FEATURE SPONSOR
NOISE REDUCTION
NOISE MEASUREMENT FOR OFFSHORE WINDFARM DEVELOPMENTS
The National Physical Laboratory (NPL) has more than 40 years of expertise in underwater acoustic measurement and has been setting the benchmark for noise mapping used in offshore development projects
Offshore wind offers the best renewable electricity source as it’s both sustainable and relatively cheap, with almost 90% of the world’s offshore windfarms in northern Europe and the bulk of them in the shallow North Sea.
Most foundations for wind turbines are steel mono-pile or tripod jacket structures, with large diameter piles. Percussive pile driving is used to hammer the piles into the seabed and some of the energy used creates a high amplitude sound that introduces significant underwater noise into the ocean.
SIGNIFICANT IMPACT The impact on marine life can be severe, from hearing damage for animals close to the pile, to behavioural changes such as aversive flight from the area. To combat this, NPL led collaborative research to produce a new international standard – ISO18405:2017 – on the measurement of radiated underwater sound from percussive pile driving. Developers are required to ensure that acoustic impact of development work can be adequately assessed and mitigated.
NOISE MAPS
NPL has worked with the Crown Estate and the major developers to perform such accurate underwater acoustic measurements. This work includes predicting the impact of underwater noise on marine life by using acoustic propagation models, or ‘noise maps’.
www.windenergynetwork.co.uk 39
The below image shows what a typical noise map looks like and clearly identifies the region where the noise may exceed the agreed threshold levels for impact, for the area around the pile.
Key features of the marine environment, such as water depth, sediment density and surface conditions, all affect how the sound propagates and must be taken into account during the installation of the windfarm.
DEMAND
The demand for accurate noise predictions and operational measurements is already proving essential for offshore windfarms expanding to the less well studied waters of East Asia and North America.
National Physical Laboratory
Image: Noise Map of piling noise in offshore windfarm.
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