The Influence Of Near-Fault Ground Motions On Response Of Wind Turbines

The growth in global wind energy suggests that wind farms will increasingly be constructed in seismically active regions.On the other hand,some ground motions near faults are pulse-type ground motions,accompanied with large velocity pulses,and near-fault ground motions are often accompanied with strong vertical ground motion,so the influence on the seismic performance of the structure can not be ignored.The initial geometric imperfections,attributable to a systematic manufacturing process may be more disadvantageous to the seismic performance of the wind turbine towers,the wind turbine tower structure will have a large deformation or even collapse directly under a major earthquake.Therefore,a 1.5MW wind turbine tower of a land wind farm was investigated to study the influence of near-fault velocity pulse and vertical ground motion on the seismic response of the wind turbine towers,and analyze the imperfection sensitivity and collapse of the wind turbine towers.Firstly,ten typical pulse ground motions and ten non-pulse ground motions are input into the wind turbine tower structure,and the time history analysis is carried out to study the influence of near-fault velocity pulse on the seismic response of the wind turbine towers.The results show that the near-fault velocity pulse has a significant influence on the top displacement,top acceleration,bottom shear force and bending moment of the tower,indicating that the fan tower is sensitive to the near-fault velocity pulse.If the proposed wind farm is located near the active fault,during an earthquake,extent of damage will be more serious.Then,in order to study the influence of vertical ground motions on the seismic response of wind turbine towers,six groups of ground motions with significant verticaleffect are selected to perform the time history analysis under two cases of seismic inputs,i.e.ground motions with only horizontal component and combination of both horizontal and vertical components.The results show that the vertical ground motion has little effect on the horizontal displacement and acceleration on the top of tower,but has a significant effect on the vertical displacement,vertical acceleration and axial force of the structure.With the increase of the ration of the vertical peak ground acceleration to peak horizontal acceleration,the vertical displacement and vertical acceleration response of the top tower increase.The less time difference between the peak acceleration of horizontal and vertical ground motion is,the greater the vertical effect of the earthquake is.The vertical ground motion would cause the increase of the axial forces at the bottom of the tower.With the increase of the ration of the vertical peak ground acceleration to peak horizontal acceleration,the maximum axial force at the base increase,while the minimum axial force decreases.Finally,the wind turbine tower is modeled by self-contact finite element method,and the tower model considering weld depression imperfection is established.The elastic-plastic incremental dynamic analysis of the structure is carried out to study the seismic collapse characteristics of the tower structure with or without depression.The results show that the FEM model considering the self-contact mechanism predicts the buckling failure mode reasonably.Once the tower changed from elasticity to the inelastic range a plastic hinge develops at a change of thickness or weld depression potentially leading to collapse,with very little prior energy dissipation.Imperfections were found to have a significant effect on the intensities of ground accelerations at which damage initiates and on the failure location.The imperfections significantly reduce the acceleration at which plastic damage initiates.An imperfect tower also exhibits more potential hinge locations,increasing the variability in the seismic response.The inclusion of vertical accelerations has the potential to shift the critical hinge location to a weaker part of the tower,particularly when imperfections are present.