Computational prediction of near and far field noise due to pile driving for offshore wind farms

Abstract

One major long-term goal of the German government is to decrease the green-

house gas emissions by 40 %. This results in a key role of offshore wind farms regarding the turnaround in energy policy. In most cases, offshore wind turbines are erected by pile driving leading to a significant noise impact. In consequence, limiting values for emitted underwater noise have been prescribed to avoid a negative influence on marine mammals. To fulfill these requirements, different sound damping systems are currently developed or under investigation. Thereby, the numerical prediction of the resulting sound pressure level is an important tool to prevent cost-intensive offshore tests.

As a general approach different numerical modeling techniques are used to study the generated pressure wave, taking into account the near and far field propagation separately. To model the area near the pile of the wind turbine, a detailed finite element approach is used. For the far field propagation, numerically highly effective methods are needed to predict the sound pressure level at large distances of several kilometers from the pile. In a combined model, results of the area close to the pile are transferred to a separate model using wavenumber integration to compute the sound pressure in the far field of the pile. Detailed investigations of the far field model and the setup of the combined near field-far field model can be found in corresponding publications of the authors [1]-[4]. The focus of this contribution is on the transformation of the near field model from the time domain to a formulation in the frequency domain to be able to consider frequency-dependent effects,

like, e.g., the damping characteristics of bubble curtains.