The double mesh method (DMM), which is a numerical technique newly developed in the numerical simulation of free surface problems by boundary element method, is applied to the finite difference solutions of Navier-Stokes equation. DMM is a numerical method in which two mesh systems are used depending on the characteristics of the equations or terms to be calculated. The viscous flow around a circular cylinder and the free surface flow around the Wigley model are calculated by DMM. It was proved that the method can greatly improve the efficiency of the finite difference method.

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The Navier-Stokes equation is directly solved by the finite-difference method to simulate 3-dimensional viscous flow fields with free-surface around a Wigley model. The body-fitted coordinates, non-staggered mesh system and the third-order upstream differencings for the convection terms are used in the present method. The solution procedure is a time-marching calculation of the velocities, followed by a solution of the pressure field in which the pressure iterations are made to reach convergence. A closer examination of the numerical scheme such as grid schemes and computing domains are made.
It is found that either a narrow domain or a coarse grid system suppresses the development of the free-surface elevation. The computational results around the bow agree well with the experimental results even though the Reynolds number is not the same, but the stern flow does not. This may be partially due to the difference in the Reynolds number.
The criterion for the sub-breaking is applied to the computed results. It detects the appearance of sub-breaking waves in the course of computation. The results corresponds to the observed free-surface flows.

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By fitting stator vanes behind a screw propeller energy loss of rotational flow in the slip stream of the propeller can be reduced and hence the propeller efficiency can be improved. Then the stator generates thrust to propel a ship. Therefore the screw propeller with the stator behind it acts as one propulsor. We call it stator-propeller in the present paper.
So far, experimental methods were used for designing stator vanes and for obtaining propulsive performances of the stator-propeller. For experiments we need scale models of the stator-propeller and the ship, and the experimental work is time-consuming and expensive.
The aims of the present research are to develop a method for theoretical calculation of propulsive performances of the stator-propeller and to develop a method for design of the stator by theoretical calculation in case that the geometry of the installed screw propeller is known.
The vortex lattice method has been employed for the above-mentioned purposes. Kerwin's roll-up model has been applied as the vortex lattice model of the screw propeller. A stator has been represented by one spanwise line vortex along with rectangular vortex rings trailing in downstream. The outside duct has been replaced by a circular vortex ring in the duct and the trailing vortex lattice cylinder in downstream.
The developed methods have been applied to two example models of the stator-propeller and the calculated performances have been compared with the results of open water tests. They have shown good agreement. The results of performance calculation show an appreciable improvement in propeller efficiency in open water and additionally the load of the screw propeller has reduced due to the effect of the stator.
The twisting angle of the stator vane designed by the developed method for theoretical design as for the same two examples has been also in good agreement with that of actual models designed by the conventional method based on experimental data of rotational angle of flow velocity in the race of the screw propeller. This fact concludes the completion of the theoretical design method of the stator-propeller.

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The singular perturbation problem of the self-similar flow around the cusped-bow ship with the circular cross-sections is discussed in the limit of vanishings of the small dimensionless parameter F, which corresponds to the Froude number. The asymptotic expansions of the velocity potential are constructed in both domains near and far from the body. In the near field, it is shown that the local waves only appear in the formal solution expanded in the ascending even powers of F. In the far field with the large spatial extent of O (1/F²), the solution satisfying the homogeneous free-surface conditions with the no appearance of the parameter F contains both the local waves and the free waves to be added up to the near field solution. The wavy potential of O (F⁷) obtained by the WKB approximation method of the solution with the satisfaction of matching to the far field solution is supplemented to the formal near field solution.

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The purpose of the present research is to develop an efficient numerical method for the calculation of potential flow and predict the wave-making hydrodynamic forces for the application to ship design. A sailing yacht is chosen for an example of practical ship, which has been designed by Nippon Challenge America's Cup Committee to aim at the next race in 1991.
The paper deals with the numerical calculation of potential flow around the sailing yacht with forward velocity and a drift angle by the new slender ship theory. Kelvin sources distributed over the hull surface are determined by solving the small matrix at each transverse section so as to satigfy the approximate hull boundary condition due to the assumption of slender body, and the calculation begins at the bow end and marches step by step to the stern end. It is seen that such a numerical procedure is efficient not only for reducing computer time but also for the accuracy of computation. Here hydrodynamic forces acting on the hull without or with a keel, wave resistance, lateral force and yaw moment are obtained by integrating pressure over the hull and the keel surface. Wave patterns in the neighborhood of the hull are calculated from the formula of wave elevation on the free surface. Thereafter those calculated results are compared with measured ones. It can be seen by the present method whether the propulsive performance of a yacht is good or not.

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A hydrofoil catamaran of 2000 displacement ton type is designed, keeping the load coefficient of the hydrofoil on the same level with that of a 200 ton type. The new system with four sets of hydrofoil shows satisfactory characteristics from the hydrodynamical viewpoints, namely, low resistance and low motion transfer functions. The experimental results suggest that the large-scale hydrofoil catamaran is one of the most feasible system for high-speed transportation. The motion control system by flaps is tested and the hydrodynamical forces in an oblique flow are studied.

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A performance index for an optimal Linear Quadratic (L Q) autopilot for minimum fuel consumption was determined. This performance index and resulting system closed-loop eigenvalues were compared with several indices (and eigenvalues) suggested by different researchers. Directives for the ideal positioning of the eigenvalues regarding the reduction of the propulsive losses and fuel consumption are discussed.

