Laminar and turbulent separated flows around a 6 : 1 prolate spheroid are investigated using an unstructured grid CFD method. The RANS equations are solved for incompressible viscous flows. The artificial compressibility is introduced in the continuity equation and cell-centered finite-volume method on unstructured grid is used for spatial discretization. The Spalart-Allmaras one-equation turbulence model is employed for the Reynolds stress. The computational results are compared with experimental data and the physics of three-dimensional turbulent flow separation is confirmed. A range of Reynolds numbers and angles of attack is considered and the effects are investigated. The modification of the Spalart-Allmaras model is added to improve the performance and examine the effects of turbulence model on the vortical flow structure.

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The influence of streamwise pressure gradients and curved surfaces on microbubble skin friction reduction was examined in cavitation tunnel at free-stream speeds of 5, 7 and 10m/sec. A 1.5m long, 0.3m width flat plate and 2D convex model were used. In order to change streamwise pressure gradient, using temporary slopping bottom changed sectional area at the test section.
The effect of skin friction reduction under favorable pressure gradients tended to rather reduce compared with the zero pressure gradient case. In opposition, the adverse pressure gradients tended to rather increase. Moreover, there was a condition that the skin friction reduction effect increased extremely under the adverse pressure gradient. Air bubbles under that condition looked like cloud and the void fraction of inner layer was high. There seems to be possible to find an effective microbubble method by the optimization with air bubble diameter and distribution.

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Recent developments of numerical techniques and computer system have enabled us to obtain a highly accurate CFD results for unsteady flow fields. However, we have some difficulties to utilize such results in a design process due to the huge amount of data. Major problem is a handling of those data in comparing with other results, archiving in a database and exchanging among the researchers. In our study, a data compression method using a characteristic feature of a flow field will be considered. Firstly, the flow field is visualized using some display-based techniques such as a volume rendering method for a scalar field and LIC (Line Integral Convolution) or PEM (Pixel Exposure Method) for a vector field. And then, a vortical structure is interactively abstracted from the flow field. In a two-dimensional case, some point-vortices are substituted for the distribution of the vorticity. Vortex sticks will be utilized in three-dimensions. Those vortex elements represent the flow fields, and are stored for the comparisons, the archives and the exchanges. It will be expected that the size of data is extremely reduced without standard techniques of data compression in computer science. In this paper, we will propose a methodology of our data compression method, and demonstrate the method for a two-dimensional incompressible flow field.

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Ground water flow in a surf zone closely relates to the purging of seawater and biological activities. Because the water flow into surf ground is transporting a kind of nutrients and oxygen to benthos in the ground.
In the present paper, visualizations of ground water flow show that the water flows into the surf ground with radial direction near the run-up point induced by waves approaching a beach. The seepage water flows out from the seabed surface near the wave breaking point. The measured pressure on the seabed surface reveals the distribution of positive pressure near the run-up point and negative pressure near the wave breaking point, which is the driving force of water percolation in the surf ground.
The measured pressure distribution is compared with the calculated by the wave set-up and set-down. Further computation on the ground water flow in the surf ground is conducted assuming Darcy's law. Laplace equation for the time-averaged pressure is solved by finite difference method. The calculated streamlines are in accordance with the visualized flow pattern. It is found that the flow rate of the purging by waves is comparable to that of tidal motion.

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A new combined diagnostic and prognostic numerical simulation method to estimate the environmental effect of very large floating structure on the water circulation is reportd.
In this method, two domains which has different size and different resolution are used. In the first step, diagnostic model is applied to wide domain to reproduce wide-range current, temperature and salinity field. In the second step, prognostic model is applied on the small area near the floating structure. The result of diagnostic calculation is used as the boundary condition for the prognostic calculation.
As an application, the evaluation of water mass exchange under the imaginary floating structure which is settled off Kansai international airport is reportd. Water particle tracing method is performed with the prognostic calculation, and as the result, it is found that there are remarkable dirrerences between the spatial distribution of water particles with floating structure and that without floating structure, but average residence time does not change widely whether the floating structure exists or not.

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The effect of the construction of a large-scale marine structure in Osaka bay is evaluated using Landsat TM data. Sea surface temperature and chlorophyll before and after building the Kansai international airport are made from the satellite image. Since the conventional formula underestimates the concentration of chlorophyll in this area, we derive a new formula. The flow stagnation around the airport, clockwise stream in the bay, a large plume in the western area is observed.

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To realize a very large floating structure (VLFS), it is indispensable to examine various effects on marine environment around a VLFS. For an assessment in the physical, chemical, and biological aspects, a numerical study by means of ecohydrodynamic model, which is an ecological-physical coupled model, is conducted. First, to validate the ecohydrodynamic model, numerical simulations of coastal ecosystem in the summer of Tokyo Bay are carried out under the boundary conditions which change every moment, and under those which are kept unchanged for computations. Additionally, the effects of an imaginary VLFS on the surrounding environment are examined in two cases : the VLFS is assumed to be installed in the sea area off Yokosuka or off Haneda in Tokyo Bay. As a result of some computations, it is concluded that predicted change of water quality agreed quantitatively with observation data, and the impacts of the VLFS on marine environment are localized in close vicinity to the floating structure. However the extent of the effects is relatively larger in the sea area off Haneda, where the residual current is weak, than off Yokosuka.

