In this work, air compressibility effects are investigated during wave interaction with an Oscillating Water Column (OWC) Wave Energy Converter (WEC). Mathematical modelling includes a thermodynamic equation for the air phase and potential flow equations for the water phase. A simple three dimensional OWC geometry with a linear Power Take Off (PTO) response is considered and both the thermodynamic and potential flow equations are linearised. Analysis of the linearised system of equations reveals a nondimensional coefficient which we name ‘‘compression number”. The flow potential is decomposed into scattering and radiation components, using an analogue of spring-dashpot response and taking into account the additional effects of air compressibility to wave interaction pro- cesses. We use these concepts to characterise the relative importance of the air compress- ibility effects inside the OWC and to derive novel scaling relations for further investigation of scaling effects in OWC physical modelling. The predictions of the methodology are val- idated against large scale experimental data, where compressibility effects are evident and further application of the methodology to a realistic OWC geometry is used to demonstrate the importance of these effects to prototype scale.
|Journal||International Journal of Marine Energy|
|Early online date||1 Sep 2017|
|Publication status||Published - Sep 2017|