Study On Mechanism And Characteristics Of Energy Conversion From Flow-induced Motion Coupled With Electromagnetic

The flow-induced motion(FIM)energy convertor to harness the current energy has a better future than the traditional generators because of its low starting flow velocity and high energy density.Until now,great majority of studies of FIM energy are about the characteristics of the oscillators or the piezoelectric materials.Available studies,which concentrate on the influences of the generator,the oscillating system and the sectional shape,are very scarce.In this thesis,the mechanism of energy extraction from FIM based on the electromagnetically generator is studied in the theoretical and experimental methods.The influences of the parameters of the motor,the mechanical system and the cross sections on the oscillation mode and the energy extraction are analyzed.The objective of this thesis is to help to design the FIM energy conversion devices.The main research works and results are listed as follows:(1)A coupled theoretical dynamic model of Hydraulic,Oscillator,Generator and Resistance(HOGR)is established.The expression of the harnessed efficiency is deduced,and the influential factors are analyzed.Then methods to predict the efficiency and to select generator are proposed for fixed excitation generators.(2)FIM characteristics of square prism are investigated experimentally.The effects of incident angle,stiffness and mass on the oscillation are analyzed,and the responses of square prisms and triangular prism are compared.Results show that triangular prism has a better performance in the FIM energy harness.Then the following studies focus on the triangular prism.(3)The increase and the decrease of the flow velocity are tested.The physical models of fixed magnetic generator and triangle prism are introduced.The variations of damping,stiffness,and mass and cross-section aspect ratio are achieved and then verified by free decay tests.(4)The FIM of triangular prism is studied experimentally.The complete responses of soft galloping(SG)and hard galloping(HG)analyzed.The evolutions of oscillation mode for damping,stiffness,mass and cross-section aspect ratio are revealed.The parameters,which improve the flexibility of energy extraction,are discussed.The main findings are listed as follows.A self-excited region can be observed in the SG response,and the VIV(Vortex-Induced Vibration)branches are incomplete;on The contrary,the self-excited region cannot be observed but a critical flow velocity can be observed in HG response,VIV branches are complete.As damping and mass increase or stiffness and aspect ratio decrease,oscillation mode of triangular prism transits from SG to HG.High stiffness,high aspect ratio or low mass will improve the flexibility of energy extraction.(5)The energy extraction of triangular prism using fixed magnetic generator is studied experimentally.The high energy response branches of triangular prism are pointed out.The influences of load resistance,stiffness,mass and aspect ratio on the efficiency are analyzed.The parameters which improve energy efficiency extraction are discussed.The main findings are listed as follows.The high energy response branches are the VIV upper branch,the VIV-galloping transition branch,and galloping branch.The variations of efficiency versus the load are different under different generators.Increase of stiffness or decrease of mass only promote to increase the efficiency in VIV,transition and initial part of galloping branch.Increase aspect ratio will promote to increase the maximum efficiency in VIV branch.For the fixed magnetic generator,forcing the triangular prism in the critical galloping(CG)mode will help energy extraction in a wide flow velocity range.(6)The influences of magnetic on the physical parameters and the generator parameters in HOGR model are discussed.A variable magnetic generator physical model is established.The FIM characteristics and energy extraction for the triangular prism under the variations of magnetic generator are studied.The main findings are listed as follows.Increase of the magnetic promotes higher damping and higher upper limit energy efficiency.As the magnetic increases,the oscillation mode transits from SG to HG.In VIV branches,as magnetic increases,efficiency first rises up and then falls down;in galloping branch,as magnetic increases,efficiency continues to increase until the galloping is suppressed.The variation of the magnetic achieves to improve the flexibility of energy extraction in HG.Compared with the CG mode,the efficiency under the variation of magnetic is increased around 20%~50%.