In the first place, the breaker type on an artificial reef is classified by using high speed video camera. Next, velocity vector fields for each breaker type is measured by using PIV, and the characteristics of internal velocity fields are clarified for each one.
In the typical case that the slope gradient is 1:3, the breaker type changes from spilling breaker to other breaker types regardless of h/L, as H/h increases. Especially in the range of H/h>0.25, the breaker type changes from plunging breaker to the plunging-surging under the same H/h, as h/L decreases. And moreover, the maximum offshore velocity on the crown at the backruch is closely connected with the transition of the breaker type.

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The objective of this study is to investigate experimentally the breaking limit of waves due to a submerged breakwater in a multi-directional random wave field. Experiments have been conducted in a 3-D wave basin equiped with a multi-directional random wave generator. In this study, a special type of wave gages has been employed to record the water surface fluctuations at wave breaking with favorable accuracy. This study investigates the influence of incident wave conditions and wave directionality parameter S_max on the wave breaking limit. An equation has been introduced to predict the wave breaking limit in regular wave field using the least square technique applied to the results. This equation has been revealed to work well over a wide domain of wave conditions ranging from crossing waves to multi-directional random waves.

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A series of laboratory tests were made on the nonlinear behavior of random waves on a rectangular step. Waves with a sharply peaked spectrum exhibited the secondary and tertiary spectral peaks at the frequencies twice and thrice the peak frequency owing to nonlinear interactions, in a manner similar with the cases of regular waves. As the peakedness of spectrum decreases, the nonlinear spectral peaks become unnoticeable.
Random waves on a rectangular step are accompanied with long-period waves, the amplitude of which increases as waves propagate from the tip of step toward the rear end. While the long-period waves moving offshore maintain the nearly constant amplitude, the waves moving onshore increase their amplitude. The mechanism of amplification could not be clarified in the present study.

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The MPS method, generally called the Particle Method, which is the Lagrangian concept to solve the Navier-Stokes equation, is applied to the plunging breaker on a uniform slope. The MPS method has a superiority in the accurate calculation of the complicated behavior of water surface. In other word, it is less affected by the numerical diffusion due to the convection term than the Eulerian methods. The characteristics of splash due to the collision of a wave with a slope and the transition of the mode from the breaking to the runup via the bore are investigated based on the detailed numerical information of the velocity field on a slope.
By introducing the additional drag term, which represents the existence of the permeable layer, into the governing equation, the wave breaking and runup on the permeable slope is also simulated. The effect of the permeability of the slope on the wave runup process is also discussed.

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This paper describes interim development of a numerical wave flume for practical use in designing maritime structures. The flume is based on a 2-D numerical wave simulation using a NASA-VOF method particularly selected because it can reproduce highly nonlinear wave profiles against various structures, e. g., impact of a breaking wave on a vertical wall. During fiscal years 1998 to 2000, a cooperative research group has been tasked with this project, having almost completed the associated computer code in 1998 and studied application of the numerical wave flume for practical design of various types of coastal structures.

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The wave observation data at ten stations along the Southern Pacific Coast of Japan were analyzed for the distribution of extreme significant wave heights for the purpose of establishing the parent distribution in this region. The wave observation at these stations has been conducted every two hours for the duration of 8 to 25 years. The peaks-over-threshold method was used to define the extreme wave heights, the number of which ranged from 151 to 409 per station with the total number of 2884.
The candidate distributions of the FT-II (four), FT-I, and Weibull (four) were subjected to rejection tests by the DOL and REC criteria proposed by Goda, and the distribution with the least case of rejection was assumed as the parent distribution. The necessity to deal with the mixed population was clearly demonstrated for this region, because storm waves by typhoons were much greater than those by other disturbances. The population of extreme waves by typhoons seems to have the FT-I distribution as the parent, but the limitation in the sample size prohibits to draw the definite conclusion.

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At present, waves and storm surges are predicted by the numerical simulation to determine the design wave and water level for designs of storm surge barriers. In the designs, maximum extreme wave and highest storm surge are employed as the design wave and water level without consideration of the possibility of their simultaneous occurrence. Possibility of the simultaneous occurrence is of great importance to check the effectiveness of the present storm barriers on the protection of storm surges.
In the present paper, the characteristics of the simultaneous occurrence of maximum storm surges and waves have been investigated by analyzing the field data in Osaka bay. The results of the investigation conclude that the simultaneous occurrence of maximum storm surges and waves depend mainly on the course and speed of typhoons.

