Waves in the North Sea: powering our future?

Ocean waves contain huge amounts of energy which almost haven’t been exploited up to now. Along the West European coastline the wave power resource is varying between 30 and 70kW/m crest length (Thorpe, 1999). These huge amounts of wave power increase the potential energy capture on the one hand but hamper installation on theother hand. Furthermore the survivability of conversion systems could be in danger in these severe wave conditions.The wave climate in the North Sea is less aggressive due to the sheltering effect of Great Britain. The wave power resource and potential areas for installation of a farm of Wave Energy Converters (WECs) in the North Sea will be discussed during the presentation.Wave energy is a renewable energy type that is becoming more and more important. Many conversion principles have been invented and are currently being developed, tested and improved. Research on power optimization, structural design, etc. is going on while interest of private investors is increasing.Although many concepts have been invented, only a limited number of systems have already been built in prototype size and have experienced real sea trials. Even fewer have reached a commercial stage. Among them is the Pelamis the converter which is probably most ahead of the others. This system, sometimes called ‘sea snake’ consists of four hinging cylinders that produce electricity via a hydraulic intermediate stage. The Portuguese consortium Enersis will shortly install three units of 750kW each in front of the Portuguese coast. Some other systems that have experienced sea trials - mostly at scaled size - are Wave Dragon, FO³, Wave Star, AquaBuOY, OPT Power Buoy, Pico power plant, Limpet device,… Some of these systems will be treated more in detail during the presentation

Numerical modelling of wave energy absorption by a floating point absorber system [POSTER]

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Bottom slamming on heaving point absorber wave energy devices

Oscillating point absorber buoys may rise out of the water and be subjected to bottom slamming upon re-entering the water. Numerical simulations are performed to estimate the power absorption, the impact velocities and the corresponding slamming forces for various slamming constraints. Three buoy shapes are considered: a hemisphere and two conical shapes with deadrise angles of 30 and 45, with a waterline diameter of 5 m. The simulations indicate that the risk of rising out of the water is largely dependent on the buoy draft and sea state. Although associated with power losses, emergence occurrence probabilities can be significantly reduced by adapting the control parameters. The magnitude of the slamming load is severely influenced by the buoy shape. The ratio between the peak impact load on the hemisphere and that on the 45 cone is approximately 2, whereas the power absorption is only 4-8% higher for the 45° cone. This work illustrates the need to include slamming considerations aside from power absorption criteria in the buoy shape design process and the control strategy

Lactate-guided resuscitation saves lives: we are not sure

SCOPUS: ed.jinfo:eu-repo/semantics/publishe