The Queen's University of Belfast: Department of Civil Engineering
Doi
Abstract
In order to assess the Queen's University device on a more realistic basis than in 1978 it has been found expedient to adopt a point absorbing device which is directly moored to the sea bed via a rigid tension leg system (shown schematically in Fig. 1). This type of mooring effectively restricts the heave motion of the device and as a consequence it corresponds closely with the fixed canopy tests which have been carried out in our upgraded test facility over the past 2 months. These tests have shown excellent repeatibility and the extraction efficiencies have been found to be considerably greater than those for the J 978 device. It was therefore considered logical at this time to concentrate our efforts on this system especially as it was estimated that the costs of moorings and overall structures would not be appreciably altered from those for a less restrained device. The other alternative of assessing a device based on the estimated drop-off in extraction efficiency, which would occur if the canopy was not fully fixed against heave motion was abandoned for this feasibility study as it would have been based on too many uncertainties. In the near future when the appropriate series of model tests on the flexible mooring system have been carried out it is intended that a comparative feasibility study will be made. At this time it is important to emphasise that the hydrodynamic model studies have not as yet yielded the optimum configuration for the form of device being considered this year and as a consequence the overall costs are still likely to be pessimistic. It is in this context and on the understanding that the consultants will attempt to take these consideration s into account that the team embarked on this further feasibility study. The main objectives of this study were to: ( 1) obtain an approximate overall estimate of the cost of the latest form of the QUB device for use in comparison with other wave energy devices and with conventional thermal power systems. and (2) assess the relative contributions of moorings, structures, electrical and turbine to the cost of the overall system. As in 1978 the device team does not consider that a comprehensive submission can be made at this time. However, attempts have been made to produce more realistic general arrangement drawings of the proposed structure and a more detailed appraisal has been made of possible mooring arrangements and the generation and transmission system
