A two-dimensional laboratory experiment was conducted to investigate the movement on the nourishment-gravel composed of sand, gravel and cobble due to huge waves. As the experimental site, the on-offshore beach profile in the surveying point No.47 in the east side of Showa-hosuiro in the Fuji coast is selected. The experimental scale of horizontal and vertical lengths, and wave conditions are adopted the Froude law. The scale of sand grain size is decided by considering the similitude law of beach profile change, and similitude laws obtained the investigation results on the two-dimensional beach profile and on-offshore sand movement by waves.
In the experiment, waves in a storm event is operated for the beach model of 1/40-sacle. The movements of beach sand and nourishment-gravel, and settling under the seabed of nourishment-gravel are measured by using experimental tools of beach profiler, boring cone for taking the sample from the sub-seabed layer, and digital camera. By the arrangement of measured experimental data, it is seen that the nourishment-gravel moves rapidly into the surf zone within 30 minutes after wave operation; and after 1 hour wave operation the moved nourishment-gravel is gradually buried under the seabed by the sedimentation of moved beach sand.

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In order to monitor the environment in the coastal zone, a monitoring system with a digital video camera, which moored to a balloon, is developed in this study. From some images captured by the developed monitoring system the diffusion coefficient over the artificial tidal flat of Hannan Second District in Osaka Bay, and the seawater purification system through use of biological intake of oyster growth promoted by bubbling in Katakami Bay in Nagasaki. The estimated values of the diffusion coefficients at the both observation sites have same order 10^-2 m²/s.

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Wind farm at sea must be one of important projects in Japan. Although several mono tower and mono pile type wind turbines are in operation in North Sea having the flat sea bed, there is a problem of how to estimate wave loads on such type of structure which would be built on a slope of the sea bed around Japan. In this study, estimation of wave forces acting on such a tower using both a simulation of wave by “CADMAS-SURF” and a calculation of Morison's equation is taken on trial. And it is found that this wave force estimation method gives good results for the condition on the slope where other estimation methods are not effective.

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To broaden utilization of wind energy, floating offshore wind farms are said to be valid because of deep, high slope of sea flour off Japan. However, a cost-effective construct is a critical matter and so necessitate the development of high capacity and easily deployable anchors, which tend to be used on trials for toutmooring of floating units in deep sea environments in Brazil. Measurements were done for dragging distance, penetration depth, inclination and pulling tension of rectangle plates in homogeneous dry sand and clay in a tank. This paper describes the analytical model taking mechanism producing holding capacity into considerations along with bearing capacity factors obtained by solving the equilibrium of forces such as gravitational force, friction, resistance force and pulling force acting on the plate fluke.

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Japan has lagged behind European countries in advancing wind turbine technologies in part due to the occurrence of frequent severe earthquakes. Therefore we conducted a 1/55 scale model test to clarify vibration characteristics of an offshore wind turbine structure during earthquake conditions (actual frequencies from 3 to 1 Hz), by using shaking table together with wind action. The test was also carried out in wind tunnel generating low frequency oscillations (0.27-0.67Hz) correspondent with the first natural period of the structure. Furthermore by fixing isolation rubbers onto the foundation of the model, we also examine the effect of seismic isolation in order to diminish vibrations caused by ground motion. The measured strains in tower and acceleration of a nacelle were compared with results of dynamic analyses by using finite element analysis. We concluded that while rubber isolators are valid for wide frequencies, the fluctuating wind forces acting on rotational blades also decrease the motion of tower as aerodynamic damper.

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This paper describes the technical feasibility study and the economical evaluation of the floating wind power system. The box-girder type floating structure installed three wind turbines is proposed as a concept. The 5MW class propeller type turbines are adopted. The box girder with simple structures is favorable in the cost performance. Moreover, the wave induced motion and the righting moment can be optimized easily. The estimations of the static inclination and the wave induced motion were carried out in technical study. The relations between wind loads and motions or inclinations were investigated by the wind tunnel test. On the numerical analysis of motions, the fluid dynamic forces were calculated using the potential theory with zero draft assumption in the estimation of motion. The floating structure model was consisted by beam elements of FEM. The calculation result showed that the motion and the inclination in an operation condition are less than 5 degrees. According to the economic estimation, it was presumed that the proposed concept can be attained to the equally cost of water-power generation and others.

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Offshore structure made of concrete in ice-covered sea areas is likely to meet an abrasion due to sea ice movement, and needs to be a light weight because of long carriage for its installation. Therefore, it is necessary to determine the thickness of covered concrete with high accuracy. The method to estimate an amount and area of abrasion is shown in considering both local ice pressure distribution and change of water level due to tide. The way to reduce the abrasion is also proposed.

