When high speed vessels are discussused, one may usually think of dynamically supported vessels such as hydrofoil crafts, hovercrafts, etc. These types of vessel, however, have restrictions in terms of deadweight and cruising range.
In order to clear these restrictions, the concept of displacement type monohull vessel suitable for high speed navigation has been investigated.
This paper presents the outlines of its conceptual design of about 10, 000 M. T. displacement calss.
This paper also discusses design problems and countermeasures regarding resistance, propulsive performance, sea worthiness, maneuverability, hull strength, propulsive machineries, etc. related to this design concept.

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A 12m long full-scale model of a new-type hydrofoil catamaran is constructed and served for experiments in the sea. The experimental results are presented for the properties on steady straight course, i.e., resistance, longitudinal stability and so forth. A 1/10-scale model is also manufactured in order to measure total forces and to study the correlation properties. The results of the tank experiments are presented and discussed.

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Investigation of flow characteristics at the stern is made for two stern forms : one is a newly-developed asymmetric stern of the letter-C-type and the other is its parent stern having usual form. Velocity distributions are measured by five-hole pilot tube at the propeller location for the two forms. Discussion is made about the flow characteristics including vorticity distributions, energy saving mechanism due to inflow rotation, and induced drag, etc. A new formula is presented for calculating induced drag due to longitudinal vortices. Discussion is also made for scale effect of induced drag.

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A new velocity measurement method was applied for the fullscale ship wake measurement. The wake distribution was measured on a 105 m long 5, 800 displacement ton training ship “SEIUN-MARU”. The 3-dimensional velocities of tracers were measured from the synchronized screen images of 3 CCD TV cameras which were installed on the hull surface. The 3-dimensional velocity distributions, i. e. wake distributions, were then calculated at the sections near the ship stern by interpolating the measured tracer velocities.
The measurements were made twice. One was in the condition of a conventional propeller equipped and the other was in the condition of a highly skewed propeller equipped. In the first experiment, a LDV measurement was also performed by another research group. Therefore, the authors could compare their results with the simultaneously measured LDV results besides the comparison between the different propeller conditions. The following results were obtained :
(1) The present measurement result is very reasonable and agrees fairly well with the LDV result. It can be said that the present method is simpler and less expensive than the LDV method. This system is also less sensitive to the hull vibration. In addition, the present system can measure the 3-dimensional velocity distribution in the measurement volume.
(2) The secondary flow distributions clearly show the development of the bilge vortex.
(3) The wake distribution in the case of the highly skewed propeller is similar to that of the conventional propeller case. However, the wake fraction is about 0.1 lower in the highly skewed propeller case than that in the conventional propeller case.

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In the first report, the authors showed a new concept to reduce turbulent frictional drag by injecting high-viscosity fluid into boundary layer. The experimental result showed a substantial reduction of shear stress by injecting sugar sirup which was used as high-vescosity fluid and water from the double slits.
In this report, the experiment of water/sugar sirup injection was done in many conditions. The injected sugar sirup looked white that was because of a large difference in index of refraction between water and sugar sirup. So Laser Doppler Velocimeter could not be used for measurement of velocity distribution. In this report, the velocity distribution was measured by cross-correlation method using a pair of hot film anemometers. The velocity gradient became less at the vicinity of the wall when the water/sugar sirup was injected. It confirmed the hypothesis of drag reduction shown in the first report. A finite difference computation was also made for different viscosity layers in boundary layer.

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A drag reduction for 3-dimensional body is attempted by microbubble injection. Two models with different lengths are used for experiments to distinguish the resistance due to on microbubble injection itself and the skin friction affected by microbubble covering. A reformed Wigley model is used to investigate the effect of microbubble injection on wave making. Measurements of the resistance and the longitudinal wave profiles are performed. The covering by microbubbles is realized by injected air through a porous pipe with pore size of 15 μm. The flow of microbubbles is obsered and the bubble sizes are estimated based on the rising velocity of a bubble in still water.
The results show that it is possible to reduce the resistance of a 3-dimensional body by use of microbubbles if the body is well covered by microbubbles. Although the resistance increases where microbubbles are injected, the local frictional resistance is reduced more than 20 % where microbubbles cover the body. The total resistance is reduced more than 5 %. Based on a wave analysis, it is found that injecting microbubbles into water does not affect on wave making resistance.

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When a body is put into waves, the waves are scattered by the body. If there is another body in the near field, the body is affected by the scattered waves and the hydrodynamic forces on the body are sometimes quite different from those on a single body.
In this paper, by actively making use of these hydrodynamic interaction effects among bodies, we optimize the arrangements of the bodies in the sense that the hydrodynamic forces on the bodies are minimized. It is shown that this can be achieved by combining the existing hydrodynamic interaction theory and the nonlinear programming techniques. Through several example problems the effectiveness of the present method is demonstrated.

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An experimental technique is developed for a vehicle moving steadily in the vicinity of the ground. The towing tank with a steadily advancing carriage is used and the unfavorable effects of the boundary layer on the wall of wind tunnel is fully removed. Experiments with a box-shaped model and a car model revealed some interesting features of lift, drag and side force at various clearance from the ground. Lift force is more sensitive to the boundary layer and it should not be measured in a wind tunnel. The flow with vortices near the bottom surface of the body gives one of the most important effects on the forces.

