Development and evaluation of the hydrodynamic design of the OWEL wave energy converter

Abstract

The conversion of ocean wave energy has the potential to supply utility magnitudes of electrical generating capacity. It has been predicted that the UK has an annual, practical wave energy resource of 50 TWh which represents 12.5 % of the total electricity consumption. The lack of convergence in the design of wave energy converters, demonstrates that there is not yet a clearly superior concept and so the development of novel technologies is continuing. OWEL’s novel wave energy converter was intended to overcome some limitations of floating OWCs whilst retaining many of the beneficial synergies. The simplicity of the collector, no submerged moving parts and a uni-directional air turbine PTO are all advantages of the technology. A review of the previous development work concluded that little was known about the operating principle of the device and that its hydraulic design was not understood. Through the extensive small scale, physical modelling of three different device geometries, the conversion process was investigated to increase knowledge and inform the hydrodynamic design. Initial studies considered a simplified duct geometry and found that the suggestions from the previous development phases of the technology were inaccurate and so were discounted. The methodologies developed were used in subsequent testing and provided initial learning on which the future experiments were based. A multi-duct model was tested in a wave basin in order to investigate whether such a configuration would be suitable as a future commercial device. Energy conversion
efficiencies exceeding 40 %, proved the potential of the configuration but the testing highlighted the many complexities of the platform that should be addressed before being further developed. A single duct was studied to evaluate and improve the design of a proposed marine demonstrator being developed consecutively with this research in a commercial project. Testing the sensitivity of performance to changes in the geometric design and naval architecture resulted in a configuration that maximised the conversion efficiency. Various numerical modelling options were considered to create a performance model. CFD was
deemed to be the most suitable method to capture all of the relevant flow physics in the conversion process and to provide a useful design tool. A preliminary model was developed to demonstrate the applicability of the method and provide the foundation for further work. Annual, large scale energy productivity analysis for the optimised device predicted that a 42 m long, single duct would be able to generate 154 MWh/yr at Wave Hub. This was equivalent to a 124 % increase over the original baseline design. Predicted electricity generation for the EMEC site was comparable to the predictions for a competing technology. Although both predictions were relatively low, it was anticipated that these would increase as the designs mature.

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Identifiers

ORCID for A.S. Bahaj: orcid.org/0000-0002-0043-6045

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