Public defence in Mechanical Engineering, MSc Yaxuan Zhu

Title of the thesis: Ship ice loads as combined effect of ice conditions and ship operations: Antarctic field measurements

Thesis defender: Yaxuan Zhu
Opponent: Prof. Bruce Quinton, Memorial University of Newfoundland, Canada
Custos: Prof. Jukka Tuhkuri,Aalto University School of Engineering

Understanding ice loads on ships is important for designing and operating icebreakers, particularly when global warming is rapidly changing the sea ice conditions in polar seas. An ice load arises when a ship hits an ice floe or breaks level ice. It is commonly recognised that ice conditions, such as ice concentration, ice thickness and floe size, and ship velocity can affect an ice load. The thesis investigates ice loads on ships using field data collected in three expeditions to Antarctic and sub-Antarctic regions onboard S.A. Agulhas II. To analyse the data, the ice loads were synchronised with ship velocity and observations of ice conditions, which were categorised into a collision with a single ice floe, a collision with ice floes under confinement, and operation in level ice. No single parameter can explain the measured ice loads, similar loads were observed in different kinds of ice conditions and at various ship velocities. The study shows that ship ice loads are a combined effect of both ice conditions and ship operations. As an example, one of the largest loads in the data is from a high velocity collision with a very small ice floe. The combined effect is a manifestation of impact energy, defined as mass multiplied by velocity squared; the ice load increases with increasing impact energy. Ice conditions change the mass term of the impact energy while ship velocity alters the velocity term. To obtain a high accuracy ice load estimation, the ice conditions need to be described in detail.

Thesis available for public display 7 days prior to the defence at Aaltodoc. 

Contact information: yaxuan.zhu@aalto.fi