Application of an extended inverse method for the determination of ice-induced loads on ships

Abstract

With the opening of more Arctic shipping routes, the motivation to design safe and efficient ice-going ships has increased. Recently, knowledge of ship-ice interactions and the mechanics of icebreaking processes has improved through numerous full-scale studies; however, the understanding of precise ice-induced pressures and load heights requires refinement to improve design methods.

This thesis aims to further the development of an inverse engineering method to determine the nature of ice loads experienced by ships. The method uses full-scale strain measurements to estimate local pressures on the ship's structures. The data studied in this thesis was collected on the oblique icebreaker Baltika while operating in the Russian Arctic over a two-year period.

The inverse method uses an influence coefficient matrix to relate the measured strain to the input pressure load. Using FEM, strain response functions are fitted at each sensor to generate the terms of the influence coefficient matrix. An optimisation routine is used to solve the inverse force-strain relationship and predict the load patch shape and pressure induced by the ice impact.

The hourly maximum strain measurements are identified and analysed to estimate the applied load and contact area during ice impact events. A general analysis of 250 significant impact events reveals that the applied pressure is on the order of 10-25 MPa and the load height is on the order of 1-3 cm. The detailed analysis of 98 individual impact events demonstrates that the load height during impact remains markedly constant for the duration of the contact. Furthermore, the pressure distribution between load carrying structures is investigated. Based on the results, the pressure distribution between structural members is random and independent of the supporting structure.