We consider the infinitesimally small vibration of two circular cylinders, which are immersed in a water region of infinite extent. Asumming the water to be an incompressible non-viscous fluid, and treating the problem as a two-dimensional potential problem, the author has made an analytical study of the problem, and made an estimation of the effect of surrounding water (in form of “virtual mass”) upon the vibration of two circular cylinders. It is noticed that the acceleratory motion of No.1 cylinder affects the acceleration of No. 2 cylinder, thus, causing an effect very much similar to the phenomenon of “mutual inductance” in the theory of coupled (inductive) electric circuits.
Many problems should be studied, when we compare measured ship motions with computed ones, such as three dimensional effect, advance speed effect, nonlinear effect and restricted water effect. Finite depth effect is investigated in this paper on the basis of Thin Ship Theory. There is little effect on hydrodynamic forces and on ship motions when water depth-ship length ratio h/L is greater than 1. but when h/L is less than 0.5, they are affected by the finite depth, and computed ship motions show a little decrease compared with those of infinite depth.
It has been considered that the purpose of the automatic steering system of ships is to maintain ships' course as far as possible. However, the author would like to point out that this definition is not proper, because, there might be reasonable limitation to the rudder angle in relation to the speed loss, that is : if an excessive rudder angle was taken to maintain the ship course too much strictly, it will induce considerable power loss. The real purpose of applying the automatic steering to a ship in a seaway is to bring her from one side to the other end of a route as fast as possible within a limited cost. Therefore, the author prefers to define the purpose of an automatic steering to be “to minimize the increase of resistance in a wide sense under the disturbance of wind or waves in the ocean.” Making the use of this definition, the author obtained the performance function of the automatic steering system of ships at sea, namely : J=θ2+λδ2 where θ2 : mean square of course error. δ2 : mean square of rudder angle. λ : a constant which shows the weight of above two values. A full scale measurement of yawing motion is also carried out on a cargo ship, “M. S. Florida-Mar” in Pacific Ocean to obtain the spectrum of angular rate which is affected by disturbance caused by wind or waves. Applying these results, some suggestions are obtained to improve the automatic steering system of ;ships, for example, 1) The rudder angle ratio has to be chosen not too large. 2) The weather adjustment of conventional system is injurious and cannot keep the rudder angle small, because it necessarily requires rather deep rate control. 3) First of all, we should pay attention not to make the rudder too much sensitive to each wave. and so on.
Aiming to reduce the viscous resistance of fat and low speed ships as tankers, new ship form encouraging buttock flow is proposed. Resistance and self-propulsion tests of Cb=0.88 and 0.84 model are proceeded. Characteristics of the new ship form are remarkably less profile drag and less wake gain. The latter defect can be improved by properly designed skeg form and bilge corner form.
By making use of the slender body theory, the author studies into the optimum configuration of the frame line form of ships. Firstly, fixing his eyes upon the energy of the secondary flow around the frame line, he finds out that there are ship forms which have no secondary flow as like as rotational bodies, the stream lines on such body become approximately geodesic and, if so, there may be no cross flow in the boundary layer by Squire's theorem. He calls them Approximate Geodesic Stream Line Ship Forms and shows some examples represented by Lewis' conformal mapping function. Secondly, he deduces some typical ship forms by setting simple characters upon the secondary flow and they contain the so-called U-frame, V-frame and bulbous bow form. Lastly, he analyses three representative practical ship forms and finds out that the aft-bodies of three ship forms are all nearly the forms of which the secondary flow is the minimum. Although the theory developed here does not foretell the resistance quantitatively, it seems very usefull to design the optimum frame line configuration of the ship.
It is the purpose of present paper to study analytically the hydrodynamic characteristics of fully cavitated hydrofoil in cascade by acceleration potential concepts. By taking the usual linearized assumptions, the problem can be reduced to a potential one of mixed boundary value type in acceleration field. The lift and drag of fully cavitated hydrofoil in cascade are expressed in the generalized form of Munk's integral known in thin wing theory. Numerical calculations are performed for the characteristics of fully cavitated hydrofoil of flat plate and cambered section in typical arrangements of cascade and comparisons are made with the former theories. In the last place, application of the present theory to supercavitating propellers and comparison withmeasured value is made.
This paper presents the results of the tank tests of a systematic series of modified AU-type five-bladed propeller models, the expanded area ratio of which is 0.80. The J-KT, KQ, η0 curves and √Bp-δ design diagram are given.
