Discrete element modeling of ice floe field-structure interaction

• Main Author: Partanen, Samuli
• Other Authors: Polojärvi, Arttu, Insinööritieteiden korkeakoulu, Aalto-yliopisto, Aalto University
• Format: Master Thesis
• Language: English
• Published: 2017
• Subjects: discrete element method; ice-structure interaction; broken ice field; ice management; ice loads; offshore structure; Arctic
• Online Access: https://aaltodoc.aalto.fi/handle/123456789/27107

Stationary offshore structures experience high loads when they interact with ice fields. In the Arctic seas, the ice field is usually either naturally broken into distinct floes, or intentionally broken with icebreakers in order to avoid high magnitude impact loads in moored platforms, such as oil drilling vessels. In this thesis, the ice floe field-structure interaction is modeled with two-dimensional discrete element method (2D DEM). Elastic-viscous-plastic contact model is applied in order to determine the interaction loads. First, the effect of floe field concentration, ice-ice friction, velocity and floe size to structure loads and deformation zone shape are determined by varying the parameter values and comparing the results. Afterwards, the impact of rate-dependent friction model is examined. Finally, the significance of ice management is studied by generating brash ice between large floes. Since the model is applied for the first time, also its applicability is discussed. The results show that highly concentrated ice field damps the impacting floes in the simulations. The concentration was also observed to be the dominating parameter dictating the area of the deformation zone. Higher friction coefficient values were correlated with so-called tangling of floes, which decreased the loads while increasing the deformation zone area. The rate-dependent friction corresponded to constant friction coefficient 0.1 in the structure loads. The simulations of brash ice, which were modeled with small floes between larger floes, demonstrated the importance of ice management to the peak load magnitudes. The small floes allowed the larger pieces to deviate around the structure. The simulations also indicate weaknesses of 2D DEM in the simulation of floe-structure interaction. Nonphysical bouncing phenomena was observed in the collisions within the deformation zone, because deformation was not modeled. Jäälauttakentät aiheuttavat suuria kuormia merellä oleviin rakenteisiin. Akrtisilla merialueilla jää on usein murtunut ...