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Article type: Cover
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Published: March 30, 1978
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Article type: Cover
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Junichi NISHIYAMA, Masaaki HASHII
Article type: Article
Pages
1-6
Published: March 30, 1978
Released on J-STAGE: March 30, 2018
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Concerning the circumstances of oil crisis, it has been a tendency to increase number of vessels, which are operated with reduced power. It is said that the reduced power running of ship will be continued for a long time. So, the study for the reduced power running will become more important and more. On the other hand, the design of ship is based on the normal power running as the most effective condition, to begin with. So, the plant efficiency will be reduced in case of running with reduced power. One of the object of reduced power running is to save fuel oil consumption. Therefore, it is very important to improve the plant efficiency in case of running with reduced power. In this paper, some discussions about the problem in case of reduced power running are made, and the countermeasure i sstudied under the condition of minimum investment.
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Hiroshi OKAMOTO, Yoshio YAMAGAMI, Kenji ITOH, Masashi NAKAGAWA, Nobuyo ...
Article type: Article
Pages
7-15
Published: March 30, 1978
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Computer simulation and simulator study based on mathematical models (equations of manoeuvring motions) are considered effective for an accurate grasp of wide range of manoeuvring performance. For this purpose, a mathematical model to be used is required which expresses accurately wide-range manoeuvring motion of full scale ships. In the previous report we introduced a new mathematical model by which wide-range manoeuvring motions such as turning motion and accelerated/decreasing motion can be expressed. This time we have verified the accuracy of the our mathematical model for turning and accelerated/decreasing motions, by comparison of the paths by computer simulation and that in full scale ship test. Furthermore, we introduce here the result of simulator study as an example of application of this mathematical model. The purpose of this study is to investigate the influence of the rudder area and time scale (L/U) on the ship's steerability (performance of a man-machine system includiog that of the navigator). According to this investigation, the settling time to a new course at course change becomes longer as the rudder area becomes smaller. That is, it has been found that the minimum rudder area is determined by the longest allowable settling time, that is determined from many factors including the personal feeling of navigators.
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Yusaku YAMAZAKI
Article type: Article
Pages
17-27
Published: March 30, 1978
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In this study, the captive model tests and the free running model tests are carried out in order to investigate the stopping ability of ships. As a result, it is confirmed that the thrust deduction factor t and the lateral force coefficient Y'_<(P)> are function of J_S(=U_s/nD), and that their signs turn over according to J_s. And, it is led that if propeller revolution n changes stepwise, the stopping motion of ships is related to J_ <SRO>(=u_o/n_aD), and that non-dimentional stopping time and distance are function of J_<SRO>. Futhermore,it is confirmed that J_<SRO> decides whether ships turn to the right or to the left, and that taking account of machinery characteristics, ships tend to turn to the left. Finally, it is verified by the digital simulation of the stopping motion that the equation of motion using the effective thrust coefficient K_<T(1-0)> is useful.
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Tadao TAKAI, Yukiharu NEKADO, Susumu UJI
Article type: Article
Pages
29-34
Published: March 30, 1978
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Full scale manoeuvring tests were carried out to evaluate the steering quality of a wide-beam tanker. These results show that if a large wide-beam tanker has a large rudder which is enough to keep the course stability, the ship has similar performance to those of the conventional one. In order to study the scale effect upon manoeuverability, ship trial results are compared with those from free running model tests, in which three geosim models (4m,10m,30m in length) were used and following conclusions are obtained. (1) In the full load condition, there is only a small scale effect in the range of large amplitude motion. While in the range of small amplitude motion, models are more stable on course and much quicker in response to rudder. (2) In the ballast condition, the difference between models and ship is remarkable.
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Masataka FUJINO, Toshihiko SARUTA, Tsutomu IDA
Article type: Article
Pages
35-44
Published: March 30, 1978
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With regard to the effectiveness of the bow thruster, there exist a number of theoretical and experimental investigations. Especially, it is well known that the forward speed of a ship has a great influence upon the effectiveness of the bow thruster: the hydrodynamic forces which are generated by operating the bow thruster and act on the ship's hull, decrease remarkably with increase of the forward speed of a ship. On the other hand, there seems exist little knowledge of the effccts of several factors, i.e.ship speed, water depth, etc., on the effectiveness of the stern thruster. Therefore, the authors decided to investigate into the influences of the ship speed and the water depth upon the effectiveness of the stern thruster by the model experiments. As the result of the experiments, it is clarified that the ship speed has a great influence on the effectiveness of the stern thruster, which is quite different from the influence of the ship speed on the bow thruster. Namely, even in deep water, the hydrodynamic forces generated by operating the stern thruster do not decrease so much as in case of the bow thruster.In particular, it should be kept in mind that in shallow water, the lateral force due to the stern thruster increases with increase of the ship speed, and it may amount to several times the lateral force at zero forward speed. In this paper, the authors try to explain the increase of the lateral force by an analogy between the stern thruster and the jet-flap wings.
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Nobuo NAGAMATSU
Article type: Article
Pages
45-50
Published: March 30, 1978
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Inhomogeneous wake fields cause serious vibration and cavitation problems. To avoid these detrimental effects, it is necessary to equalive the wake non-uniformity. It has been found possible to equalize the wake fields by means of fins, tunnels, stern-bulbs etc. In this paper, a new method to equalize the wake non-uniformity is proposed and its equalizing effects and some problems in the application of this method to ship are investigated. This method is based on effects caused by free rotaing propeller in non-uniform wake. By experiments in circulating water channel, it is shown that this method is very effective to equalize the wake non-uniformity over a large of propeller disk. So, it is expected to reduce not only surface force but also bearing force and errosion by this method.