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In this paper, hydrodynamic effects of 2-dimensional WIG (Wing In Ground effect) moving near the free surface are simulated by means of boundary element techniques. The air flow field around WIG is analyzed by the panel method, and interactions between WIG and the free surface are given as pressure distributions acting on the free surface by this method. In order to analyze the wave making phenomena of water by those pressure distributions, the boundary element method based on Cauchy's integral theorem is employed, in which nonlinearities of free surface conditions can be included. As results of those computations, however, it is verified that wave making effects of WIG are very small because of the difference of fluid density. In final examples of the present computations, simulations of lift changes of WIG moving near the incident regular waves are shown by using the combined scheme of the panel method and the discrete vortex method. In those examples, the wave surface can be treated as the rigid wavy wall, because the wave making effect of WIG is small.

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The N-S solver is applied to investigate the flow characteristics of 3-D submerged foil with free-surface. Flows of five different cases are simulated and compared each other to discuss the free-surface effects on 3-D hydrofoils where the submergence depth and angle of attack are changed. The no-slip condition used for the viscous flow realizes the shock-free condition for pressure around the trailing edge, which proves to be an advantage of the present numerical simulation over the potential method where Kutta condition is imposed. Through the numerical computation, it is found that the lift and drag are seriously influencd by the free-surface waves which are affected greatly by the submergence depth and angle of attack. The large-amplitude waves, under the suspect of breaking, have much influence on the lift and drag forces because the pressure fields are seriously affected by the waves. The righting moment, which comes from the non-symmetrical lift distribution along the span, is also calculated for the heeled case.

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The rowing of shell eight boat is studied hydrodynamically focussing on the forces generated by the oar blade. The speed and the rowing motion are analyzed by an image processing technique to provide the motion of the blade and the resultant velocity and the incident angle of the flow to the blade. The steady force acting on the blade is measured which is used for the estimation of the force generated by the blade by assuming that the rowing motion is quasi steady. Discussions are made to understand the mechanism of generation of the hydrodynamic forces by the oar blade. The steady drag coefficients by the blade are much affected by the angle of the incident flow to the blade surface and the resultant velocity; the maximum values appear when the angle of attack is between 40° and 140°. Free-surface effects are noticeable on the drag coefficients. The paths of the blade show that the blade moves mainly in the lateral direction to the still water and not so much in the longitudinal direction. The lateral motion generates the thrust. The angle of the incident flow to the blade delicately affects the thrust. The estimated thrust shows that the thrust changes during one stroke very much; high thrust is generated around the catch and the finish but it is minimum at the middle, while the efficiency is maximum around the middle. Three assumed patterns of rowing are simulated by estimating their thrusts and discussions are made for more efficient rowing techniques.

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In the previous paper, authors have developed a new technique to measure the pressure distribution around the blades of a full scale propeller. The full scale measurements were performed on the conventional propeller, CP in short, of the training ship “Seiun-Maru”. From the results of full scale measurement, the measured pressure distributions were similar at each propeller loading condition, except cavitation region. Comparing with an existing propeller lifting surface theory, good agreements were found at most of the measurement points on the back side except near the propeller tip.
This paper describes the measurement of pressure distribution on a highly skewed propeller, HSP in short, of the same ship “Seiun-Maru”. First of all, the special pressure pick-up was improved taking account of the experience in the previous measurement. The same measurement instruments were employed. The measurements were also performed with the same procedure as the previous ones under several working conditions of propeller revolution rate 70, 90, 110 and 149 rpm. At the propeller revolution rates more than 110 rpm, the thrust coefficient K_T and the advance coefficient J are 0.190 and 0.66, respectively. The accuracy of the present measurement was estimated to be the same as that of the previous one, i. e, ± 0.03 kg/cm².
The measured pressure distributions were compared with the theoretical one with using an estimated nominal full scale wake distribution. Excellent agreements with the theory were found at most of the measurement points, especially in the fore part of the blades. These results indicate the usefulness of the lifting surface theory and the estimated wake for a highly skewed propeller in full scale.
On the other hand, the following unforeseen findings were obtained. The measured pressure at 90% radial position tends to decrease toward the trailing edge and completely differs from the theory. This suggests us the hydrodynamic load in the vicinity of the trailing edge at 90% radial position was remarkably heavier than that predicted by the theory. This cyclic load might cause the break-off of the propeller tip due to rapid fatigue crack growth, if a propeller blade is damaged at the trailing edge.
The measured pressure in the region of sheet cavitation on HSP was higher than the vapor pressure while that on CP was equal to or lower than the vapor pressure.
The present full scale measurements indicated that there still exist some problems on the existing propeller theory and some improvements are necessary on the modelling of a propeller theory including separation vortex from the leading edge.
The present measurement of pressure distribution on both propellers also provides us a number of invaluable standard data to develop and validate a new propeller theory.

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This paper describes the numerical study on the cavitation problem of marine propellers by three-dimensional theory, based on the mathematical model of the trailing vortex geometry including the phenomena of the flow separation from the tips by using the vortex lattice method.
The numerical procedure is developed to solve the partial-and super-cavitating propeller problem and to predict the cavity extent and the cavity thickness distribution.
The results of the present numerical study are compared with the experimental results both in uniform and non-uniform flows. Although the comparison shows that the present method is advantageous to predict the cavity extent and the cavity thickness distribution, further problems still exist in the numerical studies to predict the propeller cavitation more accurately.

