M4 WEC development and wave basin Froude testing

Abstract

The M4 wave energy converter (WEC) is a moored, multi-float, multi-PTO (power takeoff), multi-mode, attenuator-type system designed to be capable of order MW capacity. The strategy is first described with technical requirements. Wave basin testing was undertaken to demonstrate the system and validate linear diffraction-radiation modelling, used for initial assessment and to generalise the configurations. Froude-scale modelling including power takeoff has been demonstrated for the first, possibly only, time. Further wave basin testing was undertaken to validate a multi-float generalisation. Moorings are a critical component with the elasticity of (synthetic) cables reducing snap loads markedly but with complex dynamics requiring wave basin testing and further model development. Preliminary results are presented. Limitations of wave basins with regard to the control of wave (and current) conditions and associated measurement are discussed along with suggested improvements. Computational modelling ranges from efficient linear diffraction-radiation modelling to massively resource-intensive computational fluid dynamics (CFD). The former extended to second order is of main practical importance and is well suited to generalise WEC configurations and model complexity, such as nonlinear power takeoff control and moorings, but are limited in accurately representing physics such wave nonlinearity, slamming and viscous effects. However, CFD has yet to become a practical tool for realistic irregular wave conditions. Wave basin modelling based on Froude scaling is of vital importance for both concept exploration and model validation.