Offshore wind turbines in cold sea areas can be fitted with ice cones to reduce static and dynamic loads from drifting sea ice. The effectiveness of ice cones in reducing static loads has been tested in model-scale ice basin experiments. However, only a few experiments used compliant test setups to study ice-induced vibrations on conical structures. This study explores the dynamic interaction between level ice and a downward-bending cone with a 60° slope angle through ice basin tests with a hardware-in-the-loop system based on a hybrid technique, combining a physical indenter with a numerical structure model of an offshore wind turbine. Two types of periodic ice-induced vibrations were observed for the first time in an ice basin: bending failure-induced vibrations and unexpected vibrations caused by local failure at the ice-structure interface. The local failure had characteristics of both shear failure and crushing failure and occurred at low ice-structure interaction speeds during tests. Local failure-induced vibrations were significant in the dynamic test with an ice-drift speed of 5 mm s^-1, however they also contributed to the dynamic response of the structure at higher ice-drift speeds. Bending failure-induced vibrations occurred at critical ice-drift speeds (30 mm s^-1 to 40 mm s^-1 and 70 mm s^-1 to 100 mm s^-1) where the bending failure frequency matched the 1st or 2nd natural frequency of the structure model. The results show that ice-induced vibrations on conical structures occur at various ice-drift velocities for both previously known and unexpected ice failure modes. Furthermore, the results provide new insight into conducting ice basin tests on ice-structure interaction with compliant conical structures.

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.