Study On Modal Parameter Identification Of Offshore Wind Turbine Structure Under Ambient Excitation

With the demand for energy of social development increases, the wind power, as akind of typically renewable energe shows huge development potential. Offshore windpower as an effective means of utilising wind energy has a great prospect, and offshorewind turbine structure is put into use more and more. However, the damage diagnosis ofthese structures should not be ignored considering the long-term operation in harshmarine environment. The foundation and critical link of the damage detection methodswhich are based on vibration test response information is modal parameter identification.In order not to affect the normal work of the offshore wind turbine structure, there is aneed to use the dynamic response signals under ambient excitation to identify the modalparameters. In this thesis, a modal parameter identification method of offshore windturbine structure under ambient excitation is presented. Taking the single column andtripod-piles offshore wind turbine structure as an example, we firstly study the modalparameter identification of the foundation structure under various load cases. And thenextend to the modal parameter identification of the whole structure under its operatingconditions. The main research works are as follows:1. Study on the modal parameter identification of the single column and tripod-pilesoffshore wind power foundation structure under impact load excitation. Build the finiteelement model of the foundation structure, and then use the Complex Exponential method(Prony) and the impulse response signal to identify the modal parameters. In order toimprove the accuracy of the results, we combined the MPC and MAC indicators toeliminate false modes. Numerical study results show that the method can accuratelyidentify the first six order modal parameters of the structure, and the order of theidentified modal parameters is related to the direction of the applied load.2. Study on the modal parameter identification of the single column and tripod-pilesoffshore wind turbine foundation structure under white noise load and wave loadrespectively. Firstly,get the cross-correlation function through the response signals of the finite element model of the foundation structure by using the Natural ExcitationTechnique (NExT),then use the Complex Exponential method (Prony) to identify themodal parameters of the structure, meanwhile, use the MPC and MAC indicators todistinguish the noise modal and system modal. Numerical results demonstrate that themethod is feasible to the modal parameter identification of the structure under ambientexcitation.3. After the verification of the method, extend it to the whole structure of the singlecolumn and tripod-piles offshore wind power, and study the modal parameteridentification under its operating condition. Build the finite element model of the wholestructure, and simulate the combined effect of the draught fan load and wave load to thestructure under operating environment. Finally, use the Natural ExcitationTechnique(NExT) combining with the Complex Exponential method (Prony) to identify the modalparameters of the whole wind turbine structure. This section further verified theeffectiveness of using the Natural ExcitationTechnique (NExT) combining with theComplex Exponential method (Prony) to identify the modal parameters under ambientexcitation.