衝突時の等価附加質量について

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To calculate the absorbed energy by the flacture of ship's structure in case of collision, it is necessary to estimate accurately the added mass of striken ships. Minorsky has proposed in his famous paper^<1)> to use 0.4 for the added mass coefficient of striken ships. In this paper, the authors tried to obtain an exact expression of the hydrodynamic force which will act on ships during a collision by theoretical calculations and series of model experiments on the first atomic-powered ship of Japan were conducted. As a result, the authors have shown that the ratio of external force to the acceleration of the striken ship varies with the time elapsed during the collision : i.e., the added mass of the ship is not constant during the collision. From this result, the authors introduced an equivalent added mass which, dividing the external force by it, will give an acceleration equal to the exact value of acceleration at the end of the collision. It was also shown that this equivalent added mass changes its value with the "duration" of the collision. If the duration is infinitely sma1l, the equivalent added mass is equal to the added mass for infinite high frequency. This agrees with Minorsky's assumption. However, if the duration is finite, the equivalent added mass becomes larger as the duration increases. Since the duration is only related to the initial speed of the striking ship and the amount of penetration, and lower the initial speed or deeper the penetration the longer the duration, the equivalent added mass coefficient will be much greater than 0.4 in the case when a soft structured ship is striken by a low speed ship resulting in a considerable amount of penetration.
社団法人日本船舶海洋工学会の論文

衝突時の等価附加質量について

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