Loads Analysis of Fixed-Bottom and Floating Offshore Wind Structures

Offshore wind in the United States is a rapidly growing industry. The development of both fixed bottom and floating platforms is important for the success of the industry. While monopiles are common substructures in Europe, the Atlantic Coast has a much greater risk for hurricanes. It is necessary to understand how extreme weather events will impact the structures. Meanwhile, floating offshore wind will be key for offshore wind development along the Pacific Coast, Hawaii, and Gulf of Maine. Before these projects can come to fruition, the cost of development must first decrease. A taut mooring system with multiline anchors may be able to reduce costs, specifically when deployed in deep water locations. This thesis considers these concerns for both the fixed bottom and floating wind developments. A parametric study is completed using OpenFAST for a variety of mooring systems. A taut multiline mooring system is designed for water depths ranging from 850 to 2000 meters. Further 850-meter designs explore how changing line properties impact the mooring line and multiline loading. Using these mooring designs, preliminary suction anchors are designed, focusing on the potential savings of decreasing the number of anchor installations from 3 single line anchors per turbine to 1 multiline anchor per turbine. Anchors are designed for a range of soil conditions to observe their impacts on anchor dimensions. For monopile design, four Atlantic Coast wind developments are chosen for design of monopiles at each site, using 50-year and 500-year storm conditions in the design process. These monopiles are designed using primarily hand calculations, with the assistance of OpenFAST to create a hub thrust power curve. The loads are then used to design monopile for a constant diameter and thickness from the transition piece to the mudline. The constant diameter monopiles are compared to a design that was complete for fatigue loading. In general, the fatigue loaded monopiles were required to be much larger, providing capacities larger than the monopiles designed for extreme storm conditions