Misao Hashida

LANDWARD TRANSPORT OF SPRAY GENERATED FROM A WAVE ABSORBING SEA WALL

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Field Observations of Sea-Salt Quantity Transported Landward by Winter Monsoon

Field observations of sea-salt quantity transported by winter monsoon have been performed on a reclaimed land facing Japan Sea. The landward transported sea-salt quantity and the deposit rate have been estimated quantitatively and the leeward profiles have been normalized by introducing representative scales. Especially, the normalization gives us a universal expression for the deposit rates by winter monsoon and Typhoon 9117. The transported sea-salt quantity decreases rapidly in the dimensionless distance less than 25 because of the settling of sea-salt particles. The representative scales introduced for the normalization depend strongly on the mean wind velocity at the height of 10m. The empirical expression for the deposit rates and the quantification of the representative scale enable us to predict the settling flux of sea-salt at an arbitrary place in the coastal area.

AN EXPERIMENTAL STUDY ON THE EFFECTIVE TRANSFORMATION OF WAVE ENERGY INTO POTENTIAL ENERGY

波浪エネルギーの有効利用の一つとして, 3次元構造物を用いて波を効率的に越波させることにより獲得された水位差を利用して, 一方向流れを発生させる技術が提案されている. 3次元構造物は一様法面勾配をもつ越波堤部とV字状集波堤部から構成されている. 波浪エネルギーから効率良く位置エネルギーを獲得するには, 入射波に対して構造物の最適寸法を決定することが重要となる. 入射波が規則波の場合と不規則波の場合に対して構造物の形状と寸法を広範囲に変える実験を行い, 越波量と獲得される位置エネルギーを定量的に評価した. さらに設計波に対し所要越波量を得るための構造物の設計指針を提案した.

QUANTITY OF SPRAY TRANSPORTED BY STRONG WIND OVER BREAKING WAVES

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

Volume of Wave Overtopping Gained Effectively by a 3-D Structure

For the utilization of ocean energy, we are demonstrating how to gain the difference of water head by wave overtopping and how to discharge the sea water by using the head difference. The devised artificial structure is composed of two parts. One is the dam to activate the wave overtopping and to gain effectively the head difference. The other is the walls to converge the widely distributed wave-energy. The evaluation has been given for the volume of wave overtopping gained effectively by using the structure

A Study on Amplification Rate of Two-dimensional Regular Waves by V-shaped Con verging Walls

A project has been pursued to generate uni-directional flow in the sea by utilizing the natural enegy. This flow is applicable to the development of artificial fishing grounds or to the purification of stagnant polluted sea-water. The utilization of water-head difference has been devised as a method to generate the flow, in which the head difference is effectively gained by overtopping amplified waves through converging walls. In this study, it has been investigated how two-dimensional surface waves are amplified by propagating the converging walls. The amplification rate H/Ho is strongly dependent on l /L0, where is the length of the converging walls and Lo the wavelength in deep water. The amp l ified waves are progressive at l/L0 ‹ 0.4. Partial standing waves are formed at l/L0 › 0.6. The maximum values of H/Ho take about 2.4 for the progressive waves, and they are seen at 0.7 l from the entrance of the converging walls.