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Bursting phenomenon of tip vortex cavitation of a propeller causes high frequency vibration, but its mechanism is not elucidated yet. In this study the authors made the experiment that used two kinds of propellers and changed some experimental conditions such as wake distributions, and examined the burst phenomenon with high speed video camera. We also measured flow distribution around the tip vortex. As a result we found that in the burst phenomenon big pressure fluctuations were measured twice, and it depended strongly on the flow distribution of the wake. With the bursting wake tip vortex moved below downstream and was bigger and slower than that of non-bursting wake so that it interfered in the cavitation of the next blade.

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Bursting phenomenon of tip vortex cavitation causes severe high-frequency vibration, but estimation of it by numerical computation is not yet realized. In this study the authors made model experiments to observe the bursting phenomena and measured the pressure fluctuations caused by that, changing two propellers, wake distributions, thrust coefficients and cavitation numbers parametrically. After analyzing frequency of it we found that there would be two methods to suppress the bursting phenomenon : stabilizing the tip vortex cavitation or reducing the volume of cavitation. We also did numerical fluid simulations around a propeller in non-cavitating, unsteady condition and compared the strength of tip vortex along the circumference and its derivatives. As a result the phenomena were parameterized by the time derivative of the strength of tip vortex, and if it was higher than a certain value, tip vortex cavitation bursted. Therefore there is the possibility to predict the occurrence of bursting phenomenon by numerical analysis.

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This paper presents a calculation method for the 3-D unsteady sheet cavitating hydrofoil problem. The method is based on a simplified surface panel method “SQCM”. Hess and Smith type source panels are distributed on the hydrofoil and cavity surfaces. Discrete vortices are distributed on the camber surface according to Lan's QCM (Quasi-Continuous vortex lattice Method). The boundary conditions to determine these singularities are the constant pressure condition on the cavity surface and the zero normal velocity condition on the hydrofoil and camber surfaces (except the trailing edge). We consider the unsteady Kutta condition that the pressures must coincide with each other on the upper and lower surfaces at the trailing edge. Then we introduce the normal velocity at the trailing edge. This normal velocity is obtained by iteration for the equal pressure condition. The cavity shape in each spanwise section is determined so that the zero normal velocity condition is satisfied on the cavity surface.
In the present method, a cavity length for each spanwise section is given first. Then the singularities and the cavity shapes are determined. The cavity length is corrected in order that the opening at the cavity end will get closer to the target value. By using the corrected cavity length, the calculation is repeated from the beginning. These steps are repeated until the opening at the cavity end agrees with the target value in each section and then we move to next time step.
This method is applied to the Wagner problem, heaving hydrofoil and a hydrofoil in a sinusoidal gust. We show some calculated results for partially cavitating and super cavitating hydrofoil and compare them with another calculated results.

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In the previous paper, authors presented experimental and theoretical data on open water characteristics of two side thrusters which impellers have the forward skew (type (A)) and the backward skew (type (B)).
In this report, cavitation characteristics and blade stress of these two side thrusters are investigated theoretically and experimentally. Cavity extent on the impeller blades was estimated by the propeller lifting surface theory. Then, cavitation tests were performed by using the impeller models with the duct in the cavitation tunnel. These results show that the cavity extent on the impeller blades is similar comparing these two impellers. But, the tip vortex cavitation of impeller (B) is much stronger than that of impeller (A), which causes more severe noise and vibration. The finite element method was applied for the stress analysis of the impeller blades. The stress level of impeller (B) was normal, but slightly high stress, which was acceptable, was found on the blade of impeller (A) near the leading edge of 0.7 R-0.8 R.

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For this paper, the authors designed three types of SURFACE PIERCING PROPELLERS. Each propeller was constructed with a different type of blade section, one wedge-shaped, one crescent-shaped, and one with an improved wedge shape. We checked the propeller's performance around the planned ship speed and also the performance in the astern direction. In order to study the possibility for improvement in lowermedium speed performance, additional model tests were conducted with the submersion ratio, which strongly influences lower-midium performance, changed. Lastly, the authors verified that in an actual vessel, where the submersion ratio can be adjusted by changing the propeller shaft's inclination angle, the performance of the SURFACE PIERCING PROPELLER was improved.

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In the previous paper, the wave radiation conditions in wave problems, their introduction into the variational principles and the simple numerical results are discussed, and the effectiveness of the new radiation conditions and the variational principles were shown.
In the present paper, the numerical results for one-dimensional water wave problems not included in the previous paper are given. As expected in advance, the region required for the numerical solution is reduced drastically as compared with that required by the Sommerfeld-type formulation. Furthermore, the amplitude of the diverging wave is obtained in the process of the variational solution.
Two-dimensional water wave problems are discussed briefly.

