Study On Hydrodynamic Performance And Capture Power Of Wave Energy Converter In Low Wave Energy Density

Wave energy is a kind of clean energy with significant potential for development and commercial application.At present,a variety of wave energy converters are applied in high wave energy density sea areas.In contrast,the development of low wave energy density sea area,which accounts for nearly 40% of the global sea area,is insufficient.The key technology research of the wave energy converters with the advantages of offshore,low layout and operation cost is insufficient.How to optimize the hydrodynamic performance of buoys and enhance the capture power is becoming the primary task of the wave energy converters in low wave energy density sea area.According to the characteristics of wave motion in low wave energy density sea area,a new type of sealed buoy wave energy converter suitable for the marine environment of Shandong Peninsula is studied in this paper.The numerical model of the buoy is established by the finite element software ANSYS,and the numerical analysis of wave energy conversion is carried out by the hydrodynamic calculation software AQWA.Then the hydrodynamic performance and capture power of the buoy in low wave energy density are studied,as well as the structural parameters are optimized.Firstly,the effects of buoy shape,mass and diameter changes on the hydrodynamic performance and force of buoy in frequency domain are studied.The pitching time history response of buoys based on buoy shape,mass and diameter in time domain is calculated.The law of capture power changing with buoy shape,mass and diameter is investigated,and the time history response of buoys at different mooring angles is discussed.Secondly,the relationship between the shape,mass,diameter of buoys and wave wavelength in the state of wave resonance is studied based on the frequency domain analysis method.The influence of buoy parameters on the state of wave resonance is analyzed,and the relationship between capture power and wave length is obtained.Finally,based on the relationship between buoy parameters and hydrodynamic performance and capture power under single factor,the influence of multi-buoy parameter coupling on buoy capture power is researched by orthogonal experimental method.The buoy structure parameters are optimized and analyzed with capture power as the optimization objective.Through the above research,the following conclusions are drawn:(1)In low wave energy density,the hydrodynamic performance and capture power of cylindrical buoy are better than that of hemispherical buoy.The hydrodynamic performance and capture power of buoy can be improved by increasing the mass or diameter to a certain extent.And the maximum pitch time history response value can be obtained by 45° mooring the wave energy converter.The pitch RAO of a 3~5m diameter cylindrical buoy increases gradually with the increase of mass(2.2~4.2t).The capture power increases first and then decreases.The pitch RAO of a cylindrical buoy increases first and then decreases with the increase of buoy diameter(2~5m),and reaches its maximum at a diameter of 4m.(2)For the same diameter,the most suitable wavelength of the cylindrical buoy is about 0.45 times that of the hemispherical buoy.Increasing the mass can make the buoy form a new resonance state with longer wavelength waves.When the diameter increases from 2m to 3m,the buoy forms a resonance state with longer wavelength waves.When the diameter increases from 3m to 5m,except for 4.2t and 4m diameter buoys,the buoy forms a resonance state with shorter wavelength waves.The wavelength range of the buoy with a diameter of 4~5m is about 7~14m when the maximum capture power is obtained.(3)In cylindrical buoys with a mass of 2.2~4.2t and a diameter of 2~5m,the optimal buoy structure parameters optimized by orthogonal experiment is: the sealed buoy wave energy converter with a mass of 4.2t and a diameter of 4m can achieve maximum wave energy capture in low wave energy density sea area with a wavelength of about 14 m.The combined scheme is widely applicable to the Bohai Strait and the majority of the Yellow Sea.