| Summary: |
The ocean waves may be regarded as a major energy resource worldwide, and especially in Portugal, where natural conditions (high level of wave energy, narrow continental shelf i.e. deep water near the coast) and others (electrical grid close to the coast, government-imposed high purchase price of wave-generated electrical energy) are particularly favourable. Offshore devices are basically oscillating bodies, either floating or (more rarely) fully submerged. If large-scale exploitation of wave energy is to be performed, large arrays of such devices (like wind farms) are to be deployed offshore. Compared with shoreline and near-shore devices, offshore devices exploit the more powerful wave regimes available in deep water (typically more than 40m water depth). However they are in general more complex, which, together with additional problems associated with mooring, access for maintenance and the need of long underwater electrical cables, has hindered their development, and only recently some systems have reached, or come close to, the full-scale demonstration stage. The theoretical and numerical modelling is the first stage in the development process of wave energy converters (WECs). The hydrodynamic modelling of the wave energy absorption is usually based on linear water-wave theory. This theory ignores non-linear effects that are known to be important in the more energetic sea states, and also in small WECs ("point absorbers"), whose motion amplitude is relatively large. The standard way to account for non-linear wave effects is by model testing in wave basin, usually at scales between about 1:80 to 1:10. The main function of the mooring system of a floating WEC is to keep it in place. This results in an interactive process, since the mooring forces will depend on the motions of the WEC, and such motions in turn depend on mooring forces in addition to hydrodynamic forces and power take-off forces. The mooring configuration should be adapted to the typ  |
Summary
The ocean waves may be regarded as a major energy resource worldwide, and especially in Portugal, where natural conditions (high level of wave energy, narrow continental shelf i.e. deep water near the coast) and others (electrical grid close to the coast, government-imposed high purchase price of wave-generated electrical energy) are particularly favourable. Offshore devices are basically oscillating bodies, either floating or (more rarely) fully submerged. If large-scale exploitation of wave energy is to be performed, large arrays of such devices (like wind farms) are to be deployed offshore. Compared with shoreline and near-shore devices, offshore devices exploit the more powerful wave regimes available in deep water (typically more than 40m water depth). However they are in general more complex, which, together with additional problems associated with mooring, access for maintenance and the need of long underwater electrical cables, has hindered their development, and only recently some systems have reached, or come close to, the full-scale demonstration stage. The theoretical and numerical modelling is the first stage in the development process of wave energy converters (WECs). The hydrodynamic modelling of the wave energy absorption is usually based on linear water-wave theory. This theory ignores non-linear effects that are known to be important in the more energetic sea states, and also in small WECs ("point absorbers"), whose motion amplitude is relatively large. The standard way to account for non-linear wave effects is by model testing in wave basin, usually at scales between about 1:80 to 1:10. The main function of the mooring system of a floating WEC is to keep it in place. This results in an interactive process, since the mooring forces will depend on the motions of the WEC, and such motions in turn depend on mooring forces in addition to hydrodynamic forces and power take-off forces. The mooring configuration should be adapted to the type of WEC. The capability to suitably model the energy conversion chain (from waves to electrical energy) and mooring system, and its validation by physical model testing are essential in the conception, basic studies, and design of wave energy converters, and in the optimal design/specification of their structural, mechanical and electrical components. |