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In this paper, it is shown that liquid can be treated hydrodynamically as a compressible fluid similar to gas by using the extended Tammann equation. Thus, regardless of fluid phase, the wave equation governing the hydroacoustic field can be deduced from the fundamental equations of compressible fluid. As a result it is found that the heat can be one of the sources of sound as well as mass injection, external force and Lighthill's stress.

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A theory is described on the free-surface flow slowly moving full hull forms in short waves. Under the assumption of small perturbation over the double body flow, a new function is derived which satisfies the free-surface condition including the effect of deformed flow due to the presence of the ship hull. By using the function, an expression of the velocity potential is introduced. In order to know the basic feature of the present theory, calculations are made of wave pattern generated by a pulsating source moving with constant speed below the free-surface. As a result, it is shown that steep waves appear in the region where a parameter τ₀ (= U₀ω/g ; U₀ is local velocity of the double body flow, ω the encounter frequency and g the acceleration of gravity) is close to 0.25. The wave pattern shows the similar tendency to the diffraction waves in front of a full hull form observed by Ohkusu¹¹⁾ .

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Practical method is investigated to predict hydrodynamic forces on a catamaran oscillating and running at high forward speed in waves. Assumption of relatively large variation of flow variables along the ship length leads to flow field around the ship with diverging waves. Chapman's approach is used to solve the boundary value ploblem for the unsteady velocity potentical around twin hulls' section countour with retaining all the terms of the full linear free surface condition including forward speed effect. Results show that predicted hydrodynamic forces agree generally well at high Froude number with the measured on a model ship except for the diffraction wave field around the ship.

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Estimation of directional frequency transfer functions of a running ship is important to estimate their behaviours in realistic short crested irregular waves (such waves are called as directional spectrum waves)
Of course, there are some theoretical calculation methods for such directional response functions, but it seems that there are not so many experimental results confirming such theoretical ones. For that purpose, square basins are needed.
On the other hand, recently the authors developed a wave maker which can generate directional spectrum waves in a long towing tank, and many experiments of running ships were conducted in such waves.
In those experiments, obtained results are one dimensional motion spectra and direct comparison with theoretical ones is impossible.
So we tried to make inverse estimation of directional transfer functions of a running ship using both one dimensional response spectrum measured in such waves and measured two dimensional directional wave spectrum.
Estimated results by present method on heave, pitch, roll and vertical acceleration response functions are reported here, but this method will be also applicable to other situations like motions of a running ship in actual seas by measuring its motions and incoming directional waves.

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Critical situations leading up to capsize are pointed out for a ship in severe following and quartering seas by using the aid of numerical simulation program. The effect of several parameters on the critical situation is discussed to investigate the possible causes of capsizing. In addition, Froude-Krylov force acting on a ship with large amplitude displacement are evaluated in the practical formulas to make simulation program simple.

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The Hydrofoil Catamaran (HC) concept has been developed based on the tank test at University of Tokyo. In 1990, the prototype for HC named “Exceller” was built and actual sea testing was conducted. The Exceller has flaps and ailerons for pitch, heave and roll control. This paper describes the Roll Stability and Control Augmentation System (Roll SCAS) by using ailerons and its validation at sea. The NEC-PC 32 bit computer was installed on the ship to form the data aquisition and the digital control system. The dynamics of actuators and the ship were obtained by the measurement of the actual hardware. Roll angle and roll rate were used as feedback variables with gains, and gains were tuned by the comment of seamen.
The Roll SCAS was exemplified at actual sea and showed clear distinction between its on and off.

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In the application of the linear quadratic (LQ) optimal regulator theory to the control system design, it is difficult to find suitable weighting matrices Q, R in the performance function. That is, the designer must resort to trial and error iteration to find them. And so it is rather difficult to design the optimal control systems.
On the other hand, the inverse linear quadratic (ILQ) optimal servo theory was recentry proposed. This design theory is developed from the practical view point by applying some results on the inverse problem of LQ regulator. In this method there is a close relationship between the characteristic of the transient response of the control system and the design parameters. And when the design condition is fullfilled, it is able to construct a control system which has no interaction between the controlled variables, and it is also able to express the optimal feedback gain in terms of the system matrices and the design parameters.
In this paper, we tried to apply ILQ optimal servo theory to the design of a control system for manoeuvring motion of a ship. It is shown that by ILQ design method the control system for manoeuvring motion of a ship can be designed very easily compared with usual LQ design method. Response characteristics can be selected with design parameters. A control system can be constructed not to interact between the control variables. And as the gain is expressed in terms of the system matrices and the design parameters, it is able to construct a control system which is adaptable to the change of the characteristic of the controlled object.

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The evaluation and decision making for the uncertainty problems, such that are subjective to personal likes and extremely dependent upon conceptual variations, during the conceptual design and initial planning stage are apt to depend on making use of the experience and ingenuity of engineers and specialists. It is desirable to be established the methodology of making the decision that is balanced in an overall perspective, especially when the decision is to be taken based upon multi-criteria objectives.
The process of this decision making way is broken down into a hierarchy model, a grading model and an evaluation-decision model in this report. An analytical method for decision making based on these models is proposed through the technique of management engineering using the fuzzy theory in order to consider the conceptual, qualitative and indeteminable elements. As a typical example of applying the proposed method, the process of making choice on the transportation systems between two metropolises is presented here.