Recenty, an oil tanker is becomming largar and larger and now, the enormous large tanker with over 300, 000 D. W. tons has being planed. In designing such a large tanker, it is important to determine the most efficient type and the scantlings of the midship section. For the basic study of this problem, authors tried to examine the effectiveness of the side girders attached on the bottom and the deck part both in a centre and wing tanks, that is, (1) to deduce the method of the three dimensional strength calculation for the with side girder type tanker, expanding the method explained in our previous paper, (2) to examine the effect of the side girders upon the transverse strength and on the longitudinal strength and to examine the strength of the side girder itself. Form this study we obtained the following results, that is (1) the side girders are not effective for the transverse strength but effective for the longitudinaly bending action, (2) the shearing stress of the side girder becomes much larger in the case of the rigidity of the side girder is smaller than those of the transverse members, on the contraly, the normal stress of the side girder becomes larger in the case that the rigidity of the side girder is larger than those of the transverse members, (3) it seemes to us that, it is, therefore, better not to attach the side girders on both the bottom and the deck part, and moreover, if necessary, the _??_-giders may be removed for the sake of the simplicity of the hull structure.
In our previous paper, we had examined the strength of hull structure of an oil tanker under the several load conditions. These results are all coresponding to those under the upright conditions. While the ship is exposed to the various waves and winds generally in her service conditions. Consequently, live load due to the motions both of the water particles of the waves and of the ship is acting on the hull structure in addition to dead load. It is, therefore necessary that the strength of a ship is to be examined under such the load condition mentioned above. The authors try to examine the strength of an oil tanker under the heeled condition applying the statical load for the basic study of this problems, that is, (1) to deduce the method of the three dimensional strength calculation under the heeled condition, (2) to compare the state of deformations and stresses under the heeled condition with heel angle of 20 degrees to those under the upright conditions, both in the still water. (3) to compare the state of deformations and stresses under the Tank Test Condition to those under the Normal Ballasted Condition with heel angle of 20 degrees. From this study we obtained the following results. (1) Stresses under the heeled condition are greater than those under the up right condition in the lower part of the Trans. Ring at the immersed side. The ratio of increment of stress is about 1.21.3 times in the case of this study. (2) The Tank Test Condition gives the stress in the Trans. Ring almost equal to those under the Normal Ballasted Condition inclined with heel angle of 20 degrees in still water. But the axial forces in the Struts of the Trans. Ring becomes 1.2 and 2 times larger than those under the Tank Test Condition.
In this paper, the ultimate strength of girder plate structures in oil tankers or ore carriers has been investigated from view point of plastic failure of the structures under statical loading. Problems of local buckilng failure of members in the plate structures are not taken into consideration. Based on the simplified lower bound theorem method of plasticity, theoretical analysis has been made on the plastic collapse of deep girders with round corners at both ends subjected to shear, axial force and bending, to determine the collapse load of the girders as well as the location of the plastic hinge at the round corners. A method is presented of the plastic analysis on such girder structures, by introducing the concept of “plastic span-point” in a fictitious beam with uniform cross section, of which the collapse load is equivalent to that of the given girder. Model tests have been also carried out to examine the collapse mode of the deep girders, measuring the development of yield zones in the web and the ultimate load carrying capacity of the girder specimens. Results of the tests have shown that the ultimate strength of the deep girders with round corners can be well predicted by the theoretical analysis.
An improved theory on the ultimate shear strength of plate girders with due regard to the effect of the rigidity of flanges is presented. Theoretical values obtained by the present theory are in satisfactory coincidence with those obtained by the experiments conducted in various research institutes. The defects in Basler's theory are also discussed.
For the solution of elastic-plastic buckling problems, the variational methods (Rayleigh, and Galerkin methods) have been the most powerful and useful to engineering purposes. In the recent years, the developement in high speed digital computers has been giving favor to a numerical approach that is referred to as “the finite element method”. Gallagher first applied this method to buckling of columns and Kapur established the basic approach in obtaining the solution of elastic plate buckling with the finite element method. Based on the results of the investigations mentioned above, the authors have developed the finite element method and succeded in applying the method to the solution of elastic-plastic buckling of plates with the aid of the plastic theories, the plastic deformation and the plastic flow theories. In the paper, the accuracy of the solution by the method was examined for both elastic and plastic buckling of plates at a relation to the number of finite elements divided in the plate. As a basic example of the application, elastic, elastic-plastic and plastic buckling of plates containing residual stresses was solved by the method and compared with the analytical solution obtained by the energy method. The result was quite satisfactory and suggested the usefulness of the method.
