The Mightyt Whale wave energy converter is a floating device to extract the energyfrom sea waves and convert it a nesessary form of energy. If wave energy could be completely absorbed by energy converter device, waves surrounding the device would disappear completely, resulting in a calm sea. Accordingly, it is possible to combine the use of wave energy and utilization of offshore area, the value of wave energy converter would be greatly increased. This paper deals with the influence of environment by Mighty Whale, particularly waves and wave induced nearshore current around a model of Mighty Whale on inclined bottom comparing with those around a model of detached breakwater.

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It is very important to know the precice compressive strength of sea ice in order to estimate ice force acting on marine structures. This study aims to estimate the uniaxial compressive strength of sea ice and fresh water ice.
The authors carried out systematic experiment on uniaxial compressive test and dynamic elastic modulus measurement of ice. Finally, compressive strength and static elastic modulus of ice depend on ice temparature and density, and is clarified that they can be estimated by using a dynamic elastic modulus.

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The total horizontal ice force acting on multi-legged structures in ice-infested seas is estimated by summing the force on a single pile. Non-simultaneous loading of first peak force and subsequent force acting on each pile as well as simultaneous loading of first peak force are considered in the method. It is obtained that total ice force of nonsimultaneous loading, which is more realistic case, is estimated to be approximately 80% of that of simultaneous loading.

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Estimating the ice forces acting on offshore structures constructed in cold region, it is very important to evaluate fluid force acting on the ice floes. This force is called environmental force and sea ice drift is also caused by this force. When fluid force is evaluated, the drifting velocity of sea ice floes is able to be estimated. In this paper we carried a series of experiaments with paraffin ice model and found the relationship between environmental condition (for example the verocity of wind or water), and forces acting on the ice floes, and the drifting velocity of them.

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Coefficient of friction test between sea ice and various construction materials were conducted to clarify the ice-material interaction. This ice-material properties are necessary to calculate the ice forces on sloping structures in cold coastal and offshore regions. Through the six years experimental studies, the following conclusions have been drawn (Saeki et al. 1986) The coefficient of friction have been found to be affected by the following: i) relative velocity; ii) sea ice temperature; and iii) surface roughness of construction materials. They have been found to be relatively unaffected by the following; iv) contact area; v) normal stress; vi) growth direction of sea ice; and vii) water at the sea ice-material interface.

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The abrasion of offshore structures constructed in cold regions occur when the movement of ice sheets are active during the time of thawing. Theleft-lettore, It is very important in the design of offshore structures for very cold region to estimate the abrasion amount due to a movement of sea ice sheet. Basic studies on the abrasion of various construction materials due to the movement of sea ice have been conducted by Saeki et al. Furthermore, as natural sea ice sheets contain fine sand, the authors also systematically experimented on various materials abrasion by sea ice containing sand. According to the data obtained, the authors propose an estimation method for the actual amount of abrasion on offshore structures. And the authors examined the adequacy of our abrasion estimation method, comparing it to the result of the observations of the light house in the Gulf of Bothnia.

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The authors carried out a model study to evaluate the effects for control of ice floes movement by two kinds of Ice Booms (Traditional Ice Boom and New type Ice Boom) and to investigate the ice forces acted upon them. Through these systematic experiment, the authors obtain the following results:(1) The effect of sea ice control determined by a function of Fe and h/L (Fe: Froude number; h: ice thickness; L: representative length of ice).(2) In practical situations, if the traditional type Ice Boom can control icefloes of up to 80cm/sec velocity, the New type Ice Boom can control ice floes of up to 150cm/sec.(3) Ice forces can be calculated from the area of ice floes trapped by Ice Boom, roughness coefficient of ice cover and velocity.

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The Okhotsk Sea coast of Hokkaido is covered with sea ice and drift ice for three or four months, theleft-lettore ships can't navigate, and ports are closed. All works the sea are discontinued completely except for the culture fishery. The drift ice which rushed into lagoons caused heavy damages to culture fishery, and marine products coastal areas of the Okhotsk Sea were damaged by the movement of drift ice. This paper describes the control techniques for drift ice movement.

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Coastal structures constructed in Okhotsk Sea coast of Hokkaido have been attacked by water waves and drifting sea ice floes. The weight or shape of the armor units, side slope are interrelared and comprise the principal factors in the design of artificial reef. In this report, the authors deal with the stability of armor concreat blocks on artificial reefs which are attacked by water waves and motion of ice floes.

