Study Of Influence On Horizontal Dynamic Characteristics Of Offshore Wind Turbines Supported By Pile In Heterogeneous Seabed Soil Under The SH Wave

The rich low-frequency components in the near-field earthquake and the energy they carry are the main reasons for the destruction of offshore structures.Most offshore wind farms are built in the offshore waters close to the coastline,while most of China’s offshore waters are located near the seismic fault zone.Frequent near-field earthquakes always threaten the safety of offshore wind turbine structures near the fault.At the same time,the existing research on the dynamic response of offshore wind turbine structures considers the homogeneous seabed soil,which is quite different from the actual working conditions.In view of the above research status,based on the Biot wave theory,this paper establishes an inhomogeneous seabed soil model with an exponential distribution of shear modulus along the depth direction,and obtains the horizontal displacement distribution of the free field under the action of vertically incident SH waves by the difference method.The Novak thin layer method was further introduced to obtain the horizontal dynamic impedance of the pile.On this basis,the dynamic response calculation model of pile-supported offshore wind turbines was established,and the offshore wind turbine system was divided into embedded section,submerged section and tower section,of which the horizontal displacement was obtained by analytical method and embedded The horizontal displacement of the segment is solved by the difference method.Based on the previously obtained free field displacement of the heterogeneous seabed soil and the dynamic impedance of the pile body,the tower top nacelle and blades were simplified to concentrated mass,and combined with the displacement and stress continuity conditions at the junction of the three sections,an index was established A horizontal dynamic response calculation model of the single pile fan in the heterogeneously distributed seabed soil under the action of SH waves and considering the MTMD vibration reduction effect.Furthermore,based on the principle of radiation wave propagation,the four parts of the embedded section,the submerged section,the platform,and the upper tower are coupled through continuity conditions and boundary conditions to construct a partially buried in the heterogeneous seabed soil under the action of SH waves.The calculation model of the horizontal dynamic response of the fan supported by the pile group.The influence of parameters such as tower height,tower top concentrated mass,pile spacing and MTMD on fan dynamic response is discussed.The research results of this paper are as follows:(1)When the shear modulus of the heterogeneous seabed soil is large,the resonance frequency of the fan structure decreases.At the same time,the height of the tower barrel,the concentrated mass of the tower top and the diameter of the pipe pile in the offshore fan have significant influence on the resonance frequency of the fan.The resonant frequency of the fan structure will decrease with the increase of the height of the tower,the concentrated mass of the tower top and the diameter of the pipe pile.(2)Consider the vibration reduction effect of MTMD on fan structure.The analysis shows that the narrow frequency bandwidth,more TMDs and smaller MTMD damping ratio can reduce the displacement amplitude of the fan resonance,and increase the frequency band control range of the fan structure resonance frequency.(3)In the offshore fan of pile group,the interaction force between pile and pile becomes smaller because of the too large distance between piles,which makes the change of distance between piles have little effect on the resonance frequency of fan.