Air bubble curtain for windfarm construction
An innovative air bubble curtain has been developed which can help reduce the effects of noise on marine life when building offshore windfarms.
The air bubble curtain with innovative hose system from Continental has been successfully tested in a pilot project at the Arkona Basin Southeast wind farm together with a specialist hydraulic engineering company.
“With our innovative solution, we make a contribution to the expansion of regenerative energy sources on the high seas, thereby protecting marine life from construction noise,” said David Hoffmann, who is responsible for industrial hose solutions in the EMEA and APAC region for the Continental Corporation.
For marine life, windfarm projects mean all sorts of construction noise and vibrations which interfere with certain species ability to orient themselves, communicate and to locate prey and predators.
In order to protect the animals, a noise level of no more than 160 decibels applies in German waters at a distance of 750 metres from the construction site.
This legal requirement of the Federal Ministry for Environmental Protection Building and Nuclear Safety has spurred on the development of new technologies for the quiet installation of foundations, including the air bubble curtain.
Continental’s air bubble curtain is created by using one of its heavily perforated hoses. This is placed around the construction site as a ring, before the wind turbine towers driven into the seabed.
The hose ends are connected to powerful superchargers on ship decks. During the work, they pump 10 bar of oil-free compressed air into the hoses, which escapes through the holes according to a well-defined pattern. The result is a curtain of millions of small bubbles that rise to the water surface, forming a kind of whirlpool around the construction site.
The air bubbles change the density of the water and thus break down the sound waves. Depending on the nature of the soil and water currents, hydraulic specialists also use two-ring technology.
This technology reduces the noise level by up to 18 decibels, which is a volume reduction of 95%.
The challenge comes with keeping the hose at the bottom of the sea without additional steel chains when the pressurised air provides buoyancy.
Continental solved the problem with a further development of its hoses. Each hose consists of different layers of different materials, such as rubber, as well as reinforcements.
Even with the hoses used as air bubble curtains, one of these layers consists of a wire mesh. This spring wire spiral serves as bend protection during winding and unwinding of the hose line and keeps the shape of the hose stable in case of over or under pressure at the same time.
Mr Hoffman said that air bubble curtains are also suitable for many other applications, such as mine clearance, offshore oil drilling, seismic surveys, port and coastal development, bridge construction and the construction of artificial islands.
The technology is also suitable for keeping oil spills in a particular area, or for keeping seaweed, algae, jellyfish or flotsam from beaches, harbours and shores.
By Anne-Marie Causer
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