Laboratory tests for dynamic ice-structure interaction

Abstract

The CRREL test basin is able to simulate dynamic ice-structure interaction with scale model tests which cover the whole range of structures that are considered here. For bottom-founded structure simulation, a test pile was designed so that its stiffness, natural frequencies and modes and damping could be varied. The ice movement against the pile was arranged to have constant acceleration in order to excite different modes with differing ice velocities. The flexibility of the drive system caused jerky ice movements with low velocities. Analysis of the recorded ice forces and acceleration include the refinement at measured ice forces by eliminating the response of the measuring system itself using the dynamic equilibrium or transfer function approach. The frequencies and the damping of vibrations were analysed using a Fourier signal analyser. Scaling laws are discussed and it is noted that full similitude cannot be achieved for both ice interaction force and pile and ice vibrations. Results so far show similarity with in-field ice force histograms: both random and saw-tooth like repetitious ice force fluctuations appear. The change from one interaction mode to the other occurs with increasing drive velocities. With high velocities relatively smooth random ice crushing occurs and in some cases natural modes are stable. The greatest energy content of the ice force does not always coincide with the natural frequencies of the structures.