This study analyses the results from basin tests with a vertically sided cylindrical pile loaded by ice failing in crushing. Tests were performed with a ‘rigid’ structure and with structural models representing a series of single-degree-of-freedom (SDOF) oscillators covering a wide range of mass, frequency, and damping values. The structural models were represented by a real-time hybrid test setup, which combined physical and numerical components to measure real ice forces, apply the forces to a numerical structural model, and simulate the dynamics of the tested structural models in real-time. The test results are analysed and simple numerical simulations are performed to assess the relevance of several ice force characteristics observed from the ‘rigid’ structure tests to the ice-induced vibrations in the SDOF oscillators. The results from the rigid structure tests show that the median ice forcing frequency is linearly related to the ice drift speed. The mean and standard deviation of the ice forces on the rigid structure show a negative force-velocity gradient at low ice drift speeds and indications of a positive force-velocity gradient at higher ice drift speeds. The comparison of experimental results to the simulations of the single-degree-of-freedom oscillator tests shows that the positive force-velocity gradient at higher ice drift speeds allows to best capture the dynamics during continuous brittle crushing as observed in the experiments. Furthermore, the comparison shows that frequency lock-in initiation is primarily driven by the velocity-independent spatial frequency spectrum of the ice force signal. The added damping caused by the positive force-velocity gradient must be considered to capture the frequency lock-in initiation speeds measured in the constant deceleration experiments. The consideration of the negative force-velocity gradient at low relative velocities is not needed to capture these frequency lock-in initiation speeds as observed in the experiments. However, once frequency lock-in is initiated, the negative gradient is needed to correctly capture the dynamics during frequency lock-in. Analysis of the results shows that the peak forces during intermittent crushing at the end of the load build-up phase have a dependence on relative velocity equal to the load dependence on velocity of rigid structures at low speed. This indicates that intermittent crushing is not a purely brittle type of interaction.@en

Basin tests were performed at the Aalto Ice Tank to gather data on ice-structure action and interaction from ice failing against a vertically sided cylindrical pile. The tests were performed with a real-time hybrid test setup, which combined physical and numerical components to simulate a range of test structures in real-time. The dataset includes results from tests with offshore wind turbine structures, structural models representing a series of single- and multi-degree-of-freedom oscillators, and scaled dynamic models of the Norströmsgrund lighthouse and the Molikpaq caisson structure. In addition, forced vibration tests and rigid structure tests were performed. Ice loads and structural response were measured with accelerometers, displacement sensors, potentiometers, strain gauges and load cells and the ice-structure interaction process was filmed from three different camera angles. The resulting raw data have been categorized and stored as unfiltered time series. A total of 259 different tests are included in the dataset. The model ice formation procedure and the test temperature were aimed at creating model ice that mimics the material behavior of full-scale saline ice during crushing failure, with a specific focus on the transition from brittle to ductile behavior. The data can be used for validation of models for dynamic ice-structure interaction. The offshore wind turbine data can be used to study the effect of wind loading on the interaction with ice and the effect of the specific dynamic properties of wind turbine structures with monopile foundations on the ice-structure interaction process. The forced-oscillation data can be used to quantify the time and speed dependant aspects of ice loading. The Norströmsgrund lighthouse and the Molikpaq data can be used as a reference comparison to full-scale data on ice loads.

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With the recent surge in development of offshore wind in the Baltic Sea, Bohai Sea and other ice-prone regions, a need has arisen for new basin tests to qualify the interaction between offshore wind turbines and sea ice. To this end, a series of model tests was performed at the Aalto ice basin as part of the SHIVER project. The tests were aimed at modeling the dynamic interaction between flexible, vertically-sided structures and ice failing in crushing. A real-time hybrid test setup was used which combines numerical and physical components to model the structure. This novel test setup enabled the testing of a wide range of structure types, including existing full-scale structures for which ice-induced vibrations have been documented, and a series of single-degree-of-freedom oscillators to obtain a better understanding of the fundamental processes during dynamic ice-structure interaction. The tests were primarily focused on the dynamic behavior of support structures for offshore wind turbines under ice crushing loads. First results of the campaign show that the combination of the use of cold model ice and not scaling time and deflection of the structure can yield representative ice-structure interaction in the basin. This is demonstrated with experiments during which a scaled model of the Norströmsgrund lighthouse and Molikpaq caisson were used. The offshore wind turbine tests resulted in multi-modal interaction which can be shown to be relevant for the design of the support structure. The dataset has been made publicly available for further analysis.@en

Ice-induced vibrations of offshore wind turbines on monopile foundations were investigated experimentally at the Aalto Ice Tank. A real-time hybrid test setup was developed allowing to accurately simulate the motion of a wind turbine in interaction with ice, incorporating the multi-modal aspects of the interaction and the effect of simultaneous ice and wind loading. Different vibration patterns were observed where some could be described based on the common terminology of intermittent crushing or continuous brittle crushing. However, not all resulting vibrations could be described accordingly. A combination of several global bending modes interacting with the ice resulted in high global ice loads and structural response. Such response is likely typical for an offshore wind turbine, owing to the dynamic characteristics of the structure. The type of interaction observed during the tests would be most critical for design as the largest bending moments in critical cross-sections of the foundations occur for this regime. A classification of ice-induced vibrations is proposed which encompasses the experimental observations for offshore wind turbines on the basis of the periodicity in the structural response at the ice action point. @en