A Study on Velocity Dependence of Breaking Component in Ice Resistance

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Other Title
  • 砕氷抵抗の破壊成分の速度依存性に関する研究
  • 砕氷抵抗の破壊成分の速度依存性に関する研究 : その1 模型実験による破壊成分の速度依存性の検証
  • Part 1 Experimental Evidence of Velocity Dependence of Breaking Component in Ice Resistance
  • その1 模型試験による破壊成分の速度依存性の検証

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Abstract

It is well recognized that the ice resistance in continuous breaking mode consists of several components. However, the quantitative recognition of those components in the ice resistance is poorly understood. To understand the ice resistance quantitatively, the dependency on such factors as a thickness of ice sheet, a bending strength of ice sheet, a velocity of ship and so on has to be clarified for each component. <BR>Among those components in the ice resistance, it is unanimously recognized that the breaking component is of primary importance. It has been considered by many investigators that the breaking component strongly relates to the moment capability of ice sheet, σƒh2 and does not depend on the ship velocity. However, the authors have had doubt on this recognition that the breaking component is independent of the velocity of ship. Such doubt comes partly from the experimental study by Kato et al. and partly from the theoretical study by Sorensen and Tawara & Horimizu. <BR>In order to clear this doubt, it is necessary to separate the breaking component from other components. For this purpose, a new component separation test-named the TBI test-was developed and employed to the 1/20 model test on medium size icebreaker. The TBI test can use an almost completely preserved broken ice field which has been made just before by the test of the same model in intact level ice. Thus the TBI test employs a realistic breaking patters of ice field. The model experiments were performed on three different velocities. Six or seven tests were conducted at each velocity under different combinations of ice thickness and bending strength to verify the prediction. It was found from experiments that a relationship between the breaking component and the moment capability of ice sheet is linear when the velocity is specified. It is in agreement with authors' prediction. A relationship between the submersion component and ice thickness is not strictly defined, but a linear relation is again tenable. <BR>Coefficients of both the relationship between the breaking component and the moment capability of ice sheet and the relationship between the submersion component and ice thickness were plotted with respect to velocity. It was found that both coefficients increase with velocities. This indicates that both the breaking component and the submersion component increase with velocities. It is concluded that the velocity dependence of the breaking component in ice resistance has been clearly evidenced. However, in order to understand the ice resistance more quantitatively, the authors should concern a study on the velocity dependency of the breaking component, which was not accomplished in the present study.

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