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Moriya's 1st approximate formulae to caluculate velocity distributions on blade surfaces and the lifting force of 2-dimensional blade sections in ideal flow, are popularly used in Japan. The Fourier series in the formulae, however, diverges in the calculation of blade sections with non-zero trailing edge thickness, and converges slowly in the case of non-zero trailing edge angle.
In this paper, the formulae are progressed and re-examined in some points. The main results are as follows ;
(1) Adding a logarithmic term to the mapping function, the 1st approximate formulae to caluclate the velocity on sufaces of blade sections with non-zero thickness at the trailing edge, are obtained. In the case of such blade sections, assuming that the pressure at the trailing edge surface is to be same as one at infinite distance, the thrust force is disappeared.
(2) Calculating the terms concerning to trailing edge angle separately, the Fourier series converges rapidly. The logarithmic singularity, however, appears in the terms.
(3) Formulae presented here are equivalent to the Hanaoka's formulae.
(4) The effect of blade thickness on the lifting force is disappeared, due to the approximation of the formulae shown in this paper.

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Hydrodynamic modeling of trailing vortex wake of a propeller is one of the most important factors in developing a propeller theory. A variety of trailing vortex wake models have been proposed hitherto. However, details of geometrical features have not been known clearly.
In the present study, flow fields around propeller are precisely measured in a cavitation tunnel by use of a 3-component Laser Doppler Velocimeter (LDV). Based on the experimental finding that pitch of tip vortices is smaller than that of helical trailing vortex sheets, a new wake model of trailing vortices is proposed to improve the existing surface panel methods for hydrodynamic analysis of propeller. Then, the flow fields around propeller are calculated by using the improved surface panel method, and it is shown that the predicted flow fields around propeller are in good agreement with the measured ones.

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In order to improve theoretical prediction of propeller induced pressure fluctuations, it is indispensable to investigate the behaviour of unsteady cavity on the propeller blades, since the pressure fluctuations are roughly in proportion to the second time derivative of the cavity volume. To this end, several methods of measuring cavity shape have been proposed such as using stereo photography, pin gauge and laser beam scattering.
This paper describes a highly advanced method of measuring the three-dimensional cavity shape using a laser beam coupled with a CCD (Charge Coupled Device) camera and image processor to make measurement faster and more detailed. Model experiments on two propellers-a conventional and a highly skewed propeller-of a training ship SEIUN-MARU have endorsed the usefulness of the present measurement technique both in its speed and accuracy.
Further, some features of cavity behaviour of highly skewed propellers have been found in terms of cavity thickness distribution and its variation over the blades and the blade angle positions.

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New statistical theory was developed by the authors in the previous paper, which gives probability density function (p. d. f.) and extreme values of total second order responses of moored vessels in random seas. It assumes the response represented in the form of two term Volterra functional series and is based on the generalized Laguerre polynomial expansion of p. d. f. of which the first term is a gamma p. d. f. consisting of three parameters.
This paper shows non-normality of surge responses of moored tanker and semi-submersible measured in a wave basin, and determines that the theory estimates it very well. Furthermore effect of time varying wave drift damping and other slow motion hydrodynamic force coefficients on p. d. f. and extreme values are discussed by time domain simulations. This effect cannot be represented in the form of two term Volterra functional series.

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In this paper, the characteristics of dynamic behaviour of double-articulated columns in regular waves is investigated with special emphasis being laid on the effect of static restoring force of columns on the dynamic behaviour of the column itself as well as the behaviour of total system including a moored tanker. For the numerical analysis of the behaviour of articulated columns without a moored tanker, two different methods, that is to say, double-pendulum approach and constraint matrix method are simultaneously utilized, but for the analysis of total system including a moored tanker the latter method was applied. From comparison between the predicted behaviour and the result of experiments performed in a water basin, it was found that both analytical methods are of use for predicting the dynamic behaviour of articulated columns. Furthermore, it was concluded that as far as the present investigation is concerned, the difference in the static restoring force characteristics of the column does not bring about serious differences in the response characteristics of the present mooring system in regular waves. However, it must be kept in mind that the static restoring force of the column should be large enough to avoid an excessive submersion of the buoy caused by the wave drifting force acting on a moored tanker.

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A numerical procedure is described for predicting the motions and the structural responses of huge offshore structures supported by a large number of three-dimensional floating bodies of arbitrary shape in waves. The developed numerical approach which is accurate in linear system is based on combination of a three-dimensional source distribution method, wave interaction theory and the finite element method of using the space frame element. Numerical results are compared with the experimental ones of the structural responses of a freely floating semisubmersible type structure supported by 8 lowerhulls and 16 columns in shallow water. The results of comparison confirmed the validity of the proposed approach. The method presented is applicable to huge structures for ocean space utilization which seem to be brought into practical use in the future.

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In the previous paper, the 1st-order motion responses of semi-submersibles in short-crested directional spectra waves were investigated. This paper presents results of an investigation into the 2nd-order responses such as slow drift oscillations in directional waves.
Model tests in various kinds of directional waves which have specified power spectra and directional spreading, were carried out with spring moored and catenary moored conditions. Test results in directional waves are compared with those in uni-directional (long-crested) waves, and the influence of wave directionality on drift forces, low-frequency oscillations etc. are investigated.
In order to estimate the 2nd-order responses in directional waves, new practical methods are proposed. These are based on the Pinkster's expression' of the low-frequency drift force spectrum in directional waves. By approximating the estimation of quadratic transfer functions of the mean drift force in two-directional cross regular waves, mean and low-frequency drift forces in directional spectra waves can be estimated practically. The applicability of these methods are investigated by comparing estimated 2nd-order sway responses with experimental measurements.

