Roxana Tiron

A long-term nearshore wave hindcast for Ireland: Atlantic and Irish Sea coasts (1979–2012)

The Northeast Atlantic possesses some of the highest wave energy levels in the world. The recent years have witnessed a renewed interest in harnessing this vast energy potential. Due to the complicated geomorphology of the Irish coast, there can be a significant variation in both the wave and wind climate. Long-term hindcasts with high spatial resolution, properly calibrated against available measurements, provide vital information for future deployments of ocean renewable energy installations. These can aid in the selection of adequate locations for potential deployment and for the planning and design of those marine operations. A 34-year (from 1979 to 2012), high-resolution wave hindcast was performed for Ireland including both the Atlantic and Irish Sea coasts, with a particular focus on the wave energy resource. The wave climate was estimated using the third-generation spectral wave model WAVEWATCH III®; version 4.11, the unstructured grid formulation. The wave model was forced with directional wave spectral data and 10-m winds from the European Centre for Medium Range Weather Forecasts (ECMWF) ERA-Interim reanalysis, which is available from 1979 to the present. The model was validated against available observed satellite altimeter and buoy data, particularly in the nearshore, and was found to be excellent. A strong spatial and seasonal variability was found for both significant wave heights, and the wave energy flux, particularly on the north and west coasts. A strong correlation between the North Atlantic Oscillation (NAO) teleconnection pattern and wave heights, wave periods, and peak direction in winter and also, to a lesser extent, in spring was identified.

A Detailed Investigation of the Nearshore Wave Climate and the Nearshore Wave Energy Resource on the West Coast of Ireland

The western coast of Ireland possesses one of the highest wave energy resources in the world and consequently is a promising location for the future deployment of Wave Energy Converters (WECs). Most wave climate studies for this region have focused primarily on the offshore area since it enjoys higher energy densities. However, recent studies have shown that nearshore locations offer a similar potential for the exploitation of wave energy as offshore sites [13]. Furthermore, the proximity of WEC devices to the shore will likely reduce losses in power transport, and facilitate access for maintenance activities.In this context, we analyse the wave climate over a ten year period for several nearshore sites off the Irish West Coast. The wave climate is estimated using a spectral wave model, WaveWatch III, forced with wind and spectral wave data from the ECMWF (European Centre for Medium Range Weather Forecast) operational archive. The wave model is validated with wave buoy data from intermediate to shallow depths (< 60 m).Our focus is on two aspects of the wave climate resource assessment. Firstly, we characterise the directionality of the wave energy resource (mean direction, directional spread) which affects the site selection, design and performance of nearshore WECs. Secondly, we discuss the climate data from the perspective of accessibility for maintenance. When selecting sites for the deployment of WECs, a balance needs to be found between two opposing criteria: the existence of sufficiently long, continuous time intervals of calm sea states (weather windows) which are necessary for maintenance activities to take place, and a high, consistent level of wave energy density, essential for economically viable wave energy extraction.Copyright

An Experimental Study of the Hydrodynamic Effects of Marine Growth on Wave Energy Converters

Even though the outstanding energy resource provided by ocean surface waves has long been recognized, the extraction of wave power is still in its infancy. Meanwhile, the increased interest in sustainable energy alternatives could lead to large-scale deployments of wave energy convertors (WECs) worldwide in the near future. In this context, the interaction of WECs with the marine environment is an issue that has come under increased scrutiny. In particular, the accumulation of biological deposits on the device (commonly referred to as biofouling) could lead to a modification in the behaviour and performance of the device design.For coastal devices in the North-Eastern Atlantic region, the main contributors to biofouling are likely to be the brown algae from the genus Laminaria. In the experimental study described in this paper, we have investigated the effects of algal growth on a scale model of the Oyster 800 WEC, a technology developed by Aquamarine Power. The experiments were carried out in the wave tank at Queens University Belfast. The algal growth on the device has been emulated with plastic stripes attached on the surface of the device. Several configurations with various placements and stripe dimensions were tested, in sea states typical to the targeted deployment sites. Our experiments were designed as a worst-case scenario and provide first insights into the potential effects of biofouling on the performance of a WEC. The experiments indicate that the effects of biofouling could be significant and suggest the need for further investigation.© 2013 ASME

SPATIAL VARIABILITY OF EXTREME SEA STATES ON THE IRISH WEST COAST

Recent studies have revealed a long history of large waves around Ireland, which can be attributed to persistent strong winds in this area. At the same time, due to the consistently high levels of wave energy, the West Coast of Ireland has attracted a lot of interest as a prospective site for deployment of wave energy converters (WECs) farms. The design of such devices, and in fact of any offshore installation, depends crucially on the knowledge of extreme sea states they will experience during their deployment time.With this in mind, an Extreme Value Analysis incorporating seasonality and accounting for long-term trends was performed, based on a 29 year hindcast for Ireland. The hindcast was performed using the WAVEWATCH III wave model in a 3 nested grid setup, with the largest grid covering the North Atlantic basin and the finest resolution grid (10km) focusing on Ireland. The model was forced with ERA-Interim 10m winds from the European Centre for Medium Range Weather Forecasts. The wave model was validated by comparison to buoy data from the Irish Marine Data Buoy Network.The analysis was performed on the entire fine resolution grid. This affords a characterisation of the spatial variability in extremes both along the coast and with depth gradients. This is of interest in many marine applications, and in particular WEC design and deployment. Indeed, in the nearshore, wave energy levels can be similar to those found in the offshore. This, in conjunction with the diminished risk of extreme sea states, makes nearshore areas attractive for future ocean energy sites.Copyright