This paper deals with characteristics of the wave pressure distribution on a bottom-seated hemisphere obtained by model experiments under regular waves. The obtained results are summarized as follows;
(1) The dimensionless maximum wave pressure decreases in a region of the head of the hemisphere.
(2) The maximum wave pressure increases almost linearly with the increase of the wave period T when the wave height is constant.
(3) The maximum wave pressure decreases at the circumference of the top pore of the perforated-hemisphere.

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A tsunami breakwater is constructed at the mouth of Kamaishi bay, the Iwate prefecture in the northem part of Japan.The caissons have slit members at their fronts.For the design of this type of caissons, it is important to estimate the wave pressure on the members as well as the caisson stability, The present paper experimentally studies on wave pressures of the slit members in a multi-directional wave basin.Compared wave pressures in uni directional wave with that in multi-directional one, the maximum wave pressure on a member becomes much Iager in the uni-directional wave condition.Therefore, the model test in multi-directional sea is important to get a reliable results.

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A series of model test is carried out to investigate the critical condition of the occurence of impulsive tension in offshore oil booms moored slack in waves and curre nt. The critical condition, at which the maximum tension suddenly increases with con trol parameters changing, is discussed in terms of representative dimensionless parame ters such as gap ratio or Froude number.A numerical model is proposed for predicting the critical conditoin and compared with the experiments.

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Mooring buoyes are widely employed to moor vessels in some isolated islands facing to the ocean. The impulsive tension induced by large waves may cause heavy damages to the mooring line and buoy. The application of a rubber-chain is proposed to reduce the impulsive tension. The effects of the rubber-chain are experimentally investigated. An approximate computation model for estimation of the impulsive tension on the mooring line is verified in the experimental results. The computational result for a buoy with a mooring line of 40m demonstrates that the employment of a rubber-chain only 10m long is effective to protect the occurence of the impulsive tensions.

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The time-domain analysis of the floating body dynamics in shallow water is developed based on the Green's function method. A practical method for evaluating hydrodynamic forces on a two-dimensional floating body is presented in detail. Using the numerical procedure developed here, the effect of nonlinearity of catenary mooring on the dynamics of a rectangular dock is examined. Specifically, the linearized result based on the frequency-domain analysis is compared with the one by the time-domain analysis. Also, the estimation of the equivalent spring stiffness appropriate to the frequency domain analysis is examined extensively. Finally, a series of model tests is carried out to verify the time-domain analysis and also the estimation method of the equivalent spring stiffness.

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In recent years, marinas which moor pleasure boats are widely planned and constructed in Japan. These facilities have been constructed in the calm sea where is sheltered by bay or sound. Recently, marinas are also constructed in the open sea under the influence of ocean waves. Then, motions and forces of floating piers under waves actions become more important in the design procedure of those facilities. In this paper, several methods which compute motions and forces of floating piers are compared and evaluated.

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Floating bridges with column-type floating foundations have been studied in this paper. Wave response analyses of the proto-type floating bridges have been performed for six different floating foundations, each of which has the different shape, and the effect of the shape of the floating foundations to the wave response has been examined. In the analysis, the interaction effect of the elastic deformation of the structural system with fluids are included, and the effects of the interactions to the response are also examined. The analytical results have shown that the shape effect of the floating foundations are significant. In conclusion, the possibility of the control of the wave response of floating bridges by changing the shape of floating foundations are shown.

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In Tomakomai East Port, though in calm, a moored ship has often been oscillated with long period of a few minutes. That ship oscillation called “Soko-Uneri” has often terminated cargo handling and caused break of mooring ropes. In this study, according to the simultaneous observation of ship oscillation and wave motion, it is shown that long period waves enter the harbor and cause the resonance behavior of the moored ship. The properties of such long period waves are also discussed with relation to wave setdown.