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Time domain simulations of slow drift motion are compared with model experiments in wave basin. The simulations include various slow motion hydrodynamic forces such as drag coefficient depending on Kc number, time varying wave drift damping, added mass change due to waves etc. as well as second order wave excitation. Most of them are given by slow motion forced oscillation tests in regular waves. The simulation and the model experiments are carried out for two types of floating structures moored in bi-chromatic or irregular waves.
They show excellent agreement with the experiments. It is clarified that importance of each slow motion hydrodynamic forces on the slow drift oscillation in irregular waves of a moored floating vessel depends on a type of vessel. Wave drift damping affects significantly the tuned motion amplitude of not only a barge but also a semi-submersible. Added mass change due to waves affects the tuned frequency only for a semi-submersible.

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Dynamic tensions of mooring lines may be ignored in the estimation of wave frequency motions of a floating structure, but for slow drift oscillations hydrodynamic forces acting on mooring lines are important, because drag forces acting on mooring lines act as the damping force and have a great effect on the slow drift oscillation.
When dynamic tensions of mooring lines are calculated in full consideration of added mass forces and drag forces acting on mooring lines, a numerical calculation such as Lumped Mass Method is usually used. The numerical calculation needs prohibitively long computer time and it is not practical in the early stage of the design of a floating structure. The authors had developed an Approximate Method for calculating the dynamic tension taking the added mass force and drag force into consideration. A remarkable feature of this calculation method is its short computation time, and the accuracy of the approximate method has been confirmed by comparing calculated results with experiments. The original form of the Approximate Method was applicable to the only frequency domain problem and therefore it was impossible to apply the calculation method to the problem in irregular waves.
In this paper a Modified Approximate Method extended to the time domain problem is presented. The calculated results of the slow drift oscillation of a floating structure and dynamic tensions of mooring lines obtained by using the extended approximate method are compared with the experimental ones. The calculated results are in good agreements with experimental ones.

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The wave measuring system applying laser beams for wave surface probes were recently developed by Experimental Tank of Yokohama National University. Laser spot projectors are set as the wave probe array under water, and He-Ne laser beams are projected vertically upward from each projectors. Images of laser spots on the wave surface are taken by a video camera, and that video pictures are processed and the digital informations of wave heights or wave slopes are obtained from processed video signals. These measured timeseries converted to the wave timehistories of multi positions by a personal computer in real time, and the directional wave spectrum is estimated by the Maximum Likelihood Method. Moreover the hard copies of 3-D graphs of directional spectra are got immediately.
In this paper, principles of these new measuring systems and related numerical calculus are mentioned. And the measured examples in the Experimental Tank of Yokohama National University by these systems are shown.
Consequently, these new systems showed the excellent abilities and performances.

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A new numerical evaluation scheme is developed of the Green function which is essential in the boundary-value problem of the motions of a ship with forward speed in waves. The single integral expression derived by Bessho' is used and its integration is performed along the path of steepest descent on which the integrand does not oscillate. Using this numerical steepest-descent method, we can evaluate the Green function with less computing time as well as enough accuracy, even if both of the field and source points are close to the free surface.
With this efficient scheme incorporated in the panel method, radiation and diffraction problems are solved for a submerged spheroid. Convergence and accuracy of the solution are numerically checked by increasing the number of discretized panels on the body.
In the radiation problem, contributions of the steady perturbation potential to the body boundary condition and to the unsteady pressure are consistently taken into account. These effects on the added-mass and damping coefficients are investigated by comparing the obtained results with another numerical results taking only the unform-flow contribution into consideration. In the diffraction problem, computations are performed for the wave exciting forces and the diffraction wave pattern on the free surface. These computed results are compared with corresponding experiments measured by the authors, and found to be in favorable agreement.

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Using a three dimensional source technique counted in forward speed, the heave and pitch hydrodynamic coefficients of slender ship model are evaluated. The ship model has a length to breadth ratio of 8.0, Lewis form section and block coefficient of 0.5. Matsunaga et al. show its experimental results and numerical works by slender ship theory.
Comparisons of the theoretical predictions and experimental results are discussed. The numerical results of three dimensional source technique are the best fit to the experimental ones in comparing with new strip method and Matsunaga's works by slender ship theory.
The influence of forward speed upon heave added mass distribution of the model are also discussed by three dimensional source technique.

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The added resistance in regular head waves at low forward speed acting on a huge bulk carrier is evaluated by using three dimensional source technique with forward speed. The numerical results are compared with measured data and are also compared with the calculated value of slender ship theory.
The added resistance at low forward speed predicted by three dimensional source technique is much better agreement with measured ones than that by slender ship theory.
Using added resistance data in regular waves ship speed in a seaway is also evaluated.
The evaluated ship speed in regular moderate seas based on slender ship theory is in good agreement with ones based on a measured added resistance. In rough seas, however, the estimated speed loss obtained by using slender ship theory is too high to use. This is because of the error of added resistance at low forward speed. On the other hand, speed loss in rough seas estimated by based on three dimensional source technique is fairly good.

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As a continuation to our previuos report on tank testing results of ship motions in directional spectrum waves this paper presents further test results under 'following sea' condition. Uniform irregular waves with arbitrary directional spectrum have been generated in the whole area of towing tank of Yokohama National University by the newly installed snake type wave maker and running tests have been carried out at Froude numbers 0.2 and 0.275. The experimental data have been analyzed at encounter frequency base using both Fast Fourier Transformation (FFT) and Maximum Entropy Method (MEM) to obtain the power spectrum of motions and the results are presented along with the theoretical estimates. Directional transfer functions of motions have been calculated using well known New Strip Method (NSM) and analyzed directional wave spectra obtained from experimental data by Maximum Likelihood Method (MLM) have been used to estimate theorectical motion spectra. The compared results show fairly good agreement.
This paper also presents short term prediction of motions calculated for both 'head sea' and 'following sea' conditions over venous range of wave periods.

