Research On Structural Modal And Aeroelastic Damping Analysis Method Of Wind Turbine Based On Eigenvalues

Aeroelastic coupling stability analysis of wind turbines has always been a subject of extensive attention and research by experts and scholars in the field of wind power at home and abroad.Aeroelastic coupling mainly includes the coupling between the structure of the machine’s own internal forces and external aerodynamic,structure modal analysis was carried out on the wind turbine in addition to avoid wind turbine running in structural damage to the resonance region,the more important is to aeroelastic stability analysis,because the aeroelastic instability is different from resonance and vibration,more destructive potential.In order to study the influence of geometric nonlinearity of flexible wind turbine on aeroelastic frequency.The research object selected in this paper is the 5MW horizontal axis wind turbine of the American Renewable Energy Laboratory.The wind turbine is discrete into a mixed multi-body system based on rigid flexible body,spring force element and joint.In this paper,the structure is modeled by multi-body recursive method,and the wind turbine is regarded as a bifurcation tree system with roots,and the nonlinear dynamic equation of the wind turbine is constructed by Newton-Euler.Aerodynamic load based on the modified Blade Element Momentum Method and combined with the structural model of the wind turbine,the steady-state time-domain response program of aeroelastic coupling of the wind turbine was written to calculate the steady-state deformation position and velocity of the wind turbine under various working conditions.At the same time the introduction of state space equation B-L dynamic stall model,the model is suitable for wind turbine aerodynamic elasticity,negligible compression effect and leading edge caused by flow separation,introduces four state variables to describe the effect of the unsteady aerodynamic parameters,established the nonlinear aeroelastic coupling characteristic equations of the machine,the linearization of the equation is in a stable equilibrium state.At present,there are mainly two methods for modal analysis of wind turbines.One is based on impulse excitation response,and the dynamic characteristics of the system are obtained by calculating the frequency response function.The other is to obtain the explicit expression of the mass,stiffness and damping of the system by solving the eigenvalue problem.For the corresponding eigenvalue problem,the eigenvalue and eigenvector can be calculated under any working condition,so as to obtain the natural frequency,damping and mode shape of the aeroelastic mode.The built-in multi-body recursive algorithm of Recur Dyn multi-body dynamics software was used for programming modeling.The eigenvalue method was used to analyze and calculate the natural frequencies of each order structure at the assembly position and the steady-state equilibrium position,as well as the natural frequencies at various speeds.Without considering wind shear,variable propeller Angle and tower shadow effect,the aerodynamic and elastic coupling characteristic equations of the whole machine were solved by using the eigenvalue method,and the aerodynamic and elastic frequency and damping ratio of the assembly position and the steady equilibrium position of the whole machine were calculated under the condition of fixed tip speed ratio and different rotating speeds.