Date of Award

2025

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Department

Ocean Engineering

First Advisor

James Miller

Abstract

The primary foundation type for offshore wind farms are large-diameter monopiles, which are installed with an impact hammer that produces a high-intensity, broadband impulsive signal that radiates acoustic energy in the water column and seafloor. This signal generates multiple waves such as compressional, shear and Scholte (or interface) waves. Scholte waves travel on the water-sediment interface and contain high-intensity, low-frequency energy that benthic species of fish and invertebrates could possibly detect. COMSOL Multiphysics, which is a finite element modeling software, was used to develop two transient models of impact pile driving to measure Scholte wave particle motion (displacement, velocity, acceleration) and pressure at different ranges (from the pile) and depths (from the interface). The first model represents an ideal case which confirms the validity of COMSOL and the second model utilizes field data of the Coastal Virginia Offshore Wind (CVOW) Project to provide deeper understanding of changes in Scholte wave propagation in a more complex environment. At r = 50m and z = 0m, the Scholte wave had a peak pressure and vertical acceleration of ~80kPa and ~5X10^4 mm/s^2 for the first model and ~10kPa and ~1.5X10^4 mm/s^2 for the second model. Vertical and radial acceleration power levels (dB re 1 μm/s^2) from the second model at all ranges and both levels exceeded the behavioral sensitivity curves from 30Hz to 350Hz for four different fish species. A Scholte wave attenuation model was developed which demonstrated that its transmission loss was dominated by absorption, rather than cylindrical spreading. Averaged Scholte wave absorption values were calculated for each model and utilized to estimate shear wave absorption within the sediment which proved to be plausible compared to known theory.

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