Photo: Henrik Bredmose

Floating turbine test led to surprising knowledge

Thursday 23 Apr 15
|
by Bjørn Lymann Jespersen

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Henrik Bredmose
Professor
DTU Wind Energy
+4545 25 43 15

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Robert Flemming Mikkelsen
Senior researcher
DTU Wind Energy
+4545 25 43 20

Two MSc students have tested a floating wind turbine under demanding and challenging conditions. During the extreme wave test, the turbine oscillated at unexpected frequencies.

Throughout January, a scale model of a wind turbine has been undergoing tests in a wave pool at the DHI Department of Water Resources and Environment. The wind turbine was attached to a floating base which makes it possible to install offshore turbines in locations where the water is too deep for conventional seabed foundations. During the experiments, measurements were taken of how the turbine blades, tower, and foundations reacted to different loads and wave sizes.

The float used for the wind turbine was what is known as the TLP (Tension Leg Platform) type, and was more compact and cost-efficient than previously. The rotor was newly designed as well, because the blades had to be almost 75 per cent wider to ensure correct dimensioning of the wind forces during experiments.

The experimental set-up was designed by Anders Mandrup Hansen and Robert Laugesen, master’s students at DTU Mechanical Engineering and DTU Wind Energy, respectively. The two students submitted their report on the experiment on 16 March, and according to their supervisor—Henrik Bredmose, Associate Professor at DTU Wind Energy—their work presented a good indication of where extra input is required to improve the turbine design.

Surprising frequencies
There was quite a surprise in store for the team when the turbine was subjected to extreme wave conditions:

“During the extreme wave test, the turbine oscillated at frequencies our calculations failed to predict. This is one of the areas we will need to look at more closely,” says Henrik Bredmose, who has already started two new MSc projects centred on comparing measurement data with calculation models.

“This will certainly provide even more insight, which can then be used in future designs,” he adds. Henrik expects analysis of the findings to continue until summer 2015.

The experiments were part of the INNWIND.EU research project, which focuses on innovative solutions for wind turbines in the 10–20 MW class.

Article in DTUavisen no. 4, April 2015.

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