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Inland navigation had played a key role for physical distribution in earlier times. As railway and road had developed, however, inland navigation had declined. Recently, inland navigation draw renewed attentions from the aspects of reduce of physical distribution cost and global environmental problem.
Ishikari River is located in cold region and it is known that the water is frozen in winter season. So the measurements for the ice problem are needed on the facility of inland navigation. In this study, some measures of ice buildup on lock wall are considered.

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The distribution of local ice pressure acting on offshore structure in ice-infested sea area is investigated through data obtained by the plane pressure panel sensor in in-situ ice/structure indentation test using sea ice. The local ice pressure is characterized into two types depending on indentation velocity (V) divided by ice thickness (h). This is why ice failure pattern depends on (V/h). In the paper, an approximation curve of the ice pressure distribution is proposed as a multiple of uni-axial compressive strength of sea ice.

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Ice-Scour Event is a phenomenon that occurs when deformed ice such as an ice ridge comes into contact with seabed. Ice-Scour has been reported to cause damage to communication cables and water intake pipelines. Although most of technical issues against the ice-scour have been focused on estimating the scour depth/burial depth, it will be also important to consider a sub-scour deformation, which means stress transmission or soil deformation within the seabed below the sea ice.
In this study, we carried out basic model experiments related to the sub-scour de Iformation by setting up some test conditions. We found that the stress within the seabed during ice-scouring does not depend on a drift speed of a model ice but an attack angle, and that the model ice with the smaller attack angle is though to cause the soil deformation of larger areas because of restriction/compression of a large amount of soil in front of inclined surface of an ice.

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A vacuum suction oil skimming system is investigated. Several types of suction inlets are experimentally studied with small-sized models. Their suction performances are measured in terms of liquid suction rates, oil and water fraction, pressure gradient and liquid hold-up in a vertical suction pipe in various simulated conditions. In the experiments, W/O emulsified heavy oil, whose viscosity is about 300, 000m Pa·s, is used. The results show that the vacuum suction is a potentially suitable measure for skimming spilled oil from sea surface since it has even better performance on a wavy sea surface than on a calm surface. A large-sized oil suction experiment is also conducted and its results are compared to those of the small-sized experiments to discuss the scale effects. The comparison provides a basic design strategy for a real-sized onboard oil recovery system which an oil recovery vessel will be equipped with.

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In the Nahotokha oil spill, the use of a crane bucket was found to an effective method for recovering the oil under low temperature and rough sea. However, a system for separating oil from water that is also collected in the bucket is needed for this recovery method. This paper describes the system for separating oil and water that uses conduit with a semi-circular cross section that has drainage holes in the bottom. Experiments were carried out under the conditions of unsteady flow. From the experimental results, design parameters of the system were discussed.

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A large amount of heavy fuel oil C was spilled out to the sea in the wreck of the Russian tanker “ Nakhodka ” in January, 1997, and serious damage was brought to the coasts which face to the Sea of Japan. Cleaning cost of an oil recovery vessel is very high and polluted beach is recovered by hand wiping without steam spray and detergents that kill life. So the cost reduction and new method of cleaning equipments and beaches is requested.
We experimented with cleaning heavy fuel oil from iron plates with only physical cleaning from ultrasonic power. The experiments were carried out under room temperature without detergents.
We obtained relation between the cleaning time and frequency, and between the time and power density, of ultrasonic waves. Besides, the relation between the cleaning time and the cleaning rate was approximated with theory curve of a cleaning velocity.

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This study deals with a low frequency oscillation of a large scale rigid floating body. The oscillation due to first order short period waves of an order of 10s is small. However, new free low frequency waves appear both sides of the floating body if a second order (bound) low frequency waves are considered. Due to the free low frequency waves, together with the low frequency bound waves, the floating body shows an significant oscillation. In this study characteristics of the new free low frequency waves around the floating body and the oscillation induced by the wave is clarified. The mooring system, which reduce the low frequency oscillation in principle is also explained.

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[in Japanese]

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This paper deals with the characteristics of combination resonance for submerged floating structure. The combination resonance takes place in a vibratory system having multiple degrees-of-freedom and under parametric excitation. In this study, it is assumed that the floating structure is moored by some tension legs and located in the water between seabed and water surface. Due to such a structural form, there is much possibility that complicated dynamic phenomena like parametric excitation take place. The parametric excitation is caused by the time-varying tension force of tension legs. The time-varying tension force arises when some dynamic loads such as regular waves act on the floating body and the body moves in the water. In this paper, analytical studies are carried out to confirm the possibility of the occurrence of unstable motions by introducing Mathieu equations and effects of tension leg arrangements on the combination resonance characteristics are investigated in particular.

