船首部に作用する衝撃荷重について : 第2報

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The impact pressure due to the water impact was studied experimentally and numerically. The two dimensional impact tests of a rigid flat plate, a 1-deg wedge and a 2-deg wedge were carried out under the condition that drop velocity was kept constant during the water impact. Experimentally it is confirmed that in case of the water impact of 2-deg wedge the impact pressure obeys Wagner's theory and the air layer is not formed between the wedge and water surface. In case of 1-deg wedge the air cushioning effects appear when the drop velocity is higher than 0.4 m/s. In order to investigate the mechanisms of the flat plate impact, the phenomena during the water impact were filmed with a high speed camera at 2000fr/s. The pictures show that during the impact the edges of the fiat plate doesn't touch closely the water surface, but the air-water mixture is formed between the plate and water surface near the edges. Since the density of the air-water mixture may be higher than that of the air, the high density mixture chokes the air flow under the plate. Thereby, the pressure between the plate and water surface ascends rapidly. We present a mathematical model considered the mixture leakage. Numerical simulation was carried out of this model. The air layer thickness, added mass and coefficient of the air leakage, which cause the impact pressure ascending, were estimated by means of the comparison of the numerical results with experimental results. The estimated values obtained from the simulation almost agree with the observed values.
社団法人日本船舶海洋工学会の論文

船首部に作用する衝撃荷重について : 第2報

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