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It is of importance to design a ship which has a good seakeeping performance in her sea-lane. It is, however, hard to say that an optimization of the hull form for seakeeping performance has been sufficiently carried out from the seakeeping point of view at the initial design stage of a merchant ship so far, because it has been difficult to make clear the seakeeping criteria and the correlation between the hull forms and the seakeeping qualities.
In this paper the author derives the regression equation to estimate the correlation between the hull forms and the seakeeping qualities by applying the Bales' procedure to the container ships. He provides the guidelines to optimize the hull form for the seakeeping performance and the added resistance in irregular waves. The calculation is made to determine the hull forms in accordance with the above guidelines, and finally the optimized hull form is shown for the seakeeping performance and the added resistance. It is concluded that the present method is very easy and useful in the early stage of ship design for determining the dimensions of a new ship which has a good seakeeping performance and a small added resistance.

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Ship length of VLCC is long compared with sea wave length. Hydrodynamic pressures on a full ship in short waves are measured to investigate the wave loads of VLCC. The predicted hydrodynamic pressure distributions at some sections with New Strip Method (NSM) and 3 Dimensional Source Sink Method (3DM) are compared with the measured ones. The predicted results with NSM are not in good agreement with the measured ones in short waves. But, the predicted results with NSM with longitudinal cut are in good agreement with the measured ones only in short waves and the predicted results with 3DM are in good agreement with the measured ones in whole wave frequencies. From the above results, it is found that the diffracted wave from the bow and the bottom is important term to estimate the wave loads and the hydrodynamic pressures in short waves. These diffracted waves are not taken into consideration for the strip method. The modified method for the diffracted wave term of NSM is developed with the diffracted waves calculated with 3DM for the ships with different length beam ratios. The predicted pressure distributions with this modified method for NSM are in good agreement with the measured pressure distributions in whole wave frequencies.

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A model test was conducted for models with two kinds of bow flare form in both regular and irregular waves in order to obtain information on effects of the bow flare to the deck wetness and asymmetry of the vertical wave bending moment. The model was made of synthetic resins so as to simulate bending rigidity of a full scale ship. The measured results are analysed to give the intensity of impact pressure in the bow, the frequency of the deck wetness and green sea and the asymmetry of the bending moment. Discussions are given to the effectiveness of the flare form against the deck wetness and the estimation method of nonlinearity of the bending moment.

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In the previous papers, the surf-riding of a ship in the regular following waves was examined by the self-running model tests as well as the numerical simulatione. It was clarified that the surf-riding occurs when the ship speed including the steady oscillatory component due to the surging motion, after the decay of the transitional motion, reaches the phase velocity of the wave. The numerical simulation showed that concerning the occurrence of the surf-riding there exist three ranges of the ship speed for the fixed wave condition. Under the critical speed V_1Cr, the ship never makes the surf-riding but invariably makes the periodic surging motion. At the speed between V_1Cr and another critical speed V₁, the ship sometimes makes the periodic surging motion and sometimes makes the surf-riding motion. Which motion occurs is dependent on the initial conditions of the ship position relative to the wave trough and the surging velocity of the ship. Over the critical speed V₁ the ship always drops into the surf-riding condition. It was also shown that for the low wave height, the critical speed V_1Crcoincides with another critical speed V₁ It was not clarified how the critical speed V₁ appears.
In order to make clear totally the non-linear phenomenon like the surf-riding, it is not sufficient to repeat the numerical simulations for the various initial conditions. It is necessary to use the common method of a phase plane analysis for the non-linear ordinary differential equation which expresses the surf-riding motion. In the present paper, the author examines the mechanism of the surf-riding by means of the phase plane analysis and clarifies how the speed range is separated into three parts and how the wave parameter affects the separation. The method is presented to obtain the above critical speed V_1r, which may be termed as the unconditional critical speed for the occurrence of the surf-riding. It is important to know the speed at which the ship can escape from dangerous surf-riding condition. The speed is named as the pull out speed following the analogy with the pull out torque of the synchronous motor, and the chart to obtain the pull out speed is also presented. Showing the analogy with other physical phenomena such as the Josephson effect in the superconductivity, the synchronous motor and the driven damped pendulum, the surf-riding is suggested to be one of the fundamental non-linear phenomenon in the physical science.

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This paper describes a procedure for shape design sensitivity analysis of elastoplastic structuralresponse in plane stress field using the incremental solution scheme, which is briefed as follows ;
(1) State equation in the incremental form is differentiated with respect to design variables. The co-ordinates of nodal points and the thicknesses of elements are considered as the design variables.
(2) The increments of sensitivities of nodal displacements with respect to the design variables are derived at every load step. The sensitivities of nodal displacements are evaluated as the sum of their increments.
(3) In the differentiation of stiffness matrix and stress components, the differentiation of the stress-strain matrix has to be considered for the plastic element.
The method of reanalysis is also shown based on the Taylor Series Expansion Method.
Based on a few sample calcuations, it has been found that ;
(1) For the sensitivities of the first and the second-order, satisfactory results are obtained for simple calculation models.
(2) The results of reanalysis are different from the exact solutions when large changes are imposed on the values of design variables.
(3) The CPU time to calculate first-order sensitivity is less than 10 % of that for ordinary stress analysis. On the contrary, the CPU time for second-order sensitivity rapidly increases with increase in the number of design variables.