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Submerged Floating Structure is a whole new type of strait crossing which is fixed in the water and supported by the balance between buoyancy and drag force of tension legs. This structure is expected to be widely applicable for railway, road, pedestrian walk and transportation system of material and fluid. In order to realize this construction technology, however, there are a lot of problems to be solved.
One of the most important probrems is parametric excitation which is the response caused by time-varying tension force of legs. In this paper, the parametric excitation phenomena of Submerged Floating Structure are studied analytically and characteristics of the dynamic instability are investigated

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We have partly presented a new type of floating breakwater, which is able to reduce reflection waves for comparatively short waves and also transmission waves for comparatively long waves as compared to the conventionalp ontoon-typef loatingb reakwater.T wo additionald evices are adaptedt o the pontoonb reakwater;s uch as vertical-barrier-typree flectiond issipatersa nd submergedh orizontalp lates. In this study, i n order to improvet he performance of a new breakwater for much longer waves, effect of the dimension of submerged horizontal plate is examinede xtensively.A fter such 2-D examinationsa, newly developedf loatingb reakwateri s applied to the 3-D wave field. By the use of 3-D wave tank, wave height distributions around the arrayed floating breakwaters are observedt o know the effectivenessin the open sea. In the test, we have used two differenta rrangemenmt ethods of the breakwater array to improve the performance.

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In late years, in stead of existing method of construction such as land reclamation, needs for semifloating structures are increasing. Especially, semi-floating structure are considered to be effective, because reaction of ground of seabed can be reduced by buoyancy of structure. However, response of such structures to the vertical motion of earthquake has not been understood. In this study, for the evaluation of responses of large semi-floating structures, an analysis method had been developed. This method is based on a combination of BEM with FEM. Using this method, it appeared that the response of semi-floating structure to the vertical motion of earthquake is influenced by the stiffness of structure, supports, mass and displacement. These results were examined by shaking table test in water.

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The authors developed a reduction system for low-frequency ship motions that can effectively reduce low frequency motions of moored ships, and they also proposed the system as one method for countermeasures against long-period waves. The reduction system for low-frequency ship motions can reduce the surge motions of moored ships by preventing resonance with long-period waves, and computer-controlled hybrid mooring winches make it possible to forcibly change the natural period of mooring system consisting of a ship and mooring ropes. In this study, the authorsv erifiede ffectivityo f the reductions ystemf or low-frequencysh ip motionsb y the fundamentahl ydraulic model experiment

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The field measurement of moored ship motions is necessary to decrease troubles in cargo handling. But it was difficult to measure ship motions accurately by using accelerometer.
In this paper, a 3D PTV algorithm is applied to field observation of moored fishing boat motions. As a result, six-directional ship motions are measured accurately. This observation shows that heaving, rolling and pitching have only one energy peak which is the same period as energy peak of sea wave. Surging, swaying and yawing have two energy peaks, and the energy of peak in long period is higher than the energy of peak in short period. These two peaks are the same period as peaks of sea wave.

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A rate of effective working days is calculated by frequency of wave height which is lower than the allowable value. The allowable ship motions are necessary for calculating the allowable wave height. Both allowable values for cargo ship and tanker are proposed by Ueda, but those for fishing boat are not proposed.
The purpose of this study is to propose the allowable ship motions for fishing boats by questionnaire for fisherman, and the allowable wave height for fishing boats by simulation of ship motions. The investigation of questionnaire shows that the allowable ship motions of fishing boats in Hokkaido are ±0.5m for surging, +0.5m for swaying and ±0.5m for heaving. And the simulation result of ship motion shows that the allowable wave height depends on size of ships and wave period.

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This study presents an appearance condition of resonant phenomena in a narrow gap between two modules of very large floating structure under waves. We apply a theoretical method for an estimation of natural frequency of fluid in a U-tube with different diameters to a theoretical development for the appearance condition. A natural frequency of fluid in the gap which is composed of a geometrical condition of floating structure, a gap width, a length of module, a draft and a water depth, is derived by energy conservation around a module on the side of incident wave. Then, the appearance condition is derived by substituting a dispersion relation of incident wave into the natural frequency of fluid in the gap as kl tanh kh=1 (k: incident wave number, l: geometrical condition of floating structure, h: water depth). A laboratory experiment is also conducted in order to understand characteristics of fluid resonance in the gap, and the validity of the appearance condition is verified by the arrangement of experimental results using kl tanh kh and l/λ(λ: wave length).

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