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In this paper, the application of three dimensional source technique for computations of motion responses and drift forces for multi-body floating system with zero forward speed in waves are investigated. The mean wave drift forces are obtained by far field and near field (direct pressure integration) methods. Numerical results for the first order motion responses and the mean wave drift forces for a parallel arrangement of a FPSO (Floating Production Storage and Offloading Unit) and a LNG carrier are discussed. Some comparisons are made for a single floating body (semi-submersible) as well as for a simple multi-body system of a cylindrical body with a box shaped hull. Numerical results for motion responses are compared with experimental ones for the FPSO-LNG system and also results for mean wave drift forces obtained from both of the methods are compared with experimental ones. The trend of the results as well as correlation between both of the methods found to be comparatively well in agreement. The effects of roll damping to the second order wave drift forces for sway and yaw are also discussed.

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In this paper, the tank sloshing and the vibration of the internal structure in contact with the water are discussed by extending the Boundary Element Method (BEM). The BEM has been widely used to solve the nonlinear fluid motions in a tank as well as the potential flow past an obstacle. However, when a tank is fitted with the thin internal structure, the basic BEM will give a numerical error due to the thickness of the plate in the evaluation of the pressure acting on the internal structure. Nishino et al. solved this problem by introducing the Thin Plate Boundary Element Method (TPBEM) with some manipulation of the formula.
The basic BEM, in this paper, is extended to the Multiple Domain Boundary Element Method (MDBEM) by dividing the whole fluid domain into several sub-domains. The computer program has been developed and applied to the sloshing of two-dimensional (2D) tank with internal structure and also to the vibration of the internal structure in a tank. Some of the computational results are compared with the ones in the published papers. It shows that they agree well each other and the present method is effective.

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This paper proposes a new method to simulate slamming impact. loads and ship response of a high-speed vessel in waves. Many non-linear analysis methods have been proposed and reported for simulation of slamming of ships, in which hydrodynamic impact loads are determined by means of Karman type impact model. It means that wrater pile up is not taken account of in water surface impact. process. On the other hand, model experiments and numerical analyses of water impact of wedges show very good agreements with water impact theory by Wagner, in which water pile up plays an important role. This implies that calculation of proper impact loads is not expected by these non-linear analysis methods. A new approach have been tried to improve this inconvenience.
Wagner type impact model is adopted in the new method, together with threshold velocity of water impact to judge occurrence of water impact. Threshold velocity of water impact is derived for wedges with various deadrise angles, of which model test was carried out for the validation.
A new concept of equi-added-mass lines is introduced to take account of the hull form to compute substantial relative velocity between hull and wave surface. This corresponds to a method to derive relative vertical velocity of an inclined prismatic body with a wedge section advancing forward on calm water surface. Using this method, substantial relative velocity can be computed taking account of ship speed, and loads derived by the method include the lift force induced by ship speed.
These are incorporated in a new non-linear analysis method. It is confirmed that loads derived by this method for a ship section are equivalent to the loads derived by Stavovy & Chuang's method, which is so-called an impact theory to calculate three-dimensional impact. pressure. A comparison is made between the results of this method and model tests for hull response of a 40 m patrol boat in regular waves. The results show comparatively good agreements in motions in waves. But, it shows there is much room for improvements in treatments of piled up water and waves the ship induces.
This method is applied well to simulate hull response of such high-speed vessels like patrol boats, and this method is expected to apply also to other ships like container ships.

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A model test method, a partly captured PMM test, to measure unstable motions of a planing craft induced by periodic maneuvering motion is developed. The experimental results of a planing craft at Fn=2.0 by the method demonstrates that a violent motion which is large rolling, heaving and pitching coupling motion occurs when the frequency of motion given by PMM coincides with the rolling natural frequency, and with the half of the heaving and pitching natural frequency of the craft. It should be noted that the rolling motion has the same frequency as the forced motion given by PMM, but that the heaving and pitching motions have the twice of the frequency of the forced motion.
In order to clarify the cause of the violent motion, the hydrodynamic forces acting on the hull in periodic maneuvering motions are measured by PMM tests for a captured model and obliquely towing tests. The experimental results show that the rolling displacement of the craft generates hydrodynamic heaving force and pitching moment at high speed. A non-linear time-domain simulation of the motions using the measured hydrodynamic forces is carried out. The simulated motions are in fairly good agreement with the experimental ones.

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In order to evaluate manoeuvrability of ships by analyzing manoeuvrability test at seas effects of steady wave forces and moment must be estimated correctly since it is inevitable that ships suffer those external forces at seas. Short waves induce larger steady wave forces than long waves and short waves exist anytime at seas. These are among reasons why short waves' effects on ships in manoeuvring motion must be investigated.
Formula for estimating steady wave forces and moment acting on ships in manoeuvring motion is presented by applying Ohkusu's method for calculating added resistance of ships in head wave condition to manoeuvring condition that includes oblique, turning and their combined motion. Model experiment is carried out to measure steady wave forces and moment acting on a ship in oblique and turning motion in short waves with motion of wave period not constrained.
Calculated results by present method are compared with experimental data and those by other methods of calculation. It is found that present method well describes property of steady wave forces and moment acting on ships both in oblique and turning conditions. Effects of oblique and turning motions on steady wave forces and moment are discussed based on present calculation.

