A Life-cycle Analysis On Mechanical Properties Of Offshore Wind Turbine Support Structures

This paper is based on an offshore wind turbine project. A life-cycle analysis on mechanical properties of offshore wind turbine support structures is conducted by using commercial software allowing for pile-soil interaction.Firstly, analysis of the wind turbine structure in each specific stage is conducted, including static analysis,modal analysis and seismic analysis.This course is consist of four stages, which are initial stage of service,10years of service,20years of service and30years of service.Pile-soil interaction is simulated by springs defined by p-y curves through the course.In the section of static analysis, The deformation of the structure and the stress of the structure as well as the axial force are calculated in each stage in two conditions,which are the limit state condition and the normal condition. After checking in accordance with the relevant norms,we can know the safety margin of the structure in each stage.In the modal analysis section,the whole finite element modal of the wind turbine structure is builded and analysed by ANSYS software to gain the frequency and modal shape of wind turbine structure.The first order natural frequency in each stage is reasonable.as a result,it can not suffer the resonance destruction.The seismic analysis is on the basis of the modal analysis. In this section,only the seismic load and the wave and current load in design water level are considered.It shows that the results are so small that they are within the reasonable range,which means the structure has enough safety reserve to avoid seismic damage.Then,the effects of different environmental factors on the mechanical properties of offshore wind turbine structures are compared,including cycle load and static load,soil sliding and no soil sliding and different slip magnitude as well as a variety of slip depth. It shows that,the difference betweent the deformation and stress induced by cycle load and static load is small. And the deformation and stress will get greater with the increace of slip magnitude or slip depth.