Date of Award

2022

Degree Type

Thesis

Department

Ocean Engineering

First Advisor

Chris Baxter

Abstract

Even with growing interest in developing an offshore wind industry off the east coast of the United States, there is little publicly available data for offshore wind structures. Combined with the wealth of knowledge in the US from the oil and gas industry, data from an offshore wind farm off the east coast could provide invaluable information for validating or updating policy as this new industry forms. The objective of this research was to compare the predictions of foundation and structural dynamics of the Block Island Wind Farm (BIWF) to measured values obtained from an on-going structural health monitoring program funded by the U.S. Bureau of Safety and Environmental Enforcement (BSEE). The predictions of the dynamic behavior included the natural frequency of the structure through the creation of a finite element model, vertical soil spring constants determined through a geotechnical pushover analysis, and the investigation of the sensitivity of the natural frequency to the vertical soil springs. The measured dynamics included the identification of the natural frequency through a data-driven state-stochastic identification modal analysis (SSI-DATA) of real-time accelerometer data from the BIWF during normal operation and 2 storm events, and the identification of the vertical soil springs through model updating. The vertical soil spring value was predicted to be between 1080 and 2500 MN/m depending on the analysis method, but was ultimately determined to have little influence on the overall frequency of the structure. As a result, model updating proved to be a complicated task. The identified natural frequencies were 0.29 Hz and 0.31 Hz in the side-to-side and fore-aft directions, and the associated global damping ratios were identified as between 0 and 14 percent and usually falling much lower, between 0 and 2 percent. The storm events provided the opportunity to compare the structural response during operation and when parked.

Available for download on Monday, March 06, 2023

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