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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In vitro susceptibility of six isolates of equine herpesvirus 1 to acyclovir, ganciclovir, cidofovir, adefovir, PMEDAP and foscarnet

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Settlement of Macoma balthica larvae in response to benthic diatom films

The role of multi-species benthic diatom films (BDF) in the settlement of late pediveliger larvae of the bivalve Macoma balthica was investigated in still-water bioassays and multiple choice flume experiments. Axenic diatom cultures that were isolated from a tidal mudflat inhabited by M. balthica were selected to develop BDF sediment treatments characterized by a different community structure, biomass, and amount of extracellular polymeric substances (EPS). Control sediments had no added diatoms. Although all larvae settled and initiated burrowing within the first minute after their addition in still water, regardless of treatment, only 48-52% had completely penetrated the high diatom biomass treatments after 5 min, while on average 80 and 69% of the larvae had settled and burrowed into the control sediments and BDF with a low diatom biomass (<3.5 mu g Chl a g(-1) dry sediment), respectively. The percentage of larvae settling and burrowing into the sediment was negatively correlated with the concentration of Chl a and EPS of the BDF. This suggests higher physical resistance to bivalve penetration by the BDF with higher diatom biomass and more associated sugar and protein compounds. The larval settlement rate in annular flume experiments at flow velocities of 5 and 15 cm s(-1) was distinctly lower compared to the still-water assays. Only 4.6-5.8% of the larvae were recovered from BDF and control sediments after 3 h. Nonetheless, a clear settlement preference was observed for BDF in the flume experiments; i.e., larvae settled significantly more in BDF compared to control sediments irrespective of flow speed. Comparison with the settlement of polystyrene mimics and freeze-killed larvae led to the conclusion that active selection, active secondary dispersal and, at low flow velocities (5 cm s(-1)), passive adhesion to the sediment are important mechanisms determining the settlement of M. balthica larvae in estuarine biofilms

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