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This paper deals with statistical identification problems of governor-propeller rpm control system in a marine diesel engine under operating at sea. The experiments are carried out after the ship's governor system is completely swiched to a newly developed computer control system. Pl +random input signal is given to the main engine through the governor rack in the actuator. As the statistical model, a multivariate auto regressive (MAR) model is adopted and the minimum AIC estimate method is used in order to fit the model to the actual data. A statistical bias free frequency response function, impulse response function of the governor-propeller rpm system are derived from the fitted AR model.

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One of the necessary conditions for a high speed ship is that a propulsive plant with big power has smaller size and lighter weight.
When we plan a displacement-type monohull high speed ship, in particular, it is difficult to get the hull form with the wave-making resistance minimum, because the stern shape is limited by an arrangement of propulsive machines and shafts.
If we have a small-sized and light-weight propulsive machines, we will expand the limit of hull form design.
Superconducting technology will have capability of realizing the small-sized and light-weight propulsion motor.
In this paper, we generally describe superconducting ship propulsion systems, and report the test results of the 480 kW superconducting motor which we have constructed for the purpose of developing superconducting electric propulsion system.
Showing the design of a 150, 000200, 000 PS propulsive plant for a displacement-type monohull high speed ship, we discuss the possibility of the plant realizing, and pick up the subject for a future study.

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It is important to estimate the ship manoeuvring motion at slow speed. However, the manoeuvring characteristics of ship and the hydrodynamic forces acting on ship at slow speed complicate so much, because sway velocity becomes often larger than the forward speed due to the external disturbances such as wind and current. The development of prediction method for ship manoeuvrability at slow speed condition will be expected.
In this paper, as the first step, the cross flow past rectangular cylinder in early stage from the rest condition are studied by vortex shedding model combined panel method, to analyze the characteristics of flow around ship moving transversely, taking into account the Kutta condition.
Furthermore, the flows around some types of rectangular cylinders are calculated to check the validity of this method.
From these studies, the cross flow past rectangular cylinder in the early stage from the rest condition will be affected by aspect ratio of cross section of the cylinder.

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A perturbational study is made of the shallow water flow past a rectangular flat plate at incidence to predict the nonlinear characteristics of lift acting on it. It is assumed that the flat plate is slender and its draft is nearly equal to the depth of water and the angle of attack is comparatively large. The flow field is divided into three regions for the analysis. In the flow field near the body of the flat plate Kirchhoff's dead water flow in two dimensional channel is applied to the cross flow. Free-streamlines in a cross section are regarded as three dimensional vortex layers in consideration of the longitudinal flow velocity. The flow far from the body is expressed apparently as the flow past a porous flat plate in a horizontal plane. In the intermediate field between the near and far field a depthwise averaging technique of Euler's equations with apparent stresses is used to determine the flow velocity incoming to the flat plate. The normal force coefficient, which is equal to one for a two dimensional flat plate as zeroth approximation, is simply expressed by using a drag coefficient of dead water flow. The obtained results are compared with experimental results.

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The flowfield about a horizontal cylinder advancing beneath the regular waves with its axis parallel to the crests is studied both experimentally and numerically. The force measurement shows that a component with the period double of the wave period is of significant magnitude around the resonant frequency. The flow visualization and the numerical simulation by the TUMMAC-V_WV method based on the Navier-Stokes equation reveal the variation of the complicated vortex motions due to the change of frequency relation. The interaction of waves and vortices is also elucidated.

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This paper presents measurements of transverse forces acting on oscillating cylinders towed at constant speeds and the measurements were arranged so that the results can be used in the response analyses of cylinders. The responses of spring supported cylinders and simply supported flexible cylinders were calculated. The calculated responses of the cylinders showed good agreements with the experimental results and calculations by other researchers. The experiments were systematically conducted changing combination of four parameters, oscillation amplitude, towing speed, oscillation frequency and cylinder length. The large number of the experiment cases were conducted and transverse forces and phase differences between oscillation and lift forces are arranged as functions of the four parameters.
When oscillating amplitude is small, the frequency of lift force is governed by Strouhal number. The oscillating frequency become to dominante frequency of transverse force as the oscillating amplitude is increased. When the oscillating frequency come close to the Strauhal frequency, the frequency of the lift force is controlled by the oscillating frequency and correlation length become very long. But the correlation length does not become long when the oscillating frequency is distant from the Strauhal frequency. The phase angle, which determine energy exchange between fluid and oscillating cylinder, is changed by 180 degrees as the oscillating frequency coincide with the Strouhal frequency.

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A vertical cylinder in uniform current and regular waves is analysed based on potential flow theory and low current speed approximation. The perturbation theory is formulated by expanding the velocity potential in a power series of current speed U and by neglecting the terms of order O (U²). This reduces the boundary-value problem to the integral equation, whose kernel functions involve only the Green's function with zero current speed. The solutions are derived in explicit form for the first-order wave exciting force, mean wave drift force and wave drift damping force on the cylinder, where the nonlinear coupling between the steady and unsteady potentials at the free surface is taken into account. Numerical results are also presented, which lead to the following conclusions :
i) The hydrodynamic forces on the vertical cylinder in current and waves are significantly influenced by the presence of current.
ii) The wave drift force is more sensitive to current than the first-order wave exciting force. With the increase of current speed in the wave propagation direction, the mean drift force tends to increase compared with the force without current.
iii) The nonlinear coupling between the steady and unsteady potentials at the free surface has a significant effect on the hydrodynamic forces, in particular on the wave drift force and wave drift damping. The inclusion of these effects results in an increase of the wave drift damping coefficient by one or two times the value predicted with the classical free surface condition.

