Uniaxial compression of saline columnar ice under variable strain rates Ice-induced vibrations of offshore structures
Marius Stübbe, Norwegian University of Science and Technology
With the increasing demand for sustainable energy sources to meet the EU target of climate neutrality by 2050, numerous countries are committing to invest in offshore wind farm projects, for example in the Baltic Sea, with several planned in ice-covered waters (Marienborg Convention. International standards for Arctic offshore structures (ISO 19906 2019) and design requirements for fixed offshore wind turbines (IEC 61400-3-1 2019) consider dynamic ice-structure interactions, such as ice-induced vibrations (IIV), due to concerns about fatigue and peak loads. The interaction of level ice with a structure is complex and depends on ice thickness, its time-dependent mechanical properties, and the structure’s geometry and loading conditions. For flexible, vertically sided structures such as mono piles, various ice-induced vibration regimes can occur when subjected to drifting level ice. The failure mode and resulting loads are dominated by the displacement and velocity of the interaction, with the highest global loads occurring during indentation at the ductile-to-brittle transition velocity.
To investigate the mechanical response of sea ice under conditions representative of ice-induced vibrations (IIV) on offshore structures, uniaxial compression tests were performed on naturally formed saline columnar ice from Sveabukta, Svalbard. A sinusoidal advancing strain profile was designed to replicate the displacement and velocity characteristics associated with IIV events. Horizontal ice cores were subjected to constant, stepwise, and cyclic loading to evaluate the influence of variable strain rates on the mechanical response. All tests were conducted under confined conditions using an acrylic cylinder to simulate in situ lateral pressure. Microstructure analysis under cross-polarized light was conducted on the ice samples using thin sections prepared with a CNC milling machine. Sections were produced both before testing, to document the ice texture, and after testing, to assess fracture development and failure patterns.