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The present study is concerned with the development of a finite element program for collapse analysis of three-dimensional framed structures under static loading, which has the following features :
(1) A linear Timoshenko beam-column element is employed with a variable location of an integration point, which is equivalent to the beam bending element including the effect of shear deformation in the RBSM (Rigid Bodies-Spring Models) family, and can be considered to be suitable to the analysis of highly nonlinear problems including crush analysis.
(2) The program is equipped with the updated Lagrangian formulation as well as the total Lagrangian formulation, the former of which is used in the crush analysis accompanied by extremely large rotations and strains, and the latter is used in the ultimate strength analysis with moderately large deformations.
(3) A formulation using generalized stresses is adopted for the derivation of incremental stiffness equations, and the yield functions expressed in terms of resultant forces are assumed in the elastoplastic analysis, from a point of view of the generalization of the method of limit analysis.
Numerical studies for crush as well as elastica and inelastic stability problems are conducted to show the validity of the developed code. The treatment of strain-hardening and the experimental verifications for the crush analysis will be contained in a further report.

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Load carrying capacity of a tubular member with a circumferential through-thickness crack is investigated. Firstly, a series of pure bending tests is carried out. Then, based on the experimental results, generation phase analysis is performed using the finite element method. In the analysis, both material and geometrical non-linearities are taken into account. Application phase analysis is also performed considering the J-integral and the crack opening angle as initiation and propagation conditions of a crack, respectively. It has been found that ;
(1) Load carrying capacity and rigidity decrease due to the presence of a crack.
(2) Ultimate strength is attained after the crack propagation starts.
(3) Higher ultimate strength is attained with higher critical value of J-Integral.
(4) The decrease in load carrying capacity is observed to be more with lower value of critical crack opening angle.

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A computer program is developed to assess the reliability of structural members considering the deterioration of resistance due to environmental effects (random loading, fatigue, corrosion).
Markov Chain Model (MCM) is applied as the theory which governs deterioration of resistance caused by fatigue crack or corrosion damage. Stationary MCM is applied to the reliability assessment of structures in the air. Probability of existence of initial defects and the probability distribution of the defect size are considered in the initial state vector of MCM. The crack initiation and propagation processes are incorporated into the transition matrix of a single MCM. As the absorbing event (failure event) of the matrix, leak failure, plastic collapse or brittle failure from critical component is considered. In order to deal with the uncertainty due to random load, marginal integration technique is employed. Nonstationary MCM is applied to the reliability assessment of structures in corrosive environment, where the effects of corrosion fatigue properties and the reduction of plate thickness on the reliability of structures are taken into consideration.
The advantage of using MCM is that the inspection procedure can be treated easily in the analysis. In the program, effects of pre-service inspection (PSI) and periodic or non-periodic in-service inspections (ISI) on the structural reliability can be evaluated.
The program is applicable to the actual structures as a support system for fatigue design and inspection maintenance.

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This paper is concerned with reliability assessment of ship main structures, which are modelled as spatial frame structures and subjected to quasi-static extreme loads, based on ultimate strength analysis. Ultimate strength of the structure is evaluated by using a linearized plasticity condition of the section of the structural element under the combined effect of internal forces and moments to generate the safety margins of structural failure modes, using a matrix method and plastic node method. Probabilistically dominant collapse modes are selected by applying the so-called branch-andbound method combined with heuristic operations. The above methods are successfully applied to main structures of a large tanker (240, 000DWT) under various notional loading conditions. Probabilistic properties of ultimate strength of ship main structures are investigated through the numerical examples and comparison with previous results for plane frame models.

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This paper describes the applicability of Level II method in reliability engineering to ship strength design and two application examples.
In the case of non-buckling-damaged upper deck plates, the safety index is greater than 4. In addition, the buckling strength reliability of upper deck plates does not decrease even if ship design philosophy changes from use of mild steel to use of high-tensile-strength steel.
On the other hand, in the case of fatigue-damaged cruciform joints, the critical safety index was estimated to be about 3.13.6. Furthermore, effect of load probability distribution on the fatigue strength reliability was also made clear.
Finally, the partial-safety-factor design formulas were derived for the buckling strength and the fatigue strength of ship structures considering the safety index.

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Since Bauer and the authors presented the paper showing that the sloshing of water in a tank acts as dynamic damper for reducing vibration, a lot of investigations have been carried out by civil engineers. Tuned sloshing damper (TSD) is not only simple and free of maintenance, but also available for reducing vibration. The authors showed that measured damper effect was in good agreement with one calculated by the authors' theory, in which the sloshing mechanism was simulated mass-spring systems.
This paper deals with experimental investigation into the characteristics and the damper effect of TSD. The authors carried out systematically model test by using the TSD models and the tower models. The authors obtained the conclusions that the natural frequency of TSD increases as the amplitude of excited vibration but wave height response of water in TSD decreases, and the improved theory gives theoretical coupled natural frequency and response in good agreement with the measured one.

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A numerical method is developed to simulate the bow flare slamming of fast ships. Curved ship body boundary is represented by the Porocity method within the constraints of a rectangular grid system. Numerical simulations are conducted using a cross section of a typical container ship with a large bow flare and the simulations are compared with model experiments. The results of the computed and measured pressure histories are comparable. Conventional slamming theories based on self-similarity, on the other hand, fail to predict the measured pressure on the flare. From the experiments and simulations the authors found that high pressure persists for a long duration of time without any sharp peak on the bow flare. Large scale structural damage might be caused by this pressure since it increases simultaneously over an extensive area on the flare when the upper part of the flare comes into contact with water.

