Investigation On Mechanism And Characteristics Of Dynamic Responses Of A Spar-Type Floating Wind Turbine Based On Model Testing And Numerical Simulation Methods

With the continually increasing worldwide demand for energy coupled with a growing public awareness of the need to protect the environment,clean renewable energy has become an important current research and development.The conversion of energy from the wind and solar sources are the most visible in terms of research and application to commercial enterprises.Because traditional fixed seafloor-mounted offshore wind turbines are prohibitively expensive in deep water,industry and researchers have gradually begun to focus on a variety of floating offshore wind turbines(FOWT)concepts.This research study deals with a deepwater spar-type offshore wind turbine concept that could be deployed beyond the line of sight of populous coastal regions and yet near enough to population centers that could benefit energy generating from steadier and stronger wind resources.The research with respect to floating offshore wind turbines is multidisciplinary,involving aerodynamics,hydrodynamics,multi-structure dynamics(elastic)and automatic control.Due to the complexity of these models,the accuracy and reliability of the simulation tools around the world starve for validations with measured data from real floating offshore wind turbines or model tests.However,due to the proprietary protection from corporations/research organizations,the recorded field data or model test results are rarely released for use to the general research community.Therefore,to meet the urgent vadiation demand for international FOWT simulation tools and to conduct in-depth analysis of coupled response behaviour characteristics of the spar-type wind turbine,a basin model test with respect to a spar-type floating wind turbine has been performed in Deepwater Offshore Basin at Shanghai Jiao Tong University with a 1:50 Froude scaling ratio and a prototype water depth of 200 m.The research in this dissertation has broken through the bottleneck of transferring from the model tesing technologies with respect to traditional offshore floating structures to those with respsct to the floating offshore wind turbine.A new method of model tesing technology has been innovatively proposed in this dissertation.That is involving Reynolds and Froude number simultaneously considering technology,rotor spinning controlling technology,model blade manufacturing technology,open space wind field simulating technology,tower elasticity simulating technology and system mass matching technology.And on on top of this,the dynamic behavior characteristics of the spar-type FOWT have been investigated comprehensively,and the response behaviors and couping effect between motion,turbine/tower loads and mooring tension have been analyzed.This dissertation also presents the research findings of an extensive model test investigation of the dynamic response to vortex-induced motions(VIMs)of the spar-type floating offshore wind turbine.Particulars of this research are to investigate the unique and crucial effects of wind load on the spar-type FOWT,which differs considerably from other traditional spar-type floating systems utilized in the gas and oil industry,on the VIMs.A modified model blade was innovatively utilized in this model test based on the spar-type FOWT.This modified blade shows better-matched aerodynamic performance with the prototype relative to the original NREL geometrically scaled one,which,to a large extent,compensates for the less accurately matched rotor performance drawbacks of the geometrically similar blade.The test results under various load conditions based on the thrust-matched blade system(TMBS)and geometry-matched blade system(GMBS)have been compared to underscore the unique dynamic characteristic of the TMBS and to recognize the role that thrust-matched blades can play in floating system response behaviors.Combining the study on mechanisms of aerodynamic,hydrodynamic and dymanics,and based on which,a simulation tool calculated in time domain with respect to a floating offshore wind turbine has been developed,named DARwind.A numerical model based on the basin test in SJTU has been properly established in DARwind(in-house simulation code developed by SJTU)and FAST(FOWT simulation tool from NREL),considering the effects of sensor cables,low Reynolds environment and tower elasticity.By comparing the results from test and simulation,the accuracy and reliability of these two simulation tools have been vadiated.