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The European Marine Energy Centre (EMEC) has decided to use DHI’s MIKE modelling technologies for studying water levels, currents and waves in the often rather harsh environment at EMEC’s test sites in the Orkney Islands located NW of Scotland, UK.
EMEC is a test centre created to promote the development of the wave and tidal stream energy conversion industries in the UK and wider. The established open-sea grid-connected test facility allows a ‘plug and play’ approach for testing of new wave and tidal energy devices in full scale.
Location of the EMEC’s wave and tidal test sites (left panel) and the Orkney Island computational mesh
The wave test site is located off the west coast of Mainland Orkney, 2km off Billia Croo bay. There are currently four test berths located in water depths of approximately 50m. The average significant wave height is approximately 1.9m.
The tidal test site is located to the west of Eday, one of Orkney’s North Isles, and east of Muckle Green Holm, is a tidal stream known as the Fall of Warness. This body of water is approximately 2km wide and 3.5km long. There are currently five test berths located in water depths of approximately 25-50m. Due to the narrow channel very strong tidal streams occur. During spring tides the typical strength is approximately 3.4 m/s and for neap tides approximately 1.3 m/s.
DHI will construct a numerical hydrodynamic model of the Orkney Islands using the flexible version of MIKE 21 Flow Model FM. This model permits spatial varying resolution, so that the complex tidal channels and local topographic features that may influence the tidal dynamics can be sufficiently resolved. The calibrated the model will be delivered to EMEC.
The complexity of the flow structure in Fall of Warness is also illustrated in the figure below, where the flow vectors are superimposed upon the current speed magnitude. The position of the eddy and the severe gradient in the current field is very sensitive to the local water depth and to the flow separation at the nearby War Ness point.
Map view of the Fall of Warness including the position of an ADCP and current speed vectors at peak and late flood tide
Also a fully spectral model of the Orkney Islands will be build using MIKE 21 Spectral Waves FM within special focus on the wave conditions at Billia Croo and at Fall of Warness. ADCP measurements at Fall of Warness show that the strong tidal stream has significant impact on the wind-sea and swell wave climate due to wave-current interaction processes. This is illustrated in the animation below.
Based on wave hindcast DHI will provide statistical wave analysis at Billia Croo and at Fall of Warness. Also the calibrated wave model will be delivered to EMEC.
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