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The boundary element method is extended to simulate the non-linear sloshing of liquid in a three dimensional tank. In the proposed method, higher-order element (cubic spline element) is employed for discretization of the boundary integral equation in order to improve the accuracy of numerical solutions. And, the perturbation method is introduced for the purpose of saving the computing time. The details of the boundary element technique are described in reference to formations of cubic spline element.
Several numerical examples are presented for liquid-sloshing in prismatic and spherical tanks subjected to forced oscillations, and are compared with the experimental results, furthermore, the usefulness of the proposed method is discussed.

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Various types of underwater line structures, such as mooring lines, towing lines, flexible risers and oil fences, have been used widely in the ocean. Needless to say, theoretical and/or experimental studies are important to design safe and economical line structures.
Many investigations into static and dynamic responses of underwater line structures were made and general-purpose computer programs have been developed using the numerical analysis method, i. e. the finite element method or the lumped mass method. Although, it would be difficult to frequently use these programs because of time and cost savings. At the initial stage of designing the underwater line structures, a more simple method is preferable.
In this paper, extensible catenary equations are derived and the fundamental characteristics of catenary are discussed. Next, the ways to solve the equations under various boundary conditions are described. Finally, the examples of its applications are briefly shown.

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At present, the most reliable fatigue design for structures subjected to service loading is considered to be one based on fatigue strength diagrams. These diagrams would have to be obtained from actual service loading fatigue tests or random loading fatigue tests simulating service loading. However, it would take a very long time to complete the necessary experiments, so long as to be impossible.
In the previous paper, the authors proposed a new method of developing fatigue strength diagrams under random loading conditions. This method combines random loading test plus an equation, and promises to reduce by 95-99 percent the time required for ordinary random loading fatigue tests with the Weibull distribution.
In this paper, using the proposed method, fatigue strength diagrams for butt and fillet welds of mild steel were obtained for load-controlled axial pulsating tension random loading with the Weibull distribution. Shape coefficient in the Weibull distribution was chosen to be 0.75, 1.0 and 1.25. Strength diagrams with these welds were also derived by means of UKDOE Guidance and AWS Code.
The main results obtained in this study are as follows.
1) Fatigue strength diagrams, represented by shape coefficients as a parameter, are approximated by paralell straight lines in semi-log coordinate.
2) Fatigue strength decreases by about ten precent or fatigue life about one-hundredth as shape coefficient increases by 0.25, from 0.75 to 1.25.
3) Strength diagrams for both welds, obtained by those two organizations, lead to divergent final designs.

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In order to preserve the structural integrity against brittle fracture, structural materials should be selected based on the proper evaluations of the fracture toughness of materials and of the near tip field parameters of a crack by an appropriate stress analysis. In welded structures there exist some difficulties in achieving the procedure. The precise evaluation of the fracture toughness of materials is not a simple task, if a welding process induces the spatially distributed inhomogeneous material degradation such as the locally restrained decrease of the fracture toughness in the heat affected zone. Considering a brittle crack initiated and propagating along a welded joint, it sometimes exhibits sharply curved paths and penetrates into the base material, while in other cases it propagates in a straight fashion along the welded joint. It is clear from these observations that the prediction of brittle crack paths is essential for the evaluation of fracture toughness of welded structures.
In the present paper a mathematical model is proposed for the crack path prediction, in which the combined effects of applied stresses, welding residual stresses, and material degradation in the so-called heat affected zone are taken into account. In the present model a homogeneous fracture toughness is assumed in both the base and weld materials, where the crack path is predicted by the local symmetry criterion (K_II =0) based on the first order perturbation solution of a slightly kinked and curved crack. When a curved crack propagating in a weld material intersects the heat affected zone which is modelled as a line degradation zone, a quastion arises as to whether the crack extends along the heat affected zone, or whether it penetrates into the base material. Since the local symmetry criterion does not work at this point, the crack growth direction is predicted by the minimum principle of the total potential energy. The relevant energy calculations can easily be performed by using the second order perturbation solution of a kinked crack.
Numerical results show that if brittle fracture occurs under a relatively low applied stress in comparison with the longitudinal welding residual stress, and if the average material degradation along the heat affected zone is small, crack paths tend to deviate from the welded joint. This is the case actually observed for brittle fracture of welded plates made of mild steel, where cracks extend in the base material. It is also shown that cracks tend to propagate along the heat affected zone with increasing the applied stress and materials degradation levels, which may possibly simulate certain brittle fracture of welded plates made of high tensile steel.

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The development and applications of an arc-welding robot for Shipbuilding sub-assembly works are studied here.
Robots for such purposses should require only a minimum teaching time and should be able to track out deviations in welding lines. Moreover they should be flexible enough to accommodate for larger constructions and different workpiece laying positions, according to changed production schedules.
A large gantry type Arc-welding robot with robot language capability has been newly developed and the new application engineering for this robot has been studied and incorporated in the macro program with the task level robot language functions.
The robot and the application engineering shows the following remarkable features :
(1) Teaching items for the task level macro programs are reduced to 1/35th of the original.
(2) Almost the entire weldings, including corner weldings, can be performed by robots throughout the sub-assembly works.
(3) More freedom for sub-assembly laying positions, without altering the welding programs. Thus, the sub-assembly works having complicated stiffener arrangements can be welded by the robot with a 75 % reduction in the welding man-hour.