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The experiments on this study were conducted to find the effective motion control by a flat plate attached on the pontoon, and also Wave response characteristics of several type of the pontoon were examined. Then, it was verified that the flat plate have worked effectively for motion control of a floating pontoon, especially against a wave with conparatively large wave steepness. It was confirmed that the dimension and attaching depth of flat plates are important factor for motion control of a floating pontoon. The most effective plate for motion control on these experimental condition is case 4. This method using a simple potential energy of fluid could be multiply applied to pontoon with other formed ones.

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This study is concerned with the development of numerical model for the dynamic response of flexible floating pier due to ocean waves. The numerical model was induced by improving a numerical method for rigid floating structure. The motions and the tension forces of mooring lines of the pier were calculated from the method. The results of numerical simulation were compared with those of laboratory tests. It was found that the flexibility of the joints is a dominating parameter for the vertical movements the floating pier.

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Wave equation under an elastic floating body suported by springs over an arbitrary bottom topography are derived. By using this equaton, under the condition of constant water depth, a Fortran program to obtain the dispersion relation is given, and some figures are shown for the ratio of the wavenumber of waves under an elastic floating body to that of free gravity waves.

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This paper deals with a large scale pontoon-type structure such as floating airport. Experiments have been performed for the 2-D model structure made of polyurethane plate and having the length of 10m, the width of 0.5m and the thickness of 76mm, 38mm and 19mm. The experimental results have shown that the wave response of such flexible structure clearly differ from the rigid-body motions. Some experimental results are presented and are compared with the numerical examples using BE-FE combination method for the 2-D structure.

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We have studied for a new type of Spar-Buoy boring derrick, which required to cope with two exceeding conditions, namely (1) increasing loaded weight of boring machine parts and materials for increasing boring depth, and (2) a increasing current velocity to about 4 knots.
We have studied two models, (1) double float type, and (2) larger diameter of float for increasing buoyancy, in order to utilizeparts and materials of the existing spar-Buoy boring derrick for economical choice.
We have performed numerical analysis and model experiments for two type model, and prototypes were designed and put to practical use.

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The dynamic response of caisson structure with suction force between bottom of caisson and seabed was numerically evaluated in the frequency domain by means of structureseabed interaction analysis. In this paper, caisson structure was assumed to be a rigid rectangular prism with skirt, whose base has several square compartments, and the suction force was to act on each compartment. While the seabed was assumed to be a fluidsaturated poroelastic medium whose behavior is governed by Biot's theory of wave propagation. The effects of skirt length of caisson structure and suction force type acting on compartments on the dynamic response of caisson structure were numerically investigated.

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Seabathing is very comfortable and enjoyable. Seabathing is one of the most popular sea recreation in Japan. However more than 100 people per year were dead in sea accidents. Two series of field suverys were conducted to investigate people's safety during seabathing. The first one is to investigate the accidents in 11 coasts during the summer of 1993. The second one is to observe more in detail the people's movement at I coast in Shizuoka Prefecture in the summer of 1994. The results show some relations between the accidents and winds, waves and currents.

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Flow patterns and lifting properties of air-lifts in homogeneous environments are examined in laboratory experiments. The flow patterns are classified into three ones; bubble flow, slag flow and bubble bullet. It is shown that different flow patterns can appear even for the same air-rate, which influence lifting properties. Critical lift head is formulated from the balance of buoyancy and gravity in air-lift. Non-dimensional air rate, Fb, is derived. Lifting discharge is explained with the balance between buoyancy and wall friction, and it is clarified that the characteristic buoyancy, Mp, and the characteristic Reynolds Number, Rp, are very important parameters for lifting discharge.

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Synoptic views from Landsat are useful to grasp hydrodynamic phenomena of large scale of water area. But, Landsat images can only show a temporal scene of the changing phenomena. To compensate this deficiency, numerical simulation should be introduced. This paper show an example to solve this problem through a case study of Ise bay. The authors investigate a relation between the residual current and dispersion of flood water seen on the Landsat image data.Circumstance of the current was examined by computer simulation with finite difference method. The results of this study are summarized as follows: 1) flood water are deflected to the right due to Coriolis force, 2) density current may have an important role for the management of water quality in Ise bay.

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