| Developing the study concerned with mechanism of sea-ice breakup is important in analyzing the formation of ice ridge and overlapped ice, ice riding up and piling up. And it is also one of the main principles to describe the ice loads and ice induced vibration between the interaction of ice and structure. According to the characteristics of sea-ice in Bohai, the mechanism of ice breakup on tidal fluctuation and waves is analyzed, and the physical model tests are carried out to confirm the rupture theory model of ice sheet under the action of regular waves. On the basis of the static equilibrium principle and the bending theory of beam, the theoretical model of ice breakup on shallow beach due to tidal fluctuation is set up. And the ice height, ice length, ice limit bending strength and the slope angle that influence the breaking length of sea-ice are discussed. In order to analyze the fracture of offshore large sea-ice under the action of waves, the wave equation under the infinite long ice sheets is simplified, and so the simplified formula of wave groups velocity are derived. By means of flux energy, the deformation effects of ice sheet elastic energy on wave transmitted into the ice sheets are also analyzed and discussed. And so the limited wave heights relative to the flexible failure of semi-infinite long ice sheets in different incident waves and different bending rigidity, bending strength of sea-ice are also achieved. According to the theory of floating motion, the forces that the regular waves exert on the floating sea-ice blocks are calculated by means of numerical method of finite element. Also the interior stress of sea-ice is calculated with the elastic beam theory, and the limited wave height of ice breakup is derived. The factors to control the finite- length ice breakup are discussed, and the applied range of the breaking theory is given. Under the actions of tidal fluctuation and waves, bending failure is happened in sea-ice, and the fracture is close relative to the ice bending strength, ice size and conditions outside. The results indicate that the ice breaking length increases for longer, thicker ice sheet due to the tide. Further more, the limited wave height under the ice sheet to break ice increases with the reducing of ice bending rigidity and the increasing of incident wave period for the offshore large ice sheet under the action of waves. Moreover, the limited wave height to break the floating ice block on waves lessens for larger ratio of ice length and wave length, and less ratio of ice thickness and ice length. In conclusion, the physical model tests are conducted to confirm the fracture theory model of semi-infinite long and finite long sea-ice sheets under the action of regular waves. As a result of comparing the measured results with the calculated results in the breakup of sea-ice under the action of regular wave, the theory of floating is reliable to analyze the floating ice on waves. The results of reflected coefficient and transmitted coefficient obtained in experiment show that the elastic modulus of sea-ice is one of the key factors to affect the breakup of offshore large ice sheet on waves.
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