Numerical simulations on ice-structure interaction in shallow water

• Main Author: Häsä, Riikka
• Other Authors: Polojärvi, Arttu, Insinööritieteiden korkeakoulu, Aalto-yliopisto, Aalto University
• Format: Master Thesis
• Language: English
• Published: 2015
• Subjects: ice mechanics; ice-structure interaction; grounding; arctic offshore structures; numerical modelling; combined finite-discrete element method; Arctic; Arktis*; Ice Sheet; Sea ice
• Online Access: https://aaltodoc.aalto.fi/handle/123456789/18624

Moving sea ice causes high loads on Arctic offshore structures when it breaks against them. Many of these structures are built in relatively shallow water, which affects the loading process. The ice breaking process in shallow water involves complex interactions between the intact ice sheet, the ice blocks formed in the process, the structure and the seabed. In this thesis, ice-structure interaction on a wide sloping structure in shallow water is studied using a 2D combined finite-discrete element method (FEM-DEM). The intact ice is modelled as a nonlinear Timoshenko beam and its fracture into smaller pieces is modelled using the cohesive crack model. The discrete element method is used for contact force calculation between the ice blocks, the structure and the seabed. In the work reported here, the inclination angle of the structure, the ice thickness and the water depth are varied to study how these parameters affect the ice rubble grounding and the ice loading process. The simulation results suggest that grounded rubble leads to higher loads on the structure than non-grounded rubble. The loads on the structure increase with thicker ice and decreasing water depth. In addition, a larger inclination angle induces higher loads on the structure throughout the simulation. The load events on the structure are related to simultaneous ride-up events of the rubble and the loads are transmitted to the structure along so-called force chains. Furthermore, the probability of overtopping increases in shallow water. The load increase and the increased probability of overtopping in shallow water are caused by the supporting effect of the seabed. Sudden load drops on the structure are related to buckling of the force chains. When the rubble is grounded, the force chains are supported from below by the seabed and form above by the rubble above. Thus they sustain more loads than force chains in non-grounded rubble. Liikkuva jää aiheuttaa suuria kuormia arktisille merirakenteille jään murtuessa rakennetta vasten. Monet näistä ...