A simplified interaction model for moored ships in level ice

Abstract

A one dimensional numerical model for the interaction between a moored ship and drifting level ice is presented. Elastic beam theory combined with friction theory was utilized to derive the ice force model. The ice force model took the relative motions and velocities between the ship and ice into account, such that the vessel response influenced the interaction force between the hull and the ice. The ship was modelled with a single degree of freedom, with hydrodynamic and mooring forces in addition to the ice forces. Hydrodynamic forces were derived from potential theory, while the mooring force was assumed to be a linear function of the displacement of the ship. The ice properties were sampled from probability distributions, and the equation of motion was integrated over time. Parameter sensitivity studies were performed for both the ice force model and the ice–ship interaction model. The mooring forces oscillated most at the lowest ice drift speeds and with the lowest natural period of the vessel, due to dynamic amplification and interaction effects between the ship's response and the drifting ice. The necessity of the model was assessed by comparing with a simpler model and the difference between the models increased with decreasing mass and decreasing ice drift speed.