Effects of Hydrodynamic Forces on Ice Plate Bending Failure

本文的研究结果总结如下：1。在冰模盆上进行了三种模型冰板的弯曲性能试验。分别是悬臂梁弯曲试验、三点弯曲试验和板挠曲试验。利用刚体弹簧模型进行了计算，探讨了悬臂弯曲试验中存在的问题。结果表明，通常采用的悬臂梁弯曲试验，其杨氏模量明显减小，主要是由于与悬臂梁根部连接的板的挠度造成的，而其抗弯强度给出了适当的数值。利用二维流动计算和梁理论对船舶推进水压对破冰体尺寸的影响进行了基础理论分析。结果表明，由于冰块尺寸减小，冰下压力增大。这种趋势与全尺寸船和模型船的观察结果一致。破冰力的增加与航速的平方成正比。现有的冰阻预测方法没有考虑到这一事实。在“大豆”号破冰船上进行了全尺寸和简化船模实验，以测量破冰船的破冰模式。冰的深度与长度之比在0.17 ~ 0.27之间。厚冰板增大了全尺寸船和模型船的碎冰量。全尺寸冰块与模型冰块的尺寸存在显著差异；模型中的冰块比全尺寸的冰块大几倍。考虑到这种差异是由于实尺和模型之间冰力学特性的差异。

The results obtained in this research are summarized as follows :1. Three kinds of model ice plate flexural property tests were performed at an ice model basin. Those were cantilever bending test, 3 point bending test and plate deflection test. Calculations using Rigid Body Spring Model were also made to investigate the problems in the cantilever bending test. The results showed that the generally adopted cantilever bending test gave significantly smaller Young's modulus mainly because of the deflection of the plate connected with the root of the cantilever while it gave proper values of the flexural strength.2. Fundamental theoretical analyses using two-dimensional flow calculation and beam theory were made to investigate the effect of water pressure due to ship advance on the size of the broken ice pieces. The results showed that the pressure increase under the ice plate due lessened the ice piece size. This tendency agreed with the observations on the full-scale and model ships. The force to break the ice increased in proportion to the square of the ship speed. This fact has not been taken into account in the existing ice resistance prediction methods.3. Full-scale and simplified ship model experiments on the icebreaker "Soya" were performed to measure the icebreaking patterns. The ratio of the ice piece depth to its length was in the range of 0.17 - 0.27. Thicker ice plate enlarged the broken ice pieces for both the full-scale and model ship cases. The size of the ice pieces were significantly different between the full-scale and the model ; the ice pieces in the model were some times larger than those in the full-scale. This discrepancy was considered due to the difference in the ice mechanical properties between the fullscale and the model.