| In recent years, with energy crisis and environmental problem breaking out, the development and exploitation of marine renewable energy receive more and more attention around the world. China successfully constructed the Shanghai East Sea Bridge offshore wind farm in 2010, which marks that China has entered the offshore wind power times. As China's construction of offshore wind farms, more and more engineering problems are placed in front of our engineers and scientists. At present, our country still has no professional structural design standard of offshore wind turbine. The construction and technology of offshore wind farm in China are still in its initial stage. Therefore, systematically study the dynamic response of offshore wind turbine structural system under marine environmental loads will be very meaningful for our country to construct large offshore wind farms.This paper started from two aspects, one is marine environmental loads simulation and the other one is the dynamic response analysis of offshore wind turbine under marine environmental loads. The calculation method of random wind loads, random wave loads and nonlinear wave and currents loads of offshore wind turbine were studied systematically. The dynamic responses of offshore wind turbine under aerodynamic and hydrodynamic loads were studied in time domain. The analysis method of random dynamic response of offshore wind turbine was studied based on pseudo excitation method in frequency domain. The wave impact on the offshore wind turbine tower-foundation process was simulated in three-dimensional based on the new mesh-free method-smooth particle hydrodynamics (SPH). The wave and offshore wind turbine tower-foundation interaction problems were studied based on the SPH and FEM coupling method. Specific studies of this paper are as follows:(1) Review of the offshore wind energy utilization and dynamic response analysis of offshore wind turbine structural systems. This paper started from the research background, it is very meaningful and necessary to study the dynamic response of offshore wind turbine structural system systematically under the background that our country are vigorously developing the offshore wind power in current. The current domestic and international offshore wind energy utilization and the resulting economic and environmental benefits were introduced first in the paper. Starting from the field of civil engineering, structural classification of the offshore wind turbine was introduced. And then the current status of the environmental load calculation method of offshore wind turbine structural system and dynamic response analysis of offshore wind turbine blades, tower and foundation were reviewed in the paper.(2) Research on the aerodynamic loads of offshore wind turbine blade and dynamic characteristics of blades. The aerodynamic loads of blades were studied based on blade element momentum theory (BEM) with considering the fluctuating wind speed. The blade rotating speed influence on the aerodynamic loads of blade was studied, and then the most adverse action of the blades on the tower was analyzed. The variable cross-section cantilever beam model was built for offshore turbine blade as a simplified model. The feasibility of introducing the variable cross-section cantilever beam model for dynamic analysis was verified by comparison of the modal shapes and modal frequency. The centrifugal stiffening effect influence on the dynamic characteristics of blades were studied, and the axial force plane and natural frequency plan of blade were introduced to analyze the relationship between natural frequency, time and rotating speed directly. By introducing the concept of coefficient, the centrifugal stiffening effect was studied quantitatively.(3) The dynamic response study of offshore wind turbine under aerodynamic loads. Contrary to the outline characteristics of offshore wind turbine, the simulation method of fluctuating wind with considering the spatial coherence effect was presented based on the harmonic superposition method. The correctness of the simulation method was validated by comparison of the calculation spectrum and target spectrum. The dynamic response of offshore wind turbine with considering the blade and tower coupling effect was study, and the influence of the blade and tower coupling effect on the wind induced response of tower was discussed. The paper also studied the dynamic response of offshore wind turbine with considering the centrifugal stiffening effects, and the influence of the centrifugal stiffening effects on the wind induced response of blade and tower were also studied in this paper.(4) Research on the dynamic response of offshore wind turbine under aerodynamic and hydrodynamic loads. The calculation method of random wave loads was studied, and the dynamic responses of offshore wind turbine under random environmental loads were analyzed in time domain. The influence on the environmental loads results and the dynamic response of offshore wind turbine of loads combination rules and free surface variation were discussed quantitatively. Based on the stream function wave theory, the nonlinear wave loads calculation method of offshore wind turbine was studied, and the influence of wave surface variation and pile diameters on the nonlinear wave loads were discussed quantitatively. Then the dynamic responses of offshore wind turbine under nonlinear wave loads were calculated. The nonlinear wave and currents loads of offshore wind turbine were also studied by the stream function wave theory, and the dynamic responses of offshore wind turbine under nonlinear wave loads were calculated in time domain. The influences of wave and current interaction model and wave-current combination model on the nonlinear wave current loads were investigated.(5) Study on random dynamic response of offshore wind turbine based on the pseudo excitation method. The basic theory and calculation process of pseudo excitation method were analyzed first, and it lays a foundation to study the pseudo excitation method application on analyzing the random dynamic of offshore wind turbine. The high performance calculation method of offshore wind turbine random dynamic analysis was presented based on the pseudo excitation method. Based on the structural characteristics of offshore wind turbine, the pseudo excitation load construction method of blade and tower and the calculation method of displacement power spectrum were presented. The spatial coherence of pseudo excitation load was studied by the spatial coherence function.Based on the calculation method presented in this paper, the random vibration response of wind turbine blade and tower under wind loads were analyzed in frequency domain, and the displacement power spectrum of offshore wind turbine blade and tower and the extreme response values in design life period were calculated. By introducing the pseudo excitation method, the random vibration analysis of large scale offshore wind turbine was solved efficiently, and it can provide a reference to the engineering project.(6) Study on the offshore wind turbine and wave interaction problem based on SPH method. The analysis method of offshore wind turbine dynamics and wave-structure interaction was presented based on the SPH and FEM coupling method, which includes SPH and FEM coupling method calculation process and the construction methods of numerical wave tank and three dimensional dynamic analysis models of offshore wind turbine tower and foundation. The wave impact process on the tower was simulated based on the SPH method and the velocity field and pressure field of fluid during the impact process were calculated. By combining the SPH and FEM coupling method, the dynamic response of offshore wind turbine tower and foundation and their response with considering the wave-structure interaction effect were studied in three three-dimensional.
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