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An approximate method for solving wave boundary-value problems about a harbor consisting of impermeable and permeable boundaries, such as rubble mound breakwaters and vertical breakwaters, is developed. The vertical line source Green's function method was basically used for efficient computations. Extensions of the method to the permeable boundary conditions were examined precisely. It was confirmed that the approximate method developed here is very effective for estimating wave height distributions in a harbor with permeable breakwaters.

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A Boussinesq equation model was connected with parabolic mild-slope equation model in order to relieve their burden of calculation. The method of connection was that first, the wave motions, refraction, shoaling deformation and diffraction in relatively deep water were calculated based on the parabolic mild-slope equation, and then the wave motions in shallow water were calculated by the Boussinesq equation. It was demonstrated that the connection of two models was efficient for a wide area calculation in practical use.
Moreover, in order to verify the Boussinesq equation model for the calculation of wave motion around a offshore barrier in shallow water, laboratory experiments were made with offshore detached breakwater. The wave height and depth-averaged velocity distributions were measured in detail and compared with results of numerical simulation.

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A non-linear wave-current model is presented for wave transformation analyses in a wave-current coexistence field. The model is based on Madsen et al.^{1), 2)} type extended Boussinesq equations. For the application of the governing equations in a wave-current field, a wave-current dispersion relation is also derived from a wave-current velocity potential. A semi-implicit finite difference scheme is adopted for the solution to the equations. The model is applied to a sloping bottom topography and 1D model results are compared with laboratory experiments and analytical solution. Results depict that interactions are more pronounced in the constant-depth shallow water region, and wave height increases for waves propagation against adverse currents and wave height decreases for waves propagation with following currents. Also, the wave-current field changes mean water level all over the domain, and steady current and wave motion affect the wave-current set-down.

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Wave forces on a structure installed on a submerged breakwater have been measured to investigate their characteristics. It has been observed that the impulsive wave force due to wave breaking acts on the structure located the vicinity of the leading crown of the breakwater. Them agnitude of the impulsive wave force has been revealed to be much larger than those of then on-breaking waves. Thet imev ariation of the impulsive wave force is well evaluated with the Morison equation by adopting the velocity and acceleration at the front face of the structure. Moreover, it has been revealed that the drag coefficients decrease for higher values of KC approaching the constanv talue. On the other hand, the inertia coefficients are almost constant for all the tested values of KC.

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Recently, plans of large pier structures, such as offshore airports and artificial islands, have been proposed. In order to design such structures safely and rationally, uplift pressures acting on them have to be precisely evaluated. The uplift pressures caused by regular waves have been studied and their behavior has been characterized by some researchers experimentally and theoretically.
In this paper, the uplift pressures caused by multi-directional random waves are investigated through hydraulic model tests. The effect of taking the multi-directional random waves into consideration on the maximum values of impulsive wave pressures is discussed.

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Effect of block scale and Reynolds number on model experiment of wave pressure in range of breaking wave was examined on an upright sea wall provided with wave absorbing works.
Wave pressure obtained decrease with an increase with following parameters: ratio of incident wave height to block scale, H_I/d', Reynolds number, Re, ratio of width of wave absorbing works to wave length, B/L and ratio of width of wave chamber to wave length, l/L.
The wave force at the upright seawall taken wave absorbing works is P and the wave force without a wave absorbing works is P₀, in addition the ratio of P to P₀, is found between 0.12 and 0.92.

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When the overturning jet of broken wave hits a wall of coastal structure such as a breakwater, the impact force acts on the structure, which often give a great damage to the structure. Although there have been many reports on the impact force, little is known about the quantitative properties of the force and velocity fluctuation in time. In this paper, the plunging jet attacking to the structure was numerically solved by the direct numerical scheme with the high level of accuracy. The correlations between the surface profiles, the direction of fluid velocity and the pressure were also discussed through the investigations of spatial and temporal changes of them.