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Chong Dal OH
Article type: Article
Pages
51-58
Published: March 30, 1978
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The induced velocity of the bow and stern bilge vortices generated around a wallsided model is measured using a five-hole pitot tube to study the behaviour and property of the vortices. The numerical calculation of the locus of the bow bilge vortex is also carried out by applying the line vortex approximation and the conformal mapping method. Some of the main results obtained are as follows: 1) The structure of the wake distribution deformed by the induced velocity of vortices is experimentally clarified. 2) The diffusive interaction of the counter-rotating components of vortex causes the decay of the vortex circulation. 3) The numerical calculation agrees well with the experiments.
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Yoichi HARA, Nobuyoshi MORI, Noboru SHIMIZU, Tamio KOZONO
Article type: Article
Pages
59-68
Published: March 30, 1978
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Snip ends of stiffeners in ship structures often suffer damages. So, in this paper, the strength of these stiffener ends under static water pressure is investigated. A series of experiments are carried out on model stiffened plates under static water pressure. Besides, the stresses of these stiffener ends are theoretically analyzed by the two beam theory. Comparisons are made between the test results and theoretical ones and good agreements are observed between them. Through these theoretical and experimental investigations, the following conclusions are obtained; 1) Damage patterns of stiffener ends differ with snip angles of stiffener ends. 2) This calculation method by the two beam theory is very useful for analysis of the strength of stiffener ends. 3) To prevent a crack initiation in the welding beads at stiffener ends, it is effective to make the snip angle of stiffener end smaller. 4) In the case of the snip angle of stiffener end kept constant, it is effective to make slit breadth or stiffener depth at its end smaller.
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Yoichiro OKAMURA, Hiroo OKADA, Kenichi KITAURA, Yoshio FUKUMOTO
Article type: Article
Pages
69-75
Published: March 30, 1978
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In this paper, as a basic study on the strength and rigidity of ship's deck girders or bottom girders with holes, the static strength, rigidity and fatigue strength of steel strips with circular holes arranged in saw-tooth pattern, were investigated, theoretically and experimentally. Elasto-plastic analysis by finite element method was used to calculate the static strength and rigidity of these strips under tension, and these results were in good agreement with experimental results. The fatigue test under constant repeated loads was carried out to evaluate the fatigue strength. Furthermore, the effect of the pitch of holes and the distance between rows of holes on the strength and rigidity of these strips was also discussed.
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Takeshi NAGANO, Hisayoshi YASHIMA
Article type: Article
Pages
77-87
Published: March 30, 1978
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Where the ship structural members are designed, it is one of the important items to consider the decrease of steel thickness due to corrosion. The authors introduced the procedure of fatigue fractures reliability analysis where the decrease of thickness was gradually progressed by time passing and this decrease caused the gradual increase of characteristic extreme value stress under the condition of fluctuating wave. Using above procedure and the results of fatigue model tests, the probability of fatigue crack initiation was calculated and compared on the four types of lower ends of side frames which were used in multi-purpose cargo ships; and sensitivity analysis on random variables was also performed. As the results, the following conclusions were obtained. (l) In reliability analysis of ships structure, the decrease of plate thickness due to corrosion has a great effect on the magnitude of the probability of fatigue crack initiation. (2) The probability of crack initiation is not always high when the expected corroded thickness is taken off from the original thickness for stress aanlysis in stead of consideration that the decrease of plate thickness due to corrosion is gradually progressed by time passing. (3) Under selected ranges of random variables, the mean values of coefficient of S-N curve have the most important effect upon the fatigue reliability.
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Junkichi YAGI, Toshiyasu TSUNENARI, Hideo ONO
Article type: Article
Pages
89-99
Published: March 30, 1978
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To discuss cxperimentally the validity of simplified estimation method of fatigue strength of butt welded jolnts with angular distortion and/or mis-alignment, fatigue tests were carried out on notched specimens under axial repeated stress superposed by bending stress secondarily, on the base metal specimens with modified reinforcement and angular distortion, and on the butt welded joints with angular distortion and/or mis-alignment of which reinforcements have conditions of as welded, dressing or flushing. From these tests followings are concluded. (1) If dimensions of notch in specimen are constant for various tests conditions and representation of the fatigue strength is described in terms of summation of nominal axial and bending stress at the part of crack initiation, σ_<rtb>, the fatigue strength at given crack initiation life, Nc, is presented higher as the ratio of bending stress to axial one increases. (2)σ_<rtb>-Nc diagrams of butt welded joint with various amounts of angular distortion coinside with that of the joints without angular distorsion. (3) Effects of dressing or flushing with reinforcements on the fatigue strength of butt welded joints with various amounts of angular distortion are nearly the same as that of the joint without angular distortion.
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[in Japanese], [in Japanese]
Article type: Article
Pages
101-106
Published: March 30, 1978
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Article type: Appendix
Pages
107-108
Published: March 30, 1978
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Article type: Appendix
Pages
109-113
Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Appendix
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Published: March 30, 1978
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Article type: Cover
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Published: March 30, 1978
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Article type: Cover
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Published: March 30, 1978
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