The Random Response Analysis Of Wind Turbine Based On Nonlinear Aero-elastic Coupling

Wind turbine upsizing is an inevitable tendency of modern wind turbine development. With the size increasing, it cannot be neglected that flexible components (e. g. blade) have influence on aerodynamic force of wind turbine and aerodynamic load change impacts aeroelasticity of wind turbine. So, it now becomes significant foundation of wind turbine coupling analysis to find the analysis method of wind turbine dynamic characteristics and aeroelastic coupling analysis including nonlinear deformation effect. This paper built an aeroelastic coupling model of wind turbine based on rigid and flexible hybrid multibody modeling method, combining with Blade Element-Momentum Theory (BEM) of wind turbine aerodynamic analysis. Then it made a time domain response simulation on large wind turbine through numerical solution.Firstly, a kind of superelement containing five Degrees of Freedom (DOFs) is built, the flexible components (blade, tower and shaft) which are divided into limited superelements is combined with the relative rigid bodies (hub, nacelle) which is set as rigid bodies. Then, the Hybrid Multibody System (HMBS) method is used to build aerodynamic multibody system model of wind turbine. By using Roberson-Wittenburg (R-W) modeling method combining with BEM calculating aerodynamic force of blade, using limited DOFs, nonlinear Algebraic Differential Equations (DAEs) of wind turbine are derived. A generalized aerodynamic simulation program is written and solved through default stablization solution, and time domain analysis of nonlinear aero-elastic coupling of large wind tuibine is realized. This program can automatically build and solve the constrained aerodynamic equations, DAEs, of system according to import data describing topological configuration of system. On the foundation of multibody system model of wind turbine and BEM aerodynamic model, aero-elastic coupling model is derived. On each time step of numerical integration of aerodynamic equations, the aerodynamic load can be calculated by aero-elastic coupling model according to speed, angular speed and attitude coordinates (direction cosine matrices) of each body of blade, then the load is uploaded to instantaneous deformed blades to realize time domain analysis of nonlinear aero-elastic coupling of wind turbine.Nonlinear aero-elastic coupling response under running situation is analyzed in the calculating case of this paper based on a5MW offshore wind turbine model released by National Renewable Energy Laboratory (NREL). According to the analysis, both edgewise vibration and flapewise vibration of blade under random wind are nonlinear vibration with big amplitude. And vibration of blade have a strong feedback on its aerodynamic force, their impacts on each other which means aero-elastic coupling is getting more obvious with the increasing of wind turbine power and blade flexibility.The time domain analysis of nonlinear aero-elastic coupling of large wind tuibine is significant for the blade design and the safe operation of large wind turbine, besides it is also an important foundation for aero-elastic stability analysis of wind turbine. The work done by this paper offered a referentially valuable thought and platform for building aero-elastic coupling model of whole wind turbine under the willing to have a further study on the mechanism and reason of nonlinear aero-elastic unstability.