In this paper, Instability of plates with a circular hole supported at all edges and subjected to shearing forces and/or compressive forces, is studied to investigate the buckling strength of girder web of large ships. The body of this paper consists of two parts ; one is the case where the I-Beam is supported at both ends and is loaded by a concentrated load at the center, so that web of I-Beam is subjected to simple shear and buckled mainly due to the shearing stress. (Fig. 1 and 2) Another is the case where the square plate with a circular hole is subjected to edge thrust under the supported condition along all edges, and the effect of position of the circular hole is mainly studied. (Fig. 11) The buckling loads are determined by Δ2-method and are calculated by Energy method. The conclusions obtained are as follows ; (1) It is proved theoretically and experimentally that Δ2-method (the linear relationship between load P and the square of the max deflection δ2) is also valid for the case of shear buckling (Fig. 4, and 5) (2) The behavior of I-Beam with hole in web and the effect of the hole on the shear buckling strength of the web, are clarified. (Figs. 8, 9 and 10) (3) The effect of position of a hole on the buckling strength of square plate is studied, and the hole is shifted to the transverse direction (4 A) is found to be the weakest. (Fig. 13) (4) It is proposed that to calculate the buckling load of the practical problems such as the buckling strength of a plate with a hole of irregular shape, a numerical distribution of stresses should firstly be computed by a suitable method, for example, finite element analysis, and a suitable deformed mode of the plate should be assumed so as to satisfy the given boundary conditions, then the energy method could easily give the solution with enough accuracy.
Stress concentration problems of thin elastic plates are one of the classical problems in the theory of elasticity, and since E. Goursat's work on the complex variable representation of stress functions in plane elasticity problems, much work has been done all over the world, and Muskhelishvilii and others have established the unified theory on the two dimensional elasticity problems. Unfortunately, however, the exisiting theoretical solutions obtained along this line are quite limited for the practical purpose and the development of the more practical method of analysis is definitely anticipated. One of the authors believes that the energy methods will provide the alternative procedure powerful enough to treat the more practical problems although actually no attempt along this line has been made. In this paper, the first effort is made on the stress analysis of a perforated rectangular plate, the result of which is found consistent with the famous Howland's solution on the perforated plate strip problem and some test results.
The heat affected zones (HAZ) of three kinds of high tensile steels were reproduced with a synthetic thermal cycle apparatus, and their notch toughness was evaluated by fracture stress curve test and Double Blow test in respect to the initiation of brittle fracture. As the results of the experiments it was found that the synthetic HAZs were in general remarkably notch sensitive, and the results of both tests had the same relation as previoulsly reported on many other base plates. The transition temperatures of synthetic HAZ were compared with the ones of bead welded specimen in the first report. It was revealed that Trα5 in Kinzel test and (TrEi) 2 in the synthetic HAZ varied almost in similar way with the increace in the hardness. On the other hand, a close corelation was not found between (TrEi) 2 in the synthetic HAZ and Tr15 in the bead welded specimen. Finally, the behavior of brittle fracturing of bead welded specimen was schematically discussed, and it was concluded that the existence of thin and brittle layer as seen in HAZ would obviouly have adverse influence on the notch toughness of the specimen, for the range of the temperature lower than TrS of the base plate.
In this paper, the effect of the size of a weld defect “lack of penetration” remaining in the welded butt joint of mild steel on brittle fracture initiation characteristics was investigated by using wide tensile test specimens. Three types of part-through weld defect notch are tested. Two of them are the surface notch and the internal notch with limited extension to the both directions of thickness and breadth. The other one is the internal notch through breadth on weld line. From the results of surface and internal notch tests, a change in crack extension mode from the direction of breadth into that of thickness with an increase in notch depth was observed clearly. A complicated phenomenon that the brittle fracture initiated at low stress levels in the through-breadth internal notch test specimen, in which the brittle cracks propagated only in the direction of thickness was observed. But it is remained to analyse theoretically the results of these part-through notch tests, based on the energy condition theory for brittle crack initiation, and further based on the close examination for the state of actual stress on the notch section. However, as it is considered that the deep notch test is practically effective method to investigate the brittle fracture initiation characteristics for the welded joint under one of the severest conditions, additional investigations which can be applied to the through-breadth internal notch specimens will provide another valuable basic data with respect to the brittle fracture initiation characteristics at low stress levels for the welded joint.
