Underwater sound propagation and mitigation in offshore pile driving

Wind energy is a crucial component of the transition to a carbon-free energy supply. As offshore wind farms expand into deeper waters, larger monopiles are required, posing technical and environmental challenges. High-blow energy hydraulic hammers drive these piles into the seabed, generating significant underwater noise that propagates through seawater and sediment, potentially impacting marine life. Regulatory bodies enforce noise thresholds and require environmental impact assessments to mitigate these effects.

Current underwater noise models often simplify seabed conditions, overlooking complex pile-water-soil interactions. Semi-analytical models provide accurate near-field predictions but struggle with long-range effects, while empirical models lack adaptability to varying soil conditions and mitigation measures. This thesis addresses these gaps by incorporating detailed sediment descriptions to enhance noise predictions over large distances.

The study also integrates an air bubble curtain into a noise prediction framework, considering pile, water, sediment, and bubbly layers. A noise prediction module estimates non-mitigated pile driving noise, while a noise reduction module quantifies bubble curtain effects using boundary integral equations. This enables efficient noise reduction assessment across different configurations.

Additionally, the study evaluates seabed vibrations and particle motions, crucial for benthic species often neglected in impact assessments. A comprehensive modelling framework is developed, transforming wave fields into Source levels (SL) for both fluid and sediment sources. Sound maps estimate maximum impact distances based on species-specific sensitivity thresholds, offering insights for regulatory compliance and marine conservation.