Wind Turbines at Sea Suffer Catastrophic Design Failure
Investors in wind farms around British and Danish coasts are facing financial ruin as a new study from the University of Olso affirms a catastrophic design oversight. Newly identifed flaws mean that all windmills currently in operation are in real danger of snapping like matchwood during severe storms.
Science Daily runs the story, ‘Windmills at Sea Can Break Like Matches’ (Feb. 26, 2013) highlighting the findings of a team led by Professor John Grue of the Department of Mathematics at the University of Oslo, Norway. Professor Grue warns that even medium-sized waves can break wind turbines at sea like matches. “These waves occur even in small storms, which are quite common in the Norwegian Sea,” says the report.
“The problem is, we still do not know exactly when the wind turbines may break,” says Grue, one of the world’s foremost experts on wave research. In 1989 he discovered an inexplicable wave phenomenon called ringing, which is a special type of vibration that occurs when choppy waves hit marine installations. The discovery was made in a 25-metre long wave laboratory located in the basement of the mathematics building at Blindern Campus. So far scientists have studied ringing in small and large waves, but as it turns out, ringing is more common in medium-size waves. For wind turbines at sea with a cylinder diameter of eight metres, the worst waves are those that are more than 13 metres high and have an 11-second interval between them.
Financial ruin
The ringing problem may increase significantly in the years ahead. There are plans to build tens of thousands of wind turbines at sea.
“If we do not take ringing into consideration, offshore wind turbine parks can lead to financial ruin,” warns John Grue to the research magazine Apollon at University of Oslo.
Today, the largest windmill parks at sea are outside the coasts of Denmark and Great Britain. They are nevertheless like small miniatures compared to Statkraft and Statoil’s enormous plans on the Dogger Bank outside Scotland. This windmill park is to produce as much electricity as 60 to 90 Alta power plants. A windmill park with the capacity of two Alta power plants will be built outside Møre og Romsdal in West-Norway.
“Thus far it has not been possible to measure the force exerted by ringing. Laboratory measurements show that the biggest vibrations in the wind turbines occur just after the wave has passed and not when the wave hits the turbine. Right after the crest of the wave has passed, a second force hits the structure. If the second force resonates with the structural frequency of the wind turbine, the vibration is strong. This means that the wind turbine is first exposed to one force, and is then shaken by another force. When specific types of waves are repeated this causes the wear to be especially pronounced. This increases the danger of fatigue.”
It is precisely this secondary force that creates ringing and that the mathematicians until now have not managed to calculate.
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