As a part of Aker Arctic’s personal analysis and growth work, a sequence of ice mannequin checks had been carried out in November 2023 to analyze the ice masses affecting windmill monopiles.
Offshore windmills require sturdy foundations to resist the cruel marine setting, together with ice and waves. Just like the planning of icebreakers or different ice-strengthened vessels, the testing of offshore constructions with scaled fashions is a cost-efficient methodology to confirm design adequacy earlier than building begins, making certain suitability for the supposed operational space.
Crushing energy is essential
Aker Arctic’s earlier structural ice mannequin checks have targeted on researching cone-shaped constructions the place bending energy was decided to be the very best ice scaling possibility. Nevertheless, when testing vertical constructions, resembling monopiles, it’s deemed essential to scale the mannequin ice in relation to its crushing energy.
“Mannequin ice differs from pure ice in its homogeneity,” explains Topi Leiviskä, Staff Chief, Mannequin Checks and Facility at Aker Arctic. “Moreover, mannequin ice may be scaled for both crushing forces or bending forces, however not for each concurrently.”
Analysis engineer Toni Skogström provides, “We adhere to a scientific scaling and testing method. Whereas comparable checks have been carried out earlier than, we aimed to delve deeper into vertical constructions to establish essentially the most applicable mannequin ice parameters.”
4 pillar sizes investigated
The analysis crew examined 4 totally different pillar sizes throughout 4 distinct ice thicknesses with scale ratios starting from 1:89 to 1:16. This method allowed the crew to extrapolate information tendencies for a full-scale monopile with a 6.67-metre diameter in 80 cm thick ice.
“In real-life circumstances, a windmill monopile will likely be wider than this dimension, however we opted for a diameter that yields essentially the most information for our analysis,” Leiviskä says. “It’s the scaling ratio, moderately than absolutely the dimension, that’s of higher curiosity on this case.”
Simple testing process
Each mannequin check requires a singular ice sheet which entails preparation and freezing time. In consequence, every of the monopiles was examined in separate testing slots.
(Photograph: Aker Arctic)
In November 2023, the varied pillar shapes ready for the checks had been instrumented and mounted on a cell platform. The purpose was to seize complete information on ice masses. This was achieved by shifting the setup throughout the ice basin at totally different speeds in degree ice circumstances whereas measuring the worldwide forces on the water line.
Skogström clarifies the distinctive failure patterns of pure ice in comparison with mannequin ice, highlighting why velocity is vital and the way it impacts the distribution of stress.
“Pure ice breaks in a number of methods opposite to mannequin ice. In nature, the best stress is targeted on the centreline. The sooner the velocity, the extra centred the stress turns into. Nevertheless, in low velocity, the crushing stress is unfold wider.” (See photos beneath)
He predicts that whereas the checks had been simple, analyzing the info will likely be a fancy and insightful course of.
Stress distribution at a steady sooner velocity when ice failure is brittle.
Stress distribution at a steady creep velocity when ice failure is ductile.
*Supply: Määttänen, M., Marjamaa, P., Saarinen, S. & Laakso, M. 2011. Ice crushing checks with variable structural flexibility. Chilly Areas Science and Know-how. Vol. 67. S. 120–128.
Conforming with calculations
The present monopile design calculations extensively used adhere to ISO requirements, but lack full-scale empirical information for validation.
Nevertheless, full-scale information has been gathered from the offshore lighthouse Kemi I, positioned within the Gulf of Bothnia, in 1984–1986. This space is good for checks in excessive circumstances together with quick ice, shifting ice sheets, pack ice fields and ice ridges.
“Our aim with the monopile checks is to analyze how properly the requirements align with our findings,” says Leiviskä. “By means of our analysis, we purpose to reinforce the reliability and security of windmill constructions in icy circumstances, probably resulting in extra sturdy and cost-effective designs. This might considerably contribute to the development of sustainable power options in harsh marine environments.”
The analysis crew anticipates publishing the outcomes following an in depth evaluation and overview.
(Republished with permission from Aker Arctic)