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As semi-submersible structures have smaller resonant frequency in the heaving and rolling mode compared to surface vessels, the response of a freely floating semi-submersible structure for Tsunami is studied experimentally. The solitary wave is chosen as Tsunami. The maximum displacement and inclination of the structure show easy result to understand when the maximum slope of the solitary wave or the ratio of wave height to water depth is taken as a parameter like the wave period in regular waves. Approximately speaking, the structure climbs up to the wave height, moves horizontally as the same to the water particle, and inclines to the maximum slope of the solitary wave. The structure, however, climbs up and inclines a little more than those when the height-depth ratio is small, while a little less when the height-depth ratio is large.

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Wave forces on a vertical cylinder in directional waves have been investigated. Morison equation has been utilized to express the wave force. In directional waves, the effect of the lift force may dominates over the drag and inertia forces when one component of the horizontal water particle motion dominates over the other one. Under such conditions, the Morisone quationc onfirmedt o be less accuratei n estimatingt he wave force. The effect of the lift force, however, becomes less important in estimating the wave force acting on a whole cylinder. This paper shows that the wave force on the cylinder can be evaluated with the drag and inertia coefficients obtained in this study. Moreover, it is confirmed that the wave forces in directional waves, for a given magnitude of the velocity, is larger than that of the uni-directional waves. Thus, effect of the directional spreading should be properly consideredi n the estimatingt he wavef orce.

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Nowadays, there are many research reports about submerged floating tunnel (S. F. T.). In this paper, we examined the vibration response of floating tunnel supported by tention legs. We measured angle response and vibration response of the test model of S. F. T. subjected cross flow using by parameters reduced velocity and reduced angle displacement.
From that, we can observed the flatter vibration coupled between angle response and lift motion of S. F. T. and discuss about the mechanism of flattervibration, subjected steady flow, caused by rotating vibration of ballast container mode and some amplitude (3 degrees).

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In this paper, flow structure around a circular cylinder was calculated in each cases of waves of small amplitude in long waves, in shallow water and in deep water. The Boundary Element Method with the Green's integral equation was used for numerical analysis of the potential flow in field of wave motion. Also, in case of analysis of flow structure around the circular cylinder, vorticity equation and Poisson's equation for stream function ware employed for governing equation, and flow structure with separation and fluid force acting upon the circular cylinder ware calculated numerically, using the finite differential method and spectrum method. In the result of study, it was confirmed that flow structure or fluid force was evidently different in each cases of water waves. Further, fluid force by numerical analysis was compared with Morison's equation and was discussed.

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Seasonal characteristics of current velocity with the long period were clarified from field data during the longterm in Ishikari Bay. These long period current have a high velocity even at deep water levels outside breaker zones. The fluctuations of current velocity can be estimated by the storm surge formula that assumes wind stress to be the external force and Coriolis force to be the restoring force. The compensation currents were caused by the effect of above things. These currents are dominated near the bottom layer and are larger in winter than in summer. It is seemed that these phenomena were occurred by the seasonal variations of Tsushima warm current.

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Tsunami causes extreme erosion and accretion in the bottom of a harbor.The collision force of the floating objects is also one of the problems in tsunami's disaster.To understand them, hydraulic model experiments are carried out.Flow pattern in a harbor by tsunami are measured by PTV (Particle Tracking Velocimetry), one of the flow visualization methods.
Tsunami intrudes in the harbor along the breakwater, and generates a circulation inside.In case of tsunami that has a large wave gradient, the super-critical flow and hydraulic jumps can be seen in the mouth of a harbor.
Accuracy of PTV was also verified in the experiment.The velocity by PTV is compared with that by an electromagnetic current meter.Those have quite good agreements except the space where the hydraulic jump exists.

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The diffusion of a negatively buoyant jet that issued horizontally from a pipe outlet into shallow water and fell onto the horizontal bed was investigated experimentally. The densimetric Froude number of the jets are from 6.7 to 17.0. The velocity profile and the temperature profile of the freely falling jet and those of the horizontally spreading jet on the bed floor are emerged.Those profiles keep similarity in shape in each zone. As the distance s from the outlet along the axis of the jet increases, the maximum velocity of the profile decreases in proportion to s^-1 or less in the freely falling zone. Meanwhile the maximum velocity decreases in proportion to s^-1.5in the horizontally spreading zone.When the jet impinges onto the bed floor, the freely falling jet transforms smoothly into the horizontally spreading jet, but the entrainment of jet pause for a while.