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There is no doubt that a motorboat driver's motion during its turn has a large influence in its speed and stability. Nevertheless, this mechanism has not yet been solved. In this paper, we present a novel system to analyze three dimensional motion of a driver based upon three dimensional measurement with multiple CCD cameras. Using this system, we can calculate the centre of gravity and moment of inertia of a motorboat driver in its turn.

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The annual capsizing probability was calculated for an Indonesian RoRo passenger ship in Indonesia and Japanese water areas. The calculation method is based on an uncoupled roll equation with the piece-wise linear restoring curves and the existing wave statistics. Numerical results show the quantitative difference between different water areas and positive possibility to determine the minimum metacentric height against capsizing, while they remarks the need for longer wave measurements in Indonesian waters and for the precise prediction of roll damping. Further, the simplified method for the annual capsizing probability is proposed.

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Marine disasters which cause serious environmental pollution occur frequently. Disabled ships due to marine disasters must be removed from the sea route as soon as possible. Generally disabled ships are towed by tugboats. Concerning the towing problems with tugtowed ships systems, some factors such as the length of the towing ropes, the location of the towing point and the condition of the disabled ships, etc. should be considered. However, these important factors have been left to the knowledge and the experience of towing operators up to the present time. In order to tow disabled ships safely, we need to develop the optimum method of towing systems from the viewpoint of navigational safety.
As the first stage of this research, we carried out captive model tests to measure the hydrodynamic forces acting on disabled ships. For the conditions of the disabled ships, we considered the ship which has immersed bow due to large trim angle.
Finally, applying the results of the captive model tests, we calculated the manoeuvring motions of tug and towed ships, then estimated the course stability in towing conditions.

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In a previous paper, the author showed experimental results of a ship manoeuvring control system using an actual ship, confirming the effectiveness of a learning feed-forward control system (LFFC). The experiments were mainly concerned with the follow-up control of the ship with either the bow thruster or the rudder. However, in experiments on follow-up control with the bow thruster, response had a tendency to oscillate after 8001000 sec. from the start of the experiment.
In this paper, the stability conditions of an inverse system in the LFFC are discussed, then actual ship experiments using the bow thruster with the stabilized LFFC's for follow-up control to the desired heading angle and for compensation control for wind disturbance were carried out.
The experiments proved that the LFFC's for follow-up control and compensation control can be stabilized by the stabilized inverse system and that control systems with the LFFC's are useful in the manoeuvring motion control of an actual ship.

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In this paper, the longitudinal control system for full-submerged hydrofoil based on wave prediction was proposed to exclude human operation and to improve the performance of contouring waves. The proposed control system consists of optimal preview servo system, Kalman filter and generation of future reference input and future wave disturbance.
In the proposed control system, the wave disturbance and the wave elevation were filtered and predicted by using sensor signals, Kalman filter, 30th linear prediction model and the augmented system. Then the future reference input and the future wave disturbance were generated by using predicted wave disturbance and wave elevation, and were used to calculate the feedforward control input in the optimal preview servo system. And also the future reference was modified based on the significant wave height for ship height control.
The simulation results show that the proposed control system has good performance of contouring waves in the follow sea and the hydrofoil regulates heave and pitch motion in low significant wave height and contours the waves in high significant wave height without human operation. And also the experiment was performed to confirm the algorithm of filtering of wave disturbance and hydrofoil motion, and calculation of wave elevation.

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The importance of the knowledge of ocean waves parameters for the naval and ocean engineering field is not questionable, and the limitations of the available methods to obtain this valuable information is the leading motivation to the search of better approaches and improved analysis methods. The use of conventional marine radar PPI images allows the estimation of wave parameters on a real-time basis, using both space and time information about the evolution of the ocean surface waves. In Part I, the two-dimensional (spatial information) spectral analysis of one radar PPI image was performed, and the limitations of this approach could be evaluated using radar images numerically generated. To overcome those limitations the wave number-frequency spectrum is calculated from a set of radar images through a three dimensional FFT. The understanding of the components of this spectrum and the comparison with the expected dispersion shell allows the filtering of noise and correction of aliased frequencies. In this paper, simulated radar images generated as described in Part I and experimental data are used to evaluate the analysis method. The significant wave height was recovered using a new approach based on the shadow ratio present on the radar image.

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For the design of ships or offshore structures, a reliable database of long-term wave is very import. Nowadays this valuable information is mainly available in three forms : (1) based on visual observation (ship data); (2) hindcast data, such as provided by Ship Research Institute (SRI) and (3) based on wind data, such as provided by Global Wave Statistics (GWS) system developed by N. Hogben et al. in UK. Those different approaches to create the statistical database presents significant differences for the same sea area subdivision and the designer must choose the convenient database for each area. In this work, the long-term prediction and mutual transformation were considered to give the basic information aiming at the unification of those different databases.

