In the coastal engineering field, breaking waves cause the destruction of coastal structures due to impulsive breaking wave pressure. Although the phenomenon of wave breaking is very important in terms of engineering, the occurrence condition of breaking waves is not sufficiently understood yet. In this research, to clarify the occurrence condition to the breaking of waves, the theoretical analyses of progressive waves in constant water depth are carried out. Further, the numerical simulation of wave run-up on a uniform gradient water depth is also performed. In the theoretical analysis, the characteristic phenomenon of the kinetic energy of the water surface exceeding the potential energy as the wave height depth ratio increases on the Hyperbolic wave and the solitary wave are shown. To show the validity of the theoretical analysis, the numerical simulation of wave run-up on the periodic wave and the solitary wave are conducted, and the simulation result confirms the same results as the theoretical analysis. As a conclusion of this study according to the results of the theoretical analysis and the numerical calculation, the kinetic energy of water particles on the water surface increases divergently as the wave height to depth ratio increases which leads to wave breaking; because it occurs the wave height depth ratio is the same order as the breaking wave height depth ratio in the case of constant water depth and just before the wave collapses in the case of uniform gradient water depth.

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 Based on the basic technology established in the knowledge of the flap gate type watergate, the newly developing flap gate type rising seawall was applied to the improvement of the coast protection facility of Muya port, Tokushima, Japan. It have been put to practical use by overcoming various problems due to installation of land side. It is a new type of seawall, using the buoyancy during inundation at the time of tsunami, tidal wave / storm surge, the gate body turns upright and falls without power / manual operation. In this paper, the basic idea of design and maintenance based on the applicability study of flap gate type rising seawall to Port of Muya is presented.

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 With the marine steel structure, the corrosion damage of steel materials by the seawater and degradation by the marine biofouling become the problem. In this exposure test, we made a test piece by metal spraying with Al-5% Mg alloy and copper materials, and thick anticorrosion coat. It was exposed installed on seawall of total six years. As a result, within this experiment parameters was not provided the coated specifications the anti-biofouling effect with more than two years. However, the knowledge about anti-biofouling and corrosion prevention by metal spraying with Al-5% Mg alloy and copper materials, and thick anticorrosion coat was obtained. We report a result of exposure test for the purpose of contributing to the development of the anti-biofouling and corrosion prevention coating specifications in the future marine steel structure.

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