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Recently, the high-density mud transport systems using a compressed air are utilizing in the field of coastal zone developments. This system is very useful for high-density slurry transport because it is easily to separating air from slurry. The purpose of this paper is to clarify the mechanism of slurry transpo-rting system using a compressed air in the experimentally. In the experiment, the air-liquid twophase flows have been focused on liquid of low viscosity in long distance pipelines with narrow diameter and discussed the mechanism of generating, development and breakdown of slug flows. As the results of experiments it was shown that the water depth of slug flow generating is nearly constant for all conditions of air-water mixing ratio in pipe flow.

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Lately, the breakwater where waves not only are controlled but also the water quality is purified has come to be requested. In one of such structures, there is a breakwater with the submerged mound. The offshore seawater rises on the submerged mound the water elevation, and flows into the port through the hole in the breakwater. However, the seawater-exchange function goes down in the area where the change of the tide level is large occasionally.
In this study, we developed the moving structure to tide level change, and examined the hydraulic characteristic. On the floating structure, the seawater rises the water elevation, and the seawaterexchange function does not go down even if the change of the tide level is large.

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Water-exchange performance of newly-deveroped caisson with front panel in waves is investigated by model experiment. Panel height, panel spacing from the caisson and diameter of water introducing pipe are adopted as experimental parameters.
Panel height, which is found an important parameter, should be adjusted to the still-water level. The present caisson of unit length in waves of one-meter height can introduce several hundred tons of the outer water, which seems enough quantity for improvement of water quality, to the restricted area behind the caisson per hour.

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It is important to keep sea water exchange in a fishing port especially when its internal space is utilized for aquaculture. Authors havc developed a new type permeable breakwater with a cylindrical shaped projecting tube that has large cross section, and examined their hydraulic characteristics. Experiments showed that flows in the tube are not only dependent on pressure difference by water level inside and outside the port. Entrainment flow also gives an influence on the flow in the tube. Entrainment flow is caused by vertical flow outside the port, but its velocity could not be evaluated correctly by existing energy formulae. Authors developed a numerical model that describes the characteristics of the velocity, and examined the experimental results by the model. The newly developed formula will be useful to quantify and control the flow in the tube. It is important to keep sea water exchange in a fishing port especially when its internal space is utilized for aquaculture. Authors havc developed a new type permeable breakwater with a cylindrical shaped projecting tube that has large cross section, and examined their hydraulic characteristics. Experiments showed that flows in the tube are not only dependent on pressure difference by water level inside and outside the port. Entrainment flow also gives an influence on the flow in the tube. Entrainment flow is caused by vertical flow outside the port, but its velocity could not be evaluated correctly by existing energy formulae. Authors developed a numerical model that describes the characteristics of the velocity, and examined the experimental results by the model. The newly developed formula will be useful to quantify and control the flow in the tube.

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The breakwater with hole for exchange of seawater is being constructed at Konoura fishing port in Akita prefecture. The system of this breakwater is intending to take outside seawater through the hole by differential water pressure which made by breaking wave compulsory at underwater bound It was designed to apply low wave height during summer season in order to get required seawater quantity effective way. As the breakwater has completed partially, the field investigation was conducted to consider effect of the breakwater system. This paper is stating the design method, field investigation and the result of the system for breakwater with hole.

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Beach erosion of the Hitotsumatsu beach on the Kujukuri coast in Chiba Prefecture facing the Pacific Ocean was investigated by field observations in 1997 and 1998. The Kujukuri coast has been formed by the deposition of sediment supplied from the sea cliffs located both ends of a 60km long stretch of coastline. Disappearance of sand source of the sea cliff due to the construction of wave dissipating works on foot of sea cliff as a measure against erosion and obstruction of continuous sand movement by breakwaters of the harbors caused severe beach erosion on the downcoast. Here such a situation is studied and future measures against beach erosion is discussed.

