@article{williams_bryant_agrawal_mazzoleni_granlund_ramaprabhu_bryant_2022, title={Characterization of the Steady-State Operating Conditions of Tethered Coaxial Turbines}, ISBN={["978-1-6654-6809-1"]}, ISSN={["0197-7385"]}, url={http://dx.doi.org/10.1109/oceans47191.2022.9977052}, DOI={10.1109/OCEANS47191.2022.9977052}, abstractNote={Tethered coaxial turbines (TCTs) may be a feasible configuration to extract hydrokinetic energy from the Gulf Stream’s flow. A TCT consists of two rotors attached to the halves of a rotary generator, which is moored to a mounting point via a tether. Flow causes the rotors to counter-rotate which induce power within the generator. The TCT’s steady-state operating domain and power extraction is determined by the intersection of the hydrodynamic operating domain of the rotors and electromechanic operating domain of the generator. As a result, the TCT’s operating point can be selected with an electrical load resistance, skew angle, and flow speed. Previous analytical methods for evaluating dual rotor devices have assumed ideal rotor, flow, and generator characteristics to simplify the quantification of power extraction. The proposed hydrodynamic analysis modifies traditional blade-element momentum theory (BEMT) to accept nonuniform inflow into the rotor, via a radially and azimuthally discretized BEMT method (RAD-BEMT). RAD-BEMT is leveraged alongside a momentum theory wake development factor to determine the response of the back rotor within the nonuniform wake of the front rotor. The back rotor response is determined by minimizing the difference in mass continuity and rotor torques. Our electromechanical analysis considers an AC generator, and the effects of voltage rectification, system resistance, and capacitance on the TCT’s power extraction capabilities. A case study was performed to demonstrate the ability of torque and mass continuity minimization to locate a hydrodynamic operating point, for axial and skew flow conditions. Additionally, power extraction capabilities, load resistance selection, and the qualitative effects of skew on the minimization domain are discussed.}, journal={2022 OCEANS HAMPTON ROADS}, publisher={IEEE}, author={Williams, Vinson Oliver and Bryant, Samuel and Agrawal, Saurabh and Mazzoleni, Andre P. and Granlund, Kenneth and Ramaprabhu, Praveen and Bryant, Matthew}, year={2022} }
 @article{agrawal_williams_tong_hassan_muglia_bryant_granlund_ramaprabhu_mazzoleni_2022, title={Demonstration of a Towed Coaxial Turbine Subscale Prototype for Hydrokinetic Energy Harvesting in Skew}, ISBN={["978-1-6654-6809-1"]}, ISSN={["0197-7385"]}, url={http://dx.doi.org/10.1109/oceans47191.2022.9977395}, DOI={10.1109/OCEANS47191.2022.9977395}, abstractNote={The immense potential for ocean current energy harvesting is being actively explored by researchers, exhibiting the importance of the marine hydrokinetic industry. This paper presents a towed dual rotor coaxial turbine prototype built to demonstrate the ability of tethered, underwater, hydrokinetic devices to harvest energy from ocean currents. A sub-scale test article was developed to measure fluid power conversion and serve as a platform for operational feasibility in open-water testing. Tow testing of this article was done in the freshwaters of Lake Norman in North Carolina at three tow speeds: 1 m/s, 1.25 m/s and 1.5 m/s. Preliminary results demonstrate the ability to extract power, system robustness, waterproofing capabilities, and illuminates the nuances and non-linearities unique to the tethered coaxial turbine system.}, journal={2022 OCEANS HAMPTON ROADS}, publisher={IEEE}, author={Agrawal, Saurabh and Williams, Vinson Oliver and Tong, Xinyang and Hassan, Mehedi and Muglia, Mike and Bryant, Matthew and Granlund, Kenneth and Ramaprabhu, Praveen and Mazzoleni, Andre P.}, year={2022} }