| With the gradual consumption of traditional energy and the accelerated deterioration of global warming,the green renewable energy industry has been booming all over the world.Among them,wind energy is popular because of its wide distribution,low cost and early start.In the wind energy industry,offshore wind power is particularly favored because of its high stable wind speed,low noise constraints,and small visual impact.With the gradual development of the offshore field,the development field has gradually moved to the deep-sea area where the installation cost of traditional fixed offshore wind turbine is increasing.At this time,the floating offshore wind turbine（FOWT）is more suitable.However,due to the complexity of the deep-sea environmental load,such as the combined load of wind,wave and flow,FOWT’s blades,tower and platform will suffer from the large deformation,which will damage the structure and affect the safety and durability of the FOWT.Therefore,the research on vibration control of FOWTs has become an urgent problem to be solved.In this dissertation,a complex rigid-flexible coupling multi-body dynamics model of the American National Renewable Energy Laboratory（NREL）5MW Semisubmersible FOWT（SS-FOWT）is established.A new electromagnetic double tuned double mass damper（EM-DTDMD）is proposed to reduce the vibration of the tower and platform of SS-FOWT.The vibration reduction test of classical tuned mass damper（TMD）on SS-FOWT scale model in the basin is also carried out.The main research work of this dissertation includes the following aspects:（1）The research status of related fields at home and abroad is introduced.The development status of wind energy industry in the world and China is briefly introduced.The research status of conceptual design and development of FOWTs is introduced.The research progress of multi-body dynamics modeling of FOWTs is reviewed.The research status of vibration control for offshore wind turbines is reviewed.（2）The rigid-flexible coupling multi-body dynamics model of SS-FOWT under combined wind and wave loads is established.Aiming at the multi-body coupling and multi-source excitation characteristics of SS-FOWT,considering the in-plane and out-of-plane bending deformation of blades and tower,as well as the three-dimensional translation and rotation of floating platform,the structural multi-body dynamics model of SS-FOWT is established based on Lagrange equation.The blade element momentum theory and virtual work theorem,Morrison formula and slice theory are used to propose the calculation methods of aerodynamic load and hydrodynamic load respectively.Finally,the multi-body dynamics model of structure-aerodynamic-hydrodynamic coupling system of SS-FOWT is formed.（3）The established SS-FOWT multi-body coupling dynamic model is verified and the dynamic response characteristics are analyzed.Based on the established SS-FOWT dynamic model,the simulation program is compiled by Matlab code.The numerical simulation is conducted to compare the vibration response output results with the current mainstream simulation software FAST for FOWT under different load conditions to verify the accuracy of the established model.The simulation load conditions are mainly divided into five conditions:Free decay motion,harmonic wave load,steady wind load excitation,steady wind and harmonic wave combined load,turbulent wind and harmonic wave combined load.（4）The EM-DTDMD is proposed and the parametric optimization of vibration reduction is studied.Aiming at the vibration of tower and platform of SS-FOWT,a new damping device called EM-DTDMD is proposed to control the vibration.Based on the classical TMD,the EM-DTDMD is achieved by replacing the viscous damping unit in the classical TMD with the electromagnetic tuned inerter damper,so as to realize the dual-mass and dual-tuning effect of the TMD and the electromagnetic tuned inerter damper.Compared with the classical TMD,it can effectively reduce the physical mass of the damper and improve the vibration reduction performance.In view of the design,installation and different control modes of EM-DTDMD in the nacelle and platform,the parameter optimization of single and triple EM-DTDMD for FOWT tower and platform vibration reduction is carried out respectively,and the optimization results are verified by numerical simulation.The parameter optimization method mainly includes H2 and H∞optimization theory,whose objective function are the root mean square value and peak value of the controlled structure displacement,respectively.（5）The damping performance of EM-DTDMDs on SS-FOWT is studied.Based on the established SS-FOWT dynamic model and the parametric optimization of damper,the optimal single EM-DTDMD and triple distributed EM-DTDMDs are installed in the nacelle and platform of the SS-FOWT,respectively.A new method of EM-DTDMD cooperative vibration reduction is proposed,and the dynamic model of the coupling system of the nacelle-platform EM-DTDMDs and SS-FOWT is established.Then,under the excitations of turbulent wind and random wave,the time domain simulation is conducted to analyze the vibration reduction performance under three different control strategies of nacelle EM-DTDMD,platform EM-DTDMDs and nacelle-platform EM-DTDMDs.In addition,the vibration reduction performance is compared with that of TMD with the same arrangement,to highlight the superiority of EM-DTDMD vibration reduction performance.（6）The tank vibration reduction tests of TMD on SS-FOWT scale model are carried out.Firstly,a 1:50 scale SS-FOWT scale test model is developed according to the 5MW prototype of NREL FOWT,and the accuracy of the model is verified by hydrostatic attenuation response.Then,a TMD damping device embedded in the SS-FOWT floating platform is developed,which is installed in the three columns of the platform.Finally,the TMD vibration reduction tests under different frequency harmonic wave excitation are carried out in the experimental tank of Stevens Institute of Technology,and the feasibility of TMD vibration reduction for SS-FOWT platform is verified. |
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