This paper describes the calculation of viscous flow around the tanker (Ryuko-maru) under the double model flow assumption at model scale and full scale Reynolds Numbers, in both towing and self-propulsion conditions. The CFD method used here has been originally developed by Kodama and Hinatu. As a result, difference of wake distribution between model and full scale ships is predicted well. The form factor and the thrust deduction predicted by CFD method are not depend on the Reynolds number, but effective wake fraction decreases with increase of Reynolds number. Scale effect predicted by CFD described above is basically agree with the knowledge that is used in the stage of prediction of full scale ship performance from tank test results.

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Recent ship is usually equipped with a mariner rudder, which consists of horn and movable part. In the numerical modeling of the mariner rudder, they substitute the equivalent rudder having the same height and side ares as the movable part. In order to check the validity for it, we measured the open-water characteristics (normal force and chordwise force) of the mariner rudder, the equivalent rudder and the trapezoidal rudder which is unified one of the horn and the movable part. Through comparisons of the characteristics among the three kinds of rudders, we confirm the reasonableness of that modeling. Moreover, we clarify the effect of gap between the horn and the movable part on the open-water characteristics.

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The method of speed trial analysis which evaluates the effects of encountered waves and steering as well as wind and current is proposed by SR-208 Panel of the Shipbuilding Research Association of Japan. In this paper, a new practical wave height measurement system developed for the speed trial analysis is introduced. According to the Guidelines of Standardization Speed Trial Analysis prepared by SR-208 Panel, significant wave height and mean period of waves for seas and swell are necessary. Although these data are usually based on visual observation, this system makes it possible to evaluate the wave height and mean period with reliability and to introduce a sort of objectivity. The wave height meter consists of a buoy and a pressure sensor, and the data measured by the sensor is transimitted through an electric wire to the analysis system on the fishing boat chartered for a trial. The analog data transmitted is digitalized by the AD converter for the first, and spectral analysis is made by the personal computer on the boat, which gives the information about the wave height and period of the total wave for seas and swell. The significant wave height and mean period of waves for seas can be obtained from the total wave data by introducing the relative information such as the wave height ratio and the wave length ratio of seas to swell. These relative data are based on visual observation. The significant wave height and mean priod of waves for swell can be also obtained in the same way. The use of this measurement system for the speed trial analysis was admitted for the recent trials of LNG carriers. Some applied examples are also introduced in the paper, with the more detailed explanation of the system.

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Generally, there are some advantages about a mono hull type high speed craft, such as simple structure and availability for using existing port facilities, then mono hull type is used mainly in high speed crafts. However, in regard to a mono hull type craft, it has been known to lose the transverse stability occasionally with increasing her ahead speed, even though she possesses adequate stability at rest condition. Despite the relative severity of the phenomenon, very few is known about the fundamental characteristics. There are some technical literature concerned with stability phenomenon by experimental method. However, there is few examples that approach this phenomenon by numerical calculation method. In this paper, numerical calculations on the transverse instability are carried out for dynamic pressures, rolling and yawing moment acting on a high speed craft, by applying Prof. Maruo's new slender ship theory. This paper deals with the high speed instability phenomenon on the assumption that she has constant speed, heave, trim and heel angle.

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A feasibility research project on large scale floating structures for the ocean space ulitization is undergoing now in Japan. Floating structures are superior to the reclaimed island in some points such as less impact on ocean environment. But, because the scale is huge compared with existing ones, environmental assessment of such a structure in a bay is necessary before construction. In this paper, we present a method to simulate tidal flows of a bay with a very large floating structure using muli-level model. Pressure under the pontoon is obtained by solving the Poisson equation. Effects of vertical displacement of the pontoon due to tidal force are considered in the tidal simulation. Tidal currents, residual currents and wind driven currents in a bay with/without a structure are presented graphically and discussed.

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The present paper studies the numerical methods for predicting ship's maneuvering hydrodynamic forces and proposes an improved numerical procedure. To improve such numerical methods, the effects of separation position, the initial vortex position and the shedding angle on the lateral force distribution have been studied in several separation models. The effects of body's section number and the frame's mapping parameter number have also been discussed. In the improved procedure the theoretical solution for the ellipsoid is adopted to revise the force near the bow. The calculated forces for 4 ships by the procedure agree with the measured data satisfactorily.

