Date of Award

2014

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

First Advisor

Aaron S. Bradshaw

Abstract

Increasing emission of carbon dioxide from combustion of fossil fuels its effect on the earth’s climate has led to increased research into renewable, clean energy solutions. Wind energy has been used as an alternative energy source for hundreds of years, however current research proposes the deployment of offshore wind farms in the deep waters of the oceans. A major challenge of deploying offshore wind farms is to safely and economically fix the wind turbines by means of anchors in the seabed. The objective of this study is to evaluate whether different anchoring concepts are suitable for securing floating offshore wind turbines in sandy soil conditions. For this purpose, an extensive literature review has been carried out to identify existing anchor capacity prediction models for three different anchor types. A 1-g model laboratory program was then developed and pullout tests using different anchor shapes in sand were performed. The laboratory testing program included pullout tests on shallow, vertically loaded square plate anchors, inclined square plate anchors, and drag embedment anchors in sands. For this purpose a testing facility (1.2 m width, 2.4m length and 0.9m height) was developed and a total of 11 pullout tests were carried out. The sand samples were prepared at a relative density of 22% and the tested depths varied from 0.15 m to 0.45 m. Tests results show an increase in capacity with increasing inclination angles. A comparison of the obtained test results and predicted capacities were used to evaluate the existing models. Best fit models were identified and loads derived from a state-of-the-art wind turbine were used to assess the feasibility of the proposed anchors to secure the 5-MW turbine. The results suggest that the examined anchor types are theoretically capable of mobilizing allowable capacities larger than the acting forces. The feasibility of anchor installation at the required embedment depths has to be proven in future research.

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