Miles Willis

A robust blade element momentum theory model for tidal stream turbines including tip and hub loss corrections

Blade Element Momentum Theory (BEMT) performance models for wind turbines lead to a robust BEMT model of marine current or tidal stream turbines. It is shown that numerical convergence methods for models reported in the literature are problematic when away from the normal operating range and this paper reports a robust numerical scheme using combined Monte Carlo and sequential quadratic optimisation. The model is extended by Prandtl corrections for losses at the blade tip and hub. Results are validated against an industrial code, Garrad Hassan’s Tidal Bladed Software (GH Tidal Bladed) evaluation version, and a lifting line theory model.

Comparison of underwater background noise during Spring and Neap tide in a high tidal current site: Ramsey Sound

Underwater noise monitoring of a tidal stream is an important component of any Environmental Impact Assessment to assess the potential noise disturbances that a tidal turbine may have on marine life. Before monitoring operational noise, it is crucial to characterise ambient noise at different period of a proposed site. In May 2011, an acoustic survey of Ramsey Sound was undertaken over two entire tidal cycles. Ramsey Sound is a proposed site for the installation of a tidal turbine. It is an open channel measuring 2.5km long and 1km wide, varying between 25 and 70m deep and subject to tidal streams up to 4m.s-1. Continuous recordings have been carried out from 1Hz to 22kHz. The methodology used to monitor ambient noise was to immerse the hydrophone over the board and let the boat drift with the current flow, which allowed the reduction of unwanted noise such as water flow noise, cable strum. This paper presents the impact of the tide, the biological and the physical noise on the ambient noise. Sound Pressure Level during neap tide evolves between 95 and 125dBre_1μParms. During spring tide, background noise SPL is higher and evolves between 100 and 127dB re_1μParms.