Numerical Analysis of the Hydrodynamic Loading of a Floating Tidal Turbine Undergoing the Pendulum Motion

Abstract

For a floating offshore turbine freely oscillate in the six degrees of freedom motion, the origin of the unsteady loading comes from the combination of tidal current, waves, and the platform (and turbine) motion. In literature, the pendulum (pitch) motion is viewed as the dominant contributor, in terms of the wave-induced platform motion, to the fluctuating load on a floating turbine. This paper aims to analyze the unsteady hydrodynamic loading on the floating tidal turbine oscillating in the pendulum motion. Computational fluid dynamics (CFD) analyses were carried out to investigate the performance of the floating turbine. The fluctuating load was highly in phase with the instantaneous velocity on the rotor. Loading variations increase together with the increase in motion amplitude and frequency. Flow separation occurs at higher motion amplitude and frequency cases, which is detrimental to the structural integrity of the rotor. Implementing the speed control technique by spinning the rotor faster can minimize the stalling effect on the floating turbine. The research finding can provide useful insight into understanding the unsteady loading on a floating tidal turbine oscillating in the pendulum motion.

Keywords: pitch motion, tidal turbine, stall, floating, unsteady loading, OpenFOAM