Analysis of Anthropogenic Noise due to Pile Driving Using Computational Fluid Dynamics

There has been a growing concern in recent years about the effects of anthropogenic noise due to pile driving on underwater wildlife. Current guidelines for mitigating hydroacoustic effects associated with these geotechnical events are based upon a relatively simple transmission loss formulation known as the Practical Spreading Loss Model (PSLM). This model is easy to implement, but it may produce overly conservative results. During a previous study, sound data during pile drives from two sites in Florida showed much higher sound attenuation than predicted by the PSLM at one of the sites. This study focused on explaining this discrepancy using computational fluid dynamics. Specifically, synthetic pile drives were simulated using Siemens' Star-CCM+. These models tracked sound decay from a single hammer blow that was imposed at a modeled pile using site-specific bathymetry data. Results showed that discrepancies between measured transmission loss coefficients and the practical spreading loss model could not be explained due to local bathymetry alone. However, if different sound absorption criteria were used at the sites' mudlines, the model was able to replicate results. The data therefore suggest that geotechnical conditions may play a significant role in determining anthropogenic sound loss due to pile driving.