Public defence in mechanical engineering, M.Sc. Riikka Matala

Towards better harmonized ice performance predictions of merchant ships in old unconsolidated brash ice channels 

Winter navigation ensures the year-round supply of many everyday products and is thus vital for communities living by the freezing seas. In the Baltic Sea, the winter navigation system is based on ice-capable merchant fleet assisted by icebreakers. Finnish and Swedish authorities utilize ship classification based on the Finnish-Swedish ice class rules to determine each ship’s eligibility for icebreaker assistance. This depends on, among other things, the ship's expected ice performance in the prevailing ice conditions. 

The ship’s performance may be verified with physical model-scale tests in an ice tank according to the ice class rules. The first ice model tests were performed in the 1950s and the methodology is generally well agreed. However, modern merchant ships typically have a bow optimized for good open water performance and the most common operational environment for an icebreaker-assisted merchant ship is a brash ice channel.

In such conditions, the forces resulting from hull-ice interaction differ fundamentally from those forming the ice resistance of an icebreaking bow in level ice. Consequently, reconsidering the application of current ice model testing practices for brash ice channels is crucial in ensuring accurate performance predictions for merchant ships operating in brash ice channels. The thesis analyses the processes forming the ship’s ice resistance in an old unconsolidated brash ice channel using experiments on brash ice and ship correlation tests in both full scale and model scale. The thesis scrutinises the ice properties contributing to the ship's resistance and assesses whether the current model test methodology can simulate all substantial factors sufficiently. The thesis introduces a novel methodology for model scale simulations that improves the modelling of interaction between the brash ice blocks. This new methodology aims to generate fair and more harmonized performance predictions in an old unconsolidated brash ice channel for all hull shapes.

Ship’s performance in ice is one of the key factors in the winter navigation system and a basis for the planning and controlling the system. Determination of ship’s performance in better accuracy is a substantial step towards more efficient and sustainable winter navigation in the future.

Opponent: Professor Knut Vilhelm Høyland, NTNU, Norway

Custos: Senior Advisor Pentti Kujala, Aalto University School of Engineering, Department of Mechanical Engineering

Contact information of the doctoral student: Riikka Matala, [email protected]

The public defence will be organised on campus (auditorium 215, Otakaari 4)

The thesis is publicly displayed 10 days before the defence in the publication archive Aaltodoc of Aalto University.

Electronic thesis