BORA - Predicting Underwater Noise due to Offshore Pile Driving

Motivation

Numerous offshore wind farms are planned, already granted, or currently under construction within Germany's exclusive economic zone (EEZ). Usually, the foundation of the wind turbines are planted by pile driving, e.g. for monopile, tripile, tripod constructions.
This technique induces underwater noise, which can be measured in distances of 20 km and more to the construction site. In the near surroundings of the pile, sound energy levels often exceed the present limit values prescribed by the German authorities to protect marine mammals, which are a single event sound pressure level (SEL) of 160 dB re 1 μPa and at a maximum peak level (L_peak) of 190 dB re 1 μPa in a distance of 750 m to the pile. Therefore, various sound-damping techniques are currently in development or in field trial.

Major Targets

The global target of BORA is to develop a profound calculation model to predict waterborne noise due to offshore pile driving. This includes especially models to predict:

the sound development at the source due to pile deformation and vibration.
the sound transmission into water and soil.
the consideration of the sound attenuation due to the air-water mixture produced by bubble curtains or due to other sound-damping methods.

An important step when developing such models is the thorough validation of the approaches regarding their ability to accurately account for the sound origination at the pile, the transmission into water and soil, ant the sound attenuation due to possible migitation measures. For this purpose, three extensive offshore measurement campaigns will be performed in different wind farms in the German North Sea.

After validation, the detailed simulation model will be adapted to other offshore structures with different boundary conditions. Due to the complexity of the resulting simulation model and the necessary access to substantial computing capacities and specialist simulation software, this model can only be executed by experts in the field of numerical simulation. Therefore an additional stand-alone expert system will be developed, which will enable third party users to calculate basic noise predictions for offshore pile driving. Finally, standard datasets will be compiled to allow for a review of future computation models.

For further information please visit the BORA website.