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For model experiments of nonlinear behaviors of a ship running in realistic ocean environment, it is necessary to generate short-crested irregular waves that have a specified and stationary directional spectrum in a model basin. However, the measurements of the waves generated by the double-summation method with side-wall reflections indicated that the variance of wave elevation is not stationary in space. Therefore, the authors carried out comprehensive numerical experiments to compare the double-summation method and single-summation one both with side-wall reflections. As a result, it is concluded that single-summation method even with side-wall reflections can be regarded as practically stationary in space but the double-summation method cannot.

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Model experiments and numerical simulations on motions and mooring tensions of an ocean observation platform were made for the design of the mooring system and platform. The platform is under development for the study of green house effects and is planned to be moored in very rough sea area of 5000m depth. The performance of wave power device, which is installed in the platform to supply the electric power for instruments used in the chemical, biological and physical measurements, is also discussed based on pressure variations generated in the air chamber of the platform model.
In general, results of numerical simulations showed good agreement with those of experiments, though a few points needing improvement were discussed.

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The authors proposed a very large floating structure (VLFS) installing the oscillating water column (OWC) type wave energy absorption, and the response control on VLFS and the estimation of the electric power generation on OWC type wave energy absorption system were carried out. In the present, paper, a prediction method of electric power generation and also the photovoltaic power generation equipment was considered in order to carry out the examination of compound-type ocean wave power generator.
A number of researches on the utilization system of natural environment energy in ocean have been performed. In general the electric power generation is calculated from the characteristics of generator, energy and rate of operation. In the present study, the system simulation method power generator of oscillating water column type by dividing into the primary and the secondary converters was adopted. The hydrodynamic forces on oscillating water column were calculated by three-dimensional singular distribution method, and the time history simulation on primary converter was carried out, . Secondary converter was expressed by using the equation of motion on turbine. Photovoltaic power generation used existing technique.

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A very large floating structure has hydro-elastic responses that are an elastic deformation and a slowly varying drift motion. Generally, a breakwater is established to reduce the responses. However, it is very difficult to construct it from technical point of view and costs when the water depth increases. Therefore, it is necessary to develop the response reduction system for a very large floating structure even in open seas.
In this paper, a new hydro-elastic responses reduction system of a very large floating structure by using wave energy absorption devices has been proposed. The characteristics of hydro-elastic responses of an elastic structure with wave energy absorption devices were investigated both experimentally and numerically. This new system was proved effective in reduction of hydro-elastic responses of a very large floating structure. Two numerical analysis methods were developed to estimate hydro-elastic responses of a very large floating structure. The results obtained by these methods give a good agreement with the experiment results.

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We have to study slowly varying wave drift forces on very large floating structures (VLFS) carefully when we design a mooring system, because it is possible that the frequency of the slowly varying wave drift forces will be almost the same as one of the natural frequencies of VLFS-mooring systems. The aim of our research is to develop an estimation method of such forces on VLFS in the seas. In the 1st and the 2nd report, we presented a legitimate estimation method in which we can evaluate slowly varying wave drift forces easily by means of the integration of the squared relative wave height and we validated that method with model tests and with numerical calculations.
In this 3rd report, we estimated slowly varying wave drift forces on so-called Mega-Float Phase II Model with applying the method, i.e. with using measured relative wave height, and also we attempted to evaluate the incident wave from relative wave height. That is, this report shows the possibility of the estimation of slowly varying wave drift forces on VLFS from the incident waves.

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The solution method to the problem of a floating elastic disk subject to a train of plane waves is presented. This method is based on Stoker (1957) 's work and Ohkusu & Namba (1998) 's method using the assumptions of linear long wave theory, shallow draft approximation and Bernoulli-Euler equations for a thin plate. Solving an extended differential equation of Bessel in the disk domain, its velocity potential is matched to the exterior solution in the water domain. Some numerical results using this semi-analytical method are shown for a rigid or flexible disk relative to the length.

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In the present study, an accurate general-purpose three-dimensional computer program has been developed for hydroelastic response of Very Large Floating Structures (VLFSs) due to regular waves in water area of complicated environment close to real situation. It has pursued a well-balanced analysis of fluid-structure interactions with detailed modeling of respective media. Thus, NASTRAN has been adopted for the structural modeling and analysis for complicated VLFS structures and a hybrid finite/infinite element method of domain decomposition type has been newly developed for modeling and simulating the surrounding flow field of water-waves and then a modal interaction approach has been selected to make possible separate FE discretizations for fluid and structures.
The present paper discusses the structural modeling, the fluid-structure interaction strategy and a large scale modal hydroelastic response scheme examined, following the first and the second reports on a large scale computation of water waves. Special attention has been paid to data transfer between NASTRAN and the corresponding hydroelastic interaction program and modal interaction schemes.
Calculated hydroelastic responses for a rectangular plate 4, 800 m long have agreed well with the existing results. In addition, pilot calculations for a T-shaped airport and a highly asymmetric VLFS under construction have been successfully simulated. These have proved the applicability of this scheme to a class of VLFSs under consideration, largest in size and most complicated in shape.

