Physical Mechanism of Ice-Induced Self-Excited Vibration

Abstract

Steady amplitude vibration on cylinder structures caused by dynamic ice loading has been observed during the measurements on prototype structures. Further analysis indicates that it belongs to self-excited vibration, in which the vibration amplitude stays constant and the frequency of the dynamic ice load is locked by the frequency of the structural vibration. Based on the conclusions from ice mechanics, this study proposes a physical mechanism to describe the ice-induced self-excitation process: during the loading phase within a single vibration cycle, the compressive strain rate in the ice sheet close to the structure enters a ductile-brittle transition range, and thereby the steady formation of micro cracks maintains the resistance of the ice sheet as the ice load steadily increases; when the density of cracks in the ice reaches a critical level, cracks coalesce and collapse, resulting in the unloading phase. In this way structure vibration dominates the time-variation of the ice load. The proposed mechanism is verified using field data.