Underwater acoustic propagation modeling and utilization for marine hydrokinetic devices

Abstract

Over the last two decades, there has been growing concern surrounding the increase in underwater anthropogenic sounds as expanding human populations interact with marine life and look for alternative energy production methods. That concern has led to a significant push worldwide to understand how propagated sound interacts with the surrounding marine environment. Marine hydrokinetic (MHK) devices are an alternative source of renewable energy available, which generate electricity from the motion of tidal and ocean currents, as well as ocean waves. Sounds produced by MHKs tend to overlap the frequency range common to both marine fauna communication and behavior. Preliminary measurements indicate that sound level values fall near the total sound decibel limitations presented by regulatory bodies. To date, the power optimization of MHK arrays has been prioritized over how its sound is produced, directed, and may impact the marine soundscape. There is a gap in knowledge regarding how marine fauna may respond to these sounds and what their physical and behavioral impact may be, and an absence in measured levels from insitu MHK deployments. A model for predicting the propagation of sound from an array of MHK sources in a real environment is essential for understanding potential impacts on a surrounding system. This work presents a fully three-dimensional solution to a set of coupled, linearized velocity-pressure equations in the time-domain as applied to underwater systems, and is an alternative sound propagation model to the Helmholtz and wave equation methods. The model is validated for a single source located within a series of increasingly complex two-dimensional and three-dimensional shallow water environments and compared against analytical solutions, examples from literature, and recorded sound pressure levels collected from Sequim Bay, WA. An uncertainty analysis for an array of MHK devices is presented to further understand how multiple turbine signals interact with one another in increasingly complex systems. This research presents a novel use of the velocity-pressure equations to analyze the variability associated with sound sources as sound propagates through a selected environment to inform the design and deployment of a MHK device or array of devices to minimize potential future impacts.