Study On The Conversion Efficiency Of Oscillating Water Column Wave Energy Converter With A Horizontal Plate

The ocean has a wealth of wave energy,and how to develop and exploit the wave can be one of the hottest issues all over the world.At present,the oscillating water column wave energy converter is one of the most studied and promising wave energy converters in the world.Based on the potential flow theory,the boundary value problem(BVP)of the interaction between the linear wave and the offshore oscillating water column(OWC)wave energy devices is solved by means of the matched eigenfunction expansion method.Meanwhile,by employing the FLUENT software and its associated user-defined function(UDF),a two-dimensional fully nonlinear wave-OWC numerical model was established.The effects of the immersion depth,the thickness of walls,the width of the chamber on the energy conversion efficiency were examined both in theoretical and numerical manners,and the comparison by these two manners shows a good agreement.Moreover,with the help of the numerical model,the performances of the OWC devices influenced by the incident wave heights were investigated as well.At last,this paper put forward a new type of OWC device with a horizontal plate at the bottom,the influence of the depth and length of the horizontal plate on the fluctuation of water level in the air chamber was analyzed,what's more,the effect of turbine damping coefficient on the performance of the OWC was considered.The results show that the bandwidth of highly-efficient frequencies narrows with the increase of the immersion depth,and the peak shifts to the low frequency region;the increase of walls' thickness results in the decrease of energy conversion efficiency in the high frequency region,while having little effect in the low frequency region;the bandwidth of highly-efficient frequencies widens with the increase of the chamber width,and the peak shifts to the low frequency region.In addition,the increase of the incident wave height causes the decrease of the energy conversion efficiency,especially,near the resonant frequency.The immersion depth of the horizontal plate of OWC can affect the fluctuation of water level in the air chamber,especially in the high frequency region.With the increase of immersion depth,the amplitude of water surface in the low frequency region decrease and increase in the high frequency region;meanwhile,the resonant frequency of device shifts to the high frequency region.The water outside the column and above the horizontal plate will resonances due to the incident wave,and selecting a proper horizontal plate length can aggravate the fluctuation of water level in the column,so that the frequency bandwidth corresponding to the high water surface amplitude widens.In addition,under the different wave frequencies,the optimal parameter values of air turbine are different;the damping coefficient has little effect on the wave energy conversion efficiency in the low frequency region,but sensitively in the high frequency region.