Designing impact hammers to reduce offshore pile driving noise

The cumulated capacity of all worldwide installed offshore wind turbines is growing rapidly. Most often single piles, so-called monopiles, are used as foundations. Usually, impact hammers are used to drive the monopiles into the seabed. The two main components of an impact hammer are the impact weight and the anvil. During pile driving, the impact weight is lifted up, then falls onto the anvil which transmits, at least most of the kinetic energy to the pile which is then driven deeper into the seabed. This process is repeated several hundred times until the pile is embedded deep enough to serve as the foundation for the offshore wind turbine. During pile driving, the pile radiates sound in the surrounding air, water, and seabed. The resulting underwater sound can be very high and is potentially dangerous for whales and fish. For this reason, many countries have placed limits on the resulting underwater sound pressure levels. The present thesis presents the potential of an impact hammer designed to emit less noise. The approach went twofold. First, theory combined with parameter studies served to understand how the ram impulse and the pile influence the underwater sound pressure levels. Second, an optimisation algorithm was employed to uncover the potential of the hammer design and to obtain exemplary shapes of hammer components to minimise the underwater sound pressure levels.