Study On The Hydrodynamic Performance For Two Kinds Of Point Absorbing Wave Energy Device

With the continuous exploitation of fossil energy,human beings will face the severe challenge of fossil energy depletionand environment pollutioin.Wave energy is a kind of clean ocaen renewable energy.It has the characteristics of wide spreadand rich reserves.It has become a hot field focused by industry and academic circles to use wave energy generating power.There are several styles of wave energy device,such as point absorber,oscillating water column and wave overtopping style.Point absorber is also called oscillating buoy wave energy device.It use theoscillating buoy based on the carrier to capture wave energy.Point absorber wave energy devicehas attracted wide attention due to the advantages of simpler mechanism,higher conversion efficiency and easier installation and maintenance etc.According to the carrier whether fixed,point absorberwave energy device can be divided into fixed and floating types.According to the number of buoys based on the same carrier,point absorber wave energy device can also be divided into single point absorber and multi point absorber.There bas been many research results about fixed and floating point absorber wave energy technology and device.But it is not very thorough for the basic theoretical research on the flow field characteristics,hydrodynamic and wave energy conversion mechanism.It restricts the development of point absorber wave energy utilization technology and the progress of design method of the device.The article carry out research aims to two kinds of point absorber wave energy devices.One device is swing arm buoy wave energy device based on fixed carrier,another one is coaxial column buoy wave energy device which is based cylindrical type mooring floating carrier.Through theoretical calculation and model experiment,the paper studied the hydrodynamic method,the movement performance of buoy and the energy performance of device.Through the above research work,it will provid thepretical basis and technology method for design these two kinds of wave energy device.According to the floating point absorber wave energy device with structure of coaxial column and buoy,the radiation and diffraction problems of the structure under the action of wave are studied.Based on the potential flow theory,variables separation method and series expansion method,according to the structure characteristics of the device,the fluid domain is divied into three sub domain.Radiation and diffraction velocity potential are expanded into series in different domain.The unknown coefficients of series expansions are calculated according to the boundary conditions.Then the expressions of the velocity potential are getted.Through numerical examples,the analysis hydrodynamic results are contrasted with the AQWA numerical results and uncoupled hydrodynamic calculation results.The validity of the results are verified and the differences between coupled and uncoupled hydrodynamic results are analyzed.According to the solution results,the hydrodynamic performance of loater and cylinder are analyzed,the influence of the buoy and column's scales for there hydrodynamic performance are studied.According to column buoy type wave energy device,the movement characteristic and energy conversion characteristic for the mooring wave energy device with structure of coaxial column and buoy are studied.Firstly,the buoy-PTO-column coupling dynamics model of the column buoy wave energy device is established.The buoy and column's relative motion fuction and system's energy conversion function are derived.Considering the coacial structure of column and buoy,through coupling hydrodynamic solution,the influence regular for the buoy and column's hydrodynamic performance by device scale,wave parameters,PTO damping coefficients and rigidity coefficients is studied,and the energy conversion mechanism of the system is also discussed.Based on the research,the energy conversion optimization model is established combining genetic algorithm.Through optimization,the energy conversion efficiency of the device is improved.According to the swing arm buoy wave energy device,the movement and energy conversion performance of the device are studied.Firstly,based on the analyzation for the movement characteristic of buoy,swing arm and PTO system,the PTO-swing arm-buoy coupling motion equation is established.The motion functions of different mechanism and energy conversion function of the device are getted through solving the motion equation.Then the hydrodynamic coefficients of buoy are caculated based on numerical method.The parameters including the shape of the float,the initial installation angle of swing arm,platform inclination,the installation location of PTO on the swing arm are optimized.,Based on the analyzation for the damping and the spring characters of the system,the trends of power curve and the influence law of energy output response are discussed.The energy conversion mechanism studied and summarized systematically.According to to these two kinds of point absorber wave energy device,the performance test of motion and energy conversion are carried out in ship model towing tank of Harbin Engineering University.Firstly,experiment principles,test method are introduced.Experiment models and test system are designed.Through the design of test conditions and model experiment,experiment datas are obtained.According to the experiment datas,the effect law of wave period and wave height on the motion performance of thebuoy,wave load characteristics and energy conversion characteristics are repectively analyzed.Moreover,the theory analysis results are also validated with experiment results.