Hydrodynamic And Power Performance Of A Spar Type Turbine-Wave Energy Converter Integrated System

Multi-energy complementarity and comprehensive application are one of the developmental trends of marine renewable energy.The joint development of offshore wind and wave energy has become a research hotspot,and a variety of wind-wave integrated systems have been proposed.However,most previous studies on wind-wave integrated system remain in the stage of proposing new concepts,which are lack of in-depth understanding of the wave energy conversion characteristics and mechanism during operational conditions and the influence of wave energy converter on floating offshore wind turbine.The key parameters of wave energy converter are often given through experiments without model selection basis.In this dissertation,a wind-wave integrated system composed of a Spar type wind turbine and an annular wave energy converter was taken as the subject.Numerical simulation was carried out concerning hydrodynamic and energy conversion problems.The core component of the wind-wave integrated system,a coaxial-cylinder heaving wave energy conversion unit was studied.Frequency-domain motion and wave energy conversion model was established.Analytical results of optimal generator damping and capture width ratio considering the hydrodynamic coupling between the two bodies are derived.Results revealed that the optimal capture width ratio achieves a three-peak feature and their mechanism of existence was explained.The influence of mooring stiffness on wave energy conversion was studied to determine a bad mooring stiffness that seriously affected the power performance of the wave energy unit,and the influence mechanism was clarified.The Spar-annular wave energy converter subsystem was studied.A frequency-domain multi-DOF motion and wave energy conversion model was established.The influence of the wave energy converter draft and outer radius on the power performance of the subsystem was investigated.Based on the geometry and mass properties of the Spar and the wave conditions in the target operational area,a systematic model selection study was performed and plausible schemes were given.By further comparative study,the scheme with a larger wave power peak and the scheme with wider available frequency band were retained.A fully coupled time-domain motion and wave energy conversion of the wind-wave integrated system under regular waves was established.Based on the above two selected schemes,the influence of the annular wave energy converter on the motion response of Spar,the maximum mooring loads,and turbine power was studied.The influence of the wind turbine on the heave motion response and power output of the annular wave energy converter was also studied.The interactions between the wind turbine and the annular wave energy converter were unveiled.Results showed that stability and power of the wind turbine could be improved by the presence of the annular wave energy converter whereas the mooring loads are slightly affected.Besides,the wind turbine in different operational conditions has very limited effects on the annular wave energy converter.A fully coupled time-domain motion and wave energy conversion of the wind-wave integrated system under irregular waves was established.According to the probability distribution of wind speed and wave in the target operational area,a comparative study of the two schemes was carried out.Results revealed that the two schemes have similar effects on the motion response and mooring loads of the wind turbine.Then,the average turbine power,wave power,total power of the integrated system,and the annual wave energy production of the two schemes were compared.It was found that the scheme with wider available frequency band has apparent advantages in power performance,which was selected as the final scheme.