Abstract
Ocean currents present along the western boundaries of global ocean basins represent a significant renewable energy resource, with localized energy densities off the east coast of the US exceeding 3 kW/m² in areas and a total extractable potential in the gigawatt range. Most energy-rich currents are located within the upper 100 meters of the water column in areas where total depths exceed 250 meters. To harness this energy efficiently, moored ocean current turbines (OCTs) are being investigated that use variable buoyancy control, lifting surfaces, or a combination of both for depth regulation. This research focuses on a dual-rotor OCT configuration that utilizes both variable buoyancy and lifting surfaces, such that the variable buoyancy controls the pitch of the system, which in turn impacts the lift force on a wing structure, controlling the operating depth. This study presents a numerical simulation-based performance assessment of a dual-rotor OCT operating in the Florida Straits. The turbine dynamics are modeled using a rigid-body framework with eight degrees of freedom, six associated with the main body and two corresponding to the independent rotational speeds of the dual rotors. Additionally, the mooring system is represented through a finite-element, lumped-mass cable model, where each node is assigned three degrees of freedom. The findings provide insights into the dynamic response and power production of the proposed turbine configuration under various ballast tank fill distributions and flow conditions. Specifically, open-loop simulations are conducted for (i) different buoyancy tank fill levels at constant flow speed and zero turbulence, and (ii) different flow speeds with identical tank fill levels and no turbulence. Additionally, closed-loop results are presented for varying flow speeds under a fixed fill configuration with 10% turbulence.
The poster for this paper at OREC/UMERC 2025 can be found here.