Reinvestigation of Ice Speed Effect on Ice-Induced Vibration of Conical Structure

Abstract

Offshore installations designed to withstand extreme ice actions in ice-covered waters have experienced ice-induced vibrations (IIVs). ISO 19906 states that the dynamic ice actions and the corresponding IIVs shall be considered in the design and characterized with respect to the fatigue limit state (FLS). Ice-breaking cones have been effectively adopted in several full-scale structures to reduce the magnitude of the ice loads. Full-scale experience from Bohai Bay has shown that a structure utilizing a conical waterline geometry reduces the magnitude of IIVs relative to the analogous vertical structure. The same data indicated that structures with a narrow cone at the waterline can still experience IIVs and the magnitude of acceleration varies by ice speed for a given ice thickness. Researchers have performed comprehensive model tests on sheet ice approaching flexible conical structures and found the same phenomenon. In this paper, both full-scale field data and model test data were reinvestigated in consideration of ice speed. Two dimensionless variables were constructed for this purpose, one dimensionless variable with respect to the ice velocity and the other with respect to the acceleration of the structure. It is found that these two dimensionless variables show a linear correlation. The proposed methodology can be used to investigate the ice-induced acceleration of the flexible conical structure subject to a moving ice sheet.