Laboratory experiments to study ice-induced vibrations of scaled model structures during their interaction with level ice at different ice velocities

Abstract

A simplified model of a typical bottom-founded structure was forced through ice sheets in a laboratory experiment to study ice-induced vibrations. The ice forces exerted on the structure are identified in conjunction with the response of the entire structure using a joint input-state estimation algorithm. Novel insights into ice-induced vibration phenomena are obtained by comparing, on different time scales, measured and estimated response quantities and forces/pressures. First, the identified forces, ice velocities and time-frequency maps of the measured responses are presented for a series of ice-induced vibration tests. It is shown that the ice forces excite more than one mode of the structure and that the transition ice velocity at which the vibrations shift from the first to the second mode increases with reduced foundation stiffness and reduced superstructure mass. Second, a detailed analysis of the interaction between the structure and the ice edge is performed on a smaller time scale by comparing the locally measured pressures at the ice-structure interface to the identified structural responses and forces. It is shown that structural vibrations at a frequency higher than the dominant vibration frequency cause cyclic loading of the ice edge during intermittent crushing. These vibrations led to an increasing loading rate prior to ice failure. During an event that shows the tendencies of frequency lock-in vibrations, the structural response was dominated by a single vibration frequency.