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Abstract Wind climate analysis and modelling is of most importance during site selection for offshore wind farm development. In this regard, reliable long-term wind data are required. Buoy measurements are considered as a reference source in relevant applications including evaluation and calibration of wind data obtained from less reliable sources, combined assessment, blending and homogenization of multi-source wind data, etc. Most of these applications are based on regression techniques elaborated by using the principle of ordinary least squares (OLS). However, wind data usually contain several outliers, which may question the validity of the regression analysis, if not properly considered. This study is focused on the implementation of the most important robust regression methods, which can identify and reveal outliers, and retain at the same time their efficiency. Long-term reference wind data series obtained from buoys at six locations in the Mediterranean Sea are used to calibrate hindcast (model) wind data by applying robust methods and OLS. The obtained results are compared according to several statistical measures. The effects of the calibration methods are also assessed with respect to the available wind power potential. The results clearly suggest that least trimmed squares and L1-estimator perform in all respects better than OLS.

Abstract The expanding marine renewable energy industry will increase the prevalence of electromagnetic fields (EMFs) from power cables in coastal waters. Assessments of environmental impacts are required within licensing/permitting processes and increased prevalence of cables will increase questions concerning EMF emissions and potential cumulative impacts. It is presumed that protecting a cable by burial, may also mitigate EMF emissions and potential impacts on species. Focussing on a bundled high voltage direct current (HVDC) transmission cable, we use computational and interpretive models to explore the influence of cable properties and burial depth on the DC magnetic field (DC-MF) potentially encountered by receptive species. Greater cable pair separation increased the deviations from the geomagnetic field and while deeper burial reduced the deviations, the DC-MF was present at intensities perceivable by receptive species. An animal moving along a cable route may be exposed to variable EMFs due to varied burial depth and that combined with an animal's position in the water column determines the distance from source and EMF exposure. Modelling contextually realistic scenarios would improve assessments of potential effects. We suggest developers and cable industries make cable properties and energy transmission data available, enabling realistic modelling and environmental assessment supporting future developments.

Abstract Wind turbines need to be spaced at a distance of the order of 1 km apart to reduce the effect of aerodynamic wakes. To increase the density of the power production in the farm, the deployment of wave energy converters (WECs) in the spaces between FWTs could be considered. However, the cost of energy from WECs is still very large. Therefore, the deployments of the WECs will reduce the economic value of the total project. In the present paper, a combined concept involving a combination of Spar-type FWTs and an axi-symmetric two-body WECs is considered. Compared with segregated deployments of FWTs and WECs, this combined concept would imply reduced capital costs of the total project because it will reduce the number of power cables, mooring line and the structural mass of the WECs. However, the effect of the addition of a Torus (donut-shape heaving buoy) on the FWT's motions as well as the power production should first be investigated. In the present study, coupled (wave- and wind-induced response-mooring) analysis is performed using SIMO/TDHMILL3D in the time domain to study the motion behaviour of the combined concept and to estimate the power production from both FWT and WEC under operational conditions. Mooring tension in the combined concept is also compared with the mooring tension in the Spar-type FWT alone. Hydrodynamic loads are determined using HydroD. The validated simplified method called TDHMILL is implemented to calculate the aerodynamic forces as a function of the relative wind velocity. The analysis is performed for several operational conditions according to metocean data taken in the Statfjord field in the North Sea. Finally, the behaviour of the combined concept under operational conditions is assessed, and it is shown to result in a positive synergy between wind and wave energy generation in terms of both capital investment and power production.

Abstract The OBREC is an overtopping structure which is integrated into a traditional rubble-mound breakwater to convert wave energy into electricity. The relatively simple geometry of this overtopping device, with a single frontal ramp and a reservoir, makes the technology suitable to be fully combined also with existing structures. OBREC has been deeply investigated over the last years with physical and numerical model tests, and it is still under development with the ongoing monitoring activities at full-scale in real environments focusing on the wave-OBREC interaction. A comprehensive review of the research studies during the last ten years is here presented. The paper contains some unpublished details on OBREC geometry and power take-off strategy. A special attention is also directed to the description of the full-scale prototype of OBREC at Naples harbour, where an experimental campaign is still continuing.

Abstract Satellite data are used to characterize the near-surface winds over the Northern European Shelf Seas. We compare mean winds from QuikSCAT with reanalysis fields from the Weather Research and Forecasting (WRF) model and in situ data from the FINO-1 offshore research mast. The aim is to evaluate the spatial and temporal variability of the near-surface wind field, including the inter- and intra-annual variability for resource assessment purposes. This study demonstrates the applicability of satellite observations as the means to provide information useful for selecting areas to perform higher resolution model runs or for mast installations. Comparisons between QuikSCAT and WRF reanalyses show biases ranging mostly between 0.6 and −0.6 m s−1 with a standard deviation of 1.8–2.8 m s−1. The combined analyses of inter- and intra-annual indices and the wind speed and direction distributions allow the identification of 3 sub-domains with similar intra-annual variability. Local characteristics observed from the long-term QuikSCAT wind rose distributions are depicted in high-resolution satellite Synthetic Aperture Radar (SAR) wind fields. The winds derived from the WRF reanalysis dataset miss seasonal features observed by QuikSCAT and at FINO-1.

Abstract Oscillating water column (OWC) devices equipped with an air turbine are the most extensively studied and possibly the most reliable wave energy converters (WEC). Self-rectifying air turbines are usually employed, being the key element of the power-take-off system. Experimental testing the air turbine in realistic operating conditions is a fundamental step in turbine and WEC development. These turbines are, by definition, operating under oscillating airflows. The present paper describes the development of a novel test-rig designed to test self-rectifying air turbines under both steady and variable unidirectional airflows, and subsequent demonstration tests performed on an axial-flow impulse turbine. A real-time hardware-in-the-loop flow controller was implemented, providing the means to not only experimentally characterise the turbine's performance under realistic wave conditions, but, as importantly, to develop new advanced turbine-generator control strategies that further increase overall efficiency and survivability. Results show that a unidirectional oscillating-flow test-rig with a calibrated fan and fast-actuating valve system can adequately reproduce airflows that are characteristic of an OWC air turbine's operational regime. The hardware-in-the-loop simulator implemented in an oscillating-flow test-rig appears as an innovative, integrated solution for turbine testing in realistic operating flow conditions, but in a laboratory-controlled environment at a small fraction of the costs.