High fidelity modeling of pile driving acoustic energy

Pile driving for the installation of wind farms has become a recent topic of interest as we seek to learn how to protect the marine environment while energy efficient offshore turbines are installed. For environmental compliance, propagation models for spreading from a point source are sometimes used to evaluate impact volumes. Use of a point source is problematic in that a pile (either hammered or shaken using a vibratory source) fully extends through the water column and cannot be considered a point source. In this paper we present a hybrid model solution to evaluate the sound field at close and far ranges. First, a finite element model, consisting of the hammer, pile, the nearby seawater and the sediment, is used to computed the acoustic pressure field at a short range (∼3 m). The sound pressure field versus depth and frequency at this range is used as the starter field for the Parabolic Equation and the field is then propagated to range, including range dependent environments. Impact volumes, for various marine species hearing groups are computed. [Work supported by BOEM.]