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Asphalt mats with cold ocean gravity structures is an economic construction method because the coefficients of friction can be increased. However, flexibility and the visco-elastic response of mats which contribute much to the sliding resistance decrease at sea water temperatures below 0°C. In summer, temperatures inside the asphalt mats rise at manufacturing yard. An investigation has been made to develop mix proportions of asphalt mats which are less sensitive to temperature, and so suitable for the wide change in temperatures in cold oceans.

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A series of abrasion tests of three types of concrete piles were carried out by use of a large scale U-shaped tube which generated a strong oscillatory flow with sand drift. Abrasion rates of usual concrete and underwater concrete are the same and larger than centrifugal concrete. Abrasion rate of concrete is roughly proportional to the 2nd-3rd power of amplitude of velocity. The larger the ratio of sand particle diameter to pile diameter, the larger abrasion rate.

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Composite column of PBS method consists of precast concrete blocks and filled-in concrete and steel pipe pile. The authors conducted the serial tests in order to clarify the stress changes of introduced prestress due to the drying shrinkage and creep by means of monitoring strains and carried out the mechanical tests for comparing the theoretical values. The results of this study show that the stress losses due to the drying shrinkage and creep could be taken by a few theoretical formulas and that the stress state in this composite structure could be obtained by creep factor and strain of drying shrinkage stated in the Standard Specification for Design and Construction of Concrete Structures by JSCE.

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This report gives the outline of a technical development for the under water concreting carried out at Hokkaido during the past two years.
The research for the advancement of construction technique is performed by collecting and analyzing the data as for the mix proportions, concreting, quality of concrete and others on the base of the practical construction in marine fields.
From the surveying results, it is ascertained that the characteristics concerned with concrete quality and the properties of the concreting have an influence with the compressive strenght, frost resistance and so on.
It is found that the new casing-system for under water concreting is available for a measure to prevent the segregation due to free dropping.

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Recently, caisson type structures have been employed as offshore structures in regions of extreme cold. As the liquid, sand or gravel filling proceeds, the caisson freezes and the internal pressure rises. It has previously been verified that this pressure rise, due to an increase of volume caused by ice growth, depends strongly upon the permiability coefficient of the sea ice forming within the sands and gravels. This paper deals with the variation of inner pressure in two kinds of model caissons due to ice growth.

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In-service periods of some among the facilities in coastal region have already passed the years of endurance, so that, especially, the deterioration assessment of foundation structures which bear the upper structures has become an important subject. In case of steel structures, the main evaluation factor is soil corrosion, but the actual state of soil corrosion in coastal region is not confirmed yet.
In this paper, we investigated the corrosion data of steel piles, and conducted a few experiments to obtain the basic data of soil corrosion. As the results of these experiments which were simulated the changing of ground water level, we confirmed that the corrosion rate becomes very high when the soil has good aeration.

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Softsit-on-bottom type offshore structure has been considered as one of the safest offshore structure systems against earthquake and settlement of ground. This system was developed in 1980 by the outhors and has been proposed for such purposes since then. In this paper, the structural charaeters of this structure system is described according to three casestudies of ocean city projects-Campus City in the Tokyo bay, Osaka bay marinecity and Makuhari messe island Project.

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Fishing communities have long played an important role in coastal region as the base not only for the fishries industry but also for the marine utilize system. In recent years, it very often occures to conflict between fishiry activities and marine liesure uses due to increasing demand of marine liesure. So we propose a basic idea to adjust these two uses in coastal water area.

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Weakness of coastal zone at Male island against high waves is discussed. At this island rapid economic development and population increase enhanced necessity of land reclamation. Land reclamation on coral reef greatly decreased the wave dissipating effect of natural reef. In order to increase safty for wave disasters, protective measures are needed. This study summarizes the orientation of future planning of these measures.

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Slides showing past coastal disasters collected by Prof. O. Toyoshima were analyzed. 378 pictures were selected. All photos were classified into four categories; (1) Disasters due to tsunami, storm surges and high waves and countermeasures, (2) Beach erosion and damage of coastal facilities, (3) Sea cliff erosion, and (4) Coastal utilization. Damaging process of coastal revetments is revealed for a typical example.

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DOUBLE CYRINDRICAL CAISSON BREAKWATER has been newly developed to create calm sea area in the deep and high-wave area.The 3rd District Port Construction Bureau determined to adopt this new type breakwater in Shibayama Port which is designated as a left-lettuge port. Before applying this new breakwater to Shibayama Port, in order to confirm the validity of the developed design method and security of construction work, field observation has been carried out since 1989. This paper reports some results of analysis from viewpoints of hydlaulic property of this new caisson.

