Defence in the field of mechanical engineering M.Sc. (Tech) Malith Prasanna

Opponents Professor Hayley H. Shen, Clarkson University, New York, USA and Professor Wenjun Lu, Norwegian University of Science and Technology, Norway

Custos Professor Arttu Polojärvi, Aalto University, School of Engineering, Department of Mechanical Engineering

Contact information malith.prasanna@aalto.fi

"Ice block breakage: experiments and simulations" The interest towards ice-covered sea areas has been increasing as, for example, offshore wind park developments are moving towards those areas. Sea ice ridges, which are ice feature made of ice rubble, a collection of ice blocks and ice fragments, are one of the most demanding ice conditions that could occur in first-year ice, thus, ice loads exerted by deforming ice rubble are a key factor when designing efficient structures for ice-covered sea areas. Discrete element method (DEM) simulations are widely used to estimate ice loads on ships and offshore structures. However, modeling ice fragmentation in DEM simulations is not trivial and, there are severe knowledge gaps related to the physics of ice block breakage in ice-to-ice contact and modeling of the fragmentation processes. Therefore, the present doctoral thesis studies the breakage processes through laboratory-scale experiments, high resolution numerical modeling, and development of a simplified block breakage model for DEM simulations. In the experiments, three ice blocks were set to form two ice-to-ice contacts and compressed until the failure of the three-block system. The experimental results showed that the primary failure mode of ice blocks in compressive ice-to-ice contacts was a shear failure. High resolution numerical modeling of the experiments also confirmed this hypothesis and further revealed that the Mohr-Coulomb failure criterion can be used to model the shear failures in a simple yet reliable manner. Following that, a simplified block breakage model based on shear failure and the Mohr-Coulomb failure criterion was developed and integrated in to an existing DEM code. Then direct shear box experiments on ice rubble were simulated by using the code and the simulation results were compared with experimental results, which in turn revealed that the simulations with the developed breakage model yield results more close to experiments than without the model. Therefore, the present thesis suggests that the shear failure of ice blocks at contacts need to be accounted in DEM simulations.