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At the stage of initial design, the manoeuvrability of ship is usually predicted by MMG model in Japan. The MMG model contains three interaction factors (1-t_R, a_H, x_H) which are determined by the rudder angle test. This paper proposes a method to calculate these factors hydrodynamically. We represent a ship hull and a rudder by SQCM (Source and QCM) and do a propeller by the simplified propeller theory. As to rudder model, we check the usefulness of the simplified rudder model which uses the center-plane source and vortex distributions. Instead of actual ship models SR-221 A, B, for simplicity, we adopt a simple strut having a parabolic water plane, and obtain the three factors through numerical calculations. Then we show the usefulness of this method comparing with the experimental results on SR-221 A, B models.

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From the viewpoint of marine safety, it is of importance to grasp ship manoeuvring performance, such as berthing in a harbour, drifting behaviour of a disabled ship. For the prediction of ship manoeuvrability with high accuracy, it will be required to estimate the hydrodynamic forces acting on a ship accurately not only in relatively high speed motions with small drift angle but also in low speed motions with large drift angle. So, numerical calculations have been already given to the longitudinal distribution of the cross flow forces over the length of ship at larger drift angles. This theoretical method is on basis of vortex shedding model developed by the authors. The numerical results for a container ship hull in drifting motion agree well with measured results of oblique towing model test. In this paper, the simulation calculations based on the mathematical model are compared with the results of free running model test for typical manoeuvres with tugboats. The hydordynamic forces acting on ship, which are needed for the numerical simulation of manoeuvring motion, are obtained by means of theoretical method. Form these studies, it is found that this approach will be useful for parctical prediction of manoeuvrablily for ship in low speed motions at early design stage. However, there still remain some problems to be solved, such as the effect of yawing motion on hydrofynamic forces acting on ship in large drifting motion, to perdict the manoeuvring performance more accurately.

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For predicting ship manoeuvring performance, it will be very important to estimate the hydrodynamic forces acting on a ship with high accuracy. The hydrodynamic forces can be estimated by the approximate formula as a function of principal particulars of the ship. However, it will be not able to estimate the hydrodynamic forces considering the detail hull form such as a frame line by using this prediction method. Therefore it is necessary to establish the prediction method which can be took into the effect of difference of frame line configuration in order to estimate the hydrodynamic forces more accurately. In the last paper, we examined the hydrodynamic forces acting on a ship hull in oblique motion considering the frame line configuration by using the prediction method which was based on Fuwa's method. Because of the assumption of the separation line which was set on the keel, we couldn't get a qualitative agreement between the estimated hydrodynamic forces and the measured hydrodynamic forces in manoeuvring motion with large drift angle. In this paper, we investigated the hydrodynamic forces acting on three types of model ships which were a VLCC with V type-frame aft part, a VLCC with U type-frame aft part and a VLCC with just middle frame line configuration between V type and U type. We assumed the separation line on both starboard bilge and port bilge referred to the results of captive model tests and shed the vortex lines freely. From the results of numerical calculation in the proposed method, we got the following concluding remarks. As a result of the comparison between the estimated hydrodynamic forces and the measured hydrodynamic forces, we got a good agreement in these results. Furthermore, it is considered that it will be able to estimate the hydrodynamic forces acting on a ship hull in oblique motion taking into the frame line configuration with high accuracy by using the present method.

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The study discusses the influences of different sources of wave statistical data, which were based on visual observations of ocean wave, on long-term predictions of ship responses with special emphasis given to wave data quality. It makes their tendency clearly with the quantification of wave data statistical characteristics. The influences of wave data accumulation on ship responses are also considered by a proposed simple combination methodology of Yamanouchi, Takaishi, and Watanabe's wave data, which presented with some differences in data format. Being compared with reference to the corrected GWS wave data, it shows that it is possible to obtain good estimates of long-term predictions of ship responses by observations accumulations. And it also shows that the quality of wave statistical data is mainly dominated by their collection period, collecting method and so on. A numerical example of the effect of different wave statistical data and the accumulated data for long-term prediction of ship bow vertical relative displacement based on some special sea areas is given.

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Offshore platform or cable layer ship are often required to keep their position with high accuracy under influence of external forces. In order to keep their position at deep sea, dynamic positioning system (DPS) is often used. Though the linear quadratic (LQ) optimal regulator theory is often applied to design control system of DPS, it is very difficult to select suitable weighting matrices in the performance index that is necessary to obtain optimal control input. Therefore, from a viewpoint of practical use, recently the inverse linear quadratic (ILQ) optimal servo theory that makes design process more easier has been proposed. In this paper, we applied the ILQ optimal servo theory to design the control system of DPS for ships and carried out numerical simulations of ship motion to examine the performance of the control system designed by using the ILQ optimal servo theory. From the numerical simulations, it is found that the time constant T_i should be selected to be small value considering performance of the thruster and the gain adjustment parameter σ_i would be selected as same as value of σ__-. It is also found that design process using the ILQ optimal servo theory would be more easier than using conventional LQ optimal regulator theory.

