The Seismic Behavior Of Support Structure Of Offshore Wind Turbine Considering Fluid-structure-soil Interaction

As an important content of clean energy and strategic emerging industries,offshore wind power business is thriving and flourishing."deeper waters,lager capacity and higher quality" is directing the development of offshore wind power generation,and wind turbines,whose weight,unit capacity and hub height are increasing significantly,have put forward higher requirements on support structures.At present,the attention to seismic performance of offshore wind turbine support structures has yet to reach where it deserves,and the interaction between the three fluid-structure-soil coupled subsystems has not been embodied completely,since considerations for their seismic design are still fairly half-baked,according to the current relevant standards.Therefore,the questions of fluid-solid interaction and pile-soil interaction under earthquake action was taken into consideration fully in this paper,and a numerical model of an offshore wind turbine support structure,with a unit capacity of 10MW,was constructed to analyze the dynamic behavior.First of all,some basic research work was culminated in this paper.The research status and ideas in terms of three aspects,which included the seismic behavior,the fluid-solid coupled problem and the pile-soil coupled problem of offshore wind turbine support structure,was discussed.The structural form of offshore wind turbine support structure and the gist of its selection was conveyed,so that the one that meet the requirements for the future Chinese construction of offshore wind power was done.Secondly,a theoretical study of fluid-solid interaction and pile-soil interaction analytical methods was conducted in this paper.On the basis of existing research,material nonlinearity and media damping of solid were involved,and an incremental finite element scheme of fluid-solid interaction system was deduced.Furthermore,one added mass method and two recursive algorithms were offered.On the other hand,the mass method based on Morrison equation that had been generalized to three-dimensional seismic situation in this paper was briefly described.In addition,the fluid-solid coupled finite element method,the P-y curve method concerning pile-soil interaction and the contact analysis finite element method were discussed.And then,one unabridged analysis theory about offshore wind turbine support structure’s dynamic responses was formed actually.A numerical model of an offshore wind turbine support structure,which was concerning fluid-solid interaction and pile-soil interaction,was constructed as an application of APDL.The motion equation was established,the recursive algorithm was derived,and the excitation calculation of the support structure was completed,which included the selection of seismic wave and the creation of artificial seismic wave via program,the calculation of aerodynamic loads according to BEM theory,the simulation of wind field via AR model and the calculation of wind loads,and the calculation of wave loads and current loads.Besides,the precision of the numerical model was validated based on P-y curve method.Finally,the research on the seismic behavior of offshore wind turbine support structure was done.The hysteretic behavior of pile-soil was analyzed,including effects of different parameters,such as pile diameter and undrained shear strength of soil.At the same time,the dynamic performance of the support structure was studied,including how fluid-solid interaction and pile-soil interaction effect modal parameters.The seismic response rules under different earthquake actions were summarized,and the seismic performance of the support structure was evaluated quantitatively through proposing the concept of seismic safety factor.It was on the seismic response of offshore wind turbine support structure that the influence of fluid-solid interaction,pile-soil interaction,and different excitations,including aerodynamic loads,wind loads and wave-current loads,was investigated in order to provide a reference for the seismic design.Whether the seismic response of offshore wind turbine support structure is sensitive to the depth of water was explored,and the selection of design tide levels in aseismic calculations was involved.