Ice basin experiments on mixed-mode failure on ice cones

Abstract

Increased activity in planning offshore wind farms in the northern Baltic Sea has renewed interest in studying the effect of ice cones on ice failure mechanisms. In preparation for future experiments with steep ice cones, preliminary ice basin experiments were performed at the Aalto Ice and Wave Tank to investigate how model ice fails against a 3D-printed cylindrical and a conical structure representative of wind turbine foundations. The main motivation behind the two structures is to test ice loads on a monopile foundation and a monopile foundation fitted with an upward-bending ice cone. Each structure was tested at eight different velocities in three ice sheets with varying mechanical properties, including a newly developed, crushing-optimized model ice. The force exerted by the ice on these rigid structures was measured using a six-axis load cell. The results show that ice undergoes mixed-mode failure on the cone in the form of bending, crushing, and spalling, when tested in crushing-optimized ice. Based on the observations and results, it is recommended that model-scale experiments, focused on mixed-mode ice failure, use model ice with a representative compressive to flexural strength ratio, scaled flexural and compressive strength, and the ability to fail in brittle crushing. If these criteria cannot be met, it may be possible to combine test results from different ice sheets, each focused on one ice failure mechanism. Additionally, this study successfully used 3D-printed structures, which present a new and more accessible method of preparing scale models.