OFFSHORE WIND FARMS & RENEWABLES
‘Star Wars’ Dunes March Through Offshore Windfarm
At a windfarm far, far away, rare crescent-shaped dunes have been slowly making their way across the seabed.
On land, the unusual dunes are famous for engulfing a Star Wars movie set in the Sahara, but in a new HR Wallingford study, world-renowned scientists tracked similar dunes underwater to show how they move past monopiles.
The research, published in the latest edition of the journal Earth Surface Processes and Landforms, is the most extensive study of its kind and will help support offshore wind developers. It captures the effects of the sedimentology phenomena, called marine barchan dunes, trooping across the seabed and looks at whether they cause increased erosion (scour) around the monopiles. The scouring process
A rare dune that marched through a UK windfarm
happens too quickly to observe, so the renowned team constructed an advanced 3D numerical model using the TELEMAC modelling suite.
The team did see some surprising scour pits, but luckily for the planning, installation and maintenance of windfarms, the team of experts did not find that the barchan dune increased erosion. And because the scour happened so quickly, there was never any additional sand up against the monopile, keeping the stiffness and the integrity of the foundation fairly constant.
Dr Kerry Marten, Senior Scientist at HR Wallingford, explains how the project came about: “We first spotted the
Resistant Coating Systems for Offshore Rotor Blades
Extreme Conditions for Wind Turbines In the offshore sector, rotor blades for wind turbines should be able to withstand 20 years of operation without impairment. Extreme environmental influences such as snow, hail, rain, salty seawater, heat and UV radiation put a strain on the huge blades. Wind speeds of up to 500 km/h affect the blade tips. This area is therefore a particular weakness of the rotor blade, as the coating at this point is particularly badly eroded by rain erosion, so that the aerodynamics on the blade surface change and performance can decrease.
Rain Damages Rotors The impact speed and the size of the raindrops play a major role in rain erosion. HPF The Mineral Engineers, a division of the Quarzwerke Group,
carried out rain erosion tests based on real conditions in a miniature simulator. Glass fiber reinforced plastic (GRP) test specimens were rotated around their own axis in the centrifuge at a horizontal rotational speed of 10,000 rpm. For a 22 cm long rod, this corresponds to a speed of the rod ends of 414 km/h. At the same time a vertical load from above with a continuous 3 mm wide water jet was applied to simulate rain. The aim of the tests was to find out whether the use of special high-performance mineral fillers can contribute to the durability of rotor blade coatings. The evaluation of the damage patterns that occurred on the differently coated test rods after different rotation times in the simulation chamber is impressive: These clearly show how the resistance of the coating to rain erosion depends on the filler used.
Increased Service Life of Coating Systems for Rotor Blades The talc and barium sulfate fillers contained in the starting formulation served as reference fillers in the pore filler. They were successfully replaced in the tests by the silica flours SIKRON® and SILBOND® as well as by TREMIN® wollastonite and MICROSPAR® feldspar. All the alternatives tested significantly improved the resistance of the test rods to impacting rain drops compared with the reference fillers. MICROSPAR® feldspar achieved the best resistance. It was shown that a specific surface treatment of the functional fillers further increased the resistance.
Conclusion: Using various high- performance fillers, it has been possible to develop coatings that are resistant to rain erosion.
November 2020
www.sosmagazine.biz 45
dunes in 2004 during a pre-installation site survey and, realising that not much was known about how the large submarine features would interact with the windfarm, we asked the owner if we could use the data for our internal research programme. For the next eleven years we tracked the progress of the dune, inputting the data from site surveys into our model and analysing the effects on the monopiles”
So, good news for windfarm developers as the dunes pose little threat to operations. But as the research is likely to be ongoing, it can only be said that ‘the story continues’…
Find out more:
youtu.be/0DJWeUPyM3M
q +44 (0)1491 822 8990 E
info@hrwallingford.com H
www.hrwallingford.com
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