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In this paper, the representation method of ship hull and the modification and fairing expert system is discussed.
In this research, we represent ship hull by normalized B-spline surface. Instead of representing the entire hull by a single surface, we devided it into several parts and represent them seperately. The degrees of continuity between seperate surfaces are normally Gl, and at some places only G 0 is obtainable.
It is usually generate B-spline surface from points which consist of mesh in the surface. An algorithm for generating surface from the mesh curves is developed. With it, we can use water line and station line directly to generate the hull surface. For shape modification of the ship hull surface, an object oriented shape modification and fairing paradigm is proposed to overcome the difficulty of flexibility and consistency caused by the complexity of data structures and the relations between data. Upon that paradigm, a test water line and station line modification and fairing expert system is developed and some results are provided.

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The process planning expert system for the plate structure is discussed in this paper. The partitioned structure to be built is expressed in terms of the Entity-Relationship model and the rule-based production system is applied to represent human experts for the process planning. The whole system including the rule-based production system is made on the Smalltalk-80 environment.
The proposed system is applied to the double bottom structure of the ship and results obtained seem fairly appropriate for the production.

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Nowadays integrated systems for manufacturing, namely CIM systems : Computer Integrated Manufacturing systems, are required in many industrial fields to meet their heavy requirements. Also in the shipbuilding field, we believe that CIM can be very beneficial. In this paper, it was made clear what kind of information is required for building a CIM system especially from the point of view of manufacturing planning and control of shipbuilding. Then the model representation of a shipyard, SYMFONIC, Ship Yard Model FOr PlanNIng and sCheduling, was proposed.
With the model, SYMFONIC, we propose a basic system for planning and scheduling, which is based on an Object-oriented representation, and Rule-based programming.

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Shipbuilding industry has long been devoting to complete CAD/CAM systems in the stage of design and fabrication. However it is often said even now that elaborating engineering works are needed to manage CAD/CAM systems.
In recent years, the necessity of computer integrated manufacturing system in shipbuilding industry has been recognized in our shipyards. Ship research committee 210 of Japan Shipbuilding Research Assoiation organized the feasibility study of computer integrated design and manufacturing in 1987. In order to integrate CAD/CAM system, product modeling and expert systems were taken as the most important themes in the project.
The aim of our paper is to propose one example of a product model of ship. The model should be as flexible as possible because it is used as a model not only in design stage but also in manufacturing stage.
Object oriented concept is used to represent a ship model. Two types of objects are introduced in our paper. One is body object which states geometrical properties and its attributes. The other is connection object which states the connection relation of body object A with object B.
Concepts of cutting of designed ship structure into pieces and assembling those pieces to a ship block are also introduced here.
It can be said that the ship model proposed here can be used in the design and manufacturing stages.

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Several constrained problems with a number of design factors are to be solved in the design stage of a ship equipment. Generally, the design factors connected with a ship equipment have a tendency of fuzziness and randomness. In spite of this, the actual design is usually based upon the typical values of these factors. A more practical choice for analyzing these indeterminable problems is to use the theory of fuzzy sets and extended operations.
This paper presents an analytical method which is covenient to deal with these indeterminable problems by a combinations of many small scatters in the design factors, using the Cartesian products of fuzzy sets. As an example, the proposed method is applied to the system that collects oil and water through the bottom structures in cargo oil tanks or water ballast tanks, to calculate the pumping hours and the quantity of residual fluids. Further, the drain collecting system is evaluated from the viewpoint of determining an optimal location for the bellmouth and a pattern of the drain course, using the fuzzy multi-criteria analysis.

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Growing the demand for new generation of automation in ship navigation and for various assessments in harbours and waterways, so-called fast-time simulation technique becomes important as well as man-in-the-loop simulation such as ship handling simulator experiments.
In the fast-time simulation technique, the mathematical model of the ship dynamics in various environmental conditions should be of course carefully investigated, but the modelling of navigators is another important factor which governs the inputs of simulation. In this paper the authors have developed an automatic navigation system called SAFES in combination of fuzzy theory and expert system, which is applicable to automation of ship navigation and also to the modelling of navigators in the fast-time simulation. The system can treat various ship operations in open sea and restricted waterways as well as under multi-ship encounters. Some results of the application of SAFES are shown, which were actually used for certain assessment and design of waterways.
In the modelling of ship navigators, fuzzy control and reasoning are used for the basic controls such as course-keeping, course-changing and path-keeping, and for the reasoning of collision risk between other ships and boundary of navigational lane. Further in the path-keeping algorythm, fuzzy reasoning of the nearness to the course-changing point is included. It is not necessary to introduce fuzzy control even in course-keeping, but it is found that fuzzy autopilot can operate smoothly from course-keeping to course-changing and vice versa without large overshoot nor slow settling. The describable knowledge of ship navigators for ship operation and process control is represented in the rule base of the expert system.
As conclusions of the paper, the authors can point out the following two points as well as the availability of the proposed system. As the first point, the expert system approach is essential for the description of complicated navigators' decision process, which cannot be easily implimented in the sequential programming style such as in FORTRAN. On the contrary, each function of navigators' orders and behaviour of helmsmen may be represented also by non-fuzzy description. However, the authors would like to stress as the second point that once we prepare a general-purpose fuzzy controller/reasoner which passes one fuzzy output from two fuzzy inputs, almost all functions can be easily handled by fuzzy control/reasoning, because most functions of human operation are originally given by only fuzzy descriptions.