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The objectives of the present paper are to develop a powerful numerical method for computing the second-order wave forces on a cone shaped floating structure and to clarify the nonlinear effects on the wave forces induced by the effects of the cross angles of body and water surface. In the present paper, the second-order wave exciting forces are obtained from the radiated wave potential of the double frequency and the first-order scattered wave potential by using the extended Haskind formula. The infinite integral over the free surface is evaluated by using the Fresnel and the Gaussian integrations and the effects of the cross angles of body and water surface is considered in the compuation. The numerical results for the second-order steady forces and the wave exciting forces are compared with the experimental results. The usefulness of the present method and the nonlinear effects are discussed.

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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 vessels moored in random seas. It assumes the response represented in the form of two term Volterra functional series and is based on the generalized Laguerre polynominal expansion of p. d. f. of which the first term is gamma p. d. f. consisting three parameters.
We must compute exciting force and radiation hydrodynamic force in the response transfer function to obtain p. d. f. of the total second order response.
In this paper we approached the effect of the second order potential to statistical values, using this theory. The calculation of second order potential in obtaining exciting force transfer function is very complex and takes many time to compute. Therefore, the transfer functions are generally obtained by neglecting this effect. It is investigated whether second order potential is negligible or not in statistical analysis.
Furthermore coupled motion of six degrees of freedom (DOF) is discussed. We need coupled hydrodynamic force matrix to solve equations of motion because of coupling effect. Considering each DOF independent, only diagonal terms of hydrodynamic force matrix are necessary, and few tasks are needed for calculating hydrodynamic force. So, we discuss the conditions where the coupling motion effects of a slow drift motion on statistical values are negligible or not, by comparing the computed statistical values with measured ones by model experiments of two typical moorings.

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Estimation of directional frequency transfer functions of floating offshore structures is important to estimate their behaviours in realistic short crested irregular waves (such waves are called as directional spectrum waves).
Of course, there are some theoretical calculation methods for such directional response functions, but it seems that there are not so many experimental results confirming such theoretical ones. For that purpose, square basins are needed.
In two previous reports, the authors showed the inverse estimation of directional transfer functions of a floating offshore structure only using results of a few experiments in directional spectrum waves in a long towing tank.
The response functions of wave exciting forces are treated in this paper. The precisions of estimated directional frequency response functions are confirmed using theoretical data.

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Unsteady lift acting on an oscillating wing below a free-surface is studied in two dimensional problem. Unsteady velocity potential is expressed by the distribution of singularities over the wing and the wake. A set of integral equations in terms of the forward speed Green function is solved numerically for a thick wing of arbitrary section. Hydrodynamic forces are obtained by integrating the pressure on wing surface.
Numerical calculations for a wing with several Froude numbers and the submergences are demonstrated and the results such as the pressure distribution and the hydrodynamic force coefficients are presented graphically. It is found that unsteady lift on an oscillating wing at shallow submergence shows abrupt change near the characteristic number, τ takes 0.25, which is determined by the forward speed and the oscillating frequency. This could be explained by the fact that one of four surface wave systems is possible to propagate forward for τ≤0.25.
Experimental results carried out for two wings in heaving oscillation show good agreement with the present calculations.

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Floating production, storage and offloading units (FPSO) and floating storage and offloading units (FSO) have been and will be built for small or medium size oil fields. Recently the external turret mooring systems (ETM system) for FPSO/FSO are increasing in number, because of easy installation onboard, redundancy of mooring chain (i. e. safty), easy mooring works at site, and economical cost. But there seems no report on the calculation method of maximum mooring force for ETM systems.
It is very important to estimate the maximum mooring force at early stage of the design of the mooring system. However, there is no practical calculation method.
This report proposes the calculation program of ship motion round a SPM and mooring forces, considering a low frequency surge motion. This program is evaluated by the model test of a 850, 000 bbl FSO and a new calculation method of maximum mooring force is proposed. This method is based on a statistic analysis of surge motion and offset from the initial moored point, under external forces of waves, current and wind. The predicted maximum surge and offset gives the maximum mooring force.

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This paper presents dynamic behaviors of a deep water utilization system composed of a 2 point moored barge equipped with machineries and a cold water pipe (CWP) attached to the barge. Dynamic behaviors of the floating barge of the present scale and the CWP are mutually affected by each other. The dynamic behaviors were investigated in both numerical calculations and full scale experiments.
A full scale system was tested at Toyama bay in Japan Sea of about 300 m water depth in the summer season of 1989 and 1990. Measurements were performed for motions of the barge, tensions of mooring lines and CWP behaviors.
Motions of the floating barge in waves are calculated including the effects of CWP. Dynamic behaviors of the CWP in the real sea are calculated using the discretized Lagrange's equation in the time domain. It is assumed that the CWP is excited only by the floating barge. The present numerical scheme for the CWP can be applied to the dynamic calculations of various types of line structures.

