Analysis of wave and current data in a tidal energy test site

Abstract

Characterisation of a tidal stream site before device deployment is important for the marine tidal industry, in order to optimise the device design and accurately predict its performance during operation. Understanding the short-term uctuations in tidal stream velocity, resulting from turbulence and wave-current interactions, is essential for proper evaluation of the transient performance of a tidal stream turbine. Several aerodynamic models have been proposed for the design of tidal stream turbines and energy production calculation, most of which have proved to predict accurately mean quantities within the ow regime. Unfortunately, these models cannot accurately predict the instantaneous ow variation and resulting forces within the ow regime acting on tidal stream systems which is of central importance to the tidal energy industry. The reasons for this may not be unconnected to the signi cant differences between wind and tidal turbines. Given the uncertainties which exist in the assumptions of resource modelling and the need for an accurate energy capture assessment at a speci c site, accurate on-site measurements that can predict the ow velocity (and its directional component) at a given location, are needed. This thesis is devoted to characterisation of ow in a typical tidal stream site (the Fall of Warness, of the European Marine Energy Center (EMEC), Orkney) through measured data. The high-frequency Acoustic Doppler Current Pro ler (ADCP) surveys were conducted at different locations within this site by EMEC. This dataset allows for the rst time a statistical and thorough analysis of the vertical turbulence structure at the EMEC's tidal stream test site. Detailed analyses of the directional components of the wave elds using a non-phase-locked method and in uences of seabed and tidal stream on wave elds, were performed. The bulk turbulence parameters within the tidal streams were estimated using the variance method. The results suggest a signi - cant effect of directionality and short-term uctuations in stream velocity resulting from turbulence and wave-current interactions, on the hydrodynamics in a typical tidal energy test site. The results from this study can be used to validate and improve/develop proposed hydrodynamic models and can play a vital role in tidal energy resource planning.