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Relation between configuration of a comet tail formed in the lee side of an island and the predominant wave direction was investigated at Himeshima and Mashima islands in northern Kyushu. The direction of a comet tail shows the direction of predominant wave incident to that island. Field observation was carried out at Mashima island. The difference of coastline features around this island can be well explained by oblique wave incidence predicted by the shape of a comet tail. The existence of rocky north coast covered by boulder and south coast composed by shell beach is explained by this fact. The predominant wave direction was also determined from the shoreline shape in a pocket beach and compared with that obtained from the shape of the comet tail.

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Field investigation of formative mechanism of scarp around headland built on the Chigasaki coast facing Sagami Bay in Kanagawa Prefecture was carried out. Beach nourishment was conducted at this coast against beach erosion and beach changes after the nourishment were measured. Formation of double scarps were found at the lower and upper levels of the beaches depending on eastward longshore sand transport associated with rough waves and westward longshore sand transport generated in calm wave condition.

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The characteristics of coastal processes in IRAGO-NISINOHAMA beach and the protection techniques against beach erosion are discussed. Since the beach was eroded, several structures have been constructed to protect the beach against erosion. The apparent northerly sediment transport has been found to be mainly caused by the winter wind coming from the west side. However, the wind waves coming from the Pacific Ocean south of Ise Bay are thought to be the main cause of topographic changes around the breakwater. It can be judged that the detached breakwaters and the groin work effectively to reduce the shoreline retreat in IRAGO-NISINOHAMA beach.

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The single space beach change around breakwaters in the new port of Ishikari Bay is described using the beach profiles of field surveying.
The following properties was made clear after examining the results of field surveying
(1) the shoreline and the equilibrium point of beach profile are relating to the grain size of beach sands,
(2) the trough depth is proportional to the bar depth and they are relating to the steepness of wave breaker,
(3) the changes of shoreline is effected by the wave reflection, and is related by the site of trough and bar.

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Beach changes triggered by the construction of detached breakwaters and harbor breakwaters were investigated through comparison of aerial photographs on the Yotsukura and Natsui coasts both located in a pocket beach of 11km long stretch facing the Pacific Ocean. Formation of wave calm zone behind these breakwaters induced severe beach erosion on the surrounding beaches as well as sand accumulation in the lee side of the structures. Further the construction of gently-sloping coastal revetment covered vast area of natural sandy beaches. Deep concern should be paid to the change in this coastal situation in order to preserve and recover natural coastal environment.

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Coastal geomorphology, coastal protection and management in Denmark and Sweden were investigated through a field study and collaboration with local researchers. Coastal managementregulations and protection schemes such as the right of public access to the beach and groin system have been well established in Denmark since 1241 and early 19^th century, respectively. In Sweden a few coasts are protected against waves by artificial structures and most of southern coasts are allowed to change in natural manner. In Denmark beach nourishment is preferred and becomes major coastal protection scheme in recent years. Danish experience and knowledge are useful to future activity of beach nourishment in Japan.

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Aerial photographs were taken to investigate beach changes on coral coasts and sand movement around reef gap at Sanur and Nusa Dua Beaches on Bali Island by using a ultra light plane. At Sanur dominant beach changes can be observed around groins because of obstruction of longshore sand transport. On both beaches, beach erosion has become serious problem and various measures were taken, but lack of overall comprehensive plan reduces natural sandy beach to artificial coastline protected by many kinds of structures.

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For artificial beach constructed in coastal region facing to a coral reef, the stability of sediment is most important Meanwhile, the beach should be convenient for amenity activity and valuable to natural landscape. In order to protect the beach erosion in such artificial beaches, several countermeasures are proposed and carried out. The head land method is one of the most effective way for beach stability. This paper proposes the new effective arrangement of head lands to protect the artificial beach planed in coral reef employing the three dimensional experiments. In the experiment the level of flow which caused the beach erosion are determined in the two dimensional cannel tests.

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Burrowing bivalves such as surf clams (Pseudocardium sybillae) that inhabit open sandy beaches are an important fishery resource. The main reason for the decrease in the number of bivalves is due to high waves, and the release of bivalves from the seabed into the water is thought to be the first phase in the mortality process of bivalves. Local erosion and accumulation velocities during sand ripple formation caused by the asymmetry oscillatory flow are experimentally studied.The intensity of bed deformation speed and maximum erosion velocity due to asymmetry oscillatry flow are estimated from the results due to oscillatry flow, taking into account the effect of asymmetry on Shields number.