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This paper presents theoretical development and experimental results of controlled installation technique of deep water TLP tendons. Dynamic response and deformation of a single-piece TLP tendon is controlled using wing-like appendages which generate drag force. The appendages are unfolded by servomechanism and drag force is controlled by changing the opening angle. This actuator utilizes free fall momentum of sinking tendon. Thus the actuator is efficient from viewpoint of consumed energy and the size of the actuator can be small. The system is suitable for deep water uses.
In the theoretical development LAC/HAC approach is employed to make the system robust against the nonlinearity and uncertainties in the dynamics of underwater line structure. DVFB is employed for LAC and significant modes are controlled by HAC. The line structure handled in this paper is almost neutrally buoyant and a constraint is imposed so that the moment of control forces about supporting point be zero. Otherwise there is possibility of structure do not sink and the structure can not be installed. Control parameters were chosen from computer simulations, and experiments were conducted successfully. The experiments are important to verify the theoretical development and robustness of control.

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There have occurred a world-wide anxiety about global warming due to the increasing concentration of CO₂ in atmosphere. Among various countermeasures argued is the fixation of CO₂ in deep sea. This measure seems to be promising from the viewpoint of the huge amount of CO₂ to be treated, provided that the influence on the deep-sea environment be acceptable and that the cost and/or energy consumption would not make an impact on the economic situation.
In this paper, CO₂ transportation system is studied at first, which consists of CO₂ loading on board at port, transport to planned sea area and sending CO₂ into deep sea. Three types of system are planned conceptually, each of which corresponds i) solid, ii) liquid and iii) hydrate for the CO₂ state of cargo, respectively. As a result, the fatal technical difficulties are not found so far as the transportation system. Furthermore, considering the merits and demerits of the three types comparatively, the one for liquid CO, is estimated main to be carried on to the next phase of study for the present.
Secondly, the experimental investigation is performed. A pressure vessel filled with highly pressed artificial sea water is situated in the room of steady temperature. And liquid CO₂, is slowly injected. Consequently, it is experimentally confirmed that liquid CO₂ become heavier than sea water under condition of the waterdepth of more than 3000 meters. This is an evidence of the self-sinking of liquid CO₂ in deep sea more than 3000 meters.

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A multi-level simulation program was developed to compute the ocean current. As an example of its application, tidal currents of 12 hours period in Tokyo Bay were calculated and compared with observations. As a result, it was found that computed results of tidal ellipses, amplitude and phase lag of tidal elevation agree fairly well with observed ones. The most striking characteristic feature of multi-level model is to be able to clarify the vertical structure of tidal currents, i. e., the distribution of vertical velocity and the structure of vertical shear current. In the numerical simulation of ocean currents, a part of various parameters included in governing equations are usually determined empirically. In order to examine the influence of such parameters on computed results, a series of comparative simulations were carried out varying the numerical values of such parameters in a systematic manner. Furthermore, the effects of river inflow and seasonal wind direction on the tidal residual flow were clarified. In particular, the difference in tidal currents predicted by the simulation model with different number of levels was discussed in detail.

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In order to estimate ice loads acting on ice-breakers for the design of hull structures as well as an estimation of ship performance, it is essential to grasp the mechanical characteristics of sea ice, especially under multi-axial stress conditions. However, the mechanical behavior of sea ice is more complicated as compared with that of metals, where the effect of hydrostatic pressure and anisotropy of the material are distinctive.
In this study, triaxial compression tests were conducted systematically by using laboratory grown saline ice specimens, where the salinity of specimen and the strain rate were taken as prime testing parameters. Before conducting the triaxial compression tests, several series of uniaxial compression tests were also carried out. As a result of the uniaxial compression tests, it was concluded that saline ice employed in this test program could represent the mechanical behavior of sea ice in terms of the uniaxial compressive strength under the test conditions used in the study.
24 series of triaxial compression tests were conducted in order to investigate the effect of the salinity of specimen, the strain rate at a test and the specimen type on triaxial compressive strengths. It was found that the triaxial compressive strengths of saline ice could be expressed by the Drucker-Prager failure criteria when the salinity of specimen as well as the strain rate at a test and the specimen type were specified. Using the coefficients of the said criteria obtained in a series of the triaxial compression tests, the effects of salinity of speciment and strain rate at a test on the triaxial compressive strengths were clarified. It was also found that the extent of anisotropy can be estimated by the coefficients of the said criteria.
From the coefficients of the Drucker-Prager failure criteria obtained in the present study, an empirical formula was suggested to estimate the triaxial compressive strength for an arbitrary salinity, strain rate and specimen type (being limited within those values used). However, it was realized that more work should be needed to round the equations out, especially on coefficient k of the said criteia. It was also realized that an anisotropic failure criteria such as the Pariseau failure criteria would be more realistic when it comes to express strength characteristics of saline ice (sea ice) rather than using the Drucker-Prager failure criteria. Establishment of an experimental technique to define the coefficients of the anisotropic failure criteria will be needed for better understanding the mechanical behavior of sea ice.

