| Budget Amount *help |
¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1990: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1989: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
Impact pressure by breaking waves on a vertical wall gives often rise to serious damages of coastal and harbor structures, and shows high variability in its characteristics. Thus, in this project, generation of the impact pressure is discussed both by time series data of the wave pressure on the wal and high-speed video pictures taken simultaneously with the pressure measurement.
The main findings of this project are as follows ;
(1) The impact pressure occurs when a narrow lens-shaped air pocket is trapped between the vertical wall and the breaking wave front. The impact pressure is divided into two types of the time histories, single impact pressure and damping oscillation associated with impact pressures.
(2) Prediction of the impact pressure should include aerodynamic processes of the trapped air pocket. A simple model, taken into account of the adiabatic process, was proposed. The model indicates that the pressure maxima and pressure frequency are functions of aspect ratio of the air pocket as well as the breaking wave height and water depth in front of the wall at impact.
Virtual mass scale, contributed to the impact process, is determined by comparisons between the model and experiments. The scale is given as a function of the vertical height from the bottom to the breaking wave created at instant of the impact.
(3) Experiments confirm that the single impact pressure occurs when the aspect ratio is smaller than 0.2.
(4) Simultaneous records of the impact pressure and pictures of the high speed video reveals that the damping oscillation associated with impact pressures terminates before release of the trapped air. The damping mechanism can not be specified in this study.
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