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In this paper, we developed a new automatic calculation system in addition to new concepts, which was extended from the conventional automatic calculation system (ref. 3) where shear flow on the cross-section of thin-walled uniform beam is statically deteminated. Specifically speaking, for the thin-walled variable cross-section beam with multi-cell i.e. shear flow on the cross-section is statically indeteminated, we developed the new system which can calculate for the analysis, applying the new longituginal strength of a hull girder taking into consideration of "warping in bending" (ref. 4), automatically with the minimum input data. This new system can process the figures on the results of calculation by interactive computer programs. Next, we applied this new system to two kinds of double hull ship and confirmed that the new system was operated properly. Total working hours of the new system was very short in comparison with those of the conventional system. And then, taking account of the effects of warping in bending, the new longituginal strength theory of a hull girder is considered to have reached the stage for practical application.

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In order to calculate fatigue strength of ship structure, the calculation of stress from wave loads and ship motion is needed. DIScrete Analysis Method (called DISAM for short) is an effective method for this. Using DISAM or other methods, the structural response which affect fatigue strength (e.g. combination of stress components, shape of long-term distribution of stress) is getting clarified. However, most of the studied are limited withinlongitudinal members, for example side longitudinals. First, in this study, the calculation using DISAM is carried out in order to investigate structural response of transverse members of double hulls VLCC, with respect to fatigue strength. The modeling techniques for load discretization and finite element meshing are explained. The results are shown for some members and summarized with stress at specified cumulative exceeding probability, correlation factor and Weibull shape factor. Second, the simplified method based of the obtained results is proposed for fatigue design of transverse members of double hulls VLCC. In the simplified method, the parameters which represent load characteristics are assumed same. The correlation factors and Weibull shape factors which are obtained by the analysis are used. The difference of structure is assessed with simple FEM calculation.

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What residual stresses would be retained in ships in prolonged sea service was the theme addressed by the authors, and a 20-year-old 33,375 D.W.T. tanker was selected for the measurement of residual stresses in welded joints in its upper deck, side shell, strut, bottom transverse members, and longitudinal members. The results may be capsulized as follows, (1) The butt joints in upper deck, side shell, etc. gave residual stress readings about as high as the base metal yield stress, indicating almost no changes in their residual stress levels from the 20 years of sea service. (2) Some of the boxing-fillet-welded joints joining the stiffeners or brackets to the face plates of longitudinal members exhibited the reduction in their intrinsically high levels of welding-induced tensile residual stress, probably from the effects of high tensile loads applied. It however was indeterminable whether such tensile loads had been applied in the course of ship construction or while at sea after being commissioned in service.

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Fatigue cracks start to initiate as surface cracks at high stress/strain concentration field such as structural discontinuity parts in weld steel structures. These small surface cracks lay almost on a straight line and coalesce from repetition to repetition as the cracks advance. Finally, these cracks come to be a larger one surface crack. Single edge notched specimens with a projection in which breadth is 0.3mm at a notch root are prepared. A slit is introduced into the projection in advance. In these specimens, the projection is removed just after fatigue crack propagates at the end of projection. In this test, only one surface crack propagates at a notch root, and the configuration is obtained by means of beach marks. From this test, the changes of aspect ratio as equilibrium crack growths are investigated which may relate to a stress distribution beneath a notch root. On the other hand, we carried out fatigue tests using single edge notched specimen subjected to tension with notch radius of 0.5mm, 1mm and 2mm. During testing, ink with different colors, was permeated into crack surfaces and was dried while keeping some constant loading just below maximum load for the purpose of obtaining crack shapes and sizes at some intervals of cyclic loading. It is very difficult to analyze each crack growth because of the interference each other and crack opening/closing behavior. Therefore increase rate of K value at the deepest point of the largest crack among surface craks due to the interference effect is obtained from previous studies for surface elliptical surface cracks in a semi-infinite plate subjected to tension. Then a supposed representative surface crack of which K value at the deepest point is the same as the increased K value by the interference is obtained, which has the same depth of the largest surface crack. It becomes clear that the aspect ratio of the supposed representative surface crack emanated form a notch changes along a tangent line that touches the curve of aspect ratio for equilibrium surface crack growth from a semi-circular small crack with the depth of a grain size of micro structure. Consideration of the change of aspect ratio for the supposed representative surface cracks may play a role of the indirect consideration of the crack growth behavior for plural surface cracks emanated from a notch.