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A curved double slit caisson breakwater is a kind of perforated-wall caisson withan arc-shaped slit wall. The caisson is very stable against storm waves and can dissipate large amout of wave energy.However, impulsive wave forces act on the arc-shaped slit wall with a rear chamber.
Curved double slit caisson is invented to improve the curved slit breakwater. The curved double slit caisson has the second vertical slit wall with a rear wave chamber. The curved double slit caisson can reduce the impulsive force greatly and can dissipate wave energy with a relatively small wave chamber.

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This paper reports the developement of double semicylindrical hybrid caisson using the head of breakwater at Fukui Port, where the big waves caused by winter sensonal winds attack many times and the brakewater had been required to improvement with wave dissipating concrete blocks.

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The 5th District Port Construction Bureau, Ministy of Transport has been developing Block-embedded Double-box type Caisson adapted for the deep-sea (-40m) and the large waves (H_max=16m) at the baymouth of Shimoda Port.
As compared with the caisson covered with wave dissipating blocks in the deep-sea, this caisson saves many blocks, but it has the similar characteristics of wave left-lettlection and transmission.However, in order to keep the stability of embedded blocks, it is necessary to make the upper blocks of heavy concrete. Besides, the stress caused by highest wave is so large in some members of the caisson that it is necessary to use steel-concrete composite hybrid members.

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A New type caisson structure, which has a horizontal gutter on i'ts side wall perpendicular to the breakwater alighment, can form a pipe for water interchainging beteween in and outer sea. This structure is named Crenellated Breakwater after its small holes on the front wall. In the present paper, hydraulic characteristics of crenellated breakwaters and their effects on water interchange are revealed by the results of model tests in a wave flume and numerical calculations.

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This paper deals with the characteristics of wave dissipation and wave force forthe proposed breakwater. For the characteristics of wave dissipation, random waveexperiment have been carried out to compare with the results of regular wave test which hadbeen performed before. And still more, wave forces acting on this breakwater have been investigated by experiment used regular waves. Based on results, the calculationmethod of design wave forces can be applied to this breakwater are presented as well asthe description of characteristics of wave left-lettlection and transmission.

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Wave left-lettlection from a slit-type breakwater having diamond-shape or circular-shape cylinders as a front wall is obtained theoretically and experimentally. A method of a previous study where the matched asymptotic expansions was employed is used. The blockage coefficient for the diamond-shape cylinders which has not been gotten yet is obtained by using the Boudary Integral Method (BIM). The value of the energy loss coefficient for the cylinders is decided after comparison of theoretical values with experimental data. The left-lettlection coefficients for the slit-type breakwater with diamond-shape and circular-shape cylinders calculated from the present method agree with experimental data, as are those for the one with square cylinders. The difference in the characteristics of the left-lettlection coefficients of a slit-type breakwater having diamondshape, circular-shape, and square-shape cylinders is discussed.

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Doubly arranged semi-floating breakwater is proposed. Two bodies are hanged from water bottom with hinged rod, and connected each other by a resilient rod for interaction of wave forces.
Transmission of waves, motion of bodies and forces on bottom are examined on theoretical model and experimental study. It is shown that coefficient of wave transmission and wave forces are much less than these of fixed body.

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A method of numerical analysis on the wave diffraction and radiation by a linear array of identical three-dimensional floating bodies is newly developed by a wave source Green's function method. Using the numerical method, wave transmission characteristics through an infinite array of rectangular floating breakwaters and dynamic responses of these break waters are extensively studied, including directional characteristics of the transmitted waves. It is clarified that obliquely transmitted wave components are predominant behind the floating breakwater array when an incident wave length is less than a center-to-center distance between the neighboring breakwaters.

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Wave transformations by flexible-type submerged floating breakwater have been investigated in correlation with the variation of air depth in the air-chamber and submerged water depth experimentally. As a result, it can be pointed out that the wave left-lettlection tends to be larger, the wave transmission smaller in order to generate radiation waves by dynamic behavior of the floating and membrane movement as the air depth and the submerged water depth decrease. This type of floating breakwater can contral the wave left-lettlection and transmission.

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Experiments are carried out in a wind water tunnel. Wind velocity and wind-wave height behind the breakwater are measured. In this paper, wind-waves are the newly generated waves behind the breakwater by wind. Six kinds of model breakwater areused for the study. Breakwater with the mound of precast concrete armor units shows the largest reducing effect on wind and wind-waves behind it.

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