Dynamic Reliability Of The Offshore Wind Turbine's Tower Considering The Coupling Of The Foundation

With the development of technology ,the increasing of the capacity of the indicidual offshore wind turbine calls for increasing dimension of the foundation and the wind turbine tower. However, the dynamic loading from wind and waves increase correspondingly. That means higher demands has been presented on the strength of the tower and stability of the foundation.In the thesis the structure of the offshore wind turbine was abstracted to the continuous beam with complicated boundary conditions .Considering the random load due to wind and waves ,the dynamic response of the wind turbine beam was calculated ,and the response was used to appreciate the reliability of the offshore wind turbine.In the first step,the modeling about dynamic response of the wind turbine was developed .Considering the nonlinear loads on the foundation from the soil,the foundation can be abstracted to a nonlinear spring,the restoring moment of the spring is a function of the foundation's rotation angle .The tower can be abstracted to an infinite number degree of freedom beam with varying section, the blade was abstracted to a particle with concentrated load.Secondly,calculating the random load on the offshore wind turbine.For the purpose to reduce compute capacity,the simulation of the stochastic wind load was made through AR method while the random wave load was made through harmonic superposition method.Next step is to calculate the system of partial differential equations .The wind turbine model and the time were discreted by the fully-discrete method .Then the random load was substituted into the equations for the final response of the wind turbine through the iteration method in time domain.The study has been carried out by statistical analysis of the dynamic response of the offshore wind turbine.The dynamic reliability of the wind turbine within the design life was calculated through the reliability within the computing time. As an example ,the dynamic response and reliability of an 1.5MW offshore wind turbine was calculated .The whole flow of dynamic reliability analysis of the offshore wind turbine is provided which is based on the Matlab.