Erick Johnson

Model and data comparison for a three-dimensional, finite-difference, time-domain solver in Sequim Bay

Paracousti is a three-dimensional finite-difference, time-domain solution to the governing velocity-pressure equations. This program is directed at modeling sound propagation generated by marine hydrokinetic (MHK) sources in an ocean environment. It is capable of modeling complex, multi-frequency sources propagating through water and soil that have spatially varying sound speeds, bathymetry, and bed composition. Experimental sound data collected at Sequim Bay in Washington, USA, during the winter of 2017 is compared against several simulations modeled within Paracousti for a range of frequencies and receiver locations. This measurement campaign recorded ambient noise data and the sound from a source producing three-second long, sinusoidal pulses between 20 and 5,000 Hz at a depth of 3 m. Additionally, bathymetric, sanity, and temperature data for the bay were collected in order to calculate the sound speed. Data were recorded at six locations ranging in distance between 10 and 1,000 m from the source by stationary buoys. Each simulation was created to model the collected source profiles and has a total depth of 80 m, with the average soil depth occurring at 23 m, and compared via transmission losses. Paracousti is a three-dimensional finite-difference, time-domain solution to the governing velocity-pressure equations. This program is directed at modeling sound propagation generated by marine hydrokinetic (MHK) sources in an ocean environment. It is capable of modeling complex, multi-frequency sources propagating through water and soil that have spatially varying sound speeds, bathymetry, and bed composition. Experimental sound data collected at Sequim Bay in Washington, USA, during the winter of 2017 is compared against several simulations modeled within Paracousti for a range of frequencies and receiver locations. This measurement campaign recorded ambient noise data and the sound from a source producing three-second long, sinusoidal pulses between 20 and 5,000 Hz at a depth of 3 m. Additionally, bathymetric, sanity, and temperature data for the bay were collected in order to calculate the sound speed. Data were recorded at six locations ranging in distance between 10 and 1,000 m from the source by s...

Modeling underwater noise propagation from marine hydrokinetic power devices through a time-domain, velocity-pressure solution

Marine hydrokinetic (MHK) devices generate electricity from the motion of tidal and ocean currents, as well as ocean waves, to provide an additional source of renewable energy available to the United States. These devices are a source of anthropogenic noise in the marine ecosystem and must meet regulatory guidelines that mandate a maximum amount of noise that may be generated. In the absence of measured levels from in situ deployments, a model for predicting the propagation of sound from an array of MHK sources in a real environment is essential. A set of coupled, linearized velocity-pressure equations in the time-domain are derived and presented in this paper, which are an alternative solution to the Helmholtz and wave equation methods traditionally employed. Discretizing these equations on a three-dimensional (3D), finite-difference grid ultimately permits a finite number of complex sources and spatially varying sound speeds, bathymetry, and bed composition. The solution to this system of equations has been parallelized in an acoustic-wave propagation package developed at Sandia National Labs, called Paracousti. This work presents the broadband sound pressure levels from a single source in two-dimensional (2D) ideal and Pekeris wave-guides and in a 3D domain with a sloping boundary. The paper concludes with demonstration of Paracousti for an array of MHK sources in a simple wave-guide.