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Recent progress in computer technology, especially in Al field, is remarkable and it enables the automation in judgment and decision-making by means of knowledge-based system. A big project on development of an intelligent ship has been carried out in Japan. It is a highly automated ship with an artificial intelligence onboard. For its realization, a thorough assessment and social acceptance is essential as well as the solution of the technical problems, because it is a large scaled system after an entirely new concept. Diversification for sense of value in modern society requires a rational procedure and concrete measures for the assessment when a new system is introduced. For the consensus it is preferable to make the measures as objective as possible. Concrete safety evaluation method has not been established yet, though it is strongly expected.
An evaluation method for an automatic navigation system of the intelligent ship by means of synthetic evaluation function and computer simulation has been studied. Results of the conceptual study are presented here in Part 1.
Ship safety at seas is defined by two factors. They are the potential danger of collision or stranding of the navigation area, and total ability for collision avoidance by maneuverability of the ship and skillful ship operation. Systematic approach for the safety evaluation is introduced.
Both of subjective and objective aspect of evaluation are necessary for the thorough assessment. Once the factors for evaluation and evaluation function are identified, simulation results after a well-defined scenario, which contains typical ship encounters, natural and geographical conditions and some events necessary for navigation, leads indices of safety and total performance of the system by a routine procedure. These indices are objective elements of the evaluation. Hierarchical analyses for the safety and related factors based on subjective and relative evaluation between two factors, is a powerful method to build up a rational and objective evaluation function.
On the other hand subjective factors are also important and essential for the safety evaluation. It is much more difficult to take the subjective elements into the evaluation. Computer graphics offer useful information for the judgment to the experts who perform the evaluation. Real time simulation with realistic models and environmental conditions is also helpful for the evaluation by experts because they can see and examine it as if a real system is working.
Official standard for the safety assessment should be equipped with a sufficient scientific, social and political background. A concept for the safety assessment and its standard is shown, which is helpful for the establishment of the administrative measures by the authority of the government.

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There are various factors to be taken into account for the objective safety evaluation and comprehensive performance evaluation of an automatic ship navigation system. A computer simulation is an effective tool for the safety assessment.
A new computer system suitable for the simulation of the ship navigation and marine traffic is designed and built. The simulation system is composed of a network of different kinds of computers one is for numerical calculation using FORTRAN, the second for knowledge processing and the others are graphic work-stations.
Realistic representation of environmental conditions, such as natural, geographical and vessel traffic condition, and suitable modeling of ship motion and judgment and decision-making for ship operation are essential for the evaluation. Simulation monitors by CGI technique are also effective for the subjective evaluation of the simulation results.
Composition and features of the simulation system are introduced here. The real time simulation system with multi-process type is driven by simulation scenario, which contains various for the evaluation. The simulation of an automatic ship navigation in Tokyo Bay shows satisfactory results. The system is expected as a powerful tool for the concrete safety evaluation of the navigation system.

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The Rankine bottoming plant is a cost-effective means of energy saving on motor ships. However, drastic improvement in specific fuel consumption of main diesel engines caused a large reduction in its exhaust gas energy, hence made difficult to apply conventional bottoming plant. The author carried out research & development towards advanced heat recovery systems by introducing new ideas and made success in realizing dual steam pressure system in 1978, mixed pressure turbo-generator system in 1982, hot water heat recovery & flash steam turbine system in 1984 and finally combined steam & gas turbine generator system in 1986. The overall thermal efficiency of a diesel propulsion plant was improved from 40 % to 54 % in terms of propulsive power generation and from 51 % to 62 % in terms of cogeneration. The vessels equipped with advanced heat recovery systems amount to 136 vessels at the end of September 1988.

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A study of scattering of underwater sound by a rigid object near an interface is provided. The target's scattering angular pattern versus monostatic variable angles of incidence is calculated. The method used in the calculations is the boundary integral equation method (BIEM) and the target is a semi-submerged sphere which is chosen as a special case of the boundary problem in a stratiform region.
An examination of scatterd echos by the rigid sphere on a free surface in pulsative incident waves is also presented. Angular distributions of sound pressure are shown and numerical results are compared with the experiments. It is observed that the calculated values agree qualitatively with experimental results.

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DRAKE (Depth and Roll Adjustable Kite for measuring Energy flux of the Kuroshio) is a towed vehicle developed to carry an acoustic doppler current profiler and CTD sensor (Conductibity-, temperature- and depth-sensor). The current profiler demands a high level of stability in pitch, roll and heave of the towed vehicle, so that the main wings and the tail wings are controlled automatically to maintain the submerged depth and roll stability.
In the previous report the authors discussed a simulation technique for estimating motions of the towed vehicle and cable.
In this paper the structure of the towed vehicle DRAKE and the performance confirmed by experiments on the observation line across the Kuroshio are described. In the experiments, four kinds of tests are carried out. The first one is the towing test for investigating the static characteristics of DRAKE, such as the main wing angle, trim angle and cable tension versus a command depth. The second one is the steady towing test for the study of the stability of motions of DRAKE when the mother ship is advancing in irregular waves. The third one is the depth change test for the study of the stability of DRAKE in transient motions. The fourth one is the turning test holding a constant depth controlled by automatically produced command signal. These experiments indicated that the performance obtained in experiments are in good agreements with those of theoretical estimations obtained by the previous report.

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In the previous study, basic methods to estimate motion or attitude of the vehicle (camera), i. e. ego motion, from video image data obtained continuously by a video recorder are investigated, and several alternative methods to estimate the vehicle motion are evaluated by sample pictures. From the study, possibility of the ego motion estimation at the sea bottom, where few landmarks exist and images are not so clear, is assured for the case human operator can recognize the motion visually, using full information and selecting appropriate estimating points.
In this study, more effective iterative estimating algorithm based on the Extended Kalman Filter is studied, and the availability of the method is evaluated by applying them to continuous video image data obtained from a camera moving in a two dimensional horizontal plane. By choosing appropriate filtering pamameters, it is possible to get the accurate estimation within 1/3 of computing time needed for the previous methods.

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