Application Of Absolute Node Coordinate Formulation In Blade Structure Analysis Of Large Wind Turbine

As a key component of wind turbine,wind turbine blade is an important part of wind turbine design and optimization.Its complex structure and variable load make the nonlinear deformation of blade more obvious.At the same time,with the development trend of largescale wind turbine,the blade flexibility has increased sharply,so how to accurately and effectively simulate the blade has become a hot spot in blade design research.Finite element method and multi-body system dynamics are the main methods to study this problem at present.However,finite element method has more degrees of freedom and lower solving efficiency.The multi-body method loses part of the structural information due to the equivalent transformation of the flexible blade.Aiming at the problems existing in the existing modeling methods,combining with the structural characteristics of large rotating flexible blades,this paper adopts the absolute node coordinate method based on the continuum theory to establish the structural modeling of flexible blades.The dynamic and static characteristics of the flexible blade are obtained by analyzing the blade in time domain and frequency domain.The specific research work includes:(1)In order to obtain the accurate dynamic model of the flexible blade,the structure model of complex blade was established by combining Gaussian integral and Hammer integral in this paper.Then,the stiffness matrix,mass matrix and generalized force matrix of the twodimensional beam and the three-dimensional beam were firstly derived based on the geometric nonlinear deformation method.The static model of the cantilever beam is established to calculate the nonlinear large deformation of the beam when the free end is subjected to the concentrated moment.Finally,the dynamic model of flexible pendulum was established to analyze the influence of different element numbers on the model accuracy.The numerical results show that the absolute node coordinate method has a good ability to describe the large deformation of the beam.(2)with absolute node coordinates and describes the large deformation of rotating beam movement and tiny vibration of the rotor blades for analysis of dynamic players effect and its frequency characteristic,the introduction of floating coordinate system to establish the dynamics equation of rotating beam,and pushed the mass matrix and stiffness matrix of the same features,the rotating flexible beam and the establishment of blade dynamic model and the solution is more convenient.This paper takes a two-dimensional flexible beam as an example to simulate its rotation dynamics and observe the deformation and vibration of the beam in the process of rotation.Based on the perturbation theory,the free vibration equations of the three-dimensional rotating flexible beam with hub radius were established by linearization method.The frequency domain characteristics of the beam under different rotating speeds and without hub radius were analyzed.(3)In this paper,the vibration equation of the blade is established on the basis of the structural model of the blade and the free vibration equation of the three-dimensional rotating flexible beam.Then,the proposed model was used to calculate the modal information of the blade and compared with the results of NERL and ANSYS.The simulation results verified the reliability of the proposed model.Finally,the influence of dynamic rigidity on the natural frequency and mode shape of the blade is analyzed.