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In the previous paper, the authors presented a new method for calculating vertical motions and wave loads of large high-speed ships with hydrofoils and developed the program code TSLAM-F_HF. The computational method of TSLAM-F_HF is based on the time-domain strip method taking account of the effects of the nonlinear hydrodynamic forces and dynamic lift of the hydrofoils.
In this paper, the authors apply the program code TSLAM-F_HF to a 12 m long hydrofoil catamaran in regular head seas. The computed results show that there exists a strong nonlinearity in ship motions and wave loads due to the unsteady lift of the hydrofoils and the impact forces by the hydrofoil slamming.
When we design large high-speed ships, the structural aspects are often more important than the hydrodynamical ones. The program code TSLAM-F_HF is a very useful tool for the structural design of large high-speed ships with hydrofoils.
In the next step, the author simulate motions of the ships actively controlled by the hydrofoil flaps to stabilize the ship motions in order to prevent the hydrofoil emergence which leads to strong impact forces on the hydrofoils. The feedback gains for the flap control are determined by solving the optimal state regulator problem. The result shows that the flap control is very effective in stabilizing the ship motions. It reduces the amplitide of the ship motions to about 20 % of that for the non-controlled conditions and it can also prevent the hydrofoil emergence among rough seas.

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Full-scale measurements of local stresses and wave pressure working on hull side in seaways were carried out on a VLCC. The measurements aimed at understanding the actual condition of working stresses on longitudinal members and wave pressure acting near the load water line. The findings made from the present study are as follows :
(1) So far as the results of this full-scale measurements, higher order components of wave pressure owing to wave breaking and/or impact were not remarkable.
(2) The mean periods of stresses on side longitudinals were shorter than those of deck or bottom longitudinals. This comes from the difference between the response characteristics in regular waves.
(3) It was confirmed by the comparison with the results of full-scale measurement that the prevalent wave pressure estimation based on strip method well explained the short-term characteristics of stress on longitudinals.
(4) For the evaluation of local stresses of structural members where various load elements act mutually Discrete Analysis Method (DISAM for short) was found to be effective.

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The rational and comprehensive ship structural analysis and strength evaluation based on data from a good feedback of operational service experience must be effectuated in order to secure the ship hull strength in hull structural design and establish the design criteria. For that purpose, it is important to develop the estimation method by which the ship hull stresses in ocean waves are estimated with accuracy.
In this background, the authors developed the simulation method of ship hull local stresses in ocean waves, and applied the method to the local stress estimation in the actual ship. As a result of the application, the several findings on the structural response characteristics of local structure in waves are obtained as follows.
(1) In the vertical distribution of fluctuating stresses in side longitudinal frames the hump was found to appear beneath the L. W. L. owing to nonlinearity of wave height to wave pressure, which can not be obtained by using linear treatment. This suggests that it is necessary to pay enough attention to fatigue strength of side longitudinal located in the limited part below L. W. L.
(2) Fluctuating stress level of bottom, deck and longitudinal BHD longitudinal is found to be lower than that of side longitudinal by the present estimation method.
(3) From the investigation of correlation between each components of side longitudinal fluctuating stresses caused by such loads as wave pressure, inner fluid pressure and vertical/lateral bending moment, the following results are obtained.
(a) The coefficient of correlation between fluctuating stress components owing to outer and inner pressure becomes -0.6.
(b) The coefficient of correlation between total fluctuating stresses owing to outer/inner pressure and vertical/lateral bending moment becomes 0.4.

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The deformation and dynamic instability mechanisms of submerged thin shell marine structures are in principle of a nonconservative nature since the associated loads are of the follower type hydrostatic pressure and drag forces which may persistently undergo disturbances due to several causes. In the region of large deformations, especially in the case of geometrically deep shell structures, the system could be much more accurately defined in a monoclinically convected material coordinate description than the conventional spacial description. Also, a complete analysis of a nonconservative system requires a dynamic criterion since the system can have multiple ranges of stability and instability involving both divergence and flutter.
This paper presents the basic formulations and development of the governing equations for the finite deformations of thin shells defined in a monoclinically convected coordinate description and applies the same to different cases of shell deformations. The validity of the formulations is verified for finite deformations and disturbed small vibrations of some common types of shell structures. The examples of some geometrically special shell structures are presented as well to show the feasibility of the present formulation.

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It is very important to estimate the load carrying capacity of a ship's hull as a whole from the viewpoints of safety and economy. For this purpose, a simple method was proposed to simulate the progressive collapse behaviour of a ship's hull girder subjected to longitudinal bending. In this method, the cross section of a hull girder is divided into small elements composed of a stiffener and attatched plating. For each stiffener element, the average stress-strain relationship under axial load is derived based on the equilibrium conditions of forces and moments. The buckling and yielding in both stiffener and plate are taken into account. Then, a step-by-step increase of vertical curvature is applied to the hull girder assuming that the plane cross section remains plane. At each incremental step, the tangential flexural rigidity of the cross section is evaluated using the tangential slope of the average stress-strain curves of the elements as well as the incremental bending moment due to the curvature increment.
Performing sample calculations on existing girder models tested under pure bending, the rationality of the proposed method was examined. Then, the analysis was performed on an existing bulk carrier, and the progressive collapse behaviour of the cross section under bending load was discussed. It was found that the full plastic bending moment can not be attained due to buckling of the deck plates under sagging condition and that of the bottom and inner bottom plates under hogging condition. It was also found that the maximum bending moment carried by the cross section under sagging condition is 20% lower than that under hogging condition.