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It becomes clear that residual stress at boxing fillet weld toe at the end of stiffner can be turned to be compressive due to appropriate flame line heating and at a result, fatigue strength of the boxing fillet weld joint increases very much, in the previous paper. Moreover, the selection method for conditions of flame line heating which lead to maximum compressive residual stress at the boxing fillet weld toe is also introduced, such as the situation of heating, length of line heating, gas flow rate, travel speed of flame heating and torch hight. The above specimen does not have other stress concentrated part except the boxing fillet joint. However in case of a continuous fillet weld joint with load earring girder of which fatigue crack initiation part is usually at the fillet weld toe near the girder due to high stress concentration, large tensile residual stress generates at the fillet weld toe apart from the girder near flame line heating, even if compressive residual stress generates near the girder due to line heating. Therefore it is considered that fatigue initiation part moves to the part near line heating where stress concentration is smaller than the part near the girder. Then enhancing effect of fatigue strength may be decreased, which is studied experimentally in this paper.

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A new type of steel plate with high fracture toughness has been developed by further improving TMCP (Thermo Mechanical Control Process) technology. The steel plate possesses s__-urface layers of u__-ltra f__-ine grain microstructure (SUF) of 1 to 3 micrometers in diameter, of which thickness is one sixth of the plate thickness. The SUF provides various advantages: for example, the SUF makes it difficult for unstable brittle crack to penetrate into the plate from its surface, dramatically improves crack arrest toughness against unstable brittle crack propagation, and so on. In the present report, the fracture toughness (fracture properties against unstable brittle crack initiation from through-thickness notch) of the developed plate with SUF has been investigated. The results suggest the following: (1) Fracture toughness, Kc value in the surface layer region of the developed plate is hardly deteriorated by tensile pre-strain of about 10 to 18%. (2) A new equation has been developed in order to predict Kc value from the result of Charpy V-notch impact test using sub-size specimens. (3) It is little expected that the SUF region significantly improves the fracture toughness against the unstable crack initiation from the through-thickness notch or crack.

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In this paper, BEM analyses of potential distribution on the wall of a double bottom ballast tank (5400×2700×2200) under cathodic protection are carried out, and the reasonable number and arrangement of sacrificial anodes (70×70×600) for the cathodic protection are investigated. Based on the calculated results, following concluding points may be in order; (1) Increment of the number of anodes results in a narrow area defended by one anode and decreasing the current loss due to IR descent. Therefore, the lower limit size of the sacrificial anode for complete protection of the tank wall becomes smaller. (2) In the case that the ballast tank without coatings is cathodically protected through six anodes, those anodes should be renewed after two years. In the case of cathodic protection through ten anodes, however, the renewed period may be extended to 8 years. Therefore, the latter case is economic. (3) The ballast tank coated with tar-epoxy paint can be completely protected with one anode even for the aged coatings. (4) When 9% of the coatings were striped partly at corners of the tank, two anodes are necessary for a complete protection of the ballast tank.

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During the initial planning stage, a new artificial creation has to satisfy the functional and performance requirements. However, the recent trends toward affluence show that the needs of our society are becoming relatively more susceptible in several ways. It is considered necessary to incorporate the factors of sensitivity to human feelings and emotions into the design, and the initial design as well. With this background, the concept planning and form design of ships also become increasingly important in the initial planning stage, especially for the ship types such as cruise ships built entirely for human leisure activities. Also, for a futuristic approach towards ship constructions, such a thought process is considered extremely important. This paper tries to get a grasp of the conditions and the criteria for a form creation by conducting a research on the relationship between adjective expressions and the trends toward form designs using a multivariant analysis of information which was gathered from opinion surveys. As a typical application, some type ship models made from styrene foam and the ship profiles drawn on personal computers were used to create an algorithm for the evaluation of the retrospective impressions on the minds of the general public, which could serve as a useful pointer towards the future trends in ship form designs.

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The authors discuss aesthetic and geometric considerations for the ship design. When reading histories of ships, it is easy to confirm that they have many elegant characteristics in shapes. However, papers discussed the aesthetics of ships are rarely to be seen in bibliographies of the naval architecture. This does not mean the naval architecture don't have the philosophy "a sense of the aesthetics". In fact aesthetic characteritics of new ship are always pointed out when introducing the design profile, and thorefore the authors guess that the design process involves a sense of the aesthetics. In order to prove their guess to be right, practical processes in relation to the aesthetics are extraced from the ship design procedure, and so the meaning of the aesthetics in the procedure is made to be clear by using the Golden Section and the Dynamic Symmetry. Finally, it is geometically examined whether the Dynamic Symmetry is applied to the planning of the profile (type) of ship.

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