The crack arrester is used for prevention of welded steel structures from brittle fracture. In the latest mammoth tankers, the welded crack arrester of high quality steel such as grade E steel is used instead of the riveted seam. In this paper, the brittle crack arresting characteristics for welded crack arrester was investigated by using large size specimens in 1, 300 mm width. Then the correlation between the characteristics in large size specimen and in standard ESSO test with temperature gradient as a substitute of double tension test was examined. From the test results, it was found that the modified gross stress-arresting temperature curves for arrested crack length of 500, 750 and 1, 000 mm, respectively, were common, and the effective crack length was approximately 250 mm which was obtained from the ESSO test or the double tension test with temperature gradient. In addition, the effect of width of arrester plate on the crack arrest in which the distribution of residual stress was taken into account, was found.
In this 5th report “Ditch-type” and “Stiffener-type” arresters are considered. In the former the arresting of brittle crack is effected by the mechanical factor associated with the singularities of stress field due to “ditch way” where discontinuous change in plate thickness exists and as well as to the increase in toughness of the material by plate thickness reduction. The latter type is similar to stiffener and frame which are popularly seen in the plate and shell structures. In the case of stiffener type arrester, material quality and/or dimensions of stiffener is so tough that the stiffener never breaks even when the crack in plate passes the line where the stiffener is attached and the crack arresting is effected by the crack closing action of the stiffener. Stress intensity factors with the presence of the above two types of arrester are approximately calculated and the results are compared with those of brittle crack propagation-arrest test using the double tension specimens with arresters. In connection with the analysis of Ditch-type arrester, the mechanical effect of plate thickness on fracture toughness is discussed. Further it has been found out that the stiffener type crack arrester is effective and promising from the practical point of view.
The progress of numerical control systems has been remarkable in many industries throughout the world, not least of all shipbuilding. Shipbuilders have long dreamt of ways of accomplishing complete automation in design and production and studies on numerical control systems are at last making this dream a reality. Hitachi Shipbuilding and Engineering Company have developed many types of softwares for use with numerical control systems, and have succeeded in organizing these for hull production design, thus with the aid of a digital computer are now able to fair ship lines, develop mould loft settings and prepare tapes as inputs for numerically controlled tools. Among softwares now in common use the most noteworthy is the auto programming system HIZAC (Hitachi-Zosen Auto Coding), which was developed for, and based upon the highly advanced shipbuilding techniques now used in Japan. This offers input paper tapes to the numercally controlled flamecutters and drafters by means of a digital computer from only a few design characteristics supplied by mould loftsmen, Details of numerical control systems and the software HIZAC are described in this paper, the lecture to be given at a meeting of the Society of Naval Architects of Japan.
It has been so far said that the flow line system might be applied mainly to the mass production industry, while the application of this system is difficult to the unique product production industry in view of the diversity of products. Accordingly, the flow line system has been adopted in the shipbuilding industry, in such limited cases as in the prefabrication stage of hull assemblies which compose parallel part of tanker and has failed to contribute to the improvement of general production system of shipbuilding industry. Through the study on the intrinsic nature of flow line system, however, the authors have developed a new system of control technique so that a group of techniques fostered in the mass production can be applied to shipbuilding industry which is typical in diversified products production. This new control system has been applied to shipbuilding industry, characteristically utilizing the flow line system. Accordingly, this system can be applied in a similar manner to the other territory of diversified products production, e. g., machine industry. The promotion of this new production system in shipbuilding industry has thus marked an epoch-making development through the introduction of electronic computers into the planning and control system of production and thereby maximum efficiency is realized in shipyard management including not only hull works but also outfitting works.
A revolutionary change was brought after the world war II into the production engineering of shipbuilding industry through the remarkable development of welding techniques. Following such technological innovation, the efforts for the modernization have continously been made and have recently been exerted actively in the mechanization and automation of manual operation mainly in welding, the introduction of electronic computer into production control, as well as the rationalization of production process by the adoption of conveyor system. In spite of these technical developments, more efforts have to be done in the solution of problem of the labour-intensive shipbuilding industry, which is suffering at present from the “prospertity without profit”. To cope with this difficulty of shipbuilding industry, the authors conducted the study on the characteristics of shipbuilding industry in comparison with the other modern industries. This study has revealed that the standardized production process can be settled on the basis of the steadiness of quality by the introduction of statistical quality control, and further that such work system with high productivity as is in general called “continuous flow production system” can be also adopted in the shipbuilding industry. Moreover, the authors have proved this fact by applying it actually to the hull construction works and have made a success of such modernization as is shown in the automation and specialization of welding in their company. Thus, it has been made clear that only on the basis of substantial improvement of production system through the application of mass prduction method, a series of modernization measures such as mechanization of manual labour, adoption of conveyor system and production control with use of electronic computer, will be realized on a full scale.