The research presented in this thesis utilizes Blade Element Momentum (BEM) theory with a dynamic wake model to customize the OrcaFlex numeric simulation platform in order to allow modeling of moored Ocean Current Turbines (OCTs). This work merges the advanced cable modeling tools available within OrcaFlex with well documented BEM rotor modeling approach creating a combined tool that was not previously available for predicting the performance of moored ocean current turbines. This tool allows ocean current turbine developers to predict and optimize the performance of their devices and mooring systems before deploying these systems at sea. The BEM rotor model was written in C++ to create a back-end tool that is fed continuously updated data on the OCT’s orientation and velocities as the simulation is running. The custom designed code was written specifically so that it could operate within the OrcaFlex environment. An approach for numerically modeling the entire OCT system is presented, which accounts for the additional degree of freedom (rotor rotational velocity) that is not accounted for in the OrcaFlex equations of motion. The properties of the numerically modeled OCT were then set to match those of a previously numerically modeled Southeast National Marine Renewable Energy Center (SNMREC) OCT system and comparisons were made. Evaluated conditions include: uniform axial and off axis currents, as well as axial and off axis wave fields. For comparison purposes these conditions were applied to a geodetically fixed rotor, showing nearly identical results for the steady conditions but varied, in most cases still acceptable accuracy, for the wave environment. Finally, this entire moored OCT system was evaluated in a dynamic environment to help quantify the expected behavioral response of SNMREC’s turbine under uniform current. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

Indiana University-Purdue University Indianapolis (IUPUI) / A gearless hydraulic wind energy transfer system utilizes the hydraulic power transmission principles to integrate the energy of multiple wind turbines in a central power generation location. The gearless wind power transfer technology may replace the current energy harvesting system to reduce the cost of operation and increase the reliability of wind power generation. It also allows for the integration of multiple wind turbines to one central generation unit, unlike the traditional wind power generation with dedicated generator and gearbox. A Hydraulic Transmission (HT) can transmit high power and can operate over a wide range of torque-to-speed ratios, allowing efficient transmission of intermittent wind power. The torque to speed ratios illustrates the relationship between the torque and speed of a motor (or pump) from the moment of start to when full-load torque is reached at the manufacturer recommended rated speed. In this thesis, a gearless hydraulic wind energy harvesting and transfer system is mathematically modeled and verified by experimental results. The mathematical model is therefore required to consider the system dynamics and be used in control system development. Mathematical modeling also provided a method to determine the losses of the system as well as overall efficiency. The energy is harvested by a low speed-high torque wind turbine connected to a high fixed-displacement hydraulic pump, which is connected to hydraulic motors. Through mathematical modeling of the system, an enhanced understanding of the HTS through analysis was gained that lead to a highly efficient hydraulic energy transmission system. It was determined which factors significantly influenced the system operation and its efficiency more. It was also established how the overall system operated in a multiple wind turbine configuration. The quality of transferred power from the wind turbine to the generator is important to maintaining the systems power balance, frequency droop control in grid-connected applications, and to ensure that the maximum output power is obtained. A hydraulic transmission system can transfer large amounts of power and has more flexibility than a mechanical and electrical system. However high-pressure hydraulic systems have shown low efficiency in wind power transfer when interfaced with a single turbine to a ground-level generator. HT’s generally have acceptable efficiency at full load and drop efficiency as the loading changes, typically having a peak around 60%. The efficiency of a HT is dependent on several parameters including volumetric flow rate, rotational speed and torque at the pump shaft, and the pressure difference across the inlet and outlet of the hydraulic pump and motor. It has been demonstrated that using a central generation unit for a group of wind turbines and transferring the power of each turbine through hydraulic system increases the efficiency of the overall system versus one turbine to one central generation unit. The efficiency enhancement depends on the rotational speed of the hydraulic pumps. Therefore, it is proven that the multiple-turbine hydraulic power transfer system reaches higher efficiencies at lower rotational speeds. This suggests that the gearbox can be eliminated from the wind powertrains if multiple turbines are connected to the central generation unit. Computer simulations and experimental results are provided to quantify the efficiency enhancements obtained by adding the second wind turbine hydraulic pump to the system.