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The objectives of present. paper are to develop the estimation method for the hydrodynamic forces on very large floating structures in the vicinity of a breakwater and to clarify the characteristics of elastic response on the very large floating structures (VLFS).
In the present paper. the source distribution method was applied to prediction of by hydrodynamic forces on VLFS and the elastic responses of VLFS were computed by model analysis. From the results of numerical calculation, the effects of breakwater on the elastic response of VLFS and the characteristics of elastic responses on the phase two model of VLFS were made clear.

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Experiments were carried out in a two-dimensional water flume to measure the elastic deformation and mooring force of a large-scale floating structure under solitary wave. The main purpose of the present study is to investigate the effect of hydroelastic response on the mooring force by changing the thickness and the length of model structures. The results are briefly concluded as follows. Firstly, the fission of a solitary wave under a large-scale floating structure is observed, and the maximum deformation of structure becomes smaller than incident wave height when the fission phenomenon occurs and decreases with the increase of the propagation distance of fissioned waves. Secondly, mooring force increases when flexural rigidity becomes larger for a certain scale of structure. Thirdly, mooring force exists a maximum value in the condition just when fission phenomenon occurs. Fourthly, mooring force can be predicted from provided wave and structure information by the non-dimensionalized parameters defined in this study.

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Recently, with increasing worldwide consumption of oil and the ongoing aging of transport fleets, a number of oil spill accidents have had highly negative effects on ocean and coastal environments. In 1997, for example, anacc ident involving the Russian tanker Nakhodka occurred in very rough mid -winter sea conditions in the Sea of Japan just off the Japanese coast. The recovery operation was hampered by high waves, and the biggest problem was the lack of equipment capable of c ollecting spilled oil in stormy weather.
In 1998 the Association for Structural Improvement of the Shipbuilding Industry (ASIS) initiated a research and development project on large -scale oil recovery systems for severe sea conditions, based on grants from the Japanese Ministry of Transport. One of the items included in this project is research and development for oil booms to be used in severe sea conditions. This report presents the results of associated work carried out in fiscal 1998, the goal of whi ch was to develop concepts of high performance oil boom and operation system.
First, several kinds of basic measurements on oil containment performance using pellets were carried out in an experimental tank in order to evaluate the oil boom type, and oil containment performance data were also obtained. Next, basic experiments of oil boom system in rough sea using actual oil were performed in a tank to decide the appropriate concept among them. Finally, based on these experiments, basic design for the operation system was undertaken.

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The deep sea drilling riser must be controlled as its top and bottom angles are within 4 degrees to avoid contact of drill strings and riser wall which may cause the destruction of riser system. The dynamics of the riser is complicated because of the coupling motion of drilling vessels and elastic. response of the riser. This paper deals with development of three-dimensional control method for deep sea drilling riser and its verification by numerical simulation and tank experiment. The presented control method is consisted of feedfoward and optimal feedback control. The feedfoward controller which is realized by the vessel's positioning and deformation control by thrusters is designed as to optimize the given objective function which is the sum of a square of riser angles and a square of control force. It compensates steady disturbances like current.. The feedback controller is used to compensate the fluctuated disturbances and elastic vibration of riser. To verify the presented control method, we developed experimental system and tank test of three-dimensional riser model was successfully completed.

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Ocean sequestration of the captured CO₂ from fossil fuel burning is a possible option to mitigate the increase of CO₂ concentration in the atmosphere. Moving ship type of CO₂ ocean sequestration is treated in this study. That is, liquefied CO₂ is delivered by ship to the site and injected into ocean depths of 1, 000 to 2.500m with a suspended and towed pipe by a slowly moving ship. In addition to the horizontal movement of releasing point, use of the rising journey of CO₂ droplets till they disappear by dissolution is effective for the dilution of CO₂ in seawater. The distance between the released depth of CO₂ and the disappearing depth depends on the initial size of droplets, the dissolution rate and the rising velocity. The possibility of generating relatively large size of droplets from moving nozzle was investigated in the previous report. In this report, the terminal velocity of CO₂ droplet under the deep-sea circumstances is measured in a large high-pressure tank, considering the influence of the hydrate film on droplet and the possible deformation when its size is relatively large. And the rising and dissolving behavior of CO₂ droplet is calculated to estimate the rising journey of CO₂ droplets in the scenario of the moving ship type of CO₂ ocean sequestration.

