Date of Award
2025
Degree Type
Thesis
Degree Name
Master of Science in Ocean Engineering
Department
Ocean Engineering
First Advisor
Reza Hashemi
Abstract
As renewable energies become increasingly more important, it becomes necessary to tap into new resources, such as energy from tidal or ocean currents. A recent development is the use of hydrokinetic turbines, deployed on floating plat- forms. Numerical modeling can be an important tool to determine the forces acting on the floating platform and the turbine.
In this thesis, a realistic floating hydrokinetic turbine was simulated in OpenFAST. Experimental data and hand calculations, were used to partially verify the simulation. Environmental data at a site was analyzed to determine conditions to run the simulations for different tidal current speeds and wave scenarios. Ultimately all elements were combined, and the simulation was run for the different scenarios. For the floating platform, heave, surge, and pitch motions were investigated, and as for the turbine, the rotor speed, and thrust force on the rotor were investigated. For a site in the Bay of Fundy that was selected for the simulations, tidal current speeds up to 1.5 m/s were used which was measured by [?]. The analysis of the wave data showed two thirds probability of occurrence for wave heights lower than 1.35 m. In comparison, wave heights higher than 2.8 m only occur in 5 % of the scenarios. In Table 1 in Section 4.1 the selected scenarios are given. Based on the environmental data, specific scenarios regarding wave conditions and current speeds were chosen to run the simulation on.
Floating body dynamics, more specifically Response Amplitude Operators for heave, were calculated by hand. Generally, a good match between hand calculations and the OpenFAST results were observed.
Also, the turbine that was simulated in OpenFAST, with a geometry from [?], was compared to experimental data, with an accuracy of 10 % between both data sets, for the operational settings that were intended for the turbine. In the comparison, the OpenFAST simulation assumed a fixed bottom structure, as that was the case for the given experimental data as well.
Simulations were then run for all elements combined. Heave, surge, and pitch show realistic responses to the wave spectrum. The force that can be expected on the rotor was calculated with the effective wind speed, and the simulation result shows an error of 13 % for 1.5 m/s current speed. Regular waves show less force on the turbine than irregular waves for the same wave height and wave period. The overall force on the rotor decreases with increasing wave height.
Lastly, a simple control for active mooring was implemented through an open loop system in Simulink. A force is applied to the platform through the mooring lines, with the same frequency as the incoming waves. It can be seen that the heave amplitudes of the platform are smaller with active control, though the damping varies, depending on wave period.
OpenFAST can be properly used for simulation of floating hydrokinetic devices, but some limitations have to be recognized, such as number of turbines, the limited accuracy for wake effects in the model and the missing viscous effects in the model.
Recommended Citation
Neber, Anneke, "NUMERIC SIMULATION OF A REALISTIC HYDROKINETIC TURBINE IN EXPOSED OCEAN ENVIRONMENTS" (2025). Open Access Master's Theses. Paper 2643.
https://digitalcommons.uri.edu/theses/2643