Light Structures monitors fatigue in floating offshore wind turbines

A floating offshore wind (FOW) turbine can be likened to a watermelon atop a piece of dried spaghetti, according to Sannerud. Only the watermelon weighs 400 to 500 metric tons. In addition, the turbine floats more than 100 kilometres offshore, in depths up to 300 metres, where it is moored or anchored to the seafloor.

This puts FOW turbines under enormous stress in extreme conditions. High wind and waves continually batter the floaters, creating stresses and vibrations that cause structural fatigue. “Fatigue is the enemy of floating wind turbines,” says Sannerud.

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Light Structures has introduced its proven fibre-optic structural monitoring technology to the FOW industry. “We monitor the turbines’ response to dynamic forces at sea and report back to the owners about problems that need attention,” says Sannerud.

Known as SENSFIB, the system is based on Fibre Bragg Grating (FBG) technology. SENSIB monitors stress, deflection and vibration and calculates fatigue on or in an object – in this case, on FOW turbines. These dynamics are most noticeable at sea as opposed to land.

“The FBG fibre-optic sensing technology gives SENSFIB a competitive edge compared to conventional strain gauge technology. Fibre optics provide a higher level of accuracy, no annual or biannual recalibration costs, and low maintenance costs with less intervention,” says Sannerud.

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“We engineer unique solutions tailored to each wind farm. We provide real-time data and analysis, which allows us to predict what will happen,” he adds.

The solution provides valuable information about a structure’s condition before a loss occurs. “We quantify uncertainties in structural fatigue, increasing insight,” says Sannerud.

In the FOW industry, this translates into lower operating costs and less financial risk associated with turbines. Ultimately this will increase the competitiveness of FOW, which still has a relatively high levelised cost of energy.

Moreover, by warning of potential accidents, worker safety is improved and environmental risk is reduced.

“Recent history has many examples of offshore accidents that could have been avoided. With our monitoring technology, we warn asset operators of the need for maintenance or shutdown before lives and assets are lost,” he adds.

By 2050, floating offshore wind is projected to generate 264 GW or 15 per cent of all offshore wind energy. This is the equivalent to a development over 3 000 times the size of Hywind Tampen, the world’s largest floating offshore wind farm.

Sannerud sees huge market potential in this space. “The typical cost for fibre-optic monitoring is 1 to 5 per cent of the asset cost. Who wouldn’t want to invest in a solution that could save lives and millions of dollars?”

Founded in 2001, Light Structures evolved as a spin-off from the Norwegian Defence Research Establishment. The company is the world’s leading provider of fibre optic hull stress monitoring and counts the renewable energy giant Equinor and the US Coast Guard among its many customers.