Investigating the Stability of Icebergs

Small icebergs roll and bob as they float in the ocean like damped harmonic oscillators. We present the results of experiments using low-density polyethylene cylinders as surrogate icebergs and use steel rods to represent a sediment layers within them. Their motion, translation and rotation, is measured at high frequency using a MEMS sensor. We show that the motion can be understood by calculating the potential energy of the system as a function of the iceberg’s depth and orientation. The water gives rise to an added mass term and damping by the radiation of surface waves, which can be calculated using the far-field expansion of a Greens function. We show good agreement between this model and the data. The importance of this result is that if waves of the right frequency are incoming, they may induce resonance and then even relatively small waves can give rise to large amplitudes oscillations and cause icebergs to capsize if they are not globally stable.