Research On Wave Buoy Hydrodynamic Characteristic And Wave Parameters Identification Method

Energy source is the important material fundament and restraining factor for morden economic and social development. With its rapid and continuous evolution, the comsuption of energy source for human society will continue to increase. So it forces human society to seek for fungible and susstainable new energy sources, including nuclear energy, solar energy, wind energy, biofuel energy and ocean energy et al.Ocean wave energy technology has become a hot issue of the world, the use of wave energy for power generation has broad application prospects. Very high extraction efficiency of wave power device in resonance phenomenon is not only familiar with human society, but also confirmed by a number of different types of wave energy device test. On the basis of summarizing200wave power device characteristics, Wuhan University Professor Cai Yuanqi team puts forward controllable resonant wave power generation technology. By tracing the time period, wave hight and wave length of wave in real time, such device can adjust its characteristics to maintain resonant condition with ocean waves, thus it can achieve stable wave energy extraction with strong survivability. Therefore, the fast, real-time and accurate measurement of wave parameters is the key technics of controllable resonant wave power generation technology.Analyzing the advantages and disadvantages of each technics of wave parameters identification, this paper determines to use small gravity wave buoy to measure wave parameters, which includes researches on two aspects:the hydrodynamic characteristic and wave following capacity of wave buoy; research on the identification method of wave parameters using data of wave buoy in six degrees of freedom.First, this paper establishes a complete set of wave buoy hydrodynamic numerical simulation platform, such platform can be easily used to research on the hydrodynamic characteristics of a variety shapes of wave buoy device and wave following capacity.Second, two shaps of wave buoy, cylinder and sphere buoys are designed and numerical analysis on the free damping heave and sway of these two kinds of wave buoy in numerical water tank. The heave and sway intrinsic frequencies of wave buoy can be achieved by FFT analysis of heave and sway time data. The general rules of the influence of wave buoy parameters on intrinsic heave and sway frequencies and the comparative researches on these two kinds of wave buoy are studied. On the base of analysis of wave theory, standards of increasing buoy wave following capacity, which aims to decrease the ratio between wave frequency and buoy intrinsic frequency, is put forward and numerical analysis is conducted with different wave time periods. The results agree with the proposed standards.Third, a new kind of method to fast and accurately detect wave parameters is put forward by applying wave buoy data in six degrees of freedom. Taking intoconsideration of transformation between moving coordinate and still coordinate, this method uses HHT method containing PCA method in EMD to get several IMFs from ocean wave message. By analyzing the power of these IMFs, the maining one can be gained, which contains the maining power message of waves. After Hilbert transforming, the time series instantaneous frequencies are obtained..The mathematical expectation of instantaneous frequency meeting3σ criterion is computated to abtain the wave frequency with99.74%confidence coefficient, it is more accurate compared with FFT method. Wave displacement can be abtained by integrating the vertical acceleration with instantaneous frequency and wave hight is abtained by least square fit. Similarly, wave suface angle can be gotten to calculate wave length. The standard deviation of heave and sway instantaneous frequencies can be used to judge whether wave parameters change.Finally, a small gravity wave buoy using MEMS triaxial accelerometer, bioaxial inclinometer and compass is designed. Tests of free heave and sway damping in water tank are conducted to get the heave and sway intrinsic frequencies. Wave identification tests are also conducted and the wave parameters identification method is applied to get the wave frequency, wave hight and wave length. The results are in keep with actural wave parameters and consequently verify the applicability of proposed wave parameter identification method.