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.
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EU urgently needs to increase the development of secure and green energy, and this includes renewables such as Offshore wind energy. An expansion of Offshore wind will include the Baltic where sea ice is one of the major uncertainties. To ensure that the w ind turbines are safe for people and the environment, while keeping them economically competitive better guidelines and regulations should b e developed collaboratively by European industry and academia. There are unsolved challenge s with respect to ice action on structures for offshore wind. However, in the current draft for Horizon Europe Work Programme 2023-2024 on Climate, Energy and Mobility1, the challenges related to sea ice with regards to Offshore wind energy are not mentioned. In order to meet the crucial green energy goals, it is our statement that it is imperative to include sea ice i n the final version.@en

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

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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