ABSTRACT:

Physical model tests are conducted to simulate ice-induced vibration of flexible structures by using a new non-frozen breakable synthetic material. Responses of the structure, including acceleration, displacement and strain, are recorded as ice sheet acting on the structure with different velocities. According to the dynamic load identification technique developed by the authors, time histories and Fourier spectrum of global ice load exerted on the elastic model structure are given. Some photos recording the ice failure process as well as the measured time histories of structural responses are presented. The phenomena and results are similar to the field observations, and some features different from those of ice-induced vibrations of column structures were obtained.

INTRODUCTION

Ice-breaking cones, as an effective method to reduce ice force, have been designed and added to legs of offshore jacket oil platforms in cold regions such as Bohai Sea. However, due to cyclically bending failure of an ice sheet prone to happening, severe vibrations of flexible structures may be induced when ice sheet acts continuously on them, which has been confirmed by many field observations and in-situ tests (Frederking, 1979; Engelbrekston and Janson, 1985; Karna and Wright, 1989). So it's necessary to re-evaluate the integrated effect of icebreaking cones. In-situ test is the most effective way to study ice-induced vibrations. However, it is difficult to be widely performed due to great expenses and hazards. So laboratory tests can be considered as an alternative way. Moreover, laboratory tests also have many advantages over in-situ tests, for examples, it's easy to control the environmental conditions, change size of the structure and test a model repeatedly. In the present paper a laboratory test for simulating ice-induced vibrations of flexible conical structures is performed, and an indirect method in time domain to determine dynamic ice loads is also introduced.

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