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This paper describes details of an Autonomous Underwater Vehicle (AUV) named AQUA EXPLORER 2 (AE-2) for inspection of underwater cables. AE2 can track cables by detecting the magnetic field induced by an AC current flowing in the cable, and can continuously measure the burial depth of the cable. The vehicle is monitored and controlled through an acoustic link between the vehicle and a mother vessel. The operating depth is 500 meters, and it can continuously dive up to 24 hours.
According to the precision analysis of the cable location system using the magnetometers, it became clear that installation error of magnetometers gave big influence to the precision of the cable positioning.
Using fluid characteristic measured by scale model test, motion simulations were performed using the linearized motion equation of the AUV. The results of field test and these simulations had good agreement. As a result of real submarine cable investigation, it became clear that AUV could trace the cable precisely using Fuzzy controller even if the tide from the side was big.

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Unsteady viscous flow field around an undulating advancing plate in low Reynolds number range is numerically studied. The main objective is to study the abilities of an undulating plate to produce thrust and achieve higher propulsive efficiency in low Reynolds number range. The Reynolds number based on the oncoming velocity and the plate length is 1000. The flow around an undulating plate is simulated by solving the full 3 D unsteady Navier-Stokes equation in a primitive value formulation. The numerical scheme is based on the MAC method where the Navier-Stokes equation is solved by the time marching method on a body fitted coordinate system.
The simulation shows that pressure is acting as thrusting force while frictional force is acting as resistance during the undulating motion. Strouhal number is the most important governing parameter for the propulsive efficiency. The propulsive efficiency is enhanced with the increase of the Reynolds number. The advancing thrust mainly comes from the aft part of the plate and the modification of the plate shape can improve the propulsive efficiency. The present study is expected to be applied for the development of a propulsor for micro-hydro-machine.

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This paper presents (1) development of a three-motor-driven mechanical pectoral fin (3MDMPF) based on the observation and analysis of three-dimensional motion of pectoral fin of a black bass, (2) its hydrodynamic characteristics, (3) development of an autonomous underwater vehicle equipped with a pair of 3MDMPFs named “BASS III” and its swimming performance. 3MDMPF can produce lead-lag motion, feathering motion and flapping motion independently. The flapping motion 3MDMPF can produce is effective in slightly increasing the thrust force compared with the case without the flapping motion. “BASS III” has a high maneuverability not only in the horizontal plane, but also in the vertical plane.

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This paper shows a framework that design process information is explicitly described and is implemented in the shipbuilding CIM system developing by authors. The two concepts are proposed as an elementary factor of design model in this framework. One concept is “Information of entity” and another one is “Information of attribute”. And design information processing is characterized as a progress from a rough design to detail design, so two design flows are proposed : one is “specification for model structure” and another is “specification for model status”. The specification for model structure means a structure of product model described by information models of entity and attribute. And a specification for model status means definitely description of information of relation and attribute values in the defined model and management that information.
In the prototype system, the information processing functions driving the specification for model structure and the specification for model status are defined as system component, and a designer proceeds design activities using the components combining. As a result the process are described in components network and well managed.

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The module construction system is established as an efficient production system in a shipyard. Because an efficiency and productivity of the module construction system are depends on block division plans, it is necessary to make proper block plans. A lot of design support systems for shipbuilding have been recently developed, but it seems that there is no effective support system for a block division planning. Therefore, a computer aided block division planning is a problem to be solved for shipbuilding CIM. In order to develop a computer aided block division planning system, this paper introduces a concept of candidate seam and shows that information on joint plays a significant role in block division planning. In this research, a computer aided block division planning system is introduced, and this system gives two processes with user interface;
-A block designer specifies information on joint of block seams and distributes structural members to each block to design blocks.
- A system generates information on joint at any position at cutting apart designed structural members.
- A system proposes some block division plans from specified block seams.
Above-mentioned functions for block division planning are implemented into the shipbuilding CIM system of authors. In order to select better division block, this system evaluates designed blocks by using product data and constraints of a facility. A few outputs from the block division planning system is shown in this paper.

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Accuracy management activities are significant problems in ship hull production. A block positioning operation in a erection stage is especially the key process in hull accuracy management. The qualities of block positioning determine not only final hull accuracy qualities, but also productivities and costs in erection stage.
The basic concept of computer aided accuracy management has already proposed by authors. Accuracy management activities are consisted of 'accuracy planning activities' and 'accuracy measure activities'. Accuracy measure activities are checking and coping with inaccuracy. Authors proposed the accuracy measure metrics : one is accuracy for completed (e.g. straightness, flatness) and the other is accuracy for construction (e.g. relative joint shapes of each part).
In this paper, detailed accuracy metrics for a block positioning operation in a erection stage are discussed. The quality of block positioning operation is estimated by this metrics : accuracy for completed can be evaluated by the concept of the tolerance, and accuracy for construction can be evaluated by the concept of labor cost. The prototype system of accuracy metrics system is implemented. This metrics system is combined with optimization software program iSIGHT to decide the best block positioning. Then some examples of block position optimizing process are shown.

