Underwater Acoustic Impact of a Marine Renewable Energy Device

Noise generated by renewable energy devices may impact local wildlife and interfere with military navigation techniques. Given the particular challenges posed by underwater sound propagation, careful analysis of this phenomenon is required. To conduct such an analysis, a model that is able to integrate detailed environmental descriptions and low frequency computations is sought. For these purposes, it has been found that normal mode models are the most suited to the task at hand, in particular the classical KRAKEN algorithm. In this article, the advantages of normal mode models over ray-tracing ones such as BELLHOP will be presented. Furthermore, the algorithm’s performance is numerically verified through the employment of mesh refinement studies to evaluate its numerical uncertainty convergence characteristics. Finally, the normal mode method’s capabilities are validated against experimental data measured near an energy-generating device installed off the coast of Peniche, Portugal. At frequencies above 1000 Hz, it was found that the normal mode solution closely followed the trends observable in the experimental data. Between 500 and 1000 Hz, difficulties in assembling a field solution over the domain arose. Below these frequencies, a clear break-down of the normal mode assumptions was observed. The normal mode method has been concluded to be a strong candidate to predict sound propagation from marine structures, but more work is needed to improve the calculation of near-field effects, potentially by use of Green’s function algorithms.