Modeling and numerical simulation of a buoyancy controlled ocean current turbine

Abstract

Increased global renewable power demands and the high energy density of ocean currents have motivated the development of ocean current turbines (OCTs). Compliant mooring systems will be used together with variable buoyancy, lifting surface, sub-sea winches, and/or surface buoys to maintain desired near-surface operating depths. This paper presents a complete numerical simulation of a 700 kW variable buoyancy controlled OCT that includes a detailed turbine system, inflow, actuator (i.e., generator and variable buoyancy), sensor, and fault models. Simulation predictions of OCT performance are made for normal, hurricane, and fault scenarios. Results suggest this OCT can operate between depths of 38 m to 90 m for all homogeneous flow speeds between 0.5-2.5 m/s. Fault scenarios show that rotor braking faults will result in a rapid vertical OCT system assent and blade pitch faults will create power fluctuations apparent in the frequency domain. Finally, the OCT power statistics and system behaviors are quantified under typical and extreme operations using measured ocean currents with normal and hurricane conditions.