Pages
107-115
Published: June 30, 1982
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Wind tunnel experiments on yacht sails were carried out at wind tunnel of Osaka University. The test section used for the present experiments is of closed type, measuring 1.8M×1.8m. Wind speed ranges from 7 to 10m/s. In order to keep sail shape realistic cloth sail models should be reasonably large. The wind tunnel wall effect can be serious. We made correction for it using blockage correction factor, ε. The ε is obtained through experiments for a number of rectangular wings and rigid sail models. We took "Flying Fifteen" class sail as a sample and measured its performance. The lifting-line theory calculation for a separate jib as well as mainsail is made. In case of jib alone, the theoretical result compares well with the measured data. For the mainsail, we need, however, some amount of zero-lift-angle correction to represent the disturbing effect of a mast.
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Tohru HORI
Article type: Article
Pages
117-127
Published: June 30, 1982
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The design concept of occean structures is now changing from the "design by rules" concept to the "design by analysis" concept, where starting from load analysis, various kinds of analyses such as stress-analysis and failure analyses are carried out in a same flow. And it can be pointed out as a special feature of the "design by analysis" concept that safety of structures is estimated from probabilistic points of view instead of the decisive estimation which has been adopted for long time. Carrying out probabilistic estimation of structural safety it is necessary to handle the two kinds of probability, the probability of stuctural strength which is originated from randomness of external load, and the probability of material strength caused by scatterness of material qualities. The author et al have been investigating problems mainly as to the former probability and have reported parts of the investigations. And in the present report, crack propation phenomena under random wave load are studied from stochastic point of view, that is, firstly methods of probabilistic estimation as to crack propagation are introduced base on the present states of art in crack propagation analysis, secondly, feasibility of the methods is verfied by numerical experiments, simulation of crack propagation under random load by computor, lastly, consideration is carried out to clarify stochastic pattern of crack propagation based on the methods derived.
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Masakatsu MATSUISHI, Setsuo IWATA
Article type: Article
Pages
129-134
Published: June 30, 1982
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The utilization of concrete for offshore structures gives an advantage of low maintenance cost and excellent durability. However, it is difficult to secure water tightness, once concrete cracking develops. Recent studies have shown that concrete reinforced with short lengths of steel fibres possesses some improved characteristics when compared to ordinary concrete. The safety and durability of offshore structures is ensurcd, if steel fibre reinforced concrete is placed over the surface of steel structures, or if steel fibre reinforced concrete is used at the region of concrete structures where large tensile stress is induced. In the paper, the authors carried out a series of pull-out tests on steel fibre reinforced concrete subjected to tensile loading. Both deformed and round fibres were employed in the tests. From the large amount of the tests results, the effect of fibre orientation, embedment length and the number of fibres were clarified. Theoretical analyses were carried out on peak pull-out loads of straight and/or inclined fibres. A comparison of the calculated and observed pull-out loads shows good agreement.
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Ken-ichi KITAURA, Hiroo OKADA, Yoichiro OKAMURA, Yoshio FUKUMOTO
Article type: Article
Pages
135-143
Published: June 30, 1982
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In this study, to obtain the basic data on impact fatigue behaviour of steel plates following the previous study, low-cycle impact fatigue tests are carried out on five kinds of plate specimens of mild steel SS 41, i.e., smooth specimens, circular notched specimens (stress concentration factor K_t=l.6) and V notched specimens (K_t=2.4, 3.5 and 4.8), under repeated impact tensile loads. The obtained results in this study are summarized as follows: (l) The process of fracture of the smooth and circular notched specimens having small K_t-values is creep type as well as that of circular bar specimens having small K_t-values. The process of fracture of V notched specimens having large K_t-values is local creep type in case of high stress level and is crack type in case of low stress level. (2) Pursuing permanent strain ε which evaluated by using change of plate thickness at the minimum cross section, it is found that there exist three types of cyclic behavlour of ε depending on above mentioncd types (A), (B) and (C) of the process of fracture and in each type the stable stage where permanent strain rate Δε_c is constant occupies most of fatigue life. (3) The relations between impact tensile stress σ and Δε_c, impact fatigue life N_f and Δε_c and σ and N_f for the case of the two creep types (A) and (B) are clarified (see Table 3). At the same time, it is found that these relations for the case of the crack type (C) are different from above relations because the value of Δε_c is fairly smaller than one for the creep types. (4) Comparing above results for plate specimens with those for circular bar specimens, it is found that there exjst considerable difference in effccts of shape of specimen on impact fatigue behaviour between the two.
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Toshimasa KAWANISHI, Munekazu MAEDA, Wataru KATO
Article type: Article
Pages
145-151
Published: June 30, 1982
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The SALM (single anchor leg mooring) has been applied at many locations throughout the world, both for conventional oil import and export terminals and for deepwater production storage and loading facilities. The SALM has proved to be a safe, reliable, and efficient means of mooring and loading or unloading both large and small tankers. Experience and continucd research have lead to design improvements which are now being incorporated in new SALM. The SALM mooring buoy is anchored through a single pretensioned anchor leg to a gravity type mooring base at the seafloor. This paper describes model tests of the response of a SALM subjected to earthquake excitation.
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Yoshikazu MATSUURA, Hiroyuki ZENJAKU
Article type: Article
Pages
153-165
Published: June 30, 1982
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In this paper have been assembled a number of cases of vertical vibration experiments carried out by the authors on the acrylic resin model ships of box section with deck erections. To clarify the vertical vibration characteristics of ships with erections, numerical calculations are carried out in the following manner. Firstly, nine structural parameters are defined, which are used to distinguish the structural differences among the ships with erections. Secondly, three basic ships are selected. The word "basic ship" means an imaginary ship, of which each structural parameter has an average value of those of model ships mentioned above. Using the calculation method previously reported by the present authors and starting from the basic ship, a series of numerical calculations of natural frequencies of ships in question is carried out by changing each of their parameters independently of the others. Using the results of calculations, vertical vibration characteristics of ships in question are given in the form of graphical presentation. Based on the results of calculations, a simple and practical method of estimating natural frequencies of ships with erections is proposed. Applying this method to the above-mentioned model ships, good agreement is obtained between the calculated and observed frequencies.
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Hideyuki SHURI, Tomomichi KURIHARA
Article type: Article
Pages
167-175
Published: June 30, 1982
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In this paper, experimental studies were carried out to investigate the further applicability of the SEA (Statistical Energy Analysis) method to two more practical and complex steel structures than ones examined in the 1st report. One was a steel structure model consisting of panels of the different size and thickness and air spaces of the different volume, and the other was an actual Jacket Launching Barge (L×B×D=198.12m×51.82m×12.20m). As for noise and vibration sources a small speaker system and an electrodynamic vibration exciter system were used in the case of the model, and a tapping machine was used in the case of the Barge. The calculated results agreed well with the experimental results, however, it was found to be necessary to make a few corrections of the theoretically calculated coupling loss factors and of the input source's vibration level for improvement of the accuracy of the calculation.
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[in Japanese]
Article type: Article
Pages
177-194
Published: June 30, 1982
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[in Japanese]
Article type: Article
Pages
195-201
Published: June 30, 1982
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[in Japanese]
Article type: Article
Pages
203-209
Published: June 30, 1982
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Article type: Appendix
Pages
211-213
Published: June 30, 1982
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Article type: Appendix
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Article type: Cover
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Article type: Cover
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