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The results of numerical analysis indicated that the velocity inside mat decreases when the velocity at the upper boundary becomes large. A small amount of circulating flow takes place with the occurrence of vertical flow, which seems to relate to the diffusion of suspended sediment. Sediment concentration near the bed, averaged over a wave period, is about 1-40% of that without mat. The maximum Shields parameters are about 0.16-0.65 and 0.04-0.13 with and without the mats, respectively. The maximum Shields parameter without mats is nearly equal to the critical condition of eelgrass growth obtained by Nakase et al. Meanwhile, with mats it is less than the critical value obtained by Nakase et al.
The sand-control mat presented in this study is demonstrated to be one effective means for the development of eelgrass beds.

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Beach changes of the artificial beach made in Odaiba Coastal Park of Tokyo located deep in Tokyo Port were investigated by field observations. The shoreline of this artificial beach was made in a L-shape due to the limitation of land usage in the park and predominant waves are incident obliquely at a large angle at one part of the beach. This causes shoreline recession at that site due to the action of longshore sand transport toward the inner side of the bay beaches. Shore protection using seawall made of wood was adopted, but beach erosion advanced to fail this seawall. Some measures to solve further beach changes were proposed and compared.

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Gently-sloping coastal revetments have been widely used in Japan for creating easy access to the beach. However, most of them were built on the sandy beach, whose foreshore width isaround 30m or less, and the construction of mild concrete slope of around 1: 4 with the top height of over 5m on the beach causes artificial beach erosion due to the coverage of natural sandy beach. Nevertheless gently-sloping coastal revetment is widely believed to be useful to create attractive coastal environment. Field observations were made to investigate this issue, and it is concluded that the present usage of the gently-sloping coastal revetment is a mistake.

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Beach changes around Misawa fishery harbor facing the Pacific Ocean in Aomori Prefecture were studied by field observation. The breakwaters of this harbor blocked longshore sand transport, and north coast was severely eroded to be artificial coastline protected by many coastal structures, whereas south coast was accreted. Sand supply from further south coast of Misawa fishery harbor is decreasing rapidly. This means that adoption of sand bypassing method, in which sand will be carried from the south side of the harbor to the north coast is impossible, because this newly causes beach erosion on the coasts further south of this harbor. It is needed that harbor breakwater should be regarded as a large-scale headland to stabilize the coastline and returning of sand from the harbor to the further south coast should be considered

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Beach erosion induced by construction of detached breakwaters in a pocket beach of a closed littoral cell was investigated taking the Ariake-Takahama coast facing the Pacific Ocean in Ibaraki Prefecture as the example. In order to protect houses against wave overtopping 8 detached breakwaters were built on this coast. This caused longshore sand movement toward the wave calm zones behind the detached breakwaters, whereas south beach was severely eroded by this sand movement. Advance of coastal forest and construction of sea dike to protect this forest further accelerated narrowing the sandy beach. Four measures to prevent this phenomenon are proposed and compared.

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Waterfront areas have recently come into increasing use for various purposes, including activities by the general public, and for residency. At the same time, waterfront area environmental problems have surfaced regarding compatibility with public activities, havitability and general comfort; a. e. problems precisely attributable to the coastal location of waterfront areas. To develop a waterfront area as an attractive space, it is essential to ensure that the area has a comfortable natural environment.
As previously reported, field measurements of seawater and meteorological information, coastal forms, and the distribution of aerial sea-salt particles near the coast in the Northern Kyushu natural and artificial coastal zones were conducted to obtain fundamental data. In addition to the above, a field measurement was also conducted to examine absorption effect of aerial sea-salt particles of the area within a distance of 600m from the coastline in the Northern Kyushu windbreak forest coastal zone.

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Development of oil and natural gas deposits are currently under way at the northeastern coast of Sakhalin. In the early stage of this project, it is planed to transport crude oil by surface tanker. But it is well known that the major spills in the ocean were caused by tanker incident.
In this paper, the simulation of oil spreading and drifting with the scenario of oil spill from the tanker at the Soya Straits was conducted. Based on this simulation, it is pointed out that the coast of Soya Bay could be polluted by crude oil spill, and the heavy impacts for fisheries of the coast of Hokkaido should occur. To reduce the impact of oil spill, some requirements for oil-combating plan was discussed.

