| Summary: | PhD thesis in Offshore technology The exploitation of offshore wind in deep waters by means of floating wind turbines is steadily gaining traction as a suitable option to produce renewable energy. Among the innovative technologies recently proposed, two-rotor floating wind turbines offer significant advantages in terms of smaller blades deployed offshore, cheaper operations, fewer installations, and sharing of the floating platform. Although examples of commercial prototypes currently under development are many, the scientific literature lacks thorough studies on the dynamic performance of such systems. As a consequence, a better understanding of the major design drivers of such systems leading toward the definition of a baseline design is required. Floating wind turbines are highly dynamic systems subjected to environmental loads from waves, currents, and wind. Moreover, the dynamic response of wind turbines is heavily influenced by the nonlinear behavior of the servo systems, such as cutin, cutout, and failure conditions. As such, dynamic analysis is often carried out by means of fully-coupled tools able to consider all factors in an integrated environment. To date, there is a lack of an open-source fully-coupled tool able to easily analyze the dynamics of two-rotor floating wind turbines. This PhD thesis presents the development of such a tool. Development work was mostly carried out in Modelica through the opensource environment OpenModelica and the freelyavailable Modelica Standard Library. The dynamics of the system and structural dynamics of tower and blades were implemented by means of a multibody approach. Linear hydrodynamics was solved in DNV Wadam and the associated hydrodynamic loads were imported into the tool as time realizations. Moreover, the well-known aerodynamic module AeroDyn within the NREL package FAST was integrated into the environment for the computation of aerodynamic loads based on the blade-element momentum approach. Benchmark studies showed good performance and accuracy compared ...
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