Study On The Wave Energy Capture Efficiency And Wave Damping Function Of An Integration System Of WECs With Breakwaters

Based on the concept of cost-share,the integrations of wave energy converters with other offshore platforms or breakwaters can provide a better way for reducing the high cost of manufacturing the WEC devices.Among them,the oscillating buoy WECs have a similar working principle with the floating breakwaters and they can be easy to integrate together.But such integration systems still need further study on for both the working principle and the desire design model.The OpenFOAM software is used in the present work for building the numerical wave tank(NWT)and the simulation of floating objects in it.After well verification and validation of the NWT and the heave motion of a pile-restraint floating box without extra restraint,the CFD simulations of two types integration systems of the heave oscillating buoy with the floating breakwaters are conducted in present work.The wave energy capture performance and wave damping performance of these two integration systems are studied in detail.The first type of integrating strategy is installing the PTO system into a single floating box type breakwater directly.Working on the effect of the performance of such integration system,such below parameters are studied here including the linear PTO model,the nonlinear Coulomb type PTO model as well as the structure parameters.The result shows that the capture width ratio of the device gets a significant decline compared with the analytical value owing to viscous and nonlinear effect.The present work emphasizes the optimal linear PTO coefficient under the viscous effect.The optimal linear PTO coefficient should be larger than the theoretical one which ignores the viscous effect.The nonlinear Coulomb type PTO model is developed in present work and is applied in the simulations.It shows the device with the Coulomb type PTO model can get higher CWR value and lower transmission coefficient compared with the one with linear PTO model.The change of the structure parameters can have a big effect on the performance of the device.The CWR can increase while the transmission coefficient can decrease with a wider structure along the direction of the wave.The shallower draft can also improve the CWR value of the device but the transmission coefficient will increase dramatically.The second integrates strategy is appending a buoy in front of a fixed permeable breakwater.The PTO system and the shape of the buoy are studied.From the case of the resonant wave condition,it shows such integration system can get even double CWR value than the first type device because the front buoy can absorb the wave reflecting by the back fixed breakwater.Three shapes of buoys are chosen for studying the shape effect on the performance of such a device.The round bottom one does little disturb on the wave field and no apparent vortex are generated from the boundary which means lower vicious effect and lower energy dissipation.Finally,the round bottom buoy can get higher CWR value.From the above study,the second type integration system shows better performance for both wave energy capture and wave dissipation function.With the optimal design for the shape of the buoy,the size of the device and PTO model,higher performance can be obtained for such a device.Such devices can be a benefit to some specific sea areas and regions.