ABSTRACT

The Okhotsk Sea coast of Hokkaido, Japan is covered with ice floes during winter. Aota et al. showed that the temperature in this region has been rising every winter, and in the last ten years the amount of sea ice has been decreasing. Therefore the period of coexistence of waves and ice floes has become more longer and it is very important problem to make clear the impact ice load acting on offshore, harbor and coastal structures which are constructed on Okhotsk Sea coast of Hokkaido. Saeki et al. and Takahashi et al. reported that the velocity of ice floes due to wind wave, overtopping over breakwater and tsunami was about 4–8 m/s. In this paper, the authors clarified the impact ice load when ice sheets collide vertically with a circular cross-sectional structure.

INTRODUCTION

Aota et aI. showed that the temperature in this region has been rising every winter; and in the last ten years the amount of sea ice has been decreasing. Asakawa et aI. and Sakai et aI. showed that when the surface of the sea is covered with ice, the wave height is remarkably reduced. When the sea surface is covered with sea ice approximately ten times as far as the wave length, the wave height is reduced to below 1/10. When the water in front of structures, such as breakwaters, is covered with sea ice over a certain distance from the structure, the wave height in front of structures is low enough for the movements of sea ice to be almost ignored. Therefore, the movements of sea ice caused by waves have almost no effect on structures. However, the recent decrease in the amount of ice floes lessens the effect of the sea ice on the wave height reduction, thus intensifying the movements of ice sheets near the structure. This phenomenon can be temporarily observed when ice floes approach and recede from the shore.

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