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In this paper, a posteriori error in finite element analysis for ship structure problems is considered. Error is estimated in element-wise fashion in order to decrease computing time and memory use. The major difficulties in the element-wise error estimation are satisfying the self-equilibrium condition and allocation of traction discontinuity along element boundaries. An optimal procedure is used for satisfying the self-equilibrium condition, while traction discontinuity along element boundaries is allocated based on the ratio of stiffness of adjacent elements for each degree of freedom.
Several sample problems are solved for showing the capability of the proposed method. The accuracy of the method is ensured by comparing the estimated error and referenced error. A lower stool part of a bulk carrier and transverse ring of oil tanker are analyzed as an application of the method to the real problem. A posteriori error in the averaged stress distribution is also considered.

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Owing to recent development of techniques of finite element analysis and computer hardware, the finite element method has been used more widely for the industrial products. The biggest difficulty here is modeling of complex configuration of industrial products which is most time consuming to engineers and hence takes up large amount of the cost. To overcome this, integrated finite element modeler MODIFY (MODeling tool for Integrated Finite element analYsis) that produces finite element model automatically is developed here. This modeler is based on two new concepts, part object and object oriented data struture. By assembling part objects that have simpler configuration, geometric model of complex configuration can be built up and mesh is generated part by part. The concept of part object enables the geometric configuration to be divided into parts, which are simpler object and easy to generate mesh. The concept of object orineted data structure results in easy handling of local modification of finite element data that is required in both local modification of geometric model and modification of finite element mesh such as in zooming or adaptive meshing. With these concepts, the user do not need to handle finite element model, but only geometric model.
The present proto type system is applicable to finite element modeling of two dimensional field, and three dimensional plate strucure which appear in ship structure. Several examples are presented for demonstration.

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This paper is concerned with the ultimate strength and reliability analysis of ship's hull girders, which are composed of the spatial membrane elements and subjected to combined static loads and extreme wave loads.
The linearized failure condition of an element is first introduced, which takes account of the yielding and buckling collapse under the plane stress condition. The failure criterion facilitates the generation of safety margins and the calculation of failure probabilities. Structural failure is defined as the generation of large deformation due to collapse. The socalled branch-and-bound method is applied to select the probabilistically dominant failure modes, which saves the computational efforts to perform a reliability analysis on large-scale structures.
Finally, the proposed methods are applied to spatial plate structures idealized for modelling main hull girders of an oil tanker and a bulk carrier under two loading conditions. Through numerical examples, the properties of proposed methods are investigated.

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In designing new type of structures, it is very difficult to evaluate the safety factors due to lack of previous design data and operational experiences. To solve the above mentioned problem, much attention is being focussed on rational reliability-based design approaches.
This paper deals with Weight-Optimal Reliability-Based Design (WORBD) of stiffened plates subjected to structural reliability constraints taking into account of the effect of local buckling and interactive behavior between local and global buckling.
Present method is compared with the existing optimal design method based only on safety factors. Numerical simulation reveals that the present method leads to lighter structure (4% reduction in weight compared to the existing optimal design) with the same reliability index. For larger structures (eg. ship structures) with more number of structural members and possible failure modes, the present WORBD procedure will be an efficient tool in designing cost-effective rationalized economic design.

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When designing a very thin stiffened panel subjected to axial compressive loading beyond its buckling strength, post buckling behaviour of the panel should be taken into consideration. Allowing the panel to buckle would raise two important strength aspects to be considered. One is the ultimate strength of the panel and the other is the fatigue strength of the welded panel boundaries (welded part of stiffeners) due to cyclic buckling deformation. Many researches have been conducted regarding the ultimate strength, and characteristics of panels under static axial loading have been well clarified up to the ultimate strength. Regarding the fatigue strength, however, very little is known in the field of welded ship structures.
In this paper, with the help of non-linear (elasto-plastic and large deflection) finite element analysis and the modified Miner's law, characteristics of a very thin stiffened panel subjected to cyclic axial compressive loading beyond buckling strength is studied.

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An Idealized Structural Unit is developed for predicting the elastoplastic behavior of tubular members with crack damage under combined tension and bending. This method can be easily applied to the elastoplastic analysis of frame structures containing through-thickness cracks. Ductile crack growth is considered using CTOD and CTOA as fracture parameters which rule the initiation and continuation of the crack growth, respectively.
The tangential stiffness matrix of a cracked member before reaching the ultimate strength of the cracked section is evaluated by introducing the crack spring element having the compliance of cracked section into the node of beam-column elements. The stiffness formulation after the ultimate strength of the cracked section is based on the plastic node method. The elasto-perfectly plastic material is assumed and the values of CTOD and CTOA are evaluated based on the Sanders' semi-membrane shell theory.
The results are compared with those of the finite elemet shell analysis, and the rationality and effectiveness of the proposed method are demonstrated.

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This paper concerns with the axisymmetric progressive buckling analysis of circular cylinders under axial compression using the nonlinear finite element method. The presently developed finite element program is an extended version of the original code¹⁾, which takes into account the major factors in the quasi-static crushing problems such as large displacements, large strains, contact, friction and localization of buckling patterns. For the frictional contact of boundary nodes on the cylinder, Coulomb's law is adopted with constraints of the nodal displacements⁴⁾. The contact between the surfaces of the cylinder is treated by the finite gap elements⁹⁾.
The numerical results have agreed well with the results of experiments, which were conducted by the authors¹⁾, with respect to the crushing deformation, axial load-shortening relations, mean crushing stresses, crushing strokes and plastic buckling stresses. It is concluded that the complicated progressive buckling behavior accompanied with the strong non-linearity was successfully simulated by the present numerical procedure.

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