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Authors have been developing integrated information system to support ship inspection. In the 1st report, ship inspection was classified into three stages (Plan, Do and Check), and prototype system for inspection planning stage was developed.
In this paper, in order to support the “Do (execution)” of inspection, information system to generate information on corrosion and inspection is developed. By carrying this system into inspection, inspector can generate corrosion information and inspection information only by doing easy operations. In order to realize this, some new models and functions are introduced. These are “Inspection State Model”, “Corrosion Model”, “Inspection State Generating Function”, “Corrosion Information Generating Function” and “Time Information Generating Function”. “Inspection State Model” and “Corrosion Model” are information models by which inspection state and corrosions are expressed statically. These models are generated by the use of above mentioned functions by effectively using Product Model, information on inspection planning and image information on corrosion.
In order to verify the proposed models and functions, prototype system is developed. Some examples are shown at the end of this paper.

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The present paper proposes a dynamical model of wheelchairs with their rear wheels locked in oscillatory environments, such as onboard passenger ships. The most dangerous situations of wheelchair use in oscillatory environment are forward sliding and tumbling down rearward. The authors tried to build a model of wheelchair motion so as to clarify the mechanism of these undesirable phenomena. The coefficients of static and/or kinetic friction between wheelchair rear wheels and the test floor play an important roll in determining the wheelchair motion in oscillatory environment. A series of experiments showed that the Coulomb's law of friction is not always satisfied in the case of forward sliding of wheelchairs. The coefficient of kinetic friction at zero speed is defined here in the place of the coefficient of static friction and was applied to the modelling of forward sliding. A comparison of some experiments and the computer simulation of wheelchair motion shows that the dynamical model using the coefficient of kinetic friction at zero speed can estimate the wheelchair motion in oscillatory environments qualitatively.

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A method to determine precisely the position of a transponder placed at a sea floor under a condition that the underwater environment (the sound velocity distribution) is not known is discussed. Not only the position of the transponder but also the unknown underwater parameters can be determined at the same time, if the acoustic rays whose number is equal to or more than that of the unknowns are obtained. The effectiveness of the method is verified by numerical simulations. If only the precise determination of the position of a sea bottom transponder is required, two or three horizontal layers may be sufficient, when a calculation method where underwater sound field is divided into horizontal layers is used.

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After the tragedy of ro-ro passenger ferry “Estonia”, a requirement on evaluating effectiveness of escape routes in ro-ro passenger ferries in its early design stage was added to 74 SOLAS Convention on 1 July 1997. In future, this requirement will be added in regulations for high speed craft. In this regard, establishment of a technique for evaluation of escape routes using computer simulations is highly anticipated internationally.
Flow rate of persons (or walking speed) in escape passages as well as size and physical conditions of escape routes and doorways are important parameters for escape route analysis by computer simulations. It is also necessary to consider list and trim as well as roll and pitch of ships.
In this study, a series of experiments were carried out to measure walking speed and flow rate of persons in listed escape routes and at doorway openings with coaming. These are unique conditions of ships. The same measurements were also made in case of existence of oncoming persons in simulated escape routes. Parameters such as flow rate coefficient were derived from the results of these experiments and used for computer simulations on escape route analysis in listed conditions of ships.
The simulations were carried out for a ro-ro passenger ship accommodated with 777 passengers and 55 crew. As the results of the simulation, increase of escape time (from the order of evacuation until assembling) was 24.5 % for in 10 degrees of list and 26.3% in 20 degrees of list.

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There are two kinds of method in ship maintenance. One is the corrective maintenance and the other is the preventive maintenance. For these maintenances, recently the stochastic techniques are widely used to keep ships in good conditions and in these maintenances it is most important to seek the maximum availability and the optimal maintenance period minimizing a given cost function. Thus, this paper suggests a method to decide the optimal policy of ship's maintenances by using Dynamic Programming and the effectiveness of the method is verified through several examples in which failure rates and maintenance data of ship's machineries and parts are given.

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In the former paper titled “Probabilistic Safety Assessment Method of Ship (Part 2 : A Risk Evaluation Methodology for FSA), a holistic methodology to evaluate risks of the ship in which several safety measures will be installed was introduced. As a possible problem of that methodology it was indicated that the number of disaster escalation scenarios would be increased so that to carry out disaster escalation and evacuation simulation may be impracticable. In this paper the developed method to resolve this problem and the trial application of this method are introduced. The characteristics of the method is to define probabilistic density function of success time at each event which affects disaster escalation directly. To do this event tree could be small, therefore the event sequences along which simulation should be carried out would be very few.

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The thinking faculty and operating ability of ship operators tend to be affected by their mental workload under the pressure from navigation environment. The suitable safety measures have to be taken to cope with the relation between stress degrees of operators and human errors based on the state-transition during operating man-machine systems such as a ship maneuvering system.
This paper, on the subject of the state-transition and stress degrees of operators, consists of (1) the estimation of accident incident probability based on the fault tree analysis and (2) the quantitative analysis of the tensional stresses by measuring the fractal nature of heart rate variability under mental work-load during maneuvering several kinds of ships. Then these results are compared with the environmental stress model proposed by K. Inoue et al., and the specific property of tensional stress generated under severe environment may be clarified with a view of to prevent marine accidents.

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