Performance Research Of The Floating Buoy Wave Energy Converters And Their Integrated Systems For Motion Suppression Of Deep-water Platforms

Wave energy is an abundant renewable energy resource of the global.Compared with other renewable energy sources such as wind and solar power,wave energy has larger energy flow density,less visual impact at the port and lower overall lifecycle carbon emissions.However,on one hand,as the wave energy varying dramaticly with the geographic location and time,the wave energy converter(WEC)could hardly maintain its the optimal performance.And the device are vulerable under the harsh ocean enviriment.On the other hand,in the far offshore area,although the wave energy is much abundant compare it in the nearshore area,it's much different for transmitting the power into the power grid.As a result,the cost of the wave energy power is much higher than the other energy resouces in the global energy industry at present.And the techonology of wave power is less mature compared to other renewable energy resources.Recently,the matural applications of the WEC are providing power for beacon light or beacon vessel,and also for rural area or island.As the environment pollution problem becomes more and more harsh in recent decades,the government all over the world,especially European countries and U.S.provide incline policies to the wave power technology.This makes the wave energy technology becomes more and more mature,and gradually be applied to the industry from the lab.At present,the three main problems of the wave energy conversion technology are the low conversion efficiency under random waves,the reliability of the device under extreme sea conditions and difficulty of transmiting the power to the shore.Because of the geographical position and the exsitance of the first island chain,the wave energy density of China is relatively small compared with other country in the South American and northern Europe,even it has a long coastline.As a result,the conversion efficiency of the WEC is the top-priority goal while applied in China.This paper propose two ways to improve the applicablity of WEC.In one way,an automatic shape optimization code for single buoy WECs and a feedback latching control strategy for two-body WECs are proposed for improving the conversion efficiency of the devices.In another way,two novel tuned heave plate energy harvesting system(THPEH)are proposed,working with deep-water platform as a novel combined ocean energy system.In this system,the THPEH system could convert the wave energy on the platform into electronic power for platform operating,and the THPEH system is tuned with the motion of the platform,in order to control the motion of the plate and improve the energy harvesting capacity at the same time.This article main research content is as follows,1.An automatic optimization code for the shape design of a bottom support heaving buoy WEC is established.Based on random vibration theory,the formulas for calculating the reduction effect on the power absorption of the stoke limitation of the motor and the buoy bottom out of water are deduced.Due to the maximum of annual average absorption power,the automatic shape optimization code of a single oscillating buoy WEC is established in frequency domain though the software of MATLAB and AQWA.The shape of the buoy is parameterized by revolution model base on a cubic spline curve.The numerical simulation of the optimal shape under a certain wave condition is carried out.The result proves the code's efficiency.2.A concept of a two body direct-drive WEC is proposed.And a dual-extruding hydraulic cylinder device is designed for carrying out the latching control for improving the absorption efficiency of the WEC.According to relationship between the wave exciting force and the latching control force,a feedback latching control strategy is established.According to the simulation results,the proposed feedback latching control could improve the absorption power of the WEC.3.Two novel tuned heave plate energy harvesting system are proposed for the motion control of deep-water platforms and energy-harvesting at the same time.The calculation model of the two system in time domain is established in the Simulink module of MATLAB.The parameter analysis of the size of the heave plate,tuned period and generator damping ratio are carried out.According to the numerical simulation results,the two novel tuned heave system can not only control the motion of the platform,but also provide considerable power.4.The mechanical and electronic test of the novel tuned heave plate and energy harvesting system(THPEH)are carried out.The mechanical model of the THPEH system is established,according to the hydrodynamic test of the heave plate and mechanical test of the motor.The effect of KC number,motion period and side ratio on the hydrodynamic of the heave plate are analyzed.The mechanical model of the power take-off system is established due to the mechanical test of the motor.The motion and energy absorption performances of the THPEH system under harmonic motion excitations with different period are analyzed.5.Model tests of a semi-submersible platform and the THPEH system are carried out in the State Key Laboratory of Coastal and Offshore Engineering,Dalian University of Technology,in order to verify and testify the effect of THPEH system on motion suppression of the platform and absorption of wave energy.Following the Froude similarity principle,the physical model test is conducted in 1:70 scale.Hydrodynamic and motion response of the deep-water semi-submersible platform,hydrodynamic of the heaving board,the performance of the generator and the motion response of the semi-submersible platform with THPEH system are testified in the model tests.Model tests are conducted in nonlinear wave tank,comparisons are performed between the deep-water semi-submersible platform with and without the THPEH system.6.In order to break the limitation of the small scale of the semi-submersible platform,a real-time hybrid simulation test method is proposed and realized for large scale model of the platform and the THPEH system.The scale for two THPEH system are 1:50 and 1:20 independently.By using the permanent magnet linear motor for carrying out the motion of the semi-submersible,which are numerically model and analyzed in real-time according to the force monitoring in the physical test of the THPEH system,the motion excitation of the platform motion could be loaded in realtime.In this way,the performance of the whole system under different wave conditions could be simulated.The effect of the system delay on the stability of the whole calculation system by using different algorithms with different time step are analyzed.The simulation are carried out for analyzing the effects of the tuned period,load resistance and wave conditions on motion control of the platform and energy harvesting.