Research On Seismic Response Reduction Of Wind Turbine Tower Structures Using New SMA-SMP Damping Device

Wind turbine tower structures(WTTSes)are being developed toward large scale applications to maximize the use of wind energy.As flexible towering structures,WTTSes are not only subjected to operating vibrations,but also affected by external environmental loads.The massive growth trend of the wind power industry has made it difficult for wind turbine towers to avoid seismic zones.Besides,seismic loads also have an equally strong impact on them.Therefore,how to use effective measures to reduce intelligently and economically the dynamic responses of WTTSes has become an important issue in the seismic control of engineering structures,which has important research significance and economic value in improving the reliability of such lifeline projects under the action of natural disasters such as earthquakes.The limited space inside the wind turbine tower prevents many common energy dissipations and damping measures from being implemented,and for safety reasons,lasso-type damping reinforcement measures cannot be installed around it.Based on this,this dissertation proposes a shape memory alloy-suspension mass pendulum(SMA-SMP)damping device for a WTTS based on the limited space within it,using the tensile energy dissipation performance of superelastic shape memory alloy(SMA)wire as the technical key combined with the principle of suspension mass pendulum(SMP)damping.It can "concentrate" the energy generated by the tower structure vibration to the damping device,to reduce the seismic response of the WTTS and achieve the purpose of effective response control of the highly flexible WTTS.The main work of this dissertation is as follows.(1)At the material level,the study on the superelastic properties of SMA wires under low-speed loading was carried out,and the energy dissipation characteristics of SMA wires under dynamic loading were investigated.Cyclic tension tests were conducted on superelastic SMA wires with different diameters to investigate the effects of different strain amplitudes,loading rates and number of cycles on the mechanical properties of SMA wires,and a modified Bouc-Wen model was proposed and validated.The results show that the superelastic SMA wire exhibits typical "flag-shaped" hysteresis characteristics with good energy dissipation and great deformation recoverability under low-speed loading,and the performance of SMA wire trained by cyclic stretching is more stable than before,and the modified Bouc-Wen hysteresis model is reliable and applicable.The SMA wires were installed in the diagonal direction between the stories of a steel frame model structure,and the initial pre-strain of SMA wires was considered.Shake table tests were conducted on the model with three working conditions:uncontrolled,partially controlled and fully controlled,to investigate the energy dissipation characteristics of SMA wires under different controlled working conditions.The results show that SMA wires can improve the seismic performance and deformation recoverability of the structure and reduce the seismic response of the structure,and SMA wires have good energy dissipation performance under dynamic loading,and the energy dissipation capacity is proportional to the number of SMA wires.(2)At the component level,an energy dissipating component of SMA-SMP damping device and a new type of SMA wire adjustable fixture are developed.Cyclic loading tests and numerical simulations were conducted on the SMA energy dissipation component to investigate the effects of different loading frequencies and displacement amplitudes on its mechanical properties,aiming at establishing a restoring force model of this energy dissipating component based on the modified Bouc-Wen model,and conducting numerical simulations on its mechanical properties.The results show that the energy dissipating component has a stable hysteresis curve under low-frequency cyclic loading,indicating that the energy dissipating component has good energy dissipation and deformation recoverability;the new adjustable fixture solves the problem of difficult anchorage of SMA wire and realizes the adjustment of SMA pre-strain;the numerical simulation agrees well with the experimental results,further verifying the correctness and applicability of the modified Bouc-Wen model.(3)At the structural level,the energy dissipating components are reasonably installed around the suspension mass pendulum,and an SMA-SMP damping device suitable for wind turbine tower structures is proposed,and the proposed SMA-SMP damping device is applied to the wind turbine tower structure to validate the efficiency of the seismic structural response control.A mechanical model of single degree of freedom(SDOF)based on the SMA-SMP damping device is established,the structural equations of motion are derived,the detailed measures and damping principles of the damping decice are explained,and the effects of mass ratio and frequency ratio on the damping effect are analyzed,and the damping effect of the device on different earthquake spectra and amplitudes is studied.The results show that the SMA-SMP damping device can effectively reduce the dynamic response of SDOF structures,and the force-displacement curve of this damping device presents good hysteretic dissipation performance and deformation recoverability.Taking an actual wind turbine tower structure as an example,a finite element refinement model and a multi-degree-of-freedom simplified model are established,respectively,the multi-degree-of-freedom(MDOF)equations of motion based on SMA-SMP are derived,the seismic response of the wind turbine tower structure is analyzed at no control,SMP control and SMA-SMP control,respectively,and the SMA-SMP arrangement position and control frequency of the device are optimized.The results show that the SMA-SMP damping device can effectively suppress the seismic structural response of wind turbine tower structure in multiple directions.