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In January 1997, the oil tanker “Nakhodka” spilled about 6, 200 kl of heavy oil into Japan Sea. The spilled oil was followed by mechanical and chemical techniques. Usually, physical properties of spilled oil change rapidly due to the hydrodynamic and environmental conditions, and its viscosity increases quickly. Finally, spilled oil becomes high viscosity substance such as mousse. In case of Nakhodka, mechanical recovery methods such as dredger, vacuum track and concrete placer showed good results in recovering of high viscosity oil. This paper reports the experimental results on more effective recovery method through systematic experiments.

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Development of oil and gas deposits off Sakhalin's northern coast in the sea of Okhotsk are currently under way.An accident involving a spill of crude oil could be expected to affectthe environment and economy of the Hokkaido's Okhotsk coast.If the oil spill occurred in winter season due to the accidents of pipeline, oil tanker and oil rigs, spilled oil would be trapped under the ice floes. If the operation for recovery of spilled oil will be late, spilled oil under the ice floes will be trapped in the ice sheet. In this paper the authors report the behavior of spilled oil trapped under ice sheet and the permeation of spilled oil into ice sheet.

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The fate of spilled oil in sea area is governed by complex interrelated physico-chemical processes that depend on the oil properties, hydrodynamic conditions and environmental conditions. Evaporation begins immediately after spill, and it is the main process which caused the loss in oil volume and the increases in viscosity and density during weathering. It is very important to select the recovery method to clarify the change in viscosity and density of spilled crude oil. In this paper, the authors describe the process of characteristic change of spilled oil, and newly developed simplified measurement technique of viscosity.

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The horizontal vibration induced hydrodynamic pressure or force acting on offshore structure surrounded by a large floating ice plate is explored. A numerical calculation procedure is developed using the Green's function method for compressible fluid region around an axisymmetric structure. The ice plate is considered as a rigid or deformable annular plate in the procedure. In case of deformable ice plate, thickness and rigidity of the plate are considered. Besides the analysis, physical model test using the underwater shaking table in ice sea basin is conducted.
Calculated pressure using rigid ice model shows fair agreement with the experimental results. By numerical and experimental results, it is shown that the hydrodynamic pressure on the icebound offshore structure are much greater than that without ice plate, and could be estimated by proposed numerical method.

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Vertical sided structures may have advantages over inclined structures in terms of construction costs and past experiences. Although, it is well recognized that even a massive structure may vibrate if a load exceeds certain level after the lesson of Molikpaq experienced in 1986. Designers shall know the parameters that cause vibrations while structures indent against various ice features. The vibration may inversely affect design loads and foundation stability. A five-year ice load research program was executed from 1993 to 1997 to clarify the characteristics and develop the computer code capable of simulating vibrations and associated loads. Extensive ice tank tests were performed to observe crushing phenomena and obtain the verification data for the computer code. In this paper, highlights of test results are summarized to feature the non-simultaneous and simultaneous failure modes.

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It is postulated that the failure mode of flaking with crushing is dominant for small scale laboratory indentation tests. However rubble piles accumulated in front of an indentor preclude either direct observation or video analysis that might allow an estimation of flaking length. The authors attempted to conduct indentation tests using a vertically placed ice sheet set up in the testing machine so as to measure the flaking length by video analysis. The test results and analysis are presented. It is shown that the flaking length tends to increase with increasing compliance of indentors and to decrease with increasing indentation rate

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This paper describes the experimental study on the first year ridge load. The authors attempted to estimate ridge load by the ice tank tests despite the lack of the field data setting rough assumptions. Ridges were built in the ice tank using molds. The consolidation depth was controlled with the insulation sheet and room temperature. 800mm wide rectangular indentor with segmented ice pressure panels in water line and ridge keel direction was used to measure the local pressure characteristics. The tests were performed varying the indentation velocity, compliance of the indentor. An estimation of the fist year ridge load exerted on a vertical sided structure is attempted using the test results.

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